A chromate/silicate surface treatment for providing an aluminum heat exchanger with a corrosive-resistent hydrophilic coating. The subject process includes sequentially immersing an aluminum heat exchanger in a series of chemical solutions. The chemical solutions include a cleaning solution, followed by a rinse solution, chromate solution, additional rinse solution, and a silicate solution. The chemical concentrations of the cleaning solution, chromate solution and silicate solution are precisely controlled in order to avoid producing a coating which emits a musty odor.
The present invention relates to a pickling agent for the chemical conversion coating of a heat exchanger which is capable of cleaning the complicated structure comprising fins and tubes of a heat exchanger in preparation for the successful formation of a chemical conversion film, a method of pickling a heat exchanger, a method of treating a heat exchanger comprising said pickling method, and a heat exchanger produced by using said treating method. The present invention provides pickling agent for the chemical conversion coating of a heat exchanger which comprises an acidic aqueous solution containing nitric acid and/or sulfuric acid and at least one metal and/or metal oxoanion salt derived from any metal selected from the group consisting of iron, nickel, cobalt, molybdenum and cerium.
A hydrophilic coating can be optionally corrosion resistant and/or microbial resistant for a substrate such as a heat exchanger. The coating is provided by a zeolite layer that can be formed from a synthesis solution comprising a structure directing agent, a base, a silicon source, an aluminum source, and a solvent. In one preferred embodiment, the synthesis solution comprises tetrapropylammonium hydroxide, sodium hydroxide, aluminum oxide, tetraethylorthosilicate, and water. The layer is characterized by a zeolite MFI structure and by a composition having the formula of M.sub.n/m [Al.sub.n Si.sub.(96-n) O.sub.192 ], or [Al.sub.n Si.sub.(96-n) O.sub.192 ].4[(CH.sub.3 CH.sub.2 CH.sub.2).sub.4 N--OH] wherein M is a metal ion of valence m.sup.+ (e.g., Na.sup.+) and 27>n>=0. After formation of the coating, the organic structure directing agent can be left intact inside the zeolite coating to make the coating corrosion resistant. Alternatively, and after removal of the organic structure directing agent, a biocidal metal ion can be incorporated into the coating by an ion exchange process to render the coating microbial resistant. A hydrophilic coating that is also corrosion resistant and microbial resistant can be made by a zeolite coating with two sub-layers--the bottom sub-layer being corrosion resistant and the top sub-layer being microbial resistant.
A hydrophilic coating can be optionally corrosion resistant and/or microbial resistant for a substrate such as a heat exchanger. The coating is provided by a zeolite layer that can be formed from a synthesis solution comprising a structure directing agent, a base, a silicon source, an aluminum source, and a solvent. In one preferred embodiment, the synthesis solution comprises tetrapropylammonium hydroxide, sodium hydroxide, aluminum oxide, tetraethylorthosilicate, and water. The layer is characterized by a zeolite MFI structure and by a composition having the formula of M.sub.n/m [Al.sub.n Si.sub.(96-n) O.sub.192 ], or [Al.sub.n Si.sub.(96-n) O.sub.192 ].multidot.4[(CH.sub.3 CH.sub.2 CH.sub.2).sub.4 N--OH] wherein M is a metal ion of valence m.sup.+ (e.g., Na.sup.+) and 27>n>=0. After formation of the coating, the organic structure directing agent can be left intact inside the zeolite coating to make the coating corrosion resistant. Alternatively, and after removal of the organic structure directing agent, a biocidal metal ion can be incorporated into the coating by an ion exchange process to render the coating microbial resistant. A hydrophilic coating that is also corrosion resistant and microbial resistant can be made by a zeolite coating with two sub-layers--the bottom sub-layer being corrosion resistant and the top sub-layer being microbial resistant.
