Vacuum brazing of TiAl-based intermetallics with Ti–Zr–Cu–Ni–Co amorphous alloy as filler metal

An amorphous Ti41.7–Zr26.7–Cu14.7–Ni13.8–Co3.1 (wt%) ribbon fabricated by melt spinning was used as filler to vacuum braze Ti–48Al–2Nb–2Cr (at%) intermetallics. The influences of brazing temperature and time on the microstructure and strength of the joints were investigated. It is found that intermetallic phases of Ti₃Al and γ-Ti₂Cu/Ti₂Ni form in the brazed joints. The tensile strength of the joint first increases and then decreases with the increase of the brazing temperature in the range of 900–1050 °C and the brazing time varying from 3 to 15 min. The maximum tensile strength at room temperature is 316 MPa when the joint is brazed at 950 °C for 5 min. Cleavage facets are widely observed on all of the fracture surfaces of the brazed joints. The fracture path varies with the brazing condition and cracks prefer to initiate at locations with relatively high content of γ-Ti₂Cu/Ti₂Ni phases and propagate through them.     

Accelerated exploration of multi-principal element alloys for structural applications

A strategy for accelerated discovery and exploration of multi-principal element alloys was developed and used to identify new alloys within a design window of desired microstructures and properties. As an example, the strategy was applied to analyze thousands of 3- 4-, 5- and 6-component alloys at equiatomic compositions of the alloying elements. Currently available thermodynamic databases were used to assess equilibrium phase diagrams for these alloys. The validity and reliability of the calculated phase diagrams were estimated based on the extent of experimental binary and ternary data used to build the respective thermodynamic databases. Alloys with specific characteristics, such as single-phase solid solution alloys with the use temperature above 1000 °C, were identified using an automated analysis of the calculated phase diagrams. The density, elastic moduli and costs of these alloys were estimated using the rule of mixtures of pure elements and were used as additional criteria for alloy selection. This approach allowed rapid, albeit preliminary, screening of many thousands of alloys and identification of promising candidate compositions, some of which are reported in this paper, for more time intensive experimental validations and assessments.     

广州市郊填埋场附近蔬菜重金属检测与讨论

蔬菜是人们餐桌上必不可少的食物,重金属在受污染的自然环境中又无处不在,而蔬菜中的重金属含量尤其令人担忧。本文使用原子吸收分光光度法(石墨炉)和原子荧光分光光度法检测了广州市郊某垃圾填埋场附近所种植蔬菜中重金属含量。结果:抽样由2013年10月至2014年9月共持续一年,共抽样检测12次,按平均每个月一次的频率,检测结果并未发现有蔬菜超出国家规定的限量值。     

硝酸对水质中重金属含量测定的影响研究

采用火焰原子吸收分光光度法对加硝酸和不加硝酸的浑浊和澄清水质样品中镍、锰、铜、锌、铅的浓度变化进行测定研究和对比,结果表明硝酸加入样品中能起到固定剂的作用,加入硝酸对于铜元素的浓度影响很小,对澄清水中的锰元素和铅元素影响也很小,但是加入硝酸对镍和锌元素有较大影响。     

重型装备综采工作面对接技术

111304工作面为对接工作面,埋藏深,地压大,工作面装备重型设备,对接失败将直接影响生产,处理困难。提前对接位置100m进行准备,加强现场管理,按线移架,综合运用调刀和改变推溜顺序等方法,及时调整工作面,确保了工作面顺利对接。     

稠油地下改质开采技术及发展趋势

稠油作为全球重要的非常规原油资源，是保障我国能源安全、重大工程需求的重要资源。目前常规的热采稠油油藏陆续进入开采后期，高能耗、高污染、高成本问题日趋严重，亟需依靠技术换代实现开发方式升级。稠油地下改质是通过向油藏中注入改质催化剂，使其与稠油发生化学反应，实现稠油地下不可逆降黏并高效采出的一种开采方式，是近十年来最受瞩目的下一代稠油开采技术之一。本文从技术机理、改质催化剂及开采效果影响因素三方面阐述了技术内涵，通过系统调研国内外相关学者和企业的代表性成果，按照催化剂种类、反应温度和降黏效果等进行综合性分类统计，对比了现有矿场试验的开采方式和采油效果，指出制约技术应用的两个关键问题，并展望了技术未来发展方向。     

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.     

