Main Corrosion Products Research Articles

In Vitro Corrosion of Quaternery Magnesium Alloy Foam by Addition of Zinc


 
 
 
 Magnesium alloys have been intensively studied as possible resorbable material with adequate mechanical properties similar to natural bones but very poor corrosion properties. In this analysis, the addition of Zn element to quaternary Mg-Ca-Zn alloy foam was evaluated with TiH2 as a foaming agent and manufactured with high-purity raw materials the powder metallurgy process. In Hank's solution, the rate of corrosion of specimens by direct observations with Scanning Electron Microscopy ( SEM), Electron Dispersion Spectrometry (EDS), static immersion studies, potentiodynamic evaluations, and X-Ray Diffraction (XRD). The specimens post-immersion characteristics and the corresponding Hank's solutions were examined at 2, 4, 6, 24, 48, and 72 hours of immersion. The findings show that the microstructure of alloy morphology, such as pores, pitting corrosion, needle shapes, and galvanic corrosion has the main corrosion products Mg(OH)2 and Ca10(PO4)6(OH)2. The addition of less than 6 percent wt Zn will minimize the corrosion rate but increase with 10 percent wt Zn. From this study, Mg-Zn-Ca alloy at 6 percent wt Zn has the lowest corrosion rate with slow pH changes in the process.
 
 
 

The hot corrosion behavior in vanadate environment and thermal cycling behaviors of YTZ and 2GYTZ for thermal barrier coating applications

A preliminary examination was carried out for hot corrosion resistance to V2O5 and thermal cycling behaviors of two alternative materials: zirconia co-doped with 16 mol% YO1.5 + 16 mol% TaO2.5 (YTZ) and zirconia co-doped with 14 mol% YO1.5+ 2 mol% GdO1.5 + 16 mol% TaO2.5 (2GYTZ). The compositions and microstructures of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). Results showed ZrV2O7 and YVO4/GdVO4 were the main reaction products at 750 °C and 850 °C for 2 h, while YVO4 and m-ZrO2 were detected as the main corrosion products at 850 °C for 10 h or rising temperature to 950 °C. With the depletion of V2O5, ZrV2O7 disappeared and decomposed into m-ZrO2 and V2O5. The hot corrosion mechanisms are similar for YTZ and 2GYTZ ceramics. However, the amount of m-ZrO2 in the 2GYTZ was much more than that in the YTZ at the same corrosion conditions. The weaker bonds due to partial substitution of Y3+ with larger size of Gd3+ and the size misfit between Gd3+ and Zr4+ resulted in decreasing the anti-corrosion capability of 2GYTZ ceramic. The tetragonal phase was very stable for YTZ and 2GYTZ coatings during high temperature heat treatment. The thermal durability of the YTZ and 2GYTZ TBCs can be significantly improved by using the YSZ buffer layer. While the cycling lifetimes for 2GYTZ coating was much shorter than that of YTZ coating whether designed for single-ceramic-layer structure or double-ceramic-layer structure. Failure of the 2GYTZ coating mainly resulted from the thermal expansion mismatch stress, concentrated thermal stress introduced by the severe sintering and low fracture toughness.

Iron Calcium Carbonate Instability: Structural Modification of Siderite Corrosion Films.

Corrosion research related to CO2-containing environments has focused over the past few decades on siderite formation (FeCO3) as a main corrosion product on carbon steel, yet the influence of Ca and other ions on its chemical and structural characteristics is not fully understood. Metal-localized corrosion is the biggest industrial challenge because of the unknown and unpredictable character of this phenomenon that frequently leads to failure. We report here the role of Ca and formation of iron-calcium carbonate (FexCayCO3) through a spiral growth model as in the calcite system and quantify the replacement of Fe2+ by Ca2+ ions in the structure of FeCO3 to form FexCayCO3. The incorporation of Ca2+ inhibits the completion of spiral segments on the growth of the rhombohedral crystals of FeCO3, promoting an enlargement of its structure along the c-axis. This leads to distortions in the chemical structure and morphology affecting the chemical and mechanical properties. Under flow conditions over time in an undersaturated environment, Ca is leached out from the expanded structure of FexCayCO3 increasing the solubility of the crystals, weakening the mechanical properties of the resulting corrosion films and stimulating localized corrosion.

