Ultrasound enhanced ferrite plating; bringing breakthrough in ferrite coating synthesized from aqueous solution

Applying power ultrasound waves (19.5 kHz, 600 W) to 300 ml of FeCl/sub 2/ aqueous solution (pH=7.0) at 70/spl deg/C, we successfully encapsulated polyacrylate spheres of two sizes, 0.25 /spl mu/m and 4.5 /spl mu/m in average diameter, with ferrite coatings of a magnetite-maghemite mixed solution. This broke the previous lower limit (0.3 /spl mu/m) of the size of the particles to be encapsulated; without application of the ultrasound waves, the ferrite coating became discontinuous or insular. The ultrasound waves produce on the polymer surfaces OH groups (which work as ferrite nucleation sites), and remove the isolated ferrite particles (grown from the solution) from the surface of the ferrite coatings. This improved the surface quality of the ferrite coatings. The ferrite-encapsulated particles will greatly improve the performance of the enzyme immunoassay, which has been put to clinical use as a cancer test reagent with insular-ferrite-coated particles.