FR2668173A1 - PROCESS FOR FORMING AN ELECTROLYTIC NICKEL COATING WITH REDUCTION OF THE ACCUMULATION OF NICKEL IONS. - Google Patents

Abstract

The invention relates to a method for forming an electrolytic coating of nickel on a conductive substrate, the purpose of which is to prevent the accumulation of nickel ions in the electrolyte. A sacrificial anode and an insoluble iron anode are immersed in a bath for the electrolytic coating of nickel. The current supplied to the iron anode is controlled during coating so as to reduce the amount of nickel buildup in solution.

Description

1 2668173

  The present invention relates to an improved process for forming an electrolytic coating, in which there is a reduction in the accumulation of soluble anodic metals; more particularly, it relates to the reduction of the undesirable accumulation of nickel ions in a process or an electrolytic coating bath of nickel or ferro-nickel by the use in the process of an insoluble ferrite electrode. Electroplating specialists have long recognized that the use of soluble nickel anodes in baths containing a nickel electrolyte or a ferro-nickel electrolyte can cause a large build-up of excess nickel ions in the solution. of the electrolyte The problem of metal accumulation has become much more serious in recent years due to the greater restrictions on the amount of metallic nickel allowed in the discharged effluents Therefore, most of the solution of electrolytic coating which is extracted is returned to the original solution This can be done using common methods such as evaporative recovery or reverse osmosis This accumulation of nickel ions creates several unwanted side effects in the bath and the electrolytic coating process These side effects can occur t include, for example, moiré, pitted or rough deposits which may occur due to the presence of excess amounts of nickel sulfate and nickel chloride Precipitates may also form when compliance limits are exceeded Nickel in excess also has the effect of significantly increasing the costs relating to the bath. For example, since the bath must ultimately be diluted, the existence of excess nickel ions therein is not only harmful to the environment, but increases the cost of treating

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  electrolyte waste before disposal In addition, the existence of unused nickel ions is proof of ineffectiveness. While one does not wish to be bound by theory, it appears that the technician knows that this accumulation is due to the disparity between the final efficiency of the anode and that of the cathode. For example, in a "typical" nickel bath ", the efficiency of the anode is 100% In contrast, the efficiency of the cathode is only about 95% The difference in yields has the effect that the amount of nickel ions in solution increases during electrolysis Similarly , in a typical nickel-iron bath, the anode has a yield of 100%, while that of the cathode is approximately 91%; this greater difference in yields causes an even greater increase in the nickel ions in

solution during electrolysis.

  We have tried to solve this problem in many ways For example, we have tried to solve the problem by reducing the number of anodes used in the solution However, this simply increases the current density of the anode so that more ions metal per given anode dissolve Polarization of the anode can also occur, which causes greater consumption of the brightening agent in typical baths, and in ferro-nickel baths produces unwanted ferric ions (Fe + 3 ) The polarization of the anode also leads to the rupture of the transformation agents into

  complex used in ferro-nickel baths.

  In addition, excessive generation of chlorine (also very undesirable in these baths) can occur

  when using such polarized anodes.

  Insoluble anodes, such as platinum-coated titanium anodes, have been used in nickel-plating electrolytes so as to increase the thickness of the coating in areas of low current density; such an anode can also reduce the accumulation of nickel ions. Similarly, carbon type anodes insoluble in nickel and ferro-nickel electrolytes have also been used. While the accumulation of nickel in these coating baths can be reduced. electrolytic with anodes of this type, the anodes that have been used previously in the art (for example, titanium anodes coated with platinum) tend to deteriorate rapidly; to have a high replacement cost; possibly causing increased consumption of the brightening agent; and, can contribute to the production of

  harmful decomposition products.

  It is sometimes accepted that sintered ferrite electrodes are insoluble anodes which may be useful in electrolytic coating processes of cyanide-free copper, or to reduce hexavalent chromium ions in chromium plating processes. Such uses are disclosed in the patents. United States of America No. 4,469,569; 4,466,865 and 4,933,051, which are incorporated here for reference. However, the Applicant believes that the use of these sintered anodes in nickel coating baths has not been disclosed or suggested in the art. in detail of such electrodes in S Wakabayashi and T Aoki, Characteristics of Ferrite Electrodes, journal de Physique, April 1977, Cl-241 to Cl-244. According to the present invention, an electrolytic coating process with nickel is provided, in which the accumulation of nickel ions in a nickel-based electroplating solution is substantially reduced and / or eliminated by using a selected class. insoluble anodes which can be ordered separately for the amount of current transmitted to the insoluble anode during

  electrolytic coating in the nickel bath.

