US2118395A - Process of electrolytically depositing iron - Google Patents

Description

Patented May 24,

PATENT OFFICE PROCESS OF ELECTROLYTICAILY DEPOSIT- ING IRON William Arthur Crowder. Newark, N.'J., assignor to Pyrene Manufact N. 1., a corporation of De No-Drawing. Application July Serial No. 38,

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The present invention relates to the electrodeposition of iron and has for an object to produce iron deposits in ductile form, that is, in a form which can be machined as it leaves the 5 electrolyte without prior annealing.

In accordance with the invention,'the above object is attained by the use of an electrolyte having several important operating characteristics, allot which will hereinafter appear.

The iron deposits produced from this electrolyte, besides their ductility, are of a suitable crystal structure that will flrinly adhere to the base metal as is necessary in building up worn machine parts, and may be satisfactorily produced on aluminum, aluminum alloys, zinc, zinc alloys, lead, lead alloys, steel, copper, and brass for the purpose of electroforming and a base for other types of plating. Z

According to the process of the present inventio'n, iron is electrodeposited through a heated solution of ferrous sulphate in which solution hydrofluoric acid is present. Sodium fluoride is preferably also included in the solution, and the hydrofluoric acid may then be formed in situ by causing part of the sodium fluoride to react with sulphuric acid, sodium sulphate being also formed by the reaction as shown by the following equation:

In preparing the solution, it is essential ,that ferrous sulphate be employed in amount suiflcient to bring the solution, at the temperature of operation, to a specific gravity of substantially 1.25 (referred to water at 20 centlgrade), the prei'erred temperature of operation being 70 centigrade. The quantity of hydrofluoric acid should be such as to cause the solution to be operated at a pH ranging between 3.0 and 5.0. As to the amounts of sodium fluoride and sulphuric acid for producing the hydrofluoricacid in situ, grams of sodium fluoride and 2.5 cubic centimeters of concentrated sulphuric acid (66 Baum) both per litre of water, have been found satisfactory. With the sodium fluoride and sulphuric acid employed in such amounts, the hydrofluoric acid formed by reaction is the principal agent effecting anode corrosion during electrolysis. That is, it is the hydrofluoric acid, and

Company, Newark, ware substantially such as to cause it to be saturated therewith.

The solution of the invention need not be heated above the temperature of 70 centigrade for its satisfactory operation, maximum solubility of ferrous sulphate being reached .at this temperature.

An important feature of the invention resides in the specified solution concentration corre sponding to aspeciflc gravity of 1.25 (referred to water at 20 centigrade), which concentration is exceptionally high and is made possible essentially by the high activity of fluorine, which prevents passivity at the anodes. At this concentration, it has been found that the osmotic pressure in the'solution is such as to insure its most satisfactory operation. Substantially constant conditions are maintained in the solution, secondary anode corrosion being reduced to a minimum. That is, little iron is dissolved at the anodes when.the solution is not in service, and little iron over the amount necessary to produce the deposit at the cathode is dissolved under operating conditions. This even and quantitative solution at the anodes at a concentration corresponding to a specflc gravity of 1.25 (referred to water at 20 centigrade) acts to maintain the solution at that concentration.

The stated solution concentration corresponding to a specific gravity of 1.25 (referred to water at 20 centigrade) is a critical value. Thus, if at the temperature of operation the concentration of the solution is reduced to, say, the degree corresponding to a specific gravity of 1.2 (referred to water at 20 centigrade) the osmotic pressure is correspondingly reduced to a point where appreciable secondary anode corrosion.

takes place. Due to the high activity of fluorine, the solution at the anodes is so rapid during operation that rapid changes in the acidity of the solution take place, which changes not only necessitate pH measurements at short intervals, but also exert a detrimental eflect on the ductility of the deposit. If, on the other hand, at the temperature of operation the concentration of the solution is increased to, say, the degree corresponding to the speciflc gravity of 1.3 (referred to water at 20 centigrade) the osmotic pressure is increased to a point where all anode corrosion substantially ceases. During operation not only is the acidity of the solution increased, but also the cathode emciency or rate of deposit at the cathode is lowered, the deposit here again being adversely affected in character.

