Analytische Chemie
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Zur Bestimmung des Feuchtezustands und insbesondere der Belegereife von Estrichfußböden kommen in Deutschland zerstörende Prüfverfahren zum Einsatz, die eine punktuelle Probenahme erfordern. Hierbei ergeben sich immer wieder Fehlinterpretationen, da zum einen die Probenahme selbst zu einer Veränderung des Feuchtezustands führt und zum anderen, weil die Verfahren an sich mitunter ungenau sind (z.B. abhängig von der Estrichzusammensetzung). Zusammen mit vier Forschungsinstituten und dem Industriepartner Bosch wurden an der BAM zerstörungsfreie Prüfverfahren auf deren Tauglichkeit zur Estrichfeuchtemessung untersucht und mit den herkömmlichen zerstörenden Verfahren verglichen.
Für diesen Versuch kamen verschiedene geophysikalische Verfahren zum Einsatz, darunter Nuklear Magnetische Resonanz (NMR), elektrische Widerstandsmessungen und Impulsradar (GPR). Es wurden neun verschiedene Estrichsorten hergestellt und während der Trocknungsphase bei Konstant-Normklima gelagert. Diese wurden sowohl zerstörend als auch zerstörungsfrei mit den o. g. Verfahren untersucht. Gleichzeitig wurden die Masseänderungen der Proben zur Bestimmung des integralen Feuchtehalts aufgezeichnet.
Die Ergebnisse zeigen zum einen, dass das Abtrocknungsverhalten von zementgebundenen Estrichen grundsätzlich unterschiedlich von dem anhydritgebundener Estriche ist. Während sich bei ersteren zügig ein deutlicher Feuchtegradient über die Höhe der Proben einstellt, verläuft dieser bei der zweiten Probengruppe sehr flach. Dies lässt sich vor allem in den NMR Daten räumlich hochaufgelöst nachvollziehen - die Datenakquise erfolgte mit einer NMR MOUSE PM 25. Ein ähnliches Bild ergibt sich auch aus den elektrischen Widerstandsmessungen, die mittels sog. Multi-Ring-Elektroden (MRE) durchgeführt wurden. MRE bezeichnen als Vertikalprofil angeordnete Ringelektroden mit einem Abstand von ca. 1-2 mm, zwischen denen jeweils Zwei-Punkt Widerstandsmessungen durchgeführt werden. Bei sehr geringen Feuchtegehalten (z.T. auch um die Belegereife) waren mit dieser Methode jedoch wegen der zu hohen Übergangswiderstände nur bedingt Messungen möglich. Im Gegensatz zu NMR und MRE sind mit dem Radarverfahren (2 GHz Antenne) keine tiefenbezogenen Aussagen möglich. Jedoch lässt sich über eine Amplitudenauswertung von direkter und an der Rückwand reflektierter Welle teilweise eine Aussage über Restfeuchtigkeit im Volumen treffen. Ebenso zeigt die Laufzeitdifferenz der beiden Wellen eine starke Abhängigkeit vom Feuchtegehalt.
In Germany there is an existing built infrastructure worth about 50 trillion Euros. The expected lifetimes of individual structures are up to 100 years. Considerable costs (annually about 35 billion Euros, the trend continues upwards) are involved in order to maintain and rehabilitate both residential as well as transportation infrastructure buildings. Most damages we observe on our built infrastructure are moisture-induced processes. Consequently reliable moisture measurement tools a highly needed for meaningful building diagnosis investigations. The optimal moisture measuring technique would be non-destructive, fast, repeatable, reliable, independent of steel in the vicinity, the surface condition or possible salt loads of the material under test. Since this is unfortunately not the case for any non-destructive method, it is often very difficult to decide for users which method to use for the particular testing problem. The only standardized methods in Germany are the “direct” and destructive Darr- and the CM tests. Although they can be highly accurate (when handled with care during the sampling), they deliver only punctual information and cannot be used for monitoring. The other, non-destructive methods are based on the change in humidity-dependent physical material properties. The underlying physics, their particular advantages and disadvantages are discussed in this paper.
