Higher Corrosion Rate Research Articles

Effect of strontium addition, cooling rate and T6 heat treatment on the corrosion behaviour of Al-20%Mg2Si composite

Mg2Si reinforced AMCs are considered a promising structural material as the in-situ formation of Mg2Si particle offers excellent matrix/reinforcement stability that allow effective load transfer. Addition of Strontium (Sr) could minimize sharp edges shape of Mg2Si particles in as-cast condition improving the mechanical properties. Incorporating Strontium (Sr) can reduce the sharp-edged morphology of Mg2Si particles in their initial cast state, leading to enhanced mechanical properties. However, existing research on Mg2Si reinforced AMCs does not show sufficient data on corrosion behavior. This research aims to investigate the microstructural changes and corrosion performance of as-cast Al-20 %Mg2Si under various influencing factors including varying solidification rate, addition of Sr and post- fabrication metalwork such as T6 heat treatment. The composite materials were prepared using in-situ casting procedure with high purity of the elements. Microstructure characterization was carried out by optical microscopy, in which the primary Mg2Si particle sizes were measured by image analyser. Corrosion behaviour of the fabricated composite was analysed using electrochemical test. Optical microscopic images reveals that the primary Mg2Si was refined and transform to polyhedron upon addition of 0.01w.t. % Sr into Al-20 %Mg2Si and resulted in improved corrosion resistance upon immersion testing and potentiodynamic polarization testing in 3.5 % NaCl with decreasing the Icorr from 0.80 to 0.41 μA/cm2.The Al-20 %Mg2Si which solidified under lower cooling rate have coarser dendritic primary Mg2Si which results in higher corrosion rate (Icorr = 4.98 μA/cm2). T6 heat treatment transformed the primary Mg2Si to fine dendrites with spherical secondary Mg2Si phase and consequently enhancing the corrosion resistance by decreasing the Icorr to 2.93 μA/cm2.

Corrosion Susceptibility of Blued Steel Reinforcement in Concrete by Electrochemical Impedance Spectroscopy

The main aim of this study is to quantify the rate of corrosion in reinforced steel bars embedded within concrete structures exposed to a simulated high-chloride marine environment. This involved selecting specific frequencies that corresponded to the solution resistance and charge transfer resistance, enabling faster measurements. A total of five cement mortar specimens were meticulously prepared for the investigation. The study focused on assessing the impact of variations in bluing temperature on corrosion minimization. Bluing was carried out at 450, 550, 650, and 750oC, and then immersing the specimens in a 3 wt.% NaCl solution for 21 days. Frequent tests, just after immersion, 7,14-, and 21-days immersions. Measurements through alternative current (AC) impedance were conducted across a frequency spectrum ranging from 100kHz to 10MHz. The results showed a significant decrease in the corrosion rate for specimens blued at 750, which was attributed to the development of thicker protective layers on the rebar. Higher corrosion rates were observed for bluing at lower temperatures.

The Effect of electrolyte concentration and temperature at electroplating with copper on the plate thickness and corrosion rate of plated gray cast iron

This study aims to determine the effect of variations in electrolyte solution concentration and copper electroplating temperature on gray cast iron to achieve the desired copper layer thickness and reduce the corrosion rate of gray cast iron impeller pumps. A total of 30 test specimens made from gray cast iron were used, with dimensions conforming to the ASTM G31-72 standard for corrosion rate testing. The specimens were coated with copper electroplating using three different solutions: solution 1 (195 g/L copper sulfate, 45 g/L sulfuric acid), solution 2 (205 g/L copper sulfate, 50 g/L sulfuric acid), and solution 3 (215 g/L copper sulfate, 55 g/L sulfuric acid). Each solution was used with dipping temperatures of 30 – 34 °C, 40 – 44 °C, and 50 – 54 °C. After being coated with copper, the layer thickness was measured using a digital coating thickness gauge (F&NF type). The corrosion rate was then tested using the weight loss method, following the ASTM G31-72 standard, by immersing the specimens in seawater for 240 hours. The test results showed that the highest average thickness was achieved with solution 3 and a plating temperature of 50 – 54 °C, measuring 27.46 μm. The lowest average thickness was with solution 1 and a plating temperature of 30 – 34 °C, measuring 26.23 μm. The lowest corrosion rate was observed with solution 3 and a plating temperature of 50 – 54 °C, at 0.0041 mmpy, whereas the highest corrosion rate was found with solution 1 and a plating temperature of 30 – 34 °C, at 0.0079 mmpy. For comparison, the average corrosion rate of uncoated specimens was 2.2947 mmpy.

