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In-Situ Raman Spectra Variations In Aqueous Crystallization System

Posted on:2021-04-08Degree:MasterType:Thesis
Country:ChinaCandidate:Y P ZhangFull Text:PDF
GTID:2381330602496454Subject:Inorganic Chemistry
Abstract/Summary:PDF Full Text Request
Crystallization is widely used in physics,chemistry,chemical engineering and material science and other fields.More researchers currently study the essence of solution crystallization from the perspective of kinetics or solution chemistry.However,there are few studies on the evolution of structure,the variation of chemical bonding mode and the nucleation and crystal growth driven by chemical reaction.With the development of high-resolution spectroscopy and in-situ technology,the development of in-situ Raman spectroscopy promotes a series of study of physical and chemical micro-behaviors by time-varying,which has great significance for chemical reaction mechanism and solution crystallization regulation.In this paper,we focus on in-situ Raman spectroscopic study of reaction crystallization and solution crystallization,aiming to study the variations of molecular vibration mode,solution structure and chemical bond during solution reaction or crystallization.The specific contents are as follows:1.The effect of chemical reaction on the crystallization process of gypsum(CaSO4·2H2O)was studied by in-situ micro-Raman spectra.Under the condition of equal concentration reaction,it was found that the formation time and crystallization rate of gypsum were related to the reactant concentration,which indicated that gypsum crystallization was controlled by chemical reaction kinetics and crystallization kinetics.Excess reactants in the non-isomolecular reaction clearly modified the precipitation reaction and the process of gypsum crystallization.The evolution of droplet morphology showed that the crystallization path driven by precipitation reaction was different from that driven by spontaneous solution.Information from Raman signal and morphology could conclude that the whole process consists of chemical reaction,aggregation of amorphous precursor,nucleation and crystal growth.This method is helpful to study the mechanism of gypsum precipitation and crystallization on the molecular level.2.Taking KDP(KH2PO4)and NaDP(NaH2PO4)solution as the research object,the influence of sodium and potassium ions on cluster aggregation and chemical bond vibration of H2PO4-solution was studied by in-situ micro-Raman spectra.It was discussed that the difference of monovalent ions(K+,Na+)and the concentration of the solution played an important role in the Raman shift variation and nucleation induction time of H2PO4-vibration.The results showed that the variation of Raman shift and the nucleation induction time increased with the increase of the solution-phase electronegativity of cations and the decrease of the concentration.In the Raman spectra,the reason was explained that for the shift of P(OH)2,PO2 vibration during the nucleation process.It is analysed that the evolution trend of solution cluster configuration and chemical bond with the crystallization process,which deepens the understanding of solution structure and chemical bond in the process of solution crystallization.3.The variations of symmetry and structure were identified by in-situ Raman spectra during the urea crystallization process.With the volatilization of the solvent,Raman spectra can sensitively identify the shift of the characteristic vibration peak of urea molecule with the change of chemical environment.Through the changes of Raman shift and intensity of C=O bond,C-N bond,N-H bond and water in the spectra,it was concluded that the chemical environment changed in the process of crystallization.The hydrogen bond between C=O bond and water molecule was weaker than that between C=O bond and N-H bond,and the interaction between N-H bond and water molecule was becoming weaklier,however,the ability of forming hydrogen bond between urea molecule was enhanced.That is to say,the process driven by hydrogen bond was forming polymer by the intermolecular aggregation of urea.
Keywords/Search Tags:in-situ Raman spectra, reaction crystallization, solution crystallization, crystallization time, Raman shift
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