Abstract
Iron powders of varying particle sizes and oxygen contents were manufactured from three different sources of iron oxide by hydrogen reduction at different temperatures. The morphology of the powders was studied by scanning electron microscopy and surface area analysis (BET). Powders reduced at low temperatures had fine particle sizes with high specific surface areas of up to, 18m2 g-1 and showed pyrophoric tendencies. At higher reduction temperatures, the powders had coarser particle sizes due to agglomeration of fines with a resultant decrease in specific. surface area. The effects on compact properties were investigated. Compacts were pressed at 200 MN.m-2 and sintered in hydrogen at 850°C for times of up to 150 hours. Fine powders compacted to low green densities but rapidly sintered to densities up to 97% theoretical density. As the reduction temperature of the powder was increased, the green density increased but the sintered density was reduced. The optimum reduction temperature to give a brief sintered density was found to be that which produces powder of comparable surface area to its oxide precursor. The effects of oxygen content on densification was examined. High levels of oxygen in the iron powder were found to inhibit the sintering of fine powders but for coarse powders oxygen appeared to aid densification. Other types of impurities also appeared to affect the densification but the greatest effect overall was found to be the difference in particle sizes. Grain sizes of compacts after sintering for various times at 850°C were established. The grain size of the sintered compact was controlled by the particle size and purity of the iron powder as well as the sintering time. Compacts made from fine powders showed fine grain sizes. The rate of grain growth at 850°C was low compared to that experienced in conventional powders when sintered around 1100°C. Mechanical properties of compacts made from fine powders and sintered at 850°C showed good elongation and tensile properties. Impact values however, were low when compared to high density compacts made from commercial iron powders. It is assumed that this was due to impurity contents.