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Synthesis of normal and anomalous tobermorites
CEMENT and CONCRETERESEARCH. Vol. 7, pp. 429-438, 1977. Pergamon Press, Inc Printed in the United States.
SYNTHESIS S.A.S.
OF N O R M A L
EZ-Hemaly*,
AND ANOMALOUS T. M i t s u d a
TOBERMORITES
and H.F.W.
Taylor
D e p a r t m e n t of C h e m i s t r y , U n i v e r s i t y of A b e r d e e n , M e s t o n Walk, 01d A b e r d e e n AB9 2UE, S c o t l a n d , U.K. (S.A.S.F.6-H. & H . F . W . T . ) Materials Research Laboratory, Nagoya Institute G o k i s o - c h o , S h o w a - k u , N a g o y a ~66, J a p a n * P e r m a n e n t address: Laboratory,National
of T e c h n o l o g y , (T.M.)
R e f r a c t o r i e s and B u i l d i n g M a t e r i a l s R e s e a r c h C e n t r e , Dokki, Cairo, Egypt.
(Communicated by J. Skalny) (Received April 28, 1977) AB STRAC T T o b e r m o r i t e s w e r e m a d e from s e v e r a l s t a r t i n g m a t e r i a l s at 105 - 180°C and C a/(Si + A6) 0.8 - 1.0. Reaction gives in s u c c e s s i o n C-S-H, n o r m a l , m i x e d and a n o m a l o u s 'tobermorites, and f i n a l l y x o n o t l i t e . H i g h C / S ratio (1.0), short time, low t e m p e r a t u r e , s t i r r i n g , p r e s e n c e of A6, and if q u a r t z is used, small p a r t i c l e size, all tend to stop it at n o r m a l t o b e r m o r i t e . In some cases, this effect is due to p r o m o t i o n of c r y s t a l g r o w t h of normal tobermorite. Low C / S ratio (0.8), l o n g time, h i g h t e m p e r a t u r e , no s t i r r i n g , p r e s e n c e of A6 plus alkali, and, if q u a r t z is used, l a r g e p a r t i c l e size, all tend to give a n o m a l o u s t o b e r m o r i t e . H o w e v e r , at " 180 ° C this c h a n g e s e a s i l y into x o n o t l i t e if C / S ~0.9.
.
ttC-S-H
",
429
430
Vol. 7, No. 4 S.A.S. EI-Hemaly, T. Mitsuda, H.F.W. Taylor Introduction
Tobermorite is an i m p o r t a n t c o n s t i t u e n t of s o m e k i n d s of a u t o c l a v e d c a l c i u m s i l i c a t e p r o d u c t s , s u c h as a e r a t e d c o n c r e t e s and t h e r m a l i n s u l a t i o n . S p e c i m e n s v a r y in t h e r m a l b e h a v i o u r ; in o n e e x t r e m e type, c a l l e d n o r m a l , l o s s of m o l e c u l a r w a t e r at a b o u t o 3 0 0 ~ c a u s e s a ~ e d u c t i o n in l a y e r t h i c k n e s s f r o m a b o u t 11.3 A to a b o u t 9.5 A, and in the o t h e r , c a l l e d a n o m a l o u s , it d o e s not. T h e c o n d i t i o n s u n d e r w h i c h t h e s e v a r i e $ i e s are f o r m e d h a v e n e v e r b e e n e l u c i d a t e d , t h o u g h it h a s b e e n s u g g e s t e d (1) t h a t n o r m a l t o b e r m o r i t e c a n p r o b a b l y be m a d e by p r o l o n g e d t r e a t m e n t of m i x e s w i t h C / S Ix0 at a b o u t I00°C, and t h a t to m a k e anomalous tobermorite b o t h A 6 3 + and a l k a l i m u s t be p r e s e n t and a C a / ( S i + A6) r a t i o of or b e l o w 0.8 is d e s i r a b l e . T h e aim of the p r e s e n t w o r k w a s to e s t a b l i s h the c o n d i t i o n s of f o r m a t i o n of the n o r m a l a n d a n o m a l o u s v a r i e t i e s . Experimental Starting
Materials
C a 0 w a s m a d e b y h e a t i n g e i t h e r a n a l y t i c a l or r e a g e n t g r a d e C a C 0 3 at 1000 - 1 1 0 0 ° C . T w o q u a r t z s a m p l e s w e r e used, of particle sizes (from sedimentation) b e l o w 10 ~ m and 10 - 20 ~ m respectively; b o t h c o n t a i n e d 9 9 . 9 % Si02. C o l l o i d a l s i l i c a and Y - A 6 2 0 3 w e r e e a c h the s a m e as, or s i m i l a r to s a m p l e s d e s c r i b e d e a r l i e r (1). By-product s i l i c a w a s an a m o r p h o u s m a t e r i a l w i t h 9 4 . 4 % Si02, 5 . 3 % l o s s , t r a c e s of F and NH3, a n d p a r t i c l e s i z e 10 - 15 ~m. Cristobalite w a s m a d e b y h ~ a t i n g this m a t e r i a l f o r 10 m i n at 1 3 0 0 ~ a n d h a d p a r t i c l e s i z e b e l o w 20 ~m. Silica g l a s s h a d 9 9 . 9 4 % S i 0 2 and p a r t i c l e s i z e b e l o w 10 pm. Kaolinite was highly crystalline, natural material. Sodium silicate was a commercial solution with Si02/Na20 3.4. Other starting materials were pure, laboratory preparations. Preparations A l l r e a c t i o n s w e r e d o n e at s a t u r a t e d s t e a m p r e s s u r e . T h o s e in s t i r r e d s u s p e n s i o n s w e r e c a r r i e d out u s i n g a w a t e r / s o l i d s w e i g h t r a t i o of 20 a n d a s t i r r i n g r a t e of 2 0 0 r . p . m . d u r i n g the f i r s t 4 h, a f t e r w h i c h s t i r r i n g w a s s t o p p e d ; for r u n s at 180°C a t i m e of 12 m i n w a s n e e d e d to r e a c h this t e m p erature. T h e p r o d u c t s w e r e f i l t e r e d , w a s h e d , and d r i e d in a v a c u u m at 8 0 ° C . F o r r e a c t i o n s in u n s t i r r e d s u s p e n s i o n s , the solid starting materials were mixed dry by brief grinding followed by mechanical s h a k i n g for 10 min, b e f o r e t r a n s f e r e n c e to the r e a c t i o n v e s s e l . W a t e r w a s t h e n a d d e d to g i v e a water/solids r a t i o of 2, and the s l u r r y b r i e f l y m i x e d b e f o r e sealing. T h e p r o d u c t s w e r e f i l t e r e d , w a s h e d , and d r i e d w i t h e t h a n o l and d i e t h y l e t h e r . Examination
of P r o d u c t s
All products were examined by X-ray powder diffraction, u s i n g e i t h e r a G u i n i e r c a m e r a or a d i f f r a c t o m e t e r . Those containing tobermorite were also similarly examined after b e i n g h e a t e d f o r 20 - 24 h at 300°C, a n d s o m e t i m e s a l s o f o r 20 h at 5 0 0 ° C . S o m e w e r e a l s o e x a m i n e d b y SEM, T E M i n c l u d i n g selected-area diffraction, optical microscopy (to d e t e c t u n r e a c t e d , a m o r p h o u s s i l i c a ) , or n i t r o g e n a d s o r p t i o n u s i n g the BET method for specific surface area determination.
