Microwave sintering temperature control

The formation of YAG through solid-state reaction is controlled by the diffusion of Al -" [156]. Such diffusion of Al -" was enhanced by the microwave field, so that the reaction temperature of YAG and its sintering temperature were decreased, as evidenced by the pores entrapped in grains, as shown in Fig. 7.44b. Similarly, the formation of the liquid phase was also promoted. In other words, the content of sintering aids could be reduced when using microwave sintering, which however needs further clarification. 

The microwave sintering was performed in a kitchen oven, commercially available, that has been modified by the addition of a temperature controller and an insulation box and silicon carbide susceptors. The modifications include a thermocouple (Pt-PtRh) and a power controller (with both manual and automatic options) for temperature control. The insulation box consists of a small chamber fabricated from low-density insulation board. Low density and very low dielectric loss is required for... 

To sinter the specimens, two specimens were stacked one on top of the other and centered on the floor of an insulation box fabricated from low-density insulation board. Once the insulating box was positioned in the microwave, a power level was selected from the controller and the timer on the microwave set. During the run up to 1350 °C and 1450 °C (and hold for 30 minutes), the power was manually stepped and the temperature measured every minute. When the run was complete, the microwave door was opened and it was possible to remove the box. After approximately 40 minutes of cooling, the specimens were removed from the oven. The sintering time as function of microwave heating temperature is given in Figure I. 

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