Study on Ablation Behavior of Phenolic Composites Prepared with Different Amounts of Zirconia and Asbestos Fiber

Ablative materials play a strategic role in aerospace industry. These materialsproduce a thermal protection system which protects the structure، theaerodynamic surfaces and the payload of vehicles and probes duringhypersonic flight through a planetary atmosphere. In this work، we investigatedthe effect of refractory zirconium oxide on mechanical، heat stability and ablationproperties of asbestos/phenolic/zirconia composites. The asbestos/phenolic/zirconiacomposites were produced with different percentages of zirconia filler from 7 to 21%with average size of 7 μm and different number of layers of asbestos، say 3 to 6layers. These ablative composites were made by an autoclave curing cycle process. The densities of the composites were in the range of 1. 68 to 1. 88 g/cm3. Ablation properties of composites were determined by oxy-acetylene torch environment and burn-through time، erosion rates and back surface temperature in the first required 20 seconds. Thermal stability of the produced materials was estimated by means of thermal gravimetric analysis، in both air and nitrogen which consisted of dynamic scans at a heating rate of 10°C/min from 30 to 1000°C with bulk samples of about 20±1 mg. The results showed that when the amount of zirconia was raised from 7% to 21%، the erosion rate and the back surface temperature of composites increased by about 24% and 26% respectively، and the heat capacity of the composites increased byabout 85%. Also، the result showed that when the thickness of composites of 4. 2 mm was increased to 10. 1mm the burn-through time raised by about 226% and erosion rate dropped by about 41%. These composites displayed the maximum flexural strength when the amount of zirconia was about 14%.