Corrosion Current Density Values Research Articles

The Effect of Sulfuric Acid Anodization on the Electrochemical Properties of Aluminum Alloy AlSi10Mg Prepared by Selective Laser Melting

Aluminum alloy, AlSi10Mg, prepared by selective laser melt (SLM) fabrication was anodized in 9.8% sulfuric acid (Type II) at 15 V for a total of 23 min. Experiments were performed to study the potentiostatic anodization process and its effects on the oxide coating morphology, thickness, and electrochemical properties of the alloy. Prior to anodization, the alloy microstructure is composed of aluminum cells encapsulated in a silicon network. Anodizing the abraded and polished AlSi10Mg surface produced a porous oxide layer with a thickness of 5 μm. The oxide coating weight was 698 ± 29 mg/ft2. The oxide coating forms in the aluminum cells that are isolated from one another by the silicon eutectic phase. In electrochemical tests, the anodic and cathodic potentiodynamic polarization currents were suppressed by factors of 15× and 215×, respectively, as compared to the unanodized controls. The data indicate the anodic oxide coating suppresses the cathodic more than the anodic reaction rate. Linear polarization resistance (R p) values increased by 279× after anodization. The corrosion current density values (j corr) decreased by 133× after anodization. Taken together, the electrochemical data indicate the anodic oxide coating (unsealed) increases the corrosion resistance of the SLM alloy by two orders of magnitude.

Study on corrosion characteristics and mechanism of laser powder bed fusion of Mg–Zn–Zr alloy

Laser Powder Bed Fusion (LPBF) presents novel opportunities for the processing and manufacturing of magnesium (Mg) alloys. However, Mg alloys consistently face challenges with poor corrosion resistance. Consequently, it becomes imperative to delve into the corrosion behavior and mechanisms of Mg alloys formed through LPBF. This paper investigated the electrochemical corrosion behavior, the distribution of corrosion products, and the corrosion mechanism of LPBF ZK60 Mg alloy. The results show that the corrosion current density (Icorr) value of LPBF ZK60 Mg alloy is 3.76 μA∙cm−2. The hydrogen evolution in Hank's solution steadily increases with immersion time and reaches a stable state after 24 h. The corrosion rates calculated based on hydrogen evolution and weight loss are 2.1 mm/y and 2.4 mm/y, respectively. The corrosion resistance of LPBF ZK60 Mg alloy is predominantly affected by three factors: uneven microstructure, internal crack defects, and precipitate phases. The melt pool boundary is identified as a corrosion-vulnerable zone, which extends into the columnar crystal zone after corrosion. Crevice corrosion occurs at microcracks, and the precipitate phases within the grains and matrix induces galvanic corrosion. These findings suggest that the corrosion resistance of LPBF ZK60 Mg alloy may be regulated through targeted measures, such as eliminating cracks, achieving microstructure homogenization, and controlling the precipitate phases (including quantity, composition, and distribution).

Metronidazole mediated potassium iodide as high-performance deterioration retardant for mild steel in an acidic media

As corrosion scientists all over the world struggle to discover new metal deterioration retardant which can close the performance gap created by the legislative banned toxic inhibitors, we present in this research work an azole based drug and its mediation performance with a synergistic agent as ‘green’ metal degradation retardant. The anti-deterioration performance of the azole-based drug, metronidazole (MTN) and its different concentration combinations with potassium iodide (KI) were examined with materials degradation analysis tools such as functional group, nanoindentation, weight loss and electrochemical techniques. MTN alone performed well as an anti-deterioration retardant exhibiting retardation efficiencies (η%) in the range between 73 to 85% at different temperatures and analytical techniques. However, with the introduction of KI, an escalation in (η%) was obtained in the region of 92 to 97%. In addition, improved polarization resistance of chemical retardants on substrate cross sections was achieved, manifested by the resultant elevation in values of polarization resistances (Rp) from 1.54 Ω.cm2 of the blank to 30.61 Ω.cm2 of the optimum concentration, charge transfer resistances, (Rct) improved likewise from 6.03 to 144.07 Ω.cm2 and depreciation in the values of corrosion current densities (Icorr) from 8863.86 to 228.89 µA.cm2. This work describes a method of improving the metal deterioration retardation potentials of an azole compound, bringing out new knowledge on the degradation inhibition properties of MTN and the adsorption process taking place between the substrate and the belligerent environment. We hope it opens the door for the utilization of a mixture of MTN and KI as additives for the formulation of sealants, paints, conversion coatings and primers for ferrous alloys. It also encourages more investigations, to find additives such as suitable activating and accelerating agents for MTN to make It exercise the same or more anti-corrosion potents possessed by the banned hexavalent chromium (vi), benzothiazoles (BTA) and others. Some of these potents are the ability of MTN to function at a wide region of pH and in the moment of coating failure, what can enable an azole-containing coating, to undergo some chemical activities and still maintain the substrate surface integrity?

