Alloys In Sulfuric Acid Solution Research Articles

Electrochemical behavior and passive film properties of Ce-added AlCoCrFeNi2.1 eutectic high-entropy alloys in sulfuric acid solution

Eutectic high-entropy alloys (EHEAs), represented by AlCoCrFeNi2.1, are considered to be promising materials. However, the study of the corrosion behavior of EHEAs remains limited, which hinders further development. This study investigated the effect of Ce addition on the electrochemical behavior and passive film properties of AlCoCrFeNi2.1 EHEAs in H2SO4 solutions. The results show that the addition of Ce changed the properties of the passive film formed on the alloys, resulting in reduction in the proportion of Cr2O3, and thereby reduced the corrosion resistance. Moreover, a higher Ce content in the EHEAs was found to correspond to a more pronounced deterioration in corrosion resistance. Compared with the film formed at 0.2 Vvs SCE, the film formed at 0.5 Vvs SCE exhibited more optimal physicochemical properties, leading to a decrease in the passive current density. Notably, Ce was absent in the film formed at 0.2 Vvs SCE, but present at 0.5 Vvs SCE.

The effect of chromium content on the corrosion behavior of ultrafine-grained CrxMnFeCoNi high-entropy alloys in sulfuric acid solution

Microstructures is an international peer-reviewed, open access, online journal. The journal of Microstructures publishes articles covering new research and developments, perspectives, and reviews related to the microstructures of materials, including, but not limited to metals and alloys, ceramics, polymers, composites, crystals, glasses, biomaterials, interfaces and nanomaterials.

Investigation on ultrasonic cavitation erosion of TiMo and TiNb alloys in sulfuric acid solution.

Two kinds of Ti-alloys, i.e., TiMo and TiNb alloys are manufactured in this paper, and their ultrasonic cavitation erosion behaviors in 0.1M H2SO4 solution are evaluated by the mean depth erosion (MDE), SEM and white light photograph. The results show that MDE of TiMo and TiNb alloys obviously increase with increasing the cavitation erosion time, however, they evidently decrease with the increment of Mo or Nb content at each fixed cavitation erosion time, and even some large blank areas (uneroded areas) still exist on the sample surface after ultrasonic cavitation erosion for 2h in the case of Ti10Mo and Ti20Nb samples, implying the enhanced anti-cavitation erosion property of Ti-alloy by adding Mo or Nb element. The MDE of Ti10Mo or Ti20Nb sample is lower than that of TC4 sample in the case of each cavitation erosion time, indicating the better cavitation erosion resistance of of Ti10Mo or Ti20Nb sample. The influences of Mo and Nb on the passivity of TiMo and TiNb alloys during the ultrasonic cavitation erosion are detected by potentiodynamic curves. The results display that Ti, TC4, TixMo (x=1, 5, 10) and TixNb (x=5, 10, 20) samples are all almost in the passive state within the potential region from 0VSCE to 1.5VSCE during ultrasonic cavitation erosion, and the passive current density evidently decreases with increasing Mo or Nb content, indicating the enhanced passive characteristic by adding Mo or Nb alloys during the ultrasonic cavitation erosion.

Electrochemical processing of technogenic wastes of rhenium-containing heat-resistant nickel alloys in sulfuric acid solutions

Electrochemical processing of technogenic wastes of rhenium-containing heat-resistant nickel alloys in sulfuric acid solutions

Effect of Indium Alloying with Lead on the Mechanical Properties and Corrosion Resistance of Lead-Indium Alloys in Sulfuric Acid Solution

Effect of indium alloying in various concentrations with lead on both microhardness and crystallite structure of lead-indium alloy was investigated. The corrosion behavior of lead-indium alloys in 4 M H2SO4 acid solution was investigated by Tafel plot and electrochemical impedance spectroscopy (EIS) methods. The results of both Tafel plot extrapolation and EIS measurements exhibited the same trend. Generally, the corrosion resistance of the alloy is more significant compared with that observed for pure lead. This study shows that the addition of 0.5 pct In to Pb decreases the corrosion. However, with a further increase of alloying In, the corrosion rate of alloy starts to increase up to 5 pct In compared with that of Pb-0.5 pct In alloy. Then the corrosion rate decreases gradually with the increase in the percentage of In up to 15 pct. The values of activation energy (Ea) supported this trend of the corrosion rate which is obtained for Pb and Pb-In alloys. X-ray diffraction data exhibited broadness of peaks, which is due to lattice distortion or grain refinement. Clearly the peaks shift to higher angles for Pb-15 pct In alloy which can be attributed to changes in lattice structure of Pb. Scanning electron microscope images confirmed that the microstructure is changed with indium alloying content. The solute content tends to refine the microstructure array.

