US2541721A - Process for replenishing nickel plating electrolyte - Google Patents

Process for replenishing nickel plating electrolyte Download PDF

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US2541721A
US2541721A US22727A US2272748A US2541721A US 2541721 A US2541721 A US 2541721A US 22727 A US22727 A US 22727A US 2272748 A US2272748 A US 2272748A US 2541721 A US2541721 A US 2541721A
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nickel
electrolyte
plating
replenishing
direct current
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US22727A
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Roehl Edward Judson
Wesley Andrew
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Huntington Alloys Corp
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International Nickel Co Inc
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Priority to GB10180/49A priority patent/GB659335A/en
Priority to FR984887D priority patent/FR984887A/en
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    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25DPROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D21/00Processes for servicing or operating cells for electrolytic coating
    • C25D21/16Regeneration of process solutions
    • C25D21/18Regeneration of process solutions of electrolytes

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  • the present invention relates to a process for electrodepositing nickel employing an insoluble anode wherein the nickel content and acidity of the electrolyte employed are maintained substantially contant and, more particularly, to a feasible process for nickel plating with an insoluble anode wherein the nickel content and acidity of the nickel plating electrolyte are maintained substantially constant by electrolytic means and the electrolyte is maintained -in condition to permit the production of sound nickel electrodeposits therefrom.
  • insoluble anode processes for electroplating nickel offer distinct advantages in many fields. For example, in the plating of steel strip and wire, the electroforming of fine screen material and parts of intricate or irregular shape, plating the inside of tubes, etc., it is important that the distance separating anode from cathode be kept substantially constant and this is most readily accomplished by employing anodes which are substantially insoluble in the plating bath. As recognized by those skilled in the art, the metal ions for plating must be provided by the plating bath as substantially no metal ions are supplied by the anode in the insoluble anode plating process.
  • the copper plating solution can be re' plenished simply by passing it over copper scrap, etc., as the solution reacts with the copper to increase the copper content and decrease the acidity of the solution.
  • nickel presents an entirely different problem and, when replenishment of a depleted nickel electrolyte is attempted in a similar manner, the results are unsatisfactory and the method impracticable.
  • the rate of corrosion of the nickel scrap, etc., in the electrolyte is very low and, in addition, nickel has a ⁇ strong tendency toward passivity in the electrolyte, particularly the chloride-free electrolyte.
  • the process of the invention comprises electrodepositing nickel at a plating cathode by passing a direct current through an acid aqueous nickel sulfate plating electrolyte from an insoluble anode to the plating cathode (said insoluble anode and said cathode being at least in part immersed in said electrolyte), replenishing the nickel content of depleted plating electrolyte by passing a direct current therethrough between electrodes having a nickel surface exposed to the electrolyte at a current density of about l to 25 amperes per square foot of effective anode surface exposed to the electrolyte, reversing the direction of said direct current at intervals of about 1 to about 50 seconds, and'v electrodepositing nickel from the thus-replenished electrolyte.
  • the electrolyte can be transferred from the electroplating unit to the replenishing unit and returned either at a continuous or intermittent rate of transfer.
  • the aqueous acid nickel sulfate electrolyte employed in the process contains or is comprised essentially of about 100 to aboutv 400 grams of nickel sulfate per liter of electrolyte,
  • the electrolyte buffered with labout to about 50 grams of boric acid per liter, said electrolyte having a pH of about 0.75 to about 3.5, a temperature of about 100 to about 160 F., ,fand being substantially devoid of chlorides, i. e., containing not more than about 1 gram per liter of chloride ion, preferably not more than about 0.01 to 0.1 gram per liter.
  • the electrolyte contains about 250 to 350 grams per liter of nickel sulfate, about to 40 grams per liter boric acid, and has a pH of about 1 to 2.
  • the object of the replenishing operation is to maintain the composition of the electrolyte during the electroplating operation within the aforesaid ranges in order that plating may be satisfactorily carried out for long periods of time.
  • the current density employed in the electroplating operation may be from about 25 to about 2000 amperes per square foot.
  • an aqueous electrolyte containing or comprised essentially of about 300 grams per liter of nickel sulfate and about 30 grams per liter of boric acid, operated at a pH of about 1.5 and a temperature of about F. has been found to be satisfactory and to give optimum overall eniciency for the system in a closed circuit of lseparate electroplating and replenishing operations.
  • Control of electrolyte pH is also a critical aspect of the process as a whole because it has been found that when the pH is lower than about 0.75 the efficiency of electroplating is impracticably low, while when the pH is higher than about 3.5 the net gain'of nickel dissolved in the replenishing operation is impracticably low.
  • the nickel electrodes employed in the replenishing operation are preferably made of electrolytic nickel, although the nickel electrodes can be any, anode material which will supply dissolved nickel to the electrolyte when it acts as anode during the replenishing operation, e. g., cast or Wrought nickel anodes, and which does not introduce harmful amounts of contaminants into the nickel plating electrolyte.
  • a feature of the present invention is that a satisfactory regenerative plating system for nickel plating with an insoluble anode is provided in which an electrolytic replenishing operation has been devised wherein nickel is dissolved anodically at a favorably higher rate than it is deposited cathodically, i. e., wherein the anode eiiciency is favorably higher than the cathode eciency.
  • anode efficiencies should be at least as high as about 50% and may be as high as about 100% while cathode efliciencies may be as low as about 25% or 30%, but should not be over about 70%.
  • the difference between anode and cathode eiiiciencies may be about to about 70% and preferably should be about 50% or more.
  • the process of the present invention is preferably carried out using a substantially chloridefree nickel plating bath, i. e., a bath containing less than 0.1 gram of chloride ion per liter.
  • a substantially chloridefree nickel plating bath i. e., a bath containing less than 0.1 gram of chloride ion per liter.
  • amounts of chloride up to about 1 gram per liter e. g., about 0.01 to 1 gram per liter, do not adversely aiect operation of the process. It has been found that if the chloride ion content substantially exceeds this amount, the eiiiciency of the replenishing operation with respect to net gain of nickel dissolved is markedly reduced and other difficulties may be encountered.
