Dissolution Of Alloys Research Articles

Electrochemical recovery of rhenium from W–Re alloys in the form of perrhenic acid: I. Fundamentals of the process

Linear voltammetry is used to study the anodic behavior of a VR20 alloy in sodium hydroxide solutions, and the possibility of high-rate dc electrochemical dissolution of this alloy is shown. Experimental dependences of the rate of alloy dissolution and the anode current efficiency on the anode current density are determined, and the electric power consumed for alloy dissolution under optimum conditions is determined in large-scale tests. Potassium perrhenate is removed from the formed electrolyte as an intermediate product to form perrhenic acid. The main characteristics of the electrodialysis conversion of the synthesized potassium perrhenate into perrhenic acid with a concentration of 591 g/L electrolyte are determined. A technological scheme is proposed for the recovery of rhenium from the wastes of a W–Re alloy in the form of perrhenic acid.

An Electrochemical Quartz Crystal Microbalance Study on Electrodeposition of Aluminum and Aluminum-Manganese Alloys

The electrodeposition process of aluminum and aluminum-manganese alloys was studied in situ, by using an electrochemical quartz crystal microbalance, EQCM, with damping monitoring, in AlCl3 based ionic liquids. Cyclic voltammetry, potentiostatic and galvanostatic deposition were performed at different temperatures, from 25°C up to 100°C. The morphology of the deposits was investigated by SEM and AFM, and their composition by EDX. The stoichiometry of the alloys was calculated from the EQCM data, based on Sauerbrey's equation. We could show that for thin films electrodeposited on gold electrodes, one can tune their morphology, and in the case of the alloys, also their composition, by modifying the deposition current or potential, as well as by modifying the temperature of the electrolyte. The morphology of the deposits changed gradually with increasing the amount of Mn in the electrolyte from a polyhedral like structure for Al films to round granules for the AlMn alloys. The mechanism for electrodeposition and dissolution of Al and AlMn alloys were analyzed and discussed based on the EQCM data.

Production of nickel–cobalt concentrate in rhenium-containing refractory alloy processing

The results of electrochemical processing of the ZhS32-VI refractory alloy implemented in a galvanostatic mode in the nitric acid electrolyte are described. Experiments on the electrochemical dissolution of the same alloy in the galvanostatic mode using a nitric acid solution with a concentration of 100 g/L at various current densities are carried out. It is shown that its constituent components separate quantitatively: refractory metals such as niobium, tantalum, molybdenum, and tungsten concentrate in the anodic slime, while partially cobalt and rhenium, as well as most of the aluminum, chromium, and nickel, transfer into the electrolyte. The functional process diagram for processing of the ZhS32-VI alloy is proposed, in which the formation and separation of the main mass of nickel and cobalt are performed at the first stage with the formation of the metallic Ni–Co-containing sediment.

Dissolution and characterisation studies on U–Zr and U–Pu–Zr alloys in nitric acid medium

Dissolution of metallic alloys, U–Zr and U–Pu–Zr has been investigated in HNO3 media. An electro oxidative dissolution technique was also examined. Explosive nature of metallic alloys during dissolution in nitric acid has been investigated. A method has been developed for the determination of zirconium in the presence of uranium and plutonium using a spectrophotometric technique. The influence of HNO3, uranium and plutonium during the estimation of Zr has been studied. Plutonium interferes in the estimation of Zr and it can be avoided by employing ascorbic acid. The method was employed for the estimation of Zr in samples generated during dissolution of Zr containing alloy fuels.

Role of molybdenum in corrosion of iron‐based alloys in contact with hydrogen sulfide containing solution

A sample iron molybdenum alloy with 3.4 wt% (2 at%) molybdenum, and pure iron, are exposed to hydrogen sulfide saturated saline solution for up to 56 days. In addition, their behavior under anodic polarization in the same electrolyte is investigated. The initially fast dissolution of the iron molybdenum alloy slows down significantly over time, while iron corrodes with a constant rate. The observed slow down of the corrosion rate can be described well with an exponential decay of the instantaneous corrosion rate with a time constant of (0.15 ± 0.03)/day, which implies stop in corrosion in practical terms after 2 weeks. Relationships are discussed between the instantaneous corrosion rate, and the time‐averaged integral corrosion rate. Dissolution under anodic polarization of the iron molybdenum alloy is slower than for pure iron. While at certain times, pyrite, FeS2, is found as corrosion product, the main corrosion product is mackinawite, FeS. The latter likely contains a certain fraction of molybdenum in case of the iron molybdenum alloy. On iron molybdenum, corrosion products forming a sealing layer are observed, which slow down further corrosion. The corrosion products on iron molybdenum show better adhesion to the base material surface.

