Sunday, March 16, 2008

Wetting Agents-Nickel Plating

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All all process of electroplating will merge gas on the electrode, depend on the solution use on the electroplating, if use water to dilute substance, on the electrode will merge hydrogen gas and oxygen gas. Certain anionic wetting agents are used in nickel baths to prevent bubbles of hydrogen from adhering to the cathode and causing pits in the deposit. They function by reducing the surface and inter facial tension, and with the correct wetting agent the contact angle between the liberated hydrogen bubbles and the cathode is reduced to zero. The bubbles disengage before they can grow to a size to cause pitting by blocking the plating at the point of contact of the bubbles. Sulfate of normal primary alcohols containing from 8 to 18 carbon atoms, in concentrations of 0.1 to 0.5 g/l, were the first successful wetting agents used commercially in bright nickel plating baths. Sodium lauryl sulfate, free from lauryl alcohol, was the most extensively used wetting agents have no adverse effects on the deposit, and none other in ductile dull nickel plating. Sodium lauryl ethoxy sulfate or sulfonate can be used in semi bright and bright nickel baths.

When air agitation is used in nickel plating to make possible the use of higher current densities, the chain length of the wetting agent should be six to eight carbons, and mildly branched chains of a total of eight carbons can to eight carbons can be used in these cases. The shorter chain sulfate or sulfonate wetting agents do not cause over foaming with the air agitation, and since agitation with clean air is itself active in anti pitting, the normally less effective shorter chain surfactants are usually sufficiently effective. Extremely fine bubble of air, as form air leaks in pumps causing emulsified air, can cause fine pitting. Another value derived from the use of the wetting agents is the diminished drag out of nickel salt because of the fast runoff from points and edges of the articles due to the low surface tension. Activated carbon can removed the wetting agents from the baths, especially the longer chain compounds. Bright or semi bright nickel baths containing certain unsaturated addition agents which function by depolarization of hydrogen are seldom subject to pitting when clean condition are maintained and air agitation is used.

Formaldehyde, various unsaturated aliphatic sulfonic acids, and mono-sulfobenzaldehydes are effective in this respect. Nevertheless even in most of these cases the use of wetting agents is still desirable.

Traces of non anionic wetting agents, 1 mg/l and less, have been used to suppress "honeycombing" in thick cathode deposits in the electro refining of nickel.

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