Effective thermal conductivities of fired pellets, nonfired pellets and sinter which were reduced in a stepwise manner to magnetite, wustite and metallic iron by CO-CO₂ or H₂ gas have been measured by the laser flash method in the temperature range from room temperature to 1273 K.
As the reduction proceeded, porosity of the samples changed from 23% to 62%. Measured effective thermal conductivities of the samples were remarkably smaller than those of dense materials. Thermal conductivities of metallic iron and hematite depended strongly on temperature in comparison with wustite. As the samples were reduced, the effective thermal conductivity decreased and reached a minimum value in wustite, but increased to 510 times in metallic iron. The treatment of reduction in stepwise at 1273 brought a little difference among the effective thermal conductivities of the three kinds of samples.
The influence of reducing gas, namely ; pure CO or H₂, on the temperature dependence of the effective thermal conductivity of metallic iron was observed. This is probably attributed to the generation of different structures of the samples. The data measured were correlated on the basis of the unit cell model. As a result, this model succeeded in explaining the actual bonding condition among neighbor grains and the equations obtained agreed well with the data observed.