• 대한금속재료학회지
• /
• 제47권2호
• /
• pp.99-106
• /
• 2009

The high temperature corrosion properties of heat resistant steels were investigated in oxidation atmosphere including sulfur dioxide. The heat resistant steels of T22, T92, T122, T347HFG and T304H were evaluated at 620, $670^{\circ}C$ for 400 hours. The corrosion rates showed a decreasing tendency while chrome contents of those steels increased from 2 mass.% to 19 mass.%. The in crease in temperature increasement has an more effect on the corrosion rates of low chrome steels than high chrome steels. The weight gains of T22, T92, T304H at $670^{\circ}C$ were 3.7, 1.65, 1.23 times compared with those at $620^{\circ}C$. The external scale formed on T22 was composed of hematite, magnetite and Fe-Cr spinel and internal layer including iron oxide mixed with sulfide. The scales formed on T92, T122, T304H consisted of an outer layer of hematite and inner layer of chrome oxide and hematite. The proportion of chrome oxide at inner layer was increased when the chrome contents in heat resistant steels were increased.

• Corrosion Science and Technology
• /
• 제21권1호
• /
• pp.53-61
• /
• 2022

Alloys of Fe-(5.3-29.8)%Mn-(1.1-1.9)%Al-(0.4-0.5)%C were oxidized at 550 ℃ to 650 ℃ for 20 h to understand effects of alloying elements on oxidation. Their oxidation resistance increased with increasing Mn level to a small extent. Their oxidation kinetics changed from parabolic to linear when Mn content was decreased and temperature was increasing. Oxide scales primarily consisted of Fe₂O₃, Mn₂O₃, and MnFe₂O₄ without any protective Al-bearing oxides. During oxidation, Fe, Mn, and a lesser amount of Al diffused outward, while oxygen diffused inward to form internal oxides. Both oxide scales and internal oxides consisted of Fe, Mn, and a small amount of Al. The oxidation of Mn and carbon transformed γ-matrix to α-matrix in the subscale. The oxidation led to the formation of relatively thick oxide scales due to inherently inferior oxidation resistance of alloys and the formation of voids and cracks due to evaporation of manganese, decarburization, and outward diffusion of cations across oxides.

• Journal of Microbiology and Biotechnology
• /
• 제31권11호
• /
• pp.1519-1525
• /
• 2021

Hexavalent chromium (Cr(VI)) is recognized to be carcinogenic and toxic and registered as a contaminant in many drinking water regulations. It occurs naturally and is also produced by industrial processes. The reduction of Cr(VI) to Cr(III) has been a central topic for chromium remediation since Cr(III) is less toxic and less mobile. In this study, fermentative Fe(III)-reducing bacterial strains (Cellu-2a, Cellu-5a, and Cellu-5b) were isolated from a groundwater sample and were phylogenetically related to species of Cellulomonas by 16S rRNA gene analysis. One selected strain, Cellu-2a showed its capacity of reduction of both soluble iron (ferric citrate) and solid iron (hydrous ferric oxide, HFO), as well as aqueous Cr(VI). The strain Cellu-2a was able to reduce 15 μM Cr(VI) directly with glucose or sucrose as a sole carbon source under the anaerobic condition and indirectly with one of the substrates and HFO in the same incubations. The heterogeneous reduction of Cr(VI) by the surface-associated reduced iron from HFO by Cellu-2a likely assisted the Cr(VI) reduction. Fermentative features such as large-scale cell growth may impose advantages on the application of bacterial Cr(VI) reduction over anaerobic respiratory reduction.

