V. A. Bychinskii

Extrapolation of thermodynamic functions in calculation of phase equilibria by the Gibbs energy minimization method

A separate description of polymorphs and glassy, liquid, and gaseous states makes it possible, using the isobaric-isothermal potential minimization approach, to describe both the phase transformations of an individual substance and its behavior in complex systems, which is required for the representation of metal and salt systems that have melting points lower than the melting points of the pure components. The suggested methods of extrapolation of the thermodynamic functions of an individual substance, performed assuming that of the phase transition heat is constant and that the heat capacity beyond the equilibrium temperature range is equal to the heat capacity of the preceding or subsequent (by temperature) phase state, enable to avoid thermodynamic paradoxes in all cases and reliably describe the composition of complex systems in a wide P,T range of their existence with allowance for the existence of solid phases, melts, and gases in equilibrium.

Method of approximation of dependence of isobaric heat capacity on temperature

A method of approximating temperature dependence of heat capacity has been developed on the basis of a power polynomial in variables with different exponents in combination with the Nelder-Mead simplex method. For especially complicated dependences, the method makes it possible to match polynomials at junction points with infinitesimal deviation. The method provides high reproducibility and correct interpolation of empirical and semiempirical data.

Specifics of Representation of Thermodynamic Functions in the Method of Thermodynamic Potential Minimization

The type of physicochemical model dictates the choice of a minimized thermodynamic potential that provides the most adequate description of specific features of a natural or technological process. In the developed approach, the Gibbs energy was selected as the basis potential, and other thermodynamic potentials were considered as functions of G(T, P) and thermodynamic parameters with inclusion of independent factors of state. The presented thermodynamic functions of individual substances can be used in minimization of all basic thermodynamic potentials regardless of the conditions of existence of modeled systems.

Physicochemical model as a method for calculating and making consistent thermodynamic properties of structural units in alkali silicate melts

The physicochemical modeling of formation of alkali silicate melts in the temperature range 298.15–1473 K has been performed. Correction of the results of calculations based on spectroscopic data has been performed to make consistent the thermodynamic properties of lithium, sodium, and potassium silicates and calculate the thermodynamic properties of structural units Qn, which exist in alkali silicate melts.

The unified method for computing thermodynamic properties of natural zeolites based on their crystallochemical formulas

The standard thermodynamic potentials of natural zeolites in universal stoichiometric representation are computed. The enthalpies are estimated using linear deconvolution into chemical elements for calibration minerals. The entropies are computed using the additive scheme for oxide components; the Gibbs free energies are computed based on the calculated standard thermodynamic functions and entropies of thermochemically simple compounds.

A study of acidic aluminum-containing solutions through modeling physicochemical equilibria by the thermodynamic potential minimization method

Thermodynamic modeling of physicochemical processes underlying the preparation of aluminum-containing solutions has been performed. It has been demonstrated that the major aluminum species in solution are aluminum chlorides and hydroxychlorides. Temperature-induced changes in the equilibrium composition of a solution has been studied.

Calculation of the standard thermodynamic potentials of aluminum sulfates and basic aluminum sulfates

The standard enthalpies, entropies, and Gibbs energies of formation from elements were calculated for compounds in the Al-S-O-H system. The thermodynamic parameters of minerals, aluminum sulfates and hydroxide sulfates with water of crystallization, were recommended on the basis of analysis of calculation errors. The reliability of the resulting values was tested compared to the solubility experimental data of aluminum sulfate.

Estimation of the heat capacity of individual substances on the basis of experimental enthalpy increments

A method of determination of the high-temperature (T > 298.15 K) heat capacity function of individual substances by differentiation of enthalpy increment measurements with respect to temperature has been suggested. The approach is based on approximation of enthalpy increment measurements by a polynomial without free term, which makes it possible to strictly meet the boundary conditions of differentiation determined by the properties of the enthalpy increment function. In combination with the Shomate method, the approach enables the optimal choice of the form of temperature dependence of heat capacity that is consistent best of all with the concepts of classical thermodynamics and provides the best reproducibility of enthalpy increment measurements. When low-temperature heat capacity measurements for individual substances are not available, i.e., the Shomate method is inapplicable, the suggested strategy makes it possible to obtain the heat capacity change function in the temperature range of enthalpy increment measurements and to estimate the heat capacity of the substance at standard temperature.

Basic physicochemical model of carbothermic smelting of silicon

Using a Selektor software package, a basic four-reservoir physicochemical model of silicon smelting in ore-smelting furnaces (OSF), which describes the process of Si production, is developed. In forming the model, the method of series reactors is used with the application of known thermodynamic databases. The dynamic reservoirs meeting the basic temperature zones of an OSF hearth, the matrix of compositions of entering charge components with allowance made for the discharge coefficients, and the lists of probable components of the system are determined; and a schematic of the process balance is drawn up. The results of solving the model by the reservoirs for the specified temperature range with introduction of 15 independent components are presented. The obtained thermodynamic model of Si smelting differs from the previously developed ones by introduction of numerous impurity elements and describes the actual technological process of silicon production in OSFs adequately.

Investigation of physicochemical and technological properties of sodium tetrafluoroaluminate

Physicochemical properties of condensed sodium tetrafluoroaluminate are investigated by methods of thermogravimetry, high-temperature X-ray phase analysis, and thermodynamic calculations of the phase diagram of the NaF-AlF3 system. It is shown that it is possible to use this compound as a correcting additive to electrolyte in aluminum electrolyzers instead of the mixture of cryolite and aluminum trifluoride. This replacement allows one to reduce the consumption of fluorine salts, to optimize the balance of production components, and to make aluminum production more environmentally friendly.