Thermodynamic properties of the La2O3-ZrO2 system by Knudsen effusion mass spectrometry at high temperature

RationaleZirconia doped with a lanthanum oxide system is of high interest due to its exceptional thermal stability for the development of high-performance ceramics. It possesses the beneficial properties of pure zirconia, such as heat resistance, mechanical strength and inertness, but also eliminates its main disadvantage, i.e. brittleness. At high temperatures, components of such systems may vaporize selectively, leading to significant change in composition, and hence, the thermal resistance, phase stability and performance of the ceramic materials. Therefore, information on the vaporization processes and thermodynamic properties of the La2O3-ZrO2 system is of great importance. MethodsKnudsen effusion mass spectrometry was used to study the vaporization processes and thermodynamic properties of solid solutions in the La2O3-ZrO2 system at 2110 K. Pure La2O3 was used as a reference substance. Comprehensive characterization of the precursors and ceramics was performed via SEM, STA, XRD and PSD analysis. ResultsZirconia-doped lanthania precursor powders and ceramics with La2O3 of 33.3, 50, 70 and 90 mol.% content were manufactured by solid-state synthesis and the original cryochemical technique. La, LaO, ZrO and ZrO2 were found to be the main vapor species over the samples studied. The activities and thermodynamic properties of La2O3 were calculated. Via XRD analysis it was shown that the phase composition of xLa(2)O(3)-(100-x)ZrO2 powders (x = 0.33, 0.5, 0.7 and 0.9 mol. fraction) significantly depends on the synthesis technique chosen. ConclusionsAccording to the XRD results combined with Rietveld refinement of the patterns, 33.3 La2O3-66.7 ZrO2 ceramics after solid-state synthesis are composed of well-formed cubic pyrochlore-type La2Zr2O7 with 5 wt.% admixture of monoclinic and cubic ZrO2 whereas 33.3 La2O3-66.7 ZrO2 precursor powders after cryochemical synthesis correspond to low-crystalline La(OH)(3). The components of the La2O3-ZrO2 system evaporate separately: there is no temperature range where lanthanum and zirconium gaseous species are present together. It was found that the activities of lanthania have low negative deviation from the ideal case.