High temperature vacuum sintering of plasmochemical powders based on ZrO2

The phase composition and mechanical properties of ZrO₂-based ceramics prepared by sintering plasmochemical powders of complex morphology in air and in vacuum were compared. Sintering at a high temperatures in vacuum produced material exhibiting high density and good mechanical properties, in which the zirconium dioxide was entirely in the tetragonal form.Institute of the Physics of Strength and Materials Science, Siberian Branch, Russian Academy of Sciences. Translated from Poroshkovaya Metallurgiya, Nos. 1–2, pp. 26–30, January–February, 1994.     

Thermophysical properties of materials based on silicon nitride

The heat capacity and thermal conductivity of materials based on Si₃N₄ are investigated for the first time. The temperature dependence of the thermal diffusivity of the composites studied is calculated. The influence of structural changes on the nature of the thermophysical properties of materials based on -Si₃N₄.Institute of Material Sciences, Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Pokrytiya, Nos. 3/4, pp. 43–47, March–April, 1995.     

Formation of the cubic phase of zirconium dioxide with a low concentration of stabilizing addition in a shock wave with subsequent heating

The possibility of obtaining solid solutions based on cubic ZrO₂ with a low concentration of Y₂O₃ by detonation treatment (DT) with a shock wave duration <10^–9 sec was studied. Phase formation and the defect structure of powders and sintered products after various heat treatments, including prolonged annealing at 1250°C, were studied by the methods of x-ray diffractometry and positron spectroscopy.Deceased.Institute of Materials Science Problems and Institute of Metal Physics, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3/4, pp. 73–81, March–April, 1995.     

Use of boron carbonitride in devices for rapid analysis of slag oxidation

A new method has been developed for determining the degree of oxidation in a metallurgical slag. It is based on measuring the equilibrium oxygen partial pressure PO₂ with an electrochemical sensor. The basic component is a ceramic element containing boron carbonitride developed at the Institute of Problems of Materials Science, Academy of Sciences of the Ukraine. The rapid response enables one to monitor the state of the slag in the bath and to control the oxidation conditions and provide improved performance in refining steel with slag under various technological conditions.Institute of Problems of Materials Science, Academy of Sciences of the Ukraine, Kiev. Central Heavy Engineering Research Institute, Moscow. Translated from Poroshkovaya Metallurgiya, Nos. 1–2, pp. 109–112, January–February, 1994.     

Effect of impurities on the properties of silicon nitride materials

Conclusions The presence of oxides in silicon nitride leads to the formation of an intergranular vitreous phase which has an adverse effect on the high-temperature physicomechanical characteristics of constructional silicon nitride ceramics. This phenomenon is particularly pronounced with silicon nitride contaminated with calcium, silicon, and alkaline metal oxides. Future development work on oxidation-resistant constructional materials based on silicon nitride should go in the directions of removal of impurities and use of additions forming solid solutions or refractory compounds with Si₃N₄ and SiO₂. Additions which can be employed for this purpose include oxides of AI, Mg, Y, and some rare-earth elements.Translated from Poroshkovaya Metallurgiya, No. 1(193), pp. 75–80, January, 1979.     

Wear resistance of silicon carbide and nitride based ceramic materials

Various factors that affect the nature of wear in SiC and Si₃N4₂ based ceramics have been analyzed. It is shown that adhesion, mechanochemical and diffusion interactions in the contact zone and wear due to fatigue, thermal stresses and abrasion are the predominant factors. Ceramics based on SiC and Si₃N₄ are shown to have excellent wear resistance. Poreless silicon nitride materials that have good chemical stability, heat and crack resistance appear promising as ceramic—metal friction couples and for metal machining. Silicon carbide based poreless materials are efficient ceramic—ceramic friction couples and for service under severe hydro and gas abrasive media attack.Translated from Poroshkovaya Metallurgiya, No. 5, pp. 3–8, May, 1993.     

