Simulated Marine Environment Research Articles

Imaging‐Based Lensless Polarization‐Sensitive Fluid Stream Analyzer for Automated, Label‐Free, and Cost‐Effective Microplastic Classification

The presence of microplastics in the environment is of significant concern, yet the exact extent of this pollution remains largely unknown. The ocean is of particular interest as the monitoring of microplastics presents a challenge in that in situ fluid stream solutions are not readily available and traditional sampling methods are labor‐intensive and costly. This study introduces an imaging‐based lensless polarization‐sensitive fluid stream analyzer (FSA) for automated, label‐free, and cost‐effective detection and classification of microplastics. The FSA incorporates digital in‐line holography and birefringence computation, enabling quantitative polarization‐sensitive imaging and machine‐learning‐based activities including sample classification. Birefringent textures of synthetic polymers are investigated owing to their optical anisotropy. A microplastic classifier is developed for the FSA and integrated to form an end‐to‐end workflow capable of sampling fluid streams and determining marine and microplastic particle presence. Cultures of two phytoplankton species form a simplified marine environment for FSA evaluation. The device is tested in a two‐class configuration for marine microorganisms and microplastics, as well as a five‐class configuration for marine microorganisms and four individual microplastic types (polyethylene, polyethylene terephthalate, polypropylene, and polystyrene). The results demonstrate high classification accuracy, supported by experiments in the simulated marine environment that validate the proposed implementation's efficacy.

Phyllanthus urinaria extract as a potential anti-corrosion agent for steel reinforcement in simulated marine environments

<i>Phyllanthus urinaria</i> extract as a potential anti-corrosion agent for steel reinforcement in simulated marine environments

Corrosion Inhibition Effect of Mg-Al-pAB-LDH Coating for Steel in the Marine Environment

In this study, the surface of steel was coated with a Mg-Al-pAB-LDH coating in order to enhance its corrosion resistance in the marine environment. The crystal structure, micro-morphology, and chemical composition of the Mg-Al-pAB-LDH coating were characterised using physicochemical techniques. The corrosion protection performance in a simulated marine environment was evaluated through electrochemical methods. The results indicate that the Mg-Al-pAB-LDH coating effectively adsorbs chloride ions from the environment, thereby increasing the corrosion potential of the steel in chloride environments and reducing its corrosion current density. In addition, the Mg-Al-pAB-LDH coating applied to the surface of steel not only enhances the corrosion resistance in the marine environment but also possesses self-healing capabilities in areas of local damage to the steel surface.

Inhibition of microbiologically influenced corrosion of Al alloy 5083 in the presence of Pseudomonas aeruginosa by Artemisia annua L

Microbiologically influenced corrosion (MIC1MIC, Microbiologically Influenced Corrosion1) of Al 5083 caused by P. aeruginosa was inhibited by A. annua aqueous extract (AAE2AAE, A. annuaAqueous Extract.2). Electrochemical measurements revealed that the adsorption of AAE on the electrode surface protected Al 5083 from MIC in a simulated marine environment with inhibition efficiency of 78 %. The adsorption layer was formed due to ionized chlorogenic acid interacting with charged Al 5083 surface, preventing bacterial adhesion and growth. Adding AAE promoted the formation of a protective Al2O3, and decreased the surface layer porosity. The pitting corrosion reduced considerably when AAE was added to biotic seawater, supporting the ICP-OES results.

