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Abstract

This thesis examines structure and strength of carbon fibres relative to other man-made filaments and associates variations in tensile strength with manufacturing and processing history. Methods of fibre identification using X-ray power diffraction techniques, etc. are given.

Metallic coating of fibre via vapour and liquid phases is shown to be unpromising and copper electrodeposition was chosen for close examination, the subject being introduced by description of theory and practice of fibre tensile testing, applied to bare and plated material.

Preliminary work revealed that high modulus, Type I fibres and acid electrolytes were unsuitable for production of high strength plated material and copper deposition from alkaline cyanide solutions is investigated, leading to results covering effects on tensile strength, of variations in temperature, current density, thickness of deposit and electrolyte with particular emphasis on the controlling influence of “free cyanide" cons centration. Limits of stable deposition are outlined and an unfamiliar blue compound, formed during unstable conditions, is identified and synthesized.

Next, effects of fibre surface cleaning on plated finish and final strength are explored. Contrary to expectation, pre-wetting results in poor quality, low strength deposits, due to lack of fibre separation during plating, with consequent poor penetration of fibre bundle. The effect of annealing on plated fibre is also examined and no significant change in strength noted below 700°Cs above this temperature, strength loss is observed, associated with sintering. At this stage a specification for copper electrodeposition onto carbon fibre is presented.

On the basis of this work, and other reports, copper-carbon fibre composites are prepared and evaluated. Their low strength is associated with hot-pressing, fibre mis-alignment and thermal stress and equated to an overall damage factor.

In conclusion major variables affecting strength of carbon fibres, with and without copper deposits, are assessed in relation to results described. Further techniques leading to production of better composites are also discussed, a promising development involving chopped carbon fibre being mentioned.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QD Chemistry
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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