Problems and prospects of selective layer-by-layer laser sintering of powders

The present state, problems, and prospects for the development of a new powder metallurgy technique, called selective layer-by-layer laser sintering, are considered. With this technique three-dimensional powder products can be obtained without resorting to traditional forming methods. The results of experiments in which one-component and multicomponent mixtures based on metals, ceramics, and polymers were sintered in the solid and liquid phase by this technique are discussed.Vitebsk Branch of the Institute of Solid-State and Semiconductor Physics, Belorussian Academy of Sciences. Translated from Poroshkovaya Metallurgiya, Nos. 3/4, pp. 32–37, March–April, 1995.     

Hydrides based on phases in the Ti2Ni-Zr2Ni section of the Ti-Ni-Zr system

A study has been made on the interaction of hydrogen with a phase based on the intermetallide Zr₂Ni and with the ternary Laves phase occurring in the Ti-Ni-Zr system in the temperature range between room temperature and 700°C. The Laves phase and the phase based on Zr₂Ni form two hydrides: a low-temperature unstable one, which decomposes in air, and a high-temperature one that gives up hydrogen on heating above 400°C. The hydrogen capacities of the two phases can be used to store hydrogen.Materials Science Institute, Ukrainian National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1/2(377), pp. 81–84, January–February, 1995.     

High-temperature reaction between silicon carbide and nitrogen under pressure

The effects of temperature and nitrogen pressure are studied on the SiC Si₃N₄ transformation of silicon carbide powders of various phase compositions, specific surface areas, and contents of mixtures. It is shown that the degree of transformation increases with nitrogen pressure up to 10 MPa and that, in all temperature and pressure ranges of nitrogen, it is higher for bulk free powder than the preliminarily compacted material. In 30–60 min, a complete transformation of SiC into Si₃N₄ occurs under 10 MPa nitrogen pressure and at 1650–1750°C temperature.Institute of Inorganic Chemistry, Slovakian Academy of Sciences. Institute of Superhard Materials, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, No. 4(364), pp. 1–6, April, 1993.     

Reactions in the crystallization of Ti-Ni-SC system alloys in the TiNi - Ni - ScNi region

The Ti-Ni-Sc diagram has been examined for nickel contents of 50–100 at. %. The alloys were prepared by arc melting and were examined by metallography, differential thermal analysis, and microprobe analysis. There are four nonvariant equilibria: two incongruent ones and two congruent ones. The minimum melting point of 980°C occurs in alloys with the base composition 3> + 2> + , which form a eutectic.Materials Science Institute, Ukrainian National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 134–140, July–August, 1996.     

Solidus surface and phase equilibria during the solidification of alloys in the Al2O3-ZrO2-Y2O3 system

The projection of the solidus surface in the Al₂O₃-ZrO₂-Y₂O₃ phase equilibrium diagram was plotted. The scheme of alloy solidification indicates that the primarily congruent modes of phase transformation in the limiting binary systems are retained in the ternary system.Institute of Materials Science Problems, Ukrainian Academy of Sciences. Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1/2(377), pp. 71–76, January–February, 1975.     

