Page 233 - Handbook of Adhesives and Sealants

202 Chapter Six

could also be processing aids on the surface such as rolling oils, lu-
bricants, drawing compounds, and corrosion inhibitors. Finally, the
mechanical working of the metal will probably have, to some degree,
mixed all these regions together into a non-homogeneous mixture.
Virtually all common metal surfaces exist as hydrated oxides as
shown in Fig. 6.3. Even materials such as stainless steels, nickel, and
chromium are coated with transparent metal oxides that tenaciously
bind at least one layer of water. Thus, the adhesive or sealant used
for these materials must be compatible with the firmly bound layer of
water attached to the surface metal oxide layer. The nature of the
oxide layer will depend on the metal beneath the surface and the con-
ditions that caused the oxide surface to grow. Certain adhesives or
sealants will interact more effectively with certain oxide layers. For

Figure 6.3 Metal surfaces are actually hydrated metal oxides. 2