Single-stage production of the nickel concentrate with processing of the rhenium-containing refractory alloy

The results of electrochemical processing of the ZhS32-VI refractory alloy in nitric acid solutions are discussed. The main production idea involves the performance of an electrochemical process under the controlled value of the anodic potential. This procedure provides the preferential transfer of nickel, which is the alloy base, into the solution and the formation of the cathodic product or metallic nickel with a purity no lower than 95%. Experiments on the electrochemical dissolution of the mentioned alloy at various values of the anodic potential are performed. It is determined that the cathodic product contains at Ea = 1.05 V, %: Ni 94.9, Re 0.2, Co 4.7, and Cr 0.1. It is established that the incorporation of the chloride ion (20 g/L) into the nitric acid electrolyte exerts no substantial effect on process characteristics; notably, the amount of nickel in the anodic slime decreases from 2.4 to 1.6%, and no considerable increase in the nickel content in the cathodic product takes place. The exclusion is a considerable increase in the transfer rate of rhenium into the electrolyte; notably, the rhenium concentration in the nitric acid electrolyte after the 10-h production process is 1.26 g/L, and that in the nitric acid electrolyte with the addition of the chloride ion is 8.90 g/L. It is shown that the process performance of the electrochemical dissolution of Re-containing nickel-based refractory alloys under the controlled anodic potential Ea = 1.05 V in nitric acid electrolytes provides the formation of a nickel concentrate with a purity no lower than 95% in one stage and makes it possible to concentrate rhenium in the anodic slime.

Extremely High-Rate, Uniform Dissolution of Alloy 22 in Anhydrous Organic Solutions at Room Temperature

During routine pharmaceutical development and scale-up work, severe corrosion of a Hastelloy Alloy C-22 (Alloy 22) filter dryer was observed after single, short (several hour) contact with the product slurry at room temperature. Initial investigations showed that the presence of both 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and HCl was sufficient in an acetonitrile solution to cause rapid corrosion of Alloy 22. More detailed mass loss studies showed initial corrosion rates exceeding 25 mm/y that then decreased over several hours to steady state rates of 3 mm/y to 5 mm/y. The corrosion was highly uniform. Electrochemical measurements demonstrated that although Alloy 22 is spontaneously passive in acetonitrile solution, the presence of HCl leads to the development of a transpassive region. DDQ is a sufficiently strong oxidizer, particularly in acidic solutions, to polarize the Alloy 22 well into the transpassive region, leading to the observed high-corrosion rates.

ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ФОРМООБРАЗУЮЩИХ ПРОЦЕССОВ ПРИ ОБРАБОТКЕ АЛЮМИНИЕВЫХ СПЛАВОВ

It is well known that machining aluminum and its alloys is accompanied by very considerable changes in quality parameters of parts surface layers which affect greatly performance attributes. The study of the machining conditions influence upon surface layer quality in parts allows defining optimum cutting parameters and increasing performance attributes of many parts. It is well known that there are alternative methods of shaping which are a combined treatment which can include a mechanical, electrical and chemical influence upon a surface worked. Combined methods of treatment possess a wide range of controlled factors affecting a quality level of a surface formed and that is why they are convenient and effective in use during processes of shaping in parts made of difficult-to cut and heterogeneous materials. As the investigation results have shown during edge cutting machining anodic-mechanical treatment in the course of cutting Al 2 and Al 3 silumins the oxides formation on the surface worked worsens considerably electrochemical processes. Particularly it is significant at anodic dissolution of aluminum alloys having a high capacity to oxidation. The method of electromechanical combined treatment allows managing qualitative indices in the course of surface shaping and as a result promoting the achievement of an essential level in quality parameters of a surface level.

