Electrochemical Techniques Research Articles

Growth and physical-chemical characterization of manganese oxide and graphene-manganese oxide films for potential applications in energy store devices

The need for progress in the development of energy supply devices such as batteries and large capacitors has led to the improvement and innovation of these devices so that they can store energy efficiently, and additionally, they must be small, light, with low production costs, and friendly to the environment. For these reasons, in this investigation results of the characterization of physical and chemical behaviors of graphene-manganese oxide and copper and manganese oxide-copper systems are studied. The graphene was synthesized through the electrochemical exfoliation technique and deposited as a film on common glass and silicon substrates via the spray technique, and over this film, Mn2O3 films were deposited through spin coating. The Raman results showed the presence of peaks D and G, located at 1534 and 1597 cm−1, respectively. XPS analysis demonstrated that the graphene is made up of three layers. TEM studies determined that the graphene is polycrystalline, and XRD established the manganese oxide coatings’ growth along the (222) and (440) planes of Mn2O3. The optical behavior indicated that the absorbance of the graphene-Mn2O3 system decreases the energy gap in 0.8 eV concerning Mn2O3 films. The voltage-current measurements suggest that the density current in the discharge process of the Mn2O3–Cu electrode system was improved approximately 3-fold with the graphene-Mn2O3–Cu electrode system. The obtained results conclude that the addition of graphene to manganese oxide coatings increases their electrochemical performance, so graphene-manganese oxide could be used in energy storage devices.

Fabrication of bioinspired SnO2/Few layered rGO nanocomposite coating for preserving Zn metal assets in various environments

The current study inspected the effect of incorporating two nanomaterials, namely reduced graphene oxide (rGO) and Tin oxide (SnO2), synthesized by hydrothermal method, upon improving the corrosion resistance in Zinc metal plate under different electrolytes. The XRD results confirms the formation of SnO2 nanoparticles with a crystalline tetragonal structure with 23.1 and 31.89 nm crystalline size. FE-SEM images indicated that the rGO is well embedded into the SnO2 nanoparticles. The TEM images and elemental mapping show the presence of crystalline nanoparticles embedded within the layers of graphene. In addition, the corrosion resistance of both pure SnO2 and SnO2-rGO nanocomposite is assessed using electrochemical techniques. The substrate coated with nanocomposite is exposed to three distinct electrolytes utilizing a Zn metal plate. Adding reduced graphene oxide (rGO) to the composite material creates a barrier that protects against corrosion and improves the charge transfer efficiency, resulting in lower corrosion rates and increased stability. The composite's combined impact of SnO2 and rGO provides exceptional corrosion resistance and the findings lead to the development of innovative and efficient ways to prevent corrosion, thereby ensuring materials' long-lasting and dependable performance in various industrial settings.

Detection of beta-blocker in plasma and urine

This paper presents a comprehensive overview of beta-blockers, a class of important medications used for treating various cardiovascular conditions like hypertension, angina pectoris, heart failure, and arrhythmia. The mechanism of beta-blockers involves blocking the binding of epinephrine and norepinephrine to b-adrenoceptors. Accurate targeting of beta-blockers is crucial for athletes participating in archery, billiards, and golf as it can effectively lower heart rate and reduce anxiety. To identify drug compounds, various separation techniques, including HPLC, GC, and CE, are commonly employed. Among these techniques, electrochemical approaches have gained prominence due to their significant advantage of not requiring any separation or extraction processes. Electrochemical methods are also advantageous as they remain unaffected by optically absorbing and fluorescent compounds, a limitation encountered in spectroscopy. Additionally, electrochemical methods can be quickly functionalized with nanomaterials to enhance their performance. While optical methods like spectrophotometric and spectrofluorometric techniques offer certain advantages over other analytical approaches, such as affordability, simplicity, and faster analysis times, they may not provide the same straightforward and rapid detection of beta-blockers as the electrochemical methods do. Therefore, considering the specific context and objectives of analysis, researchers can choose between electrochemical and optical techniques to effectively study and detect beta-blockers in different applications.

Electrochemiluminescence-Based Single-Particle Tracking of the Biomolecules Moving along Intercellular Membrane Nanotubes between Live Cells.

