Millimeter-long multilayer graphene nanoribbons prepared by wet chemical processing

Millimeter long multilayer graphene nanoribbons were prepared by a chemical treatment of graphite oxide (GO). To our knowledge, this is the very first report to harvest ultralong graphene ribbons with length dimension >1 mm using a wet chemical process. Scanning electron microscope (SEM) images reveal the nanoribbon length larger than 1 mm and width ∼10 μm. X-ray photoelectron spectroscopy (XPS) analysis shows that oxygen-containing functional groups decreased as the extent of the chemical treatment increased. X-ray diffraction (XRD) and Raman spectroscopy studies confirmed the XPS result and unveil more graphitic sheet like structure formed as GO was reduced by more concentrated NaOH. It is found that by adjusting NaOH/GO mass ratio during the chemical treatment, we can produce >1 mm long multilayer graphene nanoribbons and achieve controllable degree of reduction to the GO material. It is expected that this technique will make ultralong graphene nanoribbons readily available for research and applications.     

Antibacterial Properties and Corrosion Resistance of Nitrogen-doped TiO_2 Coatings on Stainless Steel

The Nitrogen-doped TiO2 (N-TiO2) coatings were fabricated on 304 austenitic stainless steel (SS) substrates by oxidation of titanium nitride coatings,which were prepared by plasma surface alloying technique.Microstructural investigation,corrosion tests and antibacterial tests were conducted to study the properties of N-TiO2 coatings.Composition analysis shows that the SS substrates were shielded by the N-TiO2 coatings entirely.The N-TiO2 coatings are anatase in structure as characterized by X-ray diffraction.The corrosion properties of N-TiO2 coated SS samples in Hanks’ solution were investigated by a series of tests.The electrochemical measurements indicate that the corrosion potential positively shifts from 0.275 V for untrated SS to 0.267 V for N-TiO2,while the corrosion current density decreases from 1.3×105 A/cm to 4.1×10 6 A/cm2.The corrosion resistance obtained by fitting the impedance spectra also reveals that the N-TiO2 coatings provide good protection for SS substrate against corrosion in Hanks’ solution.Electrochemistry noise tests indicate that the N-TiO2 coatings effectively retard the local pitting and crevice corrosion of the SS substrate.The results of the antibacterial test reveal that N-TiO2 coatings give 304 austenitic SS an excellent antibacterial property.     

Partial oxidation of ethanol on supported Pt catalysts

This work studied the effect of the nature of the support on the performance of Pt/Al₂O₃, Pt/ZrO₂, Pt/CeO₂ and Pt/Ce_0.50Zr_0.50O₂ catalysts on partial oxidation of ethanol. The reducibility and oxygen transfer capacity were evaluated by temperature-programmed reduction (TPR) and oxygen storage capacity (OSC) experiments. The results showed that the support plays an important role on the products distribution of the partial oxidation of ethanol. Acetic acid was the main product on Pt/Al₂O₃ catalyst whereas methane and acetaldehyde were the only products detected on Pt/ZrO₂, Pt/CeO₂ and Pt/Ce_0.50Zr_0.50O₂ catalysts.The products distribution obtained on Pt/ZrO₂, Pt/CeO₂ and Pt/Ce_0.50Zr_0.50O₂ catalysts was related to their redox properties. The OSC experiments showed that the oxygen exchange capacity was higher on Pt/CeO₂ and Pt/Ce_0.50Zr_0.50O₂ catalysts. A high oxygen storage capacity favored the formation of acetate species, which could be decomposed to CH₄ and/or oxidized to CO₂ via carbonate species. On the other hand, the lower oxygen exchange capacity of Pt/ZrO₂ catalyst led to a higher ethoxy species formation. These species can be dehydrogenated and desorb as acetaldehyde. Then, the higher selectivity to acetaldehyde observed on Pt/ZrO₂ catalyst could be assigned to its low oxygen storage/release capacity.In the case of Pt/Al₂O₃ catalyst, the production of acetic acid could be related to its acidic properties, since this material did not show redox properties, as revealed by OSC analysis.     

Dry Sliding Tribological Properties of a Dendrite-reinforced Zr-based Bulk Metallic Glass Matrix Composite

In-situ dendrite-reinforced metallic glass matrix （MGM） composites with the composition of Zr58.5Ti14.3Nb5.2Cu6.1Ni4.9Be11.0 were prepared with a vacuum arc melter by the copper mold suction casting. Effect of different normal loads and sliding velocities on the tribological properties of MGM composites was studied. The results showed that the friction coefficient and wear rate of composites initially descended with increasing the normal load and reached a minimum of 0.339 and 1.826 × 10^-4 mm^3/（N m） at 10 N, respectively, then ascended. Similarly, the friction coefficient and wear rate of composites initially decreased with the increase in the sliding velocity and reached a minimum of 0.330 and 2.389 × 10^-4 mm^3/（N m） at 0.4 m/s and 0.3 m/s, respectively, then raised. The wear mechanism of composites was mainly adhesive wear accompanied by abrasive wear at lower normal load and sliding velocity. However, the wear mechanism of composites was abrasive wear and adhesive wear as well as delamination at higher normal load and sliding velocity due to the nucleation and propagation of surface and subsurface cracks during the wear process. The flake-like and particle-like wear debris was the dominant shapes of debris observed.     

镁合金和钛合金表面着色工艺研究进展

表面着色技术能在材料表面形成不同颜色的保护性膜层,在提高材料表面性能的同时,又可赋予产品漂亮的外观或实现消光等目的。表面着色有两种形式:一是,所生成的化合物自身具有一定的颜色;二是,光线的反射、折射、干涉等效应而使表面呈现不同颜色。作为两类重要的结构材料,镁合金和钛合金因其各自优良的性质被应用于诸多领域。综述了镁合金和钛合金表面着色工艺研究进展,介绍了镁合金和钛合金表面着色工艺研究及应用现状。镁合金表面着色工艺包括:化学转化+喷涂、金属涂层、有机涂层、阳极氧化和微弧氧化;钛合金表面着色工艺包括:热氧化、化学氧化、阳极氧化和微弧氧化。列举了应用于镁合金和钛合金表面着色的具体工艺参数,总结了两种合金表面着色的具体应用。镁合金和钛合金部件经表面着色处理后,可以兼顾轻量化和强度要求,并实现部件外观的装饰性。基于镁合金和钛合金表面着色工艺研究的现有成果,对镁合金和钛合金表面着色的研究提出了一定展望。