Study on the kinetics of non-isothermal carbon thermal reduction of ironoxide sheet
MING Shoulu1，2，ZHANG Fang1，2，PENG Jun1，2，ZHAO Lijie1，2，LI Feifei1，2，CHANG Shiqi1，2
（1. School of Material and Metallurgy, Inner Mongolia University of Science and Technology, Bao'tou 014010,
China； 2. Inner Mongolia Key Laboratory of Advanced Ceramic Materials and Devices, Bao'tou 014010, China）
Abstract：To study the limiting step during the non-isothermal carbothermal reduction process of iron oxide with
carbon to produce porous iron, and to obtain a reduction kinetics model. The experimental raw materials were ob‐
tained by TG-DSC curve to obtain the optimal reduction temperature. The weight loss of the samples was mea‐
sured under different heating rates, and the variation in reduction rate was analyzed. The activation energy in the
kinetic parameters was calculated using the Flynn-Wall-Ozawa method (FWO) and ?atava-?esták method, and the
reaction mechanism function was determined. The microstructure of the samples was analyzed by a scanning
electron microscope(SEM) and energy dispersive spectroscope(EDS) under optimal reduction conditions. At four
different heating rates of 5 K/min, 10 K/min, 15 K/min, and 20 K/min, the mass loss at 15 K/min is slightly larg‐
er than that of the other three heating rates. Moreover, after the whole reduction reaction, the reduction rate of the
sample heated at 15 K/min is the highest. Using the FWO method to calculate the activation energy correspond‐
ing to different reduction rates (0.1-0.9), it is found that the activation energy first decreases and then increases to
381.6 kJ/mol. By linearly fitting the mathematical models corresponding to the possible limiting steps in the reac‐
tion process (carbon gasification reaction, interfacial chemical reaction, internal diffusion), it is discovered that the thermal reduction process of iron oxide-coated carbon is jointly controlled by multiple steps. The ?atava-
?esták method is used to obtain a strong linear relationship for the A3/2 reaction mechanism function, with R≥0.99,
and the minimum |(E0-Es)/E0| value of 0.0247. Using SEM and EDS analysis of the reduced sample with a heat‐
ing rate of 15 K/min, it is discovered that there exist pore structures within the substrate, and the surrounding
area appears to be smooth. EDS analysis shows that the substrate material consists of metallic iron. Under dif‐
ferent heating rate conditions, the reaction rate increases initially as the temperature rises and then decreases,
ultimately stabilizing. The activation energy for the entire process is calculated as 377.29 kJ/mol by the FWO
method. The limiting step of the entire reduction reaction is mixed control, and the carbon gasification reaction,
chemical interface reaction, and internal diffusion all have to limit effects. The most probable mechanism func‐
tion for the non-isothermal carbothermal reduction reaction of iron oxide scale at different heating rates is the A3/2
function model, and its integral and derivative function expressions are g (α ) = [-ln (1 - α ) ]2/3and f (α ) =
3/2 (1 - α ) [-ln (1 - α ) ]1 3.
2023, Vol. 33 