  • the electrochemical efticiency 'of the replenishing operation is highest when both the current density and the pH of the electrolyte are low. If either of these factors approaches the permissible maximum recited herein it is preferred that the other factor be maintained near the minimum recited herein. For example, when replenishing is carried out at a current density of 25 amperes per square foot it is preferred that the pH of the electrolyte be about 1 or less. If the current density is only 1 ampere per square foot, then the pH of the electrolyte can be fas high as about 3.5. Various means may be employed to insure meeting the various requirements set forth hercinbefore.
  • the electrode area for each set of electrodes in the replenishing operation should be at least about ve times as great as the cathode area in the plating operation if it is desired to maintain substantially equal rates of depletion and replenishment of nickel in the system.
  • a drop in nickel content or increase in acidity indicates that nickel is being depleted more rapidly in the plating operation than it is being dissolved in the replenishing operation, while an increase in nickel content and decrease in acidity indicates the opposite.
  • Control measures such as increasing the electrode area in the replenishing operation can be employed to maintain the nickel content and acidity of the electrolyte substantially constant when the process embodying the invention is in operation. Other control measures may also be employed.
  • the rate of nickel dissolution in the replenishing operation can be increased or decreased by respective increases or decreases in current density without changing conditions in the plating operation.
  • the current density in the plating operation can be controlled to increase or decrease the rate of nickel depletion in the electrolyte, etc,
  • the impurities in the electrolyte can be tolerated within the following ranges:
  • Suitable equipment for carrying out the invention comprises an electroplating unit comprising an insoluble anode and a cathode, and having a direct current supply'; a replenishing unit comprising one or more nickel electrodes of each polarity andprovided with a direct current supply having current reversing means; means for circulating electrolyte between the two units (e. g., pumps, strrers, etc.) and conventional auxiliary equipment such as heating means, etc., for controlling conditions, etc., in the equipment.
  • the electroplating unit and the replenishing unit may be contained in separate cells (or tanks) or in separate compartments of the same cell (or tank), or may even be contained in the same compartment.
  • EXAMPLE A recirculating plating and replenishing system illustrated schematically in the drawing was set up comprising a plating tank l and a replenishing tank 2 of approximately equal size connected stirring devices in each tank and heating means y. 1 to maintain the electrolyte temperature.
  • the platlng' tank was provided with a cathode 8 and an insoluble anode 9 and the replenishing tank was provided with a row of live equal electrolytic nickel electrodes I disposed in face-to-face relationship and having alternate electric polarity. In this manner, four sets of electrode surfaces of equal effective area and of opposite polarity were provided.
  • Each tank was provided with an independent direct current power supply Il and I2, that to the replenishing tank being provided with current reversing means I3.
  • a chloridefree aqueous nickel sulfate plating bath was established containing about 300 grams of nickel sulfate per liter of electrolyte (72.5 grams per liter of nickel) and-30 grams of boric acid per liter. The bath was pllled according to standard procedure.
  • the bath pH was adjusted to 1.3 and the temperature was adjusted to and maintained at about 130 F. for the duration of the run, and the electrolyte was circulated between the tanks at a rate equivalent to a complete circulation of the electrolyte every 2 hours.
  • a run of 28 hours duration was then made during which the current density in the plating cell was maintained at about 40 amperes per square foot and that in the replenishing cell was maintained at about 10 amperes per square foot.
  • the direct current flow in the replenishing cell was reversed at 5-second intervals.
  • the effective area of one set of electrodes (effective area of each polarity) in the replenishing cell was about 8.67 times the cathode area in the plating cell.
  • the electrolyte pH was 1.2 and the nickel content was '70.7 grams per liter.
  • the metal deposit obtained during the run was stripped from the cathode and machined into tensile test strip specimens. Results of tests on these specimens are shown in Table I, together with comparative results obtained on nickel electrodeposited from a standard Watts-type bath using soluble anodes.
  • Test results on deposit obtaine from standard .Watts-type bath operated at 170 F., pH 1.0, a cathode current density of 50 amperes per square foot, containing 325 grams por liter nickel sulfate, 45 grams per liter nickel chloride and30 grams per liter of boric acid.
  • insoluble anodes made of lead preferably should not be used during the electroplating operation wherever slight lead contamination would .be harmful to the mechanical and/or physical properties of the resulting electrodeposited article.
  • articles made in the plating operation using lead anodes have satisfactory strength and ductility in the as-plated condition, these articles tend-to become weak and brittle upon annealing.
  • More preferred insoluble anodes may be fashioned from platinum or from platinum-base alloys containing other platinum-group metals. Thus, platinum alloys containing iridium up to 30% or rhodium up to 40% or ruthenium up to 15% may be used.
  • platinum may also be used, but if other platinumgroup metals are present they will be included in amounts exceeding about 0.01% each. Not only may platinum-base alloys containing palladium be employed but palladium-base alloys containing y platinum will also give acceptable results. Other precious metals, such as gold, also give acceptable results. Base metals having corrosion-resistant properties similar to tungsten may also be employed as well as tungsten.
  • magnetite may be mentioned as a suitable insoluble anode material. Graphite anodes produce acceptable nickel electrodeposits, but this material is not preferred because of its tendency to gradually disintegrate when used as anode in the electrolyte.
  • insoluble anode is used herein in its conventional sense and means a conducting material which is either completely insoluble or which corrodes in the bath at such a low rate that its replacement is yeconomical and practical and that it does not build up harmful soluble or insoluble impurities in the bath at an excessive rate.
  • the electrolyte should be subjected alternately to electroplating and replenishing operations. This will normally require circulating the electrolyte between the electroplating and replenishing uriits at a rate suiiicient to maintain the nickel concentration in the replenished electrolyte at a level suitable for further electroplating in the electroplating unit.
  • the proper rate of electrolyte transfer between these units necessary to achieve this result will vary with each application .since this rate depnds upon many variable factors such as the volume of the plating electrolyte, rate of extraction of nickel from the bath in the plating operation, rate of replenishment of nickel in the replenishing opf eration, etc.
  • electrolytic nickel is a high purity nickel containing more than 99% nickel (including a small amount of cobalt which is usually less than 1%).
