• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.150.1-150.1
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• 2017

구조용 합금 중 가장 우수한 비강도를 나타내는 마그네슘 및 마그네슘 합금은 최근 자동차, 항공, 기계 및 전자산업 등 다양한 산업분야에서 이용되고 있다. 하지만 마그네슘 합금은 반응성이 매우 커서 쉽게 부식되는 단점이 있다. 따라서 최근 내식성 향상을 위한 표면처리 기술에 대한 연구의 필요성이 증대되고 있으며, 그 중 플라즈마 전해산화법(Plasma electrolytic oxidation)은 양극산화반응을 이용하여 고내식성, 고경도의 산화피막을 금속 표면에 형성시키는 방법으로 많은 연구가 진행되고 있다. 본 연구에서는 탄산이온이 포함된 수용액에서 수산화나트륨의 농도가 AZ31 마그네슘 합금의 플라즈마전해산화 피막형성에 미치는 영향에 대해 알아보았다. 다양한 농도의 수산화나트륨 용액에서 DC 전류를 인가하여 플라즈마전해산화 피막을 형성하였다. 탄산 이온이 포함된 수용액에서 수산화나트륨의 농도가 높아질수록 플라즈마 전해산화 피막의 형성전압은 낮아지며, 초기 피막 형성전압 상승 속도 또한 빠르게 증가하며 피막 형성전압 등락의 폭은 감소하는 것으로 나타났다.

• Proceedings of the Safety Management and Science Conference
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• 2011.04a
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• pp.553-557
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• 2011

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.193.2-193.2
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• 2016

본 연구에서는 탄산이온이 포함된 수용액에서 규산나트륨의 농도가 AZ31 마그네슘 합금의 플라즈마전해산화 피막형성에 미치는 영향에 대해 알아보았다. 다양한 농도의 규산나트륨 용액에서 DC와 펄스전류를 인가하여 플라즈마전해산화피막을 형성하였으며, 형성된 피막의 surface roughness와 thickness를 분석하였다. 탄산 이온이 포함된 수용액에서 플라즈마전해산화 피막의 형성전압은 규산나트륨의 농도가 높아질수록 높아지는 것으로 나타났다. 하지만 탄산이온이 존재하지 않은 규산나트륨 용액에서의 플라즈마전해산화 피막 형성전압보다 더 낮은 값을 나타내었다. 탄산 이온이 포함된 수용액에서 규산나트륨의 농도가 높아질수록 플라즈마전해산화 피막의 surface roughness와 thickness는 증가하였으며, DC와 펄스전류 모두에서 더 밝은 색상의 균일한 산화피막을 형성할 수 있었다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.329-337
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• 2019

We synthesized potassium titanates having splinter and plate shape and evaluated frictional and wear properties of brake pad using them as reinforcements in friction materials. For splinter-shaped potassium titanates, potassium tetratitanate (K₂O·4TiO₂, PT4) with plate shape was prepared, then K ion of the titanate was leached by acid to make potassium hexatitanate (K₂O·6TiO₂, PT6), which was transformed to splinter-shaped PT6 by thermal treatment at 800℃. Plate-shaped potassium magnesium titanate (K_0.8Mg_0.4Ti_1.6O₄, PMT) was prepared by adding Mg in the potassium titanate using KCl as a flux. Using PT6 and PMT as reinforcements in friction materials of brake pad, we evaluated frictional and wear properties using 1/5-scale dynamometer. According to dynamometer test results, both reinforcements shows similar friction coefficient and fade & recovery behavior to conventional material and plate-shaped PMT exhibits higher wear resistance than splinter-shaped PT6.

• Journal of the Mineralogical Society of Korea
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• v.30 no.4
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• pp.205-217
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• 2017

Mineral carbonation by indirect method has been studied by serpentinite as cation source. Through the carbonation of $CO_2$ and alkaline earth ions (calcium and magnesium) from serpentinite, the pure carbonates including $MgCO_3$ and $CaCO_3$ were synthesized. The extraction solvent used to extract magnesium (Mg) was ammonium sulfate ($(NH_4)_2SO_4$), and the investigated experimental factors were the concentration of $(NH_4)_2SO_4$, reaction temperature, and ratio of serpentinite to the extraction solvent. From this study, the Mg extraction efficiency of approximately 80 wt% was obtained under the conditions of 2 M $(NH_4)_2SO_4$, $300^{\circ}C$, and a ratio of 5 g of serpentinite/75 mL of extraction solvent. The Mg extraction efficiency was proportional to the concentration and reaction temperature. $NH_3$ produced from the Mg extraction of serpentinite was used as a pH swing agent for carbonation to increase the pH value. About 1.78 M of $NH_3$ as the form of $NH_4{^+}$ was recovered after Mg extraction from serpentinite. And, the main step in Mg extraction process of serpentinite was estimated by geochemical modeling.

