US2732321A

US2732321A - Plating processes and compositions

Info

Publication number: US2732321A
Authority: US
Publication date: 1956-01-24
Anticipated expiration: 1973-01-24

Description

nited States Patent O 2,732,321 I PLATING PROCESSES AND COMPOSITIONS Charles B. Gill, Albert W; Schlechten, and Martin E. Straumanis, Rolla, M0.

N Drawing. Application September 18, 1953, Serial No. 381,124

17 Claims. (Cl. 117--'131) This invention relates to plating processes and compositions. More particularly it concerns processesfor producing coatings of titanium and related metals upon various surfaces, especially other metal surfaces.

Titanium and related. metals, 'such as zirconium and hafnium, possess certain 'desirable properties, including corrosion resistance, which make them useful as platings for various surfaces. However, the plating of these metals onto other metals or surfaces presents serious problems and considerable work has been done in attempting to develop suitable processes for plating or coating with these metals. v f 1 An example of one known titanium plating method is described in U; S. Patent No. 2,351,798. In this method,

finely divided titanium or titanium'hydride is sprinkled on a metal surface such as copper and the combination is heated in a reducing or inert atmosphere to above the eutectic temperature of the system of titanium and copper, i. e., 878 C. until a fused alloy forms and spreads on the surface of the copper.

This method cannot be used to plate titanium directly onto ferrous metal surfaces for titanium does not form low melting point alloys with iron which will spread over the ferrous metal. The same is true for other surfaces, e. g., nickel, cobalt or porcelain.

Other proposals for forming titanium coatings on surfaces include treatment of iron in TiCLr and attempts at direct cementation of ferrotitanium powder on iron. These processes are not useful for obtaining corrosion resistant coatings.

A principal object of this invention is the provision of new processes for the coating of metal or other surfaces with adherent coatings of titanium, zirconium, hafnium, uranium or alloys thereof.

Further objects include: 7

(1) The provision of methods which permit titanium and related metals to be plated'or coated directly onto porcelain, iron, nickel, cobalt or like surfaces.

(2) The provision of titanium and related metal plating procedures which enable corrosion resistance surfaces to be formed upon ferrous and other metal surfaces.

(3) The provision of new coating compositions for use in conducting such processes.

(4) The provision of titaniumplating processes which may be operated at temperatures below the melting point of fusible alloys which may be formed between titanium and the base metal, e. g., the eutectic mixture of titanium and the base metal.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood,

however, that the detailed description and specific ex amples, while indicating preferred embodiments of the invention, are given by' way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

These objects are accomplished according to the present Patented Jan. 24, 1956 invention by immersing the surface to be coated in a fused inorganic material bath having a temperature between about 700 and 1000 C., bringing a source of titanium, zirconium, hafnium or uranium metal into close'proximity with said surface within the heated bath and maintaining the bath temperature long enough, for example, from 2 to 8 hours, to form an appreciable coating of the plating metal on the surface.

The fused inorganic bath may be formed, for example, of NaCl, KCl, LiCl, CaClz, KzTiFs, NaOH, KOH or mixtures of these materials.

The source of coating metal may be a sheet, bar, plate or the like or may be powdered metal.

A more complete understanding of the processes and products of this invention may be obtained from the following illustrative examples:

Example 1 A copper sheet is cleaned by sanding and a sheet of titanium of approximately the same surface area as the surface of the copper sheet to be plated is also similarly cleaned. a

The cleaned sheets are immersed in a molten bath of sodium chloride heated to about 850 C. and the distance between the copper surface and the titanium surface is adjusted by suitable clamping means to about one millimeter. perature is maintained at 850 C. After 4 hours, the cop-' per and titanium sheets are removed from the bath and adhering salt is washed from them after they have cooled.

A copper sheet having its surface coated with a dull gray titanium coating is obtained. The coating is found to be very adherent to the base copper sheet and to be capable of contacting boiling concentrated nitric acid without any appreciable corrosion. The dull gray coating may be easily polished to a bright finish.

Example 2 This example illustrates the coating of iron with titamum.

