(1) Raw Materials
The smelting of pink fused alumina is similar to that of brown aluminum oxide, using alumina powder as the main raw material and adding a small amount of Cr2O3. Because the amount of Cr2O3 added is small, it is first mixed in batches at a ratio of chromium oxide to alumina powder of 1:5, and then added simultaneously with the alumina powder.
(2) Segregation
During the smelting of pink fused alumina, sodium peraluminate also segregates in the upper and middle parts of the molten metal during the cooling process.
(3) Chromium Oxide Loss
The chromium oxide added to the raw materials differs significantly from that in the finished product, with a utilization rate of only 40%–60%. The main causes of chromium oxide loss in pink fused alumina smelting are:
① Reduction Loss
Carbon-containing materials such as carbon rods, electrodes, and furnace lining bricks introduce carbon into the molten metal, causing partial reduction of Cr2O3. The reduced chromium exists as a metallic phase in the interstices of corundum crystals, leading to an increase in chromium atoms in the system that are not part of the solid solution lattice structure.
② Flying Loss
Since chromium oxide is added in powder form, flying loss is significant.
③ Some chromium oxide forms chromates, which segregate along with sodium peraluminate, concentrating in the upper part of the molten metal. During crushing and classification, the segregated material is discarded as substandard, accounting for 10%–15% of the chromium oxide added to the raw materials.
(4) Measures to reduce chromium oxide loss in pink fused alumina smelting:
a. Add chromium oxide in the middle and late stages of pink fused alumina smelting.
b. Chromium oxide should be pre-mixed evenly with some alumina powder and added to the furnace along with the alumina powder.
c. Select appropriate additives to improve the completeness of chromium oxide entering the solid solution. For example, when smelting brown aluminum oxide, adding 1.5% TiO2 to the furnace charge can increase the amount of chromium oxide entering the solid solution from 50% to 80%.
