Microstructure of magnesia-carbon refractories used in ladles, converters and decarbonization devices under low pressure has a certain impact on the oxidation rate. Therefore, it is very helpful to study the microstructures of these magnesia-carbon refractories to improve their oxidation resistance. The oxidation rate of magnesia-carbon refractory cubic blocks was accurately measured by the staff of Japan Foundry and Forging Company. The relationship between the maximum particle size of magnesia and the oxidation rate of magnesia-carbon refractories was studied.
The experiments were carried out at oxygen partial pressure of 3.7 *102Pa and 2.1 *104Pa, respectively. The temperature ranges from 1200 to 1400. The oxidation process is carried out according to a local reaction simulating the oxidation process, and the oxidation rate is analyzed by the weight loss of the sample. The experimental results show that oxygen diffuses through the pore in the decarbonized layer, and the effective diffusivity of oxygen in M5-3 (maximum particle size of magnesia is 3.0mm) sample is slightly lower than that in M5-1 (maximum particle size of magnesia is 1.0mm) sample under the partial pressure of oxygen of 2.1*104Pa. The effective oxygen diffusivity of M5-3 and M5-1 decreases significantly at 1400 C. The dense layer was found in the decarbonized layer by optical microscopy, which may be due to the tortuosity of pore channels in M5-3 compared with M5-1, and the formation of dense layer in M5-3 was easier than that in M5-1.