Friction stir processing of AZ91 hybrid composites with exfoliated multi-layered graphene: A Taguchi-Grey relational analysis

Friction Stir Processing (FSP) involves the use of Silicon Carbide (SiC) and Graphite (Gr) nanoparticles as reinforcements to enhance the properties of AZ91 Mg alloy composites. The relationship between FSP processing parameters and surface properties of Mg alloy composites with SiC and Gr nanoparticles is poorly understood. The present study addresses this and investigates the impact of SiC and Gr volume percentages (%vol), tool traverse speed (TTS), and tool rotational speed (TRS) on the corrosion behavior and microhardness of AZ91 alloy composites. FSP turns graphite into layered graphene, making it more corrosion-resistant and stronger through various strengthening mechanisms. Taguchi optimization yielded optimal settings in runs H7 (1500 rpm-20 mm/min-13 %vol) and H8 (1500 rpm-40 mm/min-7 %vol) for high microhardness and low corrosion rate. Conversely, runs H1 (500 rpm-20 mm/min-7 %vol) and H3 (500 rpm-60 mm/min-13 %vol) resulted in reduced microhardness and increased corrosion rate. Integrating Taguchi and Grey Relational Analysis (GRA) optimized the multi-objective enhancement of microhardness and corrosion resistance, achieving 3rd-level values for TRS, TTS, and %vol. Notably, the reinforcement percentage, followed by TRS and TTS, simultaneously improved these responses.

Corrosion behavior of SiC coated HX with MoSi2 interlayer to be utilized in iodine–sulfur cycle for hydrogen production

In this era, renewable energy technologies are suitable to meet the challenges of fossil fuel depletion and global warming. Thus, hydrogen is gaining attention as an alternative clean energy carrier that can be produced from various methods, one of them is the iodine-sulfur (I–S) cycle which is a thermochemical process. The I–S cycle requires a material that can withstand an extremely corrosive environment at high temperatures. Immersion tests were conducted on bare superalloy Hastelloy X (HX), MoSi2, and SiC–MoSi2 coated HX, deposited in physical vapor deposition (PVD) to evaluate their corrosion resistance. Bare HX exhibited a high corrosion rate of 208.1 mm yr−1 when exposed to 98 wt% sulfuric acid at 300 °C. In contrast, HX with MoSi2 coating showed a much lower corrosion rate of 23.5 mm yr−1, and HX with SiC–MoSi2 coating demonstrated the lowest corrosion rate at 6.5 mm yr−1 under the same conditions. The coated samples were analyzed via FESEM before and after corrosion testing. The FESEM images reveal the formation of coalescent particles on the surface of the coating. The elemental analysis illustrates an increased concentration of silicon and oxygen in the corroded samples. Elemental mapping of these samples show a uniform distribution of elements over the sample. These findings contribute not only to materials science understanding but also to practical applications in hydrogen production via the I–S cycle, where corrosion-resistant materials are critical.

Effect of microstructure and texture of AZ31 magnesium alloy substrate on nucleation and growth of biomimetic calcium phosphate coating

Magnesium has a special place in biomedical applications due to its biocompatibility and biodegradability properties. The high corrosion rate of magnesium in the body environment requires the use of a biocompatible coating such as calcium phosphate. In this paper, the effect of microstructure and crystalline texture of AZ31 magnesium alloy substrate on the morphology of calcium phosphate coating and the corrosion behavior of the material was investigated. The results imply that apatite crystals can form and grow on the surfaces of the biomimetic coating after soaking in simulated body fluid (SBF). The corrosion behavior of the material was investigated using an electrochemical polarization test in SBF solution for 3 days. The results showed that changes in the microstructure and crystalline texture of the substrate changed the coating morphology so that the growth of calcium phosphate changed from a rod-shaped with a diameter of 100–150 nm to a blade-shaped with a thickness of 20–50 nm. An increase in the corrosion resistance of the coated specimens with the corrosion rate of 0.65 mm/year was obtained compared to the uncoated specimen with the corrosion rate of 2.62 mm/year.

