S. M. Solonin

Mechanism of the sintering of high-porosity materials in the presence of a volatile pore-forming agent

Conclusions1.During the sintering of compacts with a filler, their volume shrinkage is a result of the densification of the regions with the fine natural pores, but their macroporosity remains unchanged (except in the case of compacts of very high starting porosity).2.A matrix mixture of metal and voids predominates in the structure of porous solids produced with a coarse filler, while a statistical mixture is characteristic of the structure of solids produced with a fine filler. A formula is proposed for calculating the statistical weight of the matrix mixture in the structure.3.The differences in the structures of porous materials associated with the particle size of the filler lead to differences in the structural weakening of these materials (the volume viscosity is less for porous solids with a mainly statistical distribution of the large pores), and this results in a decrease in macroporosity during the sintering of compacts with a fine filler.4.The growth of interparticle contacts during the sintering of compacts with a filler is analogous to the growth of contacts in unpressed powders being sintered and is directly determined by the kinetics of the volume shrinkage of the porous solids.

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.

Permeable tungsten-copper materials

Conclusions1.A porous permeable tungsten-copper composite material can be produced by partially infiltrating with copper a high-porosity tungsten skeleton sintered with a volatile pore-forming agent.2.It has been established that during partial infiltration of a tungsten skeleton possessing a biporous structure the fine pores become completely filled with copper, while the large pores remain unfilled. As a consequence of this, at any given porosity a tungsten-copper material has larger pores and greater gas permeability than porous tungsten.3.At any given porosity the transverse rupture and impact strengths of a tungsten-copper material are much higher than those of porous tungsten.4.The surface of a porous tungsten-copper material becomes coated with a cupric oxide film which protects the material against high-temperature oxidation wear.

High-porosity tungsten-copper materials produced by liquid-phase sintering

Conclusions1.Use of a coarse pore-forming agent for the stabilization of a porous structure ensures the retention of a high final porosity in the liquid-phase sintering of tungsten-copper materials.2.The volume changes occurring during the liquid-phase sintering of high-porosity tungsten-copper materials can be virtually eliminated by combining the sintering operation with the infiltration of the fine pores in biporous tungsten compacts with copper from external or internal sources.3.During the infiltration of a biporous tungsten compact from internal sources the copper component becomes redistributed, as a result of which a coarse porous structure forms in the material.

Preparation and Properties of Highly‐Porous Rolled Product Based on Nichrome Powder

A production scheme is suggested for forming strips with a pore forming agent using high-temperature sintering followed by rolling compaction. This makes it possible to prepare highly-porous thin rolled strip based on nichrome powder with a controlled biporous structure and optimum physicomechanical properties.

Deformation Features for Highly Porous Metallic Materials

Ultralight metallic structural materials based on foamed nichrome and cellular sandwiches made from stainless steel are prepared with a porosity of 90-95% and high specific strength indices are obtained. Effects of loss of stability and nonuniform deformation over the height are detected with compression of foamed nichrome and nickel, and they are duplicated with radial deformation of model honeycomb structures. This makes it possible to establish that on the basis of these phenomena there are local structural arches in the material. A model is suggested for an arched structural element and the elastic problem is resolved for its deformation that adequately describes the effect of loss of stability.

Alloy formation during the liquid-phase sintering of tungsten-base powder composites

Conclusions1.It was demonstrated that an activator present in a liquid phase intensifies the formation of a tungsten-base alloy much more strongly than it does in solid-phase sintering. This is attributable to a better distribution of the activator on the tungsten surface, resulting from its transport by the liquid phase, which readily wets tungsten.2.In the solid-phase sintering of a mixture of tungsten and chromium powders with a large amount of a nickel activator a redistribution of the refractory alloying element may occur between the activator and tungsten. Such redistribution is largely suppressed in liquid-phase sintering thanks to the formation in tungsten-chromium-copper-nickel pseudoalloys of two binders — a copper-base liquid-phase solution and a nickel-base solid solution.

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.