Effect of SiO2/Al2O3 Ratio on the Thermal Reactions of Allophane

Teruo Henmi
Faculty of Agriculture, Ehime University, Matsuyama 790, Japan

Abstract: Differences were found in the differential thermal analysis curves and in the temperatures of new-phase development between allophanes of high (1.91–1.99) and low (1.47–1.53) SiO2/Al2O3 ratios. The endothermic peak due to continuous dehydration and dehydroxylation was at higher temperatures (153°–185°C) for allophanes with high SiO2/Al2O3 ratios and at lower temperatures (148°–165°C) for those with low SiO2/Al2O3 ratios. The temperature of the exothermic peak was lower and the height affected more by the exchangeable cation content for allophanes with high ratios than for those with low ratios. New phases did not develop in allophanes having high SiO2/Al2O3 ratios even after they were heated to 1000°C, above the temperature of the exotbermic peak. In contrast, a symptomatic development of new phases was noted in allophanes with low SiO2/Al2O3 ratios at 900°C, below the temperature of the exothermic peak. The effect of SiO2/Al2O3 ratio in the thermal behavior of allophane strongly suggests that differences in the structure are closely associated with the chemical composition of this material.

Key Words: Allophane • Dehydration • Dehydroxylation • DTA • Silica/alumina ratio • Thermal reactions

Clays and Clay Minerals; April 1980 v. 28; no. 2; p. 92-96; DOI: 10.1346/CCMN.1980.0280203
© 1980, The Clay Minerals Society
Clay Minerals Society (www.clays.org)