INFLUENCES OF DIFFERENT COMPONENTS ON VISCOSITIES OF CaO-MgO-Al 2 O 3. -SiO 2

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1 J. n. etall. ect. B-etall. 50 () B (01) Journal of nng etallurgy, ecton B: etallurgy INFLUENCE F DIFFERENT CPNENT N VICITIE F --l ELT G.H. Zhang a, b, c,*, K.C. Chou a, b, X.Y. Lv d a tate Key Laboratory of dvanced etallurgy, Unversty of cence Technology Bejng, Chna b chool of etallurgcal Ecologcal Engneerng, Unversty of cence Technology Bejng, Chna c Graduate chool of Fronter cences, The Unversty of Tokyo d teel Plant of Baoshan Iron & teel Co., Ltd bstract (Receved 19 ugust 013; accepted 16 June 01) The present study s amed to dstngush the dfferent nfluences of, as well as l on vscosty of --l melts. It s found that for melt wthout l, vscosty ncreases monotonously as s gradually replaced by. The addton of l leads to a complex varaton of vscosty. In dfferent composton ranges, vscosty may exhbt dfferent varaton tendences as changng the relatve contents of whle keepng contents of other components constant. It s also found that when replacng by equvalent mole of l, () n - l system, vscosty ncreases when l content s small relatve to content (there are enough + ons to charge compensate l 3+ ons), but decreases when content s nadequate for charge compensaton; () n -l - system, vscosty always decreases as substtutng l for. The reason for ths dfference for two systems may be resulted from the weak charge compensaton ablty of + on for l 3+ on relatve to + on. ll the vscosty varatons can be nterpreted well by our new proposed vscosty model. Keywords: Vscosty; --l ; Brdgng oxygen; Non-brdgng oxygen 1. Introducton The vscostes of alumnoslcate melts are mportant because of ther dramatc effects on pyrometallurgcal processes. For nstance, relable vscostes are needed () to guarantee smooth operaton of the blast furnace, () for foamng processng, () for the successful separaton of metal slag durng the basc oxygen steelmakng process (v) n the contnuous castng process where the slag acts as a lubrcant. Therefore, accurate vscosty values are essental for the optmzaton mprovement of metallurgcal processes. -- l slag system s a fundamental system n the pyrometallurgcal processes. Up to now, many expermental [1-19] theoretcal [0-] researches have been done for ths system. Lots of vscostes data for --l system [1, 1-17, 19] ts sub-bnary systems [1-8] (e.g. - system, system, etc.) sub-ternary systems [, 7-13, 18] (e.g. -l system, -l system etc.) have been measured. However, deep analyses about the nfluences of dfferent components on vscostes are lackng. In --l system, there are manly three questons nvolved: vscosty varaton n the cases of () substtutng by, or vce versa () substtutng l by, or vce versa, () substtutng (= or ) by l, or vce versa, whle keepng contents of the other components constant. mong these three cases, the thrd one has receved much attenton [3, 0, 3-]. It was found that there was a maxmum vscosty along the constant content lne n -l system -l system. In other words, vscosty frst ncreases then decreases when gradually replacng by l. The present study manly deals wth the vscosty varaton law of the frst second cases based on the measured vscosty data n the lterature to dstngush the dfferent nfluences of, as well as l.. Theoretcal bass In the followng sectons, when analyzng the vscosty varaton behavor, our new proposed vscosty model [-9] wll be utlzed. Ths structurally based vscosty model can well descrbe the vscosty varaton of alumnoslcate melts * Correspondng author: ghzhang_ustb@163.com DI:10.98/JB Z

