Electrodeposition of PtZn in a Lewis acidic ZnCl2-1-ethyl-3-methylimidazolium chloride ionic liquid

The electrodeposition of PtZn from a Lewis acidic 40-60 mol% zinc chloride-1-ethyl-3-methylimidazolium chloride ionic liquid containing PtCl₂ was investigated at polycrystalline tungsten substrates at 90 °C. Cyclic voltammetric data indicates that Pt(II) was reduced at a potential slightly more positive than Zn(II) was. The Pt-Zn electrodeposits exhibited multiple anodic stripping waves. The Zn-dominant deposits were stripped at a potential less positive than that of the Pt-dominant deposits. Energy-dispersive spectroscopy and scanning electron microscopy data indicated that the composition and morphology of the electrodeposited Pt-Zn alloys were affected by the deposition potential and the Pt(II) concentration in the plating solution. The electrodeposition of Zn at a Pt substrate also produced surface Pt-Zn alloys. The Pt of the electrochemically prepared Pt-Zn alloys was easier to oxidize than the bulk Pt substrate.     

Simulation of SiO2/S coating deposition in a pilot plant set-up for coking inhibition

The anti-coking SiO₂/S coating was prepared on the inner surface of HK40 alloy tube in a pilot plant set-up by atmospheric pressure chemical vapour deposition (APCVD). The coating deposition was simulated using the computational fluid dynamics code, Fluent. The reaction parameters of the surface reaction for SiO₂ formation were determined based on the comparison between the experimental and the calculated values. Further, the influences of the inlet flow rate and mass concentration of source materials on the coating deposition rate were investigated. The simulated results showed that an increase of inlet flow rate led to the decrease of mass conversion of gas intermediates. The coating deposition rate along the reactor tube increased by 1–5 times as the inlet flow rate increased from 10 to 80 g min⁻¹. The mass conversion rate of the gas intermediate, Si(OH)₄, changed little at different inlet mass concentrations of source materials when the inlet flow rate was 30 g min⁻¹, and it had an increase for sulphide intermediates. The coating deposition rate along the reactor tube increased by about 10 times with increasing the inlet mass concentration from 0.2% to 2%. In the conditions we studied, SiO₂/S coating deposition was surface reaction rate limited. When the inlet flow rate was 30–40 g min⁻¹ with the resource material concentration of 1–1.6%, the SiO₂/S coating was about 15 μm at the tube outlet with the silicon-containing intermediate conversion rate of above 30% and a good uniformity of S along the reactor. This work provides a theoretical basis for optimisation of operational parameters of the anti-coking SiO₂/S coating preparation in the pilot plant set-up.     

Electrodeposition of palladium-indium from 1-ethyl-3-methylimidazolium chloride tetrafluoroborate ionic liquid

Voltammetry at a glassy carbon electrode was used to study the electrochemical co-deposition of Pd-In from a chloride-rich 1-ethyl-3-methylimidazolium chloride/tetrafluoroborate air-stable room temperature ionic liquid at 120 °C. Deposition of Pd alone occurs prior to the overpotential deposition (OPD) of bulk In. However, underpotential deposition (UPD) of In on the deposited Pd was observed at the potential same as the deposition of Pd. The UPD of In on Pd was, however, limited by a slow charge transfer rate. Samples of Pd-In alloy coatings were prepared on nickel substrates and characterized by energy dispersive spectroscope (EDS), scanning electron microscope (SEM) and X-ray powder diffraction (XRD). The electrodeposited alloy composition was relatively independent on the deposition potential within the In UPD range. At more negative potentials where the OPD of Pd-In has reached mass-transport limited region, the alloy composition corresponds to the Pd(II)/In(III) composition in the plating bath. The Pd-In alloy coatings obtained by direct deposition of Pd and UPD of In on the deposited Pd appeared to be superior to the Pd-In alloys that were obtained via the co-deposition of Pd and bulk In at OPD potentials.     

