Preparation and properties of silicon oxycarbide fibers

Silicon oxycarbide fibers have been prepared from vinyl trimethoxysilane (VTMS) by a modified sol–gel method and with secondary cellulose acetate (SCA) as the fiber-forming aid. Its main advantage over a normal sol–gel fiber processing is that the spinning dope remains spinnable for a long period of time. The effect of the pre-hydrolysis of VTMS on the dope spinnability is studied. AtH2O/VTMS = 4, the resultant sol transforms into gel very quickly, unsuitable to obtain a spinnable dope; at H2O/VTMS = 2, too much unreacted VTMS exists in the sol, making the extruded fiber difficult to solidify; atH2O/VTMS = 3, a dope with good spinnability and stability, and thus high ceramic yield is obtainable. Pyrolysis at 1,000 C in argon/5% hydrogen results in silicon oxycarbide fibers with the maximum tensile strength (940.0 MPa), moderate Young’s modulus (63.2 GPa) and high carbon content (33.2%).