Overview: The Potential of silanes for chromate replacement in metal finishing industries

Abstract

Trialkoxysilanes (or silanes) have emerged as a very promising alternative for chromates in metal finishing industries. Compared to the conventional chromating processes, the major merits of silane-based surface treatments include: eco-compliance, easy-control processing, comparable corrosion protection of metals as well as paint adhesion to a variety of topcoats. In this overview paper, we report the recent status of silane studies including results of corrosion performance tests, the mechanism of corrosion protection of metals by silanes and the themal stabilities of silane films. We also address the new fields that we are beginning to explore such as nano-structured silane films, "self-healing" silane films, and "super-primers".

The corrosion resistance of 316L stainless steel coated with a silane hybrid nanocomposite coating

“…For this reason, a number of promising candidates, so called "green inhibitors", have been explored with the hope of replacing chromates. Among them, silanes, a group of silicon based organic-inorganic chemicals, have emerged as a very promising alternative [6].…”

“…A general silane structure is (XO) 3 Si(CH2)nY, where XO is a hydrolysable alkoxy group, which can be methoxy (OCH 3 ), ethoxy (OC 2 H5) or acetoxy (OCOCH 3 ). Y is an organofunctional group such as epoxy, vinyl (C=C) or amino (NH 2 ) which is responsible for a good adhesion of a silane treated metal surface [6,10].…”

“…3-glycidoxypropyl-trimethoxysilane (GPTMS) is one of the organofunctional silane molecules that have been used as an effective coupling agent or adhesion promoter in glass/mineral-reinforced polymeric composites for decades [6,[11][12][13]. Also it has been used in transparent abrasion-resistant hybrid coatings for polymers [14][15][16][17], metals [18][19][20] and for gas separation membranes [21,22].…”

Characterization and corrosion performance of poly(pyrrole-siloxane) films on commercial Al alloys

“…Parallel to ECPs, silane-based treatments, usually performed by dipping the metal in dilute alcohol or water-based solutions for a short period, have also been intensively studied [8][9][10][11][12]. Among these compounds, organofunctional silanes are most suitable for corrosion protection of various metals and alloys since they provide effective coupling with both metal substrate and organic topcoat [13]. However, silane coatings are likely to be ''passive'' since they act essentially as a physical barrier by hindering the penetration of aggressive species to the metallic substrate, so that doping with small amounts of chemicals is needed to provide inhibition characteristics [14][15][16].…”

Advanced chrome-free organic–inorganic hybrid pretreatments for aerospace aluminum alloy 2024-T3—application of novel bis-ureasil sol–gel precursors

“…[8][9][10][11][12] Such hybrids, also called Ormosils or Ceramers, are formed by hydrolysis and condensation of organosilanes with traditional alkoxide precursors. 11,12 It has been found that they provide good corrosion resistance because they combine the mechanical and chemical characteristics of the comprising organic-inorganic networks, producing films that are durable, scratch resistant, adherent to metal substrates, flexible, dense, and functionally compatible with organic coating systems.…”