In the above-noted co-pending application, there is disclosed a method of co-nucleating precious metal powders with a small percentage of a refractory oxide, most particularly titania or zirconia. The process involves a slow precipitation from an acidic solution with ammoniacal hydrazine, followed by a heat treatment. Such powders exhibit increased sintering temperatures, and find utility when formulated as pastes, with a small amount of glass frit as binder, in thick film electronic applications, and in catalysis.
The present invention is based, in one part, on the discovery that with a somewhat altered procedure, the process described above can be applied to nickel and the product exhibits a significantly increased oxidation resistance. The present invention is based, in a second part, on the discovery that with an essentially different process, precious metal powders of both increased density and higher sintering temperatures are produced.
In the above-mentioned co-pending application, it is noted that the addition of refractory oxides as distinct ingredients in certain thick film compositions is known, that the addition of copper oxide to gold to make a so-called "fritless" thick film conductors is known, and that it is also known to improve bulk metal properties such as creep strength and tensile strength with a refractory oxide as a distinct second phase, e.g. dispersion hardening. The surprising and novel aspect of the present invention, as well as that described in said co-pending application, is the significantly improved thermal properties of metal powders produced in accordance herewith.