Charge location effect on the hydration properties of synthetic saponite and hectorite saturated by Na(+), Ca(2+) cations: XRD investigation

This paper aims at comparing the effect of charge location on the hydration properties of two trioctahedral synthetic minerals: saponite and hectorite. The samples were characterised by a layer charge of 0.4 charge per half unit cell and were saturated with Na(+) or Ca(2+). The hydration behaviour was studied by determining the structural characteristics which were obtained by modelling XRD patterns. XRD patterns were recorded under controlled relative humidity (RH). The hydrated states of Ca-hectorite were more homogeneous than those of saponite whereas the transition from 1W to 2W occurred at lower RH rates for saponite than for hectorite. For heterogeneous samples, the 1W and 2W layers were stacked randomly fashion for hectorite. Na-saponite-0.4 and Ca-saponite-0.4 were made up of types of layer; one water layer (1W) and two-water layers (2W). The stacking of these layers showed some segregation.