Characterization of Ge–Bi–S glass by thermal, electrical, switching and optical measurements

A study of the synthesized Ge22.5Bi7S70.5 glassy system has been carried out. Differential thermal analysis data indicate the retention in the as-quenched sample of two amorphous phases. Thermal conductivity, , measurements on bulk sample reveal that the main contribution to is due to phonon thermal conductivity. Thermal evaporation of the synthesized ingot gives films with Ge20.7Bi6.8S72.5 as composition. The values of the activation energy and the pre-exponential factor calculated from the direct current electrical conductivity above 53 °C suggest that carrier conduction occurred between extended states in these films. The I–V characteristics in the off-state and the switching phenomenon are investigated. A memory switch with a threshold voltage decreasing with temperature is detected for the studied films. Optical parameters such as absorption coefficient, optical gap and refractive index are also determined. Comparison with binary Ge–S glass reveals that the addition of Bi introduces additional absorbing states at band edges. © 1998 Kluwer Academic Publishers     

Structural behavior and inter-layer displacements in CFRP plated steel beams – Optical measurements,analysis, and comparative verification

The linear elastic structural behavior of steel beams strengthened with externally bonded composite materials is experimentally and analytically investigated. The paper focuses on the full-field inter-layer relative displacements between the beam and the FRP layer. Such displacements result from the interaction between the adhesively bonded components and it is the integrated outcome of the interfacial conditions and the deformability of the adhesive. As such, it is commonly adopted as the state variable in simplified bond shear stress–slip representations. This aspect, as well as other aspects of the global and localized structural response, is analytically and experimentally quantified. The experiment includes a simply supported steel beam strengthened with a CFRP plate. A 3D image correlation technique with sequential measurements is used for the assessment of the full-field inter-layer displacements along the beam. The analysis adopts a high order modeling approach that accounts for the 2D stress and displacement fields through the depth of the adhesive and a 1D shear stress–slip approach using only a linear increasing branch. The comparison between the results provides validation of the analytical and experimental capabilities with emphasis on the inter-layer effects. One of the interesting findings which is discussed and explained in this paper is the fact that the slip values calculated with the shear stress–slip approach are notably different from the ones that can be measured experimentally and determined by the high order model.     

Annealing study of palladium–silver dental alloys: Vickers hardness measurements and SEM microstructural observations

Three Pd–Ag dental alloys for metal-ceramic restorations, W-1 (Ivoclar Vivadent), Rx 91 (Pentron) and Super Star (Heraeus Kulzer), were subjected to isothermal annealing for 0.5 hr periods in a nitrogen atmosphere at temperatures from approximately 400 ^∘ to 950 ^∘ C. The annealing behavior was investigated by Vickers hardness measurements (1 kg load) and SEM microstructural observations. The highest Vickers hardness occurred at approximately 700 ^∘ C for W-1 and 650 ^∘ C for Rx 91. For Super Star, there were two peaks in hardness at approximately 500 ^∘ and 650 ^∘ C. Additional use of light indenting loads (25 g for W-1; 10 g for Rx 91 and Super Star) revealed that hardness variations during annealing for W-1 and Rx 91 were related to the palladium solid solution matrix phase. For Super Star, the lower-temperature peak was controlled by multi-phase regions and the higher-temperature peak by the matrix phase. While microstructural changes due to annealing were evident with the SEM for Rx 91 and Super Star, no correlation was possible for W-1 because of its finer-scale microstructure. Although commercial Pd–Ag alloys have a relatively narrow composition range, their microstructures and annealing behavior can vary because of differences in proportions of secondary elements utilized for porcelain adherence and grain refinement elements, as well as other proprietary strategies employed by the manufacturers.     

Low-temperature TSD measurements on γ-irradiated polyvinylidene fluoride

As a part of the fundamental study of the relaxational behaviour of the semi-crystalline polymer polyvinylidene fluoride (-(CH₂-C₂) _n -, PVDF), thermally stimulated depolarization (TSD) measurements have been carried out on -irradiated thin films, poled in vacuo. Following irradiation, the total TSD relaxation strength below room temperature is depressed. Mathematical analysis of this region of the TSD spectrum reveals the reduction to be caused by the decrease of the -(glass-transition) relaxation peak. One also observes the irradiation-induced creation of two relaxation peaks, both with higher activation energies than their neighbours. Tentative interpretations for the different components of the relaxation spectrum are proposed.     

Through-thickness strength measurements using Arcan’s method

This paper presents results obtained from the experimental study on the behaviour of glass/epoxy butterfly-shaped specimens tested under pure shear and biaxial loadings using an Arcan device. Notch-to-notch longitudinally and perpendicularly oriented fibre specimens, respectively referred to as Mat31 and Mat32 ones have been tested with different loading angles ranging from 0° to 90°. The fracture mode was more or less repetitive for Mat31 specimens whereas it depended on the loading direction for Mat32 type, for which the number of cracks and the obliqueness relative to the notch-to-notch line, decreased as the test angle increased. The comparison of failure envelopes has demonstrated that Mat31 specimens are much more resistant whatever the loading angle. However, strengths at failure of Mat32 type are in good agreement with Hashin’s failure criterion, for pure shear tests up to 30° loading angles. Mat31 specimens’ failure stresses were overestimated by the criterion, although similarities in trends were noticed.     

