Messi Biology states that magnesium oxide (MgO) as an insulating coating for silicon steel not only provides isolation but also significantly improves the processing and magnetic properties of silicon steel through chemical reactions and physical protection. The main mechanisms are as follows:
- Isolation:During the high-temperature annealing process, silicon steel sheets undergo recrystallization and grain growth. Without an effective insulating layer, adjacent silicon steel sheets will adhere due to the diffusion of metal atoms. The MgO coating acts as a physical barrier, preventing the silicon steel sheets from bonding together and improving the stacking factor and stamping performance of the silicon steel sheets.
- Reaction to Form a Glassy Layer:During high-temperature annealing, MgO reacts with silicon dioxide (SiO₂) on the surface of the silicon steel to form magnesium silicate (Mg₂SiO₄) or a magnesium silicate glassy layer. This glassy film has good adhesion and stability, which not only enhances insulation performance but also improves the oxidation resistance of the silicon steel.
- Improvement of Magnetic Properties:The MgO coating helps suppress abnormal grain growth of secondary recrystallization in silicon steel, promoting uniform and stable grain growth, thereby improving the magnetic properties of silicon steel (such as reducing iron loss and increasing magnetic permeability).
- Lubrication and Protection:During subsequent rolling and stamping processes, the MgO coating can reduce friction and wear between the die and the silicon steel, acting as a lubricant. At the same time, it can protect the surface of the silicon steel from mechanical damage.
- Tension Adjustment:The glassy layer forms a certain amount of tension after annealing. This tension can effectively reduce the hysteresis loss of silicon steel sheets, further improving magnetic properties.