• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.300-312
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• 1993

The material deterioration of service-exposed boiler tube steels in fossil power plant was evaluated by using the electrochemical technique namely, modified electrochemical potentiokinetic reactivation(EPR). It was focused that the passivation of Mo$_{6}$C carbide which governs the mechanical properties of Mo alloyed steels did not occur even in the passivity region of steel in sodium molybdate solution and the reactivation peak current (Ip) observed as the result of non-passivation indicating the precipitation of Mo$_{6}$C carbides. To obtain the optimal test conditions for the field test by using the specially designed electrochemical cell, the effects of scan rate, the surface roughness and the pH of electrolyte on Ip value were also investigated. Furthermore, the change of mechanical properties occurred during the long time exposure at high temperature was evlauated quantitatively by small punch(SP) tests and micro hardness test taking account of the metallurgical changes. It is known that reactivation peak current (Ip) has a good relationship with Larson-Miller Parameter(LMP) which represents the information about material deterioration occurred at high temperature environment. In addition it was possible to estimate the ductile-brittle transition temperature (DBTT) by means of the SP test. The Sp test could be, therefore, suggested as a reliable test method for evaluating the material degradation of boiler tube steels. From the good correaltion between the SP DBTT and Ip values shown in this study, it was knows that the change of mechanical properties could be evaluated non-destructively by measurring only Ip values.ues.

• The Korean Journal of Food And Nutrition
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• v.10 no.3
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• pp.375-381
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• 1997

The anticoagulant polysaccharide was screened from the ediable mushrooms. Among them, alkali extract of Ganoderma lucidum showed the highest activity in aPTT. A crude polysaccharide fraction (GL-I) was prepared from the 1N NaOH solution extract of Ganoderma lucidum followed by methanol-reflux, precipitation with ethanol, dialysis and lyophilization. GL-I inhibited the intrinsic pathway in blood coagulation pathway and exhibited concentration dependent anticoagulation effects. The anticoagulant activity of GL-I was decreased greatly by periodate oxidation, but was not changed by pronase digestion. These suggest that carbohydrate moiety may be related to the anticoagulant activity. GL-I consisted of glucose, galactose, fucose, xylose, mannose, arabinose in a molar ratio of 19.3:3.0:2.3:1.3:1.0:0.3. GL-I was partially purified on the DEAE-Toyopearl 650C(GL-IalongrightarrowGL-If) and on the Sephadex G-100(GL-Ic-ilongrightarrowGL-Ic-II).

• Journal of the Korean Ceramic Society
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• v.23 no.5
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• pp.1-8
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• 1986

This paper is concerned with a gas sensor composed of semi-conducting ${\gamma}$-$Fe_2O_3$ ceramics made by oxidizing $Fe_2O_3$ sintered body. Acicular $\alpha$-FeOOH powder prepared by precipitation of $FeSO_4$.$7H_2O$ solution was transformed to $FeSO_4$ sintered at 700$^{\circ}$-850$^{\circ}$C for 1 hr. and then oxidized to ${\gamma}$-$Fe_2O_3$ The gas sensitive properties of ${\gamma}$-$Fe_2O_3$ ceramic bodies based on the lectrical resistance change was measured in 0.5-2 vol% $H_2$ and $C_2$ $H_2$ gas at 35$0^{\circ}C$ The specific surface area of sintered specimen largely dependent on the sintering temperature and grain shape directly affected the gas sensitive pro-perties of ${\gamma}$-$Fe_2O_3$gas sensor. Specimens having larger specific surface area showed better sensitivity which means the electrical resistance change due to oxidation and reduction process occurs on ly at the surface of grains microscopically in the ${\gamma}$-$Fe_2O_3$ceramics. Micropores made in $Fe_2O_3$ powder during dehydration of $\alpha$-FeOOH can not prompt the gas sensitive properties of sintered ${\gamma}$-$Fe_2O_3$ because they are sintered or closed in the grains during sintering process and dose not affect the specific surface area of sintered body.

