• Transactions of the Korean hydrogen and new energy society
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• v.17 no.1
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• pp.109-116
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• 2006

The heat treatment characteristics of natural talc sample was investigated in diverse analytical view point. The mass decrease comes to heat treatment was resulted by the continuous and the discontinuous process and the obtained result show very similar two step profiles with 8.9 % mass decrease. The dehydroxylation of -OH groups contained talc crystal was analyzed by spectroscopic method and the crystallographic variations was also observed after heat treatment. According to XPS result, the magnesium hydroxide($Mg(OH)_2$) of untreated talc powder changed to magnesium oxides(MgO) after heat treatment.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.6
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• pp.745-753
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• 2007

By struvite and hydroxyapatite crystallization, was high concentration of nitrogen and phosphorus in wastewater simultaneously. Particularly, removal of nitrogen and phosphate for crystallization have been applied to landfill leachates and animal wastewater. The purpose of this study is to decide the optimum struvite crystallization factors, sequence of $Mg^{2+}$ addition, pH control and the molar ratio of $Mg^{2+}$ over $PO_4^{3-}$. In conclusion, dosage of the magnesium followed by pH control formed magnesium hydroxide, so pH was decreased. Therefore, pH adjustment should followed by after magnesium dosage and then pH should be adjusted to 11. Over pH 10, it was not good for struvite crystallization efficiency by side reaction. Following of the $Mg^{2+}$ and the $PO_4^{3-}$ are dosed excessively, the removal efficiency of the $NH_4^+$ increased. A molar ratio of $Mg^{2+}:NH_4^+:PO_4^{3-}$, 1.3:1:1.3 was the most on effective for $NH_4^+$ removal at pH 9.5. But for the perfect removal $NH_4^+$, it is thought to be that molar ratio should be 2:1:2.

• Steel and Composite Structures
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• v.29 no.2
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• pp.201-218
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• 2018

In this study, the effects of magnesium sulfate on the mechanical performance and the durability of confined and unconfined geopolymer concrete (GPC) specimens were investigated. The carbon and basalt fiber reinforced polymer (FRP) fabrics with 1-layer and 3-layers were used to evaluate the performances of the specimens under static and cyclic loading in the ambient and magnesium sulfate environments. In addition, the use of FRP materials as a rehabilitation technique was also studied. For the geopolymerization process of GPC specimens, the alkaline activator has selected a mixture of sodium silicate solution ($Na_2SiO_3$) and sodium hydroxide solution (NaOH) with a ratio ($Na_2SiO_3/NaOH$) of 2.5. In addition to GPC specimens, an ordinary concrete (NC) specimens were also produced as a reference specimens and some of the GPC and NC specimens were immersed in 5% magnesium sulfate solutions. The mechanical performance and the durability of the specimens were evaluated by visual appearance, weight change, static and cyclic loading, and failure modes of the specimens under magnesium sulfate and ambient environments. In addition, the microscopic changes of the specimens due to sulfate attack were also assessed by scanning electron microscopy (SEM) to understand the macroscale behavior of the specimens. Results indicated that geopolymer specimens produced with nano-silica and fly ash showed superior performance than the NC specimens in the sulfate environment. In addition, confined specimens with FRP fabrics significantly improved the compressive strength, ductility and durability resistance of the specimens and the improvement was found higher with the increased number of FRP layers. Specimens wrapped with carbon FRP fabrics showed better mechanical performance and durability properties than the specimens wrapped with basalt FRP fabrics. Both FRP materials can be used as a rehabilitation material in the sulfate environment.

• Journal of the Korean institute of surface engineering
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• v.42 no.3
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• pp.109-115
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• 2009

Magnesium is one of the lightest metals, and magnesium alloys have excellent physical and mechanical properties such as high stiffness/weight ratios, good castability, good vibration and shock absorption. However their poor corrosion resistance, wear resistance, hardness and so on, have limited their application. To improve these defects, many techniques are developed. Micro arc oxidation(MAO) is a one of the surface treatments under anodic oxidation in which ceramic coating is directly formed on the surface of magnesium alloy. In this study, the characteristics of anodic film were examined after coating the AZ31B magnesium alloy through the MAO process. MAO was carried out in potassium hydroxide, potassium fluoride, and various concentration of sodium silicate in electrolyte. The morphology and chemical composition of the coating layer were characterized by SEM, XRD, EPMA and EDS. The hardness of anodic films was measured by micro-vickers hardness tester. As a result, the morphology and composition of anodic film were changed by concentration of sodium silicate. Thickness and Si composition of anodic film was increased with increasing concentration of sodium silicate in electrolyte. The hardness of anodic film was highly increased when the concentration of sodium silicate was above 40 g/l in electrolyte.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 2011.11a
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• pp.458-461
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• 2011

수산화마그네슘을 첨가한 저밀도 폴리에틸렌-에틸렌 비닐 아세테이트 복합체의 연소성을 시험하였다. 저밀도 폴리에틸렌-에틸렌 비닐 아세테이트에 수산화마그네슘을 40~80wt% 첨가하여 용융 혼합하고 성형 후 콘칼로리미터(ISO 5660-1)를 이용하여 연소성을 시험하였다. 수산화마그네슘을 첨가한 시편은 첨가하지 않은 시험편에 비하여 그의 플래시오버 가능성이 감소하였다. 수산화마그네슘을 첨가한 시험편은 첨가하지 않은 시험편에 비해 낮은 총열방출량과 낮은 CO 발생량을 나타내었고, 수산화마그네슘 함량이 증가할수록 총연기발생량과 비소화면적이 감소하였다.

• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.415-424
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• 2017

The purpose of this study is to investigate the effect of sulfate (${SO_4}^{2-}$) and magnesium ($Mg^{2+}$) ions on sulfate resistance of Alkali-activated materials using Fly ash and Ground granulated blast furnace slag (GGBFS). In this research, 30%, 50% and 100% of GGBFS was replaced by sodium silicate modules ($Ms(SiO_2/Na_2O)$, molar ratio, 1.0, 1.5 and 2.0). In order to investigate the effects of $Mg^{2+}$ and ${SO_4}^{2-}$, compression strength, weight change, lengh expansion of the samples were measured in 10% sodium sulfate ($Na_2SO_4$), 10%, 5% and 2.5% magnesium sulfate ($MgSO_4$), 10% magnesium nitrate ($Mg(NO_3)_2$), 10% [magnesium chloride ($MgCl_2$) + sodium sulfate ($Na_2SO_4$)] and 10% [magnesium nitrate $(Mg(NO_3)_2$ + sodium sulfate ($Na_2SO_4$)] solution, respectively and X-ray diffraction analysis was conducted after each experiment. As a result, when $Mg^{2+}$ and ${SO_4}^{2-}$ coexist, degradation of compressive strength and expansion of the sample were caused by sulfate erosion. It was found that the reaction of $Mg^{2+}$ with Calcium Silicate Hydrate (C-S-H) occurred and $Ca^{2+}$ was produced. Then the Gypsum ($CaSO_4{\cdot}2H_2O$) was formed due to reaction between $Ca^{2+}$ and ${SO_4}^{2-}$, and also Magnesium hydroxide ($Mg(OH)_2$, Brucite) was produced by the reaction between $Mg^{2+}$ and $OH^-$.

• Journal of Powder Materials
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• v.27 no.5
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• pp.401-405
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• 2020

Magnesium hydroxide sulfate hydrate (MHSH) whiskers were synthesized via a hydrothermal reaction by using MgO as the reactant as well as the acid solution. The effects of the H₂SO₄ amount and reaction time at the same temperature were studied. In general, MHSH whiskers were prepared using MgSO₄ in aqueous ammonia. In this work, to reduce the formation of impurities and increase the purity of MHSH, we employed a synthesis technique that did not require the addition of a basic solution. Furthermore, the pH value, which was controlled by the H₂SO₄ amount, acted as an important factor for the formation of high-purity MHSH. MgO was used as the raw material because it easily reacts in water and forms Mg⁺ and MgOH⁺ ions that bind with SO₄^2- ions to produce MHSH. Their morphologies and structures were determined using X-ray diffraction (XRD) and scanning electron microscopy (SEM).

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.39-47
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• 2015

In this study, the properties of strength and drying shrinkage of alkali-activated slag cement (AASC) with magnesium oxide (MgO) contents between 0 and 16 wt% were investigated. The ground granulated furnace blast slag (GGBFS) was activated by potassium hydroxide (KOH) and dosage of activator was 2M and 4M. The MgO was replaced with 2% to 16% of GGBFS by weight. The water-binder ratio (w/b) was 0.5. In the result, the higher MgO content leads to a slightly higher degree of reaction and thus to a higher compressive strength at all ages. The compressive strength and ultra sonic velocity (UPV) increased with increases MgO contents. The drying shrinkage of AASC was decreased as the contents of MgO increases. The results from SEM confirmed that there were densified reaction product of higher MgO content specimens.

• Advanced Composite Materials
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• v.18 no.2
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• pp.187-195
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• 2009

Much attention has been paid to the processing of inorganic whisker, especially calcium carbonate whisker, which can be used as reinforcement materials of polymer composite due to its low price. Unfortunately, the present synthesis technique of calcium carbonate whisker starts from calcinations of limestone, which involves high energy consumption and furthermore is a highly environment polluting reaction. In this report, needle-like aragonite was synthesized with a reversible solution reaction from limestone without calcination. Optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were used to characterize the morphology and crystal structure of intermediates as well as that of the product, aragonite. GCC (grinding calcium carbonate) powder was dissolved in an aqueous solution of magnesium sulfate with reflux and air flush. EDTA titration was used to evaluate reaction rate of the dissolution. A kinetics equation of the dissolution reaction was constructed, which displayed second-order kinetics with respect to the concentration of magnesium sulfate. A rate constant of $0.0015\;l^{-3}{\cdot}mol^{-1}{\cdot}h^{-1}$ was obtained. The dissolution reaction gave fiber-like magnesium hydroxide sulfate and gypsum crystal. Then needle-like aragonite with a length of $9.13\;{\pm}\;1.02\;{\mu}m$ and an aspect ratio of $5.64\;{\pm}\;1.37$ was synthesized from the dissolution product with $CO_2$ bubbling at $70^{\circ}C$.

• Journal of the Korean institute of surface engineering
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• v.47 no.4
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• pp.147-154
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• 2014

Formation behavior of PEO (Plasma Electrolytic Oxidation) films on AZ31 Mg alloy was studied in aqueous solutions containing various concentrations of hydroxide ion ($OH^-$) and silicate ion ($SiO_3{^{2-}}$) by voltage-time curves, and corrosion resistance of the PEO film-covered specimen was investigated by immersion test in 0.5 M NaCl solution. From the analyses of the voltage-time curves, it is suggested that two different types of anions are essentially needed for the formation of PEO films on AZ31 Mg alloy: film formation agent and local film breakdown agent. $SiO_3{^{2-}}$ ion acts only as a film formation agent but $OH^-$ ion acts not only as a film formation agent but also film breakdown agent. The PEO films prepared on AZ31 Mg alloy in alkaline silicate solution showed very good corrosion resistance without any pitting or filiform corrosions up to 480 h of immersion in 0.5 M NaCl.