Vol. 7, No. 4
431 NORMAL TOBERMORITE, ANOMALOUSTOBERMORITE, SYNTHESIS Results
Basal
spacings,
Definitions
and
Abbreviations
T h e b a s a l s p a c i n g ~ of the t o b e r m o r i t e s w e r e u s u a l l y b e t w e e n 11.3 and 11.6 A. F o r p r o d u c t s m a d e in s t i r r e d suspensions, the b a s a l ~ p a c i n g s w e r e u s u a l l y 11. 3 - 11.4 A if A6 w a s a b s e n t and 11.6 A f o r A 6 / ( S i + A6) 0.1 ~ these values m a y be c o m p a r e d w i t h t h o s e of 1 1 . 1 8 and 1 1 . 3 5 A f o u n d b y D i a m o n d , W h i t e and D o l c h (2). F o r p r o d u c t s m a d e in u n s t i r r e d s u s p e n s i o n t h e r e w a s l i t t l e or no c o r r e l a t i o n b e t w e e n b a s a l s p a c i n g and A6 c o n t e n t ; similar results have been observed for n a t u r a l t o b e r m o r i t e s (3) a n d f o r t o b e r m o r i t e s m a d e f r o m g e l s (I). T h e p r o d u c t s ar~ d e s c r i b e d as n o r m a l if the b a s a l s p a c i n g s d e c r e a s e d to 10.0 A or l e s s on h e ~ t i n g at 3 0 0 ° C and a n o m a l o u s if it d i d n o t s h r i n k b e l o w 11.0 A u n d e r t h e s e conditions. The term 'mixed tobermorite' is u s e d f o r p r o d u c t s s h o w i n g v a r i o u s k i n d s of i n t e r m e d i a t e b e h a v i o u r , of w h i c h the m o s t u s u a l w a s o a c h a n g e in the b a s a l r e f l e c t i o n to a b r o a d p e a k at a b o u t 10. 5 A at 3 0 0 ° C . A few preparations apparently c o n t a i n i n g b o t h n o r m a l a n d a n o m a l o u s t o b e r m o r i t e in c o m p a r a b l e a m o u n t s are a l s o d e s c r i b e d as m i x e d . T h e r e is an a p p a r e n t l y c o n t i n u o u s g r a d a t i o n in c r y s t a l l i n ity from semi-crystalline C - S - H to c r y s t a l l i n e tobermorite; in reference (I), f o u r c r y s t a l l i n i t y l e v e l s , c a l l e d A - D, w e r e defined. We ~ a l l u s e C - S - H to d e n o t e m a t e r i a l in w h i c h the 3.08 and 2 . 9 8 A l i n e s are u n r e s o l v e d ( l e v e l s A and B), p o o r t o b e r m o r i t e f o r m a t e r i a l in w h i c h t h e r e is i n c i p i e n t r e s o l u t i o n of t h e s e l i n e s ( l e v e l C), and t o b e r m o r i t e f o r m o r e h i g h l y crystalline material ( l e v e l D). L e v e l D w i l l be f u r t h e r s u b d i v i d e d on the b a s i s of the X - r a y p a t t e r n i n t o t h r e e l e v e l s , of w h i c h the l o w e s t ( l e v e l I) g a v e 10 - 15 and the ~ i g h e s t ( l e v e l 3) at l e a s t 25 l i n e s of s p a c i n g d o w n to 1.5 A w i t h the techniques used. Normal, mixed and anomalous tobermorites c o u l d all be o b t a i n e d in a n y of t h e s e l e v e l s of c r y s t a l l i n i t y . I n the t a b l e s a n d in a p p a r e n t d e c r e a s i n g standard abbreviations
f i g u r e s of r e s u l t s , p r o d u c t s are l i s t e d o r d e r of a b u n d a n c e and the f o l l o w i n g n o n are u s e d :
Q = quartz; C = cristobalite; S = by-product silica. T = tobermorite (thermal type not determinable) N,M,A = normal, mixed and anomalous tobermorites respectively. M* = m i x e d b e h a v i o u r at 3 0 0 ° C b u t n o r m a l at 5 0 0 ° C . -A* = a n o m a l o u s b e h a v i o u r at 3 0 0 ° C b u t m i x e d at 5 0 0 ° C Subscript 0 = p o o r t o b e r m o r i t e as d e f i n e d a b o v e . Subscripts I - 3 = higher crystallinity l e v e l s as d e f i n e d a b o v e X = xongtlite. 14T = 14 A t o b e r m o r i t e . Parentheses = trace. Phases
Detected
Fig. I a-c and d-e g i v e the p h a s e s d e t e c t e d in the p r o d u c t s m a d e f r o m C a 0 a n d q u a r t z ( b e l o w 10 pm) in s t i r r e d and unstirred suspensions respectively. Table I gives results for r u n s in s t i r r e d s u s p e n s i o n s at 180°C a n d C a / ( S i + A6) 0.8 w i t h v a r i o u s t y p e s of s t a r t i n g m a t e r i a l , some containing A63+. Table 2 gives results for unstirred suspensions, a l s o at 180°C a n d C a / ( S i + A6) 0.8, u s i n g q u a r t z ( b e l o w 10 ~m) a n d v a r y i n g
432
Vol. 7, No. 4 S.A.S. El-Hemaly, T. Mitsuda, H.F.W. T a y l o r
180°
-- N Q
NrQ)
N~ M
M MX
180c
XA X Xono/hte
N(X) N(X) N(X) X N
\
e
~
140 c
M"
M"
M°
M"
~ 1400
M
;=
Normal
k-
I~O) A"
A"
M
I I 3 7 days
I 2
I l 4 e weeks
\
I s
Time :
I I ~o 20 hours
A.
C/S
I 40
0"8
NormaI
M
N(Q)
,e Time:
Stirred
I
I
2
5
I
I
I
10 20 hours
B.
CIS
40
N
N
I
I
N
3 7 days
0"9
N
N
I
I
2.
4 8 weeks
I
1
16
Stirred
C-S-H + Q N(X) N(X) X(T) X
180°
FIG.
=u ~1400 eo.
N(Q)
N
N
N
NCQ) N
N
N
A(X)~
loo~
I
5 Time :
I
10 20 hours
C.
L
t
40
I
AQ
N
I
I
1
3 7 Clays
2
4 8 weeks
C/S 1"0
AQ
N
I
Phas@s detected using CaO and quartz (below 10 ~m) in stirred (a-c) and unstirred (d-e) suspensions. For key
Normal
E
,ed
Xonotlite
Mixel~ NQ ~
.+
(
to
phases,
see
text.
I
16
Stirred
A AtX
~
i
Xonotlite
~alou$
xonot lile
AnomalOUSAo~ ~14o o
~140°
+i
ACQI ACX)X(A)
I-Normal
,od Time :
MoQ f
i
t
I
I
I
I
I
I
I
z
s
,o
zo
,o
3
T
z
4
8
hours D.
CIS
days 0'8
Unstjrred
NoEO) NCQ)NN N Normal 14T NoQ ÷M N
Mixed MO M(Q)
weeks
I
100°'
f
16
S
Time : E.
I
I
10 20 hours
I
40
CIS 1.0
I
I
I
I
3
7
2
4
days Unstirred
I 8
weeks
I
16
Vol. 7, No. 4
433 NORMAL TOBERMORITE, ANOMALOUSTOBERMORITE, SYNTHESIS TABLE
Phases
Detected
I
in S t i r r e d
Suspensions
C a / ( S i + A6) = 0.8; for aluminous F o r k e y to p h a s e s , see text. Time (h)
Quartz 10-20 ~m
Quartz <10 wm + Y-A6203
C-S-H,
Colloidal silica
mixes,
at
A6(Si
Colloidal silica + Y-A6203
180°C
+ A6)
= 0.1
By-product silica
Cristobalite
2
LQ, C H
Ig-S-H, Q, C H
C-S-H
N
5
TO , Q
N,Q
C-S-H
N
N N N
C-S-H C-S-H T
N N
A. A
M M
N N
A A
M M
(X') X X
96
A, A, A, A,
X
N, ~X)
192
X,
A
N,
10 20 $0
TABLE
[~-S-H, To,
M,C
S
M
X
2
A
/(Si +
P h a s e s D e t e c t e d in U n s t i r r e d S u s p e n s i o n s at 180°C and C a ~ S i + A6) = 0.8, u s i n g Q u a r t z (below 10 ~m) and Y - A g 2 0 3 .
Time (h)
0
0.05
o.1o
0.15
4
AI, Q
A I,q
A2,q
A2, Q
For key text.
15
A2, Q
to p h a s e s ,
see
72
A2,(Q)
A3
A3
A3
A3
A3
A3
TABLE
3
P h a s e s D e t e c t e d in U n s t i r r e d S u s p e n s i o n s , U s i n g Q u a r t z ( b e l o w 10 Dm), Showing E f f e c t s o f A d d i n g A l k a l i (N/S = 0 . 0 2 ) or Y - A 6 2 0 3 ( A 6 / ( S i + Ag) = 0.10) or b o t h F o r k e y to p h a s e s , see text. ....
m
Temperature oC
Time
Ca Si + A6
120 °
14 days
0.8
120 °
14 days
1.0
180 °
15
0.8
h
No a l k a l i No A 6 2 0 3 N,Q N,
(Q)
A,Q
Alkali only C-S-H, Q To,
Q
C-S-H
Ag203 only N
Alkali and A 6 2 0 3 A,
N A
(Q) A
A
,(Q) O
180 °
15
h
1.0
~
(Q)
C-S-H
--
A , (Q) O
434
Vol. 7, No. 4 S.A.S. El-Hemaly, T. Mitsuda, H.F.W. Taylor
c o n t e n t s of A6 3+ Table 3 gives results for unstirred suspensions, in w h i c h the e f f e c t s of a l k a l i and A 6 3 + a l o n e and t o g e t h e r are c o m p a r e d . E x c e p t for u n r e a c t e d b y - p r o d u c t silica, all t h e s e r e s u l t s are b a s e d on X - r a y p o w d e r e v i d e n c e . A l k a l i , w h e r e used, w a s a d d e d as s o d i u m s i l i c a t e , due a l l o w a n c e b e i n g m a d e f o r the Si02 thus c o n t r i b u t e d . The r e s u l t s g i v e n in the t a b l e s f o r m i x e s c o n t a i n i n g A 6 3 + are all ones for w h i c h the l a t t e r was a d d e d as Y - A 6 2 0 3 . A l l the r u n s for a l u m i n o u s m i x e s in T a b l e I w e r e r e p e a t e d u s i n g k a o l i n i t e as the s o u r c e of A 6 3 + , w i t h o u t s i g n i f i c a n t differences in r e s u l t s , and m a n y of t h o s e in T a b l e s 2 and 3 w e r e r e p e a t e d u s i n g k a o l i n i t e , CA, C 3 A o r A 6 ( 0 H ) 3 , a g a i n w i t h o u t s i g n i f i c a n t effect. R u n s w e r e a l s o m a d e in s t i r r e d s u s p e n s i o n s at C / S 0.8 and 180°C u s i n g s i l i c a g l a s s ( b e l o w 10 p m and a l s o 10 - 20 pm) as starting material. The glass reacted slowly, unreacted m a t e r i a l b e i n g d e t e c t a b l e o p t i c a l l y f o r up to 40 h, the l o n g e s t time studied. The main products w e r e C - S - H at s h o r t t i m e s and x o n o t l i t e at 20 - 40 h. Poor tobermorite w a s d e t e c t e d in the p r o d u c t s of o n l y one r u n (20 h, 10 - 20 pm g l a s s ) and t o b e r m o r ite of h i g h e r c r y s t a l l i n i t y in none. Specific
Surface
Area
and
Electron
Microscopy
Fig. 2 g i v e s s p e c i f i c s u r f a c e a r e a r e s u l t s f o r p r o d u c t s m a d e in s t i r r e d s u s p e n s i o n s at C a / ( S i + A6) 0.8 and 180°C. L a y e r t h i c k n e s s e s w e r e c a l c u l a t e d ~ s s u m i n g d e n s i t i e s of 2.2 g cm -3 f o r C - S - H and 2.4 g cm -J f o r t o b e r m o r i t e . The specific surfaces show reasonable correlation with crystallini t y l e v e l s b a s e d on the X - r a y e v i d e n c e . FIG.
