Diamond CVD film formation onto WC–Co substrates using a thermally nitrided Cr diffusion-barrier

Diamond film deposition onto WC-Co substrates exhibits several limitations regarding the final diamond quality in the film and its adhesion due to the chemical interaction between the Co in the substrate and the diamond CVD environment. In the present study, the use of a ~ 1.5 μm thermally nitrided Cr interlayer was examined as an effective diffusion barrier throughout the CVD process. Nitridation of the Cr PVD layer in NH₃ environment resulted in the formation of a graded CrN/Cr₂N layer comprised mainly of the CrN phase, accompanied with the formation of a porous ‘net-like’ microstructure at the surface. During both thermal nitridation and exposure to the CVD environment up to 360 min, the diffusion of C and Co from the substrate into the interlayer was limited to the region adjacent to the Cr–N interlayer/WC–Co substrate interface, which contained the Cr₂N phase. In this region, the Co interacted with the Cr lattice to form a CoCr phase, which was suggested to enhance the chemical binding between the interlayer and the substrate. The region containing the CrN phase was suggested to act as an effective diffusion barrier due to its fully occupied interstitial sites and relatively high crystalline density compared to the underlying Cr₂N phase. It was evident that the deleterious effects of Co during the CVD process were successfully suppressed using the Cr–N interlayer and the deposited diamond film exhibited improved adhesion and higher diamond quality.The formation of phases within the interlayer during nitridation and the diamond CVD process, and diamond quality evaluation in the deposited films were investigated by complementary techniques: SEM, XRD, XPS, SIMS and Raman spectroscopy.     

Facile fabrication of stable PdCu clusters uniformly decorated on graphene as an efficient electrocatalyst for formic acid oxidation

Small-sized nanocrystals uniformly distributed on suitable supports are promising as active electrocatalysts due to their unique electronic structure and high accessible surface area. Herein, we report the synthesis of graphene supported PdCu nanoclusters with a uniform size of 2.3 nm via a facile one-pot solvothermal method. This nanohybrid exhibits much higher inherent catalytic activity and stability for formic acid oxidation in comparison to graphene supported Pd clusters and commercial Pd/C. The PdCu nanoclusters can maintain their original size and dispersity on graphene even after 200 CV cycles. This work offers an efficient low Pd-loading catalyst for formic acid oxidation, and the synthetic approach is of significance to preparing uniform metal-based clusters decorated on supports with superior catalytic properties for fuel cells and sensors.     

The effect of ceria content on the properties of Pd/CeO2/Al2O3 catalysts for steam reforming of methane

The effect of CeO₂ loading on the surface properties and catalytic behaviors of CeO₂–Al₂O₃-supported Pd catalysts was studied in the process of steam reforming of methane. The catalysts were characterized by S_BET, X-ray diffraction (XRD), temperature-programmed reduction (TPR), UV–vis diffuse reflectance spectroscopy (DRS) and Fourier transform infrared spectroscopy (FTIR). The XRD measurements indicated that palladium particles on the surface of fresh and reduced catalysts are well dispersed. TPR experiments revealed a heterogeneous distribution of PdO species over CeO₂–Al₂O₃ supports; one fraction of large particles, reducible at room temperature, another fraction interacting with CeO₂ and Al₂O₃, reducible at higher temperatures of 347 and 423 K, respectively. The PdO species reducible at room temperature showed lower CO adsorption relative to the PdO species reducible at high temperature. In contrast to Pd/Al₂O₃, the FTIR results revealed that CeO₂-containing catalyst with CeO₂ loading ≥12 wt.% show lower ratio (LF/HF) between the intensity of the CO bands in the bridging mode at low frequency (LF) and the linear mode at high frequency (HF). This ratio was constant with increasing the temperature of reduction. The FTIR spectra and the measurement of Pd dispersion suggested that Pd surface becomes partially covered with ceria at all temperature of reduction and with increasing ceria loading in Pd/CeO₂–Al₂O₃ catalysts. Although the PdO/Al₂O₃ showed higher Pd dispersion compared to that of CeO₂-containing catalysts, the addition of ceria resulted in an increase of the turnover rate and specific rate to steam reforming of methane. The CH₄ turnover rate of Pd/CeO₂–Al₂O₃ catalysts with ceria loading ≥12 wt.% was around four orders of magnitude higher compared to that of Pd/Al₂O₃ catalyst. The increase of the activity of the catalysts was attributed to various effects of CeO₂ such as: (i) change of superficial Pd structure with blocking of Pd sites; (ii) the jumping of oxygen (O^*) from ceria to Pd surface, which can decrease the carbon formation on Pd surface. Considering that these effects of CeO₂ are opposite to changes of the reaction rate, the increase of specific reaction rate with enhancing the ceria loading suggests that net effect results in the increase of the accessibility of CH₄ to metal active sites.     

