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Report No.

Expansion property of ammonium montmorillonite

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

To understand the swelling behavior of NH$$_{4}$$-montmorillonite (MMT), the expandability of monoionic Na-, K- and NH$$_{4}$$-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$$_{4}$$-MMT are similar to that of K-MMT for RH $$>$$ 30%. At RH $$<$$ 30%, however, NH$$_{4}$$-MMT expands further and has a larger basal spacing than both Na- and K-MMT. MD calculation results showed that NH$$_{4}$$-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$$_{4}$$$$^{+}$$ could result from bonds between H atoms of the NH$$_{4}$$$$^{+}$$ ion and the base O atoms of MMT. This irregular motion enabled the basal spacing of NH$$_{4}$$-MMT to increase and consequently, to expand further under low RH conditions.



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