Galvanic Dissolution Research Articles

Kinetic investigation of galvanic dissolution of ZnS and PbS with FeS2 from hydrothermal sulfides in seawater

Sulfide mineral dissolution is an important reaction controlling geochemical and environmental chemical processes in aqueous environments. In this study, we quantitatively evaluated the kinetic influence of galvanic interactions between different sulfide minerals on their dissolution in seawater. Four hydrothermal sulfides with different amounts of Fe disulfide minerals (pyrite) were reacted with artificial seawater for 144 h, and the dissolution rates of Zn and Pb were determined by an extraction method. The Zn dissolution rates from samples with high Fe/Zn molar ratios (>0.26) were 1.3–1.5 × 10−10 mol m−2 s−1; approximately one order of magnitude higher than those of samples with low Fe/Zn molar ratios (<0.002; 1.6–1.8 × 10−11 mol m−2 s−1). The Pb dissolution rates from a sample with high Fe disulfide were approximately nine orders of magnitude higher (8.4× 10−10 mol m−2 s−1) than reference data of the single galena dissolution rate (8.9 × 10−19 mol m−2 s−1). The higher solubility of PbSO4 than PbS and PbCO3 could explain the intense release of Pb from the other samples. These results and mineralogical observations with X-ray diffraction, X-ray photoelectron spectroscopy, and electron probe micro-analysis of sulfide mineral particulates provide evidence for the selective dissolution of anodic sulfide minerals (e.g., sphalerite and galena) at a higher reaction rate than cathodic sulfide minerals of Fe disulfide (e.g., pyrite).

Durable self-polishing antifouling Cu-Ti coating by a micron-scale Cu/Ti laminated microstructure design

Marine biofouling is a major issue deteriorating the service performance and lifespan of marine infrastructures. The development of a durable, long-term, and environment-friendly antifouling coating is therefore of significant importance but still a critical challenge in maritime engineering. Herein, we developed a Cu-Ti composite antifouling coating with micron-sized alternating laminated-structure of Cu/Ti by plasma spraying of mechanically mixed Cu/Ti powders. The coating was designed to enable controlled release of Cu ions through galvanic dissolution of Cu laminates from the Cu/Ti micro-galvanic cell in aqueous solution. Results showed that remarkable antifouling efficiency against bacterial survival and adhesion up to ∼100 % was achieved for the Cu-Ti coating. Cu/Ti micro-galvanic cell was in-situ formed within Cu-Ti coating and responsible for its Cu ions release. The successive dissolution of Cu laminates resulted in the formation of micro-channels under Ti laminates near surface, which contributed to controlled slow Cu ions release and self-polishing effect. Thus, environment-friendly antifouling capability and ∼200 % longer antifouling lifetime than that of the conventional organic antifouling coatings can be achieved for the Cu-Ti coating. On the other hand, as compared to the conventional organic antifouling coatings, the Cu-Ti composite coating presented much higher mechanical durability due to its strong adhesion strength, excellent mechanical properties, and two orders lower wear rate. The present laminated Cu-Ti coating exhibits combination of outstanding antifouling performance and high mechanical durability, which makes this coating very potentially candidates in marine antifouling application.

Spiny Pd/PtFe core/shell nanotubes with rich high-index facets for efficient electrocatalysis

The performance of fuel-cell related electrocatalysis is highly dependent on the morphology, size and composition of a given catalyst. In terms of rational design of Pt-based catalyst, one-dimensional (1D) ultrafine Pt alloy nanowires (NWs) are considered as a commendable model for enhanced catalysis on account of their favorable mass/charge transfer and structural durability. However, in order to achieve the noble metal catalysts in higher efficiency and lower cost, building high-index facets and shaping hollow interiors should be integrated into 1D Pt alloy NWs, which has rarely been done so far. Here, we report the first synthesis of a class of spiny Pd/PtFe core/shell nanotubes (SPCNTs) constructed by cultivating PtFe alloy branches with rich high-index facets along the 1D removable Pd supports, which is driven by the galvanic dissolution of Pd substrates concomitant with Stranski-Krastanov (S-K) growth of Pt and Fe, for achieving highly efficient fuel-cells-related electrocatalysis. This new catalyst can even deliver electrochemical active surface area (ECSA) of 62.7 m2 gPt−1, comparable to that of commercial carbon-supported Pt nanoparticles. With respect to oxygen reduction catalysis, the SPCNTs showcase the remarkable mass and specific activity of 2.71 A mg−1 and 4.32 mA cm−2, 15.9 and 16.0 times higher than those of commercial Pt/C, respectively. Also, the catalysts exhibit extraordinary resistance to the activity decay and structural degradation during 50,000 potential cycles. Moreover, the SPCNTs serve as a category of efficient and stable catalysts towards anodic alcohol oxidation.

