Some relationships governing initiation of self-propagating synthesis in direct electric heating
Tóm tắt
Self-propagating high-temperature synthesis with direct passage of current through the powder mixture is characterized by various forms of reaction initiation. Taking into account the general features, three types of initiation were detected: contact, breakdown, and volume. These types operate in all the examined powder mixtures, depending on the heating conditions, the preparation quality of the components, compacting pressure, and other parameters. Contact and breakdown initiation take place in the conditions with the nonuniform electrical resistivity of the powder mixture and lead to incomplete transformation of the initial components into the final product. Volume initiation is optimum from the viewpoint of increasing the quality of synthesized compounds; in this initiation, a cavity forms inside the synthesized specimen as a result of the maximum temperature in the central part of the volume filled with the powder mixture in heating by the direct passage of electric current.
Tài liệu tham khảo
V. K. Prokudina, V. I. Ratnikov, V. M. Maslov, et al., “Technology of titanium carbides,” in: Combustion Processes in Chemical Technology and Metallurgy [in Russian], Joint Institute of Chemical Physics, Academy of Sciences of the USSR, Chernogolovka (1975), pp. 136–141.
A. A. Anresyan, G. A. Sevinyan, and E. G. Khachatryan, “Production of carbides, borides, nitrides, and silicides of transition metals for producing wear-resistant components,” in: Sintered Wear-Resistant Materials [in Russian], Metallurgiya, Moscow (1977), pp. 5–8.
V. Ya. Belousov, A. V. Pilipchenko, and A. I. Tsitrin, “Recording temperature in direct electric heating of powder materials,” in: Proceedings of 5th All-Union Conference Temperatura-84, Lvov, September 18–20, 1984, Vol. 2, Lvov Polytechnical Institute, Lvov (1984), p. 69.
T. S. Azatyan, V. Mal'tsev, A. G. Merzhanov, and V. A. Seleznev, “Some relationships governing mixtures of titanium and silicon,” Fiz. Goreniya Vzryva,15, No. 1, 43–49 (1979).
V. V. Meshkov, N. K. Myshkin, and A. I. Sviredenok, “A method of calculating the technological parameters of the process of electric sintering of conducting powders,” Poroshk. Metall., No. 11, 8–11 (1976).
A. A. Zenin, A. G. Merzhanov, and G. A. Nersisyan, “Examination of the structure of the heat wave in SHS processes,” Fiz. Goreniya Vzryva,17, No. 21, 79–80 (1981).
A. I. Raichenko, V. I. Leshchinskii, T. I. Istomina, and A. A. Baidenko, “Examination of the process of electric sintering under pressure of metal — diamond compositions,” in: Hot Pressing in Powder Metallurgy [in Russian], Novocherkask Polytechnical Institute, Novocherkask (1979), p. 94.
A. I. Raichenko, M. Z. Kol'chinskii, and D. A. Levina, “Examination of electric discharge sintering of oxidized metallic powders,” Poroshk. Metall., No. 10, 19–26 (1979).
A. V. Pilipchenko, V. Ya. Belousov, A. I. Tsitrin, and A. N. Khomchenko, “Simulation of the temperature field in direct electric heating of powder materials,” Poroshk. Metall., No. 3, 26–29 (1987).