Study of the Pore Space Structure of Iron Ore Pellets Using Computer Tomography

The share of pellets in the total volume of agglomerated raw materials is continuously increasing, so the task of improving their quality is relevant. The metallurgical properties of pellets are determined by their porosity, the study of which is the purpose of this work. The calculation and experimental analysis based on the determination of the pore characteristics of dry and fired pellets using electron microscopy and tomography was chosen as the research methodology. It was determined that the pores in dry and fired pellets are predominantly represented by the size of 1–100 μm (at least 75%), during firing the share of this size class increases. During heat treatment, pores of different sizes behave differently: small pores, the size of which is significantly smaller than the grain size, disappear during sintering due to combining with other pores or filling with material. When small pores are absorbed by large ones (15–30 μm), the share of pores of 20–35 μm increases. Medium-sized pores (1–100 μm) increase in total volume. Large pores and defects in the amount of 5–10% remain during sintering, nothing happens to them. Some of the large pores (~100 μm in size) decrease in size during sintering due to shrinkage and pass into another size class. Some of the pores related to limestone carbonates remain. Burnt pellets inherit the pore structure of dry pellets, although they undergo modification: pores less than 1 μm are compacted first. At the same time, small pores disappear and pass (by combining with large ones) into another size class. Geometrically, the pores remain in their places. The shape of the pores changes insignificantly during sintering, although a decrease in the shape coefficient (the ratio of the radii of the semi-axes of the inscribed ellipse) is observed. At the same time, neither regular spherical nor slit-shaped pores were noted.