Electrochemiluminescence (ECL) imaging, a rapidly evolving technology, has attracted significant attention in the field of cellular imaging. However, its primary limitation lies in its inability to analyze the motion behaviors of individual particles in live cellular environments. In this study, we leveraged the exceptional ECL properties of quantum dots (QDs) and the excellent electrochemical properties of carbon dots (CDs) to develop a high-brightness ECL nanoprobe (CDs-QDs) for real-time ECL imaging between living cells. This nanoprobe has excellent signal-to-noise ratio imaging capabilities for the single-particle tracking (SPT) of biomolecules. Our finding elucidated the enhanced ECL mechanism of CDs-QDs in the presence of reactive oxygen species through photoluminescence, electrochemistry, and ECL techniques. We further tracked the movement of single particles on membrane nanotubes between live cells and confirmed that the ECL-based SPT technique using CD-QD nanoparticles is an effective approach for monitoring the transport behaviors of biomolecules on membrane nanotubes between live cells. This opens a promising avenue for the advancement of ECL-based single-particle detection and the dynamic quantitative imaging of biomolecules.

Galvanic Corrosion Behavior of the X80 Steel Welded Joint

Wire beam electrode techniques and classical electrochemical techniques were used to investigate the effect of the area ratio of each part of the welded joint on the galvanic corrosion behavior. The results showed that the order of the corrosion current density of the different regions in the simulated X80 steel welded joint was as follows: coarse-grained heat-affected zone > fine-grained heat-affected zone > intercritical heat-affected zone > base metal > weld metal. As the area ratio of weld metal increased, the galvanic potential shifted positively, the maximum anode galvanic current density increased and the main anode galvanic effect increased. On the other hand, as the area ratio of the base metal and the heat-affected zone decreased, the coupled potential shifted negatively and the maximum anode galvanic current density decreased. The galvanic corrosion intensity of the simulated X80 steel welded joint increased as the area ratio of the weld metal decreased and increased as the area ratio of the heat-affected zone and base metal increased. To enhance corrosion resistance, it is advisable to choose a shape with a larger groove to increase the WM area in the welded joint. Additionally, selecting a welding method with lower heat input and a higher energy density can help reduce the HAZ area in the welded joint.

Gold particles modified 3D printed carbon black nanonetwork electrode for improving the detection sensitivity of dopamine

Using 3-dimensional (3D) printing to create a fast and accurate electrochemical sensor has attracted the attention of analytical scientists. This study utilized a carbon black/PLA composite filament as the raw material for the construction of 3D electrodes (3DEs). Au particles were modified onto the activated surface of the carbon black nanonetwork 3DE. The physical and chemical properties of the 3DEs were evaluated through scanning electron microscopy (SEM) and X-ray spectroscopy (XPS). Additionally, a range of electrochemical techniques were employed to investigate the electrochemical performance of the 3DEs. The sensor is capable of detecting DA in the concentration range of 0.01–20 μM with the limit of detection (LOD) of 0.084 μM. The approach is also capable of being applied to the actual sample detection of DA with excellent selectivity. Hence, the method of combining noble metal particles and carbon black nanonetwork for constructing 3DE presents novel prospects towards the creation of electrochemical sensors with exceptional sensitivity.

Modelling Prospects of Bio-Electrochemical Immunosensing Platforms

Electrochemistry is a hotspot in today’s research arena. Many different domains have been extended for their role towards the Internet of Things, digital health, personalized nutrition, and/or wellness using electrochemistry. These advances have led to a substantial increase in the power and popularity of electroanalysis and its expansion into new phases and environments. The recent COVID-19 pandemic, which turned our lives upside down, has helped us to understand the need for miniaturized electrochemical diagnostic platforms. It also accelerated the role of mobile and wearable, implantable sensors as telehealth systems. The major principle behind these platforms is the role of electrochemical immunoassays, which help in overshadowing the classical gold standard methods (reverse transcriptase polymerase chain reaction) in terms of accuracy, time, manpower, and, most importantly, economics. Many research groups have endeavoured to use electrochemical and bio-electrochemical tools to overcome the limitations of classical assays (in terms of accuracy, accessibility, portability, and response time). This review mainly focuses on the electrochemical technologies used for immunosensing platforms, their fabrication requirements, mechanistic objectives, electrochemical techniques involved, and their subsequent output signal amplifications using a tagged and non-tagged system. The combination of various techniques (optical spectroscopy, Raman scattering, column chromatography, HPLC, and X-ray diffraction) has enabled the construction of high-performance electrodes. Later in the review, these combinations and their utilization will be explained in terms of their mechanistic platform along with chemical bonding and their role in signal output in the later part of article. Furthermore, the market study in terms of real prototypes will be elaborately discussed.

