Studies On Structure And Properties Of Lanthanum Phosphate Composite Of Zirconia Solid Electrolyte

Phosphorus is a destructive element in steel. It significantly reduces the quality of steel, so high-quality steel must be strictly controlled the phosphorus content. With the aim of overcoming the shortcomings on traditional method of spectral measurements of phosphorus, online measurement of phosphorus is adopted on this purpose. Typically, this method can add the right amount of dephosphorizer based on the phosphorus content in the molten steel to achieve the production requirements of low phosphorus steel.Based on the zirconia solid electrolyte has good conductivity and thermal shock resistance, and the application of the oxygen sensor in the steel industry, zirconia was used as solid electrolyte matrix material in phosphorus sensor, in which the basic principle is similar to concentration cell in oxygen sensor, to calculate the accurate phosphorus content in molten steel due to the Nernst equation.Rare earth phosphate has a high melting point and familiar with the zirconia composite, in this paper, the preparation of rare earth phosphate employs the precipitation method, and calcined phosphate into the crystalline solid. The composties of the rare earth phosphates and Ziconia oxide doped with stabilizer MgO were manufactured as the solid electrolytes through solid reaction. XRD, SEM and AC impedance analysis were used for structural characterization and performance tests. The phase composition, microstructure and electrical properties of zirconia solid electrolyte influenced by compounding lanthanum phosphate were investigated.XRD results show that the solid electrolyte involves any one of yttrium phosphate, cerium phosphate or lanthanum phosphate will change the phase composition of the zirconia. So in order to achieve the desired phase composition of the solid electrolyte, only combination of the phosphate lanthanum and zirconia meets the requirements. SEM results show that as the increasing of lanthanum phosphate, particles in solid electrolyte exhibit nonuniform size, increased the porosity, and generated the grid-like crystal. This grid-like crystal grows with the increase of lanthanum phosphate, which is probably due to the appearance of decomposition product of lanthanum phosphate and produced lanthanum oxide, which generated solid solution with zirconia. AC impedance test shown that as the increasing of lanthanum phosphate, the solid electrolyte conductivity is reduced; following the test temperature increasing, solid electrolyte resistance decrease and conductivity increase. According to the relationship between temperature and conductivity, the solid electrolyte conductivity activation energy was calculated, and the conductivity of the solid electrolyte under the actual operating temperature was also calculated based on extrapolation.Prepared with amount of20%lanthanum phosphate composite of zirconia as the solid electrolyte tube, and assembled into a set of phosphorus sensor and test it in Song Iron. Results shown the measuring time to stabilize emf platform for5to15s, the whole time in the20s,and phosphorus content was lower than spectroscopy testing of phosphorus content,error range from10%to20%, and conformed the regulation with the metallurgical physical chemistry basically, which can be applied in practical production.