The mechanism and the characteristics of electroless nickel plating

Electroless nickel for the deposition of nickel ions in solution with the reducing agent in the catalytic activity of the surface restored. Chemical nickel-plating, a number of reducing agents which are commonly sodium hypophosphite as a reducing agent nickel plating for industrial use. The widely accepted reaction mechanism is the theory of atomic hydrogen and hydrogen-theory.Atomic hydrogen theory is that the dissolution of Ni 2 atoms on the reducing agent sodium hypophosphite (NaH2P02) release of active hydrogen-reduction of the nickel, instead of the Ni 2 H2PO2-, dependent and direct role. The first magnesia oxide under heated conditions, sodium hypophosphite explaining the release of atomic hydrogen in the catalytic surface, or by H-2po2 catalytic dehydrogenation of atomic hydrogen, that is then H-atom on the surface of the active metal adsorbed restoring the case of Ni deposition tees to produce light. At the same atomic a phosphate hydrogen reduction of phosphorus, or the presence of the redox-reactive deposition of phosphorus, ie H 2, the precipitation of either H2POf a hydrolysis or a combination of atomic hydrogen modes.Hydride theory is that the decomposition of sodium hypophosphite not free state atomic hydrogen, but the release of stronger reducing power of hydride ion (hydrogen anion H) and nickel ions in order to restore the negative ions of hydrogen. In the acid bath, H2PO2-catalytic reaction with the surface of the water in the alkaline bath, compared with the hydride reduction of nickel ions, negative ions hydrogen with the H20 H or H, the reaction to release hydrogen.To date, the development of chemical nickel plating for over 50 years of history. After half a century of research and development, chemical nickel reached an advanced stage of development, the current situation be summarized as follows: The technology is mature, stable performance, versatile, wide range of nickel uses.Chemical applying the coating, which is Some characteristics which are derived from the electrodeposited layer. Hypophosphite as a reducing agent, phosphorus, the occurrence of co-precipitation of phosphorus and nickel oxide, electroless nickel-phosphorus, the dispersion state of the nickel-phosphorus alloy layer, the phosphorus content in the coating of 1% to L5% control phosphorus content of the nickel-phosphorus plating close , non-porous, corrosion resistance much higher than the nickel. Borohydride, or the amino-borane as a reducing agent for the nickel plated layer, a nickel-boron alloy coating of boron from 1% to 7%. Only hydrazine as a reducing agent to the coating a layer of pure nickel, nickel content of 99.5%.High hardness, good wear resistance. Only L60 ~ 180HV hardness of electroless nickel layer, the hardness of the electroless nickel plating layer 400 ~ 700HV after appropriate heat treatment further increased close to or exceed the hardness of the chrome, it's a good wear resistance, the less often both good corrosion resistance, wear resistance of electroless nickel plating layer. High chemical stability and coating with good adhesion. Higher than the chemical stability of the nickel layer in the atmosphere, and in other media, the chemical stability of the electroless nickel plating layer. As usual, the binding of steel, copper and good binding capacity of not less than the electroless nickel layer and substrate binding.The second electroless nickel plating layer of phosphorus (boron) and containing various heat treatment after coating, the physical and chemical properties of nickel-plating layer, such as hardness, corrosion resistance, abrasion resistance, electromagnetic properties of various changes. Therefore, industrial applications and process design of chemical nickel plating in the nature of diversity and specificity. Since electroless nickel plating with excellent physical and chemical properties, the technology has extensive applications in various industries such as electronics, computers, machinery, transport, energy, chemicals, aerospace, automobile, metallurgy, textile and mold.  Source:http://www.mhcocm.com