35
'7
250
~' 2 0 0
S p e c i f i c s u r f a c e a r e a s of p r o d u c t s m a d e in s t i r r e d suspensions at C a / ( S i + A&) 0.8 and 180°C. Starting m a t e r i a l s w e r e C a 0 and
40 =
\
(,t)
u El
o~
45
~D 50
E
150
I. 2.
50
,yLa
c .¢
.u_ =-
70
2
3. 4. 5. 6.
Colloidal silica. Colloidal silica plus Y-A~203. Q u a r t z , b e l o w 10 pm. Quartz plus Y-A6203. By-product silica. Cristobalite.
"~ 1 0 0 100 ~ 0
E
u
50
200 .
.
4
.
[
I
I
I
2
5
10
20
Time
(hours)
500 1000 40
J=
Products [] O
O •
C-S-H Poor tobermorite Tobermorite, crystallinity level Tobermorite, crystallinity level Tobermorite, crystallinity level
I 2 3
Vol. 7, No. 4
435 NORMAL TOBERMORITE, ANOMALOUSTOBERMORITE, SYNTHESIS
Electron microscopy s h o w e d that p r o d u c t s d e s c r i b e d h e r e as c o b e r m o r i t e v a r i e d in m o r p h o l o g y f r o m p l a t e y to l a t h - l i k e or fibrous. A t o t a l of 89 c r y s t a l s w e r e e x a m i n e d b y s e l e c t e d area diffraction. A l l s h o w e d (001) c l e a v a g e and g a v e p a t t e r n s t h a t c o u l d be i n d e x e d e n t i r e l y , or a l m o s t e g t i r e l y on C - c e n t r e d o r t h o r h o m b i c c e l l s w i t h ~ 11.2, ~ 7.3 A a p p r o x . ; s o m e s h o w e d w e a k s t r e a k i n g of r e f l e c t i o n s p a r a l l e l to ~*. T h e r e w e r e no v a r i a t i o n s t h a t c o u l d be r e l a t e d to n o r m a l , m i x e d or a n o m a l o u s b e h a v i o u r , and no c r y s t a l s w e r e f o u n d w i t h (100) c l e a v a g e . The abnormal pattern of electron-diffraction re,flections and (100) c l e a v a g e t h a t w e r e f o u n d f o r the o r i g i n a l anomalous tobermorite ( f r o m L o c h E y n o r t , S c o t l a n d , 4) t h u s do n o t o c c u r in all a n o m a l o u s t o b e r m o r i t e s . Discussion Sequence
of R e a c t i o n s
The sequence
results
Ca(0H)2
suggest
that
reaction
proceeds
through
the
+ Si0^ ~ C-S~ ~ normal tobermorite mixed to~ermorite ~ anomalous tobermorite ----~xonotlite.
B e l o w 140°C, at l e a s t f o r the s t a r t i n g m a t e r i a l s , times and o t h e r c o n d i t i o n s used, the s e q u e n c e p r o c e e d s b e y o n d the s t a g e of mixed tobermorite only with difficulty, and x o n o t l i t e is n o t f o r m e d at all. T h e p r o d u c t s of a n y g i v e n r u n are c o n t r o l l e d b y a n u m b e r of f a c t o r s , l a r g e l y k i n e t i c in n a t u r e . These include time, t e m p e r a t u r e , b u l k C / S r a t i o , n a t u r e and p a r t i c l e s i z e of the s i l i c a , c o n t e n t if a n y of A 6 3 + or o t h e r a d d i t i v e s , a n d w h e t h e r or n o t the m i x t u r e is s t i r r e d . It is t h e r e f o r e n o t s u r p r i s i n g t h a t the c o n d i t i o n s n e e d e d to p r o d u c e t o b e r m o r i t e of a g i v e n t h e r m a l t y p e are n o t c l e a r l y d e f i n e d . Effect
of Bulk
C/S
Ratio
T h e u s e of a h i g h C / S r a t i o (1.0 as o p p o s e d to 0.8) r e t a r d s c o n v e r s i o n of n o r m a l i n t o m i x e d or a n o m a l o u s t o b e r m o r ite, b u t a c c e l e r a t e s c o n v e r s i o n of the l a t t e r i n t o x o n o t l i t e . T h i s is c o n s i s t e n t w i t h the f a c t s t h a t the t h e o r e t i c a l c o m p o s i t i o n of x o n o t l i t e is C 6 S 6 H a n d t h a t n a t u r a l l y o c c u r r i n g tobermorites s h o w i n g n o r m a l t h e r m a l b e h a v i o u r h a v e C / S r a t i o s of a b o u t 0.9, w h e r e a s t h o s e s h o w i n g m i x e d or a n o m a l o u s b e h a v i o u r h a v e C a / ( S i + A6) r a t i o s b e l o w 0.8 (3). Crystal
Size
of N o r m a l
Tobermorite
and
Ease
of C o n v e r s i o n
F o r t o b e r m o r i t e s m a d e in s t i r r e d s u s p e n s i o n s at C a / ( S i + A6) 0.8 a n d 180°C the t h e r m a l t y p e is h i g h l y c o r r e l a t e d w i t h the s p e c i f i c s u r f a c e a r e a (Fig. 2). If the s p e c i f i c s u r f a c e a r e a is low, the t o b e r m o r i t e is n o r m a l , a n d if it is h i g h , the t o b e r m o r i t e is a n o m a l o u s . This observation, too, is c o n s i s t e n t w i t h o n e s on n a t u r a l t o b e r m o r i t e s : t h o s e t h a t are n o r m a l f o r m m a r k e d l y l a r g e r c r y s t a l s t h a n t h o s e t h a t are m i x e d or a n o m a l o u s (3). It f o l l o w s t h a t a n y f a c t o r t h a t i n c r e a s e s the r a t e of c r y s t a l g r o w t h w h i l e the p r o d u c t is at the s t a g e of n o r m a l t o b e r m o r i t e w i l l r e t a r d the c o n v e r s i o n o f the l a t t e r i n t o the m i x e d or a n o m a l o u s type.
