Initial Stage Of Immersion Research Articles

Biodegradation behaviour of Fe-based alloys in Hanks’ Balanced Salt Solutions: Part II. The evolution of local pH and dissolved oxygen concentration at metal interface

Commercially pure Fe, Fe35Mn, and (Fe35Mn)5Ag alloys were prepared by uniaxial pressing of the mixture of individual powders, followed by sintering. The influence of the alloying elements Mn and Ag on the corrosion behaviour of these Fe-based alloys was investigated in Hanks’ Balanced Salt Solution (HBSS). Furthermore, the role of the components in HBSS, particularly Ca2+ ions during alloys degradation was studied. Distribution of local pH and dissolved oxygen concentration was measured 50 μm above the interface of the degrading alloys. The results revealed that 5 wt% Ag addition to Fe35Mn alloy triggered micro-galvanic corrosion, while uniform corrosion dominated in pure Fe and Fe35Mn. Fast precipitation of Ca–P-containing products on the surface of these Fe-based alloys buffered local pH at the metal interface, and blocked oxygen diffusion at the initial stages of immersion. In the (Fe35Mn)5Ag, the detachment or structural changes of Ca–P-containing products gradually diminished their barrier property. These findings provided valuable insights into the degradation mechanism of promising biodegradable Fe-based alloys.

Exploring the corrosion behavior of Mn-implanted biomedical Mg

Many surface modification technologies have been developed on biomedical magnesium (Mg) and its alloys to expand potential clinical applications. In this study, the bio-safe manganese (Mn) element was implanted into the biomedical Mg surface by a metal vapor vacuum arc (MEVVA) technique. In the Mn-implanted layer, Mn existed in the form of both metallic and oxidized states. Besides, Mn ion implantation changed the corrosion behavior of biomedical Mg in Hank’s solution. At the initial stage of immersion, the corrosion rate was accelerated owing to the galvanic couple between metallic Mn and Mg, and micro-scale galvanic corrosion was uniformly distributed on surfaces. With the immersion time prolonging, Mn-implanted Mg displayed enhanced anti-corrosive property, presenting as a change from corrosion prone to corrosion resistance. On the one hand, the anti-corrosive and uniform Ca, P-containing products were formed on the corroded surface based on uniformly-distributed micro-scale pitting corrosion. On the other hand, the metallic Mn tended to be oxidized to stable Mn oxide so that galvanic corrosion was retarded. This research attempts to explore the effect of Mn ion implantation on the corrosion behavior of biomedical Mg, and offers new insight into novel surface modifications of biomedical Mg devices for long-time implantation.

Water Resistance Properties of Lime Soil Ground under Long-Term Soaking Environment

To explore the water resistance properties of lime soil ground, the physical and mechanical properties of lime soil with 5%, 10%, 15% and 20% lime content after long-term water immersion were studied by conducting unconfined compressive tests, density tests and water absorption tests. The results show that the stress–strain relationship curves of the lime soil during immersion are of the strain-softening type. The curves are multistage and nonlinear with evident peak values, and the lime soil achieves ductility and toughness with an increase in immersion time. The failure modes of the lime soil samples mainly include single slope shear failures, brittle splitting failures and conjugate shear failures, which are mainly affected by the lime content and immersion time. The strength of the lime soil decreases sharply in a short time while interacting with water. The strength slowly increases to 50.07–69.15% of the initial strength after immersion for a long time, i.e., still far less than the initial strength without immersion. Under long-term immersion, the water absorption of the lime soil increases gradually at the initial stage of immersion and then increases to a stable value of 16.76–21.67%. The change law of the wet density is essentially controlled by the water absorption. The strength of lime soil decreases significantly, and the water resistance capacity is poor after soaking; lime soil with 15% lime content has better engineering properties. It is recommended to apply lime soil with 15% lime content in practical engineering with a volume ratio of lime to soil of 3:7 and to avoid using lime soil materials in immersed or other dry-humid environments.

