Characterization of supported Pd-Pt catalysts by chemical probes

The temperature programmed (palladium) hydride decomposition appeared very effective method for diagnosing the extent of alloying in Pd-Pt/SiO₂ catalysts. Introduction of Pt to Pd catalysts moves the TPHD peak gradually towards lower temperatures and the shift in hydride decomposition peak is accompanied by a decrease in the amount of released hydrogen. The catalysts prepared the direct redox method showed much better alloy homogeneity than the samples prepared by coimpregnation. The results of probing with other techniques, i.e. catalytic probing with hydrodechlorination of CCl₂F₂ and XRD, were in line with TPHD data. The catalytic probing showed the presence of synergistic effect, a clear indication of Pd-Pt mixing. XRD data of post-reaction samples showed carbon incorporation into Pd-rich phase, whereas separate Pt-rich phase did not experience any bulk carbiding.     

T(x) phase diagram of the Cu2Se-Al2Se3 system

Twenty alloys of various compositions in the Cu₂Se-Al₂Se₃ system were prepared and investigated. The T(x) phase diagram of the Cu₂Se-Al₂Se₃ system was obtained from x-ray diffraction, differential thermal analysis, and microstructure investigation for the first time. The homogeneity region of the CuAlSe₂ semiconducting compound was established. Previous articles by this author were presented with the spelling of his name as B.V. Korzun.     

化学镀Ni—P镀层的X射线衍射研究

根据X射线衍射分析结果,对化学镀高P(含P>11wt％或19at％)Ni-P镀层加热时效时,镀层成分和加热温度对结构转变的影响作了研究,结果表明,高P共晶、过共晶(含P>11wt％或19at％)合金的结构转变有如下特征:(1)相同加热时效条件下,Ni-P合金的结构转变与成分有密切关系:(2)对同一成分的过共晶合金,Ni-P合金的结构转变与时效温度密切相关;(3)过共晶合金在290～360℃温度范围内时效处理,出现Ni_xP_y介稳相,X射线衍射分析认为Ni_xP_y为Ni_(12)P_5。     

Photoelectronic and transport properties of polypyrrole doped with a dianionic dye

Polypyrrole (PPy) doped with dodecylsulfate (DS) and an organic dye (indigo carmine, IC) was electrochemically prepared and characterized by Raman spectroscopy and X-ray diffraction (XRD). The photoelectrochemical properties of PPy-DS and PPy-DS-IC in contact with an electrolytic solution containing a redox couple were studied using the theories for the semiconductor ∣ electrolyte interface. Results indicate that the system containing IC presents a higher photocurrent density under polychromatic illumination and faster response time when compared with PPy-DS. This fact was assigned to the formation of molecular-scale paths in PPy-DS-IC. The IC molecules lying perpendicularly between PPy chains, as confirmed by the X-ray analysis, could facilitate the mass transport at the interface and increase the ordering degree to provide better electronic charge transfer in the bulk. Although the photoelectrochemical devices presented here do not present all the properties of inorganic-based devices, we discuss some strategies to enhance the photoelectrochemical properties and response time of conducting polymers used in these type of systems.     

Characterization of CuInS2 thin films for solar cells prepared by spray pyrolysis

We have made a study of the chemical composition, the electrical, the optical and the structural properties of polycrystalline CuInS₂ thin films prepared by spray pyrolysis to be used for thin film solar cells. These films were deposited starting from aqueous solutions with different chemical compositions ([Cu]/[In] and [S]/[Cu] ratios) and at different substrate temperatures. In all cases, the material is p-type with grains preferentially oriented in the (112) direction of the sphalerite structure. The electro-optical properties show a very strong dependence on the [Cu]/[In] ratio in the solution. Films with copper excess have smaller resistivity and better crystallinity than those which are stoichiometric or have indium excess. The results obtained in this work show the possibility of having CuInS₂ thin films with a wide range of resistivity, a fact that could be important for making solar cells based on this material.     

