Corrosion Current Density Values Research Articles

The corrosion resistance of porous Ni–Ti alloys in seawater

Porous Ni–Ti alloys were fabricated by reactive synthesis of Ni and Ti elemental powders. The corrosion behavior of porous Ni–Ti alloys was explored by electrochemical methods and weight change measurements at 298 K in seawater. The polarization curves and electrochemical impedance spectroscopy data show that porous Ni–Ti (6.5:3.5) alloys provide the best corrosion resistance. The values of corrosion current density and corrosion rate are 1.6944 × 10−4 mA/cm2 and 1.9929 mm/a, respectively. The corrosion behavior and corrosion mechanism of porous Ni–Ti alloys are also discussed.

Effect of hydroxyapatite:zirconia volume fraction ratio on mechanical and corrosive properties of Ti-matrix composite scaffolds

Ti-based scaffolds reinforced with zirconia and hydroxyapatite were produced successfully by a hybrid method with an eco-friendliness and low cost to obtain low elastic modulus (E) with sufficient physical, electrochemical and biological properties. The effect of simultaneous modification of the volume fraction of hydroxyapatite (HA) and zirconia (ZrO2) on scaffolds was investigated in terms of mechanical, corrosive, and antibacterial properties. Scanning electron microscopy with attached electron dispersive spectroscopy and X-ray diffraction were used for the characterization of scaffolds. Compression and electrochemical tests were performed to determine mechanical properties with detailed fracture mechanism and in-vitro corrosion susceptibility to simulated body fluid at 37 °C, respectively. Antibacterial tests were carried out by comparing the inhibition areas of E.coli and S.aureus bacteria. It was observed that the mechanical strength of the scaffolds decreased with increasing HA:ZrO2 volume fraction ratio. The lowest E was achieved (6.61 GPa) in 6:4 HA:ZrO2 composite scaffolds. Corrosion current density (Jcorr) values were calculated to be 21, 337, and 504 µA/cm2 for unreinforced Ti, 3:2 and 6:4 HA:ZrO2 reinforced scaffolds, respectively. The inhibition capacity of the 6:4 reinforced composite scaffold was found to be more effective against S.aureus bacteria than other scaffolds.

Study on the Microstructure and Mechanical Properties of a Ti/Mg Alloy Clad Plate Produced by Explosive Welding

In this paper, the microstructure and properties of a Ti/Mg alloy clad plate manufactured by explosive welding were studied. The bonding interface was inspected by ultrasonic examination (US). The microstructure and the composition of the clad were characterized by OM and SEM. Properties were inspected by tensile test, shearing test, microhardness test and electrochemical corrosion. The results showed that the bonding interface of the clad plate was made up of straight areas and wavy areas. In straight areas, element diffusion occurred across the bonding interface. Additionally, in wavy areas, a melting zone occurred in the Mg alloy layer near to the bonding interface. Lots of light particles embedded on the melting zone. Tensile test results were comparable with the Ti sheet and the ultimate tensile strength of the clad plate demonstrated an 18% increase. The shearing strength of the clad plate was about 68–87 MPa. The microhardness of the clad plate was higher than that of the original sheets from the interface to 300 μm away. At over 300 μm, the microhardness of the clad plate decreased and approached the original sheets. Compared with the straight area, the hardness of the Mg alloy layer in the wavy area close to the interface increased by 12%. Corrosion results showed that the corrosion potential (Ecorr) absolute value of the clad plate increased by 24%, and the corrosion current density (icorr) value was 4 orders of magnitude lower, compared with the Mg alloy sheet. It was clear that the corrosion resistance of the clad plate was higher than that of the Mg alloy sheet. Cladding Mg alloy and Ti by explosive welding would improve the industrial applications of magnesium materials.

