Application of the X-ray diffraction analysis method for in situ study of the formation processes of ultra- and nanosized iron oxide/hydroxide phases in the Fe0(Steel3)-H2O-O2 system: features and results

Abstract

The relevance of obtaining new samples of nanoscale materials and researching ways to control these processes is supported by constant progress in the fields of nanotechnology, semiconductors, biomedicine, wastewater treatment etc. The Fe0(Steel3)-H2O-O2 system, which is considered promising for use in the specified industries, allows both obtaining a number of nanoscale phases of iron oxygen-containing compounds (IOCs), in particular magnetite, cobalt ferrous ferrite, iron(III) hydroxide oxides, and controlling these processes due to changes in the physicochemical conditions of the process. Taking into account the permanent change in the specified system of phase composition on the metal surface, the method of X-ray diffraction analysis (XRD) was applied using the created additional device for the goniometric attachment GP-13 for the in situ study of IOCs formation processes on the surface of a steel disc in the system Fe0(St3)-H2O-O2. This made it possible to investigate the mechanisms and optimal conditions for the formation of individual ultradisperse and nanosized phases of IOCs under a number of physicochemical conditions. By calculating the area under the characteristic peaks on the in situ XRD patterns, quantitative ratios of IOCs formed under certain physicochemical conditions were found, and the average size of crystallites was calculated according to Scherer's formula, which provided additional information for the analysis of IOCs formation mechanisms. Along with this, the method of scanning electron microscopy (SEM) and the XRD without an additional in situ device were used. Based on the analysis of the obtained kinetic regularities, conclusions were made about the formation of IOCs by the formation of iron (II-III) hydroxycarbonate and hydroxysulfate layered double hydroxides I and II types, followed by their transformation to the final nanoscale phases of magnetite, cobalt ferrous ferrite, and iron(III) hydroxide oxides. The formation and accumulation of ferrous hydroxide phase was not recorded by the XRD in situ, however, in the Fe0(St3)-H2O-O2 system, the formation of iron (II-III) layered double hydroxides based on its monolayers is not excluded. The preference of carbonate anions over chloride anions in the formation processes of iron layered double hydroxides is shown.