PHASE TRANSITIONS OF ICE V AND VI

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PHASE TRANSITIONS OF ICE V AND VI

Y. Handa, D. Klug, E. Whalley

To cite this version:

Y. Handa, D. Klug, E. Whalley. PHASE TRANSITIONS OF ICE V AND VI. Journal de Physique Colloques, 1987, 48 (C1), pp.C1-435-C1-440. �10.1051/jphyscol:1987160�. �jpa-00226306�

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PHASE TRANSITIONS OF ICE V AND VI

Y . P . HANDA, D . D . KLUG and E . WHALLEY

Division of Chemistry, National Research Council of Canada.

Ottawa, Ontario, KIA OR9, Canada

&6sd

-

^Lestransitions de phase de la glace V et VI dans le domaine 90-175 K cnt

6~ CtudiCes par cdlorh5trie. Les transitions dans le domaine 105-140 K qui sont semblables B des transitions ordredsordre, ont Qt6 identifiks. Les variations d'enthalpie de celles-i ainsi que les transformations des glaces V et VI en glace I, plus hautes t e r a t u r e s cnt 6th &termi&es.

Abstract

-

Phase transitions of ice V and VI in the range 90-175 K have been investigated by heat-flow calorimetry. Transitions in the range 105-140 K, which are likely order-disorder, have been identified and enthalpy changes of these and the transformations of ice V and VI to ice Ic at higher temperatures have been determined.

Introduction

All known crystalline phases of ice stable below %0.5 Hbar consist of hydrogen- bonded networks of distinct water molecules. Each water molecule is hydrogen bonded to four neighboring water molecules in tetrahedral geometry. At high temperatures all phases except ice I1 are orientationally disordered and the maximum number of configurations per molecule, as implied by the well known ice rules, is -1.5. Upon cooling, ice Ih [I] doped with potassium hydroxide, I11 [2,3], and VII [4] undergo order-disorder transitions to acquire partial or nearly complete order. In addition, all phases except ice Ih transform to ice Ic when heated from 77 K at ambient pressure. A reversible order-disorder transformation in ice V in the range 105

-

¹³⁰^Khas been reported in an abstract [5] and partly ordered ice V and VI have been recognized by neutron diffraction at 110 K [ 6 , 7 ] . Diffraction methods will, of course tell the structure of a particular sample, but not the course of the ordering unless extensive measurements are made. The course of the ordering can be readily followed by calorimetry, and so this paper reports the calorimetry of ice V and VI in the region of the order-disorder transitions and of the transformation to ice Ic. The ordering transitions are sometimes very slow, and so, following Tajima et al. [1,8], samples of ice V and VI doped with potassium hydroxide also have been studied.

Ex~erimental Methods

Samples of %2.4 g of either distilled water or a 0.1 mol dm-' potassium hydroxide solution prepared from potassium hydroxide free of carbon dioxide (J.T. Baker Chemical Co.) were held in closed indium cups. Each sample was frozen in its cup at one bar in about 10 min in a freezer held at 240 K, transferred to a piston-cylinder device, cooled with an alcohol bath, and pressurized to prepare ice V while

monitoring the piston displacement with a dial gauge [9,10]. Each sample was held in the region of stability of ice V for 30 min, quenched under pressure in -10 min to 77 K with liquid nitrogen, and recovered in its indium cup.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987160

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JOURNAL DE PHY.SIQUE

Pure and potassium-hydroxide-doped samples of ice VI were prepared from ice V by pressurizing to 7.5 kbar Ill]. They were held in the region of stability of ice VI for 30 min and quenched and recovered at 77 K.

Each sample in its indium cup was transferred to an automated Tian-Calvet heat-flow calorimeter (Setaram model BT) [12] which had previously been cooled to 77 K, and was annealed at various temperatures in the range 103

-

¹²⁰^K. ^Each

sample was then cooled t o 77 K and heated at the rate of 10 K h-' through the phase transitions described below. The heat capacity and the transition enthalpies were obtained as previously described 112). T o calculate the transition enthalpies, the baselines were drawn parallel to the heat capacity of ice I and passing through the experimental points outside the high- or low-temperature ends of the transitions, as shown in Figs. 1 and 3.

