L. L. Kolomiets

Activating effect of small additions of group viii metals on alloy formation during the sintering of tungsten and molybdenum powders mixed with other refractory metals

Conclusions1.It has been established that small additions of Group VIII metals have a pronounced activating effect on alloy formation during the sintering of tungsten and molybdenum powders mixed with other refractory metals.2.Use of different Group VIII metal additions enables the phase composition of alloys to be varied.3.The mechanism of activation of alloy formation appears to be linked with the fact that additions of Group VIII metals intensify the grain boundary penetration of an alloying metal into tungsten or molybdenum.

Substructure and some processing properties of explosive-shock-treated powders of refractory materials

Conclusions1.X-ray structural examinations of powders of magnesium oxide and titanium and silicon carbides demonstrated that explosive-shock treatment had markedly decreased the size of coherent scattering regions. The resultant size of coherent scattering regions was of the order of 300 å for all the materials investigated. The powders differed in the extent of broadening of their x-ray interference lines, which was due to the fact that they exhibited different degrees of plastic deformation and hence different magnitudes of microdistortions. There is a close correlation between this finding and the plasticity of the materials investigated.2.Explosive-shock treatment enables nonporous compacts to be produced from magnesium oxide powder. The treatment substantially improves the compressibility and compactibility of titanium and silicon carbide powders at room temperature. It also produces a marked improvement in the compressibility of silicon carbide in hot pressing.3.Structural distortions produced in silicon carbide powder by explosive-shock treatment activate its densification during hot pressing only when the pressure is applied in the course of heating at a temperature much lower than that at which the defects are fully annealed out.

Making Calcium Phosphate Biomaterials

Publications and patents over recent decades on the use of hydrogenating alloys as an active material for nickel-metal hydride batteries that have successfully replaced ecologically harmful nickel-cadmium batteries are reviewed. It is shown that the main direction of scientific research into the preparation of alloys with a high electrochemical capacity, cycle life, and chemical activity towards hydrogen, is the development of multicomponent alloys by alloying whose principles are formulated in this communication.

Development of Hydrogenating Powder Alloys for the Electrodes of Alkali Batteries. Part 3. Production Characteristics of Gas-Atomized Powders of Multicomponent Intermetallic Alloys

Alloy powders containing rare earth metals are prepared by the gas atomization method and their structure, surface, technological, and electrochemical properties are studied. Powders of the alloys LaNi4.5Al0.5, LaNi2.5Co2.4Al0.1, and (Mm, La)Ni3.5Co0.7Al0.35Mn0.4Zr0.05 are prepared with different particle sizes. The morphology, oxygen content and crystal structure of powders in relation to particle size are studied by x-ray analysis, electron microscopy, and surface dispersion spectroscopy. The hydrogen capacity and electrochemical properties of different fractions are determined. It is established that all of the fractions have similar morphology and alloy lattice parameters. The surface of gas atomized powders with less particle size is less contaminated with oxygen compared with larger fractions. At the same time fractions with a particle size <50 μm have poor activity during gas and electrochemical hydrogenation. DTA curves for fractions of fine particles have an additional exothermic peak that may be caused by thermally induced transformation of the amorphous component into crystalline. The coarse fraction of gas atomized powder has the same hydrogen and electrochemical capacity as for fuzzed alloys.

HYDROGEN-SORPTION PROPERTIES OF POWDERED LANI4AL WITH DIFFERENT STATES OF THE SURFACE OF PARTICLES

The basic properties of the intermetallic compound LaNi4AI intended for storing hydrogen were investigated in [i]. When nickel in the intermetallic compound LaNis is partially replaced by aluminum, the equilibrium pressure of hydrogen in the system LaNi4AI-H 2 becomes much lower without a substantial reduction of the capacity; this compound can therefore be used in flooding systems with exactly stipulated pressure level at ordinary temperatures. Since the intermetallic compound and its hydride are highly active substances, even a low level of impurity concentration affects activity in regard to hydrogen and the speed of the reaction of hydrogenation. The most active deactivator of intermetallic hydrogen accumulators is oxygen which can be obtained from the surrounding air. The aim of the present work is therefore to study how the storing of powder in air affects the state of the surface of its particles, and consequently the change of operational characteristics, in particular the level of equilibrium pressure of the system LaNi4AI-H2, the hydrogen capacity, and the speed of the processes of sorption and desorption. An ingot of the material which according to chemical analysis had the composition Lal.0sNi~.9~Al0.s3 (0.006% oxygen content) was crushed and separated into three fractions: -40 Dm, 40-80 Dm, and 80-100 Dm. In half the freshly crushed powders we immediately investigated the sorptive properties, the other half of each batch of powders was held in air in a dry medium for 6-7 months, and then their hydrogen-sorption properties were investigated in an analogous way with the use of a Sieverts-type standard installation. The hydrogen pressure in the reaction space was measured with a mercury manometer and with a manometer valve LT-4. The batches of investigated material weighed at least i0 g, the accuracy of measurement of the hydrogen content was !0.013 cm 3. The temperature of the reaction vessel was measured with a Pt-Pt/Rh thermocouple and maintained constant with the aid of an electronic potentiometer ~PD-52. X-ray phase analysis was carried out on a diffractometer DRON-3M in Cu radiation. The change of morphology and composition of the surface of the particles was investigated by methods of scanning electron microscopy and Auger microanalysis. Although the weight of the powdered LaNi4AI powders during storage in air remained constant (accuracy of measurement !0.004 g), their sorptive properties underwent noticeable changes. The position of the isothermal lines of the disposition of the hydrides LaNi4AIH x for powders with different degree of fineness, freshly crushed or kept in air, is being compared in Fig. i. It shows the starting points of the isothermal lines of desorption ascertained on maximally saturated materials. The hydrogen capacity of freshly obtained powders is almost the same (curves 1-3), the hydrogen capacity of materials kept in air differs greatly: fairly fine powders lose the ability of becoming fully saturated with hydrogen (curve 4), the hydrogen capacity of coarse powders greatly increases (curve 6), and of powders with particle size 40-80 ~m it remains almost unchanged. Thus the air has an unequal effect on the sorptive properties of powders with different fineness. The