The ablation properties, thermal resistance and micro structural behavior of the phenolic resin (Resole) composites have been investigated in this research. Different materials, such as carbon fabrics, glass fabrics, also silica and zirconia powders have been used as reinforcements for synthesis of the composites. The specimens were prepared with three sets of compositions. The first set was produced with 37.5 wt% of Resole and 62.5 wt% of reinforcements. Another set of specimens were produced with 40wt% Resole, 40 wt% of silica and 20 wt% of zirconia. Also to achieve high insulation index in Resole/carbon fabrics composites a thin film of zirconia coated at the back side of the specimens. To explore the ablation characteristics of the composites in terms of insulation index, erosion rate and microscopic pattern of ablation, an oxyacetylene torch flame with heat flux of 10 Mw/m2 at approximately 2800°C was used. The ablation behavior and microstructure of the burnt-through specimens were also observed, using scanning electron microscopy. It was found from ablation test that the erosion rates of the Resole/carbon fabric specimens are 20% lower than the other specimens. Additionally the high insulation index of the Resole/carbon fabrics coated with zirconia indicates that these composites are the best ablative materials in the present study. It has been also reported that those specimens filled with zirconia have the highest insulation index. Although the erosion rate of the Resole/silica composites were 20% higher than the Resole/glass fabrics, but a 5mm depth hole (from 10 mm thickness of the whole specimen) was seen at the center of the Resole/glass Fabric specimens. SEM observations show that proper adhesion between reinforcements and matrix is important to achieve improved ablative properties, it was also reported many changes in diameter, shape and the surface of the carbon fibers through the ablated area. These changes can be reduced from surface to back side of the specimens.
Study on phenolic resin foam modified by montmorillonite and carbon fibers