Homogenous liquid precursor for ZrC–SiC was prepared by blending of Zr(OC4H9)4 and Poly[(methylsilylene)acetylene]. This precursor could be cured at 250°C and converted into binary ZrC–SiC composite ceramics upon heat treatment at 1700°C. The pyrolysis mechanism and optimal molar ratio of the precursor were investigated by XRD. The morphology and elements analyses were conducted by SEM and corresponding energy‐dispersive spectrometer. The evolution of carbon during ceramization was studied by Raman spectroscopy. The results showed that the precursor samples heat treated at 900°C consisted of t‐ZrO2 (main phase) and m‐ZrO2 (minor phase). The higher temperature induced phase transformation and t‐ZrO2 converted into m‐ZrO2. Further heating led to the formation of ZrC and SiC due to the carbothermal reduction, and the ceramic sample changed from compact to porous due to the generation of carbon oxides. With the increasing molar ratios of C/Zr, the residual oxides in 1700°C ceramic samples converted into ZrC and almost pure ZrC–SiC composite ceramics could be obtained in ZS‐3 sample. The Zr, Si, and C elements were well distributed in the obtained ceramics powders and particles with a distribution of 100 ~ 300 nm consisted of well‐crystallized ZrC and SiC phases.
The ceramic precursor for ZrC/SiC was prepared via solution‐based processing using polyzirconoxane, polycarbosilane, and divinylbenzene. The precursor could be transformed into ZrC/SiC ceramic powders at relative low temperature (1500°C). The cross‐linking process of precursor was studied by FT–IR. The conversion from precursor into ceramic was investigated by TGA, XRD. The ceramic compositions and microstructures were identified by element analysis, Raman spectra, SEM, and corresponding EDS. The results indicated that the ceramic samples remained amorphous below 1000°C and t–ZrO2 initially generated at 1200°C. Further heating to 1400°C led to the formation of ZrC and SiC with the phase transformation of ZrO2 and almost pure ZrC/SiC could be obtained upon heat‐treatment at 1500°C. During heat treatments, the ceramic sample changed from compact to porous due to carbothermal reduction. The ceramic powders with particle size of 100 nm~400 nm consisted of high crystalline degree ZrC and SiC phases, and Zr, Si, C were well distributed at the different sites in ceramic powders. The free carbon content was lowered to 1.60 wt% in final ZrC/SiC composite ceramics.
Soluble organometallic polymers containing zirconium and silicon were synthesized by a salt metathesis reaction. The molecular weight of the polymers was measured by GPC and the corresponding structures were identified by 13 C NMR and FT-IR. After heat treatment of the polymers under argon at 1400 °C for 2 h, ZrC/SiC composites with different molar ratios of crystalline phases were obtained and characterized by XRD, elemental analysis, SEM and Raman spectroscopy. The crystalline size of the composites was approximately 100 nm-200 nm and the elements were well distributed at the different sites in the ceramics. The Raman results indicated that the ceramic residue could be considered as ZrC/SiC/C ternary composites.
The ceramic precursor for HfB 2 /HfC/SiC/C was prepared via solution-based processing of polyhafnoxanesal, linear phenolic resin, boric acid and poly[(methylsilylene)acetylene)]. The obtained precursor could be cured at 250°C and subsequently heat treated at relative lower temperature (1500°C) to form HfB 2 /HfC/SiC/C ceramic powders. The ceramic powders were characterized by element analysis, thermal gravimetric analysis, X-ray diffraction, Raman spectroscopy, and Scanning electron microscopy. The results indicated that the ceramic powders with particle size of 200~500 nm were consisted of pure phase HfB 2 , HfC, and SiC along with free carbon as fourth phase with low crystallinity.W. Fahrenholtz-contributing editor Manuscript No. 32036.
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