Adsorption of BTSE and gamma-GPS organosilanes on different microstructural regions of 7075-T6 aluminum alloy

The adsorption of bis-1,2-(triethoxysilyl)ethane (BTSE) and gamma-glycidoxypropyltrimethoxysilane (gamma-GPS) on mirror-polished 7075-T6 aluminum alloy was studied with an emphasis on the different microstructural regions of the alloy surface, specifically the alloy matrix and the two main types of second-phase particles, as well as how the adsorption was affected by a heating pre-treatment and by changes in the pH of the gamma-GPS solution. Surface characterizations were undertaken with scanning Auger microscopy (SAM), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and time-of-flight secondary-ion mass spectrometry (TOF-SIMS). BTSE at its natural pH (4.3) adsorbed at all micro-regions of the air-oxidized surface, while gamma-GPS at its natural pH (5.7) was largely ineffective. Adsorption of gamma-GPS on all micro-regions was possible after adjusting the solution pH to a lower value (3.2), or by using the solution of natural pH after pre-treating the sample by heating at 200 degrees C for 15 min. TOF-SIMS measurements indicated that direct metal-O-Si covalent bonding occurred at each silane interface formed to the different micro-regions of the alloy surface, with Al-O-Si bonding being predominant in each case. (c) 2006 Elsevier B.V. All rights reserved.