Coatings for metal casting parts
The method is disclosed for coating or impregnating a metal tool with a metal oxide to render the metal part more resistant to liquid metal attack or micro-welds. The method includes the steps of applying a liquid metal carboxylate composition, or a solution thereof, to a substrate material, and exposing the substrate to an environment that will cause vaporization or dissipation of any excess carboxylic acids in the liquid metal carboxylate composition while the metal carboxylates are being converted to metal oxides.
1. A method for reducing liquid metal attack on a solid metal part, comprising:
(a) applying a liquid metal carboxylate composition to a solid metal part substrate, wherein the liquid metal carboxylate composition comprises a solution of a metal salt of a carboxylic acid in a solvent, and
(b) heating the part with the applied liquid carboxylate in a non-oxidizing environment that will convert at least some of the metal carboxylates to metal oxides; wherein the metal oxides penetrate the solid metal part substrate to a depth of about 200 Angstroms to about 600 Angstroms.
2. The method of claim 1 , wherein the solvent comprises a carboxylic acid, and wherein heating the metal part in a non-oxidizing environment causes vaporization or dissipation of any carboxylic acid solvent.
3. The method of claim 2 , wherein the solvent comprises at least one carboxylic acid that corresponds to a carboxylate moiety in the liquid metal carboxylate composition.
4. The method of claim 1 , wherein the carboxylic acid is a carboxylic acid having the formula
R—C(R″)(R′)—COOH
wherein:
R is selected from H and C 1 to C 24 alkyl groups; and
R′ and R″ are each independently selected from H or C 1 to C 24 alkyl groups.
5. The method of claim 4 , wherein the carboxylic acid is alpha-branched, wherein at least two of R, R′ and R″ are not H.
6. The method of claim 5 , wherein R is H, R″ is C 2 H 5 and R′ is C 4 H 9 .
7. The method of claim 1 , wherein the carboxylic acid is a mixture of carboxylic acids.
8. The method of claim 7 , wherein the average molecular weight of the acids contained in this mixture is from about 130 to 420.
9. The method of claim 7 , wherein the average molecular weight of the acids contained in this mixture is from about 220 to 270.
10. The method of claim 9 , wherein the mixture of carboxylic acids contains 2-ethylhexanoic acid as its lowest boiling acid constituent.
11. The method of claim 1 , wherein the liquid metal carboxylate composition comprises a mixture of metals.
12. The method of claim 1 , wherein the liquid metal carboxylate composition comprises one or more metals selected from the group consisting of Lithium, Beryllium, Sodium, Magnesium, Potassium, Calcium, Scandium, Titanium, Chromium, Manganese, Iron, Nickel, Cobalt, Copper, Zinc, Gallium, Rubidium, Strontium, Yttrium, Zirconium, Silver, Cadmium, Tin, Cesium, Cerium, Barium, Lanthanum, Hafnium, Tantalum, Gold, Thallium, Lead, Bismuth, Cerium, Praseodymium, Neodymium, Samarium, Europium, Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium, Lutetium, Thorium and Uranium.
13. The method of claim 1 , wherein the liquid metal carboxylate composition comprises Zirconium.
14. The method of claim 11 , wherein the liquid metal carboxylate comprises a mixture of metals comprising:
up to 10% by weight of yttrium;
up to 5% by weight of chromium; and
the balance zirconium;
wherein the minimum total amount of yttrium is at least 3% and the minimum total of chromium is at least 2%.
15. The method of claim 11 , wherein the liquid metal carboxylate comprises a mixture of metals comprising:
7 to 8% by weight of yttrium;
2 to 3% by weight of chromium; and
89 to 91% by weight of zirconium.
16. The method of claim 11 , wherein the liquid metal carboxylate comprises a mixture of metals comprising:
14-15% by weight of yttrium;
the balance cerium.
17. The method of claim 2 wherein the vaporization or dissipation of any excess carboxylic acids in the liquid metal carboxylate composition and conversion of the metal carboxylates to metal oxides is carried out by heating the coated metal part.
18. The method of claim 17 , wherein the metal part is heated at a temperature greater than about 400° C.
19. The method of claim 17 , wherein the metal part is heated at a temperature less than about 480° C.
20. The method of claim 17 , wherein the metal part is heated for about 3 to 5 minutes.
21. The method of claim 17 , wherein the metal part is heated for more than about 5 minutes and less than about 20 minutes.
22. The method of claim 1 , wherein the amount of metal in the liquid metal carboxylate composition is in the range of 30 to 80 grams of metal per kilogram of liquid metal carboxylate composition when using ceria.
23. The method of claim 1 , wherein the amount of metal in the liquid metal carboxylate composition is in the range of about 100 to about 300 grams of metal per kilogram of liquid metal carboxylate composition when using zirconia.
24. The method of claim 22 , wherein the amount of metal in the liquid metal carboxylate composition is 30 to 80 grams of metal per kilogram of liquid metal carboxylate composition.
25. The method of claim 23 , wherein the amount of metal in the liquid metal carboxylate composition is about 100 to about 300 grams of metal per kilogram of liquid metal carboxylate composition.
26. A method for reducing liquid metal attack on a solid metal part, comprising:
(a) applying a liquid metal carboxylate composition to a solid metal part substrate, wherein the liquid metal carboxylate composition comprises a solution of a metal salt of a carboxylic acid in a solvent, and
(b) heating the metal part comprising the applied liquid metal carboxylate composition in a non-oxidizing environment to a temperature of less than or equal to 450° C.; and
(c) converting at least some of the metal carboxylates to metal oxides in the non-oxidizing environment.
27. A method for reducing liquid metal attack on a solid metal part, comprising:
(a) applying a liquid metal carboxylate composition to a solid metal part substrate, wherein the liquid metal carboxylate composition comprises a solution of a metal salt of a carboxylic acid in a solvent, and
(b) heating the part with the applied liquid carboxylate in a non-oxidizing environment at a temperature of less than or equal to about 450° C. to convert at least some of the metal carboxylates to metal oxides, wherein the metal oxides penetrate the solid metal part to a depth of about 200 Angstroms to about 600 Angstroms.
28. The method of claim 27 , wherein metal part substrate is heated for about 3 minutes to about 5 minutes.
29. The method of claim 28 , wherein the metal part substrate is heated at a temperature of less than about 450° C.