A sheet of iron is cleaned by abrading and then is placed in a crucible with titanium powder packed around it. Melted sodium chloride is poured into the crucible, penetrating the powder until it covers the powder and the iron sheet.

The crucible and contents are heated to 900 C. for 4 hours after which the iron sheet is removed from thebath, cooled and then washed free of salt.

A sheet of iron having a dull gray coating of titanium about 0.001 inchin thickness is obtained. The coating is extremely adherent to the iron base sheet and may be polished to a bright finish and handled roughly without breaking loose of the base sheet.

. The process of the invention may be used to coat a large variety of surfaces. However, the surface and substructure should be capable of being heated to a temperature of at least 700 C. without destruction, i. e., without decomposing, melting, or disintegrating in the coating bath orthe like. Examples of materials of which the surfaces to be coated may be made are copper, iron, cobalt, nickel, silver, alloys of these metals, e. g.,.bronzes, steels and the like, and porcelain.

The process is particularly useful for plating surfaces with titanium. However, zirconium, hafnium and uranium coatings may also be formed using the new invention.

Preferably the plating is accomplished using titanium, or the other metal per se and bringing these into close proximity with the surface to be coated. However, alloys of these metals with themselves or with other heavy metals may be used. Also compounds which pyrolytic'ally The sheets are held in the bath while the tem-' 3, decompose into these metals at a temperature not greater than 700 C., e. g., titanium hydride which decomposes into finely divided titanium metal, may be used.

When powdered metal is used as the source of the coating metal, close proximity of the metal to the surface to be coated is obtained so long as the powder is kept uniformly distributed through the bath. Distribution of the powder may be maintained by stirring or agitating the bath, rotating the objectto be plated within'the bath, agitating the entire process vessel and contents or in similar ways.

If solid sheets or the like are used as the source, of the coating metal, they are preferably shaped to present a surface which is roughly the convo -e of the surface to be coated. These two surfaces are then placed in the fused bath and held closely together by wires, clamps or other means. The distance between the surface to be coated and the converse plating surface may be varied, but a distance of about 1 millimeter has been found to give very good results. Greater distances may be used, but the rate of coating is lower as the two surfaces are moved further apart. It is possible to satisfactorily plate irregular surfaces, such as medallions or coins, using a flat coating metal surface, indicating that the spacing is not critical. The optimum spacing is also dependent to some. extent upon bath temperature and higher temperatures permit larger spacings.

A large variety of inorganic, normally solid materials may be used to form the fused baths employed in these new processes. The inorganic material used should not destroy the surface to be coated or the coating metal at temperatures between 700 and 1000 C. Suitable materials include inorganic salts, e. g., NaCl, KCl, LiCl, CaClz, related iodides, bromides or fluorides, KzTiFs, mixtures of these salts, and inorganic bases, e. g., NaOI-I and-KOH. When mixtures of these materials are used, proportions of the mixture components are not critical and may be varied to obtain baths of different melting points as is well known.

Sufiicient inorganic bath material should be used to completely cover the surface to be coated and the coating metal in the process vessel; Where the coating metal.

is used in the form of a powder, the ratio of inorganic salt or base to powdered metal may be varied widely, e. g., the weight of powdered metal may be 1 to 100 parts for each parts of salt. The amount of powdered metal used is best controlled individually for each coating operation to ensure that, taking in consideration the contour of the surface to be coated, there will be a relatively heavy concentration of the powder in the bath throughout the area of the surface undergoing coating.

Maintenance and control of the fused bath temperature during the plating operation is important. In general, the temperature should beheld between about 700 and 1000? C. with the coating proceeding more rapidly at higher temperatures. The most desirable temperature within this range will depend to some extent upon the surface to be plated. When plating copper, it is preferable to use a lower temperature, e. g., 800 to 850 C., than with iron which is best plated at a temperature of 900 to 950 C. Obviously, the bath temperature should not; exceed the fusion point of the surface to be coated, but with many of the surfaces that can be plated using these new procedures, it is not important to Watch this for the surfaces will have a melting point above 1000 C., e. g., iron, nickel or like metals.

