Viscosity of a CaO-MgO-Al 2 O 3 -SiO 2 melt containing spinel particles at 1646K
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NTRODUCTION
VISCOUS properties of molten slags with suspended solid particles are of practical importance to metal smelting and refining processes. One most commonly used relationship describing the viscosity of liquids containing solid suspensions is the Einstein–Roscoe type equations:[1–4] h 5 h0 (1 2 af )2n
[1]
where h and h0 are the viscosity of the solid-containing and the solid-free melt, respectively; f is the volume fraction of solid particles in the melt; and a and n are constants. The reciprocal value of a represents the maximum amount of solid that the melt could accommodate before the viscosity becomes “infinite.” For spherical particles of a uniform size, Roscoe suggested[2] a and n to be 1.35 and 2.5, respectively. Reddy and Yen[5] have studied the viscosity of glass melts with xSiO2 /xNa2O 5 0.5 and xB2O3 5 0.25, 0.4, 0.5, and 0.57 (where x denotes mole fraction) at 900 to 1150 K. They found that the volume fraction of solids (NaBO2) estimated from fitting the viscosity to Eq. [1] with a 5 1.35 and n 5 2.5[2] matched the micrographically observed volume fraction of solid in their quenched glass samples. This was taken as evidence to support the applicability of Eq. [1] for the calculation of viscosity of solid-containing borosilicate glass melts. For silicate melts of geological significance (magmatic, basaltic, etc.), there have been a number of studies[6–10] on the effect of solid suspension on the viscosity of the subliquidus melts. When the liquid is cooled below the liquidus temperature, solid precipitation may start, and this usually
S. WRIGHT, Senior Experimental Scientist, L. ZHANG, Senior Research Scientist, S. SUN, Principal Research Scientist, and S. JAHANSHAHI, Research Manager and Senior Principal Research Scientist, are with the G K Williams Cooperative Researcher Center for Extractive Metallurgy, a joint venture between CSIRO Minerals and the Department of Chemical Engineering, University of Melbourne, Clayton South, Victoria 3169, Australia. Manuscript submitted December 22, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS B
leads to changes in the composition of the remaining liquid. To remove the uncertainty of changing liquid composition, Lejeune and Richet[10] carried out experiments on an aluminosilicate melt of the pyrope garnet composition, i.e., Mg3Al2Si3O12, which when annealed at around 1200 K (much lower than the liquidus of 1820 K) precipitates an isochemical aluminous enstatite crystal as spherical particles. Partially crystallized melt was thus prepared with solid volume fractions up to nearly 70 pct. Viscosity of these melts was measured at temperatures between 1030 and 1130 K. At these temperatures, the melt was highly viscous, with viscosity generally varying between 108 and 1014 Pa ? s. It was found that with solid fractions below 40 pct, the melt behaves in a Newtonian manner. Deviation from the Newtonian behavior occurs with solid fractions greater than 40 pct. The variation of viscosity vs solid loading could be reasonably well described using the Einstein–Roscoe
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