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.     

地应力条件下的凿岩爆破数值模拟

为了研究地应力对凿岩爆破的影响,采用DDA方法模拟爆炸应力波作用下考虑地应力条件时的单孔和多孔凿岩爆破破岩过程。模拟发现,随着初始地应力水平的增加,裂纹扩展半径和破岩区域面积减小,裂纹发育主方向趋于地应力的最大主应力方向,初始地应力对裂纹的抑制和引导作用明显;初始地应力水平的增加,对拉伸裂纹的抑制作用更为显著,从而降低了拉伸破坏对爆破破岩的贡献。模拟也表明,在初始地应力存在的条件下,通过对爆破载荷和炮孔布置进行针对性的优化,可以克服地应力带来的影响,并取得预期的爆破效果。本研究对地应力条件下的凿岩爆破工程具有理论和参考意义。     

离子型稀土矿山淋洗及尾水富集试验研究

对浸矿后离子型稀土原地浸矿场采用清水进行淋洗，在184天的清水淋洗过程中，尾水氨氮值从最开始的507mg/L，降低至140mg/L，淋洗尾水pH4.52~3.10。淋洗尾水采用两级反渗透膜分离，既回收有价资源稀土，又能使出水氨氮达标。结果表明，产水氨氮浓度稳定低于15mg/L，对稀土的截留率高于98.25%，浓水中稀土离子平均浓度313.4mg/L，可进一步回收稀土资源。     

Rare earth metals co-doped ZnO/CNTs composite as high performance photocatalyst for hydrogen production from water_triethanolmine mixture

This study investigated the zinc oxide (ZnO) based heterojunction photocatalysts for improved hydrogen production from water splitting. A sol-gel route was adopted to produce terbium (Tb) and samarium (Sm) co-doped ZnO/CNTs composites where CNTs worked as a support material. The built-in redox couples of lanthanides in co-doped TS-ZnO/CNTs composite showed higher hydrogen evolution activity than Sm doped (Sm-ZnO/CNTs) and Tb doped (Tb–ZnO/CNTs) photocatalysts. When triethanolamine was utilized as a sacrificial agent, the TS-ZnO/CNTs photocatalyst result in a remarkable hydrogen evolution rate of 2683 molh^?1g^?1 under visible light illumination. The optimum photocatalyst also showed high stability over five successive hydrogen evolution cycles. The better hydrogen evolution rate with TS-ZnO/CNTs was referred to its fine particle size, high reactive surface area, small optical band gap, suppressed reunification of charge carriers and built-in redox couples. The photocatalytic mechanism, involved in water splitting with TS-ZnO/CNTs photocatalyst, is also deduced in this study. This study can stimulate the attempts towards construction of lanthanides based co-doped semiconductor photocatalysts for efficient hydrogen evolution.     

成分配比对稀土钨电极材料组织及力学性能影响

通过固液掺杂、等静压压制、中频烧结的方法，制备了不同的氧化镧、氧化钇、氧化锆三元掺杂成分比例的钨电极材料烧结棒材，探究了不同成分配比对样品显微组织、第二相粒子分布以及宏观力学性能的影响。结果表明，氧化镧、氧化钇、氧化锆三元复合添加能够有效改善第二相粒子在钨基体中的分布形态，降低第二相在晶界的过度富集，提高钨电极材料的综合力学性能。并且当添加成分镧、钇、锆质量比为3:1:1时，材料具有最好的综合力学性能，致密度可达96.04%，显微硬度可达549.37HV0.3，抗压强度可达3785MPa，原因是此配比下第二相粒子最为细小均匀，弥散程度最高，对基体晶粒的细化作用最好，该配比下钨基体平均晶粒尺寸达到10.3μm。     

TiO_2/FeOOH/硅藻土纳米复合材料的制备和光催化性能研究

采用分子组装的方法,以硅藻土为基底制备TiO_2/硅藻土、TiO_2/FeOOH/硅藻土纳米复合材料,通过UV-Vis、TEM方法对材料进行表征,以甲基橙溶液为目标降解物探究纳米复合材料的光催化性能,结果表明,基底制备TiO_2/硅藻土、TiO_2/FeOOH/硅藻土纳米复合材料对甲基橙均有不错的降解率,其中TiO_2/FeOOH/硅藻土纳米复合材料降解率达到67.16%。     

