Crystal-glass phase transition induced by pulses of electric field in chalcogenide semiconductors

It is shown that the minimum power of an electric field which induces the crystal-glass phase transition in micrometer-thick films of chalcogenide semiconductors does not depend on pulse duration τ for τ>10 μs and increases, as τ decreases to τ<1–3 μs. The dependence obtained is similar to that observed for crystal-glass phase transition induced by pulses of laser radiation. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 1, 2000, pp. 93–95. Original Russian Text Copyright ? 2000 by Lebedev, Tséndin, Kazakova.     

Possibility of creating standard spectrometric gamma-ray sources with a complex decay scheme

Conclusions Multireference sources enable one to broaden the energy range of energy calibration and recording efficiency and increase the reliability of the results obtained. The nuclides⁷⁵Se, ,¹⁵²Eu,¹⁸²Ta, and⁵⁶Co are recommended as multireference sources. This set of nuclids can be supplemented naturally as new experimental data is obtained. To create standard spectrometric sources using these nuclides, it is necessary to solve the problem of checking the sources as regards their activity or quantum yield and also to check the presence of radioactive impurities in the initial raw material.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 45–48, September, 1978.     

Effect of the components' molar mass and of the mixing conditions on the compatibilization of PE–LCP blends by PE‐g‐LCP copolymers

The rheology, morphology, and mechanical properties of blends of high‐density polyethylene (HDPE) with a semiflexible liquid crystalline copolyester (SBH) were studied in order to assess the compatibilizing ability of added PE‐g‐SBH copolymers, and its dependence on the molar mass of the PE matrix, and on the technique used for blend preparation. The PE‐g‐SBH copolymers were synthesized as described in previous articles, either by the polycondensation of the SBH monomers in the presence of a functionalized PE sample containing free carboxyl groups, or by reactive blending of the latter polymer with preformed SBH. Two samples of HDPE having different molar masses, and two samples of SBH with different melt viscosity and different microstructure, were used for preparing the blends. The two components and the compatibilizer were either blended in a single batch or used to prepare binary master blends to which the third component was added at a later stage. The results indicate that the PE‐g‐SBH copolymers do, in fact, compatibilize the PE–SBH blends and that the effect is more pronounced with the lower molar mass PE matrix and with the SBH sample having lower viscosity. The experiments carried out on blends prepared with different techniques show that the compatibilizing ability of the graft copolymer is improved if the latter is first blended with either of the two main components. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 603–613, 1999     

Synthesis of PP–LCP graft copolymers and their compatibilizing activity for PP/LCP blends

The aim of this work was the synthesis of new graft copolymers consisting of polypropylene (PP) backbones and liquid crystalline polymer (LCP) branches, to be used as compatibilizing agents for PP/LCP blends. The PP-g-LCP copolymers have been prepared by polycondensation of the monomers of a semiflexible liquid crystalline polyester (SBH 1 : 1 : 2), that is, sebacic acid (S), 4,4′-dihydroxybiphenyl (B), and 4-hydroxybenzoic acid (H) in the mole ratio of 1 : 1 : 2, carried out in the presence of appropriate amounts of a commercial acrylic-acid-functionalized polypropylene (PPAA). The polycondensation products, referred to as COPP50 and COPP70, having a calculated PPAA concentration of 50 and 70 wt %, respectively, have been fractionated with boiling toluene and xylene, and the soluble and insoluble fractions have been characterized by Fourier transform infrared and nuclear magnetic resonance spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry, and X-ray diffraction. All analytical characterizations have concordantly shown that the products are formed by intricate mixtures of unreacted PPAA and SBH together with PP-g-SBH copolymers of different composition. Exploratory experiments carried out by adding small amounts of COPP50 or COPP70 into binary mixtures of isotactic polypropylene (iPP) and SBH while blending have demonstrated that this practice leads to an appreciable improvement of the dispersion of the minor LCP phase, as well as to an increase of the crystallization rate of iPP. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 391–403, 1998     

Feasibility study on developing high-nitrogen steels by refining in suspended state under high pressure

High-nitrogen steels are finding increasing use in the industrially developed nations. However, they are still not being used to their full potential. Among the reasons are the time and money needed to develop new grades of high-nitrogen steels. This article reports on the progress made in this area by the Institute of Metallurgy of the Bulgarian Academy of Sciences. As an example, it describes the quick and efficient process followed in developing a new nickel-free low-manganese austenitic stainless steel obtained by refining in the suspended state under pressure. __________ Translated from Metallurg, No. 2, pp. 37–41, February, 2007.     

Improved Ni ohmic contact on n-type 4H-SiC

This paper presents the structural, chemical and electronic properties of Al/Ni/ Al-layers evaporated on 4H silicon carbide and then annealed at 1000°C for 5 min. The structure was investigated before and after annealing by transmission electron spectroscopy from cross-sectional specimens. With x-ray photoelectron spectroscopy, both element distribution and bonding energies were followed during sputtering through the alloyed metal-semiconductor contact. Voids are found in both annealed Ni/4H-SiC and Al/Ni/Al/4H-SiC contact layers, though closer to the metal-semiconductor interface in the former case. The first aluminum-layer is believed to prevent voids to be formed at the interface and also to reduce the oxide on the semiconductor surface. The contact was found to be ohmic with a specific contact resistance ρ_c - 1.8 × 10⁻⁵ Ωcm² which is more than three times lower ρ_c than for the ordinary Ni/4H-SiC contact prepared in the same way.