Promotion Of Dissolution Research Articles

Peculiarities of Calcite Interaction with Carboxylic Acids

This research examined the interaction of calcite with carboxylic acids (formic, citric, malic, and oxalic acids) at temperatures ranging from 22 to 80 °C. Experiments were carried out using an open batch reactor to prevent the impact of aggressive CO2 byproducts. The dissolution rate was determined to be a combination of the chemical interaction of calcite with acid and the promotion of dissolution by calcium carboxylate salt. When acid concentrations are low, the surface chemical reaction acts as a limiting step with an activation energy of 42 kJ∙mol-1. Conversely, at higher acid concentrations, the formation of calcium carboxylate with reduced solubility hinders its dissolution, thereby restricting the overall calcite dissolution process. Both stages are significantly influenced by temperature. The specific functional groups present in the acids aid in the formation of surface species with Ca2+ cations. The properties of these functional groups impact the stability of the species and the dissolution of calcite.

Amine-promoted gypsum carbonation for efficient CO2 capture and selective synthesis of CaCO3 polymorph integrating with amine regeneration by bipolar membrane electrodialysis

CO2 mineralization of waste gypsum not only reduces the carbon emissions of power plants but also improves gypsum utilization by recovering high-value-added CaCO3. However, the extensive consumption of various reagents limited its development. This paper proposed an amine-promoted waste gypsum carbonation process integrating with amine regeneration by bipolar membrane electrodialysis (BMED). The alkaline amine was expected to act as a multifunctional reagent for gypsum carbonation — alkaline reagent, CO2 absorbent, gypsum dissolution promoter, and CaCO3 crystal regulator. Seven typical amines with different amino types and pKa values were selected to investigate the feasibility of this process. Results show that promising CO2 removal efficiency (>95 %) from an artificial exhausting gas, gypsum carbonation efficiency (>93 %), and CO2 sequestration capacity (>340 g-CO2/kg-gypsum) can be achieved due to the additional alkalinity, fast CO2 absorption, high CO2 concentrations, and enhanced CaSO4 dissolution in amine solutions. In addition, the interactions of amine-CO2-gypsum and the CaCO3 growth mechanism in the gas–liquid-solid system were explored. Monoethanolamine (MEA), 3-amino-1-propanol (MPA), piperazine (PZ), and 1,3-Diaminopropane (DAP) could prolong the CaCO3 precipitation due to their strong affinity for Ca2+ and CO32−. In this case, CO2 absorption by the liquid phase dominated the carbonation process in the initial 30 min for these four amines, while CaCO3 precipitation mainly occurred within 30 ∼ 120 min. Amines’ different affinities for Ca2+ and CO32− provided an approach to selective synthesis of CaCO3 polymorph: 100 % calcite by PZ, 100 % vaterite by DAP, a calcite-vaterite mixture by MEA, and a calcite-vaterite-aragonite mixture by MPA. After the carbonation process, amines were recycled from the liquid residue by BMED, which could provide OH− for amines regeneration from protonated amines, recovery of H2SO4, and decrease the solution salinity.

Direct observations of nanoscale brushite dissolution by the concentration-dependent adsorption of phosphate or phytate

With the development of agricultural intensification, phosphorus (P) accumulation in croplands and sediments has resulted in the increasingly widespread interaction between inorganic and organic P species, which has been, previously, underestimated or even ignored. We quantified the nanoscale dissolution kinetics of sparingly soluble brushite (CaHPO4·2H2O, DCPD) over a broad range of phosphate and/or phytate concentrations by using in situ atomic force microscopy (AFM). Compared to water, we found that low concentrations of phosphate (1–1000 µM) or phytate (1–100 µM) inhibited brushite dissolution by slowing single step retraction. However, with increasing phosphate or phytate concentrations to 10 mM, there was a reverse effect of dissolution promotion at brushite-water interfaces. In situ observations of the coupled dissolution-reprecipitation showed that phosphate precipitated more readily than phytate on brushite surfaces, with the formation of amorphous calcium phosphate (ACP). For a fundamental understanding, zeta potential and in situ Raman spectroscopy (RS) revealed that the concentration-dependent dissolution is attributed to the reverse of outer-sphere to inner-sphere adsorption with increasing phosphate or phytate concentrations. In addition, the mineralization of phytate with outer-sphere adsorption by phytase was higher than that with inner-spere adsorption, and the presence of phytate delayed ACP phase transformation to hydroxylapatite (HAP). These in situ observations and analyses may fill the knowledge gaps of interaction between inorganic and organic P species in P-rich terrestrial and aquatic environments, thereby implicating their biogeochemical cycling and the associated availability.

