A positron annihilation lifetime spectroscopic study of the corrosion protective properties of epoxy coatings

Miscellaneous · Wed Jan 01 00:00:00 EST 1992

OSTI ID:7275314

MacQueen, R C

Positron Annihilation Lifetime Spectroscopy (PALS) was used to measure the free volume cavity sizes and free volume fractions of crosslinked epoxy coatings on steel before and after saturation with liquid water at 23[degrees]C. A direct linear relationship between the equilibrium volume fraction of water absorbed and the dry relative free volume fraction of bisphenol A epoxy coatings was found. The free volume cavity sizes and the number of free volume cavities per unit volume of these epoxies were found to decrease after water saturation. These decreases are ascribed to the occupation of 13-17% of the free volume cavities by 2-4 water molecules per cavity. The free volume cavity size of polyglycol diepoxides was found to increase after water saturation. This increase is ascribed to the expansion of the free volume cavities by water, which is substantiated by the macroscopic swelling observed in these coatings. An inverse, linear relationship between the equilibrium water uptake and the relative free volume fraction of these coatings were observed. This result coupled with the fact that less than one molecule of nitrobenzene was determined to fit into an epoxy free volume cavity, and that nitrobenzene is quite soluble in most of the epoxides, indicates that other factors besides the magnitude of the free volume fraction affect the amount of solvent absorbed by epoxy coatings. The small percentage of free volume occupied by water and the small number of water molecules capable of filling each void of the bisphenol A epoxies after water saturation correlate to the high impedance values and the good corrosion protection of these coatings, suggesting that water passes through these coatings by slow diffusion through the connected free volume cavities in the coating. Increases in the free volume cavity sizes of the polyglycol diepoxides after water saturation correlate to the low impedance and the poor corrosion protection of these coatings.

• Research Organization: Lehigh Univ., Bethlehem, PA (United States)
• OSTI ID: 7275314
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
EPOXIDES
PORE STRUCTURE
SPECTROSCOPY
WATER SATURATION
STEELS
CORROSION PROTECTION
PROTECTIVE COATINGS
SURFACE COATING
ALLOYS
COATINGS
DEPOSITION
IRON ALLOYS
IRON BASE ALLOYS
MICROSTRUCTURE
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
SATURATION
360602* - Other Materials- Structure & Phase Studies