Guest Editorial -For Plateworld.com
Don Baudrand, Don Baudrand Consulting, e-mail:firstname.lastname@example.org
Doís and Doníts of Sulfamate Nickel Plating
Why is sulfamate nickel plating used? The deposits are ductile, yet strong. The deposits have good thermal and electrical conductivity, favorable modulus of elasticity; low coefficient of expansion, the formula is simple. It does not cause hydrogen embrittlement per se. Embrittlement, is often due to pre-treatment such as the use of hydrochloric acid, or sulfuric acid. A mild sulfamic acid or mild phosphoric acid is suggested for a very short time when treating high strength steels. The sulfamate radical is very activating of steels. There is a sulfamate nickel strike formula that will activate some stainless alloys that are difficult to activate using a Woods strike.
Sulfamate nickel solutions can plate at very high current density using mild agitation. Over 100 A/sq.ft (10.8A/dm2) is possible. With moderate agitation deposit the can be up to 400 ASF (43A/dm2 ) With high agitation, 600 or more ASF (65A/sq dm) or more is possible and with "hone plating" where agitator is in contact with the deposit surface moving at relatively high speed, 6000 ASF (646 A/sq dm) is achievable. Plating rate is about a mil per minute.
Trace metals in the plating solution can influence some of the characteristics of the sulfamate nickel deposit. For example, a small amount of manganese (Mn) decreases stress and more important, Mn can inhibit sulfur migration to grain boundaries of the nickel deposit. Also, Mn in the deposit will stop cracking at weld sites by preventing sulfur from reaching weld areas. Sulfur is a common impurity in sulfamate nickel deposits. Sources of sulfur are carbon filters, over flow from anode baskets because of the sulfur depolarized (SD) anodes required for sulfamate nickel. The particulate sulfur can co-deposit in the nickel. On heating of the deposit, sulfur migrates to grain boundaries.
Small amounts of magnesium have little or no influence on the physical characteristics of the nickel deposit.
Small amounts of chromium copper, zinc and cadmium change the properties of the nickel deposit drastically.
Cobalt additions will harden the deposit and enhance the hard magnetics.
Iron will also increase the magnet magnetic characteristics.
Sulfamate nickel deposits make a good base for bright nickel plating. It is used with diamonds particles used in cutting tools. Sulfamate nickel deposits are useful for many different applications.
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