Potentiodynamic Technique Research Articles

Electrochemical in‐situ investigations on polycrystalline gold electrodes with oscillating quartz crystals: The electrosorption valency and heterogeneity constant of halide and sulphate adlayers

AbstractThe electrochemical formation and decay of halide and sulphate adlayers on polycrystalline gold electrodes were followed in‐situ in the monolayer range with oscillating quartz crystals. In addition, potentiodynamic techniques were applied to gain information on charge transfer and interfacial capacitance for these processes. From the obtained data the electrosorption valency γ and heterogeneity constant C were evaluated. Following data were obtained. γ = −0.06; γ = −0.34; γSo4− = −0.5; CBr− = 35.5 kJ/mol.

Electrochemical behaviour of palladium/graphite and palladium/carbon systems

Palladium electrocatalysts dispersed on carbon and graphite have been studied by a potentiodynamic technique. It is shown that the hydrogen region in the voltammograms depends on the substrate nature and the palladium deposition method. The electrooxidation of formate in alkaline medium is used to evaluate the electrocatalytic activities of the different systems. They are also found to depend on the support and the preparation method.

The corrosion behavior of palladium-silver-ceramic alloys

Five commercial PdAg alloys were investigated. Their electrochemical behavior was tested with standard potentiodynamic techniques in 0.9% saline solution and an artificial saliva and compared with high-Pd systems. Corrosion characteristics of the PdAg alloys were quite similar regardless of microstructural and compositional differences. In the area of oral interest, all alloys showed a sufficient corrosion resistance. The alloys were, unlike their high-Pd counterparts, adversely affected by a high Cl- content under more extreme conditions, and a visible film formed.

Surface properties of plasma-nitrided titanium alloys

Titanium alloy WT3-1 with an σ + β structure was subjected to isothermal plasma nitriding at 730, 830 and 1030 °C, and cyclic plasma nitriding between 930 and 730 °C. The wear resistance of this alloy at a unit pressure of 400 MPa was determined using the “three rollers-taper” method whilst, for the assessment of the corrosion resistance in 15% H2SO4, the potentiodynamic technique was used. It has been found that the nitriding treatment enhances the wear resistance as well as the corrosion resistance of the alloy. Nitriding performed at 1030 °C results in a smaller increase in wear resistance than does nitriding carried out at below 930 °C. The nitriding temperature has no effect on the corrosion resistance of the layer. A comparison has been made between the properties of the differently nitrided layers produced on two opposite sides of the specimen. The layer formed on the upper side, exposed to ion bombardment, shows a higher wear resistance as well as higher corrosion resistance than that produced on the lower side. The wear resistance of the nitrided titanium alloy is higher than that of plasma-nitrided austenitic and martensitic steels. In addition to this, its corrosion resistance is higher in 0.05 M Na2So4 + 0.1 M NaCl.

The corrosion behaviour of high-palladium porcelain-bonding alloys

The corrosion behaviour of eight commercial high-Pd alloys was investigated and compared to that of PdAg systems. They were tested with standard potentiodynamic techniques in 0·9 per cent saline solution and an artificial saliva. The corrosion behaviour of the high-Pd alloys was satisfactory and essentially equivalent. In more systems anodic overloading in 0·9 per cent saline in this alloy group seemed to be superior compared to the PdAg alloy group. Within the high-Pd alloy systems compositional and constitutional variations were apparently too small to result in substantial electrochemical effects.

The influence of iodine in the electroformation of ZrO 2 films on zircaloy-4 electrodes in acid solutions

The electroformation and growth of ZrO 2 film on Zircaloy-4 electrodes in an iodide acid solution containing iodine is studied by using potentiodynamic techniques. The voltammograms involve three regions. The first one corresponds to the electroreduction of iodine followed by a potential region where the electroformation and growth of the oxide film take place. The third region extends from a critical potential related with the pitting corrosion of Zircaloy-4 upwards. The presence of iodine mainly enhances the formation of zirconium iodine species at the electrode surface and shifts the potential at which ZrO 2 film formation usually appears towards more positive values.

