1. Tabular Alumina
Tabular alumina is a high-end refractory raw material that has seen rapid growth in the refractory industry in recent years. It has been particularly popular in high-performance refractory products, particularly carbon-free refractory materials for steel refining ladles, functional refractory materials, and high-throughput iron channel castables. It has partially replaced traditional white, sub-white, and brown aluminum oxide. In recent years, as companies have optimized tabular alumina production processes, significantly increased production capacity, and continuously reduced production costs, the technical and economic advantages of tabular alumina have been further enhanced. Sub-white and brown fused alumina no longer offer price advantages, and the remaining share of brown aluminum oxide in the refractory raw material market, used in specialized applications, is expected to be further replaced.
2. Production Process
The common production process for tabular corundum involves industrial alumina powder, grinding, adding water to form pellets, drying, high-temperature calcination in a vertical kiln, crushing, and packaging. This calcination process is carried out in a high-temperature vertical kiln fueled by clean natural gas. The calcination takes place at 1900-1950°C, transforming transitional phases such as γ-Al₂O₃ in the industrial alumina powder into the most stable α-Al₂O₃ phase. Using a rapid calcination and cooling process, the grain size of tabular corundum generally ranges from 30 to 150μm.
Brown fused alumina is produced by the electric fusion process. High-alumina bauxite clinker, carbon material, and iron filings are mixed and added to an electric arc furnace. After high-temperature melting and impurity reduction, the mixture cools and crystallizes into a brown-brown fused mass. The mineral composition is primarily α-Al₂O₃ phase, with the center of the crystals displaying rhombuses, thick plates, and cracked grains. The periphery contains a significant amount of melt crystallization of titanium oxide, silicon oxide, and calcium oxide, forming long plates, with the coarsest grains forming skeletal platelets. Because impurities have not been completely removed, brown aluminum oxide also contains secondary phases such as calcium hexaaluminate, calcium plagioclase, spinel, and rutile, as well as glassy phases, iron alloys, and solid solutions. The color tone of brown fused alumina is largely dependent on the residual titanium oxide in the product.
3. Usage Characteristics
Tabular corundum is produced through a rapid firing and cooling process, resulting in a large number of intracrystalline micropores within the grains. Most of these pores are nanoscale in size. These closed micropores effectively resist thermal shock and prevent crack propagation, giving tabular corundum superior thermal shock resistance.
Brown aluminum oxide has more open pores and fewer closed pores, and forms larger single crystals during the slower cooling process. Its high content of impurities leads to larger intergranular defects. These single crystals can crack during crushing, reducing thermal shock resistance and spalling resistance.
It is particularly important to note that pulverization and cracking of brown fused alumina are also a serious concern. Because brown aluminum oxide is made from bauxite, which contains high levels of impurities such as silicon, iron, and titanium, it requires desiliconization using coke as a reducing agent. If this is not properly treated during the smelting process, high residual carbon content can form aluminum carbide impurities, which easily pulverize when exposed to water. Such brown fused alumina particles can cause cracking or spalling when used in finished products. Tabular alumina, however, does not require the use of reducing agents such as coke due to its low impurity content. Therefore, the final product contains more than 99.5% (w) Al2O3, eliminating the risk of cracking or powdering.
4. Energy Consumption, Clean Production, and Supply Capacity
The production process of tabular alumina utilizes clean natural gas. Because the processing temperature is lower than that of molten alumina, it is more energy-efficient and environmentally friendly than brown aluminum oxide. Brown fused alumina production is energy-intensive, with the energy consumption per ton of smelting being over four times that of tabular alumina. The production of brown fused alumina produces significant amounts of waste gas and slag. Tabular corundum production uses natural gas, which contains no sulfur. Only nitrogen oxide emissions are required in the exhaust, making it easier to manage. No other waste gas or slag are emitted.
Therefore, the preparation of tabular corundum is more energy-saving and environmentally friendly, while the production of brown aluminum oxide consumes huge amounts of energy and seriously pollutes the environment.