• Resources Recycling
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• v.25 no.6
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• pp.65-72
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• 2016

We studied a selective recovery condition of vanadium (V) from FALL (Fly Ash Leach Liquor) produced at a fossil fuel power station using heavy oil. By applying a spectroscopy to quantify the V in a sample, we identified a concentration range V interfered by on presence of metals such as Ni, Fe Also, the optimal vanadium precipitation rate according to the amount of 5.0M $NH_3$ loaded to the sample, solution pH and stirring time. As a result of the experiment, the maximum selective recovery ratio of V was achieved to be higher than 91.5% when the stirring duration was less than 1 minute at pH 7.0, and $25^{\circ}C$.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.6
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• pp.249-255
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• 2019

This study is intended to clarify the main microstructural factors that contribute to an increase of hardness during isothermal aging in Mg-Al alloy. For this work, Mg-9.3%Al alloy specimens were solution-treated at 688 K for 24 h followed by water quenching, and then aged at 473 K for up to 24 h. The aging at 473 K yielded nodular discontinuous precipitates (DPs) with (${\alpha}+{\beta}$) lamellar morphology at the grain boundaries, and the volume fraction of DPs increased from 0% to ~30% with increasing aging time up to 12 h. For the aging times longer than 12 h, further formation of DPs was substantially inhibited owing to the occurrence of significant continuous precipitation within the ${\alpha}-(Mg)$ matrix, and the density of continuous precipitates (CPs) becomes greater with increasing aging time. Hardness of the specimen was steadily increased with aging time up to 24 h. Microstructural examination on the aged specimens revealed that the increased overall hardness at the early stage of aging is associated with the increased volume fraction of DPs, but at the later stage of aging, where the amount of DPs was hardly changed, the increased hardness of the ${\alpha}-(Mg)$ matrix in response to the higher density of CPs within the matrix, plays a key role in increasing the overall hardness value.

• Transactions of Materials Processing
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• v.33 no.3
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• pp.161-168
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• 2024

Aluminum alloy sheets, compared to conventional steel sheets, face challenges in press forming due to their lower elongation. To enhance their formability, extensive research has focused on forming technologies at elevated temperatures, specifically warm forming at around 300℃ and hot forming at approximately 500℃. This study proposes that the formability of aluminum alloy sheets can be significantly enhanced using a multi-stage hot forming technique. The research also investigates whether the strength of the A6061 aluminum alloy, known for its precipitation hardening, can be maintained when formed below the precipitate solid solution temperature. In the experiments, the A6061-T6 sheet underwent heating and rapid cooling between 250 and 500℃. The mechanical properties were evaluated at each stage of the process. The findings revealed that when the initial heat treatment was below 350℃, the strength of the material remained unchanged. However, at temperatures above 400℃, there was a noticeable decrease in strength coupled with an increase in elongation. Conversely, when the secondary heat treatment was conducted at temperatures of 350℃ or lower, the strength remained comparable to that of the initial heat treated material. However, at higher temperatures, a reduction in strength and an increase in elongation were observed.

• Resources Recycling
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• v.8 no.1
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• pp.11-17
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• 1999

This study was carried out to investigate the efficiency of stcclmaldng slag and sludge in removing metals existing in wastewater or leachate. Laboratory experiments were performed as a function of initial concentration of metals. pH a and temperature of the background solution and the presence of che1ating agent, EDTA. The test conditions were temperatures r ranging from $25^{\circ}C$ to $50^{\circ}C$; initial concentrations varying from 5mg/L to 50 mg/L; pH between 3 and 11; and Cu. Cd‘ and Pb a as adsorbates. The results of tests showed that overall rates of metals removal were 20~30% at pH 3 and greater than 90% at p pH 7 and 11. Metals were removed from the solution predominantly via adsorption in acidic conditions, and the combined e effects of adsorption and precipitation in neutral and alkaline conditions. In view of the test results and other engineering c characteristics of steelmaking slag and sludg$\xi$, these industrial by-products from steel industry have a high potential to be used l in wastewater treatment and are particularly beneficial when used as landfill liner additives due to thelJ ability to remove heavy m metals from leachate.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.5
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• pp.191-198
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• 2022

