Investigations of continuous carbon fibre surface after modification process
Zbigniew Zarański, Ignacy Łosik, Zbigniew Bojar Wojskowa Akademia Techniczna, Instytut Materiałoznawstwa i Mechaniki Technicznej, ul. Kaliskiego 2, 00-908 Warszawa
Annals 2 No. 5, 2002 pages 318-322
DOI:
keywords:
abstract Elemental continuous carbon fibres or HMS 5236 roving of high modulus fibres in „merchant” condition (the surface of fibres covered with polymeric impregnation), in condition after removing of impregnation by initial thermal heating at the temperature of 1550oC, in argonium atmosphere (called as „raw” condition) and in condition after modification process (according to author’s proposal), were investigated in this work. Modified carbon fibres means that single roving of carbon fibres was impregnated with silicon resin solution and then thermally heated in graphite reactor. A subtle SiC layer, playing a role of diffusion barrier during producing a composite by spontaneous dampening of roving, was obtained as a result of modification process. Main goals of conducted tests were: – to identificate, by X-ray analysis (Fig. 1), a phase structure of modified carbon-fibres surface (using XRD 3003 Siefert difractometer); – to estimate morphology and geometric parameters (Fig. 2) of modified carbon fibres surface (using XL-30LaB6 SEM); – to measure braking force (Fig. 3a) and elongation for elemental fibres (using microforce tester); – to measure strength properties (Fig. 3b, c) of roving samples (using Instron 8501 universal pulsator); – to compare an oxidation resistance (Fig. 4) of fibres in „raw” and modified condition (by measuring of loss mass value after each stage of heating at temperature of 850oC, in air atmosphere). It has been shown that basic phase component of modified carbon fibres surface layer was silicon carbide SiC (a week but noticeable (004) and (110) peaks were visible in tested range of 2θ angle - Fig. 1). Packages of elemental carbon fibres in „merchant”, „raw” and modified conditions were subjected to morphological testing (Fig. 2) of their surfaces and important morphological differences were stated. The morphology differences observed were adequate to the state of carbon fibres surface layer. So fragments of polymeric coatings visible on „merchant” carbon fibres surface were not fully continuous and diverse in thickness (Fig. 2a). Heating of these „merchant” carbon fibres in oxidation atmosphere gives possibility on effective removing the preparation thus „raw”, roughly carbon surface becomes exposed (Fig. 2b). The surface layer of carbon fibres in modified condition is much more homogenous (morphologically) and has different chemical composition (visible in BSE detector picture - Fig. 2c). The results of strength properties testing of elemental carbon fibres (Fig. 3) or samples of single roving (Tab. 1) subjected to various processes of treatment are different from those given by supplier of carbon fibres in „merchant” condition. The tensile strength of modified carbon fibres (as elemental and in roving) is, in comparison to the „raw” carbon fibres, lower and their modulus of elasticity (in the same comparison) is higher. Conducted tests of „raw” and modified carbon fibre oxidation resistance proved that SiC coatings obtained during modification process effectively guard against chemical reactions in aluminium - carbon system. It is good prognosis for trials of infiltrating modified carbon fibres roving with liquid aluminium or aluminium-based alloys.