DEGREE AND STABILITY OF MAGNETIC DISPERSIONS - SEDIMENTATION, RHEOLOGICAL, AND MAGNETIC-PROPERTIES

There is a distinct correlation between the dispersion qualities of magnetic acicular particles as measured by slush grind rheology, sedimentation test, and coating magnetic properties. Sedimentation time measurement is a very sensitive tool to evaluate the degree of dispersion and dispersion stability. Sedimentation, rheology, and coating magnetic properties show that 'steric stability' is essential to maintain the excellence of magnetic particle dispersion. Some surface active agents provide excellent pigment dispersion but poor stability with time, whereas other chemical compounds adsorbed on a particle surface can provide a very high degree of dispersion with excellent dispersion stability. Results of particle size evaluation from sedimentation measurements show five to six times improvement in the degree of dispersion due to suitable surface active agents.