• Corrosion Science and Technology
• /
• 제4권3호
• /
• pp.89-94
• /
• 2005

This paper presents the results of a study that was undertaken to optimize the ratio of the components of a new multi-component inhibitor blend composed of orthophosphate/ phosphonates/ acrylate copolymer/ isothiazolone. The effects of newly developed inhibitor on carbon steel dissolution in synthetic cooling water were studied through weight loss tests, electrochemical tests, scale tests, and micro-organism tests. The obtained results were compared to blank (uninhibited specimen) and showed that developed inhibitor revealed very good corrosion, scale, and micro-organism inhibition simultaneously. All measurements indicated that the efficiency of the blended mixture exceeded 90 %. The inhibitive effects arose from formation of protective films which might contain calcium phosphate, calcium phosphonate, and iron oxide. The nature of protective films formed on the carbon steel was studied by scanning electron microscopy (SEM) and auger electron spe ctroscopy (AES). Inhibitor used in this study appeared to have better performance for scale inhibition due to their superior crystal modification effect and excellent calcium carbonate scale inhibition properties. The effect of inhibitor on microorganisms was evaluated through minimum inhibitory concentration (MIC) test. All kinds of micro-organisms used in this study were inhibited under 78ppm concentration of inhibitor.

• 상하수도학회지
• /
• 제22권3호
• /
• pp.379-387
• /
• 2008

The pH & alkalinity adjustment method by lime and carbon dioxide($CO_2$) for corrosion control in water distribution system was investigated to evaluate the corrosion characteristics of metal pipes, such as galvanized iron, copper, stainless steel, and carbon steel. When the pH in sand filtered and ozone+GAC treated water was increased with lime and $CO_2$ from 7.5 to 8.0, the concentration of residual chlorine decreased at higher pH and longer reaction time; the concentration of trihalomethane increased. The corrosion rate of coupons with corrosion control using lime and carbon dioxide was showed much smaller than those without corrosion control using pilot-scale simulated distribution system. The galvanized iron was corroded much faster than carbon steel, copper, and stainless steel. Especially, copper and stainless steel coupons were hardly corroded. The galvanized iron and carbon steel coupons with corrosion control were produced the corrosion products less than those without corrosion control by the results of environmental scanning electron microscope(ESEM) and energy dispersive x-ray spectroscopy(EDS) analyses. The galvanized iron coupon with pH and alkalinity adjustment by lime and carbon dioxide was detected about 30 percent of zinc, when the carbon steel was detected about 30 percent of calcium by calcium carbonate products formation. For the results of X-ray diffraction(XRD) analyses, the goethite(${\alpha}$-FeOOH) was identified as primary corrosion product of galvanized iron without corrosion control, while the Zinc oxide(ZnO) was found on corrosion products of galvanized iron coupon with corrosion control as the results of EDS analyses. However, the carbon steel corrosion products regardless of corrosion control were composed predominantly of maghemite(${\gamma}-Fe_2O_3$) and hematite(${\alpha}-Fe_2O_3$).

• 한국재료학회지
• /
• 제11권1호
• /
• pp.34-38
• /
• 2001

Fe-28%Al($Fe_3Al$)과 Fe-28%Al-4%Cr($Fe_3Al-4Cr$) 금속간화합물을 대기중 1073, 1273, 1473k의 온도에서 최고 17일까지 장시간 산화시켰다. $Fe_3Al-4Cr$의 산화저항은 근본적으로 $Fe_3Al$과 거의 비슷하거나, 약간 우수하였다. $Fe_3Al$ 위에 형성된 산화물은 거의 순수한 ${\alpha}-AL_2O_3$로만 구성되어 있었으며, $Fe_3Al-4Cr$ 위에 형성된 산화물은 약간의 Fe와 Cr 이온이 고용된 ${\alpha}-AL_2O_3$로 구성되어 있었다. 외부산화막을 형성하기 위해 모재원소의 외부확산에 의해 산화물-모재 계면에는 Kirkendall 기공이 존재하였다. $Fe_3Al(-4Cr)$ 표면에 형성된 산화막은 1273k가지는 비교적 얇고 치밀하였으나, 1473k에서 산화막의 박리와 함께 상대적으로 큰 무게증가가 발생하였다.