Mechanical and chemical properties of CoCrFeNiMo0.2 high entropy alloy coating fabricated on Ti6Al4V by laser cladding

CoCrFeNiMo0.2 high entropy alloy (HEA) coating was successfully synthesized on Ti6Al4V sheet by laser cladding. Microstructural characteristics of the HEA coating were investigated by the combined use of multiple characterization techniques. The results indicate that the coating consists of body-centered cubic (BCC) and σ phases with a typical uniform dendrite microstructure. The hardness of the coating is ∼900 HV0.1, about 2.3 times that of the substrate. The coated Ti6Al4V alloy presents better oxidation resistance than Ti6Al4V at 600 °C due to a compact oxide layer rich in Cr element. Compared to the Ti6Al4V substrate, a lower wear rate is noted for the coating, demonstrating greatly improved wear resistance, especially at 600 °C. The wear mechanisms of the coating are dominated by abrasive wear and oxidative wear. A more positive corrosion potential value and lower corrosion current density value are found for the coating, indicating a better corrosion resistance than the Ti6Al4V alloy. In-depth analyses suggest that the improved surface performance is associated with combined contributions from the solid-solution strengthening and grain refinement hardening, as well as the addition of Cr element.

Corrosion Behavior of Steels in LiBr–H2O–CaCl2–LiNO3 Systems

Conventional absorption and refrigeration systems use a LiBr/H2O mixture, which causes corrosion problems to the metallic components. In order to avoid this and some other problems such as crystallization and vapor pressure, some additives such as CaCl2 and/or LiNO3 are added to the LiBr/H2O mixture. In the present work, the corrosion behavior of 1018 carbon steel as well as of type 304 and 316L stainless steels was evaluated in LiBr/H2O at 80 °C with the addition of CaCl2, LiNO3, and CaCl2+LiNO3. Potentiodynamic polarization curves and electrochemical impedance spectroscopy were used for this purpose. The results showed that the corrosion current density values of all tested steels decreased with the addition of CaCl2 and/or LiNO3, which induced the formation of a passive film on carbon steel. Both types of stainless steels showed a passive film in all tested conditions, but the passive current density was the lowest, whereas the passive zone was the widest, for 316L steel. The corrosion mechanism remained unaltered for both stainless steels but was changed with the addition of CaCl2 and/or LiNO3 for carbon steel.

Pouteria sapota as green CO2-corrosion inhibition of carbon steel

Imidazoline obtained from the essential oil contained in Pouteria sapota seed was tested as an environmentally-friendly corrosion inhibitor of 1018 carbon steel in CO2 saturated 3.5 % NaCl solution using electrochemical techniques. This imidazoline contains fatty acids with the presence of long hydrophobic chains, with 52.73 % of unsaturated (oleic and linolenic acids) and 40 % of saturated (palmitic and myristic acids) compounds. Polarization curves revealed that this inhibitor is highly efficient mixed-type of inhibitor with the inhibitor efficiency of 99.9 % reached at 25 ppm. Also, the lowest pitting potential value was observed at 25 ppm of inhibitor, making the carbon steel highly susceptible to the pitting type of corrosion. Corrosion current density value decreased by nearly four orders of magnitude, and a passive film formation was induced for inhibitor concen­tra­tions higher than 5 ppm. Accordingly, polarization resistance values were increased from 100 W cm2 up to about 106 W cm2 at 25 ppm of inhibitor. The inhibitor forms a protective film of corrosion products adsorbed on the metal surface in a very strong chemical way, following a Langmuir type of adsorption isotherm. This was supported by electrochemical impedance spectra that showed two relaxation processes ascribed to electrode interface and film regions. In agre­ement with polarization resistance data, the total electrode resistance determined by inter­facial charge transfer and film resistance, increased up to 8.2 ´ 105 W cm2 in presence of 25 ppm of inhibitor. SEM images additionally showed that type of corrosion was fully changed from uniform to a localized type when 25 ppm of inhibitor was added into the solution.

