Eco-friendly modified chitosan as corrosion inhibitor for carbon steel in acidic medium: Experimental and in-depth theoretical approaches.

The industrial and medical sectors have a great interest in chitosan due to its unique properties, such as abundance, renewability, non-toxicity, antibacterial activity, biodegradability, and polyfunctionality. In this work, two modified chitosan Schiff bases (ChSB-1 and ChSB-2) were made using condensation methods, and their potential as corrosion inhibitor for carbon steel in 1 M HCl was investigated using chemical and electrochemical techniques. The ChSB-1 and ChSB-2 inhibitors exhibited remarkable inhibitory performance, as evidenced by the mass loss data, which showed 89.3 % and 91.5 % efficacy at 1 mM concentration, respectively. Because of the electron-donor substituent of methoxy (-OCH3), ChSB-2's active sites have more delocalized electrons than ChSB-1's. The PDP results showed that both ChSB-1 and ChSB-2 inhibitors have anti-corrosion characteristics because heteroatoms caused a protective layer to develop that functioned as mixed-typed inhibitors. The calculated adsorption-free energy ∆Gadso for ChSB-1 and ChSB-2, respectively, was found -36.1 and - 37.1 kJ mol-1. The ChSB-1 and ChSB-2 inhibitors adsorb on carbon steel in acidic conditions through physisorption and chemisorption interactions, and their adsorption is in line with the Langmuir adsorption model. Inhibited and uninhibited metallic surfaces were subjected to surface morphological assessments using contact angle (CA), the scanning electron microscopy and the energy dispersive X-ray (SEM/EDX) analysis. The DMol3 part of Materials Studio 7.0 software was used to perform the quantum chemical calculations based on DFT to visualize the structural features. Studies from quantum chemistry suggest the possibility of surface interaction between the unoccupied orbitals of the metal surface and the inhibitors ChSB-1, ChSB-2, ChSB-1H+, and ChSB-2H+. The results clearly show that the two inhibitors work well as environmentally friendly carbon steel corrosion inhibitors in acidic medium. This could be advantageous for industrial procedures such as pickling, cleaning, acidizing oil drilling in oil wells, and using citrus to de-sediment boilers.

Synthesis of new binary trimethoxyphenylfuran pyrimidinones as proficient and sustainable corrosion inhibitors for carbon steel in acidic medium: experimental, surface morphology analysis, and theoretical studies.

In this study, synthesis and assessment of the corrosion inhibition of four new binary heterocyclic pyrimidinones on CS in 1.0 M hydrochloric acid solutions at various temperatures (30-50 °C) were investigated. The synthesized molecules were designed and synthesized through Suzuki coupling reaction, the products were identified as 5-((5-(3,4,5-trimethoxyphenyl)furan-2-yl)methylene)pyrimidine-2,4,6(1H,3H,5H)-trione (HM-1221), 2-thioxo-5-((5-(3,4,5-trimethoxyphenyl)furan-2-yl)methylene)dihydropyrimidine-4,6(1H,5H)-dione (HM-1222), 1,3-diethyl-2-thioxo-5-((5-(3,4,5-trimethoxyphenyl)furan-2-yl)methylene)dihydropyrimidine-4,6(1H,5H)-dione (HM-1223) and 1,3-dimethyl-5-((5-(3,4,5-trimethoxyphenyl)furan-2-yl)methylene)pyrimidine-2,4,6(1H,3H,5H)-trione (HM-1224). The experiments include weight loss measurements (WL), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP). From the measurements, it can be shown that the inhibition efficiency (η) of these organic derivatives increases with increasing the doses of inhibitors. The highest η recorded from EIS technique were 89.3%, 90.0%, 92.9% and 89.7% at a concentration of 11 × 10-6 M and 298 K for HM-1221, HM-1222, HM-1223, and HM-1224, respectively. The adsorption of the considered derivatives fit to the Langmuir adsorption isotherm. Since the ΔGoads values were found to be between - 20.1 and - 26.1 kJ mol-1, the analyzed isotherm plots demonstrated that the adsorption process for these derivatives on CS surface is a mixed-type inhibitors. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), atomic force microscope (AFM) and Fourier- transform infrared spectroscopy (FTIR) were utilized to study the surface morphology, whereby, quantum chemical analysis can support the mechanism of inhibition. DFT data and experimental findings were found in consistent agreement.

