PARTICLE-SIZE EVALUATION OF FERRITE MATERIALS

In ferrite powder processing, small particle size differences are important because they can greatly influence the intrinsic grain size and ultimate electrical and physical properties of the final fired products. In addition, careful measurement of particle size is a most important step in the control of powder quality and uniformity. For this reason, a study was undertaken to compare three commercially available methods of measuring the particle size of ferrite powders. Air permeability, air sedimentation and resistance change were chosen because all three techniques are widely used in the ceramic and chemical processing industries. A 16 kg batch of the following oxides (in wt%) was the starting material: Fe//2O//3 equals 64, MgO equals 11, ZnO equals 9 and MnO equals 16. Using the air permeability method, a significant amount of particle size variation with porosity was noted. It appears that this method is also sensitive to the state of agglomeration of the material. The air sedimentation method was also somewhat affected by the state of agglomeration of the material. With this method, however, powder heat treated for 2 h at 900 degree C was magnetically active. Techniques such as degaussing, ultrasonic agitation and the addition to cationic dispersants to the heat-treated samples all failed to adequately disperse the particles.