3D reconstruction and interconnectivity quantification of the nano-porosity in the oxide layer of corroded Zr alloys

Nano-porosity development in thermally grown oxides plays a significant role in oxidation kinetics as nanopores may provide pathways for oxidizing species. As an example, Zr alloys are the most commonly used cladding materials in pressurized and boiling water nuclear reactors and are known to develop significant oxide nano-porosity. Corrosion results in the formation of an oxide layer containing nanopores while still being protective. It is still under debate whether the nanopores can provide fast diffusion paths for the oxidizing and hydriding species, and possibly accelerate corrosion. In the current study, we precisely quantify the nano-porosity in different regions of the oxide layer using a machine-learning-based method reported in a previous publication. In addition, the entire oxide layer depth and each pore within the layer are imaged, and a TEM-based 3D tomographic reconstruction is obtained. We further investigate the interconnectivity of the pores and the shortest path through the pores as functions of oxide depth, exposure time, and corrosion rate. Results demonstrate that interconnectivity is highest in the proximity of the W/O interface and gradually decreases towards the M/O interface. Specifically, higher temperatures, longer exposure times, and higher corrosion rates are correlated to increased interconnectivity among pores. This work provides essential evidence that pores in the near water/oxide interface region can provide paths for oxidizing species.

Effects of Electrolyte Composition on the Electrochemical Properties of an Aluminum Alloy Electrode for Al-Air Batteries

Aluminum-air batteries that use alkaline electrolytes have the advantage of a high operating voltage, but the aluminum alloy electrodes experience high corrosion rates. To address this issue, a promising solution is proposed, which involves mixing neutral electrolytes with the alkaline electrolyte. In this study, we analyzed the electrochemical characteristics of aluminum alloy electrodes in electrolyte solutions containing varying concentrations of NaCl added to a 1 M NaOH alkaline electrolyte solution to understand the effect of neutral electrolytes on the discharge performance of aluminum-air batteries. The results obtained from potentiodynamic polarization tests, electrochemical impedance spectroscopy, three-electrode discharge tests, and open-circuit potential tests confirmed that the corrosion reaction and discharge voltage of aluminum alloy electrodes are influenced by the concentration of NaCl in the alkaline electrolyte solution. The corrosion rates and discharge voltages decreased as the concentration of neutral electrolyte increased, indicating that the electrochemical properties of aluminum-air batteries are highly dependent on the electrolyte composition.

Experimental investigation on corroded stud connectors under strain rates effect

Shear connectors have been widely used in bridge and steel engineering to transfer the dynamic load effect between the neighbour elements. The shear connectors are exposed to moist air, and corrosion is unavoidable. An experimental investigation was conducted on the shear behaviour of corroded stud connectors with growing strain rates to study the effects of corrosion and strain rate on the shear capacity. Four series of specimens with different corrosion rates were tested. The electronic accelerating method was used to fabricate corroded studs with target corrosion rates. The corroded studs were loaded with five loading speeds to investigate the strain rate effects on the shear capacity. The fractured surfaces show that the corroded stud connectors have more tensile deformation in the loading process and a higher strain rate enhances the shear fracture other than tensile fracture. Based on the statistics of load-slip curves, we found that stud connectors with higher corrosion rates are more sensitive to dynamic load. However, corrosion cannot decrease the ultimate shear stress based on the minimum cross-section. For all corrosion rates, the relative ultimate shear strength grows with strain rate with a fixed growth rate.

Synergetic effects of cryo-FSP on microstructural, mechanical and corrosion behavior of stir cast AA5083-2 wt% SiC nanocomposite