Electrodeposition of Sb, Bi, Te, and their alloys in AlCl3-NaCl-KCl molten salt

The Electrochemistry of Sb, Bi, and Te in AlCl₃-NaCl-KCl molten salt containing SbCl₃, BiCl₃, and/or TeCl₄ at 423 K was investigated by voltammetry, and electrodeposition of the three metals was performed under constant potential control in the melt. The voltammogram on a glassy carbon (GC) electrode in a melt containing 0.025 mol dm⁻³ [M] SbCl₃ showed a couple of redox peak corresponding to the Sb/Sb(III) redox reaction, and a stable layer of pure Sb was deposited under the constant potential control. The voltammograms in the melt containing 0.025 M BiCl₃ or 0.025 M TeCl₄ showed several redox couples. Stable deposit layers of pure Bi and Te were not obtained under the constant potential control, as the deposited layers detached from the electrode and immediately dissolved into the molten salt. Binary alloy deposition was possible in a melt containing BiCl₃ and SbCl₃, and also with BiCl₃ and TeCl₄. A stable Bi-Sb alloy deposit of metallic Sb and Bi-Sb solid solution was obtained at 0.8 and 0.9 V versus Al/Al(III) in the melt containing BiCl₃ and SbCl₃. The atomic ratio of Bi in the deposit was 37% at 0.9 V and 57% at 0.8 V. A stable Bi-Te alloy deposit was also obtained with the molten salt containing BiCl₃ and TeCl₄. The deposited Bi-Te alloy consisted of a mixture of Bi₂Te₃, BiTe, and Bi₂Te. The alloy deposit had good crystallinity and the preferential orientation was the (1 1 0) plane.     

Silver-zinc electrodeposition from a thiourea solution with added EDTA or HEDTA

This paper shows the study of silver-zinc electrodeposition from a thiourea solution with added (ethylenedinitrilo)tetraacetic acid (EDTA), disodium salt and N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), trisodium salt. Voltammetric results indicated that silver-zinc alloy can be obtained applying overpotential higher than 0.495 V, in Tu solution containing 1.0 × 10⁻¹ mol L⁻¹ Zn(NO₃)₂ + 2.5 × 10⁻² mol L⁻¹ AgNO₃. This was due to silver(I) ion complexation with thiourea, which shifted the silver deposition potential to more negative value and due to silver-zinc alloy deposition, which occurred at potentials more positive than the potential to zinc deposition alone. EDTA or HEDTA did not significantly affect the silver and zinc deposition potentials, but decreased the current density for silver-zinc deposition. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses of the silver-zinc deposits showed that the morphology and composition changed as a function of the conditions of deposition, viz, deposition potential (E_d), deposition charge density (q_d) and solution composition (silver, EDTA and HEDTA concentrations). EDS analysis of the deposits showed sulphur (S) incorporated into the silver-zinc deposit, while SEM images showed that this sulphur content seemed to improve the silver-zinc morphology, as did the presence of EDTA and HEDTA in the solution, which enhanced the sulphur incorporation into the silver-zinc deposit. X-ray diffraction (XRD) analysis of the silver-zinc deposit showed that it was amorphous, irrespective of its composition and morphology.     

Study on the preparation of Mg-Li-Zn alloys by electrochemical codeposition from LiCl-KCl-MgCl2-ZnCl2 melts

Electrochemical codeposition of Mg, Li, and Zn on a molybdenum electrode in LiCl-KCl-MgCl₂-ZnCl₂ melts at 943 K to form Mg-Li-Zn alloys was investigated. Cyclic voltammograms (CVs) showed that the potential of Li metal deposition, after the addition of MgCl₂ and ZnCl₂, is more positive than the one of Li metal deposition before the addition. Chronopotentiometry measurements indicated that the codeposition of Mg, Li, and Zn occurs at current densities lower than −0.78 A cm⁻² in LiCl-KCl-MgCl₂ (8 wt.%) melts containing 1 wt.% ZnCl₂. Chronoamperograms demonstrated that the onset potential for the codeposition of Mg, Li, and Zn is −2.000 V, and the codeposition of Mg, Li, and Zn is formed when the applied potentials are more negative than −2.000 V. X-ray diffraction (XRD) indicated that Mg-Li-Zn alloys with different phases were prepared via galvanostatic electrolysis. The microstructure of typical α + β phase of Mg-Li-Zn alloy was characterized by optical microscope (OM) and scanning electron microscopy (SEM). The analysis of energy dispersive spectrometry (EDS) showed that the elements of Mg and Zn distribute homogeneously in the Mg-Li-Zn alloy. The results of inductively coupled plasma analysis showed that the chemical compositions of Mg-Li-Zn alloys are consistent with the phase structures of the XRD patterns, and that the lithium and zincum contents of Mg-Li-Zn alloys depend on the concentrations of MgCl₂ and ZnCl₂.     

