Properties of quartz-phenolic composites for thermal protection systems

Resumo

Thick composite materials are used as liners in rocket nozzles, due to its structural strength, low density and very high thermal insulation property. Carbon fiber and silica fiber based composite structures are used in the nozzles of large solid rocket motors. Since these are multiple layer structures, the commonly observed defects are delaminations, lack of adhesive material, porosity between layers, etc. In this work quartz-phenolic resin based ablative composites have been characterized, with the intention to evaluate composite materials for thermal protection systems. The study used as parameters the resin concentration in the composite and the characteristics of the quartz fabric. These materials had been processed with different phenolic resin concentrations (20, 32 and 42%) using woven and chopped fabric configurations. The option for studying different configurations of fabric and concentrations of resin lies in the possibility to solve problems of delamination and molding in thermal protection systems of large dimensions and complex formats. Therefore we focussed our interest in the evaluation of the effects of the characteristics of woven mesh quartz fibers (weaved with aligned fibers in a single plan) and chopped mesh quartz fibers (with random domains of orientation of fibers) over their ablative, thermal and microstructural properties. The processed materials had been submitted to a non transferred arc plasma torch operating in air with a flow of 5.4. 10-3 kg/s and 30 kW power transferred to the jet, that corresponds to an enthalpy of ∼5.5 of MJ/kg. The samples had been exposed to thermal flows between 0.5 and 1.7 MW/m2 during 30 seconds, and we evaluated the loss of specific mass of the samples. To study its microscopic aspects, the samples were analyzed, after the ablation process, with a scanning electron microscope (SEM). The thermal insulation properties of the samples were evaluated by measuring the temperature at some internal positions in the samples using thermocouples inserted at distances of 2, 4 and 8mm of the sample surface, where the temperature was measured using an optical pyrometer. The diffusivity of the samples was measured in a graphite furnace "Flashline 5000" from room temperature to 1500° C.