Factors Affecting Kinetics and Gel Composition of Alkali–Silica Reaction in Alkali-Activated Slag Mortars

Alkali activation of metallurgical slags produces low-carbon cementitious binders for sustainable concrete production. However, the potential deleterious reaction of internal alkalis in alkali-activated slag (AAS) with siliceous aggregates is a serious durability concern. In this work, the alkali–silica reaction (ASR) in alkali-activated ground granulated blast furnace slag mortars with various activator dosages and types, aggregate reactivity, as well as incorporation of pulverized fly ash or silica fume is studied. The ASR-induced length expansion and microstructural damage in AAS mortars are studied by a modified accelerated mortar bar test and scanning electron microscopy with X-ray energy-dispersive spectroscopy. The results show that the kinetics of ASR-induced damage, as well as the gel composition and spatial distribution, in AAS mortars is highly dependent on the alkali dosage, activator type, and aggregate reactivity. The ASR-induced length expansion is approximately proportional to the volumetric fraction of dissolved glassy aggregates. However, AAS mortars show noticeable autogenous shrinkage at the initial stage of immersion, making the conventional judgment of ASR risks using length expansion as the sole indicator invalid. The dissolution kinetics of aggregate, which is influenced by the level of alkalinity and availability of reactive silica, seems to be the rate-limiting reaction of ASR-induced damage in AAS mortars under accelerated testing conditions.

Effect of Alloying Elements on Pit Growth in AA7075

AA7075 is known to a show high strength/weight ratio but suffers from localized corrosion, such as filiform corrosion, pitting, crevice corrosion, and stress corrosion cracking in Cl-containing environments. It has been proposed that Cu-containing intermetallics deteriorate the corrosion resistance and are the initiation sites of pitting. When AA7075 is immersed in an aqueous solution containing NaCl, the intermetallic compounds dissolve, and Cu-enriched particles are formed on and around the intermetallic compounds. Then, the Cu-enriched particles act as a cathode for the oxygen reduction and hydrogen generation reactions, and a strong alkali is locally generated. As a result, it is considered that the Al matrix dissolves, and local corrosion occurs. Therefore, alloy elements that suppress the cathode reaction on the Cu-enriched particles were studied.The samples were prepared from the arc-melting of AA7075 and pure Sn. The concentration of Sn was changed from 0.1 to 5 mass%. After casting, the ingots were heated to 430°C and rolled to a thickness of 2 mm. A solution treatment was performed at 500°C for 2 h. After the heat-treatment, the sample surfaces were polished with a diamond paste down to 0.25 µm.In order to characterize the shape and distribution of the intermetallic particles in the samples, the sample surfaces were observed with an optical microscope and SEM-EDS. The open circuit potentials of AA7075 were measured in 0.1 M NaCl adjusted to pH 6.0 for 16 h. The area exposed to the electrolyte was 10 mm × 10 mm. The measurements were performed in a naturally aerated solution, and Ag/AgCl (3.33 M KCl) was used as a reference electrode. After immersion, the sample surfaces were inspected. Anodic polarization curves of AA7075 were measured in 0.1 M NaCl adjusted to pH 6.0. The measurements were performed in the aerated solution, and the electrode area was 10 mm × 10 mm. In addition, that of pure Sn was also measured. The number of intermetallic compounds in AA7075 with 0.1 mass% Sn was low compared with AA7075. In the initial stage of immersion of AA7075 and Sn-added AA7075, the open circuit potentials were located approximately – 1.0 V and increased with time. Finally, the potential reached around – 0.7 V. The lower potential duration was prolonged by the Sn addition. After immersion, filiform-like corrosion and pitting were observed on the samples. In addition, the Al-matrix and the intermetallic compounds discolored by dissolution. The pitting potential of AA7075 and the 0.1 mass% Sn-added AA7075 alloy was -0.65 V, and no difference was observed.