Alloying and brushite coating improve corrosion resistance of magnesium in a simulated physiological environment

While magnesium (Mg) and its alloys have been regarded as encouraging orthopaedic implant materials, the high corrosion rate limits their application. This study determines how alloying and brushite coating affected the corrosion rate of Mg in vitro. The corrosion behaviours of pure Mg, Mg-Nd-Zn-Zr alloy (Jiao Da Bio-Mg, JDBM) and brushite coated JDBM in a simulated physiological environment were comparatively evaluated. The evaluation included the surface morphology, roughness, chemical composition, structure, phase composition and functional groups of the corrosion products with the corrosion rate, pH value, Mg2+ concentration and osmotic pressure of the immersion solution. The following corrosion resistance trends were found: brushite coated JDBM > uncoated JDBM > pure Mg. The main corrosion product of the Mg alloys in the cell culture medium was MgCO3·3H2O. Compared with the pure Mg, the corrosion form of the JDBM alloys was uniform corrosion. The results showed that the addition of the Nd, Zn and Zr elements and brushite coating effectively improved the corrosion resistance of metal Mg. In addition, the power law function formula Δm = ρAtB was applied successfully to predict the mass loss of the JDBM alloy in an in vitro immersion test.

Effect of relative humidity on corrosion behavior of SAC305 and Sn–37Pb solders under polyvinyl chloride fire smoke atmosphere

The effect of ambient relative humidity from 50 to 98% on the corrosion characteristics of SAC305 and Sn–37Pb solders under the polyvinyl chloride fire smoke atmosphere was researched. The corrosion kinetics results reveal that the mass loss and corrosion rate of both solders show an increasing trend when the relative humidity is lower than 90%. While the mass loss and corrosion rate at 98% relative humidity present a significant decrease compared with those at 90% relative humidity, which may be ascribed to the impeded diffusion of oxygen under saturated humidity environment. The corrosion rate analysis indicates that SAC305 solder is more susceptible to corrosion. Besides, the corrosion microstructures reveal that the corrosion products grow more and more with the increase of relative humidity, but are most serious at 90% relative humidity. Sn21Cl16(OH)14O6 with SnO and SnO2 are detected as the main corrosion products of SAC305 solder by EDS, XRD and XPS analysis. While the corrosion products of Sn–37Pb solder are Sn21Cl16(OH)14O6 and PbCl2.

A study on corrosion products and processes of patinated tin bronze in formic acid

The corrosion processes of bare bronze and three types of patina-bearing tin bronze in the presence of formic acid have been explored through laboratory exposure. Following exposure time of 4, 14 and 28 days, the morphology and composition of the corrosion products on the sample were characterized to investigate their evolution by using SEM, XRD and Raman. The results indicated that Cu2O was first generated on the bare bronze surface, then Cu(OH)2 was formed at the early stage of the corrosion and as the exposure time increased, Cu(OH)(HCOO) and Cu(HCOO)2 were further generated. Bronze with Cu2O layer was destroyed by formic acid and converted into Cu(HCOO)2, which was similar to the conversion process of corrosion products of bare bronze, except that, the account of products of bronze patinated with Cu2O was more than that of bare bronze, indicating that the Cu2O layer on the sample surface was destroyed and further transformed. The main corrosion product of bronze with CuCl patina was Cu2(OH)3Cl, which was consistent with the reaction process of powdery rust. For bronze with mixed patina, two corrosion processes of Cu2O patina and CuCl patina proceed at the same time, and the corrosion products were Cu(HCOO)2 and Cu2(OH)3Cl, which were basically consistent with the corrosion behavior of bronze covered with a Cu2O and a CuCl patina.

