US2048594A - Electrodepositing metals - Google Patents

Description

Patented July 21, 1936 UNITED STATESfPATENT OFFICE ELECTRODEPOSITING METALS Charles Joseph Brockman, Athens, Ga.

No Drawing.

12 Claims.

plied. Unfortunately, the coating so formed is 5 nearly always of a spongy, poorly adherent nature and serves only to prevent the adherence of the deposit later to be made.

In order to avoid the formation of this poorly adherent deposit a number of modifications of some are now in use. In general these modifications fall into two classes. Either the object to be plated is first covered with an intermediate or strike coating of a metal that will form an ing deposited on the surface so formed, or the plating conditions are so modified that the metal with which it is desired to plate will not form a spongy deposit of the kind mentioned.

Various changes in plating conditions have been tried, including the starting of the deposition at hating the spongy coating, the cyanide baths are I probably the most common. Copper can be directly plated upon iron or steel from an alkaline copper cyanide solution, although the cathode efliciency is relatively poor, the bath is extreme- 1y poisonous and the current density must be carefully controlled. Usually a thin "strike" coating of copper, is applied by the use of a cyanide solution .and the plating then finished in a copper sulfate bath. Other metals may be similarly deposited by the, use of cyanide baths upon cathodes on. which they will not ordinarily form an the basic plating procedures have been tried and,

adherent deposit on the object and the final coat- Application January 21, 1935, Serial No. 2,837

adherent deposit. However, the disadvantages of plating from a cyanide solution are much the same regardless of the metal plated.

Because of these disadvantages at least several additional types. of baths have been developed and 5 tried under various conditions. Of these mention may here be made of two, the tartrate bath and the oxalato bath, both used for plating copper on steel or iron. A tartrate bath suggested by Brown and Mathers, J. Phys. Chem. 10 39-51 1 (1906) has the following formula:

Copper sulfate 60 grams Sodium hydroxide; 50 grams Sodiumpotassium tartrate 159 grams Water 1 liter 15 The oxala bath was suggested by Fink and Wong, Trans. Electrochem. Soc. 63 Preprint 9 (1933) It is also aqueous and has the formula:

Copper oxalato (Disodium dia- 20 qu o d i o xal a t o cuproate) Na2[Cu(CzO4) 2.(H.2O) a] 20 grams/liter Sodium sulfate 15 grams/ liter Boric acid 20 grams/liter 2r The authors tell us that their baths obviate many of the difliculties experienced with the cyanide type of bath.

Nevertheless, experiments indicate that the current efliciency, quality of the deposit and other features of the methods using these baths are still subject to improvement. Hence, it is the purpose of the present invention to provide a new method involving the use of a new bath and thus to obtain greater current efficiency, use lower current densities if desired, and yet to form a uniform adherent deposit from a non-poisonous bath. The new bath also has excellent throwing power and hence is especially well adapted to the plating of irregularly shaped articles. Further objects and advantages of this invention will ap-. pear from a consideration of the following description of the new bath and the manner of its use. 1

According to the discovery upon which this invention is predicated it appears that triethanolamine, and probably other similar compounds, formwith metals complexions somewhat similar, but more advantageous, in their affect in plating baths to the corresponding cyanides. Baths containing these lens may be used with particular advantage in the electrodeposition of metals upon cathodes on which the metals will not satisfactorily plate from the common plating solutions. Such baths are non-poisonous and plate satisfactorily throughout a wide range of Copper sulfate (51-120) 150 grams/liter Boric acid grams/liter Triethanolamine 2'70 0. c./liter This bath was compared with an aqueous cyanide bath consisting of:

Cuprous cyanide 22.5 grams/liter Sodium cyanide 34.0 grams/liter Sodium carbonate 15.0 grams/liter The results with the solutions stirred during deposition and run at 30 amperes per square foot, 5

1 volts potential were as follows:

Copper deposited mg./sq. cm. Time in seconds 0 id yan 0 New bath bath in 68 01c 30 3. 27 .138 50 6. 69 220 70 7. 74 324 90 l 9. 38 428 120 '11. 91 601 The deposit formed by the new process was bright,

hard and copper colored. It was found preferable I to use copper anodes to keep the-solution supplied with the metal.

A modification of this bath that has proved particularly advantageous because of the high current efficiency that may be obtained therewith and because the deposit therefrom is especially satisfactory as a. strike plate upon which further quantities of metal may be deposited has the following formula:

Copper sulfate (51120) 16 grams/liter,- Sodium oxalate 1O grams/liter Triethanolamine 22 c. c./liter The solution so formed is light blue and does not plate on iron by contact. A current density of 3.6

amperes per square foot at 1.5 to 2.5 volts gives I. bright plate on-steel which will hold copper from the ordinary copper sulfate bath.- Below are figures showing three test depositions under these conditions. They may be compared with the figures given above, but it should be remembered that the current density here is only aboutoneeighth of that used in obtaining those figures.

