Synthesis Technique And Characterization Of Calcium Borates By Hydrothermal Method

Some of hydrated calcium borates are useful chemical industrial materials which aremainly used in the non-alkali glass fiber and the glass industry and also widely used inceramic, enamel, material, agriculture, burning inhibitor。In order to look for theconvenient and feasible methods to synthesis useful borates, in this paper, six typecalcium borate which are CaO·3B₂O₃·5H₂O, 2CaO·B₂O₃·H₂O, 2CaO·5B₂O₃-5H₂O,4CaO·5B₂O₃·7H₂O, 2CaO·3B₂O₃·H₂O and CaO·B₂O₃ have been synthesized in thehydrothermal condition at different temperatures and the different ratio of raw materialsby starting from boric acid, borax and calcium oxide。The prepared powder waseffectively analyzed by DTA-TG, XRD, TEM, FE-SEM, chemical analysis and so on。Through changing the proportion of raw materials and the temperature, Theinfluencing factors of temperature, the molar ratio of B/Ca and water quantity wereinvestigated。From studing the influence of temperature to synthetic product, it wasconcluded that synthetic product is changed from calcium borate with high polyborate tocalcium borate with low polyborate as the temperature increasing under highconcentration of boric acid. With the increasing of temperature, the high degree ofpolymerization of polyborate would be depolymerized and it would format the simplerpolyborate under high concentration of boric acid. During the study of the influencing ofthe molar ratio of B/Ca, some results were indicated that when there were higher boricacid concentration of solution and excessive boric acid it was helpful for maintaining thestability of hexa-polyborate anions in aqueous solution。But when the solutiontemperature achieved a certainly high temperature, higher boric acid concentration ofsolution could not maintain the stability of hexa-polyborate anions in aqueous solutionand the product could be changed。Moreover, under the certain temperature, the sameconcentration of boric acid and the varying the molar ratio of B/Ca within a given rangejust a certain proportion of boron and calcium, it could improve conversion of boron withincreasing the proportion of calcium oxide。During the study of the influence of additionof water, some results were indicated that addition of water was great influence on thedevelopment of crystal structure。Under full of water, crystal structure of aqueouscalcium borate was developed very well。But under less water, the development of it wasnot good and the product would tend to non-shaping。Moreover the influences of pH value, reaction time, degree of fill and so on werealso studied。Under certain temperature and the same composition of raw material boronpolymerization degree increased with reducing the pH value of solution in the solutionand was helpful for forming the high polymerization degree of calcium borate。Along with reaction time increasing, the synthetic product was developed completely。Butreaction time increased, it almost had no effect on the synthetic ratio of calcium borate。Different degree of fill had no influence to the property of calcium borate。Degree of fillfrom 0.50 to 0.75 was suitable。From experimental result above, the hydrothermal reaction mechanisms andreaction equation of thermal analysis were proposed。...