Search

ZnO samples with an addition of 0, 0.035, 0.1, and 0.35 mol.% Bi2O3 were microwave sintered at heating rates 10 and 50°C/min to a maximum temperature of 1200°C with zero hold time. The densification curves obtained by optical dilatometry have been studied in their dependence on the dopant concentration and the heating rate. Direct volumetric absorption of microwave radiation resulted in a 50–60°C shift of the densification curves toward low temperatures compared to susceptor‐assisted heating. An analysis of the effect of the volumetrically absorbed microwave power on the formation of grain‐boundary phases that facilitate densification is presented. [ABSTRACT FROM AUTHOR]

MgAl2O4 samples were microwave sintered to near‐full density in rapid processes with heating rates on the order of 100°C/min and zero isothermal hold. The experiments were carried out using a gyrotron system for microwave processing of materials operating at a frequency of 24 GHz with a maximum power of 6 kW. In the regimes with a preset heating rate sustained by the automatically regulated microwave power, the maximum achieved density was about 95% of the theoretical value in pristine MgAl2O4 samples (maximum sintering temperature 1650°C) and about 97% in 1 wt.% Y2O3‐doped samples (1700°C). In the regimes with a fixed microwave power (about 3.5 kW), translucent spinel samples with a relative density above 99% were obtained at 1700°C. The duration of the high‐temperature stage of sintering was 1.5‐10 minutes. The suggested mechanism responsible for the enhanced densification involves development of a thermal instability and formation of transient liquid phases at grain boundaries. The estimated specific absorbed power in the samples during the high‐temperature stage of ultra‐rapid microwave sintering was 27‐80 W/cm³, similar to the values observed in dc field‐assisted flash sintering experiments. [ABSTRACT FROM AUTHOR]

Yb:(LaY)2O3 ceramic samples have been sintered to almost full density in a fast microwave heating process with zero hold time. Rapid densification is observed at heating rates ranging from 50°C to 2400°C/min. The estimated value of the power absorbed in the materials per unit volume is from 10 to 400 W/cm3, which is similar to the processes of flash sintering under an applied dc/ac voltage. The microstructure of the sintered samples exhibits traces of a liquid-like intergranular phase. The observed flash microwave sintering effect is associated with both preferential microwave absorption and enhanced mass transport within the softened grain boundaries arising due to an elevated concentration of defects and impurities therein. The volumetric nature of microwave heating gives rise to thermal stresses which can act as an additional driving force for sintering. The advantage of the microwave flash sintering process is that no electrodes are needed to supply the power to the articles undergoing sintering. [ABSTRACT FROM AUTHOR]

MgAl2O4 samples were microwave sintered to near‐full density in rapid processes with heating rates on the order of 100°C/min and zero isothermal hold. The experiments were carried out using a gyrotron system for microwave processing of materials operating at a frequency of 24 GHz with a maximum power of 6 kW. In the regimes with a preset heating rate sustained by the automatically regulated microwave power, the maximum achieved density was about 95% of the theoretical value in pristine MgAl2O4 samples (maximum sintering temperature 1650°C) and about 97% in 1 wt.% Y2O3‐doped samples (1700°C). In the regimes with a fixed microwave power (about 3.5 kW), translucent spinel samples with a relative density above 99% were obtained at 1700°C. The duration of the high‐temperature stage of sintering was 1.5‐10 minutes. The suggested mechanism responsible for the enhanced densification involves development of a thermal instability and formation of transient liquid phases at grain boundaries. The estimated specific absorbed power in the samples during the high‐temperature stage of ultra‐rapid microwave sintering was 27‐80 W/cm³, similar to the values observed in dc field‐assisted flash sintering experiments. [ABSTRACT FROM AUTHOR]