Rare-earth phosphates (REPO₄) are regarded as one of the promising thermal/environmental barrier coating (T/EBC) materials for SiC_f/SiC ceramic matrix composites (SiC-CMCs) owing to their excellent resistance to water vapor and CaO–MgO–Al₂O₃–SiO₂ (CMAS). Nevertheless, a relatively high thermal conductivity (κ) of the REPO₄ becomes the bottleneck for their practical applications. In this work, novel xenotime-type high-entropy (Dy_1/7Ho_1/7Er_1/7Tm_1/7Yb_1/7Lu_1/7Y_1/7)PO₄ (HE (7RE_1/7)PO₄) has been designed and synthesized for the first time to solve this issue. HE (7RE_1/7)PO₄ with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750 ℃ and good chemical compatibility with SiO₂ up to 1400 ℃. In addition, the thermal expansion coefficient (TEC) of HE (7RE_1/7)PO₄ (5.96×10⁻⁶ ℃⁻¹ from room temperature (RT) to 900 ℃) is close to that of the SiC-CMCs. What is more, the thermal conductivities of HE (7RE_1/7)PO₄ (from 4.38 W·m⁻¹·K⁻¹ at 100 ℃ to 2.25 W·m⁻¹·K⁻¹ at 1300 ℃) are significantly decreased compared to those of single-component REPO₄ with the minimum value ranging from 9.90 to 4.76 W·m⁻¹·K⁻¹. These results suggest that HE (7RE_1/7)PO₄ has the potential to be applied as the T/EBC materials for the SiC-CMCs in the future.

With the development of hydrogen metallurgy and hydrogen-based shaft furnace, the corresponding refractories for critical parts have higher requirements. Understanding the service environment characteristic and implementing targeted design for the performance are thus particularly important for refractories. In this paper, the temperature, pressure and gas phase concentration distribution for interior and wall surface in reduction domain of hydrogen-based shaft furnace were simulated by a software named Ansys. Also, the thermodynamic stability of typical components of traditional refractory during the process was calculated by FactSage. The results show that the high-temperature and high-pressure service area is concentrated near the gas inlet, while H₂O is concentrated in the top and bottom areas of the furnace. Increasing the temperature of inlet gas has a certain effect on the temperature field, but has little effect on the pressure field and gas phase composition. Among the typical components of conventional refractory, Al₂O₃,ZrO₂, magnesium aluminum spinel, calcium-hexaluminate and TiO₂ exhibit a thermodynamic stability, which can be used as potential refractory components of furnace walls. AlN or TiC can be used as additive materials to improve the relevant properties of these refractories. In addition, some impurity components as SiO₂, MgO, CaO, Cr₂O₃, Fe₂O₃, SiC, Si₃NN, B₄C and BN can be eliminated. This study can provide a theoretical basis and methodological support for the service environment simulation and material component selection of refractory for a hydrogen-based shaft furnace.

Mechanical properties consisting of the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, etc., are key factors in determining the practical applications of MAX phases. These mechanical properties are mainly dependent on the strength of M-X and M-A bonds. In this study, a novel strategy based on the crystal graph convolution neural network (CGCNN) model has been successfully employed to tune these mechanical properties of Ti₃AlC₂-based MAX phases via the A-site substitution (Ti₃(Al_1-xA_x)C₂). The structure-property correlation between the A-site substitution and mechanical properties of Ti₃(Al_1-xA_x)C₂ is established. The results show that the thermodynamic stability of Ti₃(Al_1-xA_x)C₂ is enhanced with substitutions A = Ga, Si, Sn, Ge, Te, As, or Sb. The stiffness of Ti₃AlC₂ increases with the substitution concentration of Si or As increasing, and the higher thermal shock resistance is closely associated with the substitution of Sn or Te. In addition, the plasticity of Ti₃AlC₂ can be greatly improved when As, Sn, or Ge is used as a substitution. The findings and understandings demonstrated herein can provide universal guidance for the individual synthesis of high-performance MAX phases for various applications.