4.1 Classical DTA ^[1], ^[2]

Differential thermal analysis, DTA, is the simplest and most widely used thermal analysis technique. The difference in temperature, ? T, between the sample and a reference material is recorded while both are subjected to the same heating programme. In classical DTA instruments, represented schematically in Figure 4.1., a single block with symmetrical cavities for the sample and reference is heated in the furnace. The block is chosen to act as a suitable heat-sink, and a sample-holder of low thermal conductivity is included between the block and the sample to ensure an adequate differential temperature signal during a thermal event.

Figure 4.1: Differential thermal analysis (DTA). (a) Classical apparatus (S = sample; R = reference); (b) heat-flux configuration; (c) typical DTA curve. (Note the DTA convention that endothermic responses are represented as negative, i.e. downward peaks.)

Should an endothermic thermal event ( ? H positive, such as melting) occur in the sample, the temperature of the sample, T _s, will lag behind the temperature of the reference, T _r, which follows the heating programme. If the output from the thermocouples, ? T= T _s- T _r, is recorded against T _r (or the furnace temperature, T _f- T _r), the result will be similar to Figure 4.1(c)). If an exothermic process ( ? H negative such as oxidation) occurs in the sample, the response will be in the opposite direction. Since the definition of