  The insoluble anode of the present invention has a surface which consists at least in part of a composition

of iron.

  The method of the present invention comprises the steps of providing an electrolytic nickel coating bath and immersing a first anode and a second anode in the bath The first anode is a sacrificial nickel anode and is connected to a first rectifier The second anode is an insoluble anode in which at least part of the surface comprises iron The second anode is connected to a second rectifier A substrate to be coated is then immersed in the electroplating bath and cathodically electrified The first anode is anodically electrified while the current flowing to the second anode is regulated so as to supply an effective amount of current to the second anode during the electrolytic coating of the substrate in order to prevent the accumulation of nickel ions in

excess in the solution.

  It has thus been found that with the new process of the present invention, it is possible to substantially reduce the accumulation of nickel, hence the increase in the life of the coating bath and the corresponding reduction in the concentrations of nickel ions which must be arranged later. In addition, the iron anode of the present invention has a significantly increased life compared to anodes of the titanium-platinum type or of the carbon type which have been used in the prior art, hence the decrease in replacement and shutdown costs caused by

  insoluble anodes of the prior art.

  In general, the method of the present invention comprises the following steps An effective nickel-based electrolytic coating bath is first supplied A first anode is immersed in the bath which is connected to a first rectifier A second anode connected to a second rectifier is immersed in the bath The second anode is an insoluble anode in which at least part of the surface comprises an iron composition A substrate to be coated is then immersed in the bath The first anode is anodically electrified and the substrate is cathodically electrified At the same time, the current flowing to the second anode is regulated by the second rectifier so as to supply an effective amount of current to the second anode, to prevent the accumulation of excess nickel ions in the

solution.

  The present invention is based on the discovery that the use of an insoluble anode containing iron, while regulating the current supplied to this anode, significantly reduces the amount of nickel ions which accumulate in these solutions of the nickel bath. The process of the present invention can be used in industrial nickel plating baths

  conventional or in coating baths with nickel-

  iron which is currently used. Thus, standard industrial baths which include appropriate concentrations of nickel ions, brighteners, complexing agents or chelating agents, level equalizers, surfactants, and other similar additives, which are generally used in nickel-plating baths, can be used in the process of the present invention. Similarly, additives and additions which are commonly used in nickel-iron baths can be used. , in the process of the present invention. The first anode used in the present invention is generally a sacrificial anode which may include, for example, a basket of titanium or the like, filled with suitable nickel pieces, which are sacrificially added to the bath solution while the plating process continues The first sacrificial anode is connected to a rectifier

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  separated from the second anode so that current can be controlled independently between the two

  anodes during the electroplating process.

  In general, the second anode used in the present invention is provided in the bath with surfaces such that from about 0.5 to 10 amperes per square meter can be supplied to the second anode In general, surfaces are provided in the baths such that from about 1 to about 5 amps per square meter can be applied through the second anode Preferably, the surfaces of the second anodes are such that from about 1.5 to about 2.5 amps per

  square meter can be applied by the second anode.

  The second anode of the present invention is an insoluble anode where at least part of the surface comprises an iron composition In a preferred embodiment, the second anode is a sintered structure of iron oxide In a coating bath typical industrial electrolytic, the effective surfaces of the second anode will generally be between 0.1 and about 12 square meters, an area between about 0.5 and about 2.0 square meters, preferably in a

typical industrial bath.

  In a preferred embodiment, the sintered structure is obtained from an intimate mixture of sintered iron oxide in combination with nickel oxide. A typical formula for the anode would include about 90 mole% Fe 203 and approximately 10 moles% of bivalent nickel oxides The other metals or metal oxides could also be used in a sintered structure insofar as the metal used will not be harmful to the coating bath Thus, copper oxides, oxides of manganese and cobalt oxides could be used in the sintered structure Such sintered anode structures are exposed in S Wakabayashi and T. Aoki Characteristics of Ferrite Electrodes, document cited above and incorporated here for reference. While some can be treated more effectively than others, the structure of the substrate to be coated is not critical in the present invention However, the substrate must be a conductive type substrate as is commonly

  used in the electroplating technique.

  The substrate can be, for example, either a plastic material substrate or a metal substrate,

  depending on the intended application.

  The sintered metal anode is connected to a rectifier which is separated from the sacrificial anode so that the current supplied to the sintered iron anode can be controlled independently. It is important in the present invention that the current can be regulated. so as to supply an effective amount of current in order to significantly reduce

  accumulation of nickel in the solution.

