Superglo Bright Nickel Process
'Superglo' is a bright nickel process developed to produce brilliant, mirror-bright and highly leveled deposits with excellent mechanical properties. The solution is easy to maintain, being quite tolerant to metallic impurities.
The process is best operated with continuous filtration through activated carbon. This ensures consistent production standards and eliminates the necessity for bath purification treatments, saving time and materials.
The standard watt's type bath composition is satisfactory. For best results the solution should be air agitated by passing clean filtered air.
The two addition agents are Nickel Additive 22 and Superglo Brightener 33, both of which are liquid. It is easy to convert other bright nickel processes to Superglo Bright Nickel. However, before such a conversion, a sample solution should be submitted for analysis and recommendations.
The initial make-up of solution is carried out by dissolving Superglo Nickel Salts preferably in deionized or distilled water. The following concentrations are recommended.
| ||Optimum ||Range |
|Superglo Bright Nickel Salt ||400 g/l ||350-450 g/l |
|Nickel Additive 22 ||7.5 ml/l ||5-10 ml/l |
|Superglo Brightener 33 ||0.4 ml/l ||0.2-0.6 ml/l |
|Antipit No.2 ||0.1 g/l ||0.05-0.5 g/l |
|(for cathode movement bath only) || || |
|Cathode Current Density ||4 A/dm2 ||2 - 8 A/dm2 |
|Anode Current Density ||2 A/dm2 ||1 - 3 A/dm2 |
|Temperature ||55 oC ||50 - 65 oC |
|pH (Electrometric) ||4.2 ||4.0 - 4.6 |
|Density ||24 oBe ||20 - 28 oBe |
|Agitation ||Air/Cathode || |
|Filtration ||Continuous || |
FUNCTION OF SOLUTION CONSTITUENTS
Nickel Sulphate provides the principal source of nickel ions for the Superglo solution. The concentration of nickel ions largely determines the limiting current density that can be used.
The Chloride ion is essential in nickel bath since it enables the anode to dissolve properly without polarization and it improves the electrical conductivity of the solution.
Boric Acid is important because it stabilizes the pH value of the solution and also it improves the brightness and ductility of the deposit.
Nickel Additive 22:
This is used in the preparation of a new solution and during the conversion of an existing process. Frequent addition with Superglo Brightener 33 is recommended. Slightly more addition of Nickel Additive 22 may be required after carbon treatment.
Superglo Brightener 33:
This is used both in the initial preparation of the solution and for subsequent maintenance. It is responsible for the brightness and leveling properties of the deposit.
A liquid addition agent is used if pitting cannot be eliminated by normal additions of Antipit No.2. It is a low foam type wetting agent and is used in an air-agitated solution without causing excessive foaming.
A solid addition agent used only when the solution is operated under cathode rod movement and should not be used in air agitated baths, because this will cause excessive foaming.
NOTES ON OPERATING CONDITIONS
To obtain best results the solution should be maintained between 50-65oC. Higher temperature permits higher current densities to be used. For high temperature operation suitability of tank linings, anode bags and agitation coils should be considered.
The pH value should be between 4.0 - 4.6. Excessively low pH values reduce the brightness and leveling of the deposit and excessively high pH values reduce the high current density ranges and ductility.
In normal working the pH value of the solution tends to rise and it should be reduced by means of additions of pure Sulphuric Acid (diluted with water). The pH value should be checked and adjusted at least once in each working shift.
If it is necessary to raise the pH value, only Nickel Carbonate should be used, and this preferably should be added by pre-coating a filter unit and circulating the solution until the required pH value is obtained. Ammonia, Sodium Hydroxide and Sodium Carbonate must not be used to raise the pH value.
Air agitation should be vigorous to achieve maximum performance from the Nickel plating process. The air must be clean and supplied by a low pressure blower. The air agitation must be directed at the work being plated. Cathode rod movement can also be used for agitation of the solution. The stroke of the cathode movement should be from 7-8 cms and 5 cycles per minute.
Superglo Nickel solution should be continuously filtered through high quality activated carbon. This will ensure consistent and reliable production. The filter unit should be of sufficient capacity to have two to four changes per hour. 100-150 gms of carbon per 1000 litres per week and 50 gms of Nickel Purifier per 1000 litres per week is usually sufficient to maintain the purity of solution.
For the initial make-up of a Nickel solution, the solution is prepared as per the following method :
This solution is in a purified condition and ready for the addition of brighteners. After these additions and the final adjustment of the pH value, the solution is ready for use.
