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Effect of burning conditions and minor components on the color of portland cement clinker
CEMENT and CONCRETE RESEARCH. Vol. 23, pp. 933-938, 1993. Printed in the USA. 0008-8846D3. $6.00+00. Copyright © 1993 Pergamon Press Ltd.
E F F E C T O F B U R N I N G C O N D I T I O N S A N D MINOR C O M P O N E N T S ON THE C O L O R O F P O R T L A N D C E M E N T C L I N K E R
M.ICHIKAWA and Y.KOMUKAI Cement&Concrete Research Dept. Central Research Laboratory Chichibu C e m e n t Co.,Ltd. 2-1 - 1, T s u k i m i - C h o , K u m a g a y a - S h i S a i t a m a , 360 J a p a n
(Communicatedby H.F.W. Taylor) (ReceivedAug. 20, 1992) ABSTRACT The s u b s t i t u t i o n of Me 2 ~(Mg,Zn) for AI a ~ and F e a ~ in the c a l c i u m a l u m i n o - f e r r i t e phase, which i n t r o d u c e s e x t r i n s i c o x y g e n v a c a n c i e s in t h e s t r u c t u r e , is e s s e n t i a l to t h e c h a n g e in c o l o r f r o m yellowish brown to dark g r e y . H o w e v e r , an i n c r e a s e of t h e r a t i o Me 4 ~(Si,Ti)/Me z ~ in t h e ferrite phase, which, for e x a m p l e , is e n c o u r a g e d by slow c o o l i n g in n i t r o g e n , r e d u c e s t h e n u m b e r of e x t r i n s i c o x y g e n v a c a n c i e s and p r e v e n t s the above color change. With C 6 A 2 F solid solutions t h e c o l o r c h a n g e is a c c o m p a n i e d by a d e f i n i t e i n c r e a s e in e l e c t r i c c o n d u c t i v i t y , i n d i c a t i n g the significance of electrons released by the oxidation of FeO in a d d i t i o n to t h e o c c u r r e n c e of o x y g e n v a c a n c i e s .
Introduction
Previous studies l) 2) showed that w i t h MgO in c l i n k e r the f e r r i t e phase is dark grey w h i l e i t is yellowish brown w i t h o u t MgO. However, w i t h o u t oxygen in the atmosphere the f e r r i t e phase remains yellowish brown even in the presence of MgO. In the present study laboratory clinkers and C 6 A z F solid solutions of different colors were prepared by systematically changing those factors relevant to the color and subjected to FeO analysis, EPMA and e l e c t r i c c o n d u c t i v i t y measurement. Discussions have been made concerning the mechanism of the color change. Materials
1. C l i n k e r s The c l i n k e r s w i t h and w i t h o u t m i n o r c o m p o n e n t s w e r e p r e p a r e d under d i f f e r e n t burning a t m o s p h e r e s and c o o li n g c o n d i t i o n s . The b asi c c l i n k e r was of t h e q u a r t e r n a r y s y s t e m : SiO2 23.396, Al2Oa 5.196, F e 2 0 3 3.tt96 and C a O 68.0% by w e i g h t . The r a w m i x e s , a f t e r being p e l l e t i z e d , w e r e h e a t e d a t 50Wmin up to 10001~ and t h e n at 30Wmin up to t h e m a x i m u m t e m p e r a t u r e l tt901~ with r e t e n t i o n for 20 and 5 min a t 1000 and 14901~, r e s p e c t i v e l y . Tab l e 1 shows t h e 933
934
Vol. 23, No. 4
M. Ichikawa and Y. Komukai
a t m o s p h e r e s , coo l in g r a t e s and q u e n c h i n g t e m p e r a t u r e s m a d e in air r e g a r d l e s s of t h e burning a t m o s p h e r e s .
employed.
