Polymer-bonded magnets: Part I. Analytic thermogravimetry to determine the effect of surface modification on dispersion of Nd–Fe–B fillers

The degree of mixing is a critical factor in controlling the magnetic properties and mechanical properties of polymer-bonded magnets. Pretreatment of the NdFeB fillers with a silane coupling agent improved the degree of mixing of the fillers in the polymer matrix. The observed improvement in the degree of mixing of the silanetreated fillers was ascribed to good wetting as evidenced by viscosity reduction of the coupled polymer-bonded magnets. However, traditional materials characterization methods could not be used to quantitatively determine the degree of mixing of the polymer-bonded magnets. This paper describes use of thermogravimetric analysis to quantify the degree of mixing of polymer-bonded magnets. The intensity of segregation of the fillers was calculated from the measured weight change of the magnetic filler in the samples. The results of this work showed that the thermogravimetric analysis method was useful in determining the degree of mixing of NdFeB fillers in polymer-bonded magnets.