오오스테나이트 스테인레스강에서 Si 첨가가 응력부식파괴에 미치는 영향

변수일,한유동 대한금속재료학회(대한금속학회) 1981 대한금속·재료학회지 Vol.19 No.6

The effect of Si addition on the stress corrosion cracking (SCC) of austenitic stainless steel was studied in the boiling aqueous solution of 42% MgCl₂. Failutre time, under constant load, remained nearly constant for the specimen with Si content up to 1.42 wt.%, however, it increased drastically as Si content increased from 1.42 to 2.21 wt.%, and further increase in Si content did not affect the failure time. Metallographic examination showed that the specimen with Si <1.42 wt.% and Si> 2.21 wt.% had austenitic single phase and austenitic-ferritic duplex phase respectively. The increased failure time caused by Si addition was explained in terms of retardation of SCC growth due to ferrite phase and formation of stable passive film. No change in pitting potential(breakdown) was observed for both unstressed and stressed specimen regardless of its Si content respectively. The stressed specimen showed lower (more anodic) pitting potential than the unstressed. Critical passivation current density (critical anodic partial current density), in pass estimated from electrochemical polarization curve and weight loss measurement decreased with Si addition and higher passivation current density was observed with the stressed specimen compared with the unstressed.

An Overview of the Activated Carbon Fibers

변수일,이경자 한국전기화학회 2006 한국전기화학회지 Vol.9 No.1

This article is concerned with the overview of the activated carbon fibers. Firstly, this review provides a comprehensive survey of the overall processes for the synthesis of the activated carbon fibers from the carbonaceous materials. Subsequently, the physicochemical properties such as pore structures and surface oxygen functional groups of the activated carbon fibers were discussed in detail. Finally, as electrochemical applications of the activated carbon fibers to electrode materials for electric double-layer capacitor (EDLC), the electrochemical characteristics of the activated carbon fiber electrodes and the various methods to improve the capacitance and rate capability were introduced. In particular, the effect of pore length distribution (PLD) on kinetics of double-layer charging/discharging was discussed based upon the experimental and theoretical results in our work. And then we discussed in detail the applications of the activated carbon fibers to adsorbent materials for purification of liquid and gas.

Equilibrium Thermodynamics of Chemical Reaction Coupled with Other Interfacial Reaction Such as Charge Transfer by Electron, Coligative Dissolution and Fine Dispersion: A Focus on Distinction between Chemical and Electrochemical Equilibria

변수일,이성재,김주식 한국전기화학회 2008 한국전기화학회지 Vol.11 No.4

This article involves a unified treatment of equilibrium thermodynamics of the chemical reaction coupled with other interfacial (phase boundary) reactions. The modified (restrictive) chemical potential μ+ k , such as electrochemical potential, hydrostatic-chemical (mechanochemical) potential (exceptionally in the presence of the pressure difference) and surface-chemical potential, was first introduced under the isothermal and isobaric conditions. This article then enlightened the equilibrium conditions in case where the release of chemical energy is counterbalanced by the supply of electrical energy, by the supply of hydrostatic work (exceptionally in the presence of Δp), and finally by the release of surface energy, respectively, at constant temperature T and pressure p in terms of the modified chemical potential μ+ k . Finally, this paper focussed on the difference between chemical and electrochemical equilibria based upon the fundamentals of the isothermal and isobaric equilibrium conditions described above

비금속개재물 (非金屬介在物) 이 용접강관 (熔接鋼管) 의 품질에 미치는 영향 : 1. 전위차법 (電位差法) 에 의한 용접강관의 황화물응력부식파괴와 비금속개재물 및 미세조직과의 의존관계 1. Dependence of Sulfide Stress-Corrosion Cracking on the Nonmetallic Inclusions and Microstructures by Electrical Potential Method

