Thermal Decomposition of Yttrium Oxalate

Abstract

Thermal decomposition of yttrium oxalate octahydrate, Y₂(C₂O₄)₃⋅8H₂O, has been studied by thermogravimetry, differential thermal analysis, infra-red absorption spectroscopy, X-ray diffraction analysis and surface area measurement. The results obtained were as follows:
(1) Yttrium oxalate octahydrate decomposed to the oxide in the order of the following five stages: (i) octahydrate→trihydrate, (ii) tihydrate→dihydrate, (iii) dihydrate→monohydrate, (iv) monohydrate→anhydrate, and anhydrate→intermediary (such as carbonate or oxycarbonate), and (v) anhydrous oxalate or intermediary→oxide.
(2) The dehydration of the octahydrate to the monohydrate took place below about 200°C, and the monohydrate was nearly stable between about 200°C and 320°C. It was unable to find out the temperature range in which the anhydrate was separately stable. The anhydrate decomposed to the oxide directly, or through the formation of the intermediary above about 350°C.
(3) Surface area of the thermal decomposition products obtained on heating the octahydrate to the various temperatures at a constant rate increased with increasing temperature below the temperature in which the monohydrate was formed due to the dehydration, being followed by a decrease with increasing temperature.
(4) Above the temperatures where the monohydrate decomposed, surface area remarkably increased and showed maximum by holding the temperature in which the formation of the intermediary was pronounced.