Coupled Thermogravimetry and Differential Thermal Analysis

The bottom of Fig. 4.192 provides information on iron(III) hydroxide, an amorphous, brown, gel-like substance. Loss of water takes place over the whole temperature range up to 1,075 K. No distinct intermediate hydrates occur until hematite, Fe20j, is obtained. The crystallization exotherm of the hematite is visible in the DTA curve at about 775 K. 

The bottom example in Fig. 4.193 represents the thermal decomposition of a silver carbonate, AgjCOj, in helium. At about 400-550 K, the carbonate loses carbon dioxide and changes into the oxide Ag20. A second, smaller loss of mass begins at a temperature of 675 K. Both mass losses are accompanied by an endotherm in the DTA trace, meaning that the reactions are entropy driven. The final decomposition product is metallic silver. 

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