Influence of KBr conditioning on the infrared hydroxyl-stretching region of saponites

In order to assess the influence of tetrahedral sheet charge on the hydroxy l-stretching vibration in clay minerals, a series of synthetic Na saponites , with increasing layer charge, was studied by infrared (IR) spectroscopy. When recorded after KBr dilution either in transmission or diffuse reflecta nce, the IR spectra exhibit a component at similar to 3710 cm(-1), the inte nsity of which increases linearly with increasing layer charge. When experi ments are carried out without any dilution of the samples, this component i s not observed, suggesting a Na+/K+ exchange upon mixing of the sample with KBr. The spectra obtained for K-saponite confirm this exchange. This shows that the dilution procedure can lead to serious misinterpretations of IR s pectra in the OH-stretching region.