Thermodynamic Properties of Melts and Phase Equilibria in the Copper–Zirconium System

The vapor composition over and thermodynamic properties of Cu–Zr melts (5.1–85.0 at. % Zr) are studied by Knudsen cell mass spectrometry between 1191 and 1823 K. The data set obtained comprises more than 1100 activity values for various compositions and temperatures. The thermodynamic behavior of Cu–Zr melts is described in terms of the associated-solution approach with an accuracy no worse than the experimental accuracy. The melts are shown to contain two molecular species: CuZr and Cu₂Zr. The contributions of different types of chemical bonding to the Gibbs energy and enthalpy of formation of Cu–Zr melts are asymmetrical and shifted from the equiatomic composition in opposite directions: the extremum of covalent bonding is shifted to the Cu-rich side, while metallic bonding is more significant in Zr-rich alloys. The rapid temperature variation of covalent bonding leads to a large excess heat capacity C _p ^E of the melts and a negative excess entropy _f S ^E, which rapidly drops with decreasing temperature. It is shown that not only C _p ^E and _f S ^E but also their temperature variations are governed by the parameters of association reactions and depend more strongly on the entropy than on the enthalpy of complex formation. This indicates that, in the general case, the glass-forming capabilities of melts are independent of the interparticle interaction and accounts for the pronounced tendency of Cu–Zr melts toward amorphization.     

Deviation from stoichiometry in α-HgI2

Measurements of lattice constants, density and transition temperature have been carried out on α-HgI₂ single crystals grown both from vapor phase and from solution under different stoichiometric conditions. Stoichiometry deviations on both Hg- and I-rich sides were found. Large supersaturations extending on the Hg-rich side up to about 4 × 10^?2$\text{I}{}_{\mathrm{Hg}}\text{HgI}{}_2$ mole ratio and on the I-rich side up to about 10^?2$\text{I}{}^{\mathrm{?}}{}_3\text{HgI}{}_2$ mole ratio were accomodated by the crystals. The interpretation of the results supports the assumption of the presence of mercury interstitials in the Hg-rich crystals and of I^?₃ anions in the I-rich crystals. The large deviations from stoichiometry are attributed to the non-stoichiometry of the mother phase and to the easiness of the crystal structure for accomodating interstitials rather than to characteristic thermodynamic equilibria of interstitials in the lattice.     

Integrated sensor array for analysis of multicomponent gas mixtures

A new device has been proposed and tested experimentally for the discrimination of gases in “electronic nose” systems. The device consists of an array of surface-acoustic wave (SAW) sensors positioned on a single anisotropic substrate with a common gas-sensitive coating for each sensor. The specificity of the sensors is provided entirely by the elastic anisotropy of the single-crystal substrate: changes in the direction of propagation of the wave through the gas-sensitive film deposited on the anisotropic substrate are accompanied by changes in the partial components of the mechanical displacement of the wave and corresponding contributions to the resultant SAW “response.” Pis’ma Zh. Tekh. Fiz. 24, 40–45 (August 26, 1998)     

Laminated beams subjected to transverse load

A simple elastic solution has been developed for predicting the shear stress distribution in a laminated beam subjected to a variety of transverse loading conditions. Photoelastic tests on composite models involving a single bonding layer have been used to validate the theory, and also to comment upon the significance of these results in interpreting the interlaminar shear strength and bending modulus of the simplest form of laminated strip.     

Continuous models in nonlinear thermomechanics of binary systems

We study some general problems connected with the construction of thermodynamic models in the mechanics of two-component elastic bodies. Principal relations of the model are established on the basis of fundamental concepts and approaches of nonlinear continuum mechanics and nonequilibrium thermodynamics. We also demonstrate that systems of this sort can be described without using chemical potentials in the explicit form.Center of Mathematical Simulation. Pidstryhach Institute for Applied Problems in Mathematics and Mechanics, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 4, pp. 7–15, July – August, 1995.     

Absorption of silicone fluid in a silicone elastomer

Measurements have been made of the absorption properties of a silicone fluid in a silicone elastomer, Aircast 3700, at temperatures between 0 and 150 °C. It was found that the diffusivity could be described by Arrhenius' law. The saturation fluid content was 20% at 0 °C, decreasing to 17% at 120 °C. The swelling was large, up to 26% at saturation, and approximately equalled the volume of fluid absorbed. A reverse thermal effect was observed and an attempt has been made to explain it.     

An efficient continuous flow helium cooling unit for mossbauer experiments

A Mossbauer continuous flow cooling unit for use with liquid helium over the temperature range 4.2–300 K is described. The cooling unit can be used for either absorber or source studies in the horizontal plane and it is positioned directly on top of a helium storage vessel. The helium transfer line forms an integral part of the cooling unit and feeds directly into the storage vessel so that helium losses are kept to the minimum. The helium consumption is 0.12 / h^-1 itat 4.2 K decreasing to 0.055 / h-1 at 40 K. The unit is top loading and the exchange gas cooled samples can be changed easily and quickly.