30 40 tlh

Figure 1. Heat capacity of ice V in Figure 2. Transition enthalpy, AH, the range 85

-

175 K when doped with for undoped samples (open circles) potassium hydroxide (upper curve) and a doped sample (closed circle) of and undoped (lower curve). The upper ice V as a function of annealing time.

curve has been translated parallel to "zero-time" results are for samples the C axis by +5 J mol-' K-'. The cooled in the calorimeter from 132 K baselynes are drawn parallel to the to 78 K in 3 h.

heat capacity of ice I.

Transition entropies, AS, were obtained from the integral over the transition region,

A C ~ AS = d T ,

where T is the sample temperature and AC is the heat capacity increment above the

baseline. P

Results

Two phase transitions occurred in ice V in the range 106

-

¹⁶⁰^K. Typical plots of the heat capacity versus sample temperature are shown in Fig. 1. There is an endothermic transition in the range 106

-

132 K, which has been identified calorimetrically for the first time. The transition occurs in two regions, a principal peak in which most of the heat is absorbed, and a tail, possibly caused by a slower process, in which the rest of the heat is absorbed.

The effect of potassium hydroxide is to decrease the width and to increase the height of the 106

-

¹³²^Kpeak. The transition is not first order as is indicated

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in the range 140

-

¹⁵⁶^Kis from ice V to ice Ic [lo]. An undoped sample of ice V

was annealed for various times in the range 0

-

60 h at 111 K and was heated from 77 K through the first transition. The heat absorbed, AH, is plotted versus the annealing time in Fig. 2. It fits well a first-order kinetic relation of the form

with a relaxation time, T , of 18 h, and an asymptotic AH at t = -, denoted by AHN, of 110 J mol-'. t is the effective annealing time of a sample cooled in the calorimeter throug[: the transition region in 3 h. This yields a AHo at t = 0 of 15 J mol-', as shown in Fig. 2.

Potassium-hydroxide-doped ice V yielded AH = 89 J mol-' after the sample was cooled in 3 h from 132 K to 77 K in the calorimeter. This is only -20 percent less than the AH of 106 J mol-' obtained after annealing an undoped sample for 60 h, which demonstrates that doping greatly increases the transition rate. The transition enthalpy obtained after annealing a doped sample for 30 h at 108 K was 229 J mol-', which is 2.2 times larger than obtained for the undoped sample annealed for 60 h and 2.1 times larger than the apparent asymptotic value of 110 J mol-' for the undoped sample in Fig. 2. The kinetics varied from sample to sample for undoped samples in a manner similar to that reported for ice Ih [8] and the AH obtained after long annealing times also varied by -20 percent. The error of the enthalpies and entropies of the endothermic transitions is estimated as +5%. In addition, an error could occur due to the placement of the baseline or to variation in kinetics from sample to sample [8].

The enthalpy change of the large exothermic transition that occurred over the temperature range 130

-

¹⁵⁸^K^{was -915}²⁵^Jmol-' and was independent of sample doping, and is in general agreement with the somewhat less precise value of -1100

+

²⁰⁰^Jmol-' [lo] reported previously.

There were two phase transitions in ice VI in the range 120

-

¹⁵³^K,as is shown in Fig. 3. The enthalpy change for the weak endothermic transition in the range 120

-

¹⁴¹^K^{was 115}^Jmol-' and did not change when the annealing time was doubled from 6 to 12 h or when the sample was doped with potassium hydroxide. The

transition in the range 141 - ¹⁵³K is from ice VI to ice Ic [Ill and the transition enthalpy is -1404 + ²⁰J mol-1, in agreement with the value reported earlier of

1200 f 200 J mol-l [ 1 1 1 and about an order of magnitude more precise.

Figure 3. Heat capacity of ice VI in the range 85

-

¹⁷⁵^K. The baseline is drawn parallel to the heat capacity of ice I.

