Abstract
Laminar pyrocarbons are used as interphases or matrices of carbon/carbon and ceramic-matrix composites in several high-temperature aerospace applications. Depending on their organization at the microscale, they can have a variety of mechanical and thermal properties. Hence, it is important to know, before thermal processing, the properties of these matrices at the micrometer scale in order to improve and control the composite behavior in a macroscopic scale. We use the scanning thermal microscopy on a silica fiber/regenerative laminar pyrocarbon matrix composite to provide an insight into the effective thermal conductivity of pyrocarbon as well as the thermal contact resistance at the interface between fiber and matrix. The conductivity of pyrocarbon is discussed as a function of its nanostructural organization.
Highlights
Carbon/carbon (C/C) composite materials are choice materials for use in extreme environments, such as space propulsion rocket nozzles, atmospheric re-entry thermal protection systems, aircraft brake discs, and Tokamak plasma-facing components[1]
The scanning thermal microscopy (SThM) method has been applied to a composite made of silica fibers embedded in a regenerative laminar pyrocarbon (RL PyC) matrix
A main advance in the field of scanning thermal microscopy is that we implemented an inverse technique in order to identify simultaneously (i) the radius of the contact area between the probe and the sample, (ii) the thermal conductivity of the sample and (iii) the effective thermal conductivity of the PyC
Summary
Carbon/carbon (C/C) composite materials are choice materials for use in extreme environments, such as space propulsion rocket nozzles, atmospheric re-entry thermal protection systems, aircraft brake discs, and Tokamak plasma-facing components[1]. It is important to know the properties of these matrices at the micrometer scale in order to improve and control the composite behavior in a macroscopic scale In this frame, a large variety of PyC samples have been prepared[8]. The general orientation of the anisotropic texture is concentric around the fibers, as exhibited, and results in orthotropic thermal properties of the matrix in the cylindrical coordinate frame following the fiber axis This is due to the fact that the graphitic sheets exhibit strong thermal anisotropy. In order (i) to overcome the drawbacks of the TR method, (ii) to provide thermal conductivity value for ReL PyC, and (iii) to measure as well the thermal boundary resistance at the interface between the PyC and the glass fiber, we have implemented the scanning thermal microscopy (SThM) experiment involving the 3ω mode[15]. 002 Lattice Fringe TEM imaging of the pyrocarbon; the inset is a Selected Area Electron Diffraction Diagram illustrating the high anisotropy through the low value of the 002 diffraction arc opening angle
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