硼酸盐热力学基元贡献模型及在MgBO_2(OH)纳米晶须水热合成过程分析中应用  

Subunit contribution model for thermodynamic properties of borates and its application in hydrothermal synthesis of MgBO_2(OH)nanowhiskers

作　　者：朱万诚[1,2,3] 张学一[1] 张强[1] 向兰[1] 朱慎林[1,3] 

机构地区：[1]清华大学化学工程系,北京100084 [2]曲阜师范大学化学工程系,山东曲阜273165 [3]化学工程联合国家重点实验室(清华大学),北京100084

出　　处：《化工学报》2013年第2期443-451,共9页CIESC Journal

基　　金：国家自然科学基金项目(21276141);化学工程联合国家重点实验室开放课题项目(SKL-ChE-09A02)~~

摘　　要：以MgCl2.6H2O、H3BO3、NaOH为原料,控制摩尔比Mg∶B∶Na=2∶3∶4,经室温共沉淀及水热转化(220～240℃,6.0～30.0h)制得了单斜相MgBO2(OH)纳米晶须。借鉴机械混合模型、基团贡献法思想,根据质量守恒原则将硼酸镁盐按照复盐分子式进行基元拆分,通过引入校正因子k,利用复盐基元的基础热力学数据拟合建立了ΔfHm及ΔfGm等硼酸盐热力学基础数据估算的基元贡献模型,估算了共沉淀产物Mg7B4O13.7H2O及水热产物MgBO2(OH)不同温度下的ΔfHm、ΔfGm热力学数据,得到了25～100℃下共沉淀反应及25～250℃下水热转化的ΔrHm、ΔrGm。结果显示,共沉淀反应在室温条件下可自发进行,水热转化须借助一定温度条件方能自发实现,且反应趋势随水热温度升高时间延长而增大。该热力学基元贡献模型有望为其他结构复杂复盐化合物纳米结构的湿化学法控制合成分析及预测提供借鉴。Pure monoclinic MgBO2（OH） nanowhiskers were synthesized by room temperature co- precipitation followed by hydrothermal treatment at 220-240℃ for 6.0--30.0 h, using MgCl2 · 6H2O, H3 BO3, and NaOH as raw materials with molar ratio of Mg ： B ： Na= 2 ： 3 ： 4. Enlightened by mechanical mixture model and group contribution method, a novel subunit contribution model for the assessment of thermodynamic properties such as △f Hm and △fGm of borates was developed, by introducing correction factor k and reasonably decomposing the complex double salt metal borates into constitutional subunits according to mass conservation. The aseveloped model was utilized to assess △fHm and △fGm at various temperatures for precipitate MgTB4 O13 · 7H2O and hydrothermal product MgBO2 （OH） , based on which the values of ArSm and ArGm of the co-precipitation of MgTB4O13 · 7H2O and hydrothermal conversion to MgBO2（OH） were obtained. The results show that, the room temperature co precipitation can occur spontaneously whereas the hydrothermal conversion can only be performed spontaneously at high temperature. The feasibility for the co-precipitation as well as the hydrothermal conversion turns to be higher with the increase in the temperature and time. The subunit contribution model is beneficial for the analysis and prediction of controllable synthesis of other complex double salt nanostructures via the soft-chemistry based method.

关 键 词：热力学性质 硼酸盐 基元贡献模型 水热 纳米晶须 

分 类 号：TQ131.1[化学工程—无机化工] TQ132.3