Polymer-bonded magnets: Part I. Analytic thermogravimetry to determine the effect of surface modification on dispersion
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Polymer-bonded magnets: Part I. Analytic thermogravimetry to determine the effect of surface modification on dispersion of Nd–Fe–B fillers Jun Xiao Department of Materials Science and Engineering, Iowa State University of Science and Technology, Ames, IA 50011
Joshua U. Otaigbea) Department of Materials Science and Engineering and Department of Chemical Engineering, Iowa State University of Science and Technology, Ames, IA 50011 (Received 3 August 1998; accepted 9 April 1999)
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.
I. INTRODUCTION
In recent years, polymer-bonded magnets have been widely used for many engineering applications because of their ease of processing, low weight, and low cost relative to permanent (metallic) magnets. The polymerbonded magnets are prepared by blending a magnetic powder with a polymeric binder in a mixer or extruder. The resulting composite material can be shaped by a conventional molding process, such as injection molding, into magnetic parts with complex shapes.1,2 Optimum properties of the polymer-bonded magnets depend on the suitable choice of magnetic filler, polymer binder, and distribution of the filler. Commercial polymer-bonded magnets are limited in their application at high temperatures because of their poor heat-resistance properties.3 The heat resistance of bonded magnets can be improved by selecting heat resistance binders and high-temperature polymers. Poly(p-phenylene sulfide), frequently referred to as PPS, is an ideal polymer for making bonded magnets because of its good combination of properties in-
Based on a paper presented at the 5th International Conference on Composites Engineering, Las Vegas, 1998. a) Address all correspondence to this author. J. Mater. Res., Vol. 14, No. 7, Jul 1999
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cluding good thermal stability, low viscosity, and resistance to chemical environments. The magnetic pathways in polymer-bonded magnets critically depend on the relative association of the magnetic fillers and their level of dis
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