The degradation of aluminium cathodes by fluoride ion during zinc electrowinning

The influence of fluoride ions on aluminium cathode surface degradation during zinc electrowinning has been studied. Electrolyte with a composition similar to that employed in plant operations has been used. A direct correlation is shown between the electrolyte fluoride content and the number of deposition cycles possible before zinc removal becomes difficult. The role of initial nucleation and starting electrode morphology is discussed in terms of the degree of adherence observed. Electrochemical tests have also been made on the electrodes at various stages of the process in an attempt to gain a better fundamental understanding of the mechanisms responsible for the adherence. The results indicate that the severity, of the adherence is generally determined by the amount of residual zinc remaining on the surface after stripping and the fluoride content of the solution during plating. The contribution of physical surface condition alone seems to be less significant than the chemical conditions imposed during deposition.     

有机酸杂质对乳酸锌初次成核速率的影响

引言 溶液结晶作为一种高效、低能耗、少污染的分离和提纯技术,在医药、食品、生物等工业生产中的应用非常广泛.特别在医药行业,溶液结晶是主要的单元操作,85%以上的医药产品的生产过程中含有结晶单元[1].结晶过程涉及成核和生长两个阶段,成核和生长的热力学和动力学决定最终晶体产品的粒度分布以及产品质量,是进行结晶器分析、设计、操作和优化的主要依据[2].     

Effect of nucleation mode on the morphology and texture of electrodeposited zinc

The effect of temperature, pH and current density on the morphology and texture of electrodeposited zinc on mechanically polished steel was studied. The electrodeposited zinc had mostly basal (0 0 0 2) and low angle planes (1014, 1013, 1012) parallel to the surface. At pH 2, increasing overvoltage (i.e., increasing current density or decreasing temperature) reduced the percentage of basal plane and increased the percentage of low angle planes parallel to the substrate surface. Increasing overvoltage decreased the zinc crystal size. At pH 4, increasing current density increased the percentage of both basal and low angle planes parallel to the surface, but increased the zinc crystal size. This variation of behaviour at pH 4 was explained by a change in nucleation mode due to hydroxide adsorption. The nucleation mode was determined by comparing dimensionless (i/i _m)² vs (t/t _m) potentiostatic current–time transient graphs with models for instantaneous and progressive nucleation. It was shown that at pH 2, instantaneous nucleation was predominant, whereas at pH 4, it was close to progressive.     

Effect of surface curvature and wettability on nucleation of methane hydrate

Natural gas hydrate nucleation is a complex physical and chemical process that is not well understood presently. In this article, an improved thermodynamic model is proposed to analyze the effects of surface curvature and wettability on methane hydrate nucleation for the first time. The results indicate that methane hydrate nucleation is more difficult on hydrophilic curvature surfaces under the same conditions, with a larger critical nucleation radius and required energy barrier than on hydrophobic surfaces. Furthermore, a convex surface is more favorable for forming methane hydrate under the same conditions than a concave surface. The model's results are critical in elucidating the microscopic mechanism of methane hydrate nucleation and providing a theoretical foundation for developing technologies for strengthening and inhibiting hydrate formation.     

Electrodeposition of indium and zinc on aluminium

Zinc and indium were deposited from sulphate and chloride electrolytes onto aluminium electrodes under potentiostatic conditions. The role of the anion, pH, cation concentration, cathodic potential and agitation were investigated. The deposit morphology and composition were studied by SEM and EDX. Potentiodynamic and galvanostatic techniques were also applied for product characterization. Once a critical amount of Zn was deposited preferred In deposition began without agitation. But under rotation or at low cathodic potentials Zn2+ discharge became the prevalent reaction. The results support the earlier hypothesis of the preferential adsorption of Zn ions [1].     