Submerged photosynthesis of TiO2-CuO hetero-nanoparticles and their multiple applications for water issues under solar light

Environmental challenges, encompassing issues like agricultural ammonia discharge, industrial organic dye misuse, and high environmental polluted water evaporation, demanded urgent attention. In response, we proposed a method for synthesizing TiO2-CuO hetero-nanoparticles capable of different environmental protection commands. Submerged Photosynthesis of Crystallites (SPSC) was adopted due to its simplicity and eco-friendliness. Hetero-nanoparticles with varying Cu-Ti ratios were prepared, characterized, and assessed. CuO dispersion within TiO2 proved consistently even. Increasing Cu content increased Cu-Ti ratio until reaching an upper limit. All nanoparticle samples demonstrated excellent solar light absorption. Combining solar illumination and electrochemical techniques synergistically boosted pollutant degradation. The nanoparticle with a Cu-Ti ratio of 0.17 exhibited optimal photo-electrochemical degradation, enhancing efficiency by 150% under solar light compared to darkness. It also outperformed solar light alone by 32% and electrochemistry alone by 2% in RhB degradation. Furthermore, it enhanced water evaporation rate under solar light. The nanoparticle with a Cu-Ti ratio of 0.52 was the highest water evaporation rate, increasing up to 104% compared to the control group. We discussed the mechanisms underlying fabrication and degradation, elucidating the observed performance. In conclusion, our research underscored the potential of TiO2-CuO hetero-nanoparticles for solar-assisted solutions to different environmental issues, highlighting their environmental applicability.

Recent Advances in Aptamer-Based Biosensors for Bacterial Detection.

The rapid and sensitive detection of pathogenic bacteria is becoming increasingly important for the timely prevention of contamination and the treatment of infections. Biosensors based on nucleic acid aptamers, integrated with optical, electrochemical, and mass-sensitive analytical techniques, have garnered intense interest because of their versatility, cost-efficiency, and ability to exhibit high affinity and specificity in binding bacterial biomarkers, toxins, and whole cells. This review highlights the development of aptamers, their structural characterization, and the chemical modifications enabling optimized recognition properties and enhanced stability in complex biological matrices. Furthermore, recent examples of aptasensors for the detection of bacterial cells, biomarkers, and toxins are discussed. Finally, we explore the barriers to and discuss perspectives on the application of aptamer-based bacterial detection.

Selective and efficient removal of As(III) from water by Ce-Mn oxide-modified biochar: Synergetic role of rapid oxidation and enhanced adsorption

Pre-oxidation of trivalent arsenic (As(III)) to pentavalent arsenic (As(V)) with subsequent in-situ adsorption serves as a viable strategy for the As(III) removal from water environment. Herein, a simple pyrolysis-impregnation-pyrolysis method was used to create the Ce-Mn oxides modified biochar (CMBC) and the as-prepared CMBC was applied to a persulfate (PS) system to establish a multiphase catalytic process for the rapid oxidation of As(III) and efficient adsorption of As(V) in aqueous solution. The maximum adsorption capacity of As(III) arrived up to 162.09 mg g−1 under CMBC/PS system, and the excellent removal performance of As(III) could be achieved in both acidic and alkaline situations (pH ranging from 3 to 11). Ionic strength, natural organic matter, as well as coexisting anions (except for phosphate) and cations did not inhibit As(III) removal in CMBC/PS system. Especially, the adsorption of As(III) under diverse coexisting ions reached adsorption dynamic equilibrium within 90 minutes, implying that the process has relatively fast adsorption kinetics and is resistant to interference. Moreover, the adsorbent could be effortlessly renewed with regenerant while retaining the desired removal rate. Persulfate activated by CMBC generated radical species, however, the free radical trapping experiments, EPR experiments, and electrochemical technique analysis revealed that there existed a non-radical-dominated electron transfer pathway in the CMBC/PS system. The ideal regeneration performance, anti-disturbance ability, and high adsorption capacity imply that CMBC/PS may serve as a promising approach to removal As(III) via adsorption method, and the results also gain insight into the electron transfer pathway in the system.

