Effect Of Phase Composition And Content Of Zirconia Metering Nozzle On Thermal Shock Resistance

With the development of continuous casting technology,the life of the tundish lining material has been greatly improved,and the service life of the fixed metering nozzle is lower than that and mismatching,resulting in the increase of production cost.The main reason for the low working life of the zirconia metering nozzle is the poor thermal shock resistance.and the thermal shock resistance is closely related to the phase composition and content of zirconia.It is very important to study the relationship between the thermal shock resistance and zirconia phase composition and content for improving the service life of zirconia.This project simulates the composition and sintering process of zirconia metering nozzle,MgO partially-stabilized zirconia particles is used as aggregates and the matrix part is made of fused zirconia powder and MgO stabilizer grinding mixture.The sample were prepared through 1710?×2h with the ratio of 65:35?matrix:aggregate?,The relationship between phase composition,content and temperature under high temperature conditions was analyzed,and the relationship between phase composition,content and thermal shock resistance was studied.The incorporation of the stabilizers in the aggregate is difficult to adjust,and the composition and content of the phase can not be controlled.The phase composition and content of the matrix part can change through the type and dosage of the stabilizer.In order to simplify the experiment,the influence of the addition amount of CaO stabilizer on the composition and properties of the matrix phase of the zirconia metering nozzle was studied by simulating zirconia metering nozzle matrix part composition with fused zirconia powder and CaO stabilizer grinding mixture.On the basis of optimizing CaO stabilizer addition,different amounts of nano zirconia powder replace the fused zirconia powder by the equivalent substitution method.The phase content and properties of sample were changed through the formation of the intragranular structure by coating the nanoparticles in the matrix grain.Effect of different stabilizers and addtion on physical properties,phase composition and microstructure of the samples were characterized by X-ray diffraction?XRD?and scanning electron microscopy?SEM?,phase composition and content was changed by high temperature conditions and the different content of the nano powder.The relationship between the composition and content of the phase and the thermal shock resistance was investigatedThe experimental study draws the following conclusions:?1?With the increase of the amount of MgO and CaO stabilizers,the content of stable cubic?c-Zr O₂?in each sample increases,and the content of monoclinic phase?m-ZrO₂?decreases.The content of cubic phase in A₃?3.0%MgO?sample reaches 82%,and the cubic content in 4Ca-PSZ sample reaches 67.8%.?2?Simulation experiment shows that the sample is subjected to high temperature again.At the same time,the higher the temperature,the more cubic phase content converts to the monoclinic phase after cooling.Compared with the effect of stabilizer dosage on phase content,temperature has little effect on phase transformation.When the content of cubic phase is about 70%in MgO stabilized zirconia,the thermal shock resistance is best.?3?The addition of nanoscale powder inhibits the abnormal growth of the matrix grain,the matrix particles take the nano particles as the nucleation and reaction,and the nano particles are encapsulated in the grain of the matrix to form the intragranular structure,which can not form solid solution with the stabilizer and keep monoclinic phase content.When the specimen is destroyed by force,the transgranular fracture is induced,the strength and the thermal shock resistance is improved.when the content of cubic phase is 45%in the CaO stabilized zirconia with nanometer powder addition,the thermal shock resistance is best.