X-ray spectroscopic investigation of the Zr-site in thin film sol-gel surface preparations

X-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (X AS) measurements were made on thin film (similar to 1000 Angstrom) sol-gel adhesion promoting surface treatments. These silicon/zirconium-containing s ol-gel coatings are possible replacement processes for traditional surface preparations that use environmentally undesirable and potentially toxic mat erials. The sol-gels were waterborne mixtures formulated with tetra-n-propo xyzirconium (TPOZ) and a silane, either 3-glycidoxypropyl-trimethoxysilane (GTMS) or 3-aminopropyl-triethoxysilane (APS). Results show that dried sol- gel powders formulated with TPOZ or TPOZ + GTMS have longer Zr-O bond lengt hs (similar to2.18 Angstrom, CN 7 or 8) than the TPOZ + silane + metal subs trate samples (similar to2.10 Angstrom, CN 6). The fraction (+/- 0.10) of Z r in a short bonded 6-fold site is highest (0.80) for TPOZ + (APS or GTMS) on (Ti or Al), at an intermediate value (0.40) for TPOZ on Ti and low (0.10 ) for the powders. For sol-gels deposited on a metal substrate, there are i ndications of a chemical bond between the thin film sol-gel and the metal s ubstrate. The TPOZ + APS coatings on Ti data suggest that this Zr-O-Ti bond is present with a Zr-Ti separation of similar to3.5 Angstrom. Only subtle differences were observed in the near-neighbor bonding due to curing treatm ent variations from room temperature to similar to 125 degreesC, alloy subs trate variations (Ti-6Al-4V/Al 2024), and age of the deposited sol-gel coat ing (up to 1 year).