Corrosion of Paint
203
TabLE 7.3
Characteristics of Pigments for Metal Protective Paints
Pigment
Specific
Gravity
Color
Opacity
Specific Contribution to
Corrosion Resistance
Active Pigments
Red lead
8.8
Orange
Fair
Neutralizes film acids
Insolubilizes sulfates and
chlorides
Renders water noncorrosive
Basic silicon lead
chromate
3.9
Orange
Poor
Neutralizes film acids
Insolubilizes sulfates and
chlorides
Renders water noncorrosive
Zinc yellow
(chromate)
3.3
Yellow
Fair
Neutralizes film acids
Anodic passivator
Renders water noncorrosive
Zinc oxide (French
process)
5.5
White
—
Neutralizes film acids
Renders water noncorrosive
Zinc dust at low
concentration in
coatings for steel
7.1
Gray
Good
Neutralizes film acids
Galvanically Protective Pigments
Zinc dust sacrificial at
high concentrations
7.1
Gray
Good
Makes electrical contact
Galvanically sacrificial
Barrier Pigments
Quartz
2.6
Nil
Translucent Inert
Compatible with vinyl ester
additives
Extenders
Mica
2.8.
Nil
Translucent Impermeability and inertness
Talc
2.8
Nil
Translucent Impermeability and inertness
Abestine
2.8
Nil
Translucent Impermeability and inertness
Baytes
4.1
Nil
Translucent Impermeability and inertness
Silica
2.3
Nil
Translucent Impermeability and inertness
Iron oxide
4.1
Red
—
Impermeability and inertness
Iron oxide
4.1
Ochre
—
Impermeability and inertness
Iron oxide
4.1
Black
—
Impermeability and inertness
Titanium dioxide
4.1
White
Excellent
Impermeability and inertness
Carbon black
1.8
Black
Good
Impermeability and inertness
Note: Titanium dioxide has better “hiding” than any other pigment.
Source: Tator, K.B., 1989, Coating, in Corrosion and Corrosion Protection Handbook, 2nd. ed.,
Schweitzer, P.A., Ed., New York: Marcel Dekker, p. 466–467.