The resulting platings or coating are found to have the best properties when the bath. temperature is conrolled to stay below about 10 C. below the melting point of any alloy which may be formed between the titanium or other coating metal and metal to be plated. For example, in plating copper. the bath temperature should stay below 868 (3., i. e., 10 C. below the 878 C. eutectic temperature of the system copper titanium.

may be varied and will depend partly upon the bath tem erature and type of s face b ing coat h r times result in thinner coatings and longer times increase the tendency of the metal being coated to diffuse into the plating metal and vice versa. However, generally times of immersion of 2 to 8 hours, and especially 3 to 5 hours, give satisfactory results.

The coatings formed by these new methods vary in thickness depending upon bath temperature, time of imm rs n in he coa ing bath an th ikee Ih ne s f a ou l mi e typical and. it hould b r cog ized h hese coa ings may no necessarily b pur t t ni m. z r m or fn m- Difiusion of, th base m tal n o th ating forms u'all yvwith the plating m tal and this a tion s t r with extende plating tim s r high temperatures,

Af er h ting op r ion has in d lo g n gh to build up a coating of appreciable thickness, e. g., a fraction of several mils, the surface being plated is removed'from the fused .bath and allowed to cool. it should then be washed to remove any salt which may have been picked up from the bath. No other special treatments to theplated surface are necessary.

Any suitable type process vessel may be employed to hold the fused bath. Common forms of crucibles, electric furnaces or the like used in the metal treating art are satisfactory.

New processes for plating of metal or other surfaces with titanium, zirconium and hafnium metal have been disclosed and described. Special compositions comprising fused mixtures of pow ered Plating metal and inorganic s r use in hose n w plating pr c s re lso d closed,

The new processes make possible the formation of corrosion resistance platings on metal surfaces and it is possible to form these platings directly onto iron or otherferrous metal surfaces Witho t, need for intermediate pper plating as in th case of th la e pl ing P e e known and used heretofore.

We claim;

l. A process for plating Of metal onto a surface which can be heated to a temperature of at least 700 C. without destruction which comprises immersing the surface to be plated in a fused bath of inorganic, normally solid onal of the group consisting of m rgani salts. and organic b s s whish oe no decomp se when h a o temperatures between about 700 and 1000 C., introducing a plating material from the group consisting of titanium metal, zirconium metal, hafnium metal, uranium metal, alloys thereof and compounds thereof which pyy ically de pose into said m t ls t a temp a not greater than the temperature of operation defined herein into said both, ringing said. p a ing m eri n h bath into close proximi y o said r ace, nd tn intr ning said bath at a temperature b t een about 700 a 1000 C- until an. appreciable a ing of d m t i formed upon said surface.

2. A-process for plating metal onto the surface of another metal havi g a melting point abo abo 7 0 C- which comprises immersing said metal surface a insod salt bath ha ing a tempera re below he m lting Point of said su face met l between abou 700 and 10-00 said bath being compose of in gani s s hich o not d compose hen heated to a tempera ur p o 1900* Q. introduci g a pla g metal from h roup on i ng. of titanium, zirconium, hafnium, ur nium and alloys thereof into said heated salt bath, ringing id p a ing metal into close proximity with said metal surface, maintaining said proximity of said surface and plating metal within said bath at a temperature above about 700 C. and below 1000 C. or the eutectic temperature of the system of said metal of said surface and said plating metal, whichever is the lesser, until an appreciable coating of said plating metal is formed upon said surface and then withdrawing said surface from said bath.

3. The process of claim 2 wherein said bath comprises an alkali metal halide.

4. The process of claim 2 wherein said bath comprises an alkaline earth metal halide.

5. The process of claim 2 wherein said hath comprises an alkali metal chloride.

6. The process of claim 2 wherein said plating metal is titanium and said proximity to said surface is obtained by introducing the titanium into said bath as powdered metal and mixing the powder uniformly into said bath.

7. The process of claim 2 wherein said plating metal is introduced into said bath as a solid body having a surface contoured roughly to the converse of the metal surface to be coated and said converse surface is matched in close proximity to said metal surface.

