Nickel Plating

Nickel is one of the most important metals applied by electrodeposition. The plate is used principally as a bright coating underneath a much thinner chromium electroplate to provide a highly lustrous and corrosion-protective finish for articles of steel, brass, zinc die castings, chemically metallized plastics, and, to a much smaller extent, for coatings on aluminum alloy and magnesium alloys. The protection of the underlying metal depends primarily on the nickel plate, with the thin chromium overlay conferring a permanently nontarnishing, hard, wear-resistant surface. To a far lesser extent, and only for mild exposures, thin gold or brass electroplate with a clear lacquer finish is used as a decorative coating on thin bright nickel deposits. Nickel coating alone are also used industrially to afford corrosion protection to prevent contamination of a product. Because of favorable mechanical properties, nickel electrodeposits are used for electroforming of printing plates, phonographs record stampers’, foil and tubes, screens, and many other articles.


The history of the electrodeposition of nickel goes back more than 125 years. It began in 1843 that describe the first apparently sound nickel plate, which obtained from a bath containing nickel and ammonium sulfates. The first do nickel plating on a truly commercial basis used double salt baths, including both sulfate and chloride, and was probably the first to recognize the importance of impurities in the plating bath. He employed cast soluble anode which contained silicon, iron, and carbon. The only early developments that have survived, however, are Weston’s introduction of boric acid into the bath, the use of chlorides and promote anode corrosion, and the discovery about 1912, that cadmium salt act as brighteners. Electrolytic nickel refining profited by the experience of the nickel platter and has made use of warm nickel sulfate-boric acid solution since 1894.

Next:

• Work process on nickel plating
• Chromium alloy plating 

Chrome Plating over Nickel Plating

Find other method of Chrome plating Process:




Bright chrome plating is the final chrome on the surface layer, while beneath of chrome plating can be other kind of plating like copper plating, nickel plating, semi bright nickle plating, micro porous nickel and the final coat is chrome plating. But the usual plating is use nickel plating as base of chrome plating because chrome easier to coat on the nickel plating and easier to be a bright plating.

Other reason of using nickel plating beneath of chrome plating because nickel have better characteristic of stand to corrode and can be plated in thick plating compare with chrome plating. The ratio of thickness and measurable difference in electrochemical potential of semibright nickel layer to bright nickel layer is designed to improve the corrosion resistance. By using a chrome brightener the end result of bright chrome plating can be in perfect result.

Bright chrome plating over the nickel plating can result a mirror bright chrome plating, the appearance can reflect like a mirror. More bright of chrome plating then more reflective the surface of chrome plating of the surface finished. Nickel plating has a white finish and the chrome plating which deposits chromium has a clear translucent finish which is hard and scratch resistant.


The thickness of chrome plating is driven by current electricity so the metal deposit can vary in thickness depend on the electric current. Nickel plating beneath the chrome plating make the thickness of chrome is no need to make thick, usually the thickness of chrome plating is setting in thin thickness because if chrome plating is too thick usually easily to crack. Beside bright chrome plating, the piece can be made for hard chrome plating and decorative plating or black chrome plating over nickel plating. This make the finished object can be vary depend on the purpose of plating on the base metal.

Nickel Plating Bath Composition

A nickel electroplating bath for obtaining a satin-finish which comprises a solution of acidic continuous phase nickel salt solution, an alcohol soluble poly-amide resin and polishing agent dissolved in bath. The polyamide resin is a member selected from the group consisting of a co-polymer of dimer acid and an aliphatic amine, a co-polymerized nylon and a modified nylon. The electroplating bath preferably contains a cation surface active agent selected from the group consisting of an aliphatic and/or aromatic Quaternary ammonium salt and an aliphatic and/or aromatic fluorosulfonylamine Quaternary ammonium salt. The use of the electroplating bath provides a means for obtaining a uniform satin-finish nickel plating surface on the material plated.