Study on Wettability and Corrosion Behavior of Al2O3 Doped Polyurea Coatings

The Al2O3 powder was added as a filler to polyurea and the effect of doping amount on Shore hardness and wetting property were investigated. The electrochemical impedance spectroscopy (EIS) was used to investigate the corrosion resistance of coating/aluminum alloy system in 0.1 mol/L NaOH solution. The results showed that with the increase of the doping amount, the Shore hardness of the coating increased and the contact angle on the aluminum alloy matrix decreased. By analyzing the results of the characteristics of EIS and the fitting results, doped Al2O3 powder can improve the coating corrosion resistance, but it may affect the density of the coating and reduce the impedance modulus during the initial stage of immersion. The relationship between the doping amount of Al2O3 powder and the corrosion resistance in this test was 5 wt % > 10 wt % > 15 wt % > 0 wt %. In general, in the doping range of this test, since the powder was uniformly distributed in the polyurea coating, the cohesive force of the polyurea can be lowered to cause an increase in the wetting property. At the same time, excessive dopped Al2O3 powder may deteriorate the compactness of the polyurea and the binding property of the polyurea itself may decrease, resulting in deterioration of corrosion resistance. However, the proper doping of Al2O3 powder in polyurea improves its overall performance.

Prominent inhibition efficiency of sodium nitrate to corrosion of Al-based amorphous alloy

The corrosion resistance of Al-based amorphous alloy can be significantly improved with the addition of NaNO3 into NaCl solution. The growth rates of passive film in the initial stage of immersion are accelerated, and the metastable pitting is inhibited. The pitting potential of Al-based amorphous alloy is increased with the concentration of NaNO3, and the pitting corrosion is completely avoided when the concentration of NaNO3 is above 0.03 M. The transition from pitting to transpassivation can be attributed to the incorporation of NO3− in passive film. Sodium nitrate is an efficient corrosion inhibitor for Al-based amorphous alloy.

Effects of bentonite content on the corrosion evolution of low carbon steel in simulated geological disposal environment

The effects of bentonite content on the corrosion behavior of low carbon steel in 5 mM NaHCO3 + 1 mM NaCl + 1 mM Na2SO4 solution were investigated by electrochemical measurements combined with X-ray diffraction (XRD) and scanning electron microscopy (SEM). In the initial immersion stage, the cathodic process of low carbon steel corrosion was dominated by the reduction of dissolved oxygen, while it transformed to the reduction of ferric corrosion products with the immersion time. The presence of bentonite colloids could suppress the cathodic reduction of oxygen due to their barrier effect on the diffusion of oxygen. However, the barrier performance of bentonite layer was gradually deteriorated due to the coagulation and separation of bentonite colloids caused by the charge neutralization of iron corrosion products dissolved from the steel substrate. More bentonite colloids could maintain the barrier effect for a long time before it was deteriorated by the accumulation of corrosion products. Conversely, it could lose the performance completely, and the corrosion behavior of low carbon steel reverted to the same as that in the blank solution.

Effect of alloyed Ca on the microstructure and corrosion behavior of extruded Mg-Bi-Al-based alloys

Microstructural characteristics and corrosion behavior of extruded Mg-1Bi-1Al-xCa (x = 0, 0.6 and 1.2 wt%) alloys were investigated. It was found that the average grain size, texture intensity and corrosion resistance of the present low-alloyed alloy system initially increased and then decreased with increasing Ca content. Intergranular corrosion was observed in the present alloy system, which was related to the higher energy of the grain boundaries. Furthermore, the corrosion mode changed from pitting corrosion in the Ca-free alloy to the mixed pitting and filiform corrosion in the Ca-containing alloys in the initial stage of immersion based on the analysis in terms of micro-galvanic corrosion and the formation of protective film. As the immersion time increased, the filiform corrosion dominated in the Mg-1Bi-1Al-0.6Ca alloy. However, the corrosion product film of the Mg-1Bi-1Al-1.2Ca alloy was quickly destroyed due to the shedding of the coarse Mg2Bi2Ca2 phase, which resulted in severe corrosion.

