Black core is an easy phenomenon in the production of high alumina brick. If the black core brick is burned in reoxidation atmosphere, the black core part can be burned white again
1) Causes and conditions of black core. The main impurities in high alumina brick are Fe2O3 and TiO2. The firing atmosphere is primary iron. Titanium oxide is the condition for black core. Iron and titanium oxide coexist and coloring is serious. Iron and titanium oxide exist alone and coloring is not significant. Under the condition of reducing atmosphere, the coexistence or separate existence of iron and titanium ions may make the brick black core. Therefore, the reducing atmosphere is easier to color the brick than the oxidizing atmosphere
2) Ways to avoid black core in high alumina brick
A. Remove iron from raw materials by strong magnetic field to reduce the coexistence of iron and titanium ions
B. Install the high alumina brick in the middle of the kiln car as far as possible, away from the fire box
C. Increase the amount of hot air, avoid reducing atmosphere and adopt oxidizing atmosphere
D. When cooling, cool down slowly, so that low valent iron and titanium ions are oxidized again and decolorized