Micro- and nano-scale intermetallic phases in AA2070-T8 and their corrosion behavior

Intermetallic phases on the as-polished surface of the Al-Cu-Li alloy AA2070-T8 were identified and characterized extensively with respect to microstructure and chemical composition using spectroscopic and microscopic techniques and atom probe tomography. This is the first comprehensive report of the intermetallic compounds in the 3rd generation of Al-Cu-Li alloys. A total of eleven compositional classifications and/or crystallographic phases and one GP zone were revealed, with Al7Cu2Fe(Mn) being the most abundant, comprising around 44% of all intermetallic particles. Seven types of large intermetallic compounds were found to be cathodic to the matrix and their nobility generally increases with their noble element content, e.g. Cu and Fe, and decreases with their Al content, which can be further correlated to the cathodic current densities supported by these particles. The intermetallic compound nobility is closely related to the Volta potential difference, which correlates with the extent of trenching around the particles during electrolyte exposure. Corrosion of this alloy in 0.1 M NaCl involves a series of chemical and electrochemical phenomena at the intermetallic compound/matrix/electrolyte interfacial region, including preferential dealloying of the intermetallic compound, galvanic dissolution of the peripheral matrix, trench development, hydrogen evolution at the bottom of trench, and pitting in the bulk alloy. However, after exposure, no clear corrosion attack on or around nm-scale precipitates was observed after exposure times comparable to that for large particles. These findings are essential to understand the material degradation mechanism of this alloy family and provide input into new alloy design.

SVET and SIET Study of Galvanic Corrosion of Al/MgZn2 in Aqueous Solutions at Different pH

The galvanic corrosion behavior of synthesized MgZn2 intermetallic particle coupled with Al in 0.1 M NaCl solutions across pH 2 to12 has been studied using the scanning vibrating electrode technique (SVET), the scanning ion-selective electrode technique (SIET) and X-ray photoelectron spectroscopy (XPS). Results indicate the galvanic dissolution of MgZn2 depends on pH as well as exposure time. SVET current density maps reveal that MgZn2 is anodic relative to Al at pH 2 but cathodic at pH 12, while self-dissolution of MgZn2 prevails at pH 4 and 6. However, the galvanic coupling effect is more pronounced at pH 2 and 12. SIET maps of H+ and Cl− ion distribution reveal evidence of local alkalization on MgZn2 and migration of Cl− ions away from MgZn2 surface at pH 4 and 6 due to significant accumulation of OH− ions. Preferential dissolution of Mg occurs leading to segregation of Mg compounds in the outer layers of the film and Zn enrichment on the matrix/solution interface. In slightly acidic and near neutral solutions MgO/Mg(OH)2 dominates the outer layers and MgO/Mg(OH)2/ZnO dominates the inner layers, however, at pH 12 a stable MgO/Mg(OH)2 passive film is formed.

Effect of friction stir welding on microstructure and corrosion behavior of LF6 aluminum alloy

The LF6 aluminum alloy plates were joined by friction stir welding method. The tool rotational (1180 rpm) and transverse speed (0.56 mm s−1) were kept constant during welding of 4 mm thick plates. The microstructural features, hardness and tensile properties of the welded samples were determined to evaluate the structural integrity in comparison with the base metal. The electrochemical behavior of base metal (BM), thermo-mechanically affected zone (TMAZ) and weld nugget zone (WNZ) was also investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl solution. The microstructural study revealed significant grain refinement and agglomeration of β (Mg2Al3) intermetallic precipitates in the WNZ. The relatively higher hardness and a decrease in the ductility (3%) also assured the formation of precipitates β precipitates in the WNZ welded samples. The fracture surface of welded sample also revealed the existence of β precipitates within the elongated dimples which may be considered as the crack initiation sites. The relatively lower corrosion rate (23.68 mpy) and higher charge transfer resistance (403 Ω cm2) of BM compared to WNZ could be associated with the galvanic dissolution of Al-matrix through competitive charge transfer and relaxation (adsorption/desorption of intermediate species) processes specifically at the vicinity of the β precipitates.

