Fast Corrosion Research Articles

Investigating machining characteristics and degradation rate of biodegradable ZM21 magnesium alloy in end milling process

Surface properties play a significant role in the biocompatibility and biodegradation of Mg-alloy implants which primarily depends on the manufacturing route followed. In the present work, the milling process has been optimized on ZM21 Mg-alloy to obtain the trade-off between the material removal rate (MRR), surface roughness (SR), and degradation rate (DR). Milling parameters vary the amount of force and pressure developed between the tool and work interface, thus, affecting the MRR and SR. The weight loss of machined samples was measured after seven days of immersion in simulated body fluid (SBF) to calculate the DR. L16 orthogonal array was used to study the effect of milling parameters such as tool rotation speed (TRS), feed rate (FR), and depth of cut (DoC). The result showed that the variation in the values of milling parameters significantly influences the surface integrity of Mg-alloy, thus affecting the DR. Chip morphology and surface cracks with scanning electron microscopy (SEM) were evaluated to correlate the influence of milling parameters on the machining performance of ZM21 Mg-alloy. The machined surface of Mg-alloy must be of very low SR and cracks-free to avoid fast corrosion. Therefore, grey relational analysis (GRA) has been employed for multi-optimization to get the best trade-off for higher MRR and lower SR and DR. The optimized setting suggested by GRA for milling of ZM21 Mg alloy is TRS: 2700 rpm, FR: 25 mm/min, and DoC: 1.25 mm.

Electrostatic adsorption facilitating dual-layer coating for stabilized cathode-electrolyte interphases and boosted lithium intercalation thereof in LiNi0.8Co0.1Mn0.1O2 cathode

Cathode-electrolyte interphases (CEIs) are determinative to the electrochemical performance of lithium-ion batteries, especially those with Ni-rich cathodes. Herein, we employed the simple electrostatic adsorption (SEA) method to generate a homogenous polydimethyldiallyl ammonium chloride/ graphene oxide (PDDA/GO) dual-layer coating on the surface of a model single-crystalline Ni-rich cathode, LiNi0.8Co0.1Mn0.1O2 (NCM811), and thus modified the CEIs in both compositions and microstructures. The PDDA/GO coating depresses the LiF component, enables a homogeneous organic-enriched CEI film with fast Li diffusion and effective corrosion protection on cathodes. Together with the mechanical confinement on cathodes, these characters of modified CEIs benefit the electrochemical stability effectively. For instance, NCM811-PDDA/GO cathodes exhibit a 77% capacity retention after 500 cycles at the current density of 50 mA g−1, against 28% for pristine NCM811. This study provides new insights in correlating the coating and CEIs, which effectively guide the development of Ni-rich cathodes for high performance. Such a simple strategy to form a homogeneous coating can also be extended into other electrode materials easily.

Non-Destructive Diagnostic Methods for Fire-Side Corrosion Risk Assessment of Industrial Scale Boilers, Burning Low Quality Solid Biofuels—A Mini Review

The use of low-emission combustion technologies in power boilers has contributed to a significant increase in the rate of high-temperature corrosion in boilers and increased risk of failure. The use of low quality biomass and waste, caused by the current policies pressing on the decarbonization of the energy generation sector, might exacerbate this problem. Additionally, all of the effects of the valorization techniques on the inorganic fraction of the solid fuel have become an additional uncertainty. As a result, fast and reliable corrosion diagnostic techniques are slowly becoming a necessity to maintain the security of the energy supply for the power grid. Non-destructive testing methods (NDT) are helpful in detecting these threats. The most important NDT methods, which can be used to assess the degree of corrosion of boiler tubes, detection of the tubes’ surface roughness and the internal structural defects, have been presented in the paper. The idea of the use of optical techniques in the initial diagnosis of boiler evaporators’ surface conditions has also been presented.

