Increasing Electrolyte Temperature Research Articles

Porous hierarchical TiO 2 nanostructures: Processing and microstructure relationships

A dual porous hierarchical coating of TiO 2 nanotubes (∼50 nm diameter) on the nanoscale and large (∼1 to 20 μm) pores on the micro-scale can be fabricated on the surface of Ti by anodic oxidation. This unique coating may have potential applications as bioactive coatings for Ti bone implants. This paper details several important aspects of the coating microstructure. TiO 2 coatings were fabricated by anodic oxidation in 1 M H 2SO 4 + 0.1 M NaF solution. Microstructure characterization was carried out using scanning electron microscopy. We also report on the observation of precipitates which form as both a continuous surface layer and of a conical geometry. The mechanism for nanotube formation, precipitate layer formation, and microscopic pitting was discussed. The effect of processing variables (i.e. time, temperature, pH) on the TiO 2 microstructure was studied. Anodization time was found to affect nanotube length and also pit size and density. Lowering the electrolyte pH decreased the nanotube length and microscopic pit density. Increasing electrolyte temperature decreased nanotube length and increased pit/pore and precipitate density. Microscopic pitting, in the nanotube coating was found to occur above grain boundaries in the Ti substrate and above Ti grains with (0 0 0 1) orientation.

Influence of electrolyte temperature on pure titanium modified by electrochemical treatment for implant

AbstractThis study examined the effect of electrolyte temperature on the surface characteristics of anodized pure titanium in DL‐α‐glycerophosphate (DL‐α‐GP) and calcium acetate (CA). The anodic oxide films contained a large proportion of anatase with some rutile. The relative intensity of the anatase peaks and the surface roughness increased with increasing electrolyte temperature. As the electrolyte temperature was increased, the pore size increased to 1–4 µm, and the apatite crystals became coarser and denser. The amount of calcium and phosphate adsorbed increased with increasing electrolyte temperature. The anodizing voltage reached the onset of constant voltage mode faster with decreasing electrolyte temperature. A higher voltage is essential for the electrolyte at lower temperature to reach the constant voltage mode during this initial period. Copyright © 2008 John Wiley & Sons, Ltd.

Influence of the anodizing temperature on the porosity and the mechanical properties of the porous anodic oxide film

The microhardness and fretting wear resistance of anodic oxide layers, produced on commercially pure aluminium by potentiostatic anodizing in sulphuric acid under conditions of controlled convection and heat transfer in a reactor with a wall-jet configuration, were evaluated as a function of the electrolyte temperatures in a wide range from 5 °C up to 55 °C. Additionally, information on the microstructure of the anodic films was acquired by FE-SEM analyses whereas image analysis of high-resolution surface images yielded quantitative information on the evolution of the surface porosity as a function of the electrolyte temperature. Hence measured mechanical properties were directly related to the corresponding microstructure. The microhardness of the anodic films progressively decreased with increasing electrolyte temperatures whereas the wear resistance remained constant for the lower considered temperatures from 5 °C to 25 °C, followed by a decreasing wear resistance with increasing electrolyte temperature from 25 °C onwards. Both mechanical properties displayed an important decrease when the electrolyte temperature was raised from 45 °C to 55 °C. FE-SEM analyses indicated the formation of porous oxides with initially equal pore diameters at the metal-oxide interface, though pore widening due to chemical dissolution of the oxide by the electrolyte led to films with cone-shaped pores. This phenomenon became more pronounced with increasing electrolyte temperature and towards the surface of the anodic layer. The deterioration of the microhardness with increasing electrolyte temperatures could mainly be attributed to the increase of the porosity in the outer region of the oxides since the rate of microhardness reduction is almost synchronous with the rate of porosity increase. In contrast, the variation of the wear resistance with increasing anodizing temperature indicates that the degradation of the wear resistance does not only depend on the oxide porosity and is also affected by other characteristics of the oxide.

Morphology of calcium phosphate coatings deposited on a Ti–6Al–4V substrate by an electrolytic method under 80 Torr

Calcium phosphate coatings were deposited on the Ti–6Al–4V alloy plate in a 0.04 M Ca(H 2PO 4) 2·H 2O (MCPM) solution at 4–10 V, 0–60 °C, 1 h, and 80 Torr. X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM) were used to identify the coating morphology and microstructure. Electrolytic deposition at 80 Torr improves the gathering of the bubbles on the cathode surface, and blocks the deposition of calcium phosphates. Under 80 Torr, the films are regularly interconnected at applied voltages greater than 7 V owing to rapid degassing. OH − increases with increasing applied voltage. When excess OH − is present, hydroxyapatite (HAP) is deposited on the Ti–6Al–4V substrate. The plate-like grains formed at applied voltages under 5 V are identified as dicalcium phosphate dehydrate (DCPD). HAP deposition occurs when the applied voltage is greater than 7 V. HAP increases with increasing electrolyte temperature.

Electrodeposition of Pt–Ir alloys on nickel-base single crystal superalloy TMS-75

Platinum–iridium alloy coatings from amidosulfuric acid solutions have successfully been electrodeposited on nickel-base single crystal superalloy TMS-75 by direct current method. The effects of electrolyte temperature, current density and mole concentration ratios of [Ir 3+]/([PtCl 6 2−]+[Ir 3+]), on the deposition rate, composition and crystallographic structures of Pt–Ir alloy coatings are investigated. It is found that with increasing electrolyte temperature, deposition rate and Ir content increase, whereas the grain size of Pt–Ir alloy coatings decreases. Smooth and dense Pt–Ir alloy coatings can be obtained at 1 A/dm 2 and 353 K. Pt–Ir alloy coatings with expected compositions can be readily fabricated by controlling the mole concentration ratios of [Ir 3+]/([PtCl 6 2−]+[Ir 3+]) in the electrolyte. A detailed investigation of the structure and morphology of electrodeposited Pt–Ir alloy coatings is also presented. XRD analysis revealed that all the coated Pt–Ir alloys have a single phase with f.c.c structure, and the lattice parameters of the coatings decrease linearly with increasing Ir content, suggesting that the coated Pt–Ir alloy system follows the Vegard's law.

