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SPECTROSCOPIC PROPERTIES OF TRANSITION ELEMENTS IN GLASSES OF GEOLOGICAL
INTEREST
G. Calas
To cite this version:
G. Calas. SPECTROSCOPIC PROPERTIES OF TRANSITION ELEMENTS IN GLASSES OF GEOLOGICAL INTEREST. Journal de Physique Colloques, 1982, 43 (C9), pp.C9-311-C9-314.
�10.1051/jphyscol:1982957�. �jpa-00222486�
JOURNAL DE PHYSIQUE
Colloque C93 supplement au n°12, Tome 42, deeembre 1982 page C9-311
SPECTROSCOPIC PROPERTIES OF TRANSITION ELEMENTS IN GLASSES OF GEOLOGICAL INTEREST
G. C^las
Laboratoire de Mineralogie-Cr-istdllographie, LA CNRS 09, Universite de Paris 6 et 7, 752SU Paris.Cedex, France
Résurne.- Les propriétés géochimiques des éléments de transition peuvent être expli- quées en partie par leur cristallochimie dans les liquides silicates. On peut reconnaître différents types de comportement et de dépendance en fonction de la variation de composition du verre, notamment la présence de complexes stables et de valences inhabituelles.
A b s t r a c t . - Geochemical b e h a v i o u r of t r a n s i t i o n m e t a l i o n s can b e p a r t l y e x p l a i n e d a t t h e l i g h t of t h e i r c r y s t a l l o c h e m i c a l p r o p e r t i e s i n s i l i c a t e m e l t s . D i f f e r e n t k i n d s of e l e m e n t s can b e d i s t i n g u i s h e d , when s t u d y i n g t h e dependence of s p e c t r a l p r o p e r t i e s on g l a s s b u l k c o m p o s i t i o n , s t a b l e complex f o r m a t i o n and e x o t i c v a l e n c i e s .
S i l i c a t e m e l t s p l a y an i m p o r t a n t r o l e as d e t e r m i n i n g t h e fundamental c h a r a c - t e r i s t i c s of n a t u r a l magmas : t r a n s p o r t p r o p e r t i e s , g a s d i s s o l u t i o n , thermodynamic p r o p e r t i e s ( c r y s t a l / l i q u i d e q u i l i b r i a , h e a t c o n t e n t s . . . ) . These s t u d i e s can b e done u s i n g t h e b u l k p r o p e r t i e s of t h e s e s y s t e m s . The geochemical b e h a v i o u r of minor and t r a c e components, which a r e c o n t a i n e d i n s i l i c a t e m e l t s , a r e m a i n l y governed b y s h o r t - r a n g e o r d e r p r o c e s s e s . I n t h e s p e c i f i c c a s e of t r a n s i t i o n e l e m e n t s , t h e y c a n be s t u d i e d w i t h v a r i o u s s p e c t r o s c o p i c t e c h n i q u e s which a l l o w t o d e t e r m i n e l o c a l s t r u c t u r e s . The r e s u l t s o b t a i n e d can be u s e d f o r m o d e l i z i n g p r e c o n c e n t r a t i o n p r o - c e s s e s of t h e s e elements'; i n ! t h e e a r t h ' s c r u s t and m a n t l e , which w i l l govern t h e i r l o c a t i o n a s o r e b o d i e s i n s p e c i f i c g e o l o g i c a l c o n d i t i o n s . We w i l l p r e s e n t t h e r e s u l t s o b t a i n e d on t r a n s i t i o n e l e m e n t s i n s y n t h e t i c g l a s s e s o f c o m p o s i t i o n s i m i l a r t o t h o s e e n c o u n t e r e d i n n a t u r a l systems b u t i r o n - f r e e t o a v o i d p e r t u r b a t i o n on t h e r e s u l t i n g s p e c t r a . S y n t h e s i s of t h e s e g l a s s e s was made i n c o n t r o l l e d oxygen p a r t i a l p r e s s u r e , s t a r t i n g from o x i d e m i x t u r e s and q u e n c h i n g from t h e m e l t . D i f f e r e n t s p e c t r o s c o p i c t e c h n i q u e s were used : o p t i c a l a b s o r p t i o n and f l u o r e s c e n c e , EPR, Mossbauer e f f e c t , EXAFS and XANES. The comparison between t h e m s e l v e s a l l o w t o d i s c u s s more c o m p l e t e l y t h e models p r o p o s e d .
