Plasma Assisted Microwave Sintering and Joining of Ceramics

Abstract

ABSTRACTDirect microwave sintering and joining of low temperature ceramics such as mullite have been extensively studied. However, it is recognised that microwave sintering and joining of high temperature oxide and non-oxide ceramics poses serious problems, primarily because of the difficulty of coupling microwave energy into these non-absorbing materials which make up the bulk of advanced ceramics. Attempts to overcome this problem by using indirect auxiliary heating or utilisation of intermediary or impure materials have been, by and large, unsatisfactory. Indeed, this fundamental physical barrier has seriously impaired the penetration of microwave heating in ceramic processing.In order to overcome this seemingly insurmountable fundamental barrier, a radical approach is required. This has been recently achieved by using a Microwave Induced Plasma (MIP) whereby microwave energy is utilised in a hybrid fashion. In this method, a microwave plasma is used to rapidly heat the ceramic to temperatures at which it becomes absorbing. At this point, microwave radiation is directly coupled to the ceramic and the plasma is extinguished since energy is no longer available to ionise the gas and sustain a plasma. This hybrid approach circumvents the limitations of conventional microwave heating for sintering and joining of advanced materials. In this review paper the fundamentals of microwave/materials interaction and conventional approach to microwave heating of ceramics will be thoroughly discussed. In addition, the new hybrid heating developed by the authors will be described and the possibility of MIP-assisted sintering/joining of industrially important materials will be demonstrated.