Electrochemical behaviour of nitrogen-implanted 4145 steel

The corrosion behaviour of nitrogen-implanted (with and without Ti-coating) 4145 steel was investigated using the potentiodynamic technique in a 0.5M sodium acetate/acetic acid buffer (pH 5.0) solution. Nitrogen ions (N + 2) were implanted at 100 keV with doses ranging from 1 × 10 16 to 3 × 10 17 ions cm −2. Parameters such as polarization resistance, anodic and cathodic Tafel slopes along with corrosion rates were evaluated. The best results were obtained with a dose of 3× 10 17 ions cm −2. Surface morphology studied by scanning electron microscopy revealed fewer pits in Ti-coated 4145 steel. Moreover, it also suggested an increase in E p = E pass − E pit compared to uncoated steel, thus protecting the surface from active corrosion. EDXA analysis was also carried out to study the constituents and possible mechanism of pitting.

Changes in the composition of the passive layer and pitting corrosion of stainless steel in phosphate—borate buffer containing chloride ions

The influence of the passive layer properties on the pitting corrosion of 316SS was studied in phosphate—borate buffer containing chloride ions by using potential step and potentiodynamic techniques complemented with scanning electron microscopy. The increase of the anodization time in the passive region decreases the nucleation rate and the mean number of corrosion pits formed onthe 316SS surface. Results are explained through changes in the structure and composition of the passive layer during anodization. Two different Cr(III) species can be voltammetrically detected at short anodization times, an outer weakly bound Cr(III) species which is electroaoxidized to soluble CrO 4 2− and an inner Cr(III) species which is electrooxidized to Cr(VI) but retained in the film at potentials lying in the transpassive region. As the anodization time in the passive region increases, the weakly bound Cr(III) species is transformed into another more stable one, probably an iron chromite, which exhibits an electooxidation potential more positive than that of Cr(III) species. The aged passive layer becomes more resistant to pit initiation, due to either a decrease in the density of active sites or a decrease in the nucleation rate constant for pit initiation.

ChemInform Abstract: Complex Processes Related to the Early Stages of Mercury Electrodeposition on Pt Electrodes.

AbstractThe underpotential deposition (UPD) and early stages of bulk Hg electrodeposition on either polycrystalline or polyfacetted single crystal Pt electrodes in acid solution containing Hg22+ are studied by using combined potentiostatic and potentiodynamic techniques.

Some X‐ray photoelectron spectroscopic measurements on Passivated Tin in some neutral media

AbstractSome ESCA measurements have been carried out on the anode film formed on BDH Sn foil by the potentiodynamic technique up to 2.5 V (SCE) in (i) phosphate buffer, pH 6.7, (ii) 0.1 M KCl, 0.1 M Na2SO4, pH 6.6, in order to identify the elements, and possibly also some compounds, present in the film. The results in phosphte buffer indicate the presence of: (i) Sn(II) and Sn(IV) oxides and hydroxides, (ii) tin phosphate species probably (HPO4)2−, (H2PO4)−, and insoluble phosphate complexes and (iii) evidence is given for the formation of soluble Sn species containing OH or phosphates before the beginning of passivity. The results in chloride solutions indicate the presence in the anode film of Sn, O and Cl in various states of combination such as: (i) Sn(II) and Sn(IV) species (oxides, chlorides and some hydroxides, (ii)) adsorbed oxygen and water, and (iii) basic or oxysalts or complexes involving Sn, O, Cl, and K. The results in Na2SO4 solutions indicate the presence in the film of Sn, O, S, and Na in the form of: (i) Sn(II) and Sn(IV) oxides and hydroxides, (ii) Na2SO4, other un‐ identified S species, and possibly also traces of PbS (from traces of Pb present in the Sn foil), (iii) adsorbed oxygen and water, and (iv) basic or oxysalts or complexes involving Sn, Na, O, sulphate and other unidentified S species.