  • the process for electrodepositing nickel which comprises establishing an aqueous nickel plating electrolyte essentially comprised of about 100 to 400 grams per liter of nickel sulfate, about to 50 grams per liter of boric acid, substantially devoid of chloride ions, ⁇ having a pH of about 0.75 .to 3.5 and a temperature of about 100 to 160 F., electrodepositing nickel from said electrolyte in an electroplating unit having a source of direct current, at least one insoluble anode and at least one cathode by passing a plating current from said direct current source through said electrolyte from said insoluble anode to said cathode to electrodeposit nickel at said cathode, ilowing said electrolyte to a replenishing unit comprising a source of reversible direct current in electrical connection with a plurality of nickel electrodes, substantially replenishing the nickel content of said plating electrolyte by passing therethrough between said electrodes direct current from said source of reversible direct current at a current density
  • aqueous nickel plating electrolyte is essentially comprised of about 250 to 350 grams of nickel sulfate per liter of electrolyte, about 20 to 40 grams per liter of boric acid, and has a pH of about l to 2, wherein the direct current in the replenishing unit ilows at a current density of about 5 to 15 amperes per square foot and wherein the direction of said current ⁇ is reversed at time intervals of about '3 to 7 seconds.
  • aqueous nickel plating electrolyte is essentially comprised of about 300 grams per liter of nickel sulfate, about 30 grams per liter of boric acid, and has a pH of about 1.5.
  • the process which comprises electrodepositing nickel by passing an electrodepositing current from an insoluble anode immersed in an aqueous vnickel sulfate plating electrolyte substantially devoid of chloride ion and having a pH of about 0.75 to 3.5 to a cathodeW likewise immersed in said electrolyte to electrodeposit nickel at said cathode, flowing said electrolyte t0 a replenishing unit.
  • the process for electrodepositing nickel which comprises establishing an aqueous nickel plating electrolyte essentially comprised of about 100 to 400 grams per liter of nickel sulfate, about 10 to 50 grams per. liter of boric acid, substantially devoid of chloride ions, having a pH of about 0.75 to 3.5 and a temperature of about 100 to 160 F., electrodepositing nickel irom said electrolyte in an electroplating unit having a source of direct current, at least one insoluble anode and at least one cathode by passing a plating current from said direct current source through said electrolyte from said insoluble anode to said cathode to electrodeposit nickel at said cathode, flowing said electrolyte to a replenishing unit comprising a source of reversible direct current in electrical connection with a plurality of electrolytic nickel electrodes, substantially replenishing the nickel content of said plating electrolyte by passing therethrough between said electrodes direct current from said source of reversible direct current at a current density of
  • aqueous nickel plating electrolyte is essentially comprised of about 250 to 350 grams of nickel sulfate per liter, about 20 to 40 grams of boric acid per liter, and has a pH of about 1 to 2, and wherein the direct current in the rel1 plenishing unit ows at a current density o! about 5 to 15 amperes per square foot and the in saidvelectrolyte a net gain of nickel Ydissolved direction of said current is reversed at intervals o1' about 3 to 7 seconds.
  • the process for electrodepositing nickel which comprises alternately subjecting to an electroplating operation and to a replenishing operation an aqueous nickel plating electrolyte containing about 100 to 400 grams of nickel sulfate per liter of electrolyte. ⁇ about to 50 grams per liter of boric acid, having a pH of about 0.75 to 3.5 and being substantially devoid of chloride ions, said electroplating operation comprising passing a plating current through said electrolyte between an insoluble anode and a cathode immersed therein to electrodeposit nickel at said cathode, said replenishing operation being conducted in a replenishing unit having a plurality of electrolytic nickel electrodes in electrical connection with a source of reversible direct current and comprising passing through said electrolyte between said electrodes Vdirect current from said source of reversible direct current at a current density of about 1 to 25 amperes per square foot
  • aqueous nickel plating electrolyte is essen# tially comprised of about 4v250 to 350 grains of nickel sulfate per liter, about 20 to 40 grams of boric acid per liter, and has a pH of about 1 to 2.

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Description

ETAL
Feb. 13, 1951 E. .1. RoEHL' PROCESS FOR REPLENISHING 'ICKEL PLATING ELECTROLYTE Filed April 22,
INVENTORS Ibn/Awa 170mm/ Foe/a wafrfwhrszy Patented Feb. 13, 1951 PROCESS FOR REPLENISHING NICKEL PLATIN G ELECTROLYTE Edward Judson Roehl, Little Silver, and Andrew Wesley, Plainfield, N. J., assignors to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware l Application April 22, 1948, Serial No.22,727
11 Claims. l
The present invention relates to a process for electrodepositing nickel employing an insoluble anode wherein the nickel content and acidity of the electrolyte employed are maintained substantially contant and, more particularly, to a feasible process for nickel plating with an insoluble anode wherein the nickel content and acidity of the nickel plating electrolyte are maintained substantially constant by electrolytic means and the electrolyte is maintained -in condition to permit the production of sound nickel electrodeposits therefrom.
It has been recognized in the art that insoluble anode processes for electroplating nickel offer distinct advantages in many fields. For example, in the plating of steel strip and wire, the electroforming of fine screen material and parts of intricate or irregular shape, plating the inside of tubes, etc., it is important that the distance separating anode from cathode be kept substantially constant and this is most readily accomplished by employing anodes which are substantially insoluble in the plating bath. As recognized by those skilled in the art, the metal ions for plating must be provided by the plating bath as substantially no metal ions are supplied by the anode in the insoluble anode plating process. This results in the disadvantage that the bat-h used for plating with an insoluble anodel becomes depleted in metal ion content and, since the metal ions plated out are replaced by an equivalent amount of hydrogen ions by electromechanical reactions, the acidity of the bath increases. Due to the combination of these factors, the bath eventually becomes unsuitable for further plating unless steps are taken to replenish the metal ion content and to decrease the acidity.
In `the plat-ing of copper using insoluble anodes, the copper plating solution can be re' plenished simply by passing it over copper scrap, etc., as the solution reacts with the copper to increase the copper content and decrease the acidity of the solution. However, nickel presents an entirely different problem and, when replenishment of a depleted nickel electrolyte is attempted in a similar manner, the results are unsatisfactory and the method impracticable. For example, the rate of corrosion of the nickel scrap, etc., in the electrolyte is very low and, in addition, nickel has a` strong tendency toward passivity in the electrolyte, particularly the chloride-free electrolyte. These and other factors require that the volume of solution and surface area of scrap used in the replenishing system be so impracticably large that no satisfactory method employing this principle hasyet been devised. Other` methods have been tried or proposed for the replenishment of depleted f are high and it is diilicult to maintain the diaphragm in good operating condition. Although many attempts have been made to remedy these and other shortcomings, none, as far as we are aware, was entirely successful when carried into commercial practice.
