Thermodynamics Analysis of Porous Crystal Formation from Phase Transition Coupling with Dissolution
Porous materials have been widely used from long ago because they possess important applications: biomaterials, filtering and purifications systems, acoustic and thermal insulation, building constructions, transportation, communications, aeronautical applications, etc. To investigate the mass transfer of ions and nucleation of crystals in multi-scales and then to explain the formation mechanism of the porous structure materials, a multi-scale mathematical model for mass transfer processes coupling with local reactions is proposed in which the chemical potential gradient 兇冚 is used as the driving force to avoid the discontinuity of the kinetics equations in the micro-channels. Meanwhile, porous structured KCl with a pore size of 10-50 microns is produced from the fractional crystallization of carnallite (as shown by SEM images in Figure 1), and the dissolution kinetics of KCl at 298.15 K is measured with ion selective electrode to determine the dissolution rate constant d k by the statistical rate theory and the average area of crystals Ac. The investigation for the fractional crystallization process of carnallite shows that the calculated mixing time versus channel width agree with the Einstein diffusion equation, which validates that the model can be used to describe the ion diffusion very well. Meanwhile, to have an accurate 兇冚 of KCl, in the channel width of or narrower than 2.0⊙10-6 m, it is enough to consider the diffusion only, while in the channel width of or wider than 2.0⊙10-5 m, diffusion should be coupled with reaction. The investigation also shows the vital of the consideration of the ionic activity coefficient for the investigated systems in micron scales. Moreover, the process simulation for the synthesis of mesoporous fiber reveals the formation mechanism of the porous structures in the inorganic material fabrication (as shown in Figure 2). This will provide a reference for the regular and ordered porous structure formation in the advanced inorganic material synthesis.
chemical potential gradient mass transfer dissolution crystallization nucleation kinetics microphase separation
Xiaohua Lu Chang Liu Yuanhui Ji Xin Feng
State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, Nanjing 210009, Jiangsu, P. R. China
国际会议
International Symposium on Crystal Engineering and Drug Delivery System 2009(2009晶体工程与药物传送系统国际会议)
天津
英文
58-59
2009-09-05（万方平台首次上网日期，不代表论文的发表时间）