Recyclable and efficient hydrate-based CH4 storage strengthened by fabrics

Due to the high storage capacity and low cost, gas hydrates have great potential in CH4 storage. In this work, four different common fabric materials were used as the CH4 hydrate carriers to enhance the gas–liquid interface and the mass transfer during hydrate growth at 278.2 K and an initial pressure of 6.7 MPa. The strengthen mechanism was further analyzed using a kinetic model and SEM images. Results showed that the water conversions ratios in different fabric materials were 76–92 % which corresponded to the storage capacities ranged from 60 to 65 v/v and the decay in storage capacity was less than 6.3 % within 6 cycles of hydrate formation. The beach pants fabric was found to be the most active in the promotion of CH4 dissolution and hydrate growth where the water conversion ratios were over 90 % and the time required for 63 % water conversion is only about 0.6 h. Kinetic analysis showed that the CH4 diffusion resistance through the hydrate layer was the rate-limiting step although some fabric materials performed well in hydrate growth. SEM images revealed that beach pants induced the hydrate formation with foamy surface which facilitated the gas transportation through the hydrate layer. Based on the multiscale analysis, an ideal fabric material for hydrate formation should be thin, light and knitted where the fibers can induce particle like or foamy hydrates instead of dense and continuous hydrate layer.

Investigation of Glycine Polymorphic Transformation by In Situ ATR-FTIR and FT-Raman Spectroscopy

The solution-mediated phase transformation of α-form to γ-form glycine, including dissolution of metastable α-form, nucleation, and growth of stable γ-form during polymorphic transformation, was investigated using in situ attenuated total-reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and Fourier transform Raman spectroscopy (FT-Raman). The mechanistic influence of operating parameters such as agitation speed, crystallization temperature, α-form seed concentration, and NaCl concentration on polymorphic phase transformation was examined. When the agitation speed, crystallization temperature, and NaCl concentration were increased, the polymorphic transformation process was improved due to the promotion of nucleation and growth of stable γ-form, in addition to the promotion of dissolution of metastable α-form. Moreover, the time to induce γ-form nucleation and complete conversion of α-form to γ-form was also reduced with increasing α-form seed concentration.

The bio-activation of pozzolanic activity of circulating fluidized-bed fly ash by Paenibacilllus mucilaginosus

The present investigation reports an eco-friendly biotechnology applying Paenibacilllus mucilaginosus (P.m), a silicate solubilizing bacteria, to activate pozzolanic activity of CFA. The results show SiO2 and Al2O3 dissolution rate of CFA treated by P.m and its Ca2+ absorption capacity in saturated Ca(OH)2 solutions are increased compared to raw CFA indicating that pozzolanic reactivity of CFA is improved by P.m. One reason is destruction of the anhydrite coating layer of CFA particles surface through P.m erosion. Another reason is promotion of SiO2 dissolution caused by deformation and destruction of Si-O-Si (Al) bonds by P.m. Carbonic anhydrase activity of P.m is one of the main factors involved in dissolution of SiO2, which also induces CaCO3 mineralization. The hardening characteristics and hydration products of CFA-15% lime system with different content of P.m further confirm the effects of P.m on pozzolanic activity of CFA. 40% P.m incorporation is conducive to promote CFA hydration, ettringite earlier formation and bio-mineralization, thereby improving the mechanical properties of hardened mortar. Incorporation of 40% P.m in cement blended with CFA results in that CFA content is increased by 5–20% and the 28d strength improved by 11.5–23.9 MPa. This is the first report of microbial activation of CFA pozzolanic activity.

