Carbon/platinum nanotextured films produced by plasma sputtering

Platinum loaded carbon layers were synthesized by a two-step plasma sputtering process. Two hundred nanometers thick columnar (columns with an average diameter of 20 nm) carbon films having a large open porosity were formed in the first step. Using the same plasma system, the films were subsequently loaded with platinum. SEM, TEM and Rutherford backscattering spectrometry analysis show that platinum diffuses into the carbon layer and forms nano-sized particles (mean diameter ca. 3 nm) along and around the carbon nanocolumns and down to the film/support interface. Optimized catalytic layers were formed at low plasma pressure operation (<1 Pa) and had an upper platinum loading limit of about 0.1 mg cm⁻².     

Optical and mass spectroscopy measurements of Ar/CH4/H2 microwave plasma for nano-crystalline diamond film deposition

Nano-crystalline diamond (NCD) thin film with grains of about 5–100 nm in size attracts much attention as new functional materials in various industrial fields, due to its unique properties that are different from the conventional microcrystalline diamond (MCD) thin film. Most commonly, NCD film can be synthesized using CH₄/Ar plasma with/without a small amount of hydrogen gas added. In this study, we carried out the measurements of quadrupole mass spectroscopy (QMS) and optical emission spectroscopy (OES) to investigate CH₄/H₂/Ar mixture plasma in detail. Combined with our experimental results of NCD film synthesis, the mechanism of CH₄ dissociation and the precursors of NCD were further explored.     

Characteristics of carbon-related materials deposited in electron-energy controlled CH4/H2 RF discharge plasmas

The influence of electron temperature T_e on the production of carbon-related materials was investigated in a hollow-type magnetron radio-frequency (RF) CH₄/H₂ plasma. Here, the electron temperature decreased along the plasma column. Since the dissociation of CH₄ is determined by the electron energy in plasmas, the density ratio of radicals CH₂/CH₃ can be varied by the electron temperature. Therefore, the change of the electron temperature is quite important for controlling the characteristics of carbon-related materials. In the experiment, the production of diamond microparticles in low T_e plasma was detected. On the other hand, thin carbon films consisting of graphitic carbons were observed in the high T_e plasma. Therefore, it is shown that control of the electron temperature in the plasma has a key effect on the film quality.     

用于吸附分离CH4/CO2的碳分子筛的制备研究

以碳分子筛(CMS)作为吸附剂,探索其对CH4/CO2混合气的分离纯化性能。采用化学气相炭沉积法,以价格便宜的商品椰壳基活性炭为原料,以苯为沉积剂,制备碳分子筛。研究了沉积时间和沉积温度对CMS的吸附性质的影响。采用容量法对CMS吸附CH4和CO2性能进行测定。结果表明,在沉积温度为700℃,沉积时间为40min时制备的CMS平衡吸附选择性系数为58.03,远高于活性炭的5.124,对CH4/CO2有良好的分离效果。     

Microstructure and electron field emission study of diamond nanorod decorated a-SiO2 nanowires by microwave Ar–CH4/H2 plasma chemical vapor deposition with addition of N2

In our recent paper [M. K. Singh et al., Chem. Mater. 20 (2008) 1725], we reported the fabrication of Nanocrystalline diamond (NCD) fibers by template (a-SiO₂ nanowires) technique. Our present work demonstrate that the addition of nitrogen of 20% by volume in the reaction gas during synthesis induce the formation of feather-like morphology of NCD on a-SiO₂ nanowires. The feather-like morphology consists oriented diamond nanorods surrounded by an sp²-bonded carbon sheath. These have been characterized by Scanning Electron Microscopy, Transmission Electron Microscopy (high-resolution mode) and Micro-Raman spectroscopy. Electron field emission (EFE) of as-synthesized NCD fibers (with 20% N₂ addition) was observed with a threshold field of 3.5 V/µm which is quite less in comparison to previous grown NCD fibers and the current density at 10 V/µm increases around 20 times with 20% nitrogen doping in the gas source during synthesis. This may be because each diamond nanorod is enveloped in a sheath of sp²-bonded nanocarbons which provides a conducting path for electron emission.     