Acidic nickel electroplating bath composition obtaining a uniform satin finish metal plate surface on the material plate surface as below:

1. Nickel 25 to 170 gm/lt
2. Polyamide resin dissolved in low molecular weight and alcohol have 1 to 3 carbon atom: 1 – 10,000 ppm
3. Polishing agent: 0.1 to 40 gm/lt

Nickel is dissolved and forms a continuous aqueous phase solution and poly-amide resin is dispersed in aqueous phase to form a stable emulsion.

Free e-book of Nickel Plating Process

To understand the theoretical about Nickel plating process, you may can download from the internet freely. The book is discussed all about Nickel electroplating with good design and good looking picture. But the point of this book just theoretical of nickel plating not practical use, so don’t try base on the theoretical because many parameter still not tell on the theory, what discussed on this e book also already discussed on this blog about 10 years ago. The theory is just for your reference if you are running plant of nickel electroplating. The real hand book should be from equipment supplier how to run the machines.

The book actually complete contain such as:

• The role of addition agents
• Bright nickel plating
• Nickel Brighteners
• Anticipating Agent
• Anti pitting agent (wetting agents)
• Semi bright nickel plating solution
• Sulphamate nickel electroplating Bath
• Anode for nickel plating
• And many other discussed about nickel electroplating

If you need addition information about nickel plating you can download this e book freely, but on this blog only talking each of the problem and little about nickel plating theory, not in detail.

Cobalt Plating over Nickel Plating

The existence of cobalt metal on nickel plating bath make the plating result more bright and lustrous. Dense and lustrous deposit of nickel can be obtained, beside also have other benefit properties like great hardness, elegant appearance and resistance to oxidation also still exist.

The difficulties of using cobalt metal as brighteners of nickel plating is the availability of this metal still difficult on the market, so make the price will higher and of course can affect to the final product price.

Many technical points in connection with the plating of cobalt have not been investigated; the corresponding investigations for nickel have been comparatively thorough.

The numerous statements have been published in the past with regard to cobalt plating, the conclusions to be drawn from the survey of the existing literature and patents would lead one to be very skeptical as to the advantages of cobalt plating over nickel plating. It is noticeable, the conditions for the production of good cobalt plates, vary tremendously among themselves.

Nickel and Silver Platting Calculation

A 0.500 amp current flowing for exactly one hour is passed through a solution of nickel (II) ions.

1. How many grams of nickel metal will plate out?
2. If this cell is hooked in series with another cell containing Ag+ ions (in series the same current passes through both cells), how many grams of Ag will plate at the same time?

First we need to know how much charge passed through the cell(s):
0.500 A x 3600 s = 1800 C

Now how many moles of electrons was that?

(1800 C x 1 mol e-) / 96500 C = 0.0187 mole e-

Since nickel (II) has a charge of +2, one atom of nickel will require 2 e- to plate:

0.0187 mole e- x 1 mole Ni / 2 mole e- = 0.00935 mole Ni

This is 0.549 grams
.
Since silver is plated by the same amount of charge, but each atom of silver requires only one electron to plate (Ag ions are +1), we should expect twice as many moles of silver atoms to plate:

0.0187 mole e- x 1 mole Ag /1 mole e- = 0.0187 mole Ag

Thus 2.02 grams of silver are produced. Note that the ratio based on charge affects the moles of silver and nickel. Their atomic masses influence the final mass plated.

Plating experiments are rather boring and this one is no exception. There is not much to do as the process takes place (especially if your calculator is recording the data...) and there is generally not much to look at. However, there is time for a fascinating diversion. You know from the activity series that zinc, which is above copper, will be displaced by copper in solution. The voltage for this process is 1.10 v as you saw in the previous experiment. The opposite process, zinc displacing copper is non-spontaneous. Or is it?

For many years chemistry teachers have done a demonstration in which they turn ordinary pennies into "gold". Traditionally the process has been done in a hot, very alkaline solution containing the ion Zn(OH)₄^2- and some solid zinc. This combination of materials caused zinc metal to spontaneously plate on the copper. When the "silver" pennies were subsequently heated in a flame, the thin coating of zinc alloyed with the copper, producing yellow brass or "gold".