Revealing the Corrosion Resistance Mechanism of Plain Carbon Steel Micro-Alloyed by La in Simulated Industrial Atmosphere.

Plain carbon steel is the most widely applied steel in current engineering construction. With the increased application property needs, the service life of plain carbon steel has been severely tested. As one of the most destructive failure modes, corrosion resistance of carbon steel has attracted wide attention. Rare earth La, as the microalloying element, was employed in plain carbon steel, Q355, to improve its corrosion resistance. As the content of La increased, the microstructure was refined. The fraction of pearlite decreased, while the content of acicular increased. Within the La addition of 230 ppm, the tensile strength and impact energy were jointly improved. Furthermore, the microalloying element of La modified the inclusion types and refined the inclusion size. The modified microstructure and inclusions by La co-improved the corrosion resistance. The formula of effective La content was proposed to estimate the effect of La on corrosion. As the effective content of La increased, the relative corrosion rate decreased. La3+ promoted the protective rust layer to increase corrosion resistance.

A New Mechanism for the Inhibition of SA106 Gr.B Carbon Steel Corrosion by Nitrite in Alkaline Water.

The purpose of this study was to investigate the composition of oxide films formed on SA106 Gr.B carbon steel in nitrite solutions at 35 °C for 1000 h. The product of the reduction of nitrite during the corrosion inhibition process was also examined. The X-ray photoelectron spectroscopy results revealed that a thin Fe3O4 film was formed and ammonium ions were adsorbed on the outermost surface of the oxide film. The presence of ammonium ions was also demonstrated by ion chromatography. These results indicate that nitrites are reduced to ammonium ions, which in turn promotes the formation of the protective Fe3O4 film.

Mechanism of Fatigue-Life Extension Due to Dynamic Strain Aging in Low-Carbon Steel at High Temperature.

An enhancement in fatigue life for ferrite-pearlite low-carbon steel (LCS) at high temperature (HT) has been discovered, where it increased from 190,873 cycles at room temperature (RT) to 10,000,000 cycles at 400 °C under the same stress conditions. To understand the mechanism behind this phenomenon, the evolution of microstructure and dislocation density during fatigue tests was comprehensively investigated. High-power X-ray diffraction (XRD) was employed to analyze the evolution of total dislocation density, while Electron Backscatter Diffraction (EBSD) and High-Resolution EBSD (HR-EBSD) were conducted to reveal the evolutions of kernel average misorientation (KAM), geometrically necessary dislocations (GND) and elastic strains. Results indicate that the enhancement was attributed to the dynamic strain aging (DSA) effect above the upper temperature limit, where serration and jerky flow disappeared but hindrance of dislocations persisted. Due to the DSA effect, periods of increase and decrease in the total dislocations were observed during HT fatigue tests, and the fraction of screw dislocations increased continuously, caused by viscous movement of the screw dislocations. Furthermore, the increased fraction of screw dislocations resulted in a lower energy configuration, reducing slip traces on sample surfaces and preventing fatigue-crack initiation.

Corrosion of Sulfate-Reducing Bacteria on L245 Steel under Different Carbon Source Conditions.

Objective Sulfate-reducing bacteria (SRB) pose a threat to the safe operation of shale-gas-gathering pipelines. Therefore, it is essential to explore the role played by SRB in dedicated pipelines. Methods In this work, the corrosion behavior of SRB was investigated by organic carbon starvation immersion experiments combined with cell number monitoring, corrosion weight loss recordings, morphology and profile observations and electrochemical measurements. Results In experiments with sodium lactate content ranging from 0-3500 ppm, the corrosion rate and pitting depth were the highest at 350 ppm. Conclusions The results indicated that the reduction in carbon sources leads to bacterial starvation, which directly obtains electrons from metals and exacerbates corrosion. It is not appropriate to use the content of bacteria to determine the strength of bacterial corrosion.

Investigation of the Crystallographic Evolution Sequence of Nano-Precipitation via HRTEM in Cu-Bearing Ultra-Low Carbon Steel.

