Effect of mechanical activation on the packed-bed, high-temperature behavior of hematite and graphite mixture in air

The present study reports the effect of mechanical activation on the reaction behavior of the Fe2O3/C powder mixture at high temperature under air atmosphere. Hematite and graphite were ground up to 150 hours using a ball mill with an alumina vial. The mixture was heated isothermally in the temperature range of 1173-1373degreesK using an electric furnace. The degree of reaction was determined by weight-loss measurement using a high accurate balance. It was found that low-energy mechanical milling at room temperature increases (the degree and) the rate of reaction at constant temperature. However, this effect was more significant at temperatures above 1273degreesK. At temperatures below 1273degreesK, the main reaction is oxidation of graphite and the total reaction process is controlled by diffusion of gases, whereas above 1273degreesK both chemical reaction (gasification reaction) and diffusion were controlling mechanisms. However, increasing milling time would shift the controlling mechanism from diffusion toward pure chemical reaction above 1273degreesK. It was observed that the mechanical milling might cause the mechanism to be changed at lower temperatures. This could be attributed to the increase of the rate of reaction due to mechanical milling. It was also observed that milling of powder mixture would decrease the difference in the average reaction rates at various degrees of reaction.