The surface chemistry / functionalization of nanomaterials and microparticles largely controls the stability of these materials as well as their solubility and subsequent biofunctionalization and their interactions with biological systems. Moreover, in the case of some nanomaterials like semiconductor quantum dots or lanthanide-based upconversion nanocrystals, the ligand shell strongly affects their optical properties, e.g., via passivation of surface states and traps that favor luminescence quenching or the protection of surface atoms from quenching water molecules. This renders analytical methods for the quantification of surface groups like functionalities very important. Targets of broad interest are here amino, carboxyl, alkine and maleimide groups used for common bioconjugation reactions and typical ligands like thiols and polyethylene glycol (PEG) molecules of varying length, used for the tuning of material hydrophilicity and biocompatibility, minimization of unspecific interactions, prevention of biofouling, and enhancement of blood circulation times as well as surface-bound biomolecules like streptavidin or other biomolecules relevant e.g., for diagnostic assays. Here, we focus on simple optical methods relying on standard laboratory instrumentation, validated by method comparison and/or mass balances and present examples for their use for the characterization of different types of nanomaterials and microparticles.
Luminescence-based detection methods, ranging from fluorescence spectroscopy for photophysical and mechanistic studies over sensing applications, chromatographic separation techniques and the microarray technology with fluorescence detection to fluorescence microscopy, flow cytometry, single molecule spectroscopy, and molecular imaging to integrating sphere spectroscopy, are among the most widely used methods in the life and material sciences. This is due to e.g., their unique sensitivity enabling the detection of single molecules, potential for multiplexing, ease of combination with spatial resolution, and suitability for remote sensing. Many of these advantages are closely linked to the choice of suitable molecular and nanoscale fluorescent reporters, typically required for signal generation. This includes organic dyes without and with sensor function, fluorophore-encoded polymeric and silica nanoparticles as well as nanocrystalline systems like semiconductor quantum dots and upconversion phosphors, emitting in the visible (vis), near-infrared (NIR), and IR (infrared). Current challenges present the environment sensitivity of most fluorophores, rendering fluorescence spectra, measured intensities/fluorescence quantum yields, and fluorescence decay kinetics matrix-dependent, and instrument-specific distortions of measured fluorescence signals that need to be considered for quantification and comparability of data, particularly fluorescence spectra.
Here, current applications of luminescence-based methods and different types of reporters will be presented. In this context, suitable spectroscopic tools for the characteri-zation of the optical properties of fluorescent reporters and fluorophore-encoded microparticles, analytical tools for the determination of the surface chemistry of different types of particles, and different multiplexing strategies will be discussed.
The reliability of wheel set axle testing is of high importance because small discontinuities caused during manufacturing or rock fall impacts during operation might cause growing cracks during the operation load cycles. While most of the axles are tested by automated UT-systems today, the basic education of railway NDT operators is still manual testing providing the basic understanding and skills for the operators. In Germany it is a common rule that NDT operators in the railway branch need to refresh their knowledge and skills every five years including a refresh examination. The testing results from these exercises and from a parallel round robin test have been sampled at the DGZfP Railway Education Centre in Wittenberge for a period of about 5 years. The results of the operators written in test record sheets were compared with the “true” test crack or notch position in the axles used for examination. In this way the testing results could be categorized into “hits” and “misses” and the “hits” were further evaluated due to correct position and adequate amplitude height. Considering some thousand indications documented by the operators during the refresh examination and comparing transition bow, shaft and seat it was a highlight to see that the operators reach their best detection rate in the transition bow of the wheel axle set while this is often the most difficult part concerning the UT-echoes. Fortunately this is due to their raised awareness in the transition bow region because this is the most dangerous region with respect to fracture mechanics.
For two selected axles the experimental set up of 45° and 70° inward and outward UT-testing were also simulated showing clearly the difficulties of the UT-echoes detection of some specific test defects.
In the last two decades automated ultrasonic inspection devices took over a lot of applications that prior have been carried out using manual inspection with the evaluation of A-scans only. In parallel phased array systems have been developed and brought to the market which offer detailed and fast control over the sound field. When applying automated inspection phased array systems for UT measurements imaging of the recorded data in combination with the probe positioning data is used for the evaluation of inspections. B-Scan, C-Scan and S-Scan images are typically used with this setup.