2 158 G.H. Zhang et al. / J 50 () B (01) nvolvng,, r, Ba, Fe, n, L, Na, K, l,, F, T, Fe P 5 components. The temperature dependence of vscosty s calculated by rrhenus equaton, ln =ln + E / RT [1] where s the vscosty, Pose; s the preexponent factor, Pose; R s the gas constant, 8.31 J/(molK); T s the absolute temperature, K; E s the actvaton energy, J/mol, whle s calculated as follows, E n ln n n l l, l, [] j n l, n j l, where n' are the mole numbers of dfferent types of oxygen ons; parameter descrbes the deformng ablty of bond around the correspondng unt, whch s optmzed from the vscosty data of smple system. The deformng abltes of chemcal bonds around dfferent types of oxygen ons are shown n Table I. The hgher the value n Table I s, the weaker the chemcal bond around ths type of oxygen on wll be. In the denomnator of Eq. [], the frst, second, thrd, fourth, ffth sxth terms represent the contrbutons of brdgng oxygen bonded wth + on; oxygen bonded wth l 3+ on not beng charge compensated; free oxygen bonded wth metal caton ; brdgng oxygen bonded wth compensated l 3+ on by caton ; non-brdgng oxygen bonded wth + on, non-brdgng oxygen bonded wth caton j l 3+ on charge balanced by caton. The numbers of dfferent types of oxygen ons are related to composton can be calculated by followng the followng assumpton [8]. ssumpton I: + on has a hgher prorty than + on to charge compensate l 3+ on. nly when the + on s exhausted, + on could be used to charge compensate l 3+ on. ssumpton II: The equlbrum constant for the charge compensaton reacton of wth l to generate 1/ l unt (oxygen on n ths unt s brdgng oxygen l, ) s nfnte. Followng ths rule, n the case of x / xl 1, all act as charge 3 balancers, whereas x n the case of x / xl 1, all l ons form the l tetrahedrons, any excess x ( x xl ) acts as a network modfer. 3 ssumpton III: When the free oxygen (n excess ) react wth brdgng oxygen (n 1/ l or ) to generate non-brdgng oxygen, t s assumed that 5- - the brdgng oxygen for l tetrahedra are equvalent, the numbers of non-brdgng oxygen bonded to l 3+ on + on are proportonal to the 5- - numbers of l tetrahedral present. ssumpton IV: The equlbrum constant for the reacton of a free oxygen (n excess ) wth a brdgng oxygen (n 1/ l or ) to generate non-brdgng oxygen s nfnte. Therefore, for a - 1 / l system, when the mole fracton of the excess basc oxde exceeds /3, t s assumed that there are no brdgng oxygens present n melt. ssumpton V: For systems ( ) -1 / l- contanng both excess, the numbers of ( dfferent types of oxygen ons can be calculated by the rom mxng rule. In practce, the calculaton makes use of frstly, ssumpton IV by consderng all the excess basc oxdes to be one basc oxde; then multply each term by the re-normalzed mole fractons of the excess basc oxdes ( ), / ( ) or 1 / l or / 1. ( ) o 3. Dfferent nfluences of on vscosty In order to dstngush the dfferent nfluences of on vscosty, vscostes of compostons wth the same contents of l should be known. The measured compostons n the lterature fulfllng ths condton are summarzed n Table II C- group The comparsons of vscostes for melts wth the same content of are shown n Fgure 1, from whch t can be seen that melt possesses a hgher vscosty value than melt. Ths phenomenon s also found by many researchers [, 3, 5]. Vscosty s related to the bond strength. elt wth a strong bond strength means a large resstance to vscous flow under the external force, so a hgh vscosty wll be. For a onc bond, the bond strength can be approxmately evaluated by the coloumbc Q force I between caton ( I, ( r Z+ r - ) where Q s the covalence of on; r are the rad of z+ Z - oxygen ons, respectvely). ccordng to the Paulng s method [30], the onc bond percentage for - - bonds are 77.% 67.8% [5]. Thereby, - - bonds are manly composed of onc bond. From the magntude of I - =1.956 I - =0.907, t could be concluded that the - bond s stronger than - bond. From Table I, the deformng ablty of chemcal bond around s weaker than that around, so, a stronger non-brdgng bond s formed n - melt relatve to melt, whch means a hgher vscosty. r Z+ r -

3 G.H. Zhang et al. / J 50 () B (01) Table 1. Deformng abltes of chemcal bonds around dfferent type of oxygen ons l l, l, l, l, l, Table. Compostons for studyng dfferent nfluences of on vscosty Group C- C--C C- -C C-C C_1 Composton No. l Refs. C ,,3 C ,5 C ,,5,6,7,8 C ,5,8 C--C ,8 C--C C--C C--C C--C ,8 C ,10 C ,11 C C C ,10,11 C C ,1 C C C C C C C C-C C-C C-C ,1 C-C C-C C-C C_ C_ C--C group The vscosty of, - melts wth the same content of are shown n Fgure. Wth the gradual ncrease of content, vscosty ncreases, whch agrees wth the concluson obtaned n C- group. Therefore, n melt wthout l, vscosty ncreases monotonously as substtutng for.