Recently a pair of chemists investigated this process more closely. Their report appeared in the Journal of Chemical Education. They found that the process was very different from what had been assumed. In fact, the very alkaline solution was not required at all! Copper placed in a heated solution of Zn²⁺ and a small amount of metallic zinc will become plated with zinc metal!! How is this? According to their research the process is driven by the alloying which occurs at the very surface of the copper. Due to thermal agitation in a heated solution, some zinc ions manage to work their way into the spaces between the copper atoms and form a very thin layer of brass.

The voltage for zinc metal plating on brass (as opposed to copper) is positive! Thus the "silver" appearance of the penny after heating is actually a type of brass (silver brass).
When heated in a flame, the silver brass is converted to yellow brass ("gold"). You can do this yourself, using the plating solution and some granular zinc.

Bring two of the shiniest (cleanest) pennies you can find. Place them in the beaker of solution provided on the hot plate and boil the solution. It takes about 10-15 minutes to plate a uniform layer of silver brass. Turning the pennies occasionally will help. When they are covered in silver brass, remove them and rinse in water. You can keep one "silver" penny and heat the other very carefully in a cool burner flame to change it to "gold". Too hot a flame will melt the brass coating, so be careful. This is just for fun, but it also points up the fact that not everything which we take for granted is happening they way we think. There are plenty of puzzles left to solve.

Problem on Plastic Electroplating

The basic problem of plastic electroplating is in attempting to electroplate onto plastics substrates is, of course, that they are electrically non-conductive and cannot be immersed in a plating solution and coated in the way that metal objects can. Some method was therefore needed whereby a conductive film could be deposited onto the plastics surface to provide the basis for subsequent electrodeposition. It was, of course, vital that this surface layer, in addition to being electrically conductive, should adhere well to the substrate if the final coating system was to show good adhesion.

Substrate Etching

Early processes, using conductive paint or chemically reduced silver on surfaces roughened either mechanically or by solvent attack, did not provide adequate adhesion. In the mid 1960s, etching solutions based on chromic acid were developed which could successfully be used with acrylonitrile butadiene styrene (ABS) copolymer. Use of these solutions resulted in selective removal of the butadiene phase from the resin to give a micro-etched surface providing bonding to the subsequent conductive layer.

Electroless Plating

This development came at a time when great improvements were also being made in the technology of electroless nickel plating and electroless copper deposition. These advances in electroless plating combined with the development of the etching technique gave rise to a system that provided a highly conductive coating exhibiting satisfactory adhesion to the plastics surface.

Cleaner Production of Electroplating

The program of Environmental Department is cleaner production for all industry in their government. This can be difficult especially for industries that use many chemicals for their production process. The main propose of this program is to produce product without any pollutant expose to the environmental. The available check on this matter just can be prevented and evaluate just on the solid and liquid waste, but on gas pollutant are difficult to check because the gases can be expelled to the air and after that will mixed with the atmosphere. The normal and continual check to exposed gas just on the continuous gas release, but on the incidental or a moment release this can't be controlled by government. This cleaner production program can be occurred just by the commitment of the management.

Electroplating industry like on chromium electroplating has many environmental aspect and have highly polluting industry, there are many resources available to help the metal plating industry improve its environmental performance. Even though trade associations have technical guidance, supplier and discussion forum where serve for all question about product and waste process and give several major programs focused specifically on helping the sector with pollution prevention, but cleaner production really as difficult aspect factor for this kind industry.

Cleaner production is not just applied to the developed countries, this regulation also should be implemented to the developing countries early, because the whole cost of this process should counting all the cost need to produce certain product like on nickel plating for example.They are not just count overhead cost but don't include the cleaner production cost even produce in developing country. If the investor don't want to invest in developing country because of this rule, developing countries should produce other product that more save for their environment.

Nickel Electroplating Problem

Ask:
I am currently doing an investigation on Nickel electroplating in school. I am having problems as every time I try to electroplate onto a Copper sheet I always get a layer of Nickel(II) Oxide and no Nickel metal. I have tried using different current densities and concentration of substrate solution ( Nickel Chloride). However, I have found out that when I use Ammonium Nickel Sulfate I get a nice shiny coating. Can someone please explain why this is the case?

