Effect of MgO and NH4OH on Formation of 5Mg(OH)2·MgSO4·3H2O Whiskers

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).