Preparation And Conductive Property Of Calcia Stabilized Zirconia Ceramics

Calcia stabilized zirconia (CSZ) ceramics have been widely used in oxygen sensors,oxygen pumps and high temperature heat generator due to their relatively high ionicconductivity, low heat conductivity, high temperature chemical stability, and outstandingthermal shock resistance. In this work, using zirconia and calcium nitrate as rawmaterials, a series of CSZ ceramics were prepared via pressureless sintering method, andtested the relative densities and open porosity of the sintered samples. The particle size ofCSZ powder was analyzed. Phase transformation was characterized by XRD and Ramanspectroscopy; microstructure was represented by SEM; electrical property was tested byAC impedance technology. In addition, the effect of CaO additive amount, sinteringtemperature, phases, and microstructure on the electrical properties are discussedemphatically. The results are as following.The sintered samples have high relative density. With the increase of CaO additiveamount, the relative density firstly increase and then decrease. Elevating the sinteringtemperature, the open porosity declines. The main phases of sintered samples is cubicZrO2(c-ZrO2) and tetragonal ZrO2(t-ZrO2). A small amount of monocliniczirconia(m-ZrO2) is present in a few of samples. By increasing either the sinteringtemperature or CaO additive amount, the phases gradually turn from c-ZrO2, t-ZrO2andm-ZrO2into c-ZrO2and t-ZrO2, finally only c-ZrO2left. Grain boundary was clear in thesection of CSZ ceramics, and grain size is relatively uniform. The main fracture mode ofCSZ ceramics is intergranular fracture.The ionic conductivity of CSZ ceramics is determined by the concentration andmobility of oxygen vacancies. Varying the CaO additive amount, the5.0wt%sinteredsamples is found to own the highest ionic conductivity, in which the concentration ofoxygen vacancies stay at an appropriate level. The sintering temperature also affects theconductivity via changing the phases and grain. The conductivity is related to the phaseratios of CSZ ceramics; and the ratios of c-ZrO2and t-ZrO2should range in anappropriate region. Small and uniform grain, as well as larger quantities of grain boundary, contribute to oxygen vacancy transfer and better conductivity of CSZ ceramicsas a result. As calculated, the conductivity activation energies are at about1.0eV, whichhas no direct relation to the conductivity of the solid electrolyte. With the sinteringtemperature of1600℃and CaO additive amount of5.0wt%, the highest conductivity of0.016S cm-1is achieved at1073K.