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Effect of fluorspar on the formation of clinker phases
CEMENT and CONCRETE RESEARCH. Vol. 14, pp. 397-406, 1984. Printed in the USA. 0008-8846/84 $3.00+00. Copyright (c) 1984 Pergamon Press, Ltd.
EFFECT OF FLUORSPARON THE FORMATIONOF CLINKER PHASES M.T. Blanco-Varela, A. Palomo and T. V~zquez
Instituto Eduardo Torroja Madrid 33, Spain (Refereed) (Received Feb. 3, 1983; in final form Jan. 26, 1984) ABSTRACT The evolution of the phases of a commercial clinker in relation to the time and temperature on the clinkerization has been studied. The influence on this evolution by the addition of a small quantity of fluorspar (~ 0.2%) has been determined. The work was basically supported by a study carried out by IR spectroscopy. Introduction The use of fluxes and mineralizers to f a c i l i t a t e the process of clinkerization goes back many years. Klemmand Skalny (1) did a good and complete review about fluxes and mineralizers. The concept of using such fluxes and mineralizers to burn normal raw mixes at a much lower temperature for the sole purpose of reducing the fuel requirements of the kiln, has begun to be seriously considered in the last few years. An effort to study these kinds of compounds has been made. Among these compounds, fluorides and silicofluorides have been studied more, although they have rarely survived commercially, owing to the rapid deterioration of refractory kiln linings and the effects on setting time and strength. The possibility of reducing energy expenses in the clinkerization process by adding to the raw mix a small quantity of fluorspar (approximately 0.2%, since the i n i t i a l criterion adopted is the weight relation CaCO3/CaF2 = 400), has been studied in this paper. For this purpose, the evolution of the s i l i cates, aluminates and ferrites in function of time and temperature of clinkerization has been compared between samples with an addition of CaF2, and with additive-free samples. The study has been basically led by the IR spectroscopy supplemented for the data obtained by XRD, DTA and TGA, optical microscopy and free (uncombined) lime analysis. Experimental Procedure The materials used were Spanish commercial raw mix, and a Spanish commercial fluorspar, of 97% purity. The composition of the raw mix was determined by chemical analyses and is given in Table I. Starting with this raw mix, which will hereafter be referred to as raw mix A (fluoride - free control samples), and of this same raw mix to which fluorspar has been added (~0.2%), which will be referred to as raw mix B, the following operations were carried out: 397
398
Vol. 14, No. 3 M.T. Blanco-Varela, et a l .
Table I L.I. 33.90 -
insol.
SiO 2
AI203
Fe203
CaO
MgO
SO3
Na20
K20
0.20
14.13
4.14
1.76
43.45
1.81
0.50
0.23
0.63
Study by DTA of the thermal behaviour of raw mixes A and B.
The curves of DTA, DTG and TG of raw mix A can be seen in Figure I . These curves, which are very s i m i l a r to those of raw mix B, have several thermal i n d i c a t i o n s between 25 and 1450°C corresponding to chemical or physical t r a n s f o r mations w i t h i n the samples. - Sixteen p e l l e t s from raw mix A and 16 from raw mix B were made up in a hyd r a u l i c press using a c y l i n d r i c a l mould of 2.5 cm inner diameter. Each p e l l e t weighed ~ 4 gr. - With the object of knowing e x a c t l y what phenomena caused the thermal i n d i c a t ions registered in the curves of DTA, DTG and TG, and the influence of f l u o r s p a r in these phenomena, a number of c l i n k e r i z a t i o n s were carried out followed by a i r quenching on the p e l l e t s of raw mixes A and B. The burning temperatures were 1160, 1200, 1250 and 1340°C r e s p e c t i v e l y (temperatures before and a f t e r the thermic i n d i c a t i o n s observed by thermal analyses) The heatings were carried out i s o t h e r m i c a l l y and the time in the furnace was 15, 20, 25 and 30 minutes for each sample. - Once the samples underwent the thermal treatment t h e i r content of free lime was determined and they were also analyzed by XRD and IR spectroscopy with the object of obtaining information about t h e i r mineralogical composition and the v a r i a t i o n of t h i s with the temperature and the time of c l i n k e r i z a t i o n . Likewise, the samples burned during the 30 minutes were submitted to treatment with methanol and s a l i c y l i c acid (Takashima attack) with the object of separating the s i l i c a t e s and free lime from the aluminates and f e r r i t e s . In t h i s way the evol u t i o n and composition of the " l i q u i d phase" could be studied through XRD and IR spectroscopy. Results Studies were made of the behaviour of raw mixes A and B, subjected in the TA furnace to a programmed thermic treatment (V : 8°C/min.) up to a temperature of 1450°C. During the heating, an exothermic descent of the base l i n e between 1160 and 1200°C, followed by a strong exothermic peak with a maximum of 1250°C, was observed in the DTA curve of the two raw mixes A and B (Fig. I ) . This i n dicates that C3S, C2S, f e r r i t e s and aluminates are being produced. At 1290 and 1320°C two endothermic peaks, due to successive melting of compositions which reach i n v a r i a n t p o i n t s , can be observed. During the cooling i t can be seen in the DTA curve two exothermic peaks: the f i r s t at 1225°C is intense and is due to the s o l i d i f i c a t i o n of the l i q u i d phase which was formed during the heating, and the second at IOIO°C is of l i t t l e i n t e n s i t y and is due to the s o l i d i f i c a t i o n of K2SO4 present in the raw mixes. The c l i n k e r s proceeding from the TA were studied by XRD, IR spectroscopy and o p t i c a l microscopy. By means of these techniques, b e t t e r c r y s t a l l i z a t i o n of the s i l i c a t e s and worse c r y s t a l l i z a t i o n of the aluminates in the c l i n k e r with the a d d i t i o n of CaF2, could be observed. In order to know e x a c t l y what phenomena caused the thermal i n d i c a t i o n s regi s t e r e d in the curve of DTA and the i n f l u e n c e of f l u o r s p a r in these phenomena, the raw mixes were heated at the temperatures and durations mentioned in the
Vol. 14, No. 3
399 FLUORSPAR, CLINKER FORMATION, PHASES, TEMPERATURE
iAi I i
!
i
i
.
Y
i
OT&,. /
i i" !
