Preparation Of ZrC By Self-propagating High Temperature Synthesis

Zirconium carbide ceramics have been put into application in the fields such as high-temperature structural ceramics, composites, refractory materials and nuclear reactor core materials, for their excellent properties such as high melting point, high bending strength, high hardness, super thermal conductivity, electrical conductivity and capability of low neutron cross-section and good irradiation-resistance.In this paper, ZrC powder was prepared by self-propagating high-temperature synthesis with two systems:Zr-C, ZrO2-C-Mg. The effects of process parameters on the combustion process and experimental results were investigated. The phase and morphology of ZrC powder were analysed.For Zr-C system, the effects of process parameters on the ignition current and combustion temperature during SHS process were investigated. Three carbon sources were selected including activated carbon, carbon black and graphite powders as carbon sources, and the influences on the microscope and chemical composition of final product were studied. Different amounts of NaCl as SHS diluents were added to control the particle size and shape of synthesized powders. The results show carbon black is the best carbon source for preparing ZrC powder. The mean particle size of the product synthesized from zirconium and carbon black is 660nm and the oxygen content is 0.38%. The combustion temperature between reaction of the zirconium and carbon black with 30% in mass NaCl decreases to 1810 K. With the increase of NaCl, the particle size of powder decreases, and its mean particle size is about 50 nm when NaCl content is 30%For ZrO2-C-Mg system, the adiabatic temperature of the system and the Gibbis free energy of every possible reaction were calculated. It is shown that the adiabatic temperature of the system is up to be 2235K and the whole reaction for the formation of ZrC powder is given in the equation and may proceed via two steps:ZrO2+ 2Mg=Zr+2MgO, Zr+C=ZrC.The effects of process parameters on the ignition current and combustion temperature during SHS process were investigated. The complete conversion of the reactants into products was obtained in samples with an excessive addition of Mg (20% excessive addition) and argon pressure of 0.4 Mpa. When the particle size of Mg was 74μm, ZrC powder had a lower oxygen content (3%) than using 154μm Mg particles(3.43%), while the grain size remained about 320 nm, which was independent of the particle size of Mg. The heat treatment results show that with the increase of temperature and holding time, the oxygen content of the powder decreases, while the grain size grows.