THE PRESSURE OF INDIUM MONOCHLORIDE VAPOUR: THE VAPOUR-GAUGE AND SPECTROPHOTOMETRIC EXPERIMENTAL DATA

Abstract

Equilibria involving indium and gallium halides are important, in particular, for the deep purifi cation 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 diffi culty. Objective. The goal of the research was to conduct the spectrophotometric and vapour-pressure investigation of the two-phase LIn – V and the three-phase LIn – LInCl – V equilibria and to fi nd the molar extinction coeffi cients of gaseous indium monochloride. (LIn and LInCl 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 LIn – V equilibrium allowed us to show the temperature dependence of the absorption coeffi cients 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 LIn – V equilibrium the concentration CInCl = const and the change in the absorption coeffi cients 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 LIn – V equilibrium. The experimental dependences of the absorption coeffi cient k(λ, T) of the InCl saturated vapour (in the three-phase equilibrium LIn – LInCl – V) on the temperature can be described by the following function: ln Tk( ,T) A ( ) T l = - + B l . It should be noted that the angular coeffi cient A is essentially independent of the wavelength and its value is almost identical to the angular coeffi cient for the temperature dependence of the pressure of saturated vapour: ln p A T= - + b. 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. Conclusion. For the latter equation the following parameters were obtained: A = – 10255 ± 69 К, b = 1095 ± 0.08 (for the atmospheric pressure as a standard for p). These values correlate well with the reported data. These results were used to calculate the molar extinction coeffi cients for the strongest absorption bands of gaseous indium monochloride. The highest value of the molar extinction coeffi cient ε(λ) 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 ε(λ)-values are also very high. Thus, the spectrophotometric method is very sensitive for both qualitative and quantitative determination of gaseous indium monochloride.

Keywords

• indium monochloride
• saturated vapour pressure
• heterogeneous equilibrium
• high temperature spectrophotometry
• tensimetry
• manometry