레이저 표면 가열 보조의 대기압 마이크로파 플라즈마를 이용한 금속 산화물의 환원 연구

Abstract

Reduction of metal oxides is an important issue in many industrial applications such as steel production, oil refinery, and catalytic processes. In the steel industry, reduction processes of metal oxides using hydrogen gas or plasma have been investigated as an alternative technology to the smelting in blast furnace. In this thesis, a method of accelerating the reduction rate of metal oxides has been developed using an atmospheric microwave non-thermal plasma assisted by laser heating. This method aims to combine the efficient surface heating of the laser and the catalytic effect of reactive species of the plasma. In order to verify the proof-of-concept, hematite powder samples have been tested with varying hydrogen gas concentration and surface temperature. The plasma gas temperatures were measured using Rayleigh scattering method and thermocouple, the surface temperature was monitored by infrared imaging, and the surface state was analyzed by Raman spectroscopy and X-ray diffraction. The atomic line emission of hydrogen (H-α) was used as a qualitative indicator for the hydrogen concentration. It is found that the surface of the hematite powder reduces to magnetite when it reaches a threshold temperature regardless of the hydrogen gas ratio. It turned out that H-α emission is not an adequate indicator for identification of active species in the reduction process of the hematite. It is confirmed that the most critical parameter in the plasma reduction reaction is the surface temperature of sample.