Continuous silicon carbide fiber-reinforced silicon carbide (SiCf/SiC) composites have been expected as next-generation highly reliable heat resistant materials. It is well-known that the interface ...between fiber and matrix acts as an important role for toughening and strengthening SiCf/SiC composites, and it should be optimally controlled to achieve high performance SiCf/SiC composites with excellent fracture tolerance. In this study, polypyrrole (Ppy) as an electric conductive polymer was coated on amorphous SiC fibers to increase their surface electric conductivity so that electrophoretic deposition (EPD) method can be applied to form the interphase on the SiC fibers, and carbon interphase was formed on the SiC fibers by EPD method. In addition, unidirectional SiCf/SiC composites were fabricated by polymer impregnation and pyrolysis (PIP) process, and their mechanical properties were evaluated. Thin Ppy coating with the thickness of around 200 nm drastically increased the surface electric conductivity of the amorphous SiC fibers, and the surface of Ppy-coated SiC fibers was wholly and uniformly coated with flaky graphite particles by EPD. The average thickness of the carbon interphase formed on the Ppy-coated SiC fibers by EPD became thicker with an increase in EPD voltage, and it was revealed that the SiCf/SiC composites with carbon interphase formed by EPD showed pseudo-ductile fracture behavior and excellent mechanical properties, and the formation of the thick carbon interphase (average thickness; 0.7 ± 0.4 µm, EPD voltage; 5 V) provided the higher bending strength and fracture energy under the experimental condition in present study. These results demonstrated that Ppy coating on the low-conductive SiC fibers was very effective to improve their surface electric conductivity, and uniform and sufficient carbon coating was successfully formed on the SiC fibers by EPD for achieving high performance SiCf/SiC composites.
Continuous silicon carbide fiber-reinforced silicon carbide (SiCf/SiC) composites have been expected as next-generation highly reliable heat resistant materials. It is well-known that the interface ...between fiber and matrix acts as an important role for toughening and strengthening SiCf/SiC composites, and it should be optimally controlled to achieve high performance SiCf/SiC composites with excellent fracture tolerance. In this study, polypyrrole (Ppy) as an electric conductive polymer was coated on amorphous SiC fibers to increase their surface electric conductivity so that electrophoretic deposition (EPD) method can be applied to form the interphase on the SiC fibers, and carbon interphase was formed on the SiC fibers by EPD method. In addition, unidirectional SiCf/SiC composites were fabricated by polymer impregnation and pyrolysis (PIP) process, and their mechanical properties were evaluated. Thin Ppy coating with the thickness of around 200 nm drastically increased the surface electric conductivity of the amorphous SiC fibers, and the surface of Ppy-coated SiC fibers was wholly and uniformly coated with flaky graphite particles by EPD. The average thickness of the carbon interphase formed on the Ppy-coated SiC fibers by EPD became thicker with an increase in EPD voltage, and it was revealed that the SiCf/SiC composites with carbon interphase formed by EPD showed pseudo-ductile fracture behavior and excellent mechanical properties, and the formation of the thick carbon interphase (average thickness; 0.7 ± 0.4 µm, EPD voltage; 5 V) provided the higher bending strength and fracture energy under the experimental condition in present study. These results demonstrated that Ppy coating on the low-conductive SiC fibers was very effective to improve their surface electric conductivity, and uniform and sufficient carbon coating was successfully formed on the SiC fibers by EPD for achieving high performance SiCf/SiC composites.
The fluorination of Yttria (Y2O3) coatings in the inner chamber wall of a plasma-etching equipment causes a process drift. In this paper, we investigate the relationship between the microstructure ...and fluoride layer of Y2O3 coatings prepared by aerosol deposition (AD) method compared with Y2O3 coatings prepared by atmospheric plasma spraying (APS) and ion plating (IP). The plasma corrosion of AD-coating, which has a highly dense microstructure without any pores, proceeded homogeneously and the specific surface area maintained its initial smooth surface. Moreover, F atoms slightly penetrated the AD-coating and formed a very thin, 45-nm fluoride layer after plasma exposure. The total area of the surface fluoride layer did not increase with plasma exposure time because the surface remained smooth. Therefore, Y2O3 coating prepared by AD can suppress surface fluorination and process drift compared with Y2O3 coatings prepared by APS and IP.
Boron carbide (B4C) powders with defined stoichiometry, high crystallinity, minimal impurity content, and a fine particle size are imperative for realizing the exceptional properties of this compound ...in advanced high-technology applications. Nevertheless, achieving the desired stoichiometry and particle size using traditional synthesis methods, which rely on prolonged high-temperature processes, can be challenging. The primary objective of this study is to synthesize fine B4C powders characterized by high crystallinity and a sub-micron particle size, employing a fast and energy-efficient method. B4C powders are synthesized from elemental boron and carbon in a high-frequency induction heating furnace using the electromagnetic induction synthesis (EMIS) method. The rapid heating rate achieved through contactless heating promotes the ignition and propagation of the exothermic chemical reaction between boron and carbon. Additionally, electromagnetic effects accelerate atomic diffusion, allowing the reaction to be completed in an exceptionally short timeframe. The grain size and crystallinity of B4C can be finely tuned by adjusting various process parameters, including the post-ignition holding temperature and the duration of heating. As a result, fine B4C powders can be synthesized in under 10 min. Moreover, these synthesized B4C powders exhibit oxidation onset temperatures higher than 500 °C when exposed to air.