Advanced Electrochemical Machining (ECM) for tungsten surface micro-structuring in blanket applications

Plasma facing components for fusion applications must have to exhibit long-term stability under extreme physical conditions, and therefore any material imperfections caused by mechanical and/or thermal stresses in the shaping processes cannot be tolerated due to a high risk of possible technical failures under fusion conditions. To avoid such defects, the method of Electrochemical Machining (ECM) enables a complete defect-free processing of removal of tungsten material during the desired shaping, also for high penetration depths. Furthermore, supported by lithographic mask pretreatment, three-dimensional distinct geometric structures can be positive-imaged via the directional galvanic dissolution applying M-ECM process into the tungsten bulk material.New required applications for tungsten components, e.g. as adhesion promotors in W-surfaces to enable sure grip and bonding of thick plasma-spraying layers for blanket components, will define the way of further miniaturization of well-established millimeter dimensioned M-ECM shaping processes to dimensions of 100μm and furthermore down to 50μm. Besides current M-ECM limits the article describes inevitable needs of further developments for mask resists, mask materials and the resulting ECM parameters, to reach the needed accuracy in tungsten microstructure. The achieved progress and observed correlations of processing parameters will be manifested by produced demonstrators made by the new “μM”-ECM process.

Serial Morphological Transformations of Au Nanocrystals via Post-Synthetic Galvanic Dissolution and Recursive Growth

Geometric modification of Au nanostructures is typically achieved in multistep reactions, where synthesis parameters need to be well-controlled. In this work, we report a facile method using IrCl3 to refine morphologically diverse Au nanostructures and trigger their morphological transformations. The synthesis is accomplished at room temperature by an iterative process of galvanic dissolution and recursive growth. Seeds retrieved after the dissolution of different Au nanostructure archetypes served in the structural recovery and morphological transformation via rapid and slow regrowth, respectively. The rapid regrowth was accomplished by adding ascorbic acid (AA), while the slow regrowth occurred spontaneously. In the structural recovery, the nanostructures regrew back to their original morphologies. Improvements in the shape quality and size distributions were observed for the rapid regrowth case. In the spontaneous slow regrowth transformation, the resulting nanostructures were encased by {111} facets, minimizing total surface energy through the more closely packed planes. Transformation of the four nanostructure archetypes showed correlation, trending toward these lower indexed facets and to twinned structures (from RDs to OCTs, OCTs to TPs, and TPs to PSs). Surveying all observations, our work of the metal cation-mediated geometric modulation of Au nanostructures delivers important clues in understanding nanoparticle synthesis and provides a new path for the fabrication of nanocrystals with high-quality size and shape distribution.

Time Evolution Degradation Physics in High Power White LEDs Under High Temperature-Humidity Conditions

A high temperature-humidity test is commonly employed to evaluate the humidity reliability of electronic devices. For an integrated circuit, the degradation mechanism under the high temperature-humidity test is metal corrosion, and Peck's model is used for extrapolating the test results at accelerated test conditions to the normal operating condition. Such extrapolation is possible as the underlying degradation physics is invariant from the accelerated test conditions to the normal operating condition for integrated circuits. However, this is not true for high power LEDs, as found in this paper. The degradation in the LEDs undergoes time evolution at either 95% or 85% relative humidity (RH) and 85 $^{\circ}\hbox{C}$ . We also found that the degradation physics are completely different among the various RH levels from 95% to 70%. The degradation process begins from bond pad contamination and Kirkendall void formation, galvanic dissolution, phosphor dissolution to encapsulant, and die attach delamination. Such time evolution degradation physics renders the inapplicability of the Peck model and presents a challenge in extrapolation of test results to the normal operating condition for lifetime prediction.

