Microscopic Structure and Binding Mechanism of the Corrosion-Protective Film of Oleylpropanediamine on Copper in Hot Water

Abstract

The structure of the film formed by oleylpropanediamine (OLDA) on the copper (Cu) metal surface in water at 150 °C was investigated by combining quantitative NMR and surface characterization methods. We succeeded in quantifying the amount of film formation by precisely determining all mass balances in the systems examined. 2D IR microscopic mapping showed that the film thickness is uneven in the horizontal direction with a length scale of ∼100 μm and hundreds of OLDA layers. This film thickness was also confirmed by AFM. The analysis of the C−H stretching vibrational frequency disclosed that the alkyl chains are highly ordered in the layers close to the Cu surface and are conformationally disordered in the layers distant from the Cu surface in the thicker portion of the film. Combining XPS measurements using argon gas cluster ion beam etching with the ICP-AES analysis, we revealed that the key to multiple layering is the formation of a coordination complex of the unprotonated amino groups of OLDA with Cu that presumably results in polymer chain-like network structures. Contact angle measurements at different OLDA concentrations and treatment times showed that the water repellency of the film originated from the thick layering of OLDA molecules with disordered hydrophobic chains.

Nuclear Magnetic Resonance Analysis of Hydrothermal Reactions of Ethyl- and Octylamine in Sub- and Supercritical Water

“…1−4 The formation of aliphatic-amine corrosion-inhibitor films is expected to ensure safe long-term operation of heat transfer from flame to hot water or steam across the metal−water interface. 5 The power generation industry today faces the challenge of balancing the introduction of massive amounts of variable renewable energy with the need to maintain a stable power supply through frequent startups and shutdowns. 6 The problem is that shutdowns accelerate corrosion due to the oxygen uptake and the localization of trace amounts of acids.…”

“…Here, we focus on how the C–N bonds of protonated and neutral amines are cleaved and how the cleavage mechanism depends on reaction conditions such as pH and temperature. Solving this problem has become increasingly desirable in recent years due to the growing interest in alkylamines for corrosion inhibition applications in steam–water power generation cycles. − The formation of aliphatic-amine corrosion-inhibitor films is expected to ensure safe long-term operation of heat transfer from flame to hot water or steam across the metal–water interface . The power generation industry today faces the challenge of balancing the introduction of massive amounts of variable renewable energy with the need to maintain a stable power supply through frequent startups and shutdowns .…”

“…To overcome this new situation, corrosion control measures need to be strengthened by a deeper understanding of the molecular sciences. In a recent study, 5 we have elucidated the film structure of alkylamines by various surface analyses; we analyzed films formed at 150 °C, a temperature sufficiently low that the effects of decomposition of amines are negligible. The reactions occurring on the water side of the water−metal interface, on the other hand, have not been fully elucidated from a physicochemical perspective.…”