Processing, physical and thermal properties of Blackglas (TM) matrix composites reinforced with Nextel (TM) fabric

The cure and pyrolysis behavior of a Blackglas(TM) resin and Nextel(TM) 440 impregnated with Blackglas(TM) resin were studied. Cure of the Blackglas(T M) resin is an exothermic process and DSC studies indicate that with an inc rease of catalyst content from 0.1 to 1.0%, the onset and peak temperature of cure are decreased coupled with an increase in the enthalpy of cure indi cating a greater extent of cross linking. However, pyrolysis char yield of the pyrolyzate is relatively insensitive to cure conditions. Cure pressure and pyrolysis environment are variables in the processing of Blackglas(TM) matrix composite reinforced with Nextel(TM) 440 plain weave f abric. Variations in cure pressure from 30 to 80 psi had no discernible eff ect on the chemistry of the pyrolyzate. However, the higher cure pressure r esulted in top and bottom ply damage. Pyrolysis in an Ar environment result ed in incorporation of up to 12 wt % C of which 8 wt % was graphitic in nat ure in the ceramic matrix. Pyrolysis in NH3 resulted in 3.9 wt % nitrogen a nd 1.5 wt % carbon in the matrix, with all the nitrogen and carbon bonded t o Si. The cured panels have to be pyrolyzed/densified between 6-7 times to achieve required density and porosity content. Oxidation behavior of the co mposites at 1000 degrees C indicate that the argon pyrolyzed CMC's lose mor e weight due to decomposition of the pyrolytic carbon, whereas, NH3 pyrolyz ed CMC's are stable as both the N and C are bonded to Si in the matrix. Die lectric constants K' and K" measured at 1 GHz in the as-processed condition are high in the argon pyrolyzed CMC, (K' = 11-28) due to the presence of p yrolytic carbon. On the other hand NH3 pyrolyzed CMC exhibit low dielectric constant (K' = 4). On oxidation, the dielectric constant in both the Ar an d NH3 pyrolyzed panels is approximately 4.0. (C) 1999 Kluwer Academic Publi shers.