Analytische Chemie
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Paper des Monats
- ja (27)
Number-average molecular weights and inherent viscosities were found for the soluble members of an alkoxy-substituted copolyester series. A liquid-crystalline (high-temperature) phase was distinguisehd by IR and wide-angle X-ray scattering on molten and quenched samples in form of a nematic sanidic phase. In this phase no relationship exists between the orientation of the aromatic polyester backbone and that of the laterally attracted alkoxy groups. Further, it was proven by IR that only the polyester backbone can be aligned by shear stress. If the applied shear stress is very strong, the orientation of the stiff backbone becomes sensitive to disturbance caused by mechanical forces.
The main component of this program is a simultaneous representation of the unit cell and the calculated powder pattern. It allows the manipulation of the Crystal structure by moving selected atoms of the asymmetric unit. The resulting powder pattern can be directly compared to experimental data in order to obtain reliable starting values for further computations in refinement programs.
PowderCell 2.0 for Windows
(1998)
PowderCell contains a comfortable, user friendly visualization and modification tool for crystal structures. It provides on-line calculation of the corresponding powder diffraction patterns simulating a variety of experimental conditions. The common ICSD and Shelx file formats are supported for importing crystal structure information. It has control of automatic cell transformation and also derivation of subgroups. More than 740 different settings of the 230 space-group types are supported. Up to ten crystal structures can be considered simultaneously. A full pattern refinement enables the direct comparison with experimental diffractograms for quantitative phase analysis, lattice parameter refinement, polynomial background estimation, etc.
PowderCell as teaching tool
(1998)
PowderCell represents a user friendly program which supports the solution of scientific problems as well as teaching and education. Especially for the last one the program offers a lot of information regarding the space-group type as well as crystal structure used. Therefore, on some universities the program is used successfully to make students familiar with x-ray crystallography. The quasi-simultaneous diffraction pattern simulation visualized the changes caused by the respective crystal structure. However, it is also possible to vary different diffraction parameters and investigate the resulting changes in the interference intensity or the reflection position. In principle, the aim of the program is the intuitive generation of structure models. Therefore, special tools have been implemented to move (rotate or shift) or transform the crystal structure.
The formation of AlN films prepared by N+2 ion implantation into aluminium was investigated using X-ray and Auger photoelectron spectroscopy ( XPS, AES) as well as cross-sectional transmission electron microscopy (XTEM). After 100-keV N+2 implantation of low doses (1×1017 cm−2), the formation of hexagonal AlN nanocrystals (crystal size <5 nm, Ncrystal=1017 cm−3) was observed. Their orientation is strongly correlated with the aluminium matrix. With the dose increasing to 3×1017 cm−2, crystal growth follows, finally forming a homogeneous AlN-layer. Furthermore, the diffraction patterns show an increasing amount of misorientation with increasing dose. From the crystal size distribution, we conclude that continuous nucleation takes place. Samples implanted with an energy of 3 keV exhibit analogous behaviour. Nitride growth was further investigated using microstructured AlN formed by 3-keV implantation through movable TEM-masks (structure size: 15–150 mm).
In the case of high N+2 doses (D&5×1017 cm−2), AlN is detected by AES in the shielded area at a distance of up to 10 mm from the exposed region. The Diffusion coefficient was calculated to be 10−10 cm2 s−1. The formation of AlN proceeds in two steps.
After a continuous nucleation, diffusion-assisted Crystal growth takes place until a homogeneous AlN layer results.
Platinum does not form any adherent oxides and can be easily wetted by tin-based solders. Platinum is also an available metallization in semiconductor laboratories. Therefore we investigated the diffusion of platinum thin-film metallizations into eutectic tin–lead solder by using a high-resolution secondary ion mass spectroscopy (SIMS) profiling from the back side. It is shown that an intermetallic phase (PtSn4) is formed during soldering, which controls the consumption of platinum during soldering and in operation. The consumption of platinum follows the well-known parabolic diffusion law. The activation energy of this process is 0.63 eV. Even at extended heating cycles of 2 min at 250°C, 190 nm from the original 300 nm of the platinum film remain undissolved. This high stability makes platinum a very attractive thin-film metallization for flip-chip (FC) bonding of new microsystems.
Our aim is the application of LIBS as a simple, quasi on-line method for the non-destructive testing of concrete. Concrete is naturally inhomogeneous. Therefore we must take into account the local variation of the element composition using a statistical analysis. Depending on how much cement and aggregate is measured with each laser pulse, a scan on the surface of a concrete specimen produces a distribution of points in the Rankin diagram which is used to characterise the concrete.
Today's civil engineering NDT needs are for quantitative, fast to apply and easy to interpret methods. They are required on site both for evaluation of existing structures/infrastructure and for quality control in new construction. With this purpose, BAM has carried out in-situ feasibility studies, using radar, impact-echo and ultrasonic-echo methods. Two examples are given of their combined application on different railway slab–track constructions, using high frequency radar, scanning impact-echo and ultrasonic array methods. The aim was to evaluate limitations and advantages, comparability and complementarity of these methods. The on-site measurements demonstrated the possibility to investigate, with good accuracy via NDT, the bonding conditions between sleepers and slab, to locate voids and measure layer thickness. The acoustic and electromagnetic methods used, were found to be complementary.
The program PowderCell is a crystallographic tool for visualization of Crystal structures. However, it offers also non-conventional features like the fulautomatical generation of subgroups or the consideration of non-standard settings of space-group types. On the one Hand the program is very useful for non-crystallographers who like to get an impression of the atomic arrangement within the unit cell. But also for crystallographers it is recommendable because it contains a lot of additional information which can be extracted and used like data given in the International Tables for Crystallography, Vol. A. However, the most important advantage of the program is the simultaneous calculation of the X-ray or neutron diffraction powder patterns for a mixture of up to 10 crystalline phases. Between more than 7 different characteristic radiations can be chosen and their influence on the resulting powder pattern can be studied. Furthermore, experimental diffractograms can be analysed using a refinement procedure. The implemented LeBail-algorithm allows the investigation of unknown phases. In combination with the refinement algorithm an interface to Shelx offers the possibility for a step by step ab initio structure analysis. Certainly, the user-friendly shell is one reason that especially users who are not so familar with space-group symmetry, crystal structure data or diffractometry use this powerful tool for the solution of scientific or analytical problems as well as in teaching.
X-ray stress analysis on crystalline materials is based on the determination of elastic lattice strains. The strains described by the shift of peak positions are converted to stresses by the means of theory of elasticity. The development of the sin2ψ-method of X-ray stress analysis introduced an enormous progress in X-ray stress analysis during the last decades. This report outlines some important elements of X-ray physics and fundamentals of theory of elasticity. The Standard measuring procedure are described and special experimental differences to the common powder diffractometry are outlined.
XTEM and TFXRD investigations of ohmic Ti/Al/Ti/Au/WSiN contacts on AlGaN/GaN HFET layer systems
(2002)
The microstructural features of the high-temperature-stable ohmic contact system Ti/Al/Ti/Au/WSiN on AlGaN/GaN were investigated using analytical transmission electron microscopy and thin film x-ray diffraction.
For two typical rapid thermal annealing steps at 750 ◦C (non-ohmic behaviour) and 850 ◦C (ohmic behaviour) the intermetallic phases at the metal–semiconductor interface are presented. Increased annealing leads to the transformation of an Al2Au-AlAuTi phase mixture to a mixture of Al2Au-Al3Au8 phases and the formation of Ti-Al-nitride layers at the interfaces. In light of these results the electrical contact properties are discussed.
This Report describes the certification of the reference material antimony implanted in Si/SiO2 intended to be used for calibration of surface and near surface analytical methods. It describes the preparation, homogeneity measurements and the analytical work performed for the certification of both Areal density of antimony Atoms (retained dose) and the isotope amount Ratio as well as giving considerations on the stability of the material.
HIIRM final report
(2002)
Accurate analytical results have become more and more an absolute essential tool for further progresses in technology and science. Precision however, often used in this context as a quality criterion for analytical methods, is not a replacement for accuracy in any way. Therefore, analytical procedures are necessary, which will generate reliable and accurate results and can be used for evaluation of other analytical procedures and certification of reference materials (RM). Especially the certification of reference materials for the amount content of trace elements requires highly accurate results with a small combined uncertainty. The best example for an analytical procedure having this capability is undoubtedly Isotope Dilution Mass Spectrometry, for inorganic as well as for organic applications. Applied on Thermal Ionization Mass Spectrometry (TIMS) isotope dilution provides results of highest quality and proven high accuracy especially in the field of RM certifications for more than 30 years.
The major drawback of this approach often is the necessity for a complex chemical separation step. A major advantage of Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is the potential to cope with a simplified or an on-line-carried-out sample preparation. A key requirement of isotope dilution analysis however is the accurate and precise determination of isotope ratios, because of its limiting factor for the accuracy and the total uncertainty of the result. Very precise isotope ratios can be determined in combination with a detection system that is capable of simultaneous detection of different isotopes, a so-called multi-collector system.
The objective of the presented project is to evaluate the advantages of such a multi-collector ICP-MS for the application of IDMS in the field of trace elemental analysis in reference materials. The focus is on the development of simple and fast procedures for isotope ratio measurements in general and IDMS analysis in particular. Furthermore, it is an objective to develop and evaluate on-line spiking procedures.
