| By introducing the structural transformation analysis into the kinetics of mechanochemical reaction and borrowing the structural macrokinetics research theory from the combustion synthesis, the structural macrokinetics of mechanochemical reaction and its research methods are put forward in this thesis. Based on the chemical reaction and material structure transformation, the mechanochemical processes were investigated and the research methods were applied successfully to the anatase TiO2, CaO+TiO2and Fe2O3+ZnO systems.The main conclusions are as follows:1. The shear force can promote the crystal transfer of anatase phase. By changing the action mode of mechanical force, the phase transformation of anatase can be expected to proceed along different courses, which is of practical reference value to synthesize TiO2ceramic material with the demands of crystal form. Results show that under our experimental conditions the anatase TiO2powder is demonstrated to induce different phase transformation phenomena with mechanical processing:a step-by-step transformation from anatase to TiO2-â…¡ and then to rutile in all three mills:a planetary ball mill, an attritor and a ring-roller mill; besides a direct transformation from anatase to rutile in the ring-roller mill.2. Under the same milling conditions, the mechanochemical reaction rates increased in turn when the alkaline-earth metal oxides MgO, CaO and BaO were milled with anatase, respectively, which indicates the existence of an alternation phenomenon along main group elements. Phase transformation might occur in anatase when it was milled with alkaline-earth metal oxides, which results in the different courses of reaction.(1) In the system MgO+TiO2, it is hard to synthesize MgTiO3directly from the reaction of MgO with anatase TiO2. Experimental results show that the TiO2-â…¡, as a newborn phase with better reactivity than anatase TiO2, is firstly transformed from anatase TiO2with mechanical force, and MgTiO3can be formed through the reaction of MgO with the TiO2-â…¡.There exist the chemical reactions in the system as follows: TiO2(Anatase)â†'TiO2-â…¡ AO+TiO2-â…¡â†'ATiO3(2) For the system CaO+TiO2and BaO+TiO2, TiO2-â…¡ was not detected during the course of milling. And experimental results show that it is easy for anatase TiO2to directly react with CaO and BaO to form CaTiO3and BaTiO3, respectively. There exists the chemical reaction in the two systems as follows: AO+TiO2(Anatase)â†'ATiO33. Under the same milling conditions, the mechanochemical reaction rates increased in turn when the metallic oxides CuO, NiO and ZnO were milled with Fe2O3, respectively. Results show that with a similar structure between the reactant and the resultant, the reaction runs smoothly; otherwise, it runs relatively hard.4. The mechanochemical kinetics of phase transformation to rutile in anatase system and reactions in both CaO+TiO2and Fe2O3+ZnO systems, are best expressed by Avrami-Erofe’ev model, which indicates the random nucleation of products phase followed by a growth of nuclei.(1) The kinetic equation of anatase system is as:[-1n(1-α)]1/1.9147=0.2484t (Ring-roller mill,710rpm)(2) The kinetic equation of CaO+TiO2system is as:[-ln(1-α)]1/08685=0.36581(Planetary ball mill,500rpm, BPR=20:1)(3) The kinetic equation of Fe2O3+ZnO system is as:[-ln(1-α)]1/13262=0.0859/(Planetary ball mill,500rpm, BPR=20:1)5. Taking the mechanochemical synthesis of ZnFe2O4by milling Fe2O3+ZnO mixed powders for example, the reaction kinetics was studied by energetic approach in this thesis. Results show that a fine effect could be obtained when Avrami-Erofe’ev kinetics model is used to fit the mechanochemical reaction. When it is under a certain BPR, the reaction conversion degree only directly relates to the energy dose. Energy-scaled knetics of mechanochemical reaction has less restriction on milling parameters than time-scaled kinetics.The kinetic equations under different BPR are as follows:[-ln(1-α)]1/1.3179=0.0254Ekum(BPR=40:1)[-ln(1-α)]1/13706=0.0151Ekum(BPR=20:1)... |
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