The Refinement of the Nanoporous Copper by Adding Third Elements

Fine nanoporous copper was fabricated from the amorphous Ti-Cu alloys with a minor addition of silver in 10 mM HF solutions. The pore sizes decreased from 100 nm to 12 nm with the increase of the Ag contents in comparison of Ti60Cu40 ribbons free of Ag. With increasing of the dealloying time, the sizes of the nanopores and ligaments increased for the nanostrucutres on Ti60Cu38Ag2 ribbons since the segregation of the Ag phase which triggered the galvanic dissolution of the adjacent Cu matrix in form of micro-couplings to further coarsen the nanoporous Cu. On the contrary, the trace formation of the Ag phase on the Ti60Cu39Ag1 ribbons had a weak ability to motivate the galvanic dissolution, indicating by the constant pore sizes and slight decrease in the ligament sizes with the increase in the dealloying time. The refinement of the nanoporous structures was ascribed to the drastic decrease in the surface diffusivity. The decrease in the surface diffusivity due to the involvement of Ag with a lower surface diffusivity in comparison of Cu was more than one order of magnitude. The involvement of Ag adatoms restricted the diffusion of Cu adatoms in the interface regions in the inward and outward directions.

Silver-Assisted Colloidal Synthesis of Stable, Plasmon Resonant Gold Patches on Silica Nanospheres

Patchy particles possessing heterogeneous surface composition show great promise as self-organizing building blocks for new classes of hierarchical functional structures. A major hurdle is the scalable synthesis of stable patches on nanosized core particles with arbitrarily defined patch number and coverage. So far, few methods have been reported which could be expected to meet these challenges. Recently, we described the heterogeneous nucleation and growth of silver patches on silica nanospheres via a template free colloidal route. The patches produced, although tunable in size and number and showing interesting plasmon resonant properties, were rather unstable and degraded rapidly during attempts to process them further. In the present work, therefore, we set out to explore if related approaches can be employed to produce patchy particles involving gold, which is known to be more stable. The differences between typical patch precursors Ag(+) and [AuCl(x)(OH)(4-x)](-) and their respective interactions with amorphous silica make this a significant challenge. We show that preformed small silver patches in addition to the presence of a reducing agent are necessary for the formation of gold patches conformal to the silica nanosphere surface. Systematic study of the process parameters and their influence on the patchy particle morphology as well as in-depth analytical transmission electron microscopy investigation of the patch composition reveal that patches spread over the silica surface via a cycle of galvanic dissolution and redeposition of silver. The resulting gold patchy particles remain stable during subsequent storage or washing and display tunable plasmon resonances within the visible and near-IR spectrum.

Corrosion relationships as a function of time and surface roughness on a structural AE44 magnesium alloy

Pit initiation, growth, and coalescence corrosion mechanisms of an AE44 magnesium alloy subjected to a salt-water environment were quantified. Stereological quantities were evaluated using optical microscopy, scanning electron microscopy, and laser beam profilometry. Three corrosion mechanisms clearly arose: pitting, intergranular, and general. Pitting began as the result of localized galvanic dissolution between the intermetallics and magnesium matrix. Intergranular corrosion arose as pits coalesced. General corrosion arose by dissolution and regeneration of a Mg(OH) 2 film at a continuous rate. Stereological quantification demonstrated that the corrosion pit number density and pit radius size distribution initially increased before decreasing due to pit coalescence.

Electrochemical impedance spectroscopic analysis of activation of Al–Zn alloy sacrificial anode by RuO 2 catalytic coating

The uniform surface activation characteristics of RuO 2-coated Al–Zn alloy sacrificial anodes were studied in the present work. Electrochemical impedance spectroscopic and SEM/EDAX analyses were carried out to evaluate the galvanic dissolution characteristics of the anodes. The conventional electrochemical methods were also followed. Persistence and retention of catalytic RuO 2 on the anode surface even after a large extent of galvanic dissolution of the anode surface was confirmed based on the EDAX spectroscopy. The anodes showed the same polarization performances even after the anodes were disintegrated to one-third of its original size, revealing the sustained catalytic activity of RuO 2.

Galvanic Dissolution Behavior of Magnesium-1 mass%manganese-0.5 mass%calcium Alloy Anode for Cathodic Protection in Fresh Water

Magnesium-1 mass%manganese-0.5 mass%calcium (Mg-1 mass%Mn-0.5 mass%Ca) alloy was used as sacrificial anode. This work was performed to investigate the galvanic dissolution behavior of the alloy anode for cathodic protection in fresh water. The microstructure and dissolved surface of the alloy anode were analyzed with an electron probe micro analyzer, a scanning electron microscope with energy dispersive X-ray spectrometer and a microscope. The current efficiency of the anode has been measured by laboratory test method of galvanic anodes for cathodic protection. It was found that calcium is present uniformly at the grain boundaries as Mg 2 Ca or Mg-Ca-Si compounds. Calcium compounds dissolve preferentially compared to the matrix of magnesium, as a result the anode uniformly dissolve compared to Mg-1 mass%Mn alloy anode. The current efficiency of the anode for the dissolution was higher than that of Mg-1 mass%Mn anode. On the other hand, manganese is added in order to decrease the local cathode to magnesium alloys, however the part of manganese compounds act as the local cathode in the alloys.