Strength, corrosion resistance and cellular response of interfaces in bioresorbable poly-lactic acid/Mg fiber composites for orthopedic applications

The shear strength and the corrosion resistance of the fiber/matrix interface after immersion in simulated body fluid was studied in poly-lactic acid/Mg fiber composites. The shear strength of the interface was measured by means of push-out tests in thin slices of the composite perpendicular to the fibers. It was found that the interface strength dropped from 15.2 ± 1.4 MPa to 7.8 ± 3.7 MPa after the composite was immersed in simulated body fluid for 148 h. The reduction of the interface strength was associated to the fast corrosion of the fibers as water diffused to the interface through the polymer. The expansion of the fibers due to the formation of corrosion products was enough to promote radial cracks in the polymer matrix which facilitate the ingress of water and the development of corrosion pitting in the fibers. Moreover, cell culture testing on the material showed that early degradation of the Mg fibers affected the proliferation of pre-osteoblasts near the Mg fibers due to the local changes in the environment produced by the fiber corrosion. Thus, surface modification of Mg fibers to delay degradation seems to be a critical point for further development of Mg/PLA composites for biomedical applications.

Electro-spark deposition in vacuum using graphite electrode at different electrode polarities: Peculiarities of microstructure, electrochemical and tribological properties

Titanium and its alloys are widely used in offshore and costal infrastructure, but need protection against wear and corrosion in saline environments. Compared to other surface engineering methods, electro-spark deposition (ESD) does not have the drawbacks of small thickness and poor adhesion of protective coatings. However, ESD in air or inert atmosphere using a graphite electrode does not provide sufficient continuity of a protective layer due to a low efficiency of carbon transfer. To enhance carbon transfer, Ti was subjected to ESD in vacuum using a graphite electrode. The main difference between vacuum and air deposition is that, in addition to spark discharges, arc evaporation occurs. It was shown that the carbon content, microstructure, and phase composition of modified Ti layer can be well controlled by changing electrode polarity and pulse energy. At cathodic polarity, arc discharge occurs on graphite electrode, which leads to increased carbon evaporation and a higher carbon content in the coating. Resulting coatings protect Ti from wear and corrosion in 3.5 wt.% NaCl solution due to formation of TiC layer. Coatings with top graphite layer show the lowest values of friction coefficient and corrosion current density, as well as fast corrosion potential recovery during tribocorrosion tests.

Renewable redox couple system for sustainable precious metal recycling from e-waste via halide-regulated potential inversion

Precious metal (PM) retrievement from e-waste is of great significance for reducing virgin mining activity and promoting rare resource sustainability. However, current PM recycling methods rely mainly on caustic aqua regia or unstable sulfur-based ligand, which has caused severe environmental damage and process inefficiency. Here, we propose an environmentally friendly halide-regulated strategy, utilizing milder and renewable oxidant—cupric/ferric ion for facile PM dissolution. This is realized by the synergistic effect of enhanced oxidizing ability of Cu(II) and reduced oxidation potential of PM with halide addition. Electrochemical tests and leaching experiment results show that Cu(II)/Cu(I) redox potential experiences great change with bromide, increasing from 0.4 to 0.75 V. Fast corrosion feature was observed for Au in Cu(II)/Fe(III)-Br- and Pd in Cu(II)/Fe(III)-Cl-, and it can be accelerated by increasing oxidant and halide concentration. Our proposed strategy outperforms traditional methods with stable and fast dissolution, where 2.5 mol/L Br- is appropriate for Au dissolution. Moreover, selective dissolution of base metal, Pd/Ag, and Au can be achieved via ligand alteration and be further combined with electrodeposition technique for multi metal recovery and oxidant regeneration. This halide-regulated strategy can lead PM recycling from pollutive status towards environmentally friendly road.

Experimental study of one-step economical retarded sandstone acid

The objective of this study is to experimentally evaluate a new acid combination of HEDP: CH3COOH as a retarded acid to minimize some limitations of high-temperature sandstone acidizing, such as fast acid-rock reaction and secondary precipitation pipeline corrosion. In this work, the acid–base titration, core-powder solubility test, scale deposition test, corrosion rate measurement and corefloods were carried out to evaluate the performances of the acid combination, including acidity characteristics, retarded performance, preventing scale rate, corrosivity and improving permeability. And then the microstructure and mineral content in sandstone samples were observed and analyzed with SEM–EDS. The results of evaluation tests indicated that the new acid combination has excellent performances on retarded rate, preventing scale deposition, permeability enhancement and lower corrosivity, comparing with conventional mud acid. The results of SEM and EDS showed that the microstructure and mineral content of sandstone changed after acid treatment. Compared with mud acid, the new acid system can react more with small particles on sandstone surface and less with the skeleton of samples and the decrease in the contents of Mg, Al, Na, K, Ca and Fe is relatively lower.

