When Should Microwaves Be Used to Process Technical Ceramics?

Abstract

This paper attempts to shed light on why the stand alone microwave processing of technical ceramics, despite being one of the most popular field with respect to volume of research performed, is still struggling to achieve priority status with respect to commercialisation. To obtain some answers to this enigma and determine when microwaves should be used to process technical ceramics, three case studies are explored. The conclusion is that microwaves should be used to process technical ceramics when specific advantage can be taken of the intrinsic nature of microwave energy and not simply as an alternative energy source. In addition, it is concluded that from a commercialisation view point hybrid processing is often a better approach than the use of pure microwaves.

Microwave Sintering of Multilayer Integrated Passive Devices

“…As can be seen, with the exception of Variance, high V nom (almost double) and acceptable values of C r , leakage current, were obtained for the microwave‐sintered IPDs due to the finer grain size and high densities achieved. This correlates well with the literature reports where almost twice the breakdown voltage was also measured for microwave‐processed single‐component and multilayer varistors compared with conventionally processed samples 21,23,25 . Extending the soaking time at temperature gradually improved the variance due to the slightly higher densities achieved; however, at longer durations the V nom slightly dropped owing to larger grain sizes in the resulted device components.…”

“…It is clear that at any given temperature the microwave process provides a much higher densification than conventional sintering, a result that has been observed before in many other systems 14,23,24 . Although the exact mechanism for the enhanced densification is not yet clearly understood, the electric field component of the EM radiation could be playing a crucial role in enhancing the densification kinetics during the microwave sintering of electroceramics 21,25,26 …”

“…14,23,24 Although the exact mechanism for the enhanced densification is not yet clearly understood, the electric field component of the EM radiation could be playing a crucial role in enhancing the densification kinetics during the microwave sintering of electroceramics. 21, 25,26 Optical microscopy of the samples microwave sintered at 10501C for 20 min revealed that the metal electrodes (average electrode spacing 5 69 mm) in these devices were fully intact, Fig. 4, without delamination and no electrode ''buckling'' was noticed.…”

“…9, was found to be remarkably uniform and the electrical properties showed a clear improvement in their variance values, bringing it closer to what was considered to be acceptable, Table III. Additional work based on the use of a genuine hybrid microwave/conventional sintering cavity 14,21,25 has improved the variance during the processing of multilayer electroceramic devices further (this method also eliminated the need for “casketing”) and showed that there is a clear potential for scaling up the process.…”

“…This correlates well with the literature reports where almost twice the breakdown voltage was also measured for microwave-processed single-component and multilayer varistors compared with conventionally processed samples. 21,23,25 Extending the soaking time at temperature gradually improved the variance due to the slightly higher densities achieved; however, at longer durations the V nom slightly dropped owing to larger grain sizes in the resulted device components. Nevertheless, the variance still remained high.…”