After brown fused aluminum oxide is roasted in an oxidizing atmosphere, the brown particles of brown fused aluminum oxide turn blue, which is caused by the solid solution Ti2O3. Ti2O3 is the only oxide of titanium that can be dissolved in α-alumina grains, and TiO2 is also the oxide with the best thermal stability of titanium. Above 1000℃, oxygen can diffuse into α-alumina grains, oxidizing Ti2O3 into more stable TiO2. Then it wraps around α-alumina grains.
The TiO2 nuclei continue to aggregate and grow at a rate that is temperature-dependent. Once the titanium dioxide grains reach a size of 0.01 to 0.1 μm, they begin to scatter light like a colloidal suspension. This selective scattering of blue light with a shorter wavelength makes α-alumina grains appear blue. This selective scattering of small particle light is called the Tyndall effect. If the TiO2 nuclei are allowed to grow to about 0.1 μm, they will no longer only scatter blue light, but scatter all wavelengths of light, and the roasted brown fused aluminum oxide will become light gray.
Only brown fused alumina oxide containing solid solution titanium oxide will turn blue after roasting. Brown fused aluminium oxide with low Ti2O3 content will not turn blue. Like many characteristics of particulate materials, the blue color after roasting is the average color of all particles in the sample. In a brown fused alumina for abrasive sample after roasting, the proportion of blue particles is in the high to medium range of typical technical conditions of titanium dioxide (TiO2) content of 2.4% to 3.0%, and non-blue particles are below the lower limit of technical conditions. There may be some brown fused aluminum oxide whose chemical composition is within the typical technical conditions range, but does not turn blue after roasting. This is mostly a mixture of low titanium dioxide particles that is doped with some high titanium dioxide particles.
First of all, we need to talk about raw materials: the main raw material of brown fused aluminum oxide is high-aluminum bauxite, which is refined and crystallized through electrofusion. It is suitable for abrasives, steel, metallurgical casting, refractory materials, and water filtration in multiple industries. However, because many silicon carbide powder manufacturers have been shut down due to environmental protection issues such as outdated equipment and illegal sewage discharge in the production of high-alumina bauxite, the supply of bauxite has become tight, which has caused many brown fused alumina oxide manufacturers to stop production due to the inability to purchase raw materials. With fewer manufacturers, the product is in short supply, and the price will naturally rise, which is the main reason for the price increase.
Currently, the country is vigorously treating the illegal mining of bauxite raw materials and environmental protection issues such as the aluminum oxide kiln and corundum smelting, shutting down outdated production facilities and illegal sewage discharge enterprises, causing upstream and downstream supplies to be tight. Therefore, some brown fused aluminum oxide manufacturers have reported that they have stopped production due to the inability to purchase raw materials. With fewer brown fused aluminum oxide manufacturers, there is a shortage of supply, which has led to a price increase. However, from the perspective of national policies, the country attaches great importance to environmental protection. In order to control pollution, it is inevitable to shut down some brown fused aluminum oxide manufacturers with outdated processes. There is also the issue of energy consumption. The abrasive industry is a high-energy-consuming industry. To meet national environmental protection regulations, the demand for electricity itself will be very large, and the rise in electricity prices has greatly increased the production cost of factories, which has forced enterprises to increase the price of brown fused aluminum oxide.