Electrochemical stability of Co–Mo intermetallic compound electrodes for hydrogen oxidation reaction in hot KOH solution

In order to obtain a hydrogen electrode with high-performance and stability for H 2–O 2 alkaline fuel cells, Brewer-type Co–Mo alloys are manufactured in the 35 to 57 wt.% Mo composition range by an arc-melting method. The electrochemical stability of alloys composed of Co 3Mo and Co 7Mo 6 phases is investigated in hot KOH solution deaerated with N 2 gas by means of electrochemical methods such as cyclic voltammetry, potentiostatic polarization and potentiodynamic polarization. Co–Mo alloy is extensively dissolved because the cobalt in alloy is soluble in hot KOH solution. The dissolution current of the alloys increases with increasing electrolyte temperature, electrolyte concentration and Mo content in the alloy.

Influence of Electrolyte Aging on Electrotinning in Phenolsulfonic Acid Bath

The influence of phenolsulfunate concentrations on electroplating characteristics and electrochemical behaviors was investigated with a viewpoint of electrolyte aging using the circulation cell and potentiostate And comparison of tinplate coating appearance such as glossiness and Image clarify has been also studied with varying of phenolsulfonic acid (PSA) solutions. As the aging of electrolyte proceeded, the limiting current density was moved to a lower current density region by the limitation of mass transfer, and higher phenolsulfunate concentrations resulted in the narrower optimum current density range and deterioration of coating surface of tinplates. The difference of the limiting current density was not remarkable with increasing electrolyte temperature. Thus the electrolyte aging was attributed to the limitation of thermally-activated process such as mass transfer of reducible ions. It has also been considered that the accumulation of phenolsulfonate suppressed normal electrotinning reaction by reducing the mobility of stannous ions, taking into account of the smaller effect of electrolyte aging. Experiments showed similar polarization behavior between the electrolyte of high phenolsufonate solution and the aged one, which comes to conclude that the accumulation of phenolsulfonate is one of the major causes of electrolyte aging.

Current efficiency in the Hall–He´roult process for aluminium electrolysis: experimental and modelling studies

Results are presented from a laboratory study of the influence of electrolyte composition, temperature, cathodic current density and interpolar distance on the current efficiency with respect to aluminium (CE). The current efficiency was determined from the weight gain of metal, in a laboratory cell designed to attain good and reproducible convective conditions, and with a flat cathode surface which ensures uniform cathodic current distribution. The cell is believed to more closely represent conditions in industrial cells than traditional small-scale cells, and is a good basis for an experimental study of the influence of isolated variable parameters on the current efficiency with respect to aluminium. The results show a nonlinear decrease of CE with increasing electrolyte temperature, a close to linear decrease of CE with increasing NaF/AlF3 ratio in the electrolyte, a slight increase of CE with increasing electrolyte CaF2 concentration, and no influence of electrolyte Al2O3 concentration on CE. A current efficiency model, based on previous work and theory of electrochemistry and mass transport, shows good agreement with the obtained results.

銅陽極不働態化に及ぼす液温の影響

The known effect of increasing electrolyte temperature in preventing anode passivation in copper refining was extensively reviewed.It has been found that a layer of anode slimes formed at a higher electrolyte temperature tends to become more porous with the simultaneous decrease in slime fall. While this increased permeability allows the diffusing ability of Cu2 ions away from the surface of a corroding anode to increase, a gravitational flow of the electrolyte also becomes more pronounced within the slime layer. That is, a more concentrated copper electrolyte at the anode surface streams downwards through the micro pores and cracks, and this type of mass transport removes excessive Cu2+ ions far more efficiently.A thorough investigation of electrolyte properties such as diffusion coefficient of Cu2+ ions, viscosity, solubility of copper sulfate and vapor pressure etc. measured using copper electrolyte of a nominal composition over the temperature range 45-65°C, proves the fact that the gravitational flow is a predominant factor contributing to the decreased tendency to passivate at a higher temperature.That anode passivation occurs more readily at a lower level of anode height is also explainable by this claim.

Effect of electrolysis conditions on the dispersion and apparent density of nickel powder

1. A study was made of the effect of electrolyte composition and electrolysis conditions on the dispersion and apparent density of nickel powder obtained from sulphate-chloride electrolytes. By using the regularities established, it is possible to prepare powder metals of any required dispersion. 2. It is demonstrated that the most effective factors governing the dispersion and apparent density of the powder are the concentration of nickel ions in the solution, current density, and electrolyte temperature. 3. It was established that, with increasing electrolyte temperature, the dispersion and apparent density of the powder decrease. The decrease in the apparent density of the powder is due to the fact that the adsorption and passivating effect of the hydrolysis products of nickel sulphate result in the deposition of strongly dendritic particles. 4. Increasing the concentration of sodium chloride and decreasing the duration of growth of loose deposits on the cathode (periods of time between the powder removal operations) are instrumental in increasing the dispersion of the powder. Both these factors may be utilized for improving the technical and economic parameters of electrolysis.