7.1.5A nodicC ontrol Protection
Noble metal coatings provide anodic control protection. They are usually
used where corrosion protection and decorative appearance are required.
Nickel, chromium, tin, lead, and their alloys are the coating metals that
provide anodic protection.
7.1.5.1 Single LayerCoatings
Singlel ayer metal coatings provide corrosion protection as ar esult of
the original barrier action of the noblem etal. With the exception of lead,
as econd barrier of corrosion products is notf ormed. Noble metals do not
provide cathodic protection to steel substances in natural atmospheres
because the corrosionpotential of the noblemetal is more noble than that of
the steel. Refer to Table7.3.
Steel
Steel
Electrolyte
Zn 2+
OH −
Zn
ee
Zn(OH) 2
Zn
O 2
FIGURE 7.4
Schematic illustration of galvanic action of sacrificialm etal coating.
Corrosion of Linings and Coatings
414
CAT8247—CHAPTER 7—17/10/2006—15:02—TRGANESH—XMLM ODEL B–pp. 403–485
Noble metal coatings provide anodic control protection. They are usually
used where corrosion protection and decorative appearance are required.
Nickel, chromium, tin, lead, and their alloys are the coating metals that
provide anodic protection.
7.1.5.1 Single LayerCoatings
Singlel ayer metal coatings provide corrosion protection as ar esult of
the original barrier action of the noblem etal. With the exception of lead,
as econd barrier of corrosion products is notf ormed. Noble metals do not
provide cathodic protection to steel substances in natural atmospheres
because the corrosionpotential of the noblemetal is more noble than that of
the steel. Refer to Table7.3.
Steel
Steel
Electrolyte
Zn 2+
OH −
Zn
ee
Zn(OH) 2
Zn
O 2
FIGURE 7.4
Schematic illustration of galvanic action of sacrificialm etal coating.
Corrosion of Linings and Coatings
414
CAT8247—CHAPTER 7—17/10/2006—15:02—TRGANESH—XMLM ODEL B–pp. 403–485