1991 Volume 8 Issue 2 Pages 59-68
Montmorillonite was synthesized by hydration of sodium, magnesium aluminosilicate glass under hydrothermal pressure of 100 MPa. The water/solid ratio of starting mixtures was varied in the range 0.155 to 2.17. If complete conversion from glass to montmorillonite is assumed, the ratios correspond to 4 (OH) and nH2O, n=5 to 80, for Na0.66 (Mg, Al) 4 (Si, Al) 8O20 (OH) 4·nH2O. The synthesis temperature ranged from 250 to 475°C. Run products were analyzed by X-ray diffraction.
Yield of montmorillonite and its crystallinity increased drastically at the water/solid ratio of 0.310 (i.e.n=10) but were saturated in more water-rich conditions. The interlayer spacings of as-grown samples before humidity-adapted de-intercalation indicated that the number of water-layers depended on the water/solid ratio: one water-layer for n <20, two for n>20, and three in excess-water synthesis.
From variations of full width at half maximum (FWHM) of 001 and 11, 02 reflections depending on the hydration of glass, the following growth mechanism for montmorillonite is suggested: two-dimensional fragments were formed by an initial hydration of the glass and appeared to be slightly interstratified by one another. Further hydration did not increase the dimensions of the fragment or the degree of interstratification, although the number of such poorly crystallized fragments was increased.
