Melting-Point Depression of Water in Sorbed State

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S t u d i e s of water i n a l l i t s phases c o n s t i t u t e an important p a r t of t h e l a b o r a t o r y s t u d i e s of t h e D i v i s i o n of B u i l d i n g Research. So important i s t h i s work t h a t a small group w i t h i n t h e B u i l d i n g l t l a t e r i a l s S e c t i o n of t h e D i v i s i o n i s d e v o t i n g a l l i t s time t o t h i s one s u b j e c t ,

t h e r e s u l t s of t h i s work being a p p l i c a b l e t o more prac- t i c a l s t u d i e s of v a r i o u s b u i l d i n g m a t e r i a l s .

T h i s t r a n s l a t i o n d e s c r i b e s solre s i g n i f i c a n t work in r e l a t i o n t o t h e d e p r e s s i o n of t h e f r e e z i n g - p o i n t of water when adsorbed i n v a r i o u s m a t e r i a l s . Piany s t u d i e s have been made of t h i s s u b j e c t with t h e o b j e c t of r e l a t i n g t h e e f f e c t of pore s t r u c t u r e t o t h e phenomenon. In t h i s work t h e d e p r e s s i o n of t h e melting-point of water adsorbed s i l i c i c a c i d g e l , pernlulite and i o n exchange r e s i n

IR-45

w a s i n v e s t i g a t e d with a d i f f e r e n t i a l c a l o r i m e t e r . The s i g n i f i c a n t r e s u l t s o b t a i n e d a r e thought t o be of i n t e r e s t n o t o n l y t o workers i n t h i s D i v i s i o n b u t t o o t h e r s concerned with t h i s i ~ n p o r t a n t a s p e c t of t h e p r o p e r t i e s of water. The t r a n s l a t i o n i s , t h e r e f o r e , p u b l i s h e d by t h e D i v i s i o n i n i t s r e g u l a r s e r i e s as a f u r t h e r c o n t r i b u t i o n t o b u i l d i n g s c i e n c e i n Canada. O t t a w a R.F. Legget February 1962 D i r e c t o r

NATIONAL RESEARCH C O U N C I L OF CANADA

T e c h n i c a l T r a n s l a t i o n 1010

T i t l e : The m e l t i n g - p o i n t d e p r e s s i o n of w a t e r i n sorbed s t a t e

Author:

Y e

I w a k m i

Reference : J. Chem. Soc. Japan, Pure Chem. Set, ( ~ ~ i p p o n Kagaku Z a s s h i ) ,

80

( 1 0 ) : 1094-1097,

1959

TIIE IJELTING-POZ\IT DEPRESS I O N OF l.JAPITEI'I

IN

SORBED STATE The a u t h o r h a s r e p o r t e d on s e v e r a l occasions t h a t t h e f a c t o r s c o n t r o l l i n g t h e d e p r e s s i o n of t h e melting-point of adsorbed m a t e r i a l a r e t h e pore s i z e d i s t r i b u t i o n , t h e n a t u r e and t h e q u a n t i t y of m a t e r i a l adsorbed. The o b j e c t of t h e p r e s e n t e x p e r i - ments w a s t o i n v e s t i g a t e t h e changes i n t h e melting-point o f t h e a d s o r b a t e when t h e adsorbent was s u b j e c t e d t o r a d i o a c t i v e r a y s which cause changes i n t h e c o n d i t i o n s of i t s s u r f a c e .

A s a d s o r b a t e , water w a s used, t h e adsorbent being s l l i c i c a c i d g e l , pernlutite, and i o n exchange r e s i n a m b e r l i t e IR-45. A s t h e source of r a d i o a c t i v e r a y s c o b a l t 60 was used. Water w a s adsorbed by exposed and unexposed m a t e r i a l , and t h e melting-point of water

i n t h e adsorbed s t a t e w a s measured by a d i f f e r e n t i a l c a l o r i m e t e r . The r e s u l t s d f f f e r e d depending on t h e adsorbent. However, t h e

experimental v a l u e s showed good agreement with t h e t h e o r e t i c a l ones, which were obtained u s i n g our e q u a t i o n r e l a t i n g t h e d e p r e s s i o n of t h e melting-point of water t o t h e s i z e of t h e pore and t h e amount of adsorbed water.

