Nitriding of nanocrystalline iron was studied under the atmosphere of pure ammonia and in the mixtures of ammonia - hydrogen - nitrogen at temperatures between 350°C and 500°C using thermogravimetry and x-ray diffraction. Three stages of nitriding were observed and have been ascribed to the following schematic reactions: (1) α-Fe → γ'-Fe4N, (2) γ'- Fe4N → ε - Fe3N and (3) ε - Fe3N → ε - Fe2N. The products of these reactions appeared in the nitrided nanocrystalline iron not sequentially but co-existed at certain reaction ranges. The dependence of a reaction rate for each nitriding stage on partial pressure of ammonia is linear. Moreover, a minimal ammonia partial pressure is required to initiate the nitriding at each stage.
Superparamagnetic iron oxide nanoparticles were obtained in the polyethylene glycol environment. An effect of precipitation and drying temperatures on the size of the prepared nanoparticles was observed. Superparamagnetic iron oxide Fe3O4, around of 15 nm, was obtained at a precipitation temperature of 80°C and a drying temperature of 60°C. The presence of functional groups characteristic for a polyethylene glycol surfactant on the surface of nanoparticles was confirmed by FTIR and XPS measurements. Silver nanoparticles were introduced by the impregnation. Fe3O4-Ag nanostructure with bactericidal properties against Escherichia coli species was produced. Interesting magnetic properties of these materials may be helpful to separate the bactericidal agent from the solution.
Utilization of spent iron catalyst for ammonia synthesis
Several methods of the utilization of spent iron catalyst for ammonia synthesis have been presented. The formation of iron nitrides of different stoichiometry by direct nitriding in ammonia in the range of temperatures between 350°C and 450°C has been shown. The preparation methods of carbon nanotubes and nanofibers where iron catalyst catalyse the decomposition of hydrocarbons have been described. The formation of magnetite embedded in a carbon material by direct oxidation of carburized iron catalyst has been also presented.