Papers by Author: Hua Zhi Gu

Abstract: With the increasing requirements for steel quality, the refining conditions are increasing strict. The high-speed movement of molten steel under mechanical or pneumatic agitation can uniform the temperature and composition, and accelerate the collision of the inclusions to eliminate. However, the electromagnetic field has an important influence on the removal of inclusions in steel and the corrosion of refractory materials. The magnetic phenomenon caused by the movement of molten steel needs to be explored. Considering the complexity of high temperature thermal simulation, this work adopted the physical modeling combined with mathematical simulation method, saturated sodium chloride solution was selected to simulate molten steel as a liquid electrolyte, the magnetic phenomenon caused by solution motion was tested and analyzed, and mathematical model of solution motion magnetization was based on discharge mechanism and magnetic vector potential superposition principle, then the variation law of spatial magnetic field generated by liquid electrolyte flow was discussed. The results show that the simulation results agree with that of the physical modeling, and the mathematical model is promising for prediction of the magnetic field generated by liquid electrolyte flow. Under a constant flow speed of 2000 r/min, a magnetic field with magnetic flux density up to 0.15 Gs was produced, which has a significant effect on the refractory corrosion and removal of impurities in the molten steel.

Abstract: Silca and its composite powders added different amount of microsilica were ground in a planetary ball mill (QM-3SP4) at various grinding period with addition of a certain number of grinding aid. The effects of mechano-chemical on particle size, crystal size and lattice deformation in grinding process were analyzed. The phase compositions and size compositions of the treated powders were investigated by X-ray Diffraction (XRD) and Laser Particle Size Analyzers. With the increase of grinding time, the particle size decrease, the specific surface area increase, and the more amount of microsilica added, the smaller particle size the powders had after grinding. The XRD results showed that the diffraction peak intensity of powders weaken and gradually widen. The surface of the particle happened to amorphization, and occurred grain refinement and lattice distortion. Comparing with other treated powders, the change of the powders with the microsilica addition of 5% was larger. Even though the grinding time reached to 30h, the crystal transformation of SiO₂ has not been detected.

Abstract: Effect of adding CaCO₃ on the microstructure and properties of corundum was studied, with corundum modified by adding CaCO₃ powder, by means of XRD, SEM etc. The experimental results show that when the quantity of CaCO₃ powder is not more than 14.1wt%, would obtain corundum-calcium hexaluminate composite aggregate. When a little hexaluminate is generated, it would not increase porosity significantly but closed porosity increase slightly, and the heat conductivity is lower than tabular corundum. Calcium hexaluminate in aggregate grow well and are flakes. There are large numbers of small pores, and distributed uniformly. Composite aggregate has preferable performance of sintered and low thermal conductivity when hexaluminate generative capacity is about 27%.

Abstract: The silica matrix specimens were prepared by adding microsilica and MoSi2 powder. The mixture were pressed to cylinder and then sintered at 1200oC, 1250oC, 1300oC and 1400oC for 8h respectively. The phase compositions of specimens were analyzed by X-ray diffusion and the tridymite crystal morphology and grain sizes were observed by SEM. The results show that with the addition amount of MoSi2 powders increase, the intensity of tridymite diffraction peaks first strengthen slightly and then decrease, becoming more and more amorphous process, while the diffraction peaks of residual quartz phase enhance. When adding 2.5% MoSi2, the precipitation of CaMoO4 phase reduces the O/Si ratio in the liquid phase, and promotes the generation of tridymite, so the number of tridymite increase, but the crystal size decreases. With the sintering temperature increase, the intensity of tridymite diffraction peaks increase, the residual quartzite amount reduces.

Abstract: Crude vermiculite is used as raw materials, heat-treated for activation, leached with a complexing acid, exchanged with sodium solution, following contacted with polyhydroxyl aluminium solution. The Al-intercalated vermiculites are prepared by ion exchange. The phase and microstructure of the composite material are analyzed by means of XRD, TEM, TG-DSC, et al. The results reveal that the basal spacing of vermiculite expanded by intercalation of Al-species, and the interlayer of vermiculite inlaid with a large amount of nanometer Al-species particles.