2 ff

H a

Figure 4. Structure of ice V shown in projection along the b axis. The occupation parameters are consistent with A2/a symmetry and the ice rules.

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D i s c u s s i o n

O r i e n t a t i o n a l l y d i s o r d e r e d i c e V belongs t o t h e s p a c e group A2/a [ I 3 1 and i t s s t r u c t u r e i s drawn i n F i g . 4. A l a r g e amount of p r o t o n o r d e r i s a l l o w e d u n d e r t h i s s p a c e group and t h e n e u t r o n - d i f f r a c t i o n r e s u l t s a t 110 K of Hamilton e t a l . [ 6 ] i n d i c a t e t h a t t h e 0 2

--

^{0 3}-- 02 c h a i n s a r e a l m o s t t o t a l l y o r d e r e d , and t h e 0 4

--

⁰⁴

c h a i n s a r e t o t a l l y d i s o r d e r e d . The o t h e r oxygen-oxygen bonds a r e s l i g h t l y o r d e r e d . The o r d e r can be d e s c r i b e d by a s e t of p a r a m e t e r s which is d e t e r m i n e d by t h e symmetry [ I n p r e p a r a t i o n ] and a r e shown i n Fig. 4. The i c e r u l e s r e q u i r e t h a t a l

-

^{a 2}⁼B1 - B2, and t h e r e p o r t e d o c c u p a n c i e s [61 r e q u i r e t h a t a l = a2 and ₌B2 w i t h i n t h e e x p e r i m e n t a l u n c e r t a i n t i e s . It is v e r y l i k e l y t h a t t h e e n d o t h e r m i c t r a n s i t i o n we o b s e r v e d is due t o p r o t o n d i s o r d e r i n g . The t r a n s i t i o n e n t r o p y f o r a n undoped sample a n n e a l e d f o r 60 h a t 110 K was 0.84 J mol-l K-l. The t r a n s i t i o n e n t r o p y f o r t h e sample i n v e s t i g a t e d by n e u t r o n d i f f r a c t i o n [61, a s c a l c u l a t e d u s i n g t h e r e l a t i o n proposed by Nagle [ 1 4 ] , i s 0.8 i 0.1 J mol-l K-l i f i t is assumed t h a t i c e V a t h i g h t e m p e r a t u r e s i s f u l l y d i s o r d e r e d w i t h i n t h e i c e r u l e s . T h i s s u g g e s t s t h a t o u r undoped sample h a s undergone t h e same o r d e r i n g p r o c e s s a s r e p o r t e d by Hamilton e t a l . , where t h e 0 2 -- 0 3

--

02 c h a i n s a r e a l m o s t f u l l y o r d e r e d and t h e o t h e r oxygen-oxygen c h a i n s a r e o n l y s l i g h t l y o r d e r e d o r remain f u l l y d i s o r d e r e d . On doping, AS i n c r e a s e s t o 1.9 -+ 0.1 J mol-l K - ~ , which i s 56 % of t h e maximum

c o n f i g u r a t i o n a l e n t r o p y change a l l o w e d . Doping t h u s i n c r e a s e s AS by 126 % and i m p l i e s t h e r e i s a d d i t i o n a l o r d e r i n g a l o n g t h e oxygen-oxygen chains. Kamb and La P l a c a [S] have claimed t h a t i c e V t r a n s f o r m s t o t h e s p a c e group Pz1/a, but a l l c o n f i g u r a t i o n a l e n t r o p y can be l o s t i n t h e s p a c e group A2/a, and s o c a l o r i m e t r y cannot c o n f i r m t h e o r d e r i n g t o P21/a. T h i s f o l l o w s s i n c e i f B i n F i g . 4 is e i t h e r z e r o o r one, which c o u l d o c c u r u n d e r A2/a symmetry, t h e n e a c h 64

--

04 c h a i n would be p o l a r i z e d randomly i n e i t h e r of two d i r e c t i o n s . T h i s would c o n t r i b u t e

i n f i n i t e s i m a l l y t o t h e c o n f i g u r a t i o n a l e n t r o p y and would n o t be d e t e c t e d c a l o r i m e t r i c a l l y ( u n p u b l i s h e d ) .

