Dual-phase rare-earth-zirconate high-entropy ceramics with glass-like thermal conductivity

A series of rare earth zirconates (RE₂Zr₂O₇) high-entropy ceramics with single- and dual-phase structure were prepared. Compared with La₂Zr₂O₇ and Yb₂Zr₂O₇, the smaller “rattling” ions (Yb³⁺, Er³⁺, Y³⁺) have been incorporated into pyrochlore lattice in (La_0.2Nd_0.2Y_0.2Er_0.2Yb_0.2)₂Zr₂O₇ (LNYEY) while larger ions (La³⁺, Nd³⁺, Sm³⁺, Eu³⁺) incorporated into fluorite lattice in (La_0.2Nd_0.2Sm_0.2Gd_0.2Yb_0.2)₂Zr₂O₇ (LNSGY). Due to high-entropy lattice distortion and resonant scattering derived from smaller ions Yb³⁺, Er³⁺, and Y³⁺, LNYEY shows a lower glass-like thermal conductivity (1.62-1.59 W m^-1 K^-1, 100-600℃) than LNSGY (1.74-1.75 W m^-1 K^-1, 100-600℃). Moreover, LNYEY and LNSGY exhibit enhanced Vickers’ hardness (LNYEY, H_v = 11.47 ± 0.41 GPa; LNSGY, H_v = 10.96 ± 0.26 GPa) and thermal expansion coefficients (LNYEY, 10.45 × 10^-6 K^-1, 1000℃; LNSGY, 11.02 × 10^-6 K^-1, 1000℃). These results indicate that dual-phase rare-earth-zirconate high-entropy ceramics could be desirable for thermal barrier coatings.     

Microstructural and electrical changes in Ca0.9R0.1CeNbMoO8 (R = Y,Sm, Nd,La) ceramics induced by rare-earth ion doping

Rare-earth ions doped Ca_0.9R_0.1CeNbMoO₈ (R = Y, Sm, Nd, La) ceramics have been successfully prepared by solid-state method, and their modifications to the microstructure and electrical properties are also investigated. The rare-earth ions doped ceramics exhibit the scheelite structure. With the increase in the radius of rare-earth ions, the lattice distortion and bond interaction will be enhanced, and the consistency of grain size will be reduced. The ceramics exhibit negative temperature coefficient (NTC) thermistor characteristics in the temperature range of 473 K-1273 K, and the activation energy decreases with the increase of the radius of rare-earth ions. Rare-earth ions doping can increase the content of Ce³⁺ ions and promote the conductivity of ceramics. Except for Sm³⁺-doped ceramics, the high-temperature aging rate of other ceramics is less than 2%. The existence of some metastable Sm²⁺ ions in Sm³⁺-doped ceramics not only increases the activation energy, but also reduces the high-temperature stability of the ceramics.     

High-entropy ferroelastic rare-earth tantalite ceramic: (Y0.2Ce0.2Sm0.2Gd0.2Dy0.2)TaO4

In this study, high-entropy rare-earth tantalate ceramics (Y_0.2Ce_0.2Sm_0.2Gd_0.2Dy_0.2)TaO₄ ((5RE_0.2)TaO₄) have been successfully fabricated. The possibility of formation of (5RE_0.2)TaO₄ was verified via first-principles calculations. In addition, the phase structure, ferroelastic toughening mechanism, thermophysical, and mechanical properties were systematically investigated. The (5RE_0.2)TaO₄ ceramics have lower phonon thermal conductivity (1.2–2.6 W·m^–1·K^–1) in the entire temperature range than that of RETaO₄ and YSZ. (5RE_0.2)TaO₄ has a higher fracture toughness and lower brittleness index than YSZ. The thermal expansion coefficients of (5RE_0.2)TaO₄ are as high as 10.3 × 10^-6 K^–1 at 1200°C and Young's modulus is 66–189 GPa, and thus, (5RE_0.2)TaO₄ possesses great potential for application in thermal barrier coatings (TBCs).     

Critical Assessment 36: Assessing differences between the use of cerium and scandium in aluminium alloying

ABSTRACT

Key factors affecting an application of two rare-earth metals cerium and scandium as alloying elements in aluminium are critically assessed. Having similar abundance in the Earth’s crust, their cost and consumption differ by three to four orders of magnitude. The spectacular increment of alloy strength, achieved by scandium through the coherent, nano-scale, L1₂-ordered Al₃Sc precipitates is faced by the prohibitive cost barrier. For cerium, the low cost is accompanied by rather limited strengthening effects: negligible solid-state solubility of cerium in aluminium makes age hardening ineffective so the alloy strength depends on the Al₁₁Ce₃ eutectic phase, formed during solidification. As a result, there are still no commercial aluminium alloys with large-scale applications that take advantage of cerium, scandium or their combination.     

