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.