Research On Chemical Preparation,Mechanical Properties And Thermal Shock Resistance Of Sr-and Mg-doped LaGaO₃

Strontium and magnesium doped lanthanum gallate with higher oxygen-ion-conducting properties was first reported by Ishihara and Goodenough in 1994 and has been expected to be potential candidate for an alternative electrolyte material for reduced-temperature operation. Since then, critical assessments regarding the basic material properties of these materials as the electrolyte in SOFCs have been discussed in the literature, including creep behavior, structure and thermal expansion. All the researches indicate that it is difficult to synthesize the single-phase perovskite. Then in present investigation, solid-state reaction technique, glycine-nitrate combustion method and polyacrylamide gel were used to synthesize the Sr- and Mg-doped LaGaC>3. Room-temperature X-ray diffractometry (XRD) was performed on the synthesized powders and sintered samples. The particle morphology was observed through scanning electron microscopy (SEM) and transmission Electron Microscopy (TEM). The particle size and its distribution were determined by using a laser diffraction particle size analyzer. The sintering behaviors were studied by observing the changes of density as a function of sintering temperature and time. The density of sample was measured using the standard Archimedes method with distillated water. The surface and fracture surface of specimen were observe through SEM too.As for the research about its mechanical property, the starting materials used for preparing the samples measured were obtained through only one synthesized method: solid-state reaction technique or combustion method. It's a well known for all ceramicist that the powders synthesized through different methods always have different properties, including morphology, powder size, specific surface area and so on and then result in different sinterabilities. In order to investigate the effect of starting materials prepared from different synthesis techniques on this promising electrolyte, such as sinterability, mechanical properties and electrical conductivity etc, the present paper was focused on the mixed powders prepared through solid-state reaction method and glycine-nitrate combustion technique as starting materials. The result shows that the flexural strength decreases gradually with theincreasing contents of powders synthesized through glycine-nitrate combustion method, And the fracture mode changes from a nearly single intergranular to transgranular.As far as thermal shock resistance is concerned, there is no report in the literature. It is well known that, in addition to the electrical conductivity, the thermal and mechanical properties of solid electrolyte are important consideration to design the structure of SOFCs. Especially for the application of SOFCs to electric vehicles with frequent heating-cooling cycles, high thermal shock resistance is required for dense solid electrolyte. So in the present study, the thermal shock resistance of the electrolyte was also investigated. The result shows that the critical thermal shock temperature, △TC, is around 75 ℃, which indicates that the thermal shock crack propagate in a quasi-static manner. Thermal fatigue test shows that it is weak in crack extension resistances. Air quench test shows that the material can be used as solid electrolyte for the SOFCs.