The long term stability of mercury based ferromagnetic liquids

The stability over very long ageing times of iron particles in mercury and the effect of coatings on this stability has been investigated. To study this, ferromagnetic liquids containing 2% by weight of iron in mercury have been prepared by electrodeposition of iron onto an agitated mercury cathode and a mercury/tin amalgam cathode. Measurements of coercivity at 77°K and at room temperature have been made on these samples and show that particle radii in the range 20Å-40Å exist in the tin-free fluid, and between 15Å-30Å in the ferrofluid containing tin. Electron microprobe analysis has shown that a tin coating is present on the iron particles after tin addition. Ageing at 425°K and plotting log(radius)/ log(time) reveals two distinct growth characteristics in both coated and uncoated samples. Previous results obtained by Luborsky can also show these two regions. Electron micrographs of coated samples after ageing show the presence of clustering and particle growth within the clusters. The short term characteristics of the log/log plot can be understood in terms of cluster formation during this period. At the longer ageing times, diffusional growth is thought to be the dominant process.