In recent past, a significant research attention has been given to the study of nanosize ceramic particles reinforced aluminium alloy composites due to its excellent mechanical and surface properties compared to unreinforced counterpart. Hence, the major aim of the present study is to investigate the effects of cryocooling friction stir processing (cryo-FSP) on microstructural evolution, and its effects on mechanical properties & corrosion behavior of a stir-cast 2 wt% nanosize SiC (n-SiC) particles reinforced AA5083 nanocomposite in comparison to the room temperature (RT) FSPed and as cast counterparts. The cryo-FSP was performed successfully using optimized process parameters of 1400 rpm and 40 mm/min traverse speed using a specially designed cryo-FSP setup extracting deformation heat efficiently by a flowing mixture of LN2 and methanol (−30 °C). Evolution of a finer equiaxed grain structure (∼2 μm) with a homogeneous distribution of n-SiC particles and precipitate phases is confirmed (through SEM-EBSD and STEM/TEM analysis) in the cryo-FSPed composite compared to RT-FSPed sample (∼4 μm). The cryo-FSPed sample exhibited a superior yield strength (i.e., YS = 230 ± 3 MPa) compared to the RT-FSPed sample (i.e., YS = 197 ± 4 MPa) with a reasonably good ductility for both (i.e., 14 %). The improved YS is attributed mainly to the grain boundary strengthening due to extra grain refinement induced by cryo-FSP and dispersion strengthening via second phase particles. Different strengthening mechanisms' analyses established a good correlation between the theoretical YS and experimentally obtained tensile YS. Fractography analysis corroborated well with the tensile properties of the corresponding samples. Compared to the interdendritic cast structure, both the FSPed samples exhibited a superior corrosion resistance due to an improved surface characteristic developed in the dynamically recrystallized matrix with uniform dispersion of second phase particles. However, due to more grain boundary active phenomenon and higher misorientation angles, a bit higher corrosion rate could be observed in the fine-grained cryo-FSPed sample compared to the RT-FSPed composite.

Chemical composition optimization of Al2O3-TiO2 composite coatings for enhanced wear and corrosion resistance

This study aimed to optimize the chemical composition of wear- and corrosion-resistant Al2O3-TiO2 composite coatings. 2-layered and 4-layered Al2O3-TiO2 coatings were fabricated on a 316L substrate with various Al2O3 and TiO2 content (20 %, 35 %, 50 %, 65 %, and 80 % in weight) at 900 °C by sol-gel technique. Wear properties were measured by dry sliding tests against an Al2O3 ball, and corrosion behavior was determined through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. All Al2O3-TiO2 composite coatings consisted of α-Al2O3 and rutile phases, regardless of the chemical composition. Increasing TiO2 content significantly increased coating thickness at the same number of layers. The 2-layered configurations resulted in lower wear rates in low-TiO2 compositions, whereas the 4-layered configurations provided higher wear resistance in high TiO2-containing coatings. The high Al2O3 concentration caused extremely high corrosion rates compared to those consisting of high TiO2. Wear and corrosion losses were decreased with increasing TiO2 content due to its nanosized structure, allowing well-adhered, continuous, and less porous coating morphology. The maximum improvement in wear and corrosion resistance was obtained in the 4-layered 65 % TiO2-containing composite coating.

Corrosion analysis of welded Nb-1% Zr-0.1% C alloy in lead-bismuth eutectic solution

This study aims at checking the suitability of Nb-1% Zr-0.1% C alloy as coolant channel for carrying molten lead-bismuth eutectic (LBE). Molten LBE is used to carry heat from the reactors to heat exchangers in the compact high temperature reactors. Corrosion properties of the base metal (BM), heat-affected zone (HAZ) and fusion zone (FZ) of the weld of niobium alloy were compared at the temperature of 1050 °C in LBE solution in open-air condition. The presence of lead and bismuth at grain-boundary and triple junctions of the grain boundaries is evitable in both the BM and FZ, and the material loss can be attributed to oxidation corrosion. Nb2O5 and NbO2 being brittle and permeable oxides of niobium did not inherit the characteristics of hindering further oxidation-corrosion at elevated temperature. The corrosion rates of FZ, HAZ and BM were observed to be equal to 24.16 mm/year, 20.83 mm/y and 27.80 mm/y, respectively, and this difference occurred mainly due to the formation of nitrides of zirconium (ZrN) and carbides of zirconium (ZrC) and niobium (NbC). ZrO2 could be confirmed by the micro-hardness profile, which appeared to be flat throughout the FZ and BM. The formation of these carbide and nitride phases was confirmed through XPS and XRD analyses. The differences of surface roughness values expressed in root mean square (Sq.) values, determined before and after the corrosion, were found to be equal to 0.267 and 0.230 for the base metal and weld zone, respectively. It signifies that FZ was more corrosion-resistant than BM. It is not recommended to use this alloy in open-air condition for the coolant channels, due to the high corrosion rate in the BM, FZ and HAZ, which leads to material loss beyond the acceptable limit.

