The electrochemistry of metal oxide additives in pasted zinc electrodes

The effect of small additions (2 w/o–4 w/o) of HgO, Tl₂O₃, PbO, CdO, In₂O₃, In(OH)₃, In and Ga₂O₃ to pasted zinc oxide electrodes has been evaluated using chronopotentiometry, cyclic voltammetry, polarization measurements and scanning electron microscopy. Additives such as PbO, In(OH)₃ and In increase the density and the polarizability of the deposit whereas additives such as Ga₂O₃ and CdO yield finely divided deposits of low polarizability. The results are attributed to a substrate effect on zinc deposition. The beneficial effect of some additives (eg a mixture of 0.5 w/o In(OH)₃ and 1 w/o PbO) is attributed to an improvement in the secondary current distribution due to an increase in electrode polarizability.     

Effects of promoters on catalytic activity and carbon deposition of Ni/γ‐Al2O3 catalysts in CO2 reforming of CH4

Catalytic reforming of methane with carbon dioxide was studied in a fixed‐bed reactor using unpromoted and promoted Ni/γ‐Al₂O₃ catalysts. The effects of promoters, such as alkali metal oxide (Na₂O), alkaline‐earth metal oxides (MgO, CaO) and rare‐earth metal oxides (La₂O₃, CeO₂), on the catalytic activity and stability in terms of coking resistance and coke reactivity were systematically examined. CaO‐, La₂O₃‐ and CeO₂‐promoted Ni/γ‐Al₂O₃ catalysts exhibited higher stability whereas MgO‐ and Na₂O‐promoted catalysts demonstrated lower activity and significant deactivation. Metal‐oxide promoters (Na₂O, MgO, La₂O₃, and CeO₂) suppressed the carbon deposition, primarily due to the enhanced basicities of the supports and highly reactive carbon species formed during the reaction. In contrast, CaO increased the carbon deposition; however, it promoted the carbon reactivity. © 2000 Society of Chemical Industry     

Study of the performance of secondary alkaline pasted zinc electrodes

Calcium zincate was prepared by a chemical coprecipitation method and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrochemical performance of pasted zinc electrodes with bismuth and calcium additives was investigated by the charge–discharge method. The addition of metallic bismuth powder improves the discharge performance of zinc electrodes due to the formation of an electronic conduction matrix. The calcium-containing zinc electrodes showed higher discharge capacity, less shape change and longer cycle lifetime. Moreover, zinc electrodes using calcium zincate as active material show better electrochemical performance than those with the physical mixture of zinc oxide and calcium hydroxide.     

钢铁件锌酸盐镀锌前处理方法

简单介绍了锌酸盐镀锌的特点及其添加剂的两种类型。对一般钢铁件进行化学除油、酸洗除锈后再次除油、预浸蚀,最后浸碱液,其间采用高压水清洗,对提高其锌酸盐镀锌的质量,起到了较好的效果。列举了酸洗除锈的一些典型配方,说明了其适用范围。     

Effect of cations and anions on properties of zinc oxide particles synthesized in supercritical water

Hydrothermal synthesis of zinc oxide fine particles from zinc salt (Zn(CH₃COO)₂, ZnSO₄, Zn(NO₃)₂) and alkali metal hydroxide (LiOH, KOH) aqueous solution was carried out with a Ti alloy batch reactor in supercritical water. Particle size synthesized in LiOH solution was relatively smaller than that in KOH. Emission spectra of the particle produced from ZnSO₄ and LiOH aqueous solution shows the highest intensity among these systems. Hydrothermal synthesis of zinc oxide fine particles from Zn(NO₃)₂ and LiOH solution was also carried out with a flow-through apparatus for continuous production and rapid heating of the starting solution to supercritical states. Nanoparticles having an average particle diameter of 16 nm was produced at 659 K and 30 MPa.     