G l a s s e s of g e o l o g i c a l i n t e r e s t have a complex c h e m i c a l c o m p o s i t i o n which v a r i e s a p p r o x i m a t e l y between a b a s a l t i c and a r h y o l i t i c c o m p o s i t i o n as d e f i n e d on Table 1 below ( v a l u e s a r e i n wt %).
T a b l e 1
S i 02 T i 02 A 1 2° 3 M8° C a° N a 2° K2 °
B a s a l t i c ^ ^ 2 6 n 8 2 4_g ] K 4 4_5 K 3
glass
Rhyolitic M_2 _ n_2 0 < 6 2_2 4 > 9 4_9
glass
The main feature is then an increase of SiO„ content and also of alkali—content of the glasses and a subsequent decrease of alkaline-earths when going from a basaltic to a rhyolitic glass, Al-content remaining quite at a constant level.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982957
C9-312 JOUFCJAL DE PHYSIQUE
The r e s u l t s we have o b t a i n e d by s t u d y i n g s p e c t r o s c o p i c p r o p e r t i e s of t r a n s i t i o n e l e m e n t s i n g l a s s e s r a n g i n g between a b a s a l t i c and a r h y o l i t i c composition c a n b e summarized i n f o u r t y p e s of b e h a v i o u r s , a s d i s c u s s e d below.
1.- C u ( I 1 ) a s a " t y p i c a l " t r a n s i t i o n m e t a l i o n . D i v a l e n t copper i s s t a b l e i n s i l i - c a t e g l a s s e s under o x i d i z i n g c o n d i t i o n s and can be c o n s i d e r e d a s r e p r e s e n t a t i v e of t h e main p a r t of 3d-elements. I t h a s t h e advantage t o be s t u d i e d b o t h w i t h EPR and o p t i c a l s p e c t r o s c o p i e s , which a l l o w a d e t a i l e d d i s c u s s i o n of t h e s i t e s i t o c c u p i e s i n o x i d e s g l a s s e s ( 1 ) . O p t i c a l a b s o r p t i o n s p e c t r a show a s l i g h t d e c r e a s e i n t h e c r y s t a l - f i e l d e n e r g y when going from b a s a l t i c t o r h y o l i t i c composition (13700 c m l and 13000 cm-I r e s p e c t i v e l y ) . EPR s p e c t r a (Fig.1) show a w e l l d e f i n e d h y p e r f i n e s t r u c t u r e p a r t i c u l a r l y d e v e l o p e d on p a r a l l e l components which p e r m i t t o s t u d y Cu-0 covalency f o l l o w i n g Imagawa's formalism. I f p e r p e n d i c u l a r components of g and A
-4 -1 t e n s o r s do n o t e x h i b i t a g r e a t v a r i a t i o n ( w i t h v a l u e s n e a r of 2.059 and 2 6 . 4 ~ 1 0 cm r e s p e c t i v e l y ) , g,/ component shows an i n c r e a s e (2.341 t o 2.366) and
-4 -1
shows a d e c r e a s e ( 1 5 1 ~ 1 0 - ~ c m - ' t o 137x10 cm ) when g o i n g from a b a s a l t i c t o a r h y o l i t i c composition.
