Electrochemical synthesis of molybdenum, tungsten, titanium, and zirconium silicides in a dispersed state

The electrolytic deposition of molybdenum, tungsten, titanium, and zirconium silicide powders from ionic melts was investigated. Conditions for the deposition of various phases were found. Electrochemical synthesis of the silicides was affected by the interrelated factors of bath composition, voltage, current density, temperature, and time. Institute of General and Inorganic Chemistry, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5/6(395), pp. 66–69, May–June, 1997.     

Finely dispersed composite iron-platinum and iron-gold powders

The physicochemical laws of the formation of Fe−Pt and Fe−Au oxalates have been determined. For the first time finely dispersed Fe−Pt and Fe−Au composite powders have been fabricated by thermal reduction. The physicochemical and biomedical properties of such powders are investigated. We show that the powders are corrosion-resistant, are almost monodisperse, have a hydrophilic surface, are nonpyrophoric, are harmless, are bactericidal, and withstand sterilization temperatures. Their magnetic properties can be controlled during formation. Colloid Chemistry and Water Chemistry Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3-4(400), pp. 1–6, March–April, 1997.     

High-dispersion iron powders produced by the thermochemical method

The problem of producing high-dispersion iron powders is very complicated because of the fact that these powders are highly pyrophoric and, consequently, the number of methods of production of these powders is limited. Another difficulty is that the majority of these methods do not make it possible to vary the properties of microcrystals in the required range and this greatly restricts the application of powders. Institute of Colloidal Chemistry of Water, National Academy of Sciences of the Ukraine. Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6, pp. 1–4, May–June, 1998.     

Highly dispersed composite iron—Copper powders obtained from oxalates by a thermochemical method

The preparation of highly dispersed composite iron—copper powders with various concentrations of copper from mixed iron and copper oxalates was studied. The physico-chemical properties of the powders were determined. The powders were corrosion resistant, hydrophilic, practically monodispersed, bacteriocidal and tolerated the sterilization at elevated temperatures. Their magnetic properties could be regulated in the process of forming the initial components. Such powders can be useful in medicine, biology and technology. Institute of Colloid and Water Chemistry, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 1–4, July–August, 1998.     

Use of powders of the tungsten—Rhenium alloys for the preparation of impregnated cathode skeletons. II. Emission capabilities of barium containing impregnated cathodes with tungsten—Rhenium alloy skeletons

The dependence of the emission properties of barium-containing impregnated cathodes on the rhenium content, phase composition, and pore structure of the metallic skeleton was studied. Skeletons were prepared from mixtures of elemental W and Re powders, as well as from W—Re alloy powders. The lowest work function (π(1300 K)=1.97–1.99 eV) was observed in cathodes containing 50–80 mass % Re. The use of W—Re alloy powders with additions of highly dispersed aluminum oxide for the preparation of skeletons increased the lifetime of impregnated cathodes by 2–2.5 times. Such cathodes possessed a stable and uniform grain structure which was resistant to recrystallization and grain growth, thus they had a stable skeleton structure. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 25–30, January–February, 1999.     

Theory, manufacturing technology, and properties of powders and fibers

The properties of ferromagnetic powders after reduction annealing are examined. It is shown that magnetite and a destructured composite organic coating ensure the resistance of such powders to external effects. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 7–8 (456), pp. 3–7, 2007.     

Deformation of materials based on thermally expanded graphite

Strain and strength in uniaxial compression have been examined for specimens with various densities made by uniaxial pressing of thermally expanded graphite powders, which have been produced by the heat treatment of intercalated graphite compounds. Low-density graphite specimens formed at 600°C have the highest strain resistance. Surface Chemistry Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurigya, Nos. 5–6, pp. 18–23, May–June, 1998.     

Finely dispersed Si3N4−SiC powders and materials based on them

The objectives of the present research were to investigate the preparation of homogeneous ultrafine composite Si₃N₄−SiC powders by a plasmochemical process and the properties of ceramics produced from them. The chemical and phase compositions of the powders depended on the particle size of the initial powder, silicon input rate, and ratio of ammonium and hydrocarbon flow rates. The particle size and specific surface area of the compounds depended on the concentration of particles in the gas jet, and the cooling rate of the products. Composite powders containing from a few up to 90 mass % SiC, with specific surface areas of 24–80 m²/g and free silicon and carbon content less than 0.5 mass % were obtained. The main phases present were α-Si₃N₄, β-Si₃N₄, β-SiC, and X-ray amorphous Si₃N₄. Dense materials were prepared both by hot pressing at 1800°C under a load of 30 MPa and gas-pressure sintering at 1600–1900°C under a pressure of 0.5 MPa nitrogen. The plasmochemical composites had smaller pore sizes, were finer grained, and densified more rapidly than materials sintered from commercial powders. Institute of Inorganic Chemistry, Latvian Academy of Sciences, Salaspils. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(405), pp. 7–12, January–February, 1999.     

