Description of dynamic viscosity depending on the alloys composition and temperature using state diagrams

The equilibrium nature of viscosity and fluidity is discovered on the basis of the Boltzmann distribution within the framework of the concept of randomized particles as a result of the virtual presence of crystal-mobile, liquid-mobile and vapor-mobile particles. It allows one to consider the viscosity and fluidity of solutions, in particular, melts of metal alloys, from the point of view of the equilibrium partial contributions of each component in the total viscosity and fluidity, despite the kinetic interpretation of natural expressions for these properties of the liquid. A linearly additive partial expression of viscosity is possible only for perfect solutions, in this case, for alloys with unrestricted mutual solubility of the components. Alloys with eutectics, chemical compounds and other features of the state diagram are characterized by viscosity dependencies that repeat the shape of liquidus curve over entire range of the alloy composition at different temperatures, with an increase in smoothness and convergence of these curves at increasing temperature. It was established that these features of viscosity temperature dependence are completely revealed within the framework of the concept of randomized particles and the virtual cluster model of viscosity in calculating the fraction of clusters determining the viscosity of the alloy. That viscosity of the alloy is found by the formula in which thermal energy RTcr at liquidus temperature is the thermal barrier of chaotization, characterizing the crystallization temperature of the melt Tcr, as well as the melting point of pure substances. On this basis, a method is proposed for calculating the alloys viscosity by phase diagrams using the temperature dependences of pure components viscosity to change the alloy’s viscosity in proportion to ratio of the clusters fractions at any temperature above liquidus line and for the pure component, taking into account the mole fraction of each component. As a result, a three-factor model of the liquid alloy viscosity has been obtained in which the thermal barrier of chaotization RTcr is used as variable for the first time. It determines the fraction of clusters for both pure substances (at RTcr = RTm ) and for alloys. This thermal barrier reflects the essence of the virtual cluster theory of liquid and adequacy of the concept of randomized particles.

Microstructure and Wear Properties of TiC/7075 Composites by In Situ Reaction Liquidus Curve Casting Method

7075 matrix alloy was fabricated by in-situ reaction liquidus curve casting method, and its as-cast microstructure was analyzed, the wear properties of these composites and matrix alloy were studied under the different conditions. The results show that the wear resistance of TiC/7075 composites is superior to 7075 matrix alloy in the same conditions (with same load or rotating velocity). Because of introduction of particle reinforcements, the wear resistance of the composite is enhanced by 1.5～4 times than that of its matrix. In addition, the wear mass loss of TiC/7075 composites increases almost with increase of load, but decreases with increase of rotating velocity. The wear resistance of the composites increases slightly at low load and high rotating velocity. The SEM analysis of the worn-out surface indicates that the wear mechanism of TiC/7075 composites is mainly abrasive wear.

Isotope Effect on Eutectic and Hydrate Melting Temperatures in the Water-THF System

Differential scanning calorimetry was used to study the effect of isotopic substitution on the eutectic and melting temperatures in the water-tetrahydrofuran (THF) system with THF molar fractions near the stoichiometry of the hydrate phase. Deuteration of the host causes an opposite effect from that of the guest with respect to the hydrate liquidus curve and eutectic melting temperature. The eutectic temperature in D2O-containing systems is approximately 3.7 K higher than that in H2O-containing systems. The melting temperatures of THF and deuterated THF hydrates increase by roughly 3.5 K with heavy water. The inclusion of deuterated THF causes a depression of the hydrate liquidus temperatures and a small but measurable effect on the eutectic temperature.

Morphological instability of a non-equilibrium ice–colloid interface

We assess the morphological stability of a non-equilibrium ice–colloidal suspension interface, and apply the theory to bentonite clay. An experimentally convenient scaling is employed that takes advantage of the vanishing segregation coefficient at low freezing velocities, and when anisotropic kinetic effects are included, the interface is shown to be unstable to travelling waves. The potential for travelling-wave modes reveals a possible mechanism for the polygonal and spiral ice lenses observed in frozen clays. A weakly nonlinear analysis yields a long-wave evolution equation for the interface shape containing a new parameter related to the highly nonlinear liquidus curve in colloidal systems. We discuss the implications of these results for the frost susceptibility of soils and the fabrication of microtailored porous materials.

Calculation of Some Thermodynamic Parameters of Non-Ideal Solutions

A computational method has been proposed for calculating the correct interaction parameters from experimental phase diagrams, despite reports that this problem was believed to be a "thermodynamically incorrect” one. It has been shown that the presumed difficulties are not of fundamental importance. An original computer program has been applied to two well-known systems Bi – Sb (1) and Bi2Te3 – Sb2Te3 (2), and a good agreement between calculated and observed values has been achieved. The values of interaction parameters s= 7.1 ± 0.4, l= 1.56 ± 0.09 kJ mol-1 for (1) and s = 5.9 ± 2.5, l = 3.9 ± 2.5 kJ mol-1 for (2) have been found. The results have been analyzed and their statistical reliability has been established. In addition, the possibilities of calculating the liquidus curve from only the solidus experimental data the solidus from the liquidus experimental data have been demonstrated. It has been found that the prediction of liquidus from solidus is much more successful than predicting the solidus from the liquidus. The results allow one to determine with reliance that the backward problem of modeling regular solutions for finding thermodynamic interaction parameters can be solved correctly. The calculated parameters can be used for both the computational restoration of missing pieces of the experimental phase equilibrium diagrams of binary and multinary systems and for the recognition of the physical nature of regular solutions.

Determination of dissociation degrees of K3NbF8 and K3TaF8 by thermodynamic analysis of subsystems of the KF-K2NbF7 and KF-K2TaF7 systems

A special form of the LeChatelier-Shreder equation describing the equilibrium between the crystalline phase and the melt in system A-AB in which the substance AB partially dissociates upon melting was applied to systems KF-K3NbF8, K2NbF7-K3NbF8 and to KF-K3TaF8, K2TaF7-K3TaF8 subsystems of the binary systems KF-K2NbF7 and KF-K2TaF7 in which the additive compounds K3NbF8 and K3TaF8 are formed. Using the phase diagram of the system KF-K2NbF7 determined by McCawley and Barclay (1971) and the values of the fusion enthalpy of K3NbF8 taken from literature, the intervals of the dissociation degree values of K3NbF8 for both branches of the liquidus curve of K3NbF8 were calculated. The calculated values of the dissociation degree depend on the coordinates of the liquidus curve of K3NbF8 of the pertinent phase diagram, on its used branch and section, and on the value of the fusion enthalpy of K3NbF8. For the measured fusion enthalpy of K3NbF8 (57 kJ mol−1), a common interval of the dissociation degree values of K3NbF8 for both branches of the liquidus curve of K3NbF8 is 0.71–0.72. Similarly, intervals of the dissociation degree values of K3TaF8 for both branches of the liquidus curve of K3TaF8 were calculated using the phase diagram of the system KF-K2TaF7 determined by Boča et al. (2007) and the measured fusion enthalpy of K3TaF8 ((52 ± 2) kJ mol−1). The error of the determination of the fusion enthalpy of K3TaF8, the common interval of the dissociation degree values of K3TaF8 for both branches of the liquidus curve of K3TaF8 is 0.68–0.69.