STRUCTURAL EFFECTS IN THE ELECTROLYTES GLASS (LiC1) xH2O AND THE NUCLEATION OF METASTABLE PHASES

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STRUCTURAL EFFECTS IN THE ELECTROLYTES

GLASS (LiC1) xH2O AND THE NUCLEATION OF

METASTABLE PHASES

A. Elarby-Aouizerat, P. Chieux, P. Claudy, J. Dupuy, J. Jal, J. Letoffe

To cite this version:

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JOURNAL

DE

PHYSIQUE

Colloque C8, suppl6ment

au

n012,

Tome

46,

d6cembt-e

1985

STRUCTURAL EFFECTS I N T H E ELECTROLYTES GLASS ( L ~ C ~ ) ~ H ~ O AND THE N U C L E A T I O N OF METASTABLE PHASES

A. Elarby-Aouizerat, P. ~hieux*, P. claudy**, J. Dupuy, J.F. Jal and J.M. ~etoffe**

L$iversit6 CZaude Bernard, Lyon I , 69622 ViZZeurbanne Ceder, France I n s t i t z i t LauB Langevin, 156 X, 38042 GrenobZe Ceder, Prance

**

_{Laboratoire de Therrnochimie, I .}_{N .}_{S .}_{A .} _{de Lyon, France}

Resume

-

L1int6r6t des 6lectrolytes aqueux pour la compr6hension de 1 '6tat

vitreux est montr6 par la diffusion ou la diffraction de neutrons et par

D.S.C.

Sur deux gammes de compositions, le verre form6 ne cris

1

allise

pas et un verre avec deux Tg differentes est obtenu. L'effet endothermique

observe par D.S.C.

pendant Tg, est attribu6 B

un rgarrangement du verre.

L'effet thermique, se produisant dans le liquide tr&s au-dessus de Tg,

est probablement dQ au rgarrangement des mol6cules d'eau.

Abstract

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The interest of aqueous electrolytes for the understanding

of the glassy state is shown by neutron scattering or neutron digfraction

and

Differential Scanning Calorimetry (D.S..C.).

In two ranges of

composition the formed glass does not crystallize, and a glass /with two

different Tg is shown. The overshot as observed by D.S.C. duriing Tg is

attributed to a reordering of the glass. The thermal effect occuring in

the liquid well above Tg is probably due to a rearrangement of the water

molecules.

I

-

INTRODUCTION

Aqueous electrolytes are very interesting for the fundamental study of glass forma-

tion since they demonstrate a large variety of situations as a function of the

nature of solute and its concentration (deep eutectics, multiple coumpoupds, systems

with two Tg's, strong undercool ing of some 1 iquidus 1

ines..

.

).

These arise because

of the competing forces between solvated ions and water. The experimental conditions

are particularly favourable for Differential Scanning Calorimetry, and non

equilibrium phase diagram lines are obtained at constant heating rates on quenched

vitrous samples. Combined with neutron diffraction and small angle scattering,

D.S.C.

is effective for investigating the domains of glass and undercooled liquid

metastability as well

as the nucleation of microheterogeneities and the

identification of the crystallization products (references

1, 2, 3,

4 , 5,

6).

I1

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GLASS WITHOUT CRYSTALLIZATION

If we consider, for example the LiC1-Hz0 phase diagram given in figure 1, there

are two concentration ranges where strong undercooling of the liquidus is easily

achieved and where a glass to liquid transition is observed at Tg on warming without

crystallization, a conclusion confirmed by neutron diffraction.

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I11

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REORDERING OF GLASS BELOW Tg

Tg and TC have been measured as shown a t x=10.9 ( f i g u r e 3). A s t r i k i n g f a c t i s t h a t t h e D.S.C. shows no o v e r s h o t a t Tg i n t h e ranges where t h e g l a s s does n o t c r y s t a l l i z e . On t h e o t h e r hand, i f t h e sample i s annealed below Tg, t h e o v e r s h o t i n c r e a s e s . A t t h i s c o n c e n t r a t i o n n e u t r o n d i f f r a c t i o n shows t h a t c u b i c i c e i s formed ( f i g u r e 2).