One of the first conclusions, which had a severe impact on the HIIRM project, arose during the early days of the project. Currently most certification experiments are accomplished by certification campaign based on a variety of participants’ results. The sample preparation, sending, analyzing and data evaluation however require lot of resources and the process may take a long time. An alternative way is given by using fewer participants with methods of higher metrological quality. For elemental amount contents such a method undoubtedly is isotope dilution analysis and multi-collector ICP-MS offers the necessary precision and matrix robustness and ruggedness as said above. Therefore, a multiple collector ICP-MS was manufactured as part of the project instead of the originally planned high-resolution instrument. Due to the novelty of the multicollector ICP-MS instrument, a lot of additional fundamental research became necessary. Especially interferences needed further attention. Fortunately, the IsoProbe is additionally equipped with a high-resolution option and with a brand new collison cell. The high-resolution option however can only be used to identify interferences but cannot be used to quantify them. On the other hand, the use of the collision cell proved to be a vital tool to overcome interferences. This is especially true because high resolution would have reduced the available sensitivity by a factor of ~100. Applying the collision cell technology the high sensitivity was maintained whilst most interferences were eliminated. However finding the right parameters of operation for the collision cell became a huge part of the method development process. A variety of gases like argon, helium, hydrogen, deuterium, nitrogen, krypton and xenon were tested for their suitability. Especially the tests accomplished for iron determinations revealed that carefully selected parameters have an incredible influence on the quality of the final results. Nonetheless collision cell technology will undoubtedly be widely used for newer ICP-MS instrumentation and contribute to eliminate wrong analytical values caused by interferences.
The enhanced sensitivity of the instrument revealed also problems not detectable by other means. The control of contaminations seems to be one of the major analytical challenges in the future. Sector field based ICP-MS will give the user an opportunity to trace sources of contamination back to their origin and eliminate them. Even lower limits of detection will be the result as well as an enhanced reliability for analysts dealing with higher amount contents. The analyst will also benefit in controlling blank levels when the method of isotopically spiked procedure blanks is used as demonstrated in this project.
Another main part of the project was the validation of the developed procedures. The first validation step was successfully accomplished by applying these procedures on the standard solutions provided by NRG. The main part of this validation however consisted of the evaluation of the fundamental parameters of the isotope dilution process and related measurements. This approach turned out to be superior compaired to the first step as a highly reliable uncertainty calculation can be easily performed. The best reputation and acceptance of the methods can however only be accomplished by participating in certification campaigns or in interlaboratory comparisons on highest metrological level. The results of the participations in general were brilliant. Not only the results but also the obtained realistic uncertainties were of superior quality. Direct comparisons at BAM with the results obtained by a multicollector TIMS applying the same calculation schemes showed the benefits of using multicollector ICP-MS. The main benefits of ICP-MS were identified, of which the first one is the enhanced precision of the isotope ratio measurement. For a variety of elements the values obtained by multicollector ICP-MS are even more precise than the ones obtainable by multicollector TIMS. The second important advantage identified was the simplified sample preparation. The laborious and time consuming analyte-matrix-separation step as necessary for TIMS measurements can either be omitted or at least be drastically reduced. Therefore, the advantages regarding time and enhanced sample throughput will result in further spread of ICP-MS in general and multicollector ICP-MS in particular.
The third major part in terms of the method development process was mainly focused on developing an online isotope dilution system. The volumetric instead of the gravimetric IDMS approach proved difficult, if the high demands necessary for RM definition measurements are to be fulfilled. The major obstacle in this case is the missing stability and precision in terms of mass flow. Consequently, the initial development failed as the system made up of two piezoelectric droplet injectors was unable to reach the required stability as well as precision. The thereupon-created system consisting of two HPLC pumps proved to be far more valuable regarding automation and particularly the quantification of transient signals. Nevertheless, such a system will probably be rarely used in certification campaigns, as the gain of time is too small compared to the loss of reliability. However, this system proved most valuable in terms of species-specific elemental analysis as preliminary investigations showed. In this context this system will be suitable for certification measurements, as the major uncertainty contributions derive from sampling, sample treatment and species distribution and as moreover all availabel methods demonstrate far beyond.
During the whole project, one of the main concerns regarding the multicollector ICP-MS instrument were software issues caused by the early development state of the original control programs. A lot of effort was necessary to accomplish the necessary data manipulations externally. The development of a new software suite by Micromass for the HIIRM project has solved this issue almost completely. With the new software suite and the validated parameters of measurement a step forward for institutes dealing with reference material certifications was achieved.
Future certifications campaigns for minor elemental contents in different matrices should be performed by a small number of participants from highly qualified institutes. These institutes should apply very reliable methods of measurement like the ones developed in the HIIRM project. Many resources may be saved that way while the outcome of the certifications may easily be improved. ICP-MC-MS has the potential to be an important method in this context. Stable isotope dilution analysis in combination with a multi-detector ICP-MS, equipped with a hexapole collision cell for the suppression of important spectral interferences and for enhanced sensitivity, proved to be an advanced method of elemental analysis with a high potential for matrix independent measurements. Since ICP mass spectrometers of this type have only recently been introduced, no systematic evaluation of the capabilities of this specific application of the ICP-IDMS method has yet been made.
The orientation relationship (OR) between the bcc and fcc phase in the plessite microstructure of the iron meteorites Watson, Agpalilik and Gibeon has been analysed in a scanning electron microscope using electron back-scattered diffraction (EBSD). A very strong OR exists, independently on the analysed plessite type and the observed spreading of single orientation data. The agreement between the experimental orientation distribution and existing models varies for each meteorite. The black plessite in the Agpalilik corresponds to the Nishiyama-Wassermann model whereas the Duplex plessite of the Gibeon meteorite shows an OR close to the Kurdjumov-Sachs model. The Watson meteorite is strongly deformed so that a general OR is difficult to determine due to the blurred experimental orientation distribution.
An extensive comparison between the conventional Vickers hardness at 500 mN and indentation hardness measured with Vickers indenters at 500 mN is presented for up to 20 different materials and for three different instruments. Additionally, the indentation modulus is compared to Young’s modulus, which was measured with alternative methods or taken from the literature. It is shown that the agreement between the results from depth-sensing indentation and the reference values can be improved by additional corrections, for the calculation of the indentation area. With corrections the mean hardness difference to the Vickers hardness reference as average of all investigated materials can be reduced to about 10 % although disturbing pile-up or sink-in effects can still not be considered. For the modulus, the mean difference was only about 6 %.
The often poor construction and low maintenance level of tailings dams has caused serious accidents. The EC funded Project TAILSAFE is aimed at the non-destructive assessment of tailings facilities for stabilization analyses and the development of better management methods.
The focus of geophysical field studies was on the discrimination of different layering and construction steps as well as the determination of the spatial (relative) water content in the dams. SIP measurements at three tailings facilities different in their geological backgrounds, composition and age have been conducted.
Electron backscatter diffraction and energy-dispersive X-ray spectrometry were used to investigate the intermixed interface produced during laser cladding of a Co-Cr-Mo alloy on a steel substrate. A multi-component system and rapid solidification conditions together lead to a complex microstructure at the interface. The solidification of the cladding starts with the formation of an interface layer, which is about 75µm in thickness and consists of randomly oriented equiaxed grains of Co-Cr-Fe solid solution and martensite. Orientation analysis of the grains in the interface layer revealed that some grains have a special orientation relationship with the former austenite grains in the heat affected zone but the cladding is not formed by epitaxial growth on the substrate. Intermixing of the materials at the interface is providing a strong bond between the substrate and the cladding. For a grain from the interface layer to emerge as columnar grain in the cladding, it was determined that its <001> crystallographic direction is not supposed to deviate more than 25° from the sample normal direction.
A Co-Cr-Mo laser cladding applied on railway wheels is characterised by a combination of EBSD and EDX. A complete pass of the cladding is investigated to achieve a better understanding of the microstructure evolution during laser cladding. A microstructure with columnar grains extending over the whole thickness of the cladding is observed. The grains have a <001>-fibre texture with the fibre axis parallel to the normal of the substrate surface, and a substructure consisting of cells/dendrites. During the cladding process, two different kinds of precipitates form in the cell walls, which can be identified as M6C and a non-equilibrium phase. Furthermore, stacking faults are observed to occur in the cladding grains and are discussed with respect to the laser cladding process.
The hydrogen influence on the microstructure of the austenitic-ferritic Cr22-Ni5-Mo3 stainless steel was investigated. Cathodic hydrogen charging was performed electrochemically from aqueous solution of 0.1M H2SO4 with hydrogen entry promoter addition. The aim of this study was to reveal microstructural changes appearing during the hydrogen charging and particularly to clarify the occurrence of phase transformations induced by hydrogen. The specific changes in both phases of steel were observed. In the ferritic phase, strong increase of dislocation density was noticed. Longer time of hydrogen charging leaded also to the strips and twin plates formation in ferrite phase. In the austenitic phase, the generation of stacking faults, followed by the formation of α' martensite was remarked.
During focused ion beam microscopy (FIB) of crystalline materials imaging contrast and milling result are effected by orientation of the crystals with respect to the incident ion beam. This is due to the possibility of ion channeling along preferred crystal directions which effects the depth at which interaction between ions and specimen atoms takes place. As a result of channeling emission of ion induced secondary electrons (iiSE) and secondary ions (SI) as well as the sputter rate decreases.
Theoretical channeling orientations and critical angles can be calculated.
These effects have been studied quantitatively for polycrystalline recrystallized Cu as a typical model case.
The competitive growth of columnar grains in a single-grain selector, which is used for directional solidification of single-crystal blades from nickel-based superalloys, has been investigated by electron backscattered diffraction and local X-ray diffraction analysis. It has been found that the competitive grain growth in a starter block is determined by the crystallographic factor: rapidly growing grains with the axial orientation close to the [001] direction dominate in this part of the casting. For the competitive grain growth in a helicoidal separator, the geometric factor (the position of a grain at the input of the separator) is also important. The results obtained suggest that an appropriate geometry of the single-grain selector was chosen. In addition, the distribution of the orientations of columnar grains obtained by electron backscattered diffraction, can be used for approximate estimation of the yield of suitable (i.e., with the deviation of the axial orientation from the [001] direction within a specified tolerance) single-crystal blades.
