PRODUCTION OF ALUMINUM OXIDE/IRON OXIDE COMPOSITE PARTICLES IN SUB- AND SUPERCRITICAL WATER
Rubrics: 1. CHEMISTRY
Authors:
1.
KNITU
2.
KNITU
3.
Kazan National Research Technological University
4.
Kazan National Research Technological University
5.
KNITU
Type:
Article
Pages:
from 28
to 34
Status:
Published
Received:
23.12.2025
Accepted:
25.12.2025
Published:
25.12.2025
Language:
Russian
Keywords:
SUPERCRITICAL WATER OXIDATION, ALUMINUM OXIDE, STRUCTURAL CHANGES, KINETICS
Abstract (English):
This article examines the kinetics of aluminum oxidation in sub- and supercritical water, which is of significant scientific and practical interest for the production of functional oxide materials. The experimental portion of the work included oxidation tests of aluminum samples in a high-pressure reactor at temperatures of 325, 350, and 375°C, followed by analysis of the mass of unreacted metal and the volume of remaining water. For mathematical modeling of the process kinetics, the Runge-Kutta-Merson method in MS Excel was used, along with macros for constructing and solving systems of differential equations based on stoichiometric matrices. During the study, a kinetic model was proposed and gradually refined, accounting for the heterogeneous nature of the process, including the stages of aluminum activation due to oxide film breakdown, the oxidation reaction itself with the formation of boehmite (2Al + 4H₂O → 2AlOOH + 3H₂), and the water decomposition reaction (2H₂O → O₂ + 2H₂) near the critical point. The most adequate model was described by a system of six differential equations, which took into account both the chemical stages and diffusion limitations. By solving the inverse kinetic problem, the rate constants of individual stages and their temperature dependence were determined. It was found that the rate constant of water decomposition is satisfactorily described by the Arrhenius equation, while the constants associated with aluminum activation and boehmite formation exhibit deviations, likely due to the significant influence of diffusion factors in the critical region. The validity of the proposed model is confirmed by high Pearson R² values (average R² 0.95) and good visual agreement between the calculated and experimental data. The calculated interval errors did not exceed 5%. The practical significance of this work lies in the development of an improved approach to modeling complex heterogeneous processes under extreme conditions, which can be used to optimize metal processing technologies and the synthesis of oxide materials in supercritical fluids.
This article examines the kinetics of aluminum oxidation in sub- and supercritical water, which is of significant scientific and practical interest for the production of functional oxide materials. The experimental portion of the work included oxidation tests of aluminum samples in a high-pressure reactor at temperatures of 325, 350, and 375°C, followed by analysis of the mass of unreacted metal and the volume of remaining water. For mathematical modeling of the process kinetics, the Runge-Kutta-Merson method in MS Excel was used, along with macros for constructing and solving systems of differential equations based on stoichiometric matrices. During the study, a kinetic model was proposed and gradually refined, accounting for the heterogeneous nature of the process, including the stages of aluminum activation due to oxide film breakdown, the oxidation reaction itself with the formation of boehmite (2Al + 4H₂O → 2AlOOH + 3H₂), and the water decomposition reaction (2H₂O → O₂ + 2H₂) near the critical point. The most adequate model was described by a system of six differential equations, which took into account both the chemical stages and diffusion limitations. By solving the inverse kinetic problem, the rate constants of individual stages and their temperature dependence were determined. It was found that the rate constant of water decomposition is satisfactorily described by the Arrhenius equation, while the constants associated with aluminum activation and boehmite formation exhibit deviations, likely due to the significant influence of diffusion factors in the critical region. The validity of the proposed model is confirmed by high Pearson R² values (average R² 0.95) and good visual agreement between the calculated and experimental data. The calculated interval errors did not exceed 5%. The practical significance of this work lies in the development of an improved approach to modeling complex heterogeneous processes under extreme conditions, which can be used to optimize metal processing technologies and the synthesis of oxide materials in supercritical fluids.
Keywords:
SUPERCRITICAL WATER OXIDATION, ALUMINUM OXIDE, STRUCTURAL CHANGES, KINETICS
SUPERCRITICAL WATER OXIDATION, ALUMINUM OXIDE, STRUCTURAL CHANGES, KINETICS