Effect of titanium on the structural, mechanical and surface properties of CoCrFeMnNiTix high entropy alloy fabricated by selective laser melting

In this study, the effect of titanium (Ti) on the microstructure, mechanical properties, wear resistance and corrosion behavior of CoCrFeMnNi high-entropy alloy (HEA) was examined. The selective laser melting (SLM) method was used to produce HEAs without Ti addition (HEA-1) and with Ti additions of 3 and 5 wt% (HEA-2 and HEA-3, respectively). While the HEA-1 sample exhibited a single-phase face-centered cubic (FCC) structure, the HEA-2 and HEA-3 samples exhibited intermetallic phase structures (Sigma and Laves) along with FCC. The addition of Ti and the presence of intermetallic phases in the HEA-2 sample revealed an improvement in mechanical properties without reducing the ductility value of the structure. However, in parallel with the increasing Ti ratio, the formation of more brittle intermetallic phases in the microstructure of the HEA-3 alloy caused a significant increase in strength but a decrease in ductility. Microstructural examinations revealed that all alloys had a cellular/dendritic structure and the relative densities of the samples were above 99%. While the ultimate tensile stress (UTS) of the HEA-1 sample was 548 MPa and the UTS of the HEA-3 alloy was 832.1 MPa, elongation values were obtained as 48% and 2%, respectively. HEA-2 sample exhibited more ideal results with an elongation value of approximately 22% and UTS values of 760.8 MPa. It was observed that the addition of Ti significantly increased the wear resistance in sliding conditions due to the increase in the hardness of the alloy. The highest hardness and lowest wear rate were obtained with HEA-3 coded samples. The HEA-1 sample exhibited the best corrosion rate, with higher corrosion potential (Ecorr) and lower corrosion current density (Icorr) values. The highest corrosion rate was observed in the HEA-3 sample.

Corrosion Behavior of Carbon Steel in LiCl/H2O Mixtures

The corrosion behavior of 1018 carbon steel in LiCl/H2O mixtures has been evaluated by using potentiodynamic polarization curves, electrochemical noise and electrochemical impedance spectroscopy techniques. Two different concentrations of LiCl were employed, namely 35 and 40 wt. %, and the testing temperatures included 25, 35 and 70 °C. It was found that the steel showed a passive zone; the corrosion current density value increased with an increase in the solution temperature and concentration. The pitting potential value decreased with an increase in the testing temperature and the solution concentration. The corrosion process was under charge transfer control. This mechanism was unaltered either by the solution temperature or concentration. The charge transfer resistance value decreased with an increase in both the solution temperature and concentration. A localized, pitting type of corrosion dominated the corrosion morphology at 25 and 35 °C, whereas at 70 °C, the main type of attack was a mixed type of corrosion.

