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Abstract Polymer‐derived amorphous SiCN has excellent high‐temperature stability and properties. To reduce the shrinkage during pyrolysis and to improve the high‐temperature oxidation resistance, Y2O3was added as a filler. In this study, polymer‐derived SiCN–Y2O3composites were fabricated by mixing a polymeric precursor of SiCN with Y2O3submicron powders in different ratios. The mixtures were cross‐linked and pyrolyzed in argon. SiCN–Y2O3composites were processed using field‐assisted sintering technology at 1350°C for 5 min under vacuum. Dense SiCN–Y2O3composite pellets were successfully made with relative density higher than 98% and homogeneous microstructure. Due to low temperature and short time of the heat‐treatment, the grain growth of Y2O3was substantially inhibited. The Y2O3grain size was ∼1 μm after sintering. The composites’ heat capacity, thermal diffusivity, and thermal expansion coefficients were characterized as a function of temperature. The thermal conductivity of the composites ceramics decreased as the amount of amorphous SiCN increased and the coefficient of thermal expansion (CTE) of the composites increased with Y2O3content. However, the thermal conductivity and CTE did not follow the rule of mixture. This is likely due to the partial oxidation of SiCN and the resultant impurity phases such as Y2SiO5, Y2Si2O7, and Y4.67(SiO4)3O.
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Critical thickness of polymer‐derived ceramic coatings with particulate fillers
Abstract In this study, we demonstrate a novel environmental barrier coating processed from polymer‐derived ceramics (PDCs) with homogeneously distributed sub‐micrometer Y2O3as the filler. Under suitable conditions, dense and crack‐free coatings can be achieved for all the designed compositions with the volumetric content of Y2O3varied from 45 to 93 vol%. To process the PDC SiC–Y2O3composite coatings, Y2O3particles and SiC liquid precursor were uniformly dispersed in hexane and then dip‐coated on SiC substrates. After cross‐linking at 250°C and heat‐treated at 900°C in argon, dense and crack‐free PDC SiC–Y2O3composite coatings were formed. The effect of coating thickness and heat‐treatment temperature on the formation of cracks due to constrained pyrolysis was studied. The critical thickness for realizing crack‐free coatings of three compositions (i.e., 93, 77, and 45 vol% Y2O3) was studied for heat treatment from 1000 to 1300°C using atomic force microscope and scanning electron microscopy. As heat‐treatment temperature increases, the critical coating thickness decreases for the same coating compositions due to enhanced shrinkage at higher temperature. With higher Y2O3content, the critical thickness of the coating increased. The inert Y2O3particles reduce the amount of polymer leading to reduction in the overall constrained shrinkage of the coating during heat treatment.
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- Award ID(s):
- 1655740
- PAR ID:
- 10479057
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- International Journal of Applied Ceramic Technology
- Volume:
- 20
- Issue:
- 1
- ISSN:
- 1546-542X
- Page Range / eLocation ID:
- 84 to 93
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/ijac.14269