Q u en ch i n g
was
T a b l e 1 Burning c o n d i t i o n s o f c l i n k e r s Atmosphere
Q u en ch i n g temp.(~)
C o o li n g r a t e (~/min)
Air, N2(O2<10 4atm)
20
1350, 1200, 300
Air, N2(O~<10 4atm)
10, 100, 500
300
2. C6A2F solid solutions For s i m p l i c i t y , C6A~z x / 2 ) M x F and CoA~2 x~MxSxF with X=0~0.#5 w e r e p r e p a r e d on a s s u m p t i o n t h a t MgO and SiO~ s u b s t i t u t e for A1203, though part of MgO m ay s u b s t i t u t e for F e 2 0 ~ . The raw m i x e s w e r e burnt in n i t r o g e n on the s a m e h e a t i n g p r o g r a m as in t h e c l i n k e r burning e x c e p t t h a t t h e m a x i m u m t e m p e r a t u r e and t h e r e t e n t i o n t i m e w e r e 1#50~ and 20rain. The fired p r o d u c t s w e r e c o o l e d at 10~/min down to 300~7 in t h e f u r n a c e and then q u e n c h e d in air. C a l c i u m a l u m i n a t e , c a l c i u m s i l i c a t e and p e r i c l a s e w e r e found to c o e x i s t in small q u a n t i t i e s by XRD. Experimental The c o l o r s w e r e m e a s u r e d using a c o l o r d i f f e r e n c e m e t e r for the p r o d u c t s ground to t h e Blaine s p e c i f i c s u r f a c e a r e a of 2 9 0 0 i 1 0 0 c m 2 / g . The r e s u l t s w e r e giv en a c c o r d i n g to t h e H u n t e r ' s e q u a t i o n . F e O was a n a l y z e d by t h e c o l o r m e t r i c method with a - a' d i p y r i d y l as an i n d i c a t o r 3 ~. In slowly cooled clinkers (10~/min) the f e r r i t e c r y s t a l s have been d e v e l o p e d large. Point analysis of the f e r r i t e phase was made using an e l e c t r o n probe m i c r o a n a l y z e r ( J E O L - 8 6 0 0 M ) with a c c e l e r a t i o n v o l t a g e of 15KV and probe c u r r e n t of 2×10 8A. The number of points measured was 10 or m o r e f o r each c l i n k e r sample and the c o r r e c t i o n f o r i n t e n s i t i e s was made by Z A F . The f e r r i t e crystals in r a p i d l y cooled c l i n k e r s (500~/min) w e r e not l a r g e enough f o r EPMA, so that w e t c h e m i c a l analyses w e r e made a f t e r e x t r a c t i n g the f e r r i t e phase 4~ The C o A 2 F solid solutions w e r e pressed i n t o disks at 1000kg/cm ~, s i n t e r e d at 1200~ in a i r or in n i t r o g e n and s u b m i t t e d to e l e c t r i c c o n d u c t i v i t y m e a s u r e m e n t b e t w e e n 50 and 250~. R e s u l t s and discussion 1. C l i n k e r s Fig. 1 shows the i n f l u e n c e of MgO, burning atmospheres and quenching t e m p e r a t u r e s on t h e b va l u e in t h e H u n t e r ' s e q u a t i o n . In a c c o r d a n c e with th e previous studies i ~ 2~ the b value was remarkably lowered in the p r e s e n c e of MgO in c l i n k e r . The c o n c e n t r a t i o n of F e O was also g r e a t l y decreased w i t h the fail in b v a l u e . The effect of q u e n c h in g t e m p e r a t u r e on the b v a l u e was n o t i c e a b l e f o r the c l i n k e r s w i t h MgO and burnt in n i t r o g e n . The clinker quenched in air from 13 50~, which is apparently higher than the crystallization temperature of the ferrite
o MgO 0% 19
( ): FeO(ppm)
• MgO 1.5%
(850)
(810)
17 15
(860)
(3200)
>~ 13 (2160) 11 9
Nitrogen
Air
7 5
(1 ) I
I
135o
1200
(14o) I
(120) !
