WANG Chao 1, SHI Yingheng 1, YU Kuiling 2, LI Huachun 2, YUAN Wenjie 1,3
(1. The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China; 2. Saint-Gobain Research (Shanghai) Co. Ltd., Shanghai 200245, China; 3. National-provincial Joint Engineering Research Center of High Temperature Materials and Lining Technology, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China)
Abstract: Silica fume has been widely used in castables for increasing flowability, due to its spherical morphology and small particle size. Characteristics, such as type, composition and particle size of silica fume and dispersants have significant influences on the rheological properties of the slurries. The rheological properties of silica fume slurries with a volume fraction of 30% were characterized by using a coaxial cylinder rheometer, while the rheological curves of the silica fume slurries were fitted with the Herschel-Bulkey model. Effects of dispersants on yield stress, viscosity and rheological index of the silica fume slurries were analyzed. It is found that the zirconia-containing silica fume is acidic and the common silica fume is weak alkaline. The zirconia-containing silica fume that is easily rubbed with the SiO2 leads to agglomerate, resulting in larger particle size and more free water flowing in the slurries to reduce the viscosity at a fixed content of water, because of the larger specific surface area of ZrO2. For acidic zirconia-containing silica fume, both the consistency coefficient (K) and the yield stress (τy) decreased significantly with the addition of alkaline polycarboxylate supported on alumina. For common silica fume, the consistency coefficient (K) and the yield stress value (τy) decreased significantly when adding polyethylene glycol. The polyacrylate type dispersants supported on calcium aluminate cement only have promising dispersion effect on some zirconia-containing silica fumes.
Key words: dispersant; silica fume; pH; rheological properties; Herschel-Bulkey model