Heat Capacity Of Mixing Research Articles

THERMODYNAMIC MIXING FUNCTIONS OF A MULTICOMPONENT LIQUID METAL AND SLAG

The work proposes a thermodynamic model of a multicomponent condensed phase applicable to metal and slag melts. The integral and partial thermodynamic mixing functions: Gibbs energy, enthalpy, entropy, heat capacity have been obtained using configurational statistical sum. Methods for estimating of model parameters using available data on activity coefficients and heats of mixing, Wagner interaction parameters have been suggested. Using binary Fe-Mn system as an example, the high accuracy of the calculation of the mixing thermodynamic functions of the metal phase in the entire concentration range has been shown. Mixing heat capacity has been shown to comply 3rd law of thermodynamics. Suggested thermodynamic model is already being used in steelmaking control system «Master» at metallurgical plant «Zaporizhstal», and in heat projecting and control system «DesigningMelt» at XuanSteel metallurgical works (PRC).

Enthalpies of mixing and intermolecular interactions in the 1-octanol-dimethylformamide system at 298–318 K

The heat effects of solution of N,N-dimethylformamide (DMF) and 1-octanol (OctOH) in the DMF (1)-OctOH (2) system are measured over the range of compositions using a variable-temperature isothermal-shell calorimeter at 298, 308, and 318 K. The partial molar enthalpies of the binary mixture components and the enthalpies and heat capacities of mixing are determined. It is found that the amide-alcohol mixing is strongly endothermic and very weakly depends on temperature. The enthalpy and specific heat parameters of binary and ternary interactions between the DMF molecules in OctOH and the OctOH molecules in DMF are determined in terms of the virial expansion technique, and it is shown that the two nonelectrolytes exhibit a tendency to homoassociation.

The enthalpy and heat capacity characteristics of the water-N,N-dimethylpropyleneurea system

A variable-temperature isothermic-shell calorimeter was used to measure the heat effects of dissolution of N,N-dimethylpropyleneurea (DMPU) in the water-N,N-dimethylpropyleneurea system at 298 and 313 K over the interval of compositions x2 = 0−0.1 mole fractions. The partial molar enthalpies of mixture components and the enthalpies and heat capacities of mixing were calculated. The results were compared with the data on water-amide systems. The exothermic effect of mixing of nonelectrolytes with water was found to increase in the series dimethylformamide < dimethylacetamide ∼ DMPU < hexamethylphosphorotriamide (HMPT). The McMillan-Mayer formalism was used to determine the enthalpy and heat capacity parameters of pair and three-particle interactions between DMPU molecules in water. The behavior of DMPU in water was to a substantial extent determined by hydrophobic interactions between nonpolar molecule moieties. This interaction was, however, noticeably weaker than in solutions of HMPT.

On the nature of the excess heat capacity of mixing

The excess vibrational entropy (ΔSvibex) of several silicate solid solutions are found to be linearly correlated with the differences in end-member volumes (ΔVi) and end-member bulk moduli (Δκi). If a substitution produces both, larger and elastically stiffer polyhedra, then the substituted ion will find itself in a strong enlarged structure. The frequency of its vibration is decreased because of the increase in bond lengths. Lowering of frequencies produces larger heat capacities, which give rise to positive excess vibrational entropies. If a substitution produces larger but elastically softer polyhedra, then increase and decrease of mean bond lengths may be similar in magnitude and their effect on the vibrational entropy tends to be compensated. The empirical relationship between ΔSvibex, ΔVi and Δκi, as described by ΔSvibex = (ΔVi + mΔκi)f, was calibrated on six silicate solid solutions (analbite–sanidine, pyrope–grossular, forsterite–fayalite, analbite–anorthite, anorthite–sanidine, CaTs–diopside) yielding m = 0.0246 and f = 2.926. It allows the prediction of ΔSvibex behaviour of a solid solution based on its volume and bulk moduli end-member data.

Thermodynamic mixing behavior of synthetic Ca-Tschermak–diopside pyroxene solid solutions: I. Volume and heat capacity of mixing

The unite cell parameters and heat capacities of a series of synthetic clinopyroxenes on the join Ca-Tschermak (CaTs)-diopside (Di) were measured using X-ray powder diffraction and calorimetric methods, respectively. The volume of mixing at 298 K shows a negative asymmetric deviation from ideality. A two-parameter Margules fit to the data yields W-CaTs-Di(V) = -0.29 +/- 0.11 cm(3) mol(-1) and W-Di-CaTs(V) = -1.14 +/- 0.14 cm(3) mol(-1). Heat capacities were determined between 5 and 923 K by heat-pulse at 5-302 K and differential-scanning calorimetry at 143-923 K. The precision of the low and high temperature C (p) data is better than +/- 1%. Polynomials of the form C (p) = a + bT(-1/2) + cT(-2) + dT(-3) were fitted to the C (p) data in the temperature range between 250 and 925 K. Thermal entropy values [S (298) - S (0)] and [S (900) -S (0)] as well as enthalpies [H (298) - H (0)] and [H (900) - H (0)] were calculated for all members of the solid solution series. No significant deviation from ideal mixing behavior was observed.

Short‐range order in miscible polymer blends: A monte carlo study

AbstractLocal ordering in miscible binary polymer blends with strong attractive interactions between the two types of chains was investigated by computer simulation of allowable conformations on an incompressible cubic lattice. A tendency toward maximum ordering (in which chains pack in alternate parallel rows) is shown by the calculation of pair correlations and in “snapshots” of the mixtures. A specific directional interaction is not necessarily required for ordering. A comparison of these results with those recently obtained using mean‐field theory is presented. The heat capacity of mixing was also calculated and found to be positive, with a value close to that reported experimentally.