• Journal of Powder Materials
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• v.18 no.3
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• pp.283-289
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• 2011

Magnesium hydroxide sulfate hydrate whiskers ($5Mg(OH)_2{\cdot}MgSO_4{\cdot}3H_2O$, abbreviated 513 MHSH) were prepared using hydrothermal reaction with magnesium oxide (MgO) and magnesium sulfate ($MgSO_4{\cdot}7H_2O$) as the starting materials. The effects of the molar ratio of $MgSO_4$/MgO and amount of $NH_4OH$ were studied. As a result, 513 MHSH whiskers co-existed with hexagonal plate $Mg(OH)_2$ at low concentration of $SO_4^{2-}$. The molar ratio of $MgSO_4{\cdot}7H_2O$/MgO was 7:1, uniform 513 MHSH whiskers were formed without impurity such as $Mg(OH)_2$. Appropriate amount of $NH_4OH$ has affected to formation of high quality MHSH. Their morphologies and structures were determined by powder X-ray diffraction (XRD) scanning electron microscopy (SEM) and thermo-gravimetric analyzer (TGA).

• Journal of the Korean Ceramic Society
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• v.50 no.3
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• pp.201-205
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• 2013

Magnesium hydroxide sulfate hydrate ($5Mg(OH)_2.MgSO_4{\cdot}3H_2O$, abbreviated 513 MHSH) whiskers were synthesized using MgO and $MgSO_4.7H_2O$ as reactants without addition of basic solution. Previously, MHSH whiskers were prepared by hydrothermal method using $MgSO_4$ in aqueous ammonia. In this work, for the first time, we synthesized a high purity MHSH via ambient pressure. In addition, a high molar ratio of $MgSO_4$ : MgO is an important key to the formation of high purity MHSH. Also, it was possible to prepare whiskers with high aspect ratio using an increasing reaction time in the reaction between the remaining $SO_4^{2-}$ ions and the ${Mg(OH)_6}^{4-}$ fragment, finally producing one-dimensional whiskers.

• 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 Powder Materials
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• v.26 no.3
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• pp.195-200
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• 2019

Whisker-type magnesium hydroxide sulfate hydrate ($5Mg(OH)_2{\cdot}MgSO_4{\cdot}3H_2O$, abbreviated 513 MHSH), is used in filler and flame-retardant composites based on its hydrate phase and its ability to undergo endothermic dehydration in fire conditions, respectively. In general, the length of whiskers is determined according to various synthetic conditions in a hydrothermal reaction with high temperature (${\sim}180^{\circ}C$). In this work, high-quality 513 MHSH whiskers are synthesized by controlling the concentration of the raw material in ambient conditions without high pressure. Particularly, the concentration of the starting material is closely related to the length, width, and purity of MHSH. In addition, a ceramic-coating system is adopted to enhance the mechanical properties and thermal stability of the MHSH whiskers. The physical properties of the silica-coated MHSH are characterized by an abrasion test, thermogravimetric analysis, and transmission electron microscopy.