7.2.1.10 Gas Plating
Some metal compounds can be decomposed by heat to form the metal.
Typicale xamples arem etal carbonyls, metalh alides,a nd metal
methyl compounds.
7.2.1.11 Fusion Bonding
Coatings of low melting metalssuch as tin, lead, zinc, and aluminum may be
appliedb yc ementing the metal as ap owder on the substrate then heating
the substrate to atemperature above the melting point of the coating metal.
7.2.1.12 Explosion Bonding
This method produces abond betweentwo metals by the exertion of astrong
force that compresses the two metals sufficiently to develop as trong
interfacial interaction.
7.2.1.13 MetalCladding
The most common method is rollbonding that produces full-sized sheets of
clad (coated) material. The bond formed is partly mechanical and partly
metallurgical; consequently,m etallurgically incompatible materials cannot
be produced.
7.3N obleC oatings
Because of the high corrosion resistance of the noble metals, these materials
are used where ah ighd egree of corrosion resistance and decorative
appearance are requirements. They find application in domestic appliances,
window frames,b icycles. motorbikes, parts for car bodies, furniture, tools,
flanges, hydraulic cylinders, shock absorbers in cars, and parts of equipment
for the chemical and food processing industries.
Noble metal coatings protect substrates from corrosion by means of
anodicc ontrol or EMF control. Coating metals that provide protection by
means of anodiccontrol includenickel, chromium, tin, lead, and their alloys.
They can protect the substrate metal as ar esult of their resistance to
corrosion insofar as they form awell-adhering and nonporous barrier layer.
However, when the coating is damaged, galvanicallyi nducedc orrosion
will lead to severe attack. This corrosion process is extremely fast for coated
systemsb ecause of the high current density in the defect as ar esult of the
large ratio between the surfacea reas of the cathodic outer surface and the
anodicd efect, as shown in Figure 7.7.T oc ompensate for these defects in
the coating, multilayer coating systems have been developed. The corrosion
resistance of as ingle layer noblem etal coating results from the original
barrier action of the noblem etal, the surface of the noble metal being
Coatings
421
CAT8247—CHAPTER 7—17/10/2006—15:02—TRGANESH—XMLM ODEL B–pp. 403–485
Some metal compounds can be decomposed by heat to form the metal.
Typicale xamples arem etal carbonyls, metalh alides,a nd metal
methyl compounds.
7.2.1.11 Fusion Bonding
Coatings of low melting metalssuch as tin, lead, zinc, and aluminum may be
appliedb yc ementing the metal as ap owder on the substrate then heating
the substrate to atemperature above the melting point of the coating metal.
7.2.1.12 Explosion Bonding
This method produces abond betweentwo metals by the exertion of astrong
force that compresses the two metals sufficiently to develop as trong
interfacial interaction.
7.2.1.13 MetalCladding
The most common method is rollbonding that produces full-sized sheets of
clad (coated) material. The bond formed is partly mechanical and partly
metallurgical; consequently,m etallurgically incompatible materials cannot
be produced.
7.3N obleC oatings
Because of the high corrosion resistance of the noble metals, these materials
are used where ah ighd egree of corrosion resistance and decorative
appearance are requirements. They find application in domestic appliances,
window frames,b icycles. motorbikes, parts for car bodies, furniture, tools,
flanges, hydraulic cylinders, shock absorbers in cars, and parts of equipment
for the chemical and food processing industries.
Noble metal coatings protect substrates from corrosion by means of
anodicc ontrol or EMF control. Coating metals that provide protection by
means of anodiccontrol includenickel, chromium, tin, lead, and their alloys.
They can protect the substrate metal as ar esult of their resistance to
corrosion insofar as they form awell-adhering and nonporous barrier layer.
However, when the coating is damaged, galvanicallyi nducedc orrosion
will lead to severe attack. This corrosion process is extremely fast for coated
systemsb ecause of the high current density in the defect as ar esult of the
large ratio between the surfacea reas of the cathodic outer surface and the
anodicd efect, as shown in Figure 7.7.T oc ompensate for these defects in
the coating, multilayer coating systems have been developed. The corrosion
resistance of as ingle layer noblem etal coating results from the original
barrier action of the noblem etal, the surface of the noble metal being
Coatings
421
CAT8247—CHAPTER 7—17/10/2006—15:02—TRGANESH—XMLM ODEL B–pp. 403–485