| The main investigated object of this work was alumina-based castables. The influences of ultra fine powders, particle size distribution and nonoxide (graphite, Sialon) on the theology and thermomechanical properties of alumina-based castables have been studied.This work could be divided into four parts: (1) The influences of micropowders, cement, magnesia, graphite and Sialon fines on rheology of castable matrix have been studied by using viscometer of model NXS-11A. (2) The influences of ratio of mcropowders, particle size distribution, magnesia, flake graphite, extruded graphite pellets and Sialon fines on castable Theological properties have been studied by using IBB Rheometer Vl.O. (3) The influences of micropowders, cement, graphite and Sialon fines on general mechanical properties (such as porosity, bulk density, MOR and CCS etc.) of castables after firing have been studied. (4) The influences of microsilica and ultra fine alumina powders ratios, contents of extruded graphite pellets (EGP) or Sialon fines on thermomechanical properties (such as HMOR, TSR ) of castables have been studied by using conventional three point bend testing and different temperature to water cycling. The results indicated that as follows:1) The studying on the matrix results showed that the rheological type of matrix was Bingham model; ultra fine powders and cement. magnesia. graphite and sialon were the principal factors influencing matrix rheology. Microsilica could improve matrix rheology noticeably-shear viscosity, shear stress and yield stress were decreased, its contributed to microsilica was of amorphous structure, with extremely fine particles of ball shape and smooth surfaces, which would fill into the very small porous of the castable structure and replace the water original in the voids; ultra fine alumina had slightly positive effect on matrix rheology, however, cement, magnesia, graphite, sialon fines had negative effect on matrix rheology.2) The studying on the castables rheology results indicated that particle size distribution, the ratio of ultra fine alumina/microsilica powders and flake graphite were remarkably influenced on the rheological behavior; the rheological properties were slightly effected by magnesia powder and ultrafine alumina; extruded graphite pellets and p-Sialon fines had slightly negative effect on the rheological properties. The rheological type of castables ininthis paper was Bingham model. With increasing microsilica content of micropowder, the self-flow value was remarkably increased, and the amount of water was decreased; the Theological properties were noticeably improved, their torque, torque viscosity and flow resistance were reduced. The results show that their Theological behavior was remarkably affected by PSD. With a decrease of q value (from q=0.29, 0.26 to 0.23), then- torque, flow resistance, torque viscosity and water demand tended to increase, indicated degradation of Theological behavior. With increase of fines, surface energy in the system would be increased, more contact and collision of particles would take place and the fines tend to agglomerate, and which needed more water to wet the surface of the fines. With increasing the amount of flake graphite, the water amount was exceedingly increased (almost 100% when added 5% flake graphite), the Theological behavior was remarkably deteriorated, because of the poor water wettability and dispersion of flake graphite. When the addition of extruded graphite pellets (EGP) and sialon fines IN castables, the water amount was slightly increased (from 4.9% to 6.4%), and their Theological behavior was gently degraded. Its contributed to improving the surface character and specific gravity of extruded graphite pellets (EGP) , and ?-sialon fines have weak polar covalent bond and wettability are much better than flake graphite.3) When the ratio of ultra fine alumina/microsilica amount varied from 100/0 to 50/50 in castables, with increase of microsilica content, the linear change of the specimens exhibited from shrinkage to little sw... |
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