Preparation Of Porous Biological Carbide/C Composite Material Using Molten Salt Media

Transition metal carbides are a class of materials with some excellent properties such as high melting point,high hardness,good chemical stability,good acid and alkali corrosion resistance,superconductivity and catalysis.Among them,chromium carbide has the highest oxidation resistance during metal carbides.Molybdenum carbide and tungsten carbide are called “eka-platinum catalyst” due to its similar electronic structure and catalytic properties of the noble metals.In this paper,porous carbon materials were prepared from three kinds of natural plants such as pine wood,bamboo and cane,which can be naturally regenerated.And porous MC/C(M = Cr,Mo,W)composite materials were prepared by molten salt synthesis(MSS),using the prepared carbon materials as templates.The structure and function were well integrated by growth of transition metal carbides in site on the biological carbon templates.The graphitization degree,morphology and pore size distribution of the three kinds of carbon templates with different pore structure were studied,and the oxidation resistance of the carbon templates were tested in air atmosphere.Porous MC/C(M = Cr,Mo,W)composite materials were prepared by MSS,which is a low-temperature and environmentally friendly technology,using Cr,Mo and W as metal sources.The effects of the reaction temperature,reaction time,type and ratio of mixed salts on the phase composition and morphology of the products were investigated.The pore size distribution and oxidation resistance of the praducts were characterized and analyzed,and the reaction mechanism was explored.(1)The graphitization degree of the carbon template increases with the increase of carbonization temperature.And the porous structure of natural wood is well retained in the carbon templates.(2)The growth of the carbides are facilitated by increasing the reaction temperature or the reaction time.(3)The oxidation activation energy of the chromium carbide/carbon composite material is higher than that of the carbon template,that is,the chromium carbide/carbon composite material shows excellent oxidation resistance.(4)Compared with the Na F/Na Cl mixed salts medium,the KF/KCl mixed salts medium is more favorable for the formation of molybdenum carbide and tungsten carbide,and the content of KF in the mixed salts should be relatively low.(5)The raw metal powders participate in the reaction in the molten salt medium in two states: one is in the solid state and another is dissolved in the liquid molten salt.With the formation of the salt melt and the increase of the reaction temperature,on the one hand,the diffusion rate of the metal powders in the reaction system is increased,so that the raw material particles can sufficiently react with the carbon template;on the other hand,the increase of the solubility of the metal powder in molten salt further promotes the reaction.