There are several physical changes that can yield exothermic peaks in DTA (differential thermal analysis) and DSC (differential scanning calorimetry), including:
Crystallization: The process of a material transitioning from a disordered, amorphous state to an ordered crystalline state can often be accompanied by an exothermic peak.
Solid-state reactions: Reactions between two or more solids can result in the release of energy, which may be detected as an exothermic peak in DTA or DSC. Examples include oxidation or combustion reactions.
Phase transitions: Changes in the crystal structure of a solid can result in the release of energy, especially if the transition is associated with a change in entropy. Melting, sublimation, and recrystallization are all examples of phase transitions that may yield exothermic peaks.
Adsorption/desorption: When a gas or liquid is adsorbed onto a solid surface, energy is typically released. This energy may be detected as an exothermic peak during desorption.
Mixing: When two or more substances are mixed together, the resulting mixture may have a lower enthalpy than the individual components due to favorable interactions between them. This mixing enthalpy may be detected as an exothermic peak during cooling.
Overall, any physical change that involves a reduction in energy or complexity has the potential to yield an exothermic peak in DTA or DSC.