1225
II
• HEATING
] [
I~ COOLING
FIG. 1 DTA, DTG and TG curves of raw mix A. experimental procedure and continuously quenched by a i r . The r e s u l t s of analyzing the c l i n k e r s proceeding from the quenchings by XRD (only those corresponding to the raw mixes which remained 30 minutes in the furnace), as well as the r e s i due of the same, by subjecting them to the Takashima a t t a c k , are given in Table II. The analyses of these c l i n k e r s by IR spectroscopy (Figs. 2 and 3) agree with the r e s u l t s obtained by XRD and also c o n t r i b u t e some other data of i n t e r e s t such as: In the spectra of the residue obtained by submitting the c l i n k e r s to the Takashima a t t a c k , the appearance of bands in 600-700 and 1100-1200 cm-I c h a r a c t e r i s t i c of sulphates, were observed. These bands are i d e n t i f i e d as syngenite, K2SO4, e t t r i n g i t e , CaSO4.2H20, etc. or mixtures of them. No i n t e r p r e t a t i o n has been made of the v a r i a t i o n s of these bands as to temperature, because there are s e r i ous doubts t h a t the Takashima attack may in some way a f f e c t the sulphates, even f a c i l i t a t i n g t h e i r meteorization. -
- The appearance of the c h a r a c t e r i s t i c bands of C12A7 in the spectra of the c l i n k e r s obtained at 1160 and 1200°C are observed; however, i t is important to note t h a t the IR spectrum of ClIA7CaF 2 is very s i m i l a r to t h a t of CI2A 7, being hard to d i f f e r e n t i a t e between them in samples l i k e the ones studied. In these spectra.bands were observed in 990, 940 and 920 cm'l, which i n d i c a t e s v i b r a t i o n s of Si04 ~- tetrahedra w i t h i n the aluminates l a t t i c e . The spectrum of the f l u o r i d e - f r e e c l i n k e r obtained at 1200°C has weak bands c h a r a c t e r i s t i c of cubic C3A. - In the spectrum of the f l u o r i d e - f r e e c l i n k e r obtained at 1250°C, the disappearance of the c h a r a c t e r i s t i c absorptions.. of Cl A is observed; however, is detected in the c l i n k e r with the a d d l t l o n of ~a~2. C12A7
400
Vol. 14, No. 3 M.T. Blanco-Varela, et al.
Table I I X-ray Data of Samples A and B Heated 30 Minutes ( I n t e n s i t y of x-ray d i f f r a c t i o n :
xxx=strong; xx=moderate; x:weak; o:no signal)
SAMPLESWITHOUTFLUORSPAR lJ
SAMPLESWITHFLUORSPAR
CLINKERINGTEMPERATURES(:C)
i,i FF=w
8
1160
1200
1250
C3S
0
X
XX
C2S
X
XX
FREE LIME
XXX
C3A
0
C4AF CI2A7 C2AS
1340
1160
1200
1250
1340
XXX
X
X
XX
XXX
XXX
XX
X
XX
XX
XX
XXX
XX
X
XXX
XXX
XX
0
0
XX
XXX
0
O
XX
XX
X
XXX
XX
XX
XX
XX
0
0
XX
XXX
XX
0
0
XX
XXX
XXX
XX
XXX
XXX
0
0
X
0
0
NC8A3 and cubic C~A is found in both c l i n k e r s , A and B, at t h i s temperature (1250°C). A broad b~nd in 970 cm-I due to vibrations of Si04-4 deformed t e t r a hedra is also found. At 1340°C, NC8A3 and orthorhombic C3A are observed in both c l i n k e r s , A and B. The two spectra have the absorption band of Si044" in 960-980 cm-l. Between the two spectra there is l i t t l e difference - the sharper bands are found in the f l u o r i d e - f r e e sample. The f e r r i t i c phase increases i t s content in A1 from 1160 to 1250°C, i . e . , while the IR spectra of the samples quenched at I160°C have the c h a r a c t e r i s t i c bands of C4AF, the ones of the samples quenched at 1250°C have altered these bands. Even new bands appear. This means that the composition of the f e r r i t i c phase is between C4AF and C6A2F. This phase is now less c r y s t a l l i z e d than before. At 1340°C the f e r r i t i c phase is C4AF, but the c r y s t a l l i z a t i o n is not as good as at I160°C. Table I I I shows the results of the analyses of free lime in the clinkers obtained a f t e r the quenchings. Discussion Evolution of the S i l i c a t e s Having analyzed the results provided by XRD and IR spectroscopy, i t may be deduced that the influence of fluorspar on the formation of the s i l i c a t e phases was as follows: According to the temperature at which the quenching took place, the stable polymorphic of C2S changes. At 1160 and 1200°C, B-C2S was found; at 1250°C,
Vol. 14, No. 3
401 FLUORSPAR, CLINKER FORMATION, PHASES, TEMPERATURE
FIG. 2 IR spectra of clinkers A and B a transition formed between B and ~'-C S and at 1340°C the stable form is ~'C2S. Due to displacements of the band~ v 3 SiO4 in 990 and 850 cm-l toward lower frequencies, ~'-C2S could be identified. - The CRS was detected in the raw mixes with fluorspar at ll60°C while in the fluorideZfree samples, the C3S was not detected until 1200°C. This fact diverges slightly from the affirmation of Gutt and Osborne (2) that when there is F- in the system the lowest limit of the field of s t a b i l i t y of C S is found at ll70°C. However, the fact agrees with Mukerjii (3) who says that tRe lowest limit of the field of s t a b i l i t y of C3S is ll07°C in the system C-S-CaF2, although this author does not take in consideration the existence of 3C3S.CaF2. The CaF2 also increases the velocity of the formation of C3S at any temperature (in the interval of those studied), a fact that is deduced by the greater intensity of the peaks of XRD and by the lessening of free lime. I t agrees with the results of several authors (4,5,6).
402
Vol. 14, No. 3 M.T. Blanco-Varela, et al.
"~
.~',
moo
mo
~
wuo
wo
~
~
~
I
FIG. 3 IR spectra corresponding to the residue obtained when submitting clinkers A and B to the Takashima attack.