Design of self-healing PEO-based protective layers containing in-situ grown LDH loaded with inhibitor on the MA8 magnesium alloy

The high corrosion rate of magnesium and its alloys in chloride-containing solution significantly reduces the potential of this material for diverse applications. Therefore, the formation of a smart protective coating was achieved in this work to prevent degradation of the MA8 magnesium alloy. A porous ceramic-like matrix was obtained on the material by plasma electrolytic oxidation (PEO). Further surface functionalization was performed using layered double hydroxides (LDH) served as nanocontainers for the corrosion inhibitor. Several methods of LDH intercalation with benzotriazole (BTA) were proposed. The composition and morphology of the formed coating were studied using SEM-EDX analysis, XRD, XPS, and Raman microspectroscopy. The corrosion behavior of the coated samples was evaluated using electrochemical impedance spectroscopy and potentiodynamic polarization. The corrosion rate was estimated using volumetry and gravimetry methods. The formed composite coating provides the Mg alloy with the lowest corrosion activity (|Z|f = 0.1 Hz = 8.48·105 Ω·cm2, Ic = 1.4·10−8 A/cm2, PH = 0.21 mm/year) and improves the protective properties of the PEO-coated sample (|Z|f = 0.1 Hz = 8.37·103 Ω·cm2, Ic = 4.1·10−7 A/cm2, PH = 0.31 mm/year). The realization of the self-healing effect of the inhibitor-containing LDH/PEO-coated system was studied using localized electrochemical methods (SVET and SIET) with two artificial defects on the surface. A mechanism involving three stages for the active corrosion protection of the alloy was proposed. These findings contribute to the follow-up work of developing modified LDH/PEO-based structures that promote the Mg alloy with high corrosion resistance, superior electrochemical performance for applications in various fields of industry and medicine.

Modeling of water film generation in up-inclined low liquid loading natural gas pipeline elbows and its implication on internal corrosion occurrence

Condensed water often accompanies natural gas in the transmission process. The water forms thin film when parameters such as temperature and pressure change. This accelerates pipeline corrosion and makes the pipeline wall become thinner. Severe corrosion can lead to pipeline rupture, endangering the pipeline safety and leading to economic losses. The distribution of a water film plays a significant role in the corrosion process, So the work of predicting the distribution of a water film and flow characteristics becomes a key priority when analyzing corrosion in a pipe elbow. In this study, Eulerian, RNG (re-normalization group) k-ε and Eulerian wall film models are employed to establish a pipe elbow model that predicts the locations of water phase accumulation. Combining with a limiting diffusion current density, this model can be used to predict the potential corrosion locations and extent. The proposed model is validated by using velocity and water film distributions and it shows substantial agreement with previous models and results in the literature. From the simulation outcomes, a water film is mainly distributed at bottom while the thickness of the water film increases significantly at the pipe elbow. At the elbow bottom the inlet gas velocity increases, this shifts the high corrosion rate zone from elbow rear to front. Corrosion at the elbow front is more serious regardless of the changes in the inlet liquid velocity, elbow angle or water holdup. Meanwhile, when the gas velocity or elbow angle is large, the water film gradually spreads from the elbow bottom to the side and top parts which are in a high corrosion rate zone and more dangerous. Therefore, weak positions where pipeline elbow corrosion failures may occur can be quickly and conveniently computed and determined by the proposed model.

Study of Atomic Layer Deposition Nano-Oxide Films on Corrosion Protection of Al-SiC Composites.

In recent years, aluminum matrix composites (AMCs) have attracted attention due to their promising properties. However, the presence of ceramic particles in the aluminum matrix renders AMCs a high corrosion rate and makes it challenging to use traditional corrosion protection methods. In this study, atomic layer deposition (ALD) techniques were used to deposit HfO2, ZrO2, TiO2, and Al2O3 thin films on AMC reinforced with 20 vol.% SiC particles. Our results indicate that the presence of micro-cracks between the Al matrix and SiC particles leads to severe micro-crack-induced corrosion in Al-SiC composites. The ALD-deposited films effectively enhance the corrosion resistance of these composites by mitigating this micro-crack-induced corrosion. Among these four atomic-layer deposited films, the HfO2 film exhibits the most effective reduction in the corrosion current density of Al-SiC composites in a 1.5 wt% NaCl solution from 1.27 × 10-6 A/cm2 to 5.89 × 10-11 A/cm2. The electrochemical impedance spectroscopy (EIS) investigation shows that HfO2 deposited on Al-SiC composites has the largest Rp value of 2.0 × 1016. The HfO2 film on Al-SiC composites also exhibits effective inhibition of pitting corrosion, remaining at grade 10 even after 96 h of a salt spray test.

