| With the exhaustion of the resources,the deepening strict of national environmental requirements and increasingly harsh service environment,higher requirements for the design and workability of monolithic refractories have been put forward in high temperature industries.The quality of microsilica and fine alumina powders produced by different manufacturers are quite different,and effects of the combination of fine powders and various superplasticizer are not the same.In this dissertation,aluminate cement bonded corundum castables are taken as the research object.The characteristic parameters such as chemical composition,particle size and p H value of different microsilica and reactive alumina powders were evaluated.The rheological properties of fine powder slurries and castable matrix slurries were analyzed,and the influence of fine powder characteristics on the flowability and performance of castables was studied.Moreover,effects of different types of water reducers were compared.Detailed conclusions are as follows:（1）The isoelectric point of fine alumina powders with higher content of Ca O and Mg O impurities is greater.The ordinary microlsilica containing more basic oxide impurities presents weakly basic.Microsilica bearing Zr O2is acidic because it contains more soluble phosphorus and less basic oxides.In microsilica bearing Zr O2,fine zirconia particles are wrapped by amorphous silica,and the particle size is larger than that of ordinary microsilica.（2）The rheological behavior of microsilica and fine alumina powders can be described by Herschel-Bulky model,and both of them have shear thinning characteristics.Among the characteristics of microsilica,the order of grey correlation degree between rheological properties of slurries without water reducers is as follows:p H>alkali metal oxide content>D90.The correlation between the viscosity of microsilica slurry and characteristics of powders does not decrease with the increase of the shear rate as same as the properties of alumina slurry.For slurries with water reducers,the specific surface area of fine alumina powders has higher grey correlation degree with rheological behavior,while the order of characteristics of microsilica with strong correlation are as follows:alkali metal oxide content>carbon content>D90.（3）Polyethylene glycol-based water reducer with more carboxyl,carboxylic ester and hydroxyl group can be used to improve the flowability of castables better.The results show that the castable matrix slurry follows Bingham model,and the relationship between rheological properties and the initial flow value of castables is not completely consistent.Compared with ordinary microsilica,the initial flow value of some castables with microsilica bearing Zr O2is higher,but its flowability decays faster.For the flowability and its attenuation of castables,the size factor of fine alumina powders(particle size D10and specific surface area)has the greatest correlation,while the composition factor（p H value and alkali metal oxide content）of microsilica has the greatest correlation.Compared with the influence of soluble impurities in fine powders,it is concluded that elements calcium and phosphorus in microsilica are dominant while calcium in fine alumina powders is most closely correlated.The particle size and soluble content of fine alumina powders and p H value of microsilica can affect the variation of setting parameters including conductivity and sound velocity of castables.（4）Due to the different effects of microsilica on the hydration of cement and the bonding of castables,the compressive strength of samples containing ordinary microsilica after curing is greater than that of samples containing microsilica bearing Zr O2,but its drying strength is lower than that of the latter.Among castables with different batches of microsilica bearing Zr O2,samples containing microsilica with small particle size and high impurity content have larger linear shrinkage and higher strength after calcination. |