|
30(1 1350 1200 Quenching Temp. ( 0(3 )
Fig. 1 Co l o r variation of clinkers
I
3(X)
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BURNINGCONDITIONS,COLOR,FERRITEPHASE
935
phase, was dark g r e y in c o l o r and g a v e t h e s a m e b v a l u e as those burnt in air. By c o n t r a s t , th e c l i n k e r s q u e n c h e d a f t e r t h e c r y s t a l l i z a t i o n of t h e f e r r i t e phase w e r e yellowish brown with t h e b v a l u e s as high as t h o se of t h e c l i n k e r s w i t h o u t MgO. Fig.2 g i v e s t h e e f f e c t of c o o l in g r a t e s on the c o l o r of c l i n k e r s w i t h MgO. The c l i n k e r s w e r e all q u e n c h e d in a ir at 300~. The b v a l u e s r e m a i n e d v i r t u a l l y un ch an g ed with c o o l i n g r a t e s for e a c h burning a t m o s p h e r e . A f t e r r e h e a t i n g in air a t 950g for 15 m i n u t e s , the F e O c o n c e n t r a t i o n in t h e c l i n k e r s burnt in nitrogen decreased to the same l e v e l as in the clinkers burnt in air i r r e s p e c t i v e of th e c o o l i n g r a t e s w h il e t he b v a l u e s did not with slow co o l i n g (100g/rain and 10g/rain). Fig.3 shows t h e e f f e c t of minor a d d i t i o n of TiOz(1.0%) and ZnO(1.0%) on t h e b value. The q u e n c h in g t e m p e r a t u r e and c o o l i n g r a t e w e r e f i x ed at 300g and 10~/min, respectively. TiO2 and ZnO are opposite in effect; i.e., TiO2 i n c r e a s e d t h e b v a l u e while ZnO d e c r e a s e d it. A f t e r r e h e a t i n g in ai r a t 950~, the c l i n k e r s burnt in n i t r o g e n showed t h e s a m e c h a n g e in t h e b v a l u e as t h e slowly c o o l e d c l i n k e r s in Fig.2 and t h e r e v e r s i o n r e m a i n e d i n c o m p l e t e .
21
MgO 1.5% ( ): FeO(ppm)
19
(2600)
17
I I
MgO 1.5% Cooling rate 10 °C/min
21
I (2740) I ~°)Nitrogen
19
A" ~
i
A Nitrogen
17
15
15
~> 13
>
" 11
,
9
(190).
i ,,,~Affer reheating
.o II
reh ating
7
13
•
O
9 7
Air
0 ~
0
Air
5 500 100 10 Cooling rate (°C/rain)
ZnO I ~
No
TiO2 1
Additive Fig.3 Effecl of minor components on clinker color
Fig.2 Effect of cooling rates on clinker color
Fig.4 g i v e s t h e r e l a t i o n b e t w e e n t h e m o l a r r a t i o Me 4*(Si,Ti)/Me 2 ~(Mg,Zn) in t he f e r r i t e phase and t h e b v a l u e . The b values of t h e c l i n k e r s burnt in nitrogen are those a f t e r reheating. The b v a l u e rises in p r o p o r t i o n to Me 4 ~ / Me 2 . , which was i n c r e a s e d by slow co o l i n g in n i t r o g e n or in t h e p r e s e n c e of TiO2. E x t r i n s i c o x y g e n v a c a n c i e s a r e f o r m e d with t h e s u b s t i t u t i o n of Me z~ for AI 3+ and F e 3. to c o m p e n s a t e for t h e d e f i c i e n c y of p o s i t i v e c h a r g e . This p r o c e s s is e x p r e s s e d as follows using t h e KrOger-Vink n o t a t i o n 5> .
gMe
O=2Me
( A , ,
F o
'
+200
+Vo ( V o : Oxygen vacancy)
The c o u p l e d s u b s t i t u t i o n Me 2 ++Me 4 ~ 2 ( A I 3 ~,Fe a ,)6) 7) is e x p e c t e d to d e c r e a s e the n u m b e r of o x y g e n v a c a n c i e s with i n c r e a s i n g Me 4 +/Me ~ ~ r a t i o . Thus, t h e M e4 ~ / Me 2~ r a t i o e x e r t s i n f l u e n c e on t h e b v a l u e through o x y g e n v a c a n c i e s in the f e r r i t e phase.
Vol. 23, No. 4
M. Ichikawa mad Y. Komukai
936
1.4 .0
1.2 '6
E
+
1.0
m
/
No Additive Burning Cooling atmosphere rate(*C/min) 10 1 TiO21o/, Nitrogen 10 2 TiO'21"/, Air 10 3 No Nitrogen 10 4 No Air 10 5 Zn01:~ Nitrogen 10 6 ZnO1'/o Air 500 7 NO. Nitrogen 500 8 No. Air
+
~o
0.8 --
0.6
/ 4 / C~/ O g(~ 5
/'~
-
/O /
" ,
5
i
I0 b value
I
15
Fig.4 Me4+/M~ + molar ratio and b value
2. C 6 A ~ F solid s o l u t io n s Fig.5 shows the influence of c o e x i s t i n g MgO and SiO2 on t h e b values for the C6A2F solid solutions. The specimens were burnt in nitrogen and subsequently reheated in air at 950~. The b value was lowered w i t h the increase in MgO content. But the coexistence of SiO2 considerably depressed this change due probably to the decrease in the number of oxygen vacancies. The C~A~F solid solutions, when unreheated in air, gave almost the same b value as C6A2F.
