Tape-shaped pitch fibers with a transverse cross-sectional size of 400 m width and ~30 m thickness, melt-spun from mesophase pitch, were adopted as a model for treatment in oxygen using various temperatures and durations to investigate their stabilization behavior. Several characterization techniques were used to systematically analyze the functional group species, oxygen content and distribution, local composition, thermal pyrolysis behavior and micro-structural changes in the various stabilized tapes. After oxidative stabilization treatment, the tape-shaped fiber exhibits uniform shrinkage behavior during subsequent heat treatments thereby maintaining its * Corresponding author. E-mail address: xkli8524@sina.com (X. Li) 2 tape shape and structural integrity. The ~30 m thick tapes can be stabilized completely by treatment in oxygen at 220 °C for ~10 h and this indicates a high efficiency of stabilization, which is, perhaps unexpectedly, higher than that of corresponding ~30 m diameter round-shaped fibers. Thermal decomposition pathways varied with the degree of stabilization and have obvious effects on the microstructure of the resulted tapes, which in turn strongly influences their final physical properties. Pitch tapes oxidized under mild conditions offered relatively higher mechanical performance. Tensile strength and Young's modulus of 2500 °C graphitized tapes, previously oxidatively stabilized at 220 °C for 20 h, were measured to be about 2 and 250 GPa, respectively.

Ultra-high temperature ceramics are desirable for applications in the hypersonic vehicle, rockets, re-entry spacecraft and defence sectors, but few materials can currently satisfy the associated high temperature ablation requirements. Here we design and fabricate a carbide (Zr0.8Ti0.2C0.74B0.26) coating by reactive melt infiltration and pack cementation onto a C/C composite. It displays superior ablation resistance at temperatures from 2,000–3,000 °C, compared to existing ultra-high temperature ceramics (for example, a rate of material loss over 12 times better than conventional zirconium carbide at 2,500 °C). The carbide is a substitutional solid solution of Zr–Ti containing carbon vacancies that are randomly occupied by boron atoms. The sealing ability of the ceramic’s oxides, slow oxygen diffusion and a dense and gradient distribution of ceramic result in much slower loss of protective oxide layers formed during ablation than other ceramic systems, leading to the superior ablation resistance.

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