Fatigue crack propagation investigations have been performed in austenitic-ferritic duplex stainless steel H22N5M3 in air and during hydrogen charging, using various frequencies of loading. Strong differences of crack propagation velocity depending on the test conditions were noticed. Lower frequency with applied hydrogen charging led to the huge increase of crack propagation velocity compared to the tests performed in air. To understand such a behaviour in each case and characterize crack mode, the samples were observed using electron back-scattered diffraction (EBSD). It was shown that in air, the fatigue crack propagation involved plastic deformation and the resulting cracks had ductile character. The presence of hydrogen led to more brittle mode of cracking. This effect was also connected with frequency of loading: lower frequency, which assured longer time for hydrogen-crack tip interaction, resulted in the highest crack propagation velocity and the brittle cracking mode with lower amount of plastic deformation. The performed observations indicated that the path of the crack went mostly transgranularly through both austenite and ferrite phases. Phase and grain boundaries were not the preferred paths for crack propagation.
Interphase boundary characterization in duplex steel and iron meteorites using EBSD technique
(2006)
The properties of materials are mainly described by the orientation distribution of the crystalline phases in a material. Beside the so considered anisotropy also the grain as well as phase boundaries are of extreme importance for a whole string of properties, e.g. the strength of a material. On the example of the interface between fcc and bcc iron the discovered and derived models are discussed. Although the common models are based on the crystal lattice description, the atomic configuration on the interface is analysed. Since experimentally a wide spread of orientations data appears the consideration of the frequency distribution is proposed to find at least the main orientation relationship between fcc and bcc. High-indexed pole figures as well as the Euler subspace are introduced in order to increase the accuracy and to compare different measurements. For the sake of simplicity EBSD measurements on iron meteorites are used since they commonly consist of large fcc single crystals which transformed to a low and very specific number of bcc grains. In special cases the described procedure could also be used for steels.
In this paper, a new method for the investigation of the degradation of ballast railway track beds is proposed. An array of antennas is used for simultaneous acquisition of reflected radar impulses, which have been transmitted from different sending positions. This array setup allows an automated CMP-measurement, which enables a direct calibration of the ballast thickness. These multiple offset measurements using the array setup are well suited for fast railway inspections. The method offers the possibility to visualize the state of degradation of the ballast in a velocity spectrum.
Dyke breaks - caused by e.g. Overflows or Slop breaks during long lasting high water gauge - Play a great role in a failure potential of extreme flood Events.
Using conventional dyke condition Monitoring dyke messengers can undertake only a visual surface inspection. Thus defective Areas can oftentimes be discovered too late.
A critical area in which failures due to soil displacement and moisture Penetration become more significant is located at a landside dyke foot. Geotextiles are integrated here as a Drainage in case of modern three-zone type of dyke.
Aflatoxins, a group of structurally related mycotoxins, are well known for their
toxic and carcinogenic effects in humans and animals. Aflatoxin derivatives and protein
conjugates are needed for diverse analytical applications. This work describes a reliable
and fast synthesis of novel aflatoxin derivatives, purification by preparative HPLC and
characterisation by ESI-MS and one- and two-dimensional NMR. Novel aflatoxin bovine
serum albumin conjugates were prepared and characterised by UV absorption and
MALDI-MS. These aflatoxin protein conjugates are potentially interesting as immunogens
for the generation of aflatoxin selective antibodies with novel specificities.
Carrying out dimensional measurements by CT means assessing coordinates in space. CT must therefore be treated as a coordinate measuring technique similar to optical or tactile Coordinate Measuring Machines (CMMs). The well-established standards and guidelines for the acceptance- and verificationtesting of CMMs require the use of calibrated reference standards to achieve measurement machine characteristics.
Hence, transferring these concepts from coordinate metrology to CT, a dedicated CT-specific reference standard was designed, manufactured and calibrated using a tactile CMM. For comparison purposes, a CAD model was created by reverse engineering using the calibration data. The calibrated model was fed into a virtual CT and the measurement process was simulated. The reference standard was measured by micro-CT.
By comparing the characteristics of the measurement output of CT and the output gained from simulation, the influences of measurement artefacts can be judged, for the first time, in analogy to existing Guidelines of coordinate metrology.
We have studied the anisotropic milling of Cu with respect to the milling rate and the milling topography, as well. The background is twofold: i) anisotropic milling has to be taken into account during the preparation of TEM specimens and in the manufacturing of micro parts from crystalline materials, and ii) the orientation depending milling behaviour can be used to generate topographies with specific properties with respect to, for example, adsorption, wear, and corrosion.
A multi-offset radar system will be presented that features the possibility to get quantitative information about the wave propagation velocity as a measure of the ballast quality. This goes beyond the regular application of conventional radar systems offering only qualitative structural information. The new approach provides a fast NDT method for the classification of ballast fouling. A main advantage of the multi-offset radar is that regular ballast digging for velocity evaluation can be avoided and travel time can be directly transformed into an equivalent depth by using the automatically evaluated velocity. The maintenance cost and interruption time can be significantly decreased by this method. The application of velocity evaluation method is common in geophysical applications but it is used for ballast inspection for the first time.
Three petrol reference materials were certified for their total sulfur content in support of Directive 2003/17/EC of the European Parliament and of the European Council, which stipulates that petrol with a maximum S content of 10 mg/kg must be available in all member states by 2009. Commercially available petrol was obtained and filled into borosilicate ampoules without further treatment. Homogeneity of the materials was tested and no heterogeneity was detected for two of the materials, whereas minor heterogeneity was observed for the third material. Stability of the materials was tested for 8-12 months at 60 °C and no degradation was observed. Characterisation was based on isotope-dilution mass spectrometry (IDMS) applied as primary method of measurement by three European metrology institutes and certified values were assigned using all results. The certified uncertainties include contributions of (potential) heterogeneity, potential degradation as well as characterisation. The final assigned values are:
ERM-EF211: 48.8 ± 1.7 mg/kg
ERM-EF212: 20.2 ± 1.1 mg/kg
ERM-EF213: 9.1 ± 0.8 mg/kg
The materials are available from IRMM (ERM-EF211), LGC (ERM-EF212) and BAM (ERMEF213)
Irrational orientation relationship derived from rational orientation relationships using EBSD data
(2008)
The determination of the orientation relationship (OR) between α-Fe matrix (bcc) and γ-Fe precipitates (fcc) is discussed using orientation data collected by electron backscatter diffraction (EBSD). The comparatively low accuracy of EBSD is compensated by the high number of measurements what allows a general statement regarding to the mean OR existing in a sample. The representation and discussion is realized on a part of the Bain zone in a {001} pole figure. A discussion of some selected rational OR which are commonly used for the phase boundary characterization between α and γ shows that the pole figures describing a transformation from γ → α are different to those for α → γ. A technique is proposed based on at least three misorientation angles between the experimental OR to the rational OR's as reference. For the misorientation angle distribution a refinement is applied to extract the mean values. They are used to detect the mean OR, what is also possible for only a few or even a single precipitate if the number of measurements describing the phase boundary is sufficiently high.
The tetragonal crystal- structure type of chalcopyrites (chemical formula AIBIIICVI2) is a superstructure of sphalerite type. The c/a ratio differs generally from the ideal value 2, i.e., the crystal structure is pseudocubically distorted. For CuInSe2 and CuGaSe2 thin films, simulations demonstrate that it is theoretically possible to reveal the tetragonality in electron backscatter-diffraction (EBSD) patterns for CuGaSe2, whereas it may not be possible for CuInSe2. EBSD experiments on CuGaSe2 thin films using the ”Advanced Fit” band-detection method show that it is possible to extract accurate misorientation-angle distributions from the CuGaSe2 thin film. Pole figures revealing the texture of the CuGaSe2 thin film are shown, which agree well with X-ray texture measurements from the same layer.
Following to a brief introduction of BAM the procedures are explained how to prepare reference materials in analytical chemistry. Examples are given for collecting and presenting data in welding, thermomechanical properties and tribology. The use of data for modelling safety in technology and chemistry is demonstrated. Finally there is in outlook on the World Materials Research Institut Forum (WMRIF) and recommendations for action.
For prediction of wave propagation in multilayered structures it is necessary to know the material properties. Important parameters are sound velocity (c) and attenuation ( ). Values found in the literature were not satisfactory mainly due to insufficient accuracy of measured attenuation. Experiments were carried out in Division VI.3 - Durability of Polymers. The ultrasonic test equipment was provided by Divisions VIII.1 - Measurement and Testing Technology; Sensors and VIII.4 - Acoustical and Electromagnetical Methods.
The class Dothideomycetes (along with Eurotiomycetes) includes numerous rock-inhabiting fungi (RIF), a group of ascomycetes that tolerates surprisingly well harsh conditions prevailing on rock surfaces. Despite their convergent morphology and physiology, RIF are phylogenetically highly diverse in Dothideomycetes. However, the positions of main groups of RIF in this class remain unclear due to the lack of a strong phylogenetic framework. Moreover, connections between rock-dwelling habit and other lifestyles found in Dothideomycetes such as plant pathogens, saprobes and lichen-forming fungi are still unexplored. Based on multigene phylogenetic analyses, we report that RIF belong to Capnodiales (particularly to the family Teratosphaeriaceae s.l.), Dothideales, Pleosporales, and Myriangiales, as well as some uncharacterised groups with affinities to Dothideomycetes. Moreover, one lineage consisting exclusively of RIF proved to be closely related to Arthoniomycetes, the sister class of Dothideomycetes. The broad phylogenetic amplitude of RIF in Dothideomycetes suggests that total species richness in this class remains underestimated. Composition of some RIF-rich lineages suggests that rock surfaces are reservoirs for plant-associated fungi or saprobes, although other data also agree with rocks as a primary substrate for ancient fungal lineages. According to the current sampling, long distance dispersal seems to be common for RIF. Dothideomycetes lineages comprising lichens also include RIF, suggesting a possible link between rock-dwelling habit and lichenisation.
