The paper describes the features of the metal oxide nanopowder obtaining by an evaporation-condensation method with pulsed heating of the material by focused subterahertz radiation. It has been experimentally shown that optimal conditions for the rapid evaporation of a substance are achieved at the highest possible pulse power and the lowest possible duty cycle at a fixed average power. Under these conditions, it is possible to realize the heating and evaporation of a substance in a focused radiation beam in a relatively short time, while the adjacent layers of the substance maintain a relatively low thermal conductivity. A linear increase in the evaporation rate with a decrease in the duty cycle of heating pulses was demonstrated, the increase reached 5 times relative to the continuous heating mode.
The temperature dependences of the absorption coefficient of Al2O3, ZnO, TiO2 powders at a frequency of 527 GHz are investigated. A gyrotron with an output power of up to 240 W in CW mode was used as a radiation source for heating the samples. The power absorbed in the samples was measured in the temperature range from 300 to 1000 ° C (for some samples). Compared with experiments at a frequency of 263 GHz, a significant increase (by a factor of 4 - 6) in the absorption coefficient is observed. The results may be of interest to researchers involved in microwave heating of materials.
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