Average Particle Size (APS)
1. Influence on the APS value of powder
In the formulation of Mn-Zn ferrite magnets, since iron oxide accounts for about 70% or so, the Average Particle Size (APS) value of iron oxide has a great impact on the APS value of ferrite magnet powder. Generally speaking, when the APS value of iron oxide is small, the APS value of ferrite magnet powder will also be relatively small. For example, a smaller APS value can accelerate the speed of chemical reactions. This is because a small particle size means that the specific surface area of the particles is relatively larger, increasing the reaction contact area and making chemical reactions easier to proceed.
2. Limitations and impacts of the APS value size
However, it is also necessary to consider the problems caused by overly fine powder particles. If the powder particles are too fine, it will be unfavorable for subsequent pressing processes and the tendency to crystallize easily during sintering. Therefore, the APS value should not be too small. When the APS value of iron oxide is too large, during the pre-sintering stage, due to its relatively large particle size, only the diffusion reaction of the spinel phase can be carried out, and the grain growth process cannot be further carried out. As a result, the activation energy required for sintering will inevitably increase, which is unfavorable for the solid-phase reaction and will hinder the smooth progress of the solid-phase reaction, thereby affecting the final performance and microstructure of the ferrite magnets.
Specific Surface Area (SSA)
The specific surface area is also an important physical property of ferrite magnets. A larger specific surface area means that the unit mass of a substance has a larger surface area, which can provide more reaction sites for chemical reactions. It has an important impact on the chemical reactions during the preparation process of ferrite magnets, such as the interaction between substances in processes like raw material mixing and sintering. It can affect the reaction rate and the degree of reaction progress, and is thus related to the performance of the final finished ferrite magnets.
Bulk Density (BD)
The bulk density reflects the mass per unit volume of ferrite magnet powder in a naturally stacked state. It has an impact on many aspects in the production process of ferrite magnets. For example, in the batching process, the amount of raw materials can be accurately controlled based on the bulk density. In the pressing process, different bulk densities will result in different filling situations of the powder during pressing, which will further affect the density and mass uniformity of the pressed green body. Ultimately, it will also have an impact on the physical properties, mechanical properties, etc. of the finished ferrite magnets after sintering.
In conclusion, these physical properties are interrelated and jointly affect the chemical reactions in the production process of ferrite magnets, the formation of the microstructure, and the performance of the final finished products.