Influence of micro-structure on corrosion behavior of a Ni-based superalloy in 3.5% NaCl

The electrochemical corrosion behavior of a Ni-based superalloy with polycrystalline (cast alloy), single-crystalline (SC (2 0 0)) and nanocrystalline (NC) micro-structures has been studied in 3.5% NaCl solution. The results indicated that among the three materials, the corrosion resistance increased in the order cast alloy < SC (2 0 0) alloy < NC coating. XPS analyses revealed that the composition of passive film on the three materials was different. In addition to Cr₂O₃ and TiO₂, some NiO was detected in the passive film on the cast alloy, little in that of the SC (2 0 0) alloy and none in that of the NC coating. The double-log plots showed the compact property of the passive film formed on the samples also varied in the order cast alloy < SC (2 0 0) alloy < NC coating, with the cast alloy displaying the worst compact property and the NC coating the best. The micro-structure influenced both the composition of passive film as well as the initial growth of passive film, which determined the compact property of the film and resulted in the observed differences in the corrosion behavior of the three materials.     

Co-deposition of Al-Cr-Ni alloys using constant potential and potential pulse techniques in AlCl3-NaCl-KCl molten salt

To improve the oxidation resistance of TiAl intermetallic compound under high temperature condition, cathodic co-deposition of Al-Cr and Al-Ni alloy was carried out by constant potential control or potential pulse control in AlCl₃-NaCl-KCl molten salt containing CrCl₂ and/or NiCl₂ at 423 K. Cathodic reduction of Ni and Cr starts at potential of 0.8 and 0.15 V versus Al/Al³⁺ in the molten salt, respectively. The co-deposition of Al, Cr, and Ni occurred at potentials more negative than −0.1 V to form a mixture of intermetallic compounds of Cr₂Al, Ni₃Al, and Al₃Ni. Concentration of Cr in the deposit was enhanced to 43 at% at −0.1 V; however, concentration of Ni in the deposit was 6 at% at the same potential. The concentration of Ni further decreased with more negative potential to 1 at% at −0.4 V. The potential pulse technique enhanced the Ni concentration in the deposit to about 30 at%, due to anodic dissolution of Al content from the deposit at the higher side of potential on the potential pulse electrolysis.     

Liquid metal corrosion resistant LaPO4 coating with metallophobic characteristics fabricated on 316 stainless steel using electrophoretic deposition technique

A liquid metal corrosion (LMC) resistant and metallophobic lanthanum phosphate (LaPO₄) coating was prepared on SUS316 stainless steel using electrophoretic deposition (EPD) technique. A specific hierarchical surface structure was created on coating surface by adjusting EPD process parameters. LMC test was performed using three different metal melts, Al–Zn–Mg alloy, Mg–Al–Mn alloy, and pure Zinc. Results indicated that steel bare surface was severely attacked by all three melts. The mechanism of corrosion process was explained in each case. After coating, the LaPO₄ covered steel showed an excellent resistance against all three liquid metals. Besides, wetting of steel surface by liquid metals was strongly decreased by application of LaPO₄ surface coating. This can be attributed to the intrinsic metallophobic characteristic of LaPO₄ as well as the hierarchical surface structure developed on coating surface.     

Development of an environmentally friendly protective coating for the depleted uranium-0.75 wt.% titanium alloy: Part I. Surface morphology and electrochemistry