Cyclic voltammetric studies of nickel hydroxide and cobalt hydroxide thin films in alkali and alkaline earth metal hydroxides

Cyclic voltammetric studies of thin films of electrosynthesized (ES)-Ni(OH)₂ and Co(OH)₂ in different alkaline electrolytes suggest that the mechanism of oxidation is different from the mechanism of reduction. While the metal ion (alkali or alkaline earth metal) intercalation-deintercalation from the electrolyte into the film provides the driving force, the reduction reaction takes place heterogeneously independent of the electrolyte concentration, whereas oxidation takes place homogeneously across a nebulously defined electrode-electrolyte interphase. ES-Ni(OH)₂ permits facile intercalationdeintercalation of alkali metal ions Li⁺, Na⁺ and K⁺, irrespective of their ionic size, while the reactions of ES-Co(OH)₂ are sensitive to ionic size, requiring larger potentials in KOH compared to LiOH. In the alkaline earth metal hydroxides, both Ni(OH)₂ and Co(OH)₂ films show greater reversible characteristics in the order Ba(OH)₂ > Sr(OH)₂ > Ca(OH)₂. This may be trivially related to the order of the solubilities of the three hydroxides.     

碱性锌酸盐体系锌及锌铁合金电镀添加剂

综述了碱性锌酸盐体系锌及锌铁合金电镀添加剂的研究和发展，添加剂产生光亮作用的机理。     

Hydrogen production during zinc deposition from alkaline zincate solutions

The determination of the amount of hydrogen produced during the electrodeposition of zinc from alkaline zincate solutions was carried out using the rotating ring-disc electrode (RRDE) technique. The experimental conditions for which the RRDE technique offers reliable results are discussed. Hydrogen production during zinc deposition was studied for a range of cathodic (disc) current densities (20–500 A m^–2) and electrolyte compositions (1–7 M KOH, 0.01–0.2 M zincate). It was found that an increasing amount of hydrogen was formed with increasing (disc) current density and decreasing KOH and zincate concentration. The impact of hydrogen formation during the charging process on nickel oxide/zinc secondary battery performance is expected to be small. It is concluded that in battery electrolytes (8 M KOH, 1 M zincate) hydrogen is formed chiefly by corrosion of the zinc electrode rather than by electrochemical formation during the electrochemical reduction of zinc.     

Electrochemical capacitive properties of cadmium oxide films

The specific capacitances (SC) of cadmium oxide (CdO) films synthesized electrochemically followed by air annealing at 673 K for 2 h onto tin-doped indium oxide (ITO) substrates, in different electrolytes, are estimated using cyclic voltammetry (CV) and galvanostatic discharge experiments and characterized for the structural and surface morphological studies using X-ray diffraction and scanning electron microscopy techniques, respectively. The flake-like surface morphology of CdO film has showed superior SC in KOH electrolyte than that of KNO₃, Na₂SO₄ and NaOH, respectively. Effect of air annealing on shape and enclosed area of CV curves is also studied. Over 1000 cycles, the film electrode was considerably stable, confirming the potentiality of CdO as a capacitive material.     

Immobilization of metal-containing waste in alkali-activated lime-RHA cementitious matrices

This research investigated the immobilization potential of alkali-activated lime-rice husk ash (RHA) for synthetic Cr(OH)₃, Fe(OH)₃, Zn(OH)₂ and zinc cyanide plating sludge. The binder consists of hydrated lime and RHA at a weight ratio of 45:55. Waterglass (Na₂SiO₃) with SiO₂/Na₂O ≈ 3 and anhydrous sodium carbonate (Na₂CO₃) were used as alkali activator between 0 and 8 wt.% of the binder. Results showed that Zn(OH)₂ addition causes a considerable strength development in control and sodium silicate-activated samples but only after 14 days. Similar observations were found for the sample loaded with 10 wt.% plating sludge but this only occurred after 28 days. A possible explanation for these phenomena is that the initial formation of calcium zincate, which has a set retarding effect, inhibits early strength development. At later ages, calcium zincate dissolves and Zn is taken up in the formation of C-S-Z-H solid solutions leading to strength development. These phenomena were not observed from the sodium carbonate-activated lime-RHA matrices. In these, it is believed that zinc/calcium carbonates readily form inhibiting calcium zincate and C-S-Z-H formation. Despite this, carbonate-containing mixes with up to 30 wt.% plating sludge gave a 14-day strength and Cr concentration in TCLP leachate that meet the regulatory limit for landfilling.     

