Studies on fluorination of Y(2)O(3) by NH(4)HF(2)

Abstract

Fluorination of Y(2)O(3) by NH(4)HF(2) to obtain pure YF(3) is studied in this work by observing the mass changes at room temperature and by employing TGA and DTA at higher temperatures, and observing the subsequent phase changes by X-ray diffraction. Fluorination begins at room temperature with the formation of (NH(4))(3)Y(2)F(9) and NH(4)F, and continues with the later further fluorinating any leftover Y(2)O(3) to ammonium yttrium fluorides with the evolution of NH(3). Similarly, on heating a mixture of Y(2)O(3) and NH(4)HF(2), the reaction proceeds sequentially through the formation of (NH(4))(3)Y(2)F(9), NH(4)Y(2)F(7) and finally YF(3). Any Y(2)O(3) still remaining reacts with YF(3) to form yttrium oxyfluorides, which continue as impurity. Substantial evaporation of NH(4)HF(2) is possible even before it could participate in the reaction. This disturbs the stoichiometry of the charge causing oxygen to remain in final YF(3). The compound reported in literature as YF(3)center dot 1.5NH(3) appears to be NH(4)Y(2)F(7). (C) 2011 Elsevier B.V. All rights reserved.