Chemical Dissolution Rate Research Articles

Observations on the cavitation of steels

The relative importance of erosion and corrosion in the cavitation phenomenon on steels was studied. The rate of chemical dissolution in the passive range of oxidation potentials was controlled by the dynamic balance between the rates of breakdown and repassivation. Work hardening was shown to cause localization of the damage into discrete pits. This is assumed to be due to the effect of etch pits arising by dislocations. Work-hardened specimens suffered a more severe cavitation then non-work-hardened specimens.

Electro-deposition of Cu and Ag from solutions of PPM concentration, followed by inductively-coupled plasma spectrometry

An examination has been made of the kinetics of electro-deposition of copper and silver from acid solution, with special reference to the rate of chemical dissolution of the deposited metal.

１３Ｍ硫酸溶液中で生成したアルミニウムのアノード酸化皮膜の組成，構造および性質について

Commercially pure aluminum specimens were anodically oxidized in a 13M H2SO4 solution at 20°C by applying a constant current density of 1A·dm-2, the voltage attained being 36-38V. The composition and properties of the oxide formed were investigated by chemical analysis, electrochemical techniques, thermogravimetric analysis, and transmission electron microscopy. The results were compared with those for oxide films formed in a 1.5M solution. (1) The content of SO42- and H2O were about 40% and 6.5% respectively for the 13M film and 15% and 5.5% for the 1.5M film. Thus, film composition is expressed by Al2O2.29 (SO4)0.71⋅;0.61H2O and Al2O2.81 (SO4)0.19⋅0.38H2O. (2) For the 13M films, the thickness of the barrier layer was 330A and that of the pore wall 270A, pore diameter was 200A. The number of pores was 19.6×109cm-2 for the 13M film and 72.1×109cm-2 for the 1.5M film. (3) The rate of chemical dissolution of both 13M and 1.5M films was higher in the 1.5M H2SO4 solution than that in the 13M solution. In both solutions, the 13M film dissolved faster than the 1.5M film, due to its larger SO42- content. (4) Microvoids were found to have been produced in the barrier layer and pore walls of the 13M film by the expansion of oxide due to the incorporation of a large number of SO42- ions. Because microvoids were present in both the barrier layer and the pore walls, density and abrasion resistance were lower for the 13M film than for the 1.5M film.

Specific chemical rate constants for the acid dissolution of oxides and silicates

Correlations relating the specific chemical rate for the acid dissolution of MgO, Mg 2SiO 4, ZnO, Zn 2SiO 4 and ZnFe 2O 4 to temperature and hydrogen ion concentration/activity have been produced from a critical analysis of published dissolution data. In determining specific chemical rates it is important that consideration is given to the means of determination of the surface area of the solid and to the likelihood of a diffusional resistance contributing to the dissolution rate. It is demonstrated that at 25°C, the chemical dissolution rates of the silicates are significantly lower than those of the corresponding oxides. This finding is discussed in terms of current theories of the oxide dissolution process.

The electrochemical behaviour of chromium plates in sulphuric acid media in the presence of selenite ions

It has been established that the presence of selenite ions at concentrations of 0.1 – 10 mg l -1 drastically increases (up to 30 – 35 times) the chemical dissolution rate of electrodeposited chromium coatings during cathodic polarization in sulphuric acid media (up to pH 3). The process can be triggered by a short cathodic pulse and dissolution proceeds spontaneously after the pulse at an ever-increasing rate until the chromium coating is completely dissolved. The relationships between the rate of the process and some basic parameters (selenite ion concentration, pH and temperature of the corrosive medium) were determined. It is presumed that the effect exerted by the selenite ions is related to their participation in the cathodic process and their enhancement of the interaction between chromium atoms and hydrogen ions by forming intermediate Cr x Se-type compounds with pronounced metallic character and high electrical conductivity.

ChemInform Abstract: EFFECT OF SURFACE PRETREATMENT ON THE GALVANOSTATIC OXIDATION OF NICKEL

AbstractDas Verhalten der Oxidfilme auf elektropolierten (H2SO4) sowie auf elektropolierten und in Sproz. HNO3 30 s lang geätzten Ni‐Elektroden bei offenem Schaltkreis während kathodischer Reduktion und anodischer Aufladung wird in wäßrigen Na2SO4‐Lösungen untersucht.