Within the last decade, silicon drift detectors (SDD) systems have become more and more popular in the field of energy-dispersive spectroscopy (EDS). The main characteristic of the SDDs is their extremely high pulse load capacity of up to 750,000 counts per second at good or reasonable energy resolution (<123eV Mn-Kα, <46eV C-Kα at 100.000 cps). These properties in conjunction with electron backscatter diffraction (EBSD) techniques and modern data processing make a range of innovative analysis options possible, not only high speed mapping but also hyperspectral imaging techniques.
Bisphenol A polycarbonate/acrylonitrile–butadiene–styrene (PC/ABS) with and without bisphenol A bis(diphenyl phosphate) (BDP) and 5 wt.% zinc borate (Znb) were investigated. The pyrolysis was studied by thermogravimetry (TG), TG-FTIR and NMR, the fire behaviour with a cone calorimeter applying different heat fluxes, LOI and UL 94. Fire residues were examined with NMR. BDP affects the decomposition of PC/ABS and acts as a flame retardant in the gas and condensed phases. The addition of Znb results in an additional hydrolysis of PC. The fire behaviour is similar to PC/ABS, aside from a slightly increased LOI and a reduced peak heat release rate, both caused by borates improving the barrier properties of the char. In PC/ABS + BDP + Znb, the addition of Znb yields a borate network and amorphous phosphates. Znb also reacts with BDP to form alpha-zinc phosphate and borophosphates that suppress the original flame retardancy mechanisms of BDP. The inorganic–organic residue formed provides more effective flame retardancy, in particular at low irradiation in the cone calorimeter, and a clear synergy in LOI, whereas for more developed fires BDP + Znb become less effective than BDP in PC/ABS with respect to the total heat evolved.
We report on three respiration sensors based on pure optical technologies developed during the FP6 EU project OFSETH. The developed smart medical textiles can sense elongation up to 3%, while maintaining the stretching properties of the textile substrates for a good comfort of the patient. The sensors, based on silica and polymer fibre, are developed for monitoring of patients during MRI examination. The OFSETH harness allows a continuous measurement of respiration movements while all vitals organs are free for medical staff actions. The sensors were tested in MRI environment and on healthy adults.
Digital radiography in the inspection of welded pipes to be installed under deep water offshore gas and oil pipelines, like a presalt in Brazil, in the paper has been investigated. The aim is to use digital radiography for nondestructive testing of welds as it is already in use in the medical, aerospace, security, automotive, and petrochemical sectors. Among the current options, the DDA (Digital Detector Array) is considered as one of the best solutions to replace industrial films, as well as to increase the sensitivity to reduce the inspection cycle time. This paper shows the results of this new technique, comparing it to radiography with industrial films systems. In this paper, 20 test specimens of longitudinal welded pipe joints, specially prepared with artificial defects like cracks, lack of fusion, lack of penetration, and porosities and slag inclusions with varying dimensions and in 06 different base metal wall thicknesses, were tested and a comparison of the techniques was made. These experiments verified the purposed rules for parameter definitions and selections to control the required digital radiographic image quality as described in the draft international standard ISO/DIS 10893-7. This draft is first standard establishing the parameters for digital radiography on weld seam of welded steel pipes for pressure purposes to be used on gas and oil pipelines.
The changes in the sonic surface wave velocity of concrete under stress were investigated in this paper. Surface wave velocities at
sonic frequency range were measured on a prismatic concrete specimen undergoing several cycles of uniaxial compression. The
loading was applied (or removed) gradually in predefined small steps (stress-controlled). The surface wave velocity was measured
at every load step during both loading and unloading phases. Acoustic Emission (AE) test was conducted simultaneously to
monitor the microcracking activities at different levels of loading. It was found that the sonic surface wave velocity is highly stress
dependent and the velocity-stress relationship follows a particular trend. The observed trend could be explained by a combination
of acoustoelasticity and microcracking theories, each valid over a certain range of applied stresses. Having measured the velocities
while unloading, when the material suffers no further damage, the effect of stress and damage could be differentiated. The slope
of the velocity-stress curves over the elastic region was calculated for different load cycles. This quantity was normalized to yield a
dimensionless nonlinear parameter. This parameter generally increases with the level of induced damage in concrete.
Statistical analysis of tomographic reconstruction algorithms by morphological image characteristics
(2010)
We suggest a procedure for quantitative quality control of tomographic reconstruction algorithms. Our task-oriented evaluation focuses on the correct reproduction of phase boundary length and has thus a clear implication for morphological image analysis of tomographic data. Indirectly the method monitors accurate reproduction of a variety of locally defined critical image features within tomograms such as interface positions and microstructures, debonding, cracks and pores. Tomographic errors of such local nature are neglected if only global integral characteristics such as mean squared deviation are considered for the evaluation of an algorithm. The significance of differences in reconstruction quality between algorithms is assessed using a sample of independent random scenes to be reconstructed. These are generated by a Boolean model and thus exhibit a substantial stochastic variability with respect to image morphology. It is demonstrated that phase boundaries in standard reconstructions by filtered backprojection exhibit substantial errors. In the setting of our simulations, these could be significantly reduced by the use of the innovative reconstruction algorithm DIRECTT.
A long period grating (LPG) mechanically imprinted in a microstructured polymer optical fibre (mPOF) is embedded in a carbon fibre reinforced polymer (CFRP) unidirectional laminate. Processing steps were established in order to ensure that mPOF does not suffer significant degradation. The strain and temperature responses of the embedded mPOF-LPG were then investigated.
Structural changes in the condensed phase of bisphenol A polycarbonate (containing 0.45 wt% poly (tetrafluoroethylene))/silicone acrylate rubber/bisphenol A bis(diphenyl-phosphate) (PC/SiR/BDP) and PC/SiR/BDP/zinc borate (PC/SiR/BDP/ZnB) during thermal treatment in nitrogen atmosphere and in fire residues were investigated by solid-state NMR. H-1, B-11, C-13 and P-31 NMR experiments using direct excitation with a single pulse and H-1-P-31 cross-polarization (CP) were carried out including 31P(1 H) and C-13{P-31}double-resonance techniques (REDOR: Rotational Echo Double Resonance) on a series of heat-treated samples (580 K-850 K). Because many amorphous phases occur in the solid residues, and solid-state NMR spectroscopy addresses the most important sites carbon, phosphorus and boron, this paper is the key analytical approach for understanding the pyrolysis and flame retarding phenomenon in the condensed phase of PC/SiR/BDP and PC/SiR/BDP/ZnB.
For the system PC/SiR/BDP it is shown that (i) at temperatures around 750-770 K (main decomposition step) carbonaceous charring of PC occurs and arylphosphate structures are still present, reacted in part with the decomposing PC; (ii) for higher temperatures from 770 K the phosphorus remaining in the solid phase increasingly converts to amorphous phosphonates and inorganic orthophosphates with a minor amount of crystalline orthophosphates; and (iii) H-1-P-31{H-1} CP REDOR and H-1-C-13{P-31} CP REDOR NMR experiments suggest that the phosphates and phosphonates are bound via oxygen to aromatic carbons, indicating the interaction with the carbonaceous char.
When ZnB is added to the system PC/SiR/BDP, (i) ZnB leads to a slightly enhanced PC decomposition for temperatures below 750 K; (ii) alpha-Zn-3(PO4)(2) and borophosphate (BPO4) are formed in small amounts at high temperatures suggesting a reaction between BDP and ZnB during thermal decomposition; and (iii) most of the borate remains in the solid residues, forming an amorphous pure borate network, with the BO3/BO4 ratio increasing with higher temperatures.
The NMR data of thermal and fire residues are highly correlated, underlining the importance of this work for understanding the pyrolysis and flame retardancy mechanisms in the condensed phase during the burning of the PC/SiR blends. (C) 2010 Elsevier Ltd. All rights reserved.
Ground penetrating radar (GPR) was used to characterize the frequency-dependent dielectric relaxation phenomena in ordinary Portland cement (OPC) hydration in concrete changing from fresh to hardened state. The study was experimented by measuring the changes of GPR A-scan waveforms over a period of 90 days, and processed the waveforms with short-time Fourier transform (STFT) in joint time-frequency analysis (JTFA) domain rather than a conventional time or frequency domain alone. The signals of the direct wave traveled at the concrete surface and the reflected wave from an embedded steel bar were transformed with STFT, in which the changes of peak frequency over ages were tracked. The peak frequencies were found to increase with ages and the patterns were found to match closely with primarily the well-known OPC hydration process and secondarily, the evaporation effect. The close match is contributed to the simultaneous effects converting free to bound water over time, on both conventional OPC hydration and dielectric relaxation mechanisms.
Shape memory polymers (SMP) belong to the class of stimuli-responsive materials and have generated significant research interest. Their capability to retain an imposed, temporary shape and to recover the initial, permanent shape upon exposure to an external stimulus depends on the "functional determinants", which in simplistic terms, can be divided into structural/morphological and processing/environmental factors. The primary aim of the first part of this review is to reflect the knowledge about these fundamental relationships. In a next step, recent advances in shape memory polymer composites are summarized. In contrast to earlier reviews, studies on the impairment of shape memory properties through various factors, such as aging, compression and hibernation, lubricants, UV light and thermo-mechanical cycling, are extensively reviewed. Apart from summarizing the state-of-the-art in SMP research, recent progress is commented.
Biofilms living on gold (Au) grains play a key role in the biogeochemical cycle of Au by promoting the dispersion of Au via the formation of Au nanoparticles as well as the formation of secondary biomorphic Au. Gold grains from Queensland, Australia, are covered by a polymorphic, organic-inorganic layer that is up to 40 μm thick. It consists of a bacterial biofilm containing Au nanoparticles associated with extracellular polymeric substances as well as bacterioform Au. Focused ion beam (FIB) sectioning through the biofilm revealed that aggregates of nanoparticulate Au line open spaces beneath the active biofilm layer. These aggregates (bacterioform Au type 1) resulted from the reprecipitation of dissolved Au, and their internal growth structures provide direct evidence for coarsening of the Au grains. At the contact between the polymorphic layer and the primary Au, bacterioform Au type 2 is present. It consists of solid rounded forms into which crystal boundaries of underlying primary Au extend, and is the result of dealloying and Ag dissolution from the primary Au. This study demonstrates that (1) microbially driven dissolution, precipitation, and aggregation lead to the formation of bacterioform Au and contribute to the growth of Au grains under supergene conditions, and (2) the microbially driven mobilization of coarse Au into nanoparticles plays a key role in mediating the mobility of Au in surface environments, because the release of nanoparticulate Au upon biofilm disintegration greatly enhances environmental mobility compared to Au complexes only.
