(230d) Finite Element Analysis of Heat Transfer in a Solid State Reaction System

Advanced materials such as nitrides, oxides and carbides have been successfully synthesized using Self-propagating High-temperature Synthesis (SHS), a highly exothermic reaction process. Because of the process’s high reaction temperature and fast reaction rate developing a mathematical simulation of the process is crucial for a safe large scale manufacture. Silicon nitride is a good structure ceramic material and a superior material used as a heat sink in LED and many other energy applications. In this work, a time dependent three-dimensional finite element analysis model is developed to study the SHS of silicon nitride via 3Si + 2 NaN₃ + 0.2 Si₃N₄→ 1.2 Si₃N₄ + 2Na + N₂. Momentum transfer, heat transfer, temperature dependent thermodynamic properties and reaction kinetics are integrated in the model. A reaction mechanism including silicon nitridation, sodium azide decomposition, sodium vaporization and silicon nitride decomposition at high temperatures are proposed and included in the reaction network. Temperature history, reaction rates, reaction conversion, combustion front movement velocity, and the impact of silicon nitride diluent on the SHS process are presented.