Some mechanical properties of silicon carbide fibers

Conclusions Electroerosion of silicon carbide fibers in contaminated mercury electrical contacts decreases their strength by between one-half and two-thirds. During prolonged holding under load at room temperature the creep of silicon carbide fibers is close to zero, while at 1173°K l/l 10^–7 l/day. X-ray structural analysis of silicon carbide fibers annealed for (1.8–10.8)·10³ sec in a hydrogen atmosphere at 1273–1773°K and for (3.6–18)·10³ sec in a nitrogen atmosphere at 1773–1973°K revealed no recrystallization in (4–5)·10^–7-m-thick layers of polycrystalline SiC deposited from a gaseous phase. A correlation was found between the strength of silicon carbide fibers and the number of flashes forming during their fracture.Translated from Poroghkovaya Metallurgiya, No. 1(253), pp. 55–59, January, 1984.     

Effects of silicon powder structure of nitriding

A study has been made on how the structural state of the silicon affects the nitriding at 1200–1400C. As the initial powder becomes more defective, the nitriding accelerates, and there is an increase in the importance of reactions in the gas phase, with an increase in the proportion of the a modification of silicon nitride, and a tendency for elongated crystals to form.Translated from Poroshkovaya Metallurgiya, No. 10, pp. 1–7, October, 1992.     

Reaction between zirconium carbide and silicon powders

Conclusions A study was made of the reaction of zirconium carbide and silicon powders over the temperature range 800–1700C.Translated from Poroshkovaya Metallurgiya, No. 11(83), pp. 61–65, November, 1969.     

Formation of the structure and properties of molybdenum disilicide films during solidification on silicon

Physical metallography is used to study the phase composition, structure, and physical properties of thin (100–600 m) molybdenum disilicide films formed on silicon. The main factors which affect film properties are the chemical composition of the starting material, sputtering conditions, heat treatment, the phase state of the substrate, and impurities. It is established that solidification kinetics depend on the orientation of the silicon single-crystal substrate.Institute of Materials Science Problems, Ukrainian National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3/4(384), pp. 50–54, March–April, 1966. Original article submitted April 25, 1994.     

Physicochemical processes occurring in nitride and oxide-nitride composites with phosphate binders during heating

Conclusions The hardening of compositions based on aluminum and silicon nitrides is a result of the chemical reaction of their phosphate binder with the nitrides, while additions of, e.g.,-corundum act as inert fillers up to a temperature of 570K. The reaction products are amorphous acid mono- and disubstituted aluminum and silicon phosphates, which on heating at first condense, forming poly- and metaphosphates, and then, at temperatures above 870K, decompose, forming (depending on their composition) aluminum orthophosphate or silicon pyrophosphate.Aluminum nitride initially, after being combined with the phosphate binder, vigorously reacts with it, which may lead to clotting or rapid swelling of the composition. However, gradual mixing under conditions of cooling (or without it) enables masses of any consistency to be obtained.In the mechanism of hardening of the compositions investigated a dominant role is played by the hydrogen bond. With rise in temperature the OH groups evaporate and the role of the hydrogen bonds diminishes, but a new, more powerful mechanism becomes operative, linked with the polymerization of the phosphates. Above 970K the polymer structure, which attains its maximum development at 870–970K, gradually disintegrates, but at the same time a new process-sintering-commences. Accordingly, as has been demonstrated by our investigation into the temperature dependence of the strength of the compositions, all the materials investigated pass through stages of hardening (470K), strengthening (470–970K), partial strength loss (by 30–40% in the range 970–1270K), and high-temperature sintering.The end products of the thermal decomposition of the polyphosphates up to 1520K are (depending on the nature of the nitride filler) aluminum orthophosphate or silicon pyrophosphate, present in amounts of 5–10%.At 1270–1370K a liquid phase (aluminum metaphosphate or silicon polyphosphate) forms in the compositions and then gradually disappears as a result of its further reaction with the fillers. Under these conditions an additional amount of AlPO₄ or SiP₂O₇ is formed.Translated from Poroshkovaya Metallurgiya, No. 5(233), pp. 50–54, May, 1982.     

