A CONTRIBUTION TO THE RARE-EARTH INTERMETALLIC CHEMISTRY - PRASEODYMIUM MAGNESIUM ALLOY SYSTEM

Pr-Mg alloys were studied in the range 0-100 at. % Mg. By using X-ray powder diffraction, optical and scanning electron microscopy, electron probe microanalysis and differential thermal analysis, the different intermediate phases were identified and their crystal structures confi rmed or determined. The following phase equilibria have been also dete rmined: PrMg (cubic, cP2, CsCl type, melting point 765-degrees-C), PrM g2 (cubic, cF24, MgCu2 type, peritectic formation 740-degrees-C), PrMg 3 (cubic, CF16-BiF3 type, melting point 790-degrees-C), Pr5Mg41 (tetra gonal, tI92 Ce5Mg41-type, peritectic formation 575-degrees-C) and PrMg 12 (tetragonal, tI26 ThMn12-type, peritectic formation 565-degrees-C). PrMg2 undergoes a eutectoidal decomposition at 670-degrees-C. Three e utectic reactions were observed to occur at 735-degrees-C and 40-0 at. % Mg, at 725-degrees-C and 59-5 at. % Mg and at 560-degrees-C and 95. 0 at. % Mg, respectively. The (beta-Pr) terminal solid solution was ob served to decompose eutectoidally at 510-degrees-C and 19.5 at. % Mg. The data obtained in this study are compared with those relating to ot her previously studied R-Mg systems. The crystallochemical characteris tics of the binary phases formed by Mg with the rare earths and with t he alkaline earths are briefly discussed.