solutions or moltens alt solutions in which the H
C ion concentration
is negligible.
Manyalloys may be electrodeposited,including copper–zinc, copper–tin,
lead–tin, cobalt–tin, nickel–cobalt, nickel–iron, and nickel–tin. The copper–
zinc alloys are used to coat steel wire used in tire-cord. Lead–tin alloys are
known as terneplate and have many corrosion resistant applications.
The thickness of coating can be accurately controlled since the amount
deposited is afunction of the number of coulombs passed.
7.2.1.2 Electroless Plating
This method is also known as chemical platingo ri mmersion plating. It is
based on the formation of metal coatings, resulting from chemical reduction
of metal ionsf roms olution. The surfacet hat is to be coated must be
catalytically active and remain catalytically active as the deposition proceeds
in asolution that must contain areducing agent. If the catalyst is areduction
product (metal), autocatalysis is ensured. In this case, it is possible to deposit
acoating, in principle, of unlimited thickness. The advantages of electroless
platinga re:
1. Deposits have fewer pinholes.
2. Electric power supplyi sn ot required.
3. Nonconductive materials are metallized.
4. Af unctional layer is deposited.
5. Au niform layer is deposited, even on complex parts.
6. The equipmentf or electroless platingi ss imple.
Electroless plating is limited by the fact that:
1. It is more expensive than electroplating because the reducing
agents cost more than an equivalent amount of electricity.
2. It is less intensive because the metal deposition rate is limited by
metal ion reduction in the bulk of the solution.
Copper,s ilver,c obalt,a nd palladium are the most commonly plated
metalsu sing this process. The silveringo fm irrors falls into this category.
Hypophosphite, amine boranes,f ormaldehyde, borohydride, and hydrozine are typical reducing agents. Deposits of nickel formed with hypophosphite as ar educing agent contain phosphorus.T his alloying constituent
determines many of the properties. Table7 .4 shows coatings obtainedb y
electroless plating.
7.2.1.3 Electrophoretic Deposition
Finely divided materials suspended in an electrolyte developacharge as
ar esult of asymmetryi nt he charge distribution caused by the selective
Corrosion of Linings and Coatings
418
CAT8247—CHAPTER 7—17/10/2006—15:02—TRGANESH—XMLM ODEL B–pp. 403–485
C ion concentration
is negligible.
Manyalloys may be electrodeposited,including copper–zinc, copper–tin,
lead–tin, cobalt–tin, nickel–cobalt, nickel–iron, and nickel–tin. The copper–
zinc alloys are used to coat steel wire used in tire-cord. Lead–tin alloys are
known as terneplate and have many corrosion resistant applications.
The thickness of coating can be accurately controlled since the amount
deposited is afunction of the number of coulombs passed.
7.2.1.2 Electroless Plating
This method is also known as chemical platingo ri mmersion plating. It is
based on the formation of metal coatings, resulting from chemical reduction
of metal ionsf roms olution. The surfacet hat is to be coated must be
catalytically active and remain catalytically active as the deposition proceeds
in asolution that must contain areducing agent. If the catalyst is areduction
product (metal), autocatalysis is ensured. In this case, it is possible to deposit
acoating, in principle, of unlimited thickness. The advantages of electroless
platinga re:
1. Deposits have fewer pinholes.
2. Electric power supplyi sn ot required.
3. Nonconductive materials are metallized.
4. Af unctional layer is deposited.
5. Au niform layer is deposited, even on complex parts.
6. The equipmentf or electroless platingi ss imple.
Electroless plating is limited by the fact that:
1. It is more expensive than electroplating because the reducing
agents cost more than an equivalent amount of electricity.
2. It is less intensive because the metal deposition rate is limited by
metal ion reduction in the bulk of the solution.
Copper,s ilver,c obalt,a nd palladium are the most commonly plated
metalsu sing this process. The silveringo fm irrors falls into this category.
Hypophosphite, amine boranes,f ormaldehyde, borohydride, and hydrozine are typical reducing agents. Deposits of nickel formed with hypophosphite as ar educing agent contain phosphorus.T his alloying constituent
determines many of the properties. Table7 .4 shows coatings obtainedb y
electroless plating.
7.2.1.3 Electrophoretic Deposition
Finely divided materials suspended in an electrolyte developacharge as
ar esult of asymmetryi nt he charge distribution caused by the selective
Corrosion of Linings and Coatings
418
CAT8247—CHAPTER 7—17/10/2006—15:02—TRGANESH—XMLM ODEL B–pp. 403–485