Validation of electrochemical device setup for detection of dual antibiotic drug release from hydrogel

Due to antimicrobial resistance that occurs throughout the world, antibiotic-releasing hydrogel with at least two drugs that synergistically treat stubborn bacteria is preferable for infection prevention. Hydrogel can serve as a drug reservoir to gradually release drugs in a therapeutic window to effectively treat microorganisms with minimal side effects. The study and development of drug releasing hydrogels requires a reliable, straightforward, cost-effective, fast, and low labor-intensive drug detection technique. In this study, we validate the electrochemical technique and device setup for real-time determination of dual antibacterial drugs released from a hydrogel. Concentrations of two representative antibacterial drugs, tetracycline (TC) and chloramphenicol (CAP), were determined using square wave voltammetry (SWV) mode that yields the lower limit of detection at 2.5 µM for both drugs. Measurement accuracy and repeatability were verified by 36 known drug combination concentrations. Capability in long-term measurement was confirmed by the measurement stability which was found to last for at least 72 h. Stirring was revealed as one of the significant factors for accurate real-time detection. Real-time measurement was ultimately performed to demonstrate the determination of multiple drug releases from a drug releasing hydrogel and validated by high-performance liquid chromatography (HPLC). All the results support that the electrochemical technique with the proposed device design and setup can be used to accurately and simultaneously determine dual drugs that are released from a hydrogel in real-time.

Furosemide drug as a corrosion inhibitor for carbon steel in 1.0 M hydrochloric acid

Furosemide (4-chloro-2-furan-2-ylmethylamino-5-sulfamoylbenzoic acid) was examined as an inhibitor for the corrosion of carbon steel (CS) in 1.0 M HCl. The investigation included mass loss (ML) and electrochemical techniques: potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM). The efficiency of inhibition rises with increasing Furosemide concentration and temperature. This compound follows the Temkin isotherm with good fit. The presence of varying quantities influences both anodic metal dissolution and cathodic hydrogen evolution. Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) were used to detect the effect of the compound on the CS surface. The molecular inhibitory effect of Furosemide was demonstrated using quantum chemical calculations, and the molecular simulation results demonstrated the adsorption on the carbon steel surface.

A high-power glucose fuel cell for potential application in implant surfaces

The glucose fuel cells (GFCs) leverage the implant surface as an electrode, representing an optimal approach for miniaturizing implantable power sources. A conductive hydrogel electrode membrane is crafted through in situ reduction and electrochemical co-deposition techniques by employing bacterial cellulose as a scaffold. This process enables the seamless integration of the GFC directly onto the implant surface. The integrated GFC exhibits an impressive open-circuit voltage peak of 0.894 V and a peak power density of 94.7 μW cm−2. Additionally, the fuel cell demonstrates resistance to chloride ion toxicity under simulated interstitial fluid conditions. Although performance within horse serum is moderate, the methodology presents a viable strategy for developing GFCs on implant surfaces.

Ethylenediamine-functionalized metal-organic frameworks for applications of electrochemical supercapacitors as an additive

In this study, the impact of incorporating ethylenediamine (ED)-functionalized metal-organic frameworks (MOFs) on enhancing the electrochemical performance of polypyrrole(PPy)-based conducting polymers as supercapacitor electrode materials was investigated. The stability of terephthalic acid-containing MOFs in different environments, including exposure to acids, relies on the specific metal ions and ligands utilized in their construction. In this research, ED treatment was chosen for its resistance to acid attack. Unlike the post-synthetic modifications observed in previous literature regarding ED-modified MOF5, this study introduces a unique approach where ED is directly integrated into the framework in a single step. The resulting materials, referred to as ED-MOF, were employed in creating a novel composite material concurrently with polypyrrole, designed for use as electrode materials in supercapacitor applications. The optimal loading in the electrochemical preparation of polypyrrole-based conducting polymers was determined using cyclic voltammetry and electrochemical impedance spectroscopy techniques. Areal capacitance for the resulting electrodes was evaluated through cyclic charge-discharge experiments. The areal capacitance of the ED-ZnMOF/1@/PPy/PGE electrode was found to be 575.2 mF.cm−2 at a charge/discharge current density of 1 mA.cm−2. This research underscores the potential advantages of combining conducting polymers and metal-organic frameworks in supercapacitors, as well as other electrochemical systems.