Zirconia and titanium alloys, which are mainly used for dental implant materials, have poor osseointegration and osteogenesis abilities due to their bioinertness with low bioactivity on surface. In order to improve their surface bioinertness, surface modification with a bioactive material is an easy and simple method. In this study, akermanite (Ca₂MgSi₂O₇), a silicate-based bioceramic material with excellent bone bonding ability, was synthesized by a solid-state reaction and investigated its bioactivity from the analysis of surface dissolution and precipitation of hydroxyapatite particles in SBF solution. Calcium carbonate (CaCO₃), magnesium carbonate (MgCO₃), and silicon dioxide (SiO₂) were used as starting materials. After homogeneous mixing of starting materials by ball milling and the drying of at oven, uniaxial pressing was performed to form a compacted disk, and then heat-treated at high temperature to induce the solid-state reaction to akermanite. Bioactivity of synthesized akermanite disk was evaluated with the reaction temperature from the immersion test in SBF solution. The higher the reaction temperature, the more pronounced the akermanite phase and the less the surface dissolution at particle surface. It resulted that synthesized akermanite particles had high bioactivity on particle surface, but it depended on reacted temperature and phase composition. Moderate dissolution occurred at particle surfaces and observed the new precipitated hydroxyapatite particles in synthetic akermanite with solid-state reaction at 1100℃.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.4
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• pp.562-572
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• 2005

Statement of problem : Titanium is widely used as an implant material lot artificial teeth. Also, studies on surface treatment to form a fine passive film on the surface of commercial titanium or its alloys and improving bioactivity with bone have been carried out. However, there is insufficient data about the biocompatibility of the implant materials in the body. Purpose: The purpose of this study was to examine whether the precipitation of apatite on titanium metal is affected by surface modification. Materials and methods: Specimens chemically washed for 2 minute in a 1:1:1.5 (in vol%) mixture of 48% HF 60% $HNO_3$ and distilled water. Specimens were then chemically treated with a solution containing 97% $H_2SO_4$ and 30% $H_2O_2$ at $40^{\circ}C$S for 1 hour, and subsequently heat-treated at $400^{\circ}C$ for 1 hour. All specimens were immersed in the HBSS with pH 7.4 at $36.5^{\circ}C$ for 15 days, and the surface were examined with TF-XRD, SEM, EDX and XPS. Also, commercial purity Ti specimens with and without surface treatment were implanted in the abdominal connective tissue of mice for 4 weeks. Conventional aluminium and stainless steel 316L were also implanted for comparison. Results and conclusions : The results obtained were summarized as follows. 1. An amorphous titania gel layer was formed on the titanium surface after the titanium specimen was treated with a $H_2SO_4$ and $H_2O_2$ solution. The average roughness was $2.175{\mu}m$ after chemical surface treatment. 2. The amorphous titania was subsequently transformed into anatase by heat treatment at $400^{\circ}C$ for 1 hour. 3. The average thickness of the fibrous capsule surrounding the specimens implanted in the connective tissue was $46.98{\mu}m$ in chemically-treated Ti, and 52.20, 168.65 and $100.95{\mu}m$ respectively in commercial pure Ti, aluminum and stainless steel 316L without any treatment.

• Journal of Surface Science and Engineering
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• v.47 no.1
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• pp.39-47
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• 2014

The peculiar feature of cathodic protection in seawater has the capability to form mineral calcareous deposits such as magnesium and calcium on metal surfaces. It is assumed that $OH^-$ ions are generated close to the metal surface as a result of cathodic protection and generated $OH^-$ ions increases the pH of the metal/seawater interface outlined as the following formulae. (1) $O_2+2H_2O+4e{\rightarrow}4OH^-$, or (2) $2H_2O+2e{\rightarrow}H_2+2OH^-$. And high pH causes precipitation of $Mg(OH)_2$ and $CaCO_3$ in accordance with the following formulae. (1) $Mg^{2+}+2OH^-{\rightarrow}Mg(OH)_2$, (2) $Ca^{2+}+CO{_3}^{2-}{\rightarrow}CaCO_3$. The focus of this study was to increase the amount of $CO{_3}^{2-}$ with the injection of $CO_2$ gas to the solution for accelerating process of the following formulae. (1) $H_2O+CO_2{\rightarrow}H_2CO_3$, (2) $HCO^{3-}{\rightarrow}{H^+}+CO{_3}^{2-}$. Electrodeposit films were formed by an electro-deposition technique on steel substrates in solutions of both natural seawater and natural seawater dissolved $CO_2$ gas with different current densities, over different time periods. The contents of films were investigated by scanning electron microscopy(SEM) and X-ray diffraction(XRD). The adhesion and corrosion resistance of the coating films were evaluated by anodic polarization. From an experimental result, only $CaCO_3$ were found in solution where injected $CO_2$ gas regardless of current density. In case of injecting the $CO_2$ gas, weight gain of electrodeposits films hugely increased and it had appropriate physical properties.