Vol. 14, No. 3
403 FLUORSPAR, CLINKER FORMATION, PHASES, TEMPERATURE
Table I I I Results of the free lime analyses made in the c l i n k e r s A and B CLINKERING TEMPERATURES (°C) 1200
1160
i AGE I (minutes)
15
A
% FREE LIME
27.8
B
% FREE LIME 2 5 . 9
30
1250
1340
30
15
30
15
30
25.5 23.1
19.6
9.4
7.1
4.8
3.2
21.7'1 18.2
15.1
7.8
6.0
4.5
2.7
15
I
I
- F i n a l l y , the form of the bands of the IR spectra due to s i l i c a t e s indicates a greater s t r u c t u r a l order provoked by the F-. Evolution of the L i q u i d Phase The e v o l u t i o n of the components of the s o - c a l l e d " l i q u i d phase" with temperature and the presence or absence of f l u o r s p a r may be described in the f o l lowing manner: F e r r i t i c phase. The f e r r i t i c phase may be considered as a s o l i d s o l u t i o n of a general formula C2(AI_xFx ) in which x may have values between 1 and 0.33. The formation of t h i s phase may be from C2F and l a t e r Fe s u b s t i t u t e d by AI. The s t r u c t u r e is orthorhombic, having t e t r a h e d r a l and octahedral coordinations. I n i t i a l l y the A1 s u b s t i t u t e s Fe in the tetrahedral coordination and l a t e r t e t r a h e d r a l l y and o c t a h e d r a l l y . In t h i s manner composites are formed according to the f o l l o w i n g sequence: A1 A1 A1 C2F
> C6AF2
> C4AF
> C6A2F
As the proportion of A1 increases in the general formula of the f e r r i t i c phase C2(AI_xFx), the f o l l o w i n g are observed in the corresponding spectra (7): 1°, - Appearance of bands c h a r a c t e r i s t i c of AIO4, i . e . absorptions in 780 and 830 cm-~ and perhaps bands c h a r a c t e r i s t i c of AIO~ in 400-600cm -1. Simultaneously, a lessening of the absorptions in 60~:700 cm- I ( v i brations of FeO4) and also in 400-450 and 300-400 cm- I ( v i b r a t i o n s of FeO6) i s observed. 2°. - As the s u b s t i t u t i o n of Fe by A1 increases, the i n t e n s i t y of the bands in 700-800 cm-I increases and above a l l the i n t e n s i t y increases in 450 cm-l. The o u t l i n e of the bands varies p r o g r e s s i v e l y . 3° . - The bands vary toward higher frequencies as the proportion of A1 i n creases. On comparing the v a r i a t i o n s which, in the IR spectra, are experienced by the bands of adsorption corresnonding to the f e r r i t i c phase when the temperature i n creases from 1160 to 1250°C i t i s deduced t h a t i n i t i a l l y at I160°C there e x i s t s a f e r r i t i c phase with a composition l i k e C4AF and as the temperature increases, the phase reaches a composition compressed between C4AF and C6A2F. I t may be affirmed (from the form of the bands) t h a t the f e r r i t i c phase is well c r y s t a l l i z e d at low temperatures (up to 1250°C).
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Vol. 14, No. 3 M.T. Blanco-Varela, et al.
On reaching 1340°C, the i n t e r s t i t i a l phase melted and on quenching there remained a f e r r i t i c phase very rich in Fe and a poorly crystallized and vitreous phase rich in Al. Aluminates. C ~ Pure C3A is cubic with a parameter of unit element = 15.263 + 0.003 X . . , , s compound admits oxides as impurities Cup to certain proportion~) in i t s l a t t i c e , which substitutes atoms of Al and/or Ca and which provokes variations in the size of the parameter of the l a t t i c e but which does not cause a change of symmetry from cubic to orthorhombic. Thus, the Al may be substituted by Fe (8,9) or Si (lO) up to certain limits causing increases in the size of the unit element as in the case of Fe, or reductions in the case of Si. Naturally, for a correct balance of loads when i t is the Si which replaces Al, there are two options: one atom of Si replaces two atoms of Al. In this way, the remaining one extra oxygen must be accommodated in the structure or 4 atoms of Al replaced by 3 of Si, a vacant hole thus remaining. The Na20 replaces the CaO, and as this replacement is taking place, the parameter "a" of the unit element slowly lessons until the concentration of Na20 reaches 3%. From this moment, the C3A, which is s t i l l cubic, changes to orthorhombic (lO). In the IR spectra of the residue obtained after submitting the fluoridefree clinkers to the Takashima attack, the appearance of the characteristic bands of C3A was not observed in those samples heated below 1200°C. The spectum of the sample heated at 1200°C has weak bands which are characteristic of the ring Al6018 of the cubic C3A. In the spectrum B (sample with fluoride) at this temperature, these absorptions do not exist. At 1250°C, both spectra A and B have the absorptions of the cubic C3A. Perhaps the effect of the fluoride in these samples is not a strong one, nevertheless a variation is observed in the band in 910 cm-l which can be assigned to the vibrations stretching O-Al-O i l l ) . I t is also observed in the two spectra the appearance of a broad band in 970 cm-l due to deformed tetrahedra SiO4 which replaces AIO4, also deformed within the structure of the cubic C3A. In the spectra of the samples heated to 1340°C, l i t t l e bands, due to orthor. hombic C3A, are seen. This is due to the presence of impurities (for example Na+) and the substitutions of SiO4 - AlO4 in the l a t t i c e of the C3A. NC8A3: The existence of NCsA3 in the clinkers is a function of two variables: content of Na20 and speea of cooling. Suzukawa (12), in his studies of NC8A3 affirms that with the presence of an excess of Na20 and rapid cooling, th~s-composite is obtained, while i f the cooling is slow, C3A and Na2SO4 are obtained. In the opinion of this author, the NC8A3 contains some SiO2 in i t s structure due to partial substitutions of lime-aluminium by sodium-silicon. Thus, in the clinkers of high temperature (1250 and 1340°C), since there already existed C3A with SiO4 in i t s l a t t i c e and the Na20 was present, NC8A3 was formed, which on being subjected to rapid cooling remained stabilized as such and was not transformed into C3A. of dlffractlon The lines " " " of NC8A3 are very sl"milar to that of C3A; thus the NC8A3 was identified as C3A by XRD. However, in the IR spectra, the bands appearing in 865, 798, 725, 530, 520, and 400 cm-l are interpreted as characteri s t i c of NC8A3 (13). C2AS: The gehlenite is an intermediate compound within the process of clinkerization which is i n i t i a l l y formed by solid state reactions. As the temperature is increased, gehlenite reacts to produce C3A and C2S (14). The content of gehlenite in the clinkers diminishes progressively when the temperature increases. At 1250°C gehlenite was not found. At ll60 and 1200°C, a higher
