Use of X-ray transmission diffractometry for the study of clay-particle orientation at different water contents

Homoionic Ca-saturated clay pastes were prepared and drying curves were obt ained by applying suction pressures from 1 kPa to 100 MPa. A transmission d evice was used to study particle orientation by placing the clay in a cell specially designed to obtain diagrams corresponding to different sample ori entations. The 00l and hk0 reflections were compared to determine the best reflections for studying clay-particle orientation. Depending on the clay, 00l reflections or the 020 reflection and/or hkl bands can be used to analy ze orientation. In many cases the 020 reflection is preferred because the i ntensity of the peak is high and appears to be independent of the H2O conte nt and the degree of stacking order of layers along the [001] direction. For interstratified clays, the conditions required to obtain 001 reflection s depended on several factors, the most important of which is the water con tent. Also, the intensity relating to particle orientation depends on (1) p article extension (size) in the (001) plane and (2) the crystal structure. Illite crystals of <1000 <Angstrom> gave a poorly oriented clay matrix. In contrast, large aggregates of illite, smectite, and kaolinite particles (>1 0,000 Angstrom) showed a strongly oriented system. The particles of smectit es may be curved and the dry material was poorly oriented owing to weak coh esion forces between the layers in comparison to illite. The study of the orientation of particles by X-ray diffraction on hydrated samples may be affected by sample mounting techniques. Any change in the co ntent or the way the sample is mounted may modify the microstructure of a m aterial. Clay containing a high water content affects the disorientation of particle s, whereas, for the dry samples, pore size, pore volume, and solid continui ty are associated with the geometry and crystal structure of the clay matri x.