Mechanical characterization of sol-gel-derived silicon oxycarbide glasses

Silicon oxycarbide glasses have been fabricated, in the shape of thin rods suitable for flexural test experiments, by pyrolysis in an inert atmosphere at 1000 degrees and 1200 degrees C of sol-gel precursors containing SI-CH3 and SI-H bonds. The amount of carbon in the silicon oxycarbide network has been controlled by varying the carbon load in the precursor gel. Density and surface area analysis revealed that all of the samples pyrolyzed at 1200 degrees C were well-densified silicon oxycarbide glasses whereas for the glasses treated at 1000 degrees C, compositions with low carbon loads showed the presence of a residual fine porous phase. The elastic modulus (E), flexural strength (MOR), and Vickers hardness (H-v) increase markedly with the amount of carbon in the oxycarbide glasses reaching the maximum values (E approximate to 115 GPa, MOR approximate to 550 MPa, and H-v approximate to 9 GPa) for samples with the highest carbon content. The experimental elastic modulus values of the silicon oxycarbide glasses compare well with the theoretical estimations obtained using the Voigt and Reuss models assuming the disordered network formed by the corresponding thermodynamic compositions.