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Vol. 7, No. 4 S.A.S. EI-Hemaly, T. Mitsuda, H.F.W. Taylor
Effects
of
Stirring
and
of Q u a r t z
Particle
Size
V a r i a t i o n s in the r a t e of c r y s t a l g r o w t h of the n o r m a l t o b e r m o r i t e p r o b a b l y a c c o u n t f o r the d i f f e r e n c e s o b s e r v e d b e t w e e n s t i r r e d and u n s t i r r e d s u s p e n s i o n s (Fig. I). One m i g h t r e a s o n a b l y e x p e c t that c r y s t a l g r o w t h w o u l d be s l o w e r in u n s t i r r e d s u s p e n s i o n s , and t h a t t h i s w o u l d f a v o u r c o n v e r s i o n of n o r m a l i n t o m i x e d or a n o m a l o u s t o b e r m o r i t e , a n d this is w h a t is a c t u a l l y o b s e r v e d . T h e u s e of c o a r s e q u a r t z (10 - 20 vm) s e e m s to h a v e a s i m i l a r e f f e c t ( T a b l e I), t h o u g h the r e a s o n f o r this is n o t c l e a r . At C / S 0.9 - 1.0, the f i n a l s t a g e s of the r e a c t i o n s e q u e n c e l e a d i n g f r o m m i x e d t o b e r m o r i t e to x o n o t l i t e are r e l a t i v e l y fast, e s p e c i a l l y in stirred suspensions, and m i x e d or a n o m a l o u s t o b e r m o r i t e is rarely obtained free from other phases. Effect
of A l u m i n i u m
I n the p r e s e n t e x p e r i m e n t s , a d d i t i o n of A 6 3 + a c c e l e r a t e d crystal growth of normal tobermorite. For reactions starting w i t h q u a r t z , this e f f e c t is m o s t c l e a r l y s e e n in the s p e c i f i c s u r f a c e a r e a r e s u l t s f o r p r o d u c t s m a d e in s t i r r e d s u s p e n s i o n s (Fig. 2). A d d i t i o n of A 6 3 + l o w e r e d the s u r f a c e a r e a s and p r e v e n t e d the c o n v e r s i o n of n o r m a l i n t o m i x e d t o b e r m o r i t e w i t h i n 40 h at 180°C a n d C a / ( S i + A6) 0.8 ( T a b l e I). For u n s t i r r e d s u s p e n s i o n s at the s a m e t e m p e r a t u r e and c o m p o s i t i o n , the e f f e c t on c r y s t a l l i n i t y c a n be s e e n in the X - r a y r e s u l t s ( T a b l e 2), but w a s i n s u f f i c i e n t in this c a s e to p r e v e n t the conversion from occurring. These results may explain apparent inconsistencies in the l i t e r a t u r e (1,2) r e g a r d i n g the effect of A63+o T h e y s u g g e s t that A 6 3 + w i l l a l w a y s p r o m o t e crystallization of n o r m a l t o b e r m o r i t e and thus h i n d e r its c o n v e r s i o n i n t o the m i x e d or a n o m a l o u s type. However, opposing factors may limit crystallization and thus a l l o w the c o n v e r s i o n to o c c u r . One s u c h f a c t o r is a b s e n c e of s t i r r i n g , a n d a n o t h e r , as w i l l be s e e n l a t e r , is the p r e s e n c e of a l k a l i . C a u t i o n is n e e d e d in g e n e r a l i z i n g a b o u t the e f f e c t of A 6 3 + for another reason: t h e r e are a p p a r e n t i n c o n s i s t e n c i e s in the l i t e r a t u r e as to its e f f e c t on c r y s t a l size. Kalousek (5) r e p o r t e d that e l e c t r o n m i c r o s c o p y s h o w e d that the c r y s t a l s of Ag-substituted tobermorites were markedly smaller than those of u n s u b s t i t u t e d tobermorites, while Diamond, White and Dolch (2) f o u n d t h a t s p e c i f i c s u r f a c e a r e a s , m e a s u r e d by w a t e r v a p o u r a d s o r p t i o n , w e r e u s u a l l y h i g h e r (up to a b o u t 50%) t h a n t h o s e of unsubstituted specimens. Further investigation of t h e s e d i s c r e p a n c i e s w o u l d be of i n t e r e s t . Reactions
Using
Amorphous
Silica
I f a m o r p h o u s t y p e s of s i l i c a are u s e d , the i n i t i a l r e a c t i o n to g i v e C - S - H is u s u a l l y fast, b u t the s u b s e q u e n t c r y s t a l l i z a t i o n of t o b e r m o r i t e is s l o w e r t h a n w i t h q u a r t z . With silica g l a s s , the i n i t i a l r e a c t i o n is a l s o slow. With colloidal s i l i c a , a d d i t i o n of A g 3 + m a r k e d l y a c c e l e r a t e s b o t h c o n v e r s i o n o f C - S - H i n t o n o r m a l t o b e r m o r i t e a n d c r y s t a l g r o w t h of this p r o d u c t ( T a b l e I and Fig. 2). M o s t of t h e s e o b s e r v a t i o n s w e r e m a d e b y e a r l i e r w o r k e r s (1,6 e t c . ) . T h e e f f e c t of Ag 3+ in s t i r r e d s u s p e n s i o n s at 180oc a n d C a / ( S i + Ag) 0.8 w a s s u f f i c i e n t in the p r e s e n t c a s e to p r e v e n t c o n v e r s i o n of n o r m a l i n t o m i x e d or
Vol. 7, No. 4
437 NORMAL TOBERMORITE, ANOMALOUSTOBERMORITE, SYNTHESIS
anomalous
tobermorite
Effect
Aluminium
of
within Plus
40
hours.
Alkali
The present results ( T a b l e 3) c o n f i r m e a r l i e r o b s e r v a t i o n s (7) t h a t a d d i t i o n of a l k a l i w i t h o u t A 6 3 + g r e a t l y r e t a r d s crzstallization of t o b e r m o r i t e f r o m C - S - H . If alkali and A 6 3 + are b o t h p r e s e n t , anomalous t o b e r m o r i t e w a s f o r m e d in all the c a s e s s t u d i e d , i n c l u d i n g t h r e e f o r w h i c h the p r o d u c t obtained in the a b s e n c e of A 6 3 + or a l k a l i w a s n o r m a l or m i x e d . Earlier observations on crystallization of t o b e r m o r i t e f r o m g e l s (I) g a v e s i m i l a r r e s u l t s . T h e s e r e s u l t s c a n be e x p l a i n e d by supposing t h a t A 6 3 + c o u n t e r s the e f f e c t o f a l k a l i to a limited extent; a n o r m a l t o b e r m o r i t e is p r o d u c e d r e a s o n a b l y q u i c k l y , b u t c r y s t a l g r o w t h is too s l o w to p r e v e n t its c o n v e r s i o n i n t o the m i x e d or a n o m a l o u s form. T h e s e r e s u l t s are c o n s i s t e n t w i t h the o b s e r v a t i o n that naturally occurring mixed and anomalous tobermorites all c o n t a i n b o t h A 6 3 + a n d a l k a l i (3). It a p p e a r s p r o b a b l e t h a t this combination of additives permits anomalous t o b e r m o r i t e to be f o r m e d at t e m p e r a t u r e s t h a t are too l o w to a l l o w s u b s e q u e n t conversion into xonotlite. T h e r e s u l t s o f the p r e s e n t w o r k s h o w that, c o n t r a r y to a p r e v i o u s s u g g e s t i o n (I), the p r e s e n c e o f A 6 3 + a n d a l k a l i is n o t n e c e s s a r y f o r the f o r m a t i o n of anomalous tobermorite, t h o u g h it m a y m a k e it p o s s i b l e to o b t a i n it as a s t a b l e p h a s e . Preparative
Conditions
Normal t o b e r m o r i t e c a n p r o b a b l y be m a d e r e p r o d u c i b l y by reaction using quartz of particle s i z e b e l o w 10 p m in u n s t i r r e d suspensions at C / S 1.0 a n d 120 ° f o r I - 2 m o n t h s ; in s t i r r e d suspensions, t h i s t i m e c a n be r e d u c e d to I - 2 weeks. Anomalous t o b e r m o r i t e c a n be m a d e f r o m t h e s a m e s t a r t i n g materials at C / S 0 ° 8 a n d 1 8 0 ° C in 2 - 3 days using unstirred suspensions, b u t at t h i s t e m p e r a t u r e it is d i f f i c u l t to e n s u r e a b s e n c e o f x o n o t l i t e , a n d to p r e p a r e t h i s p h a s e r e p r o d u c i b l y it m a y be m o r e s a t i s f a c t o r y to u s e s t a r t i n g m a t e r i a l s c o n t a i n i n g A~3+ plus alkali. In o n e s i n g l e e x p e r i m e n t i n the p r e s e n t w o r k (at I 0 5 ° C ) , 14 ~ t o b e r m o r i t e was formed. To m a k e this phase reproducibly, it is p r o b a b l y n e c e s s a r y to u s e l o w e r temperatures a n d l o n g e r t i m e s at C / S = 1o0, e.g. 6 m o n t h s at 6 0 ° C as f o u n d b y K a l o u s e k a n d R o y (8). Structural
Considerations
In naturally occurring anomalous tobermorites the c o n t e n t o f (Si + A6) a p p r o a c h e s the theoretical v a l u e (6per p s e u d o cell) r e q u i r e d b y the c r y s t a l s t r u c t u r e , whereas in n a t u r a l l y occurring normal tobermorites it is b e l o w 5 . 5 (3). This indicates that, i n n o r m a l t o b e r m o r i t e s , the s i l i c a t e c h a i n s are h i g h l y defective; to c o n v e r t a n o r m a l i n t o an a n o m a l o u s tobermorite, it is n e c e s s a r y either that complete recrystallization should occur, or that additional s i l i c a t e or a l u m i n a t e groups should be i n t r o d u c e d into existing crystals. I n e i t h e r c a s e the p r o c e s s is l i k e l y to o c c u r m o r e e a s i l y i f the c r y s t a l s h a v e n o t g r o w n too l a r g e .
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Vol. 7, No. 4 S.A.S. EI-Hemaly, T. Mitsuda, H.F.W. Taylor
T h e r e is no e v i d e n c e that x o n o t l i t e c a n be s i m i l a r l y d e f e c t i v e in silicon; this is c o n s i s t e n t w i t h the o b s e r v a t i o n that c o n v e r s i o n of a n o m a l o u s t o b e r m o r i t e into x o n o t l i t e o c c u r s r e l a t i v e l y easily. T o b e r m o r i t e can a p p a r e n t l y i n c o r p o r a t e c o n s i d e r a b l y m o r e Ag3+ (2,5) than x o n o t l i t e (9); this w o u l d e x p l a i n the o b s e r v a t i o n that A 6 - s u b s t i t u t i o n r a i s e s the m i n i m u m t e m p e r a t u r e n e e d e d for c o n v e r s i o n of t o b e r m o r i t e into x o n o t l i t e (5, 10). The s l o w n e s s of c r y s t a l l i z a t i o n of t o b e r m o r i t e from the C - S - H f o r m e d u s i n g a m o r p h o u s s i l i c a has b e e n noted. At least two e x p l a n a t i o n s are p o s s i b l e . One is that the c o n c e n t r a t i o n of s i l i c a in s o l u t i o n m a y be h i g h e r than if quartz is used, and that this i n h i b i t s the f o r m a t i o n of t o b e r m o r i t e . A n o t h e r is that, b e c a u s e of the r e l a t i v e l y r a p i d r e a c t i o n of the silica, a type of C - S - H is f o r m e d that is s t r u c t u r a l l y less s i m i l a r to tobermorite a n d t h e r e f o r e less r e a d i l y c o n v e r t e d into it. One m i g h t s u p p o s e that a C - S - H h a v i n g a d e g e n e r a t e g y r o l i t e s t r u c t u r e c o u l d be formed, and the r e a d y f o r m a t i o n of g y r o l i t e from m i x e s c o n t a i n i n g a m o r p h o u s s i l i c a gives some s u p p o r t to this view. Acknowledgment Dr.
