Synthesis and thermal stability of rare earth compounds REF3, REF3·nH2O and (H3O)RE3F10·nH2O (REu202f=u202fTb ? Lu, Y), obtained from sulphide precursors

Article abstract of DOI:10.1016/j.jfluchem.2017.12.001

The nature of the interaction between sulphides of the rare-earth elements (RE) of the yttrium subgroup RE₂S₃ (Dy ? Lu, Y) with hydrofluoric acid (concentration of 49%) was studied. Powders of RE₂S₃ compounds were obtained by the reaction between RE₂O₃ (Dy ? Lu, Y) and Tb₄O₇ with a stream of H₂S and CS₂ in the 1000–1050 °C temperature range. The reaction between RE₂S₃ and HF was carried out in a glassy carbon crucible in the 21–25 °C temperature range in solution, and the precipitate was washed with H₂O and dried at 90–100 °C. For the hydrates of RE fluorides with decreasing RE radius, the RE content increases the sorption of water for TbF₃·0.5H₂O; DyF₃·0.5H₂O; YF₃·0.5H₂O; HoF₃·0.8H₂O; and ErF₃·0.9H₂O. The powders of REF₃·nH₂O consisted of micro- and nano-sized particles containing the amorphous phase. Water loss occurs in the 50–180 °C temperature range and is accompanied by a natural increase in enthalpy: from 23.6 J/g for TbF₃ · 0.5H₂O to 97.8 J/g for ErF₃·0.9H₂O and from 51.1 J/g for (H₃O)Tm₃F₁₀·1.7H₂O to 64.5 J/g for (H₃O)Lu₃F₁₀·0.9H₂O. Exothermic effects of formation of polycrystalline phase REF₃ were recorded in the 200–300 °C temperature range. The reaction of RE₂S₃ (Tm, Yb, Lu) powders with HF proceeds with the formation of the zeolite type compounds (H₃O)Tm₃F₁₀·1.7H₂O, (H₃O)Yb₃F₁₀·1.0H₂O and (H₃O)Lu₃F₁₀·0.9H₂O. Thermal dissociation occurs with gradual loss of water and HF to form RE fluorides with the β-YF₃ structure as described by