Exploring the effects of self-lubricating MoS2 in magnesium metal matrix composite: Investigation on wear, corrosion, and mechanical properties

The prime focus of this experimentation is to develop a lightweight self-lubricating surface composite with superior wear resistance. This article inquires into the consequences of Molybdenum di Sulphide (MoS2) for its 2, 4, and 6 vol% dispersion on magnesium surface by applying friction stir processing (FSP). The prepared composites were analysed for their microstructure, mechanical, and wear characteristics. The observation of the microstructure reveals the smaller grain size as a result crystallization process occurring during FSP and the uniform dispersion of reinforced particles. The surface composite shows a growing tendency in its hardness which can be assumed as the outcome of the reduced grain size and reinforcement dispersion. On the other hand, the developed composite exhibited lower tensile characteristics than the base matrix. The composite shows constructive enhancement in wear resistance with the increase in the vol% of MoS2 particles whereas the increase in load increases the wear rate. The value of the corrosion rate is decreased up to 60 % with 2 % reinforcement addition whereas further addition resulted in a higher corrosion rate.

Corrosion processes at the GGG40 steel–bentonite interface

Abstract. Spheroidal graphite cast iron (GGG40/0.7040) is used as an overpack material for the reference Pollux 10 container, a prototype for the storage of fuel elements in different types of host rocks (Hassel et al., 2019). Corrosion processes are expected to be triggered after some decades, as the contacting bentonite, which is used as fill material, becomes soggy because of the decay of the fission heat generation and the intrusion of pore water as the temperature decreases under the condensation point (King and Padovani, 2011). The distinct electrochemical reactivities of the graphite, ferrite, pearlite, and cementite phases exposed by this material introduce local galvanic elements which influence the topographic evolution of degradation (Spence, 2005). The aim of this work is to elucidate the corrosion dynamics of active and passive areas by following the chemical evolution at the interface of cast iron–bentonite during the first stages after its saturation with geological pore water. Polarization experiments and electrochemical impedance spectroscopy were applied to monitor the corrosion process in a bentonite cell, where GGG40 steel is put into contact with a light compacted Wyoming bentonite slurry 1 : 10 w/w of bentonite to Opalinus Clay pore water (Fig. 1a). Experiments were performed at 30 and 50 ∘C for longer than 3 months. The surface chemistry and morphological changes were investigated by local XPS, SEM-EDX, and TEM (X-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive X-ray, and transmission electron microscopy, respectively). These experiments were complemented with corrosion studies performed in pore water under different temperatures, hydrostatic pressures, and pH and with and without dissolved oxygen. The polarization curves indicate a constant corrosion rate of GGG40 steel in saturated bentonite after 30 d. SEM micrographs reveal a preferential dissolution of the ferrite phase around the graphite spheres and the ferrite lamellae contained in the pearlitic eutectic. A strong localized dissolution of ferrite along the graphite boundary can be also observed; this is a typical case of crevice corrosion caused by the unhindered access of oxygen to the graphitic cathodic areas (Wang et al., 2022). The surface chemical studies indicate the accumulation of iron oxides, which can be attributed to a hydrated magnetite and the formation of iron silicates (Zhang et al., 2021). TEM pictures of a cross-sectional lamella, including part of graphite sphere, show the formation of a silicate film covering the corroding surface with an irregular adherence (Fig. 1b). The initial relatively high corrosion rate of GGG40 steel can be attributed to the dissolution of the more active ferrite with the formation of poorly passivating iron oxides and silicates. The system is driven towards the dissolution of pearlite at more positive electrode potentials. The bentonite slurry limits the access of oxygen to the graphitic cathodic areas, reducing the corrosion rate by 1 order of magnitude in comparison with that in aerated pore water. A surface enrichment of cementite with superior passive properties and the neutralization of the local elements by approaching the corrosion potential of graphite (Kadowaki et al., 2019) is also expected. Thus, the consumption of oxygen and the transport limitation of the cathodic reaction by bentonite forecast a considerable reduction in the degradation of the container after a sacrificial corrosion phase.