At the stated solution concentration corre produced. Moreoven evcn at those high ourrent densities, variation in rate of deposit is ef-v fectively prevented because of the substantially constant conditions maintained in the solution.

-It has been found that as the proportion of sodium fluoride is increased above 30 grams per litre, the solubility of the ferrous sulphate is correspondingly reduced, which has the effect of diminishing the range of current densities that may be satisfactorily employed.

Because of the presence of hydrofiuoricacid in the solution, any ferric salt with which the ferrous sulphate employed may have been contaminated, is immediately dissolved by reduction to the ferrous state, and during electrolysis any ferric salt which, because of oxidation of ferrous iron, may tend to precipitate out of the solution, is also reduced to the ferrous state, whereby the solution is maintained clear at all times. Hitherto the precipitation of basic iron salts has been the source of considerable difficulty in some electrolytes. Thus, these insoluble salts, it allowed to accumulate in the solution, cause rough deposits, as well as inclusions in such deposits, and must therefore be removed as fast as they are formed, as by continuously circulating the electrolyte through a suitable filter. Not only is the solution of the invention free from suspended particles and sediment at any time, but the necessity of continuous filtration is entirely eliminated.

As already stated, the solution of the inven tion is operated at a pH ranging between 3.0 and 5.0. These low acidities are-made possible because of the use of hydrofluoric acid as the active acid agent, complex ions being formed in the solution. And they may be used even when high densities of current are passed through the solution. Satisfactory deposits have thus been obtained from electrolytes operated within the range of pH values specified, and at a current density of 30 amperes per square decimeter.

Several advantages are obtained as a result of the low acidity values of the solution which may be employed;- One advantage is that the amount of hydrogen generated at the cathode is reduced to a minimum, which prevents the formation of brittle deposits normally caused by absorption of hydrogen. Another advantage is that the use of expensive diaphragms, such as asbestos bags or specially made porous pots, which has hitherto been required for collecting the insoluble impurities,such as gr phitic carbon, from the anodes, is eliminatedy/ 'hat is, simple canvas bags may be used to enclose the anodes, the collected impurities of course settling to the bottom of such bags so that they in no way hinder anode corrosion. Moreover, the use of elaborate ventilating systems and of expensive containers for containing the solution is also eliminated.

It is well known that the pH of an electrolyte is apt to change due to varying anodic conditions or other causes, such as accidental ccntamina tion with alkali or acid, and that such changes greatly minimized by the invention, there being several factors contributing to this effect. One factor has already been stated, namely, the even and quantitative solution at the anodes at the specified solution concentration corresponding to a specific gravity of 1.25 (referred to water at centigrade), which factor maintains the solution at that concentration. Another factor is the action of the sodium fluoride in the solution. That is, the sodium fluoride, when this substance is employed, acts as a buffer salt controlling the pH of the solution against any great variation due to any cause. It is to be particularly noted, however, that this buffer action is almost entirely eliminated in solutions having a degree of concentration appreciably less than that corresponding to a specific gravity of 1.25 (referred to water at 20 centigrade) In the practice of the invention, it has been found that, due to the fact that the iron in the anodes is completely dissolved, periodic cleaning of the anodes is unnecessary; there being no formation of insoluble coatings on their active surfaces.

The following procedure may be followed for producing an iron deposit in accordance with the invention:

A lead-lined tank suitably equipped with heating facilities is'filled approximately 80% full of water, which water is heated to a temperature of 70 centigrade. The precalculated amount of sodium fluoride, in the proportion of grams per litre of water, is then added to the water and dissolved therein; and, for the purpose of forming hydrofluoric acid, there is admixed with the resulting solution an amount of concentrated sulphuric acid (66 Baum) precalculated in the approximate proportion of 2.5 cubic centimeters per litre of water. Bags of ferrous sulphate are then suspended in the solution and are maintained therein until suificient ferrous sulphate has been dissolved to bring the specific gravity of the solution to 1.25 (referred to water at 20 centigrade), at the temperature of 70 centigrade. Upon removal of they ferrous sulphate bags, iron anodes contained in canvas bags and the object or objects to be electroplated are suspended in the solution; and, at the temperature of 70 centigrade, the anode and cathode terminal bars are connected to an electroplating generator of suitable capacity.

