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Zirconium carbide ( ZrC) was synthesized by solution-based processing using versatile starting reagents including zirconium oxychloride octahydrate ( Zr O Cl2·8 H2 O, ZOC), acetylacetone (Hacac), and phenolic resin. Polyzirconoxane ( PZO), obtained by chelation of Hacac to zirconium, was used to combine with phenolic resin to form a precursor for ZrC. It generated ZrC at a relatively low temperature (1550°C) and in a low C/ Zr molar ratio of 2 assuming that phenolic resin was the only carbon source. As a comparison, synthesis of ZrC only using ZOC and phenolic resin was also conducted. Besides, the pyrolysis of PZO was carried out and the transformation mechanism during the pyrolysis was studied, during which ZrC was obtained at 1550°C in flowing argon. The conversions from as-synthesized preceramic precursors to ceramics were studied by means of FTIR, DSC- TG, SEM, EDS, and XRD. [ABSTRACT FROM AUTHOR]

Highlights: [•] C/ZrC, C/SiC and C/ZrC–SiC with different SiC content are fabricated by PIP process. [•] C/ZrC has the superior anti-ablation property but the poor anti-oxidation property. [•] The introduction of SiC improves oxidation resistance but degrades ablation property. [•] The C/ZrC–SiC with a certain content of SiC shows superiority over other composites. [•] A high temperature self-healing mechanism has been achieved by C/ZrC–SiC composite. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) needle-punched C/ZrC–SiC composites were successfully fabricated by infiltration and pyrolysis of a novel liquid ZrC precursor and polycarbosilane (PCS) separately. The effects of PIP cycles of PCS on the microstructures and mechanical property of the composites were studied. The C/ZrC–SiC composite with more PIP cycles of PCS had a high performance in mechanical property due to its higher density. The C/ZrC–SiC composite with 6 PIP cycles of PCS had a flexural strength of 142.4±17.5MPa and a fracture toughness of 7.6±0.3MPam1/2, which was superior to C/ZrC composites with the same total 20 PIP cycles. The ablation behaviors of the C/ZrC–SiC composite were studied using an oxyacetylene torch. The formation of continuous molten ZrO2 layer contributed mainly the high ablation resistance in the center region, while the SiC matrix accounted for the improved oxidation resistance beyond the center and transition regions. Moreover, the ZrC matrix homogeneously distributed in composite can act as a reservoir of the ZrO2 phase, and then supplemented the ZrO2 loss continuously in the whole testing. [ABSTRACT FROM AUTHOR]

Abstract: Three-dimensional (3D) Cf/ZrC–SiC composites were successfully prepared by the polymer infiltration and pyrolysis (PIP) process using polycarbosilane (PCS) and a novel ZrC precursor. The Cf/ZrC–SiC composite with relatively more PIP cycles of PCS has a higher density and a lower porosity, which account for the improved mechanical property of the composite. The composite with 6 PIP cycles of PCS has a flexural strength of 136.0±13.1MPa, and a fracture toughness of 7.3±0.3MPam1/2, which is superior to the monolithic ultrahigh temperature ceramics. The relatively low flexural strength and elastic modulus of the Cf/ZrC–SiC composites are attributed to the small stiffness of the matrix because of the debonding feature of the ZrC matrix. The high temperature oxidation testing of the S6-Cf/ZrC-SiC composite reveals that the surface molten ZrO2 layer contributes mainly to the improved anti-ablation property. [Copyright &y& Elsevier]

Abstract: Chitosan–zirconium complex, obtained by chelation of chitosan to zirconium, formed a novel precursor for zirconium carbide (ZrC). ZrC was synthesized via carbothermal reduction reaction using zirconium oxychloride (ZrOCl2·8H2O), and chitosan as sources of zirconium and carbon. The initiation of carbothermal reduction process was at about 1400°C, and the reaction was substantially completed at a relatively lower temperature (∼1550°C), compared with that using ZrOCl2·8H2O and phenolic resin as a carbon source. The conversions from as-synthesized preceramic precursors to ceramics were studied by means of FTIR, DSC-TG, SEM, EDS and XRD. [Copyright &y& Elsevier]

Three-dimensional (3D) braided C/ZrC–SiC composites with various SiC/ZrC ratios were fabricated by precursor infiltration and pyrolysis (PIP) process. The effects of SiC/ZrC ratios on the ablation and mechanical properties were investigated systematically. The flexural strength of 3D C/ZrC–SiC grows with the increase of SiC/ZrC ratios. The compact and stiff ZrC-SiC matrix, moreover, the carbon fiber and PyC interphase with the less reaction damage account for the improved flexural strength of C/ZrC–SiC with higher SiC/ZrC ratios. As for the ablation properties, both mass and linear ablation rates drop with the decrease of SiC/ZrC ratios at the beginning. However, the ablation rates start to increase with the further decrease of SiC/ZrC ratio, where the high open porosity deteriorates the ablation properties. Herein, in order to obtain a balance between ablation and mechanical properties, an appropriate SiC/ZrC ratio should be considered. [ABSTRACT FROM AUTHOR]