Numerical simulation and error analysis for thermal diffusivity measurements using laser-induced thermal grating technique

The laser-induced thermal grating technique has been used to determine the thermal diffusivity of liquids and liquid mixtures. But the dynamic behaviour of the transient thermal grating has not yet been thoroughly investigated, and the systematic errors, which result from the departures from one-dimensional heat conduction, have scarcely been studied quantitatively. In this paper. a three-dimensional numerical simulation and results of the transient thermal grating technique are presented, which enable a good understanding of the dynamic behaviour of the transient thermal grating. The results of this simulation are important for the proper design of the experimental setup to keep the systematic errors for the diffusivity measurement small. Based on the simulation method, the systematic errors were analyzed quantitatively. Here, the following effects were studied: (I) sample thickness, (2) intersection angle, (3) absorption, (4) Gaussian beam intensity distribution and focusing of heating laser beam, and (5) heating pulse duration and laser power. This error analysis makes it possible to specify the criteria for optimum measuring conditions, to correct the measured thermal-diffusivity values for systematic errors, and to estimate the accuracy of the measurements.     

Current ISI and monitoring technologies in European energy industries

This paper reviews available information on the state of practice of inservice material property monitoring performed in European energy industries. Current practice includes a range of standard nondestructive testing and monitoring methods, improved remote sampling and surveillance specimen testing, and new monitoring techniques which are emerging from ongoing development programs. These new technologies include ultrasonic, positron annihilation, neutron diffraction, and magnetic techniques.     

Fluctuation X-ray microscopy: a novel approach for the structural study of disordered materials

Measuring medium‐range order is a challenging and important problem in the structural study of disordered materials. We have developed a new technique, fluctuation x‐ray microscopy, that offers quantitative insight into medium‐range correlations in disordered materials at nanometre and larger length scales.In this technique, which requires a spatially coherent x‐ray beam, a series of speckle patterns are measured at a large number of locations in a sample using various illumination sizes. Examination of the speckle variance as a function of the illumination spot size allows the structural correlation length to be measured. To demonstrate this technique we have studied polystyrene latex spheres, which serve as a model for a dense random‐packed glass, and for the first time have measured the correlation length in a disordered system by fluctuation X‐ray microscopy. We discuss data analysis and procedures to correct for shot noise and detector noise. This approach could be used to explore medium‐range order and subtle spatial structural changes in a wide range of disordered materials, from soft matter to nanowire arrays, semiconductor quantum dot arrays and magnetic materials.     

Progress in near-field photothermal infra-red microspectroscopy

Near‐field photothermal Fourier transform infra‐red microspectroscopy, which utilizes atomic force microscopy (AFM)‐type temperature sensors, is being developed with the aim of achieving a spatial resolution higher than the diffraction limit. Here we report on a new implementation of the technique. Sensitivity of the technique is assessed by recording infra‐red spectra from small quantities of analytes and thin films. A photothermomechanical approach, which utilizes conventional AFM probes as temperature sensors, is also discussed based on preliminary results. Early indication suggests that the photothermal approach is more sensitive than the thermomechanical one.     

双能X射线骨密度仪测定技术研究

以Ｌｕｎａｒ公司ＤＰＸ－Ｌ型双能Ｘ射线骨密度仪为例，研究引起测量误差的主要因素并提出质控措施。用自检模块、腰椎体膜评定仪器的体外测量精度好于１％。对１０位志愿者重复２次测量，体内精度对腰椎，ＭＰＤ（平均百分差）为０．４６，ＣＶ（变异系数）为０．７５；对股骨颈，ＭＰＤ为１．２６、ＣＶ为０．４７；Ｗａｒｄ’ｓ三角区ＭＰＤ为２．０１、ＣＶ为１．１４；大转子ＭＰＤ为１．６６、ＣＶ为０．７２。扫描图像由２位