Study On The Effect Of Nano ZnO Additive On The Structure And Properties Of Low Carbon MgO-C Refractory

With the development of the technology of clean steel, the requirements of refractories used at steel ladle lingings are increasing. To reduce the pollution of carbon to molten steel, the carbon content in refractories should be strictly confined, however, the reduction of carbon content have a negative effect on thermal shock resistance (TSR) and slag corrosion of MgO-C bricks, so how to make up the decrease of properties resulted from carbon content reducing is one of the main subjects. In this work, various contents of nano ZnO (0.5%、1%、2%、3%、4%) addition in low carbon MgO-C refractories is investigated; meanwhile, the active gaseous phases catalyzed by nano ZnO, the promotion of whisker formed by in-situ reactions and the mechanism of microstructure improved in low carbon MgO-C refractories are disscused through the analysis of phase composition, microstructure characteristics and comprehensive performances of specimens heated at 1000℃,1300℃and 1500℃. Furthermore, the effect of different contents of Al (0%、0.5%、1%、2%、3%、4%) in low carbon MgO-C refractories with addition of nano ZnO on the structure and properties of refractories are studied.The results show that:appropriate addition of nano ZnO in low carbon MgO-C refractories could improve the mechanical properties of materials at room temperature and high temperature, when added 0.5% of nano ZnO, mechanical properties of low carbon MgO-C refractory improves heated at 1000℃,1300℃and 1500℃. However, the mechanical properties of low carbon MgO-C refractory decrease when the addition of nano ZnO is more than 1%.The results of SEM and EDAX show that:the morphology of formation of spinel sintered at 1000℃、1300℃、1500℃without nano ZnO addition in low carbon MgO-C refractory is granular. When adding 0.5% nano ZnO, the shape of spinel is changed. After sintered at 1000℃, some in-situ spinel fibers are found in the sample. When temperature rises to 1300℃, some in-situ spinel fibers are found obviously. The fibers are formed via the vapor-liquid-solid and vapor-solid mechanisms when sintered at 1500℃. The twists spinel fiber and needle-shape spinel fiber could fill in the interstrices of periclase skeleton structure, which is contributed to strengthening and toughening effects.The mechanism of adding nano ZnO into low carbon MgO-C refractory to improve the properties of material is that:The active Zn vapor produced by reduction of nano ZnO by carbon catalyzed the gaseous phases reactions in matrix, which results in the formation of in-situ fibers, and these fibers can be beneficial to the improvement of properties of MgO-C refractory. Rising the addition of nano ZnO above 1%, the Zn vapor volatilized out of simple, result in the increasing of the apparent porosity of MgO-C refractory, which is harmful to the material.Mechanical properties at room temperature and high temperature are improved by adding appropriate Al powders into low carbon MgO-C refractories modified by nano ZnO powders. With the increasing contents of Al powder into low carbon MgO-C refractories modified by nano ZnO heated at 1000℃、1300℃and 1500℃, the modulus of rupture(MOR) of specimens increases at first and then decreases, When the content of Al is about 2%, the specimens have lower apparent porosity, higher bulk density, and higher cold MOR. Hot modulus of rupture (HMOR) of specimens increases with increase of Al powder. The refractories have good thermal shock resistance (TSR) and HMOR (16MPa) with 2% Al addition. With increase of Al powder, the residual MOR and residual strength ratio of specimens after thermal shock tests are increase. Whereas TSR of refractories is decreased with Al content more than 3%.The observation of SEM show that:the compound and the fiber of in-situ Mg-Al spinel increase with the increasing of Al addition. A small quantity of in-situ Mg-Al spinel could block up the pores in refractories and densify the material, however, excessive spinel result in volume expansion, the loosened structure and finally destruct the materials. With 2% addition of Al into low carbon MgO-C refractories modified by nano ZnO, the materials have a better physical properties、thermal shock resistance properties and higher HMOR.