Shear magnetometry for the analysis of magnetic tape dispersions

Applying mechanical shear to a magnetic dispersion during a magnetic measurement breaks up flocculates and particle networks and thus greatly simplifies the interpretation of the magnetization behaviour. Without the hysteresis due to the thixotropy of the dispersion, the area between the initial and subsequent magnetization curves is a simple measure of the amount of material in primary agglomerates and therefore the quality of the dispersion. The orientability of the dispersion can be determined from the approach to saturation of the magnetization curve. Groups of a few particles can be better oriented than large agglomerates, so a qualitative estimate of the size of the agglomerates can be made. There is good correlation between these simple measurements on dispersions and the properties of the resulting tapes. Despite small particle sizes, metal particle formulations can be dispersed to single particles by kneading, confirming that the function of kneading lies in wetting and dispersing the particles rather than in compressing aggregates.