Expansion property of ammonium montmorillonite

Saito, Akito*; Kawakita, Ryohei*  ; Sakuma, Hiroshi*; Oda, Chie  ; Honda, Akira; Sato, Tsutomu*

To understand the swelling behavior of NH-montmorillonite (MMT), the expandability of monoionic Na-, K- and NH-MMT was investigated by XRD under controlled relative humidity (RH) conditions and molecular dynamics (MD) calculations. XRD results indicate that the expansion properties of NH-MMT are similar to that of K-MMT for RH 30%. At RH 30%, however, NH-MMT expands further and has a larger basal spacing than both Na- and K-MMT. MD calculation results showed that NH-MMT reaches a one-layer hydration state under lower RH conditions than that of Na- and K-MMT, and was entirely consistent with the above observations by XRD. It was also confirmed that an irregular motion of interlayer NH could result from bonds between H atoms of the NH ion and the base O atoms of MMT. This irregular motion enabled the basal spacing of NH-MMT to increase and consequently, to expand further under low RH conditions.