Simulation of Porous Magnetite Deposits on Steam Generator Tubes in Circulating Water at 270 °C

In the secondary side of pressurized water reactors (PWRs), the main corrosion product accumulated on the steam generator (SG) tubes is magnetite, which has a porous structure. The purpose of this work is to simulate the porous magnetite deposited to the SG tubes using a loop system. We newly developed a circulating loop system for a porous magnetite deposition test. A test section was designed as a single hydraulic flow channel, and a cartridge heater was fabricated and mounted into a commercial SG tube to provide an equal heating source for the primary water. After the deposition test, the simulated magnetite deposits were characterized for comparison to real SG tube deposits collected from an operating PWR plant. The magnetite deposits produced using the loop system were appropriate for simulating the real SG tube deposits because the particle characteristics, phase, and porous morphology are closely similar to those of real deposit samples. Using the loop system, the chemical impurities such as Na and Cl can be easily concentrated within the pores of the simulated magnetite deposits. These simulated magnetite samples are expected to be widely utilized in various research fields such as the heat transfer degradation and magnetite accelerated corrosion of SG tubes.

Study of Microbially Influenced Corrosion in the Presence of Iron-Oxidizing Bacteria (Strain DASEWM2)

The present study deals with the investigation of microbially influenced corrosion of mild steel by the iron-oxidizing bacterium (IOB), Pseudomonas sp. strain DASEWM2, using electrochemical tests, immersion tests, and surface analysis. The corrosion rate obtained by Tafel plots was higher after exposure of ~ 24 h to 72 h when the concentration of sessile cells and constituents of extracellular polymeric substances were high. In inoculated media, cyclic polarization curves show lower pitting potential, repassivation potential, and large area under the hysteresis loop, indicating higher susceptibility of steel to localized corrosion. Immersion tests show higher corrosion rate (0.252 ± 0.05 mpy) and large deep pits in the open area (maximum pit depth 140 ± 8 µm) and under crevice (maximum pit depth 95 ± 4 µm) indicating a higher degree of corrosion in inoculated media. Corrosion products formed on corroded steel samples were analyzed using EDAX, XRD, and FTIR techniques. Goethite and lepidocrocite are the main corrosion products in the case of inoculated media. In contrast, lepidocrocite and iron hydrogen phosphate are the main corrosion products in the case of control media. The absence of iron hydrogen phosphate, a protective type of corrosion product, on steel exposed to inoculated media may be responsible for observing a higher degree of corrosion due to bacteria.

High Temperature Corrosion Behaviors of 20G Steel, Hastelloy C22 Alloy and C22 Laser Coating under Reducing Atmosphere with H2S

High-temperature corrosion behaviors of 20G steel, Hastelloy C22 alloy and C22 laser coating was evaluated by corrosion mass gain measurements at 450 °C. The corrosive atmosphere is 0.2 vol% H2S–0.1 vol% O2–N2, which simulated the severe high-temperature corrosion environment occurred under low-NOx combustion in pulverized-coal furnaces. Experimental results showed that the corrosion resistance of the C22 laser coating and the C22 alloy was obviously better than 20G steel. Furthermore, it should be noted that the C22 laser coating fabricated in this study displayed a higher corrosion resistance than the commercial C22 alloy although they had the same chemical composition. The severe pitting corrosion was observed in 20G steel with the corrosion products consisting of FeS2, Fe2O3 and Fe3O4. The C22 alloy and C22 laser coating exhibited the uniform corrosion and their main corrosion products were NiS2, CrS and a small amount of chromium and manganese oxides.

Dynamic Corrosion Test Using LiNO3 Containing Molten Salt for CSP Applications

Low melting point thermal energy storage (TES) materials have been proposed in the last years to reduce the storage cost in concentrating solar power (CSP) technology. One of the most interesting additive due to the enhancement in thermal properties is lithium nitrate. However, there is a lack of dynamic corrosion tests to simulate real operation conditions in CSP plants. In this work, we present a dynamic reactor set up where a mixture of 30 wt.% LiNO3 + 57 wt.% KNO3 + 13 wt.%. NaNO3 is moved through a mechanical stirrer obtaining a lineal speed of 0.30 m/s. A commercial carbon steel A516 was tested as container material at 390 °C during 1000 h. Fe2O3 and Fe3O4 were obtained as the main corrosion products by scanning electron microscopy (SEM) and x-ray diffraction (XRD) with a metallographic corrosion rate of 0.015 mm/year.