Effect of admixed chloride and molarity of NaOH solution on early-age strength and reinforcement corrosion in FA/GGBS geopolymer concrete

Chloride persuaded steel reinforcement corrosion is an important durability issue in concrete structures. In this present study, the corrosion of reinforcing steel was evaluated in 0% and 3% sodium chloride admixed fly ash (FA)/ground granulated blast furnace slag (GGBS) GPC mixes. Two different molarities of NaOH solution i.e. 8 M and 10 M were used for preparing the GPC mixes with FA/GGBS proportions of 100/0 (wt.%), and 70/30 (wt.%). Reinforced geopolymer concrete prismatic specimens were prepared for half-cell potential and linear polarization resistance (i.e. LPR) measurements after 28 days and 180 days of its manufacturing. The obtained results showed that the early age 7 days compressive strength of GPC mixtures reduced with the existence of NaCl. The higher value of compressive strength was detected in GPC prepared with FA/GGBS proportion of 70/30 as compared to that made with FA/GGBS proportion of 100/0. Further, GPC made with higher molarity (10 M) of NaOH solution showed greater strength than that made with lower molarity (8 M) of NaOH solution. The less negative half-cell potential value and lower corrosion current density (Icorr) value of steel reinforcement in GPC was observed at the later age i.e., at 180 days in all GPC mixes as compared to 28 days. The higher chance of rate of corrosion, and the higher Icorr of steel reinforcement was detected in 3.0% NaCl added geopolymer concrete. Further, more negative half-cell potential and higher Icorr of steel reinforcement were detected with a rise in molarity of NaOH solution in GPC made with FA/GGBS proportion of 70/30 at both ages (i.e. at 28 days and 180 days). However, mostly less negative half-cell potential and lower Icorr of reinforcing steel were detected with a rise in molarity of NaOH solution in GPC made with FA/GGBS proportion of 100/0 at both ages.

Organic additives based alkaline alumina slurry for selective removal of barrier layer metals

In the present work, tantalum (Ta) and copper (Cu) chemical mechanical polishing (CMP) has been carried out using a polishing slurry containing 2 wt% alumina (abrasive), 1 wt% potassium carbonate (oxidizer), and 0.25 wt% each urea and citric acid (additives). The Cu removal rate (RR) decreases with an increase in pH and is found to be minimum at pH 11 while Ta RR increases till neutral pH and then decreases till pH 11 having maximum RR at pH 7. Ta to Cu removal rate selectivity of 1:1.02 is attained at pH 11. Other parameters such as the effect of additives concentration, applied pressure, and platen rotational speed are also studied and results are reported to get a clear scenario. Surface charge analysis reveals that with change in pH, zeta potential alters and 30mV zeta potential is found at pH 11 which confirms the stability of the formulated slurry. To comprehend the removal mechanism of the metals, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) are employed. The same trend is encountered for both corrosion current density (Icorr) and film resistance (Rfilm)values resulting from Tafel and EIS. Based on the research conducted a plausible material removal mechanism is suggested.

Texture evolution and corrosion behaviour of Sn–1.5 wt% Cr coatings containing Graphene oxide

ABSTRACT Sn–1.5 wt% Cr coating incorporated with varying quantity of Graphene oxide (GO) were deposited using electrodeposition technique on mild steel strip using aqueous electrolyte bath. The aqueous bath was dispersed with GO with increasing concentrations in mg/L (31.2, 62.5, 93.7, 125 and 156.2). All the coatings exhibited compact morphology and contained Sn and Cr-oxide phases (CrO2 and Cr2O3). Potentiodynamic polarisation and impedance spectroscopy techniques showed that the coating corrosion resistance increased for the initial addition of GO till Sn–Cr–GO2 coating (from 62.5 mg/L of GO) and it decreased thereafter for higher GO additions. The corrosion current density value exhibited by pristine Sn–Cr, Sn–Cr–GO2 and Sn–Cr–GO5 (from 156.2 mg/L of GO) was 1.38, 0.5 and 4.09 µA/cm2, respectively. Characterisation of the coating texture showed that between all the coatings, low angle grain boundary fraction was highest for Sn–Cr–GO2 coatings. The highest corrosion resistance was on account of special impermeable and inert properties of GO which was uniformly distributed in the coating matrix and the presence of a large fraction of low energy low angle grain boundaries. High corrosion rate in the case of Sn–Cr–GO5 coatings was attributed to the agglomeration of GO in the coating matrix which resulted in non-uniform coating morphology with high surface defects.