Nanoporous PdCu alloys as highly active and methanol-tolerant oxygen reduction electrocatalysts

Nanoporous (NP) PdCu alloys with three different bimetallic ratios are fabricated by selectively dealloying PdCuAl ternary alloys in sulfuric acid solution. Electron microscopy and X-ray diffraction characterizations demonstrate that selective etching of Al from ternary PdCuAl source alloys in acid medium generates three-dimensional bicontinuous ligament-pore nanostructures with a single-phase face-centered-cubic crystalline structure. NP-PdCu alloys show superior electrocatalytic activity and structure stability toward oxygen reduction reaction (ORR) compared with the commercial Pt/C catalyst. The specific and mass activities for ORR follow the order of NP-Pd50Cu50 > NP-Pd75Cu25 > NP-Pd30Cu70 > Pt/C. It is found that among three PdCu samples NP-Pd50Cu50 exhibits the highest methanol tolerance and catalytic durability for ORR. These experimental observations indicate that incorporation of 50 at.% Cu into Pd accompanied with the network nanoarchitecture is beneficial to maximize the ORR performances of Pd.

Influence of Cu on the Passivation Behavior of Fe-20Cr-xCu (x = 0, 2, 4 wt%) Alloys in Sulfuric Acid Solution

Effects of Cu on the polarization behavior of Fe-20Cr-xCu (x = 0, 2, 4 wt%) were examined in deaerated 0.1 M sulfuric acid (H2SO4) solution. In the active region, corrosion resistance of the alloys is improved with Cu content as a result of the enrichment of Cu on the surface of the alloys that occurs by the preferential dissolution of Fe. In the passive region, the effects of Cu on the passivation behavior of the alloys was dependent on the applied potential. At potentials active to −100 mV vs. saturated calomel electrode (SCE), the passivity of the alloys is improved with Cu content, which is confirmed by the increase in passivation rate with a decrease in oxidation tendency. In contrast, above −100 mVSCE, where the oxidation reaction of Cu+ to Cu2+ occurs, the passivity of the alloys was degraded significantly with Cu content, as confirmed by the increase in passive current density as well as the significant decrease in passivation rate. The deleterious effects of Cu on the passivation behavior of Fe-20Cr-xCu (x = 0, 2, 4 wt%) decreased at potentials noble to 500 mVSCE, primarily as a result of the significant decrease in Cu content in passive film and hence of the decrease in the oxidation reaction of Cu+ to Cu2+.

The Effect of the Nickel Sulphide Alloys Structure on Their Electrochemical Oxidation Parameters

The granulation of nickel sulphide alloys results in formation of the ultrafine structure because of their reactivity is increased in the hydrometallurgical processing. The phase composition and phase size of nickel sulphide alloys granulated was studied by X-ray and optical microscopy methods. It is shown the high cooling rate leads to the crystallization of non-equilibrium phase and dispersion of a metal component. The parameters of the electrochemical oxidation of nickel sulfide granular alloys in sulfuric acid solution were estimated. The initial potentials of phase components oxidation of nickel sulfide alloys granulated were defined. The rate of electrochemical oxidation of nickel sulfide alloys granulated is higher than that at slow-rate cooling.

Effect of potential cycling on dissolution of equimolar Pt–M (M: Co, Ni, Fe) alloys in sulfuric acid solution

Dissolution of equimolar Pt–M (M: Co, Ni, Fe) alloys covered with a Pt-enriched layer on the surface has been studied under potential cycling in 0.5M H2SO4 solution at 25°C. The Pt-enriched layer was formed on the surface of Pt–M alloys by a selective dissolution treatment of M under immersion condition in the solution. The amounts of Pt and M dissolved under potential cycling with various combinations of upper potential limit Eupper and lower potential limit Elower were determined with an inductively coupled plasma mass spectrometry (ICP-MS). During the selective dissolution treatment, rest potential Erest of the Pt–M alloys approaches to that of pure Pt, indicating the enrichment of Pt on the surface. The Pt-enriched layer strongly suppresses further selective dissolution of M under the immersion condition. However, when the Pt–M alloys are exposed under potential cycling in the potential ranges of Eupper>Erest (≈1.0V vs. SHE) and Elower<0.5V, the selective dissolution of M takes place again, although it is suppressed at the initial stage of the potential cycling by formation of the thicker Pt-enriched layer.