The effect of anodizing temperature on the oxygen evolution reaction activity of anodized FeNiCo alloy in alkaline electrolyte

This study investigates the oxygen evolution reaction (OER) activity of the FeNiCo alloy anodized at several temperatures in a fluoride-containing ethylene glycol electrolyte. When the alloy is anodized at 10 V, the OER activity in KOH electrolyte is highly enhanced on the alloy anodized at 15 and 20 °C, at which non-uniform film growth proceeds. The fraction of the locally thick film regions increases with anodizing time, enhancing the OER activity. Only thin porous films are formed at ≥30 °C even though the anodizing current is high because of the promotion of film dissolution at high electrolyte temperatures. Because of the thickness limitation, the OER activity is relatively low when the anodic films are formed at ≥30 °C. A good correlation is found between the OER activity and the electric double-layer capacitance; thicker porous anodic films enhance the OER activity. The anodic film formed at each temperature consists of a rutile-type (FeNiCo)F2 phase, but in KOH electrolyte, it is converted readily to an oxyhydroxide phase, which is OER active. A ∼2 μm-thick film obtained under the optimum anodizing condition reduces the overpotential of OER to 245 mV at 10 mA cm–2 in 1.0 mol dm–3 KOH electrolyte.

Efficient extracting germanium and gallium from zinc residue by sulfuric and tartaric complex acid

This paper introduces an efficient extraction method based on organic and sulfuric complex acid system, to achieve the clean recovery of scattered metals from zinc leaching residue. The tartaric (TAR) and sulfuric complex acid significantly improved the leaching of Ge but had little effect on the leaching efficiency of Ga. A maximum extraction efficiency of 93.1% of Ge and 84.3% of Ga, was obtained at a sulfuric acid concentration of 100 g/L, TAR concentration of 20 g/L, leaching time of 1 h, and temperature of 80 °C, with a liquid-solid ratio of 10 mL/g, and a mixing rate of 250 rpm. The leaching process and mechanism were investigated by XRD, SEM, EPMA and UV–Vis. The findings showed that TAR acid plays a key role in the dissociation of the mineral phase containing Ge, as well as the promotion of Ge dissolution. Compared with the conventional sulfuric acid system, the TAR containing complex acid could effectively promote the decomposition of some iron ore phases, like beaverite, in which Ge tends to be embedded and enriched, in association with Fe. Additionally, the improved leaching efficiency of Ge was attributed to the formation of soluble TAR-Ge complexes, which were confirmed by UV–Vis.

Insight into the Effect of LiNO3 Additive in High‐Voltage NCA Cathode with a Cylindrical 18650 Lithium-Metal Battery

Lithium metal is an attractive anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mA h g−1) and low density (0.59 g cm−3). Unfortunately, lithium metal itself faces huge problems including inhomogeneous lithium deposition, infinite volume expansion, increased polarization, and dendrite formation. To overcome these drawbacks, many researchers have employed LiNO3 additive in the ether-based electrolyte to modify the properties of the solid electrolyte interface (SEI) film formed on the lithium metal surface. The LiNO3 can improve an ionically conductive, dense, and stable SEI formation through Li stripping and plating. However, LiNO3 has low solubility in carbonate based. Thus, LiNO3 was applied as an additive in carbonate electrolyte using CuF2 as a dissolution promoter. Herein, we demonstrate carbonate electrolyte system using LiNO3 and CuF2 with different ratios in high‐voltage Ni‐rich cathode with a cylindrical shape (18650). To achieve fundamental understanding of the effect of electrolyte additive molecules on the SEI formation at the lithium anode, reactive molecular dynamic simulation (Reaxff) has been used to investigate the mechanism and property of the SEI layer on the lithium anode.

