Effects of hyperthermal atomic oxygen on a cyanate ester and its carbon fiber-reinforced composite

The durability of cyanate ester (CE) to hyperthermal atomic oxygen (AO) attack in low Earth orbit may be enhanced by the addition of carbon fiber to form a carbon fiber-reinforced cyanate ester composite (CFCE). To investigate the durability of CFCE relative to CE, samples were exposed to a pulsed hyperthermal AO beam in two distinct types of experiments. In one type of experiment, samples were exposed to the beam, with pre- and post-characterization of mass (microbalance), surface topography (scanning electron microscopy (SEM)), and surface chemistry (X-ray photoelectron spectroscopy (XPS)). In the second type of experiment, the beam was directed at a sample surface, and volatile products that scattered from the surface were detected in situ with the use of a rotatable mass spectrometer detector. CFCE exhibited less mass loss than pure CE with a given AO fluence, confirming that the incorporation of carbon fiber adds AO resistance to CE. Erosion yields of CE and CFCE were 2.63 +/- 0.16 x 10(-24) and 1.46 +/- 0.08 x 10(-24) cm(3) O-atom(-1), respectively. The reduced reactivity of CFCE in comparison to CE was manifested in less oxidation of the CFCE surface in XPS measurements and reduced CO, CO2, and OH reaction products in beam-surface scattering experiments. The surface topographical images collected by SEM implied different surface deterioration processes for CE and CFCE. A change of surface topography with increasing AO fluence for CE indicated a threshold AO fluence, above which the erosion mechanism changed qualitatively. CFCE showed almost intact carbon fibers after relatively low AO fluences, and while the fibers eventually eroded, they did not erode as rapidly as the CE component of the composite.