Messi Biology stated that the particle size of magnesium oxide has a significant impact on the suspension and coating properties of magnesium oxide. Silicon steel grade magnesium oxide is generally made into spherical particles, which are easy to roll, have small movement resistance between particles, and have good fluidity. On the coating, the filling performance between particles is good, and the coating is dense and uniform. In addition, magnesium oxide must have a certain particle size distribution to ensure the circulation of moisture and annealing ambient gas during the high-temperature annealing process of silicon steel grade steel coils. Generally, the particle size is required to reach 70% below 5 μm.
In the preparation process of silicon steel grade magnesium oxide, particle size control has always been a difficult problem. Since the preparation of magnesium oxide is obtained by calcining intermediates, it is first necessary to control the particle size and shape of magnesium hydroxide or basic magnesium carbonate intermediates. The study of crystal morphology shows that when the temperature is too low, the crystal formation is incomplete, and it is easy to agglomerate into larger crystal grains. When the temperature is too high, the formation rate of crystal nuclei becomes smaller, the growth rate of crystals becomes larger, and large grains are easily formed. In addition, the thermal movement of particles is intensified at high temperature, and it is easy to collide to form larger particles.
In the preparation of the basic magnesium carbonate intermediate, the reaction temperature is generally controlled at 70-80°C to obtain a suitable particle size of the basic magnesium carbonate. If the thermal decomposition temperature is higher than 85°C, the product particles will increase significantly, and the average particle size of magnesium oxide is >5μm; if the thermal decomposition temperature is lower than 55°C, the decomposition will be incomplete in the decomposer, resulting in a decrease in yield. The particle size of magnesium oxide not only depends on the particle size of the intermediate, but also has a great influence on it during the calcination process. Magnesium oxide may agglomerate at high temperatures, resulting in excessively large particle sizes. Some studies have found that when the basic magnesium carbonate intermediate is roasted, the method of gradually increasing the temperature from low temperature can effectively avoid product sintering and ensure that the particle size of magnesium oxide is small.