Modern EBSD systems perform diffraction pattern “quality” (PQ) calculations, essentially measurements of the contrast of the brighter bands in the pattern above background, for every pattern analyzed. Since the calculations are independent of EBSD indexing, data are generated from all points on the analyzed sample surface, regardless of indexability or the state of the material beneath. EBSD maps generated from PQ data are like microstructurally sensitive SEM images, collected at EBSD speeds and grid resolutions, with contrast arising from phase density, crystal structure, crystallographic orientation, grain boundary location, near-surface plastic strain, coating density/thickness, and to some extent topography. Grain boundaries and other aspects of sample microstructure are readily revealed, so the PQ map is a very useful characterization tool in its own right, and serves as a reference for EBSD maps generated from indexing-derived data, such as orientation, grain boundary character, phase distribution and strain maps.
EBSD is nowadays a common technique for the characterization of crystalline microstructures in scanning electron microscopy. The diffraction patterns are often interpreted by superimposing individual Kikuchi bands which are geometrically described by band edges derived from Braggs law. For the typically very simple crystal structures of technically applied materials, such a simplification of the Kikuchi pattern interpretation works sufficiently well, especially for orientation determinations as a main application of EBSD. The more complex crystal structures, however, are a challenge for EBSD indexing routines which in such cases often fail unpredictably. The use of only the intensities of single reflectors for a description of the Kikuchi band intensity and as a cut-off criterion for a pre-selection of the strongest bands are not satisfactory. Often the result will match too many phases, or there are certain deviations in the intensity prediction which must be adapted manually. This is already problematic if one is absolutely sure that the patterns are originating from the expected phase and it becomes a very questionable procedure for an unknown phase.
Certification report for the reference materials ERM-AE102a, -AE104a, -AE120, -AE121 and -AE122
(2010)
Isotope reference materials are essential to enable reliable and comparable isotope data. Besides the correction of mass fractionation or mass discrimination isotope reference materials are indispensible for validation and quality control of analytical procedures. This article describes the production and certification of a set of five isotope reference materials ERM-AE102a, 104a, AE120, 121 and 122, for boron isotope analysis. The isotopic composition of all materials has been adjusted by mixing boron mother solutions enriched in 10B or 11B with a boron mother solution having natural-like isotopic composition under full gravimetric control. All mother solutions have been analysed for their boron mass fraction as well as their boron isotopic composition by TIMS using IDMS as calibration technique. For all five reference materials the isotopic composition obtained on the basis of the gravimetric data agrees very well with the isotopic composition obtained from different TIMS techniques. Performed stability and homogeneity studies show no significant influence on the isotopic composition as well as on the related uncertainties.
The certified isotope abundances for 10B are 0.29995 (27) for ERM-AE102a and 0.31488 (28) for ERM-AE104a. The certified δ11B values are -20.2 (6) ‰ for ERM-AE120, 19.9(6) ‰ for ERM-AE121 and 39.7 (6) ‰ for ERM-AE122.
Together with the formerly certified ERM-AE101 and -AE103 a unique set of seven certified reference materials (CRM) for boron isotope analysis is now available from BAM.
Neutrons are absorbed particularly by hydrogen containing materials so
they can be used as a tool for visualising heterogeneous density distributions of organic materials. Penetration limits are set by the layer thicknesses and the neutron energies applied. In case of specimens with a flat shape the situation may be encountered that the object only could be penetrated in selected directions. In addition, the overall size may exceed the beam diameter and thus the viewing window if a certain region of interest should be studied by tomography without destroying the integrity of the specimen.
This study shows the capabilities and limits of thermal and fast neutrons to investigate flat wooden specimens such as boards and girders by neutron tomography under such circumstances. Taking projections was impaired either by the limits of penetrability or by the total size of the object. As a consequence, projections were included for reconstruction only from a limited angular range of 90°. It could be shown that an approach based on the slice theorem was capable to visualise structural features along the beam directions while simply omitting the perpendicular ones without causing additional artefacts.
Small samples with a thickness of up to 2 cm but several times broader could be studied with the ANTARES facility of the FRM II neutron source in Garching providing thermal neutrons while larger objects required a beam of higher energy as available in the NECTAR facility of the same institution. The fast (fission) neutrons (1.5 – 2 MeV) of this site allowed investigating an area of interest inside a girder with a cross section of 23.5 x 49 cm². Internal features such as inclusions could be detected as well as a heterogeneous density distribution in glue layers.
In a mutual framework agreement, the two German national institutes BAM (Federal Institute of Materials Research and Testing) and PTB (Physikalisch-Technische Bundesanstalt) agreed upon the development, provision, and dissemination of national measurement standards for chemical analysis via primary reference measuring systems.
Traceability to national standards and international comparability is of key importance for the acceptance of measurement results in metrology.
Nondestructive testing (NDT) methods are applicable in many ways for defect detection as well as optimization of packaging production processes. The visual inspection method is the technique which is mostly used, although neither the customer nor a skilled inspector may be aware of this.
Techniques like ultrasound for wall thickness measurement, the application of x-ray techniques or the use of dye penetrant techniques for crack detection are rather well known to the NDT family. However, acoustic emission techniques can also be helpful for the characterization of packaging materials. In this paper the employment of x-ray computer tomography (CT) for measurement of wall thickness in plastic jerrycans, especially on the edges, and its possible optimization of production processes will be discussed.
A comparison of the CT and ultrasonic examinations of wall thickness and the reliability of this measured data are also important points for the discussion, especially if some safety factors can be derived from the results.
The leakage test is also good for jerrycans, IBCs or other kinds of drums for the transportation and storage of dangerous goods. The disadvantage of this kind of test is that a lack of quality, e.g. wall thickness deterioration, cannot be detected if the wall thickness withstands the internal pressure. Therefore, especially for Quality assurance, the other, previously mentioned techniques are better for a statistical assessment of a batch. This paper is focused on the comparison of different NDT results with special emphasis on the large range of material mechanical properties.
The European research project i-Protect “Intelligent PPE system for personnel in high-risk and complex environments”, supported by the EU 7th Framework Programme, develops an advanced personal protective equipment (PPE) system that will ensure active protection and information support for personnel operating in high risk and complex environments in fire fighting, chemical and mining rescue operations.
Within the project an intelligent underwear for monitoring the rescuers heart rate, body temperature, and respiratory rate will be developed.
Triacetone triperoxide (TATP) is a primary explosive, which was used in various terrorist attacks in the past. For the development of biosensors, immunochemical µ-TAS, electronic noses, immunological test kits, or test strips, the availability of antibodies of high quality is crucial. Recently, we presented the successful immunization of mice, based on the design, synthesis, and conjugation of a novel TATP derivative. Here, the long-term immunization of rabbits is shown, which resulted in antibodies of extreme selectivity and more than 1,000 times better affinity in relation to the antibodies from mice. Detection limits below 10 ng L-1 (water) were achieved. The working range covers more than four decades, calculated from a precision profile. The cross-reactivity tests revealed an extraordinary selectivity of the antibodies—not a single compound could be identified as a relevant cross-reactant. The presented immunoreagent might be a major step for the development of highly sensitive and selective TATP detectors particularly for security applications.
A GPR antenna array was investigated for automated measurement of wave propagation velocity as a measure of the ballast quality. This goes beyond the regular application of conventional radar systems offering only qualitative structural information. The new approach provides a fast NDT method for the classification of ballast fouling. A main advantage of the multi-offset radar is that regular ballast digging for velocity evaluation can be avoided and travel time can be directly transformed into an equivalent depth by using the automatically evaluated velocity. Fast monitoring of ballast fouling condition can reduce maintenance cost significantly by supporting the works necessary for ballast cleaning and furthermore this method reduces interruption time for a better railway service.
A unifying review of bioassay-guided fractionation, effect-directed analysis and related techniques
(2012)
The success of modern methods in analytical chemistry sometimes obscures the problem that the ever increasing amount of analytical data does not necessarily give more insight of practical relevance. As alternative approaches, toxicity- and bioactivity-based assays can deliver valuable information about biological effects of complex materials in humans, other species or even ecosystems. However, the observed effects often cannot be clearly assigned to specific chemical compounds. In these cases, the establishment of an unambiguous cause-effect relationship is not possible. Effect-directed analysis tries to interconnect instrumental analytical techniques with a biological/biochemical entity, which identifies or isolates substances of biological relevance. Successful application has been demonstrated in many fields, either as proof-of-principle studies or even for complex samples. This review discusses the different approaches, advantages and limitations and finally shows some practical examples. The broad emergence of effect-directed analytical concepts might lead to a true paradigm shift in analytical chemistry, away from ever growing lists of chemical compounds. The connection of biological effects with the identification and quantification of molecular entities leads to relevant answers to many real life questions.
GMR sensors are widely used in many industrial segments such as information technology, automotive, automation and production, and safety applications. Each area requires an adaption of the sensor arrangement in terms of size adaption and alignment with respect to the field source involved. This paper deals with an analysis of geometric sensor parameters and the arrangement of GMR sensors providing a design roadmap for non-destructive testing (NDT) applications. For this purpose we use an analytical model simulating the magnetic flux leakage (MFL) distribution of surface breaking defects and investigate the flux leakage signal as a function of various sensor parameters. Our calculations show both the influence of sensor length and height and that when detecting the magnetic flux leakage of µm sized defects a gradiometer base line of 250 µm leads to a signal strength loss of less than 10% in comparison with a magnetometer response. To validate the simulation results we finally performed measurements with a GMR magnetometer sensor on a test plate with artificial µm-range cracks. The differences between simulation and measurement are below 6%. We report on the routes for a GMR gradiometer design as a basis for the fabrication of NDT-adapted sensor arrays. The results are also helpful for the use of GMR in other application when it comes to measure positions, lengths, angles or electrical currents.