The surface of the depleted uranium (DU)-0.75 wt.% titanium alloy has been studied using scanning electron microscopy, energy dispersive spectroscopy and optical microscopy. The samples were examined after mechanical polishing and again after nitric acid cleaning. The acicular martensitic microstructure is revealed after chemical etching. Several of the impurities have been identified and their prevalence has been found to change depending on the surface treatments. The impurities have also been found to vary from sample to sample and within the same sample.The electrochemistry and corrosion characteristics of the alloy were studied using open circuit potential measurements and potentiodynamic polarization techniques. This study has been directed towards developing environmentally friendly protective coatings for this alloy. In this paper, we discuss our efforts in finding suitable chemical species to act as inhibitors and activators during coating formation. The effect of various oxyanions, MoO₄²⁻, PO₄³⁻, VO₄³⁻, MnO4⁻, SiO₄⁴⁻ and WO₄²⁻, on the electrochemical behavior of the depleted uranium alloy in quiescent nitric acid has been explored including their ability to inhibit corrosion. Results indicate that chemical or electrochemical activation of the DU alloy in 0.1 M HNO₃ + 0.025 M MoO₄²⁻ can lead to the formation of a rudimentary coating. The effect of several fluorine compounds was also examined and their electrochemical response indicates that several of them may have a potential use as a surface activator.     

Mechanism of formation and electronic structure of semiconducting ZnSb nanoclusters electrodeposited from an ionic liquid

Electrocrystallization of Sb and the compound semiconductor ZnSb has been investigated by in situ SPM methods at the electrified ionic liquid/Au(1 1 1) interface at an elevated temperature of 50 °C for the first time employing the ionic liquid ZnCl₂-[C₄mim]⁺Cl⁻ (45:55). Prior to the underpotential deposition (UPD) process of Sb, ZnCl₃⁻ anions adsorb on the gold surface at the open-circuit potential (OCP). An ordered region - showing the characteristic of a Moiré-like pattern - coexists with a disordered region indicative of an interfacial phase transition. When the potential is reduced to −0.40 V versus Pt/Pt(II), 2D electrocrystallization of Sb starts showing a typical structure of the first monolayer. Further decreasing the potential to −0.5 V a second layer of Sb islands occurs. Stepping the potential from the UPD region to −0.60 V, the OPD of Sb sets in showing randomly dispersed clusters of homogeneous size. Near the ZnSb deposition potential, at ∼−0.95 V, a nearly homogeneous distribution of clusters of spherical shape with diameters up to 15 nm is found. Their corresponding STS curves exhibit an obvious semiconducting behaviour with a gap-energy of ∼0.6 ± 0.2 eV. Experiments at deposition conditions on the Sb-rich or Zn-rich side relative to the ZnSb deposition potential show an obvious doping effect - in the case of Zn excess - which is revealed by the corresponding normalized conductance (NC) spectra.     

Deposition behavior and characteristics of hydroxyapatite coatings on Al2O3, Ti,and Ti6Al4V formed by a chemical bath method

A simple chemical bath method was used to deposit hydroxyapatite (HA) coatings on Al₂O₃, Ti, and Ti6Al4V substrates at ambient pressure by heating to 65–95 °C in an aqueous solution prepared with Ca(NO₃)₂·4H₂O, KH₂PO₄, KOH, and EDTA. The deposition behavior, morphology, thickness, and phase of the coatings were investigated using scanning electron microscopy and X-ray diffractometry. The bonding strength of the coatings was measured using an epoxy resin method. The HA coatings deposited on the three kinds of substrates were fairly dense and uniform and exhibited good crystallinity without any additional heat treatment. A coating thickness of 1–1.8 μm was obtained for the samples coated once. By repeating the coating process three times, the thickness could be increased to 4.5 μm on the Al₂O₃ substrate. The bonding strength of these coatings was 18 MPa.     

An in situ scanning tunneling microscopic study of electrodeposition of bismuth on Au(1 1 1) in a 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid: Precursor adsorption and underpotential deposition