DFT simulations of pyrite galvanic interactions with bulk, solid-solution and nanoparticle Au occurrences – Insights into gold cyanidation

Gold cyanidation is an important hydrometallurgical route central to which are the gold/mineral galvanic interactions which pose perennial challenges to understanding gold dissolution. In this study, Density Functional Theory simulations have been performed to unveil some important electronic features of gold/pyrite associations on gold cyanidation. Three typical gold/pyrite occurrences have been considered, namely, model_1) gold slab/pyrite slab association to emulate contactless liberated gold and pyrite with up to a few Å separations; model_2) gold-substituted pyrite solid-solution slab to emulate atomically dispersed gold in a sulfidic matrix; and model_3) pyrite slab with tethered gold nanocluster, in addition to isolated gold nanocluster and to pure pyrite slab. Gold/pyrite associations for all three studied models have been shown to induce electron transfer from gold to both pyrite’s sulfur and iron atoms. Model_1 revealed that galvanic interactions between liberated gold and pyrite can occur up to 10 Å separation distance between the metal and the sulfide slabs. However, the efficacy of galvanic interactions decreased with increasing the inter-slab separation distances. Model_2 divulged that S-substitutive incorporation of Au in the pyrite structure resulted in expanded crystal dimensions as well as changes in electron properties of gold, iron and sulfur atoms in the solid-solution structure. Occurrence of gold nanocluster on pyrite surface (model_3) led to the formation of metal-metal Au-Fe bond and covalent Au-S bond. Sorption interactions of cyanide with gold and pyrite surfaces in presence of dioxygen were investigated with the three model variants. The DFT simulations showed that CN− preferentially adsorbed on gold instead of pyrite sites provided gold/pyrite galvanic interactions deprived gold from electron density at the expense of pyrite. The cyanide adsorption energies were found to follow the sequence: model_1 with substituted Au+ > model_2 > model_3 with substituted Au+ > model_1 (short distance) > model_3 > pure pyrite (1 0 0) & model_1 (long distance contact) > isolated Au9 nanocluster. As Au electron deficiency via galvanic interactions or gold oxidation was enhanced, gold-cyanide interaction energy increased portending the promotion of gold dissolution in cyanidation processes.

Mechanism of birnessite-promoted oxidative dissolution of antimony trioxide

Environmental contextThe release of antimony and its compounds to the environment can present a toxic hazard for humans. We evaluated the use of birnessite to dissolve antimony trioxide and found that birnessite accelerated the dissolution process, and ~50% of the oxidised antimony was absorbed. The results can help evaluate the bioavailability of antimony in the environment. AbstractThe most important naturally occurring forms of antimony (Sb) are the ore mineral stibnite (Sb2S3) and its principal weathering product antimony trioxide (Sb2O3). Moreover, most Sb is released into the environment as Sb2O3 from manufacturing, formulations, processing, and the use and disposal of Sb products. In this study, birnessite (δ-MnO2) was employed to promote Sb2O3 dissolution. The Sb2O3 dissolution rate accelerated from ~2% to >99% after 9 days of reaction, and more than 98% of the dissolved SbIII was oxidised into SbV in the presence of birnessite. The birnessite-promoted oxidative dissolution mechanism of Sb2O3 was studied through experiments on the effects of the reaction time and pH. The release rate of Sb in the aqueous phase at the initial stage (335.4 μmol L−1 day−1, pH 6.5) was much higher than that at the late stage (13.28 μmol L−1 day−1, pH 6.5), and when the pH increased from 4.7 to 8.0, the Sb release rate decreased from 351.2 μmol L−1 day−1 to 257.7 μmol L−1 day−1. The dissolution promotion effects of birnessite on Sb2O3 were the most evident under acidic and neutral conditions (the percentages of dissolved Sb2O3 under acidic and neutral conditions were 98.3% and 100.0% after 9 days of reaction). Not all of the produced SbV was released in the reaction solution because ~50% of it was adsorbed by birnessite, and the amount of Sb adsorbed increased with increasing pH. Therefore, alkaline conditions are shown to reduce the release of SbV by inhibiting Sb2O3 dissolution (86.7%) and enhancing SbV adsorption. These results could help clarify the geochemical cycle and fate of Sb in the environment.