Effect of relative humidity on the corrosion behavior of Sn–0.7Cu solder under polyvinyl chloride fire smoke atmosphere

AbstractThe effect of environment relative humidity (RH) on the corrosion behavior of Sn–0.7Cu solder was investigated by the weight loss method and surface characterization techniques. In this study, RH ranging from 50% to 98% was researched. The results show that the corrosion degree is getting worse from 50% RH to 90% RH. However, the corrosion rate at 98% RH is lower than that at 90% RH, which may be ascribed to the degree of oxygen diffusion in electrolyte layers of different thicknesses. The microstructure characterization proved that the corrosion products exhibit a superimposed growth and present the same corrosion degree variation trend as the corrosion kinetics. The compositions of corrosion products are examined, and Sn21Cl16(OH)14O6, SnO, and SnO2 are the main corrosion products.

Synchrotron X-ray diffraction investigation of the surface condition of artefacts from King Henry VIII's warship the Mary Rose.

Synchrotron X-ray diffraction (XRD) measured on the XMaS beamline at the ESRF was used to characterize the alloy composition and crystalline surface corrosion of three copper alloy Tudor artefacts recovered from the undersea wreck of King Henry VIII's warship the Mary Rose. The XRD method adopted has a dynamic range ∼1:105 and allows reflections <0.002% of the height of major reflections in the pattern to be discerned above the background without smoothing. Laboratory XRD, scanning electron microscopy-energy dispersive spectroscopy, synchrotron X-ray fluorescence and X-ray excited optical luminescence-X-ray near-edge absorption structure were used as supporting techniques, and the combination revealed structural and compositional features of importance to both archaeology and conservation. The artefacts were brass links believed to be fragments of chainmail and were excavated from the seabed during 1981 and 1982. Their condition reflects very different treatment just after recovery, viz. complete cleaning and conservation, chemical corrosion inhibition and chloride removal only, and distilled water soaking only (to remove the chlorides). The brass composition has been determined for all three at least in the top 7 µm or so as Cu(73%)Zn(27%) from the lattice constant. Measurement of the peak widths showed significant differences in the crystallite size and microstrain between the three samples. All of the links are found to be almost chloride-free with the main corrosion products being spertiniite, sphalerite, zincite, covellite and chalcocite. The balance of corrosion products between the links reflects the conservation treatment applied to one and points to different corrosion environments for the other two.

Zinc/Silver Particle (Zn/AgP) Composite Coatings: Evaluation of Corrosion in Physiological Environments and Antibacterial Activity against P. aeruginosa

In this work, zinc/silver particle (Zn/AgP) composite coatings were manufactured by electrodeposition to investigate their antibacterial capacity and corrosion rate in physiological environments. The morphology and composition of the coatings were analysed by glow-discharge optical emission spectroscopy and scanning electron microscopy coupled to an energy dispersive spectrometer. The results showed the formation of Zn/AgP composite coatings with a homogeneous distribution of Ag throughout the coating surface and depth. Additionally, the Ag content in the coatings increased with increasing concentrations of AgP in the electrolytic solution. The Zn/AgP composite coatings with 0.30 wt.% Ag on the surface (0.30 wt.% Agsurf) showed efficiencies close to 100% growth inhibition of the bacteria Pseudomonas aeruginosa after 10 min of contact. The corrosion rate of the Zn and the Zn/AgP (0.30 wt.% Agsurf) coatings in Hank’s, Ringer’s and Phosphate buffered saline (PBS) solutions was evaluated by polarization curves and by immersion tests over different time periods (7, 30, and 40 days). The corrosion rate of the Zn/AgP (0.30 wt.% Agsurf) coatings was on the order of tenths of microns per year and the amount of zinc mass dissolving per day was in the range of 0.15 to 0.7 mg cm−2. Additionally, the surface of the coatings was analysed by X-ray diffraction (XRD) after 40 days of immersion. These results showed the formation of ZnO, as the main corrosion product, in the samples immersed in Hank’s and Ringer’s solutions. In the samples immersed in PBS, the formation of a passivating film of Zn2(PO4)3·2H2O was detected.