Effect of Titanium and Boron on the Stability of Grain Refinement of Al-Cu Alloy

Abstract The present research was conducted on thin-walled castings with 5 mm wall thicknesses. This study addresses the effect of the influence of different master alloys, namely: (1) Al-5%Ti-1%B, (2) Al-5%Ti and (3) Al-3%B, respectively on the structure and the degree of undercooling (ΔTα = Tα−Tmin, where Tα - the equilibrium solidification temperature, Tmin - the minimum temperature at the beginning of α(Al) solidification) of an Al-Cu alloy. The process of fading has been investigated at different times spent on the refinement treatment ie. from 3, 20, 45 and 90 minutes respectively, from the dissolution of master alloys. A thermal analysis was performed (using a type-S thermocouple) to determine cooling curves. The degree of undercooling and recalescence were determined from cooling and solidification curves, whereas macrostructure characteristics were conducted based on a metallographic examination. The fading effect of the refinement of the primary structure is accompanied by a significant change in the number (dimension) of primary grains, which is strongly correlated to solidification parameters, determined by thermal analysis. In addition to that, the analysis of grain refinement stability has been shown with relation to different grain refinements and initial titanium concentration in Al-Cu base alloy. Finally, it has been shown that the refinement process of the primary structure is unstable and requires strict metallurgical control.

Magnesium Alloy Corrosion Under Thin Electrolyte Layer Using Electrochemical Impedance Spectroscopy and Polarization Curve

Here, we reported some simulated atmospheric corrosion studies of magnesium alloy (including AZ91D and AM60) based on electrochemical impedance spectroscopy and polarization technology, and the effect of rare earth element Ce or La on corrosion behavior of magnesium alloy. In the case of AZ91D magnesium alloy, the electrochemical results reveal that the corrosion rate of AZ91D under thin electrolyte layers (TELs) is slower than that in bulk solution and decreases with the TEL thickness thinning. Bothe the anodic and cathodic reactions are restrained under TELs, especially in thickness thinning to around 200 μm and lower. For AM60 magnesium alloy and pure magnesium, the corrosion processes are also inhibited by decreasing thickness of TEL. All those corrosion rates and behavior of magnesium and its alloy are different from that of aluminum, copper and zinc alloy, which are due to the special cathodic reaction for magnesium alloy. Rare earth elements Ce or La have a strong effect on the dissolution of AM60 magnesium alloy under TEL. Typical impedance diagrams consist of two capacitive arcs at high and intermediate frequencies in all cases. At low frequencies, an arc or tail in the Nyquist plots appears sometimes disappears due to the complex corrosion reaction. Comparing to AM60, AM60 with rare earth element addition presents the 3rd capacitive loop sometimes instead of an inductive tail under the TEL thicknesses of 200 and 300 μm, which is associated with reaction taking place on the cathodic intermetallic compounds formed with rare earth elements. The EIS and polarization measurements indicate the rare earth element alloying can reduce corrosion rate of AM60 and AZ91D both under TEL and in bulk electrolyte.