• 대한환경공학회지
• /
• 제37권4호
• /
• pp.246-252
• /
• 2015

철강공장의 열연공정에서 발생하는 폐부산물인 mill scale을 원료로 하여 인흡착에 효율적인 무기흡착제인 magnetite를 생산하고자 하였다. Mill scale의 주요 구성성분은 wustite (FeO), magnetite (FeO), hematite (FeO)였으며, 산처리를 수행할 경우 대부분의 wustite가 magnetite와 hematite로 전환되었다. Mill scale의 산처리는 HCl과 $H_2O_2$를 이용하여, 염기처리는 NaOH 이용하여, 산-염기 복합처리는 $H_2SO_4$와 NaOH를 이용하여 수행하였다. Oil 제거 및 DI water로 rinsing만 한 경우, 인 흡착용량은 0.28 mgP/g으로 나타난 반면, 염기처리를 한 경우 0.68, 산처리를 한 경우 1.19 mgP/g으로 인 흡착용량이 증가하였다. 산-염기 복합처리 과정을 통해 단일상의 magnetite 입자를 얻을 수 있었으며, 이 입자의 인 흡착용량은 3.11 mgP/g 이상인 것으로 파악되었다. 산화철의 인 흡착에 대한 동력학적 특성 분석결과 Freundlich와 Langmuir 두 등온 흡착모델 모두 magnetite의 인 흡착 거동을 잘 모사하였다. Freundlich 모델의 흡착능(K)과 흡착강도(1/n)를 조사한 결과, 온도가 증가할수록 강한 흡착능을 보이는 것으로 나타났다. Langmuir 모델 적용결과 최대 흡착용량은 $20^{\circ}C$에서 5.1 mgP/g인 것으로 파악되었다.

• 한국인터넷방송통신학회논문지
• /
• 제10권5호
• /
• pp.1-5
• /
• 2010

본 논문은 열연 공정을 거친 철강 강판에 형성된 산화철 층, 즉 scale 층의 두께를 유전체 렌즈 안테나를 이용하여 측정하는 방법을 소개하였다. 유전체 렌즈 안테나는 X 밴드 대역에서 주파수에 독립적인 특성을 가지며, 혼 안테나에서 방사되는 구면파를 초점이 형성되는 평면에 평면파를 형성하는 역할을 한다. 이러한 동작원리를 이용하여 철강 강판에 형성된 scale 층에 완전 도체와 유전체로 형성된 two-layer 구조에 직각 입사하는 평면파의 이론적 해석이 적용될 수 있다. Scale의 두께를 도출해 내는 과정에서 유전체 렌즈의 영향을 최소화하기 위한 calibration 과정이 삽입되었으며, 이로 인한 반사 계수 위상의 오차가 발생하였다. 이러한 위상 오차에 의한 scale 두께의 오차를 줄이기 위하여, 수치적으로 regression 방법을 사용하였으며, 기존의 iteration 방법과 비교하여, 주기적으로 얻어지는 두께의 값이 아닌 단일 두께 값을 얻어낼 수 있었다.

• 한국재료학회지
• /
• 제13권12호
• /
• pp.791-795
• /
• 2003

The oxidation behaviour of Fe-XAl-0.1Y(X= 5, 10, 14 wt.%) alloys were investigated at 1073, 1173 and 1273 K in oxygen/ nitrogen gas atmosphere for 1∼24 hrs using SEM/EDX, XRD and EPMA. The weight changes of Fe-XAl-0.1Y alloys followed the parabolic rate law. Oxidation rates of 10Al and 14Al alloys were ten times lower than that of 5Al alloys. This is attributed to the formations of protective $A1_2$$O_3$oxides on the surface of 10Al and 14Al alloys. The oxidation product scales of the 5Al alloy showed that thick iron oxide scales($Fe_2$$O_3$, $Fe_3$$O_4$) containing porosities formed during early stages of oxidation. With continued oxidation, aluminum oxide was formed at the alloy/scale interface.

• 한국세라믹학회지
• /
• 제47권1호
• /
• pp.8-18
• /
• 2010

When metal oxides are exposed to chemical potential gradients, ions are driven to diffusive mass transport. During this transport process, the divergence of ionic fluxes offers the formation/annihilation of oxides. Therefore, the divergence of ionic flux may play an important role in the void formation in oxides. Kinetic equations were derived for describing chemical potential distribution, ionic fluxes and their divergence in oxides. The divergence was found to be the measure of void formation. Defect chemistry in scales is directly related to the sign of divergence and gives an indication of the void formation behavior. The quantitative estimation on the void formation was successfully applied to a growing magnetite scale in high temperature oxidation of iron at 823 K.