Investigation of moisture diffusion in epoxy system: Experiments and molecular dynamics simulations

Corrosion Inhibition Mechanism of Ultra-High-Temperature Acidizing Corrosion Inhibitor for 2205 Duplex Stainless Steel

The acidizing corrosion inhibitors reported so far have a poor effect on duplex stainless steel in high-temperature and high-concentration acid systems and cannot effectively inhibit the occurrence of selective corrosion. In this paper, a new acidizing corrosion inhibitor was designed, which was mainly composed of Mannich base and antimony salt. The inorganic substance in the corrosion inhibitor had good stability at high temperatures and could quickly form a complex with the metal matrix to enhance the binding ability. The organic substance can make up for the non-dense part of the inorganic film. The properties of developed corrosion inhibitors were analyzed by quantum chemical calculation, molecular dynamics simulation, and scanning electron microscopy. The results showed that a double-layer membrane structure could be constructed after adding the corrosion inhibitor, which could play a good role in blocking the diffusion of acid solution at high-temperature. The uniform corrosion rate of 2205 duplex stainless steel after adding acidizing corrosion inhibitor immersion in a simulated service condition (9 wt.% HCl + 1.5 wt.% HF + 3 wt.% CH₃COOH + 4~6 wt.%) at 140 °C, 160 °C and 180 °C for a 4 h test is 6.9350 g·m^-2·h^-1, 6.3899 g·m^-2·h^-1 and 12.1881 g·m^-2·h^-1, respectively, which shows excellent corrosion inhibition effect and is far lower than that of the commonly accepted 81 g·m^-2·h^-1 and no selective corrosion could be detected.

Corrosion Resistance of Li-Al LDHs Film Modified by Methionine for 6063 Al Alloy in 3.5 wt.% NaCl Solution

Methionine (Met) was introduced to modify the Li-Al layered double hydroxides (LDHs) film prepared on 6063 aluminum alloy by in situ method for the first time. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Scanning electron microscopy, and X-ray diffraction confirmed the successful insertion of Met into LDHs film and revealed that the introduction of Met could make the LDHs film much denser. Electrochemical tests illustrated that the corrosion rate of the Met modified LDHs film was reduced by more than an order of magnitude compared with the bare Al alloy. Moreover, the corrosion rate of the modified LDHs film after immersion in 3.5 wt.% NaCl solution for 21 days was almost the same as that without immersion, which indicates that the modified film has good corrosion durability. The corrosion resistance of the scratched modified film could recover to the level without a scratch on the 14th day based on the scratch test results, meaning the modified film has a good self-healing property. Finally, the anti-corrosion mechanism of the Met was proved by molecular dynamic simulations and found that the enhanced corrosion resistance may be attributed to the addition of Met that slowed the diffusion of the corrosive medium Cl− and water molecules.

Exploring secondary interactions and the role of temperature in moisture-contaminated polymer networks through molecular simulations

Leveraging the state of absorbed moisture within a polymer network to identify physical and chemical features of the host material is predicated upon a clear understanding of the interaction between the polymer and a penetrant water molecule; an understanding that has remained elusive. Recent work has revealed that a novel damage detection method that exploits the very low baseline levels of water typically found in polymer matrix composites (PMC) may be a valuable tool in the composite NDE arsenal, provided that a clear understanding of polymer-water interaction can be obtained. Precise detection, location, and possible quantification of the extent of damage can be performed by characterizing the physical and chemical states of moisture present in an in-service PMC. Composite structures have a locally elevated dielectric constant near the damage sites due to a higher fraction of bulk ("free") water, which has a higher dielectric constant when compared to water molecules bound to the polymer network through secondary bonding interactions. In this study, we aim to get a clear atomistic scale picture of the interactions which drive the dielectric signature variations necessary for tracking damage. Molecular Dynamics (MD) simulations were used to explore the effect of temperature on the state of moisture in two epoxy matrices with identical chemical constituents but different morphologies. The motivation was to understand whether higher polarity binds a greater fraction of moisture even at higher temperatures, leading to suppressed dielectric activity. Consequently, the influence of secondary bonding interactions was investigated to understand the impact of temperature on the absorbed water molecules in a composite epoxy matrix.

Kinetic analysis of an anion exchange absorbent for CO2 capture from ambient air

This study reports a preparation method of a new moisture swing sorbent for CO2 capture from air. The new sorbent components include ion exchange resin (IER) and polyvinyl chloride (PVC) as a binder. The IER can absorb CO2 when surrounding is dry and release CO2 when surrounding is wet. The manuscript presents the studies of membrane structure, kinetic model of absorption process, performance of desorption process and the diffusivity of water molecules in the CO2 absorbent. It has been proved that the kinetic performance of CO2 absorption/desorption can be improved by using thin binder and hot water treatment. The fast kinetics of P-100-90C absorbent is due to the thin PVC binder, and high diffusion rate of H2O molecules in the sample. The impressive is this new CO2 absorbent has the fastest CO2 absorption rate among all absorbents which have been reported by other up-to-date literatures.

CNT/polymer interface in polymeric composites and its sensitivity study at different environments

The environmental durability of polymer based composites has always been a critical concern over its short- and long-term performances. The degree of environmental degradation is supposed to have different mechanisms and kinetics at the polymer/reinforcement interfaces in comparison to the bulk polymer matrix. Differential degradation could possibly attribute a stressed state in the material, especially at the interfaces. Present review is focused on the roles of reinforcing CNT on the performance of the polymeric nanocomposites in different in-service environments (the environmental parameters include temperature, moisture, UV light, low earth orbit space environment, electromagnetic waves). It is essential to understand how the addition of CNTs in polymeric material alters the microstructure at micro- and nano-scale, and how these modifications influence the overall macroscopic behaviour, not only in its as fabricated form, but also its continuous alteration with time in the in-service environment. The technological superiority with CNT addition to polymeric materials may be advantageous, but scientific merits are here to be explored critically for a reliable and sustainable interfacial durability and structural integrity in different in-service environmental conditions.