Preparation of Basis Metal (Nickel Plating)

Find the right Base Metal:





In preparation for applying a plated finish to an article, polishing is often used to smooth the surface before more refined finishing procedures. Subsequent buffing is usually used on such metals as copper, brass, zinc die castings, and article aluminum alloys before plating. Because of high cost, steel is seldom buffed before nickel plating. Where a buffed surface is desired, a common practice has been to apply a copper plate before buffing. More recently, the use of high leveling bright nickel baths, or a combination leveling semi bright bath and a bright nickel bath, or a high leveling, bright, ductile acid copper plating bath eliminates or reduces appreciably the amount of buffing required to produce a lustrous finish.

Polishing and Buffing
The nature of surface condition of the metal can have a profound effect on the performance of the nickel plate. Proper preparation of articles to plated with nickel start with the manufacture of the basis metal. Many investigators have shown that rolling scams, slag inclusions, blow holes, sand inclusions, and the like effect the protective value of nickel plate. Moreover the manner in which the metal is processed, either before or after being form into articles of manufacture, has been proved to affect the porosity of the nickel deposit. In general, the result show that rough grinding was detrimental to the protective value of nickel plate, and in addition, that smoothing out and rounding of the tops of scratch, as for example, with a well lubricated, final polishing wheel, was important from the stand point of enhancing the protective value of nickel. A final sisal wheel accomplishes the same result, especially of eliminating slivers.

Cleaning and Pickling
The purpose of cleaning before plating is to remove all the interfering substance from the surface to be plated. Adhesion, smoothness and corrosion resistance of nickel plate depend on a proper cleaning cycle. Diffusion of one metal into other (alloying) is not necessary for adhesion and may be detrimental when the alloy layer or any part of it is weaker or more brittle than the individual metals. Harmful substances which cause poor adhesion are oxides, graphite, oils, grease and immersion coating of copper or lead from contaminated acid dips or from the presence of chromates, even in small concentrations, in the rinse water or in the plating baths. If cathode cleaners are used that are contaminated with dissolved zinc, copper, or lead and thus plate out a non adherent film, or when cathodic cleaners are used in the cleaning or activating sequence for longer than 1 minute without an anodic activation, or when bipolar or intermediate electrode effects occur in the plating steps, poor adhesion will result.

Wire Mesh Anode

With the introduction of perforated and wire mesh titanium anode baskets, the use of primarily nickel has become the predominant nickel anode material. Small squares of electrolytic nickel, usually about 2.6 x 2.6 cm or small squares or buttons of sulfur depolarized electrolyte nickel (designated SD nickel or S nickel), or Mond nickel pellets are the forms used.

Electrolytic nickel is the least expensive and purest form of anode nickel and about 90% of all the nickel anodes now used in the U.S. are these electrolytic squares, the SD type amounting to about 50% of the total. The SD electrolytic nickel, like regular electrolytic nickel, has very low (about 0.01%) iron and copper impurities, but contains about 0.02% sulfur dispersed through its structure, which makes the nickel anode material with respect to pH, anode current density, and very low chloride concentration. Regular electrolytic nickel contains no depolarizer and is the least active nickel anode material.

The SD nickel can be used for chloride-free and high pH baths of sulfate and sulfamate type. There is no metallic sludge with SD nickel, but the nickel sulfide formed, while not voluminous and voluminous, nevertheless can be carried out into the bath if the anode bags are not kept above the solution level, which should be the general anyway. The best bag for regular electrolytic nickel are not necessarily the best bags for SD nickel, for which a tighter weave is preferred. Double bagging is especially preferred for titanium baskets over 1 m long, the outside bag being made of approved plastic fibers and of a more open weave. Cotton bags, when used without an auxiliary outer plastic bag, must in general be changed about every six to eight weeks of service due to deterioration which may lead to breaks in the bag. Great care should be exercised in changing bags to keep anode sludge from falling into the tank. it is for these reasons that plastic bags which do not rot are tested to find combinations that are as good in holding back the sludge as the best cotton bags.