• YAKHAK HOEJI
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• v.15 no.1
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• pp.32-40
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• 1971

Optimum reactons for the preparation of extra-light magnesium carbonate from magnesium chloride and sodium carbonate solutions were found by observing the difference of crystalline shapes under an electromicroscope. Reaction temperature the and washing temperature were main factors affecting the crystalline shapes, and drying temperature was found to be of secondary importance. Optimum temperatures for reaction and washing ranged from $20^{\circ}C$ to $30^{\circ}C$ and the temperature over $40^{\circ}C$ should be avoided for the reaction and washing. It was found that the higher the drying temperature, the lighter the crsytal of the produced magnesium carbonate. Reaction time, molar ratio (Mg$^{2+}/CO_{3}^{2-}$ ) and the concentrations of magnesium chloride and sodium carbonate solutions have only a slight effect on the form of the product.

• YAKHAK HOEJI
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• v.15 no.1
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• pp.24-31
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• 1971

Optimum reaction conditions for the preparation of extra-light magnesium carbonate from bittern by the reaction with sodium carbonate solution was found to be as follows: reaction temperature 33.deg. molar ratio(Mg$^{+2}/CO$^{2-}_{3}$)0.8, reaction time 14 minutes, drying temperature 99.deg. and bittern concentration 17%. While Korean pharmacopeia regulates the bulkiness above 12 mililiters per gm., our experimental result shows above 45 mililiters. Electron microscopic shapes were compared with products prepared under various reaction conditions, and it was found that there exists lighter the powder the more pillar crystalline, the heavier the powder the more amorphous and the intermediate was mixture of them.

• Proceedings of the Materials Research Society of Korea Conference
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• 1998.11a
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• pp.27-27
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• 1998

• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.1
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• pp.18-24
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• 2016

Mineral carbonation is a technology for permanently storing carbon dioxide by reacting with metal oxides containing calcium and magnesium. In this study, we used sea water and alkaline industrial by-product such as paper sludge ash (PSA) for the storage of carbon dioxide through direct carbonation. We found the optimum conditions of both sea water content (mixing ratio of sea water and PSA) and reaction time required in the direct carbonation through various experiments using sea water and PSA. In addition, we compared the amounts of carbon dioxide storage with the cases when sea water and ultra-pure water were separately used as solvents in the direct carbonation with PSA. The amount of carbon dioxide storage was calculated by using both solid weight increase through the carbonation reaction and the contents of carbonate salts from thermal gravimetric analysis. PSA particle used in this study contained 67.2% of calcium. The optimum sea water content and reaction time in the carbonation reaction using sea water and PSA were 5 mL/g and 2 hours, respectively, under the conditions of 0.05 L/min flow rate of carbon dioxide injected at $25^{\circ}C$ and 1 atm. The amounts of carbon dioxide stored when sea water and ultra-pure water were separately used as solvents in the direct carbonation with PSA were 113 and $101kg\;CO_2/(ton\;PSA)$, respectively. The solid obtained through the carbonation reaction using sea water and PSA was composed of mainly calcium carbonate in the form of calcite and a small amount of magnesium carbonate. The solid obtained by using ultra-pure water, also, was found to be carbonate salt in the form of calcite.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.3
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• pp.149-154
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• 2017

We investigate the availability of $CO_2$ ocean storage by means of chemical conversion of $CO_2$ to the dissolved inorganic carbon (mainly the bicarbonate ion) in seawater. The accelerated weathering of limestone (AWL) technique, which is accelerating the natural $CO_2$ uptake process through the chemical conversion using limestone and seawater, was proposed as an alternative method for reducing energy-related $CO_2$ emission. The method presented in this paper is slightly different from the AWL method. It involves reacting $CO_2$ with seawater and quicklime obtained from alkaline wastes to produce the bicarbonate-rich solution over 100 times more than seawater, which could be released and diluted into the ocean. The released dense bicarbonate-enriched water mass could subside into the deeper layer because of the density flow, and could be sequestrated stably in the ocean.