We than/< the E g y p t i a n G o v e r n m e n t for a r e s e a r c h g r a n t E Z - H e m a l y , w h i c h a l l o w e d h i m to w o r k in A b e r d e e n .
to
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To M i t s u d a and H . F . W o T a y l o r (in R u s s i a n ) , Proc. 6th Int. Cong. Chem. Cement, M o s c o w , 1974, [ (I), 213 (1976).
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G.L.
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OF N O R M A L
EZ-Hemaly*,
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Taylor
D e p a r t m e n t of C h e m i s t r y , U n i v e r s i t y of A b e r d e e n , M e s t o n Walk, 01d A b e r d e e n AB9 2UE, S c o t l a n d , U.K. (S.A.S.F.6-H. & H . F . W . T . ) Materials Research Laboratory, Nagoya Institute G o k i s o - c h o , S h o w a - k u , N a g o y a ~66, J a p a n * P e r m a n e n t address: Laboratory,National
of T e c h n o l o g y , (T.M.)
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(Communicated by J. Skalny) (Received April 28, 1977) AB STRAC T T o b e r m o r i t e s w e r e m a d e from s e v e r a l s t a r t i n g m a t e r i a l s at 105 - 180°C and C a/(Si + A6) 0.8 - 1.0. Reaction gives in s u c c e s s i o n C-S-H, n o r m a l , m i x e d and a n o m a l o u s 'tobermorites, and f i n a l l y x o n o t l i t e . H i g h C / S ratio (1.0), short time, low t e m p e r a t u r e , s t i r r i n g , p r e s e n c e of A6, and if q u a r t z is used, small p a r t i c l e size, all tend to stop it at n o r m a l t o b e r m o r i t e . In some cases, this effect is due to p r o m o t i o n of c r y s t a l g r o w t h of normal tobermorite. Low C / S ratio (0.8), l o n g time, h i g h t e m p e r a t u r e , no s t i r r i n g , p r e s e n c e of A6 plus alkali, and, if q u a r t z is used, l a r g e p a r t i c l e size, all tend to give a n o m a l o u s t o b e r m o r i t e . H o w e v e r , at " 180 ° C this c h a n g e s e a s i l y into x o n o t l i t e if C / S ~0.9.
.
ttC-S-H
",
429
430
Vol. 7, No. 4 S.A.S. EI-Hemaly, T. Mitsuda, H.F.W. Taylor Introduction
Tobermorite is an i m p o r t a n t c o n s t i t u e n t of s o m e k i n d s of a u t o c l a v e d c a l c i u m s i l i c a t e p r o d u c t s , s u c h as a e r a t e d c o n c r e t e s and t h e r m a l i n s u l a t i o n . S p e c i m e n s v a r y in t h e r m a l b e h a v i o u r ; in o n e e x t r e m e type, c a l l e d n o r m a l , l o s s of m o l e c u l a r w a t e r at a b o u t o 3 0 0 ~ c a u s e s a ~ e d u c t i o n in l a y e r t h i c k n e s s f r o m a b o u t 11.3 A to a b o u t 9.5 A, and in the o t h e r , c a l l e d a n o m a l o u s , it d o e s not. T h e c o n d i t i o n s u n d e r w h i c h t h e s e v a r i e $ i e s are f o r m e d h a v e n e v e r b e e n e l u c i d a t e d , t h o u g h it h a s b e e n s u g g e s t e d (1) t h a t n o r m a l t o b e r m o r i t e c a n p r o b a b l y be m a d e by p r o l o n g e d t r e a t m e n t of m i x e s w i t h C / S Ix0 at a b o u t I00°C, and t h a t to m a k e anomalous tobermorite b o t h A 6 3 + and a l k a l i m u s t be p r e s e n t and a C a / ( S i + A6) r a t i o of or b e l o w 0.8 is d e s i r a b l e . T h e aim of the p r e s e n t w o r k w a s to e s t a b l i s h the c o n d i t i o n s of f o r m a t i o n of the n o r m a l a n d a n o m a l o u s v a r i e t i e s . Experimental Starting
Materials
C a 0 w a s m a d e b y h e a t i n g e i t h e r a n a l y t i c a l or r e a g e n t g r a d e C a C 0 3 at 1000 - 1 1 0 0 ° C . T w o q u a r t z s a m p l e s w e r e used, of particle sizes (from sedimentation) b e l o w 10 ~ m and 10 - 20 ~ m respectively; b o t h c o n t a i n e d 9 9 . 9 % Si02. C o l l o i d a l s i l i c a and Y - A 6 2 0 3 w e r e e a c h the s a m e as, or s i m i l a r to s a m p l e s d e s c r i b e d e a r l i e r (1). By-product s i l i c a w a s an a m o r p h o u s m a t e r i a l w i t h 9 4 . 4 % Si02, 5 . 3 % l o s s , t r a c e s of F and NH3, a n d p a r t i c l e s i z e 10 - 15 ~m. Cristobalite w a s m a d e b y h ~ a t i n g this m a t e r i a l f o r 10 m i n at 1 3 0 0 ~ a n d h a d p a r t i c l e s i z e b e l o w 20 ~m. Silica g l a s s h a d 9 9 . 9 4 % S i 0 2 and p a r t i c l e s i z e b e l o w 10 pm. Kaolinite was highly crystalline, natural material. Sodium silicate was a commercial solution with Si02/Na20 3.4. Other starting materials were pure, laboratory preparations. Preparations A l l r e a c t i o n s w e r e d o n e at s a t u r a t e d s t e a m p r e s s u r e . T h o s e in s t i r r e d s u s p e n s i o n s w e r e c a r r i e d out u s i n g a w a t e r / s o l i d s w e i g h t r a t i o of 20 a n d a s t i r r i n g r a t e of 2 0 0 r . p . m . d u r i n g the f i r s t 4 h, a f t e r w h i c h s t i r r i n g w a s s t o p p e d ; for r u n s at 180°C a t i m e of 12 m i n w a s n e e d e d to r e a c h this t e m p erature. T h e p r o d u c t s w e r e f i l t e r e d , w a s h e d , and d r i e d in a v a c u u m at 8 0 ° C . F o r r e a c t i o n s in u n s t i r r e d s u s p e n s i o n s , the solid starting materials were mixed dry by brief grinding followed by mechanical s h a k i n g for 10 min, b e f o r e t r a n s f e r e n c e to the r e a c t i o n v e s s e l . W a t e r w a s t h e n a d d e d to g i v e a water/solids r a t i o of 2, and the s l u r r y b r i e f l y m i x e d b e f o r e sealing. T h e p r o d u c t s w e r e f i l t e r e d , w a s h e d , and d r i e d w i t h e t h a n o l and d i e t h y l e t h e r . Examination
of P r o d u c t s
All products were examined by X-ray powder diffraction, u s i n g e i t h e r a G u i n i e r c a m e r a or a d i f f r a c t o m e t e r . Those containing tobermorite were also similarly examined after b e i n g h e a t e d f o r 20 - 24 h at 300°C, a n d s o m e t i m e s a l s o f o r 20 h at 5 0 0 ° C . S o m e w e r e a l s o e x a m i n e d b y SEM, T E M i n c l u d i n g selected-area diffraction, optical microscopy (to d e t e c t u n r e a c t e d , a m o r p h o u s s i l i c a ) , or n i t r o g e n a d s o r p t i o n u s i n g the BET method for specific surface area determination.
