Enhanced dehydration and amorphization of Mg(OH) 2 in the presence of ultrafine SiO 2 under mechanochemical conditions

Abstract

Mechanochemical amorphization and dehydration of fine particulate crystalline Mg(OH) 2 was substantially accelerated by the presence of amorphous SiO 2. The TG-DTA profile of the mixture consisting of fine powders of Mg(OH) 2 and SiO 2 changed significantly with grinding time whereas only a slight change was observed on grinding pure Mg(OH) 2. Enhanced mechanochemical dehydration of Mg(OH) 2 in the mixture was explained by assuming the following complex processes: intimate mixing, agglutination at the contact points of unlike particles promoted by the higher affinity of silica over magnesia towards hydroxyl groups and initiation of simultaneous solid-state reactions, i.e. addition-reaction between two ingredients and dehydration to form a precursor of magnesium silicate in an amorphous state. The proposed mechanisms were compared with those for the mechanochemical change of talc.