The effect of glow-discharge plasma and muffle furnace heating on the surface chemistry of kaolinite

Abstract

Kaolinite is commonly used as a coating in the paper industry, and as a filler in the plastics industry. Therefore it is crucial that the particles are not flocculated. In order to achieve a stable system the surface chemistry is manipulated such that strong repulsive inter-particle forces are present. This paper then investigates the changes in the surface chemistry of a commercial kaolinite after treatment in a muffle furnace and in glow-discharge plasma. The effect of the surface treatment on the zeta potential of the kaolinite was investigated by electroacoustic means. Furnace heating lead to a decrease in the magnitude of the zeta potential at the natural pH, and the zeta potential was always negative over the pH range studied. No iso-electric point was found, rather a minima in the magnitude of the zeta potential was observed at a pH of 3.5. This minima was shifted to higher pH values after treatment. Analysis of the surfaces of the kaolinite particles was also performed by the use of a DVS Advantage (SMS UK Ltd). The muffle furnace heated kaolinite had a lower water uptake than the untreated kaolinite implying changes to the hydrophobic/ hydrophilic nature of the kaolinite surfaces. Normally dispersants are added to kaolinite suspensions to aid dispersions. As kaolinite is processed at a rate of several millions of tonnes per annum, a small reduction in the amount of dispersant required could result in a significant economic saving.