Thus, a definite need exists in the art to pro vide a successful method whereby nickel electrodeposits can be produced employing an insoluble anode, and at the same time, the nickel ion content and acidity of the electrolyte are maintained substantially constant in ranges where the production of sound nickel deposits at a satisfactory rate is feasible.
It is an object of the present invention to provide a process for electrodepositing nickel from a cell having an insoluble anode wherein the nickel content and pH of the electrolyte are maintained substantially constant.
It is still another object of the present invention to provide a method for replenishing the nickel content and maintaining the acidity of the electrolyte used in electrodepositing nickel employing an insoluble anode.
It is a further object of the present invention to provide an electrochemical method for simultaneously providing a supply of nickel ions to and diminishing the acidity of a nickel plating electrolyte.
It is a still further object of the present invention to provide a method for emciently dissolving nickel electrolytically. It is another object of the present invention to provide a method whereby electrolytic nickel may be dissolved electrolytically at high edlciency in a chloride-free nickel plating bath and, at the same time, to maintainthe bath in condition that satisfactory nickel electrodeposits may be produced therefrom at feasible rates of deposition and over long periods of time.
Other objects and advantages of the presen invention will become apparent from the following description taken in conjunction with the drawing which depicts schematically an embodiment of the invention.
Broadly stated, the process of the invention comprises electrodepositing nickel at a plating cathode by passing a direct current through an acid aqueous nickel sulfate plating electrolyte from an insoluble anode to the plating cathode (said insoluble anode and said cathode being at least in part immersed in said electrolyte), replenishing the nickel content of depleted plating electrolyte by passing a direct current therethrough between electrodes having a nickel surface exposed to the electrolyte at a current density of about l to 25 amperes per square foot of effective anode surface exposed to the electrolyte, reversing the direction of said direct current at intervals of about 1 to about 50 seconds, and'v electrodepositing nickel from the thus-replenished electrolyte. The reversal of direct current flow during the replenishing operation will usually be repeated as often as required to replace nickel removed from tlie electrolyte in prior electrodeposition and to provide the nickel concentration required for further electrodeposition of nickel from the replenished electrolyte. In practice, the electrolyte can be transferred from the electroplating unit to the replenishing unit and returned either at a continuous or intermittent rate of transfer. I
It is critical that three separate operating factors-be met in carrying outthe present invention. That is, in the replenishing operation the nickel `surface of the anode "must be maintained in an active condition and there must be an economically feasible difference between anode eiciency and a. lower cathode eiciency, while in the plating operation an opposing high electroplating efficiency, e. g., cathode efciency, must be maintained. Inability to meet any one of these operating factors would vitiate the entire process, and the present invention resides in the unexpected discovery of a set of conditions which enables satisfying these critical factors simultaneously.
These factors are met simultaneously by the cona nickel sulfate plating electrolyte such as described herein. Y
In practice, the aqueous acid nickel sulfate electrolyte employed in the process contains or is comprised essentially of about 100 to aboutv 400 grams of nickel sulfate per liter of electrolyte,
buffered with labout to about 50 grams of boric acid per liter, said electrolyte having a pH of about 0.75 to about 3.5, a temperature of about 100 to about 160 F., ,fand being substantially devoid of chlorides, i. e., containing not more than about 1 gram per liter of chloride ion, preferably not more than about 0.01 to 0.1 gram per liter. Preferably, the electrolyte contains about 250 to 350 grams per liter of nickel sulfate, about to 40 grams per liter boric acid, and has a pH of about 1 to 2. It is to be pointed out that the object of the replenishing operation is to maintain the composition of the electrolyte during the electroplating operation within the aforesaid ranges in order that plating may be satisfactorily carried out for long periods of time. The current density employed in the electroplating operation may be from about 25 to about 2000 amperes per square foot. By way of example, it may be said that an aqueous electrolyte containing or comprised essentially of about 300 grams per liter of nickel sulfate and about 30 grams per liter of boric acid, operated at a pH of about 1.5 and a temperature of about F., has been found to be satisfactory and to give optimum overall eniciency for the system in a closed circuit of lseparate electroplating and replenishing operations.
Control of electrolyte pH is also a critical aspect of the process as a whole because it has been found that when the pH is lower than about 0.75 the efficiency of electroplating is impracticably low, while when the pH is higher than about 3.5 the net gain'of nickel dissolved in the replenishing operation is impracticably low.
The nickel electrodes employed in the replenishing operation are preferably made of electrolytic nickel, although the nickel electrodes can be any, anode material which will supply dissolved nickel to the electrolyte when it acts as anode during the replenishing operation, e. g., cast or Wrought nickel anodes, and which does not introduce harmful amounts of contaminants into the nickel plating electrolyte.
A feature of the present invention is that a satisfactory regenerative plating system for nickel plating with an insoluble anode is provided in which an electrolytic replenishing operation has been devised wherein nickel is dissolved anodically at a favorably higher rate than it is deposited cathodically, i. e., wherein the anode eiiciency is favorably higher than the cathode eciency. When this condition is achieved, the
.function of the replenishing operation to supply nickelions and to decrease the acidity in-the platingl electrolyte which has been depleted in nickel ions and has become more acid in the plating operation is realized. In the present invention, this has been provided by control of critical features affecting the replenishing operation and including the reversal of the flow of the direct current applied between the electrodes employed in the replenishing operation, the time cycle of current reversal, the current density effective upon the electrodes, the pH and composition of the electrolyte. etc. It has been found that reversal ofthe direct current is essential and that the direct current must be reversed at intervals of from about 1 to about 50 seconds (cycles of about 2 to about 100 seconds), preferably at intervals of about 3 to 7 seconds e. g., 5 seconds. It is important to avoid reversing intervals shorter than about l second (for example, as represented by 60-cycle alternating current) or longer than about 50 seconds, as it has been found that both conditions produce low electrochemical e'iciency in the replenishing operation with the result that the net gain of nickel dissolved becomes too low for successful operation.' In addition to the foregoing, it is critical that the net current density applied on each electrode in each direction of current now be maintained within the aforementioned range of about 1 .to about 25 amperes per square foot in the replenishing operation, preferably about 5 to l5 amperes per square foot, e. g., 10 amperes per square foot, because at current density values below the minimum the rate of dissolution of nickel becomes impracticably low, while at current density values above the maximum the rate of deposition of nickel in the replenishing operation approaches and may even exceed the rate of dissolution of nickel therein, with the result that the net gain of nickel dissolved in the electrolyte decreases below practicable limits. It is preferred that 'the time intervals and current density in the replenishing operation be so chosen that the same number of ampere hours per square foot is alternately applied on the cathode side in each direction of current flow, e. g., the same current density and the same time interval for each reversal of current flow, as otherwise one set of electrodes would dissolve faster than the other set or might even grow at the expense of the other. In addition, some difficulties might be encountered by way of growths on one set of electrodes which might produce short circuits, particularly when the electrodes are closely spaced. From a practical standpoint, it is desirable to replace both sets of electrodes at the same time and to employ electrodes of substantially the same area.