Phase equilibria in the zirconia–yttria/gadolinia–silica systems

Phase equilibria in ZrO₂-YO_1.5-SiO₂ (ZYS) and ZrO₂-GdO_1.5-SiO₂ (ZGS) were experimentally assessed at 1400?°C and 1600?°C as they can offer insight on reactions between thermal barrier coatings (TBCs) based on ZrO₂-YO_1.5/GdO_1.5 and molten silicate deposits in gas turbine engines. Features shared in both systems include the absence of ternary compounds and no ternary solubility in the binary phases. In ZYS however, a quaternary invariant reaction was observed that eliminates the zircon-disilicate equilibrium at higher temperatures. The results suggest no appreciable difference in the reactions between silica and thermal barrier oxides based on ZrO₂-YO_1.5 or ZrO₂-GdO_1.5, or environmental barrier coatings based on the corresponding Y/Gd silicates. The phase diagrams derived from these experiments are part of a broader effort to develop thermodynamic databases that can help guide the design of next-generation TBCs.     

含La2O3奥氏体不锈钢堆焊合金层晶粒细化机制及对其耐腐蚀、磨损性能的影响

目的 通过在超低碳Cr19Ni10不锈钢堆焊合金中加入稀土氧化物La2O3，细化其微观组织，获得力学性能、耐腐蚀性能和耐磨性能等综合性能优良的堆焊合金层。方法 采用添加La2O3的超低碳Cr19Ni10不锈钢焊条制备了四种不锈钢堆焊合金。采用X射线荧光光谱、红外碳硫分析仪和X射线衍射分析仪，对堆焊合金层的元素组成和相组成进行了测定。采用金相显微镜和晶粒度统计软件，对堆焊合金层的微观组织形貌进行观察，并对晶粒度进行了统计分析。采用显微维氏硬度计和纳米压痕仪对堆焊合金层的硬度和杨氏模量进行了测定。采用电化学工作站和CSM摩擦磨损试验机对堆焊合金层的耐腐蚀性能和耐磨性能进行了评价，并且采用白光共聚焦显微镜对磨损后的磨痕形貌和尺寸进行了观察和测定。采用二维晶格错配度理论，对La2O3/γ-Fe界面间的晶格错配关系进行了计算。结果 在堆焊合金层中加入La2O3，随着La2O3加入量的增加，堆焊合金层奥氏体晶粒细化越明显。当La2O3的添加量由0%增加至1.5%时，奥氏体晶粒平均面积由400 μm²减少为210 μm²。堆焊合金层加入La2O3，可以明显提高其力学性能、耐腐蚀性能和耐磨损性能。当La2O3的添加量由0%增加至1.0%时，堆焊合金层的微观硬度由180HV增加到225HV，宏观硬度由125HBS增加到150HBS，杨氏模量由186 GPa左右增加到217 GPa，腐蚀电位由?0.4 V增加到?0.25 V，磨痕深度由50 μm减小到10 μm。La2O3(001)面和γ-Fe(110)面的二维晶格错配度为8.7%(<12%)，说明La2O3可以作为γ-Fe的中等有效异质形核基底，从而细化了堆焊合金层中的奥氏体晶粒。结论 La2O3可以有效地细化奥氏体晶粒，改善堆焊合金层的力学性能，提高其耐腐蚀和耐磨损性能。但是，La2O3加入量存在一个最佳值，当La2O3的加入量为1.0%时，堆焊合金层的综合性能最好。     

夜光粉表面包覆的研究

介绍了国内夜光粉表面包覆技术的现状,并指出了引起夜光粉水解的原因,夜光粉SrAl2O4：Eu,Dy经包覆后在水中浸泡5天仍有1500 mcd/m2的初始亮度,未经处理的夜光粉几乎失去发光性能.经包覆处理后的夜光粉表面有一层连续致密的保护层,大大提高了它的化学稳定性和发光亮度,拓宽了夜光粉的应用领域.     

离子稀土矿山环境影响评价中的生态修复体系研究

分析堆池浸工艺废弃矿山土壤的主要问题,对某离子型稀土矿生态修复方案进行设计,将废弃地恶劣基质转变成能够生长植物的土壤是修复的关键,为同类型稀土矿山生态修复方案的编制提供参考。     

掺Pr3+,Lu3+氟化镓铟玻璃系统玻色峰的研究

将拉曼光谱与热分析方法相结合，研究了在20GaF3-15InF3-20CdF2-15ZnF2-20PbF2-10SnF2玻璃系统中玻色峰与稀土离子Pr^3 ，Lu^3 掺杂浓度的关系．结果表明：稀土离子Pr^3 ，Lu^3 的加入不会使玻璃结构发生质的变化，玻璃的玻色峰峰值强度随Pr^3 和Lu^3 掺杂浓度变化的趋势与At随Pr^3 和Lu^3 掺杂浓度变化的趋势相一致；掺Pr^3 系列可用“软势模型”来解释玻色峰，而掺Lu^3 系列玻色峰的成因更加复杂，谐波近似的软势模型不再适用；非桥氟决定了玻色峰的峰值强度及稀土离子在玻璃中的溶解度．