| SiC one-dimensional nanomaterials have become a research focus at home and abroad in recent years. This is not only because of their good performance, such as high melting point and hardness, low density, good thermal stability, excellent high temperature performance and mechanical properties, inherited from the bulk SiC materials, but also due to their some unique physical and chemical properties resulting from special morphology and structural features, which make them have a broad application prospects in high-temperature structural materials, micro-nano electronics, catalytic etc. Therefore, the study of SiC one-dimensional nanomaterials is of great importance.SiC nanowires were synthesised by carbon thermal reduction at1100～1500℃from graphite, silicon and silica micro-nano powders, which were prepared by ball milling. In this process alumina, ferrocene, iron nitrate, nickel nitrate were used as catalysts. The composition, morphology and structure of the products were analyzed and studied in details by a variety of tests and characterization methods, such as scanning electron spectroscopy (SEM), energy disperse spectrum (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD) and so on.The influence of different variables, which include temperature, holding time, vacuum degree, catalyst, and reactants, on the growth process and morphology of SiC nanowires were researched. Combined with the literature reports and experimental verification, we analyzed the factors of constraining the growth of nanowires with controlled microstructures. Based on the thermodynamic calculations and characterization of the experimental products, the growth process and mechanism of SiC nanowires were also analyzed.Through a variety of tests and characterization methods, we found these:①The longest of SiC nanowires were length up to the millimeter and even centimeter level by this method, which is a ultra-long nanowires prepared by the inorganic powders as raw materials so far.②The diameter of the nanowires is in dozens to hundreds of nanometer level, the thickness is almost uniform.③In addition to a few of bifurcate, most of the nanowires are in the straight line and bending shape.④The nanowires mainly contain carbon, silicon, oxygen, and a small amount of alloy elements which are from catalyst.⑤The main composition of the nanowires is beta SiC by this method.⑥There are a lots of stacking faults in the SiC nanowires, which are coated by a thickness of2-4nm SiOx amorphous layer on the surface.⑦The nanowires grow along <111> direction.We found that different variables have a great effect on the growth of the nanowires though the study.①For using silicon and graphite powders as raw materials, the optimal growth temperature of nanowires is1400℃in the sintering furnace. The nanowires mostly grow in a bending shape and the yield is low at low temperture. With the increase of temperature, the nanowires will grow in a straight shape and the yield will be improved. When the temperature exceeds the optimal growth temperature, the product will in a short clavite nanorods growth. As reaction temperture increased, the diameter of nanowires will become thick.②The output of the nanowires will increase gradually as the extension of holding time.③Different catalysts have different effects on the result, and the effect of ferrocene and alumina is better.④The influence of vacuum (pressure) on the growth of nanowires is great, which should consider the reaction temperature and gas of supersaturation together.⑤Added silica nanopowders to the silicon and graphite system, the yield of the nanowires is improved obviously.⑥Nanowires, which length up to the millimeter, can be prepared by using silicon, silica and graphite micro-nano powders with a small amount of catalyst in the tube furnace.Based on the thermodynamic calculations and characterization of the nanowires, we found these:big droplets containing the elements of catalyst alloy did not find in the tip of nanowires, although the catalyst is added in the experiment. The catalyst plays an important role in the growth of nanowires. SiC nanowires is primarily generated by gas-solid reaction. So we put forward a catalyst-assisted gas-solid growth mechanism to explain the nanowire growth process in this paper... |
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