Use of dispersants to enhance incorporation rate of nano-particles into electrodeposited films

The effect of a cationic dispersant, polyethyleneimine (PEI) on the co-deposition of 45-55 nm and 1.0 μm SiC particles with Ni on a rotating disk electrode is investigated. Addition of 500 ppm of PEI into a Watts bath increases the SiC fraction in the nano-composites without affecting the electrodeposition kinetics, however films have undesired properties, as evidenced by cracks. A pre-coating procedure, in which nano-particles are treated with 500 ppm PEI prior to introduction into the plating bath is described. The pre-coating method increases the SiC incorporation to values as high as 23 vol%, one of the highest reported values for nano-particles in electrodeposited films, without decreasing the current efficiency. In addition, the pre-coating method facilitates bath-composition optimization when, for example, leveling agents are employed; otherwise the leveling agent and PEI competitively adsorb onto the SiC particles. The efficacy of employing the pre-coating procedure in manufacturing, where plating baths need a long life, may be satisfactory. Strategies where dispersants are first attached to ceramic particles prior to integration into a plating bath containing other additives may lead to high volume fractions of particles thus harder deposits. The detailed procedures to achieve high-volume fractions required modification when transitioning from micron- to nano-sized particles.