High pressure synthesis of magnesium aluminate composites with MoSi<sub>2sub> and Mo<sub>5sub>Si<sub>3sub> in a self-sustaining manner
- 作者：Z.I. Zaki<sup>asup><sup> ; sup><sup>bsup><sup> ; sup><sup>zakimohamed2000@yahoo.comsup> ; Nasser Y. Mostafa<sup>asup><sup> ; sup><sup>csup> ; M.M. Rashad<sup>bsup>
- 关键词：D. Silicides ; MoSi2 ; Mo5Si3 ; MgAl2O4 ; Combustion
- 刊名：Ceramics International
- 出版年：2012
- 期刊代码：13_02728842
- 类别：ms
- 出版时间：August, 2012
- 卷：38
- 期：6
- 页码：5231-5237
- 文件大小：1041 K
摘要
Magnesium aluminate/MoSi<sub>2sub> and magnesium aluminate/Mo<sub>5sub>Si<sub>3sub> composites were successfully prepared by combustion synthesis with a special emphasis on the thermodynamic of the reactions involved in the process. The process involves loading of a very weak exothermic formation reaction of MgAl<sub>2sub>O<sub>4sub> onto a highly exothermic formation reaction of MoSi<sub>2sub> and Mo<sub>5sub>Si<sub>3sub>. The starting material was a blend of MoO<sub>3sub>, SiO<sub>2sub>, Al and MgO. The effect of Al grain size (鈭? to 鈭?1 渭m), MoO<sub>3sub> stoichiometric value (0.7-1.25x), MgO additions (15-25 wt%) and working pressure (50 bar) on the synthesis process were investigated. Microstructure of the combustion products was inspected by SEM. It was found that using 鈭? 渭m grain size Al was necessary for reaction completion. Higher stoichiometric value of MoO<sub>3sub> was found to be necessary to compensate for its volatilization from the reaction media. Addition of MgO as diluents reduced combustion temperature but unexpectedly it reacted with some amounts of SiO<sub>2sub> and formed Mg<sub>2sub>SiO<sub>2sub> phase and Mo<sub>5sub>Si<sub>3sub> instead of MoSi<sub>2sub>. However, increasing the reaction pressure was found to be the most effective factor to suppress the MoO<sub>3sub> volatilization. Thermodynamic study of the process revealed the production of entire phases in molten states whereas the adiabatic temperatures of the formation reaction of MgAl<sub>2sub>O<sub>4sub>/MoSi<sub>2sub> and MgAl<sub>2sub>O<sub>4sub>/Mo<sub>5sub>Si<sub>3sub> composites were 2408 and 3210 K, respectively.