THE PRASEODYMIUM-GOLD SYSTEM

The phase diagram of the Pr-An system was examined over the whole comp osition range by differential thermal analysis, X-ray diffraction, opt ical and scanning electron microscopy, and electron probe microanalysi s. Seven intermetallic compounds form in the Pr-Au system. Their melti ng behaviour was determined and their crystal structures confirmed or determined as follows: (1) Pr2Au, orthorhombic, oP12, Co2Si-type (anti -PbCl2-type), peritectic formation 750 degrees C; (2) PrAu, m.p. 1420 degrees C (alpha form, orthorhombic, oP8, FeB-type; beta form, orthorh ombic, oC8, CrB-type; gamma form, cubic, cP2, CsCl-type); (3) Pr3Au4, trigonal, hR42, Pu3Pd4-type, peritectic decomposition 1250 degrees C; (4) PrAu2, orthorhombic, oI12, CeCu2-type, peritectoidal decomposition 1100 degrees C; (5) Pr17Au36, tetragonal, tP106, Nd17Au36-type, m.p. 1180 degrees C; (6) Pr14Au51, hexagonal, hP65, Gd14Ag51-type, m.p. 121 0 degrees C; (7) PrAu6, monoclinic, mC28, PrAu6-type, peritectic decom position 900 degrees C. Four eutectic points exist at 610 degrees C an d 18.0 at.% Au, 1100 degrees C and 62.0 at.% Au, 1050 degrees C and 72 .5 at.% Au, and 790 degrees C and 90.5 at.% Au. A catatectic reaction of the (beta Pr) phase was also found.