Changes in layer organization of Na- and Ca-exchanged smectite materials during solvent exchanges for embedment in resin

The embedding process designed for impregnation in resin of hydrated clays for TEM observation comprises four steps of exchange by solvents and resin. Clay pastes of Na- and Ca-exchanged Wyoming smectite were prepared at low suction pressures (3.2 and 100 kPa, respectively), and their layer organiza tion was examined at different steps of the embedding process. X-ray diffra ction was used in order to follow the evolution of layer distances and part icle orientation during solvent exchanges. At 3.2 kPa as well as at 100 kPa , the water-saturated clay exhibits interlayer distances of 1.9 nm. After m ethanol exchange, interlayer distances collapsed to 1.6-1.7 nm. With 1,2-ep oxypropane and resin saturation, clays behave in a similar way as with meth anol. Examination of layer-stacking coherency by measurement of peak widths indicates that the first exchange by methanol is the most critical step in the embedding process because it induces reduction of the layer distances and aggregation, especially in the case of dilute Na-exchanged clay. The fi nal polymerization of resin introduces further slight changes in organizati on of the clay.