Time-of-flight SIMS characterization of hydrolysed organofunctional and non-organofunctional silanes deposited on Al, Zn and Al-43.4Zn-1.6Si alloy-coated steel

In this paper Al, Zn and Al-43.4Zn-1.6Si (AlZn) alloy-coated steel have been treated with the organufunctional silane gamma-mercaptopropyltrimethoxysilane (gamma-MPS) and the non-organofunctional silane 1,2-bis(triethoxysilyl)ethane (BTSE). Also, a two-step treatment of metal substrates was performed: the metal substrates were treated with the BTSE silane followed by a gamma-MPS treatment. The influence of metal substrate and the pH value of the silane film properties were investigated using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results show that the BTSE silane is fully hydrolysed but the gamma-MPS silane is not. The presence of negative ions of the type HSixOy- indicates that both types of silane films are highly cross-linked via Si-O-Si bonds. The two-step treatment gave gamma-MPS silane layer on top of the BTSE silane layer but the thickness of the total silane film become thinner than for a single BTSE film, indicating that some of the BTSE is dissolved during the gamma-MPS deposition step. Furthermore, the ToF-SIMS results show that the thiol group of the gamma-MPS silane is oxidized. Finally, no major influence, either in the positive or the negative mass spectra, from the different metal substrates could be detected for the silane films investigated. Copyright (C) 2003 John Wiley Sons, Ltd.