Synthesis Method of Magnesia-alumina Spinel
Synthesis method of magnesia-alumina spinel
Natural magnesia-alumina spinel resources cannot meet the needs of industrial production, and the commonly used magnesia-alumina spinel is synthetic. The synthesis methods mainly include sintering method, electrofusion method, precipitation method, drying and rinsing method, and the like. Among them, the first two methods of producing magnesia-alumina spinel are suitable for industrial use. Compared with the electrofusion method, the sintering method has the advantages of simple synthesis process, low production cost, and the advantages of natural raw material synthesis, and thus rapid development.
The main method of synthesis of magnesia-alumina spinel:
(1) Sintering method: refers to raw materials such as aluminum hydroxide and sintered alumina, and magnesium-containing raw materials such as magnesium carbonate and magnesium hydroxide, which are compounded according to requirements, and are finely ground together to press the ball (blank) at 1750 ° C or higher. The high-temperature calcination in a rotary kiln or a shaft kiln can obtain a magnesia-alumina spinel synthesized by sintering. Specifically, it can be divided into a one-step sintering method and a two-step sintering method.
One-step sintering synthetic magnesite / synthetic light burnt magnesium powder + bauxite raw material → dry co-grinding → forming → firing → spinel clinker
Two-step sintering synthetic magnesite and bauxite raw material → dry co-grinding → forming → light burning (about 1300 ° C) → crushing → forming → firing → spinel clinker
Theoretically, the more the number of repeated calcinations in the synthesis of magnesia alumina spinel, and the finer grinding of the product after each calcination, the better the synthesis effect.
(2) Electrofusion method: Synthetic magnesia-alumina spinel sand can be selected from magnesium-containing aluminum-containing raw materials of various purities. In the raw material for synthesizing spinel, the MgO content is always selected within the range of 35% to 50%. The highest or too low MgO content is detrimental to the melting of the synthetic sand. The high viscosity makes the melt difficult to cast, and the addition of chromium ore is beneficial to the melting and pouring of the melt. The formulated mixture can be melted in a tilting electric furnace or a vortex melting furnace.
By controlling the cooling rate of the furnace body, an fused spinel having a different degree of crystallization can be obtained. When a magnesia-alumina spinel product is produced using a spinel having a high structural defect, it is ensured that the desired sintering activity is obtained at the time of firing.