The Role Monovalent and divalent cations in the Dehydroxylation of Kaolinite

Abstract

Homo-ionic forms of kaolinite exhibit difference in peak shapes of dehydroxylation reaction in differential thermal analysis. H-forms are found to give higher amplitudes, A/w and slope ratios of dehydroxylation peak than divalent cations in general. Na+- forms tend more towards hydrogen forms in their behavior. The peak temperatures of the various homo-ionic forms are not much affected when the furnace is controlled and temperature measured with a thermocouple in the centre of the sample while the furnace temperature is raised according to a predetermined heating cycle by changing the input energy. The difference in the dehydroxylation peaks of homo-ionic forms are consideration to be due to change in the rate of dehydroxylation. The divalent cations though not in an orderly way are found to decrease the rate of dehydroxylation and this is considered to be the formation of oxide linkages which bring down the interparticle porosity and obstruct the easy escape of water vapour. Slight pressure due to entrapped water vapour is considered to cause retardation of the forward reaction. No rigid order of cations regarding dehydroxylation is to be found and perhaps work with close sized fractions may throw greater light on this aspect.