For more sophisticated applications with linear arrays echo tomography and syntethic aperture focusing technique (SAFT) are well known methods and often applied for high resolution image reconstruction. Since channel count of phased array systems is constantly rising, matrix arrays with up to 256 elements entered the market. Signal processing in the matrix domain became 3D. Since some years the Total Focusing Method (TFM) is an additional imaging tool for these type of application. It is based on the Full Matrix Capture (FMC) using the elements of phased array probes as separate transmitters and receivers.
In this contribution we discuss the common ground of SAFT and TFM as well as the differences between these imaging tools. The combined use of automated inspection, matrix arrays and signal processing for high resolution measurements is a challenging task where a very long parameter list has to be taken into account. Under which conditions which elements of the full matrix should be taken for the reconstruction for best results?
Based on examples taken from measured and simulated echo signals it will be shown how image resolution can be optimized in dependence of different parameters like the distance between transmitters and receivers and their directivity patterns, the depth of echo source and the specimen geometry.
Ray tracing boudary value problems: simulation and SAFT reconstruction for ultrasonic testing
(2016)
The application of advanced imaging techniques for the ultrasonic inspection of inhomogeneous anisotropic materials like austenitic and dissimilar welds requires information about acoustic wave propagation through the material, in particular travel times between two points in the material. Forward ray tracing is a popular approach to determine traveling paths and arrival times but is ill suited for inverse problems since a large number of rays have to be computed in order to arrive at prescribed end points. In this contribution we discuss boundary value problems for acoustic rays, where the ray path between two given points is determined by solving the eikonal equation. The implementation of such a two point boundary value ray tracer for sound field simulations through an austenitic weld is described and its efficiency as well as the obtained results are compared to those of a forward ray tracer. The results are validated by comparison with experimental results and commercially available UT simulation tools. As an application, we discuss an implementation of the method for SAFT (Synthetic Aperture Focusing Technique) reconstruction. The ray tracer calculates the required travel time through the anisotropic columnar grain structure of the austenitic weld. There, the formulation of ray tracing as a boundary value problem allows a straightforward derivation of the ray path from a given transducer position to any pixel in the reconstruction area and reduces the computational cost considerably.
Quantification of rock structures with high resolution X-Ray μ-CT for laboratory SIP measurements
(2016)
Spectral Induced Polarization (SIP) measurements are used in many different ways to characterize natural rocks and soils. Main foci of interest are the enhanced characterization of the causes of IP-effects in clastic rocks (especially sandstones), the interactions between the matrix-fluid-system and within the electrical double layers as well as the correlation with “classical” petrophysical parameters, such as specific surface area, permeability, mercury intrusion capillary pressure (MICP) and others. Nevertheless, for all of these investigations, knowledge of the inner structure of the sample material is essential in order to create reliable and validated models as well as to interpret and to assess the data most completely. Unfortunately, many of the methods used, to get access to the inner structure of rocks are destructive (e.g. MICP, thin sectioning, etc.) and the valuable sample is lost. In addition, data is either of volume integrated nature or only available for the 2D case and the usage of sister cores does not necessarily lead to reliable results. In this paper, the authors showcase the possibilities of non-destructive and three dimensional X-ray computed tomography and of enhanced image analysis capabilities for the quantification of rock structures at the pore scale.
Permeability estimation from spectral induced polarization (SIP) measurements is based on a fundamental premise that the characteristic relaxation time (t) is related to the effective hydraulic radius (reff) controlling fluid flow. The approach requires a reliable estimate of the diffusion coefficient of the ions in the electrical double layer. Others have assumed a value for the diffusion coefficient, or postulated different values for clay versus clay-free rocks. We examine the link between t and reff for an extensive database of sandstone samples where mercury porosimetry data confirm that reff is reliably determined from a modification of the Hagen-Poiseuille equation assuming that the electrical tortuosity is equal to the hydraulic tortuosity. Our database does not support the existence of 1 or 2 distinct representative diffusion coefficients but instead demonstrates strong evidence for 6 orders of magnitude of variation in an apparent diffusion coefficient that is well correlated with both reff and the specific surface area per unit pore volume (Spor). Two scenarios can explain our findings: (1) the length-scale defined by t is not equal to reff and is likely much longer due to the control of pore surface roughness; (2) the range of diffusion coefficients is large and likely determined by the relative proportions of the different minerals (e.g. silica, clays) making up the rock. In either case, the estimation of reff (and hence permeability) is inherently uncertain from SIP relaxation time.
