Novel insights into MgO hydroxylation: Effects of testing temperature, samples׳ volume and solid load

Magnesium hydroxide (Mg(OH)2 or brucite) can be formed from the hydroxylation of magnesium oxide (MgO or magnesia). Depending on the application aimed, this reaction must either occur rapidly and in a controlled and efficient way (as in the production of anti-flame additives for polymer composites) or be avoided (as in magnesia-containing refractory bricks). Many studies have investigated the physical–chemical parameters of the magnesia particle that affect this reaction, namely: average particle and crystallite size, sintering degree, impurities, specific surface area and additives. An effect that has not been completely understood is the self-catalytic heat release that occurs during the reaction. It can significantly affect the hydroxylation test results and lead to inconsistent conclusions. In this study, the effects of heat release in magnesia hydration are investigated by temperature monitoring and thermogravimetry. Three main variables directly hamper the heat withdrawal and increase the samples׳ inner temperature: the nominal time–temperature conditions of the test, the volume of the samples and their solid load.