Enhanced heterogeneous uptake of sulfur dioxide on mineral particles through modification of iron speciation during simulated cloud processing

Abstract. Iron-containing mineral aerosols play a key role in the oxidation of sulfur species in the atmosphere. Simulated cloud processing (CP) of typical mineral particles, such as illite (IMt-2), nontronite (NAu-2), smectite (SWy-2) and Arizona Test Dust (ATD) is shown here to modify sulfur dioxide (SO2) uptake onto mineral surfaces. Heterogeneous oxidation of SO2 on particle surfaces was firstly investigated using an in situ DRIFTS apparatus (diffuse reflectance infrared Fourier transform spectroscopy). Our results showed that the Brunauer–Emmett–Teller (BET) surface area normalized uptake coefficients (γBET) of SO2 on the IMt-2, NAu-2, SWy-2 and ATD samples after CP were 2.2, 4.1, 1.5 and 1.4 times higher than the corresponding ones before CP, respectively. The DRIFTS results suggested that CP increased the amounts of reactive sites (e.g., surface OH groups) on the particle surfaces and thus enhanced the uptake of SO2. Transmission electron microscopy (TEM) showed that the particles broke up into smaller pieces after CP, and thus produced more active sites. The “free-Fe” measurements confirmed that more reactive Fe species were present after CP, which could enhance the SO2 uptake more effectively. Mössbauer spectroscopy further revealed that the formed Fe phases were amorphous Fe(III) and nanosized ferrihydrite hybridized with Al ∕ Si, which were possibly transformed from the Fe in the aluminosilicate lattice. The modification of Fe speciation was driven by the pH-dependent fluctuation coupling with Fe dissolution–precipitation cycles repeatedly during the experiment. Considering both the enhanced SO2 uptake and subsequent promotion of iron dissolution along with more active Fe formation, which in turn led to more SO2 uptake, it was proposed that there may be a positive feedback between SO2 uptake and iron mobilized on particle surfaces during CP, thereby affecting climate and biogeochemical cycles. This self-amplifying mechanism generated on the particle surfaces may also serve as the basis of high sulfate loading in severe fog–haze events observed recently in China.

Combined effects of jarosite and visible light on chalcopyrite dissolution mediated by Acidithiobacillus ferrooxidans

Although jarosite and visible light are important factors for the formation of acid mine drainage (AMD), the effects of combined jarosite and visible light on chalcopyrite biodissolution have not been explored until now. In order to fill this knowledge gap, the combined effects of jarosite and visible light on chalcopyrite dissolution mediated by Acidithiobacillus ferrooxidans were investigated. The results indicated that jarosite and visible light could significantly accelerate chalcopyrite biodissolution, thus releasing more copper ions, iron ions and producing more acid. This in turn suggests enhanced generation of AMD under these conditions. Biodissolution results, mineral surface morphology, mineralogical phase and elemental composition analyses revealed that the promotion of chalcopyrite dissolution by additional jarosite and visible light was mainly attributed to the acceleration of ferric iron/ferrous iron cycling and the inhibition of the formation of a passivation layer (jarosite and Sn2−/S0) on the surface of chalcopyrite. This study provides a better understanding of the effects of jarosite and visible light on chalcopyrite biodissolution. In the future, the influences of jarosite and visible light on chalcopyrite dissolution should be considered in AMD evaluation to ensure reliability.