Moisture measurement methods
(2016)
Moisture can cause imperfect sealings, faulty roof constructions, cracks and other kind of damages. For measuring the moisture in construction materials like concrete and screed, there are destructive(direct) and non-destructive(indirect) methods, that can be used. This presentation gives an overview and a comparison of these methods.
Die regelmäßige Überprüfung von Eisenbahnradsatzwellen auf betriebsbedingte Schädigungen ist ein fester Bestandteil des Instandhaltungskonzeptes von Eisenbahnfahrzeugen. Insbesondere bei hohen Achslasten und hohen Rotationsgeschwindigkeiten ist eine detaillierte regelmäßige Prüfung notwendig. In den letzten Jahren wurden für diese Prüfaufgabe mechanisierte Ultraschallprüfsysteme entwickelt, erfolgreich eingeführt und etabliert. Für eine Weiterentwicklung dieser Technologie stehen die Themen Erhöhung der Auflösung, Reduzierung von Oberflächen- und Störeinflüssen, Verkürzung von Prüfzeiten, Verbesserung der POD, Verlängerung von Inspektionsintervallen, Vereinfachung der Auswertung und die Möglichkeit der Durchführung von Analyseprüfungen im Vordergrund. Es werden Ansätze und neue Konzepte zur Lösung dieser Herausforderungen vorgestellt.
Der einwandfreie Zustand der Radsätze von Schienenfahrzeugen ist von größter Bedeutung für den sicheren Betrieb. Die Radsatzwellen werden durch eine große Zahl von Lastwechseln individuell unterschiedlich beansprucht. Dabei spielen viele Einflüsse wie äußere statische und dynamische Lasten, innere Lasten aufgrund von Unwuchten und inneren Spannungen und Umweltbedingungen entscheidende Rollen. Eine regelmäßige Prüfung ist daher obligatorisch. BTD entwickelt im Rahmen eines MNPQ-Projektes in Kooperation mit der BAM eine Phased Array Technik zur automatisierten Prüfung von Radsatzwellen im eingebauten Zustand. Die schwierigen Ankoppelbedingungen aufgrund der begrenzten Zugänglichkeit, der komplexen Geometrie sowie Farbschichten und Schmutz auf der Radsatzwelle stellen hierbei große Herausforderungen dar. Zu deren Bewältigung werden neben optimierten Prüfköpfen, einer in die Wasservorlaufstrecke integrierten akustischen Linse und einer speziellen Ankoppeltechnik auch Signalverarbeitungsalgorithmen eingesetzt. Die Darstellung der Signalverarbeitung ist der Schwerpunkt dieses Beitrages. Mit Hilfe von Messdatensätzen präparierter Testwellen werden verschiedene Algorithmen erprobt und hinsichtlich der Stabilität, dem Verhalten bezüglich der Ankoppelschwankungen und veränderter Wellengeometrien und der Fähigkeit zur automatischen Unterscheidung von Fehler- und Formanzeigen bewertet. Letztlich wird die beste Lösung im entwickelten Prüfsystem eingesetzt.
A comprehensive characterization of plasma modified polymer surfaces or plasma-polymerized thin films needs access to parameters as
- concentration of saturated/unsaturated carbon species (e.g. aromaticity) or other double bonds as C=N or C=O,
- branching, and
- losses of crystallinty or other degrees of structural order.
