Effect of cleaning and abrasion-induced damage on the room temperature tensile strength of sapphire fibers

Room temperature tensile strengths of sapphire fibers were evaluated in the as-received condition (Dow Methocell^TM sizing applied by Saphikon), after flame cleaning, after cold water washing, and after a chemical cleaning procedure. Flame cleaning yielded an approximately 30% degradation in strength compared to the other surface treatments. Fractographic analysis revealed surface deposits at the failure origins of flame cleaned fibers; EDS analysis revealed the presence of Na, Cl, Ca, Fe, and Ce, impurities in the deposits. Tensile strengths were also evaluated for unsized fibers in the as-received condition, after flame cleaning, and after self-abrasion. Flame cleaning of unsized fibers yielded a less significant strength degradation than was observed for sized fibers and self-abrasion resulted in a 30% degradation in strength. Results indicate that use of sizing is imperative for preventing fiber damage during handling, but that improved procedures for sizing removal are required.