Inhibition of corrosion of API K55 steel by tannin from Acacia mearnsii bark in highly acidic medium

AbstractThe corrosion inhibiting effect of the tannin from Acacia mearnsii bark on API 5CT K55 steel, used for casing in the oil and gas industry, was investigated in 1 M HCl medium with different tannin concentrations. Corrosion was monitored by electrochemical tests using potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS). Complementary analyses of the corroded surfaces were performed by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X‐ray diffraction (XRD). With the application of A. mearnsii tannin, the cathodic branch of the PP curves shifted to lower corrosion current density values. EIS analysis indicated that inhibitor molecules were adsorbed on the steel surface, which provided protection against corrosion. The SEM, AFM, and XRD data showed that in the presence of the inhibitor, a film and amorphous material were adsorbed on the steel surface, plausibly associated with the formation of tannates. The highest inhibition efficiency was obtained at an inhibitor concentration of 0.7 5 g L−1 (92% determined by PP and 98% by EIS), and a high degree of surface coverage was observed, compared with that obtained using the other concentrations of tannin.

Role of layered double hydroxide in enhancing wear and corrosion performance of self-lubricating hydrophobic Ni-B composite coatings on aluminium alloy

A layered double hydroxide reinforced nickel boride (LDH/Ni-B) hydrophobic composite coating was deposited on the A356 aluminium alloy surface by the electroless method. The anti-corrosion and anti-wearing performances were studied with varying amounts (0–5 wt%) of LDH in the nickel boride matrix. The composite coating with the highest water contact angle having a value of 120° was observed for Ni-B containing 0.5 wt% of LDH. This could be attributed to the increased surface roughness offered by the LDH layers. Potentiodynamic polarization measurements in 3.5 wt% NaCl solution indicate a significant decrease in the corrosion current density (icorr) values for LDH added composite coating with a lowest of 3.96 × 10−6 A/cm2 for 0.5 wt% of LDH. This may be due to the combined effect of both coating hydrophobicity and feasibility for chloride ion intake by the ion-exchange mechanism of LDH. Improved wear resistance was obtained for composite coated aluminium with a minimum wear rate for 1% LDH added coating. Self-lubricating tribolayer formation in the presence of LDH gave higher wear resistance.

Corrosion Behavior of Chromium Coated Zy-4 Cladding under CANDU Primary Circuit Conditions

The manuscript is focused on corrosion behavior of a Cr coating under CANada Deuterium Uranium(CANDU) primary circuit conditions. The Cr coating is obtained via the thermionic vacuum arc procedure on Zircaloy -4 cladding. The surface coating characterization was performed using metallographic analysis and scanning electron microscopy (SEM) with an energy dispersive spectra detector (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) investigations. The thickness of the Cr coating determined from SEM images is around 500 nm layers After the autoclaving period, the thickness of the samples increased in time slowly. The kinetic of oxidation established a logarithmic oxidation law. The corrosion tests for various autoclaving periods of time include electrochemical impedance spectroscopy (EIS) and potentiodynamic tests, permitting computing porosity and efficiency of protection. All surface investigations sustain electrochemical results and promote the Cr coating on Zircaloy-4 alloy autoclaved for 3024 h as the best corrosion resistance based on decrease in corrosion current density values simultaneously with the increase of the time spent in autoclave. A slow increase of Vickers micro hardness was observed as a function of the autoclaved period as well. The value reached for 3024 h being 219 Kgf/mm2 compared with 210 Kgf/mm2 value before autoclaving.