Anode for Nickel Plating

Anode for Nickel Plating Can Use Several Kind:





With the first introduced in 1916 and subsequent widespread use of the Watts bath, the old 90 to 94 % or the 95 to 97 % nickel anode (balance iron) used in the cold, low speed, pH 5.5 nickel bath, gave way to the chill-cast 99 % nickel anode. Next came the rolled 99 % nickel anode depolarized with small amounts of nickel oxide. This anode corrodes smoothly, forming a light brown film that washes off as it is formed. Since small amounts of loose nickel are formed on corrosion in all solutions based on the Watts formula, anode bags are generally necessary to prevent formation of nodular deposits as a resulat of the physical inclusion of these particles. This 99% nickel rolled anode is used in baths of PH above 4.

After the rolled depolarization anode came the cast carbon nickel anode, and still later, the rolled carbon nickel anode. Both of these contain more than 99% nickel and have the feature of forming their own bag on corrosion. This bag consists of a rather tenaciously adhering but porous carbon silica film that holds back loose anode particles provided they do not form in excessive amounts. The high purity carbon type anode are used only when the pH of the bath is 4.5 or lower. Such anode are sometimes used without any cloth bags in baths that are not air agitated.

The corrosion behavior of an anode depends on the pH and the chloride content of the bath. The uniformity of corrosion (sometimes called anode activity) should not be confused with anode efficiency. Only a small chloride content, 15 to 33 g/l nickel chloride is necessary to make the latter 100 % for all types of nickel anodes under the usual conditions where the anode area is at least equal to the cathode area. The selection of the best type of nickel anode for a given process is based not only on the purity of the anode current densities to be encountered.

Removal Organic and Inorganic Contaminant

Remove Organic Contaminants
In plant processing steel, iron is the usual contaminant and with constant good filtration. Iron usually presents few problems. High pH treatments in an auxiliary tank with moist nickel carbonate dispersed with good agitation of the bath are used to remove excessive concentrations of iron, as well as aluminum, trivalent chromium, or phosphate ions. The addition of about 0.5 to 1 ml of 30 % hydrogen peroxide with the high pH treatment removes all the iron as ferric hydroxide, provided at least 2 hr of agitation is used and the temperature of the bath is kept at around 60 to 65oC. Also carbon dioxide evolved from the use of nickel carbonate is removed by agitation and heating.

In plants processing copper, brass or zinc die casting, the contaminants copper and zinc are best removed by low-current density purification, preferable continuously. Zinc, copper and lead may all be removed at the same time by electrolyzing at about 0.2 A/dm2. The faster agitation, the higher is the current density that can be used to remove these metallic impurities.

Removal of Organic Contaminants
Organic contaminants may be introduced by improperly chosen tank linings, rack coatings, filter hose, patching rubber, by airborne contamination from thick dust lint, or oil spray or drippings from loose welding scale on work pieces, from inferior cleaning methods, and by breakdown at the anode or cathode of certain class II addition agents.

If the bath is excessively contaminated with organic material, the best method of removal is by adsorption on activated carbon in the auxiliary tank, after correcting as far as possible the sources of the organic contamination. Addition of hydrogen peroxide as previously described, and agitation of the bath for several hours with 1 to 3 g/l of the activated carbonate, will help the purification. After settling with filter aid and testing a sample of the treated solution in the laboratory for the condition of the plate, the solution if approved is filtered back into the plating tank.

The use of small amounts of activated carbon in the filters, such as 2 to 4 g/100 lt of solution and adding similar amounts to the filter once or twice a week is an excellent method of avoiding or minimizing costly bath treatment of plain, semibright, or bright nickel plating baths. A check must be made at regular intervals to be sure that the wetting agent or other brighteners are not excessively absorbed.

Effect of Contaminants

In the modern acidic nickel plating baths, small percentages of metallic contaminants such as copper, lead, zinc, or tin exert profound effects on the appearance and properties of the nickel deposit, especially in the low current density plating range. The harmful effects of these impurities are additive.

Copper in concentrations over about 5 mg/l is detrimental to adhesion to steel, or leads to poor adhesion when current is interrupted or decreased to very low current density during the nickel plating. This is also true far similar concentrations of lead. Copper in these and higher concentrations cause dark, low current density plate especially evident in bright nickel plating.

