Borohydride and its derivatives may also be used as reducing agents.
When borohydride is used in the reduction, temperatures of 1408 F/608 Ct o
1948 F/908 Care required. The use of dimethylaminoborane(DMAB)enables
the deposition of Ni–B coatings with asmallamount of boron (0.5–1.0 mass
percent) at temperatures in the range of 868 F/308 Ct o1 048 F/608 C. Neutral
and alkaline solutions may be used.
Depending upon exposure conditions, certain minimum coating thicknesses to control porosity are recommended for the coating to maintain its
appearance and have as atisfactory life:
Indoor exposures
0.3–0.5 mil (0.008–0.013 mm)
Outdoor exposures
0.5–1.5 mil (0.013–0.04 mm)
Chemical industry
1–10 mil (0.025–0.25 mm)
For applications near the seacoast, thicknesses in the range of 1.5 mil
(0.04 mm) should be considered. This also appliest oa utomobile bumpers
and applications in general industrial atmospheres.
Nickel is sensitivetoattackbyindustrial atmospheres and formsafilm of
basic nickels ulfate that causes the surface to “fog”o rl ose its brightness.
To overcome this fogging, athin coating of chromium (0.01–0.03 mil/0.003–
0.0007 mm) is electrodeposited over the nickel.T his finish is applied to all
materials for which continued brightness is desired.
Single-layer coatings of nickel exhibitl ess corrosion resistance than
multilayer coatings because of their discontinuities. The electroless plating
process produces ac oating with fewer discontinuous deposits. Therefore,
the single layer deposited by electroless platingp rovides more corrosion
resistance than does an electroplated single layer.
Most electroless plated nickel deposits contain phosphorus that enhances
corrosion resistance. In the same manner,a ne lectroplated nickel deposit
containing phosphorus willa lso be more protective.
7.3.2S atin-Finish Nickel Coating
As atin-finish nickelc oating consists of nonconductive materials sucha s
aluminum oxide, kaolin, and quartz that are codeposited with chromium on
the nickeldeposit. Some particles are exposed on the surfaceofthe chromium
deposit, so the deposith as ar ough surface. Because the reflectance of the
deposit is decreased to less than half of that of al evel surface, the surface
appearance lookslike satin.
Asatin finish nickelcoating provides good corrosionresistance because of
the discontinuity of the topc oat of chromium.
7.3.3N ickel–Iron AlloyC oating
To reduce production costs of bright nickel, the nickel–iron alloy coating was
developed. The nickel–iron alloydeposits full brightness, high leveling, and
excellent ductility and good reception for chromium.
Corrosion of Linings and Coatings
426
CAT8247—CHAPTER 7—17/10/2006—15:02—TRGANESH—XMLM ODEL B–pp. 403–485
When borohydride is used in the reduction, temperatures of 1408 F/608 Ct o
1948 F/908 Care required. The use of dimethylaminoborane(DMAB)enables
the deposition of Ni–B coatings with asmallamount of boron (0.5–1.0 mass
percent) at temperatures in the range of 868 F/308 Ct o1 048 F/608 C. Neutral
and alkaline solutions may be used.
Depending upon exposure conditions, certain minimum coating thicknesses to control porosity are recommended for the coating to maintain its
appearance and have as atisfactory life:
Indoor exposures
0.3–0.5 mil (0.008–0.013 mm)
Outdoor exposures
0.5–1.5 mil (0.013–0.04 mm)
Chemical industry
1–10 mil (0.025–0.25 mm)
For applications near the seacoast, thicknesses in the range of 1.5 mil
(0.04 mm) should be considered. This also appliest oa utomobile bumpers
and applications in general industrial atmospheres.
Nickel is sensitivetoattackbyindustrial atmospheres and formsafilm of
basic nickels ulfate that causes the surface to “fog”o rl ose its brightness.
To overcome this fogging, athin coating of chromium (0.01–0.03 mil/0.003–
0.0007 mm) is electrodeposited over the nickel.T his finish is applied to all
materials for which continued brightness is desired.
Single-layer coatings of nickel exhibitl ess corrosion resistance than
multilayer coatings because of their discontinuities. The electroless plating
process produces ac oating with fewer discontinuous deposits. Therefore,
the single layer deposited by electroless platingp rovides more corrosion
resistance than does an electroplated single layer.
Most electroless plated nickel deposits contain phosphorus that enhances
corrosion resistance. In the same manner,a ne lectroplated nickel deposit
containing phosphorus willa lso be more protective.
7.3.2S atin-Finish Nickel Coating
As atin-finish nickelc oating consists of nonconductive materials sucha s
aluminum oxide, kaolin, and quartz that are codeposited with chromium on
the nickeldeposit. Some particles are exposed on the surfaceofthe chromium
deposit, so the deposith as ar ough surface. Because the reflectance of the
deposit is decreased to less than half of that of al evel surface, the surface
appearance lookslike satin.
Asatin finish nickelcoating provides good corrosionresistance because of
the discontinuity of the topc oat of chromium.
7.3.3N ickel–Iron AlloyC oating
To reduce production costs of bright nickel, the nickel–iron alloy coating was
developed. The nickel–iron alloydeposits full brightness, high leveling, and
excellent ductility and good reception for chromium.
Corrosion of Linings and Coatings
426
CAT8247—CHAPTER 7—17/10/2006—15:02—TRGANESH—XMLM ODEL B–pp. 403–485