Effect of Particle Size on Differential Thermal Analysis

Abstract

IN a review of quantitative differential thermal analyses of clay, van der Marel1 quotes numerous workers (which include Speil2 on kaolinite, and Kulp et al.3 on calcite), who have observed that the recorded temperature of transformation is lowered with a decrease in the particle size of the sample. This result was obtained from material which is either fractionated or ground. With regard to the fractionated material, the coarse portion of a sample contains the particles with better crystallinity because of their greater ability to grow. A recent example of this is the concentration of dickite in the coarse fraction and kaolinite in the fine fraction as recorded by Bayliss et al.4. In addition fractionated samples of a kaolinite are shown by Carthew5 to have similar transformation temperatures, which again indicates that crystallinity and not particle size causes the variation in transformation temperature. In the grinding of a sample, internal disruptions as well as a decrease in particle size may occur. Since clay minerals have only one cleavage, which is a perfect basal type, it is easy for disruptions to occur along these planes during grinding so that a decrease in particle size is accompanied by a reduction in crystallinity.