20 Ig 16 ® >
~
Formula of raw materials A CsA(2-x)MxSxF ~ ~I'i C6A(2-xt2)MxF k
C6A.2F
14 12 I0 8 6 4
SiO2
~
SJO2
E l e c t r i c c o n d u c t i v i t y measurement was i • I i i f made f o r the C6A2F solid solutions 0 0.1 0.2 0.3 0.4 0.5 burnt in nitrogen. The specimens X sintered in a i r at 1200~ also gave the same b values as those reheated in a i r Fig.5 at 950~, while those sintered in Effect of MgO and coexistent of Si02_ nitrogen showed almost as high b v a l u e s as C 6 A 2 F . It is c o n s i d e r e d t h a t this d i f f e r e n c e in color comes f r o m the degree of FeO o x i d a t i o n during sintering as in the clinkers. Fig.6 shows the l o g a r i t h m i c plot o f the specific c o n d u c t i v i t y at 200~ against the b value. The specific c o n d u c t i v i t y f or the specimens sintered in air increases w i t h decreasing b value along a straight line, Whereas the specific c o n d u c t i v i t y f o r the specimens sintered in nitrogen lies widely o f f below the line as that of C6A2F. Between 50 and 250~ the logarithmic plots of the specific conductivity against reciprocal absolute
Vol. 23, No. 4
BURNINGCONDITIONS,COLOR,FERRITEPHASE
937
temperatures gave a straight line fo r each specimen, indicating that the t yp i c a l semi-conduction prevails at these temperatures. Furthermore, the specific c o n d u c t i v i t y rapidly became constant in spite of the d i r e c t i o n of current f l o w, meaning that the c a r r i e r w i l l be electron.
10_3 -
1
2
10 4 -~
10-5 No. Formula of
~0 10_6 0
O
0 ¢,0
10-7 10 -8
Sintering
raw materials
1 2 3 4 5 6 7 8 9
atmosphere
CeA1rtsMo,~F C,sA~5sMo4sSo4d= C,~ 9sM0~F CsAIeMolSolF C~1 ~7~MoosF C~I~Mo o'~Soo~ CoAl77sMI0,~F C~1~sMo~.qo C~F
Air
x,
70 8 (339
Nitrogen Air
I
I
I
5
l0
15
b value Fig.6 Relation between specific conductivity and b value
These results suggest that the presence of electrons released by the o x i d a t i o n of FeO, in association w i t h the occurrence of ex t r in s ic oxygen vacancies, is essential to the darkening of the color of the f e r r i t e phase.
Conclusions I) The f o r m a t i o n of extrinsic oxygen vacancies w i t h the substitution of Me2~(Mg,Zn) f or AI a+ and Fe 3., when coupled w i t h the o x i d a t i o n of FeO during cooling, produces the color change of the f e r r i t e phase from yellowish blown to dark grey. 2) The ferrite phase w i t h yellowish brown even i f FeO r a t i o influences the number phase.
a high Me 4 +(Si,Ti)/Me 2 +(Mg,Zn) ratio remains is oxidized. This indicates that the Me 4 ÷/Me 2 of e x tr i ns ic oxygen vacancies in the f e r r i t e
3) With Co A2 F solid solutions the electric conductivity has a close relationship w i t h the number of oxygen vacancies and electrons released by the o x i d a t i o n o f FeO.
