Deposition Of Carbon Layers Research Articles

Chemistry and kinetics of chemical vapor infiltration of pyrocarbon

Abstract Capillaries, 1 mm in diameter and 17 mm in depth, were infiltrated at a temperature of 1100°C and pressures of 20 kPa (pure methane) and 30 kPa (methane–hydrogen mixture (7:1)). The residence time of the gas in the deposition reactor was 0.5 s, at the lower pressure of 20 kPa, residence times of 1 and 2 s were studied additonally. The thickness of the deposited carbon layers was determined using a X-ray microscope, i.e., without cutting the samples. In the experiments with 0.5 and 1 s residence times an increase of the deposition rate from the mouth to the depth of the pores was obtained. The gradient of the deposition rate decreases with increasing residence time of the gas and becomes negative at 2 s. Hydrogen, either formed by decomposition of methane or added to the feed gas, leads to an increase in the gradient. The homogeneous–heterogeneous model of carbon deposition from methane is used to interpret the results with special consideration of deposition chemistry and diffusivity of the relevant hydrocarbon species.

Study of the influence of surface carbon on the tribological properties of ion-treated steels

Samples of 100Cr6 steel were treated by different ion beams in order to study the evolution of their tribological properties. A strong correlation was found between the amount of surface carbon, whatever its origin (contamination, direct C implantation or ion-beam mixing of a deposited carbon layer), and the reduction of the friction coefficient as well as the improvement of the wear resistance. These results are discussed in the framework of a recent statistical model founded on the asperity concept and describing the tribological behaviour of bilayer systems.

Thin carbon films as electrodes for bioelectronic applications

Thin film diamond-like carbon (DLC) electrodes were fabricated by radio frequency (RF) magnetron sputtering on silicon, silicon oxide, and platinum substrates. The dependence of physical and electrochemical properties on process parameters like temperature, pressure, and incident power was investigated. We deposited carbon layers with hydrogen concentrations below 1%. Therefore, the resistivity was minimized to a value of 30 mΩcm. The low surface roughness of all DLC films leaded to a small double-layer capacity of 37 μF/cm 2. A large electrochemical bandwidth and a nearly ideal reversibility was shown and compared to the properties of conventional glassy carbon electrodes. The applicability of the DLC electrodes to electrochemical investigations and bioelectronic applications was demonstrated.

On the Possibility of Surface Modification of an Alumina Support with Amphiphilic Carbonaceous Material

A carbon-coated support has been prepared by the impregnation of commercial alumina with an ammoniacal solution of amphiphilic carbonaceous material. It was established that the method used for the deposition of the carbon coating on the support allowed control of both the layer thickness and the degree of filling of the surface in the low carbon content region. Equations proposed for the approximate determination of the thickness of the deposited carbon layer and of the surface occupied by this layer enabled a tentative prediction to be made of the most desirable parameters for such a system.

Stacking nature of graphene layers in carbon nanotubes and nanofibres

The structure of multilayer carbon nanotubes is studied using digital image analysis to interpret high resolution TEM lattice images containing 002 and 100 fringes, in comparision with very thin vapour-grown carbon fibres with nanometer-sized diameter (nanofibres). The results show that the stacking of graphene shells in a multilayer nanotube glide with respect to one another, which is in contrast to the stacking fidelity of three-dimensional graphite. The diffraction patterns derived from the fast Fourier transform of the lattice images yield angles of 0 °–17 ° for the 100 lattice planes relative to the ideal 100 direction. The median inter-shell spacing d 002 between carbon nanotubes is also characterized, by using the 100 spacing as an internal standard, and d 002 range from 3.4 to 3.6Å. The inter-shell spacing d 002 decreases with increasing carbon nanotube diameter, which could be due to a size effect. The so-called vapour-grown carbon fibres (VGCFs), obtained by pyrolytic decomposition of hydrocarbon, are grown through spontaneous deposition of carbon layers on primarily formed nanotubes. In order to clarify the size effect for layer stacking, very thin VGCFs with diameter ~500Å, named nanofibers as well as submicron diameter VGCFs, are compared with carbon nanotubes, and are discussed in relation with the curvature of graphene layers. Some gently pulverized VGCFs with nm as well as μm size diameters possess an exposed carbon nanotube at the core of the broken portion, suggesting a difference in the stacking structure of the graphene layers between the central core nanotube and the outer pyrolytic sections.

