Thermal transformation of yttrium hydroxides to yttrium oxides

The reaction between aqueous solutions of yttrium salts (chloride and nitrate) at constant concentration and alkaline solutions (sodium and ammonium hydroxides) were investigated under different conditions. As a result, amorphous and hexagonal yttrium hydroxides, Y(OH) 3, were formed and in addition monoclinic yttrium hydroxide, α-Y(OH) 3, was prepared hydrothermally from amorphous yttrium hydroxide. The materials so obtained were examined by thermogravimetry and differential thermal analysis (TG and DTA), and yttrium hydroxides and their thermal decomposition products by X-ray diffraction study and infrared spectrophotometry. The sequence for the thermal decomposition of those materials is proposed on the basis of the results obtained.