Amino acid as a biodegradation accelerator of mesoporous silica nanoparticles

Abstract In order to avoid cumulative toxicity of the remained mesoporous silica nanoparticles (MSNs) in biological systems, three amino acids (aâs), i.e., glycine (Gly), aspartic acid (Asp) and cysteine (Cys), were incorporated into MSNs for accelerating their biodegradation. Aâ was conjugated with 3-isocyanatopropyl triethoxysilane (ICPTES) before reacting with tetraethyl orthosilicate to form aâ-MSNs via the sol-gel process based co-condensation. FTIR spectra confirmed the urea bond formation in aâ-ICPTES, whereas silicon resonances of T2 and T3 in 29Si NMR spectrum indicated the incorporation of aâ in MSNs. Spherical bare-MSNs (112 nm) were obtained while the rod-like particles were formed in the case of Gly-MSNs (73 nm in length), Asp-MSNs (90 nm in length), and Cys-MSNs (163 nm in length). The trend of %Si dissolution rate analyzed from microwave plasma-atomic emission spectrometer (MP-AES) of aâ-MSNs in phosphate buffer saline (PBS)/trypsin enzyme (pH 7.4) was 3–5 times higher than in PBS (pH 7.4) and 7–8 times higher than in acetate buffer (pH 5.2), respectively. The Asp-MSNs having two carboxylic groups showed the highest degradability, followed by Cys-MSNs, Gly-MSNs, and bare-MSNs in all three media. By capability of aâ as a dissolution promoter, the aâ-MSNs would be an effective and alternative material used as drug carrier in biomedical applications.

Lithium Nitrate Solvation Chemistry in Carbonate Electrolyte Sustains High-Voltage Lithium Metal Batteries.

The lithium metal anode is regarded as a promising candidate in next-generation energy storage devices. Lithium nitrate (LiNO3 ) is widely applied as an effective additive in ether electrolyte to increase the interfacial stability in batteries containing lithium metal anodes. However, because of its poor solubility LiNO3 is rarely utilized in the high-voltage window provided by carbonate electrolyte. Dissolution of LiNO3 in carbonate electrolyte is realized through an effective solvation regulation strategy. LiNO3 can be directly dissolved in an ethylene carbonate/diethyl carbonate electrolyte mixture by adding trace amounts of copper fluoride as a dissolution promoter. LiNO3 protects the Li metal anode in a working high-voltage Li metal battery. When a LiNi0.80 Co0.15 Al0.05 O2 cathode is paired with a Li metal anode, an extraordinary capacity retention of 53 % is achieved after 300 cycles (13 % after 200 cycles for LiNO3 -free electrolyte) and a very high average Coulombic efficiency above 99.5 % is achieved at 0.5 C. The solvation chemistry of LiNO3 -containing carbonate electrolyte may sustain high-voltage Li metal anodes operating in corrosive carbonate electrolytes.

Lithium Nitrate Solvation Chemistry in Carbonate Electrolyte Sustains High‐Voltage Lithium Metal Batteries

AbstractThe lithium metal anode is regarded as a promising candidate in next‐generation energy storage devices. Lithium nitrate (LiNO3) is widely applied as an effective additive in ether electrolyte to increase the interfacial stability in batteries containing lithium metal anodes. However, because of its poor solubility LiNO3 is rarely utilized in the high‐voltage window provided by carbonate electrolyte. Dissolution of LiNO3 in carbonate electrolyte is realized through an effective solvation regulation strategy. LiNO3 can be directly dissolved in an ethylene carbonate/diethyl carbonate electrolyte mixture by adding trace amounts of copper fluoride as a dissolution promoter. LiNO3 protects the Li metal anode in a working high‐voltage Li metal battery. When a LiNi0.80Co0.15Al0.05O2 cathode is paired with a Li metal anode, an extraordinary capacity retention of 53 % is achieved after 300 cycles (13 % after 200 cycles for LiNO3‐free electrolyte) and a very high average Coulombic efficiency above 99.5 % is achieved at 0.5 C. The solvation chemistry of LiNO3‐containing carbonate electrolyte may sustain high‐voltage Li metal anodes operating in corrosive carbonate electrolytes.