변수일,최종교,김홍표 대한금속재료학회(대한금속학회) 1986 대한금속·재료학회지 Vol.24 No.1

The effects of nonmetallic infusions and microstructures on the sulfide stress-corrosion cracking (SSCC) of welded line-pipe steels have been investigated by using electrical potential method. SSCC tests were conducted in H₂S-saturated aqueous solution containing 5 wt.% NaCl and 0.5 wt.% CH₃ COOH at temperature of 35±2℃ by using smooth U-bend specimens. Sulfide stress-corrosion (SSC) crack initiation and propagation took place in the weld fusion zone (WFZ) of two different kinds of American Petroleum Institute (API) grade X-65 due to the presence of elongated nonmetallic inclusions such as manganese sulfides. However, SSC crack of API grade J-55 initiated and also propagated along the pearlite band nearly perpendicular to the specimen surface of heat affected zone (HAZ) of both upper and lower half regions of the full thickness due to the globular morphology of nonmetallic inclusions such as calcium sulfides in WFZ produced by Ca treatment. And the unstable crack propagation was arrested in the midthickness region due to the orientation change of pearlite band nearly by 90˚, which gives rise to the occurrence of the stripes in the SSCC fracture surface. The SSCC kinetics of line-pipe steel weldments have been divided into the three distinct stages, namely crack incubation, slow crack propagation and unstable crack propagation stages, and were discussed in terms of nonmetallic inclusions and microstructures. It is suggested that the susceptibility to SSCC was rather affected by nonmetallic inclusions than microstructures.

다성분계 산화물의 요업재료 제조를 위한 석유 증발 건조 방법

변수일 한국세라믹학회 1977 한국세라믹학회지 Vol.14 No.3

As a wet chemical drying process "hot petroleum drying method" was applied and developed for preparing uniformly fine oxide powder with high purity and sinterreactivity. Using this method solution of sulfates was dried in hot petroleum bath (~17$0^{\circ}C$) to sulfate powder from which corresponding mullite doped by Fe3+ ion was formed. Particle size, shape, decomposition by heat, and phase identification of sulfate andoxide powders determined by DTA, TGA, X-ray diffraction, analysis and electron microscopy: sulfate powder prepared by this drying method is an intimate mixture of the amorphous form of uniformly and finely distributed spherical particles (0.05-0.1$\mu$). Mullitization with the sulfate powder occurs at 110$0^{\circ}C$ in air. The morphology of mullite particle made by firing the sulfate powder at 135$0^{\circ}C$ in oxygen atmosphere is granular of 0.1-0.3$\mu$ in size. This drying process proved to be a very effective method for preparing fine, homogeneous, and highly sinterreactive multicomponent oxide powder without conventional ceramic process of mixing, milling, and granulating. This process can be also applied for preparing electronic ceramic materials which are requisite for high purity and homogeneity.mogeneity.

안정된 $ZrO^2$의 소결에 대하여

변수일 한국세라믹학회 1976 한국세라믹학회지 Vol.13 No.4

The Fundamentals of Reduction of UO22+ Ions on a Pt Electrode and Methods for Improving Reduction Current Efficiency

변수일,연제원 한국전기화학회 2007 한국전기화학회지 Vol.10 No.2

Abstract : This review article considered the electrochemical reduction of uranyl ions on a Pt surface. Specifically, we focussed on the improvement in its reduction current efficiency. First, this article briefly explained the fundamentals of the reduction of uranyl (UO2 2+) ions on a Pt surface. Namely, they involved the electrochemical behaviour of uranium species, and electrochemical cell configurations for the reduction of UO2 2+ ions. In addition, the effects of adsorbed hydrogen atoms were investigated on the reduction of UO2 2+ ions. Finally, this article presented the methods for improving current efficiency of the reduction of UO2 2+ ions on a Pt surface. Three different kinds of methods are introduced, which include electrochemical surface treatments of Pt electrode involving hydrogenation and anodisation, the use of catalyst poisons, and formation of thin mercury film on a Pt electrode. Moreover, this article provided some clues about how hydrogenation and catalyst poisons work on the reduction of UO2 2+ ions.

