The effect of the coupling agent on the packing density and corrosion behavior of NdFeB and SmCo bonded magnets

The effects of the coupling agent addition on the specific density and corr osion behavior of NdFeB and SmCo bonded magnets have been investigated. The application of LICA44, a titanate coupling agent, improved the filled volu me of the epoxy-based bonded magnets, especially at high compression pressu res. When molded at 10.5 T/cm(2), specific densities of 6.2 and 6.5 g/cm(3) have been obtained for the NdFeB and SmCo bonded magnets, respectively. In corporating a coupling agent was found to eliminate visible cracks on the S mCo bonded magnets, possibly due to the improvements in the wettability and compatibility of the system. The percentage of the filled volume was incre ased by 2%-7%. Incorporating LICA44 also improved corrosion resistance of t he bonded magnets. For NdFeB, LICA44 reduced the steady state corrosion cur rent I-corr from 69 to 38 mu A/cm(2). No significant changes in the I-corr were observed for SmCo due to the stable nature of SmCo. (C) 1999 American Institute of Physics. [S0021-8979(99)44908-4].