Michel Trinquecoste

Film boiling chemical vapor infiltration. An experimental study on carbon/carbon composite materials

Several chemical vapor infiltration (CVI) processes have been developed to increase both the carbon yield and the densification rate for a controlled type of pyrocarbon deposit. Recently, the ‘film boiling technique’ (so-called Kalamazoo) has been successfully developed for making in particular C/C composite materials. To get a better insight on this process, we have built up two small laboratory reactors with an internal resistive heating. In-situ and ex-situ experiments have been carried out with various liquid carbon precursors. The kinetics analysis has shown that the nature of the precursor plays a role but that the fundamental point is the chemical–hydrodynamical coupling. This process is based on a moving reactive hot frontier with a steep densification profile. From our analysis, it results that the precursor feed comes mainly from the molecular diffusion through the porous preform. The balance between chemical and hydrodynamical constraints leads to different types of pyrocarbon microstructures.

High temperature thermal and mechanical properties of high tensile carbon single filaments

The final quality of carbon/carbon composite materials depends strongly on the tight fit of the components. This could be predicted with a better knowledge of the intrinsic thermal and mechanical behavior of the carbon fibers. With this object, we have built-up an experimental set-up for in situ studying of dimensional variations and the bending strain at failure of single filaments from high tensile carbon fibers at temperature up to 2500 °C. We have shown off and separated the purely physical and the chemical parts of the dimensional evolution of these PAN-based filaments, in comparison to the fundamental behavior of pure graphite.

Physical properties of plasma-enhanced chemically vapour deposited hydrogenated and nitrogenated amorphous carbons

Abstract There is a fundamental interest in using a reactive plasma to produce a large variety of pure and alloyed carbons exhibiting very different properties. Hydrogenated amorphous carbons (a-C:H) and diamond-like crystals have been prepared by plasma enhanced chemical vapour deposition. Applying the r.f. plasma processing technique, we have prepared a series of a-C:H materials by varying different controlled parameters, among which we have also used nitrogen for doping these materials. In these “nitrogenated” carbons we add extra π electrons which develop the sp 2 and sp 1 bondings with respect to the sp 3 bonding usually stabilized by the hydrogen content; simultaneously the basic structure and the thermostability of these deposited films might be modified. WE have therefore prepared and investigated a series of a-C films in order to control the influence of nitrogen doping on their physical properties.

Submicronic powders containing carbon, boron and nitrogen : their preparation by chemical vapour deposition and their characterization

Abstract Submicronic powders containing carbon, boron and nitrogen have been prepared by thermal chemical vapour deposition. The precursors of carbon, boron and nitrogen are acetylene, boron trichloride and ammonia, respectively. Hydrogen is the carrier gas. The conditions of preparation of these powders are rather different from those of thin films containing the same elements. Using X-ray photoelectron spectroscopy and transmission electron microscopy, both chemical analysis and microtexture are studied. It is shown that ex-acetylene carbon blacks with a concentric ‘onion-like’ texture, quasi stoichiometric boron nitrides with a platelet texture, boron–carbon solid solutions with a low boron content (3–19 at.%) and boron carbonitride powders with either carbon or boron and nitrogen excesses have been prepared.

Thermal conductivity of submicrometre particles: carbon blacks and solid solutions containing C, B and N

Small particles of carbon blacks, of boron nitrides, of binary (Cx By ) and of ternary (Cx By Nz ) solid solutions have been prepared and then investigated as good thermal insulators at high temperature. Using a flash method with a short uniform and intense thermal pulse, the thermal diffusivity of the samples has been determined at room temperature. Following an analytical technique, the different contributions of the thermal conductivity (conduction in solid and gas phases, convective and radiative transfers) have been investigated. After analysing the different parameters as functions of the gas pressure and the particle size, we are able to express the intrinsic thermal conductivity of these submicrometre powders.