Selective Dissolution of Binary Pt Alloys in Sulfuric Acid Solution

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The effect of rare earth metals on the microstructure and electrochemical corrosion behavior of lead calcium grid alloys in sulfuric acid solution

The effect of the rare earth element lanthanum (La) on the microstructure of lead–calcium grid alloys was studied by the metallographic microscope. A comparison of the electrochemical corrosion behavior of the new and traditional grid alloys was investigated by cyclic voltammetry (CV), A.C. impedance and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to study the surface morphology of anodic films of Pb–Ca–Sn–Al–Re alloys formed in sulfuric acid solution at 1.3 and 0.9 V for 2 h. The morphology of the corrosion layer was analyzed by SEM after the constant current corrosion test. The results show that an appropriate content of La can effectively (1) increase the fineness of the grain of Pb–Ca–Sn–Al alloys, (2) increase the growth of PbO 2 film, and (3) make the anodic film formed at 1.3 V become fine and compact. Alloys with contents of 0.01 wt.%, 0.03 wt.% and 0.1 wt.% La were shown satisfactory results. La also can decrease the growth of Pb(II) film, purify and increase the density of the anodic film at 0.9 V, especially for La content of 0.03 wt.% and 0.1 wt.%. Moreover, La can improve the corrosion resistance of Pb–Ca–Sn–Al alloys, particularly for a La content of 0.01 wt.%.

Influences of temperature, H2SO4 concentration and Sn content on corrosion behaviors of PbSn alloy in sulfuric acid solution

The influences of temperature, H2SO4 concentration and Sn content on corrosion behaviors of PbSn alloys in sulfuric acid solution were investigated by potentiodynamic curve, cyclic voltammetry (CV), linear sweeping voltage (LSV), electrochemical impedance spectra (EIS), a.c. voltammetry (ACV) and Mott–Schottky analysis. The microstructure of the corrosion layer on PbSn alloy was analyzed by scanning electron microscopy (SEM). The results showed that the corrosion resistance of PbSn alloy increased with ascending Sn content and H2SO4 concentration, the increment of temperature can decrease the corrosion resistance of PbSn alloy in H2SO4 solution. The conductivity of the anodic film on PbSn alloy was enhanced with increasing temperature, ascending Sn content and descending H2SO4 concentration. SEM result revealed that the corrosion film after cyclic voltammetry was consisted of tetragonal crystal, the porosity enlarged with decreasing temperature, Sn content and H2SO4 concentration.

Dissolution of Pt–M (M: Cu, Co, Ni, Fe) binary alloys in sulfuric acid solution

The dissolution behavior of equimolar Pt–M (M: Cu, Co, Ni, Fe) alloys has been studied under conditions of immersion, potentiostatic polarization, and potential cycling in 0.5 M H 2SO 4 solution at 25 °C. The quantity of dissolved ions under these conditions has been determined with inductively coupled plasma mass spectrometry (ICP-MS). In 3-h immersion tests, selective dissolution of M atoms occurs immediately after immersion and is quickly suppressed. The rest potential shifts rapidly in the noble direction and approaches that for pure Pt. The general features of cyclic voltammograms of the alloys are very similar to those for pure Pt, although the current is considerably larger for the Pt–Fe alloy. These results indicate that the surfaces of these alloys are covered with a Pt-enriched layer because of preferential dissolution of M atoms. The resulting suppression of dissolution is reversed by potentiostatic polarization at 1.4 V. The enhancement at 1.4 V is more remarkable under the condition of potential cycling.

Relation between individual properties of alloy components and anodic behavior of multicomponent alloys in acidic environments: I. Active dissolution and passivation of Fe-Cr alloys in sulfuric acid solutions

The active dissolution and passivation of Fe-Cr alloys are analyzed with the use of concepts of the appearance, operation, and blockade of active dissolution sites on the actual metal surface. General regularities of the effect of chromium on the rate of the anodic process at the change in the alloy composition and electrode potential are considered. The less noble, but easily passivable chromium component provides a dual effect on the anodic behavior of the binary alloys; it stimulates the anodic reaction at the low content in the alloy and suppresses the process at the high content. The principally different electrochemical properties of the alloy components result in the step-by-step passivation of the alloy with an increase in the potential, which is reflected by regular breaks in perfect anodic curves.

