Chemical diffusion of fluorine in melts in the system Na2OAl2O3SiO2
نویسندگان
چکیده
The volatilization of fluorine from three melts in the system N a 2 0 A 1 2 0 3 S i O 2 has been investigated at 1 atm pressure and 1200-1400°C. The melts chosen have base compositions corresponding to albite, jadeite and a peraluminous melt with 75 mole % SiO 2. Melt spheres were suspended from platinum loops in a vertical tube furnace in a flow of oxygen gas, then quenched, sectioned and analysed by electron microprobe. The microprobe scans indicate that transport of fluorine to the melt-vapor interface is by binary, concentration-independent interdiffusion of fluorine and oxygen. F-O interdiffusivity increases in the order albite < peraluminous<jadeite. There is no simple reciprocal relationship between F-O interdiffusivity and melt viscosity. Comparison with data on high-pressure interdiffusivity of fluorine and oxygen in jadeite melt indicates that F-O interdiffusivity increases with pressure from 0.001 to 10 kbar while the activation energy remains unchanged. Fluorine chemical diffusivity in albite melt is substantially lower than H20 chemical diffusivity in obsidian melts suggesting that different diffusive mechanisms are responsible for the transport of F and H20 in igneous melts. Fluorine diffuses in albite melt via an anionic exchange with oxygen whereas water probably diffuses in obsidian melt via an alkali exchange mechanism.
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Chemical diffusion of fluorine in jadeite melt at high pressure
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