Microwave Sintering: Fundamentals and Modeling

Abstract

This paper reviews the basic physical notions underlying microwave sintering and the theoretical and numerical models of the microwave sintering process. The propagation and absorption of electromagnetic waves in materials, and the distribution of electromagnetic field in cavity resonators that serve as applicators for microwave processing are discussed and the electromagnetic modeling of such applicators is reviewed. The microwave absorption properties of ceramic and metal powder materials and the methods of their description are addressed. Self‐consistent electromagnetic and thermal models that are capable of predicting the temperature distribution in the microwave‐heated materials and dynamic effects such as thermal runaway instabilities are reviewed. The multiphysics simulations that combine electromagnetic, thermal, and sintering models and result in predicting densification, shrinkage, and grain structure evolution are discussed in detail. The significance of microwave nonthermal effects in sintering is demonstrated based on the experimental results, and the models of such effects are reviewed.

Flash sintering of ceramic materials

“…300MHz-300GHz) electromagnetic radiation to sinter ceramic materials at temperatures below conventional sintering temperatures and in short sintering times [58]. Ceramics produced by microwave sintering have high density and small grain size [59], though the mechanisms for the evolution of the microstructure during densification are not well understood [58] and extensive modelling efforts are in progress. It has been suggested by some researchers that densification during flash sintering occurs by a similar mechanism to microwave sintering [60,61].…”

Critical assessment 28: Electrical field/current application – a revolution in materials processing/sintering?

“…A simplified classification has been proposed by Grasso et al [3] and is presented in modified form in Table 1. This list does not even include microwave sintering [9] and the recently introduced flash sintering [10], as these techniques involve experimental layouts that are quite different from SPS. All the techniques listed in Table 1, on the other hand, present layouts that are quite similar, with the main difference being mostly associated to the characteristics of the electric current that is applied to the sample [2,3].…”

Propiedades mecánicas y coeficiente de dilatación térmica de la β-eucriptita sinterizada por la técnica de microondas

“…En nuestro caso, el aluminosilicato de litio (LAS) es un material dieléctrico absorbente de microondas desde temperaturas bajas (∼25 ºC) hasta altas temperaturas (>1200 ºC). Este hecho resulta una importante ventaja frente a otros materiales cerámicos donde las propiedades intrínsecas del material hace que sean, o bien transparentes a las microondas (tipo la alúmina), o bien absorbentes solo a alta temperatura (tipo la circona) (21,22). Lo cual hace que sea necesario el uso de susceptores, como el carburo de silicio, para poder sinterizar el material en cuestión.…”

“…Por lo tanto, la zona más energética se encuentra en el centro del propio grano, estando menos favorecida la difusión a través de los límites de grano (21). El calentamiento por microondas inhibe el crecimiento de grano, lo cual implica unas mejoras considerables en las propiedades mecánicas de las muestras, como se discute a continuación.…”