Patent ID: 7575694

Claim:
A process of selectively stripping a metallic coating on an external surface of a substrate without attacking an internal surface defined by an internal passage within the substrate, the process comprising the steps of: depositing within the internal passage a molten wax of a thermally-decomposable polyethylene wax having a melting temperature above 75° C.; allowing the molten wax to cool and solidify to form a solid mask of the polyethylene wax within the internal passage and mask the internal surface defined by the internal passage; treating the substrate with an aqueous solution at a temperature below the melting temperature of the polyethylene wax, the aqueous solution containing an acid having the formula H x AF 6 where A is silicon, germanium, titanium, zirconium, aluminum, or gallium, and x has a value of one to six, the aqueous solution substantially removing the metallic coating from the external surface of the substrate, the polyethylene wax being substantially unreactive with the aqueous solution and preventing the aqueous solution from contacting the internal surface of the substrate; and then heating the substrate to melt the polyethylene wax and remove a portion thereof and then further heating the substrate to thermally decompose a remaining portion of the polyethylene wax without producing a hazardous byproduct.