The same phenomena i s observed a t x=0.14 where no c r y s t a l l i s a t i o n o c c u r s . The o v e r s h o t i s t h e n i n t e r p r e t e d as b e i n g due t o t h e d e s t r u c t i o n o f t h e o r d e r i n g o f t h e g l a s s . F i g u r e 3 I V

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TWO Tg GLASS

L e t u s f o c u s now on t h e c o n c e n t r a t i o n s between LiC1-5H20 and LiC1-3H20 which a r e w e l l - d e f i n e d compounds ( 9 ) . Here two T g ' s have been i d e n t i f i e d . They m i g h t have been produced b y a phase s e p a r a t e d s o l i d b u t ( i ) t h e a m p l i t u d e o f t h e s p e c i f i c h e a t v a r i a t i o n a t each Tg i s a f u n c t i o n o f c o n c e n t r a t i o n (see t h e DSC c u r v e on f i g u r e 4 and t h e Tamman diagram on f i g u r e 5 ) , and ( i i ) t h e absence o f m i c r o h e t e r o g e n e i t y r e v e a l e d by n e u t r o n s m a l l a n g l e s c a t t e r i n g experiments seem t o c o n t r a d i c t t h i s ( 8 ) .

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C8-632 JOURNAL DE PHYSIQUE

0.s.t curves o f Tg versus molar f r a c t i o n x

0.l5 47 T R 8.25 10 4 1 R Z 173 163 1S3 Figure 5 F i g u r e 4 V

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LIQUID-LIQUID TRANSITION

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F i g u r e 6

V I

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CONCLUSION

A c o m b i n a t i o n o f c a r e f u l c a l o r i m e t r i c d a t a and s t r u c t u r a l i n v e s t i g a t i o n s l e a d t o a w e a l t h o f i n f o r m a t i o n on t h e s e a p p a r e n t l y complex systems : t h e system LiC1- Hz0 has been w e l l d e f i n e d and i t shows a g r e a t v a r i e t y o f b e h a v i o u r .

The e f f e c t o f i m p u r i t i e s can be k e p t t o a minimum, due t o t h e s i m p l i c i t y o f t h e compounds i n v o l v e d and t o t h e ease o f o b t a i n i n g t h e g l a s s y s t a t e . However, a p r o p e r d e s c r i p t i o n o f t h e i n t e r a c t i o n between t h e h y d r a t i o n spheres i s necessary i f t h e d e t a i l e d b e h a v i o u r o f t h e g l a s s y s t a t e i s t o be f u l l y understood.

REFERENCES

1

-

J. DUPUY, J.F. JAL, C. FERRADOU, P. CHIEUX, A.F. WRIGHT, R. CALEMCZUK, C.A. ANGELL

n a t u r e , Vol. 396 n o 5853 (1982) 138-140

2

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A. ELARBY, J.F. JAL, J. DUPUY, P. CHIEUX, A. WRIGHT, R. PARREINS J. Physique L e t t r e s 43 (1982) L-355-L363

3

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A. ELARBY-AOUIZERAT, These n o 1171 Lyon 2 j u i l l e t 1982

4

-

A. ELARBY AOUIZERAT, J.F. JAL, J. DUPUY,

P.

CHIEUX, A. WRIGHT, R. PARREINS J. de Physique C9-205 13 Supl. 43 (1982)

5

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A. ELARBY-AOUIZERAT, J.F. JAL, C. FERRADOU, J. DUPUY, P. CHIEUX, A. WRIGHT J . o f P h y s i c a l Chem. 87 (1983) 2 1 p. 4170

6

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J. DUPUY, A. ELARBY-AOUIZERAT, J.F. JAL, P. CHIEUX, P. CLAUDY, J.M. LETOFFE R i v i s t a d e l l a Staz. Sper. V e t r o n o 5 (1984)

7

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P. CLAUDY, J.M. LETOFFE, J.J. COUNIOUX, R. COHEN-ADAD J. Thermal Anal. 29 (1984)