Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Patent
1995-11-30
1998-02-03
Turner, Archene
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
427343, 427372, 427375, 4273761, 4273762, 4283066, 4283073, 428408, 428426, 428701, 428702, 501 44, 501 45, 501 46, C04B 4189
Patent
active
057142440
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns the protection of porous carbon-containing materials against oxidation and catalytic oxidation of the carbon.
The field of the invention is that of carbon-containing porous materials for use at temperatures above the temperature at which oxidation of carbon commences, i.e., about 350.degree. C., up to about 1000.degree. C.
These materials are solid materials such as porous graphites and carbons, and also composite carbon-containing materials. In particular, these latter materials are composite materials constituted by reinforcing fibers densified by a matrix, carbon being present in the fibers, in the matrix and/or in a matching or interphase layer between the fibers and the matrix. In particular, composite materials of this type are thermostructural composite materials in which the reinforcing fibers and the matrix are formed from carbon or a ceramic with the possible interposition of a pyrolytic carbon interphase between the fibers and the matrix. These materials are characterized by their good mechanical properties. When they contain carbon, retaining these properties at high temperature in an oxidizing environment requires the presence of effective protection against oxidation. This is also the case when the carbon is present only in a pyrolytic carbon interphase between ceramic reinforcing fibers and a ceramic matrix, where the interphase is essential to the mechanical properties of the material, as described in European patent EP-0 172 082. Further, regardless of the manufacturing process used for thermostructural composite materials--densification from a liquid consisting of impregnating the reinforcing fibers with a precursor and then transforming the precursor by heat treatment, or densification by chemical vapor infiltration--the materials obtained have a residual open pore space, giving oxygen from the surroundings access to the core of the material.
Thus a first aim of the invention is to provide effective protection against oxidation to solid or composite carbon-containing materials with an internal pore space which is accessible from the outside.
A further aim of the invention is to provide effective protection against catalytic oxidation of carbon.
The reaction between carbon and oxygen is known to be accelerated by the presence of certain elements, such as alkalis and alkaline-earths, which are introduced by or provided by, for example, sodium chloride (sea water), potassium acetate, etc., which act as oxidation catalysts. These catalysts may be impurities from the surroundings (pollution, soiling, exposure to a marine environment, etc.) or impurities from a manufacturing process, for example residues from the manufacture of carbon fibers (precursors, sizing substances added prior to weaving).
A well-known process for protecting a carbon-containing material against oxidation consists of forming a coating which constitutes a barrier against oxygen from its surroundings. When the material is used at a relatively high temperature and/or is subjected to large stresses, it is important to prevent cracks or faults in the protective barrier due to differential thermal expansion or mechanical strain from allowing access for oxygen. Therefore, self-healing oxidation protection, or protection which is completed by an additional covering layer with such a property, is also used. The term "self-healing" here means the ability to fill in automatically any crack of fault which may appear during use of the material.
Coatings in the form of glasses are used to constitute self-healing protection for materials for use at relatively high temperatures. By becoming viscous at the working temperature of the material to be protected, glasses are able to fill in any cracks. The composition of the glass is selected so that it has the desired viscous character at the intended working temperature. The publication "Ceramic Coatings for Carbon Materials" by James E. Sheehan in "Proceedings of the Fourth Annual Conference on Materials Technology", May 5, 1987, reviews different types of gl
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Delaval Rodolphe
Laxague Michel
Palavit Gerard
Rey Jacques
Thebault Jacques
Societe Europeenne de Propulsion
Turner Archene
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