Preparation and Investigation of BaSO 4 KMnO 4 Crystals

BaSO 4 crystals containing KMnO 4 prepared by precipitation were investigated morphologically, chemically and by X‐ray diffraction. The colour of the preparations is homogeneous and stable. The colour intensity and also the amount of dissolved KMnO 4 (maximum approx. 30 Mol%) increases with concentration of KMnO 4 in the reaction solution to a limiting value dependent on the temperature. The lattice constants or the unit cell volume of the BaSO 4 –KMnO 4 crystals increase with the proportion of KMnO 4 . The experimental values agree well with the Vegard rule for preparations up to 18 Mol% KMnO 4 , but with higher proportions significant departures were observed. They may easily be explained by adsorption phenomena. Because the experimental possibilities for preparation of BaSO 4 ‐KMnO 4 crystals are narrowly limited, the miscibility gap ‐ infered from chemical results ‐ cannot be determined. The system BaSO 4 ‐KMnO 4 is regarded as a true mixed crystal system, nevertheless to explain all observations an adsorption of KMnO 4 on BaSO 4 must also be considered.