As indicated hereinbefore, it is important that conditions in the replenishing operation be such that the rate of solution of nickel at the anode is favorably higher than the rate of deposition of nickel at the cathode, i. e., the anodic eficiency of the operation must be higher than the cathodic efiiciency. Thus, anode efficiencies should be at least as high as about 50% and may be as high as about 100% while cathode efliciencies may be as low as about 25% or 30%, but should not be over about 70%. The difference between anode and cathode eiiiciencies may be about to about 70% and preferably should be about 50% or more.
The process of the present invention is preferably carried out using a substantially chloridefree nickel plating bath, i. e., a bath containing less than 0.1 gram of chloride ion per liter. However, amounts of chloride up to about 1 gram per liter, e. g., about 0.01 to 1 gram per liter, do not adversely aiect operation of the process. It has been found that if the chloride ion content substantially exceeds this amount, the eiiiciency of the replenishing operation with respect to net gain of nickel dissolved is markedly reduced and other difficulties may be encountered.
It has been found that the electrochemical efticiency 'of the replenishing operation is highest when both the current density and the pH of the electrolyte are low. If either of these factors approaches the permissible maximum recited herein it is preferred that the other factor be maintained near the minimum recited herein. For example, when replenishing is carried out at a current density of 25 amperes per square foot it is preferred that the pH of the electrolyte be about 1 or less. If the current density is only 1 ampere per square foot, then the pH of the electrolyte can be fas high as about 3.5. Various means may be employed to insure meeting the various requirements set forth hercinbefore. For example, in a case where the current eiciency with respect to net gain of dissolved nickel in the replenishing operation is the same as the current emciency with respect to deposition of nickel in the plating operation and the replenishing operation is conducted with a current density of l0 amperes per square foot and the plating operation is operated at 50 amperes per square foot, the electrode area for each set of electrodes in the replenishing operation should be at least about ve times as great as the cathode area in the plating operation if it is desired to maintain substantially equal rates of depletion and replenishment of nickel in the system. By observing any-changes in the nickel ion content and/or pH of the electrolyte, it is possible to maintain control of the overall performance of the system. For example, a drop in nickel content or increase in acidity indicates that nickel is being depleted more rapidly in the plating operation than it is being dissolved in the replenishing operation, while an increase in nickel content and decrease in acidity indicates the opposite. Control measures such as increasing the electrode area in the replenishing operation can be employed to maintain the nickel content and acidity of the electrolyte substantially constant when the process embodying the invention is in operation. Other control measures may also be employed. For example, the rate of nickel dissolution in the replenishing operation can be increased or decreased by respective increases or decreases in current density without changing conditions in the plating operation. Likewise, the current density in the plating operation can be controlled to increase or decrease the rate of nickel depletion in the electrolyte, etc,
It is to be noted that small amounts of impurities which do not interfere with the working of the plating operation can be tolerated in the nickel sulfate electrolyte. In order to conform with accepted standards for good nickel plating practice, the impurities in the electrolyte can be tolerated within the following ranges:
Grams per liter If calcium is present, it may be included in amounts from about 0.002 gram per liter up to the concentration at which CaSO4 precipitates.
Suitable equipment for carrying out the invention comprises an electroplating unit comprising an insoluble anode and a cathode, and having a direct current supply'; a replenishing unit comprising one or more nickel electrodes of each polarity andprovided with a direct current supply having current reversing means; means for circulating electrolyte between the two units (e. g., pumps, strrers, etc.) and conventional auxiliary equipment such as heating means, etc., for controlling conditions, etc., in the equipment. The electroplating unit and the replenishing unit may be contained in separate cells (or tanks) or in separate compartments of the same cell (or tank), or may even be contained in the same compartment.
In order that those skilled in the art may have a better understanding of the present invention, the following illustrative example is given describing the operation of a regenerative plating system for plating nickel using an insoluble anode.
EXAMPLE A recirculating plating and replenishing system illustrated schematically in the drawing was set up comprising a plating tank l and a replenishing tank 2 of approximately equal size connected stirring devices in each tank and heating means y. 1 to maintain the electrolyte temperature.
The platlng' tank was provided with a cathode 8 and an insoluble anode 9 and the replenishing tank was provided with a row of live equal electrolytic nickel electrodes I disposed in face-to-face relationship and having alternate electric polarity. In this manner, four sets of electrode surfaces of equal effective area and of opposite polarity were provided. Each tank was provided with an independent direct current power supply Il and I2, that to the replenishing tank being provided with current reversing means I3. A chloridefree aqueous nickel sulfate plating bath was established containing about 300 grams of nickel sulfate per liter of electrolyte (72.5 grams per liter of nickel) and-30 grams of boric acid per liter. The bath was pllled according to standard procedure. Thereafter, the bath pH was adjusted to 1.3 and the temperature was adjusted to and maintained at about 130 F. for the duration of the run, and the electrolyte was circulated between the tanks at a rate equivalent to a complete circulation of the electrolyte every 2 hours. A run of 28 hours duration was then made during which the current density in the plating cell was maintained at about 40 amperes per square foot and that in the replenishing cell was maintained at about 10 amperes per square foot. The direct current flow in the replenishing cell was reversed at 5-second intervals. The effective area of one set of electrodes (effective area of each polarity) in the replenishing cell was about 8.67 times the cathode area in the plating cell. At the end of the run, the electrolyte pH was 1.2 and the nickel content was '70.7 grams per liter. The metal deposit obtained during the run was stripped from the cathode and machined into tensile test strip specimens. Results of tests on these specimens are shown in Table I, together with comparative results obtained on nickel electrodeposited from a standard Watts-type bath using soluble anodes.
