In the production process of tabular alumina , the variegated color problem has always been an important factor affecting the quality and appearance of the product. These variegated colors not only affect the aesthetics of the product, but may also have an adverse effect on the performance of the product.
1. The influence of raw materials
The main raw material of tabular corundum is alumina, and its purity and chemical composition have a decisive role in the color of the final product. First, if alumina contains trace amounts of impurity elements such as MgO and CuO, these elements may react with alumina at high temperatures, resulting in the product appearing in variegated colors such as light yellow or lavender. In addition, if the content of iron metal (such as Fe2O3) in the raw material is too high or is not effectively removed, impurities such as black and gray will also be left in the product.
In addition to the impurity content, the sulfur content of the raw material is also a key factor affecting the color of tabular corundum. Studies have shown that when the sulfur content in alumina is too high, sulfur ions will penetrate into the lattice of alumina during high-temperature calcination, affecting the growth and color change of the crystal. Especially when the crystal size is large, the influence of sulfur ions is more significant, which can easily cause the product to turn yellow.
2. Influence of production equipment and process
The production process of tabular alumina involves multiple links, including grinding, molding, drying, sintering, etc. In these links, the irregular operation of equipment and process may introduce impurities, thus affecting the color of the product.
1. Equipment material: The silos and conveying equipment used in the production of tabular corundum are mostly made of metal, containing iron, titanium, nickel, chromium and other components. If the equipment is not operated properly during maintenance, metal debris such as welding heads and steel plate scraps may be mixed into the raw materials and enter the high-temperature vertical kiln. Under high temperature conditions, these metal debris will gasify, producing metal vapor containing iron, titanium, nickel, chromium and other components, which will penetrate into the semi-molten tabular corundum balls, resulting in the product appearing in black gray, rose red or blue and other colors.
2. Atmosphere control: The atmosphere distribution in the kiln also has an important influence on the color of tabular alumina . In a reducing atmosphere (such as a high CO concentration), the combined effect of ferrous ions and titanium ions will make the tabular corundum appear blue or black; in an oxidizing atmosphere, affected by iron ions, chromium ions, and manganese ions, the tabular corundum may appear rose red or darker. Therefore, it is crucial to reasonably control the atmosphere distribution in the kiln to reduce the production of variegated balls.
3. Balling technology: Domestic production factories generally use drum balling machines for balling, but the control of parameters such as speed, water addition, and powder addition during the balling process is not accurate enough, which can easily lead to stratification during the balling process, thereby affecting the color uniformity of the product. In addition, the method of drying the spheres may also affect the color of the product.
3. Influence of smelting process
The length of smelting time and the maturity of the process are also important factors affecting the color of tabular alumina. Insufficient smelting time or immature process may result in the failure to fully remove impurities in the raw materials or the failure to fully form alumina crystals, leaving variegated colors in the product. Especially when the smelting temperature is not high enough or the insulation time is not long enough, the growth of alumina crystals is restricted and is more susceptible to color changes caused by impurity elements.