Vol. 7, No. 4
431 NORMAL TOBERMORITE, ANOMALOUSTOBERMORITE, SYNTHESIS Results
Basal
spacings,
Definitions
and
Abbreviations
T h e b a s a l s p a c i n g ~ of the t o b e r m o r i t e s w e r e u s u a l l y b e t w e e n 11.3 and 11.6 A. F o r p r o d u c t s m a d e in s t i r r e d suspensions, the b a s a l ~ p a c i n g s w e r e u s u a l l y 11. 3 - 11.4 A if A6 w a s a b s e n t and 11.6 A f o r A 6 / ( S i + A6) 0.1 ~ these values m a y be c o m p a r e d w i t h t h o s e of 1 1 . 1 8 and 1 1 . 3 5 A f o u n d b y D i a m o n d , W h i t e and D o l c h (2). F o r p r o d u c t s m a d e in u n s t i r r e d s u s p e n s i o n t h e r e w a s l i t t l e or no c o r r e l a t i o n b e t w e e n b a s a l s p a c i n g and A6 c o n t e n t ; similar results have been observed for n a t u r a l t o b e r m o r i t e s (3) a n d f o r t o b e r m o r i t e s m a d e f r o m g e l s (I). T h e p r o d u c t s ar~ d e s c r i b e d as n o r m a l if the b a s a l s p a c i n g s d e c r e a s e d to 10.0 A or l e s s on h e ~ t i n g at 3 0 0 ° C and a n o m a l o u s if it d i d n o t s h r i n k b e l o w 11.0 A u n d e r t h e s e conditions. The term 'mixed tobermorite' is u s e d f o r p r o d u c t s s h o w i n g v a r i o u s k i n d s of i n t e r m e d i a t e b e h a v i o u r , of w h i c h the m o s t u s u a l w a s o a c h a n g e in the b a s a l r e f l e c t i o n to a b r o a d p e a k at a b o u t 10. 5 A at 3 0 0 ° C . A few preparations apparently c o n t a i n i n g b o t h n o r m a l a n d a n o m a l o u s t o b e r m o r i t e in c o m p a r a b l e a m o u n t s are a l s o d e s c r i b e d as m i x e d . T h e r e is an a p p a r e n t l y c o n t i n u o u s g r a d a t i o n in c r y s t a l l i n ity from semi-crystalline C - S - H to c r y s t a l l i n e tobermorite; in reference (I), f o u r c r y s t a l l i n i t y l e v e l s , c a l l e d A - D, w e r e defined. We ~ a l l u s e C - S - H to d e n o t e m a t e r i a l in w h i c h the 3.08 and 2 . 9 8 A l i n e s are u n r e s o l v e d ( l e v e l s A and B), p o o r t o b e r m o r i t e f o r m a t e r i a l in w h i c h t h e r e is i n c i p i e n t r e s o l u t i o n of t h e s e l i n e s ( l e v e l C), and t o b e r m o r i t e f o r m o r e h i g h l y crystalline material ( l e v e l D). L e v e l D w i l l be f u r t h e r s u b d i v i d e d on the b a s i s of the X - r a y p a t t e r n i n t o t h r e e l e v e l s , of w h i c h the l o w e s t ( l e v e l I) g a v e 10 - 15 and the ~ i g h e s t ( l e v e l 3) at l e a s t 25 l i n e s of s p a c i n g d o w n to 1.5 A w i t h the techniques used. Normal, mixed and anomalous tobermorites c o u l d all be o b t a i n e d in a n y of t h e s e l e v e l s of c r y s t a l l i n i t y . I n the t a b l e s a n d in a p p a r e n t d e c r e a s i n g standard abbreviations
f i g u r e s of r e s u l t s , p r o d u c t s are l i s t e d o r d e r of a b u n d a n c e and the f o l l o w i n g n o n are u s e d :
Q = quartz; C = cristobalite; S = by-product silica. T = tobermorite (thermal type not determinable) N,M,A = normal, mixed and anomalous tobermorites respectively. M* = m i x e d b e h a v i o u r at 3 0 0 ° C b u t n o r m a l at 5 0 0 ° C . -A* = a n o m a l o u s b e h a v i o u r at 3 0 0 ° C b u t m i x e d at 5 0 0 ° C Subscript 0 = p o o r t o b e r m o r i t e as d e f i n e d a b o v e . Subscripts I - 3 = higher crystallinity l e v e l s as d e f i n e d a b o v e X = xongtlite. 14T = 14 A t o b e r m o r i t e . Parentheses = trace. Phases
Detected
Fig. I a-c and d-e g i v e the p h a s e s d e t e c t e d in the p r o d u c t s m a d e f r o m C a 0 a n d q u a r t z ( b e l o w 10 pm) in s t i r r e d and unstirred suspensions respectively. Table I gives results for r u n s in s t i r r e d s u s p e n s i o n s at 180°C a n d C a / ( S i + A6) 0.8 w i t h v a r i o u s t y p e s of s t a r t i n g m a t e r i a l , some containing A63+. Table 2 gives results for unstirred suspensions, a l s o at 180°C a n d C a / ( S i + A6) 0.8, u s i n g q u a r t z ( b e l o w 10 ~m) a n d v a r y i n g
432
Vol. 7, No. 4 S.A.S. El-Hemaly, T. Mitsuda, H.F.W. T a y l o r
180°
-- N Q
NrQ)
N~ M
M MX
180c
XA X Xono/hte
N(X) N(X) N(X) X N
\
e
~
140 c
M"
M"
M°
M"
~ 1400
M
;=
Normal
k-
I~O) A"
A"
M
I I 3 7 days
I 2
I l 4 e weeks
\
I s
Time :
I I ~o 20 hours
A.
C/S
I 40
0"8
NormaI
M
N(Q)
,e Time:
Stirred
I
I
2
5
I
I
I
10 20 hours
B.
CIS
40
N
N
I
I
N
3 7 days
0"9
N
N
I
I
2.
4 8 weeks
I
1
16
Stirred
C-S-H + Q N(X) N(X) X(T) X
180°
FIG.
=u ~1400 eo.
N(Q)
N
N
N
NCQ) N
N
N
A(X)~
loo~
I
5 Time :
I
10 20 hours
C.
L
t
40
I
AQ
N
I
I
1
3 7 Clays
2
4 8 weeks
C/S 1"0
AQ
N
I
Phas@s detected using CaO and quartz (below 10 ~m) in stirred (a-c) and unstirred (d-e) suspensions. For key
Normal
E
,ed
Xonotlite
Mixel~ NQ ~
.+
(
to
phases,
see
text.
I
16
Stirred
A AtX
~
i
Xonotlite
~alou$
xonot lile
AnomalOUSAo~ ~14o o
~140°
+i
ACQI ACX)X(A)
I-Normal
,od Time :
MoQ f
i
t
I
I
I
I
I
I
I
z
s
,o
zo
,o
3
T
z
4
8
hours D.
CIS
days 0'8
Unstjrred
NoEO) NCQ)NN N Normal 14T NoQ ÷M N
Mixed MO M(Q)
weeks
I
100°'
f
16
S
Time : E.
I
I
10 20 hours
I
40
CIS 1.0
I
I
I
I
3
7
2
4
days Unstirred
I 8
weeks
I
16
Vol. 7, No. 4
433 NORMAL TOBERMORITE, ANOMALOUSTOBERMORITE, SYNTHESIS TABLE
Phases
Detected
I
in S t i r r e d
Suspensions
C a / ( S i + A6) = 0.8; for aluminous F o r k e y to p h a s e s , see text. Time (h)
Quartz 10-20 ~m
Quartz <10 wm + Y-A6203
C-S-H,
Colloidal silica
mixes,
at
A6(Si
Colloidal silica + Y-A6203
180°C
+ A6)
= 0.1
By-product silica
Cristobalite
2
LQ, C H
Ig-S-H, Q, C H
C-S-H
N
5
TO , Q
N,Q
C-S-H
N
N N N
C-S-H C-S-H T
N N
A. A
M M
N N
A A
M M
(X') X X
96
A, A, A, A,
X
N, ~X)
192
X,
A
N,
10 20 $0
TABLE
[~-S-H, To,
M,C
S
M
X
2
A
/(Si +
P h a s e s D e t e c t e d in U n s t i r r e d S u s p e n s i o n s at 180°C and C a ~ S i + A6) = 0.8, u s i n g Q u a r t z (below 10 ~m) and Y - A g 2 0 3 .
Time (h)
0
0.05
o.1o
0.15
4
AI, Q
A I,q
A2,q
A2, Q
For key text.
15
A2, Q
to p h a s e s ,
see
72
A2,(Q)
A3
A3
A3
A3
A3
A3
TABLE
3
P h a s e s D e t e c t e d in U n s t i r r e d S u s p e n s i o n s , U s i n g Q u a r t z ( b e l o w 10 Dm), Showing E f f e c t s o f A d d i n g A l k a l i (N/S = 0 . 0 2 ) or Y - A 6 2 0 3 ( A 6 / ( S i + Ag) = 0.10) or b o t h F o r k e y to p h a s e s , see text. ....
m
Temperature oC
Time
Ca Si + A6
120 °
14 days
0.8
120 °
14 days
1.0
180 °
15
0.8
h
No a l k a l i No A 6 2 0 3 N,Q N,
(Q)
A,Q
Alkali only C-S-H, Q To,
Q
C-S-H
Ag203 only N
Alkali and A 6 2 0 3 A,
N A
(Q) A
A
,(Q) O
180 °
15
h
1.0
~
(Q)
C-S-H
--
A , (Q) O
434
Vol. 7, No. 4 S.A.S. El-Hemaly, T. Mitsuda, H.F.W. Taylor
c o n t e n t s of A6 3+ Table 3 gives results for unstirred suspensions, in w h i c h the e f f e c t s of a l k a l i and A 6 3 + a l o n e and t o g e t h e r are c o m p a r e d . E x c e p t for u n r e a c t e d b y - p r o d u c t silica, all t h e s e r e s u l t s are b a s e d on X - r a y p o w d e r e v i d e n c e . A l k a l i , w h e r e used, w a s a d d e d as s o d i u m s i l i c a t e , due a l l o w a n c e b e i n g m a d e f o r the Si02 thus c o n t r i b u t e d . The r e s u l t s g i v e n in the t a b l e s f o r m i x e s c o n t a i n i n g A 6 3 + are all ones for w h i c h the l a t t e r was a d d e d as Y - A 6 2 0 3 . A l l the r u n s for a l u m i n o u s m i x e s in T a b l e I w e r e r e p e a t e d u s i n g k a o l i n i t e as the s o u r c e of A 6 3 + , w i t h o u t s i g n i f i c a n t differences in r e s u l t s , and m a n y of t h o s e in T a b l e s 2 and 3 w e r e r e p e a t e d u s i n g k a o l i n i t e , CA, C 3 A o r A 6 ( 0 H ) 3 , a g a i n w i t h o u t s i g n i f i c a n t effect. R u n s w e r e a l s o m a d e in s t i r r e d s u s p e n s i o n s at C / S 0.8 and 180°C u s i n g s i l i c a g l a s s ( b e l o w 10 p m and a l s o 10 - 20 pm) as starting material. The glass reacted slowly, unreacted m a t e r i a l b e i n g d e t e c t a b l e o p t i c a l l y f o r up to 40 h, the l o n g e s t time studied. The main products w e r e C - S - H at s h o r t t i m e s and x o n o t l i t e at 20 - 40 h. Poor tobermorite w a s d e t e c t e d in the p r o d u c t s of o n l y one r u n (20 h, 10 - 20 pm g l a s s ) and t o b e r m o r ite of h i g h e r c r y s t a l l i n i t y in none. Specific
Surface
Area
and
Electron
Microscopy
Fig. 2 g i v e s s p e c i f i c s u r f a c e a r e a r e s u l t s f o r p r o d u c t s m a d e in s t i r r e d s u s p e n s i o n s at C a / ( S i + A6) 0.8 and 180°C. L a y e r t h i c k n e s s e s w e r e c a l c u l a t e d ~ s s u m i n g d e n s i t i e s of 2.2 g cm -3 f o r C - S - H and 2.4 g cm -J f o r t o b e r m o r i t e . The specific surfaces show reasonable correlation with crystallini t y l e v e l s b a s e d on the X - r a y e v i d e n c e . FIG.
