Combination of Silica Sol and Potassium Silicate via Isothermal Heat Conduction Microcalorimetry  

作　　者：Tian Hebao Zhang Chaocan Liu Peng Li Xi Wu Lili Chen Yanjun 

机构地区：[1]School of Materials Science and Engineering, Wuhan University of Technology, Wuhan, Hubei 430070, China [2]Department of Chemistry, School of Sciences, Wuhan University of Technology, Wuhan, Hubei 430070, China

出　　处：《Chinese Journal of Chemistry》2011年第2期356-362,共7页中国化学（英文版）

基　　金：Project supported by the National Natural Science Foundation of China （No. 50673080）.

摘　　要：Isothermal heat conduction microcalorimetry was utilized as a novel characterization method to investigate the polymerization processes of silica with both thermodynamic and kinetic parameters when the combination of silica sol and potassium silicate was stirred at temperatures of 25.0, 35.0, and 45.0 ℃. The silica polymerization was characterized by the greater enthalpy change at each higher temperature and by the reaction orders of the silica sol and potassium silicate, which varied rapidly, instantaneously, and constantly from low to high all the time, up and down in an alternate manner. When the reaction order of the silica sol and potassium silicate was 3.0, the maximum rate constant occurred at 25.0℃ （k= 1.22 × 10 ^-4 mol-2·dm6·s-1）. The two temperature regions （25.0-35.0 ℃ region with a faster rate and 35.0-45.0℃ region with a lower rate） reflected a two-stage oligomerization of silica monomers with different oligomers formed in a two-step anionic mechanism. The measurements of particle size and pH value showed that the colloidal particles in the mixed silica sol and potassium silicate first dissolved, then ＂active＂ silica in the potassium silicate redeposited to make a distinct particle size distribution （Z-average size, 33.0-14.9 nm at 25.0 ℃） influenced both by pH value （9.82--11.97 at 25.0 ℃） and the mass fraction （53, 65, 75, and 85 mass/%） of the silica sol in the mixture. The processes of combination of the silica sol and potassium silicate did not result from acid-base neutralization reactions but from a complex polymerization of the ＂active＂ silica components which relate to silica monomers oligomerization with heat evolved （the total enthalpy changes, 1.6234-3.3882 J）.Isothermal heat conduction microcalorimetry was utilized as a novel characterization method to investigate the polymerization processes of silica with both thermodynamic and kinetic parameters when the combination of silica sol and potassium silicate was stirred at temperatures of 25.0, 35.0, and 45.0 ℃. The silica polymerization was characterized by the greater enthalpy change at each higher temperature and by the reaction orders of the silica sol and potassium silicate, which varied rapidly, instantaneously, and constantly from low to high all the time, up and down in an alternate manner. When the reaction order of the silica sol and potassium silicate was 3.0, the maximum rate constant occurred at 25.0℃ （k= 1.22 × 10 ^-4 mol-2·dm6·s-1）. The two temperature regions （25.0-35.0 ℃ region with a faster rate and 35.0-45.0℃ region with a lower rate） reflected a two-stage oligomerization of silica monomers with different oligomers formed in a two-step anionic mechanism. The measurements of particle size and pH value showed that the colloidal particles in the mixed silica sol and potassium silicate first dissolved, then ＂active＂ silica in the potassium silicate redeposited to make a distinct particle size distribution （Z-average size, 33.0-14.9 nm at 25.0 ℃） influenced both by pH value （9.82--11.97 at 25.0 ℃） and the mass fraction （53, 65, 75, and 85 mass/%） of the silica sol in the mixture. The processes of combination of the silica sol and potassium silicate did not result from acid-base neutralization reactions but from a complex polymerization of the ＂active＂ silica components which relate to silica monomers oligomerization with heat evolved （the total enthalpy changes, 1.6234-3.3882 J）.

关 键 词：silica sol SILICATES nanoparticles MICROCALORIMETRY THERMODYNAMICS KINETICS 

分 类 号：TQ638[化学工程—精细化工] TQ127.2