DESIGN, ASSEMBLY AND CHARACTERIZATION OF COMPOSITE ...

metal inks have been reported for Robocasting and this is likely due to lack of a readily
available powder source and difficulty in sintering. This thesis project seeks to assemble
BaTiO3-Ni composite structures using an aqueous BaTiO3 ink and requires development
of an aqueous colloidal ink of Ni to serve as the metal phase. Of critical importance is
matching the flow behavior of the inks, the amount of shrinkage during drying, the rate
and amount of shrinkage during sintering, and the chemical stability of both species
during the sintering operation.
Ni has outstanding corrosion resistance and relatively low cost. Commercial
production of Ni powder usually involves hydrothermal reduction of Ni salt 140 or
decomposition of nickel carbonyl (Mond Process), 141 through which particles as small as
100 nm with controlled shape and morphology may be synthesized. In electronics
industry, Ni powder has generally been used with organic solvents or polymeric binders
for screen printing, tape casting, or conductive trace printing. At room temperature in air,
Ni spontaneously develops a NiO surface layer of several atoms thick in air 133, 134 and this
layer is electrically conductive. After equilibrium in water, Ni particles present a stable
surface chemistry of NiO and is relatively stable in basic condition. 135 This suggests that
Ni powder may be processed via aqueous colloidal route and should possess an
amphoteric surface chemistry typical of most metal oxides. Aqueous Ni suspensions have
been studied with the use of various polymeric dispersants 136-139 for fabrication of Ni
objects through injection molding or slip casting to achieve up to 97% of theoretical
density after sintering. 136
Here, an aqueous colloidal Ni gel is developed for use in the Robocasting process.
Complex nickel structures are printed and pressureless sintered to achieve >99.0%
113