  It has been found in the present invention that the amount of current supplied to the second anode for it to be effective in reducing nickel ions is generally between about 1% and about 16% of the total current applied during the electrolytic coating of the substrate. In general, the regulated current flowing to the second anode is between about 2% and about 12% of the total current applied during the electrolytic coating process. Preferably, between about 4% and about 8% of the total current applied is by

  through the iron sintered anode.

  Thus, in accordance with the process of the present invention, the insoluble iron sintered anode when used in accordance with the present disclosure has been found to significantly reduce the amount of nickel buildup in these coating baths. with nickel and nickel-iron In addition, it has been found that the sintered-type anode has a significantly longer lifetime, for example several years compared to the insoluble auxiliary anodes of the prior art whose duration was significantly longer short, usually lasting only weeks or months. The present invention will be better understood by

referring to the following examples.

EXAMPLE I

  An electrolytic coating bath is prepared with nickel according to the constituents indicated in Table I.

TABLE I

Constituents of the coating bath

electrolytic with nickel.

  Ni SO 4 6 H 20 290 g / l Ni C 12 6 H 2 O 60 g / l Boric acid 44 g / l UDYLITEO, brightening agent 63 ** 2.0% UDYLITE, brightening agent 610 ** 1.0 % p H 4.00 Temperature 600 C The preceding electrolyte bath was placed in a four (4) liter coating cell, equipped with a titanium basket anode which was filled with pieces of anode of sacrificial nickel and the anode was connected to a first rectifier which was itself connected to a current source A second sintered ferrite anode (having an area of approximately 51 cm 2) was immersed in the coating container and we connected this anode to a second

  * UDYLITE is a registered trademark of ENTHONE-

OMI, INC of Warren, Michigan.

  ** UDYLITE, brighteners 63 and 610 are available from ENTHONE-OMI in Warren, Michigan. rectifier in series with the current source The anodes were connected to separate rectifiers and to a common anode for the electrolytic coating The bath was electrolysed for more than 350 ampere-hours using standard additions of brightening agent during this duration The composition of the solution was rigorously analyzed; the appearance and integrity of the deposit were periodically measured and found to be acceptable The total current supplied to the sintered ferrite anode was between about 4% and 8% of the total current used in the process of coating. The results showed that no degradation product was formed, and that the p H could be maintained by the distribution of the current on the anodes. The consumption of the brightening agent was only slightly higher and it was found that the ferrite anode was very stable with a weight loss of less than 0.1% There was no detestable accumulation of nickel during the test period While a little chlorine escaped from the anode in ferrite, the quantity was not appreciable and we eliminated it

  with small additions of sodium bromide.

EXAMPLE II

  A solution of an industrial nickel-iron coating bath (NIRON *) was placed in a 4-liter coating cell provided with nickel and iron anodes which were connected to a first rectifier, which was connected in turn to a current source In addition, a sintered ferrite anode as described in Example I was immersed in the coating cell and connected to a second rectifier in series with a current source As in Example I, a common cathode was used for the electrolytic coating. The bath was electrolysed for 891

  * NIRON is a registered trademark of ENTHONE-

OMI, INC of Warren, Michigan.

  amp hour using standard additions of brightener and stabilizer during this time The composition of the solution was rigorously analyzed; the appearance and integrity of the deposit were periodically measured and found to be acceptable In general, approximately 6% of the total current was applied to the sintered ferrite anode although at some times during the test this current varied between 2% and% In this case, the current density of the anode

  insoluble varied from 1 A / m 2 to 5 A / m 2 Table II below

  after gives representative analytical results.

TABLE II

Analysis of the nickel bath

  Component O Amp-h 275 Amp-h 891 Amp-h.

  Ni + 2 60.31 g / l 59.75 g / l 55.23 g / l Ni SO 4 6 H 20 161.30 g / l 161.72 g / l 157.90 g / l Ni C 12 6 H 20 115.93 g / l 105.57 g / l 85.22 g / l H 3 B 03 45.91 g / l 44.30 g / l 42.97 g / l Fe + 2 2.40 g / 1 3, 82 g / l 3.20 g / l Fe + 3 0.18 g / l 0.27 g / l 0.50 g / l Stabilizer H * 14.62 g / l 14.75 g / l 14.32 g / l

Agent of brilliance

tage FN-1 * 3.23%

Agent of brilliance

tage FN-2 (Index) * 2.44% w H 3.0

3.16%

0.68%

2.5

3.34%

2.10%

  3.4 * Stabilizer H (stabilizer) and Brighteners FN-1 and FN-2 (agents) are available

  brightening) from ENTHONE-OMI, INC.

from Warren, Michigan.

