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Supercooled sulphuric acid solutions : Desorption of water, mass accommodation and residence time of HCl at 213, 218 and 228 K
The escaping deuterium oxide molecules from a liquid and a solid surface of the sulphuric acid solutions can be monitored by using the vacuum evaporation experiments. The measurements are performed in different spectral angles and temperatures of the solution. The energy distribution of the desorbing molecules is governed by the state of the surface. The observed discrepancy was tried to be explained using the capillary wave theory. In addition, this distribution is influenced only by the temperature. In contrast, the intensity of the velocity distribution decreases as the values of spectral angle and concentration increase. The reduction in the intensity of the velocity distribution for the molecules desorbing from the liquid and solid surface is as a function of the angular cosine of spectral angle (cos ).
Time- of- flight molecular beam technique is used to investigate the mass accommodation coefficient and the residence time of HCl gas molecules, which collide with the binary sulphuric acid water solution. These experiments are carried out in a concentration range from 52 to 75 wt% at temperatures of 213, 218 and 228 K. The measurements demonstrate that the behaviour of the mass accommodation coefficient and the residence time depend not only on the concentration of the sulphuric acid solution but also on the temperature of this solution.
On the one hand, in the concentrations between (50- 64 wt%), the measured values of the mass accommodation coefficient of HCl increases with decreasing temperature of the surface of the sulphuric acid solution, because the temperature affects on the desorption rate constant more than that on the solvation rate constant. On the other hand, in the concentrations above 67 wt%, the mass accommodation coefficient decreases as the temperature of the sulphuric acid solution decreases. The reason of this unexpected behaviour is that the solvation rate constant is stronger influenced by temperature than the desorption rate constant. This discrepancy in the demeanor of the mass accommodation coefficient can be explained using the capillary wave theory.
The residence time of the staying molecules in the fluid phase is equal to the solubility residence time and the transport time of the gas molecules in the solution. The interfacial transport time regarding to the capillary wave theory can be described the increase in the residence time of HCl gas molecules in a concentration range from 63 wt% to 75 wt%.