Wei Xie,Qiangang Fu,Chunyu Cheng,Pei Zhang,Ningning Yan
The medium-entropy oxide (Y 1/3 Yb 1/3 Lu 1/3 ) 2 O 3 with a body-centered cubic structure was successfully synthesized by solid-state reaction process, and then it was introduced into SiC ceramic to study its effect on the oxidation behavior of SiC ceramic at 1700 °C. The (Y 1/3 Yb 1/3 Lu 1/3 ) 2 O 3 -modified SiC ceramic exhibited better oxidation resistance than its individual oxides (Y 2 O 3 , Yb 2 O 3 , and Lu 2 O 3 ) modified SiC ceramic. The experimental and calculated results all indicate that the rare-earth atoms had the tendency to diffuse into the SiO 2 structure and occupy the interstitial positions within SiO 2 structure. The introduction of medium-entropy oxide (Y 1/3 Yb 1/3 Lu 1/3 ) 2 O 3 reduced the initial oxidation rate of the ceramic samples (1−3 h), and enhanced the stability of SiO 2 structure, thus resulting in a better oxidation resistance at 1700 °C.
Al-doped-SiOC ceramics were fabricated via condensation polymerization and then pyrolysis of preceramic precursor in this study. The Al cation induced the formation of mullite, SiO 2 and graphitic carbon. Results showed that the incorporation of Al element enhanced the thermal stability of SiOC ceramics under Ar atmosphere via suppressing carbothermal reduction. This was consistent with the observation from Raman spectra by curve-fitting according to the D-to-G peak intensity ratio. In addition, the thermal stability of the SiAlOC ceramics under air atmosphere was also investigated. The formation of the mullite phase under the air atmosphere indicated that the SiAlOC ceramics possessed better oxidation resistance properties than the pure SiOC ceramics. This work provides a new guide to fabricating metal-modified SiOC ceramics with desired structures. Graphical Abstract
The introducing Al element greatly enhanced the thermal stability of SiOC ceramics via restraining in-situ formation of SiC. The structural evolutions of Al cation-modified-SiOC ceramics both in argon and air atmospheres were investigated systematically.
Weixiang Yang,Jincui Ren,Yanzi Tang,Yidan Wang,Yunuo Yang
To improve oxidation resistance of alumina-carbon refractories, SiO 2 -B 4 C-glass composite coating was prepared by slurry brushing method. The coated sample was heat treated in argon atmosphere to improve compactness and oxidation resistance of the coating. Effects of heat treatment temperature and time on microstructure and oxidation resistance of the coating were studied. Results showed that after heat treatment at 800 °C, borosilicate glass powder in the coating melted into glass phase, which could fill holes and cracks of the coating. As heat treatment temperature increased to 900 °C, viscosity of the glass phase decreased, resulting in the better self-healing ability and oxidation resistance of the coating. When heat treatment time increased to 1.5 h, some glass phases flowed away from the coating surface due to its large fluidity, so oxidation resistance of the coating decreased. When heat treatment temperature was too high (1000 °C), B 2 O 3 in the glass powder was eutectic with SiO 2 , more glass phase with larger fluidity generated, which leaded to that thickness and oxidation resistance of the coating both decreased. After heat treatment at 900 °C for 0.5 h, microstructure of the coating was smooth and compact, leading to its good oxidation resistance. Weight loss of the coated sample was only −1.041 % after oxidation at 800 °C for 80 h.
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