Declining European natural gas resources and increasing legislation mean that diversification towards ‘non-conventional gases’ is essential. Accurate and traceable measurements of the composition of non- conventional gases are required to ensure gases can be transported in existing pipeline networks, and used with existing appliances. The EMRP ‘Characterisation of energy gases’ project is successfully developing a metrology infrastructure to underpin these measurements. New standards and methods have been developed for biogas composition, biogas impurities, coal mine gases, refinery gases and environmentally-friendly odorants. The project is set to conclude in 2013 with the challenging analysis of a series of real non-conventional gas samples.
Meteorites are a unique and inspiring material for microstructural studies because if their very specific genesis. Iron meteorites have been formed under unimaginable cooling rates of a few ten Kelvins per million years so that the observable transformation of the formerly huge Fe-Ni single crystals of taenite occurred under nearly-equilibrium conditions. Octahedrites (meteorites having a Ni content between 6...15%) are characterized by ribbons of the low-temperature Fe-Ni phase kamacite separated by rims of residual taenite. This very specific feature is known as Widmanstaetten structure and has been investigated by synchrotron radiation in order to cover a higher volume fraction for a statistically relevant description of orientation relationships. However, plessite – a microstructure mainly consisting of the same phases – reflects the orientation relationship between kamacite and taenite as well. For their characterization, a scanning electron microscope is very suitable in order to investigate crystal orientations or identify phases. Despite the apparently ideal formation circumstances of iron meteorites, Ni concentration profiles prove non-equilibrium conditions. Combined EDS (energy dispersive spectroscopy) and EBSD (electron backscatter diffraction) measurements at a selected plessitic region of the Cape York iron shows that a correlation exists between Ni-concentration and the locally detected orientation relationship.
Globally, cement and concrete experts are at the cutting-edge to sustainable, green, healthy but nonetheless high-performance concrete. Today concrete is not yet well established in Africa, which offers the unique opportunity to build up a cement and concrete market based on the highest available state of technology. As this industry needs high level expertise, a central issue in implementation of skilled technology is crosslinking research institutions and laboratories. It should not be neglected that concrete is a product with low transport ranges. This means that an improved concrete market mainly supports the local economy without exceeding financial drains to the international market. Thus it fosters the fight against poverty, which is an urgent need in most African countries. The project aims to cross-link experts with industry and policy making bodies, aiming to establish sustainable cement and concrete construction in Africa.
A facile and versatile synthetic route for controlling the size and surface potential of organic–inorganic hybrid silica nanoparticles (NPs) is introduced in this paper. For polymer-grafted NPs, the density of polymer chains on the surface is strongly affected by the concentration of precursor. Nevertheless, for condensed NPs, the precursor concentration determines the particle size but not the density of polymer chains on the surface or the adsorption of bovine serum albumin (BSA). Results presented here may have Major implications in biomedical and colloidal chemistry since interfacial and colloidal properties are known to drive several processes associated with nanoparticles in biological media.
The presentation was an invited talk for the final meeting of the Mara Nord Project. Projects purpose is to demonstrate the potential of GPR method use in road condition measurement and rehabilitation planning to the Nordic market. This will be achieved through cooperation between Finland, Sweden and Norway.
The presentation gives an overview of road condition measurement and rehabilitation planning in Germany and several different kind of GPR applications in Germany.
Ultrasonic echo and transmission techniques are used in civil engineering on a regular basis. New sensors and data processing techniques have lead to many new applications in the structural investigation as well as quality control. But concrete structures in the nuclear sector have special features and parameters, which pose problems for the methods and instrumentation currently available, e.g. extreme thickness, dense reinforcement, steel liners or special materials. Several innovative ultrasonic techniques have been developed to deal with these issues at least partly in lab experiments and pilot studies. Modern imaging techniques as multi-offset SAFT have been used e. g. to map delaminations. Thick concrete walls have successfully been inspected, partly through a steel liner. Embedded ultrasonic sensors have been designed which will be used in monitoring networks of large concrete structures above and below ground. In addition, sensitive mathematical methods as coda wave interferometry have been successfully evaluated to detect subtle changes in material properties. Examples of measurements and data evaluation are presented.
A major requirement for the validation of methods assessing the risk associated with engineered nanoparticles (ENPs) is the use of reference materials (RMs). In the present contribution we review available RMs, ongoing projects and characterisation trends in the field. The conclusion is that actual approaches to RMs mostly deal with metrological considerations about single properties of the ENPs, typically their primary size, which can hardly be representative of nanoparticles characteristics in real testing media and therefore, not valid for reliable and comparable toxicological studies. As an alternative, we discussed the convenience and feasibility of establishing multi-parametric RMs for a series of ENPs, focusing on silica nanoparticles (SNPs). As a future perspective, the need to develop RMs based on hybrid nanoparticles is also discussed.
Indirect UV-absorption spectrometry was shown to be a valuable tool for chemical characterization of functionalized carbon nanotubes (CNTs). It complements data from X-ray photoelectron spectroscopy (XPS) or FTIR analysis since it helps to clarify the type and concentration of functional groups. The principles of indirect application of UV-spectrometry and its mathematical interpretation are discussed. Their facile application, together with their adequate sensitivity and high flexibility, make UV-absorption-based approaches a valuable alternative to fluorescence spectrometry. Here, the approach was applied to the chemical analysis of oxidizing substances on CNTs. For this, pristine CNTs of low but finite oxygen content as well as brominated CNTs were analyzed by reaction in suspension with UV-active thiol reagents and a styrene derivative. It was shown that carefully selected reagents allow differentiation and quantification of bromine and generally oxidizing entities like oxygen. For brominated CNTs, it was shown that physisorbed bromine may dominate the overall bromine content.
Luminescence techniques are among the most widely used detection methods in the life and material sciences. At the core of these methods is an ever-increasing variety of fluorescent reporters (i.e., simple dyes, fluorescent labels, probes, sensors and switches) from different fluorophore classes ranging from small organic dyes and metal ion complexes, quantum dots and upconversion nanocrystals to differently sized fluorophore-doped or fluorophore-labeled polymeric particles. A key parameter for fluorophore comparison is the fluorescence quantum yield (Φf), which is the direct measure for the efficiency of the conversion of absorbed light into emitted light. In this protocol, we describe procedures for relative and absolute determinations of Φf values of fluorophores in transparent solution using optical methods, and we address typical sources of uncertainty and fluorophore class-specific challenges. For relative determinations of Φf, the sample is analyzed using a conventional fluorescence spectrometer. For absolute determinations of Φf, a calibrated stand-alone integrating sphere setup is used. To reduce standard-related uncertainties for relative measurements, we introduce a series of eight candidate quantum yield standards for the wavelength region of ~350950 nm, which we have assessed with commercial and custom-designed instrumentation. With these protocols and standards, uncertainties of 5–10% can be achieved within 2 h.
Algal blooms are a frequent phenomenon in nearly all kinds of fresh water. Global warming and eutrophication by waste water, air pollution and fertilizers seem to lead to an increased frequency of occurrence. Many cyanobacteria produce hazardous and quite persistent toxins, which can contaminate the respective water bodies. This may limit the use of the raw water for many purposes. The purification of the contaminated water might be quite costly, which makes a continuous and large scale treatment economically unfeasible in many cases. Due to the obvious risks of algal toxins, an online or mobile detection method would be highly desirable. Several biosensor systems have been presented in the literature for this purpose. In this review, their mode of operation, performance and general suitability for the intended purpose will be described and critically discussed. Finally, an outlook on current developments and future prospects will be given.
One of the important analytical challenges is the fast and reliable trace detection of explosives in the context of security issues, ammunition disposal, and environmental pollution. Antibodies (Ab) are a promising tool for this purpose and the combination with a
surface acoustic wave (SAW) sensor opens the opportunity of highly selective and fast, label-free detection. A robust and sensitive method for the detection of the explosive trinitrotoluene (TNT) was developed. The detection limit was determined to be around 0.5 μg/L. The fast signal response of less than 1 minute shows that this approach is suitable for security and other time-critical applications. In addition, the very low crossreactivity highly reduces the number of false-positives in relation to competing techniques, including sniffer dogs. Due to the multianalyte ability of the SAW system, several explosives might be detected in parallel. Terminal amino groups were functionalized with trinitrophenyl (TNP) groups by reaction with trinitrobenzene sulfonic acid (TNBS). In less than 1 minute, a good signal response was obtained. 50 μL of sample was used. No non-specific interaction with the SAM surface was observed. A complete measuring cycle needed 19 minutes including a surface regeneration step with 50 μL of acetonitrile/water/propionic acid (50:50:1) and 150 μL of SDS solution (0.1 %, pH 1 with 100 mM glycine and 100 mM NaCl). A good long-term stability could be shown for at least 6 hours. Two polyclonal antibodies (R1, R2, affinity purified with Protein A) and a monoclonal antibody (A1.1.1) were tested successfully. A commercially available SAW sensor (sam5 blue, SAW Instruments) was used for liquid handling and detection. Self-assembled monolayers (SAM) of alkanethiol derivatives were
prepared on gold surfaces leading to non-fouling and hydrophilic properties, due to attached polyethylene glycol (PEG) residues. A continuous flow of buffer (phosphate-buffered saline, PBS plus Tween 20) of 100 μL/min was applied to the sensor system. TNT antibodies were pre-incubated with the samples containing traces of explosives. Polyclonal and monoclonal antibodies were tested.
The limit of detection (LOD) was determined to 0.5 μg/L for all three antibodies (3s from 12 replicates).