Protection of carbon materials from high-temperature gas corrosion

A study is made of composite carbon -borosilicide on carbon materials prepared by gas phase deposition, diffusion impregnation, liquid-phase impregnation, and fusion. It is shown that muldlayer coatings prepared from carbon-borosilicide materials, particularly silicon and titanium carbides, and molybdenum, tungsten, and hafnium borides and silicides have greater heat resistance in the temperature range 1500–2000°C in air. Their protective properties are strongly dependent on composition, coating structure, and preparation methods as well of the grade of the original carbon materials.NNTs Kharkov Physicotechnical Institute. Translated from Poroshkovaya Metallurgiya, Nos. 3/4(384), pp. 47–50, March–April, 1996. Original article submitted October 17, 1994.     

Strength and thermophysical properties of porous silicon nitride materials

Conclusions A slurry casting process has been developed for the production of porous silicon nitride specimens of 40–60%. It has been established that the strength and thermal conductivity of such specimens sharply decrease with increasing porosity. However, porous Si₃N₄ possesses fairly high resistance to oxidation in air, which suggests the possibility of employing it as a heat insulating material.Translated from Poroshkovaya Metallurgiya, No. 11(263), pp. 67–70, November, 1984.     

The wetting of self-bonded polycrystalline silicon carbide by silicon I. Effect of phase composition on wetting

Conclusions It is shown that the character of variation of in and out with free silicon concentration in base plates in the wetting of self-bonded polycrystalline silicon carbide by silicon is in qualitative agreement with Johnson and Dettre's model [6], which links the wetting behavior of two-phase base plates with their energy heterogeneity.Translated from Poroshkovaya Metallurgiya, No. 10(178), pp. 47–51, October, 1977.     

Resistance of materials based on silicon nitride to corrosion by solutions of some acids and alkalis

Conclusions Hot-pressed silicon nitride parts of 1.5–4% porosity containing a 10 wt. % activating addition of MgO are resistant to corrosion by nitric acid at room temperature and by 1% NaOH solution at 100°C under steady-state conditions. The presence of 1–20 wt. % CaF₂ added with the aim of improving antifriction properties results in corrosion in nitric acid, obeying the law m²=K, where K 5.5·10^–5· C³ %²/h). The corrosion is due to attack on specimens by hydrofluoric acid forming during the reaction between the CaF₂ and HNO₃.Translated from Poroshkovaya Metallurgiya, No. 1(205), pp. 70–72, January, 1980.     

Simultaneous nitriding of silicon and aluminum

Conclusions During the high-temperature nitriding of silicon-aluminum mixtures in nitrogen and ammonia the mixture components undergo nitriding separately, first aluminum and then silicon. Aluminum inhibits the nitriding of silicon, shifting the process toward higher temperatures. The inhibition is apparently due to a reaction between the silicon nitride and aluminum, with the formation of aluminum nitride films on the silicon particles. The nitriding of silicon and aluminum in nitrogen results in the formation of a limited solid solution of aluminum in a silicon nitride based on-Si₃N₄.Translated from Poroshkovaya Metallurgiya, No. 7(211), pp. 1–6, July, 1980.     

Enthalpies of Solution and Mixing for Graphite in Molten Silicon at 2000 K

Partial and integral enthalpies of mixing have been determined in an isoperibolic calorimeter for liquid alloys in the silicon – carbon binary system at 2000 K. These enthalpies of mixing are small exothermic quantities which agree with published data. The enthalpy of mixing _f Hº₂₉₈ has been calculated for silicon carbide.     

Electrophysical properties of a porous silicon carbide ceramic

The electrical resistance and thermal electromotive force have been measured for porous silicon carbide resistance materials. It has been established that the range of controlled variation in the electrical resistance is 5·10^–2 to 1·10⁴ · cm, and that the composition of the conducting SiC phase and the concentration of added dielectric constituents have a decisive influence on the electrical characteristics examined.Material Science Problems Institute, Academy of Sciences of the Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, No. 4(364), pp. 85–89, April, 1993.     

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.     

Preparation and study of rhombic iron carbide

Conclusions The authos investigated the K-spectrum of iron absorption in steel carbides, containing silicon and chromium. It is shown that the K-edge of iron absorption in steel carbide, alloyed with silicon and tempered at a high temperature (650), is similar to the K-edge of iron absorption in the carbide of carbon steek, tempered at 400. The presence of chromium in the carbide changes the form and energetic position of K-edge absorption in it. This change depends on the temperature of tempering and chromium concentration in the steel.Translated from Poroshkovaya Metallurgiya, No. 8(44), pp. 29–32, August, 1966.     

