HETEROGENEITY IN SILICON-IRON MIXED HYDROXIDES

Several mixed hydroxides obtained by co‐precipitation of FeCl2 or FeCl2 with Na2SiO2 followed by ageing and purification were studied by X‐ray diffraction, infra‐red spectroscopy, and surface‐area measurements. The compounds with molecular ratios SiO2/Fe2O3 ranging from 0·1 to 1·17 are essentially amorphous. Silica, which is not to be considered as an integral part of the gel, is chemi‐sorbed on the ferric or‘ferrosic’ phase. The good agreement between IR, DTA, and surface‐area measurements with increasing molecular ratios permits the distinction between two ranges of silica contents. In the first range, MR <·1, silica is directly chemisorbed on the adsorbant. In the MR >0·1 range, silica polymerizes as a separate phase growing upon the‘ferrosic’ or‘ferric’ phase. Copyright © 1969, Wiley Blackwell. All rights reserved