US1277761A - Bronzing or coloring of metallic surfaces. - Google Patents

Description

UNITED STATES PATENT OFFICE.

QUIBINO SESTINI AND TITORONDELLI, OF BERG-Alto, ITALY.

BIIiOlil'ZIN(:rv R COLORING OF METALLIC SURFACES.

To all whom it may concern;

Be'it known that we, QUmINo SEs'rIm and Trro RONDELLI, subjects of the King of Italy, residing at Bergamo, Italy, have inv vented certain new and useful Improvements ,out this specification and in the claims to denote not merely the production of the coloration known as bronzin but the formation of'a coating of an oxi of copper or of iron which serves as a protection to the surface beneath it to prevent further oxidation or corrosion thereof. Prominent among the objects of the'present invention is the provision of a process whereby the desired results can be obtained more rapidly than hitherto. To this end the surface to be protected or colored is preliminarily coated with an electrolytic deposit of iron or copper.

According to the present invention a surface is bronzed or colored by depositing co per or iron electrolytically thereon and subsequently oxidizing the said deposited metal; by oxidizing is meant not merely the production of a simple oxid but the production'of any compound obtained by a process which in the broadest chenncal sense may be described as an oxidizing process.

The bath employed according to this invention is preferably 'a hot dense alkaline solution containing an oxid either of copper or of iron combined with an oxid of the alkaline metal present; and the bronzing or coloring is conveniently effected by first electrolytically depositing the iron or copper on the surface to be treated in a bath of the kind just stated and subsequently coloring the said deposit by reversing the current. The density of the solution varies between about 1.25 and 1.55 and the temperature at which it is worked is from about 115 C. u

ward, the term density being used .111 this Specification of Letters Patent.

Patented Sept. a, 1918.

Application filed May 15, 1917. Serial No. 168,763

instance, as in all others herein, to indicate the specific weight of the solution as compared with that of water.

The process may be carried out by, making the conductin surface anode, or alternately cathode an anode, but finally anode in an electrolytethat is a hot dense alkaline solution such as has been above referred to and that contains'an oxid either of copper or .of iron combined with an oxid of the alkaline metal present, the said combined substance being either a ferrite of the alkali metal, or a similar copper compound thereof- The temperature of the bath is conveniently between about 120 C. and 140 C.

and its density between 1.3 and 1.5 due to the alkaline content.

In order to provide a bath for the purposes of the present invention, the bath may be prepared, as part of the present invention, by repeatedly reversing the current through a hot dense alkaline solution between electrodes that are both ofiron or both of copper; the alkaline solution may be either a caustic alkali or an alkaline carbonate and have a density between 1.3 and 1.4 and a temperature between about 120 C. and 130 C.

A further step provided by the present invention, to be used as and when desired, consists in immersing the surface that is bein treated, after it has been electrolytically co ored in a solution of caustic alkali containing between about 10% and 20% of a metallic nitrate, or an aromatic nitrate derivative as nitrophenols or nitronaphthols; the density of the solution should be about 1.4 and its temperature about 140 C.

All or any of the above described steps may be followed by drying the colored surface and leaving it long immersed in a bath of oil at a temperature of between about 150 C. and 180 0.; the period of immersion may be in the-neighborhood of about ten minutes and the oil employed is conveniently olive'oil, or a mixture of linseed or mineral oils.

The following examples serve further to disclose the present invention:

An electrolyte is prepared by passing current and repeatedly reversing it between electrodes of the metal to be used, namely either iron or copper in a bath of hot concentrated alkali. The density of the bath,

minutes.

for a caustic alkali, is between 1.3 and 1.4; equivalent quantities of caustic potash or an alkaline carbonate may equally be used.

The temperature of the bath is raised to a point between about 120 C. and 130 C. If the electrodes are of wrought or castiron, or of steel, the repeated reversals of current through it causes an oxid of iron to, be formed and dissolved in or to be combined with the alkali in the bath; apparently the result is the formation of an alka-' line ferrite having the formula Fe O .Na O or NaFeO If the electrodes are of copper .it is an oxid of copper which is formed and enters into the electrolyte and forms a solution of a compound whose formula is similar to that of the iron compound above referred to but with copper as its metallic element.

vVhen once the electrolyte has thus been prepared it may be used indefinitely and does not undergo exhaustion.

Assuming iron electrodes to have been used so that the electrolyte contains an iron oxid and the article to be colored is to-be colored a bright black, it is immersed in the bath, the bath is brought to a temperature of about 120 C. to 130 C. and the article is made to act as cathode for about 1 to 2 The article does not need to be preliminarily cleaned but may be immersed whether smooth or rusty direct in the bath. The current density employed is about 5 amperes per square decimeter of the surface to be colored.

