Title:
Electrodeposition of silver
United States Patent 2113517


Abstract:
450,979. Electroplating. POWELL, A. R., DAVIES, E. C., and JOHNSON, MATTHEY, & CO., Ltd., 78, Hatton Garden, London. Jan. 26, 1935, Nos. 2626 and 2627. [Class 41] A bath for the deposition of hard bright deposits of silver, copper, or other metal contains a double cyanide of the metal and an alkali metal, excess of free cyanide, an organic sulphide such as carbon bisulphide or a mercaptan soluble in the bath, to which is added a colloidal solution of either alkali metal silicate or an alkali metal salt of a soap-forming acid or of a sulphonic acid derived from such an acid or from the corresponding alcohol. The soap-forming acid may be a monobasic saturated or unsaturated carboxylic or hydroxycarboxylic aliphatic acid having not less than eight carbon atoms in the molecule. Suitable additions are waterglass, Castile soap, and Turkey red oil. The free cyanide content may be 1-16 oz. per gallon. The baths are operated at room temperature with current density 1-8 amps. per sq. ft. A solution of carbon bisulphide in the bath liquor or in alkali metal cyanide solution is added from time to time.



Inventors:
Richard, Powell Alan
Conwy, Davies Emyr
Application Number:
US10414936A
Publication Date:
04/05/1938
Filing Date:
10/05/1936
Assignee:
JOHNSON MATTHEY CO LTD
Primary Class:
International Classes:
C25D3/46
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Description:

This invention relates to the electrodeposition, of silver and has for its main object to provide a plating bath from which hard bright deposits of silver of any desired thickness can be obtained. Present practice in silver plating from cyanide baths produces a matt deposit which requires polishing to develop a bright lustrous surface and this polishing not only adds to the cost of plating but removes a considerable proportion of silver which is lost.

It is well known that the addition of organic sulphides, such as carbon disulphide, to the normal plating bath tends to produce smoother and brighter deposits of silver but the advantages to 5 be obtained are not sufficiently marked nor so constant as to warrant its use being generally adopted.

It is also well known that silver plating baths containing excessive amounts of free alkali metal cyanide produce very hard matt deposits which are difficult and costly to polish. For this reason the amount of free alkali metal cyanide is usually kept down to the minimum required for satisfactory plating.

We have now found that the advantage to be obtained by the use of organic sulphides selected from the group carbon disulphide and mercaptans which are soluble in the bath, in respect to brightness of deposit and the advantage of increased amounts of free alkali metal cyanide as regards hardness of deposit can be combined and considerably enhanced by the further addition to the normal plating bath of a colloidal solution of a detergent. The term detergent in the specification and claims means an alkali metal salt of a soap-forming acid, such as a monobasic saturated or unsaturated carboxylic 6r hydroxycarboxyllc acid of the aliphatic series containing not less than eight carbon atoms in the molecule, or of an alkali metal salt of a sulphonic acid derived from one of the said soap-forming acids or from the corresponding alcohol. The addition made to a cyanide bath to produce a bright silver plate may thus consist of any of the commercial forms of soap, including sulphonated soaps. All these compounds tend to hydrolyze in solution with the production of a small quantity of the free acid in a colloidal form which appears to be adsorbed to a small extent by the deposit, thus producing a fine-grained structure consisting of almost sub-microscopic crystals.

When a soap is used, the amount required depends on the'nature of the soap, but should be sufficient to produce a permanent lather when the solution is shaken and should of course not exceed the solubility of the soap in the solution.

When the bath is made up with soft water, about 0.1 ounce of soap per gallon is sufficient, but when made up with hard water more is required since part is converted into the corresponding calcium or magnesium compound which forms a silky precipitate and gives the bath an opalescent appearance which, however, does not interfere with the production of bright silver plates. A small quantity of glycerine or of a glycol may be added to the bath to reduce still further the grain size of the deposit. Obviously, the soap may be produced in situ in the bath by the addition of free acid, as for example sulphonated acid in the form commonly known as Turkey red oil. Deposits obtained from the improved baths according to this invention are much harder than those obtained in the ordinary silver bath and have a brilliant white lustre which requires little or no polishing. There are therefore no losses of silver due to polishing and silver plating costs are consequently very substantially reduced.

The free alkali metal cyanide content of the plating bath may vary within wide limits, for example from 1 to 16 ounces per gallon, with corresponding effects upon the hardness of the deposited silver.

The sulphide brightening solution is added to the plating solution from time to time as required.

This brightening solution is prepared by saturating a portion of the plating liquor or alternatively an alkali metal cyanide solution with carbon disulphide and returning the sulphide solution obtained to the plating bath.

The following examples will further illustrate how the said invention may be carried out in practice, but the invention is not restricted to these examples.