Furthermore the complex ageing phenomena of plasma modified polymers/plasma-polymers and the measurement of an in-depth distribution of chemical species are challenges for the analyst. The talk will display selected examples where such challenges have been met by using advanced methods of surface chemical analyses as Photoelectron Spectroscopy with variable excitation energy (“SyncXPS”), X-ray Absorption Spectroscopy (NEXAFS) at C, N and O K-edges and Time-of-Flight Secondary Mass Spectroscopy (ToF-SIMS) combined with Principal Component analysis (PCA).
Der Einsatz moderner Prozessanalysentechnik führt zu einer Datenflut, deren Verarbeitung und Nutzung häufig nicht ohne den Einsatz von Chemometrie zu realisieren ist. Dafür stehen zahlreiche multivariate Verfahren, wie z.B. Hauptkomponentenanalyse (PCA) und Regressionsanalyse (PLSR) für die Klassifizierung und für die quantitative Analyse zur Verfügung. Darüber hinaus können in Spezialfällen, insbesondere in der Spektroskopie, Methoden des „Indirect Hard Modeling“ eingesetzt werden. Anhand einer Industrie-relevanten Reaktion, der Hydroformylierungsreaktion zur Bildung langkettiger Aldehyde aus der Reaktion von Alkenen und Synthesegas, die sowohl im Labormaßstab als auch in einer Miniplant in Kooperation mit der TU Berlin untersucht wurde, werden Kalibrationsstrategien (Design of Experiment, DoE) und Auswertungsansätze mittels PLSR prozessbegleitender Raman Spektren dargelegt. Auf Grundlage des chemometrischen Ansatzes ist eine on-line Überwachung der Reaktion hinsichtlich der Hauptreaktanden, 1-Dodecene und 1-Tridecanal, möglich. Weiterhin konnte mittels Raman Spektroskopie die Bildung eines unerwünschten Nebenprodukts nachgewiesen werden.
A round robin test on flash thermography was organized within the scope of a standardization research project. This test gives information on reliability, comparability and efficiency of different testing situations. Data recorded on metal and CFRP test specimens with flat bottom holes (FBH) were analysed by evaluating the detectability and by calculating the signal-to-noise ratio (SNR) of the defect signatures as a function of defect parameters. For the investigation of the influence of material properties on the spatial resolution as well as on penetration depth, test specimens made of steel and copper with crossed notches and a notch ramp were constructed and investigated. Here, the minimum resolvable notch distance and the maximum detectable depth of the ramp were analysed.
Novel air-coupled ultrasonic transducer combining the thermoacoustic with the piezoelectric effect
(2016)
In recent years, there has been an increasing industrial demand for one-sided inspection of various structures by means of air-coupled ultrasonic technique. Lightweight structures based on carbon-fibre-reinforced polymers may have very complex shapes, making air-coupled transmission difficult or even impossible. The inspection of concrete structures is another example where one-sided inspection is required.
To address these challenges a new type of transducer for air-coupled pulse-echo inspection was developed, which unites two principles: thermoacoustic emission and piezoelectric reception. The thermoacoustic emitter is a titanium electrode with a thickness of several tens of nanometer. This electrode was deposited onto charged cellular polypropylene, which serves as a piezoelectric receiver. The thermoacoustic transmission is based on a transformation of the thermal energy of an electrically heated electrode into the acoustic energy of an ultrasonic wave. Thermoacoustic emitters provide resonance-free behaviour and thus extremely broadband pulses. Charged cellular polypropylene is piezoelectric due to the polarization of its cells and it is well matched to air, with a Young modulus in the order of magnitude of MPa. In this contribution we present some pulse-echo measurements with the first prototypes of the combined thermoacoustic-piezoelectric transducer.
Dual orthogonal functionality in a single material is highly desirable in many fields such as bio-imaging, sensing, coating or diagnostic and therapy. However, combining two different functionalities in a precise and controlled way is still a challenging task.
Here we present how simply dual functional hybrid nanoparticles consisting of a silica core with a fluorescent and a thermoresponsive polymeric layers can be prepared. As a first step of this work, silica core particles were coated by a fluorescent layer using surface-initiated reversible addition-fragmentation chain transfer polymerization. Afterwards, the fluorescent silica nanoparticles were completely enclosed in a switchable protective coating made of thermoresponsive poly(N-isopropylacrylamide). The thermoresponsive poly(N-isopropylacrylamide) changes its properties with varying the surroundings temperature and this behavior is reversible and controllable. To the best of our knowledge these types of hybrid dual functional core-shell-shell nanoparticles have not yet been prepared, despite the prospect of many potential applications.