Cold crucible melting and characterization of titanate-zirconate pyrochlore as a potential rare earth/actinide waste form

La-Ce-Gd titanate-zirconate pyrochlore-based ceramics was synthesized at the lab-scale inductive melting unit with a 56?mm inner diameter cold crucible. Batch feeding rate and melting ratio were 3?kg/h and 3?kW?h/kg respectively. The ceramics is composed of 85–90?vol% zoned grains of the pyrochlore structure phase, the sample has excellent chemical durability in hot water and may be considered as a promising matrix for actinide – rare earth fraction of high level waste.     

Role of a low level of La2O3 dopant on the tetragonal-to-monoclinic phase transformation of ceria-yttria co-stabilized zirconia

Yttria, yttria-ceria and yttria-ceria-lanthana stabilized zirconia powders were prepared by coprecipitation. Their tetragonal-to-monoclinic phase (t→m) transformation was investigated by calcining the powders in a temperature range of 400–1400 °C for 2 h. The results show that after doping with 0.1 to 0.3 mol.% La₂O₃ and calcining at 1400 °C in air, unusual redox behaviours of cerium were detected in the 1.5 mol.% Y₂O₃+5.5 mol.% CeO₂ co-stabilized zirconia. Grain refinement and a sharp reduction in oxygen vacancy concentration were observed simultaneously. The t→m transition was not found in the 0.1 mol.% La₂O₃ doped zirconia but appeared in the cases with a higher dopant content. The changes are discussed with regards to the grain size, valence change of cerium, presence of oxygen vacancies, and segregation of the dopants at grain boundaries.     

The effects of the modification of the BST-system solid solutions with rare earth elements

The conditions for the preparation of the solid solutions of a binary system of barium-strontium titanates with the substitutions in the A-sublattice with the rare-earth elements (REE), including the solid-phase synthesis, mechanical activation and sintering of dispersed-crystalline products by the conventional ceramic technology, were optimized. The presence (absence) of the impurity phases was established depending on the size effect of the REE. The precision X-ray diffraction analysis revealed the features of the phase formation in the studied solid solutions and showed that the “behavior” of the structural characteristics of the solid solutions with the participation of the REE is determined by the limiting conditions of the isomorphism and anion excess of the media under study. An assumption is made about the nature of the formation of a fine-grained landscape of the modified solid solutions, associated with the multicluster structure of the crystallite structure and the formation of the ballast phases during their synthesis. The dependences of the dielectric properties of the solid-state solution on the external influences – temperature, frequency of an alternating electric field and strength of a constant field – have been established. The possibility of choosing on the basis of the obtained data, promising for practical applications of the compositions is shown.     

Energy storage performance of 0.55Bi0.5Na0.5TiO3-0.45SrTiO3 ceramics doped with lanthanide elements (Ln = La,Nd, Dy,Sm) using a viscous polymer processing route

Lead-free bismuth sodium titanate-strontium titanate (NBT-ST) dielectric ceramic materials have been extensively investigated energy storage materials because of their relaxor characteristics. In this study, four different lanthanide elements were introduced into the ferroelectric NBT-ST ceramic to improve their relaxor properties. The introduction of the lanthanide resulted in an increase in disorder at location A within the perovskite lattice and improved relaxor characteristics, leading to a stored energy density of more than 3.5 J/cm³. In particular, an ultrahigh recoverable stored energy density of 4.94 J/cm³ and efficiency of 88.45% were achieved at 440 kV/cm when the NBT-ST ceramic was modified with neodymium. The modified ceramic also exhibited good thermal stability in the range of 30–120 °C, as well as a fast discharge time of ～153 ns, indicating that Nd-incorporated NBT-ST is a promising candidate for electrical energy storage ceramic.