Retention of nitrogen atoms implanted into carbon

The retention of nitrogen atoms implanted into carbon was measured by means of Rutherford backscattering spectrometry (RBS). The samples from commercial graphite as well as carbon layers deposited by rf-sputtering in Ar, Ar + N and N plasma were used. The results show that, after room temperature nitrogen ion implantation, the maximum N to C ratio in graphite layers was about 0.25. However, in the deposited carbon layers after nitrogen implantation this ratio reaches 0.54.

形彫り放電加工における工作物形状シミュレーション

This paper describes a simulation of workpiece geometry eroded by the die-sinking EDM. The geometry of workpiece is determined by the worn geometry of the tool electrode and the gap width distribution. The paper found that the local gap width is a function of the curvature and the inclination of the surface of the tool electrode from the feed direction, and that the local wear ratio of the tool electrode is affected by the local gap width. Moreover, the geometrical factors such as the curvature and the inclination are closely related to the local wear of the tool electrode. Starting with given contours of thin plate electrodes, the change of the workpiece geometry was simulated considering the tool wear and the gap width distribution. The erosion experiment was carried out by placing the tool and workpiece electrodes in a level position and feeding the tool electrode in a horizontal direction. Under these conditions, the debris concentration and the deposited carbon layer thickness, which influence the gap width and the anode wear, respectively, are thought to be uniform over the working surface. The simulation result coincided well with the measured geometry of the workpiece.

Depth profiles of C, N and O on carbon coated steel surfaces made by IBAD

The nitrogen ion implantation into steel surfaces by using an oil diffusion vacuum pumping system is superimposed with an ion beam assisted deposition process of a very thin carbon layer. The application of Bragg-curve spectroscopy to elastic recoil detection analysis (ERDA) of ion beam assisted deposited carbon layers on steel surfaces is described. The ERDA is used for simultaneous depth profiling of the light elements carbon, nitrogen and oxygen. Typical results are good selectivity of the atomic charge number Z up to 20 with a depth resolution on the order of 5 to 10 nm and submonolayer sensitivity. The low background in the operative region allows the analysis of profiles down to concentrations of about 0.01% of the stoichiometric ones. The ERDA depth profiling results are shown in correlation to measurements with Auger electron spectroscopy (AES).

Carbon monoxide methanation over FeTi 1+ x intermetallics

FeTi 1+ x intermetallics (0 ≤ x ≤ 0.15), well-known hydrogen absorption materials, have been found to be active catalysts for CO methanation. The initial activity for H 2 absorption, CO disproportionation, and CO hydrogenation increased significantly with increasing Ti content. However, the catalysts rapidly lost their activity because of carbon layer deposition at the surface. Mössbauer and X-ray diffraction studies indicate that no surface or bulk carbides are formed during CO H 2 reaction. Auger electron spectroscopy data have revealed that for all the titanium compositions, the surface is rich in iron, and conversion electron Mössbauer results showed that the surface becomes enriched with iron metal clusters during catalytic reaction. Thus, the catalytic activity is attributed to α-iron centers at the surface which are responsible for the formation of different carbonaceous precursor species. Excess Ti concentration results in the formation of secondary iron titanium suboxide phases which help in the generation of additional active sites during the activation process. The activity of surface carbon species and the reaction routes involved in CO methanation are discussed in detail.

Steam gasification of residues catalyzed by alumina-supported potassium carbonate and calcium oxide.

Steam reforming of atmospheric, vacuum and solvent-deasphalting residues was investigated using a fluidized bed reactor, where alumina-supported potassium and calcium oxide catalysts were packed. Atmospheric residues were gasified with high efficiency on CaO above 850°C. The catalytic activity, however, decreased markedly with increasing Conradson carbon residue (CCR) of the feed residues. On the other hand, high activity of potassium catalyst was attained even in the gasification of very heavy residues from solvent deasphalting. The decrease in catalytic activity of CaO was not due to sulfur-poisoning of active sites, but was attributed to increasing carbon deposition or to decreasing reactivity of the deposited carbon. Carbon deposited on CaO, especially from residues having large CCR, was less reactive than carbon on the potassium catalyst. The mobility of catalytically active species in deposited carbon layers is a possible explanation for the superior catalytic activity of potassium to CaO.