Identifying Lamé parameters from time-dependent elastic wave measurements

In many sectors of today’s industry it is of utmost importance to detect defects in elastic structures contained in technical devices to guarantee their failure-free operation. As currently used signal processing techniques have natural limits with respect to accuracy and significance, modern mathematical methods are crucial to improve current algorithms. We consider in this paper a parameter identification approach for isotropic and linear elastic structures described by their Lamé parameters and a material density. This approach can be employed for non-destructive defect detection, location and characterization from time-dependent measurements of one elastic wave. To this end, we show that the operator linking the static parameters with the wave measurements is Fréchet differentiable, which allows to set up Newton-like methods for the non-linear parameter identification problem. We indicate the performance of a specific inexact Newton-like regularization method by numerical examples for a testing problem of a thin plate from measurements of the normal component of the displacement field on the boundary. As an extension, we further augment this method with a total variation regularization and thereby improve reconstructed parameters that feature edges.     

RBS,XRR and optical reflectivity measurements of Ti–TiO2 thin films deposited by magnetron sputtering

Single-, bi- and tri-layered films of Ti–TiO₂ system were deposited by d.c. pulsed magnetron sputtering from metallic Ti target in an inert Ar or reactive Ar + O₂ atmosphere. The nominal thickness of each layer was 50 nm. The chemical composition and its depth profile were determined by Rutherford backscattering spectroscopy (RBS). Crystallographic structure was analysed by means of X-ray diffraction (XRD) at glancing incidence. X-ray reflectometry (XRR) was used as a complementary method for the film thickness and density evaluation. Modelling of the optical reflectivity spectra of Ti–TiO₂ thin films deposited onto Si(1 1 1) substrates provided an independent estimate of the layer thickness. The combined analysis of RBS, XRR and reflectivity spectra indicated the real thickness of each layer less than 50 nm with TiO₂ film density slightly lower than the corresponding bulk value. Scanning Electron Microscopy (SEM) cross-sectional images revealed the columnar growth of TiO₂ layers. Thickness estimated directly from SEM studies was found to be in a good agreement with the results of RBS, XRR and reflectivity spectra.     

Simultaneous multidimensional deformation measurements using digital holographic moiré

This paper proposes an elegant technique for the simultaneous measurement of in-plane and out-of-plane displacements of a deformed object in digital holographic interferometry. The measurement relies on simultaneously illuminating the object from multiple directions and using a single reference beam to interfere with the scattered object beams on the CCD plane. Numerical reconstruction provides the complex object wave-fields or complex amplitudes corresponding to prior and postdeformation states of the object. These complex amplitudes are used to generate the complex reconstructed interference field whose real part constitutes a moiré interference fringe pattern. Moiré fringes encode information about multiple phases which are extracted by introducing a spatial carrier in one of the object beams and subsequently using a Fourier transform operation. The information about the in-plane and out-of-plane displacements is then ascertained from the estimated multiple phases using sensitivity vectors of the optical configuration.     

Quasi-isochoricpπT measurements and second virial coefficient ofn-heptane

Quasi-isochoricpT measurements onn-heptane vapor were carried out in the low density region using an improved apparatus that was originally proposed by Opel and Schaffenger (Wiss. Z. Univ. Rostock N18:871, 1969). The experimental results extend over the temperature range between 350 and 600 K and the density range between 11.5 and 52.2 mol · m^–3. Above 473 K a small but significant influence of decomposition was found. Accordingly, a correction scheme assuming a trace of decomposition products was applied to these data. Second virial coefficients were derived with an assumed maximum uncertainty of ±3%.. The results are compared with others in the literature and used to develop an improved correlation function for the temperature dependence ofB(T).     

Compressibility measurements of β- and β″ -alumina

The compressibilities of the a- and c-axes for sodium - and -aluminas were determined up to 10 GPa from the pressure dependence of powder X-ray diffraction measured at room temperature using synchrotron radiation as an X-ray source. Powders of sodium - and -aluminas which were prepared from grinding synthesized single crystals were used as the specimens for X-ray diffraction. The compressibilities of - and -aluminas are 1.5 ± 0.2 ×10^–12 and 1.7 ± 0.2 × 10^–12 Pa^–1 for the a-axis and 2.9 ± 0.2x10^–12 and 1.6 ± 0.2 ×10^–12 Pa^–1 for the c-axis, respectively. For the c-axis, the compressibility of -alumina is larger than that of -alumina. This experimental fact is explained by the different stacking of oxygen layers and the different content in sodium ion between - and -aluminas.     

In situ measurements of ion-exchange processes in single polymer particles: laser trapping microspectroscopy and confocal fluorescence microspectroscopy

Ion-exchange processes of a cationic dye (Rhodamine B; RhB) were studied for individual polymer particles (diameter of 16-20 μm) by laser trapping microspectroscopy and confocal fluorescence laser microspectroscopy. The absorbance of RhB at 565 nm adsorbed on a cation-exchange particle increased linearly with the concentration of RhB in the aqueous phase, while it was independent of the particle diameter. Fluorescence intensity profile measurements of RhB along the particle diameter by confocal fluorescence microspectroscopy directly proved that ion exchange took place in the surface layer (～2-μm thickness) of the particle in the initial stage (1 h). Diffusion of RhB in the particle was very slow, and ion exchange proceeded gradually to the inner volume in the order of days. The ion-exchange processes were analyzed on the basis of simulation of the time course of the concentration profile of RhB in the particle, and the diffusion coefficient of RhB was determined to be (2-4) × 10(-11) cm(2)·s(-1).