Structural state and mechanical properties of the material in the sialon-titanium nitride system after radiant heating

Conclusions Short-term radiant heating of the material of the Sialon-titanium nitride system in the temperature range 1230–2300°C is accompanied by oxidation of the titanium nitride with oxidation of rutile and titanium oxynitride (the lattice spacing of these compounds increases with increasing temperature) and also by the breakdown of '-Si₃N₄ to -Si₃N₄ and '-phase with a higher aluminum and oxygen content. The formation of rutile reduces the hardness of the material whereas formation of the oxynitride increases this parameter. A liquid phase consisting mainly of silicon and titanium disilicate appears on the surface of the specimens at temperatures above 1500°C. The material retains satisfactory strength in air at temperatures of up to 1200°C.Translated from Poroshkovaya Metallurgiya, No. 5(305), pp. 60–66, May, 1988.The authors are grateful to V. V. Kovylyaev and V. V. Traskovskii for help in the experiments.     

Production of hard-alloy blanks for very small tools

Conclusions A study was made of the character of flow of plasticized hard-alloy mixtures in the extrusion of blanks ranging from 100 to 1000 in diameter. It was established that the optimum flow rates, resulting in sound blanks for hard-alloy tools, are 130–150 and 230–250 mm/min, respectively, for mixtures plasticized with a solution of SR in benzine and paraffin wax.Translated from Poroshkovaya Metallurgiya, No. 2 (110), pp. 98–100, February, 1972.     

Influence of grain size and porosity on the high-temperature friction of titanium carbide

Conclusions It was established that in friction of a TiC-TiC pair in vacuum the coefficient of friction at 250C and the wear rate at 1250C are practically independent of grain size. At higher temperatures these characteristics have an inverse relationship to grain size.It was shown that with an increase in porosity both the wear rate and the coefficient of friction increase. With an increase in temperature the influence of porosity on the wear rate decreases.With variations in porosity in the 1–10% range, in grain size in the 1–50 m range, and in temperature in the 20–1500C range the wear rate changes within limits of 10–45% and the coefficient of friction within limits of 3–35%.Translated from Poroshkovaya Metallurgiya, No. 9(297), pp. 56–61, September, 1987.     

Mechanical characteristics of electrotechnical materials of the system Si3N4-SiC

Conclusions With selected optimal technology of producing materials Si₃N₄,-SiC, their mechanical characteristics may change within fairly broad limits, and they are determined primarily by the composition of the initial charge. Material with optimal composition has a bending strength of 500 MPa and a critical stress intensity factor 6.8 MN/m^3/2.To obtain ceramics with high values of _b and K_1c, it is expedient to use finely disperse highly active silicon carbide (10–30 volume%), and also oxide-free-activators for hot pressing.Increasing the grain size of the conducting phase SiC to 120 m and the amount of activating additive leads to reduced _b of the materials, however, the overall level of strength remains fairly high (>200 MPa).Translated from Poroshkovaya Metallurgiya, No. 1(313), pp. 57–61, January, 1989.     

Development of a higher-density pressing technology using gas drainage. II. Device for evaluating the efficiency of gas drainage from molding dies and experimental assessment of factors affecting it

A device designed specifically to determine the efficiency of gas drainage during ejection from a molding die and the intrapore gas pressure in compacts is described. This device was used to study how the morphology of iron powder particles, the size and shape of the molded parts, the compact rate and production run, as well as amount of plasticizer affect the parameters studied. Recommendations are made for developing technologies for pressing high-density briquets.Scientific Industrial Firm Bakkonditsioner. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 19–26, July–August, 1994.     

Laser chemical production of thin iron films,powders, and fibers from the carbonyl gaseous phase

Conclusions Healing a quartz substrate in a medium of IPC to a temperature above 500 K. by pulsed (> 5·10^–1 sec) radiation of a CO₂ laser with intensity of 50–100 W·cm^–2 yields thin (up to 3 m) iron films at a rate of 2 m·sec^–1 on a surface bounded by the cross section of the laser beam.When the intensity of the radiation is increased to 250 W·cm^–2, the process of decomposition of the IPC spreads to the gaseous phase. Together with intense crystallization of iron on the surface of the substrate (the surface temperature is 1500 K) a finely disperse (0.1–0.3 m) iron powder also forms.Translated from Poroshkovaya Metallurgiya, No. 1(325), pp. 85–89, January, 1990.