Electrodeposition of Al-W Alloys in AlCl3-NaCl-KCl Molten Salt Containing WCl4

Introduction Aluminum and aluminum alloys are widely used in a variety of industrial products like cars and electric appliances due to the lightweight and excellent electrical and thermal conductivity. Furthermore, aluminum oxide which is very thin and chemically stable forms on the surface. The oxide film contributes the corrosion resistant property of the surface. However, in the presence of halogen ions (ex. Cl-, F-, I- and Br- ions), corrosion takes place for the oxide surface. Al‐transition metal alloys have better corrosion resistance for chloride solution. Al-W alloys especially show the good corrosion resistance for pitting corrosion of the surface. Al-W alloys are also expected the increase of the hardness compared with pure Al. One of the available method to obtain Al alloys is an electrodeposition. Tsuda et al. previously reported the electrodeposition of Al-W alloy in the Lewis acidic AlCl3-[EtMeIm]Cl room temperature ionic liquid1). When higher temperature molten salts are used for electrodeposition of Al-W alloys, rapid electrodeposition may be achieved. AlCl3-NaCl-KCl molten salt is useful melt because the eutectic point of this system is 366 K at the composition of AlCl3 : NaCl : KCl = 61 : 26 : 13 (molar ratio). In this study, we report the mechanism of electrodeposition of Al-W alloys in the AlCl3-NaCl-KCl melt and discuss the relationship between the composition of the electrodeposit and the electrolysis potential. Experimental Electrodeposition of Al-W alloys was carried out in AlCl3-NaCl-KCl melt containing 10 mM WCl4 at 423 K. The electrochemical cell was used three-electrode system. A glassy carbon plate or a pure copper plate was used as working electrode at the voltammogram measurements or constant current electrolysis, respectively. An aluminum plate or a tungsten plate was used as counter electrode. Pure aluminum wire placed in a Pyrex glass tube filled with the AlCl3-NaCl-KCl melt was used as a reference electrode. All electrochemical measurements were performed under air atmosphere. The composition, surface morphology and identification of the electrodeposits were used X-ray fluorescence spectrometer (XRF), scanning electron microscope (SEM) and X-ray diffraction (XRD) instrument. Results and discussion A voltammogram was measured between 1.5 V and -0.2 V vs. Al/Al (III) at a sweep rate of 0.01 Vs-1 on a glassy carbon electrode in the AlCl3-NaCl-KCl melt with or without WCl4. In the melt without WCl4, the voltammogram showed a cathodic current at lower than -0.03 V with steep increase. An anodic current was observed from -0.02 V in the reverse scan. The cathodic and anodic currents correspond to the Al deposition and dissolution reactions, respectively. In the melt containing WCl4, two small cathodic currents were observed from 1.05 V and 0.45 V in the cathodic scan. The two cathodic currents correspond to a reduction of tungsten ions. When the potential is reversed at -0.2 V, an anodic current appeared from 0 V. The anodic current corresponds to dissolution of Al and Al-W alloy formed by the previous cathodic scan. In the results, the reduction steps of W ions lower than 1.05 V may occur from W (IV) to W (III), and from W (III) to W (0) below 0.45 V. To examine the relation between the electrolysis potential and the composition of the electrodeposits, constant potential electrolysis of Al-W alloys was carried out on Cu substrate at the potential range from -0.05 V to 0.4 V with electric charge of -30 Ccm-2(theoretical film thickness, 10 μm). The results suggested that when the electrolysis potential becomes higher, the W content in the electrodeposits increases. SEM images of the Al-W alloy prepared at -0.05 V and -0.025 V showed size of particle of about 5 μm, and cover the entire surface uniformly. On the other hand, it was found that a relatively small electrodeposit was formed on the substrate at higher than 0 V. The results of XRD showed the peaks corresponding to Al when the W content is less than 1 at%. When the W content is higher than 19 at%, Al peaks disappeared. However, broad peak showing the presence of an amorphous phase of W was observed at 0.4 V. Reference 1) Tetsuya Tsuda et al, J. Electrochem.Soc. 161, D405 (2014). Acknowledgment This paper is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Electrochemical Behavior of NiTi Alloys during Rapid Straining

Ni-Ti alloy is one of the most investigated alloys as a biomaterial due to its favorable mechanical properties such as superelasticity and shape memory effect. Due to the toxicity of nickel, the dissolution of nickel is one of the most severe problems when Ni-Ti alloy is used in the body. Protective passive films mainly consisting of TiO2 are formed on the alloy, which suppresses the dissolution of nickel. However, the breakdown of the passive films incudes the metal dissolution. Therefore, the metal dissolution from Ni-Ti alloy has been examined using several techniques. In the present work we examine the dissolution and repassivation behavior of NiTi alloys in Hanks’ solution using rapid straining technique.

Investigation of the electrochemical behaviour of AA1050 aluminium alloy in aqueous alkaline solutions using Dynamic Electrochemical Impedance Spectroscopy

The paper presents the electrochemical behaviour of aluminium alloy AA1050 in aqueous alkaline media in the pH range 14–8.5. Electrochemical study was applied in order to obtain comprehensive information on the mechanism and kinetics of the process of anodic dissolution of aluminium, supplemented by monitoring of surface topography using an electron microscope. The corrosion rate of AA1050 increases with increasing concentration of hydroxyl ions OH−. Cathodic reaction occurs in the form of two competing processes, oxygen depolarization and hydrogen evolution. During anodic polarization process up to +8V vs Ag|Ag2O, activation control of the electrochemical process is converted to diffusion control upon reaching the potential approx. 0V. Instantaneous impedance spectra in Nyquist projection had at least two time constants: high–frequency loop of capacitive character associated with charge transfer process during anodic dissolution and negative low-frequency capacitance loop. Dynamic processes occurring during anodic dissolution of aluminium alloy can be concluded on the base of instantaneous change of electric parameters. Dynamic Electrochemical Impedance Spectroscopy (DEIS) enables continuous impedance monitoring of non–stationary processes, such as anodic dissolution of aluminium in aqueous alkaline environments.

