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Submitted on 1 Jan 1987
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GRAIN GROWTH IN LABORATORY PREPARED ICE : SOLUTE EFFECTS
E. de Achaval, O. Nasello, E. Ceppi
To cite this version:
E. de Achaval, O. Nasello, E. Ceppi. GRAIN GROWTH IN LABORATORY PREPARED ICE : SOLUTE EFFECTS. Journal de Physique Colloques, 1987, 48 (C1), pp.C1-283-C1-288.
�10.1051/jphyscol:1987140�. �jpa-00226286�
GRAIN GROWTH IN LABORATORY PREPARED ICE : SOLUTE EFFECTS
E.M. de ACHAVAL, O.B. NASELLO* and E.A. CEPPI*
CEFA, Servicio ~ e t e o r o l 6 g i c o Nacional, Buenos Aires, Argentina
* F A M A F , Universidad Nacional de ~ 6 r d o b a , ~ 6 r d o b a , Argentina
RESUME. On a effectud unegtude exp&imentale d e croissance d e grainsdans la glace pure e t dans l a glace dop6e a v e c NaC1, NH4 OH e t HF. On a employe des solutions dans l e domaine de concentration d e lo-' M ~ o - ~ M . Les &chantillons ont EtE recuits 2 des temp6ratures comprises e n t r e -Z°C e t -16°C.
Les rdsultats montrent que l a croissance e s t plus rapide dans l a glace dop'ee a v e c certains constituants. C e comportement doit % r e e n rapport a v e c la s t r u c t u r e e t la mobilitd des joints d e grains.
ABSTRACT. Grain growth experiments were carried out using cylindrical i c e samples grown from pure w a t e r and from w a t e r solutions of NaCl, N H 4 0 H and HF. Solute concentrations were varied from 10" M t o ~ o ' ~ M and annealing was performed within t h e range -2°C t o -16°C.
The results obtained show t h a t t h e grain growth r a t e is increased when solutes a r e added t o ice. This behaviour may b e related t o changes in grain boundary s t r u c t u r e and mobility.
1. Introduccion
T h e grain growth process is a useful tool for studying t h e average grain boundary migration behaviour. Several papers (1-5) have been written about grain growth in ice, describing t h e process in polycrystalline samples of pure i c e prepared in t h e laboratory.
However, l i t t l e attention has been paid t o t h e e f f e c t s of impurities on boundary migration. Jellinek and Gouda (3) made some experiments with thin i c e sheets doped with l o e 2 M of NaCl. They found t h a t under -lO.S°C t h e grain growth r a t e was below t h a t of pure ice, while t h e contraty was t r u e for temperatures above -10.5"C.
On t h e o t h e r hand, t h e r e i s a n extensive literature on grain boundary migration on doped metals and alloys, both theoretical and experimental. In fact, many theories (6,7) developed for grain boundary migration in metals, show t h a t d r a m a t i c changes should occur in grain boundary migration if small quantities of solutes a r e present.
This has also been experimentally demonstrated (see for example Chalmers e t a1.(8)) In general, grain boundary migration is slowed down a s a result of t h e impurity drag.
Recently, Ceppi (9) has shown t h a t grain boundary migration in i c e is also a f f e c t e d by t h e presence of solutes, but in a different way with respect t o metals.
Solutes like H F o r NH40H tend t o speed up boundary migration.
T h e present work is an experimental study of grain growth in i c e samples doped with NaCI, NH40H and HF. Its principal aims a r e t o describe and discuss t h e problem of boundary-solute interactions in ice.
2. Experimental procedures and d a t a elaboration
The samples were grown following a similar technique reported by Levi and Ceppi (4). Water solutions were made t o f r e e z e rapidly, inside cylindrical tubes 28cm long and l c m radius, immersed in a cold b a t h a t -25°C. In most samples, t h e tube was mede t o spin around i t s axis while freezing, in order t o improve heat transport t o t h e bath.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987140
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Solutions were prepared with quartz double distilled w a t e r with t h e following solutes and concentrations:
i. NaCl : ~ O I ~ M , 10-:M and
ii. NH,OH : 10 M, 10- M and ~ o - ~ M iii. & : 1 0 - ' ~ , I O - ~ M and ~ o - ~ M
T h e i c e rods w e r e c u t into two pieces about 4.5 c m long, a f t e r discarding two 5 cn long pieces from t h e ends of t h e cylinders due t o inhomogeneities in crystalline structure. Then, disks 0.5 c n thick w e r e c u t a t t h e ends of e a c h sample, in order t o control t h e sample homogeneity. This also provided t h e initial conditions. T h e remaining p a r t was wrapped with paraffin film t o prevent evaporation and placed inside thermo- s t a t i z e d containers.
T h e crystalline evolution was monitored by cutting, a t predetermined intervals o f time, small disks from t h e sample which was being annealed. The. t e m p e r a t u r e was recorded using thermocouples.
The analysis of t h e disks was made by using t h e usual replica technique and by photographing thin sheets under natural light and between crossed polarizers.