CH4-CO2重整反应过程中积炭的研究方法综述

介绍了热分析（TG—DTA）、气相色谱（GC）、扫描电镜（SEM）、透视电镜（TEM）、X光电子能谱（XPS）、X射线衍射（XRD）和喇曼光谱（RS）等方法在研究积炭方面的应用,并且指出了各种方法在研究积炭过程中的作用。     

Nano-scale diamond tips: Synthesis in the CH4/N2/H2 plasma

We report the discovery of vertically aligned nano-scale diamond tips grown on the polycrystalline diamond substrates in a CH₄/N₂/H₂ mixed plasma. The best diamond quality occurs at the top part of the nanotip, which is single crystalline diamond. The quality of the diamond nanotip is justified by the diamond characteristic peak at 1332 cm^− 1 in the Raman spectrum, the discrete electron diffraction pattern of diamond along [011] zone axis, and the electron energy loss spectra. Single crystalline diamond with poor quality appears at the center and the bottom part of the nanotip. No nitrogen K edge signal appears in the electron energy loss spectra, suggesting that nitrogen is very difficult to incorporate into the diamond nanotip. The roles of nitrogen in the formation of diamond nanotips are discussed.     

Density control of carbon nanowalls grown by CH4/H2 plasma and their electrical properties

We report on successful control of the density of carbon nanowalls (CNWs) synthesized using radical-injection plasma-enhanced chemical vapor deposition (RI-PECVD) employing CH₄/H₂ plasma, by varying the total pressure and discharge power during growth. As the total pressure was decreased or the power was increased, the density of CNWs decreased in conjunction with an increase in the H atom density measured using actinometric optical emission spectroscopy. The electrical conductivity of the films was found to be determined by the number of CNWs per unit length, i.e., the linear density. We demonstrated that the electrical properties could be controlled while maintaining the crystal quality and chemical bonding state of the synthesized CNWs in the RI-PECVD.     

量热法多孔沉积物内CH4水合物生成过程中的放热行为

掌握天然气水合物在多孔沉积物生成过程中的放热规律对于天然气水合物的资源开发和了解水合物的成藏规律都具有重要意义。本研究通过高压微量热仪考察了石英砂粒径、初始含水率、温度及含盐条件对CH₄水合物在多孔沉积物内生成过程中放热行为的影响。实验结果表明,随着石英砂粒径的减小,水合物生成的放热速率随之增加。随着初始含水率的降低,水合物的放热峰明显增大,但在实验考察时间内,最终的累积放热量和含水率并没有呈现出明显的相关性。当温度在263.15K时,CH₄水合物生成过程中不存在明显的放热。对于在3.35% NaCl盐溶液体系中进行的甲烷水合物生长放热实验,发现其放热规律与在纯水体系下的放热规律具有较高的一致性,但其总体放热速率和累积放热量较纯水体系更低。实验结果呈现了良好的规律性,对进一步开发量热仪在水合物生成动力学方面的应用具有一定的参考价值。     

Effects of diluents on NO x formation in coflow CH4/air diffusion flames

The effect of diluent addition on NO _x formation in a laminar CH₄/air coflow diffusion flame was investigated by numerical simulation with experimental verification. The hydrocarbon fuel stream was diluted with N₂, CO₂, and Ar. The volume fraction of diluents systematically changed from 0.0 to 0.5. The simulation data agree well with the experimental one. The computational results indicate that overall the three diluents reduce the formation of NO and the effects vary from weak to strong in the order: N₂, Ar and CO₂. Differences between the influences of the various diluents are discussed in terms of the thermal, the dilution and the direct chemical effects, respectively. Further, the addition of CO₂ reduces the formation of NO₂, while the addition of N₂ or Ar has little effect on it. However, the formation rate of N₂O increases by each of the added diluents.     

