The effect of oxygen catalytic recombination on metal-, metal-oxide-, silicon- carbide-, and carbon-coated surfaces has been experimentally investigated. The experiments were conducted in a shock tube located in the Hypersonic Laboratory at the Korea Advanced Institute of Science and Technology. The test gas considered was a mixture of 21% oxygen and 79% argon by volume. Surface heat-transfer rates at shock tube end-wall were measured using a thin-film gauge. During the testing, the surface of the gauges was polished to a high degree of smoothness and maintained at or near the room temperature. Eight different surfaces, coated with aluminum, iron, titanium, aluminum oxide, iron oxide, titanium dioxide, silicon carbide, and carbon were considered during experiments. Prior to testing, the surface quality was examined using tools for microscopic and macroscopic analyses, thereby characterizing the initial condition. Three different levels of surface roughness of the test samples were also considered to investigate the effect of surface roughness on catalytic phenomena. Efficiency of the oxygen catalytic recombination was determined by evaluating the measured heat-transfer rates whilst referring to existing theories based on binary and tertiary gas mixtures. As observed, catalytic efficiencies corresponding to the aluminium-, iron-, and titanium-coated smooth surfaces measured 0.0034, 0.0036, and 0.0039, respectively, whereas those corresponding to aluminum-oxide-, iron-oxide-, and titanium-oxide-coated surfaces measured 0.0015, 0.0011, and 0.0022, respectively. For the silicon-carbide- and carbon-coated wall, the efficiency were determined to be about 0.0031 and 0.0027, respectively. In the case of the roughened wall, it was found that with an increase in the level of surface roughness, the catalytic activity at the surface is increased. Additionally, an electrical preheating technique applied to a silicon-dioxide-, titanium-, silicon-carbide-, and carbon-coated test model in a shock tube has demonstrated surface temperature around 500 K. The measurement of surface heat-transfer rate at such elevated surface temperatures was also achieved. With the $SiO_2$ data at such preheated surface temperatures, it was found that the present efficiency is comparable to the existing data.
본 논문에서는 금속, 산화금속, 탄화규소, 그리고 탄소 표면에서의 산소 촉매 재결합 현상에 대해 실험적으로 고찰하고자 한다. 실험은 충격파 관을 이용하여, 21%의 산소와 79%의 아르곤 (부피비) 혼합기체를 시험기체로 사용하였다. 충격파 끝단에서 박막 센서를 사용하여 표면 열전달량을 측정하였으며, 실험 전 박막 센서의 표면은 나노미터 단위의 평활성을 유지하도록 연마하고 상온을 유지하였다. 실험에는 알루미늄, 철, 티타늄, 산화알루미늄, 산화철, 산화티타늄, 탄화규소, 그리고 탄소가 표면에 증착된 서로 다른 박막 센서가 고려되었다. 증착이 완료된 박막 센서의 표면은 분석 장비를 통해 초기 성분, 상태, 그리고 표면 조도가 정량적으로 특성화 되었다. 표면 거칠기에 따른 산소 촉매 재결합 현상을 고찰하기 위하여, 서로 다른 세 가지의 조도를 갖는 표면이 고려되었다. 각 소재가 증착된 센서로 부터 획득한 표면 열전달량과 정체점 열전달량 이론식과의 교점에서 산소 촉매 재결합 효율을 도출하였다. 알루미늄, 철, 그리고 티타늄의 촉매 재결합 효율은 각각 0.0034, 0.0036, 그리고 0.0039 값으로 도출되었으며, 산화알루미늄, 산화철, 그리고 산화티타늄의 촉매 효율은 각각 0.0015, 0.0011, 그리고 0.0022 값으로 도출되었다. 탄화규소와 탄소는 각각 0.0031 그리고 0.0027 값으로 도출되었다. 또한, 표면 거칠기가 증가할수록 산소 촉매 재결합 효율이 증가하는 것이 실험적으로 규명되었다. 추가적으로, 전기회로 시스템을 기반으로 하는 표면가열 시스템이 고안되어 이산화규소, 티타늄, 탄화규소, 그리고 탄소 표면에서 500 K 까지 증가됨이 확인되었다. 해당 표면온도에서 표면 열전달량을 측정하였으며, 이산화규소 표면에서의 산소 촉매도가 기존 문헌과 유사한 값을 나타내었다.
