THERMODYNAMIC OF EVAPORATION OF DIMETHYLCADMIUM, DIMETHYLTELLURIUM AND THEIR EQUIMOLECULAR SOLUTION

2018;
23-27
1
Lviv Polytechnic National University
2
Lviv Polytechnic National University
3
Lviv Polytechnic National University
4
Lviv Polytechnic National University
5
Lviv Polytechnic National University

Element Organic Compounds (EOC) are widely used as intermediate volatile compounds for the production of high-purity substances and semiconductor materials. The practical use of EOC, which is accompanied by the evaporation of individual substances and their solutions, requires knowledge of reliable thermodynamic parameters which characterizing the phase transition of liquid-vapor. A special place among these parameters is the temperature dependence of the saturated vapor pressure and the heat of evaporation.

The total content of impurities in samples of dimethylcadmium and dimethyltellurium, determined by a decrease in the fusion point, was 0.03 ± 0.02 mol.%. According to the gas-liquid chromatography the contaminants of organic substances were not determined. The equimolar solution was prepared by mixing pre-selected weights (accuracy ± 1 · 10-4 g) of the initial components. Taking into account the high reactivity of dimethylcadmium, dimethyltellurium as well as their solution, the temperature dependence of the pressure of the saturated vapor of the substances was determined by a static method with an enhanced membrane zero-manometer. The accuracy of the temperature and pressure measurement is 0.1 K and 130 Pa, respectively.

Experimental data of the temperature dependence of the saturated vapor pressure are processed by the least squares method and approximated by the equation lnp=f(1/T): for dimethylcadmium –

lnр=-3870±432/T+21,77±1,38; for dimethyltellurium – ln р=-3620±53/T+21,372±0.176; for the equimolecular solution Cd(CH3)2:Te(CH3)2  – ln р=-5021±233/T +24,838±0.759.     By the Clapeyron-Clausius equation the enthalpies and entropy of the evaporation of are calculated: for dimethylcadmium –  ΔvapH= 32,2±3,6 kJ/mol, ΔvapS=101,0±11,3 kJ/mol К; for dimethyltellurium – ΔvapH=30,10±0.44 kJ/mol, ΔvapS=98,37±1.44 kJ/mol К; for their equimolecular solution –  ΔvapH=83,5±3,9 kJ/mol, ΔvapS=268,9±12,5 kJ/mol К. The obtained data are in agreement with the data obtained by calorimetric method. Analyzing the temperature dependences of the vapor pressure, we conclude that there is a complex compound in the liquid phase of the equimolecular solution.

The obtained results can be used in thermodynamic calculations when developing EOC purification technologies and obtaining high-purity coatings and slice by the method of conducting gas transport reactions.

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