| In recent years,with the service life of tundish increased greatly,the working life of metering nozzle is much lower than the tundish.It is very important to study the wear mechanism of metering nozzle and improve its service life,in order to achieve the same service life with the tundish lining materials.Now in the continuous casting of iron and steel industry,the partially stabilized zirconia(PSZ)particles with a particle size of about 50?m is widely used for the metering nozzle as aggregates and the matrix part is made of monoclinic zirconia with a smaller particle size and stabilizers grinding mixture,through the sintering reaction above 1700? to form PSZ metering nozzle.The incorporation of the stabilizers in the aggregate is difficult to adjust according to the needs of the metering nozzle.In the light of the above thinking,the matrix composition and process of sinterig for zirconia metering nozzle were simulated.The zirconia metering nozzle were prepared with monoclinic zirconia powders as raw materials and adding different kinds and contents of oxides(i.e.,2%(in mass fraction)CaO(A1),4% CaO(A2),6% CaO(A3),2% MgO(B1),2.5% MgO(B2),3% MgO(B3),1.8% Y2O3(C1),3.6% Y2O3(C2)and 5.4% Y2O3(C3))as stabilizers,respectively.The physical properties,phase composition and microstructure of the samples sintered at 1710? for 2h were characterized by X-ray diffractometer,energy dispersive spectroscopy and scanning electron microscope,respectively.The conductivity of zirconia materials prepared from room temperature to 1350? was determined according to the area and temperature range of impurity diffusion in the use of metering nozzle.The crucibles of zirconia wereused as samples for corrosion experiments,which simulated the temperature for metering nozzle in using process.Which provides a theoretical basis for exploring the relationship between oxygen vacancy migration,impurity ion diffusion and corrosion resistance for PSZ metering nozzle.The experimental study draws the following conclusions:(1)The content of zirconia(c+t-ZrO2)in the stable phase increases and the content of the monoclinic phase(m-ZrO2)decreases obviously with the increase of the addition amount of stabilizers in all the sintered samples.(2)The variation of grain size is not obvious for the sintered samples which adding the same one stabilizer of different incorporation.The difference between bulk density,apparent porosity and microstructure for samples with different kinds of stabilizers is obvious.The sintered samples for the yttria-stabilized zirconia have the advantages of compact structure and low uniformly distributed pore.The sintered samples for the magnesia-stabilized zirconia have the less dense structure between grains and more cracks but no pores exist.The sintered samples for the calcium-stabilized zirconia with dense structure but have the lowest bulk density due to the large number of interstellar pores and small amount of interconnected pores.(3)The conductivity of the sintered samples increases with the increase of content of stabilizer(in a certain range)and testing temperature.The difference of phase composition results in the different conductivity whenever at lower or higher temperature zones for the sintered samples,and the increase of the cubic or tetragonal phase content is helpful to improve the conductivity value.(4)The phase composition of erosion layer is almost the stabilized zirconia(c+t-ZrO2)for the sintered samples after corrosion,and the phase composition of the original brick layer and the transition layer is not obvious.The sintered samples for Y-PSZ have the best erosion resistance,followed by Mg-PSZ,and Ca-PSZ have the poorest erosion resistance.The diffusion of slag and the desolvation of the stabilizers mainly occur through the pores and cracks,the poor conductivity and erosion resistance of samples are due to the high porosity. |
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