A pH test of the solution should then be made in order to determine whether it is necessary to add so-called addition reagents to correct the solution to the pH value desired. That is, an acidic correcting substance should be added if the acidity of the solution is to be increased, and an alkaline correcting substance should be added if the acidity of the solution is to be decreased. By this means, if necessary, the pH of the solution is preferably adjusted to 3.4, as measured by colorimetric methods, this value having been found most satisfactory in practice. As the correcting substances, sulphuric acid and sodium hydroxide are preferably employed. It is not advisable'to employ ammoniumihydroxide, as this substance has been found to have a deleterious effect on the machining properties of the deposit. As to the current density which may be employed, 20 amperes per square decimeter will produce satisfactory deposits for building up worn machine parts of for e1ectroforming.

When it is necessary to employ correcting substances, it has been found that if they are added to the solution by merely pouring them into the tank, they do not mix satisfactorily, thereby causing a detrimental localized condition to exist until the solution is stirred thoroughly. This difficulty can be overcome by employing a lead pipe for adding the correcting substances to the solution, in which pipe perforations have been provided at regular intervals. This pipe is placed in the corner of the tank, and is so formed as to also extend along the bottom of the tank. When the correcting, substances are poured through the upper end of the pipe, they are distributed through the perforations at several points in the solution, which insures their mixing with the solution before coming in contact with the object or objects being electroplated. This method of adding the correcting substances eliminates'the necessity of removing the object or objects being electroplated for the purpose of adlusting the solution.

It is to be understood that various modifications may be made in the electroplating process which has been described, without departing from the spirit of the invention.

What is claimed is:

1. The process of electrolytically depositing iron which comprises electroplating through a heated solution of ferrous sulphate containing hydrofluoric acid and sodium fluoride, the quantity of ferrous sulphate present in said solution? being sumcient to bring it at the temperature of operation to a specific gravity of substantially 1.25 referred to water at 20 centigrade, the quan tity of hydrofluoric acid present in said solution being such as to cause it to be operated at a pH ranging between 3.0 and 5.0, and the quantity of sodium fluoride present in said solution being substantially such as to cause it to be saturated therewith.

2. The process of electrolytically depositing iron which comprises electroplating through a heated solution of ferrous sulphate containing hydrofluoric acid formed by reacting sodium fluoride and sulphuric acid therein, the sodium fluoride being employed in excess of the quantity required for the reaction, the quantity of ferrous sulphate present in said solution being sufllcient Patent no. 2,118,595.

to bring it at the temperature of operation to a speciflc gravity of substantially 1.25 referred to water at 20- centigrade, the quantity of hydrofluoric acid formed in said solution being such as to cause it to be operated at a pH ranging between 3.0 and 5.0, and the excess of sodium fluoride present in said solution being substantially such as to cause it to be saturated therewith.

3. The process of electrolytically depositing iron which comprises electroplating through a heated solution formed by adding to water sodium fluoride substantially in the proportion of 30 grams per litre of water, sulphuric acid in amount to form by reaction with sodium fluoride sufflcient hydrofluoric acid to cause the solution to be operated at a pH ranging between 3.0 and 5.0, and ferrous sulphate in amount to bring the solution at the temperature of operation to a specific gravity of substantially 1.25 referred to water at 20 centigrade.

4. The process of electrolytically depositing. iron which comprises electroplating through a heated solution formed by adding to water sodium fluoride substantially in the proportion of 30 grams per litre of water, concentrated sulphuric acid substantially in the proportion of 2.5 cubic centimeters per litre of water, and ferrous sulphate in amount to bring the solution at the temperature of operation to a speciflc gravity of substantially 1.25 referred to water at 20 centigrade,

"said solution being maintained during operation 'at a pH of substantially 3.4.

5. .The process of electrolytically depositing iron which comprises electroplating through a heated solution formed by adding to water sodium fluoride in the proportion of 30 grams per litre of water, concentrated sulphuric acid in the proportion of 2.5 cubic centimeters per litre of water, and ferrous sulphate in amount to bring the solution at the temperature of operation to a speciflc gravity of 1.25 referred to water at 20 centigrade, said solution being operated at a temperature of centigrade, at a pH ranging between 3.0 and 5.0, and at a current density ranging between 15 and 30 amperes per square decimeter.

