Study On Fabrication Of Nanostructures On Ti₃SiC₂ And Ti By Anodic Oxidation

Regular nanostructures can be fabricated in situ on the surface of metal or alloy by anodic oxidation which is a simple and rapid method for the preparation of nanomaterials and has become a hot topic in China and other foreign countries. Layered Ternary Carbide Ti₃SiC₂ not only has high melting point, high chemical stability and excellent thermal shock resistance of ceramics, but also has excellent electrical and thermal conductivities of metals. In this study, Ti₃SiC₂ were fabricated by reactive hot pressing method using Ti, TiC, Si as raw materials. Nanostructures were fabricated in ethylene glycol and NH4 F electrolyte by anodic oxidation using Ti₃SiC₂ or Ti as anode and graphite as cathode. The influences of anodizing potential, NH4 F content and anodizing time on the micrograph of the nanostructures were investigated. And formation process of nanostructures was monitored by the electrochemical current-time curve during anodic oxidation. Formation process of nanopore arrays on Ti₃SiC₂ and nanotube arrays on Ti by anodic oxidation was discussed and compared initially.（1） Ti₃SiC₂ was prepared by reactive hot pressing method using Ti, TiC, Si as raw materials, and its performance parameters showed that: porosity: 0.15%; bulk density: 4.60 g/cm3, flexural strength: 480.4 MPa, fracture toughness: 6.36 MPa?m1/2, conductivity: 3.03×106 S?m-1. It indicated that Ti₃SiC₂ sample by reactive hot pressing method is dense and has good electrical conductivity.（2） Nanopore arrays were fabricated on the surface of Ti₃SiC₂ by anodic oxidation. The influences of anodizing potential, NH4 F content and anodizing time on the micrograph of the nanopore arrays were investigated. The results showed that: the average diameter increases with anodizing voltage and the deviation of the nanopore diameter reduced with anodizing time extending. With the NH4 F content from 1.0wt% to 2.0wt%, the nanopore diameter increased slightly. In addition to containing Ti, Si, C element, nanopore arrays on the surface of Ti₃SiC₂ by anodic oxidation contained a small amount of O element, and it existed in the form of TiO₂.（3） Nanotube arrays were fabricated on the surface of Ti by anodic oxidation. The influences of anodizing potential, NH4 F content and water content on the micrograph of the nanotube arrays were investigated. The results showed that: when the oxidation voltage is small, nanotubes are not regular and the diameters are not uniform. But when increasing the oxidation voltage the diameter of nanotubes gradually increased. With the NH4 F content from 0.5wt% to 1.5wt%, the diameter of the nanotubes is increased slightly. When the NH4 F content reached to 2.5wt%, the diameter increased accordingly. TiO₂ nanotubes before heat treated are amorphous. The nanotube arrays are thin, so the typical XRD patterns of amorphous characteristic diffraction peaks do not exist. When TiO₂ nanotubes were heated at 600℃, the new TiO₂ characteristic diffraction peaks appear. The strong diffraction peaks are the characteristic diffraction peaks of anatase, and the weak diffraction peaks are the characteristic diffraction peaks of rutile. TiO₂ nanotube array is the mixture of anatase and rutile at 600℃.（4） The required time of stable growth of nanostructures can be obtained by electrochemical current-time curve. Within a certain range, reducing the voltage and increasing NH4 F content are beneficial to obtain stable nanostructures in a short time.（5） Under the same conditions, the morphology and I-t curve of nanostructures on Ti₃SiC₂ and Ti by anodic oxidation are different, and the key reason is the difference of the anode materials（Ti₃SiC₂ and Ti） in structure and composition.