Vol. 14, No. 3
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FLUORSPAR, CLINKER FORMATION, PHASES, TEMPERATURE
proportion of gehlenite was found in the fluoride-free samples, i.e. fluorides i n h i b i t , partially at least, the formation of gehlenite. I t was also observed that the CI2A7 formed, increased as the gehlenite diminished (in those samples with CaF2). This is probably because the addition of CaF2 to the system extends the primary field of CI2A7 ss (15). CI2A7 and CIIA7CaF2: As reported in the results, the IR spectra of our clinker: have the bands of the CI2A7• We also found three bands in 990, 940 and 920 cm-~ which can be assigned to different vibrations of tetrahedra of SiO4 within the structure of the aluminates. The highest frequency absorption is due to tetrahedra of SiO4, probably deformed, which replaces tetrahedra of AlO4, also deformed. This band in 990 cm-l does not change either when the temperature changes or with the addition of CaF2. However, the bands in 920 and 940 cm-l change as the temperature increases and for the same temperature with the addition of CaF2. These facts are interpreted in the following manner: The CI2A7 can introduce within i t s l a t t i c e , tetrahedra of SiO4 which replaces tetrahedra of AlO4. I t originates the absorptions in 990, 940 and 920 cm-i. When there is fluoride in the system, the compound formed is the CIIATCaF2 which prevents the tetrahedra of SiO4 (those responsible for the vibrations In 940 and 920 cm- I ) to be icluded within i t s lattice. To summarize the evolution of the aluminates, i t can be said that at ll60 and 1200°C, the clinkers have a phase similar to CI2A7; at 1250°C they have cubic C3A and at 1340°C a phase like NC8A3 with orthorhombic structure. All the phases mentioned are not pure ones. All have SiO4 which replaces AlO4. Of course, because of the correct balance of loads, the substitutions can be multiple ones, for example CaAI-NaSi giving in the case of the C3A a phase like (16): ((Ca72_(n+m))(Na(2n+m))72+n(A148_mSim)480144) Han, et al. (16), considered that the multiple substitutions involve the formation of a solid solution in C3A with this general formula: ((Ca)72-(n+m)(Na(2n+m)))72+n((Al)48_(m_z)(Si(m+3/4z))48_i/4z)O144 With regard to CI2A7, Jeevaratnam, et al. say that CI2A7 contains two reactive 02- per cell which may be wholly or partly replaced by up to four univalent ions with only slight concomitant changes in cell size and density. Thus, by mean of the substitution of one of these 0~-, the CIIA7.CaF2 may be formed. In the samples under study, substitutions of Si04-AlO4 within the lattice of the CI2A7 are observed. These substitutions may be like Si X-CaAI (X=Na,K). I t would produce a phase like Ca12_nAl14_nSinXn033. The substitutions Si04-AlO4 are not admitted in the lattice of the CIIA7CaF2 as easily as with the CI2A7. Finally, in the IR spectra of the samples heated at 1340°C, i t is observed that the incorporation of strange ions within the lattice of C3A produces a strong change in the symmetry of the rings A I t is explained as a change C3-Ci. I t agrees with Boikova, et al. ( l l ) _ 16018" .I.nfluence of the Time Clinkerization in the Speed of Reaction All the thermic treatment applied to the samples under study were carried out at different times (15, 20, 25 and 30 minutes) with the object of studying the influence of the time of clinkerization in the velocity of the reactions. The results obtained on anlayzing all the clinkers by XRD, those obtained by analyses of the free lime given in Table I l l , and those obtained on analyzing the free lime at the temperatures already mentioned but during 5 and lO minutes,
406
Vol. 14, No. 3 M.T. Blanco-Varela, et al.
show that at low temperatures (up to 1200°C) the reactions are t o t a l l y completed between the f i r s t I0 and 15 minutes of the reaction; at worst, the difference of the lime combined at I0 and 30 minutes, is in the order of 4%. At high temperatures (1250 and 1340°C), when we compare the combined lime at 15 and at 30 minutes, the difference of 4% decreases by ~2% in r e l a t i v e value. This 2% difference now has a greater importance since the lime must be t o t a l l y combined. At a high temperature, the formation of phases is carried out in i t s majority during the f i r s t 15 minutes of reaction, although the effects on the samples of greater period in the furnace is more important than lower temperatures. Conclusions From this work, the following conclusions can be made: I) Fluorspar, even when used in a small proportion, lowers the temperature of the formation of C~S and increases the speed of the formation of the s i l i c a t e s 2) Fluorspar stlmulates the discomposition of the gehlenite favouring simultaneously the formation of ClIA7CaF2 between 1160 and 1200°C. 3) As the gehlenite decomposes in the presence of fluorspar between 1160 and 1200°C, C2S, cubic CRA and/or CIIA7CaF 2 are formed. 4) Substitutions S~04-AI04 are admitted w i t h i n the l a t t i c e of C12A7. These s u b s t i t u t i o n s are p a r t l y prevented when s u b s t i t u t i o n s F--O 2-12 take place within the C12A7 to produce CllA7CaF 2. Thus be means of IR spectroscopy, i t is possible to discern between C12A7 and CIIA7CaF 2 in s i m i l a r samples to those already studied. 5) An increase of the temperature from I160°C u n t i l the formation of the l i q u i d phase, produces in the f e r r i t i c phase of these c l i n k e r s , a progressive enrichment in aluminium. On passing the melting temperatures of the f e r r i t e s and aluminates and l a t e r cooling the c l i n k e r r a p i d l y , a c r y s t a l l i z a t i o n (poor) of a f e r r i t i c phase rich in Fe is produced. 6) The reactions are mainly produced before the f i r s t 15 minutes of keeping the samples inside the furnace. 7) I t w i l l be necessary to study the way of increasing the speed of reaction between 1160 and 1250°C and attempting to lower the temperature of formation of euthectics. References 1 2 3 4 5 6 7. 8. 9. I0. II. 12. 13. 14. 15. 16. 17.