TABLE I Test results 'on electrolytic nickel from sulfate bath.
Thickness, Hardness, Tensile Percent Elongaton in* in. VHN 1 Strength lll 1%!! 2l .033 167 76,000 as 20 1s .osa 162 18,000 29 22 19 .030 o 71.000 s0 22 19 1.034 14s v68,250 24 20 n. d.
n. d.=not determined.
l Vickers hardness number-l0 k load.
1 Test results on deposit obtaine from standard .Watts-type bath operated at 170 F., pH 1.0, a cathode current density of 50 amperes per square foot, containing 325 grams por liter nickel sulfate, 45 grams per liter nickel chloride and30 grams per liter of boric acid.
electroformed articles and the like. Operation of the present process is attended by numerous practical advantages. Thus, no anode bags are needed in the plating operation; undesirable contaminants can readily be excluded or eliminated from the electrolyte; close control of the anode to cathode distance in the plating operation can be maintained; electrodes may be closely spaced in the replenishing operation; nickel is supplied to the electrolyte from nickel electrodes which can ,be'of high purity, e. g., electrolytic nickel, and
',ode plating process, comparing favoroably even with soluble anode plating processes.
It is to be pointed out that insoluble anodes made of lead preferably should not be used during the electroplating operation wherever slight lead contamination would .be harmful to the mechanical and/or physical properties of the resulting electrodeposited article. For example, although articles made in the plating operation using lead anodes have satisfactory strength and ductility in the as-plated condition, these articles tend-to become weak and brittle upon annealing. More preferred insoluble anodes may be fashioned from platinum or from platinum-base alloys containing other platinum-group metals. Thus, platinum alloys containing iridium up to 30% or rhodium up to 40% or ruthenium up to 15% may be used. As previously indicated, pure platinum may also be used, but if other platinumgroup metals are present they will be included in amounts exceeding about 0.01% each. Not only may platinum-base alloys containing palladium be employed but palladium-base alloys containing y platinum will also give acceptable results. Other precious metals, such as gold, also give acceptable results. Base metals having corrosion-resistant properties similar to tungsten may also be employed as well as tungsten. Among the nonmetallic materials, magnetite may be mentioned as a suitable insoluble anode material. Graphite anodes produce acceptable nickel electrodeposits, but this material is not preferred because of its tendency to gradually disintegrate when used as anode in the electrolyte. The term insoluble anode is used herein in its conventional sense and means a conducting material which is either completely insoluble or which corrodes in the bath at such a low rate that its replacement is yeconomical and practical and that it does not build up harmful soluble or insoluble impurities in the bath at an excessive rate.
It will be recognized from the foregoing that the electrolyte should be subjected alternately to electroplating and replenishing operations. This will normally require circulating the electrolyte between the electroplating and replenishing uriits at a rate suiiicient to maintain the nickel concentration in the replenished electrolyte at a level suitable for further electroplating in the electroplating unit. The proper rate of electrolyte transfer between these units necessary to achieve this result will vary with each application .since this rate depnds upon many variable factors such as the volume of the plating electrolyte, rate of extraction of nickel from the bath in the plating operation, rate of replenishment of nickel in the replenishing opf eration, etc. As indicated hereinbefore, these factors are controlled by the current densities employed in both the electroplating and replenishing operations, the number of current reversals during the replenishing operation and the intervals at which the current is reversed in the replenishing operation and the pH and composition of the plating bath.
As indicated hereinbefore, any anode materials which will supply dissolved nickel to the electrolyte when acting as anode therein and which do not introduce harmful amounts of impurities such as iron, zinc, etc., into the electrolyte may be employed as electrodes in the replenishing operation, but it is preferred that electrolytic nickel anodes be used. As those skilled in the art know, electrolytic nickel is a high purity nickel containing more than 99% nickel (including a small amount of cobalt which is usually less than 1%).
Other satisfactory soluble anodes (i. e., anodes which show good activity and which dissolve readily in the nickel electrolyte)v which may be employed in the replenishing operation are cast and wrought nickel anodes usually having analyses within the following ranges:
Although the present invention has been described in conjunction with preferred embodiments. it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such variations and modifications are to be considered within the purview and scope of the invention and the appended claims.
We claim:
l. The process for electrodepositing nickel which comprises establishing an aqueous nickel plating electrolyte essentially comprised of about 100 to 400 grams per liter of nickel sulfate, about to 50 grams per liter of boric acid, substantially devoid of chloride ions,` having a pH of about 0.75 .to 3.5 and a temperature of about 100 to 160 F., electrodepositing nickel from said electrolyte in an electroplating unit having a source of direct current, at least one insoluble anode and at least one cathode by passing a plating current from said direct current source through said electrolyte from said insoluble anode to said cathode to electrodeposit nickel at said cathode, ilowing said electrolyte to a replenishing unit comprising a source of reversible direct current in electrical connection with a plurality of nickel electrodes, substantially replenishing the nickel content of said plating electrolyte by passing therethrough between said electrodes direct current from said source of reversible direct current at a current density of about l to 25 amperes per square foot while repeatedly reversing the direction of said direct current at time intervals of about l to 50 seconds to obtain a net gain of nickel dissolved from said electrodes, flowing the thus-replenished electrolyte to an electroplating unit and electrodepositing nickel from the thus-replenished electrolyte.
2. The process according to claim i wherein the aqueous nickel plating electrolyte is essentially comprised of about 250 to 350 grams of nickel sulfate per liter of electrolyte, about 20 to 40 grams per liter of boric acid, and has a pH of about l to 2, wherein the direct current in the replenishing unit ilows at a current density of about 5 to 15 amperes per square foot and wherein the direction of said current` is reversed at time intervals of about '3 to 7 seconds.
3. The process according to claim 2 wherein the current in the replenishing unit ilows at a current density of about 10 amperes per square foot and wherein the direction of said current is reversed at intervals of about 5 seconds.
