| Research Abstract |
Rhabdophane-type RPO_4・nH_2O(n=0.5 to 1.0, R=La-Gd, Tb, Dy, Y, Er, or R=Ce+Y) were synthesized by precipitation from the mixed solution of T-salt and orthophosphoric acid at 20-90 C and pH 1-3, or by grinding weinschenkite-type RPO_4・2H_2O(R=Dy, Y, or Er) at room temperature for 10 days. Rhabdophane-type phosphates were dehydrated at 190 C to 250 C. The water corresponding to nH_2O was zeolitic water. Thermal changes of Rhabdophane-type anhydrous RPO_4, when heated in air under atmosheric pressure, were as follows:(1)rhabdophane-type RPO_4(R=La-Gd, or <=Ce+Y) monazite, (2)rhabdophane-type RPO_4(R=Tb of Dy) monazite xenotime, (3)rhabdophane-type RPO_4 (R=Y or Er) xenotime. The transformation from monazite into xenotime(2) was monotropic when heated in air under atmospheric pressure. Xenotime-type DyPO_4, however, transformed into monazite-type DyPO_4 when heated at 650 C to 1000 C in air under the pressure of 7.5 to 12.5GPa.
Weinschenkite-type RPO_4・2H_2O(R=Dy, Y, Er, or Yb) were synthesized by precipitation from the mixed solution of R-salt and orthophosphoric acid at 20-90 C and pH 1-3. Weinschenkite-type RPO_4・2H_2O gradually converted to xenotime when heated in air under atmospheric pressure.
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