35
'7
250
~' 2 0 0
S p e c i f i c s u r f a c e a r e a s of p r o d u c t s m a d e in s t i r r e d suspensions at C a / ( S i + A&) 0.8 and 180°C. Starting m a t e r i a l s w e r e C a 0 and
40 =
\
(,t)
u El
o~
45
~D 50
E
150
I. 2.
50
,yLa
c .¢
.u_ =-
70
2
3. 4. 5. 6.
Colloidal silica. Colloidal silica plus Y-A~203. Q u a r t z , b e l o w 10 pm. Quartz plus Y-A6203. By-product silica. Cristobalite.
"~ 1 0 0 100 ~ 0
E
u
50
200 .
.
4
.
[
I
I
I
2
5
10
20
Time
(hours)
500 1000 40
J=
Products [] O
O •
C-S-H Poor tobermorite Tobermorite, crystallinity level Tobermorite, crystallinity level Tobermorite, crystallinity level
I 2 3
Vol. 7, No. 4
435 NORMAL TOBERMORITE, ANOMALOUSTOBERMORITE, SYNTHESIS
Electron microscopy s h o w e d that p r o d u c t s d e s c r i b e d h e r e as c o b e r m o r i t e v a r i e d in m o r p h o l o g y f r o m p l a t e y to l a t h - l i k e or fibrous. A t o t a l of 89 c r y s t a l s w e r e e x a m i n e d b y s e l e c t e d area diffraction. A l l s h o w e d (001) c l e a v a g e and g a v e p a t t e r n s t h a t c o u l d be i n d e x e d e n t i r e l y , or a l m o s t e g t i r e l y on C - c e n t r e d o r t h o r h o m b i c c e l l s w i t h ~ 11.2, ~ 7.3 A a p p r o x . ; s o m e s h o w e d w e a k s t r e a k i n g of r e f l e c t i o n s p a r a l l e l to ~*. T h e r e w e r e no v a r i a t i o n s t h a t c o u l d be r e l a t e d to n o r m a l , m i x e d or a n o m a l o u s b e h a v i o u r , and no c r y s t a l s w e r e f o u n d w i t h (100) c l e a v a g e . The abnormal pattern of electron-diffraction re,flections and (100) c l e a v a g e t h a t w e r e f o u n d f o r the o r i g i n a l anomalous tobermorite ( f r o m L o c h E y n o r t , S c o t l a n d , 4) t h u s do n o t o c c u r in all a n o m a l o u s t o b e r m o r i t e s . Discussion Sequence
of R e a c t i o n s
The sequence
results
Ca(0H)2
suggest
that
reaction
proceeds
through
the
+ Si0^ ~ C-S~ ~ normal tobermorite mixed to~ermorite ~ anomalous tobermorite ----~xonotlite.
B e l o w 140°C, at l e a s t f o r the s t a r t i n g m a t e r i a l s , times and o t h e r c o n d i t i o n s used, the s e q u e n c e p r o c e e d s b e y o n d the s t a g e of mixed tobermorite only with difficulty, and x o n o t l i t e is n o t f o r m e d at all. T h e p r o d u c t s of a n y g i v e n r u n are c o n t r o l l e d b y a n u m b e r of f a c t o r s , l a r g e l y k i n e t i c in n a t u r e . These include time, t e m p e r a t u r e , b u l k C / S r a t i o , n a t u r e and p a r t i c l e s i z e of the s i l i c a , c o n t e n t if a n y of A 6 3 + or o t h e r a d d i t i v e s , a n d w h e t h e r or n o t the m i x t u r e is s t i r r e d . It is t h e r e f o r e n o t s u r p r i s i n g t h a t the c o n d i t i o n s n e e d e d to p r o d u c e t o b e r m o r i t e of a g i v e n t h e r m a l t y p e are n o t c l e a r l y d e f i n e d . Effect
of Bulk
C/S
Ratio
T h e u s e of a h i g h C / S r a t i o (1.0 as o p p o s e d to 0.8) r e t a r d s c o n v e r s i o n of n o r m a l i n t o m i x e d or a n o m a l o u s t o b e r m o r ite, b u t a c c e l e r a t e s c o n v e r s i o n of the l a t t e r i n t o x o n o t l i t e . T h i s is c o n s i s t e n t w i t h the f a c t s t h a t the t h e o r e t i c a l c o m p o s i t i o n of x o n o t l i t e is C 6 S 6 H a n d t h a t n a t u r a l l y o c c u r r i n g tobermorites s h o w i n g n o r m a l t h e r m a l b e h a v i o u r h a v e C / S r a t i o s of a b o u t 0.9, w h e r e a s t h o s e s h o w i n g m i x e d or a n o m a l o u s b e h a v i o u r h a v e C a / ( S i + A6) r a t i o s b e l o w 0.8 (3). Crystal
Size
of N o r m a l
Tobermorite
and
Ease
of C o n v e r s i o n
F o r t o b e r m o r i t e s m a d e in s t i r r e d s u s p e n s i o n s at C a / ( S i + A6) 0.8 a n d 180°C the t h e r m a l t y p e is h i g h l y c o r r e l a t e d w i t h the s p e c i f i c s u r f a c e a r e a (Fig. 2). If the s p e c i f i c s u r f a c e a r e a is low, the t o b e r m o r i t e is n o r m a l , a n d if it is h i g h , the t o b e r m o r i t e is a n o m a l o u s . This observation, too, is c o n s i s t e n t w i t h o n e s on n a t u r a l t o b e r m o r i t e s : t h o s e t h a t are n o r m a l f o r m m a r k e d l y l a r g e r c r y s t a l s t h a n t h o s e t h a t are m i x e d or a n o m a l o u s (3). It f o l l o w s t h a t a n y f a c t o r t h a t i n c r e a s e s the r a t e of c r y s t a l g r o w t h w h i l e the p r o d u c t is at the s t a g e of n o r m a l t o b e r m o r i t e w i l l r e t a r d the c o n v e r s i o n o f the l a t t e r i n t o the m i x e d or a n o m a l o u s type.
