Aluminum slurry coatings and methods of their formation and use

Patent metadata

Field	Value
Publication number	US-11925988-B2
Application number	US-202117410512-A
Country	US
Kind code	B2
Filing date	Aug 24, 2021
Priority date	Aug 24, 2021
Publication date	Mar 12, 2024
Grant date	Mar 12, 2024

Abstract

Methods for reducing a concentration of hexavalent chromium within a first aluminum slurry by adding a reducing agent to form a second aluminum slurry are provided. The reducing agent causes a chemical reduction reaction with the hexavalent chromium compound of the first aluminum slurry to form a trivalent chromium compound within the second aluminum slurry such that a first weight ratio of hexavalent chromium to trivalent chromium in the first aluminum slurry is decreased to a second weight ratio of hexavalent chromium to trivalent chromium in the second aluminum slurry, with the second weight ratio being less than the first weight ratio.

First claim

What is claimed is:

1. A method of reducing a concentration of hexavalent chromium within a first aluminum slurry containing a first aluminum powder, a phosphoric acid, a hexavalent chromium compound, and water, the method comprising:
adding a reducing agent to the first aluminum slurry to form a second aluminum slurry, wherein the reducing agent causes a chemical reduction reaction with the hexavalent chromium compound to form a trivalent chromium compound within the second aluminum slurry such that a first weight ratio of hexavalent chromium to trivalent chromium in the first aluminum slurry is decreased to a second weight ratio of hexavalent chromium to trivalent chromium in the second aluminum slurry, with the second weight ratio being less than the first weight ratio, wherein the first aluminum slurry, prior to the addition of the reducing agent, comprises: the first aluminum powder, the phosphoric acid, 1% by weight to 5% by weight hexavalent chromium, 0.1% by weight to 1% by weight trivalent chromium, and water.

2. The method of claim 1 , further comprising:
prior to adding the reducing agent, determining an amount of hexavalent chromium present in the first aluminum slurry, wherein the reducing agent is added in an amount based on the determined amount of hexavalent chromium present in the first aluminum slurry.

3. The method of claim 2 , wherein the reducing agent is added in an amount of 100% by weight to 115% by weight of hexavalent chromium present to reduce the determined amount of hexavalent chromium present in the first aluminum slurry to trivalent chromium.

4. The method of claim 2 , wherein adding the reducing agent to the first aluminum slurry comprises:
titrating the reducing agent based on the determined amount of hexavalent chromium present in the first aluminum slurry.

5. The method of claim 1 , wherein the reducing agent is added in an amount sufficient to reduce the concentration of hexavalent chromium to 0.1% by weight or less within the second aluminum slurry.

6. The method of claim 1 , wherein the reducing agent is added in an amount sufficient to reduce the concentration of hexavalent chromium to 0.01% by weight or less within the second aluminum slurry.

7. The method of claim 1 , wherein adding the reducing agent to the first aluminum slurry comprises:
titrating the reducing agent until a response indicator signals that the first weight ratio of hexavalent chromium is decreased to the second weight ratio.

8. The method of claim 7 , wherein the response indicator is a color change from a first color of the first aluminum slurry to a second color of the second aluminum slurry that is different than the first color.

9. The method of claim 1 , wherein the reducing agent comprises aluminum, iron, zinc, or a mixture thereof.

10. The method of claim 1 , wherein the reducing agent comprises a second aluminum powder.

11. The method of claim 10 , wherein adding the second aluminum powder to the first aluminum slurry increases a total aluminum concentration in the first aluminum slurry by 1% to 20% from a first aluminum concentration.

12. The method of claim 10 , wherein the second aluminum slurry, after the addition of the second aluminum powder and resulting chemical reduction reaction, comprises: the first aluminum powder, the second aluminum powder, the phosphoric acid, less than 0.1% by weight hexavalent chromium, 0.5% by weight to 3% by weight trivalent chromium, and water.

13. The method of claim 10 , wherein the second aluminum powder added to the first aluminum slurry is an unoxidized aluminum powder.

14. The method of claim 10 , wherein the second aluminum powder added to the first aluminum slurry is an oxidized aluminum powder.

15. The method of claim 1 , further comprising:
heating the first aluminum slurry to facilitate the chemical reduction reaction.

16. The method of claim 1 , wherein the first weight ratio is 5 or greater, and wherein the second weight ratio is 5 or less.

17. The method of claim 1 , further comprising:
after adding the reducing agent, applying the second aluminum slurry to a surface of a substrate to form a coating thereon.

Assignees

• Gen Electric

Inventors

• Kool Lawrence Bernard
• Rhoads Mark Alan

Classifications

• B22F9/18 Primary

  with reduction of metal compounds · CPC title

• B22F1/145

  Chemical treatment, e.g. passivation or decarburisation · CPC title

• B22F1/147

  Making a dispersion · CPC title

• B22F2301/052

  Aluminium · CPC title

• B22F2302/25

  Oxide · CPC title