Self-Assembled Monolayer Formation on a Dental Orthodontic Stainless Steel Wire Surface to Suppress Metal Ion Elution

Thin Protective Coatings on Metals Formed by Organic Corrosion Inhibitors in Neutral Media

Protection of metals in neutral media with pH 5.0–9.0 (in humid atmospheres and various aqueous solutions) can be achieved by formation of thin coatings (up to several tens of nm) on their surfaces due to adsorption and more complex chemical interactions of organic corrosion inhibitors (OCIs) with the metal to be protected. The review contains three sections. The first section deals with coatings formed in aqueous solutions, while the second one, with those formed in organic and water-organic solvents. Here we consider metal protection by coatings mainly formed by the best-known classes of OCI (carboxylates, organophosphates and phosphonates) and estimation of its efficiency. The third section discusses the peculiarities of protection of metals in the vapor-gas phase, i.e., by volatile OCIs, and a relatively new type of metal protection against atmospheric corrosion by the so-called chamber inhibitors. OCIs with relatively low volatility under normal conditions can be used as chamber OCIs. To obtain a protective coating on the surfaces of metal items, they are placed in a chamber inside which an increased concentration of vapors of a chamber OCI is maintained by increasing the temperature. This review mainly focuses on the protection of iron, steels, copper and zinc.

The nature of self-assembled octadecylphosphonic acid (ODPA) layers on copper substrates

HYPOTHESIS

The self-assembly of amphiphilic molecules onto solid substrates can result both in the formation of monolayers and multilayers. However, on oxidized and non-oxidized copper (Cu), only monolayer formation was reported for phosphonic acids possessing one phosphate head group. Here, the adsorption of octadecylphosphonic acid (ODPA) on Cu substrates through a self-assembly process was investigated with the initial hypothesis of monolayer formation.

EXPERIMENTS

The relative amount of ODPA adsorbed on a Cu substrate was determined by infrared reflection/absorption spectroscopy (IRRAS) and by atomic force microscopy (AFM) investigations before and after ODPA deposition. X-ray photoelectron spectroscopy (XPS) with sputtering was used to characterize the nature of the layers.

FINDINGS

The results show that the thickness of the ODPA layer increased with deposition time, and after 1 h a multilayer film with a thickness of some tens of nm was formed. The film was robust and required long-time sonication for removal. The origin of the film robustness was attributed to the release of Cu ions, resulting in the formation of Cu-ODPA complexes with Cu ions in the form of Cu(I). Preadsorbing a monolayer of octadecylthiol (ODT) onto the Cu resulted in no ODPA adsorption, since the release of Cu(I) ions was abolished.