SiC‐fiber–reinforced binary Si eutectic alloy composites have been developed for aerospace applications using the melt infiltration method. In this study, the oxidation mechanisms of various binary ...Si eutectic alloys were evaluated at elevated temperatures. We suggest that the oxidation resistance of eutectic alloys could be predicted using the Gibbs energy change for the oxidation reaction. Based on these calculations, eutectic alloys of Si‐16at%Ti, Si‐17at%Cr, Si‐22at%Co, Si‐38at%Co, and Si‐27at%Fe were prepared. These alloys produced uniform SiO2 layers and showed the same oxidation resistance as Si at 1000°C under humid conditions. Therefore, SiC composites using Si alloys with excellent oxidation resistance can be predicted using thermodynamic calculations.
Amorphous SiC-fiber-reinforced Si-CoSi2 and CoSi2–CoSi eutectic alloys composites have been developed by a melt infiltration method, and their mechanical properties were evaluated at elevated ...temperatures up to 1220 °C. As compared to polycrystalline Si, Si–Co ingots showed a ductile transition at a lower temperature (200–400 °C) due to the ductile transition of CoSi2 and the presence of a debonding interface. Moreover, the composites using Si–Co alloys showed superior bending behavior at elevated temperatures around 1000 °C as compared to composites using Si because of the ductile behavior of the Si–Co alloys and the prevention of the degradation of the SiC fibers.
The fabrication of Tyranno ZMI fiber/SiC-based matrix composites by a melt infiltration (MI) process using Si−8.5at%Hf alloy was investigated. The Si−Hf alloy was utilized instead of pure Si for MI ...processing in order to lower the MI temperature to below 1400°C as well as to inhibit the thermal degradation of amorphous SiC fibers. Microstructural characterization revealed that the composite fabricated by Si−8.5at%Hf alloy MI at 1375°C had a highly dense matrix comprising reaction-formed SiC and unreacted Si−HfSi2 phases. The Si−Hf alloy melt-infiltrated composite exhibited approximately 35% higher bending strength than a conventional Si melt-infiltrated composite fabricated at 1450°C. Further, it was confirmed that Si−Hf alloy melt-infiltrated composite maintained its strength up to 1200°C in an Ar atmosphere. These results clearly demonstrated that the Si−8.5at%Hf alloy offers sufficient infiltration ability and reactivity to form a dense SiC-based matrix at 1375°C.
In this study, the flexural strength of three kinds of alumina-strengthened porcelains (ASPs), which were recently developed with both small water absorption (WA) and small pyroplastic deformation ...(PD), was examined using a three-point bending test. The strength of the porcelains was as large as or slightly larger than that of conventional ASPs except for the porcelain made with fine talc powders, in which the accelerated cordierite crystallization suppressed the PD. In addition, the conducted X-ray diffraction, which was analyzed using the Rietveld method, revealed that a lot of alumina particles in the porcelain were consumed for the cordierite crystallization, leading to a decrease in the porcelain strength. This indicates that to realize both small WA and small PD in the material design of porcelains, maintaining the alumina amount as large as possible is important to produce strong porcelains.
The human ether-a-go-go-related gene (HERG) protein forms the ion channel responsible for the rapidly acting delayed rectifier potassium current, I(Kr), and its blockade is a significant contributor ...to prolongation of the QT interval. Using descriptors which have clear physicochemical meanings and are familiar to medicinal chemists, we have carried out 2D-quantitative structure-activity relationship (2D-QSAR) studies on 104 HERG channel blockers with diverse structures collected from the literature, and we have formulated interpretable models to guide chemical-modification studies and virtual screening. Statistically significant descriptors were selected by a genetic algorithm, and the final model included the octanol/water partition coefficient, topological polar surface area, diameter, summed surface area of atoms with partial charges from -0.25 to -0.20, and an indicator variable representing the experimental conditions. The statistics were r = 0.839, r2 = 0.704, q2 = 0.671, s = 0.763, and F = 46.6. The correspondence of the molecular determinants derived from the 2D-QSAR models with the 3D structural characteristics of the putative binding site in a homology-modeled HERG channel is also discussed.
Microstructures of monolithic high purity SiC and SiC with sintering additives after neutron irradiation to a fluence of 2.0–2.5 × 1024 n/m2 (E > 0.1 MeV) at 333–363 K and after post-irradiation ...annealing up to 1673 K were observed using a transmission electron microscopy. Results showed that no black spot defects or dislocation loops in SiC grains were found after the neutron irradiation for all of the specimens owing to the moderate fluence at low irradiation temperature. Thus, it is confirmed that these specimens were swelled mostly by the formation of point defects. Black spots and small dislocation loops were discovered only after the annealing process in PureBeta-SiC and CVD-SiC, where the swelling almost diminished. Anomalous-shaped YAG grains were found in SiC ceramics containing sintering additives. These grains contained dense black spots defects and might lose crystallinity after the neutron irradiation, while these defects may annihilate by recrystallization during annealing up to 1673 K. Amorphous grain boundary phase was also presented in this ceramic, and a large part of it was crystallized through post-irradiation annealing and could affect their recovery behavior.
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