1. I n t r o d u c t i o n

S i l i c i c a c i d g e l , p e r m u t i t e and i o n exchange r e s i n arnberlite IR-45 a r e a l l good adsorbents; v~hen water 1 3 adsorbed t h e phenomenon of d e p r e s s i o n of t h e melting-point of water can be observed.

However, t h e e x t e n t of d e p r e s s i o n depends on t h e pore s i z e d i s t r i b u - t i o n of t h e adsorbent. Thus, i f changes a r e introduced i n t h e pore s i z e d i s t r i b u t i o n of t h e s e c a p i l l a r i e s by sorne rneans, i t seer113 reasonable t o assume t h a t t h e r e w i l l be a change i n t h e melting- p o i n t of water adsorbcd by t h e adsorbent. The p r e s e n t r e p o r t i s

concerned with t h e melting-point of water i n t h e adsorbed s t a t e ~~11ich vras rrleasured by means of a d i f f e r e n t i a l calorirrietcr. S i l i c i c a c i d g e l , perniutite and i o n exchange r e s i n a m b e r l i t e IK-45 were

exposed n i a t e r i a l werc cor~lpared t o t h o s e from unexposed m a t e r i a l .

Comnlercially a v a i l a b l e s i l i c i c a c i d g e l , p e r m u t i t e and amber- l i t e IR-45 were d r i e d i n a n a i r d r y e r a t

l l o O ,

130° and go0 f o r approximately

6

_{hours, r e s p e c t i v e l y . They were t h e n s e a l e d i n} s e v e r a l g l a s s t u b e s and used as une,qosed n ~ a t e r i a l . Sonie of t h e s e t u b e s were placed n e a r a s o u r c e of c o b a l t 60 i n s e a l e d g l a s s t u b e s and were exposed t o t h e ganlrna r a y s f o r 48 h o u r s a t 10000 r-unit/min. T h i s w a s used as exposed m a t e r i a l .

For t h e exposed and unexposed n l a t e r i a l t h u s p r e p a r e d a d s o r p t i o n isotherrns a t O°C were o b t a i n e d u s i n g benzene a d s o r b a t e . From t h e s e i s o t h e r m s t h e p o r e s i z e d i s t r i b u t i o n f o r each a d s o r b e n t w a s c a l c u - l a t e d . These a r e shown i n F i g . 1 t o

3.

In F i g . 1, t h e maximum p o i n t s show good agreement i n exposed and unexposed c a s e s ; however, t h e r e a r e d i s c r e p a n c i e s i n o t h e r

p a r t s . In F i g . 2, t h e r e i s a s m a l l d i s c r e p a n c y even a t t h e maxinlum p o i n t s . I n F i g .

3,

one n o t e s a marked i n f l u e n c e a t t h e maxirnun~ p o i n t due t o exposure. It a p p e a r s r e a s o n a b l e t o assume t h a t t h e r e

w i l l b e a d i f f e r e n c e i n m e l t i n g - p o i n t s i f a s u b s t a n c e i s adsorbed by unexposed and exposed m a t e r i a l w l t h d i f f e r e n t p o r e s i z e d i s t r i b u -

t i o n even i f t h e a d s o r b a t e i s t h e same and i s adsorbed i n e q u a l amounts. Thus, a p p r o x i ~ n a t e l y a n e q u a l amount of water was allowed

t o be adsorbed by unexposed and exposed a d s o r b e n t s , and t h e melting- p o i n t of t h i s w a t e r w a s measured by means of a d i f f e r e n t i a l

c a l o r i m e t e r . The s t r u c t u r e of t h e c a l o r i m e t e r which vias used i n t h e p r e s e n t experiments i s shown i n F i g . 4.

A and B a r e b o t h v e s s e l s made of copper; t h e upper p o r t i o n s a r e connected by f u s e d g l a s s c a p i l l a r i e s . Equal amounts of a d s o r - b e n t a r e i n t r o d u c e d i n t o t h e s e c o n t a i n e r s , A and B, through C and D. A f t e r i n s e r t i n g thermocouples 11: and F', as shown i n t h e f i g u r e , t h e y a r e evacuated through G, IT and I. IText, s i l i c i c a c i d g e l , p c r r ~ l u t i t e and m l b e r l l t e II-i-45 were h e a t e d t o 1 1 0 ~ C , 130°C and 30°C, r e s p e c -

