Preparation of novel titanium-niobium-oxygen composite ceramic with excellent thermoelectric properties using the high-pressure and high-temperature method

Titanium oxide is a promising thermoelectric material because of its high stability and low cost. We synthesize novel titanium-niobium-oxygen composite ceramics directly from elementary substance Nb and TiO₂ under high-pressure and high-temperature (HPHT) in this work. Elemental substance Nb will reduce TiO₂ to Magnèli phase titanium oxide at high pressure and high temperature. In this process, elemental substance Nb is oxidized to various niobium oxides. The experimental results show that the composite ceramics have a special 'pore' microstructure, and their thermoelectric and mechanical properties are very prominent among metal oxide thermoelectric materials. After repeated tests, the optimum concentration sample zT value is 0.313 at 973 k, with a Vickers hardness of 7.06. This work provides a novel concept for improving the performance of TiO₂ by reducing it with metal elementary substances other than Ti.     

添加SnAl元素与中温烧结对Cr/Zr膜基界面结合强度的影响

目的 通过在Cr膜中添加SnAl元素及中温液相烧结,提高锆合金膜基界面结合强度。方法 在Cr靶中添加SnAl元素,制备一种均匀分布的CrSnAl合金靶材（原子比Cr:Sn:Al=95:4:1）,并利用直流磁控溅射（DCMS）技术在锆合金表面制备约5 μm厚的CrSnAl膜层,再将CrSnAl膜层试样放入Ar保护气氛炉中进行中温烧结（温度为600 ℃,时间为30 min）,随炉冷却至室温。利用XRD、SEM、EDS及体式显微镜分析中温烧结对CrSnAl膜层形貌、组织结构及元素扩散的影响;根据涂层弯曲断裂形貌、切削划痕力和切屑形貌综合评价膜基界面结合强度。结果 添加SnAl后,Cr膜层表面孔隙等缺陷明显减少,膜基界面结合强度得到较大提升,从41.7 MPa提升到了45.8 MPa。600 ℃烧结后,CrSnAl膜层韧性增强,并出现韧窝形貌,剪切唇仅为烧结前CrSnAl膜层的1/2,CrSnAl/Zr界面结合强度进一步提升到52.1 MPa。结论 Cr膜中添加SnAl有利于膜基界面元素扩散,对膜基界面结合强度提高有较大影响;中温烧结CrSnAl膜层韧性及膜基界面结合强度均有较大提升,进而改善了膜基界面结合性能。     

Hydrogen interaction characteristics of a Cr2O3Y2O3 coating formed on stainless steel in an ultra-low oxygen environment

Ceramics are the most promising candidates for tritium permeation barriers for fusion reactors due to their high thermal and chemical stabilities and low hydrogen isotope permeation reduction factors. However, hydrogen embrittlement and a large number of defects in ceramic coatings are new challenges for first wall materials in nuclear reactors. To address this issue, a new Cr₂O₃Y₂O₃ coating with a thickness of about 100 nm was synthesized and placed in an ultra-low oxygen partial pressure (8 × 10⁻²⁰ Pa) environment, in which a compact CrY alloy coating was successfully deposited on the stainless-steel substrate by pulsed electrochemical deposition. The interactions between the coating and hydrogen plasma were comprehensively analyzed and compared via surface analysis techniques, including TEM, XPS and electrochemical impedance spectroscopy (EIS). The mechanical properties of the coating before and after hydrogen permeation were studied by tensile testing. It was found that this ceramic coating effectively reduced the defect concentration and retained a high protective performance upon hydrogen exposure. Therefore, this new Cr₂O₃Y₂O₃ coating has potential as a promising hydrogen permeation barrier.     

Hydrogen interaction characteristic of nanoscale oxide films grown on iron–nickel based stainless steel by selective thermal oxidation

Hydrogen isotopes, the reaction ingredients in the nuclear fusion plant, can easily permeate through the stainless steel (SS) substrate, leading to the so-called hydrogen degradation. Generally, a widely accepted way to reduce the hydrogen permeation is to prepare a barrier coating on the substrate. Nevertheless, the coated layer has the inherent problem of incompatibility with the heterogeneous base materials. In this work, in-situ selective oxidation was used to explore the optimal oxides with the improved hydrogen resistance. Two types of layers thermally formed at 450 °C and 750 °C, respectively, were selected to investigate their hydrogen interaction characteristics. Comprehensive analyses, including Raman spectra, XPS, EIS and AES, indicate that the oxide formed at 450 °C is a better candidate of hydrogen permeation barriers, probably due to the formation of protective layers of chromia and FeCr₂O₄, while the oxides obtained at 750 °C, though exhibiting a much more stable phase, can rarely reduce hydrogen diffusion through the shortcuts of defects. This finding provides a potential new way to prepare a hydrogen permeation barrier.     

High temperature creep behaviour of glass-ceramic joined Nextel 610™/Al2O3-ZrO2 composites

Ox/ox CMC based on Nextel 610? fibers with 75 wt% alumina – 25 wt% zirconia matrix have been joined by a glass-ceramic and tested in creep in four-point bending (DIN EN 820–4) up to 50 h at 850 °C and 1000 °C, between 32 and 41 MPa. As a comparison, the creep limit of the non-joined ox/ox CMC was investigated in this range and also at higher temperatures and stresses. The creep experiments at 850 °C did not show any significant difference between joined and ox/ox CMC after 50 h, while a certain one was detected at 1000 °C on joined ox/ox CMC, suggesting that its creep mechanism is dominated by visco-elastic flow of the glass-ceramic.     

Critical evaluation and thermodynamic optimization of the Si-N,Si-C,C-N and Si-C-N systems and its applications to high purity SiC production

Thermodynamic optimization of the Si-N, Si-C, C-N and Si-C-N systems were performed using the CALculation of PHAse Diagrams (CALPHAD) method based on critical evaluation of all available experimental data. The liquid and solid solutions within the Si-C-N system were described using the Modified Quasichemical Model and Compound Energy Formalism, respectively. The Gibbs energies of β-Si₃N₄ and β-SiC were carefully optimized to resolve inconsistencies among existing thermodynamic properties and phase equilibria data. The solubilities of C and N in both solid and liquid Si solutions were critically optimized. Besides, the solubility of N in β-SiC to form a narrow homogeneity range of β-Si(C,N) solid solution is considered for the first time in the present thermodynamic modeling. Based on the present thermodynamic database, experimentally unexplored phase diagrams and thermodynamic properties within the Si-C-N alloys were predicted. As an application of the database, the influences of various operation conditions on high purity SiC production using sublimation process were calculated.     

关于智能电网发展的几点思考

  [目的]  为了理清智能电网作为新一代能源体系核心平台的相关概念和发展思路。  [方法]  利用文献综述法梳理了微电网、泛能网和能源互联网的概念及其与智能电网的关系。结合我国的能源发展现状和战略需求,探讨了我国智能电网的建设思路和重点。  [结果]  智能电网是传统电力系统和现代信息技术的深度融合,而能源互联网是智能电网和互联网思维模式、技术的深度融合。智能电网是能源互联网的基础平台,微电网、泛能网、智能电网和能源互联网都以实现更加清洁、高效、灵活的用能为目标。  [结论]  智能电网建设应在强调高压侧智能化控制的同时,同步建设智能配电网,鼓励以多能互补为核心的泛能网的发展。