Daniel Ersoy

Carbon coatings produced by high temperature chlorination of silicon carbide ceramics

Abstract Carbon coatings are widely used to modify surfaces of materials and improve their tribological properties. In this work, carbon layers were formed on various types of sintered and CVD silicon carbide (SiC) using a novel technique involving a reaction with chlorine and chlorine-hydrogen gas mixtures at 1000 °C. Following the work done on powders and fibers, this method successfully produced adherent coatings on SiC ceramics, which could be grown to thickness above 200 µm. Highly disordered carbon with contributions from nanocrystalline graphite was identified by Raman spectroscopy, x-ray diffraction, and energy dispersive spectroscopy. The kinetics of the chlorination reaction at 1000 °C for different gas mixtures fit to a linear reaction rate equation. Coatings produced in pure Cl2 are graphitic and demonstrate a low hardness (1.8 GPa), Young’s modulus (18 GPa), low wear rate, and a friction coefficient of ∼0.1, which is almost constant for any testing conditions in dry or humid air. Coatings produced in Cl2/H2 mixtures have microhardness up to 50 GPa and Young’s modulus up to 800 GPa. Although the presence of hydrogen had little effect on the Raman spectrum of the carbon layers, its presence changed the structure and permeability of the carbon film.

Tribological Properties of Carbon Coatings Produced by High Temperature Chlorination of Silicon Carbide

The tribological properties of highly disordered graphitic carbon layers formed on silicon carbide (SiC) substrates by reaction with chlorine and chlorine-hydrogen gas mixtures at 1000 °C were studied. Si was selectively removed from the near surface of SiC by chlorine gas, leaving behind a layer of carbon having high structural density and strong bonding characteristics. Tribological tests showed that the carbon films were highly adherent and able to reduce friction coefficients of the base SiC by factors of up to seven. There was little or no change in the factional behavior of carbon layers when sliding velocity and load were increased. Low friction coefficients (∼0.1) could be obtained under wet, dry, polished, and rough conditions. The initially rough carbon surface underwent plastic flow producing a smooth, self-adjusting carbon layer. Structural morphology and the amount of disorder in the carbon layers were correlated with the friction and wear performance of the resultant films. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Seattle, Washington, October 1–4, 2000

Platinum Reactions with Carbon Coatings Produced by High Temperature Chlorination of Silicon Carbide

Highly disordered graphitic carbon layers were formed on various types of commercially available silicon carbide (SiC) ceramics by reaction with chlorine and chlorine-hydrogen gas mixtures at 1000°C. The carbon was produced ranging from only a few micrometers to hundreds of micrometers thick. When a platinum sample holder was employed (instead of fused silica), platinum was found dispersed in the carbon layer concentrated near the SiC/C interface. This process can be used for incorporating platinum in porous carbon films for catalytic and other applications. In addition, the platinum resulted in a smoother physical interface between the SiC and carbon sublayer. The morphology of the platinum dispersion, its effect on the carbon layer, and its proposed formation mechanism are presented in this paper.

Nano-structured carbide-derived carbon films and their tribology

Carbide-derived carbon (CDC) is a form of carbon produced by reacting metal carbides, such as SiC or TiC, with halogens at temperatures high enough to produce fast kinetics, but too low to permit the rearrangement of the carbon atoms into an equilibrium graphitic structure. The structure of CDC is derivative of the original carbide structure and contains nanoscale porosity and both sp2 and sp3 bonded carbon in a variety of nanoscale structures. CDC can be produced as a thin film on hard carbides to improve their tribological performance. CDC coatings are distinguished by their low friction coefficients and high wear resistance in many important industrial environments and by their resistance to spallation and delamination. The tribology of CDC coatings on SiC surfaces is described in detail.

Nanostructured Carbon Coatings on Silicon Carbide: Experimental and Theoretical Study

Nanotechnology has been recognized as an emerging technology of the new century. Control over the structure of materials on nanoscale can open opportunities for the development of nanostructured materials with controlled properties, if the structure/property relations are known. This paper describes a technique that can produce a broad range of potentially important carbon nanostructures that may be used in future technologies. Nanostructured carbon coatings can be obtained either by deposition from the gas phase onto a substrate, or by surface treatment of a carbon-containing substrate. The method presented in this paper is accomplished through the extraction of metals from carbides (SiC and TiC) using chlorine or chlorine-hydrogen mixtures. This is a versatile technology because a variety of carbon structures can be obtained on the surface of carbides in the same reactor. Not only simple shapes, but also fibers, powders and components with complex shapes and surface morphologies can be coated. This technology allows the control of coating growth on the atomic level, monolayer by monolayer, with high accuracy and controlled structures.