Development of Manufacturing Principle of Porous Iron by Carbothermic Reduction of Composite of Hematite and Biomass Char

抄録

Iron-based porous metals have several advantages such as high strength and low cost compared with aluminum alloy foams. In recent years, a number of manufacturing technologies for iron-based porous metals have been proposed. However, a practical process could not be developed because of lower porosity, higher cost of raw materials, and so on. In this study, a new manufacturing principle of porous iron was proposed by applying carbothermic reduction using a composite of hematite and carbonaceous material. In the reduction experiment, graphite, coal, and three different charcoals were used as reductants. Based on the results, the characteristics and mechanism of the volume change of the composite were investigated under different pressures.

Reduction behavior significantly varied among the different types of reductants. The composites containing graphite and coal shrank during the reduction process when heated up to 1373 K. However, swelling behavior was observed for the composite prepared using charcoal containing some amounts of sodium and sulfur as ash components. When this composite was heated up to 1273 K at a rate of 0.167 K s⁻¹ at 0.3 MPa, porous iron with a maximum porosity of 97.7% was successfully obtained. The bulk density of the composite changed during the reduction of wustite to metallic iron and formed iron whiskers. The formation of the whiskered iron texture led to a considerable swelling of the composite. On the other hand, the composite prepared using charcoal with low sodium and sulfur concentrations in the ash did not swell after the formation of metallic iron. Furthermore, when such elements in the charcoal were preliminarily removed, the composite did not swell.