Constructing yeast-modified polypropylene amidoxime membrane toward highly-selective adsorption of U(VI) from seawater

To extract uranium from seawater, the adsorbent needs to have high selectivity for uranium and good hydrophilicity, and could resist biological pollution and prevent Marine microorganisms from blocking chelate sites. For effective uranium extraction, a straightforward crosslinking technique is used to create a highly selective and biofouling-resistant poly(amidoxime) (PAO-Y) membrane. PAO-Y is characterized by FT-IR, SEM, EDS, XPS, BET, WCA and NMR techniques. The effects of solution acidity, concentration, and adsorption time on its adsorption of uranyl ions and vanadyl ions are investigated. The composite material (PAO-Y) exhibits higher selective adsorption and affinity towards U(VI) compared to V(V). In simulated marine environment experiments, the material exhibited an adsorption capacity of 10.39 mg·g−1 for U(Ⅵ), which is five times higher than that for V(V). Furthermore, the adsorption partition constant for U(Ⅵ) is 1.44 × 105 mL·g−1, two orders of magnitude greater than that for V(V). The DFT calculations revealed specific coordination modes between PAO-Y and uranyl/vanadyl ions, elucidating the selective adsorption mechanism of uranium. The pentadentate coordination mode is shown by DFT calculations to be the most stable one. DFT calculations also show that the increase in the number of amino acid groups increases the interaction between the coordinating ligands and uranyl, but decreases the interaction between the coordinating ligands and vanadyl. These findings suggest that PAO-Y effectively enhance the selectivity and affinity towards uranyl ions during uranium extraction from marine environments and may find practical applications. After 15 days of continuous flow of 30 L natural seawater, PAO-Y obtained a total uranium capture capacity of 1.969 mg·g−1 in the fixed-bed adsorption system, making it a suitable candidate for uranium extraction from natural seawater.

Study on Corrosion Behavior of B30 Cu-Ni Alloy in Simulated Marine Environments

Study on Corrosion Behavior of B30 Cu-Ni Alloy in Simulated Marine Environments

Corrosion fatigue cracking behaviors of Q690qE high‐strength bridge steel as a weld joint in simulated marine environment

AbstractCorrosion fatigue behavior and mechanism of the weld joint of Q690qE high‐strength bridge steel was investigated in a simulated marine environment. It reveals the sub‐critical heat‐affected zone (SCHAZ) and coarse‐grained heat‐affected zone (CGHAZ) are the most vulnerable sites to corrosion fatigue cracking. The CGHAZ of the Q690qE steel weld joint was prone to corrosion fatigue initiation mainly because of micro‐galvanic corrosion between CGHAZ and weld metal (WM). The corrosion fatigue failure in SCHAZ mainly resulted from local stress/strain concentration due to weld softening. The final fracture location was determined by the competition between these two effects.

The effect of dissolved oxygen and Shewanella algae on the corrosion mechanism of titanium in a simulated marine environment

The influence of dissolved oxygen (DO) and Shewanella algae on the corrosion behavior of pure titanium were systematically studied in this work. The formation of S. algae biofilms on titanium surface was facilitated by the anaerobic environment, which accelerated titanium corrosion. Upon the breakdown of passive film, S. algae acquired electrons from the titanium base substrate through extracellular electron transfer (EET) processes. Various EET-related genes were overexpressed by the low DO condition, leading to enhanced EET kinetics. High concentration DO increased TiO2 content and the thickness of passive film, which enhanced the protective effect and mitigated microbiologically influenced corrosion.

Influence of Ce on the corrosion resistance of high-strength low-alloy steel in simulated marine environments

Steel with enhanced corrosion resistance in both simulated deep sea and shallow sea environments was developed by adding cerium (Ce) to high-strength low-alloy (HSLA) steel. Through conventional characterization techniques, the electrochemical performance, rust layer composition, and protective properties of the steel were analyzed. The study found that the steel exhibited superior corrosion resistance when the Ce content was 0.2 wt%. This improvement is largely attributed to Ce's role in promoting the formation of α-FeOOH, which results in a dense and protective rust layer. Additionally, Ce consumes oxygen and inhibit the cathodic depolarization reaction. Furthermore, due to the low oxygen solubility in the simulated deep sea environment, the cathode reaction is further inhibited, leading to a lower corrosion degree in the deep sea environment compared to the shallow sea environment.