Engineering a Bioactive Hybrid Coating for In Vitro Corrosion Control of Magnesium and Its Alloy

Magnesium (Mg) and its alloys are promising biodegradable metallic implant materials. However, their clinical applications are limited by their fast corrosion rate in the biological environment. In this work, with an outlook to improve the in vitro corrosion resistance of Mg and WE43 Mg alloy, a layer-by-layer interfacially engineered anticorrosive and bioactive coating consisting of a natural oxide lower layer, hydroxyapatite (HA) middle layer, and silk fibroin (SF) top layer was fabricated and investigated. Anodization was used to create natural oxide layer induced microroughness on substrates. The electrochemically deposited HA layer improved the surface microroughness and microhardness but significantly decreased Mg ion release, hydrogen gas evolution, and weight loss in simulated body fluid. The spin-coated SF layer further decreased hydrophilicity, in vitro degradation, and corrosion rate. The nonspecific and specific intermolecular interactions between fabricated layers along with their mechanical interlocking interface contributed to improved adhesion strength and integrity of the coating. The SF+HA-coated samples showed enhanced degradation and corrosion resistance due to a synergistic effect of the underlying HA layer, hindering the ingress of aggressive ions and the top hydrophobic SF layer, preventing the ingress of corrosive solution. The SF+HA-coated Mg and WE43 Mg alloy samples exhibited 50 and 26 times decreased corrosion rate, respectively, compared to uncoated samples. Moreover, in vitro cytotoxicity and cell culture studies using a mouse fibroblast cell showed that the SF+HA hybrid coating improved the cell viability, attachment, and proliferation, with cells exhibiting elongated morphology on coated samples as compared to a round shape on uncoated samples.

Electrochemical testing of thermal spray coatings using gel electrolytes

The use of electrochemical methods allows fast and inexpensive corrosion measurements of bulk materials with high significance. In the case of thermal spray coatings, electrolyte penetration into open pores up to the substrate material can cause undesired mixed potentials. Furthermore, the implementation of complex geometries or rough surfaces remains a problem. Preconditioning of the surface or the use of the electrochemical cell is required to eliminate leakage. Therefore, reliably measuring corrosion is still a challenging task. This undermines fast monitoring of corrosion performance as a part of the production process. Gelling agents are investigated to increase the viscosity of many electrolytes. A procedure has been developed to determine the concentration level and the mixing conditions. Passivation and pitting-corrosion testing are performed on thermal spray AISI 316L coatings. The electrochemical potential curves as well as the corroded surface layers were studied in comparison to a liquid electrolyte. The suitability of the test on rough surfaces in the sprayed condition was investigated. The results prove the novel approach as an alternative to established electrochemical test methods with extended application range.

Bioactivity Performance of Pure Mg after Plasma Electrolytic Oxidation in Silicate-Based Solutions.

The biodegradable metals, including magnesium (Mg), are a convenient alternative to permanent metals but fast uncontrolled corrosion limited wide clinical application. Formation of a barrier coating on Mg alloys could be a successful strategy for the production of a stable external layer that prevents fast corrosion. Our research was aimed to develop an Mg stable oxide coating using plasma electrolytic oxidation (PEO) in silicate-based solutions. 99.9% pure Mg alloy was anodized in electrolytes contained mixtures of sodium silicate and sodium fluoride, calcium hydroxide and sodium hydroxide. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), contact angle (CA), Photoluminescence analysis and immersion tests were performed to assess structural and long-term corrosion properties of the new coating. Biocompatibility and antibacterial potential of the new coating were evaluated using U2OS cell culture and the gram-positive Staphylococcus aureus (S. aureus, strain B 918). PEO provided the formation of a porous oxide layer with relatively high roughness. It was shown that Ca(OH)2 was a crucial compound for oxidation and surface modification of Mg implants, treated with the PEO method. The addition of Ca2+ ions resulted in more intense oxidation of the Mg surface and growth of the oxide layer with a higher active surface area. Cell culture experiments demonstrated appropriate cell adhesion to all investigated coatings with a significantly better proliferation rate for the samples treated in Ca(OH)2-containing electrolyte. In contrast, NaOH-based electrolyte provided more relevant antibacterial effects but did not support cell proliferation. In conclusion, it should be noted that PEO of Mg alloy in silicate baths containing Ca(OH)2 provided the formation of stable biocompatible oxide coatings that could be used in the development of commercial degradable implants.