Exploring cinnamon extract’s potential as a green corrosion inhibitor for X65 carbon steel in sulfuric acid: a comprehensive investigation

The effectiveness of cinnamon extract as an environmentally friendly corrosion inhibitor for X65 carbon steel (X65CSt) in a 1 mol/L H2SO4 solution was examined using electrochemical, chemical, and computational techniques. This inhibitor has many advantages, it is safe, environmentally friendly, harmless to human health, and economically feasible. The anticorrosion efficacy rises with rising the concentration of the cinnamon extract and reducing temperature and reaches 95.83% at 450 mg l−1 of cinnamon extract using potentiodynamic polarization. All the investigated methods confirm the anticorrosion ability of cinnamon extract as indicated by the reduced the corrosion current density values and mass loss as well as the greater charge transfer resistance. In addition, the values of the pitting potentials were also transformed in a more noble direction implying the resistance of pitting attack. The polarization technique categorized the cinnamon extract as a mixed inhibitor. The mechanism of inhibition was demonstrated in terms of adsorption of the main components of cinnamon extract onto the surface of X65CSt. of the adsorption of the main components of the cinnamon extract on the surface of the X65CSt and this adsorption is of combined type between both physical and chemical modes, as determined by the computed values of free energy of adsorption, which range between −46.96 and −37.42 kJ. mol−1. The adsorption is exposed to Langmuir isotherm. The four components of cinnamon extract were investigated through density functional theory, Monte Carlo, and Molecular dynamic simulation. The quantum parameters and the adsorption of these components on the Fe(110) reveals that cinnamaldehyde and cinnamic acid inhibitors are more effective as corrosion inhibitors.

Investigating the effect of Zr content on electrochemical and tribological properties of newly developed near β-type Ti-alloys (Ti–25Nb-xZr) for biomedical applications

In order to create alloys with exceptional properties for orthopedic uses, this study focuses on the impact of zirconium (Zr) content on the structural, electrochemical, and tribological qualities of nanostructured Ti–25Nb-xZr [x = 5, 10, 15, 20, 25, and 30 atomic (at.) %] alloys. The structural evolution was investigated using XRD and SEM techniques. The mechanical characteristics of the produced alloys, including Vickers hardness and Young's modulus, were measured. In addition, the corrosion tests were performed using the OCP, EIS, and PD methods in Ringer's solution within the independent pH range at 37 °C. A ball-on-disc tribometer was used to investigate the tribological behavior of the alloys under various loads and wet conditions using the Ringer solution. It has been verified that Zr content (at. %) in the alloys had an impact on their morphologies, structural evolution, and mechanical characteristics. According to the morphological analysis, the particle and crystallite size decreases with increasing Zr content. Young's modulus and Vickers hardness show the same tendency. The EIS data demonstrated that a single passive film formed on the alloy surfaces, and the addition of Zr enhanced the corrosion resistance of the passive films. The polarization curves demonstrate that the alloys had low corrosion current densities and large passive areas without the passive films disintegrating. Likewise, the inclusion of Zr resulted in a reduction in the corrosion and passive current density values. All of these results suggested that the titanium alloys exhibit a more noble electrochemical activity caused by Zr. From the tribological perspective, it was found that the friction coefficient of the alloys reduced with increasing Zr content.

Effect of a Substrate’s Preheating Temperature on the Microstructure and Properties of Ni-Based Alloy Coatings

Laser cladding is a new technology to fabricate a coating on the surface of a metal substrate. The properties on copper substrates are usually not very good due to the high thermal conductivity and reflectivity. The appropriate preheating temperature is helpful to fabricate coatings with good quality and properties, especially for copper substrates. In order to investigate the effect of different preheating temperatures, four coatings with different preheating temperatures (100, 200, 300 and 400 °C) were fabricated via a laser on a copper substrate. The microstructures and properties of four coatings were investigated using SEM, XRD, EDS, a Vickers microhardness meter, a wear tester and an electrochemical workstation. The results show that the elements from Ni-based alloy powder were uniformly distributed among the binding region, which obtained a good metallurgical bonding. The microstructure was mainly composited of cellular, dendrite and plane crystals, and the main reinforced phases were γ (Fe, Ni), Cr0.09Fe0.7Ni0.21, WC and Ni3B. The values of average microhardness of the four coatings were 614.3, 941.6, 668.1 and 663.1 HV0.5, respectively. The wear rates of the four coatings were 9.7, 4.9, 12.5 and 13.3 × 10−5 mm3·N−1·m−1, respectively, which were less than that of the copper substrate (4.3 × 10−3 mm3·N−1·m−1). The decrease in wear rate was due to the existence of the reinforced phases, such as WC, Ni3B, M7C3 (M=Fe, Cr) and Cr0.09Fe0.7Ni0.21. The fine crystals in the coating preheated at 200 °C also improved the wear resistance. Additionally, the minimum values of corrosion current density were 3.26 × 10−5, 2.34 × 10−7, 4.02 × 10−6 and 4.21 × 10−6 mA·mm−2, respectively. It can be seen that the coating preheated at 200 °C had higher microhardness, lower wear rates and better corrosion resistance due to the existence of reinforced phases and fine and uniform crystals.