While thus operating as cathode the article is both cleaned and plated with electrolytic iron. At the end of this period the current is reversed and the article made to serve as anodefor from six to eight minutes.

The result of this step is to form a bright black coating of oxid upon the article which may, however, be further strengthened and rendered more adhesive by subsequently immersing it for a few minutes in a solution of caustic soda having a density ofl/l, heated to about 140 C. and containing from 10% to 20% of sodium nitrate. Instead of sodium nitrate almost any metallic nitrate or aromatic nitro derivative may be employed in this solution.

If a dull black is desired the current should be reversed at least two or three times, taking care, however, to make the final direction such that the article acts as anode and that the current is continued for at least two minutes after the oxidation is complete. The completion of the oxidizing action is indicated by the voltage at the terminals of the bath; during the oxidizing process the voltage is in the neighborhood of 0.6 volts but rises to between 1.8 and 2 volts when oxidation is complete.

The colored articles, whether bright or dull, are dried and immersed for ten minutes oxidizing agents may also be added.

in a bath of olive oil heated to between 150 C. and 180 C. Instead of olive oil a mixture of linseed oil and mineral oil may be employed. Brushing the colored surface causes it to become brighter and brighter.

. If red or yellow shades of coloration are desired, the concentration of the bath must be increased to about 1.5 and the temperature to about 140 C. Nitrate of soda or other When arrangements have been made to deal with articles by a regular routine .the complete treatment of each batch takes from ten to fifteen minutes so that a batch is fully treated in approximately that time.

If it is desired to use a copper surface and color it the above processes described with reference to iron may be employed, using, however, copper electrodes and employing the conditions of temperature and concentration of the electrolyte given above for the black coloration of iron. The coloration is understood to be due to the formation of a closely adhering layer of oxid of iron or of copper as the case may be on the surface of the anode.

In a modified form of the process, the surface to be colored is covered with a deposit of electrolytic iron or copper which is subsequently oxidized by a simple immersion in an alkaline oxidizing solution, such as a solution of nitrate of sodium or other metallic nitrate, or aromatic nitro derivative.

' Theprocess, according to this invention, is easy to carry out and economical; the consumption of energy does not ordinarily exceed one watt hour per square decimeter of the surface treated. The consumption of the electrolyte is so slight as to be negligible.

The-heating of the bath may be carried out in any desired manner, but preferably by means of gas or electricity.

Havingnow particularly described and ascertainedthe nature of our said invention, and in what manner the same is to be performed, we declare that what we claim is:

1. The herein-described process of electrolytically coloring metallic surfaces, which consists in temporarily inserting the object to be treated, as a cathode, in a hot, dense alkaline solution containing an oxid of the metal to be deposited combined with an oxid of the alkali metal present; passing current through the electrolytic bath to deposit on the surface of said object a film of the first-mentioned metal; and exposing the surface so treated to oxidizing conditions in an alkaline bath. V

2. The herein-described process of electrolytically coloring metallic surfaces, which consists in temporarily inserting the object to be treated, as a cathode,-in a hot, dense alkaline solution containing an oxid of the metal to be deposited combined with an oxid of the alkali metal present; passing current through the electrolytic bath de osit on the surface of said object a film of t e firstmentioned metal; and temporarily'reversing the passage of the current through the bath and inserting the said object therein a s an. anode, so as to set up an oxidizing condition in the said bathfor action on the surface so treated.

mentioned metal and oxidizing the surfaceso treated in an alkaline bath containing an oxidizing compound. a

4. The herein-described process of electrolytically coloring metallic surfaces, which consists in temporarily inserting the object to be treated, as a cathode, in. a hot,

- dense alkaline solution containing an oxid of the metal to be deposited combined with an 'tures.

oxid of the alkali metal present and an alkaline nitrate; passin current through the electrolytic bath to eposit on the surface of said object a film of the first-mentioned metal and exposing the surface so treated to oxidizing conditions in an alkaline bath.

' 5. The herein-described process of electrolytically coloring metallic surfaces, which consists in passing current and repeatedly reversing it between electrodes of the metal to be deposited in, a bath of hot concentrated alkali to form an electrolyte comprising an oxid of the first-named metal combined with an oxid of the alkali metal present; temporarily inserting the object to be treated, as a cathode, in said electrolytic bath to deposit a film of said first named metal on the surface of said object; and exposing the surface'so treated to oxidizing conditions in an alkaline bath.---

In testimony whereof we aflix our signaraor. QUIRINO SEST'INT. DR; TITO RONDELLI.