The gd-pb (gadolinium-lead) system

Abstract

[69Dem] studied the Gd-Pb system by means of differential thermal analysis (DTA), optical metallography, and X-ray methods. [69Dem] prepared their Gd by Ca reduction of the fuoride, followed with distillation. Four different batches were used; their analyses are reported in Table 2. The Pb contained Mg, Si, Ca, Fe, Cu, Ag, and Bi as impurities, but the amount of each did not exceed 1 ppm (weight?). The samples were prepared in sealed tantalum crucibles by direct melting of Gd and Pb. The alloys were maintained in the liquid state for 30 min, cooled, inverted, and remelted at least twice. Micrographic examination showed the samples to be homogeneous. DTA was used to determine the liquidus curves and reaction isotherms of the system (heating and cooling rates not stated). Liquidus temperatures were obtained from cooling arrest data while both heating and cooling data were used to establish the reaction horizontals. Temperatures for eutectic and peritectic equilibria were reproducible to + 2 *C below 1140 *C and to  7 *C above 1140 *C, Liquidus temperatures were accurate to  10 *C. The liquidus curve in the region GdsPb 4 to GdPb2 of the assessed diagram has been drawn to fulfdl thermodynamic requirements. Due to their reactivity in air, the specimens for X-ray diffraction (XRD) were prepared by crushing or filing the alloys in an inert gas atmosphere. Also, metaUographic specimens were prepared and protected from air under kerosene. Addition of Pb to Gd gives rise to a catatectic equilibrium and to two solid solutions whose extension [69Dem] determined from photomicrographs of several alloys quenched from 1080 *C (ctGd) or from thermal data ([3Gd). Despite the very good melting point of the Gd used, the ct ,-~ 13 transformation was 23 *C higher than the accepted value listed in [86Gsc]. In such instances, correction of both the transformation temperature of the pure metal and the catatectic equilibrium sometimes is made to compensate for the difference. However, in the absence of reliable experimental data, we prefer to retain the original catatectic equilibrium at the reported temperature. The Pb melting point was raised about 1 *C by Gd additions, yielding a periteetic reaction that was verified by DTAwith a pure Pb sample as reference against an alloy at 97.44 at.% Pb. XRD experiments showed the solubility of Gd in (Pb) to be less than 0.5 at.%.