Condensed rare earth poly-phosphate prodn. esp. for optical glass mfr. - involves mixing oxide with poly-phosphoric acid, adding urea to viscous mixt. and heating

摘要

Prodn. of condensed rare earth phosphates (I) of the compsn. (RE(PO3)n, esp. La, Gd and Y polyphosphates (IA), is carried out by (a) mixing the rare earth oxide (RE203) with polyphosphoric acid (II) contg. over 70% P2O5 in RE2O3:P2O5 molar ratio = 1:3; and (b) heating the viscous reaction mixt. to 300-500 deg. C after adding urea. Pref. area is added in an amt. of 1.5-3.3 (wt.) pts/pt. water introduced with the starting materials. USE/ADVANTAGE - The process is esp. useful for producing very pure (IA) for optical glass mfr.. It is simple, uses economical, easily handled raw materials, which do not attack the reactor and gives (I) in porous, easily pulverised form. In an example, 49.5 g La2O3 (99.95%) were added to 81.0 g liquefied (II) 79.8% P2O5 = 64.6 g PwO2) at 30 deg. C in a porcelain basin and homogenised quickly. A strongly exothermic reaction started after 3 min. and the temp. rose to 300 deg. C.. 33.5 g prilled urea were stirred into the viscous liq. when the temp. fell to 200 deg. C and gas was evolved. The mixt. was kept 20 min. at 260 deg. C and the resultant coarsely porous block was heated 60 min. at 500 deg. C, until the evolution of gases (NH3, CO2, P2O5 vapour) ceased. The prod. was easily removed from the basin and pulverised. 114.0 g La polyphosphate were obtd., with 56.5% P2O5, 42.6% La2O3 and 0.9% calcination loss.