Thermal behaviour of clays and clay-water mixtures for pelotherapy

• Specific heat capacities were determined for a set of clays and clay-water pastes.
• An equation is proposed to calculate the heat capacity of peloids.
• The cooling curves of different clays are dependent of clay mineral properties.
• The relaxation time parameter lets to compare the thermal behaviour of peloides.

To prepare peloids for thermotherapy, the thermal behaviour of their component clay pastes needs to be known. This study was designed to experimentally determine the specific heat capacity and cooling kinetics of pastes prepared by adding different proportions of water to eight commercially available clays of different composition. According to exponential equations fitted to the cooling curves for the pastes, a new parameter designated the relaxation time is proposed. Using this parameter, the clayey pastes could be classified on the basis of rate of heat release. According to its specific heat capacity and relaxation time, Na-activated magnesium bentonite emerged as the most suitable clay material to prepare peloids with applications in thermotherapy.