Degradable magnesium implants: improving bioactive and antibacterial performance by designed hybrid coatings

Magnesium and its alloys are promising material candidates for degradable fracture fixation devices due to their suitable mechanical properties and biocompatibility; however, their fast corrosion in aqueous media causes pain and swelling. In this study, a hybrid coating system composed by a sol–gel silica-based matrix with bioactive glass microparticles and silica–gentamicin nanoparticles was deposited by spray technology on magnesium AZ91D alloy. The coating was homogeneously distributed on the surface and protected the degradation of AZ91D alloy in simulated body fluid for at least 28 days, preventing the pH increase of the solution and accelerating the formation of calcium phosphate-related compounds on the surface. Moreover, inhibition of bacteria growth was proved for Staphylococcus aureus and Escherichia coli and increased cell adhesion and proliferation of ST-2 and differentiated MC3T3-E1 cells was shown. The generated coating is a promising surface treatment for providing bioactive and antibacterial proprieties to new degradable implants.

Green, Template-Less Synthesis of Honeycomb-like Porous Micron-Sized Red Phosphorus for High-Performance Lithium Storage.

Large-volume-expansion-induced material pulverization severely limits the electrochemical performance of high-capacity red phosphorus (RP) in alkali-ion batteries. Honeycomb-like porous materials can effectively solve the issues due to their abundant interconnected pore structures. Nevertheless, it is difficult and greatly challenging to fabricate a honeycomb-like porous RP that has not yet been fabricated via chemical synthesis. Herein, we successfully fabricate a honeycomb-like porous micron-sized red phosphorus (HPRP) with a controlled pore structure via a large-scale green and template-less hydrothermal strategy. It is demonstrated that dissolved oxygen in the solution can accelerate the destruction of P9 cages of RP, thus forming abundant active defects with a faster reaction rate, so the fast corrosion forms the honeycomb-like porous structure. Owing to the free volume, interconnected porous structure, and strong robustness, the optimized HPRP-36 can mitigate drastic volume variation and prevent pulverization during cycling resulting in tiny particle-level outward expansion, demonstrated by in situ TEM and ex situ SEM analysis. Thus, the HPRP-36 anode delivers a large reversible capacity (2587.4 mAh g-1 at 0.05 A g-1) and long-cycling stability with over 500 cycles (∼81.9% capacity retention at 0.5 A g-1) in lithium-ion batteries. This generally scalable, green strategy and deep insights provide a good entry point in designing honeycomb-like porous micron-sized materials for high-performance electrochemical energy storage and conversion.

Structure-modulated CaFe-LDHs with superior simultaneous removal of deleterious anions and corrosion protection of steel rebar.

The three anionic species; chloride (Cl−), sulfate (SO42−), and carbonate (CO32−), are typical chemical factors that environmentally accelerate failure of concrete structures with steel rebar through long-term exposure. Efficient removal of these deleterious anions at the early stage of penetration is crucial to enhance the lifespan and durability of concrete structures. Here, we synthesize CaFe-layered double hydroxide (CaFe-LDHs) by a simple one-step co-precipitation technique and structural modulation by calcination process. It is applied for the removal of Cl−, SO42−, and CO32− anions as well as corrosion inhibition on steel rebar in aqueous solutions. The synthesized CaFe-LDHs with phase transfer show notable improvement of removal capacity (Qmax) toward Cl− and SO42− over 3.4 times and over 5.69 times, respectably, then those of previous literatures. Furthermore, the steel rebar exposed to an aqueous solution containing the three anionic sources shows a fast corrosion rate (1876.56 × 10−3 mm per year), which can be remarkably inhibited showing 98.83% of corrosion inhibition efficiency when it is surrounded by those CaFe-LDHs. The novel adsorption mechanisms of these CaFe-LDHs-induced crystals and corresponding corrosion protection properties are elucidated drawing on synergy of memory effects and chemical reactions.