WILLIAM ARTHUR WILLIAM ARTHUR CHOWDER It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, first column, line 17, after the word "and" insert as; page 2, second column, lineYh, for "of" read or; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the'Patent Office.

Signed and sealed this 28th day of June, A. D. 1958.

(Seal) Henry Van Arsdale, Acting Commissioner of Patents.

stances, it has been found that if they are added to the solution by merely pouring them into the tank, they do not mix satisfactorily, thereby causing a detrimental localized condition to exist until the solution is stirred thoroughly. This difficulty can be overcome by employing a lead pipe for adding the correcting substances to the solution, in which pipe perforations have been provided at regular intervals. This pipe is placed in the corner of the tank, and is so formed as to also extend along the bottom of the tank. When the correcting, substances are poured through the upper end of the pipe, they are distributed through the perforations at several points in the solution, which insures their mixing with the solution before coming in contact with the object or objects being electroplated. This method of adding the correcting substances eliminates'the necessity of removing the object or objects being electroplated for the purpose of adlusting the solution.

It is to be understood that various modifications may be made in the electroplating process which has been described, without departing from the spirit of the invention.

What is claimed is:

1. The process of electrolytically depositing iron which comprises electroplating through a heated solution of ferrous sulphate containing hydrofluoric acid and sodium fluoride, the quantity of ferrous sulphate present in said solution? being sumcient to bring it at the temperature of operation to a specific gravity of substantially 1.25 referred to water at 20 centigrade, the quan tity of hydrofluoric acid present in said solution being such as to cause it to be operated at a pH ranging between 3.0 and 5.0, and the quantity of sodium fluoride present in said solution being substantially such as to cause it to be saturated therewith.

2. The process of electrolytically depositing iron which comprises electroplating through a heated solution of ferrous sulphate containing hydrofluoric acid formed by reacting sodium fluoride and sulphuric acid therein, the sodium fluoride being employed in excess of the quantity required for the reaction, the quantity of ferrous sulphate present in said solution being sufllcient Patent no. 2,118,595.

to bring it at the temperature of operation to a speciflc gravity of substantially 1.25 referred to water at 20- centigrade, the quantity of hydrofluoric acid formed in said solution being such as to cause it to be operated at a pH ranging between 3.0 and 5.0, and the excess of sodium fluoride present in said solution being substantially such as to cause it to be saturated therewith.

3. The process of electrolytically depositing iron which comprises electroplating through a heated solution formed by adding to water sodium fluoride substantially in the proportion of 30 grams per litre of water, sulphuric acid in amount to form by reaction with sodium fluoride sufflcient hydrofluoric acid to cause the solution to be operated at a pH ranging between 3.0 and 5.0, and ferrous sulphate in amount to bring the solution at the temperature of operation to a specific gravity of substantially 1.25 referred to water at 20 centigrade.

4. The process of electrolytically depositing. iron which comprises electroplating through a heated solution formed by adding to water sodium fluoride substantially in the proportion of 30 grams per litre of water, concentrated sulphuric acid substantially in the proportion of 2.5 cubic centimeters per litre of water, and ferrous sulphate in amount to bring the solution at the temperature of operation to a speciflc gravity of substantially 1.25 referred to water at 20 centigrade,

"said solution being maintained during operation 'at a pH of substantially 3.4.

5. .The process of electrolytically depositing iron which comprises electroplating through a heated solution formed by adding to water sodium fluoride in the proportion of 30 grams per litre of water, concentrated sulphuric acid in the proportion of 2.5 cubic centimeters per litre of water, and ferrous sulphate in amount to bring the solution at the temperature of operation to a speciflc gravity of 1.25 referred to water at 20 centigrade, said solution being operated at a temperature of centigrade, at a pH ranging between 3.0 and 5.0, and at a current density ranging between 15 and 30 amperes per square decimeter.

WILLIAM ARTHUR WILLIAM ARTHUR CHOWDER It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, first column, line 17, after the word "and" insert as; page 2, second column, lineYh, for "of" read or; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the'Patent Office.

Signed and sealed this 28th day of June, A. D. 1958.

(Seal) Henry Van Arsdale, Acting Commissioner of Patents.