Autonomous Underwater Vehicle Path Planning Based on Improved Salp Swarm Algorithm

Aiming at the problem of path planning for autonomous underwater vehicle (AUV) to cope with the influence of obstacles and eddies in complex marine environments, a path planning method based on an improved salp swarm algorithm (ISSA) is proposed. Firstly, the motion model of the AUV and eddy current model are constructed, including the relationship between position, velocity, attitude, and control inputs. Secondly, the improved SSA is proposed, which introduces the Levy flight strategy to enhance the algorithm’s optimization seeking ability and adds a nonlinear convergence factor to enhance the convergence ability of the algorithm. The stability and robustness of the improved algorithm are verified by test functions. Finally, the ISSA is applied to AUV path planning, which optimizes the AUV travel distance, improves the search efficiency and accuracy, and avoids the local optimum of the algorithm. The ISSA enhances the adaptive ability and robustness of the algorithm by introducing a dynamic adjustment strategy and feedback mechanism. Experimental verification is carried out using a simulated marine environment. The results show that the ISSA is better than the traditional algorithm in terms of path length as well as algorithm stability, and can effectively improve the navigation performance of AUV.

Study on microbiologically influenced corrosion of HSLA-65 steel

In the current study, the corrosion behavior of HSLA-65 steel was investigated in a simulated marine environment inoculated with P. aeruginosa. In the electrochemical measurements, the negative shift in OCP, lower values of corrosion potential, pitting potential, and increased corrosion current density of the HSLA-65 steel in the biotic medium signified its low corrosion resistance in the presence of P. aeruginosa. The observation of the surface morphology revealed biofilm formation on the steel surface in the P. aeruginosa-inoculated culture medium, which significantly accelerated the pitting corrosion of the steel. The pit observed on the steel surface in the biotic medium was about 3.9 times deeper than in the sterile medium. In addition, the weight loss of the steel in the biotic medium was about 2.4 times higher compared to that in the sterile medium. These findings suggest that the P. aeruginosa biofilm significantly accelerated the corrosion of HSLA-65 steel in the simulated marine environment.

Oxidation behavior and corrosion resistance of CoCrFeNi high entropy alloy compared with FeCoNi medium entropy alloy

The entropy-based alloy with excellent oxidation and corrosion resistance is of great significance for practical applications in high-temperature environments. Thus, the difference in anti-oxidation property and corrosion behavior of FeCoNi MEA and CoCrFeNi HEA in a simulated marine environment was studied via a series of measurements. The results reveal that the HEA possesses superior oxidation and corrosion resistance in comparison with the MEA, which can be demonstrated by comparing the oxidation rate and thickness of oxide layer, corrosion current density (icorr) as well as corrosion morphology after polarization. The microstructure and composition of the oxide layer are the primary reasons resulting in the difference of oxidation and corrosion behaviors of the two alloys. The oxide layer with a compact, even and intact structure is produced on the HEA surface, which hinders the diffusion of detrimental ions and oxygen, whereas the loose, porous and cracked oxide layer consisting of inner Fe3O4 and outer CoO exhibits poor protection against corrosion and oxidation of the MEA. For the HEA, the preferential combination of Cr and O elements forms the protective oxide of Cr2O3, effectively enhancing corrosion resistance and inhibiting oxidation. However, the low protective CoO and relatively active Fe3O4 grow on the MEA surface, which cannot provide a good barrier to restrain oxidation and corrosion.

Reinforcing steels in low-carbon mortars subjected to chloride attack and natural carbonation: Contradictory trends in passivation ability and corrosion resistance

After a 7-year exposure to simulated marine environments with chloride attack and natural carbonation, the passivation ability and corrosion resistance of carbon steel and 2304 duplex stainless steel in two types of low-carbon mortars, designed with alkali-activated slag and Bayer red mud, were investigated, which were compared with those observed in ordinary Portland cement (OPC) mortar. Although a reduced passivation ability was confirmed for steels in the low-carbon mortars, an improved corrosion resistance was highlighted after long-term exposure. Accordingly, the underlying mechanisms for the detrimental impacts and beneficial effects on the corrosion resistance of steels provided by these low-carbon mortars were discussed in terms of pore solution chemistry, pore structure as well as electrical resistivity, which will shed new lights on the design of novel cementitious materials with low carbon footprint and high corrosion protection.