W . A . Klemm and J. Skalny, Cements Research Progress, 259-291 (1976). W. Gutt and G.J. Osborne, Trans. B r i t . Ceram. Soc. 69, 3, 125-129 (1970). M u k e r j i i , Memoires S c i e n t i f i q u e s , Rev. Metallurgh; IF, No. I I , 785~96 (1963). W.A. Klemm, I. Jawed and K.L. Holub, Cem. Concr. Res. 9, 489-496 (1979). S.G. Ampian and E.P. F l i n t , Am. Ceram. Soc. Bull. 52, 8, 604-620 (1973). N.H. Christensen and V. Johansen, 7th I n t l . Congre~ on the Chemistry of Cement, Vol. I I , 1.1-1.5, Paris (1980). P. Tarte, S i l . Indust. Vol. 33, No. I I , p. 333 (1968). A.J. Majumdar, B r i t . Ceram. Soc. Vol. 64, No. 2, p. 105 (1965). P. Tarte, Nature 207, N. 5000, 973 ( 1 9 ~ ) . M.A.E. Moore, S i l . Indust. Vol. 32, p. 87 (1967). A . I . Boikova, A . I . Domansky, V.A.---Paramonova, G.P. Stavitskaja and V.M. Nikushchenko, Cem. Concr. Res. 7, 483-492 (1977). Y. Suzukawa, Zement Kalk Gips 9~ 345, 390, 433 (1956). T: V6zquez, Monograf~a No. 297, I n s t i t u t o Eduardo Torroja de la Construcclon y del Cemento. Madrid (Espa~a) (1971). S. Chromy, VI Intern. Congress Chem. Cem. S e c . - l l l - l l l - 8 Moscow (1984). K. Asok Sarkar, D.M. Roy and R.M. Smart, 7th I n t l . Congress of Chemistry of Cement, Vol. I I 1-195 1-201, Paris (1980). K.S. Han, J.A. Garg and F.P. Glasser, Cem. Concr. Res. __II, 79-74 (1981). J. Jeevaratnam, F.P. Glasser and L.S. Glasser, J. Am. Ceram. Soc. 47, 105106 (1964).
EFFECT OF FLUORSPARON THE FORMATIONOF CLINKER PHASES M.T. Blanco-Varela, A. Palomo and T. V~zquez
Instituto Eduardo Torroja Madrid 33, Spain (Refereed) (Received Feb. 3, 1983; in final form Jan. 26, 1984) ABSTRACT The evolution of the phases of a commercial clinker in relation to the time and temperature on the clinkerization has been studied. The influence on this evolution by the addition of a small quantity of fluorspar (~ 0.2%) has been determined. The work was basically supported by a study carried out by IR spectroscopy. Introduction The use of fluxes and mineralizers to f a c i l i t a t e the process of clinkerization goes back many years. Klemmand Skalny (1) did a good and complete review about fluxes and mineralizers. The concept of using such fluxes and mineralizers to burn normal raw mixes at a much lower temperature for the sole purpose of reducing the fuel requirements of the kiln, has begun to be seriously considered in the last few years. An effort to study these kinds of compounds has been made. Among these compounds, fluorides and silicofluorides have been studied more, although they have rarely survived commercially, owing to the rapid deterioration of refractory kiln linings and the effects on setting time and strength. The possibility of reducing energy expenses in the clinkerization process by adding to the raw mix a small quantity of fluorspar (approximately 0.2%, since the i n i t i a l criterion adopted is the weight relation CaCO3/CaF2 = 400), has been studied in this paper. For this purpose, the evolution of the s i l i cates, aluminates and ferrites in function of time and temperature of clinkerization has been compared between samples with an addition of CaF2, and with additive-free samples. The study has been basically led by the IR spectroscopy supplemented for the data obtained by XRD, DTA and TGA, optical microscopy and free (uncombined) lime analysis. Experimental Procedure The materials used were Spanish commercial raw mix, and a Spanish commercial fluorspar, of 97% purity. The composition of the raw mix was determined by chemical analyses and is given in Table I. Starting with this raw mix, which will hereafter be referred to as raw mix A (fluoride - free control samples), and of this same raw mix to which fluorspar has been added (~0.2%), which will be referred to as raw mix B, the following operations were carried out: 397
398
Vol. 14, No. 3 M.T. Blanco-Varela, et a l .
Table I L.I. 33.90 -
insol.
SiO 2
AI203
Fe203
CaO
MgO
SO3
Na20
K20
0.20
14.13
4.14
1.76
43.45
1.81
0.50
0.23
0.63
Study by DTA of the thermal behaviour of raw mixes A and B.
The curves of DTA, DTG and TG of raw mix A can be seen in Figure I . These curves, which are very s i m i l a r to those of raw mix B, have several thermal i n d i c a t i o n s between 25 and 1450°C corresponding to chemical or physical t r a n s f o r mations w i t h i n the samples. - Sixteen p e l l e t s from raw mix A and 16 from raw mix B were made up in a hyd r a u l i c press using a c y l i n d r i c a l mould of 2.5 cm inner diameter. Each p e l l e t weighed ~ 4 gr. - With the object of knowing e x a c t l y what phenomena caused the thermal i n d i c a t ions registered in the curves of DTA, DTG and TG, and the influence of f l u o r s p a r in these phenomena, a number of c l i n k e r i z a t i o n s were carried out followed by a i r quenching on the p e l l e t s of raw mixes A and B. The burning temperatures were 1160, 1200, 1250 and 1340°C r e s p e c t i v e l y (temperatures before and a f t e r the thermic i n d i c a t i o n s observed by thermal analyses) The heatings were carried out i s o t h e r m i c a l l y and the time in the furnace was 15, 20, 25 and 30 minutes for each sample. - Once the samples underwent the thermal treatment t h e i r content of free lime was determined and they were also analyzed by XRD and IR spectroscopy with the object of obtaining information about t h e i r mineralogical composition and the v a r i a t i o n of t h i s with the temperature and the time of c l i n k e r i z a t i o n . Likewise, the samples burned during the 30 minutes were submitted to treatment with methanol and s a l i c y l i c acid (Takashima attack) with the object of separating the s i l i c a t e s and free lime from the aluminates and f e r r i t e s . In t h i s way the evol u t i o n and composition of the " l i q u i d phase" could be studied through XRD and IR spectroscopy. Results Studies were made of the behaviour of raw mixes A and B, subjected in the TA furnace to a programmed thermic treatment (V : 8°C/min.) up to a temperature of 1450°C. During the heating, an exothermic descent of the base l i n e between 1160 and 1200°C, followed by a strong exothermic peak with a maximum of 1250°C, was observed in the DTA curve of the two raw mixes A and B (Fig. I ) . This i n dicates that C3S, C2S, f e r r i t e s and aluminates are being produced. At 1290 and 1320°C two endothermic peaks, due to successive melting of compositions which reach i n v a r i a n t p o i n t s , can be observed. During the cooling i t can be seen in the DTA curve two exothermic peaks: the f i r s t at 1225°C is intense and is due to the s o l i d i f i c a t i o n of the l i q u i d phase which was formed during the heating, and the second at IOIO°C is of l i t t l e i n t e n s i t y and is due to the s o l i d i f i c a t i o n of K2SO4 present in the raw mixes. The c l i n k e r s proceeding from the TA were studied by XRD, IR spectroscopy and o p t i c a l microscopy. By means of these techniques, b e t t e r c r y s t a l l i z a t i o n of the s i l i c a t e s and worse c r y s t a l l i z a t i o n of the aluminates in the c l i n k e r with the a d d i t i o n of CaF2, could be observed. In order to know e x a c t l y what phenomena caused the thermal i n d i c a t i o n s regi s t e r e d in the curve of DTA and the i n f l u e n c e of f l u o r s p a r in these phenomena, the raw mixes were heated at the temperatures and durations mentioned in the
Vol. 14, No. 3
399 FLUORSPAR, CLINKER FORMATION, PHASES, TEMPERATURE
iAi I i
!
i
i
.
