Thermobalance examination, differential thermal analysis and X-ray diffraction studies were made of the various alumina trihydrates prepared by seeding decomposition, auto-precipitation and decomposition by passage of carbon dioxide into alkali aluminate solutions. It was observed that thermal decomposition of both hydrargillite and bayerite was of two types. The effect of the amount of hydrargillite and bayerite contained in the sample for dehydration and the effect of the particle size were investigated. It was concluded that dehydration of hydrargillite at about 300° is different from that of bayerite, and that the particle size of the samples affects the type of thermal decomposition.
It is suggested that dehydration of alumina trihydrates proceeds by the following process:.