Preparación de materiales compuestos carbono/carbono a partir de breas de alquitrán de hulla. Modificación química de las breas mediante tratamientos previos

Resumen

[EN] This study describes the design and optimization of equipments (a prepregger and a hot-press machine) necessary for the preparation of unidirectional Carbon/Carbon composites by liquid impregnation of the fibres with solutions/suspensions of pitches in TI-IF. The results of a preliminary study of the parameters relevant for the processing of these materials are described. To improve the properties of coal-tar pitches as precursors of carbonaceous matrices, two commercial pitches, a binder and an impregnating pitch, were previously subjected to air-blowing at temperatures of250-300° C. The effects of this treatment on the chemical composition and properties of pitches, and mechanisms involved in their processing, were followed by spectroscopic and chromatographic techniques, X-ray diffraction, XPS, elemental analysis, solubility tests, thermogravimetric analysis and hot-stage microscopy. Results show that the oxygen from the air promoted pitch polymerization, with a subsequent increase in pitch carbon yields. Prior to the preparation of the C/C composites the effect of pitch air-blowing on the structure and properties of resultant cokes was also studied. In the same way, the impregnating pitch was treated with a selected carbon black at temperatures of 400-450° C. The effects of this treatment were also controlled from characterizations of subsequent products by using techniques similar to those for air blowing treatment, and also from the study of the structure and properties of cokes obtained by carbonization of pitches. Results show that carbon black not only retained pitch volatile components, but also promoted the polymerization of pitch molecules and improved the solubility of pitch in hexane, these two effects being temperature dependent. The pitch was also subjected to thermal treatment, without carbon black, under the same conditions, in an inert atmosphere, to control the effect of the thermal treatment itself. Unidirectional laminar C/C composites were prepared with the original and treated pitches, and PAN-based carbon fibres. The experimental conditions used for the preparation of composites were the same, the matrix precursor being the only variable considered. Composites were characterized in terms of their microstructure (optical texture and porosity) and properties (density, flexural strength and interlaminar shear strength). The behaviour of the different materials is explained from their main structural features and the chemical composition of pitch-based precursors. Some of the applied pitch treatments produced C/C composites of improved properties, even without further densifications.