Combined study of phase transitions in the P2-type NaXNi1/3Mn2/3O2 cathode material: experimental, ab-initio and multiphase-field results

The research of new electrode materials such as sodium intercalation compounds is key to meet the challenges of future demands of sustainable energy storage. For these batteries, the intercalation behavior on the micro-scale is governed by a complex interplay of chemical, electrical and mechanical forces strongly influencing the overall cell performance. The multiphase-field method is a suitable tool to study these multi-physics and bridge the scale from ab-initio methods to the cell level. In this work, we follow a combined approach of experiments, density functional theory (DFT) calculations and multiphase-field simulations to predict thermodynamic and kinetic properties for the P2-type NaXNi1/3Mn2/3O2 sodium-ion cathode material. Experimentally, we obtain the thermodynamic potential and diffusion coefficients at various sodium contents using electrochemical techniques and discuss limitations of the experimentally applied methods. DFT is used to identify stable phases by calculating an energy hull curve. Then, the influence of long-range dispersion interactions and the exchange-correlation functional on the voltage curve is investigated by comparison with experimental results. Finally, multiphase-field simulations are performed based on inputs from experiments and DFT. The fitting of phase-specific chemical free energies from DFT calculations and experimental data is discussed. Our results highlight the thermodynamic consistency of all three approaches close to thermodynamic equilibrium. Furthermore, the phase-field method accurately describes the kinetics of the system including multiple phase transitions, by which we unravel the mechanism of the P2-O2 phase transition in a single crystal under the influence of intercalation reaction, bulk diffusion and elastic deformation. The model is able to predict the kinetic capacity loss depending on charging rate in agreement with C-rate experiments.

Electropolishing of gold and gold alloys in HCl-glycerol-ethanol electrolytes

Electropolishing or electrochemical polishing (EP) is an ultrafinishing process that improves esthetic, technical and functional properties of metallic surfaces by reducing their roughness. This process is based on anodic dissolution of the workpiece through an oxidation reaction. For many years, cyanide-based electrolytes were used to electropolish precious metals like gold and its alloys. The need for safer working conditions encouraged the replacement of cyanide by other complexing agents, mainly thiourea. However, the latter is also harmful. Therefore, the aim of this work is to electropolish pure gold and 18k jewelry gold alloys (yellow, rose, red and gray) in a cyanide-free electrolyte, to evaluate the electrochemical behavior and the influence of different parameters. For this purpose, a previously reported solution based on hydrochloric acid and glycerol was used. In the first part of the study, the influence of chloride concentration on pure gold EP was determined by electrochemical techniques and surface properties analysis. The effects of adding ethanol to electrolyte composition and of variating rotation speed were also evaluated. The best results were obtained for a HCl 50% vol. - Glycerol 25 % vol. - Ethanol 25 % vol. electrolyte at a rotation speed of 1000 rpm. In the second part of the study, this solution was used to electropolish 18 K gold alloys. Silver-containing alloys were not uniformly polished due to the formation of an AgCl film on the surface that partially masks the substrates.

Strategy, Design, and Fabrication of Electrochemical Biosensors: A Tutorial.

Advanced healthcare requires novel technologies capable of real-time sensing to monitor acute and long-term health. The challenge relies on converting a real-time quantitative biological and chemical signal into a desired measurable output. Given the success in detecting glucose and the commercialization of glucometers, electrochemical biosensors continue to be a mainstay of academic and industrial research activities. Despite the wealth of literature on electrochemical biosensors, reports are often specific to a particular application (e.g., pathogens, cancer markers, glucose, etc.), and most fail to convey the underlying strategy and design, and if it is transferable to detection of a different analyte. Here we present a tutorial review for those entering this research area that summarizes the basic electrochemical techniques utilized as well as discusses the designs and optimization strategies employed to improve sensitivity and maximize signal output.

