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Structure Of Aqueous Cesium Borate Solution

Posted on:2017-11-01Degree:MasterType:Thesis
Country:ChinaCandidate:P C SunFull Text:PDF
GTID:2311330533451663Subject:Analytical Chemistry
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The borate were the classical electron-defect compounds,two or more than two plane triangle BO3 and tetrahedron BO4 were joined together though vertexes,further forming very complex borate mineral and compounds.Their chemical forms and interactions among these different polyborate anions in solutions mainly depended on temperature,p H,concentrations and the type of cation in solutions.Therefore,the complexity and difficulty of the solution structure for borate were greatly more than its crystal.Up to now,the solution structure of borate lithium,borate sodium and borate potassium had been reported in the relative literatures.But for the biggest hydration distance of Cs+ ion in periodic table of elements,the structure of borate cesium solutions had not been studied.The hydration structure of Cs+ ion in the solutions affected the whole structure of borate cesium solutions system,still remained to be explored.This thesis reported the direct EXAFS?Extended X-ray Absorption Fine Structure?study of hydration structure of Cs+ ion,the indirect Raman and NMR study of polyborate anions in the borate cesium solutions.This work also probed the hydration structure information of the first hydration shell of Cs+ ion and the interactions of the main polyborate anions in the solutions.?1?Density,electrical conductivity and p H of tetraborate cesium and pentaborate cesium solutions were measured accurately at 298.15 K and 333.15 K,and the chemical species distribution were calculated by p H values and Newton iteration method.The chemical species distribution indicated that,B-4O5?OH?42-occupied at most,second for B3O3?OH?4-and B3O3?OH?52-,the least for B?OH?4-and B?OH?3 in higher concentrations of cesium tetraborate solutions.However,the B3O3?OH?4-ion was the main species in the higher concentrations of cesium pentaborate solutions.The B3O3?OH?52-and B?OH?4-shown second,the least for B?OH?3 in sample solutions.But B-4O5?OH?42-and B5O6?OH?4-were less than 1%.?2?The experiment of NMR and Raman spectra also supported the calculated species results.The Raman spectra of tetraborate cesium solutions confirmed that the characteristic peak of B-4O5?OH?42-occurred at 569 cm-1,B?OH?3 at 941cm-1 B?OH?4-at 774 cm-1;It cannot be observed the characteristic peak of B5O6?OH?4-whose reason that the low solubility,thinner concentrations and secondary hydrolysis of pentaborate cesium solutions.The chemical shift at 7.8 ppm was attributed to B3O3?OH?4-,the B-4O5?OH?42-peak occurred at 1.5 ppm in the NMR spectra of tetraborate cesium solutions;The assignment of the resonances at 18.1,13.1,1.2 ppm in the pentaborate cesium solutions corresponded to B?OH?3/B?OH?4-,B3O3?OH?4-and B5O6?OH?4-based on NMR spectra.?3?The EXAFS results of tetraborate cesium solutions indicated that the Cs-O hydration number were 6.5-7.6 and the corresponding distance are 3.22-3.28 ? around the first hydration shell of Cs+ ion within different concentrations;And the Cs-O distance of the first hydration shell were 3.22-3.26 ?,with the hydration number of 7.5-7.9 in the pentaborate cesium solutions.?4?EXAFS,NMR,Raman spectra and the chemical species distribution were used to study the mian polyborate anions and the hydration structure information of Cs+ ion comprehensively in this thesis.Cs+ ion in the borate cesium solutions can form a quite loose hydration shell and further change the B-O hexatomic ring structure of these polyborate anions.In summary,the hydration number from 7 to 8,making that the configuration of its first hydration shell present voronoi polyhedron.
Keywords/Search Tags:cesium tetraborate, cesium pentaborate, solution structure, species distribution, EXAFS, NMR
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