Galvanic removal of metallic wrought iron from marine encrustations

Historic shipwrecks frequently contain a large proportion of wrought-iron tools, fasteners, and other types of artefacts. Encrustations readily form around such objects in many marine environments. Depending on many factors, the iron objects inside these encrustations may be well preserved, completely disintegrated, or poorly preserved but still present. The latter type of encrustation is every conservator's nightmare because removing the encrustation yields merely a poorly preserved artefact still in need of extensive additional conservation. Neatly separating the artefact from its encrustation in order to obtain a natural mould for casting is generally impossible. Having encountered this problem many times, the authors began to experiment with the extraction of metallic iron from poorly preserved encrusted artefacts using galvanic dissolution. Data on rates of dissolution were gathered for three experimental configurations. The results of a test conducted on an encrusted artefact were promising, but inconclusive.

Galvanic removal of metallic wrought iron from marine encrustations

Historic shipwrecks frequently contain a large proportion of wrought-iron tools, fasteners, and other types of artefacts. Encrustations readily form around such objects in many marine environments. Depending on many factors, the iron objects inside these encrustations may be well preserved, completely disintegrated, or poorly preserved but still present. The latter type of encrustation is every conservator's nightmare because removing the encrustation yields merely a poorly preserved artefact still in need of extensive additional conservation. Neatly separating the artefact from its encrustation in order to obtain a natural mould for casting is generally impossible. Having encountered this problem many times, the authors began to experiment with the extraction of metallic iron from poorly preserved encrusted artefacts using galvanic dissolution. Data on rates of dissolution were gathered for three experimental configurations. The results of a test conducted on an encrusted artefact were promising, but inconclusive.

Ruthenium oxide for effective activation of aluminium sacrificial anodes: a new approach

Ruthenium oxide, one of the excellent electrocatalysts having high conductivity and high chemical and thermodynamic stability, has been coated onto the surface of an electrode made from a Al–5 wt-%Zn alloy. The activated aluminium ion was able to diffuse through the porous catalytic hydrophilic layer. Ruthenium oxide coated Al–Zn alloy anodes displayed high open circuit potential and high closed circuit potential during galvanic exposure with mild steel cathodes. A galvanic efficiency as high as 86% with an actual current capacity of 2573 A h kg-1 was achieved. The RuO2 film underwent very little deterioration and a considerable mass of the ruthenium oxide film persisted on the anode surface, even after the electrode size had been reduced to one third of its original size owing to galvanic dissolution. These electrodes are economically efficient, as convenient to prepare, install and use as other conventional electrodes, are tolerable of very aggressive media and highly efficient, even under high galvanic current loads.

Etude du mecanisme d'extraction du combustible nucleaire de sa gaine

A study was made of galvanic and cathodic corrosion at the interface between nuclear fuel and cans of stainless steel, zircaloy and aluminium. The corrosion rate was determined as a function of cathodic current density, nitric acid concentration and temperature. The E.M.F. of the fuel/can cell and the variations of E.M.F. with acid concentration and current density were determined. In 5.4 N nitric acid, the uranium potential rose sharply, probably owing to the formation of a “double layer”. Interfacial corrosion liberated N 2O, N 2, H 2 and O 2 in the cathodic region. The results can be regarded as galvanic dissolution of uranium in a uranium/can cell, to a degree determined by the E.M.F. of the cell. The dissolution of the fuel takes place at a regular rate along the fuel/can interface; radiography has confirmed this. Such dissolution allows irradiated fuel (uranium or uranium compounds) to be extracted from its can (stainless steel, zircaloy or aluminium) without the necessity of dissolving the can. This method can reduce the expense of treating irradiated nuclear fuels by reducing the volume of effluent of medium activity which would result from that operation. Moreover, this allows fuels to be treated irrespective of the material of which the can is made.