[Application of FTIR technique in microwave-hydrothermal synthesis of saponite]

FTIR was employed in the structure analysis of the saponites with an ideal chermical formula [Si6.5Al1.5]IV [Mg6]VI O20(OH)4 the starting gel synthesized by microwave-hydrothermally under different pressures (1 x 10(5), 5 x 10(5), 1.5 x 10(6), 2.5 x 10(6) and .5 x 10(6) Pa). It was found that low frequency absorption region in infrared spectrum was sensitive to the crystallization of the product and the amorphous materials produced in synthesis of saponite under the radiation of microwave. The absorptions belong to amorphous materials were decreased with increasing pressure. Saponite synthesized at 3.5 x 10(6) Pa showed no amorphous absorptions (1240, 90-602 cm(-1)), indicating the purity and quality of the synthetic mineral. It was worthy to note that Si(AI)-O stretching vibration infrared absorption could be regarded as an index in assessing the quality of synthetic 2:1 trioctahedral smectite sample with the same chemical compositions. With the increasing pressure, this strong vibration shifted to low frequency (1022, 1020, 1016, 1016, 1005 cm(-1)) in the medium frequency of the whole infrared spectrum. Since the sensitivity, easiness and simplicity, this infrared index would be meaningful in practical saponite-related minerals analysis. In addition, powder X-ray diffraction and scanning electronic microscopy were employed in charactering the saponite synthesized by microwave-hydrothermal method in this work.