对苯二甲酸锌初级成核过程研究

为研究对苯二甲酸锌的成核过程,实验采用平衡法测量对苯二甲酸锌在苯二甲酸钠溶液中的溶解度计算成核过程的过饱和度;298.15 K下用聚焦光束发射测量仪在线监测对苯二甲酸锌反应结晶过程中诱导期,并计算临界成核半径和临界成核自由能与过饱和度的关系。结果表明:过饱和度越大,诱导期时间越短;根据经典成核理论,在过饱和度S大于8.16时,发生的是均相成核过程,过饱和度S小于6.66时,发生的是非均相成核过程;其中在均相成核中,临界成核半径和临界成核自由能都是随着过饱和度的增加不断减小。因此,提高过饱和度使成核过程更加容易进行。     

A MIS transistor using the nucleation surface of polycrystalline diamond

In this work, the nucleation surface of a polycrystalline diamond film was used for the first time to fabricate a MISFET structure using standard photolithographic procedures, with a channel length of 100 μm. The resulting structure works as an enhancement-type p-type MOSFET. The I_ON/I_OFF ratio is about three orders of magnitude. The saturation of the current is clearly observed, with I_DS currents of about 20 nA for V_DS of 20 V. The smoothness of the nucleation surface allows a higher control of the electrodes, as well as their size decrease. The results show that, even though in an early stage, this investigation opens the door for a new generation of devices built on free-standing diamond films.     

Effect of surface pre-treatment on surface characteristics and adhesive bond strength of aluminium alloy

In this work aluminium alloy surfaces have been subjected to three different methods of surface pre-treatments such as solvent degreasing, FPL (Forest Products Laboratory) etching and priming using an epoxy based primer. The treated surfaces were evaluated for surface energy, contact angle, surface topography, surface roughness and adhesive strength characteristics. The influence of surface pre-treatments on the variation of polar, dispersive and total surface energy of the surfaces is addressed. A wettability test was performed on the surfaces using an epoxy adhesive in order to assess the influence of the pre-treatment techniques on substrate/adhesive interaction. Theoretical work of adhesion values for the various pre-treated surfaces were calculated using the contact angle data and further tested experimentally by adhesive bond strength evaluation by tensile testing of a single lap aluminium-epoxy-aluminium assembly. The method of surface pre-treatment showed a profound effect on the surface topography and roughness by AFM. This study reveals that a combination of high surface energy and high surface roughness of the substrate along with good wettability of the adhesive contributed to the highest joint strength for the aluminium alloy through the FPL etching pre-treatment.     

Energy consumption of aluminium smelting cells containing solid wetted cathodes

Tests with 10 kA pilot cells show that substituting a wetted, dimensionally stable cathode for the turbulent metal cathode allows the anode-cathode distance (ACD) to be decreased, with an attendant voltage reduction of about 1 V, depending on current density. Since high current efficiency is retained, specific energy consumption is decreased by about 20%. These savings are not as great as anticipated, however, because the effective electrical resistivity of the electrolyte increases as the ACD is lowered. This effect is ascribed to an increased void fraction of anode gas in the interpolar space, which appears to be dependent on anode size.     

Hydrothermal nucleation of hydroxyapatite on titanium surface

Titanium plates were submitted to nucleation and growth of hydroxyapatite (HAp) under hydrothermal conditions. A group of these plates were submitted to nucleation without any previous treatment and another group was treated with NaOH 1 M at 130°C inside an autoclave followed by heat-treatment at 600°C. The nucleation were performed by soaking all these titanium pieces, in a simulated body fluid (SBF) solution, containing calcium, phosphate and other ions, in order to promote the nucleation and growth of hydroxyapatite under hydrothermal conditions on the titanium surface. The results show that hydrothermal nucleation and growth of HAp occurs even on the non-treated titanium surface at 150°C. However, a better uniformity of the hydroxyapatite layer was observed on the pre-treated titanium surface, at 80°C, with the renewal of the SBF solution.     

