Guest Editorial -For Plateworld.com
Don Baudrand, Don Baudrand Consulting, e-mail:firstname.lastname@example.org
IMPURITIES IN NICKEL PLATING SOLUTIONS
Bright Nickel plating solutions are especially sensitive to impurities that can cause numerous defects in the nickel deposit. Likewise, Sulfamate nickel plating solutions are very sensitive to impurities that change the physical characteristics of the deposit. The same is true for the "Watts "formulation used for engineering. Strongly acidic nickel strike solutions that are used for preparation of stainless steel, titanium and other metals and alloys that require a severe activation process are sensitive to certain impurities.
Sulfamate nickel plating solutions
Nickel as metal (from nickel sulfamate concentrate) 76.5 g/L
Chloride or bromide 2.2 g/L
Boric acid 45 g/L
Chloride and/or bromide are actually impurities that have a negative influence, since the internal stress in the deposit is moved toward a higher tensile stress. In many cases that is not desirable. But the operating data sheet formula tells us that is desirable to add 2.2 g/L of a chloride or bromide. The reason for adding either of these is to help to keep the anodes from polarizing while allowing the use of higher current densities, at the sacrifice of raising the internal stress. If the lowest internal stress is a goal, lower or eliminate the chloride or bromide. But if you do that, plating must be at lower current density than perhaps you want to use. My guess is that the current density should be below 60 amps/sq. ft. (6.45 amps/sq. dm). For many applications the lower CD is not a problem, just plate a little longer.
pH of about 5 will result in a harder less ductile deposit.
Temperature of between 35 and 50C (95 – 126F) the stress is at its minimum.
Sulfamate nickel, Watts Nickel, and bright nickel (based on the Watts nickel formulation)
Nickel as metal (using nickel sulfate) 75 g/L (10 oz. /gal.)
Nickel chloride 60 " (8 oz. /gal.)
Boric acid 45 " (6 oz/gal.)
Woods nickel strike
Nickel chloride 45-60 g/L as nickel metal (6-8 oz/gal.)
Hydrochloric acid 22 Baume 10-12% by vol.
The impurities act similarly for all the above nickel plating solutions
Impurities in nickel plating solutions and result
Ammonium ions above 2500 ppm can cause tensile stress and lower ductility.
Cadmium, 1000 ppm, Source: Safraneck, dark low CD area and brittle deposit.
Chromium, starting at 3 ppm of hexavalent chromium or 8 ppm of trivalent chromium, extreme stress in the deposits, cracking of the deposit, rough deposits and dark deposits can result. A Woods nickel strike can tolerate more than 8 ppm of chromium. The amount of Chrome tolerated by the nickel strike is dependent on the age of the bath. Nickel tends to build up in the bath because the anode efficiency is greater than the cathode efficiency. Nickel sulfate may salt out.
Cobalt is sometimes added to sulfamate nickel and to Watts' nickels to form a cobalt- nickel alloy. The result is increased tensile stress, but a strong harder alloy that is useful for many applications.
Copper of 50 ppm or more causes dark deposits in the low current density region
Iron, 300 to 900 ppm whitens the deposit and can cause roughness, and reduces ductility.
If the pH of the nickel plating solution is kept at or above 3.9, there will be no iron. Iron will precipitate in the bath and be removed by filtration
A Woods nickel strike can tolerate more than 900 ppm iron
Lead causes dark low current density areas and increases tensile stress.
Nitrates above 5 ppm cause tensile stress. Above 0.3 g/L results in very high tensile stress.
Organic impurities can: cause brittle, dark, or pitted deposits. Sources are breakdown products from brighteners, or other organic addition agents used to reduce stress, harden the deposit, lower surface tension. Oils from poor cleaning, or entrapment in seams, cracks or other recessed areas. Organic impurities take many forms. In Bright nickel solutions over addition of brighteners and/or other addition agents used for brightening and other modifications of the deposit can act as impurities causing loss of brightness, increased hardness, and brittle deposits discolored deposits, even gray to black deposits.
Magnesium has little effect on the deposit properties. However, it is beneficial as is manganese in preventing sulfur from migrating to stress or heated areas of the deposit. Sulfur causes cracking of heated areas and fatigue failure.
Sodium in the amount of 25-30 g/L causes brittle deposits. Lower amounts of sodium have little effect.
Sulfur containing compounds in the range of 25 ppm or higher causes high compressive stress, brittle, fatigue failure, and bright deposits.
Tin has two common valence numbers, 2 and 4. Tin 2 has little effect on the deposit, but tin4 can cause high tensile stress
Zinc is tolerated up to about 250 ppm. Higher concentrations cause dark streaks, ease of burning and brittle deposits; and lowers cathode efficiency.
The alphabet soup of impurities can be removed from nickel plating solutions by various means, the subject of other papers.
Monitor impurities in your nickel plating solutions.
Everything in you power to prevent introducing impurities into the plating solutions.
Be sure that all items to be plated are clean. Watch out for seams, cracks, blind holes that can entrap oil, and/or other impurities.
Maintain the amount of all the constituents of the plating solution to optimum concentration.
Carbon treat when organics are likely to be present. Follow the supplier’s instructions for treating and maintenance.
Maintain the brighteners in good balance in bright nickel solutions. Don’t over add brighteners in the bright nickel.
Do not add organic materials to Watts or sulfamate solutions if used for engineering, or for the specific properties of the pure deposits. (Except surfactants that are suitable for nickel plating use.)
Keep the cover on the tank when not in use to prevent foreign material to fall into the plating tank. Cover the tank when cleaning the bus bars to prevent anything to enter the plating tank the bus bars over the tank.
High temperatures can breakdown brighteners leaving organic impurities that cause off color, and harden the deposit, that cause brittle deposits.
Enjoy good nickel plating that will meet requirements.
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