Abstract: Superfine nanometer SrTiO3 with size of near 50-60nm was prepared by citrate process and sol-gel method. XRD and TEM characterizations indicate that sol-gel method is appropriate to prepare high-purity powders at far lower temperature than other methods. The Ni-based catalysts were prepared by using SrTiO3 powder as support through impregnation and sol-gel method. These catalysts were applied to the reaction of CO2 reforming CH4 to synas and showed high activity. The catalytic activity of Ni-based catalyst is investigated by reaction temperature, the method of support preparation, and the method of catalyst preparation; It shows that the catalyst possesses higher catalytic activity with the increasing of temperature; and the catalytic rate is near 90% at 973 K; and the catalyst show higher catalytic activity when support is prepared by sol-gel method than by citrate process; and the catalyst shows better catalytic activity when catalyst is prepared by sol-gel method than by impregnation method.

Abstract: According to the practical physical dimension and processing parameters of ladle with bottom gas blowing in a factory, a geometrical model was established and mesh structure was completed, Eulerian multiphase model and porous media model were adopted for the two-phase flow in ladle, which was coupled, the effect of temperature field and thermal stress in course of working process of permeable- gas refractory ceramic was studied by finite element approach. The correlations between processing, structure, and high-temperature mechanical properties were discussed, and the material and structure of permeable-gas ceramic were designed to optimum. The results show that: The steady gas flow rate can avoid wearing of permeable-gas refractory ceramic from cataclysm of temperature-stress; After the material and structure of permeable-gas refractory ceramic are optimized, the effect on ceramic wearing of temperature-stress in condition of oxygen washing is weakened. It is an important guiding for prepara- tion of permeable-gas refractory ceramic with long life, which will make for highly active refining ladle.

Abstract: The resistance coefficients through which gas flow permeable refractory are important properties and have great effect on the gas blowing parameters and gas-liquid two phase flowing characteristics in the metallurgy furnace such as ladles, tundish. In this paper, the resistance coefficients were measured according to the Forchheimer’s law. The results show when the gas flow rate is fixed, the viscosity resistance coefficient and inertia resistance coefficient decrease as the apparent porosity and average pore diameter increase. The viscous resistance coefficient is more lager than the inertial resistance coefficient. The resistance coefficients were analyzed by dimensional analysis and the statistical correlations between the resistance coefficients and parameters of porous permeable refractory were got based on the experimental data. In order to get high strength at low resistance coefficients, the raw materials particle degree were adjusted.

Abstract: The temperature distribution of the permeable brick was modeled using CFX software. The influence of magnesia and corundum on thermal shock resistance of non-cement bonded alumina-based permeable brick was investigated. The results indicated that, in the gas blow process, the high temperature regions near the working face of the brick gradually expanded with the increase of the gas flow rate. Therefore the inner part of the brick had the complex and large change of thermal stress. Further experiments demonstrated that thermal shock resistance of alumina-magnesia based castable refractory was better than that of alumina-chrome based castable refractory. With the increase of magnesia amount, the alumina-magnesia based castable refractory had more cycles of heating and water-cooling. When different kinds of corundum were added in the raw materials, the sample with tabular corundum showed the best thermal shock resistance, the one with white fused corundum performed worse and the one with fused dense corundum performed worst.

Abstract: The Al2O3-mullite system porous refractories were fabricated, and then pretreated by sol-gel. The samples were sintered at 1200°C for 3 hours. The microstructures and phases of the samples were analyzed by SEM and XRD respectively. The physical properties of the samples were measured according to National Standard of Refractory. Mullite-whiskers were formed in the pores of the samples. The pretreated samples were more permeable, and were greatly strengthened.