Self-sustaining synthesis

The technique, now named self-sustaining high-temperature synthesis (SHS) - on the grounds that long names drive out short ones - was later taken up in the West, and has gradually become more sophisticated. The synthesis of TiC, by Holt and Munir (1986) marks the beginning of detailed analysis of heat generation and... 

Intermetallic compound formation may be observed as the result from the diffusion across an interface between the two solids. The transient formation of a liquid phase may aid the synthesis and densification processes. A further aid to the reaction speed and completeness may come from the non-negligible volatility of the component(s). An important factor influencing the feasibility of the reactions between mixed powders is represented by the heat of formation of the desired alloy the reaction will be easier if it is more exothermic. Heat must generally be supplied to start the reaction but then an exothermic reaction can become self-sustaining. Such reactions are also known as combustion synthesis, reactive synthesis, self-propagating high-temperature synthesis. 

Combustion Synthesis. Besides solid-state reactions requiring heating even for several days at high temperatures to be completed, fast reactions are also known which give their products in minutes or seconds. Several nearly equivalent names are used for these reactions such as solid-state combustion, combustion synthesis, self-propagating (self-sustained) high-temperature synthesis. Solid state direct combinations and solid-state metathesis have been described. 

Glagovsky, E. M., Yudintsev, S. V., Kuprin, A. V., Pelevin, L. P., Konovalov, E. E., Velichkin, V. I. Myasoedov, B. F. 2001. A study of actinide crystalline matrices produced by self-sustaining high-temperature synthesis. Radiochemistry, 43, 557-562 (in Russian). 

Postnikov, A. Yu., Levakov, E. V., Gavrilov, P. I., Glagovsky, E. V. Kuprin, A. V. 2001. Self-sustaining high temperature synthesis of zirco-nolite-based materials for radioactive waste immobilization. Physics and Chemistry of Materials Treatment, 5, 58-63 (in Russian). 

A theoretical analysis of combustion synthesis of refractory nitrides was presented by Munir and Holt in 1987.37 They predicted the existence of an activation energy due to chemical reaction or mass-transport. Glassman et al. in 1987,38 in their thermodynamic analysis of TiN formation, examined the possibility of creating TiN by a self-sustained reaction of the metal particles and nitrogen gas in a rocket motor. They reported that for the stoichiometric ratio of 0.5 mole N2/mole titanium, the reaction has... 

The second assay makes use of the isothermal self-sustained sequence replication reaction of RNA (3SR Fahy et al., 1991). Instead of double strand melting to yield single strands the RNA DNA hybrid obtained through reverse transcription is converted into single stranded DNA by RNA digestion making use of RNase H. DNA double strand synthesis and transcription complete the cycle. Here, transcription by T7 polymerase represents the amplification step. 

Mershanov A. Self-sustaining high-temperature synthesis. In Physical Chemistry. Modem Problem, ed. Kolotirkin Ya., Moskva Khimia, 1983. 

The combustion synthesis technique consists of bringing a saturated aqueous solution of the desired metal salts and a suitable organic fuel to the boil, until the mixture ignites a self-sustaining and rather fast combustion reaction, resulting in a dry, usually crystalline, fine oxide powder. By simple calcination, the metal nitrates can, of course, be decomposed into melt oxides upon heating to or above the phase transformation temperature. 

Historically, combustion synthesis (both SHS and VCS) is a direct descendant of classic works on combustion and thermal explosion (e.g.. Mallard and Le Chatelier, 1883 Semenov, 1929 Zeldovich and Frank-Kamenetskii, 1938 Williams, 1965 Glassman, 1977) see Hlavacek (1991) and Merzhanov (1995) for additional comments in this regard. We discuss later in Section IV how the theory of SHS grew directly from these works. The progress in combustion science made it possible to organize self-sustained exothermic reactions in powder mixtures that were controllable and predictable, hence avoiding the uncontrollable evolution of the reaction that is commonly associated with the terms combustion, fire, and explosion. 

In arriving at this synthesis comprehensive studies were summarized of initiation by stimuli such as heat, light, shock, and nuclear radiation. In spite of earlier suggestions to the contrary (see Chapter 9), little evidence was found that tribo-chemical fracture of crystals leads to detonation. Nitrogen tri-iodide was the only substance known to explode under ionizing radiation. The failure to achieve initiation in other substances was discussed in terms of the limited-size hot spots introduced by nuclear particles. This interpretation was consistent with the observation that hot spots of 10" -10" cm diameter are necessary to produce self-sustaining decomposition. 

Hydrazine (N2H4) Synthesis from N2-H2 Mixture in Non-Self-Sustained Stationary Discharge Supported by Electron Beam... 

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