Abstract
ESCA and ellipsometry have been used to determine the film thickness, molecular orientation, and chemical bonding of an organic phosphate on polished steel substrates. The organic phosphate studied was formed as a reaction product of one mole of the diglycidyl ether of bis-phenol-A (DGEBA) with two moles of phosphoric acid, and comprised the mono- and diphosphate adducts of DGEBA. The steel substrates were found to bear an iron oxide layer that was 19 ± 4 Å in thickness as determined with the use of angle-resolved ESCA depth analysis. Ellipsometry measurements gave an iron oxide thickness of 26 ± 3 Å. Surface treatment of steel with the organic phosphate homogeneously covered the surface with 30 ± 5 Å of the coating as determined with the use of the ESCA depth analysis. The phosphate end-groups of the organic phosphate were concentrated at the coating/iron oxide interface. A shift in the phosphorus (2p) spectra from 135.2 to 134.2 eV was observed when the organic phosphate coating bonded to the iron oxide substrate. The binding energy of 134.2 eV was close to that observed for an iron organophosphate reference material at 134.0 eV. A shift in the iron (2p) spectra from 711.0 to 711.7 eV at a sampling depth of approximately 35 Å indicates the possible formation of an iron organic phosphate at the iron oxide/coating interface. The carbon and oxygen spectra confirmed the spatial orientation of the organic phosphate on the surface.
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