Electrochemical behavior of some copper alloys in sulfuric acid solutions

AbstractIn this article, the corrosion behavior of CuFe and CuAlFe was studied in H2SO4 solutions in the absence and presence of different concentrations of some inorganic additives, Na2MoO4, K2Cr2O7, KIO3, and Na2B4O7. The techniques of measurements used were open‐circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy. The polarization measurements indicated that the corrosion current, Icorr, of CuFe is less than that of CuAlFe. The investigated additives in H2SO4 shifted Ecorr to more positive values and increases Icorr. Impedance measurements indicated that Nyquist plots for CuFe may be regarded as a semi‐circle in early stages of immersion and tends to be a part of semi‐circle with elapse of time and a well‐defined inductive loop appears. In case of CuAlFe, the Nyquist plots tends to be semi‐circle or depressed semi‐circle. The values of Rp for CuFe are higher than those for CuAlFe. On the other hand, the values of Cdl for CuFe are lower than those obtained for CuAlFe. The presence of these additives in H2SO4 solutions decreases the values of polarization resistance (Rp) and increases the values of corrosion current density (Icorr) and capacitance of double layer (Cdl).

The influence of tin and silver as microstructure modifiers on the corrosion rate of Pb-Ca alloys in sulfuric acid solutions

The effect of microstructure modifiers, Sn and Ag, on the corrosion rate of commercial Pb–Ca alloy in H2SO4 electrolyte was investigated by the potentiodynamic polarization and by the weight loss corrosion rate measurement at the open circuit potential. The effect of microstructure modification of the Pb–Ca alloy, provoked by the alloying with tin and silver as well as by the proper thermo-mechanical treatment, is recorded by optical microscopy. The weight loss experiments have shown three- to five-fold decreases in the corrosion rate of ternary Pb–Ca–Sn and quaternary Pb–Ca–Sn–Ag alloys, compared to the results for primary Pb–Ca alloy. It is largely in accordance with the results of potentiodynamic polarization measurements that showed comparable decrease in the passive current density of the modified alloys. The obtained results are discussed in terms of the synergetic effect of the addition of modifiers and the thermo-mechanical treatment on to the Pb–Ca alloy microstructure refinement, and accordingly the increase in their corrosion resistance.

Anodic oxidation of Ag-Cu alloys in sulfuric acid solutions when reaction products are unstable

Based on the impedance models of porous layer, anodic behavior of silver as a component of Ag-Cu alloys in aqueous sulfuric acid solutions is analyzed. It is shown that, in order to adequately describe the electrochemical process, chemical decomposition of superficial passivating silver-sulfate layer should be taken into account. Decomposition rate constants of the layer on silver-copper alloys of diverse composition are calculated.

Pitting Corrosion of Cast Metallurgy Aluminum-Beryllium Alloys in Sulfuric Acid Solutions

Abstract Four casting alloys of aluminum-beryllium ranging in a Be composition from 15 wt% to 68 wt% were tested in sulfuric acid (H2SO4) solutions of pH 2 and 4. Cyclic potentiodynamic polarization tests of the Al-Be alloys demonstrated passive behavior and positive hysteresis. Following cyclic polarization testing, all alloys showed preferential corrosion of the Be-rich phase in the forms of pitting or phase boundary attack with evidence of crystallographic etching. Total pit surface area in the Be phase was proportional to the volume fraction of the Al phase. Immersion test specimens showed uniform corrosion of the Al phase at pH 4, while the Be phase showed phase boundary and crystallographic attack at pH 2. Corrosion potentials were most noble for alloys with the highest Be wt% while corrosion current density decreased with Be wt%. A lower pH increased the corrosion rate for all alloys.

Effect of Sn content on the properties of passive film on PbSn alloy in sulfuric acid solution

The effect of Sn content on properties of anodic film formed on PbSn alloys in sulfuric acid solution was investigated using linear sweeping voltage (LSV), cyclic voltammetry (CV), and a.c. voltammetry (ACV), based on the Mott-Schottky analysis. The results revealed that the addition of Sn into lead alloys can promote the corrosion resistance property and could decrease the impedance of anodic film; these results were more remarkable with enhancing the Sn content. The over potential of oxygen evolution on lead alloys enhanced with the increase of Sn content. The Mott-Schottky analysis indicated that the passive film appeared an n-type semiconductor, and the donor density of passive film increased with increasing Sn content. The increased vacancies in the passive film with Sn content increasing could illustrate this trend.

Specifities of forming electrochemical dissolution zones at ferrite-cementite-structured alloys in sulfuric acid solutions

Specific features of the formation of electrochemical dissolution zones at steels C T 20 and C T 45 with a ferrite-cementite structure, were revealed by combining electrochemical and metallographic methods. A possibility of developing the self-dissolution process at the ferrite/cementite boundary is shown. A spontaneous sequence of the anodic dissolution of structural constituents of the alloys is found.