Pressure-induced Hydrogen Bond Relaxation And Phase Transition In Salt And Alkali Solutions

Saline and alkali solutions under high pressure are widely used in geological sciences,Greenhouse Effect,energy development and storage,material synthesis and mineral smelting.Although salt and alkali solutions have different components and different applications,they are all dissolved in water to form ionic solutions,and ions or ion groups or ion hydrate layers interact with the target substance in the hydrogen bond network.However,how the ions,protons,lone pairs of electrons in the solution interact with the hydrogen bond network of the water solvent,how the pressure changes these interactions to modulate the phase transition,and what common mechanism is involved,these issues have not been clarified.Therefore,it is a challenging and meaningful work to study the internal forces and relaxation behaviors of hydrogen bonds in saline-alkali solutions under high pressure from the point of ion diffusion injection into the solvent hydrogen bond network,in order to obtain universal laws.both solutes dissolve in water to form ionic solutions,which are ions or ionic clusters,or the ionic hydration layer interacts with the target materials.solute-solvent interaction plays an important role in it.Therefore,the study of the properties of solvent（water）under high pressure and the change of hydrogen bond network structure will be our starting point.The research work of this thesis is mainly based on the hydrogen bond cooperative relaxation theory,combined with Raman spectroscopy and the high-pressure experimental technology of diamond anvil（DAC）,and explored the different concentrations（Mg,Ca,Sr）（Cl,Br）₂of divalent salts under high pressure,the solute-solvent interaction caused by the formation of a hydrated layer induced by ions in Na OH solution,as well as the effects of different ions and concentrations on the critical pressure and mode of phase transition at high pressure.The effects of different ions and pressures on hydrogen bond relaxation were compared.The specific research contents of this paper are as follows:（1）（Mg,Ca,Sr）（Cl,Br）₂ divalent salt forms a hydration layer with the water molecules through solvation,and the electric field with the ion as the center polarizes and stretches the surrounding water molecules,so that the O:H bond becomes longer and weaker,the phonon red shifts,while the H—O becomes shorter and longer,and the phonon blue shifts.However,the opposite is played under pressure.Under the action of pressure,the water and solution at room temperature will undergo the transformation of liquid-VI phase-ice VII phase.The implantation of solute ions increases the critical phase transition pressure and obeys Hoffmeister sequence Br^->Cl^-,and Sr²⁺>Ca²⁺>Mg²⁺.Compression will reduce the distance between water molecules,increase the coordination number of low coordination water molecules,and realize the transformation from dangling bond to epidermis and from epidermis to block.The relaxation behavior of bulk water molecules in solution is almost not affected by ionic polarization,but ionic polarization affects the amount of bulk water.（2）Sr Cl₂ dissolves in water and dissociates to form a Sr²⁺and Cl^-ion point source electric field,which polarizes and stretches the surrounding water molecules.After pressure is applied,the O:H non-bond is compressed and shortened,the phonons are hardened,and the H—O covalent bond is elongated and softened.When the concentration of the solution is low,the application of pressure will cause the（Mg,Ca,Sr）（Cl,Br）₂ solution to undergo a phase transition according to the phase transition route of liquid/iceⅥ/ice VII;and when the concentration is 0.05,the phase transition route is converted to a liquid/ice VII phase transition,skipping the ice VI phase.No matter which phase transition route occur,the critical phase transition pressure increases as the concentration increases.（3）Na OH dissolves in water,Na⁺ion point source electric field and O:（?）:O super hydrogen bond point compression source is formed by solvation.The O:（?）:O super hydrogen bond point compression source and the mechanical compression have the same effect on the hydrogen bond relaxation and polarization,which shorten and harden its phonon frequency,and make the H—O bond stretch and soften.The liquid/ice VI/ice VII phase transition occurs when Na OH solution has a concentration of 0.01 at room temperature,and the liquid/ice VII phase transition occurs when the concentration is 0.02 and above.The critical phase transition pressure increases as the concentration increases.When pressure is applied,the water molecules in the Na OH solution are more difficult to compress than the salt solution,because the O:（?）:O super hydrogen bond has pre-compressed the surrounding hydrogen bonds to harden it.Due to the compression of super hydrogen bonds,the liquid-ice phase transition occurs more easily in the solution.