Study On Al₂O₃-SiO₂-CaF₂ Nano-Glass Powder By Liquid Precipitating

Al₂O₃-SiO₂-CaF₂ nano-glass powder was prepared by liquid phase precipitation method with several inorganic salts containing Al³⁺, SiO₃²⁺, Ca²⁺, F^-, Na⁺, Cl^- as processed materials. By means of XRD, TEM, IR, EDAX and DSC, the influences of technics parameters on synthesis and characteristic of Al₂O₃-SiO₂-CaF₂ powder were studied, and the synthesis mechanism of the powder was put forward. Also, the micromorphology, crystalline status, microstructure, chemical component and crystallization behavior of the powder were studied. The similarities and differences between liquid precipitation powder and melting-quenching-grinding powder were analyzed. The main results of the thesis are showed as follow:1. The influences of technics parameters, such as component proportion, solution mol-density, dispersant and PH value, ultrasonic field, cleaning and drying means, on the synthesis and characteristic of Al₂O₃-SiO₂-CaF₂ powder were studied. The component proportion has little effect on synthesize processing and the characteristic of powder. The particle becomes smaller in size and easier to agglomerate with the solution density increasing. When the PH value is in the range of 5.3-6.4, particles agglomerate slightly. Adding dispersant PA and PB in the ultrasonic field, cleaning by ethanol and drying by infrared light are in favor of obtaining disperse powder.2. In the condition of normal temperature and intensity of pressure, the optimized preparation technology for Al₂O₃-SiO₂-CaF₂ powder is obtained. Solution: Na₂SiO₃ of 0.7mol/L, AlCl₃ of 0.8mol/L, CaCl₂ of 1.0mol/L and NaF of 0.3mol/L, dispersant: PA of 0.05mol/L and PB of 0.2m ol/L, controlling the PH value in 5.3, cleaning the precipitation by non-ion water and pure ethanol for 4-6 times, finally dry the precipitation by infrared light. According to the way above, nano-glass powder can be obtained.3. The micromorphology, crystallization status, microstructure, chemical component and the liquid synthesis mechanism of Al₂O₃-SiO₂-CaF₂ powder were proved up. The powder is constituted by near spheroidic particles that size is in therange of 30⁷0nm, the powder belongs to amorphous compounds containing Al, Ca, Si, O and F atoms. After simple and multilevel chemical reactions occurred in the mix-solution system in which contains several kinds of ions such as Al3+ > SiC>32 -. Ca2+ > F > Na+ -. Cland so on, the inorganic polymer is precipitated with its complex microstructure formed by the linking of-O-Si-O-, -O-Si-F-, -Si-O-Al- and so on.4. The crystallization characteristic of Al2(>3-SiO2-CaF2 powder treated in different temperatures was studied. The results show that, in the range of 500^0 800 °C, several crystal phases are precipitated from the powder. The crystal phase CaF2 is precipitated firstly in about 545 °C, with the temperature rising, crystal phases such as A^SiOs and Ca2SiC>4 are precipitated sequentially.5. The similarities and differences between liquid precipitation powder's characteristic and melting-quenching-grinding powder's were studied. The results show that melting-quenching-grinding powder is constituted by disperse and micron-size particles which present abnormity polyhedron in shape. Both of the two powder belong to amorphous compounds and contain the same chemical elements, and they also have similar network structure with [SiO4] and [AIO4] linking together to form the base network, some of F entering the network while some of Ca2+, Al3+ and F staying as the network modifiers.