Abstract

The fine fraction of particles or the so-called matrix plays an important role for the physical properties of refractory bricks. In this study micro-fine MgO particles were added to magnesia-spinel formulations. The aim was to reduce porosity and permeability as well as to improve the sintering behaviour and to promote the in-situ spinel formation. Micro-fine MgO particles were produced from very pure Brazilian magnesia sinter with a purity of typically > 98 %. The micro-fine particles had a diameter from 0.5 to 4 µm with a d50-value of 1.6 µm as measured with a laser diffraction analyzer. These micro-fine MgO particles were added to a standard magnesia-spinel formulation during mixing. Test cylinders were produced on the laboratory scale to optimise the necessary quantity to achieve the lowest possible porosity. Having found the optimum quantity test bricks were produced on an industrial scale. The standard physical properties bulk density, apparent porosity, gas permeability and cold crushing strength as well as the hot properties refractoriness-under-load (RuL), creep-in-compression (CiC) and hot modulus of rupture (HMoR) of the finished products were tested in comparison to the reference brick formulation. For a field trial the bricks were installed in the lower transition zone of a 4.8 m diameter cement rotary kiln to assess the performance of the bricks compared to the reference material. The comparison with the reference magnesia-spinel bricks revealed that the fired density of the bricks increased significantly by 0.05 g/cm³. The apparent porosity decreased by 0.7 % absolute. This trend was accompanied by a decrease in gas permeability and an increase in cold crushing strength. The RuL T05 was kept > 1700 °C. The CiC decreased to low values of < 1 % after 25 h at 1500 °C. The HMoR was measured in 100 K intervals from 1200 °C to 1500 °C and showed an increase of the values by a factor of approximately 1.6 in average compared to the reference. The maximum strain in the HMoR measurement is a measure of the flexibility of the material. The maximum strain was increased by a factor of approximately 1.7 compared to the reference. From all figures tested it can be concluded that the addition of micro-fine MgO particles to a standard magnesia-spinel brick formulation lead to a significant improvement of the physical brick properties. Finally, these improvements should increase the performance of the refractory bricks in service.