F i g . 1 : X-band EPR spectrum of a MgO-CaO- 2Si0 ( d i o p s i d e ) g l a s s
2
c o n t a i n i n g lwt% CuO ( a i r - m e l t e d )
.
structure perpdiculoire
Following t h e work o f HOSONO e t a l . (2) t h i s c o r r e s p o n d s t o an e q u i v a l e n t v a r i a t i o n from 40 t o 10 mo1.Z Na 0 i n t h e b i n a r y s i l i c a t e g l a s s e s , which i s a way f o r compa-
2
r i n g n a t u r a l - l i k e multicomponent g l a s s e s t o s i m p l e b i n a r y s y s t e m s . Many o t h e r t r a n - s i t i o n m e t a l i o n s e x h i b i t t h e same t y p e of b e h a v i o u r ( e . g . C r ( I I I ) , N i ( I I ) ,
F e ( I 1 ) ...) which c o r r e s p o n d s t o a d e c r e a s e i n l o c a l s t a b i l i t y when g o i n g from ba- s a l t i c t o r h y o l i t i c c o m p o s i t i o n s . This e x p l a i n s some well-known chemical charac- t e r i s t i c s a s c r y s t a l - l i q u i d p a r t i t i o n c o e f f i c i e n t , which i n c r e a s e s markedly when c o n s i d e r i n g t h e same chemical v a r i a t i o n ( 3 ) .
2.- Molecular complexes : t h e c a s e of VO ++
.
Some of t r a n s i t i o n m e t a l i o n s e x i s t a s d i s c r e t e m o l e c u l a r complexes, u s u a l l y i n e x t r e m e l y o x i d i z i n g c o n d i t i o n s--
(Cr04
,
~ 0 2 -...
) . I n more r e d u c i n g c o n d i t i o n s e n c o u n t e r e d i n n a t u r a l magmas, o n l y a few p a r t i s s t a b l e , among which i s t h e i m p o r t a n t vanadyl group, VO++. T h i s can be s t u d i e d u s i n g t h e same formalism a s f o r Cu(I1) by comparing b o t h EPR and o p t i c a l s p e c t r a . A t y p i c a l EPR s p e c t r u m i s shown on F i g . 2 w i t h a w e l l marked h y p e r f i n e s t r u c t u r e . The f o l l o w i n g v a l u e s were o b t a i n e d : f o r b a s a l t i c g l a s s , g l l = 1.942, gL = 1.995, All = 1 6 0 x l 0 - ~ c m - ~ , AL = 6 l x i 0 - ~ c ~ ~ ; f o r r h y o l i t i cg l a s s , gii = 1.935, gL = 2.005, Ail = 173~10-~c;', AL = 7 0 ~ 1 0 - ~ c m - ~ . The g l a s s e s of i n t e r m e d i a t e composition range between t h e s e v a l u e s , which shows a n i n c r e a s e of t h e d i f f e r e n c e gl-g,, when going t o t h e r h y o l i t i c composition. T h i s i n d i c a t e s a p r o g r e s s i v e a x i a l compression of t h e complex i o n , due t o a s t r o n g e r vanadyl II-bonding. The o p t i c a l a b s o r p t i o n s p e c t r a e x h i b i t t h e two bands c h a r a c t e r i s t i c o f vanady 1 complexes. The main t r a n s i t i o n (b + e i ) i s s h i f t e d toward g r e a t e r e n e r g i e s (8700 cm-' t o 10300 c ~ l ) when g o i n g from b a s a l t i c t o r h y o l i t i c cornposi- t i o n : t h i s i s o p p o s i t e t o what i s o b s e r v e d i n Cu(I1) c o n t a i n i n g g l a s s e s .
Slructu~e perpondcuhtrc
F i g . 2 : EPR s p e c t r u m of a d i o p s i d e g l a s s c o n t a i n i n g lwt% V205
2000G + 1 2 G 3000G (000 G
I ( a i r m e l t e d ) .
