Preliminary analysis of the thermal behaviour of an industrially used Ecuadorian clay

Abstract

A clay mineral from Ecuador has been analysed mineralogically by X-ray, thermal and infrared analyses and shown to contain approximately 35% of a disordered kaolin phase. Following a dilatometric analysis the vitrification range is established as 1025–1350°C and an isothermal vitrification rate study is reported. The vitrification follows Arrhenius behaviour with E a=147 kJ mol −1 suggesting a viscous flow control process. Further analysis of the vitrification rate process leads to an equation enabling optimum firing conditions to be calculated: V= ∫ h o h e 0.0085rh+ e 13.23 e 17,171 T h s where V is the total relative degree of vitrification, r is the heating rate, h is the heating time above 1298 K, T is the maximum firing temperature and h s is the soaking period. Mechanical strengths of fired samples have maximum value for the optimum conditions. A detailed athermal DTA analysis of the kaolin dehydroxylation and metakaolin to spinel/mullite transformation is presented and indicates that the shift in peak maximum temperature occurring with changing heating rate can be used to determine activation energies and provide insight into the transformation mechanisms.