Phase characterization and burning rate in the self-propagating high-temperature synthesis of titanium borides
- PDF / 881,449 Bytes
- 6 Pages / 576 x 792 pts Page_size
- 37 Downloads / 147 Views
Hong Yong Sohn Department of Metallurgical Engineering, University of Utah, Salt Lake City, Utah 84112-1183
Hyung-Bock Lee Department of Inorganic Materials, Myung-Ji University, Yongin, Korea (Received 3 March 1995; accepted 10 August 1995)
Combustion synthesis of titanium borides from Ti and B binary powder mixtures having molar ratios B/Ti of 1.9 to 2.4 resulted in the formation of TiB2 as the primary phase and TiB as the secondary phase. The amount of TiB decreased when the particle size of the Ti in the powder mixtures became small and when the B content was increased. The results are discussed in terms of the homogeneity of reactant powder mixtures and the degree of boron saturation of the Ti-B melt. The burning rate increased from 11 to 15 mm/s as the titanium particle size decreased from —100 to —325 mesh with the same boron particle size of —325 mesh.
I. INTRODUCTION The self-propagating high-temperature synthesis (SHS) method, also referred to as combustion synthesis, is a process for synthesizing inorganic materials using the large thermal energy generated by the exothermic reactions taking place during the process. Extensive studies on this process have been carried out over the past twenty years.' 3 Many inorganic materials including intermetallics, ceramics, and ceramic composites have been synthesized using this method. This process has many advantages over other hightemperature synthesis processes such as the relative simplicity of process equipment,4 self-purification effect due to the volatilization of impurities,5 and in some cases the formation of rare metastable phases6 and products with high defect concentration because of the nonequilibrium nature of the process. Several articles7"12 on the combustion synthesis of titanium borides, mostly TiB2, have appeared recently, mainly dealing with the microstructure of product phases and the effects of initial particle sizes of the reactants, compact density, and diluent contents on the synthesis process, especially with respect to the combustion temperature and the combustion rate. 81112 The activation energy for the combustion synthesis of TiB was obtained from the analysis of the combustion temperature and the combustion rate data.12"17 In the present work, the effects of Ti particle size and the B content in the reactant mixture in the vicinity of the stoichiometric value for TiB2 formation on the forJ. Mater. Res., Vol. 10, No. 12, Dec 1995 http://journals.cambridge.org
Downloaded: 24 Mar 2015
mation of product phases were investigated. A particular emphasis was placed on the amount of TiB phase formed relative to that of TiB2 as a function of these variables. The burning rate was determined for a stoichiometric mixture (for TiB2 formation) using titanium particles of different sizes. II. EXPERIMENTAL PROCEDURE Powders of crystalline Ti and crystalline B were used as the reactants. Table I lists the particle sizes and the purities of the reactants. The compositions of the reactant powder mixtures (molar ratios of Ti: B) investigated in the pr
Data Loading...
