Adsorption of stearic acid by allophane

IR spectra and DTA-TG curves showed that molten stearic acid was partially converted to the ionic form on adsorption by allophane. The process was not affected by grinding the samples. In this respect allophane is unique among the Al-rich clays, which generally cause little or no conversion unless the clay-carboxylic acid associations are well ground. Stearic acid was adsorbed on the surface of allophane through water molecules. On heating, water was lost together with some of the acid; the remaining acid became coordinated to surface Al. In both open and semi-closed systems stearate ions were retained to higher temperatures than the acidic form. Allophane catalysed oxidation of part of the organic matter.