The precipitation behavior of Cu-bearing ultra-low carbon steel after step quenching and tempering at 923 K for 0.5-2.5 h was investigated. The size, quantity, and characteristic distribution of nano-precipitates were analyzed using transmission electron microscopy, and the microstructure of B2 (an ordered structure belonging to the body-centered cubic structure), 9R (a special triclinic lattice that has characteristics of rhombohedral structure), 3R (a special triclinic lattice like 9R), and FCT (face-centered tetragonal lattices) were accurately determined. The relationship between nano-precipitates and mechanical properties under different heat treatment processes was obtained, revealing that nano-precipitates effectively enhanced the yield strength of Cu-bearing ultra-low carbon steel. There were two forms of crystal structure evolution sequence of precipitation: B2→multi twin 9R→detwined 9R→FCT→FCC and B2→multi-twin 9R→detwinned 9R→3R→FCT→FCC. The morphology of the precipitated particles during the growth process changed from spherical to ellipsoidal and finally to rod-shaped. It was proven that a stable 3R structure existed due to the coexistence of 9R, 3R, and FCT structures in the same precipitate particle.

Effect of Crevice Size on Crevice Corrosion of N80 Carbon Steel in CO2-Saturated NaCl-HAc Solution.

The effect of crevice size on the crevice corrosion of N80 carbon steel was investigated by electrochemical measurements and surface analysis in a CO2-saturated NaCl-HAc solution. The N80 carbon steel exhibits a high susceptibility to crevice corrosion in this environment, which can be initiated immediately without an induction period for specimens with crevice sizes of 100 µm, 300 µm, and 500 µm. Typically, crevice solutions become more acidic during crevice corrosion; however, in this study, the crevice solution became alkaline, resulting in galvanic corrosion between the inner and outer steel surfaces and leading to severe crevice corrosion. The pH levels of the crevice solution for specimens with 100 µm and 300 µm crevice sizes are similar, but both are notably higher than that of the specimen with a 500 µm crevice size. As a result, there is no significant difference in the crevice corrosion phenomenon between specimens with 100 µm and 300 µm crevice sizes, but it is more severe than in the specimen with a 500 µm crevice size.

Effect of seawater salinity, pH, and temperature on external corrosion behavior and microhardness of offshore oil and gas pipeline: RSM modelling and optimization.

This research aims to investigate the effects of seawater parameters like salinity, pH, and temperature on the external corrosion behaviour and microhardness of offshore oil and gas carbon steel pipes. The immersion tests were performed for 28 days following ASTM G-1 standards, simulating controlled artificial marine environments with varying pH levels, salinities, and temperatures. Besides, Field emission scanning electron microscopy (FESEM) analysis is performed to study the corrosion morphology. Additionally, a Vickers microhardness tester was used for microhardness analysis. The results revealed that an increase in salinity from 33.18 to 61.10 ppt can reduce the corrosion rate by 28%. In contrast, variations in seawater pH have a significant effect on corrosion rate, with a pH decrease from 8.50 to 7 causing a 42.54% increase in corrosion rate. However, the temperature of seawater was found to be the most prominent parameter, resulting in a 76.13% increase in corrosion rate and a 10.99% reduction in the microhardness of offshore pipelines. Moreover, the response surface methodology (RSM) modelling is used to determine the optimal seawater parameters for carbon steel pipes. Furthermore, the desirability factor for these parameters was 0.999, and the experimental validation displays a good agreement with predicted model values, with around 4.65% error for corrosion rate and 1.36% error for microhardness.

Multi-Objective Optimization of Laser Cleaning Quality of Q390 Steel Rust Layer Based on Response Surface Methodology and NSGA-II Algorithm.

To improve the laser cleaning surface quality of rust layers in Q390 steel, a method of determining the optimal cleaning parameters is proposed that is based on response surface methodology and the second-generation non-dominated sorting genetic algorithm (NSGA-II). It involves constructing a mathematical model of the input variables (laser power, cleaning speed, scanning speed, and repetition frequency) and the objective values (surface oxygen content, rust layer removal rate, and surface roughness). The effects of the laser cleaning process parameters on the cleaning surface quality were analyzed in our study, and accordingly, NSGA-II was used to determine the optimal process parameters. The results indicate that the optimal process parameters are as follows: a laser power of 44.99 W, cleaning speed of 174.01 mm/min, scanning speed of 3852.03 mm/s, and repetition frequency of 116 kHz. With these parameters, the surface corrosion is effectively removed, revealing a distinct metal luster and meeting the standard for surface treatment before welding.