Uso del extracto de litchi chinensis como inhibidor de la corrosión del aluminio 2024-T3 en 3.5% NaCl

The corrosion inhibition of AA2024-T3 Aluminium alloy in 3.5 % NaCl solution by using Litchi chinensis seed ethanolic extract has been evaluated by using potentiodynamic polarization curves, linear polarization resistance and electrochemical impedance spectroscopy tests. Results have shown that the extract was a good corrosion inhibitor with an efficiency that increased with its concentration. Corrosion and passivation current density values were decreased indicating that the extract behaves as an anodic type of corrosion inhibitor. Inhibitor was adsorbed on to the metal surface in a combination of physical and chemical, dominated by a physical type of adsorption following a Langmuir adsorption isotherm. Corrosion rate was decreased due to the formation of a protective corrosion products layer which blocked further corrosion of metal by electrolyte.

Low-temperature Sn electrodeposition: Texture evolution, grain boundary constitution and corrosion behavior

Electrodeposition of Sn was conducted at three different electrolyte bath temperatures: 25 °C, 20 °C, and 15 °C in galvanostatic conditions. Corrosion analysis using the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization revealed that decreasing the electrodeposition bath temperature reduced the corrosion resistance of Sn coatings. The 25 °C coating exhibited the highest polarization resistance (Rp) value of 71,460 Ω.cm2 and lowest corrosion current density (icorr) value of 0.251 μA.cm−2, whereas the 15 °C coating exhibited Rp value of 16,120 Ω.cm2 and icorr value of 0.891 μA.cm−2. The electrochemical response was correlated with the texture and grain boundary constitution using the electron backscatter diffraction (EBSD) technique. It was observed that decreasing the electrodeposition temperature decreased the predominance of the (100) texture, increased the strain, and reduced the average grain size of Sn grains. The Sn coating with the lowest corrosion resistance displayed a predominant (501) texture, lowest grain size, and highest strain within the Sn grains.

Comparing the corrosion behaviour of AA2050 and AA7050 aluminium alloys by scanning vibrating electrode and scanning ion-selective electrode techniques

ABSTRACT The susceptibility to localised corrosion of the high strength alloys, AA2050-T84 and AA7050-T7451, used in the aerospace industry, was investigated in this study by localised electrochemical techniques, specifically, scanning vibrating electrode technique (SVET) and scanning ion-selective electrode technique (SIET), in 0.005 mol L−1 NaCl solution. The study was initially carried out using both alloys individually and then, coupling the two alloys and evaluating the effect of galvanic coupling between them. The results revealed that the AA2050-T84, being nobler than the AA7050-T7451, presented higher corrosion current density values when tested in isolation and the depth of corrosion penetration was significantly deeper in the AA2050-T84 alloy than in the AA7050-T7451. However, galvanic coupling of the two alloys resulted in cathodic protection of the AA2050-T84 alloy and a reduction in corrosion current densities on both alloys.

Corrosion Resistance of a Plasma-Oxidized Ti6Al4V Alloy for Dental Applications

A Ti6Al4V alloy was plasma-oxidized at 600 °C during 1, 2, 3, 5 and 8 h and corroded in an artificial saliva solution. Electrochemical evaluation was performed by using potentiodynamic polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) measurements during 100 h. Corroded specimens were characterized by using Raman spectroscopy and scanning electronic microscopy (SEM). All tests indicated that the highest corrosion resistance was obtained for specimen oxidized during 3 h since the noblest free corrosion potential, lowest passive and corrosion current density values, as well as the highest polarization resistance values were obtained under these circumstances. EIS measurements indicated that the highest impedance and phase angle values obtained for this specimen exhibited a high capacitive behavior typical of a very compact passive film.