F i g u r e 5. S t r u c t u r e of i c e V I shown i n p r o j e c t i o n a l o n g t h e c a x i s . The p r o t o n - o c c u p a t i o n p a r a m e t e r s a r e f o r t h e s p a c e group Pmmn. For t h e s p a c e group P42/nmc, a = 112.

I c e V I belongs t o t h e s p a c e g r o u p P42/nmc [ 1 5 ] , which i m p l i e s f u l l p r o t o n d i s o r d e r . Its s t r u c t u r e i s shown i n Fig. 5. P a r t i a l p r o t o n o r d e r was found i n samples s t u d i e d a t 110 K by n e u t r o n d i f f r a c t i o n [7], and t h e s p a c e group c o n s i s t e n t w i t h t h e s e r e s u l t s is Pmmn. The p r o t o n o c c u p a n c i e s a l o n g hydrogen bonds can be d e s c r i b e d by a s i n g l e p a r a m e t e r , a , a s shown i n F i g . 5. For t h e s p a c e group P42/nmc, a = 112, and f o r Pmmn, a can t a k e any v a l u e between 0 and 1.

The t r a n s i t i o n e n t r o p y f o r i c e V I i s 0.86 J mol-l K-l and t h e c o r r e s p o n d i n g o r d e r p a r a m e t e r , a , f o r p r o t o n occupancy d e r i v e d from Nagle's e q u a t i o n [ 1 4 ] i s 0.11 which i s t h e same a s t h e v a l u e o b t a i n e d from t h e p r o t o n o c c u p a n c i e s r e p o r t e d by Kamb.

Doping h a s no e f f e c t because r e o r i e n t a t i o n i n i c e V I i s f a s t enough t h a t maximum o r i e n t a t i o n a l o r d e r i s p r o b a b l y a c h i e v e d . The r a t e of o r i e n t a t i o n a l r e l a x a t i o n u n d e r p r e s s u r e i s c o n s i s t e n t w i t h t h i s s u g g e s t i o n [ 161.

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COMMENTS

J . P . DEVLIN

Did you u s e KOH e x c l u s i v e l y a n d i f s o , c a n y o u o r someone e l s e g i v e a r e a s o n a b l e e x p l a n a t i o n why KOH is t h e d o p a n t o f c h o i c e ( o v e r a c i d s , f o r e x a m p l e ) .

Answer :

We h a v e u s e d KOH e x c l u s i v e l y f o r t h e r e a s o n d e s c r i b e d i n t h e p u b l i c a t i o n s o f H. S u g a a n d c o w o r k e r s a n d t o b e d e s c r i b e d a g a i n i n t h e t a l k by T. M a t s u o t h i s a f t e r n o o n .

Remark o f J . DUPUY :

W i t h e l e c t r o l y t i c g l a s s e s by a n n e a l i n g o r c h a n g i n g t h e i o n s we c a n p r o d u c e a n d c o n t r o l e n d o t h e r m a l e v e n t o n DSC n e a r t h e g l a s s t r a n s i t i o n . The n e u t r o n d i f f r a c t i o n

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in connection with this phenomena, could be explained as a formation of a desorderea phase appearing before the ice crystallization.

J. DUPUY

Behaviour of DSC ? The relative importance of exothermic peaks is surprising.

Answer :

We have used a Tian-Calvet heat-flow calorimeter (Setaram Model/B'T) with isoperibal operating conditions. The exothermic transitions for ice V and VI to ice Ic have rather large transition enthalpies of

-

⁹¹⁵^T^{5 J}mol-' and

-

¹⁴⁰⁴^f²⁰^J^mol-l

respectively.

T. MATSUO

Is the order-disorder change reversible ? Answer :

Yes. The exothermic transition which is shown for ice V and VI when an annealed sample is warmed are seen on exothermic transition on cooling. We have also seen the transformation on the same sample after cycling through the 77

-

¹³²^K^{region at}

least five times.