Lead in concentration higher than 5 mg/l cause dark, fine grained, brittle, poorly adherent deposits. Stannous tin in low concentrations cause dark, low current density plate, it can be removed by oxidation to the insoluble stannic form, and thus this impurity can be confused with an organic impurity in the rate case where a tin anode get mixed in with nickel. Zinc impurity in bright nickel baths, while not as eritical as copper, lead and tin can cause whitish and with higher concentrations, dark plate in the low current density areas and even cause shiny black streaks in the plate. In general, the bright nickel baths can tolerate about 20 to at least 100 mg/l of zinc, depending on the configuration of the work. Iron (III) impurity tends to precipitate readily at pH values of about 3.5 and higher, and can cause speckling on settling surfaces, unlike the case of iron (II) which codeposits compatibly with nickel. Good filtration minimized this iron (III) problem.

Hexavalent chromium in concentrations of 3 to 5 mg/l introduced from spray from chromium plating baths or dragin from faulty rack coatings causes skip plating in low current density areas, and in higher concentrations, streaked, peeled plate. Small concentrations of sodium bisulfite reduce the hexavalent chromium to the very much less harmful trivalent form. Tirvalent chromium and aluminum in appreciable quantities lower the limiting cathode current density and tend to precipitate out at pH values above about 3.5 and cause roughness especially on settling areas of a cathode. Nitrate ion is reduced to ammonium ion at the cathode and, like anodizing agents, decreases the cathode efficiency and in appreciable concentrations causes skips plating in the low current density areas. Nitrate is not nearly as critical as hexavalent chromium. Phosphate ion lowers the limiting current density through formation of ion nickel phosphate in the cathode film and the precipitated phosphate particles also cause roughness.

Many organic compounds in small concentrations as well as large excesses of many class II brighteners can cause brittle plate and dark low current density plate. Grease, oil, improper surfactants, rubber accelerators, and so on, can cause brittle, cloudy plate.

Maintenance and Control of Nickel Baths

Maintenance and control should start with the installation of the tank and its auxiliary equipment. Satisfactory thoroughly tested tank linings and internal heating elements are available. Heating the solution by means of an external heat-exchanger is much preferred. As materials for internal heating elements, lead was at one time used almost exclusively. It has been replaced by either impervious carbon or glass in order to avoid the possibility of metallic contamination. Since lead is soluble in high chloride nickel baths, lead coils should not be used where the nickel chloride content is higher than 60 g/l. They should also not be used in baths containing organic acid that form soluble lead salt such as acetic and formic acids, or in baths with high concentrations of sulfonic acids. They can't be used in sulfamate, flouborate, all-chloride, or high-chloride baths.

Impervious carbon heating elements are widely used in such baths, and since they have good heat transfer properties, they may be employed in any type of nickel plating solution. The one disadvantage of such heating elements is their fragility. Special precaution is required to place them in the tank so that danger of physical damage is minimized. Glass heating coils avoid both metallic contamination and stray electrical current, but have the disadvantage of a relatively poor coefficient of heat transfer.

Since insulated defects may be the direct cause of poor adhesion and may result in current loss or poor plate distribution, tanks should be mounted on positive insulator such as glass or glazed ceramics. All piping connections for water, steam, and air exhaust should be equipped with permanent insulating joint in order to avoid electrical grounds and short circuits. All anode and cathode bats, racks, and contact points should be kept reasonably free from encrusted salts for good electrical contact. Contamination of the bath with copper must be avoided. Wrapping the anode bars with polyethylene sheeting is a step in that direction.

High Sulfate Bath and Black Nickel Bath

High Sulfate solution is of the type developed by Thomson for plating nickel directly upon zinc alloys. The high content of sodium sulfate suppresses ionization of the nickel sulfate and thus ends to prevent the deposition of granular nickel by chemical displacement on the zinc surface. Live entry (hot contact) is usually used. Brighteners other than small concentrations of cadmium ions are not suitable in this bath because of the high concentration of ammonium ions and in general thickness less than about 15 μm are used with this cold bath. The covering and throwing powers through superior to a Watt bath are not compatible to the cyanide copper bath, and the later is practically universally used as the first plate on top of zinc die castings. This solution is useful when copper is not desired for desired for plating on aluminum and magnesium alloys which have been coated with zinc by an immersion process.

