What Does Bond Mean?
A bond is the state of adhesion between a coating and substrate. Bond strength depends on the details of the spraying process and the materials used. Bonding mechanisms may be mechanical, physical, chemical, metallurgical or a combination of these.
An adhesive is used to form bonds between two parts when the final object consists of two sections that are bonded together. Bonds must be durable throughout the useful service life of a part, which may be years.
A bond failure in coating causes coating failure and corrosion. A properly designed bond applied using valid processes should never fail.
Corrosionpedia Explains Bond
A bond is the union or joining of materials by adhesives. It is the attachment at the interface between an adhesive and an adherend. The strength of the adhesion between the coating and the substrate is measured by bond strength. A number of test methods are used to measure the bond strength of coatings.
Bonding is a chemical process (ionic, covalent, metallic and attractive bonds). Bond failure can occur in two possible modes:
- Cohesion by fracture of the adhesive (design):
- Inadequate overlap length
- Thermal stresses
- Gross void defects (production)
- Adhesion by failure of the interface (processing):
- Inadequate surface preparation
- Ineffective surface preparation process
Adequate surface treatments, process and proper design of a substrate can achieve longer-lasting adhesive bonding.
Corrosion causes bond degradation; for example, steel corrosion causes bond performance degradation between steel and concrete. Migration of water to adhesive joints is the most common form of bond degradation.
Corrosion can occur by a chemical reaction along the paint/metallic coating interface, which can cause the chemical adhesion bond to be degraded, or by bulk corrosion of the metallic coating, leaving the paint totally "unconnected" to the steel sheet.