Analytische Chemie
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- 2010 (14) (entfernen)
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- Englisch (14) (entfernen)
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- Electron backscatter diffraction (3)
- Zinc borate (2)
- Acoustoelasticity (1)
- Active polymer (1)
- Aging (1)
- Aryl phosphate (1)
- Bisphenol-A bis(diphenyl)phosphate (BDP) (1)
- Boron (1)
- Computed tomography (1)
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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.
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.
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.
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.
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.
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.
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.
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.
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.