Effect of fluoride ions on the corrosion of aluminium in sulphuric acid and zinc electrolyte

The effect of fluoride ions on the corrosion of aluminium in sulphuric acid and zinc electrolyte has been investigated through thermodynamic analysis and corrosion experiments. The solution chemistry of aluminium, zinc, and iron in aqueous solution in the absence and in the presence of fluoride ions was studied with the construction of the Eh-pH diagrams for the Al–F–H₂O, Zn–F–H₂O and Fe–F–H₂O systems at 25°C. In the presence of fluoride ions, aluminium can form a series of aluminium-fluoride complexes depending on the fluoride concentration and pH whereas zinc and iron can form soluble or insoluble metal-fluoride complex species only at relatively high fluoride concentration and at higher pH values. Experimental results show that in the presence of fluoride ions, the corrosion of pure aluminium in sulphuric acid is due to uniform dissolution and the reaction rate depends on the fluoride concentration. In zinc electrolyte containing fluoride ions, zinc deposits onto the pure aluminium substrate spontaneously and the amount of deposited zinc also depends on the fluoride concentration. On the other hand, the presence of iron in the Al–Fe alloy accelerates the corrosion of aluminium in H₂SO₄ and zinc electrolyte significantly and prevents the deposition of zinc on the aluminium surface. The effect of fluoride ions on zinc adherence to the aluminium is also discussed.     

Effect of surface roughness on methane hydrate formation and its implications in nucleation design

As a new form of energy with substantial potential, natural gas hydrate will play a crucial strategic role in the future due to its vast reserves and broad industrial application prospects. To better comprehend the nucleation and growth mechanism of clathrate hydrate, an enhanced thermodynamic model was proposed based on the wall roughness model and nucleation theory. In general, we discovered that the nucleation of hydrate on a smooth wall surface conforms to the conclusion of classical nucleation theory. However, curvature and surface roughness are frequently characterized by hydrophilicity's inhibition of hydrate and hydrophobicity's enhancement. The specific situation is more complex and requires specific analysis and discussion. Nonetheless, this also explains the uneven distribution of hydrate nucleation induction time. Our research reveals a fundamental method for designing or manipulating the heterogeneous nucleation of hydrates. We foresee promising applications in hydrate-related technologies based on the fractal structure of the substrate's surface.     

Synthesis of aluminium titanate by means of isostructural heterogeneous nucleation

The synthesis of tialite was carried out by means of the solid state reaction technique using heterogeneous nucleation. The influence of the temperature of synthesis and simultaneous sintering (1250–1350 °C) on the yield of reaction and densification of the systems was investigated. Reference samples, consisting of stoichiometric mixture of titanium and aluminium oxides as well as the samples containing such additives as MgO, SiO₂ and MgTi₂O₅ were prepared. Applying the DSC analysis the synthesis temperatures of systems differing in the substrate composition were determined. The phase composition of synthesis products was determined by means of XRD analysis combined with Rietveld's method. The density of the obtained materials was determined by the Archimedes method. SEM observations enabled microstructures and homogeneity of sinters to be compared.On the basis of the conducted research it was found that using oxide additives containing magnesium cations allows the synthesis efficiency exceeding 95% as early as at the temperature of characterized by a homogeneous microstructure with a lower number and a smaller size of microcracks.     

Effect of surface nucleation on isothermal crystallization kinetics: Theory, simulation and experiment

Surface nucleation of poly(l/d-lactide) at the interface with aluminum was studied by performing isothermal DSC analysis of amorphous samples of varying thickness between 100 °C and 130 °C. To ensure complete wetting of the aluminum surface, a hot melt laminating process was used to prepare the samples. Theoretical aspects of surface crystallization kinetics were explored and the resulting model was compared with the results of Monte-Carlo simulations. Three stages of surface crystallization were identified depending on the growth geometry: (1) impingement-free growth, (2) increasingly laterally-constrained transverse growth, and (3) interstitial growth. By fitting the Monte-Carlo simulation to the experimental half-times of crystallization the surface nucleation concentration and the bulk nucleation rate was estimated at 4 different temperatures. It was found that both surface nucleation concentration and the bulk nucleation concentration decrease with increasing crystallization temperature.     

The effect of nickel on the mechanism of the initial stages of zinc electrowinning from sulphate electrolytes. Part II. Investigations on aluminium cathodes alloyed with iron impurities

The effect of the alloying element Fe on the electrochemical behaviour of Al cathodes during the initial stages of zinc electrowinning was studied, using scanning electron microscopy, cyclic voltammetry, atomic absorption and X-ray microprobe analysis techniques. It is shown that underpotentially deposited zinc submonolayer inhibits the discharge of hydrogen ions onto Fe aggregates — alloying element.     