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M. Ichikawa and Y. Komukai
Vol. 23, No. 4
Acknowledgments The authors thank Professor h Maki of the Nagoya Institute of Technology for his helpful discussions. References 1) F.W.Locher; World Cement Technology, 11,[ 2),67 (1980) 2) K.Miyazawa,K,Tomita; Proc. 5th.lnt.Congr~Chem.Cement,Tokyo, 1,252 (1968) 3) H.Ishii,H.Einaga,T.Watanuki; CA3 Review of the 19th General-Meeting, Tokyo,87 (1965) 4) S.Sato,T.Tamura; CA3 Review of the 23rd General Meeting,Tokyo,Lt2 (1969) 5) F.A.KrOger,H.3.Vink; Solid State Physics,3,F.Seitz and O.Turnbull,ED. Academic Press Inc.,New York,307 (1956] 6) A.Katoh; CA3 Review of the 13th General Meeting,Tokyo, 1 (1959) 7) A.Palomo, F.P.Glasser; Advances in Cement Research,2,16~,55 (1989)
E F F E C T O F B U R N I N G C O N D I T I O N S A N D MINOR C O M P O N E N T S ON THE C O L O R O F P O R T L A N D C E M E N T C L I N K E R
M.ICHIKAWA and Y.KOMUKAI Cement&Concrete Research Dept. Central Research Laboratory Chichibu C e m e n t Co.,Ltd. 2-1 - 1, T s u k i m i - C h o , K u m a g a y a - S h i S a i t a m a , 360 J a p a n
(Communicatedby H.F.W. Taylor) (ReceivedAug. 20, 1992) ABSTRACT The s u b s t i t u t i o n of Me 2 ~(Mg,Zn) for AI a ~ and F e a ~ in the c a l c i u m a l u m i n o - f e r r i t e phase, which i n t r o d u c e s e x t r i n s i c o x y g e n v a c a n c i e s in t h e s t r u c t u r e , is e s s e n t i a l to t h e c h a n g e in c o l o r f r o m yellowish brown to dark g r e y . H o w e v e r , an i n c r e a s e of t h e r a t i o Me 4 ~(Si,Ti)/Me z ~ in t h e ferrite phase, which, for e x a m p l e , is e n c o u r a g e d by slow c o o l i n g in n i t r o g e n , r e d u c e s t h e n u m b e r of e x t r i n s i c o x y g e n v a c a n c i e s and p r e v e n t s the above color change. With C 6 A 2 F solid solutions t h e c o l o r c h a n g e is a c c o m p a n i e d by a d e f i n i t e i n c r e a s e in e l e c t r i c c o n d u c t i v i t y , i n d i c a t i n g the significance of electrons released by the oxidation of FeO in a d d i t i o n to t h e o c c u r r e n c e of o x y g e n v a c a n c i e s .
Introduction
Previous studies l) 2) showed that w i t h MgO in c l i n k e r the f e r r i t e phase is dark grey w h i l e i t is yellowish brown w i t h o u t MgO. However, w i t h o u t oxygen in the atmosphere the f e r r i t e phase remains yellowish brown even in the presence of MgO. In the present study laboratory clinkers and C 6 A z F solid solutions of different colors were prepared by systematically changing those factors relevant to the color and subjected to FeO analysis, EPMA and e l e c t r i c c o n d u c t i v i t y measurement. Discussions have been made concerning the mechanism of the color change. Materials
1. C l i n k e r s The c l i n k e r s w i t h and w i t h o u t m i n o r c o m p o n e n t s w e r e p r e p a r e d under d i f f e r e n t burning a t m o s p h e r e s and c o o li n g c o n d i t i o n s . The b asi c c l i n k e r was of t h e q u a r t e r n a r y s y s t e m : SiO2 23.396, Al2Oa 5.196, F e 2 0 3 3.tt96 and C a O 68.0% by w e i g h t . The r a w m i x e s , a f t e r being p e l l e t i z e d , w e r e h e a t e d a t 50Wmin up to 10001~ and t h e n at 30Wmin up to t h e m a x i m u m t e m p e r a t u r e l tt901~ with r e t e n t i o n for 20 and 5 min a t 1000 and 14901~, r e s p e c t i v e l y . Tab l e 1 shows t h e 933
934
Vol. 23, No. 4
M. Ichikawa and Y. Komukai
a t m o s p h e r e s , coo l in g r a t e s and q u e n c h i n g t e m p e r a t u r e s m a d e in air r e g a r d l e s s of t h e burning a t m o s p h e r e s .
employed.
