高温下通过 Knudsen 蒸发质谱法测定 La O-ZrO 体系的热力学性质。

Institute of Chemistry, St Petersburg State University, 26 Universitetskii avenu, 198504, St Petersburg, Russian Federation.

Rapid Commun Mass Spectrom. 2017 Dec 15;31(23):2021-2029. doi: 10.1002/rcm.7997.

RATIONALE

Zirconia 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 La O -ZrO system is of great importance.

METHODS

Knudsen effusion mass spectrometry was used to study the vaporization processes and thermodynamic properties of solid solutions in the La O -ZrO system at 2110 K. Pure La O was used as a reference substance. Comprehensive characterization of the precursors and ceramics was performed via SEM, STA, XRD and PSD analysis.

RESULTS

Zirconia-doped lanthania precursor powders and ceramics with La O of 33.3, 50, 70 and 90 mol.% content were manufactured by solid-state synthesis and the original cryochemical technique. La, LaO, ZrO and ZrO were found to be the main vapor species over the samples studied. The activities and thermodynamic properties of La O were calculated. Via XRD analysis it was shown that the phase composition of xLa O -(100-x)ZrO powders (x = 0.33, 0.5, 0.7 and 0.9 mol. fraction) significantly depends on the synthesis technique chosen.

CONCLUSIONS

According to the XRD results combined with Rietveld refinement of the patterns, 33.3 La O -66.7 ZrO ceramics after solid-state synthesis are composed of well-formed cubic pyrochlore-type La Zr O with 5 wt.% admixture of monoclinic and cubic ZrO whereas 33.3 La O -66.7 ZrO precursor powders after cryochemical synthesis correspond to low-crystalline La(OH) . The components of the La O -ZrO 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.

背景

氧化镧掺杂氧化锆体系因其在高性能陶瓷开发方面具有出色的热稳定性而备受关注。它具有纯氧化锆的有益特性，如耐热性、机械强度和惰性，但也消除了其主要缺点，即脆性。在高温下，此类系统的成分可能会选择性地蒸发，导致组成发生重大变化，从而影响陶瓷材料的耐热性、相稳定性和性能。因此，了解 La O-ZrO 系统的蒸发过程和热力学性质非常重要。

方法

采用 Knudsen 蒸发质谱法研究了 2110 K 下 La O-ZrO 固溶体的蒸发过程和热力学性质。纯 La O 用作参考物质。通过 SEM、STA、XRD 和 PSD 分析对前驱体和陶瓷进行了全面表征。

结果

采用固态合成和原始 cryochemical 技术制备了 La O 含量为 33.3、50、70 和 90 mol.%的氧化锆掺杂氧化镧前驱体粉末和陶瓷。研究样品中主要的气相物种为 La、LaO、ZrO 和 ZrO。计算了 La O 的活度和热力学性质。通过 XRD 分析表明，xLa O-(100-x)ZrO 粉末（x = 0.33、0.5、0.7 和 0.9 摩尔分数）的相组成显著取决于所选择的合成技术。

结论

根据 XRD 结果结合图谱的 Rietveld 精修，固态合成后的 33.3 La O-66.7 ZrO 陶瓷由形成良好的立方萤石型 LaZr O 组成，其中含有 5 wt.%的单斜和立方 ZrO，而 cryochemical 合成后的 33.3 La O-66.7 ZrO 前驱体粉末则对应于低结晶度的 La(OH) 。La O-ZrO 系统的各组分单独蒸发：不存在镧和锆气态物种同时存在的温度范围。发现氧化镧的活度具有低的负偏离理想情况。