SYSTEMS FOR SHOCK-ASSISTED AND DETONATION-DRIVEN SYNTHESIS: REACTIVITY OF Ti– С POWDER MIXTURES

1. SYSTEMS FOR SHOCK-ASSISTED AND DETONATION-DRIVEN SYNTHESIS: REACTIVITY OF Ti–С POWDER MIXTURES V. A.Veretennikov Institute of Structural Macrokinetics and Materials Science, Chernogolovka, Moscow, 142432 Russia e-mail: veret@ism.ac.ru

2. As is known [1,2], a prerequisite for gasless detonation in media with positive coefficient of thermal expansion is either a non-zero isobaric-isochoric thermal effect of reaction (QP,V 0) or physically equivalent positive volume change at constant pressure P and enthalpy H (VP,H 0). However the reaction rate also becomes a necessary condition for detonation when we deal with charges of finite dimensions. This work aimed at elaborating a method for reliable estimation of reactivity (reaction rate) of metal–nonmetal powder mixtures as candidate systems for self-sustained gasless detonation. The experimental data [3] on high-temperature reaction of Ti pow-der (mean particle size 65 µm) with crystalline flake graphite were obtained by the technique of current-induced thermal explosion [4,5]. Upon reaction ignition at 1300 K, the evolution of the sample temperature has been recorded with a high time resolution. Within the temperature range 1500–2000 K, the reaction rate was found to change by as much as a factor of ten.

3. The reaction rate (dT/dt) was found to be proportional (in terms of the approach suggested in [6]) to a set of structural characteristics of flake graphite that can be determined experimentally (see the Table). The empirical expression for this set of structural parame-ters Kr can be written in the form: where Cg is the extent of graphitization, М the fraction of graphite-like carbon, Тx the texturization factor (ordering of crystallites in a flake), La and Lc the size of crystallites along the а and с axes, d002 the interlaminar separation in a crystallite, dg1 and dg2 the interpla-nar spacing in ideal graphite and turbostratic pyrocarbon (3.354 and 3.44 Å, respectively).

4. Cgextent of graphitization Мfraction of graphite-like carbon Тxtexturization factor (ordering of crystallites in a flake) La, Lcsize of crystallites along the а and с axes d002interlaminar separation in a crystallite dg1, dg2 interplanar spacing in ideal graphite and turbostratic pyrocarbon (3.354 and 3.44 Å, respectively)

5. Figure shows the linear interpolation plot ln(dT/dt)–Kr. In essence, this plot reflects the exponential dependence of reation rate on the structure of carbon material. Physical meaning of this observation still remains unclear.

6. References • A.S. Shteinberg, V.A. Knyazik, V.E. Fortov. 1994. On the Feasibility of Gasless Detonation in Condensed Systems. Dokl. Akad. Nauk 336(1): 71. • Yu.A. Gordopolov, V.S. Trofimov, A.G. Merzhanov. 1995. On the Feasibility of Gasless Detonation in Condensed Systems. Dokl. Akad. Nauk 341(3): 327. • V.A. Veretennikov, S.E. Zakiev, V.T. Popov, K.V. Popov. 2002. Mesostructure of carbon black and reactivity of Ti–C mixtures. Probl. Materialoved. 1(29): 403. • V.A. Knyazik, A.E. Denisenko, E.A. Chernomorskaya, A.S. Shteinberg. Automated Apparatus for Investigating SHS Kinetics. 1991, Prib. Tekh. Eksper., (4): 164. • K.V. Popov, V.A. Knyazik, A.S. Shteinberg. 1993. High-temperature reaction of Ti with B as studied by current-induced thermal explosion technique. 1993. Fiz. Goeniya Vzryva 29(1): 82. • A.A. Zenin, Yu.M. Korolev, V.T. Popov, Yu.V. Tyurkin. 1986. Non-isothermal carbonization of titanium. Dokl. Akad. Nauk SSSR 287(1): 111.