Guest Editorial -For Plateworld.com                                                 

 Don Baudrand, Don Baudrand Consulting,   e-mail:donwb@tscnet.com

BRIGHT NICKEL PLATING

I have had a number of inquiries about trouble shooting bright nickel plating in the last few months, so I decided to contribute the following. It is notes from a talk I gave last year. This includes a trouble shooting chart.

Bright nickel plating solutions are based on a Watts nickel formulation, sometimes with variations.

                                            Watts Nickel                 High chloride

Nickel sulfate                         40 ozlgal.                         15 ozlgal.
Nickel chloride                         8 “                                  25 “
Boric Acid                                6 “                                    6 “
pH                                          3.5-4.5                             3.5-4.5 (Optimum 4.0)

High chloride baths have higher conductivity than Watts nickel, can operate at lower temperature (energy saving) and have slightly better throwing power than Watts. But not all brighteners can stand the high Chloride

Brighteners

Primary
(Class I) Anionic sulfonic acids, sulfonamides sulfonimides (saccharine +sulfonimides)
These compounds adsorbed on the nickel surface, give up sulfur to the deposit (up to 0.04%)and thus act as grain refiners, reducing stress (toward compressive). Certain compounds tolerate zinc more than others. (sulfinic acid, for example)

Secondary Brighteners (Class II) Cationic compounds, Acetlylinic (C=C), pyridine and sometimes both. These compounds are strong inhibitors. Cathode polarization increases, an increase in tensile stress occurs, and carbon is incorporated into the deposit. They are used in the lowest concentration and have the highest consumption rate. They deposit preferentially in low current density areas.

Leveling agents, (Class I) Sulfones and unsaturated carbon groups. (C=C) Cumarin is an example.
These compounds function as both primary and secondary brighteners. They move stress toward compressive, increases cathode polarization, and concentrate is less in valleys than peaks. The nickel ion is small compared with levelers and can pass through into valleys. Low concentration of levelers allows secondary brightener into valleys inhibiting leveling.

Stress and ductility
Typical bright nickel stress is about 4000 psi compressive. (sulfamate nickel is about 300 to 4000 psi tensile. But the elongation of a bright nickel is about 4% while sulfamate deposits are 25% or better.) Elongation is one way to judge ductility. Zero stress does not mean the deposit is ductile. It often means the deposit is brittle due to both tensile causing and compressive causing materials are present.

Advantages of low total organics in a Bright nickel

Low occluded organics in the deposit; better ductility
Improved chrome reception and appearance
Reduces flaking and blistering
Better mileage
Easier to treat when necessary, usually less often.

Maintenance

Add brighteners, leveling agents and wetting agents in small amounts and often. Prefer automatic additions based on ampere-hours.

Filtration: Continuous filtration is strongly recommended through a filter with high capacity (4-20 turns per hour, the more the better), through a suitable distribution piping system. Agitation is necessary. Solution agitation is the most efficient when it is uniformly distributed toward the parts to be plated. Air agitation is used, but has many problems and is not as uniform or efficient as solution movement. Mechanical is the least efficient method; Filtration through a carbon pack or cartridge is recommended for many bright nickel systems. 1 lb of carbon per week per 1000 gallons of solution is often used. (Some brighteners are removed or lowered in concentration by carbon filtration)

Impurities

Chrome - As little as 2 ppm can cause serious problems: stress -extremely high tensile- dark streaked deposits, no coverage in low CD. 5 ppm can cause the deposit to crack spontaneously.
Zinc, copper & lead - Dark low CD areas, Streaks, increased tensile stress (Zn & Pb) and brittleness.
Organics - All of the above.

TREATMENTS

Carbon treat: Heat to 150F, pump into a storage tank; add 2 to 4 lbs of activated carbon per 100 gallons of solution. Stir well for 30 minutes or more. Add 2 lbs of filter aid per 100 gallons. Let settle for 2-4 hours filter back into the plating tank. Keep the intake hose just below the surface while filtering to minimize clogging the filter. When filtration-transfer is complete, check for any carbon that may have passed through the filter. (Extract a sample and pour through a white filter paper in a funnel). Add brighteners, check analysis, make and other adds necessary, lower temperature to normal. Filtering tests are recommended periodically during filtration process. (140 F).

Peroxide high pH treatment
For organic contamination and iron removal:
In the storage tank containing nickel solution, add 3 gallons of 30% (100 volume) hydrogen peroxide. Heat to 150 F. stir for 1/2 hour. Add, using hot water slurry, nickel carbonate (2-7 lbs/100 gal) to raise the pH to 4.5 to 5.0; add carbon. Stir for 1 hour (Mixer). Add filter aid as above; settle for 8 hours, to destroy excess peroxide. Filter back into plating tank. Adjust by and add brighteners and surfactants.