Black Nickel Bath
Black Nickel solution for deposition of a decorative black finish which contains not only nickel but also large amount of zinc and sulfur. A modification of this bath, which contain chlorides in place of sulfate, is said to be easier to control. Black nickel is a thin decorative finish which reproduces the underlying surface, lustrous black on smooth surface, and dull black on mat surface. It is used to achieved color effect and should not be considered corrosion resistant. A nickel undercoat is used protect the basis metal.

Alkaline Nickel Bath
Nickel can be deposited from alkaline baths, and baths of this type have been developed mainly for direct plating of zinc die castings with the view of eliminating the need for cyanide copper as the first plate and also for obtaining generally better throwing power. These baths in general give rather brittle plate. The bond to zinc is good but not always the best. It is mainly for this reasons that these bath are seldom used. However, an early bath consisting of ammoniac pyrophosphate and citrate complexes of nickel with some added bisulfite, and known as the Zialite bath, has been in small scale use for many years. It is used to plate directly and protect intricate zinc base castings such as spray guns, because of its very good covering power. The pH of bath is usually kept at about 8 to 9 and temperature at about 35 oC. The plate is lustrous semibright and usually is not chromium plated.

Electrotyping Baths, Double Salt Baths and Barrel Plating Baths: Special Purpose Baths

A number of applications for nickel plate require baths of special composition. Bath fomulas and preferred operation conditions are shown in the table Special Purpose Nickel Bath.

Electrotyping Baths
The ammonium salt increases conductivity and provides buffer action at high pH. Boric acid is not included because it leads to undesirable stress and to cracking of the plate at the low temperature high pH conditions necessary for covering or spreading over the surface of a treated was mold. Air agitation is commonly employed to permit operation at the upper end of the current density range. Modern practice for electrotypes and stereotypes is to apply nickel from standard warm florborate or especially sulfamate baths on sheet of vinyl plastic, leads or aluminum backed instead of on waxes.

The Double Salt Baths
Double salt bath solution of the oldest nickel plating baths, finds little application in the country. It can be employed only at room temperature (20 – 30 oC) and low current densities. It was used for deposition of tin coating on, for example, brass, costume jewelry and novelties. Brighteners like gum tragacanth, gum arabic or cadmium salt was often used.

Barrel Plating Baths
Barrel Nickel Plating is carried out with large numbers of small parts which are too difficult to rack. This solution being somewhat more concentrated than double salt solution, has the wider range necessary for the barrel plating of small parts in bulk. The brighteners used same as on the double salt baths. Modern proprietary warm bright nickel baths based on the Watts solution, usually with higher nickel chloride content and using some of the same brighteners used in rack plating but in different proportions, are now available for barrel plating to yield a superior product at higher rates of plating. The modern baths are required to give bright deposits over a very broad current density range down very lowest. Usually a very low foaming surfactant, similar to the ones used in the air-agitated baths, is added to decrease drag out.

Sulfamate Baths

Sulfamate baths are increasingly used for electroforms because their deposits have low tensile stress. The Watts baths require the use of a stress reduces for low internal stress, and because of the sulfur content of such deposits, it is necessary to avoid temperatures above about 370 oC for such electroforms. At about this temperature and higher, the sulfide-containing nickel suffers severe embrittlement. In general, for electroforming operations, the stress reducers should be used at the lowest concetrations to accomplish minimum stress.

Electrotypes are the oldest kind of electroformed article. Electrotyping is a process for producing duplicate printing plates to eliminate the need to reuse the expensive original, usually a composite of photoengraving and type. In modern methods a plastic mold, usually vinyl, is made from the original and made conductive with a reduced silver film and then plated 150 to 200 μm thick which is the required nickel shell thickness. A low stress bath is necessary to start the plating on the silver film without preliminary copper plating. Nickel sulfamate baths are generally used on both lead and plastic molds. After an initial plate of about 7.5 μm is deposited at medium current densities on the vinyl mold, the rate of plating can be increased to 20 to 30 A/dm2 to produce an all nickel electrotype shell in 30 to 40 min. Small concentrations of nickel fluoborate can be added to the sulfamate to prevent burning at the edge of the mold. In stereotypes, a soft low-melting lead-based metal is used for printing and is protected against wear by nickel electroplate about 13 μm thick, usually from the sulfamate bath.