approximately 6 hours t o a hlgh vacuum, A f t e r b e i n g r e s t o r e d t o room temperature, a c o o l i n g a g e n t of a mixture of d r y i c e and

methanol w a s introduced i n t o t h e Dewarts v e s s e l , K, t h e c a l o r i m e t e r w a s cooled from o u t s i d e , and t h e temperature i n s i d e A and B was lowered t o approximately -60°C. The t e s t m a t e r i a l i n s i d e A and B

w a s heated by means o f h e a t e r J, m a i n t a i n i n g a d i f f e r e n c e i n temper- a t u r e between A, B and t h e h e a t e r J as c l o s e as p o s s i b l e t o 3OC. No. 0 i n Fig. 5-7 shows t h e d i f f e r e n c e between t h e temperatures of v e s s e l s A and B, i . e . t h e d i f f e r e n t i a l temperature corresponding t o t h e temperature o f e i t h e r A o r B. Next, a known q u a n t i t y of water i s allowed t o be adsorbed by t h e adsorbent i n e i t h e r A o r B. The system

i s

then cooled t o approximately -60°C and heated i n t h e same way as before. T h i s g i v e s t h e d i f f e r e n t i a l temperature curve No. 1.

The temperature a t t h e maximum of t h i s curve i s t h e m e l t i n g - p o i n t of water In t h e adsorbed s t a t e . S i m i l a r procedures were r e p e a t e d with d i f f e r e n t amounts of water. The r e s u l t s a r e curves No. 2 and No.

3 ,

3.

R e s u l t s and Discussion

Fig.

5

( 1 ) and ( 2 ) resemble each o t h e r except f o r curve No. 1.

T h i s shows t h a t t h e r e i s h a r d l y any e f f e c t due t o exposure. F i g .

6

( 1 ) and ( 2 ) show t h a t t h e maximum p o i n t s h i f t s t o t h e l e f t due t o exposure. I n Fig. 7 ( 1 ) and ( 2 ) t h e m a x i m u m p o i n t s h i f t s t o t h e r i g h t due t o exposure and t h e s l o p e of t h e curves i n c r e a s e s . This could i n d i c a t e p o s s i b l y a change i n t h e p o r e s i z e d i s t r i b u t i o n due t o exposure keeping i n mind t h a t t h e melting-point of adsorbed water

i s lowered with t h e d e c r e a s e In t h e r a d i u s of t h e c a p i l l a r i e s , However, i n t h e p r e s e n t paper, i n o r d e r t o t r e a t t h e phenomenon i n

a q u a n t i t a t i v e way, t h e curve r e l a t i n g

r2

A q / A r and r, i . e . t h e r e l a t i o n between t h e amount melted and r a d i u s , w a s o b t a i n e d as i n t h e previous r e p o r t s (2-4). These a r e shown i n Fig.

8-10.

I n t h e c a s e of s i l i c i c a c i d g e l In Fig.

8,

t h e maximum p o i n t appears a t t h e same p l a c e i n exposed and unexposed m a t e r i a l ; t h e curves a r e

similar. Thus, i t resembles Fig.

5

( 1 ) and ( 2 ) . I n t h e c a s e of perrnutite i n Fig. 9, t h e maximum p o i n t , which e x i s t s i n t h e c a s e of

unexposed m a t e r i a l , d i s a p p e a r s with exposure. Thus, t h i s means

t h a t t h e maximum p o i n t i n Fig.

6

( 2 ) c o n t i n u e s t o s h i f t t o t h e l e f t . I n t h e case of a m b e r l i t e IR-45 i n Fig. 10, t h e maximum p o i n t be- comes marlcely h i g h e r due t o exposure and a t t h e same time s h i f t s i n t h e d i r e c t i o n i n which

r

d e c r e a s e s . On t h e b a s i s of t h i s t h e i n c r e a s e i n s l o p e and t h e s h i f t i n g of t h e maximum p o i n t t o t h e r i g h t i n Fig.

7

( 2 ) can be explained. Since t h e r e has been a

change in t h e r e l a t i o n between r 2

.

