STUDIES ON THE DEHYDRATION AND DECOMPOSITION OF CALCIUM AND DICALCIUMMAGNESIUM ACONITATE HYDRATES

The thermal decomposition of calcium and dicalcium magnesium aconitate hydrates were studied by TG/DTG, DTA, EGA, SEM and other physico-chem ical techniques. The decomposition proceeds in four stages: dehydratio n; oxidation of the carboxylic acid portion of the salt; complete frag mentation of the hydrocarbon portion; and finally, decarboxylation of the metal carbonate to the oxide. The crystal morphologies of the hydr ate and anhydrous salts of each compound are very similar. Tricalcium aconitate consists of well-developed twinned crystals and stellate clu sters intergrown with flat platy crystals. On the other hand, dicalciu m magnesium aconitate crystals are monoclinic with well-developed pina coidal faces. The activation energy, E(d)(43 +/- 2 kJ mol(-1) water), calculated from Borchardt and Daniels' method, for the dehydration pro cess of calcium aconitate trihydrate is of the same order of magnitude as some simple metal salt hydrates. The rate constant, k(d) increased from 0.04/min at 238 degrees C to greater than 0.86/min at 295 degree s C. It is concluded that the dehydration process is due to cation bou nd water.