Corrosion behavior and oxide layer of selective-laser-melted Al-Mg-Sc-Zr alloy in marine atmospheric environment with different Cl−concentration

In this study, the corrosion response of the Al-Mg-Sc-Zr alloy produced by selective laser-melting in marine atmospheric environments with different Cl− concentrations was studied by electrochemical and immersion. Microstructural observations showed the microstructural of Al-Mg- Sc -Zr alloy featured a double grain microstructure, making up a coarse and fine grain area. TEM showed that some white precipitates enriched with Zr and Sc were dispersed in the samples. The potentiodynamic polarization test indicated increasing the Cl− concentration led to a negative shift of corrosion potential and narrowed the potential range of the passive zone, which also caused the increase of corrosion current density value. The electrochemical impedance spectroscopy showed that higher Cl− concentration was greatly detrimental to generating a compact and dense oxide film on the Al-Mg-Sc-Zr alloys, as indicated by decreasing the resistance of the corrosion product layer and charge transfer resistance. The immersion test demonstrated that the samples suffered serious pit corrosion when the Cl− content increased to 1.5 and 3.5 wt%, showing a larger size and more depth of corrosion pits. This study is expected to provide data to determine the reliability of the SLM-manufactured Al-Mg-Sc-Zr alloy in marine atmospheric conditions.

Effect of co on mechanical and electrochemical properties of powder synthesized cellular Ti-Al alloy

ABSTRACT This work describes the effect of Co content on the compressive and electrochemical behaviour of cellular Ti4AlxCo (x = 2%, 4%, 6% and 8 wt%) alloy. Cellular products were prepared through powder metallurgy route by adding 70 v% of ammonium bicarbonate as space holder in Ti4AlxCo powder mixture. Relative density of the final products slightly upsurged due to increment of Co amount and it was found in the range of 0.32–0.35. Microstructure represented the interconnecting pores which will be advantageous to circulate the body fluid, if used as a bone implant. Plastic collapse stress of Ti4Al8Co was about 45% higher than Ti4Al2Co. Also, the elastic modulus was under the range of modulus of natural bone (11 ± 1 GPa). In Tafel plot, value of corrosion current density shifted from 8 μA/cm2 to 15 μA/cm2 by increasing the Co content from 2 wt% to 8 wt% which indicates the hampering of corrosion resistance. Corrosion rate followed the linear relationship with Co content. Best fitted electrochemical circuit showed the double layer oxide formation during corrosion. Micrographs of corroded cellular samples also represent that the surface of material is more prone to corrosion containing higher amount of Co.

Experimental and DFT studies on corrosion behaviors of laser-cladded (FeCoNi)75−xCrxB15Si10 high-entropy alloy coatings

The effects of Cr doping on microstructure evolutions and corrosion behaviors of laser-cladded (FeCoNi)75−xCrxB15Si10 (denoted as Crx hereafter, x = 0, 4, 8, 12, 16 at%) high-entropy alloy coatings (HEACs) were investigated. The composition and shape of the borides in interdendrite regions are modified by adding Cr, alleviating the localized corrosion behavior. The corrosion resistance of the HEACs increases continuously as a function of Cr level in 3.5 wt% NaCl solution. The Cr16 coating outperforms the previously reported Ni alloys, stainless steel, and some other high entropy alloys in terms of corrosion resistance, with the highest pitting potential (0.233 V), the lowest corrosion current density value of 9.9 × 10−9 A/cm2 and passive current density (2.138 ×10−8 A/cm2). Based on the experimental analysis and density functional theory (DFT) simulations, the corrosion mechanisms of the Crx HEACs were discussed. The exceptional corrosion resistance of the Cr16 coating can be attributed to its high oxygen adsorption energy and thus facilitates the rapid formation of protective and compact passive films with few defects.

