SYNTHESIS AND THERMAL-DECOMPOSITION OF SOME RARE EARTH(III) DIMETHYLAMMONIUM SULFATE CRYSTALLOHYDRATES .2. RESULTS OF INVESTIGATIONS OF [(CH3)2NH2]3LN(SO4)3.3H2O

Double sulphates of rare earths(III) with dimethylammonium were obtain ed by evaporation of aqueous reaction mixtures of rare earth(III) sulp hates and dimethylammonium sulphate in molar ratios greater than 1:20. By means of X-ray powder diffraction patterns, it was found that they are isostructural. From the TG curve of the thermal decompositions of the obtained compounds in the temperature interval from 20 to 700-deg rees-C, their general empirical formula was established as [(CH3)2NH2] 3Ln(SO4)3 . 3H2O (where Ln is Nd, Sm, Eu, Gd, Tb). The thermal decompo sition of the anhydrous double salts takes place with thermal effects on the DTA curve, which means that this process is not a simple dissoc iation, but that intermediate products are possibly involved. The equa tions of the thermal decomposition are also presented.