Electroless plating of silver onto graphite
A one-pot process for the electroless-plating of silver onto graphite powder is disclosed. No powder pretreatment steps for the graphite, which typically require filtration, washing or rinsing, are required. The inventive process comprises mixing together three reactant compositions in water: an aqueous graphite activation composition comprising graphite powder and a functional silane, a silver-plating composition comprising a silver salt and a silver complexing agent, and a reducing agent composition.
1. An aqueous electroless plating composition for plating graphite with silver, comprising:
(A) graphite powder, present in the range of 0.1-100 g/L;
(B) a silver salt, present in the range of 0.01-50 g/L;
(C) a silver complexing agent, present in the range of 0.01-35 g/L;
(D) a nitrogen-containing silane present in the range of 0.01-20 w % of the graphite weight; and
(E) a reducing agent for the silver salt, present in the range of 1-50 times the moles of silver salt,
wherein the graphite powder of (A) is not pretreated by wet chemical activation, oxidation or heating, and
wherein the nitrogen-containing silane of (D) is selected from the group consisting of 3-isocyanatopropyltriethoxy-silane, 3-isocyanatopropyltrimethoxysilane, 2-cyano-ethyltrimethoxysilane; 2-cyanoethyl-triethoxysilane, 3-cyanopropyl-trimethoxy-silane, 3-cyanopropyltriethoxysilane, 3-cyanopropylmethyldi-methoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyl-methyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 4-aminobutyl-triethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-amino-ethyl)-3-aminopropyltriethoxy-silane, N-(2-aminoethyl)-3-aminopropyl-methyl-dimethoxysilane, aminopropylsilanetriol, N-(2-aminoethyl)-3-aminopropyl-silanetriol, aminophenyltrimethoxysilane, 3-thiocyanatopropyl-triethoxysilane, 3-(2-imidazolin-1-yl)propyltriethoxysilane, and any combination of the above.
2. The plating composition of claim 1 in which the silver salt is selected from the group consisting of silver nitrate, silver sulfate, and silver chloride.
3. The plating composition of claim 1 in which the silver complexing agent is selected from the group consisting of ammonium hydroxide, ethylenediamine, methylamine, and ethylamine.
4. The plating composition of claim 1 wherein the reducing agent is selected from the group consisting of aldehydes, polyols, tartrate, tartaric acid, monosaccharides, disaccharides, polysaccharides, hydrazine, and hydrazine hydrate.