In order to further understand the effect of Y 2 O 3 doping on the electrical conductivity of CaHf 1− x Y x O 3−δ , which was prepared by conventional solid-state reaction. The electrical conductivity of CaHf 1− x Y x O 3−δ was measured by two-terminal AC method in an oxygen-rich atmosphere, hydrogen-rich atmosphere and water vapor-rich atmosphere at the temperature between 973 and 1373 K. The test results show that the conductivity of CaHf 1− x Y x O 3−δ first increases and then decreases with x from 0.08 to 0.20, and its total conductivity and conductivity activation energy are 3.88 × 10 −7 to 5.34 × 10 −5 S/m and 0.76–0.92eV respectively. Combined with the test results of the H / D isotope effect, it is found that protons are the main conductive carriers in the three different atmosphere at temperatures range of 973–1173 K. In addition, in the temperatures range of 1273–1373 K, the positive holes are the main conductive carriers in the oxygen rich atmosphere, and the vacancies participates in the conductive process as the main conductive carriers in the water vapor rich atmosphere. The chemical diffusion coefficients of CaHf 1− x Y x O 3−δ is 3.9 × 10 −6 to 2.4 × 10 −5 cm 2 / s in the temperature range of 973–1373 K. According to the test results of electromotive force, the theoretical electromotive force is consistent with the measured electromotive force. The proton transfer number of CaHf 1− x Y x O 3−δ exceeded 97% in hydrogen atmosphere at temperatures from 973 to 1173 K. In sum, these findings of CaHf 1− x Y x O 3−δ can be used as alternative materials for hydrogen sensor electrolytes.
Liyu Li,Tao Dong,Chunhuan Guo,Fengchun Jiang,Zilong Shen,Yang Liu,Mingxia Diao,Haolun Song
To reduce cracking in Mar-M247 superalloy of Selective Laser Melting (SLM) manufacturing, this research explores the impact of the core–shell structure formed by adding different contents (0.5 and 1.0 wt%) of Y 2 O 3 nanoparticles on the microstructure, crack behavior, and mechanical properties. Y 2 O 3 -doping facilitates the transition from columnar to equiaxed grains in the SLM process. The reaction of Y 2 O 3 nanoparticles with oxide-forming elements in Mar-M247 alloy promotes the formation of Y 2 Hf 2 O 7 , which could act as the nucleation sites for MC carbides, forming a core–shell structure with Y 2 Hf 2 O 7 as the core and MC carbides as the shell. The dispersed core–shell nanoparticles lead to the distribution of carbides both inside cells and at the cell boundaries, contribute to the reduction of dislocations pinned by MC carbides near the core–shell structure, and reduce the formation of dislocation walls, which helps to inhibit cracking. Moreover, both the γ′ phase and the core–shell structures can impede dislocation motion, alleviating local stress concentration at cell boundaries. The effect of Y 2 O 3 nanoparticles on the metallurgical behavior of the molten pool and precipitation characteristics during the SLM process is analyzed to reveal the mechanism of the interactions between precipitates and dislocations as well as the crack inhibition.
Element-hybrid phenolic aerogel composites are often utilized as lightweight thermal protection materials for aerospace craft. Zr-phenolic (Zr-PR) aerogels have been extensively studied due to their exceptional high-temperature resistance. However, the phase transformation of ZrO2, the pyrolysis product of Zr-PR, caused the volume changes and internal stresses, greatly limiting the application of Zr-PR. In this work, a small amount of nano-Y2O3 particles was directly doped into the Zr-PR aerogel composites to form the nanoscale mosaic structure. This aerogel composite exhibited properties of low density (0.51 g/cm3) and low thermal conductivity (<0.151 W/(m K)); moreover, it showed a significant improvement in oxidative ablation resistance with a 33% reduction in the linear ablation rate. The research indicated that the doping of nano-Y2O3 effectively addressed the adverse effects associated with ZrO2 phase transformation by in situ rapidly forming (<60s) the dense yttria-stabilized zirconia (YSZ) thermal barrier layer on the ablation surface, which significantly delayed the thermal-oxidative ablation of the composites. Additionally, the pyrolytic carbon (PyC) on the ablation surface can form abundant multilayered graphene structures due to the catalytic graphitization effect produced by the solid-solution reaction of YSZ, which further enhanced the oxidation resistance. This work provides a simple and efficient approach to improve the ablation performance of Zr-PR aerogel composites, broadening their application in extreme thermal environments.
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