Diffusion in Microwave-Heated Ceramics

Abstract

Microwave heating is an increasingly important method of chemical activation in both the laboratory and industrial processing. The increased breadth of microwave applications has not, however, been accompanied by a corresponding depth of understanding of microwave heating. The question of what constitutes a "microwave effect" remains unresolved, and that of whether "nonthermal" microwave activation takes place remains controversial. The effects of microwaves in solid materials and in biomolecules, in particular, are incompletely understood. In this paper, a method is described in which the effects of microwave heating may be investigated during the sintering of ceramic materials. By comparison of the diffusion rates parallel with, and perpendicular to, a polarized microwave field, the effects of thermal energy may be separated from those that are directly due to the microwaves. The results suggest that there is an enhanced sintering rate that is due to the presence of the microwave field, which becomes less significant as the sintering time increases. The results are consistent with a "ponderomotive" model that has been suggested previously and may have implications for reduced energy use in solid-state processing and for the rate at which thermally sensitive materials may be processed.

Rapid, energy-efficient synthesis of the layered carbide, Al4C3

“…17 Further attractions of MW processing are the opportunities offered to access new and metastable materials 22 and to rationalise the interaction of solids with electromagnetic fields. 23 The development of microwave synthesis in the solution state has been more rapid given the challenges associated with homogeneity and scale up in MW solid-state synthesis and materials processing. 24 To advance solid-state microwave process design there is a requirement both to develop an underpinning understanding of how microwave reactions proceed and to design instrumentation optimised for chemical reactions.…”

Facile synthesis of Ca-α-SiAlON:Eu2+ phosphor by the microwave sintering method and its photoluminescence properties

“…During the heating process, the electromagnetic wave can penetrate into materials and heat them owing to the interaction between polarized molecular (or ions) and electromagnetic field, finally resulting in volumetric heating to make it possible to achieve a rapid and uniform heating. In the past decades, the microwave heating method has been widely used for processing and drying solutions [12], sintering ceramics [13], fabricating functional materials [14]. However, to our best knowledge, there are rare reports that conduct researches on microwave sintering of nitride phosphors.…”

Effect of 24GHz microwave heating on creep deformation of yttria partially stabilised zirconia ceramics with titania and tin oxide additives

“…At $ 24 GHz, ε″ was approximately the same for both SS-3YSZ and TS-3YSZ, suggesting almost identical local heating, which was proportional to ε″. However, ε 0 for TS-3YSZ was larger than that for SS-3YSZ, suggesting that nonthermal effects proportional to ε 0 in TS-3YSZ were more significant than those for SS-3YSZ [19][20][21]. Such a relationship in dielectric constants between dispersed SnO 2 and TiO 2 should be maintained during the creep test because no abnormal variation in the MMW absorption was observed at the elevated temperatures, in contrast to the monolithic structures [22].…”