Zein-Bioactive Glass nanocomposite Coating on Magnesium Alloy Substrate for Orthopedic Applications

Excellent mechanical strength and biodegradable characteristics of magnesium alloys have sparked considerable interest in orthopedic applications. The utilization of magnesium alloys in orthopedic applications has been restricted due to their brittleness caused by high corrosion rate in biological environments. One of the best techniques for increasing corrosion resistance of these alloys is surface coating. For the first time, the present work aims to dip-coat zein-bioactive glass (BG) nanocomposite on AZ31B magnesium alloy. The alloy surface was also coated by native zein as a control coating. BG nanoparticles required for zein and BG (zein_BG) composite were synthesized by a bio-inspired method using cetyltrimethylammonium bromide (CTAB) as a template. The formation of BG particles was affirmed by FTIR showing characteristic Si-O-Si and Si-O– peaks. Nano-size of BG particles with an average diameter of 6.67 ± 0.06 nm was reported by TEM. SEM micrographs revealed successful deposition of zein and zein_BG coatings on the magnesium alloy surfaces. High-resolution XPS analysis on zein_BG-coated Mg alloy immersed in HBSS revealed the corrosion deposition of Mg(OH)2, MgHPO4.H2O, CaHPO4.H2O, SiO2, MgCO3, and CaCO3 on the substrate surface. More than twofold wettability, 95% adhesion strength and 14-fold increase in surface roughness were reported for zein_BG-coated magnesium alloy compared to the bare surface. Measurements of weight loss in zein and zein_BG-coated alloy substrates in Hanks Balanced Salt Solution (HBSS) for 10 d at 37°C showed a drastic decrease in weight loss of substrates after coating. As a result, zein_BG-coated substrate was observed to possess the maximum protective efficacy (95.99%) against corrosion. Interestingly, electrochemical measurements revealed a vast decrease in corrosion current density (2.41 E−6 A.cm−2) of zein_BG-coated substrate compared to the uncoated substrate (3.04 E−4 A.cm−2). Electrochemical impedance spectra (EIS) confirmed capacitive behavior of zein_BG-coated alloy substrate. These findings demonstrated that simple zein_BG composite dip coating was a successful corrosion-resistant implant coating on magnesium alloy surface for orthopedic applications.

Application of organo-tin based complexes in transesterification reaction for biodiesel production- A review

The primary energy source utilized worldwide is derived from fossil fuels. Among all fields, the transportation sector accounts 54% of total energy consumption. The overuse and scarcity of fossil fuels demand the researchers to seek out a sustainable energy source. Among various renewable resources like solar, water, wind etc., biofuel is also an alternative pollution free energy source. Biodiesel are the fatty acid of methyl esters obtained from animal fat or vegetable oil. To achieve a similar viscosity as petrodiesel, the raw oil or fat is trans esterified to biodiesel. Transesterification is a well-known chemical process wherein the reaction takes place between oil and alcohol, facilitated by the presence of acid or base catalysts. Although the base catalyst has a high conversion rate, soap is generated as a by-product. As a result, acid catalysts are a feasible alternative source for transesterification, but with lower conversion and a high corrosion rate. As traditional acid catalysts, organotin catalysts possess good Lewis acidic character for the production of biodiesel. In this study, we have studied how different substituents on organotin (IV) complexes influence the catalytic activity in biodiesel production as well as in converting by-products of biodiesel into value added products.

Corrosion of Reinforced A630-420H Steel in Direct Contact with NaCl Solution.

The deterioration of reinforced concrete structures in marine environments presents multiple problems due to the premature degradation of reinforced steel. This work aimed to study the corrosion of reinforced A630-420H steel when exposed to a 0.5 M NaCl solution. Although this carbon steel is the most widely used material for reinforced concrete structures in Chile, there is limited research on its resistance to corrosion when in contact with saline solutions. The electrochemical reactions and their roles in the corrosion rate were studied using linear sweep voltammetry, weight loss, scanning electron microscopy, and X-ray diffraction techniques. This analysis is unique as it used the superposition model based on mixed potential theory to determine the electrochemical and corrosion parameters. The outcomes of this study show that A630-420H steel has a higher corrosion rate than those of the other commercial carbon steels studied. This fact can be attributed to the competition between the cathodic oxygen reduction reaction and hydrogen evolution reaction, which also depends on the environmental conditions, exposure time, stabilization of the corrosion products layer, and presence of chloride ions. Additionally, the results under mechanical stress conditions show a brittle fracture of the corrosion product oriented longitudinally in the direction of the bend section, where the presence of pores and cracks were also observed. The corrosion products after corrosion were mainly composed of magnetite and lepidocrocite oxide phases, which is in concordance with the electrochemical results.