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Effects
of
Stirring
and
of Q u a r t z
Particle
Size
V a r i a t i o n s in the r a t e of c r y s t a l g r o w t h of the n o r m a l t o b e r m o r i t e p r o b a b l y a c c o u n t f o r the d i f f e r e n c e s o b s e r v e d b e t w e e n s t i r r e d and u n s t i r r e d s u s p e n s i o n s (Fig. I). One m i g h t r e a s o n a b l y e x p e c t that c r y s t a l g r o w t h w o u l d be s l o w e r in u n s t i r r e d s u s p e n s i o n s , and t h a t t h i s w o u l d f a v o u r c o n v e r s i o n of n o r m a l i n t o m i x e d or a n o m a l o u s t o b e r m o r i t e , a n d this is w h a t is a c t u a l l y o b s e r v e d . T h e u s e of c o a r s e q u a r t z (10 - 20 vm) s e e m s to h a v e a s i m i l a r e f f e c t ( T a b l e I), t h o u g h the r e a s o n f o r this is n o t c l e a r . At C / S 0.9 - 1.0, the f i n a l s t a g e s of the r e a c t i o n s e q u e n c e l e a d i n g f r o m m i x e d t o b e r m o r i t e to x o n o t l i t e are r e l a t i v e l y fast, e s p e c i a l l y in stirred suspensions, and m i x e d or a n o m a l o u s t o b e r m o r i t e is rarely obtained free from other phases. Effect
of A l u m i n i u m
I n the p r e s e n t e x p e r i m e n t s , a d d i t i o n of A 6 3 + a c c e l e r a t e d crystal growth of normal tobermorite. For reactions starting w i t h q u a r t z , this e f f e c t is m o s t c l e a r l y s e e n in the s p e c i f i c s u r f a c e a r e a r e s u l t s f o r p r o d u c t s m a d e in s t i r r e d s u s p e n s i o n s (Fig. 2). A d d i t i o n of A 6 3 + l o w e r e d the s u r f a c e a r e a s and p r e v e n t e d the c o n v e r s i o n of n o r m a l i n t o m i x e d t o b e r m o r i t e w i t h i n 40 h at 180°C a n d C a / ( S i + A6) 0.8 ( T a b l e I). For u n s t i r r e d s u s p e n s i o n s at the s a m e t e m p e r a t u r e and c o m p o s i t i o n , the e f f e c t on c r y s t a l l i n i t y c a n be s e e n in the X - r a y r e s u l t s ( T a b l e 2), but w a s i n s u f f i c i e n t in this c a s e to p r e v e n t the conversion from occurring. These results may explain apparent inconsistencies in the l i t e r a t u r e (1,2) r e g a r d i n g the effect of A63+o T h e y s u g g e s t that A 6 3 + w i l l a l w a y s p r o m o t e crystallization of n o r m a l t o b e r m o r i t e and thus h i n d e r its c o n v e r s i o n i n t o the m i x e d or a n o m a l o u s type. However, opposing factors may limit crystallization and thus a l l o w the c o n v e r s i o n to o c c u r . One s u c h f a c t o r is a b s e n c e of s t i r r i n g , a n d a n o t h e r , as w i l l be s e e n l a t e r , is the p r e s e n c e of a l k a l i . C a u t i o n is n e e d e d in g e n e r a l i z i n g a b o u t the e f f e c t of A 6 3 + for another reason: t h e r e are a p p a r e n t i n c o n s i s t e n c i e s in the l i t e r a t u r e as to its e f f e c t on c r y s t a l size. Kalousek (5) r e p o r t e d that e l e c t r o n m i c r o s c o p y s h o w e d that the c r y s t a l s of Ag-substituted tobermorites were markedly smaller than those of u n s u b s t i t u t e d tobermorites, while Diamond, White and Dolch (2) f o u n d t h a t s p e c i f i c s u r f a c e a r e a s , m e a s u r e d by w a t e r v a p o u r a d s o r p t i o n , w e r e u s u a l l y h i g h e r (up to a b o u t 50%) t h a n t h o s e of unsubstituted specimens. Further investigation of t h e s e d i s c r e p a n c i e s w o u l d be of i n t e r e s t . Reactions
Using
Amorphous
Silica
I f a m o r p h o u s t y p e s of s i l i c a are u s e d , the i n i t i a l r e a c t i o n to g i v e C - S - H is u s u a l l y fast, b u t the s u b s e q u e n t c r y s t a l l i z a t i o n of t o b e r m o r i t e is s l o w e r t h a n w i t h q u a r t z . With silica g l a s s , the i n i t i a l r e a c t i o n is a l s o slow. With colloidal s i l i c a , a d d i t i o n of A g 3 + m a r k e d l y a c c e l e r a t e s b o t h c o n v e r s i o n o f C - S - H i n t o n o r m a l t o b e r m o r i t e a n d c r y s t a l g r o w t h of this p r o d u c t ( T a b l e I and Fig. 2). M o s t of t h e s e o b s e r v a t i o n s w e r e m a d e b y e a r l i e r w o r k e r s (1,6 e t c . ) . T h e e f f e c t of Ag 3+ in s t i r r e d s u s p e n s i o n s at 180oc a n d C a / ( S i + Ag) 0.8 w a s s u f f i c i e n t in the p r e s e n t c a s e to p r e v e n t c o n v e r s i o n of n o r m a l i n t o m i x e d or
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437 NORMAL TOBERMORITE, ANOMALOUSTOBERMORITE, SYNTHESIS
anomalous
tobermorite
Effect
Aluminium
of
within Plus
40
hours.
Alkali
The present results ( T a b l e 3) c o n f i r m e a r l i e r o b s e r v a t i o n s (7) t h a t a d d i t i o n of a l k a l i w i t h o u t A 6 3 + g r e a t l y r e t a r d s crzstallization of t o b e r m o r i t e f r o m C - S - H . If alkali and A 6 3 + are b o t h p r e s e n t , anomalous t o b e r m o r i t e w a s f o r m e d in all the c a s e s s t u d i e d , i n c l u d i n g t h r e e f o r w h i c h the p r o d u c t obtained in the a b s e n c e of A 6 3 + or a l k a l i w a s n o r m a l or m i x e d . Earlier observations on crystallization of t o b e r m o r i t e f r o m g e l s (I) g a v e s i m i l a r r e s u l t s . T h e s e r e s u l t s c a n be e x p l a i n e d by supposing t h a t A 6 3 + c o u n t e r s the e f f e c t o f a l k a l i to a limited extent; a n o r m a l t o b e r m o r i t e is p r o d u c e d r e a s o n a b l y q u i c k l y , b u t c r y s t a l g r o w t h is too s l o w to p r e v e n t its c o n v e r s i o n i n t o the m i x e d or a n o m a l o u s form. T h e s e r e s u l t s are c o n s i s t e n t w i t h the o b s e r v a t i o n that naturally occurring mixed and anomalous tobermorites all c o n t a i n b o t h A 6 3 + a n d a l k a l i (3). It a p p e a r s p r o b a b l e t h a t this combination of additives permits anomalous t o b e r m o r i t e to be f o r m e d at t e m p e r a t u r e s t h a t are too l o w to a l l o w s u b s e q u e n t conversion into xonotlite. T h e r e s u l t s o f the p r e s e n t w o r k s h o w that, c o n t r a r y to a p r e v i o u s s u g g e s t i o n (I), the p r e s e n c e o f A 6 3 + a n d a l k a l i is n o t n e c e s s a r y f o r the f o r m a t i o n of anomalous tobermorite, t h o u g h it m a y m a k e it p o s s i b l e to o b t a i n it as a s t a b l e p h a s e . Preparative
Conditions
Normal t o b e r m o r i t e c a n p r o b a b l y be m a d e r e p r o d u c i b l y by reaction using quartz of particle s i z e b e l o w 10 p m in u n s t i r r e d suspensions at C / S 1.0 a n d 120 ° f o r I - 2 m o n t h s ; in s t i r r e d suspensions, t h i s t i m e c a n be r e d u c e d to I - 2 weeks. Anomalous t o b e r m o r i t e c a n be m a d e f r o m t h e s a m e s t a r t i n g materials at C / S 0 ° 8 a n d 1 8 0 ° C in 2 - 3 days using unstirred suspensions, b u t at t h i s t e m p e r a t u r e it is d i f f i c u l t to e n s u r e a b s e n c e o f x o n o t l i t e , a n d to p r e p a r e t h i s p h a s e r e p r o d u c i b l y it m a y be m o r e s a t i s f a c t o r y to u s e s t a r t i n g m a t e r i a l s c o n t a i n i n g A~3+ plus alkali. In o n e s i n g l e e x p e r i m e n t i n the p r e s e n t w o r k (at I 0 5 ° C ) , 14 ~ t o b e r m o r i t e was formed. To m a k e this phase reproducibly, it is p r o b a b l y n e c e s s a r y to u s e l o w e r temperatures a n d l o n g e r t i m e s at C / S = 1o0, e.g. 6 m o n t h s at 6 0 ° C as f o u n d b y K a l o u s e k a n d R o y (8). Structural
Considerations
In naturally occurring anomalous tobermorites the c o n t e n t o f (Si + A6) a p p r o a c h e s the theoretical v a l u e (6per p s e u d o cell) r e q u i r e d b y the c r y s t a l s t r u c t u r e , whereas in n a t u r a l l y occurring normal tobermorites it is b e l o w 5 . 5 (3). This indicates that, i n n o r m a l t o b e r m o r i t e s , the s i l i c a t e c h a i n s are h i g h l y defective; to c o n v e r t a n o r m a l i n t o an a n o m a l o u s tobermorite, it is n e c e s s a r y either that complete recrystallization should occur, or that additional s i l i c a t e or a l u m i n a t e groups should be i n t r o d u c e d into existing crystals. I n e i t h e r c a s e the p r o c e s s is l i k e l y to o c c u r m o r e e a s i l y i f the c r y s t a l s h a v e n o t g r o w n too l a r g e .
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T h e r e is no e v i d e n c e that x o n o t l i t e c a n be s i m i l a r l y d e f e c t i v e in silicon; this is c o n s i s t e n t w i t h the o b s e r v a t i o n that c o n v e r s i o n of a n o m a l o u s t o b e r m o r i t e into x o n o t l i t e o c c u r s r e l a t i v e l y easily. T o b e r m o r i t e can a p p a r e n t l y i n c o r p o r a t e c o n s i d e r a b l y m o r e Ag3+ (2,5) than x o n o t l i t e (9); this w o u l d e x p l a i n the o b s e r v a t i o n that A 6 - s u b s t i t u t i o n r a i s e s the m i n i m u m t e m p e r a t u r e n e e d e d for c o n v e r s i o n of t o b e r m o r i t e into x o n o t l i t e (5, 10). The s l o w n e s s of c r y s t a l l i z a t i o n of t o b e r m o r i t e from the C - S - H f o r m e d u s i n g a m o r p h o u s s i l i c a has b e e n noted. At least two e x p l a n a t i o n s are p o s s i b l e . One is that the c o n c e n t r a t i o n of s i l i c a in s o l u t i o n m a y be h i g h e r than if quartz is used, and that this i n h i b i t s the f o r m a t i o n of t o b e r m o r i t e . A n o t h e r is that, b e c a u s e of the r e l a t i v e l y r a p i d r e a c t i o n of the silica, a type of C - S - H is f o r m e d that is s t r u c t u r a l l y less s i m i l a r to tobermorite a n d t h e r e f o r e less r e a d i l y c o n v e r t e d into it. One m i g h t s u p p o s e that a C - S - H h a v i n g a d e g e n e r a t e g y r o l i t e s t r u c t u r e c o u l d be formed, and the r e a d y f o r m a t i o n of g y r o l i t e from m i x e s c o n t a i n i n g a m o r p h o u s s i l i c a gives some s u p p o r t to this view. Acknowledgment Dr.
We than/< the E g y p t i a n G o v e r n m e n t for a r e s e a r c h g r a n t E Z - H e m a l y , w h i c h a l l o w e d h i m to w o r k in A b e r d e e n .
to
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