EFFECT OF HYDROGEN ON THE POLYMORPHIC TRANSFORMATION IN YTTERBIUM

Differential thermal analysis is used for determining the temperatures of polymorphic transformations in ytterbium and in the Yb-YbH2 system . On transition from ytterbium to the solid solution of hydrogen in yt terbium the temperature of the fee --> bce polymorphic transformation decreases from 730+/-5 to 632+/-8 degrees C. The latter is the eutecto id temperature for the Yb-YbH2 system. The temperature of the hcp --> fee polymorphic transformation, irrespective of the hydrogen level, is 310+/-5 degrees C. The region of the solid solution of hydrogen in yt terbium at 632 degrees C is limited to the range H:Yb = 0.25+/-0.05; t he homogeneity region of ytterbium dihydride is limited to the range H :Yb = 1.90+/-0.05.