The paper deals with application of numerical methods to processing the experimental data on the thermophysical properties of several chemical substances and their compounds (cryolites, rare earth compounds, and alkali halides). The main aim of investigations is in estimating the parameters of dependencies between the heat of fusion and the melting temperature of these chemical substances. The data are corrupted by the measuring errors. Procession is implemented under conditions of uncertainty: there is no any information on probabilistic properties of the corrupting factors, samples of measurements are short, and only approximate functions are known that describes mentioned dependencies. Under such conditions, the standard statistical methods can be applied formally. To obtain guarantied results in parameters estimation, the interval analysis methods and procedures are used.

The heat of fusion of eutectic mixtures of sodium cryolite with alumina and calcium fluoride was measured using differential scanning calorimetry. Melting temperatures were found to be in good agreement with literature data. The molar heat of fusion of cryolite salts and eutectic mixtures was found to be directly dependent on melting temperature. The temperature dependence coefficient is the same as that of alkali halides.

The density of low melting cryolite melts based on the KF-NaF-AlF3 system was studied by the Archimedean technique at temperatures in the 920-1160 K range. The effect of temperature, cryolite ratio (1.3 and 1.5), alumina and calcium fluoride additions was investigated. The density was determined to decrease with the cryolite ratio rise and to increase with the calcium fluoride additions. The alumina additions up to 6 mol.% proved insignificant to affect the density of the melts studied. The molar volume change for the KF-NaF-AlF3 melts was calculated and deduced depending on the temperature, cryolite ratio, alumina and calcium fluoride additions.

The solubility of silica in fluoride-chloride electrolytes for use in the electrolysis of solar-grade silicon was studied. The visual method was used for the investigation. Liquidus temperatures were investigated by thermal analysis. The silica solubility rises with KF content and temperature. The densities of the compositions with high silica solubility were determined.

Laboratory study of interaction SiC-Si3N4 with low melting electrolyte based on potassium cryolite at temperature 800 degrees C are presented. The investigation has been carried out by two techniques: 1) thermal gravimetric - continuous weighing of the sample in molten salt; 2) 100-hours electrolysis test. The values of the corrosion rate were obtained and the interaction mechanism of the material with electrolyte was proposed. Recommendations for applicability of the SiC-Si3N4 composite in potassium containing electrolyte as lining bricks in the aluminum electrolysis cell were made.

1,2,3-Triphenylcyclopropenylphosphonium bromide reacts with sodium polyphosphides to give sodium 3,4,5-triphenyl-1,2-diphosphacyclopentadienide in high yield.

Tetrasodium tetradecaphosphide Na4P14 was obtained either from the reaction of PCl3 with sodium in refluxing THF or from the reaction of red phosphorus and sodium in ethylenediamine at room temperature. The solid-state structures of Na-4(DME)(7.5)P-14 (1a) and Na-4(en)(6)P-14 (1b) (DME = 1,2-dimethoxyethane; en = ethylenediamine) are described.

Protonation of sodium 1,2-diphospha-3,4,5-triphenylcyclopentadienide occurs with a [1,5]-proton shift and leads to rac-trans-1,2,6,7-tetraphosphatricyclo[5.3.0.0(2,6)]-3,9-decadiene, the product of an unusual [2 + 2] cycloaddition reaction.

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