Y
i
OT&,. /
i i" !
1225
II
• HEATING
] [
I~ COOLING
FIG. 1 DTA, DTG and TG curves of raw mix A. experimental procedure and continuously quenched by a i r . The r e s u l t s of analyzing the c l i n k e r s proceeding from the quenchings by XRD (only those corresponding to the raw mixes which remained 30 minutes in the furnace), as well as the r e s i due of the same, by subjecting them to the Takashima a t t a c k , are given in Table II. The analyses of these c l i n k e r s by IR spectroscopy (Figs. 2 and 3) agree with the r e s u l t s obtained by XRD and also c o n t r i b u t e some other data of i n t e r e s t such as: In the spectra of the residue obtained by submitting the c l i n k e r s to the Takashima a t t a c k , the appearance of bands in 600-700 and 1100-1200 cm-I c h a r a c t e r i s t i c of sulphates, were observed. These bands are i d e n t i f i e d as syngenite, K2SO4, e t t r i n g i t e , CaSO4.2H20, etc. or mixtures of them. No i n t e r p r e t a t i o n has been made of the v a r i a t i o n s of these bands as to temperature, because there are s e r i ous doubts t h a t the Takashima attack may in some way a f f e c t the sulphates, even f a c i l i t a t i n g t h e i r meteorization. -
- The appearance of the c h a r a c t e r i s t i c bands of C12A7 in the spectra of the c l i n k e r s obtained at 1160 and 1200°C are observed; however, i t is important to note t h a t the IR spectrum of ClIA7CaF 2 is very s i m i l a r to t h a t of CI2A 7, being hard to d i f f e r e n t i a t e between them in samples l i k e the ones studied. In these spectra.bands were observed in 990, 940 and 920 cm'l, which i n d i c a t e s v i b r a t i o n s of Si04 ~- tetrahedra w i t h i n the aluminates l a t t i c e . The spectrum of the f l u o r i d e - f r e e c l i n k e r obtained at 1200°C has weak bands c h a r a c t e r i s t i c of cubic C3A. - In the spectrum of the f l u o r i d e - f r e e c l i n k e r obtained at 1250°C, the disappearance of the c h a r a c t e r i s t i c absorptions.. of Cl A is observed; however, is detected in the c l i n k e r with the a d d l t l o n of ~a~2. C12A7
400
Vol. 14, No. 3 M.T. Blanco-Varela, et al.
Table I I X-ray Data of Samples A and B Heated 30 Minutes ( I n t e n s i t y of x-ray d i f f r a c t i o n :
xxx=strong; xx=moderate; x:weak; o:no signal)
SAMPLESWITHOUTFLUORSPAR lJ
SAMPLESWITHFLUORSPAR
CLINKERINGTEMPERATURES(:C)
i,i FF=w
8
1160
1200
1250
C3S
0
X
XX
C2S
X
XX
FREE LIME
XXX
C3A
0
C4AF CI2A7 C2AS
1340
1160
1200
1250
1340
XXX
X
X
XX
XXX
XXX
XX
X
XX
XX
XX
XXX
XX
X
XXX
XXX
XX
0
0
XX
XXX
0
O
XX
XX
X
XXX
XX
XX
XX
XX
0
0
XX
XXX
XX
0
0
XX
XXX
XXX
XX
XXX
XXX
0
0
X
0
0
NC8A3 and cubic C~A is found in both c l i n k e r s , A and B, at t h i s temperature (1250°C). A broad b~nd in 970 cm-I due to vibrations of Si04-4 deformed t e t r a hedra is also found. At 1340°C, NC8A3 and orthorhombic C3A are observed in both c l i n k e r s , A and B. The two spectra have the absorption band of Si044" in 960-980 cm-l. Between the two spectra there is l i t t l e difference - the sharper bands are found in the f l u o r i d e - f r e e sample. The f e r r i t i c phase increases i t s content in A1 from 1160 to 1250°C, i . e . , while the IR spectra of the samples quenched at I160°C have the c h a r a c t e r i s t i c bands of C4AF, the ones of the samples quenched at 1250°C have altered these bands. Even new bands appear. This means that the composition of the f e r r i t i c phase is between C4AF and C6A2F. This phase is now less c r y s t a l l i z e d than before. At 1340°C the f e r r i t i c phase is C4AF, but the c r y s t a l l i z a t i o n is not as good as at I160°C. Table I I I shows the results of the analyses of free lime in the clinkers obtained a f t e r the quenchings. Discussion Evolution of the S i l i c a t e s Having analyzed the results provided by XRD and IR spectroscopy, i t may be deduced that the influence of fluorspar on the formation of the s i l i c a t e phases was as follows: According to the temperature at which the quenching took place, the stable polymorphic of C2S changes. At 1160 and 1200°C, B-C2S was found; at 1250°C,
Vol. 14, No. 3
401 FLUORSPAR, CLINKER FORMATION, PHASES, TEMPERATURE
FIG. 2 IR spectra of clinkers A and B a transition formed between B and ~'-C S and at 1340°C the stable form is ~'C2S. Due to displacements of the band~ v 3 SiO4 in 990 and 850 cm-l toward lower frequencies, ~'-C2S could be identified. - The CRS was detected in the raw mixes with fluorspar at ll60°C while in the fluorideZfree samples, the C3S was not detected until 1200°C. This fact diverges slightly from the affirmation of Gutt and Osborne (2) that when there is F- in the system the lowest limit of the field of s t a b i l i t y of C S is found at ll70°C. However, the fact agrees with Mukerjii (3) who says that tRe lowest limit of the field of s t a b i l i t y of C3S is ll07°C in the system C-S-CaF2, although this author does not take in consideration the existence of 3C3S.CaF2. The CaF2 also increases the velocity of the formation of C3S at any temperature (in the interval of those studied), a fact that is deduced by the greater intensity of the peaks of XRD and by the lessening of free lime. I t agrees with the results of several authors (4,5,6).
