Surface treatment to passivate sublimation surfaces to hydrophobic contaminants

Patent metadata

Field	Value
Publication number	US-9988723-B2
Application number	US-201514957413-A
Country	US
Kind code	B2
Filing date	Dec 2, 2015
Priority date	May 17, 2012
Publication date	Jun 5, 2018
Grant date	Jun 5, 2018

Abstract

The sublimation capability of a porous metal plate used in a sublimator is maintained by heating the porous metal plate at an elevated temperature in a flowing stream of oxygen for an extended period of time to form an oxidized surface. A short chain molecule, such as citric acid, is attached to the oxidized surface having multiple functional carboxylate groups and no hydrophobic tail.

First claim

The invention claimed is:

1. A method of maintaining sublimation capability of a porous metal plate having a porous passivated surface for use in a sublimator, the method comprising:
heating the porous metal plate at an elevated temperature in a flowing stream of oxygen for an extended period of time to form a first portion of the passivated surface with an uncharged oxide; and
after the heating step, attaching a plurality of short chain molecules to form a second portion of the passivated surface, each short chain molecule having multiple functional carboxylate groups and no hydrophobic tail;
wherein the plurality of short chain molecules include a four carbon or less organic acid having at least one carboxylate group.

2. The method of claim 1 , wherein the elevated temperature ranges from about 900° F. (482° C.) to about 1200° F. (649° C.).

3. The method of claim 1 , wherein the porous plate is heated at the elevated temperature for at least four hours.

4. The method of claim 1 , wherein the porous plate is made from a metal selected from the group consisting of stainless steel and nickel based alloys.

5. The method of claim 4 , wherein the porous plate is made from stainless steel.

6. The method of claim 1 , wherein the plurality of short chain molecules comprise citric acid.

7. The method of claim 6 , wherein the attaching step comprises:
submerging the porous plate in a dilute solution of citric acid for at least two hours.

8. The method of claim 7 , wherein the dilute solution is less than 0.1 molar citric acid in water.

9. A method of maintaining sublimation capability of a porous stainless steel plate having a porous passivated surface for use in a sublimator, the method comprising:
heating the porous stainless steel plate at an elevated temperature from about 900° F. (482° C.) to about 1200° F. (649° C.) in a flowing stream of oxygen for at least four hours to form a first portion of the passivated surface with an uncharged oxide; and
after the heating step, submerging the plate in a dilute solution of citric acid for at least two hours to attach citric acid to form a second portion of the passivated surface.

10. The method of claim 9 , wherein the dilute solution is less than 0.1 molar citric acid in water.

Assignees

• Hamilton Sundstrand Space Sys

Inventors

• Steele John W
• Oehler William F
• Rector Tony

Classifications

• C23C8/14

  Oxidising of ferrous surfaces · CPC title

• C23C28/00

  Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D · CPC title

• C23C8/12 Primary

  using elemental oxygen or ozone · CPC title

• C23C8/80

  After-treatment · CPC title

• C23C28/04 Primary

  only coatings of inorganic non-metallic material · CPC title