  Regular panel tests during this period showed that no serious degradation product was found Consumption of H-stabilizer and FN-2 brightener was not influenced Consumption of FN-1 Index was slightly higher than normal The very low value of the FN-1 Index at 275 ampere-hours was due to

  errors in adding the brightening agent.

  The concentration of metallic nickel fell during the test, which is contrary to the typical nickel-iron coating baths. However, there was no appreciable accumulation of ferric iron; there was a significant drop in the chloride ion as indicated by the reduction of Ni C 12 6 H 20 from 115.93 g / l to 85.22 g / l This was probably due to the evolution of chlorine at insoluble anode There was only a slight odor of chlorine during the test The addition of l g / l of Na Br to the

  end of the test further reduced the odor of chlorine.

  The ferrite anode was periodically weighed after operating at various current densities The total weight loss during the test period was only 2.6% The higher the current density over the insoluble anode, the greater was the weight loss, although, even at 5 A / m 2,

  weight loss was not significant.

EXAMPLE III

  An industrial ferro-nickel bath (UDYLITE NIRON) has historically suffered from the serious problem of the accumulation of metallic nickel, and the bath had to be diluted by 20% to 30% every four (4) to six (6) weeks. that we do not wish to be bound by theory, we believe that the reason for the rapid accumulation of metallic nickel is due to: 1) a disparity of 10% between the efficiency of the anode and that of the cathode; 2) entraining the metal from another nickel bath; and 3) the use of an efficient recovery which brings almost all of the entrained nickel bath back into the NIRON coating bath. As a result, the bath was generally diluted when the concentration of metallic nickel (measured as

of NI + 2) exceeded 110 g / l.

  Using a conventional commercial nickel-iron bath (NIRON) already in place, approximately six percent (6%) of the total surface of the anode in the tank were replaced by insoluble ferrite electrodes, in the present case of 50 cm 2 The anode rail, on which the insoluble ferrite anodes were placed, was separated from the main buses and connected to a rectifier

  separate The cathode was common to the two rectifiers.

  The current was applied separately to the insoluble anodes. First, the amount of current supplied to the ferrite anodes was only about 4% of the total current; finally it had to be increased to 10% to control the accumulation of metallic nickel. A little chlorine was released, and 1 g / l of Na Br was added. Tests carried out indicated that the chlorine present in the air was at acceptable values The test was carried out under typical production conditions between approximately 55,000 and 60,000 ampere-hours per day, the bath operating continuously with normal downtime The test was carried out for 2.5

about months.

  The analysis of the NIRON coating bath, including the additives, at the beginning, at 26 days, and at the end of a 75-day trial period is

  indicated below in Table III.

TABLE III

  Analysis of the NIRON O bath Component Start 26 Days 75 days Metallic nickel 90 g / 1 91 g / l 89 g / l Chloride 29.5 g / l 31.5 g / l 33 g / l Ni SO 4 6 H 20 295 g / l 294 g / l 278 g / l Ni C 12 6 H 20 99 g / l 105 g / l 110 g / l Boric acid * 42.7 g / l 41.7 g / l 42, 7 g / l Stabilizer C * Nicron 81.4 g / l 82 g / l 75.5 g / l

Agent of brilliance

lantage FN i * 4.0% 3.72% 3.8%

Agent of brilliance

  lantage 84 * 1.5% 1.51% 1.4% w H ** 3.0 3.0 3.2 As can be seen from the previous analysis, the amount of nickel, without any dilution of the bath, stabilized at around 88.5 g / l In the past, the bath would have been normally diluted twice

during this time.

  The consumption rates of the organic additives were carefully monitored during the test. In all cases, they did not change.

  essentially not compared to normal values.

  Bath performance has not been affected The examples show that the use of the ferrite electrodes described here constitutes a viable method for controlling the accumulation of metallic nickel in industrial nickel and nickel coating baths. The examples also show that the use of anodes of this type has no harmful effect on the consumption of the additives and does not * These concentrations of these materials are maintained by means of regular additions so as to keep within prescribed operating range

by the supplier.

  ** Maintained via periodic additions

hydrochloric acid.

  also produces unacceptable amounts of

chlorine or harmful products.

  The present invention is not limited to the exemplary embodiments which have just been described, it is on the contrary liable to modifications and

  variants which will appear to those skilled in the art.