Influence of zirconia and ceria nanoparticles on structure and properties of electrodeposited Ni-W nanocomposites

Ni-W-ZrO2-CeO2 nanocomposites were prepared by pulse electrodeposition for high wear and corrosion resistance as a protective coating. The structure (morphology, phase composition, roughness, crystallite size, surface feature) and properties (hardness, wear and corrosion resistance) of the nanocomposites were evaluated by various methods. The formation mechanism of the nanocomposites were proposed. The results show that the nanocomposite coatings are dense with nodular-like structure. The cauliflower-like protrusion clusters were formed due to the ‘tip discharge effect’ in the uneven distribution of electric field. It demonstrated that these nanoparticles were homogeneously distributed in the Ni-W matrix. The presence of the nanoparticles in Ni-W matrix improved the hardness, wear and corrosion resistance. The combination of ceramic particles and rare earth oxide particles was an excellent reinforcement phase for Ni-W matrix. The sample obtained at 1000 Hz has the optimal hardness and wear resistance, as well as the satisfying corrosion resistance. The nanocomposite deposited for 10 min owns the superior corrosion resistance in the initial stage of immersion. Ni-W-ZrO2-CeO2 nanocomposites own excellent performance and exhibit potential application values in harsh conditions.

Long time corrosion test of AZ31B Mg alloy via micro-arc oxidation (MAO) technology

Micro-arc oxidation (MAO) ceramic coatings of AZ31B Mg alloy were formed in phosphate-silicate based electrolyte with the addition of K2ZrF6. The effect of treatment time on physical and chemical properties of the coatings were thoroughly investigated. The results showed that the micropores on the surface of the coatings increased on size and decreased on porosity with the increasing MAO treatment time. The ZrO2 was inclined to absorbed into the outer porous layer than that of the inner dense layer. The corrosion study presents that the corrosion resistance increased with the increasing treatment time, which was proved directly proved by 150 h salt immersion test. The potentiodynamic polarization test proved that the coating with the MAO treatment time of 40 min is of the most superior corrosion resistance. In addition, the long time electrochemical impedance spectroscopy (EIS) test of the coating formed in the electrolyte with the treatment time of 40 min showed that, the corrosion resistance of the coating decreases in the initial immersion stage (64 h) little by little is because of the MgO decomposition in the outer porous layer. With the immersion time increased, the blocking effect of the outer porous layer postpone the deterioration of the inner dense layer.

Alkaline Corrosion-Resistant Anodic Aluminum Oxide Formed By Etidronic Acid Anodizing

A newly discovered electrolyte for anodizing aluminum, etidronic acid (CH3C(OH)[PO(OH)2]2), operates at high voltages of more than 200 V, and ordered porous alumina measuring 400-670 nm in cell diameter (interpore distance) can be fabricated via constant voltage anodizing. Because such porous alumina film formed at high voltages possesses a thick barrier layer, etidronic acid anodizing may be useful for corrosion protection of aluminum. Here, we describe the alkaline corrosion-resistant porous alumina formed by high voltage anodizing in an etidronic acid solution, and its hydration behavior in boiling water was investigated. Highly pure aluminum plates (99.999 wt%) were anodized in 0.3 M sulfuric acid, 0.3 M oxalic acid, 0.3 M citric acid, and 0.3 M etidronic acid solutions (293 K) at a constant current density of 30 Am-2 or a constant voltage of 250 V. The anodized specimens were immersed in a 2.5 M NaOH solution (293 K). The nanostructural changes were examined by electrochemical impedance spectroscopy (EIS). The anodized specimens were immersed in boiling water to seal the pores in the porous alumina film. The surface and cross-section of the specimens were characterized by field-emission scanning electron microscopy (FE-SEM) The plateau voltages during anodizing aluminum at a constant current density of 30 Am-2 in sulfuric and etidronic acid solutions exhibited approximately 16 V and 197 V, respectively. As the specimen anodized in sulfuric acid was immersed in a 2.5 M sodium hydroxide solution, H2 gas evolution was observed from the surface at the beginning of immersion, and the amount increased with the immersion time. In contrast, the specimen anodized in etidronic acid did not result in hydrogen gas evolution during immersion until 8 min. Here, the capacitance (Cb ) is inversely proportional to the thickness of the barrier layer. Figure 1 shows the changes in the reciprocal Cb with the immersion time, ti . Complete dissolution of porous alumina formed in etidronic acid takes 15 times longer than dissolution of the alumina formed by sulfuric acid anodizing due to the formation of a thick barrier layer. As the porous alumina formed by etidronic acid anodizing is immersed in boiling water, plate-like hydroxides were formed at the bottom of the pores in the initial immersion stage. The thickness of the hydroxide layer increased with the immersion time, and the nanopores are completely sealed by long-term immersion. Figure 1

