Temperature amorphization

Calcined alumina, a-Al202, and naturally occurring comndum are practically insoluble in acids and bases, but partially calcined and low temperature amorphous oxide, such as that which forms on nacent commercial aluminum surfaces, is soluble... 

Balabanov et al. [499] found an endothermic effect in the thermographic pattern of the decomposition of niobium hydroxide at 435°C that corresponds to complete removal of water. At the above temperature, amorphous niobium hydroxide also converts into amorphous niobium oxide. Ciystallization of the amorphous oxide occurs at a higher temperature with the release of energy [28]. Researchers [499] reported on another exothermal effect at 549°C that was attributed to the crystallization temperature of amorphous niobium oxide. Decomposition of tantalum hydroxide and its conversion into crystalline tantalum oxide occurs at about 710°C [502] or at 670-700°C according to another source [132]. 

THE MICROSCOPIC QUANTUM THEORY OF LOW TEMPERATURE AMORPHOUS SOLIDS... 

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