Naphthenic Acid Corrosion Mitigation: The Role of Niobium in Low-Carbon Steel.

Naphthenic acid corrosion is a well-recognized factor contributing to corrosion in the construction of offshore industry pipelines. To mitigate the corrosive effects, minor quantities of alloying elements are introduced into the steel. This research specifically explores the corrosion effects arising from immersing low-carbon steel, specifically A333 Grade 6, in a naphthenic acid solution. Various weight percentages of niobium were incorporated, and the resulting properties were observed. It was noted that the addition of 2% niobium in low-carbon steel exhibited the least mass loss and a lower corrosion rate after a 12 h immersion in naphthenic acid. Microstructural analysis using scanning electron microscopy (SEM) revealed small white particles, indicating the presence of oil sediment residue, along with corrosion pits. Following the addition of 2% niobium, the occurrence of corrosion pits markedly decreased, and only minor voids were observed. Additionally, the chemical composition analysis using energy-dispersive X-Ray analysis (EDX) showed that the black spot exhibited the highest percentage of carbon, resembling high corrosion attack. Meanwhile, the whitish regions with low carbon content indicated the lowest corrosion attack. The results demonstrated that the addition of 2% niobium yielded optimal properties for justifying corrosion effects. Therefore, low-carbon steel with a 2% niobium addition can be regarded as a superior corrosion-resistant material for offshore platform pipeline applications.

Mechanical anisotropic behavior of low-carbon steel processed by asymmetric rolling.

In the present work, the mechanical anisotropic behavior of low-carbon (Fe-0.07C) steel processed by asymmetric cold rolling was investigated. Three different types of dynamic recrystallization (DRX) mechanisms (continuous, discontinuous, and geometric) were observed in the microstructure of the 75 % cold-rolled sheet. The average intensity of γ-fiber was remarkably enhanced to 2.8 × R as rolling deformation increased to 50 % due to the formation of many deformation bands. After 75 % cold rolling, the average intensity of γ-fiber was significantly decreased to 1.4 × R due to the creation of new recrystallized grains. The results exhibited that the hardness of the low-carbon steel sheet was 260.1 HV by 75 % cold rolling, which was 1.75 times larger than the initial low-carbon steel sheet. With increasing deformation degree, the average yield and tensile strengths gradually improved and reached a peak value of 844.8 MPa and 881.7 MPa after 75 % cold rolling, respectively, which were 2.8 and 2.1 times that of the initial low-carbon steel sheet. By increasing the rolling reduction up to 50 %, the mechanical anisotropy gradually enhanced and by further increasing the cold deformation to 75 %, the anisotropy rapidly decreased due to the weakening of the γ-fiber texture. The strength was the highest along the transverse direction (90°) in all low-carbon steel sheets, and decreased at 0° and 45°. The dσ/dε-ε curves of the 50 % cold-rolled low-carbon steel sheet for the 45° and 90° tensile directions exhibited two distinct stages during the loading, however, that for the 0° revealed only one stage. A large number of parallel striations were present on the fracture surface of the 50 % deformed low-carbon steel sheet at 90° due to the presence of parallel deformation bands.

New approach for processing chitosan as low cost protective hybrid coating for C-steel in acid media.

The novelty of this study is that it the first time blending and formulation of chitosan as a new hybrid (organometallic) protective coatings for achieving synergistic protection for carbon steel alloy during acid pickling. The role of coated silica (by 0.1 wt % stearic acid lubricant) in the improvement of coating performance was highlighted. Variable weight percentage of chitosan and silica in addition to a fixed weight percentage (35 %) of guar gum natural plant resin, 5 × 10-6 mmol (2-Hydrazinyl-6-methyl (or phenyl) -4, 5-di-H pyrimidinone) as organic corrosion inhibitors were compounding as hot melt in the presence of a low cost surfactant as an emulsifying agent improved compatibility between coating constituents. Guar gum increased coating flow during application and grafted chitosan into high molecular copolymer resin insoluble in acid media. Phosphorous acid improved coating flexibility during application by hot dipping. Hybrid coating decreased corrosion potential of carbon steel and retarded both redox reactions of corrosion acting as adsorbed mixed-type inhibitor. Percentages protection (%P) approached hundred percentage as confirmed from the agreement between impedance and polarization parameters. Guar gum plant resin and slice powder increased gloss of coating. The coated silica filled the pores and increased stiffness of coating. Super hydrophobicity of coating was confirmed by the measured contact angle above 150oC indicating good spreading of coating sample as insulating adherent surface film.