A a / ~ r and r due t o exposure, as w a s sl~own above, t h e o r e t i c a l v a l u e s of t h e melting-point based on

t h e e q u a t i o n r e l a t i n g t h e d e p r e s s i o n . i n melting-point ( A T ) t o t h e amount adsorbed ( a ) were c a l c u l a t e d i n t h e same way as shown i n p r e v i o u s r e p o r t s . These were compared with experimental v a l u e s and

shown in Table I. It i s observed t h a t t h e r e i s a good agreement between t h e experimental v a l u e s and t h e t h e o r e t i c a l values. The r a d i u s , r, shown i n t h e t a b l e i s t h e one trhich has been used i n c a l c u l a t i n g t h e melting-points and corresponds t o t h e maximum amount of water melted. With d i f f e r e n t amounts of adsorbed water t h e melting-point a l s o changes. T h i s i s e v i d e n t i n t h e t a b l e .

F u r t h e r , t h e t a b l e shows t h a t , even i n t h e same adsorbent, t h e r e i s

a marked change i n melting-point even f o r t h e same adsorbed amount depending on whether t h e adsorbent had been exposed t o ganma r a y s o r not. The f a c t t h a t t h e r e i s a good agreement between t h e theo- r e t i c a l v a l u e s t h u s o b t a i n e d and observed v a l u e s means t h a t i t i s p o s s i b l e t o e x p l a i n t h e change in melting-point with r e s p e c t t o each adsorbent by t h e a p p l i c a t i o n of t h e melting-point d e p r e s s i o n equation, t a k i n g i n t o account t h e pore s i z e d i s t r i b u t i o n of t h e adsorbent both i n exposed and unexposed cases. It can a l s o be s a i d t h a t t h e above experimental evidence confirms t h e melting-point

d e p r e s s i o n e q u a t i o n mentioned i n p r e v i o u s r e p o r t s based on t h e t h e o r y of c a p i l l a r y condensation.

The a u t h o r wishes t o e x p r e s s h i s a p p r e c i a t i o n t o D r . Masaichiro S a i t o f o r h i s generous a s s i s t a n c e .

References

1. Ivrakan~i. Nikka,

72: 259, 1951.

2 . Iwakanli. Nikka,

72: 707, 1-351.

3 .

Iwakami.

N i k k a ,

77: 1499, 1956.

4.

I~iakami. ?!?.kka,

79: 610, 1958.

5. Spalayis,

C . N . ,

Bupp,

L.P.,

Gflbert,

E.C. J. Phys.

Chem. 61:

Table I

0 0 0 1

1To. 2

No. 3

Unexposed H a t e r i a l Exposed Piaterial

Adsorbed Radius r n.p. m.p.

a obs. theor.

m

d

~

_'A

o

c

o

c

Adsorbed R a d i u s r m.p. m.p.

amt. a obs. theor.

m d g

II

o

c

o

c

S i l i c i c Acid Gel Permutite S i l i c i c Acid Gel 0 4 c 8 0 0 398 -37.0 -36.1 512 47.4 -32.5 -31.8 920 49.0 -31.0 -30.5 I

SD

Permut i t e Amberlite IR-45

,-

(A) o: unexposed X: exposed F i g . 1 S i l i c i c a c i d g e l 4 0

3

--.

E"

-

+.

20 P \ C) P @O ;10 40 60 80 r (A) o: unexposed X : exposed Fig.

3

Arnberlite

IR-45

r ( A )

o:

unexposed x : exposed F i g . 2 P e r m u t i t e Fig.

4

Temperature ( O C ) S i l i c i c a c i d g e l ( ~ n e ~ x p o s e d ) Temperature ( O C ) S i l i c i c a c i d g e l ( e x p o s e d ) 1.0

-

_u 0

-

0 8 rl cd 0.6 -P E: 0.4 Q) 6-4

2

0.2

c

l

0 - I 0 -70 -30 -40 -50 Temperature ( O C ) P e r m u t i t e (unexposed) Temperature ( O C ) F i g .

6

( 2 ) P e r m u t i t e ( e x p o s e d )

Temperature ( O C ) Fig. 7 (1) Amberlite

W-45

(unexposed) r ( A ) o: unexposed x: exyosed F i g .

8

S i l i c i c a c i d g e l Temperature (

"

C ) Fig. 7 (2.) Amberlite IR-45 (exposed ) fl ( A ) o: unexposed x: exposed Fig.

9

Pernlut i t e

r (A)

0 : unexposed x: exposed

F i g . 10 A m b e r l i t e

IR-45