Thermal effects induced by grinding in dolomite

Abstract

Differential Scanning Calorimetry (DSC) curves of ground samples of dolomite show an exothermic peak at ca . 300°C. Analysis of the released energy, ΔH, shows that the maximum is reached at 35 h of milling ( ca . 5 J/g) with a subsequent declination as grinding time progresses. No significant loss of specific surface is observed when the ground samples are heated at temperatures above the peak, and therefore the exothermic peak cannot be ascribed to a surface reordering. On the other hand, a recovery of crystallinity, as shown by the intensity of the X-ray diffraction lines and changes in crystallite size and microstrains calculated from the variance of the (104) line profiles, takes place between 200 and 300°C, the interval of temperature at which the exothermic peak appears. Thus, the energy released during heating is due to a restoration of ground dolomite crystallinity.