The influence of hot extrusion deformation on microstructure evolution, tensile properties and corrosion behavior of Mg–3Al–0.5Mn–0.5Sr alloy

A novel microalloyed Mg–3Al–0.5Mn–0.5Sr (AMJ300) alloy was designed and prepared. Then the original structure of as-cast alloy was optimized by hot extrusion. The influence of extrusion on microstructure, corrosion and tensile properties of as-cast AMJ300 alloy were studied by OM, SEM, EDS, XRD, TEM, electrochemical workstation and tensile tests. The results indicated that α-Mg, Al8Mn5 and Al4Sr phases constitute the AMJ300 alloy. Furthermore, the microstructure of alloy was further refined after extrusion, which indicates that the microstructural evolution during extrusion was governed by dynamic recrystallization. The fine and close of structure and the morphology change of intermetallic compounds greatly improved the corrosion resistance of AMJ300 alloy. The results of corrosion rate, corrosion current and corrosion morphology showed that the corrosion resistance of as-cast alloy could be significantly improved by extrusion. The main corrosion products of AMJ300 alloy in 3.5 wt.% NaCl solution was Mg(OH)2. After extrusion, the tensile properties of AMJ300 alloy was significantly improved. The tensile strength reached 349 MPa, the yield strength reached 229 MPa, and the elongation reached 13.2%. Compared with the as-cast alloy, the tensile strength, the yield strength and the elongation increased by 218.1%, 248.9% and 173.7% respectively

Study on stress corrosion behavior of C110 steel by electrochemical hydrogenation

In this study, the effects of hydrogen on the electrochemical behavior and stress corrosion behavior of C110 steel in CO2 environment was explored by electrochemical hydrogen charging, four-point bending stress loading and electrochemical test. The results show that with the raise of applied stress, the film resistance, transfer resistance of corrosion products decrease, and Icorr increases. After hydrogen charging, C110 steel has greater activity, and the combined action of external stress further promotes the corrosion reaction. The application of stress will destroy the formation of corrosion product film and reduce its protection. However, when the stress is further increased to 102%σs, the larger grains will be broken into smaller grains, so that the surface area of the film will be increased again and the protection of the substrate will be enhanced. The main corrosion products analyzed by XRD are α-Fe, Fe2O3 and MgFe2O4. The applied stress will not change the phase composition of the corrosion products.

Effect of Temperature on Corrosion Behavior of Low-Alloy Steel Exposed to a Simulated Marine Atmospheric Environment

The corrosion behavior of steel exposed to a simulated marine atmosphere at different temperatures (from 30 to 60 °C) has been investigated. The corroded specimens were analyzed gravimetrically and by scanning electron microscopy, x-ray diffraction and electrochemical techniques. The results revealed that the morphology of volcanic bulge can be observed on the sample surface at 60 °C, which can be attributed to the effect of temperature on the diffusion rate of ions. As the exposure temperature is increased, the relative content of the main corrosion products changed greatly. The increase in temperature not only promoted the transport of aggressive ions Cl− and the formation of local corrosion, but also affected the solubility of oxygen gas in the thin film, leading to the increase in the relative content of Fe3O4 and the acceleration of corrosion.

Investigating local corrosion behavior and mechanism of MAO coated 7075 aluminum alloy

In order to study the effect of defects on the corrosion behavior of MAO coatings, global electrochemical method including potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) was used to measure the corrosion resistance of MAO coatings. Local electrochemical measurements including local impedance spectroscopy (LEIS) and scanning vibrating electrode technique (SVET) were used to study the local corrosion mechanism. The confocal microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to observe the microstructure and phases of the samples. Results of global electrochemical measurement demonstrate that the scratches cause the reduction of the impedance and the increase of the corrosion current density. LEIS results show the impedance value distribution of the coating with the scratch. With the changes over time, the minimum impedance value of the scratch decreases first and then increases from the third hour. SVET results show the corrosion current density distribution of the scratched coating. The maximum corrosion current density at the scratch increases first and then decreases. The results of local electrochemical measurements show that the corrosion rate at the scratch decreases when the reaction lasted 3 h. Confocal microscopy found that the scratch is expanding with increasing time, and the depth and cross-sectional area of the coating is 5 times deeper and 10 times larger than that of 7075Al with scratch at the first 6 h. The 6-day immersion test proved that the scratch coating still has the protective effect on the substrate. The main corrosion product is Al(OH)3. A physical model reflecting the mechanism of the scratch propagation and the formation of the corrosion product film is proposed.