Claims (14)

  1 Method for forming an electrolytic coating of nickel on a conductive substrate in a manner which prevents the harmful accumulation of unused nickel ions in the electrolyte bath, characterized in that it comprises the steps consisting in: (A) providing an effective nickel-based electrolyte coating bath; (B) immersing in the bath a first anode connected to a first rectifier, this anode comprising a sacrificial nickel anode; (C) immersing in the bath a second anode connected to a second rectifier, this anode comprising an insoluble anode in which at least part of the surface comprises iron or an iron-containing composition; (D) immersing in the bath a substrate to be coated; and (E) anodically electrifying the first anode and cathodically electrifying the substrate while controlling the current applied to the second anode by the second rectifier in order to supply an effective amount of current to this second anode during the electrolytic coating of the substrate for the purpose of 'avoid   accumulation of excess nickel ions in the solution.   2 Method according to claim 1, characterized in that the controlled current going to the second anode is between about 1% and about 16% of the total current supplied during the   electrolytic coating of the substrate.   3 Method according to claim 1, characterized in that the controlled current going to the second anode is between about 2% and about 12% of the total current applied during the   electrolytic coating of the substrate.   4 Method according to claim 1, characterized in that the controlled current which is applied to the second anode is between approximately 4% and approximately 10% of the total current applied during the electrolytic coating.   Method according to claim 1, characterized in that the second anode further comprises an iron sintered structure.   6 Method according to claim 5, characterized in that the sintered iron structure further comprises a mixture of nickel and oxides of iron.   7 Method according to claim 5, characterized in that the surface of the iron sintered structure is chosen so that a current can be supplied to said structure which is between approximately   0.5 and around 10 amps per square meter.   8 Method according to claim 5, characterized in that the surface of the iron sintered structure is chosen so that a current can be supplied to this structure which is between approximately 1 and 5 amps per square meter.   9 Method according to claim 5, characterized in that the surface of the iron sintered structure is chosen so that a current can be supplied to the structure which is between about 1.5   and about 2.5 amps per square meter.   Method according to claim 1, characterized in that the second anode is a sintered structure comprising iron oxides and nickel oxides. ll Method for forming an electrolytic coating of nickel on a conductive substrate in a manner which prevents the harmful accumulation of unused nickel ions in the electrolyte bath, characterized in that it comprises the steps of at:   (a) providing an effective nickel-based electrolyte coating bath; 17 2668173   (b) immersing in the bath a first anode connected to a first rectifier, this anode comprising a sacrificial nickel anode; (c) immersing a second anode connected to a second rectifier, this anode comprising a sintered iron oxide structure having an available surface making it possible to supply a current of approximately 0.5 to approximately amperes per square meter; (d) immersing in the bath a substrate to be coated and connecting it cathodically to the first and second rectifiers; (e) Anodically electrifying the first anode and cathodically the substrate while supplying approximately 0.5 to approximately 10 amperes per square meter to the second anode so that the current applied to this second anode is between approximately 1% and approximately 16% of the total current applied during coating substrate electrolytic.   12 Method according to claim 11, characterized in that between approximately 2% and approximately 12% of the total current are applied via the second anode.   13 Method according to claim 11, characterized in that between approximately 4% and approximately 8% of the total current are applied via the second anode.   14 Method according to claim 11, characterized in that between approximately 1 and approximately 5 amperes per square meter are applied per second anode.   Method according to claim 11, characterized in that between approximately 1.5 and 2.5 amps   per square meter are applied to the second anode.   16 Method according to claim 11, characterized in that the second anode further comprises a sintered structure which is a mixture of iron oxide and nickel oxide.   17 A method of forming an electrolytic coating of nickel on a conductive substrate in a manner which prevents the harmful accumulation of unused nickel ions in the electrolyte bath, characterized in that it comprises the steps of: (a ) providing an effective nickel-based electrolyte coating bath; (b) immersing in the bath a first anode connected to a first rectifier, this anode comprising a sacrificial nickel anode; (c) immersing a second anode connected to a second rectifier, this second anode comprising a sintered structure of iron oxide and nickel oxide having an available surface which makes it possible to supply a current of approximately 1.5 to approximately 2 , 5 amps per square meter; (d) immersing in the bath a substrate to be coated and connecting it cathodically to the first and second rectifiers; (e) anodically electrifying the first anode and cathodically electrifying the substrate while supplying from about 1.5 to about 2.5 amperes per square meter to the second anode so that the current applied to the anode is between about 2 % and approximately 8% of the total current supplied during the   electrolytic coating of the substrate.