Permanganate treatment
Heat solution to 150F. Using 2-4 lbs of potassium permanganate per 100 gallons of nickel solution dissolved in hot water, add to solution in storage tank. Stir for 30 minutes. Add carbon, stir for 30 mm. Add filter aid. Settle 2-4 hours. Filter into plating tank. Test for excess permanganate. If found, add small amounts of hydrogen peroxide until no more permanganate remains.

Electrolytic Purification (Dummy plating)
Removal of copper, zinc, cadmium, lead and some organics”
Add 1-gallon hydrogen peroxide per 1000 gal. Adjust pH to 2.5-3.0 using sulfuric acid.
Plate on as large a cathode area as possible (usually corrugated sheet steel with 3”
Corrugations) at 2-6 amps/sq ft , with good agitation. Dummy time is usually 8-16 hours. Adjust pH to operating level (4.0)

Chrome removal
In a storage tank, lower the pH to 3-3.5 using sulfuric acid. Add 5 gallons of hydrogen peroxide/1000 gallons. Raise temperature to 150 F. Stir for 2 hours. (If there is no iron in the solution, add a small amount of ferrous sulfate, about 0.1 g/L). (Peroxide aids the Iron, which then reduces chromium.)
Add slurry of nickel carbonate to adjust the pH to 5.0-5.2. Nickel carbonate can be added through the filter followed by recirculating the nickel solution through the filter. Stir for 1/2 hr. Add 4-6 lbs/100 gal carbon, stir for 1 hr. add filter aid. Settle for 2-4 hours and filter back into plating tank. Adjust pH and add brighteners. (also removes iron)

Plating
At 97% efficiency, 1.06 grams of nickel will deposit per hour-hour.
For example, 100 amps for 12 minutes will deposit 0.OO1” on a square foot of surface
area.

The plating thickness will not be uniform on most parts plated. Current flows to the point nearest the anode. Anode to cathode spacing should be 6” or more. Robbers and shielding are often necessary to make the deposit thickness more evenly distributed.


NICKEL PLATING TROUBLE SHOOTING CHART (CORRECTED 9/24/01)

DULL DEPOSIT (BRIGHT NICKEL BATHS)

Possible Source of Trouble Suggested Cure
pH out of proper range The pH should be adjusted to an optimum value
Secondary brightener low Analysis, if available, indicates addition that is required. The bath should be tested with a Hull Cell for the optimum bright range.
Temperature out of range The temperature should be kept at proper range within +/_ 20F .
Brightener additions out of balance Where two or more addition agents are used, the proper proportions must be present. Adjustments should be made to the correct values.
Organic impurities The bath should be tested with a Hull Cell for the presence of organic impurities from rack coating, tank lining or buffing compounds. When found, they are removed by carbon treatment, with or without preliminary oxidation, as tests may indicate.
Metallic impurities The bath should be analyzed for presence of copper, zinc, lead, and cadmium. Dummy plating, precipitation, filtration or both remove these impurities.
Drag-in contamination The bath should be checked for contaminating drag-in from cleaners, acid dips, dirty rinses, etc., by cracked or loose tank lining and plating rack coatings, or by improper rinsing of recessed work. The source of trouble should be eliminated.


DARK DEPOSITS (SEMI-BRIGHT NICKEL BATHS)

Possible Source of Trouble Suggested Cure
Metallic impurities Excessive amounts of copper, zinc, lead, or cadmium may be present. They are removed by dummy plating.
Concentrations not in proper range. A dull nickel plate may plate dark when used diluted and at higher current densities. The bath should be analyzed to test for this condition, and it should be adjusted then
pH too high A dull nickel bath will plate dark at a high pH where basic nickel salts will plate out. Adjustment of pH to proper level corrects the difficulty.