Electrochemical behavior and surface stability of dental zirconia ceramics in acidic environments

Dental zirconia ceramics, widely employed in dentistry for their biocompatibility and mechanical properties, face challenges in long-term viability within the oral cavity. This study focuses on analyzing the electrochemical behavior of a commercial dental zirconia ceramic type in acidic environments. Through extensive electrochemical investigations, including Electrochemical Impedance Spectroscopy (EIS) and cyclic polarization resistance (Cpol), corrosion resistance was assessed. Despite indications of material dissolution, our results demonstrate significant corrosion resistance, as reflected in low corrosion current density (Icorr) values. Notably, the study reveals the development of a protective oxide layer at the ceramic-electrolyte interface, contributing to material stability. XRD analysis confirms the presence of stable crystallographic phases (t-ZrO2) even after exposure to acidic media. Surface characterizations utilizing scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) affirm minimal surface damage and maintained elemental composition. These findings illuminate the intricate electrochemical behavior of dental zirconia ceramics in challenging environments, underscoring their potential for durable dental restorations. This interdisciplinary research bridges dentistry and materials science, providing valuable insights for optimizing material properties and advancing dental materials and restorative techniques.

Electrochemical corrosion study of chitosan-hydroxyapatite coated dental implant

Chitosan (Ch) is a naturally occurring biocompatible and bio-degradable material with high corrosion protective capacities for metals in various corrosive media. Hydroxyapatite (HA) is a significant biodegradable and bioactive material. In the present work, chitosan-hydroxyapatite (Ch-HA) composite coatings with various concentrations of chitosan were made on 316L stainless steel (316L SS) using sol–gel dip coating technique. The coatings were characterized by X-ray diffraction (XRD), FTIR, SEM, and electrochemical measurements. The surface morphology results (SEM) of coated implants exposed the fairly dense microstructures having uniformity without cracks and pores indicating that coating was successfully deposited. From electrochemical analyses, it was observed that the value of corrosion current density and the corrosion rate decreased from 6.03 to 0.15 and 5.56-0.13 respectively indicating that 1.5gCh-HA is the best coating concentration. The electrochemical results demonstrated an improvement in the corrosion resistance of 316L SS than the bare one. The decrease in slope and loop area of cyclic voltammograms reveals about improvement in corrosion resistance. This increment in corrosion resistance of the Ch-HA coated SS implant in the artificial saliva is as 1.5gCh-HA > 2gCh-HA >1gCh-HA >0.5gCh-HA. Furthermore, Ch-HA coatings revealed appropriate adhesion with 316L SS substrate for its use in dental implants.

Anti-corrosion property of multilayer Ti3C2Tx reinforced chemically bonded silicate ceramic coatings in salt, alkaline and acid environments

Great potential has been exhibited by MXene (Ti3C2Tx) for improving the anti-corrosion property of polymeric matrixes. However, the anti-corrosion performance of Ti3C2Tx as a filler introduced into silicate bonded ceramic coating in H2SO4, NaOH and NaCl solutions still remains elusive. Herein, the effect of Ti3C2Tx introduction on the contact angle and water uptake of silicate bonded ceramic coatings was illustrated. The anti-corrosion property of ceramic coatings was investigated by using electrochemistry measurements. The results exhibited that the silicate bonded ceramic coating with 1.6 wt% Ti3C2Tx possesses the best anticorrosion in three different solutions respectively. Interestingly, it exhibited the highest impedance modulus (|Z|0.01Hz) of 3.45 × 106 Ω cm2 and the lowest corrosion current density (Icorr) value of 1.18 × 10−8 A/cm2 in the 5 wt% H2SO4 solution. This work also elucidated the anti-corrosion mechanism of Ti3C2Tx reinforced silicate bonded ceramic coating in three different solutions.

