Electrical Resistance Measurements of Kaolinite and Serpentine Powders during Dehydroxylation*

Direct current resistance measurements were made of kaolinite and serpentine powders to follow the changes in resistances during their dehydroxylation processes in air. The resistance of kaolinite remained almost constant during the dehydroxylation, whereas that of serpentine showed a rapid decrease. The formation of distorted lattice sites where the charge carriers are scattered under an electric field was assumed in the former case. On the other hand, the result in the latter case was interpreted in terms of an increasing cation mobility. I N T R O D U C T I O N LITTLE work has been done so far on the electrical properties of clay mineral powders in relation to their thermal decomposition and transformation processes. Freund (1960) at tempted to follow the change in tile electrical resistance of metakaolin to the subsequent phases over a temperature range 700 to 1300~ More recently, Toussaint (1961) and Fripiat and Toussaint (1963) have studied the dehydroxylation process of kaolinite by measuring tile change in a.c. conductivities in vacuum as well as under various water vapour pressures, together with parallel infrared observations; they have put forward a concept of proton delocalization to explain their experimental results. The present author has at tempted to obtain experimental information concerning the d.c. conductivities of kaolinite and serpentine with the main object of seeing whether a suspected difference in the dehydroxylation behaviors of these minerals might be followed by electrical resistance measurements. Difficulties inherent in making d.c. measurements on powder specimens have been encountered, however, in interpreting the experimental data. No attempts are made, therefore, to draw quantitative *Contribution No. 63-57, College of Mineral Industries, The Pennsylvania State University, University Park, Pa.