The mechanism of generating nanoporous Au by de-alloying amorphous alloys

De-alloying, i.e. selective dissolution of alloys, is currently studied to produce nanoporous gold items suited for use in catalysis, electrochemical applications, sensors and actuators. Both crystalline and amorphous alloys can be selectively etched. In the former, less noble atoms are removed from surface terraces of grains layer by layer, while noble ones form mounds. These evolve by undercutting and electrolyte percolation to form a ligament network. The mechanism of ligament development by de-alloying amorphous alloys is unknown. Here we show that for de-alloying a Au-based glass, in this case Au40Cu28Ag7Pd5Si20, percolation of the electrolyte through cracks of the native surface oxide initiates the formation of protuberances which are soon undercut. An interlayer develops, where Au crystals germinate, grow to nanometer size by diffusion and impinge. This is how ligaments start to coarsen. The interlayer is found at all stages between coarsened ligaments and amorphous phase. The ligaments are defective polycrystals, as opposed to single crystals obtained from crystalline alloys.

Electrodeposited Co-W alloys and their prospects as effective anode for methanol oxidation in acidic media

Abstract Electrodeposited Co-W alloys having different composition and structure were tested as anodes for methanol electrooxidation. The structure of electrodeposited Co-W alloys having various tungsten content is either nanocrystalline (3 and 18 at.% of W) or “amorphous-like” (30 at.% of W). The electrodeposition was performed on the stainless steel substrate from citrate-borate bath at 60 °C and a cathodic current density 10 mA ∙ cm − 2 . Alloys having different compositions were obtained by varying pH from 5 to 8. A well-defined crystalline structure was indicated for Co-W having 3 at.% and 18 at.% of W: these deposits have a hexagonal close packed (hpc) structure typical for electrodeposited pure Co. The high content of W in the alloy (~ 30 at.%) leads to the formation of nanocrystalline structure (“amorphous-like”). The electrocatalytic activity of prepared Co-W alloys was examined by means of cyclic voltammetry in the mixture of 1 M CH 3 OH and 0.1 M H 2 SO 4 . The electrooxidation of methanol depends on the content of W in the alloy. It was found that the crystalline Co-3 W and Co-18 W alloys are inactive for methanol oxidation, and the electrochemical alloys dissolution occurs in the tested media. Whereas, the high content of W (~ 30 at.%) in the Co-W coating prevents the continuous Co-W alloy dissolution and it might be used as anode for the methanol oxidation in the acidic media. The annealing of Co-W deposits was performed at 600 °C for 1 h in the air and formation of Co 3 O 4 and CoWO 4 compounds with simultaneous decrease of tungsten content in the alloys were detected. The annealed Co-W coatings show lower activity toward methanol electroxidation compared to as-deposited Co-30 at.% W.

Evaluation of Pb–17Li compatibility of ODS Fe-12Cr-5Al alloys

The Dual Coolant Lead Lithium (DCLL: eutectic Pb–17Li and He) blanket concept requires improved Pb–17Li compatibility with ferritic steels in order to demonstrate acceptable performance in fusion reactors. As an initial step, static Pb-17at.%Li (Pb-17Li) capsule experiments were conducted on new oxide dispersion strengthened (ODS) FeCrAl alloys ((1) Y2O3 (125Y), (2) Y2O3+ZrO2 (125YZ), (3) Y2O3+HfO2 (125YH), and (4) Y2O3+TiO2 (125YT)) produced at ORNL via mechanical alloying (MA). Tests were conducted in static Pb–17Li for 1000 h at 700 °C. Alloys showed promising compatibility with Pb–17Li with small mass change after testing for 125YZ, 125YH and 125YT, while the 125Y alloy experienced the highest mass loss associated with some oxide spallation and subsequent alloy dissolution. X-ray diffraction methods identified the surface reaction product as LiAlO2 on all four alloys. A small decrease (∼1 at.%) in Al content beneath the oxide scale was observed in all four ODS alloys, which extended 60 μm beneath the oxide/metal interface. This indicates improvements in alloy dissolution by decreasing the amount of Al loss from the alloy. Scales formed on 125YZ, 125YH and 125YT were examined via scanning transmission electron microscopy (S/TEM) and revealed incorporation of Zr-, Hf-, and Ti-rich precipitates within the LiAlO2 product, respectively. This indicates an inward scale growth mechanism. Future work in flowing Pb–17Li is needed to further evaluate the effectiveness of this strategy in a test blanket module.