Defect structure for the ultra-nanocrystalline diamond films synthesized in H2-containing Ar/CH4 plasma

The modification on the microstructure of diamond films due to the addition of H₂ species into the Ar/CH₄ plasma was investigated. While the Ar/CH₄ plasma produced UNCD films with equiaxed grains (about 5 nm in size), the (Ar-H₂)/CH₄ plasma produced acicular-shaped grains (about 5 × 20 nm in size). Transmission electron microscopy studies indicate that these acicular-shaped grains actually are agglomerates of diamond flakes, which contain stacking faults lying on the (111) lattice plane. Presumably, the incorporation of H₂ species in the plasma leads to partial etching of hydrocarbons adhered onto the diamond clusters, such that the C₂- (or active carbon) species contained in the plasma can attach to the diamond surface anisotropically, leading to diamond flakes. The incorporation of H₂ in Ar plasma can also suppress the formation of i-carbons, an allotropic phase of diamonds. The critical proportion of H₂ in Ar plasma for inducing the changes in the granular structure is around 0.03%. The proportion of grain boundaries was thus reduced and the electron field emission properties of the materials were thus degraded. However, the suppression of the film electrical conductivity without sacrificing the smooth surface characteristic has the applications as high-thermal-conductivity heat spreaders and substrates for surface-acoustic-wave devices.     

Pit formation on stainless steel surfaces pre-treated with biosurfactants produced by Pseudomonas fluorescens

Today, it is widely established that the surface tension of water can be reduced by some microorganisms capable of synthesizing surface-active compounds called biosurfactants (BS). BS characteristics depend on the microorganism that produces them and therefore, on the microorganism culture conditions.Some studies on chemical surfactants have shown that the adsorption of surface-active compounds plays a major role in corrosion; indeed they are used as a good corrosion inhibition tool.The purpose of this study was first, to estimate the importance and behavior of the stainless steels passive film on the adsorption of BS, produced by the Gram negative bacteria Pseudomonas fluorescens, and secondly, to study the impact of these treatments on the pitting corrosion.In this paper, the galvanostatic polarization technique, used as accelerated method for determining the characteristic pit potentials on stainless steels, is examined. Pit growth, shape and cover formation were also observed. The surface topography of the corroded specimens was investigated using field emission scanning electron microscopy (FESEM).     

变压吸附浓缩甲烷/氮气中甲烷的研究进展

介绍了变压吸附(PSA)技术浓缩煤层气、油田气以及垃圾填埋气中甲烷(CH4)的国内外研究和应用状况,分析了吸附剂以及PSA工艺对CH4/N2分离效果的影响,着重讨论了活性炭与碳分子筛(CMS)吸附剂在分离CH4/N2混合物中的应用,指出了目前PSA用于浓缩CH4/N2中CH4研究中存在的不足,并展望了其发展趋势.     

Inductively coupled plasma etching of Ta,Co, Fe,NiFe, NiFeCo,and MnNi with Cl<Subscript>2</Subscript>/Ar discharges

Dry etching of the magnetic thin films such as Ta, Fe, Co, NiFe, NiFeCo, and MnNi was carried out in inductively coupled plasmas of Cl₂/Ar mixture. All the magnetic materials went through a maximum etch rate at 25% Cl₂. The effects of the ICP source power and the rf chuck power on the etch rate and the surface roughness were quite dependent of the materials. An ion-enhanced chemical etch mechanism was important for the magnetic films. The surface roughness of the etched samples was relatively constant of the rf chuck power up to 200 W, but a rougher surface at a higher rf power was obtained. Post-etch cleaning of the etched samples in de-ionized water reduced the chlorine residues substantially.     