Electrochemical and quantum mechanical investigation of various small molecule organic compounds as corrosion inhibitors in mild steel

The corrosion inhibition property of selected small organic compounds was investigated using electrochemical measurements, including potentiodynamic polarization (PDP), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and density functional theory (DFT) calculations. The inhibition efficiency (IE %) of the inhibitor on mild steel (MS) in 1 M HCl was then determined. Results show that the presence of the inhibitors resulted in decreased corrosion current density (Icorr) values and increased polarization resistance (Rp). Furthermore, the use of higher concentrations of inhibitors led to an increased inhibition efficiency. Tafel slopes and shifts in the Ecorr values suggested that the inhibitors tested are mixed-type inhibitors that form a protective layer on the surface of the substrate. Of the organic compound inhibitors tested, the inhibitor 4-ethylpyridine (EP) exhibited the highest Rp values and inhibition efficiency values from the PDP, LPR, and EIS analyses, respectively. DFT calculations showed negative adsorption energies and confirmed the chemisorption of the inhibitors allowing for the formation of a hydrophobic protective film against corrosion and correlations between the quantum chemical values and electrochemical data were demonstrated. The results show the influence of the presence of electronegative O, S, and N atoms, as well as the role of aromatic rings in the promotion of surface protection by preventing aggressive ionic species from binding onto MS.

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.

The effect of the ultrasound agitation and source of ceria particles on the morphology and structure of the Zn–Co–CeO2 composite coatings

The goal of this research was to develop and analyse novel Zn–Co–CeO 2 protective coatings on steel. Two different sources of ceria (CeO 2 ) particles were employed: commercial powder and synthesized stable colloidal dispersion-sol. The plating solution was agitated by ultrasounds (20 and 30 W cm −2 ) or by magnetic stirrer (300 rpm) during electrodeposition. The CeO 2 particles used were characterized by different methods, namely scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) to compare the morphology, crystallinity and particle size. The morphology of developed composite coatings was analysed by SEM, the preferred texture was calculated based on XRD results and corrosion behaviour was evaluated by electrochemical impedance spectroscopy (EIS) and polarization measurements. Utilizing ultrasounds during electrodeposition resulted in advanced properties of the nanocomposite coatings compared to magnetic stirring. The particle content in the coatings increased to ~5 wt% when ultrasounds were applied and ceria sol used as a source of particles. Presence of ceria in composite coatings offered favourable action in corrosion behaviour increasing barrier properties of composite coatings, thereby providing a prolonged lifetime of Zn–Co alloy coatings. The benefit was more pronounced in the case of ceria sol, and deposition at 20 W cm −2 , when values of impedance modulus at low frequencies reached four times higher values after 4 days exposure to 3 wt% NaCl solution than for coatings deposited with magnetic stirring for both ceria source. The lowest value of corrosion current density (2.15 μA cm −2 ) was determined for Zn–Co–CeO 2 (CeO 2 sol) composite coatings deposited under 20 W cm −2 US power.

Electroless codeposition of GO incorporated silane nanocomposite coating onto AZ91 Mg alloy: Effect of GO content on its morphology, mechanical and corrosion protection properties

The corrosion of Mg alloys is a significant concern in practical applications, and silane-based protective organic coatings are promising to protect the Mg alloys from corrosion. The (3-glycidyloxypropyl) trimethoxysilane/graphene oxide (GPTMS/GO) coating was developed using electroless codeposition technique on AZ91 Mg alloy such that GO sheets were grafted with silanol groups. The coating was prepared by dipping AZ91 Mg alloy in GPTMS/GO solution and then curing at 120 °C. The electrochemical measurement results showed an increased corrosion resistance of AZ91 Mg alloy in 3.5% NaCl solution. The decrease in the corrosion current density value of 0.016 µA cm−2 is attributed to the formation of a passive layer of GO grafted GPTMS on the surface of AZ91 Mg alloy. The enhanced hydrophobicity of 108°, the improved adhesion (5 A) and high hardness (52 HV) were attained due to covalent metallic siloxane bonds (MgOSi) and the laminate structure of GO developed on AZ91 substrate.