Secondary spreading of acidified aerosols on the surface of Zn

Secondary spreading of acidified sodium chloride (NaCl) aerosol droplets on the surface of zinc have been studied. The in-situ observation of the secondary spreading, corrosion morphology, corrosion products under different position and volume loss are used to understand the secondary spreading of the acidified aerosol. The results reveal that the secondary spreading effect of NaCl aerosol droplet is more pronounced compared to the acidified aerosol droplets which are mainly embodied in larger spreading region and faster spreading rate. The difference of the secondary spreading effect is associated with acidification which inhibits the increase in the pH at the periphery. Furthermore, lower corrosion rate was observed for the acidified aerosol droplets due to smaller secondary spreading area (cathodic region). The main corrosion product in the center of NaCl aerosol droplet and the aerosol droplet acidified by HCl is Simonkolleite, while for the aerosol droplet acidified by H2SO4 which shows several different corrosion morphologies in the center, the main corrosion products are Gordaite, Simonkolleite and Zn4Cl2(OH)4SO4 ∙ 5H2O. The formation of protective corrosion products Gordaite that can inhibit the anodic reaction leads to the smallest spreading area and the lowest corrosion rate for the aerosol droplet acidified by H2SO4.

Effects of Al content on the corrosion properties of Mg–4Y–xAl alloys

AbstractThe corrosion performances of Mg–4Y–xAl (x = 1, 2, 3, and 4 wt%) alloys in the 3.5% NaCl electrolyte solution are investigated by electrochemical tests, weight loss measurement and corrosion morphology observation. The results indicate that corrosion modes for the alloys are localized corrosion and the filiform type of attack. With Al concentration increasing from 1 to 4 wt%, the corrosion rate of Mg–4Y–xAl alloys decreases firstly and then increases, and WA42 alloy shows the best corrosion resistance. The addition of Al element to Mg–4Y alloys leads to the formation of Al2Y and Al11Y3 intermetallic compounds and reduces the proportion of Mg24Y5 phase. Corrosion resistance of the Mg–4Y–xAl alloys mainly depends on the size and distribution of the second phases. Besides, the addition of excessive Al can greatly consumes the Y element in the matrix, thus leading to a less protective film on the alloys. The effect of the relative Volta potential changes between the second phases and α‐Mg on corrosion resistance of Mg–4Y–xAl alloys is insignificant. The main corrosion products of the Mg–4Y–xAl alloys are Mg(OH)2, Mg3(OH)5Cl·4H2O, Mg0.72Al0.28(CO3)0.15(OH)1.98(H2O)0.48, and Mg4Al2(OH)12CO3·3H2O.

Mg-Phenolic Network Strategy for Enhancing Corrosion Resistance and Osteocompatibility of Degradable Magnesium Alloys.

Magnesium-based alloys are the most widely used materials for degradable metallic implants and have considerable potential for bone applications owing to their excellent stimulating effect on osteogenesis. However, their high corrosion rate limits their structural stability and causes oxygen deficiency and an excessive increase in the pH around the defect area during bone healing. Magnesium oxides, which are the main corrosion products of Mg, are nontoxic materials with useful effects on new bone formation and pH neutralization. Metal–phenolic networks were introduced recently as a cost-effective and efficient surface modifier and were fabricated by deposition of nanosized metal oxides on different types of substrates using the chemical reaction between phenolic groups and metallic ions. In this study, magnesium oxide films were formed successfully on a Mg-based substrate using Mg–phenolic networks. The effects of various coating parameters on the surface morphology, corrosion resistance, degradation behavior, wettability, and osteocompatibility of degradable metallic materials after surface modification with Mg–phenolic networks were thoroughly investigated for the first time. The results showed that the initial concentration of Mg ions was the main parameter affecting the corrosion resistance, which was almost as much as 3 times that of uncoated samples. Additionally, cytotoxicity and viability assessment and observation of the morphological changes in bonelike cells showed that the in vitro osteocompatibility was significantly enhanced by coatings with Mg concentrations of 2.4–3.6 mg mL–1. Finally, in vivo animal studies using the rat calvarial defect model confirmed that the proposed coating method mitigated the formation of gas cavities around the implantation area by reducing the corrosion rate of the Mg-based implant. The nanosized metal oxides produced by the Mg–phenolic network significantly improved the biodegradability and osteocompatibility of Mg alloys, suggesting a potential approach to advancing the clinical application of Mg alloys.