Selective dissolution of an amorphous Mg65Cu25Y10 alloy in organic acids and dilute HCl solution

Selective dissolution behavior of an amorphous Mg65Cu25Y10 precursor alloy in organic acids has been investigated. Nanoporous copper (NPC) with a pore size of 11–19 nm and ligament of 16–19 nm is obtained after dealloying in 0.01 M formic and acetic acids. NPC formed in formic acid has a larger pore size and similar ligament size than that in acetic acid. Plot of nanopore size versus dealloying time demonstrates the formation of NPC is controlled by the surface diffusion of Cu adatoms. Low diffusion ability of anions with more CH chains from organic acids results in the formation of finer NPCs. On the other hand, NPC is unable to form in 0.01 M HCl solution and corrosion products consist of Y2O3, Y(OH)3, Mg(OH)2 and metallic Cu. The thick corrosion products passivate the surface to prevent from the further aggregation of corrosion. The formation of the finer NPC in organic acids benefits from slow surface diffusion of Cu adatoms, the buffer ability of the organic solutions and the low mobility of the organic molecule.

The effect of pin profiles on the microstructure and mechanical properties of underwater friction stir welded AA2519-T87 aluminium alloy

AA2519-T87 is a new armour grade aluminium alloy employed in the fabrication of light combat military vehicles. Joining of this material using fusion welding processes, results in the formation of solidification defects like porosity, alloy segregation and hot cracking. In order to overcome the solidification related problems, solid state welding processes such as friction stir welding (FSW) can be used. Though the joining takes place below the melting temperature of the material, the thermal cycle experienced by the thermo-mechanical-affected zone (TMAZ) and heat-affected zone (HAZ) is causing grain coarsening and precipitates dissolution in the age-hardenable aluminium alloys, which deteriorate the joint properties. To get rid of this problem, underwater friction stir welding (UWFSW) process can be employed. The water cooling reduces the heat, and thus, the thermal softening required taking place in TMAZ and HAZ. Therefore, the material flow is entirely different in FSW and UWFSW. In this investigation, a comparative study is made to understand the influence of tool pin profiles, namely straight cylindrical (STC), taper cylindrical (TAC), straight threaded cylindrical (THC) and taper threaded cylindrical (TTC) on stir zone characteristics and the resultant tensile properties of both FSW and UWFSW joints. From this investigation, it is found that the joint made by taper threaded pin profiled tool underwater cooling medium exhibited higher tensile properties of 345 MPa and joint efficiency of 76 %. The enhancement in the strength is attributed to the precipitation hardening, grain boundary strengthening and narrowing of lower hardness distribution region (LHDR).

Effect of Pb-underpotential deposition on anodic dissolution and passivation of pure Fe and Fe-Ni alloys in acidic perchlorate solution

The potentio-dynamic polarization curves of pure Fe, Fe-30 Ni, and Fe-70 Ni alloys in acidic perchlorate solutions (pH 1.9) without and with 10−3 M Pb2+ were measured to investigate the effect of Pb-underpotential deposition (Pb-UPD) on anodic dissolution and passivation in relation to Pb-induced stress corrosion cracking (Pb-SCC) of Ni base alloys. The addition of 10−3 M Pb2+ shifts the open circuit potentials of pure Fe and Fe-Ni alloys toward noble direction to inhibit the anodic dissolution and promote the passivation, which results from Pb-UPD on substrate metals. The electro-desorption of Pb proceeds with anodic potential sweep and the anodic dissolution is enhanced when the surface coverage of Pb is reduced to a critical level. Tafel slopes (b + = 8.5∼15 mV decade−1) of anodic dissolution for pure Fe and Fe-Ni alloys in the presence of Pb2+ are significantly low as compared with those (b + = 34∼40 mV decade−1) in the absence of Pb2+, which reflects on the rapid enhancement in surface reactivity as a result of electro-desorption of Pb. It is found that the potential region in which anodic dissolution is inhibited by Pb-UPD is located within the potential window of Pb-UPD estimated from the differences in work-function between substrate metals and Pb.

Corrosion-resistant composite coatings on biodegradable magnesium alloys: In vitro studies

A composite coating was formed on MA8, MA14, and MA12 magnesium alloys by plasma electrolytic oxidation with subsequent immersion of samples into a superdispersed polytetrafluoroethylene suspension. In vitro volumetry determined that using this coating significantly reduces the magnesium alloy dissolution rate. It was shown that superdispersed polytetrafluoroethylene seals pores of the coating, thus reducing the corrosion rate in an artificial medium that mimics human blood by ionic composition. However, the surface of the calcium phosphate coating (Ca: P = 1.61) containing hydroxyapatite remains open for contact with the environment. The obtained data suggested that the proposed method for surface treatment of MA8, MA14, and MA12 alloys is promising for producing biodegradable protective coatings on magnesium medical implants.