Synthesis and properties of regularly interstratified (R=2) margarite (0.67)-beidellite, a 34 angstrom phase

A regularly interstratified (R=2) margarite(0.67) - beidellite was hydrothe rmally synthesized at 400-500 degrees C under 1 kbar pressure. The starting material was a mixture of kaolinite, calcium oxide or calcium carbonate, a nd alumina gel. X-ray powder-diffraction data of a sample saturated with Mg showed that the spacings of basal reflections vary depending on sample pre paration. The first-order reflection was observed at 34.6 Angstrom under ai r-dry condition with 60% relative humidity, 29.1 Angstrom after heating to 600 degrees C, 36.4 and 37.0 Angstrom after solvation with ethylene glycol and glycerol, respectively. The spacing of the 060 reflection was 1.478 Ang strom, indicating its dioctahedral nature. Chemical data gave a structural formula of Mg-0.18 (Ca1.84Na0.22K0.12) (Al5.97Fe0.013+Mg0.03Ti0.06) (Si7.35 Al4.65) O-30 (OH)(6). A differential thermal analysis showed a few endother mic peaks below 200 degrees C and in the range 500-650 degrees C, and an ex othermic peak at 1070 degrees C. XRD and chemical data indicate that the sa mple is composed of margarite-like and beidellite-like layers in a proporti on 0.67:0.33. Infrared absorption of the sample showed major bands at 670-7 00 cm(-1) and 900-930 cm(-1) regions, which are similar to the known values of margarite. These data suggest that the phase exhibits a large extent of substitution of Si by Al.