Kwang-Tae Kim

Corrosion Inhibiting Mechanism of Nitrite Ion on the Passivation of Carbon Steel and Ductile Cast Iron for Nuclear Power Plants

While NaNO2 addition can greatly inhibit the corrosion of carbon steel and ductile cast iron, in order to improve the similar corrosion resistance, ca. 100 times more NaNO2 addition is needed for ductile cast iron compared to carbon steel. A corrosion and inhibition mechanism is proposed whereby ion is added to oxidize. The ion can be reduced to nitrogen compounds and these compounds may be absorbed on the surface of graphite. Therefore, since nitrite ion needs to oxidize the surface of matrix and needs to passivate the galvanic corroded area and since it is absorbed on the surface of graphite, a greater amount of corrosion inhibitor needs to be added to ductile cast iron compared to carbon steel. The passive film of carbon steel and ductile cast iron, formed by NaNO2 addition showed N-type semiconductive properties and its resistance, is increased; the passive current density is thus decreased and the corrosion rate is then lowered. In addition, the film is mainly composed of iron oxide due to the oxidation by ion; however, regardless of the alloys, nitrogen compounds (not nitrite) were detected at the outermost surface but were not incorporated in the inner oxide.

Development Trends of Duplex Stainless Steels for the Process Industries and It's Weldability

2상 스테인리스강는 금속 조직적으로 페라이트와 오스테나이트 상이 거의 1:1의 동등한 비율로 혼합된 미세조직을 갖는 스테인리스강이다. 2상 스테인리스강은 1930년에 개발되어 약 80년의 개발 역사를 가지고 있으나, 실질적으로는 C, N 정련기술이 확립된 1970년 대에 이르러 현재와 같은 야금학적 특성을 갖는 2상 스테인리스강이 상용화되었다고 할 수 있다. 또 1980년대 초에는 슈퍼 2상 스테인리스강과 2304 Lean급 2상 스테인리스강이 연속해서 개발되었다. 특히 근래에는 Ni 원료 가격의 폭등으로 Ni 함량이 높은 304, 316 뿐만 아니라 슈퍼 오스테나이트계 스테인리스강에 이르기까지 상대적으로 Ni 을 적게 첨가함으로써 저 원가인 2상 스테인리스강으로 대체하려는 움직임이 전반적인 추세라고 할 수 있다. 이 때문에 최근 2상 스테인리스강의 개발 니즈(Needs)증가하고, 시장 확대가 가속되고 있다고 해도 지나친 것은 아니다. 실제로 최근에는 2상 스테인리스강이 년간 20% 이상 해마다 그 수요가 증가하고 있다는 보고도 있다

TWO MOLECULAR CLOUDS WITH ANOMALOUS VELOCITIES IN THE GALACTIC ANTICENTER

We map two molecular clouds located in the exact anticenter region emitting in the (J = 1-0) transition of 12 CO and 13 CO using the 3-mm SIS mixer receiver on the 14-m radio telescope at Taeduk Radio Astronomy Observatory. The target clouds with anomalous velocities of V LSR ~ -20 km s -1 are distinguished from other clouds in this direction. In addition, they are located in the interarm region between the Orion Arm and the Perseus Arm. Sizes of the clouds are estimated to be about 8.6 and 10.8 pc, respectively. The total mass is estimated to be about 4 x 10³ M ⊙ using CO luminosity of the clouds. Several cores are detected, but no sign of star formation is found according to the IRAS point sources. Their larger linewidths, anomalous velocities, and their location at the interarm region make these clouds more distinguished, though their physical properties are similar to the dark clouds in the solar neighborhood in terms of mass and size.