Natural Product-Derived Phosphonic Acids as Corrosion Inhibitors for Iron and Steel

Abstract

Organic acids, typically derived from an oil-based value chain, are frequently used as corrosion inhibitors in industrial metal working fluids. The criteria for selection of these corrosion inhibitors have changed in the last decades, and are today not only performance-driven, but influenced by ecological considerations, toxicity and regulatory standards. We present scalable semisynthetic approaches to organic corrosion inhibitors based on phosphonic acids from renewable resources. They have been evaluated by chip filter assay, potentiodynamic polarization measurements, electrochemical impedance measurements and gravimetry for corrosion protection of iron and steel in an aqueous environment at slightly alkaline pH. The efficacy of several phosphonic acids tested was found to be strongly dependent on structural features influencing molecular self-assembly of protective layers, and the solubility of salts formed with di- and trivalent cations from the media or formed during corrosion. A carboxyphosphonic acid (derived from castor oil) was found to have remarkable anticorrosive effects in all media tested. We attribute the anticorrosion properties of this carboxyphosphonic acid to the formation of particularly stable protective layers on the metal surface. It might thus serve as a commercially attractive substitute for current acidic corrosion inhibitors, derived from renewable resources.

Glucamines as green alternatives to conventional amino alcohols in metalworking fluids

“…Tricarboxylic acid 1 is an ineffective acidic corrosion inhibitor in chloride‐containing solutions. Therefore, mixtures of DEGA with 10‐carboxyundecylphosphonic acid 2 , an efficient acidic corrosion inhibitor in various corrosive media, [ 18 ] have been evaluated. Selected results from the potentiodynamic measurements are summarized in Table 2.…”

“…We attribute this finding to the formation of stable layers of 2 on the metal surface, which protects the metal from contact with chloride by charge repulsion through the carboxylate side chains. [ 18 ] Only small defects in this protective layer caused by too low concentrations of 2 lead to pitting corrosion and rapidly growing corrosion rates.…”

“…1,3,5‐Triazine‐2,4,6‐tri aminocaproic acid 1 : TC 85, 85% 1 /15% water; TEA: >93% purity; EDEA: reagent grade, >98% purity; DEEA: for synthesis, >99% purity; AMP: for synthesis, 93%–98% purity; MIPA: >93% purity; glucamine: reagent grade, >97% purity. Carboxyphosphonic acid 2 [ 18 ] and DMGA [ 19 ] were synthesized according to literature protocols.…”

“…Each amino alcohol was combined with the acidic corrosion inhibitor 1, a tricarboxylic acid, which is a powerful commercial corrosion inhibitor for application in hard water. [18,24] S235JR-steel slide coupons were used as test specimens. A summary of data derived from potentiodynamic polarization measurements is given in Table 1.…”

Contact-Biocide TiO2 Surfaces by Surface-Initiated Atom Transfer Radical Polymerization with Chemically Stable Phosphonate Initiators

“…Phosphonate anchors are particularly attractive for SI-ATRP on TiO 2 , since they are known to form stable covalent bonds with TiO 2 − and a number of other metals and metal oxides. − The most widely used phosphonate initiator is 11-(2-bromo-2-methylpropanoyloxy)­undecyl phosphonic acid (BUPA). − Two other bromoisobutyrates have been described but are used less frequently for SI-ATRP on metals. − The effect of the initiator structure on SI-ATRP has not yet been investigated for phosphonate anchors. However, it is known that layer stability and loading density of phosphonates on metals and metal oxides depend on steric bulk and alkyl chain length. − One might therefore expect that the same would apply to the efficiency of SI-ATRP. In this context, Green and co-workers investigated the effect of the alkyl spacer length of alkoxysilane initiators on SI-ATRP of (neutral) methyl methacrylate on silica particles and found an increased polymer grafting density with increased spacer length of the initiator. − These findings can be attributed to an increased tendency of long alkyl chains to form stable SAMS on surfaces and thus higher loading densities of initiators with increasing alkyl chain length.…”