A large new application for electroformed nickel is the cylindrical screens that are used for textile printing. These screens are about 125 μm thick, 12.5 to 30 cm in diameter, and 2.5 to 6 m long. They are used in tandem with each roll applying a pattern of single color to the fabric.
Important applications of nickel electroforming include Pilot-static tubes for air-speed indicators, precision tubing of rectangular Eros section, and radar fittings, waveguides, computing cams, large searchlight reflectors, constant mesh screens, and Venturi tubes used in the jet propulsion program. Electroforming plastic dies and casting dies has an advantage owing to the high cost of bobbing them out of solid metal. Electroformed molds are used for nylon gears, ratchets, cams, and plastic toys and dolls.

Resizing of Nickel Plating

The long standing British practice of building up worn or mismachined parts by heavy nickel plating is in use in this country on a modest scale, particularly in connection with maintenance of trucks, buses, and airplane. There is nothing unusual about the nickel plating operation itself, the bath being selected to give deposits of the desired mechanical properties. Preparation of the basis metal to guarantee perfect adhesion, setting up the anodes, and stopping off or shielding the work to secure good metal distribution can be exacting.

There are numerous advantages in using nickel for salvage. It can be deposited rapidly, uniformly, and economically, the metal can be ground and, in addition, machined by conventional methods; it is corrosion resistant and tough, and it withstands shocks. Where heavy deposits with a hard surface are required, it is good practice to make up the major portion of the desired thickness with nickel and then finish with several micrometers of chromium.

Electroforming
Electroforming has inherent advantages over other processes of fabrication for parts which:
1. Require a very high surface finish, especially on internal surface contours.
2. Require high precision in certain dimensions.
3. Incorporate intricate details.
4. Needed in quantities too small for die casting run.

Sulfamate baths are increasingly used for electroforms because their deposits have low tensile stress. The Watts baths require the use of a stress reducer for low internal stress, and because of the sulfur content of such deposits. It is necessary to avoid temperatures above about 370 oC for such electroforms. At about this temperatures and higher, the sulfide containing nickel suffer severe reducers should be used at the lowest concentrations to accomplish minimum stress.

Corrosion and Wear Resistance

Thick nickel coating are used on process equipment to resist corrosion or combined corrosion, wear and fatigue. Nickel-lined steel pipe is available commercially and is in service in corrosive oil wells and in the chemical industry. An old application is the coating of huge, highly polished, cast iron drums used in this service is so high that it cannot be attained with wrought metals because they contain non metallic inclusions which cause tiny pits on buffing. The coating now used on these drums are deposited from a high chloride Watts bath under conditions giving nickel of moderate hardness. Nickel lined food processing kettles, nickel coated paper mill rolls, and nickel coated filter pressed for viscose rayon solutions are outstanding examples of heavy nickel plating on large units.

In applications where steel trends to fail by corrosion fatigue, a nickel coating has a great beneficial effect, for example, the life of sucker rods in corrosive oil wells is lengthened many times by application of 150 µm of nickel from the Watt bath. Nickel coating seem to be particularly effective in preventing "fretting corrosion." Nickel plating, like chromium plating, can reduce the fatigue strength of plated steel components subject to alternating stressing or vibration. A compressive stress in the nickel favor a minimum loss of fatigue strength.

Hard nickel is generally specified for application involving wear. The performance of nickel from the other baths, however, is better than might be expected, because this metal work-hardness rapidly under sliding action. Thus the life of hardened steel gasoline pump gears, which failed by seizure and dragging, was multiplied more than fivefold by application of 5 to 7.5 µm of nickel. For the most severe conditions of contact with steel under high pressure, it is preferable to use a composite coating consisting of nickel plated with a few micrometers of chromium.