Predictive kinetics-based model for shock-activated reaction synthesis of Ti 3 SiC 2
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John A. Pelesko Department of Mathematical Sciences, University of Delaware, Newark, Delaware 19716-2553
Naresh N. Thadhanib) School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0245 (Received 29 August 2004; accepted 2 March 2005)
A kinetics model based on mass and heat transport has been developed for Ti3SiC2 formation via shock-activated reaction synthesis of powder precursors. The model allows prediction of heat treatment conditions under which an otherwise steady-state reaction is taken over by a “run-away” combustion-type reaction during post-shock reaction synthesis of Ti3SiC2. Shock compression of Ti, SiC, and graphite precursors generates a densely packed highly activated state of reactants, which lowers the activation energy and results in an increased rate of formation of Ti3SiC2 at a lower temperature and in shorter times. The predictive model correlated with experimental results of fraction reacted as a function of time at heat-treatment temperatures of 1400 and 1600 °C illustrates an increased rate of reaction due to lowering activation energy, which also results in the reaction at 1600 °C being taken over by a “run-away” combustion-type reaction, as the rate of heat release due to reaction exceeds the rate of heat dissipation through the compact. Correlation of the model with experimental results illustrates that the predictive model can be used to optimize reaction synthesis conditions in shock-densified compacts of Ti3SiC2-forming powder precursors, to better understand the processes leading to a steady-state reaction being taken over by the combustion mode.
I. INTRODUCTION
Titanium-silicon carbide (Ti3SiC2) is a unique ceramic because of its high-temperature oxidation and wear resistance, combined with metal-like properties including electrical conductivity, thermal conductivity, and easy machinability. Its elastic modulus is typical of that of other carbide-based ceramics, but its hardness is lower and similar to that of high carbon steels. It has a hexagonal crystal structure with TiC octahedra separated by layers of Si atoms. Many attempts have been made to synthesize Ti3SiC2 ternary carbide. The methods include isothermal heat treatment of reactant powders1 and pellets2 and self-propagating high temperature synthesis (SHS) reactions between precursor powders.3 However, a)
Present address: Air Force Research Laboratory, AFRL/MNME, 2306 Perimeter Road, Eglin AFB, FL 32542 b) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0192 1476
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 6, Jun 2005 Downloaded: 16 Mar 2015
most of these methods typically produce TiC and/or SiC phases in addition to Ti3SiC2. Barsoum et al.4 have used hot pressing for producing pure, bulk Ti3SiC2 starting with a mixture of Ti, SiC, and graphite powders. A controlled rate of heating, which ensures reaction occurring in the solid state, has been found to be essential for the synthesis of single phase Ti
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