Q u en ch i n g
was
T a b l e 1 Burning c o n d i t i o n s o f c l i n k e r s Atmosphere
Q u en ch i n g temp.(~)
C o o li n g r a t e (~/min)
Air, N2(O2<10 4atm)
20
1350, 1200, 300
Air, N2(O~<10 4atm)
10, 100, 500
300
2. C6A2F solid solutions For s i m p l i c i t y , C6A~z x / 2 ) M x F and CoA~2 x~MxSxF with X=0~0.#5 w e r e p r e p a r e d on a s s u m p t i o n t h a t MgO and SiO~ s u b s t i t u t e for A1203, though part of MgO m ay s u b s t i t u t e for F e 2 0 ~ . The raw m i x e s w e r e burnt in n i t r o g e n on the s a m e h e a t i n g p r o g r a m as in t h e c l i n k e r burning e x c e p t t h a t t h e m a x i m u m t e m p e r a t u r e and t h e r e t e n t i o n t i m e w e r e 1#50~ and 20rain. The fired p r o d u c t s w e r e c o o l e d at 10~/min down to 300~7 in t h e f u r n a c e and then q u e n c h e d in air. C a l c i u m a l u m i n a t e , c a l c i u m s i l i c a t e and p e r i c l a s e w e r e found to c o e x i s t in small q u a n t i t i e s by XRD. Experimental The c o l o r s w e r e m e a s u r e d using a c o l o r d i f f e r e n c e m e t e r for the p r o d u c t s ground to t h e Blaine s p e c i f i c s u r f a c e a r e a of 2 9 0 0 i 1 0 0 c m 2 / g . The r e s u l t s w e r e giv en a c c o r d i n g to t h e H u n t e r ' s e q u a t i o n . F e O was a n a l y z e d by t h e c o l o r m e t r i c method with a - a' d i p y r i d y l as an i n d i c a t o r 3 ~. In slowly cooled clinkers (10~/min) the f e r r i t e c r y s t a l s have been d e v e l o p e d large. Point analysis of the f e r r i t e phase was made using an e l e c t r o n probe m i c r o a n a l y z e r ( J E O L - 8 6 0 0 M ) with a c c e l e r a t i o n v o l t a g e of 15KV and probe c u r r e n t of 2×10 8A. The number of points measured was 10 or m o r e f o r each c l i n k e r sample and the c o r r e c t i o n f o r i n t e n s i t i e s was made by Z A F . The f e r r i t e crystals in r a p i d l y cooled c l i n k e r s (500~/min) w e r e not l a r g e enough f o r EPMA, so that w e t c h e m i c a l analyses w e r e made a f t e r e x t r a c t i n g the f e r r i t e phase 4~ The C o A 2 F solid solutions w e r e pressed i n t o disks at 1000kg/cm ~, s i n t e r e d at 1200~ in a i r or in n i t r o g e n and s u b m i t t e d to e l e c t r i c c o n d u c t i v i t y m e a s u r e m e n t b e t w e e n 50 and 250~. R e s u l t s and discussion 1. C l i n k e r s Fig. 1 shows the i n f l u e n c e of MgO, burning atmospheres and quenching t e m p e r a t u r e s on t h e b va l u e in t h e H u n t e r ' s e q u a t i o n . In a c c o r d a n c e with th e previous studies i ~ 2~ the b value was remarkably lowered in the p r e s e n c e of MgO in c l i n k e r . The c o n c e n t r a t i o n of F e O was also g r e a t l y decreased w i t h the fail in b v a l u e . The effect of q u e n c h in g t e m p e r a t u r e on the b v a l u e was n o t i c e a b l e f o r the c l i n k e r s w i t h MgO and burnt in n i t r o g e n . The clinker quenched in air from 13 50~, which is apparently higher than the crystallization temperature of the ferrite
o MgO 0% 19
( ): FeO(ppm)
• MgO 1.5%
(850)
(810)
17 15
(860)
(3200)
>~ 13 (2160) 11 9
Nitrogen
Air
7 5
(1 ) I
I
135o
1200
(14o) I
(120) !
|
30(1 1350 1200 Quenching Temp. ( 0(3 )
Fig. 1 Co l o r variation of clinkers
I
3(X)
Vol. 23, No. 4
BURNINGCONDITIONS,COLOR,FERRITEPHASE
935
phase, was dark g r e y in c o l o r and g a v e t h e s a m e b v a l u e as those burnt in air. By c o n t r a s t , th e c l i n k e r s q u e n c h e d a f t e r t h e c r y s t a l l i z a t i o n of t h e f e r r i t e phase w e r e yellowish brown with t h e b v a l u e s as high as t h o se of t h e c l i n k e r s w i t h o u t MgO. Fig.2 g i v e s t h e e f f e c t of c o o l in g r a t e s on the c o l o r of c l i n k e r s w i t h MgO. The c l i n k e r s w e r e all q u e n c h e d in a ir at 300~. The b v a l u e s r e m a i n e d v i r t u a l l y un ch an g ed with c o o l i n g r a t e s for e a c h burning a t m o s p h e r e . A f t e r r e h e a t i n g in air a t 950g for 15 m i n u t e s , the F e O c o n c e n t r a t i o n in t h e c l i n k e r s burnt in nitrogen decreased to the same l e v e l as in the clinkers burnt in air i r r e s p e c t i v e of th e c o o l i n g r a t e s w h il e t he b v a l u e s did not with slow co o l i n g (100g/rain and 10g/rain). Fig.3 shows t h e e f f e c t of minor a d d i t i o n of TiOz(1.0%) and ZnO(1.0%) on t h e b value. The q u e n c h in g t e m p e r a t u r e and c o o l i n g r a t e w e r e f i x ed at 300g and 10~/min, respectively. TiO2 and ZnO are opposite in effect; i.e., TiO2 i n c r e a s e d t h e b v a l u e while ZnO d e c r e a s e d it. A f t e r r e h e a t i n g in ai r a t 950~, the c l i n k e r s burnt in n i t r o g e n showed t h e s a m e c h a n g e in t h e b v a l u e as t h e slowly c o o l e d c l i n k e r s in Fig.2 and t h e r e v e r s i o n r e m a i n e d i n c o m p l e t e .
