Gabriele Cacciamani

Contribution to the study of the alloys and intermetallic compounds of aluminium with the rare-earth metals

General properties of aluminium alloys of the rare earth metals are briefly summarised. Their phase equilibria and the crystal structures of the different intermediate phases are presented and discussed. The results obtained in the experimental investigation of the YAl and SmAl systems are reported. The formation enthalpies of YAl2 and SmAl2 have been re-measured, resulting in −50.5 kJ/(mol at) and −55.0 kJ/(mol at) at room temperature, in a good agreement with literature data. Phase equilibria investigation in the SmAl system has been carried out and the results obtained via thermal analysis, micrographic examination, microprobe and X-ray diffraction analyses described and discussed in the framework of the general behaviour of the rare earth alloys. The experimental Sm-Al phase diagram, collated with previous literature data, is compared with the results of a thermodynamic optimisation. The following intermetallic compounds exist: Sm2Al (peritectic decomposition, at 860 °C) SmAl (per.dec.960 °C), SmAl2 (melting point 1480 °C), SmAl3 (peritectoidal decomposition at 1130 °C), Sm3Al11 (melting point ~1380 °C). The following eutectic equilibria have also been determined or confirmed: 20 at% Al and 760 °C, 75 at% Al and 1340 °C, 97.0 at% Al and 635 °C. A eutectoidal equilibrium occurs at 10 at% Al and 700 °C.

On a simple high temperature direct reaction calorimeter

Several commercial and laboratory-made instruments have been described in the literature based on a drop technique and containing an isoperibolic differential detector. The instrument presented here consists of two cells set one above the other and located in ceramic and metallic tubes for thermal equalization. The temperature difference between the two cells (working and reference cells) is measured by a 20-couple thermopile. The calorimeter is enclosed in a furnace with three independently controlled zones which can be heated up to 1200 °C. A typical run consists of dropping from a room temperature thermostat a small capsule containing about 2 g of a metal mixture. The heat effect is evaluated by dropping, before and after the capsule, a number of weighed Ag specimens. Subsequently, in a second run, the same capsule containing the reacted sample is dropped again into the calorimeter. The difference between the heat effects obtained in the two runs gives the room temperature heat of formation of the alloy. A brief description of the instrument, of the calibration procedure and of the necessary auxiliary examinations is reported and the results obtained in a first set of measurements on a number of alloys are given.

Aluminium compounds of the rare earths: enthalpies of formation of YbAl and LaAl alloys

Abstract The standard molar enthalpies of formation for the different solid LaAl and YbAl alloys have been measured by means of direct calorimetrr. The composition and equilibrium state of the samples were checcked by micrographic and X-ray diffraction techniques. The following values have been obtained 1kJ (mol atoms)1): LaAl, ΔformH° = −46±2; LaAl2 ΔformH° = −50.5±2; LaAl3 ΔformH° = −44.0±2; La3Al11 ΔformH° = −41.0±2; Ybal2 ΔformH° = −39.5±2; YbAl2 Δform H° = −32.5±2. Experimental results are discussed and compared with literature data.

Systematics of rare earth-palladium alloys: Revision of a few systems and forecast of the tb-pd phase diagram

Abstract A summary is given of the general constitutional properties of the palladium alloys with the heavy rare earths. Slightly revised versions of the Gd-Pd, Dy-Pd, Ho-Pd and Er-Pd systems are proposed. On the basis of the trend of properties observed for the different alloys as a function of the atomic number of the involved rare earths, the shape of the Tb-Pd system has been predicted by interpolation. The results are here discussed and compared with the available thermodynamic data by means of the Lukas software.

Remarks about data reliability in experimental and computational alloy thermochemistry

Abstract The determination of phase equilibria in multi-component systems, which is fundamental to the synthesis, thermal treatments and application of several materials, may be efficiently approached through a combination of experimental measurements and computational methods. To this end, however, reliable experimental data should be available, even if obtained for a reduced set of crucial composition and temperature conditions. Among these experiments a relevant and pre-eminent role is played by thermal and thermodynamic measurements. The estimation of uncertainties in thermochemical measurements, however, is especially difficult due to the presence of errors from different sources (such as sample impurities, side reactions, deviations from equilibrium, etc.) which, mainly in alloy science, are generally larger than the instrumental errors and not easy to evaluate. On the basis also of the research carried out in the Authors laboratory, various sources of errors related to a few experimental techniques in alloy thermochemistry are examined. Some comments on the reliability and consistency of results from thermochemical optimisation, which are heavily affected by the experimental data uncertainty, (especially when large temperature and/or composition extrapolations are needed) are also given. A few comments about the overall coherence of the data concerning a certain alloy system are presented and the need for enhancing and developing experimental alloy thermodynamics underlined.

Effect of Cu and Zn on the melting and transformation temperatures of Pr and Gd

Abstract Phase equilibria in the R-rich regions of the R-Cu and R-Zn binary systems (R=Pr and Gd) have been investigated by differential thermal analysis, X-ray powder diffractometry, metallographic analysis and quantitative electron probe microanalysis. In these regions, the lowering (Δ T ) of the melting and transformation temperatures of the rare earth metals by addition of copper and zinc resulted in eutectic and catatectic or eutectoidal type reactions. The Δ T observed in these systems are discussed and compared with those reported in the literature for the binary systems of Pr and Gd with Mg and with the elements from the 9th to the 14th group of the Periodic Table. In order to complete this systematics, a few Pr-rich Pr–Cd alloys have also been prepared and analysed.

Preparation and characterization of ternary NdPrSb alloys

Ternary Nd-Pr-Sb alloys were studied using X-ray powder diffraction and optical and electron microscopy. (Nd, Pr) 2 Sb (tI12-La 2 Sb type), (Nd, Pr) 4 Sb 3 (cI28-anti-Th 3 P 4 type), (Nd, Pr)Sb (cF8-NaCl type) and (Nd, Pr)Sb 2 (oC24-SmSb 2 type) show complete solubility between Nd and Pr. The variation of the lattice parameters as a function of the Nd to Pr ratio was determined. In addition, the alloy Nd 0.475 Pr 0.475 Sb 0.05 was investigated by differential thermal analysis (DTA). The results obtained confirm a previous thermodynamic prediction of the Nd-Pr-Sb phase equilibria

Carbon – Hafnium – Silicon

The C-Hf-Si system is characterized by very high melting temperatures which make experimental investigations quite difficult. Only one ternary compound, of unknown structure, is reported in literature. [1966Bru] investigated the isothermal section at 1300°C; its results were summarized by [1969Rud]. More than 50 samples were prepared by [1966Bru] from powders of the elements: 99.57 mass% C, 99.7 to 99.9 mass% Si, 97.5 to 99.7 mass% Hf (lower purity of Hf was mainly due to Zr contamination). HfSi2 and SiC master alloys were first prepared by cold pressing the element powders with camphor as a binder. After heating at 110°C for 12 h under vacuum to remove camphor, alloys were sintered at 1250 for 2 h (HfSi2) or 1350°C for 1 h (SiC) in a Mo boat under hydrogen. Samples were prepared by hot pressing pellets of master alloy and other element powders and annealing at 1300°C for 64-65 h under helium. Samples were then examined by X-ray powder diffraction, metallography and chemical analysis.