The basal spacings of the homoionic (Na⁺, K⁺ and Ca2⁺) montmorillonite (T1) and saponite (SapCa-1) were examined by X-ray powder diffraction (XRD) analysis under the atmospheres of relative humidity (RH). RH was controlled by ReCX (Relative humidity Control system for X-ray diffractometer) precisely in the range of 0 to 100% RH.
The variations of basal spacing were almost similar in both minerals at the range of 0 to 80% RH. However, noticeable differences between the hydration state of T1 and SapCa-1 were observed at 100% RH. It was explained that the differences were caused by charge localization and hydroxyl orientation in silicate layer because of these specimens having similar layer charge.
In the region between 2 hydration states, irrational and asymmetrical reflections were observed. These reflections indicated interstratified structure of 2 hydration states. Especially at 60% RH, that the segregation structure was recognized. The existence of 2 phases indicates that there is heterogeneity in its charge density of layer.