The high-temperature phase equilibria of the Ni–Sn–Zn system: Isothermal sections

AbstractIn this work three complete isothermal sections of the Ni–Sn–Zn system at 700, 800 and 900 °C are presented. They were constructed based on experimental investigation of more than 60 alloy samples. Powder XRD, single crystal XRD, EPMA, and DTA measurements on selected samples were carried out. Two new ternary compounds, designated as τ2 (Ni5Sn4Zn) and τ3 (Ni7Sn9Zn5), were identified and their homogeneity ranges and crystal structures could be described. Whereas τ3 is only present at 700 °C, the τ2-phase was found at both 700 and 800 °C. No truly ternary compound could be found in the isothermal section at 900 °C. A seemingly ternary compound at 20 at% Sn in the Ni-rich part of Ni–Sn–Zn was found at 800 and 900 °C. Our XRD results, however, indicate that this phase is a ternary solid solution of Ni3Sn-HT from constituent binary Ni–Sn. It is stabilized to lower temperatures by additions of Zn. These new experimental results will provide valuable information to the thermodynamic description of alloy systems relevant for high-temperature lead-free soldering

A thermodynamic study of the cadmium–neodymium system

ABSTRACT: Cd vapor pressures were determined over Cd–Nd samples by an isopiestic method. The measurements were carried out in the temperature range from about 690 to 1200 K and over a composition range between 48 and 92 at % Cd. From the vapor pressures, thermodynamic activities of Cd were derived for all samples at their respective sample temperatures, and partial molar enthalpies of Cd were obtained from the temperature dependence of the activities. With these partial molar enthalpies, the Cd activities were converted to a common temperature of 873 K. By means of a Gibbs–Duhem integration Nd activities and integral Gibbs energies were calculated, using a literature value of Δ(f)G for the phase Cd(6)Nd as integration constant. A minimum of Δ(f)G ≈ −38 kJ g-atom(−1) at 873 K was obtained for the phase CdNd, a value that compares well with other CdRE compounds. GRAPHICAL ABSTRACT: [Image: see text

Pressure dependence of the tin–phosphorus phase diagram

The pressure dependence of the binary Sn–P phase diagram was investigated using an isopiestic equilibration method. Successful experiments were carried out at nine different pressures in the range from 0.006 to 0.69 bar, and the corresponding phase diagrams for these pressures were created up to a content of x P = 70 %. The change of the equilibrium temperatures of the formation reactions for the three binary compounds (Sn4P3, Sn3P4, SnP3) with increasing pressure was analyzed and extrapolated to 1 bar. The pressure-dependent maximum solubility of phosphorus in the tin-rich liquid was investigated and partial thermodynamic properties of P were derived for the liquid phase. Standard molar Gibbs energies of formation were derived for all three stable compounds

Experimental investigation of the Cd-Pr phase diagram.

The complete Cd-Pr equilibrium phase diagram was investigated with a combination of powder-XRD, SEM and DTA. All intermetallic compounds within this system, already reported in literature, could be confirmed: CdPr, Cd2Pr, Cd3Pr, Cd45Pr11, Cd58Pr13, Cd6Pr and Cd11Pr. The corresponding phase boundaries were determined at distinct temperatures. The homogeneity range of the high-temperature allotropic modification of Pr could be determined precisely and a limited solubility of 22.1 at.% Cd was derived. Additionally, single-crystal X-ray diffraction was employed to investigate structural details of Cd2Pr; it is isotypic to the AlB2-type structure with a z value of the Cd site of 0.5. DTA results of alloys located in the adjacent two-phase fields of Cd2Pr suggested a phase transformation between 893 and 930°C. For the phase Cd3Pr it was found that the lattice parameter a changes linearly with increasing Cd content, following Vegard's rule. The corresponding defect mechanism could be evaluated from structural data collected with single-crystal XRD. Introduction of a significant amount of vacancies on the Pr site and the reduction in symmetry of one Cd position (8c to 32f) resulted in a noticeable decrease of all R-values

Thermochemical investigations in the tin-phosphorus system

Phosphorus vapor pressures were measured over tin-phosphorus samples using two independent experimental techniques. Using an isopiestic method, data points were obtained between approximately 0 and 71 at.% P in the temperature interval from 618 to 998 K. Vapor pressures were also measured at lower temperatures over two two-phase fields, i. e. in (L + Sn4P3) between 559 and 677 K and in (Sn4P3 + Sn3P4) between 552 and 621 K, by a Knud-sen cell based mass loss technique. Based on these measurements partial thermodynamic properties and integral Gibbs energies were derived. The composition dependence of the phosphorus activity was also derived for three selected temperatures, 650, 700, and 750 K. Standard molar Gibbs energies of formation of Sn4P3,Sn3P 4 and SnP3 were determined and are given by: (equation Presented). © Carl Hanser Verlag GmbH & Co. KG