Morphology Of SiC Nanowires Research Articles

Formation and growth of in-situ SiC nanowires in Al2O3–C materials under various atmospheres

The Al2O3–C materials were fabricated using tabular alumina aggregates and fines, Si powder and resin powder as starting materials. The effect of firing atmosphere on the in-situ formation of SiC nanowires (NWs) at elevated temperatures was investigated. The results show that Al2O3–C samples with superior performance were prepared via a simple process using phenolic resin powder as carbon source and binder. Si reacted with resin powder to form SiC NWs in Al2O3–C materials at high temperature, which created strengthening and toughening effects resulted in increasing mechanical properties. Firing atmosphere had great effect on formation and growth of in-situ SiC NWs, reducing atmosphere could promote Si reacting completely at lower temperature, and morphology of SiC NWs was different under various atmosphere. The linear SiC NWs with relatively smooth surface formed under weak oxidizing atmosphere, SiC NWs with rough surface and irregular diameter formed under reducing atmosphere, and SiC NWs with bamboo-like and chain-bead morphologies formed under weak reducing atmosphere. The length of SiC NWs was in micrometer scale and less than 200 nm in diameter. The growth process of SiC NWs was governed by solid-vapor between Si (s) and CO (g) or C (s) and SiO (g), liquid-vapor between Si (l) and CO (g), and vapor-vapor between SiO (g) and CO (g).

Effects of pyrocarbon on morphology stability of SiC nanowires at high temperatures

AbstractTo understand the effect of pyrocarbon (PyC) on the morphology stability of SiC nanowires at high temperatures (1800‐2100°C), a PyC layer was prepared to wrap the 3C‐SiC nanowire by chemical vapor deposition. The results showed that the existence and thickness of PyC layer played a crucial role in stabilizing the structures and morphology of SiC nanowires. The SiC nanowires without PyC layer transformed to platelet‐shaped structures above 1800°C. The SiC nanowires with a ~1.5 μm PyC layer could keep their structures and morphology at 2100°C, while the SiC nanowires with a ~1 μm PyC layer could not maintain their microstructures at this temperature. The stability of SiC nanowires at high temperature might be related to the vapor phase nucleation, thermodynamics phase transformation and the stacking faults (SFs) expansion, which could be limited by the PyC layer. Therefore, preparing a protective PyC layer with an appropriate thickness might be a potential method to extend the practical applications of SiC nanowires at high temperatures.

Fabrication of SiC Composites with Synergistic Toughening of Carbon Whisker andIn Situ3C-SiC Nanowire

The SiC composites with synergistic toughening of carbon whisker andin situ3C-SiC nanowire have been fabricated by hot press sinter technology and annealed treatment technology. Effect of annealed time on the morphology of SiC nanowires and mechanical properties of theCw/SiC composites was surveyed in detail. The appropriate annealed time improved mechanical properties of theCw/SiC composites. The synergistic effect of carbon whisker and SiC nanowire can improve the fracture toughness forCw/SiC composites. The vapor-liquid-solid growth (VLS) mechanism was proposed. TEM photo showed that 3C-SiC nanowire can be obtained with preferential growth plane ({111}), which corresponded to interplanar spacing about 0.25 nm.

Microstructure characterization of SiC nanowires as reinforcements in composites

SiC nanowires have been rarely investigated or explored along their axial direction by transmission electron microscopy (TEM). Here we report the investigation of the cross-section microstructure of SiC nanowires by embedding them into Al matrix. Morphology of SiC nanowires was cylindrical with smooth surface or bamboo shape. Cubic (3C-SiC) and hexagonal structure (2H-SiC) phases were detected by X-ray diffraction (XRD) analysis. High density stacking faults were observed in both the cylindrical and bamboo shaped nanowires which were perpendicular to their axial direction. Selected area electron diffraction (SAED) patterns of the cylindrical and bamboo shaped SiC nanowires both in the perpendicular and parallel direction to the axial direction were equivalent in the structure. After calculation and remodeling, it has been found that the SAED patterns were composed of two sets of diffraction patterns, corresponding to 2H-SiC and 3C-SiC, respectively. Therefore, it could be concluded that the SiC nanowires are composed of a large number of small fragments that are formed by hybrid 3C-SiC and 2H-SiC structures.