微小型凹腔燃烧器内甲烷/空气预混火焰特性

对有凹腔的微细通道内甲烷/空气的预混燃烧进行了实验研究,并与无凹腔的情况进行了比较。结果表明,无凹腔时,只出现了稳定或振荡的倾斜火焰;有凹腔时,在很宽的速度范围内火焰均能被有效地稳定,当进气速度接近吹出极限时,火焰锋面发生弯曲和脉动。当量比为0.8、0.9和1.0时有凹腔的微细通道的吹出极限分别为0.8、1.35和1.75 m·s^-1,是对应进气条件下燃烧速度的几倍,这表明凹腔具有很强的稳燃能力。数值模拟结果表明,凹腔的斜壁与下游的水平壁面之间的转折点存在很大的速度梯度和剪应力,导致了火焰在高速下被拉断而吹出。总之,有凹腔的微细通道内火焰的稳定性主要由反应区和流场之间的相互作用决定。     

CH4/CO2混合气置换强化含氮低品质甲烷的浓缩

针对CO₂置换吸附分离CH₄/N₂过程中CO₂再生困难的问题,采用少量产品气CH₄真空吹扫以提高CO₂的解吸效果,并以解吸得到的CH₄/CO₂混合气为置换步骤的置换气,通过置换来强化含氮低品质甲烷的浓缩过程。以自制椰壳活性炭为吸附剂,对CH₄/CO₂混合气置换强化吸附回收含氮低品质甲烷工艺过程进行了实验与模拟研究。在gPROMS软件中建立并求解固定床吸附分离模型方程,预测了CH₄、N₂ 和CO₂在自制椰壳活性炭上的竞争吸附穿透曲线,通过预测结果和实验的对比,验证了数学模型方程的准确性。对比了不同置换气强化吸附分离低品质甲烷的效果,结果表明CH₄/CO₂混合气置换强化相对于CO₂置换强化可获得更高纯度产品。进行了CH₄/CO₂混合气置换强化真空变压吸附循环实验,可以将14%的CH₄/N₂和53%的CH₄/CO₂联合富集到98.8%,同时获得77.8%的回收率。     

Intensification of low-grade methane enrichment in nitrogen mixture by CH4/CO2 displacement

To solve the problem of CO₂ uncompleted desorption in the process of CO₂ displacement enhancing the adsorption separation of CH₄/N₂, a small amount of product gas CH₄ was used as purge gas to improve the CO₂ desorption. CH₄/CO₂ mixture gas obtained from desorption step was recycled as the displacement gas to enhance the enrichment of low-grade methane in nitrogen mixture. In this work, the research conducted the experiments for CH₄/N₂ separation using CH₄/CO₂ displacement intensification adsorption and the laboratory-made coconut shell activated carbon as sorbent. The mathematical models were built in gPROMS and the accuracy of models was verified by comparison of simulations and CH₄/N₂/CO₂ breakthrough experiments. The performance of enrichment of low-grade methane with displacement intensification using different displacer was compared. The result showed that the process with CH₄/CO₂ displacement had higher purity product than CO₂ displacement. The CH₄/ CO₂ mixed gas replacement enhanced vacuum pressure swing adsorption cycle experiment was carried out, which can jointly enrich 14% CH₄/ N₂ and 53% CH₄/CO₂ to 98.8%, and at the same time obtain a recovery rate of 77.8%.     

Marked Role of Carbon Monoxide in the Formation of Benzene During CH4-CO Reaction Over Rh/SiO2 Catalysts

Temperature-programmed desorption (He-TPD) and temperature-programmed reaction with hydrogen (H₂-TPR), carbon monoxide (CO-TPR) or methane (CH₄-TPR) were carried out to elucidate the benzene formation mechanism as well as the role of CO during CH₄-CO reaction over SiO₂-supported Rh catalysts. The steady-state surface for the CH₄-CO reaction was different from that of the CH₄ decomposition reaction. The existence of benzene-like adsorbed species as building blocks was demonstrated on the CH₄-CO reaction surface, while no such higher hydrocarbon adsorbed species was detected in the case of the CH₄ decomposition surface. On the contrary, in CO-TPR experiments various unsaturated hydrocarbons were released from the steady-state CH₄ decomposition surface, which was not the case from the CH₄-CO reaction surface. It is concluded that adsorbed CO may play an important role to enhance the C-C bond formation of carbonaceous species, which correlates deeply with the novel phenomenon of selective benzene formation in the CH₄-CO reaction.