In this article, the electrodeposition of Bi on Au(1 1 1) surface in the underpotential region in BMIBF₄ ionic liquid containing BiCl₃ is studied by cyclic voltammetry and in situ scanning tunneling microscopy (STM). The cyclic voltammogram shows several cathodic and anodic peaks associated with underpotential deposition (UPD) of Bi and dissolution of the UPD deposit, respectively, in the potential region between −0.38 and −0.7 V versus Pt quasi-reference electrode. In situ STM results indicate there is a BiCl₃ precursor adsorption stage prior to the Bi UPD. The adsorption of BiCl₃ leads to the formation of unique hexagonal and trigonal supramolecular assembly with a Au(1 1 1)(10 × 10) structure. The initial stage of Bi UPD proceeds with the formation of Au(1 1 1)(7 × 7) R21.8° adlayer structure composed of Bi trigonal clusters at −0.5 V. A structural transformation occurred at −0.6 V resulting in a unique “zipper-like” double-chain pattern composed of well-aligned Bi trigonal clusters which can be denoted by Au(1 1 1)(5 × 25√3/3) structural model. The trigonal clusters composed of six Bi atoms seem to be the main characteristic elemental units of Bi UPD adlayer regardless of underpotential shift. These features are dramatically different from those observed in Bi(III)-containing acidic aqueous solutions as well as in chloroaluminated ionic liquid, but are similar to those of Sb UPD in BMIBF₄ ionic liquid, which reveals profound solvent effects on the electrodeposition of semimetals.     

Zn electrodeposition in the presence of surfactants: Part I. Voltammetric and structural studies

The zinc electrodeposition onto steel substrates in the presence of surfactants with different charged head groups, namely anionic sodium dodecylsulphate (SDS), cationic dodecyltrimethylammonium bromide (CTAB), and non-ionic octylphenolpoly(ethyleneglycolether)_n, n = 10 (Triton X-100) was studied by cyclic voltammetry. The effect of the switching potential and scanning rate on the deposition process was investigated. The structural characterisation and the chemical composition of the samples prepared potentiostaticaly, in the potential range where the voltammetric cathodic peaks appear, was performed by X-ray powder diffraction (XRD) and by energy-dispersive X-ray analysis (EDS), respectively. The experimental results show that the voltammetric behaviour, namely the deposition potential depends on the presence, nature and concentration of the tested surfactants. Zn deposition occurs at potential values more positive than the estimated equilibrium potential, peak C1, simultaneously with hydrogen formation. This fact is confirmed by XRD measurements. Zn bulk deposits prepared in the absence of surfactants and in the presence of SDS are more crystalline and with a higher grain size than the ones obtained in the presence of CTAB and Triton X-100. These facts may be justified by an increase on the overpotential deposition as the electrochemical study confirms.     

Electrodeposition behavior of nickel and nickel-zinc alloys from the zinc chloride-1-ethyl-3-methylimidazolium chloride low temperature molten salt

The electrodeposition of nickel and nickel-zinc alloys was investigated at polycrystalline tungsten electrode in the zinc chloride-1-ethyl-3-methylimidazolium chloride molten salt. Although nickel(II) chloride dissolved easily into the pure chloride-rich 1-ethyl-3-methylimidazolium chloride ionic melt, metallic nickel could not be obtained by electrochemical reduction of this solution. The addition of zinc chloride to this solution shifted the reduction of nickel(II) to more positive potential making the electrodeposition of nickel possible. The electrodeposition of nickel, however, requires an overpotential driven nucleation process. Dense and compact nickel deposits with good adherence could be prepared by controlling the deposition potential. X-ray powder diffraction measurements indicated the presence of crystalline nickel deposits. Non-anomalous electrodeposition of nickel-zinc alloys was achieved through the underpotential deposition of zinc on the deposited nickel at a potential more negative than that of the deposition of nickel. X-ray powder diffraction and energy-dispersive spectrometry measurements of the electrodeposits indicated that the composition and the phase types of the nickel-zinc alloys are dependent on the deposition potential. For the Ni-Zn alloy deposits prepared by underpotential deposition of Zn on Ni, the Zn content in the Ni-Zn was always less than 50 atom%.     

Fabrication of Pd-Ni alloy nanowire arrays on HOPG surface by electrodeposition

Pd-Ni alloy nanowires with diameters 50-300 nm and lengths of over 250 μm have been obtained by electrochemical step edge decoration (ESED). The fabrication by ESED is accomplished on highly oriented pyrolytic graphite by applying three potential pulses in succession: an oxidizing “activation” pulse, a reducing “nucleation” pulse, and a reducing “growth” pulse. The alloy composition is controlled by adjusting the ion concentration ratio of palladium and nickel, and the deposition processes. The scanning electron microscopy (SEM) images reveal that the alloy nanowires fabricated by this procedure are separate, parallel, and continuous. The composition of alloy nanowires can be controlled in the range of 8-15 wt.% Ni when the ion concentration ratio of palladium and nickel is 7:3 in the solution containing 70 mmol dm⁻³ Pd(NH₃)₄Cl₂. The reaction mechanism involves nucleation at potential of −1.1 V_SCE to −2.0 V_SCE and growth at potential of −0.3 V_SCE to −0.5 V_SCE.     

