Ultra-long SiC nanowires with the lengths ranging from several millimeters to one centimeter were successfully prepared by the raw materials of graphite, silicon, silica and alumina via a simple carbon thermal reduction method in a tube furnace at 1300 o C. Scanning electron microscopy (SEM), electron energy scattering (EDX), Xray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR) were employed to characterize the morphology and microstructure of the obtained products. The results showed that the nanowires mostly consisted of 3C-SiC and exhibited mainly a straight-line shape with diameters in the range of 30-150 nm. Alumina may be as a novel and highly effective mediator playing an important role in controlling the concentration of SiO during the growth of ultra-long SiC nanowires and an alumina-assisted growth of vapor-solid (VS)mechanism was proposed for the growth mode of the ultra-long SiC nanowires.
Several-millimeter long SiC nanowires (NWs) with unique optical properties, excellent thermal stability and flexible nanomechanical properties were synthesized using a simple method with silicon and phenolic resin as the raw materials. The SiC NWs displayed special optical properties that were attributed to their large size and Al-doping. They displayed broad green emission at 527.8 nm (2.35 eV) and purple emission concentrated at 438.9 nm (2.83 eV), in contrast to the other results, and the synthesized SiC NWs could also remain relatively stable in air up to 1000 °C indicating excellent thermal stability. The Young’s moduli of the SiC NWs with a wide range of NW diameters (215–400 nm) were measured using an in situ nanoindentation method with a hybrid scanning electron microscopy/scanning probe microscopy (SEM/SPM) system for the first time. The results suggested that the values of the Young’s modulus of the SiC NWs showed no clear size dependence, and the corresponding Young’s moduli of the SiC NWs with diameters of 215 nm, 320 nm, and 400 nm were approximately 559.1 GPa, 540.0 GPa and 576.5 GPa, respectively. These findings provide value and guidance for studying and understanding the properties of SiC nanomaterials and for expanding their possible applications.
ZrB 2 -SiC/ZrSi 2 ceramics containing 30 vol% carbon fiber (C f ) additive were fabricated by hot pressing at low temperature (1500 ℃) using submicron ZrB 2 powders, and their microstructural evolution and performance were investigated. The addition of SiC or ZrSi 2 significantly reduced the onset sintering temperature and enhanced the densification of ZrB 2 . ZrB 2 -ZrSi 2 -C f showed poor performance owing to the serious fiber degradation, while the fiber degradation was effectively inhibited in ZrB 2 -SiC-C f resulting in high fracture toughness, substantial fiber pull-out, and non-brittle fracture mode for such material. The critical thermal shock temperature difference of ZrB 2 -SiC-C f was up to 741 ℃, significantly higher than those of ZrB 2 -SiC/ZrSi 2 and ZrB 2 -ZrSi 2 -C f . Moreover, this composite displayed a good oxidation resistance at 1500 ℃ in air.
ZrB 2 -SiC-C f composites containing 20-50 vol% short carbon fibers were hot pressed at low sintering temperature (1450 ℃) using nanosized ZrB 2 powders, in which the fiber degradation was effectively inhibited. The strain-to-failure values of such composites increased with increasing fiber content, and the value for the composite with 50 vol% C f was even more than 3 times higher than that of the composite with 20 vol% C f . Furthermore, the composite exhibited non-brittle fracture mode when the fiber content was above 30 vol%, and the thermal shock critical temperature difference of the composite with 30 vol% C f was up to 727 ℃, revealing excellent thermal shock resistance of this composite. Additionally, ZrB 2 -SiC-C f composites displayed good oxidation resistance when the fiber content was below 40 vol%, suggesting that this method provides a promising way for preparation of high-performance ZrB 2 -SiC-C f composites at low temperature.
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