STUDY OF THE AQUEOUS SOLUBILITY AND THERMAL-DECOMPOSITION OF MIXTURES OF THE COMPLEX OXALATES (NH4)(3)M(C2O4)(3), M=AL, FE, CR

The 25 degrees C isotherm of H2O-(NH4)(3)Al(C2O4)(3)-(NH4)(3)Fe(C2O4)(3); H2O-(NH4)(3)Al(C2O4)(3)-(NH4)(3)Cr(C2O4)(3) ternary systems and the 25 degrees C quaternary section H2O-(NH4)(3)Al(C2O4)(3)-1/2[(NH4)(3)Fe(C2O4)(3)]-1/2[(NH4)(3) Cr(C2O4)(3)] have been investigated using conductivity and X-Ray techniques. For all of them it has been established that the solids in equilibrium with the liquid are mixed crystals for the whole domain. The solid solutions exhibit a triclinic structure with a P ($) over bar 1 space group. The thermal decomposition of [(NH4)(3)Al1-xCrx(C2O4)(3)].3H2O and [(NH4)(3)Al1-xFex/Cr-2(x)/(2)(C2O4)(3)].3H2O yield (Al1-xCrx)(2)O-3 and (Al1-xFex/2 Cr-x/2)(2)O-3 solid solutions respectively.