Study of structure development of Titanium Nitride on inclined substrates

For magnetron sputter deposited coatings, the structure development during growth mostly depends on the mobility of the adatom over the substrate. The mobility is significantly affected by the orientation of the substrate with respect to the direction of the incident flux of sputtered atoms. The structural properties like crystallite size, crystallographic structure, column orientation, etc., are therefore influenced. This is relevant as the real work pieces over which the overlay functional coatings has to be applied are three dimensional in nature with the surfaces being off-normal to the incident flux. In the present investigation, the effect of incident angle on the various aspects of the structure development of Titanium Nitride coatings, having wide tribological applications, deposited on Si substrates by reactive magnetron sputter deposition was studied. A planar magnetron, with cathode diameter 75 mm and mounted with pure Ti target was used and TiN was deposited in a mixture of argon and nitrogen gas. The deposition was done for different durations. The deposited coatings were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results indicate the formation of well defined columnar microstructure in the coatings. The column inclination is compared with the well known ‘Tangent rule’.     

铝合金微弧氧化的研究进展

综述了微弧氧化技术的发展历程、成膜机理,论述了铝合金微弧氧化的特点。基于铝合金微弧氧化工艺研究现状,详细阐述了氧化时间、占空比、电压、电流密度、电解液浓度、基体粗糙度、纳米颗粒添加剂以及复合工艺等对铝合金微弧氧化膜层的组织与性能的影响。如电流密度会影响涂层的生长机理,使膜层的表面结构和内部缺陷产生较大的差异;采用不同的电解液所得到的膜层的厚度和粗糙度有明显的区别;在不同的电压参数下膜层的均匀性及膜层中微孔的尺寸大不相同;制备微弧氧化复合涂层以及采用纳米增强颗粒可使膜层的结构和性能有大幅提升。通过改变以上影响因素对铝合金微弧氧化膜层组织和结构加以调控,从而实现了对膜层性能的优化,如膜层的硬度、耐磨性、耐腐蚀性、抗疲劳性能的提高。最后对铝合金微弧氧化的发展方向提出了展望。     

Effects of bias voltage and gas pressure on orientation and microstructure of iridium coating by double glow plasma

Iridium coating was produced on various substrates using a double glow plasma. The effects of bias voltage and gas pressure on orientation and microstructure of the coating were studied. The orientation, microstructure and composition of the coating were evaluated by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The results showed that iridium coatings on various substrates all exhibited the preferred (220) orientation under the same deposition conditions. The microstructure of the coating was affected by bias voltage, gas pressure and substrate effects. The bias voltages had a significant impact on the crystal orientation of the coating. The increase of bias voltage resulted in high substrate temperature and large deposition rate. An increase in the coating thickness can affect the microstructure and orientation of the coating.     

Effects of environmental factors on atmospheric corrosion of aluminium and its alloys under constant dew point conditions

Environmental factors, such as chloride deposition rate, dew point and the addition of sulphate ions, were investigated under constant dew point conditions. Corrosion mass losses of AA1100 increased with increasing chloride deposition rates, dew points and with the absence of sulphate ions. Sulphate ions were shown to have an inhibition effect on pitting corrosion of aluminium alloys. High-purity aluminium was not sensitive to an increase of chloride deposition or dew point. As dew point increased from 5 to 28 °C, the corrosion mass loss of AA6061 decreased. The pitting susceptibility of AA6061 was rather high under low dew point conditions.     

磨料水射流-离子氮化复合处理对316不锈钢表面摩擦性能的影响

目的研究磨料水射流-离子渗氮复合处理对316不锈钢摩擦学性能的影响。方法采用磨料水射流、离子氮化技术分别在316不锈钢表面进行喷丸(WJ-316SS)、渗氮(PN-316SS)、喷丸+渗氮(WJ-PN-316SS)表面强化处理,并采用扫描电镜(SEM)、X射线衍射仪(XRD)、洛氏硬度计、粗糙度测试仪、超景深显微镜、划痕仪和摩擦磨损仪等研究复合处理试样的表面形貌、表层相结构与韧性,并讨论了不同表面处理试样的力学性能以及在干摩擦条件下的摩擦学行为。结果复合处理后的试样表面形成了连续密排的凹槽织构,表面改性层含有Fe_2N、Cr_2N、CrN等化合物,离子渗氮层厚度大约为10μm,表面显微硬度(79HRC)和表面粗糙度(1.10μm)高于单一表面处理试样。在与Si_3N_4摩擦配副进行干摩擦的实验中,316SS、WJ-316SS、PN-316SS的摩擦因数分别为0.8、0.4、0.5,磨损质量分别为7.1、3.3、3.7 mg。而WJ-PN-316SS的摩擦因数在0.25附近波动,磨损质量为0.3 mg,明显低于单一表面处理试样,耐磨性能更加优异,其磨损机理主要为疲劳磨损和氧化磨损。结论磨料水射流-离子渗氮复合处理能显著改善316不锈钢的摩擦学性能。     

A new encoding technique for peptide classification

Research on peptide classification problems has focused mainly on the study of different encodings and the application of several classification algorithms to achieve improved prediction accuracies. The main drawback of the literature is the lack of an extensive comparison among the available encoding methods on a wide range of classification problems. This paper addresses the fundamental issue of which peptide encoding promises the best results for machine learning classifiers. Two novel encoding methods based on physicochemical properties of the amino acids are proposed and an extensive comparison with several standard encoding methods is performed on three different classification problems (HIV-protease, recognition of T-cell epitopes and prediction of peptides that bind human leukocyte antigens). The experimental results demonstrate the effectiveness of the new encodings and show that the frequently used orthonormal encoding is inferior compared to other methods.