Electrochemical deposition and characterization of ZnCo alloys and corrosion protection by electrodeposited epoxy coating on ZnCo alloy

ZnCo alloys electrochemically deposited on steel under various deposition conditions were investigated. The influence of deposition current density, temperature and composition of deposition solution on the phase structure and corrosion properties of ZnCo alloys were studied. It was found that ZnCo alloy obtained from chloride solution at 5 A dm⁻² showed the best corrosion properties, so this alloy was chosen for further examination. Epoxy coating was electrodeposited on steel and steel modified by ZnCo alloy using constant voltage method. The effect of ZnCo alloy on the corrosion behavior of the protective system based on epoxy coating is interpreted in terms of electrochemical and transport properties, as well as of thermal stability.     

ChCl-urea-ZnO-Cu2O低共熔溶剂电镀铜锌合金

以ChCl-urea-ZnO-Cu₂O低共熔溶剂为电解质在343 K镍基体上电沉积制备得到了铜锌合金镀层。伏安曲线测试表明在沉积过程中,镍基体能够诱导金属Zn发生欠电位沉积,从而实现了Cu-Zn合金的共沉积。同时研究了沉积电势对镀层成分和形貌的影响,结果表明：沉积电势由-0.85 V （vs Ag）增加到-1.3 V （vs Ag）时,合金镀层中Zn原子百分数从0升高到76.29%。在沉积电势为-1.10～-1.15 V范围内,Zn原子百分数为12.5%～20.81%时,镀层平整致密,颜色为金色,达到仿金镀的效果。     

An elevated temperature infrared emissivity ceramic coating formed on 2024 aluminium alloy by microarc oxidation

An infrared emissivity coating material containing γ-Al₂O₃ was prepared on 2024 aluminium alloy surface by the microarc oxidation (MAO) method. The microstructure of the coatings was analysed by SEM, XRD and EDS techniques. The infrared emissivity properties tested at 500 °C were investigated by an infrared radiometer based on a Fourier transform infrared spectrometer. The results show that the infrared emissivity values of coated Al samples depend on the phase composition and surface roughness of the coatings. Corresponding to increasing coatings thickness, the gradually increasing γ-Al₂O₃ content and some oxide compounds containing Si and P contribute to the higher infrared emissivity value (about 0.85) in the wavelength range of 8–20 μm. The increasing surface roughness leads to an obvious increase in emissivity from 0.2 to 0.4 at wavelength 3–5 μm.     

Extraction of europium and electrodeposition of Al–Li–Eu alloy from Eu2O3 assisted by AlCl3 in LiCl–KCl melt

The work presents an electrochemical study on preparation of Al–Li–Eu alloys on a tungsten electrode in molten LiCl–KCl–AlCl₃–Eu₂O₃ system at 753 K and 953 K. Gibbs energy shows that AlCl₃ can chloridize Eu₂O₃, with a discharge in the form of Eu(III) ions on the cathode. The electrochemical behavior of Al(III), Li(I) and Eu(III) and alloy formation processes were investigated by cyclic voltammetry, square wave voltammetry, and chronopotentiometry. Cyclic voltammetry indicated that the underpotential deposition of europium on pre-deposited Al forms two Al–Eu intermetallic compounds at electrode potentials around ?2.00 V and ?2.34 V, respectively. And the underpotential deposition of lithium on Al surface at about ?2.24 V leads to a formation of Al–Li alloy. X-ray diffraction (XRD) indicated that Al–Li–Eu alloys with different phases were obtained via galvanostatic electrolysis. The microstructure and micro-zone chemical analysis of Al–Li–Eu alloy were characterized by scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS), respectively. The analysis of EDS showed that element Eu mainly distributes on needle-like precipitate, and not homogeneously in the Al–Li–Eu alloy. Composition of the alloys was analyzed by inductive coupled plasma analysis, and current efficiency was also determined with respect to the alloy composition.