입계 편석된 불순물 황 (S) 과 인(P) 이 강내의 수소 트랩 거동에 미치는 영향

변수일,임찬 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.9

The effects of sulphur and phosphorus segregated at grain boundaries on the hydrogen trapping in S-steel and Ni-Cr-steel as compared to pure iron have been studied using gas phase hydrogen charging and electrochemical detection techniques. The segregation of sulphur and phosphorus was performed by tempering the Fe-S and the Fe-Ni-Cr-P specimens, respectively. This was ensured form AES spectroscopy and SEM micrography, respectively. The hydrogen trap densities and trap binding energies were determined from plots of time lag against inverse square of input hydrogen pressures. The trap densities for the annealed Fe-S specimen and the tempered Fe-S specimen were found to be about 1.1×10^(-7) and 3.0×10^(-7)㏖/㎤, respectively, and the trap binding energy for the both specimens was determined to be about -57kJ/㏖. In the case of pure iron specimen, the trap density and trap binding energy were 1.2×10^(-7)㏖/㎤ and -56kJ/㏖, respectively. The annealed Fe-Ni-Cr specimen and the tempered Fe-Ni-Cr-P specimen showed the trap binding energies of -53 and -55kJ/㏖, respectively, and the both specimens had approximately the same trap density of 1×10^(-6)㏖/㎤. From the experimental results, it is suggested that sulphur and phosphorus segregated at grain boundaries act as saturable deep trap sites for hydrogen in S-steel and Ni-Cr-steel, respectively.

일정변형율속도법에 의한 고순도 Al-Zn-Mg 합금의 응력부식파괴에 대한 속도론적 고찰

변수일,김홍균 대한금속재료학회(대한금속학회) 1984 대한금속·재료학회지 Vol.22 No.7

The kinetics of stress-corrosion cracking (SCC) of a high purity Al-Zn-Mg alloy was studied as a function of applied potential, temperature and kind of corrosive media. The SCC tests were carried out in the range of applied potential from -550 to -2150 mV_(SHE) and at the temperatures between 288 and 318 K. 3.5 wt.% NaCl solution (PH=1), air and transformer oil were used as corrosive medium. The percentage elongation and the fracture energy due to SCC increased with decreasing applied potential from -550 to -1150 mV_(SHE) and then decreased. The SCC fractography correspondingly revealed a decreased intergranular-brittle fracture fraction with decreasing applied potential up to -1150 mV_(SHE) and then increased one with decreasing applied potential up to -2150 mV_(SHE). Average SC crack propagation rate, γ, was calculated by introducing a new function related to the σ-εcurve in the inert environment. It was also observed to be 100×10^(-6), 39×10^(-6) and 2.1×10^(-4) ㎜ sec^(-1) at the applied potential of -550, -750 and -1150 mV_(SHE), respectively, tested under the strain rate 8.3×10^(-7) sec^(-1) with the underaged specimen. The observed values are in good accord with the calculated values. The intergranular-brittle fracture mode was also observed in oil, probably caused by the water in oil. Stress-corrosion (SC) fracture mode varied from a simply corroded fracture near the surface/subsurface, followed by an intergranular-brittle fracture over the mixed fracture, composed of the intergranular-brittle fracture and a dimpled rupture, to the pure dimpled rupture in the interior of specimen. It is suggested, on the basis of the observation of potential dependence of the fracture energy and SCC fractography, that SCC is caused by hydrogen-assisted embrittlement. Activation energy for hydrogen-assisted embrittlement in the NaCl solution was found to be 18-20 kJ mole^(-1) for the specimen aged at 180℃ for 0.5h (underaged stage).

Al-Zn-Mg 합금의 전노출취성과 응력부식파괴 사이의 관계에 대한 연구

변수일,김홍표,이성민 대한금속재료학회(대한금속학회) 1990 대한금속·재료학회지 Vol.28 No.11

The stress-corrosion cracking (SCC) mechanism of Al-Zn-Mg alloy has been studied in terms of the relationship between pre-exposure embrittlement (PEE) and SCC. PEE and SCC susceptibilities were measured as a function of ageing state, pre-exposure time and applied potential by means of the slow strain rate method. The specimen pre-exposed to water vapour-saturated air, followed by reheat treatment (re-solutionized in vacuum and aged in dry air) showed a pronounced increase in fracture energy as compared to the pre-exposed specimen. This suggests that PEE is caused by reversible embrittlement, i.e., by hydrogen embrittlement. The similar trends in SCC susceptibility were obtained with respect to ageing state as well as to applied potential. This implies that the SCC mechanism remains unchanged regardless of ageing state and applied potential. When pre-exposure time was large enough than 120 h, the susceptibility to PEE and fracture surface of PEE were very similar to those associated with SCC. On the basis of experimental results, it is believed that SCC as well as PEE is caused by hydrogen embrittlement