The advent of simultaneous energy dispersive X-ray spectroscopy (EDS) data collection has vastly improved the phase separation capabilities for electron backscatter diffraction (EBSD) mapping. A major problem remains, however, in distinguishing between multiple cubic phases in a specimen, especially when the compositions of the phases are similar or their particle sizes are small because the EDS interaction volume is much larger than that of EBSD, and the EDS spectra collected during spatial mapping are generally noisy due to time limitations and the need to minimize sample drift. The backscatter electron (BSE) signal is very sensitive to the local composition due to its atomic number (Z) dependence. BSE imaging is investigated as a complimentary tool to EDS to assist phase segmentation and identification in EBSD through examination of specimens of meteorite, Cu dross, and steel oxidation layers. The results demonstrate that the simultaneous acquisition of EBSD patterns, EDS spectra, and the BSE signal can provide new potential for advancing multiphase material characterization in the scanning electron microscope.
Mechanism of porosity growth during homogenisation in single crystal nickel-based superalloys
(2013)
Several mechanisms for porosity growth in single crystal nickel-based superalloys during homogenisation heat treatment have been proposed in the literature. They were carefully checked using different experimental methods, namely quantitative light microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and density measurements. It is shown that the main mechanism is the Kirkendall–Frenkel effect, i.e. generation of voids due to uncompensated efflux of Al atoms from dissolving γ/γ′-eutectic areas. The Al diffusion is supported by the afflux of vacancies from surrounding γ-matrix which results in porosity growth. This conclusion is confirmed by the estimation of the vacancy afflux towards the dissolving eutectic.
Automated electron backscatter diffraction (EBSD) is generally unable to distinguish between multiple cubic phases in a specimen without additional information, such as that obtained by simultaneous energy dispersive X-ray spectroscopy (EDS). Small particles of phases with relatively similar compositions push the limits of phase identification using simultaneous EBSD and EDS, and a mismatch exists between the spatial resolutions of these two techniques due to them having different electron interaction volumes. In a recent paper, the present authors explored using backscatter detectors mounted on top of the EBSD detector to obtain atomic number (Z) contrast images that could be used for phase segmentation in cases where the results from the EBSD and EDS signals remain ambiguous. In the present work, we show that similar information can be obtained from the raw EBSD patterns themselves at higher spatial resolution than was obtained from the backscatter detectors, with the additional advantage of having no spatial mismatch between the data collection grids.
Since the BSE signal depends on many factors, like the chemistry of the phase and the acceleration voltage, the size and position of the detector array is (slightly) different from phase to phase so that an (iterative) post-processing of the stored patterns is highly recommended. The derived BSE signal can be used for phase assignment in high resolution and high speed maps when EBSD fails and/or EDS (energy dispersive spectroscopy) needs too much time for a suitable and parallel signal acquisition.
A concept based on the application of a cube as a general polyhedron is presented for the visualization of point group symmetry. The cube is used to represent both the highest and lowest crystal symmetries, with differences observable as patterns characteristic to each point group. Patterns are generated using direction-specific color keys, which enable the recognition of point group-specific distribution of vectors in an external reference frame. For the visualization of the incoherent hexagonal crystal classes, two twinned cubes are applied in order to generate symmetry operators that would otherwise be missing. The resulting hexagonal dipyramid is described in the frame of a cube, reducing the number of used symmetry operators from 72 to 60. The complete set of 32 polyhedra are suitable, for example, as a visual aid for understanding the crystal symmetry and/or sub- and supergroup relationships.
Pole figures are often used to present crystal orientation data. The huge number of single orientation measurements acquired by electron backscatter diffraction (EBSD) poses a challenge for pole figure representation due to the large number of calculations required. This significantly reduces the speed at which the data may be rotated and affects the ability to switch between different projection types. In the present work, it will be shown that satisfactory representation of orientation data in different projection types can generally be achieved by an imaging of a spherical projection. With this approach, explicit calculation of the projections is no longer required, allowing for both real-time dataset rotation and real-time switching between all projection types relevant to materials science. The technique can be applied to any other directional property distribution, for example, not only for EBSD orientation presentation.
The macro- and microstructure of iron meteorites provide valuable insights into both the inner structure of our planet and the history of our solar system. High speed collision events in the asteroid belt send the meteorites careening toward Earth. The collisions produce unique deformation microstructures. With cooling rates on the scale of a few degrees per million years, iron meteorites can consist of crystal sizes on the order of meters prior to the collision events. These extremely slow cooling rates result in phase transformations occurring at conditions near thermodynamic equilibrium. Preserving meteorite fragments is important for future studies of phase transformations, material behavior at high strain rates, and the origin of the universe.
Among the borates in the Middle European Zechstein Salt Succession boracite Mg3[B7O13Cl] is the most common mineral in quantity and local distribution. An exceptional enrichment is observed in Stassfurt Serie Z2) in the Stassfurth seam K2H. Boracite is to be found in two varieties: individual crystals in cubic, tetrahedral or dodecahedral habit on the one hand and fibrous crystals so-called “stassfurtite” on the other hand. The formation conditions such widely spread borates in the salt succession are ambiguous in two respects. First of all the synthetic formation of boracites is to be made by hydrothermal or melt conditions. Both processes can be suspended for the salt succession. Furthermore the cubic modification is stable above 265°C for the Mg-boracite. The cubic, tetrahedral or dodecahedral habit could be used as a geothermometer, but such conditions can be exclude by the paragenetic minerals, esp. carnallite (MgKCl3 x 6H2O). The chemical composition of orthorhombic, pseudo-cubic boracite depends on the location. Pure Mg-boracite in hexahedral habit and in fibrous habit, so-called “stassfurtite”, occurs in the North Harz region, whereas the Fe-, Mn-, Mg-boracite appears in the South Harz region. Until now the source of boron, the time of formation of crystals, but also the reasons for the differences in habit of the single hexahedral crystals are still unclear. The formation during a diagenetic/metamorphic process is evident. However, the preferred formation in Stassfurt seam could be an indication for the boron enrichment in an early diagenetic process. Furthermore permit the determination of the thermal stability and the volatile content of crystals conclusions to the chemical composition of the fluid. The observed variation suggests that the condition of crystal growth as well as the chemical composition of fluid repeatedly changed over the time. Randomly occuring xenomorpheous anhydrite and magnesite inclusions within single boracite crystals have been interpreted as an indication to factors of chemical milieu during the formation of crystals. The reversible phase transition temperature of the boracite is a linearly function of the iron and manganese content and varies from 265°C for Mg-boracite to 330°C for Fe(Mn)-boracite. The thermal decomposition of boracite is determined by two processes. The decomposition started with a boron-chlorine release (BOCl?), having a maximum rate at 1050°C. Additionally to this release one observes a simultaneous emission of H2O, HCl, HF, CO2 , N2 , SO2 , H2 , and hydro carbons. The results give evidence for the aged approach of a secondary formation of boracite within the complete Stassfurt seam, possibly in connection with the formation of salt diapirs in the Jura and Cretaceous period. The wider environmental distribution of borates is an indication of chemical transport processes within the salt succession. This should be a more important issue in the discussion about the utilisation of salt diapirs for the storage of nuclear waste.
Applications of X-ray refraction to non-destructive characterization of ceramics and composites
(2013)
X-ray refraction is analogous to visible light deflection by matter, with two main differences: 1- convex objects cause divergence (i.e., the refraction index n is smaller than 1), and 2- deflection angles are very small, from a few seconds to a few minutes of arc (i.e., n is near to 1). Trivially but importantly, deflection of X-rays is also sensitive to the orientation of the object boundaries. These features make X-ray refraction techniques extremely suitable to a) detect defects such as pores and microcracks, and quantify their densities in bulk (light) materials, and b) evaluate porosity and particle properties such as orientation, size, and spatial distribution (by mapping). While X-ray refraction techniques cannot in general image single defects, their detectability is simply limited by the wavelength of the radiation.
We will thereby show the application of X-ray refraction 2D mapping (topography) and tomography to different sorts of problems in ceramic science and technology: 1) Sintering of SiC green bodies; 2) Porosity analysis in diesel particulate filter silicates; 3) fiber de-bonding in metal and polymer matrix composites; 4) micro-cracking of glass-precursor -eucryptite. We will see that the use of X-ray refraction analysis yields quantitative results, also directly usable in available models.
Quantifying degradation of collagen in ancient manuscripts: the case of the Dead Sea Temple Scroll
(2013)
Since their discovery in the late 1940s, the Dead Sea Scrolls, some 900 ancient Jewish texts, have never stopped attracting the attention of scholars and the broad public alike, because they were created towards the end of the Second Temple period and the 'time of Christ'. Most of the work on them has been dedicated to the information contained in the scrolls' text, leaving physical aspects of the writing materials unexamined. They are, however, crucial for both historical insight and preservation of the scrolls. Although scientific analysis requires handling, it is essential to establish the state of degradation of these valued documents. Polarized Raman Spectroscopy (PRS) is a powerful tool for obtaining information on both the composition and the level of disorder of molecular units. In this study, we developed a non-invasive and non-destructive methodology that allows a quantification of the disorder (that can be related to the degradation) of protein molecular units in collagen fibers. Not restricted to collagen, this method can be applied also to other protein-based fibrous materials such as ancient silk, wool or hair. We used PRS to quantify the degradation of the collagen fibers in a number of fragments of the Temple Scroll (11Q19a). We found that collagen fibers degrade heterogeneously, with the ones on the surface more degraded than those in the core.
Computer modelling of non-destructive testing methods has come a long
way from the beginnings in the mid 90s to today. Radiographic modelling for
components with higher wall thicknesses, as they are typical for nuclear
applications, must include precise predictions of scattered radiation and its impact
in terms of contrast reduction. Dedicated or general purpose Monte Carlo methods
with the ability to calculate higher order scattering events are the state of the art for
these applications. Aerospace applications, on the other hand, have stronger
requirements on the modelling code's capabilities to import complex CAD
geometries, and can benefit from faster analytical scatter models, limited to first or
second order scattering events. Similar distinctions can be made for the various
approaches proposed to accurately model geometrical and film unsharpness, film
granularity, film responses, film/foil cartridges and photon noise. This article
presents a state-of-the-art review of radiographic modelling from the perspective of
two important application domains with very different requirements, nuclear and
aerospace.
