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Investigation on the Crystallization of Na2SO4 under Ultrasound

Author: ChenXia
Tutor: LiHong
School: Tianjin University
Course: Materials Physics and Chemistry
Keywords: ultrasonic cavitation numerical analysis Na2SO4 induction time artifical neural network
CLC: O781
Type: Master's thesis
Year: 2008
Downloads: 100
Quote: 1
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Abstract


In order to research the dynamics of ultrasonic cavitation and ultrasonic effects on the thermodynamics and kinetics properties of crystallization, four–step Runge–Kutta is used for numerical analysis. The solubility of Na2SO4 and induction time of its crystallization insonated have been investigated. A kinetics model of the crystallization has been constructed by advanced BP network.The numerical analysis of ultrasonic bubble dynamics indicates that collapsing bubbles could produce high temperature and pressure, strong microstreaming or microjets, which can improve the state, combination, function or structure of the solution to prompt nucleation of crystal. With respect of thermodynamic properties of crystallization, in insonated solution crystallization would happen at a lower temperature, and the metastable zone width was greatly narrowed. In the view of kinetics of crystallization ultrasound makes lots of notable influences in crystallization of many substances, that is, quickening nucleation speed, shortening induction time, remarkably improving the yield and so on.The analyzing for solubility and induction time measurements show that Na2SO4 solubility increases with temperature at the beginning and descends afer 34 oC. In the same conditions, the induction time of Na2SO4 solution insonated was obviously shorter than that stirred. That is ultrasound promotes nucleation.The BP network of one connotative layer, three input parameters(ΔC, T and P), and an output parameter (tind) was an advanced tool for constructing a model of the kinetics properties of crystallization, which predicting induction time according with experimental datas. We used linearity relations between ln-2s and ln(tind) measured at the same final temperature and different supersaturation to calculate interface energy by drawing. With local high temperature and pressure when ultrasound bubbles collapse, the interface energy was reduced and nucleation was hastened.

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CLC: > Mathematical sciences and chemical > Crystallography > Crystal growth > Theories of crystal growth
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