Fig. 1: Photograph of a thin section of a n a s grown cylindrical sample (10-I M NH40H).
(a) transniited light (b) between crossed polarizers (x3).
As is shown in Fig. l a , small bubbles, determining some i c e opacity, w e r e always present in t h e samples, sometimes forming concentric rings c e n t e r e d a t t h e cylinder axis. The example of Fig. l b shows t h a t t h e samples w e r e composed by crystals elongated in t h e radial direction with a preferential orientation, revealed by t h e dark cross. T h e mean orientation measured was with t h e "c" axis nearly normal t o t h e radial direction.
The large lengthlwidth ratio of t h e crystals makes t h e width a n interesting parameter t o evaluate t h e changes due t o annealing. As a m a t t e r of f a c t , w e measur- e d t h e mean crystal width w a t a distance of 0.5 c m from t h e cylinder axis.
Since t h e presence of bubbles could a f f e c t t h e boundary migration (4), w e used
t h e following expression t o approximate t h e grain growth kinetics:
by Burke (10) c o r r e c t e d a s suggested by Nasello and Ceppi (11).
Experimental d a t a w e r e f i t t e d with exmession (1) by using t h e simplex non-linear least square z ~ e t h o d (12).
3. Results
It i s convenient for t h e description of t h e experimental results, t o show t h e ~ i separately according t o t h e doping solute used.
3.1. P u r e I c e
In order t o obtain a reference t o discuss .the results with doped ice, some anneal- ing experiments were performed using i c e grown from quartz double distilled water.
Fig. 2: Evaluation of t h e mean crystal width w in t h e
samples of pure ice: (+) -2OC, (0 -6OC and (0) -16°C.
Fig. 2 shows t h e experimental points of w vs. annealing t i m e t for t h r e e tempera- tures: -2"C, -6°C and -16°C. The curve drawn across t h e points is t h e best fit obtained by using expresion (1). I t i s interesting t o note t h a t t h e slope of each curve a t t = 0 is different being higher for higher temperature. This behaviour is evidenced by t h e Arrhenius plot of K in Fig. 3, where t h e values of ln(K) a r e nearly aligned on a straight line with activation energy of (2.1 + O.l)eV and a value of K a t 0°C equal t o (1.1 5 0.2) x low3 mm2/h.
3.2. NaCl doped i c e
Fig. 4 shows a n Arrhenius plot for the values of K for t h e three concentrations used. I t may be seen t h a t all t h e points a r e above t h e straight line obtained for pure ice, indicating a higher r a t e of grain growth. a t t h e s a m e temperature. As t h e r e a r e no significant differences from one concentration t o another, only one best f i t curve has been drawn.
The activation energy obtained with the best f i t is (1.2 5 0.2) eV and t h e ordinate a t 0°C corresponds t o a value of (1.4 0.2) x mm2/h.
3.3 NH OH doped i c e
In this c a s e a s in t h e NaCl case, no concentration dependence is observed. In fact, t h e Arrhenius plot of Fig.5 shows t h a t all the points a r e nearly along t h e straight line of (0.9 5 0.2) eV of activation energy and (2.2 0.7) x mm2/h a s the value of K a t 0°C.
However, t h e values of K a r e generally higher than those of NaCl and always
higher than those of pure ice.
Cl-286 JOURNAL DE PHYSIQUE
3.4. !-IF doped ice
Fig.6 shows a n Arrhenius plot for t h e values of K found from t h e e::peri-- . f . e ~ ~ t ~ with HF. There is a high s c a t t e r of points here, showing no apparent trend. The scatterring is probably due t o t h e irregular shape of t h e crystals present in t h e samples which made difficult t h e measurements.
Fig. 3: Arrhenius piot of K vs. 1000/T for Fig. 4: Arrhenius plot of .< vs 1000/T for
pure ice. NaC1: (0) lG-2M; (0)lO-"M; (-:-)10-'~i4.
Fig. 5: Arrhenius plot of K vs 1000/T f o r Fig. 6: Arrhenius plot of K vs 1000/T for
NH OH: (~)10-' M; (u) 1Oq2M; (9) 1Om3M. HF: (A) 10'1 M; (0) ~ o - ~ M ; (0) ~ o - ~ M .
in one of t h e fastest samples a t -2"C, t h e mean width w increased from 0.19 mm a t t = 0 h t o 0.68 mm a t t = 23 h, while a t t h e s a m e temperature, with pure ice, w increased from 0.18 rnm a t t = 0 h t o 0.23 rnm a t t = 22 h.
4. Discussion
The results given in t h e last section show t h a t t h e addition of solutes t o i c e leads t o a n increase of the grain growth rate.
This behaviour is different from t h a t expected for metals where, in general, t h e impurities slow down t h e grain growth rate. As shown by t h e theories of Cahn (6) and Hillert (7), t h e e f f e c t of solutes is t o reduce the e f f e c t i v e driving force because of t h e impurity drag. In fact, if Po is t h e driving force and p (X) is t h e solute density a t a distance x from t h e boundary, the e f f e c t i v e driving f o r c e P is, according to Cahn:
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