Diamond nucleation on Ni3Al substrate using bias enhanced nucleation method

Diamond deposition with positive and negative bias enhanced nucleation (BEN) pretreatments on mirror-polished polycrystalline Ni₃Al substrates has been investigated, respectively. It was found that diamond deposition on the substrates under both biasing exhibited significant variations among grains of different orientations. The substrate surface was found to be rough in the case of negative biasing, whereas it was smooth in the case of positive biasing. Thus, the correlation of the crystallographic orientation of grains on the samples with the diamond nucleation behavior was systematically characterized for the case of positive biasing by electron backscattered diffraction method with scanning electron microscopy. Diamond deposition on Ni₃Al grains near (111) orientation results in higher nucleation densities, while the densities are low on (110) and (100) oriented grains. Also, the interfacial microstructure between diamond deposited and Ni₃Al was characterized by cross-sectional transmission electron microscopy.     

Effect of fluctuations on the surface tension of liquid droplets and gas bubbles and their nucleation

Correlations are established between the surface tension of liquid droplets and gas bubbles, and fluctuations in the volume, density, and number of particles in their core,. The smallest droplet or bubble size below which the homogeneity of its core starts to disturb is estimated. It is shown that, for the nuclei containing as few as several tens of microparticles (molecules or atoms), the surface tension is a probabilistic parameter, and this is expected to influence the course of processes.     

Effect of substrate surface treatment on the hydrothermal synthesis of zinc oxide nanostructures

In this investigation, ZnO nanostructures were coated via hydrothermal process on glass substrate surfaces, which were treated by acidic and alkaline solutions. Furthermore, the ZnO structure was doped by different amounts of Al⁺³ ions to investigate the microstructural variation. Characteristics of the samples by XRD and SEM analyses confirmed the formation of different morphologies and various crystal sizes for the nanostructured ZnO on the substrates including nanoflower, nanorod, and nanopanel morphologies. Furthermore, XRD results showed that the Zn²⁺ concentration was a crucial factor in changing the grain size. EDS analysis confirmed the uniform distribution of Al dopant, while the FTIR spectra revealed the presence of Al–O and Zn–O stretching bonds in the coatings. The results confirmed that the sample, which was etched by fused NaOH had a uniform and compacted structure. Moreover, it was evident the proposed treatment and synthesis process was successful in the formation of uniform nanostructured ZnO film on the glass substrate without the requirement for seed layer deposition.     

非均匀成核法石墨表面改性的研究

以ZrOCl2·8H2O为前驱物,采用非均匀成核法对鳞片石墨进行了表面改性处理,并研究了pH值(2.4～5.1)、前驱物溶液的浓度(0.005～0.1mol·L-1)、石墨与前驱物溶液的混合方式等工艺因素对石墨表面改性效果的影响。结果表明:1)石墨悬浮液先与浓度为0.025mol·L-1的前驱物溶液充分混合,然后滴加氨水调节pH值为3.6是非均匀成核法改性石墨的最佳工艺条件,能在石墨表面形成均匀的ZrO2包覆层;2)石墨经过表面改性后,在其表面均匀包覆的ZrO2包覆层提高了其抗氧化性和分散性,减少了团聚。     

Effects of carbon surface area on performance of lithium sulfur battery cathodes

The effect of carbon surface area on capacity is investigated in cathodes for lithium sulfur batteries. Carbon additives help overcome the low electrical conductivity of sulfur. Cathodes were prepared at 30 wt% sulfur on different activated carbons having unloaded BET surface areas of 1200–3200 m²/g. Sulfur utilization ranged from 33% to 83% of the theoretical capacity (1672 mAh/g) with a strong correlation to the accessible pore volumes having pore widths between 1 and 5 nm. Additionally, cathodes prepared at 12.5–68 wt% on an activated carbon having unloaded BET surface area of 3200 m²/g showed excessive sulfur loading provided little additional capacity.