Influence of Aluminum Additives on the Content and Parameters of the Fine Structure of Titanium Silicon Carbide in SHS Powders

The dependence of the phase composition and parameters of a fine structure of titanium silicon carbide in powders formed by the self-propagating high-temperature synthesis on the aluminum concentration in the 5Ti/2Si/1C reaction mixture is investigated. The aluminum content is varied in a range of 0.1–0.4 mole fraction with the conservation of the total carbon content. It is established that the additives of aluminum not only affect the yield of titanium silicon carbide, but also promote the preferential formation of Ti5Si3 in synthesis products instead of TiSi2 identified in powders containing no aluminum. The introduction of a small amount of aluminum (0.1 mole fraction) leads to the formation of the Ti3Si1 – xAlxC2 solid solution and makes it possible to decrease the content of impurity phases in SHS powders by 6%. The silicon carbide concentration in SHS powders decrease at a higher aluminum content in the reaction mixture, while that of binary compounds (TiC, Ti5Si3, TiAl) correspondingly increases. No noticeable effect from the introduction of aluminum on the parameters of the crystal lattice of titanium silicon carbide in SHS powders is found in concentration limits of 0.1–0.25 mol %. A noticeable increase in parameters of a and c for Ti3Si1 – xAlxC2 (from a = 3.067 Å, c = 17.67 Å to a = 3.07 Å, c = 17.73 Å) with the conservation of the c/a ratio in limits of known values (c/a = 5.78) is observed only with the aluminum concentration of 0.4 mole fraction. The crystallite size of titanium silicon carbide depends, first and foremost, on the combustion parameters. At the same time, the deformation of the crystal lattice of Ti3Si1 – xAlxC2 in SHS powders increases monotonically with an increase in the aluminum content in the reaction mixture in the concentration range under study.     

Influence of Shock Wave Treatment of Boron Carbide Powders on the Structure and Properties of Hot-Pressed Polycrystals Based on Such Powders

The influence of deformation pre-treatment (milling in a planetary mill and shock-wave treatment) of B₄C powders of different size composition on their structure as well as the structure and mechanical properties of samples that have been hot-pressed from these powders is investigated. It is shown that treatment by shock waves produces a substantial change in the structure of the powders, and this tends to increase the mechanical properties of the polycrystalline cakes. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(444), pp. 118–127, July–August, 2005.     

Ceramic humidity sensors based on magnesium aluminate spinel. II. Relation between the parameters of water adsorption kinetics and the service characteristics of ceramic humidity sensors in the MgAl2O4 system

he parameters of water vapor adsorption on the surfaces of powders and compacted powders (compacts) are compared with data on the variation of the electrical resistance of the same compacts in media with various water vapor contents. A study of the kinetic features of water vapor adsorption from the air indicated that powders with small specific surfaces adsorb water vapor and are saturated more rapidly than do powders with large specific surfaces, while their absolute moisture content is lower. The amount of water vapor adsorbed on the surface varies in the same way. The data are consistent with the results from porous structure studies. The rate of water vapor adsorption and the amount adsorbed increase for smaller pores, in which the water vapor condenses more quickly. Data on the specific surface of compacted and sintered materials, their porous structure and their adsorptivity of water vapor provide a basis for making a prior choice of technological parameters of the ceramic treatment so as to enhance the quality of humidity meters. Deceased. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos 7–8(402), pp. 46–50, July–August, 1998.     

Industrial production of powders of copper alloys by impact atomization of a jet of melt

A plant for use in impact atomization of a jet of a metallic melt by fast turning impact blades is described. Using as an example industrial production of powders of copper alloys at a rate of 2–2.5 t/h, several positive elements of the method of impact atomization are demonstrated including high yield of satisfactory fractions (90–92%) with comparatively low electricity consumption (4–8 W per kilogram of melt), as well as small overall dimensions, simplicity, and low cost of the impact atomization plant. The characteristics of deposited bronze powders are presented. It is demonstrated that application of impact atomization for large-scale production of powders of copper, iron, and nickel alloys as well as special nickel-and copper-based powders in an inert medium is highly promising. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 112–117, January–February, 2006.     