LACK OF ADEQUATE ADHESION AND PEELING

Possible Source of Trouble Suggested Cure
Cleaning cycle Cleaners should be tested routinely for concentration, temperature, current density, chromic acid or other contamination. When hexavalent chromium is found, it may be overcome by sodium hyposulfite (Na2S2O4), treatment1. Water rinses should be checked for cleanliness.
Weak or lack of acid dip A proper concentration acid dip and a clean water rinse should be used as final steps before the work is being plated to neutralize any residual alkalinity or remove any oxides present on the surface.
Current interrupted Breaking of current should be avoided, as the laminated deposit may not be adherent, especially when the plated ware is bent.
Repair work (replating)  Repair work should be stripped clean before it is replated, or the old nickel surface must be activated. Activation of the work is accomplished in either of two ways. Preferred method is the cathodic treatment with sulfuric acid for between a few seconds to two minutes2. Activation also can be done in the Wood chloride-strike bath. Or in an obsolete, but effective, cyanide activator, the work is made cathodic for 30 - 60 seconds at 70-800 F in a 12 oz/gl NaCN solution. At least 6 V are needed to produce vigorous gassing on the work being activated.
Over-cleaning Surface of the work should be checked after cleaning for films or stains from an over-concentrated cleaner. Excessive CD, especially in anodic cleaning, should be avoided.
Under-cleaning Water breaks from a below concentration cleaner indicate under-cleaning. CD, concentration or temperature may be too low.
Improper acid dipping Inspection should be made for stains or films from an over-concentration acid dip, or lack of neutralization from an under concentrated acid dip. Muriatic (hydrochloric) acid may be more suitable than sulfuric, or vice versa, for the particular job at the particular
Impurities The plating bath should be tested for metallic impurities such as lead, chromium, or for foreign organics. Metallics such as lead are removed by dummy plating. Chromium is removed by a high pH treatment and sometimes with the additional use of potassium permanganate and lead carbonate3. Organics are removed by carbon treatment, either with or without previous oxidation with potassium permanganate, hydrogen peroxide or sodium hypochlorite, as indicated by tests.
Passive base metal Alloys, such as stainless steel, heat-treated steel and nickel alloys, may have to be activated by use of the Wood strike or by cathodic acid treatment2.
Porosity of base metal Thorough rinsing is required to remove entrapped cleaner, acid, etc.


DEPOSIT LACKS DUCTILITY

Possible Source of Trouble Suggested Cure
pH too low The pH should be tested and adjusted with nickel carbonate. Never use ammonia or alkali carbonates in bright nickels for this adjustment.
Peroxide in excess Where hydrogen peroxide is being used for removal of organic impurities, excesses should be avoided. When accidental excess occurs, it is removed by heating of the bath. Hydrogen in excess may cause pitting or may result in a deposit that is passive to subsequent chromium plate; also the ductility of the deposit may be impaired.
Low boric acid Boric acid may be very much below normal; analysis will indicate the additions that are required
Organic contamination Organic impurities should be checked and removed. The effect of organic impurities should be determined by use of Hull Cell tests. They are removed by carbon treatment, with or without preliminary oxidation, as tests may indicate.
Excess brighteners Lack of ductility in bright Ni baths results from brighteners, especially of secondary (leveling) type, being in excess. The amount of excess should be determined and then reduced in optimum concentration to the proper level. Secondary brighteners are those that give the greatest brightness as well a leveling. They require more frequently additions to a bath and normally are present in a small concentration as compared to the other additives. They require frequent Hull cell testing in order to be kept in optimum range.

STREAKY DEPOSITS

Possible Source of Trouble Suggested Cure
Concentrations in the nickel bath not normal  The solution should be tested for low concentrations of nickel, chloride, and boric acid and adjusted to the correct values.
Gassing due to dirt in crevices and holes Adhering buffing compounds and dirt can cause this trouble and should be eliminated.
Contamination present Cleaner may be retained in holes or crevices through improper rinsing. Steps should be taken to eliminate such a condition if they are found.
Foreign material suspended in bath Acid may be retained in holes or crevices due to improper rinsing. Thorough rinses will help to avoid this condition
Localized low pH Acid may be retained in holes or crevices due to improper rinsing. Hydrogen gassing may cause vertical streaks. Agitation, redesign of racks and other stops may be taken to correct this. Thorough rinses will help to avoid this condition
Excess of brightener After additions of brightener, the bath should be thoroughly mixed.

SPOTTY DEPOSITS

Possible Source of Trouble Suggested Cure
At bottom of work The bath should be stirred well or agitated to avoid stratification, non-uniform temperature layers, or both.
Foreign solid material in the bath Filtration of the bath eliminates this source of contamination. Calcium sulfate is less soluble in a hot bath than in a cold one and may precipitate out to cause roughness.
Poor rinsing Cleaners not thoroughly rinsed off, or not neutralized by acid dip, or silicates precipitated on the work will cause spotty deposits. Thorough rinses are advised. Additional spray rinsing may be required.
Undissolved boric acid Heat the bath to dissolve boric acid crystals formed when the bath is cooled.

DEPOSIT DARK IN RECESSES AND LOW CURRENT DENSITY AREAS

Possible Source of Trouble Suggested Cure
Metallic contaminations present in bath The bath should be tested for contamination by copper, zinc, cadmium, and lead. If found, they are removed by dummy plating. Hull Cell tests indicate these impurities at the backside of the panel.
Organic impurities Hull Cell tests indicate these impurities as dark streaks. They are removed, if found present, by carbon/peroxide treatment, as outlined in 1H.
Low current density Increases of current density as high as possible without burning of the work is advised.


POOR THROWING POWER AND POOR METAL COVERAGE

Possible Source of Trouble Suggested Cure
Nickel metal content low Analysis for nickel concentration and increases to the proper level are in order.
Conductivity poor A check of chloride content and an increase to the proper level is indicated.
Current density low An increase in current, as high as possible without burning the work is advised. Bipolar or auxiliary anodes may be needed
Impurities present The bath should be tested for metallic impurities (Cu, Zn, Cd, and Pb) and organic impurities. These are removed, if found present, by dummying to eliminate the metals and by carbon treatment to remove organics.
Loose contacts A check of all electrical connections to tank, rack, and anodes is advised. Cleanliness to insure full flow of current is a must.
Anodes An inspection of anodes for adequate number, spacing and proper anode area is suggested. Normally 2-3 anodes per foot of anode bar are sufficient. Check anodes for black adherent polarized film. Clean anodes.


BURNT EDGES OR FROSTY PLATE

Possible Source of Trouble Suggested Cure
Excessive current density A reduction of current or an increase of agitation and a higher temperature are in order. Work should not be too close to anodes.
Bath concentrations low The bath should be routinely analyzed and build up to the prescribed limits.
Ammonium salts present Ammonium salts limit maximum current density and never should be introduced as they can only be reduced by drag-out.
Excess brighteners Brighteners in excess may limit maximum practical current density. Brighteners should be kept within proper limits.
Chemical contaminations A test for chromates or nitrates is advised. Chromium is removed by high pH method4. Dummy plating at 50-60 A/ft2, and pH of 2-3 reduces nitrates. Aluminum and iron are removed by high pH treatment.
Organic contamination Hull Cell tests and their removal, as in 3H, are in order.
Excess iron in bath Analysis for iron in the solution should be made. It is removed by rising of the pH and followed up with filtration of the solution.

PITTING

Possible Source of Trouble Suggested Cure
Antipit agent out of concentration If a surfactant is used, pitting may occur if concentration is too low, but in some cases also if too high. The operators have a tendency to keep them at high levels. It is cautioned to avoid excesses if possible.
Antipit agent low If proprietary antipit is used, the concentration maybe adjusted.
Organic contamination Organic contaminants may cause pitting and are removed with activated carbon as outlined in 1H.
Rough deposit pits Foreign solid materials, such as precipitated iron, dirt or carbon, are removed by filtration.
Air pits If pH and concentrations are normal and bath is clean, tests should be made for air being introduced by the leaking filter. Also, when everything else is normal, air pits can be obtained from the bath by the large addition of cold water while plating is being performed.
Gassing while plating Zinc base metal, not completely covered with copper, will be dissolving with release hydrogen evolution and contaminate the bath.
Low pH Too low a pH will attack zinc base metal through a thin copper plate. Adjustment to best operating level is advocated.
Low temperature Adjustment of temperature to optimum range is necessary.
Low boric acid Analysis for boric acid and a build up to proper concentration are required for proper buffering of the solution.
Excessive Current Lowered current, or increased agitation and raised temperature are suggested.
When heating up bath A cold bath, especially if not used for some time, will have absorbed air that will pass off after the bath is heated.
After raising pH Carbon dioxide, produced when the pH is raised with nickel carbonate, is removed by heating of the bath.


ROUGH DEPOSITS

Possible Source of Trouble Suggested Cure
High current density Adjustment of the CD is required, as excessively high current may cause co-deposition of minute solid particles that are suspended in bath. Each nickel bath has his intrinsic limiting maximum CD.
Low bath concentration Too low a concentration of nickel, chloride, and boric acid will promote rough deposits. Analysis of the bath and adjustments to proper concentration are in order.
Low temperature Very low temperature, below about 600F, depending on current density, will cause roughness. The bath temperature should be adjusted to a practical value.
High pH A pH > 5.0 may promote inclusion of basic nickel salts in the deposit, depending on current density. A pH adjustment to a proper level is advised.
Iron and aluminum An excess of dissolved iron and aluminum will promote precipitation under electrolysis at the high pH. High pH precipitation plus filtration remove the impurities.
Solids in bath Filtration of the bath is recommended. Operators are cautioned to avoid the presence of anode sludge, dirt, buffing compounds, filter-aids, and activated carbon in the solution. For best performances of the bath, continuous filtration with the properly sized filter is a must.

Note: a bright pit with a vertical tail characterizes hydrogen pits. Very fine pits with no tails characterize gas pits from air or carbon dioxide. Rough deposits are sometimes confused with pitting.

REFERENCES:

1. M. M. Beckwith, Proc. Am. Electroplaters Soc. 29, 80(1941).
2. W. A. Wesley & W. H. Prine, "Practical Nickel Plating," p30, International Nickel Co., NY( 1952).
3. N.V. Mandich, Plat.Surf.Finish., (1998)
4. W. A. Wesley & W. H. Prine, "Practical Nickel Plating," p30, International Nickel Co., NY (1952).

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