4 160 G.H. Zhang et al. / J 50 () B (01) Fgure 1. Varaton of vscosty for C- group melt. The content of (or ) s less or equal to the content of l for compostons C--1~ C--6, so almost all the wll partcpate n charge compensatng l 3+ on but not formng non-brdgng oxygen. In ths case, content of non-brdgng free oxygen can be neglected. The melt s manly composed of brdgng oxygen l, for -l system (or l, for -l system). For -l -l melts wth the same contents of l, concentraton of s the same. Therefore, the vscosty dfference s manly determned by the dfference between the deformng Fgure. Varaton of vscosty for C--C group 3.3. C- group l s an amphoterc oxde, t can form 5 l tetrahedron, be ncorporated nto the network provded there are enough metal catons present to charge balance the l 3+ ons. When l s absent, basc oxdes manly act as network modfers partcpate n formng nonbrdgng oxygen whch decreases the vscosty; whle when l s added, some parts of basc oxde wll charge compensate l 3+ on to form more brdgng oxygen whch ncreases vscosty. o, the vscosty varaton wll exhbt complex behavor when l s present. Varatons of vscosty wth temperature for compostons n C- group are shown n Fgure 3. By comparng the vscostes of compostons C--1 C--, C- -3 C--, as well as C--5 C--6 for whch the mole fracton of s lower than that of l, t can be seen that - l melt has a lower vscosty than - l melt (wth the same contents of l ). However, by comparng vscostes of compostons C--7 C--8, as well as C--9 C--10, -l melt for whch the mole fracton of s hgher than that of l has a hgher vscosty than -l - Fgure 3. Varaton of vscosty for C- group abltes of chemcal bond around brdgng oxygen l, l,. From Table I, t can be seen that the deformng ablty of chemcal bond around s l, lower than that around l,. Therefore, a hgher vscosty wll be antcpated for -l melt than -l melt when the content of s less than that of l. The contents of s hgher than that of l for compostons C--7~C--10. In ths case, part of or (= xl ) charge compensate l 3+ 3 x on to form brdgng oxygen, whle the other part (= x xl 3 ) form non - brdgng oxygen l, (=, ). The values n Table I show that deformng abltes around l, are weaker than, l, whle t s stronger for brdgng oxygen than 5 l, l, snce the l tetrahedron charge balanced by + on s much more stable than that balanced by + on [11]. o, from -l melt to -l melt wth the same contents of l, there wll be two changes: brdgng oxygen l, transforms to; l, non-brdgng oxygen l, transforms to l,. The frst change decreases vscosty, whle the later one ncreases vscosty. The vscosty ncrement wll exceed the decrement when there s enough extra basc oxde x xl3to generate enough non-brdgng oxygen. o, x-l melt has a

5 G.H. Zhang et al. / J 50 () B (01) hgher vscosty than -l melt when content of s hgher than that of l. Furthermore, the larger the x xl 3 s, the larger the vscosty ncrement wll be xfor -l melt relatve to -l melt. The x xl value s hgher for compostons C--7 C- -8 than compostons C--9 C- -10, so n Fgure 3, the vscosty ncrement s hgher for the former group C group Fgure shows that vscosty decreases when partly replacng n -l ternary system by to form a quaternary system - -l ( x xl ). The reason for the 3 phenomenon s that content s hgher than l 3 content, so after substtuton, all l 3+ ons orgnally x compensated by + ons wll be compensated by + ons for the hgher prorty of + on relatve to + on []. Ths leads to the form of more stable 5 l tetrahedron whch ncreases the vscosty. But, accordng to the above analyss, the non-brdgng oxygen bonded wth + on s weaker than that bonded wth + on. content s hgher than l content, so nonbrdgng oxygen bonded wth + on wll be formed. Ths factor wll decrease vscosty. Furthermore, the larger the value of x