The corrosion behavior of carbon steel under coexistence of carbon dioxide and SRB.

The corrosion behavior of carbon steel under the coexistence of carbon dioxide and SRB was studied by means of corrosion weight loss, SEM, EDS, in situ pH test, and other methods. The results showed that Chloride ions, temperature, pH, and oxygen coexist with iron bacteria will affect the corrosion under the coexistence of CO2 and SRB, and SRB tends to grow in a favorable environment for itself, and the corrosion rate of X52N at 42 days is slightly higher than that at 21 days. However, the pitting depth increased sharply from 21.20 µm in 21 days to 39.79 µm in 42 days. So that the corrosion can be divided into two stages. First, SRB catalyze the dissolution of FeCO3, leading to local uniform corrosion. Second, SRB directly obtain electrons from the metal surface, resulting in local pitting. In addition, the environment under the stable mineralized biofilm was found to be slightly alkaline.

The Influence of Heat Treatment on the Microstructure and Properties of a Cu-Bearing Ultra-Low Carbon Steel.

This study reveals the relationship between the Cu precipitates and mechanical properties of a Cu-baring ultra-low carbon steel after two-phase zone quenching and tempering at 923 K for 0.5-2.5 h. The tensile and microstructural properties were investigated as a function of heat treatment time. The contribution of the precipitation-strengthening mechanism to yield strength was calculated. The size, morphology, and distribution of the precipitated particles were observed using TEM. As the heat treatment time increased, the strength gradually decreased and then remained stable, and the elongation gradually increased and then remained stable. Additionally, the contributions of each strengthening mechanism to the yield strength under different heat treatments were 117, 107, 102, and 89 MPa, respectively. The size and quantity of the precipitates increased with the increase in heat treatment time. After tempering for more than 2 h, the precipitates continued to coarsen, but their quantity decreased. The precipitated Cu had a 3R structure with a length of approximately 17.1 nm and a width of approximately 9.7 nm, with no twinning inside. The stacking order was ABC/ABC. The stable Cu precipitation structure was FCC, maintaining a K-S orientation relationship 11¯1FCC Cu //(0 1 1) α, 1¯10FCC Cu//[11¯1] α.

Effect of a Hybrid Pumice-Portland Cement Extract on Corrosion Activity of Stainless Steel SS304 and Carbon Mild Steel A36.

The change in the corrosion activities of SS304 and the carbon steel A36 were studied during their exposure for 30 days to hybrid pumice-Portland cement extract (CE), to simulate the concrete-pore environment. The ionic composition and the initial pH (12.99) of the CE were influenced by the reduction of Portland cement (PC) content, volcanic pumice oxides and alkaline activators. Because of the air CO2 dissolution, the pH decreased and maintained a constant value ≈ 9.10 (established dynamic ionic equilibrium). The CE promoted the passivation of both steels and their free corrosion potential (OCP) reached positive values. On the surfaces, Fe and Cr oxides were formed, according to the nature of the steel. Over the time of exposure, the presence of chloride ions in the pumice caused a localized pitting attack, and for carbon steel, this fact may indicate an intermediate risk of corrosion. The chloride effect was retarded by the accumulation of SO42- ions at the steel surfaces. Based on electrochemical impedance (EIS), the polarization resistance (Rp) and the thickness of the passive layers were calculated. Their values were compared with those previously reported for the steels exposed to CEs of Portland and supersulfated cements, and the hybrid cement was considered as a PC "green" alternative.

An electrochemical, and surface studies of synthesized Gemini ionic liquid as corrosion inhibitor for carbon steel in petroleum field.