402
Vol. 14, No. 3 M.T. Blanco-Varela, et al.
"~
.~',
moo
mo
~
wuo
wo
~
~
~
I
FIG. 3 IR spectra corresponding to the residue obtained when submitting clinkers A and B to the Takashima attack.
Vol. 14, No. 3
403 FLUORSPAR, CLINKER FORMATION, PHASES, TEMPERATURE
Table I I I Results of the free lime analyses made in the c l i n k e r s A and B CLINKERING TEMPERATURES (°C) 1200
1160
i AGE I (minutes)
15
A
% FREE LIME
27.8
B
% FREE LIME 2 5 . 9
30
1250
1340
30
15
30
15
30
25.5 23.1
19.6
9.4
7.1
4.8
3.2
21.7'1 18.2
15.1
7.8
6.0
4.5
2.7
15
I
I
- F i n a l l y , the form of the bands of the IR spectra due to s i l i c a t e s indicates a greater s t r u c t u r a l order provoked by the F-. Evolution of the L i q u i d Phase The e v o l u t i o n of the components of the s o - c a l l e d " l i q u i d phase" with temperature and the presence or absence of f l u o r s p a r may be described in the f o l lowing manner: F e r r i t i c phase. The f e r r i t i c phase may be considered as a s o l i d s o l u t i o n of a general formula C2(AI_xFx ) in which x may have values between 1 and 0.33. The formation of t h i s phase may be from C2F and l a t e r Fe s u b s t i t u t e d by AI. The s t r u c t u r e is orthorhombic, having t e t r a h e d r a l and octahedral coordinations. I n i t i a l l y the A1 s u b s t i t u t e s Fe in the tetrahedral coordination and l a t e r t e t r a h e d r a l l y and o c t a h e d r a l l y . In t h i s manner composites are formed according to the f o l l o w i n g sequence: A1 A1 A1 C2F
> C6AF2
> C4AF
> C6A2F
As the proportion of A1 increases in the general formula of the f e r r i t i c phase C2(AI_xFx), the f o l l o w i n g are observed in the corresponding spectra (7): 1°, - Appearance of bands c h a r a c t e r i s t i c of AIO4, i . e . absorptions in 780 and 830 cm-~ and perhaps bands c h a r a c t e r i s t i c of AIO~ in 400-600cm -1. Simultaneously, a lessening of the absorptions in 60~:700 cm- I ( v i brations of FeO4) and also in 400-450 and 300-400 cm- I ( v i b r a t i o n s of FeO6) i s observed. 2°. - As the s u b s t i t u t i o n of Fe by A1 increases, the i n t e n s i t y of the bands in 700-800 cm-I increases and above a l l the i n t e n s i t y increases in 450 cm-l. The o u t l i n e of the bands varies p r o g r e s s i v e l y . 3° . - The bands vary toward higher frequencies as the proportion of A1 i n creases. On comparing the v a r i a t i o n s which, in the IR spectra, are experienced by the bands of adsorption corresnonding to the f e r r i t i c phase when the temperature i n creases from 1160 to 1250°C i t i s deduced t h a t i n i t i a l l y at I160°C there e x i s t s a f e r r i t i c phase with a composition l i k e C4AF and as the temperature increases, the phase reaches a composition compressed between C4AF and C6A2F. I t may be affirmed (from the form of the bands) t h a t the f e r r i t i c phase is well c r y s t a l l i z e d at low temperatures (up to 1250°C).
404
Vol. 14, No. 3 M.T. Blanco-Varela, et al.
On reaching 1340°C, the i n t e r s t i t i a l phase melted and on quenching there remained a f e r r i t i c phase very rich in Fe and a poorly crystallized and vitreous phase rich in Al. Aluminates. C ~ Pure C3A is cubic with a parameter of unit element = 15.263 + 0.003 X . . , , s compound admits oxides as impurities Cup to certain proportion~) in i t s l a t t i c e , which substitutes atoms of Al and/or Ca and which provokes variations in the size of the parameter of the l a t t i c e but which does not cause a change of symmetry from cubic to orthorhombic. Thus, the Al may be substituted by Fe (8,9) or Si (lO) up to certain limits causing increases in the size of the unit element as in the case of Fe, or reductions in the case of Si. Naturally, for a correct balance of loads when i t is the Si which replaces Al, there are two options: one atom of Si replaces two atoms of Al. In this way, the remaining one extra oxygen must be accommodated in the structure or 4 atoms of Al replaced by 3 of Si, a vacant hole thus remaining. The Na20 replaces the CaO, and as this replacement is taking place, the parameter "a" of the unit element slowly lessons until the concentration of Na20 reaches 3%. From this moment, the C3A, which is s t i l l cubic, changes to orthorhombic (lO). In the IR spectra of the residue obtained after submitting the fluoridefree clinkers to the Takashima attack, the appearance of the characteristic bands of C3A was not observed in those samples heated below 1200°C. The spectum of the sample heated at 1200°C has weak bands which are characteristic of the ring Al6018 of the cubic C3A. In the spectrum B (sample with fluoride) at this temperature, these absorptions do not exist. At 1250°C, both spectra A and B have the absorptions of the cubic C3A. Perhaps the effect of the fluoride in these samples is not a strong one, nevertheless a variation is observed in the band in 910 cm-l which can be assigned to the vibrations stretching O-Al-O i l l ) . I t is also observed in the two spectra the appearance of a broad band in 970 cm-l due to deformed tetrahedra SiO4 which replaces AIO4, also deformed within the structure of the cubic C3A. In the spectra of the samples heated to 1340°C, l i t t l e bands, due to orthor. hombic C3A, are seen. This is due to the presence of impurities (for example Na+) and the substitutions of SiO4 - AlO4 in the l a t t i c e of the C3A. NC8A3: The existence of NCsA3 in the clinkers is a function of two variables: content of Na20 and speea of cooling. Suzukawa (12), in his studies of NC8A3 affirms that with the presence of an excess of Na20 and rapid cooling, th~s-composite is obtained, while i f the cooling is slow, C3A and Na2SO4 are obtained. In the opinion of this author, the NC8A3 contains some SiO2 in i t s structure due to partial substitutions of lime-aluminium by sodium-silicon. Thus, in the clinkers of high temperature (1250 and 1340°C), since there already existed C3A with SiO4 in i t s l a t t i c e and the Na20 was present, NC8A3 was formed, which on being subjected to rapid cooling remained stabilized as such and was not transformed into C3A. of dlffractlon The lines " " " of NC8A3 are very sl"milar to that of C3A; thus the NC8A3 was identified as C3A by XRD. However, in the IR spectra, the bands appearing in 865, 798, 725, 530, 520, and 400 cm-l are interpreted as characteri s t i c of NC8A3 (13). C2AS: The gehlenite is an intermediate compound within the process of clinkerization which is i n i t i a l l y formed by solid state reactions. As the temperature is increased, gehlenite reacts to produce C3A and C2S (14). The content of gehlenite in the clinkers diminishes progressively when the temperature increases. At 1250°C gehlenite was not found. At ll60 and 1200°C, a higher