The impact of oxygen availability on steel corrosion considering the self-balance between anodic and cathodic corrosion cells

An advanced model is developed to elucidate relationship between availability of oxygen and active corrosion, considering the equilibrium between gaseous and dissolved oxygen, as well as the equilibrium of oxygen diffusion and consumption. This research notably incorporates self-regulation mechanisms of cathodes and anodes in both macrocell and microcell corrosion. Accelerated corrosion experiments were performed under simulated marine environment, monitoring variations in corrosive medium concentration and electrochemical corrosion processes. Results indicate significant reduction in oxygen concentration following the activation of rebar. Potential inaccuracies in predicting corrosion rate arise from the adoption of a static cathodic to anodic area ratio was highlighted.

A Study on the Corrosion Behavior of Ti-Containing Weathering Steel in a Simulated Marine Environment

A Study on the Corrosion Behavior of Ti-Containing Weathering Steel in a Simulated Marine Environment

Degradation Behaviors of Polylactic Acid, Polyglycolic Acid, and Their Copolymer Films in Simulated Marine Environments.

Poly(lactic acid) (PLA) and poly(glycolic acid) (PGA) are extensively studied biodegradable polymers. However, the degradation behavior of their copolymer, poly(lactic-co-glycolic acid) (PLGA), in marine environments has not yet been confirmed. In this study, the changes in macroscopic and microscopic morphology, thermal properties, aggregation, and chemical structure of PLA, PGA, PLGA-85, and PLGA-75 (with 85% and 75% LA content) in simulated marine environments were investigated. Results revealed that degradation occurred through hydrolysis of ester bonds, and the degradation rate of PGA was faster than that of PLA. The amorphous region degraded preferentially over the crystalline region, leading to cleavage-induced crystallization and decreased thermal stability of PLA, PLGA-85, and PLGA-75. The crystal structures of PLGAs were similar to those of PLA, and the higher GA content, the faster was the degradation rate. This study provides a deeper understanding of the seawater degradation behaviors of PLA, PGA, and their copolymers, and provides guidance for the preparation of materials with controllable degradation performance.

Flexural durability of BFRP bars reinforced geopolymer-based coral aggregate concrete beams conditioned in marine environments

Geopolymer is an environmentally friendly material that utilizes industrial solid waste, boasting reduced greenhouse gas emissions and energy consumption. It exhibits superior performance in terms of corrosion resistance and thermal stability compared to ordinary Portland cement (OPC). These excellent properties are crucial for marine engineering construction, offering significant value and application potential in marine engineering materials. In this study, geopolymer was employed as the cementitious material, with marine resources like seawater and coral aggregates sourced from remote island areas effectively utilized, and basalt fiber-reinforced polymer (BFRP) bars were incorporated as reinforcements to develop BFRP bars reinforced geopolymer-based coral aggregate concrete (GPCAC) beams. Laboratory aging procedures were employed to investigate the deterioration patterns and damage mechanisms affecting the flexural behavior of GPCAC beams under seawater immersion and dry-wet cycling conditions, comparing them with cement-based coral aggregate concrete (CAC) beams. The experimental results indicated that both CAC and GPCAC beams under simulated marine environments experienced a reduction in the number of cracks upon damage, but their crack spacing and width increased. Moreover, the flexural stiffness of CAC and GPCAC beams after seawater attacks tended to increase, but this increased stiffness did not translate to a higher loading capacity. Conversely, as the corrosion age increased, the ultimate load and deflection values of both CAC and GPCAC beams decreased to varying extents, with the load-carrying capacity degradation more pronounced in seawater dry-wet cycling environments than in seawater immersion conditions. Compared to CAC beams, GPCAC beams exhibited superior resistance to seawater erosion. Following 12 months of seawater dry-wet cycling, the ultimate loading capacity of CAC beams decreased by 12.2%, while that of GPCAC beams only degraded by 9.5%. Predictions of the flexural capacity of GPCAC beams using equations from existing FRP-reinforced normal aggregate concrete (NAC) specifications indicated slightly higher values than the experimental values, with an error margin of less than 15%. Overall, the formulas for the flexural capacity of NAC beams in existing FRP-reinforced NAC codes remained applicable to CAC and GPCAC beams.

