Thermodynamics Analysis Of The Relationship Between Pressure And Filling Factor Of Alkali Hydroxide In Hydrothermal Vessel

Hydrothermal technology has a history of two hundred years. Today, hydrothermal technology is widely applied to grow of various single crystals, preparation of ceramic powder, deal with organic pollution, produce nano-materials, and so on.The pressure in autoclaves is very high because the hydrothermal reactions occur in a closed system. So it should be rugged enough to bear high pressure and temperature experiments for long duration. When selecting a suitable autoclave, the first and foremost parameter is the experimental temperature and pressure conditions and the corrosion resistance in the pressure-temperature range in a given solvent or hydrothermal fluid. At the same time, the extreme condition makes it difficult to measure the parameters. The"black box"nature of the hydrothermal system hinders the development of the hydrothermal industry. In this thesis, the safety and limitation of the mechanism are thought to the key factor in handicap the application of hydrothermal technology. Determination of the pressure and the real concentration is the precondition of solving the safety problem and the further study of the mechanism of hydrothermal reaction. Consequently, the idea of building a thermodynamics model that relates pressure and initial filling factor is raised.In this thesis, both hydration and association effects are taken into account to build an activity coefficient model of aqueous NaOH and KOH solution under hydrothermal conditions. In order to satisfy the consistency of thermodynamics, the parameters of this model are regressed by activities of water and mean activity coefficients of solutes and fitted as the function of temperature and pressure. The research on NaOH at 323.15~523.15K, 1.013~400bar and KOH at 348.15~573.15K,1.013~85.879bar show that the predicted values are reliable.The model proposed in this paper is combined with phase equilibria and mass balance to build the model of filling factor to predict the pressure, liquid volume in the vessel and real concentration of ions.