Abstract
The mechanism of thermal decomposition of neodymium(III) acetate monohydrate and its anhydrides was studied by TG, DTA, X-ray diffraction, infrared spectroscopy, mass spectro-scopy and chemical analysis. The monohydrate begins to lose its water of crystallization at about 120° C, and the dehydration occurs only in one step. The anhydrous acetate dehydrated below 160° C shows a X-ray diffraction pattern of amorphous nature, crystallization taking place at 170° C to yield the anhydride of stable lower temperature type. The anhydride shows another crystallographic transformation at 220° C, giving the anhydride of stable higher tern-perature type. Both anhydrides of the stable lower and higher temperature types have a strong hygroscopic character, increasing their weigh by about 7-8% in air within several hours, and yields perfect monohydrate. The anhydrous neodymium(III) acetate releases acetone and carbon dioxide in the temperature range of 240-400°C, passing through two intermediate compounds in the course of decomposition, and yields neodymium(III) carbonate oxide as a final product. Both new intermediate compounds are insoluble in water. Presumably they have the same composition as neodymium(III) acetate oxide. The anhydride prepared from neodymium(III) acetate and acetic anhydride by a wet process exhibits a crystallographic transi-tion at 270°C, conventing to the anhydride of higher temperature type mentioned. Both anhydrous nedymium(III) acetates of the stable lower and higher temperature types are of new polymorphs of anhydride, and a heat of transition is given 2.8 kcal/mol.