21
MgO 1.5% ( ): FeO(ppm)
19
(2600)
17
I I
MgO 1.5% Cooling rate 10 °C/min
21
I (2740) I ~°)Nitrogen
19
A" ~
i
A Nitrogen
17
15
15
~> 13
>
" 11
,
9
(190).
i ,,,~Affer reheating
.o II
reh ating
7
13
•
O
9 7
Air
0 ~
0
Air
5 500 100 10 Cooling rate (°C/rain)
ZnO I ~
No
TiO2 1
Additive Fig.3 Effecl of minor components on clinker color
Fig.2 Effect of cooling rates on clinker color
Fig.4 g i v e s t h e r e l a t i o n b e t w e e n t h e m o l a r r a t i o Me 4*(Si,Ti)/Me 2 ~(Mg,Zn) in t he f e r r i t e phase and t h e b v a l u e . The b values of t h e c l i n k e r s burnt in nitrogen are those a f t e r reheating. The b v a l u e rises in p r o p o r t i o n to Me 4 ~ / Me 2 . , which was i n c r e a s e d by slow co o l i n g in n i t r o g e n or in t h e p r e s e n c e of TiO2. E x t r i n s i c o x y g e n v a c a n c i e s a r e f o r m e d with t h e s u b s t i t u t i o n of Me z~ for AI 3+ and F e 3. to c o m p e n s a t e for t h e d e f i c i e n c y of p o s i t i v e c h a r g e . This p r o c e s s is e x p r e s s e d as follows using t h e KrOger-Vink n o t a t i o n 5> .
gMe
O=2Me
( A , ,
F o
'
+200
+Vo ( V o : Oxygen vacancy)
The c o u p l e d s u b s t i t u t i o n Me 2 ++Me 4 ~ 2 ( A I 3 ~,Fe a ,)6) 7) is e x p e c t e d to d e c r e a s e the n u m b e r of o x y g e n v a c a n c i e s with i n c r e a s i n g Me 4 +/Me ~ ~ r a t i o . Thus, t h e M e4 ~ / Me 2~ r a t i o e x e r t s i n f l u e n c e on t h e b v a l u e through o x y g e n v a c a n c i e s in the f e r r i t e phase.
Vol. 23, No. 4
M. Ichikawa mad Y. Komukai
936
1.4 .0
1.2 '6
E
+
1.0
m
/
No Additive Burning Cooling atmosphere rate(*C/min) 10 1 TiO21o/, Nitrogen 10 2 TiO'21"/, Air 10 3 No Nitrogen 10 4 No Air 10 5 Zn01:~ Nitrogen 10 6 ZnO1'/o Air 500 7 NO. Nitrogen 500 8 No. Air
+
~o
0.8 --
0.6
/ 4 / C~/ O g(~ 5
/'~
-
/O /
" ,
5
i
I0 b value
I
15
Fig.4 Me4+/M~ + molar ratio and b value
2. C 6 A ~ F solid s o l u t io n s Fig.5 shows the influence of c o e x i s t i n g MgO and SiO2 on t h e b values for the C6A2F solid solutions. The specimens were burnt in nitrogen and subsequently reheated in air at 950~. The b value was lowered w i t h the increase in MgO content. But the coexistence of SiO2 considerably depressed this change due probably to the decrease in the number of oxygen vacancies. The C~A~F solid solutions, when unreheated in air, gave almost the same b value as C6A2F.
