Effects of alkalis and zinc on the damage of the tuyere composite brick of a blast furnace

The distribution of foreign elements and its true mineral forms in the tuyere composite brick extracted from a 2800 m3 industrial blast furnace were examined to gain a better understanding of the damage mechanism of the brick. The X-ray diffraction (XRD) and the scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) were applied to characterize the brick. The results show that the potassium is easier to permeate into the brick than zinc. The potassium is prone to react with Al-Si compounds in the brick to form kalsilite or leucite while the zinc is apt to react with the corundum in the brick to produce zinc-aluminum spinel. In addition, the zinc can interact with the blast furnace gas to form zinc oxide and zinc sulfide filled in the cracks of the brick. The mineral phases of the residual brick change from the original corundum and mullite to corundum, gahnite, zincite, sphalerite, kalsilite and leucite. The main cause of the damage of the brick is found to be potassium and zinc attack. In the case of degradation of the raw materials, it can choose the micro corundum brick instead of the corundum-mullite or mullite brick to prolong the life of the tuyere composite brick.