Ionic conduction in BaxCe0.8Pr0.2O3-

[1]Iwahara H,Yajima T,Ushida H.Effect of ionic radii of dopants on mixed ionic conductions (H++O2) in BaCeO3-based electrolytes.SolidState Ionics,1994,70/71:267. [2]Taniguchi N,Yasumoto E,Nakagiri Y,Gamo T.Sensing properties of an oxygen sensor using BaCe0.8Gd0.2O3-a ceram-ics as electrolytes.J.Electrochem.Soc.,1998,145(5):1744. [3]de Arcllano-Lopez A R,Goretta K C,Park E T,Dorris S E,Balchandran U,Routbort J L.High-temperature deformation of a BaCe0.8Y0.2O3-y+Ni composite.J.Fur.Ceram.Soc.,2002,22:2555. [4]Ma G L,Shimura T,Iwahara H.Ionic conduction and non-stoichiometry in BaxCe0.90Y0.10O3-a.Solid State lonics,1998,110:103. [5]Ma G L,Matsumoto H,Iwahara H.Ionic conduction and non-stoichiometry in non-doped BaxCeO3-a.Solid State Ionics,1999,122:237. [6]Ma Guilin,Qiu Ligan,Chen Rong.Performance of the solid oxide fuel cell based on BaxCe0.8Sm0.2O3-a.Acta Chimica Sinica (in Chin.),2002,60(12):2135. [7]Ma G L,Qiu L G,Tao W H,Zhou L,Chen R.Ionic conduc-tion in BaxCe0.8Sm0.2O3-a solid electrolyte.J.Chin.Rare Earths Soc.(in Chin.),2003,21(2):236. [8]Qiu L G,Ma G L,Wen D J.Study on preparation and electri-cal properties of Ba1.03Ce0.8Eu0.2O3-a solid electrolyte.J.Rare Earths,2004,22(5):678. [9]Qiu L G,Ma G L,Wen D J.Ionic conduction in BaxCe0.8Er0.2O3-a.Solid State lonics,2004,166:69. [10]Wang M Y,Qin L G.Mixed conduction in BaCe0.8Pr0.2O3-a ceramic.Chin.J.Chem.Phys.,2008,21:286. [11]Bonanos N.Transport properties and conduction mechanism in high-temperature protonic conductots.Solid State Ionics,1992,53-56:967. [12]Ma G L,Shimura T,Iwahara H.Simultaneous doping with La3+ and y3+ for Ba2+-and Ce4+-sites in BaCeO3 and the ionic conduction.Solid State Ionics,1999,120:51. [13]Shima D,Halle S M.The influence of cation non-stoichiome-try on the properties of undoped and gadolinia-doped barium ceres.Solid State Ionics,1997,97:443.     

Change in the porous structure of ceramics based on Al2O3-ZrO2 during microwave sintering

Compaction of specimens consisting of 70% Al₂O₃ and 30% of ZrO₂(2Y₂O₃) has been studied during UHF sintering and furnace heating (FH). Kinetics of the change in density and pore size distribution at 1500 and 1600°C have been studied. The compaction rate is higher with UHF heating than with FH over the whole range of temperature and exposure time. Retention of small pores with UHF heating for a long time supports the high level of capillary forces and promotes ceramic material compaction.Institute of Materials Science Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4, pp. 16–19, March–April, 1994.     

Electrochemical synthesis of tungsten and molybdenum borides in a dispersed condition

Electrolytic deposition of tungsten and molybdenum boride particles from ionic melts is studied. Conditions are found for preparing different boride phases. If the anode material is graphite and the voltage in the bath does not exceed 2.5 V the cathode deposit consists mainly of tungsten and molybdenum metals. A mixture of phases (M, M₂B, MB, MB₂, M₂B₅) is produced on the cathode with U=2.5–3.5 V, while with U=2.3–3.5 V, while with U=3.5–4.5 V the deposit consists of the higher boride MB₄. On the whole the process of electrochemical synthesis for molybdenum and tungsten borides is governed by the following interconnected parameters: electrolytic bath composition, voltage in the bath, temperature, and duration of electrolysis.Institute of General and Inorganic Chemistry, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, No. 1 (361), pp. 8–11, January, 1993.     

Effect of the composition of sn1−xsbxo2 solid solutions on the sensitivity of semiconductor gas sensors

We have studied the effect of the composition of semiconductor material based on Sn_1–xSb_xO₂ solutions on the sensitivity of semiconductor gas sensors (the ratio of the conductivity of the sensitive element in the presence of gas to its conductivity in air). We have shown that the sensitivity of the sensors increases when the Sb concentration in the semiconductor decreases. We have established that sensors containing solid solutions with 0.001 × 0.01 have optimal sensitivity.Institute of Materials Science, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6, pp. 96–99, May-June, 1996. Original article submitted May 25, 1994.     