Influences of albumin on in vitro corrosion of pure Zn in artificial plasma

Influences of albumin on in vitro corrosion behaviour of pure Zn in artificial plasma up to 28 days were investigated. Pure Zn undergoes uniform corrosion and a complex of albumin and zinc oxide/hydroxide forms on the surface. At the initial immersion stage, rapid adsorption of albumin retards the corrosion of pure Zn. However, the corrosion is promoted due to dissolution of metal matrix after 3 days. And 7 days later, Zn corrosion is obstructed by the complex accumulation on the surfaces. Profound understanding of pure Zn corrosion will encourage further exploration of Zn alloys in potential clinical application.

Corrosion-Resistant Porous Alumina Formed via Anodizing Aluminum in Etidronic Acid and Its Pore-Sealing Behavior in Boiling Water

Alkaline corrosion-resistant porous alumina was fabricated by anodizing aluminum in etidronic acid, and its hydration behavior during pore sealing in boiling water was investigated. High-purity aluminum plates were anodized in sulfuric, oxalic, citric, and etidronic acid solutions. Anodizing with etidronic acid caused stable growth of a uniform, porous alumina layer at a high voltage of approximately 200 V. This porous alumina possessed a thick barrier layer with an inner layer of pure aluminum oxide and exhibited a 10-fold increase in the corrosion resistance in a 2.5 M sodium hydroxide solution. When the porous alumina film formed by sulfuric acid anodizing was immersed in boiling water, plate-like hydroxide scales rapidly formed on the whole surface, and the pores were sealed within 10 min. In the case of etidronic acid, the hydroxides formed at the bottom of the pores in the initial stage of immersion, and the thickness of the hydroxide layer gradually increased with the immersion time. The porous layer was completely sealed by long-term immersion. Although the barrier layer was reduced to approximately 80% of its original size due to hydration, a thick barrier layer was still maintained at the bottom of the pores after immersion.

Characterization of films fabricated on AZ31 magnesium alloy by heat treatment and immersion methods

Thin films were fabricated on the surface of AZ31 magnesium alloy by heat treatment and subsequent immersion in deionized water or a NaOH solution. In this study, dense films were synthesized during the initial stage of immersion by increasing the (OH)− concentration at the interface of the high-temperature substrate and the solution. The surface of the magnesium substrates was covered by dense films aligned with the surface during the initial stages of immersion. The surface features of these films were different from those of the films formed simply by immersion in aqueous solutions. The cross-sectional results showed that the films formed in a NaOH solution with heat treatment were denser than those grown by DI water immersion with heat treatment. The X-ray photoelectron spectroscopy results revealed that the films fabricated by immersing the heat-treated substrates were mostly composed of MgO and Mg(OH)2 in both the outer and inner layers. Potentiodynamic polarization measurements showed that the films formed by the immersion of heat-treated substrates showed passive regions, and hence could act as passive layers.The morphology and structure of the films were observed by field-emission scanning electron microscopy and transmission electron microscopy. The compositions of the films were investigated using scanning transmission electron microscopy-energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Potentiodynamic polarization measurements were conducted to investigate the corrosion behavior of the films.

Adsorption Behavior of Gold Nanoparticles on Amino-terminated Micro Domains Fabricated on Quartz Substrate by Vacuum Ultra-violet Photolithography

Immobilization of gold nanoparticles (AuNPs) onto quartz is of considerable interest in optoelectronic applications. In this paper, we demonstrated a linear arrangement of AuNPs by controlling the function and optical properties at the microstructure of a quartz surface through formation of a 3-aminopropyltriethoxysilane (APS) self-assembled monolayer and the subsequent vacuum ultraviolet lithography. Citrate-capped AuNPs have been arranged on an APS-terminated surface by electrostatic attraction and in a VUV irradiated area by electrostatic repulsion. In addition, the density of AuNPs on along the boundary of the linear feature was higher than that in the center during the initial stage of immersion. The density of AuNPs along the linear feature became uniform over the entire surface with increasing immobilization time. These results induced the electrostatic interaction of negatively charged AuNPs on the interface between differently charged surfaces.

