| Tundish, as one of the most important equipment, is used for the production ofcontinuous casting. And the sizing nozzle, as one of the important functional refractory,is used for continuous cast of small square billet. It must be kept stabilization of the fluxof molten steel, in order to meet the demand of the production of continuous casting.Zirconia is used for the best raw material for the production of sizing nozzle, because itsexcellent performance, such as high melting point, high temperature stability, slagresisitance and so on.While, it is commonly to be expended diameter, crackled andjammed for zirconia sizing nozzle caused by the continuous washing of hightemperature molten steel, which affects the production of continuous casting. Thus,improving the texture of zirconia sizing nozzle, and optimizing the material preparationprocess and microstructure,which is an effective way to improve the efficiency of theproduction of the continuous casting.This subject is divided into there steps.First of all, adopting sol-gel methodprepared four kinds of Al2O3-ZrO2composite powder,which ratio of the Al2O3/ZrO2ofcomposite powder were56/44,46/54,36/64and26/74respectivily.Secondly,using fourkinds of Al2O3-ZrO2composite powder replace PSZ powder,in order to improve theproperties of sizing nozzle,and carrying out the physical properties test,which areporosity,body density,compressive strength and thermal shock resistant.Finally,adopting x-ray diffractometer and SEM to detect the mineral composition andmicrostructure of sizing nozzle samples.This study can be concluded from the following four aspects. Firstly, when thesame amount of Al2O3was introduced to partly stabilized zirconia, the addition of composite powder was increased with the reducing of ratio of Al2O3/ZrO2compositepowder.Thus, the amount of the Al2O3-ZrO2composite powder additive was less than6wt%to ensure the molding process, because of the low bulk density of the compositepowder.Secondly, too much stabilizer of MgO will be consumed when excessiveamount of Al2O3was introduced to partly stabilized zirconia.The results showed thatthe best addition of the Al2O3was1.68wt%to control the c-ZrO2phase variable,and toprevent samples from resulting in cracking and reducing of the compressivestrength.Thirdly, When B2samples (the addition of Al2O3-ZrO2composite powder was3.65wt%,the ratio of the Al2O3/ZrO2was equal to46/54, the content of the alumina was1.68wt%)sintering at1710℃, the sample’s porosity was5.47%, which was reduced by15%than based sample, and the body density was5.32g.cm-3, which was improved by0.95%than that of based sample, and the compressive strength was778MPa,whichwas improved by39.18%,meanwhile its thermal shock resistance is36times, whichwas5times as many as the based sample.Finally,the result showed that the particle sizedistribution of B composite powder was closer to the PSZ powder,which can be betterfilled in the gap of the PSZ particle to increased the body density of sample. When B2samples sintering at1710℃, which can be generated some contractedmicropores.Meanwhile, the thermal shock resistance of B2sample was improvedbecause of some micropores.The microstructure of B2samples showed that Al2O3incomposite powder reacts with the stabilizer MgO to form magnesium aluminate spinel,which distribution was uniform.While ZrO2in composite powder was formed into akind of columnar enhancement phase.Meanwhile, the combination of magnesiumaluminate spinel and zirconia particle was very well,and the sample’s structure wasdensity. In conclusion, B2sample’s optical physical properties were proved by itsmicrostructure. |
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