xl 3s, the more non-brdgng oxygen bonded wth x + on wll be formed, the C larger the vscosty decrease wll be. In Fgure 3, from composton Fgure. Varaton of vscosty for -C group -C-1 to -C-, there s only a lttle decrease of vscosty for the small value of x xl 3. But from composton -C-3 xto - C C-, vscosty decreases dramatcally for ts large x xl 3value. xc 3.5. C-C group ll the sx compostons n ths group fulfll x x >0. o, all l 3+ l 3 ons n ths group are compensated by + ons. It can be seen from Fgure C 5 that vscosty ncreases when substtutng part of for (from C-C-1 to C-C-, from C-C-3 to C-C-, from C-C-5 to C-C-6). Fgure 5. Varaton of vscosty for C-C group Replacng part of by but keepng x xl >0 can leads to two changes: part of transform to bond; part of l, transform to l,. The two changes coexst durng the substtuton process. The vscosty varaton of the melt s determned by the deformng abltes dfferences (between, as well as ), l, l, as well as the relatve concentraton of a. l, From Table I, t can be seen that bond s stronger than bond, whle l, bond s weaker than l, bond. Furthermore, the bond strength ncrement from l to s smaller the bond strength decrement from l, to l,. eanwhle, the concentraton rato of to s decded by the content rato of to l, [] l, so, when there s enough l n melt, 5 enough l l, wll be formed to decrease vscosty. But f the content of l s smaller relatve to, more wll be formed than l,. Therefore, n ths case, the vscosty ncreasng tendency resulted from transformng of to g wll be domnated, whch leads to the ncrease of vscosty. In ths group, the content of l for every composton s very small relatve to, so vscosty ncreases when replacng part of by C_1 group It can be seen from Fgure 6 that vscosty decreases as replacng part of n composton C_1-1 by to form composton C_1- (whle keepng the mole fracton of remanng hgher than that of l ). ccordng to the analyses n C-C group, t can be concluded that more l, wll be formed when there s a hgher value of xl / x (1mol l s equvalent to mol 3 after beng charge compensated). The rato of x / x n ths group s approxmately to be 1, so l3 l

6 16 G.H. Zhang et al. / J 50 () B (01) the concentratons of are almost the l, same []. However, the 5 bond strength ncrement from l to s smaller the bond strength decrement from to l, l,, so the vscosty decrement wll be domnated. Therefore, there s a decrease for vscosty from C_1-1 to C_1-. Fgure 6. Varaton of vscosty for C_1 group. Dfferent nfluences of l on vscosty The nfluence of l on vscosty s dscussed n -l, -l --l system by replacng part of by l whle keepng the contents of unchanged..1. C group Fgure 7. Varaton of vscosty for C group Fgure 7 shows that vscosty decreases from C-1 to C-, C-3 to C-, but ncreases from C-5 to C-6. Combnng wth the composton n Table III, t can be seen the l content s hgher than content for compostons C-1, C-, C-3 C-, but lower than content for compostons C-5 C-6. Therefore, t can be concluded that when there s enough to charge compensate l 3+ on, the Table 3. Compostons for studyng dfferent nfluences of l on vscosty Group C C_ No. substtuton of l for wll ncrease vscosty, whle when content s not adequate, the substtuton wll decrease vscosty. The reason for ths s that when content of s hgher than l, the new added l can lead to two aspects of nfluences on vscosty. Frst, t consumes equvalent mole of (whch orgnally acts as the network modfer) to charge compensate l 3+ on. The compensated l 3+ on ncorporates nto the network of. Ths aspect ncreases vscosty. However, as substtutng l for, strong - bond s replaced by weak l- bond. Ths factor decreases vscosty. s the content of l s small relatve to, all the l 3+ ons wll be charge compensated the vscosty ncrement wll be larger than the