In this work, we study the efficiency of N1, N3-dibenzyl-N1, N1, N3, N3-tetramethylpropane-1,3-diaminium chloride, as anticorrosion. This compound exhibits potential as a prospective remedy to stop the deterioration of carbon steel caused by corrosion in 1.0 M HCl. The synthesis of this compound is described in a comprehensive manner, and its composition is supported by a range of precise analytical approaches such as elemental analysis, and mass spectroscopy. Based on the findings of the investigation, the synthesized Gemini ionic liquid demonstrates a robust capacity to slow down the rate at which the metal corrodes. The Prepared compound was evaluation by electrochemical and morphology study. Our results revealed that elevating the inhibitor concentration led to an augmentation in inhibition effectiveness, reaching up to 94.8% at 200 ppm of the synthesized compound at 298 K. It is crucial to emphasize that the recently prepared Gemini ionic liquid is consistent with the Langmuir adsorption model and function as a mixed inhibitor, participating in the physio-chemisorption process of adsorption.

Examining the ability of palm kernel shell extract to control corrosion and assess its economic value on thermo-mechanically treated steel in artificial seawater: a sustainable and environmentally friendly approach.

Each year, the rising demand for palm oil generates large amounts of palm kernel shell waste. Discarded palm kernel shells can produce activated carbon, crushed shells, liquified fumes, and other derivatives; however, their indiscriminate disposal persists, raising issues related to the environment and economy. Therefore, the purpose of this study is to investigate the use of palm kernel shell as a corrosion inhibitor for thermo-mechanically treated steel in a seawater environment using gravimetric and electrochemical techniques, as well as surface tests at varying concentrations. The findings demonstrated that the palm kernel shell inhibited the cathodic and anodic processes by adsorption on the steel surface, which followed the Langmuir adsorption isotherm. The inhibitor exhibited a 98% inhibitory efficiency at 500 ppm concentration. Scanning electron microscopy analysis verified the thin films of the inhibitor on steel surface in seawater solution. Fourier transform infrared spectroscopy results show that the extract's components prevent the steel corrosion through an adsorptive mechanism. According to the inhibitor economic evaluation, employing the palm kernel shell extract is less expensive than utilizing conventional inhibitors.

Effect of neem oil biodiesel on the surface and structural integrity of carbon steel alloy: Chromatographic, spectroscopic, and morphological investigations.

This study explores the impacts of neem oil biodiesel (BD), which was produced and characterized using GC-MS, FTIR, and UV-Vis spectroscopic techniques to elucidate pure and corrosion-product neem oil BD at room temperature (25 °C) and different immersion durations of 0, 28, 42, and 56 days. The OM and SEM were also employed to study the surface, structural integrity, and interphase interaction between the BD and the carbon steel (C1020) before and after immersion for different durations. The dominant fatty acid (FA) group in both pure and corrosion-product neem oil BD was C18, with a total composition of 72.3 %, hence determining the nature of the BD interaction with the carbon steel. The study revealed that carbon steel (C1020) was susceptible to attacks by neem oil BD, and the duration of immersion had substantial influence on the surface morphology and structural integrity of the steel. It is therefore anticipated that this study will significantly advance the field of alternative fuel research.

The Role of Metallurgical Features in the Microbially Influenced Corrosion of Carbon Steel: A Critical Review.

Microbially influenced corrosion (MIC) is a potentially critical degradation mechanism for a wide range of materials exposed to environments that contain relevant microorganisms. The likelihood and rate of MIC are affected by microbiological, chemical, and metallurgical factors; hence, the understanding of the mechanisms involved, verification of the presence of MIC, and the development of mitigation methods require a multidisciplinary approach. Much of the recent focus in MIC research has been on the microbiological and chemical aspects, with less attention given to metallurgical attributes. Here, we address this knowledge gap by providing a critical synthesis of the literature on the metallurgical aspects of MIC of carbon steel, a material frequently associated with MIC failures and widely used in construction and infrastructure globally. The article begins by introducing the process of MIC, then progresses to explore the complexities of various metallurgical factors relevant to MIC in carbon steel. These factors include chemical composition, grain size, grain boundaries, microstructural phases, inclusions, and welds, highlighting their potential influence on MIC processes. This review systematically presents key discoveries, trends, and the limitations of prior research, offering some novel insights into the impact of metallurgical factors on MIC, particularly for the benefit of those already familiar with other aspects of MIC. The article concludes with recommendations for documenting metallurgical data in MIC research. An appreciation of relevant metallurgical attributes is essential for a critical assessment of a material's vulnerability to MIC to advance research practices and to broaden the collective knowledge in this rapidly evolving area of study.