silane crosslinkers

The corrosion behaviour of amine-cured epoxy silane sol-gel coatings has been studied by different authors The diethylenetriamine (DETA) is one of the most common epoxy crosslinkers used and an optimum amine concentration in terms of the best anticorrosive properties achieved by the coatings was reported by Vreugdenhil et al.  and by Davis et al.  of, respectively, 1.3 and 1 relative to the molar ratio ''epoxy group/amine reactive hydrogen''. Khramov et al.  also studied epoxy silane sol-gel coatings crosslinked with epoxy silanes and found significant improvement in these coatings corrosion performance in comparison to those of DETA crosslinked ones. In another study involving the addition of amino-silane crosslinkers , the above optimum molar ratio found ranged between 1 and 1.5. The aminosilanes present the advantage of contributing also to the inorganic network formation. Besides amino-silanes, other amines have been studied as alternative to DETA like di-amines of longer carbon chain  or branched amines , the resultant coatings showed better corrosion protection properties compared to those derived from formulations containing DETA as crosslinking agent. The epoxy-silane based coatings curing process (by heating or by the addition of crosslinking agents) is determinant for the establishment of both inorganic and organic networks of these hybrid coatings and should be appropriate to the precursors used in their synthesis. All the studies referred are focused on solely silane derived sol-gel coatings. In this work, a zirconium alkoxide precursor is used in addition to the epoxy silane one to produce the hybrid sol-gel coating for corrosion protection of the aluminium alloy EN AW 6063. This type of sol-gel coatings usually is thermally cured. The aim of this work is to study the corrosion properties of epoxy-silica-zirconia hybrid sol-gel coatings cured at room temperature by the addition of amine crosslinkers. Therefore, in the present work, epoxy-silica-zirconia hybrid sol-gel coatings were synthesized from glycidoxypropyltrimethoxysilane (GPTMS) and zirconium n-propoxide (TPOZ) precursors, applied to the aluminium alloy by dip-coating and cured at room temperature using two types of amine crosslinkers: diethylenetriamine (DETA), in different concentrations (GPTMS/amine-Hreactive molar ratios: 1.5 and 1), and a tri-functional amino-silane in that molar ratio of 1. A sol-gel coating prepared from the same precursors but without amine addition was also synthesized for comparison. The evolution of the curing process and the corrosion behaviour of the hybrid coated aluminium alloy specimens were evaluated by Electrochemical Impedance Spectroscopy (EIS). The morphology and surface chemistry of the hybrid coatings were also characterized by Energy Dispersive Spectroscopy (EDS) coupled to Scanning Electron Microscopy (SEM) and by Fourier Transform Infrared Spectroscopy (FTIR).