| Type II carbon fibers (PAN-based) have been electrochemically treated in aqueous potassium nitrate at varying electron charge densities (0-4112 C/g) by Jiang. The fibers were subsequently characterized by angle-resolved x-ray photoelectron spectroscopy (ARXPS) and ion scattering spectroscopy (ISS) and the results were correlated to acid/base surface titrations and BET surface area measurements. Relative to the as-received fibers (commercially treated, but unsized), the electrochemical treatments increased the ARXPS O/C atomic ratios by approximately 50-100% and the concentration of oxidized carbon became more uniform within the XPS sampling depth ({dollar}approx{dollar}100A). At the same time, the number of acidic functions titrated by sodium hydroxide rose from about 2.64 to near 1048 {dollar}mu{dollar}eq/g, and the BET surface area increased from 0.67 to 2.1 m{dollar}sp2{dollar}/g. These experiments were done by Jiang. It is hypothesized that the large increase in acidic groups must be due to increased fiber oxidation below the XPS sampling depth. The ISS spectra suggest that the surface density of carbon/oxygen groups was also increased. Single fiber fragmentation tests (using epoxy) revealed that in most cases the interfacial shear strengths (IFSS) increased (partially done by Jiang) with increasing ARXPS O/C atomic ratio probably due to enhanced fiber/matrix chemical bonding and/or mechanical interlocking. As the electrochemical treatments progressed to higher electron charge densities, it is believed that decreased fiber integrity acts to decrease the IFSS. |
