Microstructure and compressive properties of carbon microballoons

Carbon microballoons (CMBs) with tap densities of 0.143, 0.161, and 0.177 g/cm(3), as measured per ASTM B 527-93, were characterized in terms of individual balloon diameter, wall thickness, and mechanical behavior in compression through a novel uniaxial compression test technique. This compression test, performed on an IVITS Nanoindenter XP II, utilized a flat-ended cylindrical tip rather than the common Berkovich indenter. Quantitative microscopy techniques were used to obtain diameter and wall thickness measurements on the polished cross-sections of individual CMBs that had been cold mounted in epoxy resin. Though there was significant overlap in the three populations, a trend toward increasing average wall thickness-from 1.32 to 2.16 mu m-with increasing tap density was observed. Compressive property data including failure load, failure strain, fracture energy, and stiffness were obtained for individual microballoons. Comparison of these data, both inter- and intra-tap density, has yielded some viable trends. CMB failure strain exhibited a dependence upon the inverse square root of the CMB diameter, and CMB failure load depended linearly upon CMB stiffness. Averages for each tap density's failure load, pseudo-stiffness, and fracture energy were also calculated and observed to increase with tap density. (c) 2006 Springer Science + Business Media, Inc.