Silane coatings modified with hydroxyapatite nanoparticles to enhance the biocompatibility and corrosion resistance of a magnesium alloy.

The fast corrosion rate of magnesium alloys has restricted their use as biodegradable implants. Hence developing a practical approach to retard the corrosion rate of the AZ31 magnesium alloy, as well as promoting cell adhesion and proliferation is of great importance. Silane coatings were applied through dip coating, on samples pretreated in hydrofluoric acid. Samples were immersed in simulated body fluid at 37 °C, and the coating performance was assessed by electrochemical impedance spectroscopy. The coating morphologies of samples were investigated through field emission scanning electron microscopy and a cell viability/proliferation (MTT) test was performed to evaluate cellular response. A 2.2 μm-thick coating was accomplished, which increased the corrosion resistance to three orders of magnitude higher than that of the bare sample. Hydroxyapatite nanoparticles were added to the silane coating to improve biocompatibility and facilitate bone formation. Changing the concentration of hydroxyapatite nanoparticles not only helped to optimize the barrier properties of the silane coating but also ameliorated MG-63 osteoblastic cell growth. The findings showed great promise to enhance and maintain the corrosion barrier property and induce high osteoblastic differentiation by employing 1000 mg L−1 of hydroxyapatite nanoparticles.

Corrosion behavior of pure magnesium processed by accumulative roll bonding for biomaterial application

Magnesium is one of the materials that can be used as an implant for the human body. It is because the daily intake ofmagnesium for an adult is 240-420 mg/day. Also, the elastic modulus (41 – 45 GPa) and density (1.74 g/cm3) of magnesiumis closer to that of natural bone. However, pure magnesium in the as-cast condition has a very fast corrosion rate,2,89mmPY in 0.9% NaCl solution. Accumulative roll bonding (ARB) is done in this recent study to improve the corrosionrate of pure magnesium. ARB is one of the severe plastic deformations (SPD) method, which provides the possibility toobtain high strained materials without a macroscopic change after a cyclic roll-bonding process (stacking, preheating androlling). Magnesium is annealed at 250°C and 350°C for 25 minutes, and then the ARB process is done with variation; one,two, three and four cycles. The composition was tested using SEM-EDS, showing that the content of a pure magnesiumplate (as annealed) is 99.77%. The grain size is observed using the optic microscope and measured by ImageJ, while thecorrosion rate was measured with an electrochemical and immersion test. The result showed the smallest grain size achievedis 7.204 ± 1,185 μm and that the lowest corrosion rate is 0,0012mmPY. The polarization resistance determined the thicknessand the ability of passivation area obtained with the increasing number of ARB cycles. The higher plastic deformation isrecommended for improve the corrosion resistance of the metallic material for future works.

Effects of pre-oxidation on the corrosion behavior of pure Ti under coexistence of solid NaCl deposit and humid oxygen at 600\xa0\xb0C: the diffusion of chlorine

The effect of pre-oxidation on the corrosion behavior of pure Ti covered with a solid NaCl deposit in the humid O2 flow at 600 °C is studied. The oxide scale, formed by pre-oxidation, protects the substrate from the NaCl induced corrosion during the initial stage. However, the corrosion of the pre-oxidized sample is severely accelerated by solid NaCl after an incubation period. The chlorine, generated from the decomposition of solid NaCl, diffuses into the oxide/substrate interface as ions during the incubation period, which was observed by ToF–SIMS. The chlorine at the oxide/substrate interface induces the fast corrosion after the incubation period although the pre-oxidation scale is complete and compact.

Alternating Current Electrophoretic Deposition of Chitosan-Gelatin-Bioactive Glass on Mg-Si-Sr Alloy for Corrosion Protection.