Influence of the secondary phase on micro galvanic corrosion of low carbon bainitic steel in NaCl solution

The corrosion behavior of lath bainitic and granular bainitic steels in 0.01 mol/L NaCl solution was studied by SEM and TEM observation, electrochemical monitoring and weight loss test. The results indicate that the micro galvanic couple forms between the steel matrix and the secondary phase, which causes non-uniform micro corrosion on surfaces of two steels. In lath bainitic steel, the secondary phase ω acts as the micro anode. While in granular bainitic steel, the secondary phase M acts as the micro cathode. Moreover, the corrosion acceleration caused by micro galvanic couple is obvious in the initial immersion stage, and then it becomes weak during the long term corrosion.

Influence of albumin on in vitro degradation behavior of biodegradable Mg-1.5Zn-0.6Zr-0.2Sc alloy

The immersion and electrochemical degradation behaviors of as-extruded Mg-1.5Zn-0.6Zr-0.2Sc (ZK21-0.2Sc) alloy in Hank’s solution with and without albumins were investigated and the influencing mechanism was elucidated. The immersion experiment showed that the presence of albumins could inhibit the corrosion of the ZK21-0.2Sc alloy through the adsorption effect at the initial immersion stage. With immersing on, the albumins underwent denaturation and began to show the chelation effect, which accelerated the corrosion of the ZK21-0.2Sc alloy. With increasing albumin concentration, the corrosion potential of the ZK21-0.2Sc alloy increased while the corrosion current density greatly reduced. The electrochemical test showed the presence of albumins had nearly no change to the cathodic Tafel slops, but the anodic Tafel slops increased obviously with increasing albumin concentration.

Evaluation of Early Degradation and Corrosion Resistance of Modified Zinc Coating with $$\hbox {SiO}_{2}$$ SiO 2 Nanoparticles

The electrochemical properties of zinc plate modified with different concentrations of nanoparticles in 3-(aminopropyl) triethoxysilane and 3-(trimethoxysilyl) propyl methacrylate solutions were investigated. Scanning electrochemical microscopy (SECM) was employed to examine the initial degradation of the samples in the electrolytes. The morphologies of passive films formed before and after immersion were characterised by means of scanning electron microscopy. Complementary electrochemical impedance spectroscopy (EIS) and neutral salt spray test techniques were carried out for further investigation. The results reveal that the films remained stable during the initial stage of immersion despite the occurrence of slow degradation. The SECM results together with those of EIS show that the performance of the films has been enhanced with increased $$\hbox {SiO}_{2}$$ nanoparticle concentration, leading to enhance corrosion resistance in return by amount of formation of corrosion product.

Effect of residual dissolved oxygen on the corrosion behavior of low carbon steel in 0.1 M NaHCO3 solution

The effect of residual dissolved oxygen (DO) on the corrosion behavior of carbon steel in 0.1M NaHCO3 solution was investigated by electrochemical measurements, corrosion mass loss test, scanning electron microscopy (SEM) and X-ray diffraction (XRD). In the initial immersion stage, the increase of the dissolved oxygen concentration led to the change of from a reductive state of active dissolution to an oxidizing state of pseudo passivation in low carbon steel. While in the final stage, all the steels transformed into the steady state of pseudo passivation. In the anaerobic solution, the formation of α-FeOOH was attributed to the chemical oxidization of the ferrous corrosion products and the final cathodic process only included the reduction of α-FeOOH, while in the aerobic solution, it included the reduction of oxygen and α-FeOOH simultaneously. As the main corrosion products, the content of α-FeOOH was increased while that of Fe6(OH)12CO3 was decreased with increasing concentration of dissolved oxygen. The total corrosion mass loss of the steel was promoted with the increase of dissolved oxygen concentration.