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ISIJ International, Vol. 30 (1990), No. 4, pp. 298-304 The Molar Volumesand the Surface Tensions CaF2-MF(M:Li, Na) and CaF2-MF2(M: Mg, of Melts Sr, Ba) in the Systems Shigeta HARA,Hideharu SHIBAIKE1)and KazumiOGINO 1)Graduate School, Osaka University. Faculty of Engineering, OsakaUniversity, Yamadaoka,Suita, Osaka-fu, 565 Japan. lronmaking Technical Div., Technical Administration Bureau, Nippon Steel Corporation, Otemachi, Chiyoda-ku, Tokyo, 100 Japan. (Received on June 21. 1989; accepted in the final form on November 17, 1989) Nowat Surface tension anddensity of molten CaF2-basedbinary systemweremeasured. From the measurement,the fo!lowing results were obtained, (1 )Molar volumes of the melts in the systemsCaF2-NaF,andCaF2-BaF2are deviated possitively from the additive rule, while for CaF2-LiFandCaF2-MgF2melts negative deviation from the additive rule on volume is found, but CaF2-SrF2melt behaves ideally on volume. (2) Surtace tensions of the melts in the binary systemscan be expressed by Guggenheims equatibn for regular solution, if a suitable interaction energy co of each binarysystem is selected. (3) The interaction energy (,), estimated from surface tension of binary fluoride systems, is related to the excess volume on mixing for CaF2-M.F2equi-molar composition (x=1 for divalent andx=2 for monovalent fluoride). (4) Liquidus lines for the systems, calculated from the interaction energy co in combination with the thermochemical data are fairly in good agreementwith those reported, but that for CaF2-NaFsystem is exceptional. (5) Surface tentions of binary fluoride melts are strongly dependedon packing density of fluorine ions on the surface. KEYWORDS:surtace tension; molar volume; calcium fluoride; binary fluoride; melt; regular solution. 1. Introductron Currently, alkaline metal and alkali-earth metal fluorides are used as additives or main components of pyrometallurgical slags and fluxes. Janz and co- workers have already published the collective works related t