Research On Reduction Of Fe₂O₃ By Plasma At Room Temperature

At present,the metal oxides are reduced by plasma with hydrogen or hydrogen and inert gases.Hydrogen is a green reducing gas medium that water is a product in reduction reaction,there are a lot of reductive substances in hydrogen plasma,such as H,H+,H*and H2*,which could reduce the metal oxides quickly and efficiently.However,there are some safety problems in the production and transportation of hydrogen.If the ammonia gas is used as the working gas in plasma,the disadvantages of using hydrogen can be avoided.So far using of ammonia and nitrogen mixed gas as the working gas in atmospheric pressure cold plasma to reduce the metal oxide rarely.The work aims to study effect of ammonia gas constant and the process parameters on reduction of Fe₂O₃ by atmospheric pressure cold plasma jet.Phases of the samples treated by plasma were analyzed by virtue of X-ray diffraction?XRD?,and morphology of the samples was observed by virtue of a scanning electron microscopy?SEM?.And the reduction law is explained from the viewpoint of dynamics.The result show: the Fe₂O₃ couldn't be reduced by atmospheric pressure cold plasma jet with N2 in this experiment,while was reduced by plasma with NH3-N2.If the reduction time and output power were the same,when the content of NH3 is 1%,the sample surface color was black and the reduction product is Fe3O4;when the amount of NH3 was 3⁷%,the reduction products were Fe3O4 and Fe.The content of reduction products increased with the increase of NH3 content in the range of 0⁷%.If the amount of NH3 and the output power were the same,when the reduction time was 20 s,the surface color of the sample became black,and the reduction product was Fe3O4;when the reduction time was 40 s,the reduction products were Fe3O4 and Fe.The content of the product increased with the increase of time,and the reaction rate decreased with the increase of time.The reduction reaction showed a transitional reduction with time,i.e.Fe₂O₃ ? Fe3O4 ? Fe.The output power affects the ionization rate of the gas in the plasma,and the content of the product increased with the increase of the output power.The process of plasma reduction Fe₂O₃ could be described by the cracking core model.With the reduction reaction,the solid particles would be broken into small particles to continue to react.The final reduction product showed the porous structure.During the whole reaction process,NH3 was formed into a lot of active substances after being ionized into plasma,and some of them could be reduced to Fe3O4 or Fe at normal temperature and atmospheric pressure quickly.Through theoretical analysis,it is found that the main reducing particles in atmospheric pressure cold plasma with NH3 were N2H4,H and H2*,and the reduction reaction is completed under the synergistic action of many particles.