Effect of Al2O3 on non-Newtonian property and its relation to structure of mold fluxes during shear stress field at 1573 K

The effect of Al2O3 on non-Newtonian property and structure of mold fluxes was examined with a rotating cylinder method combined with Raman and magic-angle spinning nuclear magnetic resonance technology. Oswald-De Wael'e power-law model was used to quantify the shear-thinning behavior. The results indicated that a shear-thinning behavior formed and first improved and then decreased with increasing Al2O3. The sample with 9.5% Al2O3 revealed the strongest shear-thinning behavior, and its flow behavior index reached a minimum of 0.76. Raman result illustrated the Si-O-Al linkages first became prominent with adding Al2O3, and then depressed with raising shear stresses. Al-27 MAS-NMR analysis suggested that AlO4 increased with adding Al2O3. However, AlO4 reduced, AlO3F and AlO5 increased with increasing shear stresses. Si-29 MAS-NMR analysis indicated that with increasing shear stress, Q(3)(1Al) and Q(2)(1Al) in AlO4 species decreased, and the reduction of Q(3)(1Al) was larger than that of Q(2)(1Al), Q(2)(0Al), Q(1), and Q(0) units increased.