T h i s s h i f t i s r e l a t e d t o t h e e v o l u t i o n o f e f f e c t i v e charges o f t h e oxygen l i g a n d s s u r r o u n d i n g t h e vanadyl group. I n SiO - r i c h g l a s s e s t h e s t r o n g p o l a r i z a t i o n of
2
t h e oxygens p r e v e n t s them from y i e l d i n g e l e c t r o n s t o t h e c e n t r a l vanadium, whose c h a r g e remains h i g h , t h u s g i v i n g r i s e t o a s t r o n g e r vanadyl E-bonding. T h i s e x p l a i n s t h e s t a b i l i t y o f t h e s e groups i n s i l i c a t e m e l t s . and i n f l u e n c e s vanadium - - c r y s t a l - l i q u i d p a r t i t i o n c o e f f i c i e n t s which s t r o n g l y dec;ease i n t h e s t a b i l i t y f i e l d o f V(1V) ( 3 ) .
3 . - S t a b i l i z a t i o n o f e x o t i c o x i d a t i o n s t a t e s : p e n t a v a l e n t uranium. O p t i c a l a b s o r p t i o n s p e c t r a o f uranium-doped s i l i c a t e g l a s s e s show, t o g e t h e r w i t h t h e w e l l known o x i d a t i o n s t a t e s U(IV) ( a s u r a n y l i o n s ) and U(IV)
,
t h e p r e s e n c e o f U(V) i n o x i d i z i n g t o moderately r e d u c i n g s y n t h e s i s c o n d i t i o n s ( 4 ) . The well-marked c h a r g e o f t h e s e s p e c t r a a s a f u n c t i o n of g l a s s composition ( F i g . 3) were e x p l a i n e d a s a m o d i f i c a t i o n of l o c a l geometry, from an o c t a h e d r a l U(V) i n b a s a l t i c g l a s s e s10000 n o (cm-I) 5000
' I ' 1 1
F i g . 3 : O p t i c a l a b s o r p t i o n s p e c t r u m of U-containing g l a s s e s .
a ) b a s a l t i c g l a s s e s (synthe- s i s a t 1420°c and
C9-3 14 JOURNAL DE PHYSIQUE
t o an a x i a l complex (UO ) + i n r h y o l i t i c g l a s s e s . The same e x p l a n a t i o n can be made 2
a s f o r vanadyl complexes : t h e weakening o f e f f e c t i v e c h a r g e of s u r r o u n d i n g oxy- gens f a v o u r s t h e i n t e r n a l 11-bonding 0-U-0 g i v i n g r i s e t o an a x i a l complex. T h i s e x p l a i n s t h e p r e s e n c e of uranium i n SiO - r i c h n a t u r a l magmas.
2 4.- Conclusion.
C r y s t a l l o c h e m i s t r y o f t r a n s i t i o n e l e m e n t s i n complex s i l i c a t e g l a s s e s de- pends s t r o n g l y on t h e n a t u r e and o x i d a t i o n s t a t e of t h e c o n s i d e r e d i o n . The v a r i a t i o n s o b s e r v e d a s a f u n c t i o n of g l a s s composition show t h a t t h e s e i o n s s e n s e r e g u l a r l y t h e b u l k chemical changes, b u t t h e d i f f e r e n c e s o b s e r v e d between t h e b e h a v i o u r o f d i f f e r e n t i o n s do n o t a l l o w t o use them a s s t r u c t u r a l p r o b e s t o modelize t h e b e h a v i o u r of s p e c t r o s c o p i c a l l y i n a c t i v e components a s Mg. The d a t a o b t a i n e d p e r m i t t o e x p l a i n t h e measured c r y s t a l l l i q u i d p a r t i t i o n c o e f f i c i e n t s and t h e p r e f e r e n c e o f some elements f o r w e l l - d e f i n e d magmatic c o m p o s i t i o n s .
R e f e r e n c e s
( 1 ) IMAGAWA, H. (1968)
-
Phys. S t a t . S o l . , 30, 469.( 2 ) HOSONO, H., KAWAZOE, H . , KANAZAWA, T. ( 1 9 7 9 ) , J . Non C r y s t . S o l i d s , 34, 339.
( 3 ) I R V I N G , A. (1978)
-
Geochim. Cosmochim. A c t a , 4 2 , 743.( 4 ) CALAS, G. (1979)