4. The process according to claim 3 wherein the aqueous nickel plating electrolyte is essentially comprised of about 300 grams per liter of nickel sulfate, about 30 grams per liter of boric acid, and has a pH of about 1.5.
5. The process which comprises electrodepositing nickel by passing an electrodepositing current from an insoluble anode immersed in an aqueous vnickel sulfate plating electrolyte substantially devoid of chloride ion and having a pH of about 0.75 to 3.5 to a cathodeW likewise immersed in said electrolyte to electrodeposit nickel at said cathode, flowing said electrolyte t0 a replenishing unit. replenishing the nickel content of said plating electrolyte insaid re\ plenishing unit by owing therethrough between nickel electrodes direct current at a current density of about 1 to 25 amperes per square foot from a source of reversible direct current while reversing the direction of said direct cfirrent at intervals of about 1 to 50 seconds. iiowing the thus-replenished electrolyte to an electrodepositing unit comprising an insoluble anode and a cathode and electrocienositing nickel from the thus-replenished electrolyte.
6. The process for electrodepositing nickel which comprises establishing an aqueous nickel plating electrolyte essentially comprised of about 100 to 400 grams per liter of nickel sulfate, about 10 to 50 grams per. liter of boric acid, substantially devoid of chloride ions, having a pH of about 0.75 to 3.5 and a temperature of about 100 to 160 F., electrodepositing nickel irom said electrolyte in an electroplating unit having a source of direct current, at least one insoluble anode and at least one cathode by passing a plating current from said direct current source through said electrolyte from said insoluble anode to said cathode to electrodeposit nickel at said cathode, flowing said electrolyte to a replenishing unit comprising a source of reversible direct current in electrical connection with a plurality of electrolytic nickel electrodes, substantially replenishing the nickel content of said plating electrolyte by passing therethrough between said electrodes direct current from said source of reversible direct current at a current density of about 1 to 25 amperes per square footmwhile repeatedly reversing the direction of said direct current at time intervals of' about 1 to 50 seconds to obtain a net gain of nickel dissolved from said electrodes, flowing the thus-replenished electrolyte to an electroplatingl unit and electrodepositing nickel from the thus-replenished electrolyte.
7. Theprocess according to claim 6 wherein the aqueous nickel plating electrolyte is essentially comprised of about 250 to 350 grams of nickel sulfate per liter, about 20 to 40 grams of boric acid per liter, and has a pH of about 1 to 2, and wherein the direct current in the rel1 plenishing unit ows at a current density o! about 5 to 15 amperes per square foot and the in saidvelectrolyte a net gain of nickel Ydissolved direction of said current is reversed at intervals o1' about 3 to 7 seconds.
8. The process according to' lclaim 7 whereinthe current in the replenishing unit iiows at' a 10. The process for electrodepositing nickel which comprises alternately subjecting to an electroplating operation and to a replenishing operation an aqueous nickel plating electrolyte containing about 100 to 400 grams of nickel sulfate per liter of electrolyte.` about to 50 grams per liter of boric acid, having a pH of about 0.75 to 3.5 and being substantially devoid of chloride ions, said electroplating operation comprising passing a plating current through said electrolyte between an insoluble anode and a cathode immersed therein to electrodeposit nickel at said cathode, said replenishing operation being conducted in a replenishing unit having a plurality of electrolytic nickel electrodes in electrical connection with a source of reversible direct current and comprising passing through said electrolyte between said electrodes Vdirect current from said source of reversible direct current at a current density of about 1 to 25 amperes per square foot while reversing the direction of iiow of said direct current at least once at intervals of about 1 to 50 seconds to' obtain from said electrodes.
11. The process according to claim 10 wherein the aqueous nickel plating electrolyte is essen# tially comprised of about 4v250 to 350 grains of nickel sulfate per liter, about 20 to 40 grams of boric acid per liter, and has a pH of about 1 to 2.
EDWARD JUDSON ROEI-IL. ANDREW WESLEY.
nErEltE-Ncns CITED The following references are ofrecord inthe le of this patent:
UNITEDl STATES PATENTS Number Name Date 1,003,092 Dow et al Sept. 12, 1911 1,144,680 Allers June 29, 1915 1,885,148 Smith Nov. 1, 1932 2,431,949 Martz Dec. 2, 1947 2,449,422 Smith Sept. 14, 1948 2,449,495 Lum Sept. 14, 1948 2,451,341 Jernstedt Oct. 12, 1948 2,470,775 Jernstedt et al May 24, 1949 FOREIGN PATENTS Number Country Date 310,099 Great Britain Apr. 25, 1929 y 49,384 f Denmark Oct. 15, 1934 OTHER. REFERENCES Transactions of the Electrochemical Society, Watts, vol. 59 (1931), page 381.
Blum et al., Transactions of the Faraday Society, vol. 31 (1935), page 1208.
Finch et al., Transactions of the Faraday Society, vol. 33 (1937) page 566.

Claims (1)

1. THE PROCESS FOR ELECTRODEPOSITING NICKEL WHICH COMPRISES ESTABLISHING AN AQUEOUS NICKEL PLATING ELECTROLYTE ESSENTIALLY COMPRISED OF ABOUT 100 TO 400 GRAMS PER LITER OF NICKEL SULFATE, ABOUT 10 TO 50 GRAMS PER LITER OF BORIC ACID, SUBSTANTIALLY DEVOID OF CHLORIDE IONS, HAVING A PH OF ABOUT 0.75 TO 3.5 AND A TEMPERATURE OF ABOUT 100* TO 160* F., ELECTRODEPOSITING NICKEL FROM SAID ELECTROLYTE IN AN ELECTROPLATING UNIT HAVING A SOURCE OF DIRECT CURRENT, AT LEAST ONE INSOLUBLE ANODE AND AT LEAST ONE CATHODE BY PASSING A PLATING CURRENT FROM SAID DIRECT CURRENT SOURCE THROUGH SAID ELECTROLYTE FROM SAID INSOLUBLE ANODE TO SAID CATHODE TO ELECTRODEPOSIT NICKEL AT SAID CATHODE, FLOWING SAID ELECTROLYTE TO A REPLENISHING UNIT COMPRISING A SOURCE OF REVERSIBLE DIRECT CURRENT IN ELECTRICAL CONNECTION WITH A PLURALITY OF NICKEL ELECTRODES, SUBSTANTIALLY REPLENISHING THE NICKEL CONTENT OF SAID PLATING ELECTROLYTE BY PASSING THERETHROUGH BETWEEN SAID ELECTRODES DIRECT CURRENT FROM SAID SOURCE OF REVERSIBLE DIRECT CURRENT AT A CURRENT DENSITY OF ABOUT 1 TO 25 AMPERES PER SQUARE FOOT WHILE REPEATEDLY REVERSING THE DIRECTION OF SAID DIRECT CURRENT AT TIME INTERVALS OF ABOUT 1 TO 50 SECONDS TO OBTAIN A NET GAIN OF NICKEL DISSOLVED FROM SAID ELECTRODES, FLOWING THE THUS-REPLENISHED ELECTROLYTE TO AN ELECTROPLATING UNIT AND ELECTRODEPOSITING NICKEL FROM THE THUS-REPLENISHED ELECTROLYTE.