Stainless-steel porous-layered and framework fiber-powder composites

Porous layered and framework composites have been made from stainless-steel fibers and powders in the form of sheets. Measurements have been made on the electrical conductivity, elastic modulus, and ultrasound speed as dependent on the porosity, fiber and powder dispersions, and the structural features of the composites. Framework composites are better than layered ones throughout the porosity range, while purely fiber materials are better with porosity less than 60%. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 45–50, January–February, 2006.     

Phase composition and structure of composite powders based on solid solutions of SiC and AlN

The structure of SiC–AlN powders is investigated by x-ray diffraction and transmission electron microscopy methods. The powders were produced by joint carbon reduction and nitriding of silicon and aluminum oxide mixtures. The results show that a mixture of solid solutions forms during joint SiC and AlN synthesis at 1700°C, with SiC forming β (3C) and α (2H) modifications with different grain morphology. The fiber form is characteristic of β-SiC, whereas the grains of the solid solution based on SiC have a predominantly equiaxed form. α-SiC grain dimensions are considerablys smaller than those of AlN. Institute of Materials Science, National Academy of Sciences of Ukraine. Kiev Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 81–86, July–August, 1997.     

Tool ceramics based on Al2O3–ZrO2–TiCN composite

Powder Metallurgy and Metal Ceramics - Oxide composite Al2O3–ZrO2(Y2O3) powders containing 50 and 70 vol.% Al2O3, are deposited from salt solutions. The surface area of the deposited powders...     

Thermal stability of finely dispersed ferromagnetic powders

The oxidation mechanism and kinetics have been examined for finely dispersed powders of iron and compounds containing it and noble and platinum metals; these powders were made by a thermochemical method and examined at 20–400°C. The powders do not change in composition and magnetic characteristics up to 110°C because the surfaces of the particles are protected by iron oxides and carbide. This allows the powders to be used to make materials for medical purposes, since they can be sterilized at that temperature. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(413), pp. 1–4, May–June, 2000.     

Properties and structure features of nanocomposite powders based on SiC

Features of the synthesis of SiC−Si₃N₄−Si₂N₂O composite powders are studied. The characteristics of the powders are examined on the basis of x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The structure features and mechanical properties of a ceramics formed on the basis of the synthesized powders are also studied. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Traslated from Poroshkovaya Metallurgiya, Nos. 7–8(408), pp. 12–16, July–August, 1999.     

Microstructures and properties of nanocomposites obtained through SPTS consolidation of powders

The microstructures and properties of copper- and aluminum-based nanocomposites processed through severe plastic torsional straining (SPTS) consolidation of metallic micrometer powders and ceramic nanopowders were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), microhardness and electrical resistivity measurements, and mechanical tests. It was shown that the SPTS consolidation of powders is an effective technique for fabricating metal-ceramic nanocomposites with a high density, ultrafine grain size, and high strength. Copper samples processed under a high pressure of 6 GPa exhibited high failure strength and strain as well as unusual strain hardening. Superplastic-like behavior was found in Al-Al₂O₃ nanocomposite samples. This article is based on a presentation made in the symposium “Mechanical Behavior of Bulk Nanocrystalline Solids,” presented at the 1997 Fall TMS Meeting and Materials Week, September 14–18, 1997, in Indianapolis, Indiana, under the auspices of the Mechanical Metallurgy (SMD), Powder Materials (MDMD), and Chemistry and Physics of Materials (EMPMD/SMD) Committees.     

Dependence of the Structure of Sintered Boron Carbonitride on the Defect Level in the Starting BN Powder

We have carried out a comparative x-ray analysis of boron nitride powders with different degrees of ordering and sintered specimens of boron carbonitride based on such powders. We have established that an indicator of sintering activity for the boron carbonitride specimens is the rate of formation of the r-BN phase, the content of which depends on the degree of ordering of the starting BN powder. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 100–107, May–June, 2005.     

Characterization of Hypereutectic Al-Si Powders Solidified under Far-From Equilibrium Conditions

The rapid solidification microstructure of gas-atomized Al-Si powders of 15, 18, 25, and 50 wt pct Si were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In order of increasing particle size, the powders exhibited microcellular Al, cellular/dendritic Al, eutectic Al, and primary Si growth morphologies. Interface velocity and undercooling were estimated from measured eutectic spacing based on the Trivedi–Magnin–Kurz (TMK) model, permitting a direct comparison with theoretical predictions of solidification morphology. Based on our observations, additional conditions for high-undercooling morphological transitions are proposed as an extension of coupled-zone predictions. This article is based on a presentation made in the symposium entitled “Solidification Modeling and Microstructure Formation: In Honor of Prof. John Hunt,” which occurred March 13–15, 2006, during the TMS Spring Meeting in San Antonio, Texas, under the auspices of the TMS Materials Processing and Manufacturing Division, Solidification Committee.