Combined Effect of Alternating Current Interference and Cathodic Protection on Pitting Corrosion and Stress Corrosion Cracking Behavior of X70 Pipeline Steel in Near-Neutral pH Environment.

Influence of alternating current (AC) on pitting corrosion and stress corrosion cracking (SCC) behavior of X70 pipeline steel in the near-neutral pH environment under cathodic protection (CP) was investigated. Both corrosion and SCC are inhibited by −0.775 VSCE CP without AC interference. With the superimposition of AC current (1–10 mA/cm2), the direct current (DC) potential shifts negatively under the CP of −0.775 VSCE and the cathodic DC current decreases and shifts to the anodic direction. Under the CP potential of −0.95 VSCE and −1.2 VSCE, the applied AC current promotes the cathodic reaction and leads to the positive shift of DC potential and increase of cathodic current. Local anodic dissolution occurs attributing to the generated anodic current transients in the positive half-cycle of the AC current, resulting in the initiation of corrosion pits (0.6–2 μm in diameter). AC enhances the SCC susceptibility of X70 steel under −0.775 VSCE CP, attributing to the promotion of anodic dissolution and hydrogen evolution. Even an AC current as low as 1 mA/cm2 can enhance the SCC susceptibility.

Corrosion and Critical Solute Content of Corrosion-Resistant Binary Solid Solution Cu-Al Alloys in Artificial Perspiration Solution: Implications Towards Tunable Cu-Based Alloys for Antimicrobial Surfaces

Copper and its alloys as high-touch surfaces can be antimicrobial, capable of killing even antibiotic-resistant superbugs including Methicillin-resistant Staphylococcus aureus (MRSA)1–5 through controlled release of Cu(I)/Cu(II) cations as a result of corrosion. Therefore, there is interest in designing tunable Cu alloys with regulated dissolution and passivation properties. The inability to predict electrochemical behavior as a function of alloying content remains a critical challenge in both corrosion and electrochemical materials science. Yet, a lack of scientific understanding persists concerning how alloying controls soluble Cu cation release (antimicrobial function) of Cu-based alloys.6–10 A tunable alloy system is needed to balance antimicrobial efficacy, i.e. soluble Cu cation release, with tarnish-resistance which can both be regulated using alloy content optimization. Aluminum bronzes are of interest to study in this context for their relatively improved corrosion resistance due in part to formation of a tarnish-resistant oxide film.11–14The focus of this work is to investigate critical governing mechanisms associated with alloyed Al on protective oxide layer formation in FCC α-Cu, as a function of Al content. This investigation specifically addresses behavior in a realistic environment for high-touch surfaces where these pathogenic bacteria proliferate: human perspiration. To quantitatively interrogate the effect of alloying FCC α-Cu with Al on corrosion and cation release, commercially pure Cu (Cu), and high-purity arc-melted solid solution alloys consisting of Cu-0.1Al, Cu-1Al and Cu-5Al (wt%) were evaluated in modified artificial human perspiration solution.15 Open circuit corrosion exposures were conducted for up to 130 hours to determine corrosion rate and the fate of Cu and Al. Released aqueous ion concentrations were monitored via inductively-coupled plasma – optical emission spectroscopy (ICP-OES). Al was not observed as a soluble ionic species within ICP-OES limits of detection (LOD). Corrosion products were characterized using grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, and quantified with coulometric reduction (CR). Corrosion rates were assessed with mass loss and electrochemical impedance spectroscopy (EIS). Quantitative results of total anodic charge, from both mass loss and calculated from EIS-determined corrosion rates were converted to charge and directly compared to corrosion product charge (CR) and dissolution charge (ICP-OES) to determine the fate of the elements: Cu and Al, through charge balance as a function of Al alloying content. Diagnostic chemical environments were employed where only selected corrosion products are stable e.g., Al2O3 in citric/citrate buffer. For instance, HCl and deaerated citric/citrate buffer solution (CBS) were employed to determine the individual roles of Al in the metal as a metal solute and as an oxidized surface film, respectively. Primary corrosion products were revealed to be Cu2O and an inner layer of Al2O3 for Al-containing alloys. Cu was dissolved as cuprous (Cu+) ions. Minor Al alloying in solid solution catalyzed Cu dissolution which was counteracted at higher Al contents by a partially passivating layer of Al2O3, achieving complete passivity at ~6 wt% Al according to graph theory.16,17 In contrast, Cu-Al alloys corroded more readily with increasing Al content in the absence of a protective oxide film. The effect of alloyed Al as a dissolution promoter for electrochemical Cu ion release, critical Al contents for stable passivity, and subsequent implications for functional antimicrobial alloys are discussed. These results point to the possibility of making tunable Cu-based alloys for antimicrobial function.