Vol. 14, No. 3
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FLUORSPAR, CLINKER FORMATION, PHASES, TEMPERATURE
proportion of gehlenite was found in the fluoride-free samples, i.e. fluorides i n h i b i t , partially at least, the formation of gehlenite. I t was also observed that the CI2A7 formed, increased as the gehlenite diminished (in those samples with CaF2). This is probably because the addition of CaF2 to the system extends the primary field of CI2A7 ss (15). CI2A7 and CIIA7CaF2: As reported in the results, the IR spectra of our clinker: have the bands of the CI2A7• We also found three bands in 990, 940 and 920 cm-~ which can be assigned to different vibrations of tetrahedra of SiO4 within the structure of the aluminates. The highest frequency absorption is due to tetrahedra of SiO4, probably deformed, which replaces tetrahedra of AlO4, also deformed. This band in 990 cm-l does not change either when the temperature changes or with the addition of CaF2. However, the bands in 920 and 940 cm-l change as the temperature increases and for the same temperature with the addition of CaF2. These facts are interpreted in the following manner: The CI2A7 can introduce within i t s l a t t i c e , tetrahedra of SiO4 which replaces tetrahedra of AlO4. I t originates the absorptions in 990, 940 and 920 cm-i. When there is fluoride in the system, the compound formed is the CIIATCaF2 which prevents the tetrahedra of SiO4 (those responsible for the vibrations In 940 and 920 cm- I ) to be icluded within i t s lattice. To summarize the evolution of the aluminates, i t can be said that at ll60 and 1200°C, the clinkers have a phase similar to CI2A7; at 1250°C they have cubic C3A and at 1340°C a phase like NC8A3 with orthorhombic structure. All the phases mentioned are not pure ones. All have SiO4 which replaces AlO4. Of course, because of the correct balance of loads, the substitutions can be multiple ones, for example CaAI-NaSi giving in the case of the C3A a phase like (16): ((Ca72_(n+m))(Na(2n+m))72+n(A148_mSim)480144) Han, et al. (16), considered that the multiple substitutions involve the formation of a solid solution in C3A with this general formula: ((Ca)72-(n+m)(Na(2n+m)))72+n((Al)48_(m_z)(Si(m+3/4z))48_i/4z)O144 With regard to CI2A7, Jeevaratnam, et al. say that CI2A7 contains two reactive 02- per cell which may be wholly or partly replaced by up to four univalent ions with only slight concomitant changes in cell size and density. Thus, by mean of the substitution of one of these 0~-, the CIIA7.CaF2 may be formed. In the samples under study, substitutions of Si04-AlO4 within the lattice of the CI2A7 are observed. These substitutions may be like Si X-CaAI (X=Na,K). I t would produce a phase like Ca12_nAl14_nSinXn033. The substitutions Si04-AlO4 are not admitted in the lattice of the CIIA7CaF2 as easily as with the CI2A7. Finally, in the IR spectra of the samples heated at 1340°C, i t is observed that the incorporation of strange ions within the lattice of C3A produces a strong change in the symmetry of the rings A I t is explained as a change C3-Ci. I t agrees with Boikova, et al. ( l l ) _ 16018" .I.nfluence of the Time Clinkerization in the Speed of Reaction All the thermic treatment applied to the samples under study were carried out at different times (15, 20, 25 and 30 minutes) with the object of studying the influence of the time of clinkerization in the velocity of the reactions. The results obtained on anlayzing all the clinkers by XRD, those obtained by analyses of the free lime given in Table I l l , and those obtained on analyzing the free lime at the temperatures already mentioned but during 5 and lO minutes,
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Vol. 14, No. 3 M.T. Blanco-Varela, et al.
show that at low temperatures (up to 1200°C) the reactions are t o t a l l y completed between the f i r s t I0 and 15 minutes of the reaction; at worst, the difference of the lime combined at I0 and 30 minutes, is in the order of 4%. At high temperatures (1250 and 1340°C), when we compare the combined lime at 15 and at 30 minutes, the difference of 4% decreases by ~2% in r e l a t i v e value. This 2% difference now has a greater importance since the lime must be t o t a l l y combined. At a high temperature, the formation of phases is carried out in i t s majority during the f i r s t 15 minutes of reaction, although the effects on the samples of greater period in the furnace is more important than lower temperatures. Conclusions From this work, the following conclusions can be made: I) Fluorspar, even when used in a small proportion, lowers the temperature of the formation of C~S and increases the speed of the formation of the s i l i c a t e s 2) Fluorspar stlmulates the discomposition of the gehlenite favouring simultaneously the formation of ClIA7CaF2 between 1160 and 1200°C. 3) As the gehlenite decomposes in the presence of fluorspar between 1160 and 1200°C, C2S, cubic CRA and/or CIIA7CaF 2 are formed. 4) Substitutions S~04-AI04 are admitted w i t h i n the l a t t i c e of C12A7. These s u b s t i t u t i o n s are p a r t l y prevented when s u b s t i t u t i o n s F--O 2-12 take place within the C12A7 to produce CllA7CaF 2. Thus be means of IR spectroscopy, i t is possible to discern between C12A7 and CIIA7CaF 2 in s i m i l a r samples to those already studied. 5) An increase of the temperature from I160°C u n t i l the formation of the l i q u i d phase, produces in the f e r r i t i c phase of these c l i n k e r s , a progressive enrichment in aluminium. On passing the melting temperatures of the f e r r i t e s and aluminates and l a t e r cooling the c l i n k e r r a p i d l y , a c r y s t a l l i z a t i o n (poor) of a f e r r i t i c phase rich in Fe is produced. 6) The reactions are mainly produced before the f i r s t 15 minutes of keeping the samples inside the furnace. 7) I t w i l l be necessary to study the way of increasing the speed of reaction between 1160 and 1250°C and attempting to lower the temperature of formation of euthectics. References 1 2 3 4 5 6 7. 8. 9. I0. II. 12. 13. 14. 15. 16. 17.
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