Copper deposited Tim in mgJsq. cm. seconds I,

' All deposits of 50 seconds or over from this bath were capable of holding a plate from an acid sulfate bath and deposits of '70 seconds or over were particularly well suited to this purpose.

As another example of the general principlesor 5 the invention theplating of nickel on zinc. may be mentioned. Nickel will not ordinarily form an adherent deposit on zinc. However, good deposits on zinc can be obtained by the use of any one of several solutions containing a nickel salt and tri ethanolamine. The following solutions, which have been tried and found satisfactory may be cited as illustrative. Good throwing power is a characteristic of the solutions so that the deposit is smooth and uniform even though the cathode is irregularly shaped.

Nickel ammonium sulfate 120' grams/liter, Triethanolamine 200 c. c./liter Water Remainder 20,

(Boric acid may be added in small amounts but seems to have no appreciableeifect.)

Still further examples are furnished by the following aqueous solutions used for plating zinc, cobalt and cadmium respectively on copper, or other metals:

Zinc sulfate (71-120) 75 trams/liter Triethanolamine 25 c. c./liter White precipitate filtered out before use.

Cobaltus sulfate 75 grams/liter Triethanolamlne c. cJIi'ter Current density 17 amps/sq. dm. Cobaltous nitrate (61-120) 75 grams/liter Triethanolamine 50 c.c./liter Current density l 25 amps ./sq. dm. 50 Cobaltous sulfate (611:0) 75 grams/liter 'lriethanolamine 125 c. c. lliter Current density 11 amps./sq. dm.

Plates well on zinc. 55 Cadmium sulfate '15 grams/1i Triethanolamine 25 c. c./liter White precipitate filtered out .before use;

Cadmium nitrate (4Ha0) 75 grams/liter 6o Triethanolamine 25 c. c./liter Current density; 11 to 22 amps/sq. dm.

' White precipitate filtered out before use.

While the invention has been described specifically by examples using triethanolamine in 65 I formulas in order to give a concrete understanding thereof, it is to be understood that aosasc receive the deposit. Also. although the invention is most advantageously used where the metal will not plate in an ordinary acid bath it may be used even though the metal will so plate when for any other reason it may be desired to plate the metal from the new type of solution.

As an example of the compounds that may replace triethanolamine in the practice or this invention diand mono-ethanolamine may be mentioned and the use or other hydroxy alkyl amines .and their substitution products and homologues particularly those having properties fis similar to triethanolamine are also contemplated. Other changes may be made to adapt the principles of this invention to various technical situations all within the skill oi! the chemist and the broadest scope of this invention.

We claim;

1. A method of electroplating that comprises contacting the'obiect to be plated with a solution containing the metal to be deposited and an ethanolamine, and passing an electric current through said solution'and object to deposit the .metal thereon.

, 2. A method of electroplating that comprises contacting the object to ,be plated with asolution containing the metal to be deposited and an alkylolamine'and passing an electric current through said solution and object to deposit the metal thereon.

x 3. A method of electroplating that comprises contacting the object to be plated with a solution containing the metal to be deposited and a trialkylolamine and passing an electric current through said solution and object to deposit the 5. A method of electroplating that comprises and an alkylolamine and an electric cur rent through said solution and object to deposit the metal thereon.

6. A method of electxodepositing copper that comprises contacting the object to be plated with a solution containing copper and an alkylolamine,

and passing an electric current through the solution and object to deposit the'copper thereon.

'l. A method oif electrodepositing copper that comprises contacting the object to be plated with a solution containing around 150 grams per liter oi copper sulfate and around 270 c. c. per liter of triethanolamine, and passing an electric current,

through the solution and object to deposit the copper thereon.

8. A methodof electrodepositing copper that comprises contacting the object to be plated with a solution containing around 16 grams per liter of copper sulfate, around 10 grams per liter of sodium oxalate and around 22 c. e. per liter of 20 triethanolamine. and passing an electric current through the solution and object to deposit the copper thereon.

9. A method of electrodepositing copper on iron that comprises contacting the iron with a solution containing copper, an oxalate and triethanolamine and passing an electric current through the solution and iron to deposit copper on the iron.

10. A method of electroplating that comprises contacting a zinc object to be plated with a solu- =tion containing nickel ammonium sulfate and around 100 to 200 c. c. per liter of triethanolamine and passing an electric current through said solution and object to deposit the nickel thereon.

11. A method oi! electroplating zinc that comprises contacting the object to be plated with a solution containing zinc and triethanolamine, and passing an electric current through the solution and object to'deposit the zinc thereon.

12.. A method of electroplatingthat comprises contacting a zinc object with a solution containing nickel and triethanolamine and passing an electric current through the solutionto deposit the nlckel'thereon. I

JOSEPH BROCKMAN.