Magnesium alloys have gained significant attention as degradable implant materials, but the fast and localized corrosion behavior leading to hydrogen gas evolution and alkaline poisoning limits their clinical application. In this research, the possibility of controlling the fast degradation rate of an experimental Mg-Si-Sr alloy by applying hybrid biopolymer chitosan (CS)-gelatin (G)-bioactive glass (BG) coatings was investigated. Electrophoretic deposition using alternating current fields (AC-EPD) was employed for surface coating and the influence of suspension parameters (biopolymer type and concentration, BG particle size), and key AC-EPD parameters (voltage amplitude, frequency, and time) on the coating quality were investigated. Stable suspensions of positively charged biopolymer/BG particles deposited on the Mg alloy coupled as a cathode during the high-amplitude peak. Furthermore, coating homogeneity improved with increasing peak-to-peak-voltage and the hybrid nature of the coatings was confirmed by scanning electron microscopy and Fourier transform infrared spectroscopy. Corrosion studies revealed a significantly decreased corrosion rate down to 0.08 mm/year for the Mg-Si-Sr alloy incorporating CS-G-BG b AC-EPD coating.

Improving the performance of zinc-rich coatings using conductive pigments and silane

ABSTRACT By analysing the results of corrosion potential, EIS, SEM and XRD test of zinc-rich coatings (ZRCs) in 3.5wt-% NaCl solution, it was found that conductive pigment (di-iron phosphide, Fe2P) can accelerate the activation and corrosion rate of zinc powders in ZRCs, but too fast corrosion rate can reduce the cathodic protection and shielding of ZRCs. Silane improves the mechanical properties and shielding effect of coatings, but reduces the activation and corrosion rate of zinc powders. The synergy effect of the two strengthens both the cathodic protection and the shielding effect. Finally, the synergy mechanism of Fe2P and silane to improve the performance of ZRCs is proposed. These mechanisms provide references for solving the galvanic corrosion of conductive fillers (Fe2P, graphite, carbon black, carbon nanotubes, graphene, etc.) in ZRCs.

Effect of Lithium and Aluminum on the Mechanical Properties, In Vivo and In Vitro Degradation, and Toxicity of Multiphase Ultrahigh Ductility Mg-Li-Al-Zn Quaternary Alloys for Vascular Stent Application.

Magnesium alloys are the most widely studied biodegradable metals for biodegradable vascular stent application. Two major issues with current magnesium alloy based stents are their low ductility and fast corrosion rates. Several studies have validated that introduction of Li into the magnesium alloys will significantly improve the ductility while alloying with Al will improve the corrosion resistance and strength. In the present study, we studied the effects of alloying different amounts of Li and Al on the Mg-Li-Al-Zn (LAZ) quaternary alloy system. Rods were made from four different LAZ alloys, namely, LAZ611, LAZ631, LAZ911, and LAZ931 following melting, casting, and then extrusion. Systematic assessment of mechanical properties, in vitro corrosion, cytotoxicity, and in vivo degradation including local and systemic toxicity conducted demonstrated the beneficial effects of Li and Al on the mechanical properties. Our results specifically suggest that alloying with Li significantly improved the ductility while Al enhanced the strength of the LAZ alloys. Four of the LAZ alloys exhibited different corrosion rates in Hank's balanced salt solution depending on the chemical composition. Indirect in vitro cytotoxicity tests also showed lower cytotoxicity for the alloys exhibiting higher corrosion resistance. In vivo corrosion rates in the mouse subcutaneous model showed different corrosion rates compared to the in vitro tests. Nevertheless, all of the four LAZ alloys displayed no local and systemic toxicity based on the histology analysis. This research study, therefore, demonstrated the benefits of using Li and Al as alloying elements in LAZ alloys and the potential use of LAZ alloys for vascular stent application.

Study of some basic operation conditions of an Al-air battery using technical grade commercial aluminum

Commercial Al-6061 has been used as anode electrode to construct alkaline Al-air batteries. Functional batteries with satisfactory operation record have been constructed by using air-breathing Pt-free cathode electrodes simply made by depositing carbon black on carbon cloth. The devices were functional also in the absence of oxygen either by water reduction or by using hydrogen peroxide as oxidant, thus providing a variety of operation conditions. Al-6061 corroded fast in the alkaline electrolyte producing hydrogen at rates that approached the theoretical maximum. Fast corrosion was associated with the presence of grain impurities in the alloy and the existence of extensive grain boundaries. In this respect, corrosion of pure aluminum was much slower under the same conditions and resulted into a slower rate of hydrogen production.