Formation of dysprosium oxide from the thermal decomposition of hydrated dysprosium acetate and oxalate Thermoanalytical and microscopic studies

摘要

Thermogravimetry, differential thermal analysis, X-ray diffractometry, gas chromatogra-phy-mass spectrometry and scanning electron microscopy were used to characterize the course of Dy_2O_3 from hydrated acetate and oxalate of dysprosium in an atmosphere of air. The results show that Dy(CH_3COO)_3 · 4H_2O dehydrates completely in two steps at 90 and 150℃ and decomposes to Dy_2O_3 at 580℃ through a noncrystalline intermediate, Dy(OH)(CH_3COO)_2, at 355℃, Dy(O)(CH_3COO) at 380℃, and crystalline Dy_2O_2CO_3 at 415℃. For Dy_2(C_2O_4)_3 · 7H_2O, the dehydration occurs in five steps at 100, 196, 227, 300 and 380℃, forming an anhydrous oxalate, which is amorphous and unstable. The anhydrous oxalate immediately decomposes to Dy_2O_3 at 610? through two amorphous intermediates, Dy_2(CO_3)_3 and Dy_2O_2CO_3, that form at 436 and 455℃, respectively. The crystalline oxide obtained from the acetate precursor contains large pores compared to the oxide obtained from the oxalate precursor. The volatile decomposition products from the acetate and oxalate precursors are water vapor, acetic acid, ketene, acetone and methane.