Dispersions of magnetic particles in non-aqueous media

Abstract

The dispersion quality of magnetic inks made from iron based metal particles and cobalt modified iron oxide particles has been investigated using a magnetic probing technique known as DIMAG (Dispersion by MAGnetic measurement). Di(2-ethyl hexyl) phosphoric acid is used as a model dispersant while a vinyl acetatevinyl chloride copolymer that combined the functionality of a dispersant and a binder is used as a wetting binder. A comparison of the DCON values measured at different binder levels to the tape characteristics shows that dispersions with large negative DCON signals result in good quality tapes. To study the degradation of magnetic particles, the interaction of water vapor with iron based metal particles was measured under different temperature and humidity conditions using a flow microcalorimetric (FMC) technique. Water uptake by iron based metal particles increased linearly with relative humidity ranging from 30% to 70% RH in the temperature range 30°C to 70°C. Mossbauer measurements showed that the ratio of core iron to oxide iron decreased during aging. Particles coated with hydrophobic PVC exhibited much less water uptake than particles coated with a less hydrophobic polymer, poly(vinyl alcohol). A computational investigation using the method of molecular dynamics was also undertaken to characterize the state of magnetic particle dispersions. The simulations revealed that the microstructure of the spherical particulate dispersions consists of chain-like clusters resulting from magnetic dipole alignment. Acicular particles formed clusters such as dimers, chains and rings. The effect of fluid viscosity on the dispersion quality and the response of the magnetic dispersions to an external DC magnetic field are also reported.