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DE1145889B (en) * 1952-07-19 1963-03-21 Gen Am Transport Process for the regeneration of continuously working baths for chemical nickel plating
US3256165A (en) * 1961-06-19 1966-06-14 Anocut Eng Co Method and apparatus for use in electrolytic shaping
DE1262728B (en) * 1952-07-19 1968-03-07 Gen Am Transport Device for carrying out a continuous chemical nickel plating process
US3474011A (en) * 1967-08-03 1969-10-21 American Bank Note Co Electroplating method and apparatus
US3496082A (en) * 1964-10-19 1970-02-17 Ransburg Electro Coating Corp Electrophoretic coating method and apparatus utilizing bath circulation to minimize impurities
DE3002520A1 (en) * 1979-01-25 1980-08-07 Inoue Japax Res GALVANOPLASTIC DEVICE
EP0079032A1 (en) * 1981-11-06 1983-05-18 Bayerische Motoren Werke Aktiengesellschaft, Patentabteilung AJ-3 Apparatus for electroplating a metallic workpiece
EP0398735A2 (en) * 1989-05-19 1990-11-22 Sun Industrial Coatings Private Limited Plating system
US5804053A (en) * 1995-12-07 1998-09-08 Eltech Systems Corporation Continuously electroplated foam of improved weight distribution
US6056862A (en) * 1997-10-30 2000-05-02 Daiki Engineering Co., Ltd. Process and apparatus for supplying metal ions to alloy electroplating bath
US6251255B1 (en) * 1998-12-22 2001-06-26 Precision Process Equipment, Inc. Apparatus and method for electroplating tin with insoluble anodes
WO2010043776A1 (en) * 2008-10-14 2010-04-22 Siemens Vai Metals Technologies Sas Method and installation for electrolytic tinning of a continuously running steel strip in an electrodeposition unit
US20150136609A1 (en) * 2013-10-31 2015-05-21 Ebara Corporation Sn ALLOY PLATING APPARATUS AND Sn ALLOY PLATING METHOD
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GB310099A (en) * 1928-01-26 1929-04-25 George Lawton Electro copper (or other metal similarly deposited) lined hollow drill steel, for goldmining and similar purposes
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DE1145889B (en) * 1952-07-19 1963-03-21 Gen Am Transport Process for the regeneration of continuously working baths for chemical nickel plating
DE1262728B (en) * 1952-07-19 1968-03-07 Gen Am Transport Device for carrying out a continuous chemical nickel plating process
US2955944A (en) * 1953-07-03 1960-10-11 Gen Motors Corp Electroless nickel plating bath control
US3256165A (en) * 1961-06-19 1966-06-14 Anocut Eng Co Method and apparatus for use in electrolytic shaping
US3496082A (en) * 1964-10-19 1970-02-17 Ransburg Electro Coating Corp Electrophoretic coating method and apparatus utilizing bath circulation to minimize impurities
US3474011A (en) * 1967-08-03 1969-10-21 American Bank Note Co Electroplating method and apparatus
DE3002520A1 (en) * 1979-01-25 1980-08-07 Inoue Japax Res GALVANOPLASTIC DEVICE
EP0079032A1 (en) * 1981-11-06 1983-05-18 Bayerische Motoren Werke Aktiengesellschaft, Patentabteilung AJ-3 Apparatus for electroplating a metallic workpiece
US5087333A (en) * 1989-05-19 1992-02-11 Sun Industrial Coatings Private Limited Method and apparatus for electroplating
EP0398735A3 (en) * 1989-05-19 1990-12-19 Sun Industrial Coatings Private Limited Plating system
EP0398735A2 (en) * 1989-05-19 1990-11-22 Sun Industrial Coatings Private Limited Plating system
US5804053A (en) * 1995-12-07 1998-09-08 Eltech Systems Corporation Continuously electroplated foam of improved weight distribution
US6056862A (en) * 1997-10-30 2000-05-02 Daiki Engineering Co., Ltd. Process and apparatus for supplying metal ions to alloy electroplating bath
US6251255B1 (en) * 1998-12-22 2001-06-26 Precision Process Equipment, Inc. Apparatus and method for electroplating tin with insoluble anodes
WO2010043776A1 (en) * 2008-10-14 2010-04-22 Siemens Vai Metals Technologies Sas Method and installation for electrolytic tinning of a continuously running steel strip in an electrodeposition unit
WO2010043774A1 (en) * 2008-10-14 2010-04-22 Siemens Vai Metals Technolo Ies Sas Method and installation for electrolytic tinning of a continuously running steel strip in an electrodeposition unit
RU2476630C2 (en) * 2008-10-14 2013-02-27 Сименс Фаи Металз Текнолоджиз Сас Method and device for electrolytic tinning of continuously moving steel strip in electrodeposition module
EP2606163A4 (en) * 2010-08-18 2015-10-07 Macdermid Inc NICKEL pH ADJUSTMENT METHOD AND APPARATUS
US20150136609A1 (en) * 2013-10-31 2015-05-21 Ebara Corporation Sn ALLOY PLATING APPARATUS AND Sn ALLOY PLATING METHOD
US9551084B2 (en) * 2013-10-31 2017-01-24 Ebara Corporation Sn alloy plating apparatus and Sn alloy plating method

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