Chlorophyll derivatives/MXene hybrids for photocatalytic hydrogen evolution: Dependence of performance on the central coordinating metals

Development of efficient photocatalytic hydrogen evolution reaction (HER) with illumination of visible light is challenging. In this work, five chlorophyll derivatives (M-Chls; M = H₂/Cu/Ni/Co/Zn) with different central ions in its cyclic tetrapyrrole ring including free base, copper, nickel, cobalt, and zinc were synthesized and employed as the effective visible-light harvester for efficient HER. In addition, two-dimensional (2D) noble metal-free co-catalyst Ti₃C₂T_x MXene was used as an excellent electron capturer due to its outstanding conductivity property. These M-Chls are modified on the surface of Ti₃C₂T_x MXene with 2D accordion-like morphology by means of a simple deposition process to form noble metal-free Chl/Ti₃C₂T_x-based photocatalysts for HER. It is found that the best HER performance as high as 49 μmol/h/g_cat was achieved with the Co-Chl@Ti₃C₂T_x hybrid, which was much higher than those of other M-Chl@Ti₃C₂T_x composites. This research provides a specific way to synthesize low-cost and environmentally friendly natural Chls for developing highly efficient photocatalytic HER through molecular engineering.     

Plasma-assisted CO2 reforming of methane over Ni-based catalysts: Promoting role of Ag and Sn secondary metals

Carbon dioxide (CO₂) and methane (CH₄) are the primary greenhouse gases (GHGs) that drive global climate change. CO₂ reforming of CH₄ or dry reforming of CH₄ (DRM) is used for the simultaneous conversion of CO₂ and CH₄ into syngas and higher hydrocarbons. In this study, DRM was investigated using Ag–Ni/Al₂O₃ packing and Sn–Ni/Al₂O₃ packing in a parallel plate dielectric barrier discharge (DBD) reactor. The performance of the DBD reactor was significantly enhanced when applying Ag–Ni/Al₂O₃ and Sn–Ni/Al₂O₃ due to the relatively high electrical conductivity of Ag and Sn as well as their anti-coke performances. Using Ag–Ni/Al₂O₃ consisting of 1.5 wt% Ag and 5 wt% Ni/Al₂O₃ as the catalyst in the DBD reactor, 19% CH₄ conversion, 21% CO₂ conversion, 60% H₂ selectivity, 81% CO selectivity, energy efficiency of 7.9% and 0.74% (by mole) coke formation were achieved. In addition, using Sn–Ni/Al₂O₃, consisting of 0.5 wt% Sn and 5 wt% Ni/Al₂O₃, 15% CH₄ conversion, 19% CO₂ conversion, 64% H₂ selectivity, 70% CO selectivity, energy efficiency of 6.0%, and 2.1% (by mole) coke formation were achieved. Sn enhanced the reactant conversions and energy efficiency, and resulted in a reduction in coke formation; these results are comparable to that achieved when using the noble metal Ag. The decrease in the formation of coke could be correlated to the increase in the CO selectivity of the catalyst. Good dispersion of the secondary metals on Ni was found to be an important factor for the observed increases in the catalyst surface area and catalytic activities. Furthermore, the stability of the catalytic reactions was investigated for 1800 min over the 0.5 wt% Ag-5 wt% Ni/Al₂O₃ and 0.5 wt% Sn-5 wt% Ni/Al₂O₃ catalysts. The results showed an increase in the reactant conversions with an increase in the reaction time.