20 Ig 16 ® >
~
Formula of raw materials A CsA(2-x)MxSxF ~ ~I'i C6A(2-xt2)MxF k
C6A.2F
14 12 I0 8 6 4
SiO2
~
SJO2
E l e c t r i c c o n d u c t i v i t y measurement was i • I i i f made f o r the C6A2F solid solutions 0 0.1 0.2 0.3 0.4 0.5 burnt in nitrogen. The specimens X sintered in a i r at 1200~ also gave the same b values as those reheated in a i r Fig.5 at 950~, while those sintered in Effect of MgO and coexistent of Si02_ nitrogen showed almost as high b v a l u e s as C 6 A 2 F . It is c o n s i d e r e d t h a t this d i f f e r e n c e in color comes f r o m the degree of FeO o x i d a t i o n during sintering as in the clinkers. Fig.6 shows the l o g a r i t h m i c plot o f the specific c o n d u c t i v i t y at 200~ against the b value. The specific c o n d u c t i v i t y f or the specimens sintered in air increases w i t h decreasing b value along a straight line, Whereas the specific c o n d u c t i v i t y f o r the specimens sintered in nitrogen lies widely o f f below the line as that of C6A2F. Between 50 and 250~ the logarithmic plots of the specific conductivity against reciprocal absolute
Vol. 23, No. 4
BURNINGCONDITIONS,COLOR,FERRITEPHASE
937
temperatures gave a straight line fo r each specimen, indicating that the t yp i c a l semi-conduction prevails at these temperatures. Furthermore, the specific c o n d u c t i v i t y rapidly became constant in spite of the d i r e c t i o n of current f l o w, meaning that the c a r r i e r w i l l be electron.
10_3 -
1
2
10 4 -~
10-5 No. Formula of
~0 10_6 0
O
0 ¢,0
10-7 10 -8
Sintering
raw materials
1 2 3 4 5 6 7 8 9
atmosphere
CeA1rtsMo,~F C,sA~5sMo4sSo4d= C,~ 9sM0~F CsAIeMolSolF C~1 ~7~MoosF C~I~Mo o'~Soo~ CoAl77sMI0,~F C~1~sMo~.qo C~F
Air
x,
70 8 (339
Nitrogen Air
I
I
I
5
l0
15
b value Fig.6 Relation between specific conductivity and b value
These results suggest that the presence of electrons released by the o x i d a t i o n of FeO, in association w i t h the occurrence of ex t r in s ic oxygen vacancies, is essential to the darkening of the color of the f e r r i t e phase.
Conclusions I) The f o r m a t i o n of extrinsic oxygen vacancies w i t h the substitution of Me2~(Mg,Zn) f or AI a+ and Fe 3., when coupled w i t h the o x i d a t i o n of FeO during cooling, produces the color change of the f e r r i t e phase from yellowish blown to dark grey. 2) The ferrite phase w i t h yellowish brown even i f FeO r a t i o influences the number phase.
a high Me 4 +(Si,Ti)/Me 2 +(Mg,Zn) ratio remains is oxidized. This indicates that the Me 4 ÷/Me 2 of e x tr i ns ic oxygen vacancies in the f e r r i t e
3) With Co A2 F solid solutions the electric conductivity has a close relationship w i t h the number of oxygen vacancies and electrons released by the o x i d a t i o n o f FeO.
938
M. Ichikawa and Y. Komukai
Vol. 23, No. 4
Acknowledgments The authors thank Professor h Maki of the Nagoya Institute of Technology for his helpful discussions. References 1) F.W.Locher; World Cement Technology, 11,[ 2),67 (1980) 2) K.Miyazawa,K,Tomita; Proc. 5th.lnt.Congr~Chem.Cement,Tokyo, 1,252 (1968) 3) H.Ishii,H.Einaga,T.Watanuki; CA3 Review of the 19th General-Meeting, Tokyo,87 (1965) 4) S.Sato,T.Tamura; CA3 Review of the 23rd General Meeting,Tokyo,Lt2 (1969) 5) F.A.KrOger,H.3.Vink; Solid State Physics,3,F.Seitz and O.Turnbull,ED. Academic Press Inc.,New York,307 (1956] 6) A.Katoh; CA3 Review of the 13th General Meeting,Tokyo, 1 (1959) 7) A.Palomo, F.P.Glasser; Advances in Cement Research,2,16~,55 (1989)