Preparation And Properties Of Carbides Nanomaterials

Transition metal carbides have found extensive applications in many fields, such as cutting tools, wear-resistant parts and hightemperature structural materials because of their outstanding properties, such as high hardness, high melting point, high thermal conductivity, high strength even at high temperatures, high wear and corrosion resistance, and a high degree of chemical stability.In this paper, some common carbides (VC, TiC, Mo2C, NbC, WC) nanomaterials have been synthesized by chemical synthesis route. The products were analyzed by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive Spectrometer (EDS) and the thermogravimetric analysis (TGA). Main research content and conclusions are as follow:(1) Vanadium carbide (VC) was prepared via a simple and novel route by the reaction of metallic magnesium powders with vanadium pentoxide (V2O5), citric acid (C6H8O7) at650℃or potassium acetate (CH3COOK) at500℃in an autoclave. The latter temperature is150℃lower than the former, which may find potential industrial applications due to the economy and efficiency of the synthesis of VC nanopowders. The results indicated that all the products were cubic VC, which consisted of particles with an average size of about50nm and80nm in diameter, respectively.(2) Titanium carbide (TiC) was prepared via one simple route by the reaction of metallic magnesium powders with titanium dioxide (TiO2), potassium acetate (CH3COOK) at600℃for4h or oxalic acid (C2H2O4) at650℃for4h. They consisted of particles with an average size of about100nm and200nm in diameter, respectively. The product was also studied by the thermo gravimetric analysis (TGA). It had good thermal stability and oxidation resistance below350℃in air.(3) Nanocrystalline molybdenum carbide (Mo2C) was prepared via one simple route by the reaction of metallic magnesium powders with molybdenum trioxide and potassium acetate in an autoclave at the condition of600℃and4h. Scanning electron microscopy (SEM) image showed that the sample consisted of particles with an average size of about100nm in diameter. The product was also studied by the thermo gravimetric analysis (TGA). It had good thermal stability and oxidation resistance below450℃in air.(4) Niobium carbide (NbC) powders were prepared via a novel route, using metallic magnesium powders, niobium pentoxide (Nb2O5), and potassium acetate (CH3COOK) as starting materials at550℃for4h. The structures and morphologies of the products were characterized by X-ray powder diffraction (XRD) and Scanning electron microscopy (SEM). The results indicated that as-prepared products were crystallized in pure cubic NbC phase and the size of the samples was estimated to be around120nm. These particles exhibit slightly agglomerated particle morphology due to the ultrafine size of the sample. According to the Scherrer formula, the real grain size was about70nm The BET surface area of the sample was ca.29.3m2/g. The grain size distribution of the sample was about467nm, which was characterized by N4PLUS submicron Particle Size Analyzer.(5) The W2C-WC mixed powders in the range of200-400nm can be obtained by using metallic magnesium powders, tungsten trioxide (WO3) and oxalic acid (C2H2O4) as starting materials at650℃in a stainless steel autoclave under argon atmosphere. Then, the mixed W2C-WC powders were transferred to a crucible under the molten salt, followed by raising the reaction temperature to1100℃for lh. We have successfully synthesized WC powders by the method. It had good thermal stability and oxidation resistance below550℃in air.