Measurement of particulates formed during thermal protection system spallation in an arc-jet environment

An arc-jet campaign conducted in the Aerodynamic Heating Facility at NASA Ames was conducted to investigate the spallation of thermal protection system materials by estimating the size of particles ejected from these materials, as well as the corresponding mass loss. Particle sizes were determined both from analysis of particle tracking velocimetry, utilizing a force balance on the particulates, and by direct measurement of particles captured through targeted design of the test articles. Analysis of the captured particles revealed that they took on different geometries consisting of fine particulates, individual fibers, and clumps of multiple fibers. Different methods were required for each particle sizing approach to determine particle quantities, and corresponding mass loss. However, similar values for mass loss were determined using both techniques. In addition, it was found that the particle size distributions were independent of surface heat flux, and whether the carbon preform contained additional phenolic resin. It was found, however, that the presence of phenolic resin caused a measurable reduction in the rate of particle production, potentially due to its pyrolysis reducing the diffusion of oxygen from the free stream into the sample.