The influence of sorbitol on zinc film deposition, zinc dissolution process and morphology of deposits obtained from alkaline bath

A novel cyanide-free zinc deposition bath was developed in which sorbitol was added at various concentrations. Voltammetric studies indicated that the reduction process is influenced thermodynamically and kinetically by the sorbitol concentration. Also, two cathodic processes were observed, one (wave) associated with the hydrogen evolution reaction (HER) on 1010 steel, the other (peak) with zinc bulk reduction, simultaneous to the HER. Furthermore, the plating-process kinetics was controlled by mass transport. The presence of sorbitol in the bath led to formation of light-grey zinc films, even during the HER, without cracks and dendrites. Plating current efficiency decreased from ∼ ∼62% to 43% on increasing the sorbitol concentration in the plating bath. In the presence of 0.1 M and/or sorbitol concentrations higher than 0.2 M, Zn electrode dissolution was inhibited. However, a small dissolution of zinc electrode was observed with 0.05 M sorbitol in alkaline solution without zincate. SEM micrographs showed that the 1010 steel substrate was fully covered by Zn film and that the sorbitol affected the morphology of zinc films, acting as a grain refiner.     

Methanol Synthesis from CO2 Using Skeletal Copper Catalysts Containing Co-precipitated Cr2O3 and ZnO

Skeletal Cu-Cr₂O₃-ZnO catalysts have been prepared by leaching CuAl₂ alloy particles at 273 K using 6.1 M aqueous NaOH solutions containing sodium chromate (Na₂CrO₄) and sodium zincate (Na₂Zn(OH)₄). The presence of sodium chromate and sodium zincate in the caustic solution was found to affect the pore structure and surface areas of the resulting catalysts. Both BET and Cu surface areas were increased by increasing the concentration of Na₂CrO₄ and of Na₂Zn(OH)₄.Increasing the Na₂CrO₄ level from 0 to 0.06 M in a 6.1M NaOH solution containing 0.2M Na₂Zn(OH)₄ caused the content of ZnO in the catalyst to decrease from 8.8 to 3.0 wt% whilst increasing the Cr₂ O₃ content from 0 to 1.7 wt%, indicating that the presence of Na₂CrO₄ in the leach liquor not only resulted in deposition of a Cr compound but also inhibited precipitation of zinc hydroxide onto skeletal Cu catalysts. On the other hand, increasing the concentration of Na₂Zn(OH)₄ from 0 to 0.6 M in a 6.1 M NaOH solution containing 0.008 M Na₂ CrO₄ resulted in increasing the ZnO loading from 0 to 8.9wt% with an almost constant content of Cr₂ O₃ (1.3 ± 0.2%) in the catalysts, revealing that sodium zincate only led to precipitation of zinc hydroxide and did not suppress Cr₂O₃ formation.Hydrogenation of CO₂ was studied using a gas mixture of 24% CO₂ in H₂ at a total pressure of 4MPa, space velocities up to 210000L kg^-1h^-1 and temperatures in the range 493-533K. The catalysts were found to be both highly active and selective for methanol synthesis. This study confirms the role of ZnO in promoting the activity of copper for methanol synthesis from CO₂ and improving the selectivity by inhibiting the reverse water-gas shift reaction. The role of Cr₂O₃ is to improve the structural development of high surface area skeletal copper.     

Structural and catalytic promotion of skeletal copper catalysts by zinc and chromium oxides

ZnO and Cr₂O₃ promoted skeletal copper catalysts have been prepared by leaching CuAl₂ alloy particles in aqueous sodium hydroxide containing various concentrations of sodium zincate (Na₂Zn(OH)₄) (0–0.62 M), of sodium chromite (NaCrO₂) (0–0.1 M) or of a mixture of sodium zincate (0.005 M) and sodium chromite (0.02 M). Both sodium zincate and sodium chromite in the caustic solution were found to affect the leaching process. The presence of sodium zincate retarded the leaching rate and enhanced the specific surface area of the catalyst but did not protect copper rearrangement on extended leaching. On the other hand, sodium chromite in the leachant did not influence the leaching rate but the leached catalyst was more stable with the structure and surface area of the skeletal copper being maintained. The activities of ZnO and Cr₂O₃ promoted skeletal copper catalysts for the reactions of methanol synthesis, water gas shift and methanol steam reforming were determined separately. The results indicated that deposition of both ZnO and Cr₂O₃ on skeletal copper catalysts significantly improved the activities for these reactions. Chromia is found to act mainly as a structural promoter. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effect of foreign atoms on the properties of electrolytic zinc powders