Recent advances in graphene oxide-based electrochemical sensors

Graphene oxide-based nanomaterials are garnering significant attention from various fields due to their unique physical and chemical properties, which make them attractive for myriad applications. This feature article stems from Dr. Aicheng Chen’s Lecture for the 2023 Ricardo Aroca Award of the Canadian Society for Chemistry and focuses primarily on the synthesis and applications of graphene oxide-based nanomaterials for electrochemical sensing. Graphene oxide (GO), reduced graphene oxide, and functionalized and doped GO-based nanomaterials are emerging as promising enablers of broad applications in electrochemical sensors. This is due to their distinctive functional groups and novel properties, which include high electrical conductivities, large surface areas, and enhanced catalytic activities. Several strategies for the synthesis of these nanomaterials are described in this feature article, encompassing the modified Hummers method, electrochemical, thermal, and microwave reactor methods. The characterization of these GO-based nanomaterials is highlighted, employing techniques such as scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman, and X-ray photoelectron spectroscopy to study their morphologies, structures, and chemical compositions. The development of GO-based electrochemical sensors and their pharmaceutical, medical, environmental, and food safety applications are discussed. Further, the effects of these GO-based nanomaterials and different electrochemical techniques (e.g., cyclic voltammetry, square wave voltammetry, linear sweep voltammetry, and differential pulse voltammetry) on the performance of various electrochemical sensors are addressed.

High‐Power‐Density Hybrid Acid/Alkali Zinc–Air Battery for High‐Efficiency Desalination

AbstractThe electrochemical desalination technique is recognized as a promising solution to alleviate freshwater shortages, challenges yet persists in achieving optimal energy efficiency and cost‐effectiveness. Herein, a hybrid acid/alkali zinc air desalination battery (hAA‐ZADB) capable of concurrent desalination and high‐power density is reported. To improve cathodic efficiency and cost‐effectiveness, an electrocatalyst with dual atomic Fe–Mn sites on porous dodecahedral carbon (Mn‐Fe/p‐DC) is fabricated through a simple direct pyrolysis strategy for oxygen reduction reaction (ORR). The Mn–Fe/p‐DC‐900 electrocatalyst demonstrates exceptional electrocatalytic activity (E1/2 = 0.8 V in 0.5 m H2SO4) for ORR. This innovative hybrid acid/alkali cell design, coupled with advanced electrocatalysts, empowers the hAA‐ZADB system to achieve outstanding performance benchmarks with a high open circuit voltage of 2.22 V, an impressive power density of 375 mW cm−2, and notably elevated energy output of 106.9 kJ mol−1 even at a current density of 100 mA cm−2 during desalination. Distinguishing this work is its additional functionality, evident in a rapid salt removal rate of 3.64 mg cm−2 min−1 during desalination, achieving an impressive 88.67% removal of 0.6 M NaCl. This study highlights the promising potential of employing metallic air batteries for a self‐powered desalination technique applicable to specific scenarios.

Corrosion Induced on Aluminum by Biodiesel Components in Non-Oxygen Environments.

Biodiesel is a mixture of saturated and unsaturated Fatty Acid Methyl Esters (FAMEs) whose composition affects the corrosion behavior of metal containers during storage. This study examines the effect of the C=C bond present in selected FAMEs (Methyl Stearate, Methyl Oleate, and Methyl Linoleate) in aluminum corrosion in the absence of oxygen. First, mass loss assays were carried out at 100, 200, and 280 °C for 1000 h using pure Methyl Stearate (MS), 5% Methyl Oleate in Methyl Stearate (MS-5% MO), and 5% Methyl Linoleate in Methyl Stearate (MS-5% ML). Next, chemical changes in FAMEs were studied using FTIR, TGA, and GC/MS. SEM/EDS analysis allowed us to inspect the aluminum surfaces and their chemical characterization. We estimated higher corrosion rates for MS assays than those of unsaturated methyl ester mixtures. In a separate set of experiments, we used electrochemical techniques (potentiodynamic polarization, linear polarization resistance, and electrochemical impedance spectroscopy) to investigate aluminum corrosion induced by thermal-degraded products from FAMEs at 100, 200, and 280 °C for 300 h able to dissolve in aqueous extracts. These electrochemical experiments revealed that the products in the aqueous extracts from the unsaturated methyl ester mixture form a passive layer on the Al surface thicker than pure MS at the corresponding degradation temperatures.