Madhuchhanda Bhattacharya

Susceptor-Assisted Enhanced Microwave Processing of Ceramics - A Review

ABSTRACT Susceptor-assisted microwave processing is a rapidly growing technology due to its superiority over the conventional processing. In contrast to the conventional heating from the surface, the microwave heating occurs volumetrically via direct interaction with the material. Correspondingly, the microwave heating rates are in general much faster than the heating rates in the conventional furnaces, where heat has to be transferred from the heat sources to the material via conduction, convection and radiation. The need for the susceptor stems from the fact that the majority of the ceramics are low lossy materials and they cannot couple well with the microwave at room temperatures. The susceptor provides an easy and non-invasive technique to exploit the rapid microwave processing even for the highly microwave transparent ceramics, such as alumina, silicon nitride, quartz, etc. This article critically evaluates the susceptor-assisted microwave sintering and solid state synthesis of ceramics which have been reported over the last two decades. A wide range of ceramics has been considered and each case has been analyzed in terms of the enhancement of the processing rates and product qualities (grain structure, material properties, etc.) compared to the conventional processing. It has been shown that the susceptor-assisted microwave processing can greatly reduce the processing time while providing an easy pathway to achieve the desired product qualities. The use of the appropriate susceptor is the key to achieve the fast, smooth, and reliable microwave processing of ceramics and this article provides the required database for the appropriate design of the susceptor based on the process requirement.

Linear stability analysis for the onset of convection during microwave heating of oil confined within horizontal plates

This work performs linear stability analysis to investigate the onset of convection due to microwave incidences in a horizontal oil layer. The probability of onset has been characterized in terms of critical Rayleigh number (Rac), while the microwave power required to initiate convection has been quantified in terms of modified Rayleigh number (Ra¯c). The associated convection cell size has been illustrated by critical wave number (kc). These critical numbers (Rac, Ra¯c, and kc) have been determined for the entire spectrum of oil thicknesses ranging from thin to thick samples and various possible microwave source configurations starting from one sided to distributed incidences. It has been shown that the critical numbers oscillate with oil thickness in intermediate regime indicating preferential onset for specific oil thicknesses. It has also been shown that microwave source configuration plays an important role in controlling the onset of convection. Finally, the variations of Rac and kc have been correl...

Linear Stability Analysis for the Onset of Convection During Microwave Heating of Samples Confined Within Horizontal Plates

This work performs linear stability analysis to investigate the onset of convection due to microwave incidences in water and oil confined between two semiinfinite horizontal plates. The onset has been characterized in terms of critical Rayleigh (Rac ) and wave (kc ) numbers, which are determined for the entire spectrum sample thickness varying from thin to thick samples exposed to various microwave source configurations including one sided to distributed incidences. The main finding of this work is the oscillatory variations of Rac and kc with sample thickness in sinusoidal regime of microwave heating, which indicates preferential onset for specific sample thicknesses. It has also been shown that materials as well as microwave source configuration play important roles in the onset of convection in this regime. The variation patterns of Rac and kc have been correlated to the spatial patterns of absorbed microwave power within the sample. These results are useful not only for forecasting the onset but also for controlling onset of convection by selecting suitable experimental parameters.Copyright

Analysis on the onset of microwave induced convection within a horizontal water layer

This work is concerned with the onset of convection due to microwave incidence in a horizontal water layer. The onset characteristics in terms of critical Rayleigh (Rac) and wave (kc) numbers have been determined for various regimes of microwave heating, namely thin, sinusoidal and thick samples. It has been shown that both Rac and kc exhibit oscillatory patterns in sinusoidal regimes of microwave heating, while they attain asymptotes in thin and thick sample regimes. The variation patterns of critical Rayleigh and wave numbers from thin to thick samples have been correlated with the degree of asymmetry in internal heat source profiles. The analysis is carried out over the entire spectrum of microwave source configurations. It has been shown that there exists a one-to-one correlation between the variation patterns of Rac and kc with the degree of symmetry in internal heat source profiles. The total power required to initiate the convection has also been analysed in terms of the modified Rayleigh number .