Characteristics of coreduction of nickel and molybdenum from oxide systems

We have studied the kinetic characteristics of reduction of nickel and molybdenum from their oxide mixtures. We have monitored the development of the specific surface area during reduction. We calculate the nucleation rate and the apparent activation energy. The reduction temperature for molybdenum in the presence of nickel was shown to decrease appreciably; and unlike the conventional scheme, in which during the first reduction stage MoO₃ transforms into MoO₂ or molybdenum suboxide, metallic molybdenum appears. Such reduction conditions made it possible to produce fine (S_sp=20 m²/g) powder of the nickel-based solid solution and pure molybdenum from the oxide mixtures precipitated from the salt solutions at 650°C.Institute of Materials Science, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5/6, pp. 52–56, May–June, 1995.     

Creep of Al2O3-AlN and Y2O3-AlN ceramics

Conclusions An investigation into the creep of Al₂O₃-AlN and Y₂O₃-AlN ceramics has demostrated that the addition of 20–80% AlN reduces the creep rate of Al₂O₃. In the system Y₂O₃-AlN the existence of a creep rate maximum has been discovered, which may be a manifestation of structural superplasticity.Translated from Poroshkovaya Metallurgiya, No. 2(158), pp. 76–82, February, 1976.The authors wish to thank Prof. R. A. Andrievskii for his interest in this work.     

Buckingham-potential parameters and relations between them for solids

Parameters m and n in the Buckingham potential in the form =[U₀mn/(m – n)]{(1/m)Y^–m – (1/n)exp[n(1–Y)]} have been calculated for 79 elements and 35 compounds, which have been compared with data on =c_v/(U₀) and =KV₀/c_v, in which U₀ is the cohesion energy, Y=(V/V₀)_1/3, V a volume with equilibrium value V₀, ... c_v the specific heat, the thermal-expansion coefficient, and K is the bulk elastic modulus. It is found that m is dependent essentially on and n on . These relationships have been approximated, and conclusions are drawn from them about the most reliable input data, particularly K because of the large spread in published values. A study is made on the relation of m and n to the positions of the elements in the periodic system and the electron structures.Institute of Problems of Materials Sciences, National Academy of Sciences of the Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, No. 5–6, pp. 118–126, May–June, 1994.     

Reaction kinetics and change in composition during heating of some powder materials for plasma heat-protective coatings

Aluminum powder and Al₂O₃-Al, Al₂O₃-SiO₂-Al, Ni-Al composites are studied within the range 20–1000°C by means of derivatography. Temperature ranges are determined for the reaction of components, interaction with each other and with the reaction medium, as well the dehydration of Al₂O₃ and NiO. The kinetics of these processes are explained and their thermal effect is described. X-ray methods show that Al₂O₃-Al, Al₂O₃-SiO₂-Al composites do not change their phase composition qualitatively after heating in the derivatograph. The thermite composite NiO-Al becomes multiphase as a result of heating (NiO, Al₂O₃, NiAl₂O₄, Ni, Al, NiAl₃, NiAl).Nizhnegorod Branch, Engineering Institute, Russian Academy of Sciences. Translated from Poroshkovaya Metallurgiya, No. 5–6, pp. 45–48, May–June, 1994.     

Phase Equilibria in the Ni - Sc - Ti System in the Region TiNi - Ni - Sc1.13Ni At 900°C

Physicochemical analysis methods have been applied to TiNi - Ni - Sc_1.13Ni alloys at 900°C. It is shown that the phase interactions under these conditions are unaltered by comparison with those at subsolidus temperatures. The phase based on TiNi₃, which is the most thermally and thermodynamically stable, is in equilibrium with all the other phases in the TiNi - Ni - Sc_1.13Ni subsystem. The solubilities of the components in the phases based on Ti_{50– x} NiSc_x, TiNi₃, and the Laves phase are reduced at 900°C. The temperature of the polymorphic transformation in the phase based on ScNi₅ is raised by the dissolution of titanium in it to 930°C. An isothermal section is constructed of the phase diagram for the TiNi - Ni - Sc_1.13Ni subsystem together with two polysections.__________Translated from Poroshkovaya Metallurgiya, Nos. 1–2(441), pp. 39–46, January–February, 2005.