Synthesis Process And Characterization Of Al₂O₃-SiO₂-CaF₂-P₂O₅ Ultrafine Glass Powder By Liquid Precipitation

Al₂O₃-SiO₂-CaF₂-P₂O₅ ultrafine glass powder was prepared by liquid phase precipitation method with several inorganic salts containing Al³⁺, SiO₃²⁺, Ca²⁺, F^-, P₃O₁₀^5-, Na⁺, Cl^-as starting-reagents. By means of XRD, TEM, EDAX, IR and DSC, the influences of technics parameters on synthesis and characteristic of Al₂O₃-SiO₂-CaF₂-P₂O₅ powder were studied; the chemical composition, micromorphology, crystalline status, glass structure and crystallization transformation behavior of the powder were characterized. The similarities and differences between liquid precipitation powder and melting-quenching-grinding powder were analyzed, and the synthesis mechanism of the powder was also discussed. The main results of the thesis are showed as follow:1,The influences of process parameters, such as reactant proportion, solution concentration, PH value, cleaning and drying means, on the synthesis and characteristic of Al₂O₃-SiO₂-CaF₂-P₂O₅ powder were proved up. The results show that the reactant proportion have great effect on relative content of chemical elements, but it has little effect on chemical elements, micromorphology, powder size and crystalline status. The solution concentration has little effect on chemical composition and crystal status, the particle decreases slightly in size, but agglomerates phenomenon becomes severer with increasing the solution concentration. Adding some organic additive PA and inorganic additive PB so that controlling PH value of mixed solution in the proper range can improve the dispersed state of powder. Using ethanol cleaning and infrared drying can not only effectively eliminate impurity ions, but also improve the dispersion effection of powder.2,Under the condition of room temperature and normal pressure, the optimized synthesis processes for Al₂O₃-SiO₂-CaF₂-P₂O₅ powder is put forward. Confecting Na₂SiO₃ of 0.7mol/L, AlCl₃ of 0.8mol/L, CaCl₂ of 1.0mol/L, NaF of 0.3mol/L and Na₅P₃O₁₀ of 0.1mol/L, adding organic additive PA of 0.05mol/L and inorganic additive PB of 0.2mol/L, controlling PH value in the range of 5.4～6.4, cleaning the precipitation by deionized water and pure ethanol for above 5 times, finally drying the precipitation by infrared light. Based on above parameters, nano-glass powder with well-proportioned particle size and well dispersed state can be obtained.3,The chemical composition, micromorphology, crystalline status, glass structure of Al₂O₃-SiO₂-CaF₂-P₂O₅ powder were characterized. The Al₂O₃-SiO₂-CaF₂-P₂O₅ powder prepared by liquid phase precipitation method is amorphous compounds containing Al,Si,Ca,F,P,O atoms and constituted by near spheroidic nano particles that the size is in the range of 20-60nm. The glass structure is constituted by different chemical bonds containing Si-O-Si,O-P-O,Si-O-Al,P-O-Al,Si-O-Ca,P-O-Ca,Si-O,Si-F,Al-F and Ca-F.4,The crystallization transformation characteristic of Al₂O₃-SiO₂-CaF₂-P₂O₅ ultrafine glass powder during heat treatment was studied. The results show that in the range of 500℃～900℃, some crystal phases are precipitated from the glass. The crystal phase CaF₂ is precipitated firstly about 600℃, crystal phases such as Al₂SiO₅,Ca₂SiO₄ and Ca₃(PO₄)₂ are precipitated sequentially with the temperature rising.5,The similarities and differences between liquid precipitation powder and melting-quenching-grinding powder were studied. The results show that melting-quenching-grinding powder is constituted by micron-scale particles which present irregular polyhedron, the most of particles size is in the range of 0.5～2μm. Both liquid precipitation powder and melting-quenching-grinding powder have similar chemical composition,crystallization status and glass structure, but glass transformation temperature T_g and precipitation temperature T_p of liquid precipitation powder is obviously lower than those of melting-quenching-grinding powder.6,The liquid synthesis mechanism of Al₂O₃-SiO₂-CaF₂-P₂O₅ ultrafine glass powder was discussed, and the microstructure model was speculated. It is pointed out that after the anion and cation except Na⁺ and Cl^-occur rapid co-precipitation reactions in the mix-ion solution system which contains Al³⁺,SiO₃^2-,Ca²⁺,F^-,P₃O₁₀^5-,Na⁺,Cl^-, the nano inorganic polymer is precipitated with its complex microstructure. [SiO₄],[AlO₄] and [PO₄] are linked to form the basic network of this inorganic glass. Some ions Ca²⁺ and F^-enter the basic network, and other ions Ca²⁺ and F^-are located as the network modifiers.