| There are many kinds of borates with complex structures, whichprovide rich resources for searching useful borates, such asβ-BaB2O4 (BBO) which isan important NLO material because it has a variety of favorable properties and SrB4O7(SBO) which is an useful material with some excellent mechanical and opticalproperties. So the studies of strontium and barium borates have attracted much attentionin recent years. As part of the continuing study of alkaline-earth metal borates, we havesynthesized 11 strontium and barium borates by the different methods, and the standardmolar enthalpies of formation of those strontium and barium borates have beenmeasured.Seven strontium and barium borates, SrB2O4·4H2O, SrB4O7·3.5 H2O, SrB6O10·5H2O, K2Sr[B4O5(OH)4]2·10H2O, BaB6O10·4.5H2O, BaB2O4·4H2O, K2Ba[B4O5(OH)4]2·8H2O have been synthesized by solution method at different temperatures and differentcompositions. Using the Sr(OH)2·8H2O, H3BO3 as materials, we prepared two hydratedSr-borates, SrB2O4·2.5H2O and SrB4O7·3H2O by the methods of hydrothermal reaction.Through the dehydration of SrB2O4·4H2O and BaB2O4·4H2O, SrB2O4 andβ-BaB2O4were prepared, respectively.All of the products have been characterized by chemical analysis, XRD, FT-IR andsimultaneous DTA-TG and have been proved to be the pure samples, including fourkinds of new borates: SrB2O4·2.5H2O, SrB4O7·3H2O, SrB4O7·3.5 H2O, BaB6O10·4.5H2O,and seven kinds of reported borates: SrB2O4, SrB2O4·4H2O, SrB6O10·5H2O,K2Sr[B4O5(OH)4]2·10H2O,β-BaB2O4, BaB2O4·4H2O, and K2Ba[B4O5(OH)4]2·8H2O.The enthalpy of solution of these eleven synthesized pure strontium and bariumborates in 1mol·L-1 HCl(aq) were determined by heat conduction microcalorimeter. Thestandard molar enthalpies of formation of these borates were obtained throughdesigning thermochemical cycles. The thermodynamic properties of K2Sr[B4O5(OH)4]2·10H2O and K2Ba[B4O5(OH)4]2·8H2O were also calculated by group contribution method.The research results of this thesis enrich the contents of borate chemistry, andprovide synthetic methods and physic-chemical data for the application of some strontium and barium borates, which are of significance to the exploitation of thestrontium and barium borates material. |
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