8. The process of claim 2 wherein said plating metal is zirconium metal.

9. The process of claim 2 wherein said plating metal is hafnium.

10. The process of claim 2 wherein said plating metal exists as an alloy with another heavy metal.

11. A process for plating titanium onto a surface which can be heated to a temperature between 700 and 1000 C. without being destroyed which comprises immersing the surface to be coated in a fused inorganic salt bath having a temperature of between about 700 and 1000 C., introducing titanium metal into said salt bath and in close proximity to said surface, so maintaining said bath at a temperature between 700 and 1000 C. until an appreciable coating of titanium has formed on said surface and then removing said surface from said bath.

12. A process for plating titanium onto a metal surface having a melting point not less than 700 C. which comprises providing a fused bath consisting essentially of a mixture of alkali metal halides and powdered titanium metal, maintaining said fused bath at a temperature between about 700" and X 0., wherein X is the lesser 6 4 between 1000 or the eutectic temperature minus ten of the system of titanium with the metal of said metal surface, immersing said metal surface in said fused bath and holding it immersed therein for 2 to 8 hours until an appreciable coating of titanium is formed on said surface and then withdrawing said surface from said bath.

13. The process of claim 12 wherein the metal of said surface is one selected from the group consisting of copper, iron, cobalt, nickel, silver and alloys thereof.

14. A process for plating titanium onto copper which comprises immersing a copper surfaced body in a fused bath consisting essentially of a mixture of alkali metal halides and powdered titanium metal, maintaining the temperature of the bath at between about 800 and 850 C. with said body immersed therein for about 3 to 5 hours, withdrawing the copper surfaced body from said bath, allowing said body to cool and then washing olf salt from the surface of said body.

15. A process for plating titanium onto iron which comprises immersing an iron surfaced body in a fused bath consisting essentially of a mixture of alkali metal halides and powdered titanium metal, maintaining the temperature of the bath at a temperature between about 900 and 950 C. with said body immersed therein for about 3 to 5 hours, withdrawing the iron surfaced body from said bath, allowing said body to cool and then washing off salt from the surface of said body.

16. A surface coating composition consisting essentially of a fused mixture of alkali metal halides and a powdered metal selected from the group consisting of titanium metal, zirconium metal, hafnium metal and alloys thereof.

17. A composition for plating surfaces with titanium which consists essentially of a fused mixture of alkali metal halides and powdered titanium metal.

Hoge: Metal Progress (November 1947), vol. 52, pp. 819-23.

Electromotive Series, Metal Finishing, vol. 50, No. 4, p. 89.

Claims

1. A PROCESS FOR PLATING OF METAL ONTO A SURFACE WHICH CAN BE HEATED TO A TEMPERATURE OF AT LEAST 700* C. WITHOUT DESTRUCTION WHICH COMPRISES IMMERSING THE SURFACE TO BE PLATED IN A FUSED BATH OF INORGANIC, NORMALLY SOLID MATERIAL OF THE GROUP CONSISTING OF INORGANIC SALTS AND INORGANIC BASES WHICH DOES NOT DECOMPOSE WHEN HEATED TO TEMPERATURES BETWEEN ABOUT 700* AND 1000* C., INTRODUCING A PLATING MATERIAL FROM THE GROUP CONSISTING OF TITANIUM METAL, ZIRCONIUM METAL, HAFNIUM METAL, URANIUM METAL, ALLOYS THEREOF AND COMPOUNDS THEREOF WHICH PYROLYTICALLY DECOMPOSE INTO SAID METALS AT A TEMPERATURE NOT GREATER THAN THE TEMPERATURE OF OPERATION DEFINED HEREIN INTO SAID BATH, BRINGING SAID PLATING MATERIAL IN THE BATH INTO CLOSE PROXIMITY TO SAID SURFACE, AND MAINTAINING SAID BATH AT A TEMPERATURE BETWEEN ABOUT 700* AND 1000* C. UNTIL AN APPRECIABLE COATING OF SAID METAL IS FORMED UPON SAID SURFACE.