Electrochemical machining for micro holes with high aspect ratio on metal alloys using three-electrode PPS in neutral salt solution

To get micro holes with high aspect ratio on metal alloys by electrochemical machining (ECM) process, the mutual restricted problems between machining localization and efficiency are researched. By analyzing the thickening process of passive film, the mechanism of gas inhibition and dissolution promotion (GIDP) is explored. Thereby, a three-electrode pulse power supply (PPS) is designed to acidize on the workpiece/solution interface, for both better machining localization and efficiency. Micro ECM experiments, using the three-electrode PPS in neutral salt solution as electrolyte, are carried out on 304 stainless steel and 18CrNi8 alloy, in which a micro hollow electrode is used to flush electrolyte under high-pressure supply. It is found that the material removal rate (MRR) is increased by at least 80% and surface roughness R a is dropped by 40%, compared to those of two-electrode PPS. Micro array holes with diameter of about 175 μm are machined through metallic plates with thickness of 0.5 and 1.1 mm respectively. The micro array holes obtained have high consistent precision, good surface quality, and aspect ratio up to 6.5. Experimental results show the feasibility of micro ECM techniques proposed for micro hole with high aspect ratio.

Enhanced Electrochemical Cu Release from Commercial Cu-Sn Alloys: Fate of the Alloying Elements in Artificial Perspiration

Commercially pure Cu (Cu), Cu-4.5Sn-0.1Zn, and Cu-9.7Sn-0.1Zn (wt%) were evaluated for corrosion and cation release in modified artificial human perspiration solution. Open circuit corrosion exposures were conducted for up to 130hours to determine corrosion rate and the fate of Cu and Sn. Released aqueous ion concentrations were monitored via inductively-coupled plasma − optical emission spectroscopy (ICP-OES). Operando atomic emission spectroelectrochemistry (AESEC) analysis was utilized to elucidate the fate of Cu, whether in oxides or solution and deduce the dominant valence states, Cu(I)/Cu(II), of soluble Cu in artificial perspiration. Sn was not observed as a soluble ionic species within ICP-OES or AESEC limits of detection (LOD). Corrosion products were characterized using grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), and quantified with coulometric reduction (CR). Cu-4.5Sn-0.1Zn displayed the highest corrosion rates in artificial perspiration, followed by Cu-9.7Sn-0.1Zn, and then Cu. Primary corrosion products were Cu2O, with CuCl as an outer solid product, and an inner layer of SnO2 for Sn-containing alloys. Cu was dissolved as cuprous (Cu+) ions. Minor Sn alloying in solid solution catalyzed Cu dissolution which is counteracted at higher Sn contents by a passivating layer of SnO2, achieving complete passivity at 10.3wt% Sn according to graph theory. Cu-9.7Sn-0.1Zn indicated semi-passive behavior, speculated to be due a SnO2 layer and close proximity (9.7wt%) to this critical value for passivation (10.3wt%). The effect of alloyed Sn as a dissolution promoter for electrochemical Cu ion release, critical Sn contents for passivity, and subsequent implications of antimicrobial function are discussed. Oxidized Zn was not detected above LOD nor demonstrated any measurable effect on corrosion in artificial perspiration.