Thermo-Programmed Reduction of Cobalt Ferrite with Hydrogen

• Published in: Russian journal of general chemistry 2023-06, Vol.93 (6), p.1616-1621
• Main Authors: Sakharova, Yu. N., Il’in, A. A., Ptitsyna, K. O., Seyoum, M. B., Smirnov, N. N., Astrakhantseva, I. A.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Cobalt; Cobalt ferrites; Diffraction; Ferric oxide; Gas mixtures; Heating rate; High temperature; Hydrogen; Hydrogen reduction; Iron compounds; Iron oxides; Low temperature; Oxygen; Potassium; Potassium oxides; Qualitative analysis; Selected articles originally published in Russian in Rossiiskii Khimicheskii Zhurnal (Russian Chemistry Journal); Spinel group; Thermal analysis; Thermogravimetric analysis; X ray analysis; X-rays
• ISSN: 1070-3632; 1608-3350
• DOI: 10.1134/S1070363223060373

The reduction process of cobalt ferrite has been studied, and its stages have been identified. Four primary temperature ranges of hydrogen absorption have been distinguished. In the initial stage, the restoration of surface oxygen occurs. The second stage proceeds stepwise with the formation of iron ions and an iron(III) oxide phase. The third stage involves the reduction of iron oxide(III) to iron oxide(II). The fourth stage leads to the formation of metallic iron phase Fe 0 . The materials were characterized by X-ray diffraction and synchronous thermal analysis in the mode of thermally programmed hydrogen reduction (H 2 -TPR). This method made it possible to establish that with an increase in the content of the alkali metal phase, an increase in the reactivity of the samples occurs, which is expressed in an increase in the proportion of weakly bound forms of lattice oxygen in the low-temperature regions of 343–442°C and an increase in the contribution of the oxygen form in the high-temperature region of 590–627°C. Curves of thermogravimetric analysis of the process of thermally programmed reduction of potassium-promoted CoFe 2 O 4 samples in a 5%H 2 +95%Ar gas mixture (heating rate 5°C/min) were also presented. Qualitative X-ray analysis of the studied samples of promoted cobalt ferrite was carried out on a DRON-3M diffractometer using CuKα radiation. All X-ray reflections were attributed to the spinel structure, which indicates that no other crystalline phases, except for CoFe 2 O 4 , were formed. When potassium oxide is added to the system, the content of the X-ray amorphous phase increases, but no peak shifts were observed, which indicates that potassium ions are highly dispersed in the CoFe 2 O 4 matrix.