Example 1 A bath is prepared as follows:Ounces per gallon Silver (as KAg(CN) 2) ------------------ 2.0 Free potassium cyanide----------------- 8.0 Turkey red oil-.------------------------- 0.75 Sulphide brightening solution (obtained as described above)----------------------- 0.75 Example 2 A bath is prepared as follows:- 45 Ounces per gallon Silver (as KAg(CN)2)------------------- 3.0 Free potassium cyanide-----------------6.0 Castile soap (sodium oleate) ------------- 3.0 Sulphide brightening solution (obtained as described above)--------------------- 0.75 The baths described are preferably operated at room temperature and with a current density between 1 and 8 amperes per square foot. Higher current densities tend to produce "burnt deposits".

What w; claim is:1. A process for the electrodeposition of silver, in the form of hard bright deposits requiring little or no polishing, from an alkali metal cyanide 5. A plating bath comprising an alkali metal argento-cyanide, argento-cyanidi an excess of free alkali metal cyanide and an cyanide, an org organic sulphide of the group consisting of car- sisting of carl bon disulphide and mercaptans which are solu- soluble in the bt ble in the bath, which consists in adding to the acid of the gr said bath a colloidal solution of an alkali metal containing no li salt of an acid of the group consisting of all- molecule, sulph phatic acids containing no less than eight car- phatic acids, a bon atoms in the molecule, sulphonic acids de- the alcohols cor rived from said aliphatic acids, and sulphonic 6. A plating acids derived from the alcohols corresponding to gento-cyanide, said aliphatic acids. nide, carbon di 2. A process for the electrodeposition of silver, 7. A plating in the form of hard bright deposits requiring little gento-cyanide, or no polishing, from an alkali metal cyanide nide, carbon di bath comprising an alkali metal argento-cyanide, oleate (castile s an excess of free alkali metal cyanide and an 8. A process organic sulphide of the group consisting of car- in the form oJ bon disulphide and mercaptans which are solu- little or no poll ble in the bath, which consists in adding to the nide bath comn said bath a commercial soap, including sul- cyanide, an exc phonated soaps. organic sulphid 3. In the process of electrodepositing silver bon disulphide from a bath comprising an alkali metal argento- bath, which co cyanide, an excess of free alkali metal cyanide, an alkali metal an organic sulphide of the group consisting of sisting of aliphi carbon disulphide and mercaptans which are eight carbon at soluble in the bath and an alkali metal salt of 9. A process an acid of the group consisting of aliphatic acids in the form ol containing no less than eight carbon atoms in itte no the molecule, sulphonic acids derived from said nide bath corn aliphatic acids, and sulphonic acids derived from cyanide an ex the'alcohols corresponding to said aliphatic acids, cyanid, an ex the step of introducing the organic sulphide in aof can organi the form of a sulphide brightening solution pre- soluble n thsu pared by saturating a portion of the plating liquor soe aid th with carbon disulphide and returning the sul- the said bat phide solution to the plating bath. metal salt of a 4. In the process of electrodepositing silver to hydrolize in from a bath comprising an alkali metal argento- small quantity cyanide, an excess of free alkali metal cyanide, which appears an organic sulphide of the group consisting of by the deposit carbon disulphide and mercaptans which are structure consi soluble in the bath and an alkali metal salt of crystals, said s an acid of the group consisting of aliphatic acids from the group containing no less than eight carbon atoms in or unsaturated the molecule, sulphonic. acids derived from said acids of the all aliphatic acids, and sulphonic acids derived from than eight carl the alcohols corresponding to said aliphatic acids, phonic acids der the step of introducing the organic sulphide in and sulphonic the form of a sulphide brightening solution pre- corresponding t pared by saturating an alkali metal cyanide solution with carbon disulphide and returning the sulphide solution to the plating bath.

CERTIFPCATE OP CORREOTION.' Patent No. 2,113,517.

bath comprising an alkali metal e, an excess of free alkali metal ;anic sulphide of the group conbon disulphide and mercaptans ath, and an alkali metal salt of an oup consisting of aliphatic acids ess than eight carbon atoms in the onic acids derived from said allnd sulphonic acids derived from responding to said aliphatic acids. bath comprising a potassium aran excess of free potassium cyasulphide and Turkey red oil.

bath comprising a potassium aran excess of free potassium cyasulphide and commercial sodium ;oap).

for the electrodeposition of silver, f hard bright deposits requiring shing, from an alkali metal cyaprising an alkali metal argentoess of free metal cyanide, and an e of the group consisting of carand mercaptans soluble in the nsists in adding to the said batti salt of an acid of the group conatic acids containing no less than oms in the molecule.

for the electrodeposition of silver f hard bright deposits requiring shing, from an alkali metal cyaprising an alkali metal argentocess of free alkali metal cyanide sulphide of the group consisting 35 phide and mercaptans which are bath, which consists in adding to a colloidal solution of an alkali soap forming acid which tends solution with the production of a of the free acid in a colloidal form to be adsorbed to a small extent , thus producing a fine grained sting of almost sub-nicroscopic oap forming acid being selected consisting of monobasic saturated carboxylic or hydroxycarboxylic iphatic series containing not less bon atoms in the molecule, sulrived from the said aliphatic acids, 60 acids derived from the alcohols .o said aliphatic acids.

ALAN RICHARD POWELL.

EMYR CONWY DAVIES.

SApril , 1938.

