Cryoscopic studies in fluoride-Oxide-Silica systems: Part II. systems containing Mg 2+ , Ca 2+ , Ba 2+ and Pb 2+
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T H E r e s u l t s of a n i n v e s t i g a t i o n o f t h e f l u o r i d e l i q u i d u s b e h a v i o r in a l k a l i f l u o r i d e - a l k a l i o x i d e - s i l i c a s y s t e m s w e r e p r e s e n t e d i n P a r t I. t I n t h e p r e s e n t p a p e r a r e r e p o r t e d t h e r e s u l t s of a n i n v e s t i g a t i o n of the liquidus behavior in alkaline earth and lead fluoride-silicate systems.
w h e r e zkHm i s t h e m o l a r h e a t of f u s i o n o f t h e p u r e f l u o r i d e , T m i s t h e m e l t i n g t e m p e r a t u r e of t h e p u r e fluoride and T is the liquidus temperature. The measured freezing temperatures of M g F z , C a F 2 , Table I. Alkaline Earth Fluoride and Lead Fluoride Liquidus States and Activities in Fluoride-Silicate Systems
EXPERIMENTAL
MgF~-2MgO"SiO~
C o m m e r c i a l g e n e r a l r e a g e n t g r a d e s of M g F e , C a F 2 and BaF2 were purified by mixing intimately with NH4F . H F a n d h e a t i n g , i n g r a p h i t e c r u c i b l e s , t o 300~ T h e u n r e a c t e d NH4F 9H F w a s t h e n r e m o v e d b y h e a t i n g t o 800~ u n d e r f l o w i n g a r g o n . L e a d f l u o r i d e ( M e r c k "Suprapur") was used without further purification. Alkaline earth fluoride-silicate melts were prep a r e d b y m e l t i n g m i x t u r e s of t h e a p p r o p r i a t e d r i e d c a r b o n a t e , s i l i c a a n d f l u o r i d e . L e a d s i l i c a t e of P b O / SiO2 R a t i o s 2, 1.5 a n d 1 w e r e p r e p a r e d b y m e l t i n g m i x t u r e s of A R g r a d e P b O a n d SiO2 i n P t - R h c r u c i b l e s a t 800 t o 9 0 0 ~ The experimental procedures used were the same a s t h o s e d e s c r i b e d i n P a r t I. 1
NMgF2 1 0.9899 0.9800 0.9687 0.9592
T~ 1260.0 1259.2 1256.5 1252.6 1250.3
MgF2-2MgO"3SIO2 aMgF~
NMgF~
1 0.998 0.990 0.978 0.971
0.9894 0.9847 0.9767 0.9665 0.9621 0.9544
MgF:-3MgO-2SIO2
In
'hHm [ T - T m ] aMF 2 = RT Tm
[1]
HIDEAKI SUITO is Lecturer, Research Institute of Tohoku University, Sendai, Japan. D. R. GASKELL is Associate Professor of Metallurgy, Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, PA 19174. Manuscript submitted May 6, 1976. METALLURGICAL TRANSACTIONS B
1254.9 1251.9 1246.0 1241.8 1238.5 1237.7
aMgFz 0.985 0.976 0.959 0.947 0.937 0_935
MgF2-MgO"2SIO2
NMgF2
T~
aMgF2
NMgF2
T~
aMgF~
0.9872 0.9748 0.9627 0.9508
1256.2 1250.5 1243.4 1242.4
0.989 0.972 0.951 0.949
0.9810 0.9626 0.9528 0.9450 0.9355 0.9279 0.9188 0.9115 0.8803
1253.9 1245.1 1242.5 1238.2 1236.7 1235.0 1235.2 1233.4 1232.0
0.982 0.956 0_949 0.936 0.932 0.927 0.928 0.923 0.919
RESULTS The experimental results are listed in Table I tog e t h e r w i t h t h e a c t i v i t i e s of t h e a l k a l i n e e a r t h f l u o r i d e s and PbFz (with respect to the pure supercooled liquid) in the alkaline earth fluoride and PbF2 liquidus melts, obtained as
T~
MgF2-MgO"SiO2
CaFz-2CaO'SiO2
NMgF~
T~
aMgF~
NCaF~
T~C
aCaF2
0.9727 0.9700 0.9610 0.935
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