Effect of Copper and Nickel Content on the Corrosion Mechanisms in Ferritic Matrix Gray Cast Irons under Simulated Marine Environments

This article investigated the influence of copper (Cu) and nickel (Ni) on atmospheric corrosion in gray cast iron under simulated marine conditions. The goal was to compare the effect of Cu and Ni addition in castings with weathering steels. Selected alloys were cast, cut, prepared, and heat-treated for microstructure homogenization. Accelerated corrosion tests were conducted using a salt spray chamber. Corroded samples were analyzed for corrosion thickness and deposits using scanning electron microscopy, X-ray diffraction, and electrochemical techniques. The results indicate that alloying elements significantly affect corrosion processes. In the long-term, Cu had a greater impact on the corrosion mechanisms than Ni. Both Cu and Ni exhibited similar effects on the corrosion mechanisms in gray cast iron and weathering steels. In the initial and final stages, the behavior was comparable to that of weathering steels, but in the intermediate stage, it differed from the literature, suggesting the presence of an additional mechanism between these stages.

Comparative study on the corrosion behavior of two arc spraying coatings in simulated marine environments

The corrosion behaviors of arc spraying 5083Al and Zn15Al coatings in a simulated marine environment were comparatively analyzed. The 5083Al coating exhibited lower corrosion rates and higher polarization resistance than the Zn15Al coating. Due to the lower solubility and higher supersaturation of Al(OH)3, the corrosion products of 5083Al coating presents a faster deposition rate and causes a denser and blocky corrosion products layer, which inhibits the penetration of Cl−, thereby enhancing corrosion resistances. Furthermore, in the case of coating cracking, the 5083Al coating, with lower potentials than EH36 steel matrix and lower self-discharge rate than the Zn15Al coating, acting as the sacrificial anode, is more suitable to provide durable protection for steels in marine environments.

Microbial communities colonising plastics during transition from the wastewater treatment plant to marine waters

BackgroundPlastics pollution and antimicrobial resistance (AMR) are two major environmental threats, but potential connections between plastic associated biofilms, the ‘plastisphere’, and dissemination of AMR genes are not well explored.ResultsWe conducted mesocosm experiments tracking microbial community changes on plastic surfaces transitioning from wastewater effluent to marine environments over 16 weeks. Commonly used plastics, polypropylene (PP), high density polyethylene (HDPE), low density polyethylene (LDPE) and polyethylene terephthalate (PET) incubated in wastewater effluent, river water, estuarine water, and in the seawater for 16 weeks, were analysed via 16S rRNA gene amplicon and shotgun metagenome sequencing. Within one week, plastic-colonizing communities shifted from wastewater effluent-associated microorganisms to marine taxa, some members of which (e.g. Oleibacter-Thalassolituus and Sphingomonas spp., on PET, Alcanivoracaceae on PET and PP, or Oleiphilaceae, on all polymers), were selectively enriched from levels undetectable in the starting communities. Remarkably, microbial biofilms were also susceptible to parasitism, with Saprospiraceae feeding on biofilms at late colonisation stages (from week 6 onwards), while Bdellovibrionaceae were prominently present on HDPE from week 2 and LDPE from day 1. Relative AMR gene abundance declined over time, and plastics did not become enriched for key AMR genes after wastewater exposure.ConclusionAlthough some resistance genes occurred during the mesocosm transition on plastic substrata, those originated from the seawater organisms. Overall, plastic surfaces incubated in wastewater did not act as hotspots for AMR proliferation in simulated marine environments.