AIAN RICHIRB POWELL, -ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page l, second :column, line 9, before the word "acid" insert ricinolelo and that the said Letters Patent shouldbe read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 3lst day bf May, A. D. 1938.

Herry-'Van -rsdale, (Seal' Acting Canaaisaq o of Patents.

little or no polishing, from an alkali metal cyanide 5. A plating bath comprising an alkali metal argento-cyanide, argento-cyanidi an excess of free alkali metal cyanide and an cyanide, an org organic sulphide of the group consisting of car- sisting of carl bon disulphide and mercaptans which are solu- soluble in the bt ble in the bath, which consists in adding to the acid of the gr said bath a colloidal solution of an alkali metal containing no li salt of an acid of the group consisting of all- molecule, sulph phatic acids containing no less than eight car- phatic acids, a bon atoms in the molecule, sulphonic acids de- the alcohols cor rived from said aliphatic acids, and sulphonic 6. A plating acids derived from the alcohols corresponding to gento-cyanide, said aliphatic acids. nide, carbon di 2. A process for the electrodeposition of silver, 7. A plating in the form of hard bright deposits requiring little gento-cyanide, or no polishing, from an alkali metal cyanide nide, carbon di bath comprising an alkali metal argento-cyanide, oleate (castile s an excess of free alkali metal cyanide and an 8. A process organic sulphide of the group consisting of car- in the form oJ bon disulphide and mercaptans which are solu- little or no poll ble in the bath, which consists in adding to the nide bath comn said bath a commercial soap, including sul- cyanide, an exc phonated soaps. organic sulphid 3. In the process of electrodepositing silver bon disulphide from a bath comprising an alkali metal argento- bath, which co cyanide, an excess of free alkali metal cyanide, an alkali metal an organic sulphide of the group consisting of sisting of aliphi carbon disulphide and mercaptans which are eight carbon at soluble in the bath and an alkali metal salt of 9. A process an acid of the group consisting of aliphatic acids in the form ol containing no less than eight carbon atoms in itte no the molecule, sulphonic acids derived from said nide bath corn aliphatic acids, and sulphonic acids derived from cyanide an ex the'alcohols corresponding to said aliphatic acids, cyanid, an ex the step of introducing the organic sulphide in aof can organi the form of a sulphide brightening solution pre- soluble n thsu pared by saturating a portion of the plating liquor soe aid th with carbon disulphide and returning the sul- the said bat phide solution to the plating bath. metal salt of a 4. In the process of electrodepositing silver to hydrolize in from a bath comprising an alkali metal argento- small quantity cyanide, an excess of free alkali metal cyanide, which appears an organic sulphide of the group consisting of by the deposit carbon disulphide and mercaptans which are structure consi soluble in the bath and an alkali metal salt of crystals, said s an acid of the group consisting of aliphatic acids from the group containing no less than eight carbon atoms in or unsaturated the molecule, sulphonic. acids derived from said acids of the all aliphatic acids, and sulphonic acids derived from than eight carl the alcohols corresponding to said aliphatic acids, phonic acids der the step of introducing the organic sulphide in and sulphonic the form of a sulphide brightening solution pre- corresponding t pared by saturating an alkali metal cyanide solution with carbon disulphide and returning the sulphide solution to the plating bath.

CERTIFPCATE OP CORREOTION.' Patent No. 2,113,517.

bath comprising an alkali metal e, an excess of free alkali metal ;anic sulphide of the group conbon disulphide and mercaptans ath, and an alkali metal salt of an oup consisting of aliphatic acids ess than eight carbon atoms in the onic acids derived from said allnd sulphonic acids derived from responding to said aliphatic acids. bath comprising a potassium aran excess of free potassium cyasulphide and Turkey red oil.

bath comprising a potassium aran excess of free potassium cyasulphide and commercial sodium ;oap).

for the electrodeposition of silver, f hard bright deposits requiring shing, from an alkali metal cyaprising an alkali metal argentoess of free metal cyanide, and an e of the group consisting of carand mercaptans soluble in the nsists in adding to the said batti salt of an acid of the group conatic acids containing no less than oms in the molecule.

for the electrodeposition of silver f hard bright deposits requiring shing, from an alkali metal cyaprising an alkali metal argentocess of free alkali metal cyanide sulphide of the group consisting 35 phide and mercaptans which are bath, which consists in adding to a colloidal solution of an alkali soap forming acid which tends solution with the production of a of the free acid in a colloidal form to be adsorbed to a small extent , thus producing a fine grained sting of almost sub-nicroscopic oap forming acid being selected consisting of monobasic saturated carboxylic or hydroxycarboxylic iphatic series containing not less bon atoms in the molecule, sulrived from the said aliphatic acids, 60 acids derived from the alcohols .o said aliphatic acids.

ALAN RICHARD POWELL.

EMYR CONWY DAVIES.

SApril , 1938.

AIAN RICHIRB POWELL, -ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page l, second :column, line 9, before the word "acid" insert ricinolelo and that the said Letters Patent shouldbe read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 3lst day bf May, A. D. 1938.

Herry-'Van -rsdale, (Seal' Acting Canaaisaq o of Patents.