Meso- and nano-scale investigation of carbon fibers coated by nano-crystalline diamond
Introduction
Carbon fibers represent an extremely important technological material [1] and extensive efforts have been dedicated over the past decade to the research and development of new types of meso- and micro-structured C fibers [2], [3].
Exploiting potential applications in various strategic fields, such as energy saving, thermal management and space technology, caused researchers to develop strategies apt to produce meso- and micro-sized fibers with enhanced properties in terms of hardness, chemical inertness, high thermal conductivity, high sputter-resistance [4], [5].
The coupling of carbon fibers with diamond, indeed, may offer significant advantages. However, one major concern in producing diamond-coated micro-sized carbon fibers is the strong control of the structural features of the outermost diamond phase in terms of size, texture and crystalline quality of grains, but also of the inner fiber at the end of the coating process. Diamond-coated carbon-fibers can be considered an innovative diamond-based composite material for which many possible technological applications can be envisaged [6], [7], [8], [9], [10].
In the present Letter, the coating of vapour grown carbon fibers by layers of nanocrystalline diamond is reported. In particular, we investigated and identified the stacking sequence of the different carbon-based material when diamond coating of a carbon fiber is carried out. VGCF fibers were chosen in view of their outstanding properties (in primis thermal and electrical conductivity) which make them a widely used functional material [11].
Section snippets
Experimental
The objective of our research was to monitor the stability of the fibers under the conditions of the CVD process, to investigate the crystallographic features of the deposited diamond phase and to detail the microstructure of the fiber/diamond systems.
The nanocrystalline diamond deposits have been produced by CVD technique on isolate fibers, as well as on textures formed by woven filaments. The deposition runs were performed in a hot filament CVD reactor using CH4/H2 mixtures. A detailed
Results and discussion
The results reported in this Section refer to sample produced using a 0.5% CH4 in H2 and at substrate temperature of 650 °C. These were, indeed, the suitable experimental conditions for the formation of nanosized diamond.
The SEM images of Fig. 1 shows the typical morphologies of as-received textured (a and b) and single (c and d) VGCFs, before (a and c) and after (b and d) diamond deposition. The fibers were originally assembled as a cross-texture and the structural analysis by electron
Conclusions
In the course of the present research proper procedures have been selected for the coating of carbon fibers by homogeneous diamond layers formed by nano-grains with sizes in the range 5–50 nm. The structure of the external coating and of the inner carbon phases has been detailed using high resolution electron microscopy and electron diffraction in both transmission and reflection conditions. The coating process was found to generate an intermediate layer of turbostratic graphite at the
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