La2O3对铜基自润滑复合材料高温摩擦磨损性能的影响

为进一步提高铜基自润滑复合材料的硬度和高温摩擦磨损性能,采用粉末冶金热压法向铜-石墨烯-WS2复合材料中引入La2O3增强相颗粒,并对铜-石墨烯-WS2复合材料和La2O3增强铜-石墨烯-WS2复合材料在不同温度下的摩擦磨损性能进行对比研究。结果表明:复合材料烧结过程中各组元没有发生分解或互相反应,烧结后材料结构致密并且各组元均匀分布于基体中,La2O3增强相的引入在提高复合材料硬度的同时会降低材料热导率;室温下2种复合材料摩擦因数和磨损率比较相近,而高温下石墨烯和WS2的氧化导致Cu-RGO-WS2复合材料摩擦磨损性能下降,而La2O3则能发挥增强相作用和高温自润滑作用,使Cu-RGO-WS2-La2O3复合材料的高温摩擦磨损性能更优异。室温下铜-石墨烯-WS2复合材料的磨痕处仅发生了轻微的塑性变形,而La2O3增强铜-石墨烯-WS2复合材料的磨损机制主要是磨粒磨损;高温下铜-石墨烯-WS2复合材料的磨损机制为黏着磨损,而La2O3增强铜-石墨烯-WS2复合材料的磨损机制则为磨粒磨损和疲劳磨损。     

Adsorption of γ-picoline onto acid-activated bentonite from aqueous solution

The adsorption of γ-picoline onto acid-activated bentonite was investigated. The adsorption reached a maximum at pH = 7. Pseudo-first-order, pseudo-second-order, the Elovich equation, and intraparticle diffusion models were used to analyze the kinetic data obtained at different concentrations. The pseudo-second-order model was best applicable to describe the adsorption of γ-picoline on acid-activated bentonite. The Langmuir model provided good correlation with the experimental data. The adsorption of γ-picoline was endothermic with ∆H° = 29 J/mol.     

Oxidation and creep behavior of textured Ti2AlC and Ti3AlC2

The oxidation and creep behaviors of textured Ti₂AlC and Ti₃AlC₂ ceramics were characterized. The oxidation behavior of the two materials, which was studied in air at temperatures ranging from1000 to 1300 °C, was observed to be anisotropic and the materials exhibited a better oxidation resistance along a direction transverse to the c-axis. The correlation between the overall parabolic rate constant and oxidation temperature of both textured materials was characterized, providing new insights into the oxidation kinetics. The results indicate that the texturing has a negligible influence on the creep behavior in the assessed temperature range of 1000?1200 °C in air, for the applied stresses ranging from 40 to 80 MPa. In this stress regime, the creep behavior of textured Ti₂AlC and Ti₃AlC₂ appears to be controlled by grain boundary sliding. This behavior can be rationalized based on a model for superplastic deformation, indicating pure-shear motion under stationary conditions accommodated by lattice or grain-boundary diffusion.     

Stabilization of emulsions and foams using barley β-glucan

Barley β-glucan (BBG) is receiving increasing attention as a food hydrocolloid. Stability of foams and emulsions was assessed using whey protein concentrate (WPC) as an emulsifier and foaming agent, and BBG gum extracted at pilot plant or laboratory scale as a stabilizer. WPC had a significant lowering effect (P⩽0.05) on surface tension of water and water–oil interfacial tension, while the effect of β-glucan was time dependent. Differential scanning calorimetry (DSC) showed that BBG formed a gelled network, responsible for stabilizing, that melts at 58–62°C. Reversible gels of BBG melt around 63°C. Emulsion (50% o/w) droplet size decreased several fold when prepared with BBG gum and phase separation was substantially decreased. Foam volume and 50% drainage were significantly (P⩽0.05) improved upon addition of β-glucan. Sugar significantly enhanced foam stability only when used together with β-glucan. BBG shows potential as a stabilizer in foam- and emulsion-type food products.     

In situ W/O Co-doped hollow carbon nitride tubular structures with enhanced visible-light-driven photocatalytic performance for hydrogen evolution

Heteroatom co-doping has been considered as an effective strategy to simultaneously overcome intrinsic shortcomings of g-C₃N₄ to achieve enhanced photocatalytic properties, in which the involved dopants could play its role in altering electronic structure, optical absorption and charge separation of the catalyst. Herein, W/O co-doped hollow g-C₃N₄ tubular structures are successfully obtained for the first time via a one-step thermal decomposition. By W/O co-doping, architecture of g-C₃N₄ is able to be modulated with enhanced optical absorption towards visible region. In addition, narrowed band gap and restrained charge recombination are conducive for the excitation of electron-hole pairs and transportation. Photocatalytic water splitting tests indicate that the co-doped hollow tubular g-C₃N₄ structures enable superior activity for generating hydrogen up to 403.57 μmol g^?1 h^?1 driven by visible light, nearly 2.5 times as high as that of pristine g-C₃N₄. This work presents a rational strategy to design co-doped g-C₃N₄ as an efficient visible-light-driven photocatalyst.     

High-voltage arc erosion behavior and mechanism of Ti3AlC2 under different ambient atmospheres

The arc erosion behavior of Ti₃AlC₂ in oxygen, air, nitrogen, carbon dioxide, argon, and sulfur hexafluoride atmospheres at 9 kV voltage was studied. The breakdown strength increased in the order of oxygen, air, carbon dioxide, nitrogen, argon, and sulfur hexafluoride, whereas the arc energy decreased. Cracks, pits, and bulges on the eroded surface were investigated using scanning electron microscopy and three-dimensional (3D) laser confocal scanning microscopy. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to determine the composition of the eroded surface. The arc energy and electromagnetic force lead to the formation of erosion characteristics. The mechanism of erosion under the different atmospheres is discussed systematically, and is called the “decomposition-oxidation” process in oxygen, air, and carbon dioxide and the “decomposition-rereaction” process in nitrogen and sulfur hexafluoride. This study provides a reference for the application of MAX phase materials in high-voltage electrical appliances.     

Effects of MO_x(M=Mn,Cu,Sb,La)on V-Mo-Ce/Ti selective catalytic reduction catalysts

A series of MO_x-V_2O_5-MoO_3-CeO_2/TiO_2(M=Mn,Cu,Sb,and La) catalysts were prepared via an impregnation method.The physico-chemical properties of the catalysts were characterized and their NH_3-SCR of NO performance was compared.The Mn-loaded catalyst(Mn5V1Mo3Ce7/Ti) exhibits a large number of acid sites of varying strength,and together with good reducibility of the catalyst,contributes to the optimal SCR performance.The sulphate species formed in the presence of SO_2 significantly enhance the H_2O and SO_2 tolerance of Mn5V1Mo3Ce7/Ti.The Cu-loaded catalyst(Cu5V1Mo3Ce7/Ti)demonstrates potential in flue gas applications in the absence of SO_2 at low temperatures because of the excellent redox ability observed and the high degree of weak acid sites.The Sb and La loaded catalysts(Sb5V1Mo3Ce7/Ti and La5V1Mo3Ce7/Ti),especially La5V1Mo3 Ce7/Ti,exhibit the largest number of acid sites and the lowest reducibility,and therefore,may be suitable for use in high temperature denitrification applications.