Complex processes related to the early stages of mercury electrodeposition on Pt electrodes

The underpotential deposition and early stages of bulk mercury electrodeposition on platinum from aqueous solution containing Hg 2+ 2 ions were studied by using combined potentiostatic and potentiodynamic techniques. The simultaneous electroreduction of the O-containing surface species and the underpotential deposition of Hg 2+ 2 ions render an electrode surface containing an O/Hg atom ratio which depends on both the applied potential and Hg 2+ 2 ion concentration in solution. The nucleation and growth of bulk mercury is impeded by the presence of O-containing surface species, whereas it is markedly enhanced by the presence of Hg-adatoms on the electrode surface. A small number of sites are involved in the nucleation process. Apparently defective points at the UPD Hg layer act as preferred sites for nucleation. It takes potentials more negative than the reversible potential of the Hg/Hg 2+ 2 ion electrode and relatively long electrodeposition times to achieve a degree of surface coverage by mercury atoms greater than 1. It is possible to observe that a fraction of them penetrates into bulk platinum to form a skin-type HgPt alloy.

ChemInform Abstract: The Pitting Corrosion Characteristics of Borides‐Strengthened Nickeland Iron‐Based Microcrystalline Alloys

Abstractis studied by the cyclic potentiodynamic technique in 1 M NaCl solution at 25‐80 °C. A higher Cr content in the microcrystalline alloys is found to provide greater resistance to pitting.

The galvanic corrosion of steel coatings: aluminum in comparison to cadmium and zinc

Galvanic interaction between carbon steel and six galvanic coating materials including SIGAL®-aluminum, cadmium, zinc and duplex combinations with copper, nickel and tin has been studied by potentiodynamic techniques and continuous monitoring of the galvanic current. Results for 12 galvanic couples are reported here for immersion in argon and air saturated sulfate and chloride solutions of various acidity. Steel can cathodically be protected not only by cadmium and zinc, but also by SIGAL®-aluminum, in moist urban, industrial, and marine atmospheres. Ultrathin intermediate layers in duplex coatings, of e.g. nickel or tin, have practically negligible influence on the aluminum top layer and the steel base.

Implicit calculation of boundary values in digital simulation applied to several types of electrochemical experiment

In the digital simulation of chronopotentiometry, potentiodynamic techniques and adsorption kinetics involving both diffusion and adsorption isotherms, the problem of species boundary concentrations at a given new time step can be eliminated by including these in the implicit equation systems for the Crank-Nicolson scheme. This greatly improves simulation efficiency. The respective expressions for the various types of experiment are developed and tested.

The pitting corrosion characteristics of boride-strengthened nickel- and iron-based microcrystalline alloys

The pitting corrosion characteristics of four boride-strengthened microcrystalline alloys, two Ni-based and two Fe-based, were studied in 1 M NaCl solution at 25–80°C, using the cyclic potentiodynamic technique. Two commercial materials, namely Alloy 600 and AISI Type 316 stainless steel, were also tested for comparison. As in the case of conventional materials, a higher content of Cr in the microcrystalline alloy was found to provide greater resistance to pitting. Mo contents also had beneficial effects. Alloys with the highest Cr contents exhibited the highest pitting potential in each group of the materials tested. Because of the formation of pits covered with Cr-rich oxidation products, repassivation of pits on these alloys was more difficult than on those with less Cr. The presence of boride precipitates in microcrystalline alloys appeared to promote rather than inhibit pit initiation and growth.

Electrochemical Behavior of AISI 304 Stainless Steel: Corrosion, Passivity, and Pitting in Alcohols + H2SO4Mixtures

Abstract The electrochemical behavior of austenitic AISI 304 stainless steel (SS) in alcoholic solutions (ethanol, iso-propanol, and t-butanol) containing different concentrations of sulfuric acid (0.001 to 1.0 M) has been investigated using potentiostatic and potentiodynamic techniques. Frequent active-passive transitions are observed and the critical current density (CD) for passivity is found to be dependent on the concentration of acid in ethanol, iso-propanol, and t-butanol solutions. Scanning electron microscopy (SEM) examination of electrode surfaces after the polarization studies showed severe pitting of SS in high concentrations of acid in ethanol, while etch type pitting is found in the case of iso-propanol and t-butanol containing respective concentrations of acid. The different corrosion parameters and pitting potentials have been evaluated. Repassivation has also been observed. The protection potential tended to shift in the noble direction as the scanning rate decreased.

