Methods for both coating a substrate with aluminum oxide and infusing the substrate with elemental aluminum
Methods of aluminizing the surface of a metal substrate. The methods of the present invention do not require establishment of a vacuum or a reducing atmosphere, as is typically necessary. Accordingly, aluminization can occur in the presence of oxygen, which greatly simplifies and reduces processing costs by allowing deposition of the aluminum coating to be performed, for example, in air. Embodiments of the present invention can be characterized by applying a slurry that includes a binder and powder granules containing aluminum to the metal substrate surface. Then, in a combined step, a portion of the aluminum is diffused into the substrate and a portion of the aluminum is oxidized by heating the slurry to a temperature greater than the melting point of the aluminum in an oxygen-containing atmosphere.
1. A method for both coating a substrate with aluminum oxide and infusing the substrate with elemental aluminum, the method comprising:
providing a substrate having a Cr-containing surface;
providing a metal powder/polymer binder slurry, the slurry comprising a solvent, an organic binder, and metal granules;
dispersing the slurry upon the Cr-containing surface;
after dispersing the slurry, exposing the slurry to air and maintaining the temperature of the slurry and substrate below 80° C. to remove at least a portion of the solvent from the slurry; and
after removing at least a portion of the solvent from the slurry, in a combined step, both exposing the binder, metal granules and substrate to air and heating the remaining slurry and substrate to a temperature of from 1000° C. to 1200° C. to both diffuse the at least a portion of the metal of the metal granules into the substrate and coat the substrate with aluminum oxide.
2. The method of claim 1 wherein the substrate has a Cr—Fe-containing surface.
3. The method of claim 2 wherein the Cr—Fe-containing surface further comprises one or both of Co and/or Ni.
4. The method of claim 1 wherein the metal of the metal granules comprise aluminum.
5. The method of claim 4 the granules are from between 0.1 and 45 um in diameter.
6. The method of claim 1 wherein the metal powder/polymer binder slurry comprises organic constituents that carburize and/or volatilize at temperatures near or above the melting point of the metal.
7. The method of claim 1 wherein during the combined step at least a portion of the aluminum is oxidized.
8. The method of claim 1 wherein the metal of the metal granules comprise an aluminum alloy.
9. The method of claim 1 wherein the binder of the metal powder/polymer binder slurry is an organic based system having a final evaporation or decomposition temperature greater than 100° C.
10. The method of claim 9 wherein during the exposing the slurry to air and maintaining the temperature of the slurry and substrate below 80° C. the metal of the metal powder/polymer binder slurry remains unoxidized.
11. The method of claim 1 wherein the metal powder/polymer binder slurry comprises a ratio of binder to powder within the range of 10:1 to 1:10 by volume.
12. The method of claim 1 wherein the dispersing the slurry upon the Cr-containing surface comprises applying the slurry by spray dispensing, paste dispensing, painting, dip coating, stencil printing, or screen printing.
13. The method of claim 1 operating as a continuous process on a plurality of substrates.
14. The method of claim 1 wherein the metal substrate is a component of a solid oxide fuel cell stack or a boiler device.