Electrochemical and surface characterization studies of winged bean extracts doped TEOS-PDMS sol-gel protective coatings on reinforcing bar in acidic medium

Hybrid sol-gel coatings consisting of tetraethoxysilane (TEOS)-polydimethylsiloxane (PDMS) molecular precursors doped with winged bean extracts were synthesized for the corrosion protection of reinforcing steel in a 0.5 M HCl medium. The incorporation of winged bean extracts doped into hybrid TEOS-PDMS composite coatings on reinforcing steel resulted in a protective system with superior corrosion protection performance, as determined by electrochemical impedance spectroscopy, electrochemical noise measurement and potentiodynamic polarization. When compared to the undoped TEOS-PDMS silanol coating, the corrosion current density and electrochemical current noise resistance values of the winged bean extracts doped hybrid coatings were much lower, whereas charge transfer resistance values were significantly higher. Scanning electron microscopy, Fourier transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy techniques were used to analyse the morphology and structure of developed sol-gel coatings. In addition, atomic force microscopy and wettability analyses were exploited to further understand the characteristics of hybrid silanol coatings. The outcome of this study corroborates that winged bean extracts doped TEOS-PDMS hybrid coatings could be adopted as potential coatings for reinforcing steel.

Developing the inhibition mechanism for amide-based amino acids in carbonated concrete environment and assessing the migration ability in concrete

The corrosion inhibition mechanism of amide-based amino acids, Asparagine (Asn) and Glutamine (Gln) for steel in concrete pore solution simulating carbonated environment was explored by the means of gravimetric, electrochemical and surface characterization techniques. Thereafter, percolation ability of Asn and Gln was assessed through OPC and PPC concretes by UV–visible spectroscopy technique for their application as migratory corrosion inhibitors in concrete. The results revealed that Asn as well as Gln can be efficiently used in carbonated corrosive environment for steel inhibition. The protection ability of Gln was however, higher than Asn. Gln exhibited 50% lower corrosion current density values than Asn. Also, the charge transfer resistance of Gln inhibited specimens was 3 times higher than Asn inhibited specimens. The layer developed on steel with Gln as corrosion inhibitor was thermodynamically more stable than Asn as equilibrium constant of adsorption (kads) was 2.11 times higher for Gln. Optical and SEM images revealed the formation of a thin layer in the case of Asn while a thick layer was seen to form on Gln inhibited specimens. Surface layer characterization by FTIR and XPS evinced the formation of Asn-Fecomplex and Gln-Fecomplex on steel surface. Both the compounds bound the Fe ions by chelation through O atom from amide and carboxylate functional groups. Higher efficiency of Gln was attributed to development of more adherent protective film due to its longer carbon chain length than Asn. Gln’s chelate ring experienced lower steric hindrance than Asn’s ring. Asn and Gln percolated through concrete and reached upto a depth of 25mm within 15 days of application. Conclusively, it can be said that Asn and Gln can be employed as corrosion inhibitors for concrete subjected to carbonation-induced corrosion.

Mechanical, wear and corrosion behavior of Ti–6Al–xNb (x = 3.5–21 wt%) alloys manufactured by powder metallurgy

In this study, Ti–6Al–xNb alloys with different Nb percentages (x = 3.5–21 wt%) were produced by the conventional powder metallurgy technique. After mixing and pressing the alloy powders in appropriate proportions, the green samples were sintered in a tube furnace under a vacuum atmosphere at 1200 °C for 2 h. The X-ray diffraction analysis (XRD) showed that all the alloys consist of α–Ti, TiNb (β–Ti) and AlNb2 phases. The results showed that the Ti–6Al–14Nb alloy among all alloys has the best mechanical properties, and the microhardness, tensile and flexural strength are 276.4 Vickers hardness (Hv0.2), 453 MPa and 1682 MPa, respectively. Tribological tests were carried out in both dry and wet conditions with Hanks' Balanced Salt Solution. While generally, the specific wear rates of the samples increased with Nb content up to 17.5 wt% under dry conditions, on the other hand, they increased with increasing Nb content under wet conditions. On the other hand, the specific wear rate increased with increasing the sliding distance. The best corrosion resistance alloy among all the samples was Ti–6Al–7Nb with −0.0968 V corrosion potential (Ecorr), 0.015 μA/cm2 corrosion current density (Icorr) values.