- Leach a new rubber lined tank with 5% Sulphuric Acid (by volume) and 1 ml/l of Antipit No.1 at 50-70oC. Agitate the solution for 2-3 hours, maintaining the temperature at 70oC. The dilute acid is allowed to stand overnight. Afterwards the tank is cleaned with water and mixed with Antipit No.1 at the rate of 2 ml/l and then flushed with clean soft water.
- Fill the plating tank with two-thirds of water. Softened or demineralized water is preferred. Heat at a temperature of 65-70oC.
- Add calculated quantity of Superglo Bright Nickel Salt and stir vigorously until completely dissolved.
- Dilute the solution to the working level and adjust the pH value to 2.5 - 3.5 with pure Sulphuric Acid (25% volume). For dilution of Sulphuric Acid always add the acid in water with stirring and cooling.
- Suspend a few Nickel anodes on the anode bars and as many dummy cathodes as possible from the 2 cathode bar. Electrolyze the solution at 0.3 Amp/dm2 for 12-24 hours with vigorous air agitation to remove metallic impurities. Remove the anodes and dummy plates.
- Pump the hot solution to the storage tank and add sufficient Nickel Carbonate powder and stir the solution vigorously to raise the pH value to 5.0-5.5 and add 2 ml/l (20%) Hydrogen Peroxide. Stir vigorously at 60-70oC for two hours.
- Add 2 g/l activated carbon. Air agitate or stir the solution vigorously for 2 hours.
- Allow the solution to stand overnight to enable the carbon and other residues to settle.
- Filter the solution back into the clean plating tank, taking care not to disturb the layer of sludge on the bottom of the tank.
Nickel Plating Tank:
The plating tank should be of mild steel lined with an approved grade of semi-hard or hard rubber. The quality of the rubber is very important for good performance of solution and hence it is advisable to consult the Growel Laboratory / Local Representative before getting the tank lined. Thermal lagging is recommended though not essential, as it is already insulated inside by rubber lining.
Mixing and Purification Tank:
This tank is meant for the preparation and purification of the solution. This tank is suitably lined with a good quality of rubber and should have a capacity sufficient to accommodate solution of the plating tank. This should also have heating and agitation accessories.
The plating tank should be equipped with a suitable heating device, thermostatically controlled to heat the solut ion. Fol lowing heat ing equipment s are recommended:
- Titanium Heating Coil: This can be used where steam or thermic fluid is used for heating purpose.
- Silica cased electric immersion heaters with suitable protective cages can be used for heating where electrical heating is necessary.
It is essential to use continuous filtration during the process. The capacity of the filter unit should be selected so as to have two to four changes of solution per hour. All the parts of the filter unit coming into contact with the solution, should be of approved rubber or stainless steel, chemical resistant type SS 316.
Low pressure oil-free air agitation equipment is recommended to give a vigorous agitation to the solution. The air agitation coil should be made of either Ebonite or Polypropylene to have sufficient temperature resistance. The polythene and PVC coils are not suitable and should not be used.
Compressed air coming from an oil compressor, should not be used since oil will get into the solution resulting in faulty deposits such as pitting and peeling.
- Lead lined equipment "Should not be used" with Superglo Bright Nickel Plating solution.
- In general, all materials that come in contact with Superglo Bright Nickel solution, should be approved by Growel Laboratory or Growel Local Representative to avoid contamination of solution.
Cast or Rolled Depolarized Nickel Anodes are recommended. The anode area should be as high as possible. Titanium anode baskets are strongly recommended as it gives minimum wastage, resulting in high economy due to less rejection as well as less material consumption. Anode should be essentially covered with anode bags made of cotton spun woven Terylene or polypropylene to prevent the anode sludge creeping into the tank and causing roughness to deposit.
Hard water should not be used for preparation of solution and for making up of working level of solution as the calcium salts present get crystallized and give roughness and overall dullness to plating deposits.
Where the anode dissolution is proper, the nickel salt is generally lost only by drag-out and by general wastage. It is strongly recommended that small daily addition of nickel salt be made and that analytical control is used to adjust the amounts of the daily additions. Adjust the bath contents as given below :
|Nickel as metal ||: ||60 - 80 g/l |
|Chloride as Nickel Chloride ||: ||35 - 70 g/l |
|Boric Acid ||: ||35 - 45 g/l |
When it is required to make large additions of Nickel Salt, the addition should be followed by low current density electrolysis to remove metallic impurities.