This study focuses on concrete flow in presence of obstacles and develops a mathematical model and a computational approach for SCC flow through reinforced formworks. In order to decrease high computational times needed to simulate castings through reinforced elements, an innovative approach to model the reinforced sections as porous media is proposed here. In the previous work, this numerical model is proved able to simulate the free-surface flow of non-Newtonian fluids through the reinforcement networks. In the present study, the applicability of the model on the concrete flow will finally be proved. The large-scale form-filling experiments with SCC will be conducted and the experiments will be simulated using the proposed numerical model. The numerical model will then be validated through the comparison of the experimental results and the results of the numerical simulations.
The study of protein corona formation on nanoparticles (NPs) represents an actual main issue in colloidal, biomedical and toxicological sciences. However, little is known about the influence of polymer shells on the formation and time evolution of protein corona onto functionalized NPs. Therefore, silicapoly(ethylene glycol) core–shell nanohybrids (SNPs@PEG) with different polymer molecular weights (MW) were synthesized and exhaustively characterized. Bovine serum albumin (BSA) at different concentrations (0.1–6 wt%) was used as model protein to study protein corona formation and time evolution. For pristine SNPs and SNPs@PEG (MW = 350 g/mol), zeta potential at different incubation times show a dynamical evolution of the nanoparticle–protein corona. Oppositely, for SNPs@PEG with MW ≥2000 g/mol a significant suppression of corona formation and time evolution was observed.
Furthermore, AFM investigations suggest a different orientation (side-chain or perpendicular) and Penetration depth of BSA toward PEGylated surfaces depending on the polymer length which may explain differences in protein corona evolution.
We use a dynamic scanning electron microscope (DySEM) to analyze the movement of oscillating micromechanical structures. A dynamic secondary electron (SE) signal is recorded and correlated to the oscillatory excitation of scanning force microscope (SFM) cantilever by means of lock-in amplifiers. We show, how the relative phase of the oscillations modulate the resulting real part and phase pictures of the DySEM mapping. This can be used to obtain information about the underlying oscillatory dynamics. We apply the theory to the case of a cantilever in oscillation, driven at different flexural and torsional resonance modes. This is an extension of a recent work (Schr¨oter et al 2012 Nanotechnology 23 435501), where we
reported on a general methodology to distinguish nonlinear features caused by the Imaging process from those caused by cantilever motion.
Mechanically interlocked molecules (MIMs) such as rotaxanes and catenanes are capable of mechanical motion on the nanoscale and are therefore promising prototypes for molecular machines in recent nanotechnology. However, most of the existing examples are isotropically distributed in solution, which prohibits concerted movement and with it the generation of macroscopic effects. Thus, arranging them in ordered arrays is of huge interest in recent research. We report the deposition of quite densely packed multilayers of tetralactam macrocycles on gold surfaces by metal-coordinated layer-by-layer self-assembly. Linear dichroism effects in angle-resolved NEXAFS spectra indicate a preferential orientation of the macrocycles. The sequence of the metal ions can be programmed by the use of different transition metal ions at each deposition step. Additionally, reversible on-surface pseudorotaxane formation was successfully realized by repeated uptake and release of axle molecules inside the macrocycles cavities.
Isotope reference materials are essential to enable reliable and comparable isotope data. Besides the correction of mass fractionation or mass discrimination, isotope reference materials are indispensible for validation and quality control of analytical procedures. This report describes the production and certification of two isotope reference materials, ERM-AE123 and ERM-AE124, for boron isotope analysis. The isotopic composition of ERM-AE123 is the unaltered natural-like isotopic composition of the base material. The isotopic composition of ERM-AE124 has been adjusted by mixing two boron stock solutions enriched in 10B and 11B respectively under full gravimetric control. All stock solutions have been prepared fully under gravimetrical control. The corresponding boron isotopic composition has been analysed by TIMS. For both reference materials the isotopic composition obtained on the basis of the gravimetric data agrees very well with the isotopic composition obtained by TIMS. The certified isotope abundances for 10B are 0.19832 (21) for ERM-AE123 and 0.96006 (6) for ERM-AE124. Together with the formerly certified ERM-AE101, -AE102a, -AE103, -AE104a, -AE120, -AE121 and AE122, a unique set of nine certified reference materials (CRM) for boron isotope analysis is now available from BAM covering a range for the 10B isotope amount fraction from 0.2 to 0.96 and for the δ11B value from -20 ‰ to +40 ‰.
This survey will discuss current and emerging isothermal and rapid polymerase chain reaction (PCR) based nucleic acid amplification methods for patient near diagnostics. To assess the clinical need of rapid diagnostics for infectious diseases based on nucleic acid tests (NATs) we performed and analysed a questionnaire among laboratories participating in corresponding INSTAND ring trials for external quality assurance. The questions concerning new amplification technologies like isothermal nucleic acid amplification, potentially suited to significantly decrease turnaround times, were complemented by questions to evaluate the present status of NATs. Besides end-users, companies were also addressed by sending out a manufacturer specific questionnaire. Analysis of the answers from 48 laboratories in 14 European countries revealed that a much shorter turnaround time is requested for selected pathogens compared to about 2 h or longer when applying temperature cycling amplification, i.e. PCR. In this context, most frequently mentioned were MRSA, norovirus, influenza A and B viruses, cytomegalovirus (CMV) as well as hepatitis B virus (HBV) and hepatitis C virus (HCV). At present, 8% of the laboratories having participated in this survey apply isothermal amplification of nucleic acid to identify infectious pathogens.
The synthesis of the polymorphic cocrystal caffeine:anthranilic acid was investigated to obtain a better understanding of the processes leading to the formation of different polymorphic forms. In the case of these cocrystal polymorphs synthesized by liquid-assisted grinding a distinct influence of the dipole moment of the solvent was found. A pre-coordination between the solvent molecules and the caffeine:anthranilic acid cocrystal could be identified in the formation of form II. In the case of form II the solvent can be regarded as a catalyst. The formation pathway of each polymorph was evaluated using synchrotron X-ray diffraction.
The vibrational density of states of a series of homologous triphenylene-based discotic liquid crystals HATn (n = 5, 6, 8, 10, 12) depending on the length of the aliphatic side chain is investigated by means of inelastic neutron scattering. All studied materials have a plastic crystalline phase at low temperatures, followed by a hexagonally ordered liquid crystalline phase at higher temperatures and a quasi isotropic phase at the highest temperatures. The X-ray scattering pattern for the plastic crystalline phase of all materials shows a sharp Bragg reflection corresponding to the intercolumnar distance in the lower q-range and a peak at circa 17 nm-1 related to intracolumnar distances between the cores perpendicular to the columns as well as a broad amorphous halo related to the disordered structure of the methylene groups in the side chains in the higher q-range. The intercolumnar distance increases linearly with increasing chain length for the hexagonal columnar ordered liquid crystalline phase. A similar behaviour is assumed for the plastic crystalline phase. Besides n = 8 all materials under study exhibit a Boson peak. With increasing chain length, the frequency of the Boson peak decreases and its intensity increases. This can be explained by a self-organized confinement model. The peaks for n = 10, 12 are much narrower than for n = 5, 6 which might imply the transformation from a rigid system to a softer one with increasing chain length. Moreover the results can also be discussed in the framework of a transition from an uncorrelated to a correlated disorder with increasing n where n = 8 might be speculatively considered as a transitional state.
The current furfural production yield is low due to the use of non-selective homogeneous catalysts and expensive separation. In this work, partially hydroxylated MgF2 catalysts, synthesized using different water contents, were screened during xylose dehydration in watertoluene at 160 °C. The different Lewis/Brønsted ratios on the MgF2 catalysts showed that under-coordinated Mg can isomerize xylose to xylulose, whilst the surface OH-groups were responsible for the dehydration reactions. The presence of glucose as a co-carbohydrate reduced the furfural selectivity from 86 to 81%, whilst it also led to high 5-hydroxymethylfurfural selectivity. The tests catalyzed by MgF2 in combination with simultaneous N2-stripping showed that a furfural selectivity of 87% could be achieved using low xylose loadings. Moreover, the catalysts regenerated by H2O2 showed high activity during the dehydration tests in watertoluene at 160 °C.
Genetic transformation of Knufia petricola A95 - a model organism for biofilm-material interactions
(2014)
We established a protoplast-based system to transfer DNA to Knufia petricola strain A95, a melanised rock-inhabiting microcolonial fungus that is also a component of a model sub-aerial biofilm (SAB) system. To test whether the desiccation resistant, highly melanised cell walls would hinder protoplast formation, we treated a melanin-minus mutant of A95 as well as the type-strain with a variety of cell-degrading enzymes. Of the different enzymes tested, lysing enzymes from Trichoderma harzianum were most effective in producing protoplasts. This mixture was equally effective on the melanin-minus mutant and the type-strain. Protoplasts produced using lysing enzymes were mixed with polyethyleneglycol (PEG) and plasmid pCB1004 which contains the hygromycin B (HmB) phosphotransferase (hph) gene under the control of the Aspergillus nidulans trpC. Integration and expression of hph into the A95 genome conferred hygromycin resistance upon the transformants. Two weeks after plating out on selective agar containing HmB, the protoplasts developed cell-walls and formed colonies. Transformation frequencies were in the range 36 to 87 transformants per 10 µg of vector DNA and 106 protoplasts. Stability of transformation was confirmed by sub-culturing the putative transformants on selective agar containing HmB as well as by PCR-detection of the hph gene in the colonies. The hph gene was stably integrated as shown by five subsequent passages with and without selection pressure.
Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes.