Solution Alloys Research Articles

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.

A composite coating formed on AZ91D magnesium alloy by micro-arc oxidation and electrochemical deposition

A composite coating was prepared by micro-arc oxidation and electrochemical deposition onto the polished magnesium alloy substrate. The effects of deposition voltage and deposition time on the surface morphologies, deposition mass and thickness of the biological composite coating were studied. The phase compositions, surface morphologies, element contents and thickness of the coatings were investigated by X-ray diffraction, scanning electron microscope with energy dispersive spectroscopy and thickness gauge, respectively. The corrosion resistance of the coatings in the simulated body fluid (SBF) was evaluated by potentiodynamic polarisation tests and immersion tests. Finally, the mechanical properties of the coatings after immersion were characterised by tensile fatigue testing machine (INSTRON8801). The results showed that the optimal deposition voltage and deposition time was 5 V and 120 min. The duplex treatment dramatically improved the corrosion resistance and the fatigue life of the magnesium alloys in SBF solution. Therefore, the composite coating with potential bioactivity can be a candidate for magnesium alloys as biomedical materials.

Electrochemical Behavior of Magnesium and its Alloys in non-Aqueous Solutions

<p>Magnesium and its alloys are widely used in creation of chemical sources of current, because possesses a number of characteristics: highly negative standart potential, low equivalent weight, high melting point, low cost, relative abundance, ease of handling, machining, and disposal, and low toxicity of most its compounds. Therefore study of magnesium behavior and isolation is actually and perspective. However results of researches in this area are separated and have no a general direction. In this connection, the given article supposes by the purpose to generalize last achievements, available in the modern literature in electrochemistry of magnesium and its alloys in non-aqueous media.</p>

Influence of anions, pH and coating on the localized corrosion behavior of AZ31 magnesium alloy in physiological environments

Purpose The purpose of this paper was to clarify the influence of H2PO4-, HCO3-, pH increase and phosphate coating on corrosion rate and localized corrosion tendency of AZ31 magnesium alloy. Design/methodology/approach The corrosion behavior of AZ31 magnesium alloy in physiological environments was investigated by hydrogen evolution collection measurements, electrochemical techniques and by use of a three-dimensional digital microscope. Findings H2PO4- and HCO3- have corrosion inhibition effects on AZ31 magnesium alloy in normal saline solutions. After immersing for 54 h, the surface undulations decrease from 100 to about 60 μm and 45 μm. The average corrosion rate decreased with increasing pH value. The localized corrosion tendency, however, increased significantly. CaHPO4·2H2O [dicalcium phosphate dehydrate (DCPD)] coating could decrease the initial icorr of AZ31 substrate in Hank’s solution. With partial dissolution of the coating, localized corrosion was readily evident on the AZ31 substrate surface, and a large corrosion pit with depth of over 350 μm appeared. The combined effect of the presence of inhibited ions, the increase in pH during corrosion process and the DCPD coating caused the decrease in the average corrosion rate while enhancing the localized corrosion tendency, resulting in the observed localized attack. Originality/value The paper provides an essential insight into the localized corrosion mechanism of AZ31 magnesium alloy in physiological environments.

Microstructural and Corrosion Properties of Atmospheric Plasma Sprayed Alumina Coatings on AZ31B Magnesium Alloy Under Sodium Chloride Environment

AbstractThe corrosion deterioration process of plasma sprayed alumina coatings on AZ31B magnesium alloy was investigated using immersion corrosion test in NaCl solution at different chloride ion concentrations, pH value and immersion time. The experiments were conducted based on a three factor, five level, central composite rotatable design matrix with full replications technique. Response surface methodology was used to develop the relationship. The developed relationship can be effectively used to predict the corrosion rate of plasma sprayed alumina coatings on AZ31B magnesium alloy at 95 % confidence level. The results showed that the corrosion deterioration of alumina coated magnesium alloy in NaCl solutions was significantly influenced by chloride ion concentration and pH value. The alumina coatings were found to be highly susceptible to localized damage, and could not provide an effective corrosion protection to Mg alloy substrate in solutions containing acidic environments (pH3), higher chloride concentrations and immersion time.

Kinetics of Corrosion Process in H2SO4 and HNO3 Aqueous Solutions of Lead Free Sn-Ag-Cu Solder Alloys

Abstract This paper presents the results of the corrosion resistance of Sn-Ag-Cu alloys in air-saturated aqueous solutions containing NO3-, SO42- ions, whose concentration was equivalent to their contents in acid rains and in concentrations 10 - 100 times higher. The Ag, Cu and Sn concentrations in the corrosive media were determined using the Atomic Absorption Spectrometry. The specific dissolution rate and corrosion current were derived using the a rotating disc technique. The corrosion rate of Sn- Ag-Cu alloys depends on pH of the examined solutions and on the concentration of oxygen near the phase boundary. In the whole range of concentrations of the applied H2SO4 + HNO3 mixtures of acids, the pure Sn was more corrosion resistant than eutectic alloy as well as the near eutectic one, following the sequence: Sn>Sn3.66Ag0.91Cu>3.8Ag0.7Cu.

Effect of hydride formation on corrosion behaviour of Zr–1%Nb alloy in sulphuric acid solution

The effect of hydride formation on the corrosion behaviour of Zr–1%Nb alloy was investigated by potentiodynamic polarisation (PDP) and electrochemical impedance spectroscopy (EIS) measurements in 1M H2SO4 solution. Hydride phase was created by electrochemical charging method in 0.02M H2SO4 solution at room temperature. Hydrogen atoms adsorb on the sample, and then diffuse to the bulk, which causes formation of the hydride phase. The results of the X-ray diffraction and scanning electron microscopy (SEM) confirm the formation of hydride phases in the samples. By long charging time (72 h) and high current density (100 mA/cm2), a massive hydride phase formed, which induced cracks on the surface with 30 μm depth. These cracks along with the variations of the ionic and electronic properties of the oxide layer dramatically increase the corrosion rate of the hydrided sample (∼46 times).

The corrosion of AA2037 aluminum alloy in alkaline aqueous solution studied using slow positron beam spectroscopy

Corrosion behavior of AA2037 T8 Al alloy in a 1 M NaOH aqueous solution was investigated using slow positron beam, together with microscopy techniques and electrochemical tests. The alloy was homogenized at 510 °C for 2 h and 30 s, respectively, before final peak aging, so that one Sample A had more dispersoids than Sample B after homogenization. It was found that S parameter of the Doppler-broadened annihilation was significantly decreased near the surface in both samples in the alkaline solution. With increasing the dissolution time, Sample A showed a slower decrease rate than Sample B, which might imply that the preexistence of more dispersoids might hinder the corrosion process in Sample A. Scanning electron microscopy and atomic force microscopy observations found that the surfaces of both samples were uniformly thinned due to intense chemical dissolution by the attack of OH−. With increasing the dissolution time, Sample B was corroded more substantially and produced more and larger pits in a short dissolution time than Sample A. Furthermore, polarization curves showed that Sample A had a lower corrosion current and corrosion rate than Sample B, which revealed that the presence of the dispersoids was responsible for the better corrosion resistance in the alloy.

Areas of concern in an anodised dissimilar friction stir weld of AA5083 and AA6082 aluminium alloys

The major areas of concern when anodising a dissimilar friction stir weld of AA5083-O and AA6082-T6 aluminium alloys in sulphuric acid solution have been investigated. As expected, variations in the specific volumes of structurally transformed substrate materials across the weld zones were observed. Nonetheless, the greatest area of concern is the boundary region between the materials from the advancing side and materials from the retreating side. Mg–Si rich particles were observed to be distributed along the boundary between the two alloys and they possibly contribute to the dissolution in the boundary region when the weld is anodised in 4 M sulphuric acid solution. However, this dissolution was not observed when the weld is anodised in 0.4 M H2SO4 solution.

A multichannel electrochemical cell with glycerin-based liquid electrolyte

An electrochemical cell has been developed for determining the thermodynamical activity of a component in a solid solution (alloy) depending on its concentration at a temperature of up to 150°С and atmospheric pressure. A salt solution of glycerin is used as an electrolyte. Measurements can be simultaneously performed on 10–15 different samples in the cell under identical conditions for all compositions of the solid solution studied. This is ensured by using an inert electrode being displaced from sample to sample. In this case, the comparison electrode is common and immobile, thus substantially increasing the accuracy and reliability of experimental results, since this allows one to perform repeated (check) measurements of the EMF at a constant temperature on any sample with a specified composition.

Effect of temperature on corrosion and semiconducting properties of oxide films formed on M5 zirconium alloy

Nuclear fuel cladding for pressurised water reactors is commonly manufactured with zirconium alloys. The M5 alloy is a relatively new cladding material for in-reactor used with enhanced performance compared to traditional zircaloys. In this work, the influence of temperature on the corrosion resistance and semiconducting properties of the passive film formed on the M5 alloy in a borate buffer solution has been evaluated. The electrochemical behaviour of the zirconium alloy was assessed by potentiodynamic polarisation tests, electrochemical impedance spectroscopy and Mott–Schottky plots. The results indicated that the corrosion resistance of the M5 alloy decreased with temperature due to the formation of a less stable and more defective passive film. The Mott–Schottky approach used in combination with polarisation tests and impedance measurements was effective to reveal the protective state of the passive film on the M5 alloy.

Reaction behavior of Ni–Re alloys during direct current polarization in sulfuric acid solutions

The macrokinetic regularities of the reactivity of synthesized Ni–Re (20 and 60 wt %) alloys in a sulfuric acid solution (100 g/L, 25–40°C) during direct current polarization are studied using physicochemical methods. The phase composition of the synthesized alloys is determined by the formation of solid solutions as a function of the initial Ni/Re weight ratio. These are two types of nickel solid solutions (Ni16Re0.2 and Ni14Re0.9) and one rhenium solution (Ni1.1Re). These solid solutions are anodically oxidized in the sequence of their structural rearrangement Ni16Re0.2 → Ni14Re0.9 → Ni1.1Re with a combined transition of the metals into an electrolyte solution. These solid solutions provide the reduction of Ni3+ to Ni2+ due to the depolarization ability of rhenium, being their component.

Studies of Corrosion and Electrochemical Behavior of Cu-Zn Alloys in H2SO4 and HNO3 Acid Solutions

Studies of Corrosion and Electrochemical Behavior of Cu-Zn Alloys in H2SO4 and HNO3 Acid Solutions

Corrosion resistance of titanium alloys in the artificial saliva solution

Corrosion resistance of titanium alloys in the artificial saliva solution

Corrosion performance of 5182 aluminium alloy in calcium chloride solution

Corrosion behaviour of 5182 aluminium was evaluated in terms of weight change in a 30% calcium chloride solution at temperatures ranging from 0°C to 65°C. The test results indicate that there is a critical temperature (35°C) above which the alloy experiences weight gain and below which the alloy experiences weight loss during the corrosion processes. Optical light microscopy (OLM), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were carried out to characterise the corrosion behaviour of this alloy. The results indicate that weight gain and weight loss occur under different corrosion mechanisms.

Corrosion behaviour of magnesium alloys in ringer's solution

Corrosion behaviour of magnesium alloys in ringer's solution

Preparation and Performance of Electroless Nickel on AZ91D Magnesium Alloy

The corrosion of magnesium alloy in different plating solutions was researched. The results demonstrated that corrosive condition of the alloy immersed in nickel chloride solution and nickel sulfate solution is serious and in nickel acetate solution and nickel nitrate solution is less. Magnesium alloy was handled with four acid pickling formulas and two activation formulas and the effects of different pickling formulas and activation formulas were researched through comparative experiment. The experimental results indicated that after handed with pickling formula about 500 mL L−1 H3PO4 (85%), 110 mL L−1 HNO3 (68%), room temperature for 30 s and activation formula about 375 mL L−1 HF (40%), room temperature for 10 min, magnesium alloy could realize electroless nickel plating directly and the performance of the prepared plating was much better. The properties of the nickel-plating coating were researched by electrochemical workstation, scanning electron microscope, and X-ray diffraction. The results demonstrated that this Ni–P coating was very uniform and meticulous; the structure of Ni–P coating was amorphous; and comparing with magnesium alloy, the corrosion potential of this plating increased about 799 V and the corrosion current density declined obviously. The nickel-plating coating effectively improved the anticorrosion performance of magnesium alloy.

Influence of Al Content on the Corrosion Behavior of Biodegradable Magnesium Alloys in Simulated Physiological Solution

Influence of Al Content on the Corrosion Behavior of Biodegradable Magnesium Alloys in Simulated Physiological Solution

Effects of heat treatment on microstructure and microhardness of laser melting deposited Ti-22Al-25Nb alloy

The microstructural evolutions of the laser melting deposited Ti-22Al-25Nb (at.-%) orthorhombic alloy in different solutions and during different aging treatments were quantitatively investigated. The volume fraction of aggregate precipitates and B2 grain size under different annealing temperatures and holding time had been measured using the image analysis software. The relationships among heat treatment, microstructure and microhardness were established. The experimental results indicate that all heat-treated microstructure exhibited a majority of Widmanstatten O phase precipitates within B2 grains and a minority of α2 phase at grain boundaries. The volume fraction of total precipitates for samples heat-treated with different schedules could be controlled in the range of 65–74%. On the premise of this volume fraction and constituent phases, the microhardness mainly depended on the size of precipitates, where the finer the precipitates within grains are, the higher the value of microhardness is. The maximum microhardness was 429 HV0.5 for samples which were solution-treated at 940°C for 0.5 hours and then aged at 760°C for 12 hours.

ELECTROCHEMICAL BEHAVIOR OF ELECTRODEPOSITED NANOCRYSTALLINE COBALT-IRON ALLOY COATING IN DIFFERENT PH

The electrochemical behavior of a cobalt-iron (CoFe) alloy electrode in 0.1 M Na2SO4 (sodium sulphate) aqueous solution of different pH was investigated. The presence of a different concentration of dissolved sulphide ions with different pH on the corrosion of electrodeposited cobalt-iron was investigated using the EQCM technique. The corrosion rates of the alloys in acidic solutions are pronouncedly high, compared to those measured in neutral or basic solutions. The presence of sulphide ions accelerates markedly the anodic reaction for all deposits in the basic medium. The dissolution rate was twice two times faster when S2− was added. By employing the EQCM, it was observed that the mass decrease or dissolution rate was significant with an increase in pH concentration.