The Brightener 33 is consumed by electrolysis and drag-out and by general wastage. It is not appreciably removed by the recommended filtration through carbon treatment. The consumption rate of Brightener 33 is 150-200 ml per 1,000 ampere-hour and the Brightener should, accordingly, be added at this rate. Regular addition of Nickel Additive 22 is recommended, depending on dragout rates. Addition rate of Nickel Additive 22 is 75 - 125 ml per 1000 Ampere-hour. In some very specific applications the requirement of Nickel additive 22 may be higher.
Most common metallic impurities found in Nickel Salts are Copper, Zinc, Chromium, Lead and Iron. Copper, Zinc and Lead can be effectively removed by electrolytic purification, accomplished by using corrugated dummy 2 cathodes at current density of 0.3 Amp/dm2 High agitation, low pH and high temperature will help in quick elimination of these impurities. Chromium contamination of Hexavalent Chrome is precipitated by adding exact equivalent quantity of Lead Carbonate so that Lead Chromate precipitates and is removed by filtration. Iron can be removed by oxidizing carbon treatment as enumerated in the following paragraphs :
An insoluble filter media for use in filter packs to remove metallic impurities from Nickel plating solution. Regular use of this product will keep the plating bath virtually free of metallic impurities, assuring maximum brightness of the electroplated nickel, and will also eliminate costly down time, high pH treatments and electrolytic dummying.
During plating, organic impurities creep in the solution by decomposition of organic brightener during electrolysis and also by drag-in of pre-treatment solutions.
Oxidation carbon treatment:
When the contamination is not severe, the solution can be continuously filtered through a small amount of carbon packed in the filter. Should the solution become seriously contaminated with organic impurities, an oxidizing carbon treatment is required to remove the same and should be carried out as follows :
Heat the solution to 70oC and pump it into a storage tank. Add sufficient Nickel Carbonate powder and stir well to raise the pH value to more than 5.2.
Add 1-2 grams per litre of Potassium Permanganate dissolved in water or 2-3 ml per litre of Hydrogen Peroxide (20%), stir well for 30 minutes. Add 3 grams per litre of Growel Activated Carbon. Air agitate vigorously for at least 2 hours. Allow the solution to stand without stirring for overnight so as to allow the carbon and other impurities to settle. Filter the solution back into the plating tank, taking care not to disturb the layer of sludge settled at the bottom of the tank.
This treatment will remove Nickel Additive 22 and Superglo Brightener 33 partially and it is therefore recommended to add at the rate of 2-6 ml/litre of Nickel additive 22 and 0.1 - 0.2 ml/l of Superglo Brightener 33.
CONVERSION OF EXISTING SOLUTIONS
Mostly, conversion is easily carried out by giving purification treatment and the adjustment of Nickel Ion, Chloride Ion and Boric Acid contents to the required level by the addition of Nickel Sulphate, Nickel Chloride and Boric Acid. The organic contaminants are removed by Hydrogen Peroxide, Carbon or Permanganate - Carbon and then Nickel Additive 22 and Superglo Brightener 33 added to make up the required concentration level. However, before such a conversion, a sample should be submitted to G&W Laboratory for necessary recommendations.
Analysis of Nickel:
Pipette 1 ml of the plating solution into a 500 ml conical flask. Dilute it with a small quantity of distilled water. Add about 5 ml of Ammonium Hydroxide solution and a few grains of Murexide Indicator. Shake the flask well and titrate against 0.1 M.E.D.T.A. to purple colour end point. Note the reading, let it be "a"ml of E.D.T.A.
"a" ml of E.D.T.A. x 5.869 = gm/l Nickel metal
Analysis of Nickel Chloride:
Pipette 5 ml of the solution into a 500 ml conical flask and dilute with distilled water. Add few drops of Potassium Chromate Indicator and titrate against 0.1 N Silver Nitrate until the white precipitate of Silver Chloride takes on a very faint reddish-brown tint. It requires practice to detect the exact end point easily. Note the reading.
ml of 0.1 NAgNO3 used x 2.378 = gm/l NiCl26 H2O
Analysis of Nickel Sulphate:
From total nickel metal and Nickel Chloride concentration Nickel Sulphate can be calculated as follows:
[gm/lit. of Nickel Metal - (gm/lit. of Nickel Chloride x 0.247)] x 4.79 = gm/l NiSO4.7H2O
Analysis of Boric Acid:
Pipette out 1 ml of the plating solution into a 500 ml conical flask. Add 2-3 gms of Mannitol Powder and shake well to make a slurry. Titrate with N/10 Sodium Hydroxide after adding 2-3 drops of Bromocresol purple as indicator. The end point is yellow to blue.
ml of N/10 NaOH used x 6.184 = gm/l Boric Acid