Effects of the Adsorbed Dispersant Layer on Steric Stabilization in Multicomponent Nickel Pastes.

In multilayer ceramic capacitors, the internal electrodes are fabricated by printing thin layers of nickel paste, which contains a dispersant to prevent the agglomeration of nickel powder particles within the paste. We used molecular dynamics simulations and cryogenic focused ion beam-scanning electron microscopy to investigate the effects of microscopic structures in the adsorbed dispersant layer on the steric stabilization of nickel powder particles. Three dispersants were considered with different molecular structures. The simulation results indicated that stearic acid (SA) resulted in the highest steric stabilization efficiency, followed by lauric acid (LA) and oleic acid (OA). The high crystallinity of the SA and LA layers resulted in compressed molecular chains that induced strong repulsion between nickel powder particles, and the high effective thickness of the SA layer induced a stronger repulsion. The OA layer offered less steric stabilization because the molecular chains exhibited interpenetration rather than compression. The experimental results confirmed that the steric stabilization of nickel paste samples qualitatively aligned with the simulation results. Thus, multicomponent nickel pastes containing a polar solvent require a dispersant that forms a thick and highly crystalline adsorbed layer on nickel powder particles for effective steric stabilization.