Energiedispersive Röntgenspektroskopie (EDX) ist eine der meist verbreiteten Methoden zur Bestimmung der chemischen Zusammensetzung von Festkörpern und dünnen Schichten. Durch die technologische Weiterentwicklung energiedispersiver Röntgenspektrometer wurde die Leistungsfähigkeit auch im niederenergetischen Bereich unter 1 keV verbessert. Geeignete Testmaterialien zur Überprüfung der Leistungsfähigkeit im niederenergetischen Bereich in Übereinstimmung mit ISO 15632 sind kaum vorhanden und basieren hauptsächlich auf C K und F K Linien. Um gültige Resultate aus akkreditierten und zertifizierten Prüf- und Kalibrierlaboratorien in Übereinstimmung mit ISO/IEC 17025 zu gewährleisten sind regelmäßige Funktionsprüfungen der Spektrometer notwendig.
In einer Machbarkeitsstudie wurde die Eignung einer bestimmten Substanz-klasse, nämlich ionische Flüssigkeiten, als Referenzmaterial zur routinemäßi-gen Überprüfung der Energieskala, der Energieauflösung und der Spektrometer Effizienz untersucht. Es kann gezeigt werden, dass mit einer einzigen Messung an einem einzigen Referenzmaterial mehrere Geräteparameter überprüft werden können. Damit ist es im niederenergetischen Bereich möglich regelmäßige Funktionsprüfungen von Spektrometern durchzuführen, aber auch die Leistungsfähigkeit verschiedener Spektrometer zu vergleichen. Beides kann sehr effizient durch einen einfachen qualitativen Vergleich mehrerer Spektren erreicht werden. Durch die Verwendung von ionischen Flüssigkeiten als Referenzmaterial, deren Stöchiometrie genau bekannt ist bzw. zertifiziert werden kann, können eventuell sogar die gängigen Modelle zur Matrixkorrektur validiert werden. Auch wäre eine Neubewertung von Fundamentalparametern (Fluoreszenzausbeute, Massenschwächungskoeffizienten usw.) von Elementen niedriger Ordnungszahl möglich.
Scanning Electron Microscopy (SEM) represents the mostly widespread method available in analytical laboratories dedicated to the characterization of physical properties such as morphology of various solid materials from ‘micro-’ down to the nanometre scale. The use of secondary electrons excited by a sharply, nm-focussed primary electron beam enables at any modern SEM to image objects with high in-depth and lateral sensitivity, i.e. with high spatial resolution. Hence, e. g. nanoparticles (NPs) are able to be easily characterized with respect to their individual size and shape, but also to the morphology of their surface.
By preparing the nano-objects on thin membranes as electron transparent samples it is possible to perform electron microscopy in the transmission mode (TEM and TSEM). The corresponding transmission (i.e. mass-thickness) contrast reveals in-depth information, but is also well suited for dimensional measurements in the 2D projection image. Both the surface sensitive mode and the transmission one are meanwhile available at any modern SEM. If an X-ray spectrometer is attached to an electron microscope, it is possible to analyse the characteristic X-rays induced by electron bombardment. Most electron microscopes have attached an energy dispersive X-ray spectrometer (EDX) so that EDX elemental maps can be carried out. Recent technological developments of high throughput EDS detectors and their advantages regarding high-resolution X-ray analysis down to the nm range are reviewed.
High-resolution micrographs (SEM, TSEM, TEM) and corresponding X-ray elemental maps on various representative nanoparticles, but also layered samples prepared in cross-section, will be presented and discussed. The importance of selecting the best suited analysis conditions will be highlighted. Also other, often challenging, topics such as sample preparation and image data processing will be critically addressed by practical examples. Further analytical techniques able to be employed at an electron microscope, like cathodoluminescence (CL) or micro-X-ray fluorescence (µXRF) will be briefly surveyed.