Indium monochloride vapor pressure: the vapor-gauge and spectrophotometric experimaental data

Abstract

Equilibria involving indium and gallium halides are important, in particular, for the deep purification of the metallic indium and gallium. At the same time, while gallium can be easily transported during the halide CVT, a similar indium transfer is practically impossible. The following study was carried out to as an endeavour to identify the causes of this difficulty.

Objective. The goal of the research was to conduct the spectrophotometric and vapour-pressure investigation of the two-phase L_In – V and the three-phase L_In – L_InCl – V equilibria and to find the molar extinction coefficients of gaseous indium monochloride. (L_In and L_InCl are liquids based on metallic In and InCl respectively).

Methods and methodology. To investigate the above-mentioned equilibria, the following optical vapour pressure methods were used: pressure gauge technique and high-temperature spectrophotometry (MDR-41 monochromator, combined with the cylindrical furnace). Electronic absorption spectra of indium monochloride vapour were obtained in the wavelength range of 200 – 400 nm and a temperature range of 225 – 850 °C.

Results. The spectrophotometric studies of the L_In – V equilibrium allowed us to show the temperature dependence of the absorption coefficients at wavelengths corresponding to the absorption bands maxima under conditions when the indium monochloride concentration in a vapour remained constant. It was shown that in the L_In – V equilibrium the concentration C_InCl = const and the change in the absorption coefficients could only be associated with the temperature dependence of the InCl extinction. The fact is that the characteristic absorption bands of other possible species, In₂Cl₄ and InCl₃, were not observed.  Therefore, we can assume that only InCl molecules are present in the vapour in the L_In – V equilibrium.

For three-phase equilibrium L_In – L_InCl – V the experimental dependences of the absorption coefficient k(l, T) of the InCl saturated vapour on the temperature were found. These dependences have the linear form in the ln Tk(l, T) – 1/T coordinates.

It should be noted that the angular coefficient A is essentially independent of the wavelength and its value is almost identical to the angular coefficient for the temperature dependence of the pressure of saturated vapour, which is given as a simple form of the Clausius–Clapeyron equation. The latter dependency was found in the course of the vapour pressure experiments for the three-phase equilibrium with the use of a quartz membrane null-manometer and the following parameters were obtained:  A = – 10255 ± 69 К, b = 10.95 ± 0.08, where A is an angular coefficient and b is free term (here the atmospheric pressure as a standard for p).

Conclusion. The collected data correlate well with the reported data. These results were used to calculate the molar extinction coefficients for the strongest absorption bands of gaseous indium monochloride. The highest value of the molar extinction coefficient e(l) was found for the band at 267.0 nm which is 1.17×10⁸ сm²/mol at the temperature of 327 °С. For other bands in the range of 262–280 nm the e(l)- values are also very high. Thus, the spectrophotometric method is very sensitive for both qualitative and quantitative determination of gaseous indium monochloride.

 SOURCE OF FINANCING

The study was supported by the Russian Foundation for Basic Research (project No. 18-33-00900-mol-a).

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