vscosty decrement, so vscosty ncreases from C-5 to C-6. But when l content s hgher than content, part of l (= x x l ) can not be ncorporated nto the network. Ths part of l can dramatcally decrease vscosty for the weak l- bond relatve to -. Therefore, vscostes decrease from C-1 to C-, C-3 to C-. In our prevous paper [31], t s also found from experments that n -l melt, vscosty frst ncreases then decreases as gradually replacng by l, whch agrees wth the concluson of the present study... group Composton l Refs. C C C C C C C_ C_ C_ C_ Fgure 8 shows that vscosty always decreases n -l system when substtutng l for

7 G.H. Zhang et al. / J 50 () B (01) regardless of x xl or x. In - l system, when the 3 xl l content s small, the substtuton wll ncrease vscosty. Why the opposed varaton tendency of vscosty s present n -l system. It has been ponted out above that the man factor for vscosty ncrease n -l melt are that all l 3+ ons enter nto 5 stable l tetrahedron after beng charge compensated by + ons part of (= xl ) orgnally actng as network modfer now charge compensate l 3+ on. But the charge compensaton ablty of + s weak (t can be seen from Table I that l, bond has larger deformng ablty than l, bond) whch means a large deformng ablty under external force. Therefore, n ths case, durng the substtuton of l for, the vscosty ncrement wll be smaller than the vscosty decrement resulted from the substtuton of weak l- bond for strong - bond, so vscosty decreases. Therefore, the vscosty varaton law s the same as group. C_-3 C_- only contan small content of, content s enough to charge compensate all l 3+ ons, so vscosty ncreases when substtutng l for as the case of C group. 5. ummary The present study focuses on the nfluences of dfferent components on --l melt by combnng the expermental data n the lterature our theoretcal vscosty model. From the above examples, t can be seen that the complex varaton behavor of vscosty s resulted from the exstence of l. When substtutng for, vscosty changes monotonously for melt wthout l. However, the vscosty varaton becomes very complcated when l s added. The present study also found that as substtutng l for n - l melt, vscosty ncreases when the content of l s small relatve to that of, but decreases when there s a large substtuton. However, the vscosty always decreases for -l melt as substtutng l for. The weak charge compensaton ablty of + on for l 3+ on may be the reason for ths phenomenon. cknowledgement Fgure 8. Varaton of vscosty for group.3. C_ group From Fgure 9, t can be seen that from C_- 1 to C_-, vscosty decreases; whle from C_-5 to C_-6, vscosty ncreases. The reason for ths may be that composton C_-1 C_- only contan small content of whch s not enough to charge compensate all the l 3+ ons. Ths case s smlar to the case of group. Fgure 9. Varaton of vscosty for C_ group Thanks are gven to the fnancal supports from Chna Postdoctoral cence Foundaton ( T60061) the Fundamental Research Funds for the Central Unverstes (FRF-TP-13-00) as well as the Natonal Natural cence Foundaton of Chna ( ). References [1] J... Bockrs D.C. Lowe, Proc. Roy. oc. Lond., 6 (195) 3. [] J.. achn T. B. Yee, J. m. Ceram. oc., 31 (198) 00. [3] P. Kozakevtch, Rev. metall., 57 (1960) 19 [] G. Urban, Y. Bottnga P. Rchet,Geochm. Cosmochm. cta, 6 (198) [5] G. Urban,Rev. Int. Hautes Temp. Refract., 11 (197) 133. [6]. Kawahara, K. zoguch Y. ugnohara, Bull. Kyushu Inst. Technol. c. Technol., 3 (1981) 53. [7] T. Lcko V. Danek, Phys. Chem. Glasses, 7 (1986). [8] V. G. Hofmaer, Berg und Hutterun. onatsh., 113 (1968) 70. [9] D. ykes, J. Dcknson, E. James, R.W. Luth C.. carfe, Geochm. Cosmochm. cta, 57 (1993) 191. [10] R. Rossn, J. Bersan G. Urban, Revue Hautes

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