Plasma-solution synthesis of iron (iii) oxide

The process of formation of insoluble iron compounds, initiated by the action of a direct current discharge of atmospheric pressure in air on an aqueous solution of iron (III) sulfate, has been investigated. It was found that when the solution is the anode, the action of the discharge leads to the formation of a colloidal solution of iron hydroxosulfates and iron hydroxide. The colloidal solution, as shown by the DLS method, consists of two fractions 47 nm (73%) and 950 nm in size. The kinetics of the formation of colloidal particles was investigated by the turbodimetric method. It turned out that the rate of formation increases with an increase in the discharge current from 30 to 70 mA. At concentrations of iron (III) sulfate 5 mmol/l the rate constant of the process increases from 7.10(-3) to 2.2.10(-2) s(-1). When this solution is destroyed, a precipitate of the corresponding compounds is formed. X-ray analysis showed that the precipitate is amorphous. The resulting precipitate, as shown by SEM, has a dense structure. The particle size is 100 nm on average. As a result of calcining the precipitate, as shown by X-ray analysis and EDX, it turns into crystalline iron (III) oxide of the trigonal system (hematite). The resulting oxide powder has a developed surface, with a particle size of less than 50 nm on average.