Kinetic and morphological studies have been made of the deposition of zinc powder on steel substrate, from pure alkaline zincate electrolytes and with small amounts of lead and tin ions in the electrolyte. The rate of co-deposition of hydrogen has been followed volumetrically and the current efficiency of zinc deposition calculated as a function of potential.The addition of lead and tin was found to have a profound effect on the properties of the powder. The dendritic powder, obtained from pure zincate solutions, changes with the addition of lead into a mossy deposit consisting of very small crystallites. Both additives increase the specific surface area of the powder and the average lattice parameters. Hydrogen evolution per unit real surface area and hence the corrosion of the powder are somewhat inhibited by both additives.Reported at the Symposium on Electrocrystallization, 140th Meeting of the Electrochemical Society, Cleveland, Ohio, October 1971.     

碱性锌酸盐镀锌层起泡故障浅析

碱性锌酸盐镀锌常会出现镀层起泡故障,严重影响镀层质量。分析了碱性锌酸盐镀锌各个工序中镀层起泡的原因,并介绍了相应的控制方法：碱性镀锌镀层起泡的原因很多,实际电镀中需要有针对性地排除故障。     

The effect of silicate ion on the anodic behaviour of zinc in concentrated alkali

The anodic behaviour of zinc in 8 M NaOH/1 M Na₂Zn(OH)₄, containing 0.1, 1 and 10 v/o sodium silicate solution, has been studied under quiescent conditions at ambient temperature using cyclic linear sweep voltammetry in conjunction with darkfield illumination optical photo-microscopy. Results, together with measurements of the double layer capacitance of the zinc/alkali interphase as a function of potential, suggest the presence of a surface film of silicate which induces early passivation in the anodic potential excursion.     

Recovery of Zinc Ions From the Resulting Solution after Copper Cementation with Metallic Zinc

In this study, recovering of zinc ions in the residual solution occurring after copper cementation by zinc metal was investigated. The zinc ions in the solution were recovered by using sodium bicarbonate as precipitation agent. After the precipitated product was separated from the solution, it was dried at 80°C for 5 h in an oven and was subjected to the calcination process to obtain zinc oxide. The XRD and SEM analyses of the precipitated and calcined products were carried out. It was determined that the precipitated solid was Zn₅(CO₃)₂(OH)₆ (hydrozincite) and the calcined product was ZnO.     

Impedance measurements during the cycling of a zinc electrode

Impedance spectra have been obtained during the cycling of a zinc electrode both in a Leclanché-cell-type electrolyte and in an alkaline zincate solution. Changes in impedance plots indicate an increase in the electrode area and a variation of the electrode kinetics with cycling. The kinetics of zinc deposition appear to be very sensitive to the contamination of electrolytes by dissolution products. The results confirm a correlation between the presence of an additive such as NBu₄ Br and the increase of the cycle life of the zinc electrode.     

Structural and electrochemical characterization of mechanochemically synthesized calcium zincate as rechargeable anodic materials

Hydrated calcium zincate was synthesized by mechanical ball milling of ZnO and Ca(OH)₂ in water at room temperature. The structural and electrochemical properties of this material used as rechargeable anodic material were examined by microelectrode voltammetry, charge–discharge measurements and structural analysis. The results showed that during mechanical milling, ZnO, Ca(OH)₂ and H₂O reacted rapidly to form Ca[Zn(OH)₃]₂ · 2H₂O which was subsequently transformed to a stable structure CaZn₂(OH)₆ · 2H₂O. Since this composite oxide has lower solubility in KOH solution (<35 wt %) and better electrochemical reversibility than ZnO-based negative materials, the zinc anodes using this material can overcome the problems of shape changes and dendritc formation, and therefore exhibit improved cycling life.     

Oxidation of methanol on nickel—zinc catalysts

The activity of nickel—zinc and smooth nickel electrodes for methanol oxidation is investigated in KOH 1 M + CH₃OH 1 M at 60°C. Nickel—zinc alloys of different composition are easily obtained from electrodeposition. After their attack in KOH 1 M, the electrodes contain about 50% of zinc and they have the βNiZn alloy structure. The I(V) curves are compared. On smooth nickel the oxidation of methanol is strongly inhibited by the superficial oxides whereas on nickel—zinc electrodes superficial oxides are easier to reduce. The effect of adsorbed hydrogen and of mixed oxides is discussed.