Group optical basicities of polymerized anions in slags
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gens, respectively. The latter two are incorporated into the five basic structural entities in silicate melts: O
O-
O
O
I
I
I
I
O---Si---O
I
REFERENCES 1. J.H. Swisher: Trans. TMS-AIME, 1968, vol. 242, pp. 2033-37. 2. H.G. Schubert and K. Schwerdtfeger: Arch. Eisenhiittenwes, 1974, vol. 45, pp. 437-39. 3. K. Schwerdffeger and H.G. Schubert: Metall. Trans. B., 1977, vol. 8B, pp. 535-40. 4. A.G. Ponomarenko and Yu E. Kozlov: Russ. Metall., 1974, no. 5, pp. 61-66. 5. E.T. Turkdogan: Physicochemical Properties of Molten Slags and Glasses, The Metals Society, London, 1983. 6. E.T. Turkdogan: private communication, Apr. 1988. 7. G.L. Hawkes and D.R. Morris: Trans. TMS-AIME, 1968, vol. 242, pp. 1083-89. 8. K. Schwerdtfeger and H.G. Schubert: Metall. Trans. B., 1977, vol. 8B, pp. 689-91. 9. I.D. Sommerville: Proc. Int. Symp. on Foundry Processes: Their Chemistry and Physics, General Motors Research Laboratories, Warren, MI, 1986, pp. 101-22. 10. E.T. Turkdogan: Physical Chemistry of High Temperature Technology, Academic Press, New York, NY, 1980. 11. R. Rein and J. Chipman: Trans. TMS-AIME, 1965, vol. 233, pp. 415-25.
O Network A = 0.48
O--Si---O
O--Si--O
I
I
O Branching A = 0.58
OMiddle )t = 0.65
O-
O---Si---O
I
I
O---Si--O-
I
O End A = 0.70
O Ortho A = 0.74
where O represents a bridging oxygen and O - a nonbridging oxygen. Dron [4,5] has shown that the equilibria between these groupings can be described in terms of four independent equilibrium constants, while Duffy and Ingram TM have calculated the group optical basicity, A, of these units to have the values shown under each. These values were obtained using A = 0.74 for nonbridging oxygens and A = 0.48 for bridging oxygens. Taking the group called "middle" as an example, it has two nonbridging and two bridging oxygens, each of which is shared with one other silicon. Thus, A =
2 • 0.74+2
• 0.5 • 0.48
2+2x0.5
= 0.65
Generalizing this approach to any silicate ion with the formula Si,OXm- , it is seen that there are X nonbridging oxygens and (m - X) bridging oxygens. Thus, by analogy with the formula used above, its optical basicity will be given by the expression
Group Optical Basicities of Polymerized Anions in Slags I.D. S O M M E R V I L L E and C.R. MASSON Since its introduction to the metallurgical literature in 1978, [1] the concept of optical basicity has been widely applied to rationalize and predict data on a range of chemical properties of slags and fluxes. The various correlations for slags have recently been reviewed elsewhere. [2] The macroscopic or average value of optical basicity of a slag Of any given composition is governed by the cations and anions of which the slag is composed. Duffy and Ingram TM have shown how the microscopic optical basicities of individual oxygen "ions" and the group optical basicities of units such as SiO44- may be calculated. The purpose of this short communication is to show how the optical basicities of these individual anions may also be calculated very simply using their approach. In general, s
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