Papers by Keyword: Micropyretic Synthesis

Abstract: The principle of maximum entropy generation rate principle is reviewed for its applicability in Materials Science. The principle of MEPR states that, if there are sufficient degrees of freedom within a system, it will adopt a stable state at which the entropy generation (production) rate is maximized. Where feasible, the system will also try and adopt a steady state. MEPR determines the most probable state. MEPR thus allows for pathway selections that can occur in an open thermodynamic system. Recent work also shows that isolated systems and closed thermodynamic systems also display this principle. The Belousov-Zhabitonsky reaction is also described in the Sgen context. Both solidification morphologies and micropyretic process generated morphologies are studied as examples of the Sgen and MEPR.

Abstract: The influence of ignition parameters for energy efficient processing of high temperature non-oxide ceramics by the micropyretic synthesis route is studied numerically in this article. The simulation results show that a lower ignition power leads to longer ignition time to initiate reactions. An increase in the ignition time also increases the length of pre-heating zone before propagating, which further changes the initiate propagation velocity and oscillatory frequency of the temperature variations. Such changes in the initiate propagation velocity and temperature variations result in inhomogeneous structures at the ignition spot. The simulation also indicates that using a higher power to ignite the micropyretic reactions can lower the ignition time and further prevent the inhomogeneous structures from being formed at the ignition spot. However, more heat loss is noted to occur due to a high temperature gradient and the energy required to ignite the reaction. The numerical calculation indicates that there is a 20 % increase in the required energy and a 90% decrease in the required time to ignite the specimen when the ignition power is increased from 87.5 kJ/(g･s) to 962.5 kJ/(g ･s). In addition, the effect of the individual material property on ignition is also investigated.

Abstract: Experiments on combustion synthesis for the Ti-2B and Ti-C systems diluted with an inert metal are presented. The paper shows the influence of geometry, composition, density and particle size of diluent on the combustion front velocity. A Ti-2B reactant mixture diluted with Al and Cu and a Ti-C reactant mixture diluted with Al are studied. The metallic diluent and its concentration are varied. Besides, each experiment is based on a stack of cylinders with decreasing diameter in order to vary the heat losses. In some experiments the eventual quenching of the combustion reaction has been observed. Furthermore these experimental results are compared with theoretical calculations based on analytical expressions derived for such systems.