Effect of surface pretreatment on the galvanostatic oxidation of nickel

The open-circuit, cathodic reduction and anodic charging characteristics of oxide films on both electropolished and electropolished + HNO 3 etched nickel electrodes have been studied in aqueous Na 2SO 4 solutions. While the oxide film thicknesses are approximately the same, the film on etched nickel dissolves much more rapidly than that on electropolished nickel. To galvanostatically passivate etched nickel at charging rates in the range 20–200 μA cm −2 in pH 2.8 Na 2SO 4, the rate of oxide chemical dissolution has to be substantially decreased and this is achieved by lowering the electrolyte temperature from 25°C to 5°C. The transient anodic passivation charge thus observed for etched nickel is ∼ 2 x larger than that for electropolished nickel. With either pretreatment, the current efficiency for oxide formation is low (∼ 20%), the majority of the transient charge (∼ 80%) accounted for by Ni 2+ in solution. Chemical dissolution of the oxide alone cannot explain the observed charging differences between etched and electropolished nickel since the individual charges and oxide formation current efficiencies are not influenced by anodic charging rate or solution aggressiveness. The results are best explained in terms of a continual breakdown and repair of the oxide film at defect areas during anodic charging, with most of the charge consumed by inefficient film repair. The influence of the oxide defects and the reason for the differences in behaviour between electropolished and etched nickel are discussed.

Study by Nuclear Microanalysis and O18 Tracer Techniques of the Oxygen Transport Processes and the Growth Laws for Porous Anodic Oxide Layers on Aluminum

The method of nuclear microanalysis of stable oxygen isotopes by the reactions was used to investigate the mechanisms of growth, dissolution, and transport associated with oxygen during the formation of relatively thin (≤7000Aå) porous anodic layers on aluminum. The average charge associated with an oxygen ion fixed in the film was calculated on. the basis of the direct measurement of sulfur incorporation in the films. The current efficiency of the oxidation was determined (and found to be low, ∼55%) by comparing the amount of oxygen fixed on the metal surface deduced from nuclear microanalysis to that deduced from the amount of charge fed into the circuit. The rate of chemical dissolution of the oxide was measured in open circuit and under polarization and was found to be two orders of magnitude lower than that which would explain the low current efficiency. Hence the existence of an electrochemical process of cation transfer must be assumed. It was found, by using oxygen 18 tracer techniques, that the growing oxide layer is formed at the metal/oxide interface by oxygen transport through the base layer. The results show that about 60% of the ionic current is transported by oxygen ions and about 40% by cations during the growth of porous oxide layers on aluminum.

Electrodeposition of Gold by Pulsed Current

A diffusion model was developed to calculate the rate of deposition of metals by a periodically pulsed current. The results indicate that although the magnitude of the instantaneous applied current for deposition can be considerably higher than that of direct current plating under suitable conditions, the limiting over‐all plating rate was in general lower. Experimental confirmation was established using the phosphate, citrate, and cyanide gold solutions. The diffusion coefficient of the complexed gold cyanide ion was measured. The values were , and at 60°C for the phosphate, citrate, and cyanide solutions, respectively. The pH value, specific conductance, and kinematic viscosity of these solutions were also measured and tabulated. The rate of chemical dissolution of gold in the cyanide solution was also investigated.

Method for Evaluating Dissolution Characteristics of Capsules

A simple device is described which is useful for dissolution determinations of capsule formulations. It may be utilized in a visual inspection for capsule dispersion or disintegration, and also in the usual chemical dissolution rate determination for predicting possible problems of drug availability from capsules.

Pitting and Uniform Corrosion of Aluminum by pH 3.5 Citrate Buffer Solution

Corrosion of 3003 aluminum in citrate buffer solution in the presence of air may be by pitting or by uniform attack. Polarization data indicate that uniform attack is controlled by the rate of chemical dissolution of the oxide film. There is a simultaneous thickening of the film by a tarnishing‐type reaction at the same rate to maintain the film at constant thickness. Values of ΔD/ΔE determined from polarization data at constant potential were indicated to be the same for a film being formed principally by the tarnishing mechanism as for a film being formed entirely by anodic action. It was found possible to determine whether or not pitting was occurring from anodic polarization data.

The Anodic Treatment of Aluminum in Sulfuric Acid Solutions

High purity aluminum was anodized in sulfuric acid solutions at various concentrations (5– 50%), temperatures (10°– 50°C), time periods (2 – 60 min), and current densities (1.7 – 6.2 amp/dm2). The coating weight, metal loss, coating ratio, sealing weight gain, dyed color, density, and coating chemical dissolution rate were determined.