Effect of Plasma Nitriding and Oxidation on the Corrosion Resistance of 304 Stainless Steel in LiBr/H2O and CaCl2-LiBr-LiNO3-H2O Mixtures

The effect of plasma nitriding and oxidation on the corrosion resistance of AISI 304 type stainless steel in LiBr/H2O and CaCl2-LiBr-LiNO3-H2O mixtures at 80 °C has been evaluated by using potentiodynamic polarization curves and electrochemical impedance spectroscopy techniques (EIS). Steel was plasma treated at 500 °C during 8 h under different atmospheres, nominally 20% N2 + 80% H2, 100% N2 and 100% O2. X-ray diffraction analysis (XRD) showed the presence of a CrN layer in nitrided specimens, whereas scanning electronic microscopy analysis revealed that specimen treated in the 20% N2 + 80% H2 atmosphere showed the thickest nitride layer. Specimens nitrided in the 20% N2 + 80% H2 atmosphere had the noblest open circuit potential value in both solutions, whereas potentiodynamic polarization curves indicated the formation of a passive layer. These specimens exhibited the lowest corrosion and passivation current density values. Corrosion process was under charge transfer control in both solutions regardless of the plasma treatment. The type of corrosion suffered by the steel under all treatments was the pitting type of corrosion. Pits density was the lowest for nitrides steels rather than that for untreated or pre-oxidized ones.

Corrosion behavior and immobilization of pure aluminum and Al−Mg alloy LLRW in magnesium potassium phosphate cements

Magnesium potassium phosphate cement (MKPC) is a candidate material to replace ordinary Portland cement (OPC) for the encapsulation of metallic low-level radioactive waste (LLRW) and improve the corrosion behavior of encapsulated reactive metals such as aluminum. The objectives of this research were to study the corrosion behavior of pure Al (A1050) and Al−Mg alloy (AA5754) embedded in MKPC and OPC mortars, to assess the effect of curing conditions on hardening properties and on the reactivity of Al and Al−Mg alloy. Results were obtained with measurements of compressive strength, X-ray diffraction and polarization resistance and the proposed interpretation was based on Faraday´s law. In the first 15 days of interaction in water immersion the corrosion rate and the volume of hydrogen evolved were seen to be at least one order of magnitude lower for AA5754 in MKPC than in OPC mortar, yielding average corrosion current density values of 1.85 and 109.0 × 10−6 A/cm2, and hydrogen volumes of 0.33 L/m2 and 17.8 L/m2 for AA5754/MKPC and AA5754/OPC, respectively. The pore pH was close to neutral and the hardening properties were highly dependent on the curing conditions.

Tetra-functional multilayer coatings for cardiovascular stent materials

Functional coatings have been of great interest in enhancing the performance of implants in recent years. Here, for the first time, preparation and characterization of a tetra-functional coating is reported, exhibiting anticorrosion, antibacterial, biocompatible, and anticoagulant behaviors. Poly(2-ethyl-2-oxazoline)-co-polyethyleneimine (PEOX-co-PEI) stabilized silver nanoparticles (AgNPs) and heparin were used to prepare the multifunctional multilayers. The coatings were deposited on nitinol and 316 L stainless steel substrates, the most used materials in coronary stents, via layer-by-layer (LbL) technique. Corrosion current density values obtained from Tafel plots are 1.61×10−9A/cm2 and 6.79×10−8A/cm2 for coated and uncoated 316 L substrate, respectively. Similarly, the corrosion current density values shifted from 1.00×10−8A/cm2 for uncoated nitinol to 4.77×10−10A/cm2 after coating. Contact killing method against gram-positive (Staphylococcus aureus) and gram-negative (Pseudomonas aeruginosa) bacterial species concluded that the presence of the coating on the surfaces of the materials reduces the number of the survived colonies (in CFU/mL) for more than 99.9% independent of the underlying metal within 3 hours of incubation time. Prepared coatings demonstrated above 90% relative viability compared to the positive control in MTT assay using human umbilical vein endothelial cells (HUVEC), indicating no cytotoxic effect on adjacent healthy cells. The coagulation assay also exhibited a 50% reduction in the coagulation rate after coating compared to the bare substrates, confirming the antithrombogenicity of the coatings.