Environmental regulations of the International Maritime Organization (IMO) are getting stricter, and the demand for replacing the fuel of ships with eco-friendly fuels instead of heavy oil in the shipbuilding and marine industries is increasing. Among eco-friendly fuels, LNG (liquefied natural gas) is currently the most popular fuel. This is because it is an alternative that can avoid the IMO's environmental regulations by replacing fuel. In PART 1, as a basic study of laser welding of high manganese steel materials, a fiber laser bead-on-plate experiment was conducted using nitrogen protective gas, and the effect of each factor on the penetration shape was analyzed through cross-sectional observation. In PART II, argon and helium shielding gases, not the nitrogen shielding gas used in PART I, were tested under the same experimental conditions and the effect of the shielding gas on penetration during laser welding was conducted.

Environmental regulations of the IMO (International Maritime Organization) are becoming more and more conservative. In order to respond to IMO, the demand for replacing the fuel of ships with eco-friendly fuels instead of conventional heavy oil is increasing in the shipbuilding and offshore industries. Among eco-friendly fuels, LNG (Liquefied Natural Gas) is currently the most popular fuel. LNG is characteristically liquefied at -163 degrees, and at this time, its volume is reduced to 1/600, so it is transported in a cryogenic liquefied state for transport efficiency. A tank for storing this should have sufficient mechanical/thermal performance at cryogenic temperatures, and among them, high manganese steel is known as a material with high price competitiveness and satisfying these performance. However, high manganese steel has a limitation in that the mechanical performance of the filler metal is lower than that of the base metal called ‘under matching’. In this study, to overcome this limitation, a basic study was conducted to apply the fiber laser welding method without filler metal to high manganese steel. To obtain efficient welding conditions, in this study, bead-on-plate welding was performed by changing the fiber laser welding speed and output using helium shielding gas, and the effect of each factor on the penetration shape was analyzed through cross-sectional observation.

고주파 스피터 방법으로 제조된 SnO2감지막 위에 에어로졸 화염 증착법으로 알루미나 표면 보호층을 증착하여 SnO2박막 가스 센서의 감지 특성에 미치는 영향에 대햐여 조사하였고, 표면 보호층에 귀금속 Pt를 도핑하여 Pt의 함량이 CO 및 CH(sub)4 가스들의 선택성에 미치는 영향에 대하여 조사하였다. SnO2박막은 R.F power 50 W, 공정 압력 4 mtorr, 기판온도 200˚C에서 30분간 0.3μm 두께로 Pt 전극 위에 제조하였고, 질산알루미늄(Al(NO3).9H2O) 용액을 희석하여 에어로졸 화염증착법으로 알루미나 표면 보호층을 만든후 600˚C에서 6시간동안 산소분위기에서 열처리하였다. 알루미나 표면 보호층이 증착된 SnO2가스 센서소자의 경우 보호층이 없는 가스 센서와 비교하여 CO 가스에 대한 감도는 매우 감소하였으나 CH4가스에 대한 감도 특성은 순수한 SnO2센서 소자와 비슷하였다. 결과적으로 보호층을 이용하여 CH4가스에 대한 상대적인 선택성 증가를 이룰 수 있었다. 특히 표면 보호층에 Pt가 첨가된 센서 소자의 경우 CO 가스에 대해서는 낮은 감도 특성을 나타내었으나 CH4에 대한 감도는 매우 증가하여 CH4가스의 선택성을 더욱 증대시킬 수 있었다. CH4가스 선택성 향상에 미치는 알루미나 표면 보호층과 Pt의 역할에 대하여 고찰해 보았다.