Mechanistic approach to electrochemical processes in the passive and pitting corrosion regions of carbon steel in dilute NaOH solutions containing Na 2SO 4

Passive film growth, electrodissolution and pitting corrosion of prepassivated carbon steel in dilute NaOH solutions containing Na 2SO 4 are studied by using potentiostatic and potentiodynamic techniques. Two kinetic reaction models implying different passive film growth mechanisms are proposed to describe the passive film growth, the electrodissolution process through the passive film and pitting corrosion. Current transients at constant potential recorded in the passive and pitting region can be satisfactorily reproduced by assuming the occurrence of simultaneous processes. The physical interpretation of adjusting parameters derived from the two models is consistent with a duplex structure for the passive film and with the nucleation and growth of pits when the applied potential exceeds the breakdown potential although both mechanisms for the passive layer growth seem to be equally probable.

Corrosion of ferromagnetic alloys used for magnetic retention of overdentures.

Three ferromagnetic casting alloys intended for use with magnetically retained overdentures (compositions in wt%: #1, Pd 50, Co 47, Ga 2, Pt 1; #2, Pd 60, Co 37, Ga 2, Pt 2; #3, Pd 49, Co 46, Ga 2, Pt 2) were investigated. A 0.9% saline solution and an artificial saliva (Meyer) were used for evaluation of the electrochemical corrosion behavior of these alloys, utilizing standard potentiodynamic techniques. All alloys investigated possessed a good corrosion resistance in the potential range of the oral environment (from -100 to 300 mV versus SCE). In addition, alloys #1 and 3 appeared to be susceptible to pitting above +300 mV (SCE), while #2 was resistant to pitting and was found to passivate in 0.9% saline solution.

Electrochemical behaviour of copper in aqueous solution containing potassium ethylxanthate

The electrochemical behaviour of copper in aqueous potassium ethylxanthate (KEX) is studied by using potentiodynamic techniques at different sweep rates, complemented with SEM and EDAX. In NaCl solutions a cuprous xanthate film is formed at low potentials, the initial stage of this reaction being the electroadsorption of KEX on copper competing with the adsorption of chloride ions and water. At low surface coverages for electroadsorbed KEX the electrodissolution of copper is partially inhibited as compared to plain NaCl solutions. As the KEX monolayer is completed, a tri-dimensional cuprous xanthate film grows in the electrode surface. On subsequent increase of the applied potential a complex anodic layer is formed leading to copper passivity. Passivity breakdown promoted by either chloride ions or electro-oxidation of the organic film can be observed when the potential exceeds a certain critical value.

Pitting Potential of stainless steels in artificial sweat

AbstractThe pitting potentials of 12/12, 316 PX, AISI 303, 304, 316F and 316L austenitic stainless steels were determined in artificial sweat (perspiration) at room temperature. Two compositions of sweat were used: the BAM composition which contains two malodorous organic acids and the composition proposed in an ISO standard which does not contain them. The quasi‐potentiostatic method (10 mV potential steps per min), potentiodynamic technique (1 V/min linear sweep) and scratch test were used on mechanically polished and HNO3‐passivated surfaces. The aggressivity of the two artificial sweats with respect to stainless steels was found to be practically the same. The pitting potentials and the classification of the stainless steels according to their pitting potential values were found to depend on the surface preparation and, to a lesser extent, on the test method. The experimental techniques were often complementary and a combination of two or three methods in conjunction may increase the confidence with which the conclusions can be applied. The lowest pitting corrosion resistance was found for AISI 303 and the highest for AISI 316L. As expected stainless steels with the lowest concentration of nonmetallic inclusions (sulfides and oxides) exhibited the best pitting corrosion resistance.