Magnesium oxide, also known as magnesia (MgO), when used in refractory castable compositions, gives excellent refractoriness and high resistance to basic slags. However, in the presence of water, MgO undergoes an expansive hydration reaction with the formation of Mg(OH)_2, which can lead to cracking and swelling. In this work, additives called chelants are added to magnesia sinter suspensions in order to prevent its hydration. Zeta potential and ionic conductivity measurements are used to provide information on magnesia surface and chelant adsorption. Assessment of the hydration degree and volumetric expansion give indications on the amount of Mg(OH)_2 formed as well as its likelihood to damage the ceramic bodies. The results show that citric acid can inhibit MgO hydration to some extent, whereas EDTA is more effective in preventing volume expansion.
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