Potentiostatic behaviour of dental amalgam alloys in salvia

The behaviour of Ag-Sn alloy and Ag-Sn-Hg dental amalgam alloy has been studied under potentiostatic conditions in artificial saliva and in sodium chloride solutions containing 0.2% NaCl (alone or mixed with sodium hydrogen phosphate). It has been shown that Sn and Ag as well as the intermetallic compound reveal themselves through maxima in the E/I curves and through the total shift of these curves toward higher currents. The role of γ₂-phase in enhancing corrosion and of hydrogen phosphate ions (and of other constituents of saliva) in counteracting the aggressiveness of Cl^? ions have been demonstrated.     

Crevice corrosion monitoring of titanium and its alloys using microelectrodes

Crevice corrosion of titanium and its alloys in 10% sodium chloride was investigated at 100°C with the aid of microelectrodes. Potential, pH and chloride ion concentration inside the crevice were monitored using an Ag/AgCl electrode, a tungsten microelectrode and a Ag/AgCl chloride ion selective microelectrode, respectively. The pH and Cl^? concentrations within the crevice were calculated from the standard potential‐pH and potential‐log[Cl^?] calibration curves. The effect of Mo on the crevice corrosion of titanium was also studied. The passivation behavior on the titanium and Ti‐15%Mo alloy was studied using electrochemical impedance studies. There was no apparent change in pH and Cl^? ion activity inside the crevice for the alloy at 100°C, whereas a marginal decrease in pH and increase in Cl^? ion concentration were observed for pure titanium. Thus pure titanium is susceptible to crevice corrosion in hot 10% NaCl solutions at 100°C. The chloride ion activity was found to be reduced for the alloy so that the pH inside the crevice increased. The corrosion reaction resistance (R_t) was found to increase with the addition of Mo as an alloying element. It also increases with externally applied anodic potential. Hence, Mo is an effective alloying element, which enhances the crevice corrosion resistance of titanium.     

The relation between individual properties of alloy components and anodic behavior of multicomponent alloys in acidic environments. III. The effect of halide ions on active dissolution and passivation of Fe-Cr, Ni-Cr, and Fe-Cr-Ni alloys

The anodic behavior of alloy components in the presence of ions added to the solution is considered on the basis of concepts about the operation and blockade of active dissolution sites. Halide ions selectively change the anodic behavior of only nickel and iron components. The ions suppress reactions in which OH-ions are involved and promote new anodic processes, which is especially pronounced in the case of a nickel component in the presence of Cl^?.     

Electrochemical behaviour of nickel anode in H2SO4 solutions and the effect of halide ions

The electrochemical behaviour of pure nickel in H₂SO₄ solutions has been potentiodynamically investigated. The effects of the following factors on the anodic dissolution and passivation of the metal are discussed: potential scan rate, successive cyclic voltammetry and progressive additions of Cl^?, Br^? and I^? ions. Increasing the potential scan rate increases the critical current density i_cc, denoting that the active dissolution of nickel in H₂SO₄ is a diffusion controlled process. Cyclic voltammetry shows that the reverse excursion does not restore the anode to its active state. On successive cycling, the height of i_cc decreases; this could be attributed to the decrease in the reduction efficiency of passivating oxide film during the cathodic half cycles. The presence of the halogen ions below a certain concentration specific to each anion inhibits the anodic dissolution both in the active and passive states. The inhibitive action of these additives decreases in the order I^?, Br^?, Cl^?. Beyond the specific concentrations, the halogen ions accelerate the anodic dissolution and shift the active passive transition to more positive values. The aggressiveness of these anions decreases in the sequence Cl^?, Br^?, I^?, Further increase in the halogen ion concentrations can lead to breakdown of the passive film and initiate pitting. The susceptibility of nickel to pitting attack enhances with increasing H₂SO₄ concentration.     

Adsorption properties of Ag（Ⅰ）, Au（Ⅲ）, Pd（Ⅱ） and Pt（Ⅳ） ions on commercial 717 anion-exchange resin

The adsorption properties of the four precious metal ions (Ag(I), Au(II), Pd(III) and Pt(IV)) on the commercial Cl^?-form 717 strongly basic anion-exchange resin were studied in detail. The effects of the contact time, solution acidity, and concentrations of Cl^? and Pb²⁺ ions on the adsorption properties were studied by the batch method. Then, the column method was conducted under the optimized adsorption conditions (pH=3.0). The effects of the sample loading flow rate and the length-to-diameter ratios of the columns were investigated. The precious metal ions adsorbed could not be eluted completely after the saturated adsorption because the precious metal ions were found to be reduced to their metallic states during the adsorption process. So, it is recommended that the commercial Cl^?-form 717 strongly basic anion-exchange resin should be decomposed directly to recovery the precious metals after the saturated adsorption.     

Effects of coolant chemistry on corrosion of 3003 aluminum alloy in automotive cooling system

In this work, effects of coolant chemistry, including concentrations of chloride ions and ethylene glycol and addition of various ions, on corrosion of 3003 Al alloy were investigated by electrochemical impedance spectroscopy measurements and scanning electron microscopy characterization. In chloride‐free, ethylene glycol–water solution, a layer of Al‐alcohol film is proposed to form on the electrode surface. With the increase of ethylene glycol concentration, more Al‐alcohol film is formed, resulting in the increase in film resistance and charge‐transfer resistance. In the presence of Cl^? ions, they would be involved in the film formation, decreasing the stability of the film. In 50% ethylene glycol–water solution, the threshold value of Cl^? concentration for pitting initiation is within the range of 100 ppm to 0.01 M. When the ethylene glycol concentration increases to 70%, the threshold Cl^? concentration for pitting is from 0.01 to 0.1 M. In 100% ethylene glycol, there is no pitting of 3003 Al alloy even at 0.1 M of Cl^?. Even a trace amount of impurity cation could affect significantly the corrosion behavior of 3003 Al alloy in ethylene glycol–water solution. Addition of Zn²⁺ is capable of increasing the corrosion resistance of Al alloy electrode, while Cu²⁺ ions containing in the solution would enhance corrosion, especially pitting corrosion, of Al alloy. The effect of Mg²⁺ on Al alloy corrosion is only slight.     

Galvanic cells encountered in the corrosion of steel reinforcement —I. Differential pH cells

Corrosion cells resulting from differential pH values have been investigated in the absence and presence of Cl⁻ ions. Measurements of potential, galvanic current for separate and coupled electrodes, as well as experimental determination of Evans diagrams, were carried out. The results of coupling rvealed that the steel at lower pH (7 and 8) suffered from corrosion while that at the. higher pH (12 and 12·5) was completely protected even in presence of high chloride concentrations The increase in the pH range caused a relative enhancement of the anodic process. The presence of 10⁻³ or 10⁻¹M Cl⁻ ions increased the rate of the anodic reaction by 8- or 12-fold. The rate of the cathodic reaction was of the same order of magnitude both in presence or absence of Cl⁻ ions. The % anodic and cathodic control were found to be 6·4 and 93.6, respectively, in the presence of Cl⁻ ions as compared with 34·3 and 65·7 in the absence of Cl⁻ ions.     

Electrochemical Investigation of the Nucleation and Propagation of Pits in Iron-Chromium Alloys

Abstract

Electrochemical measurements performed on single crystals and polycrystalline samples of Fe 13 Cr and Fe 16 Cr alloys in Na₂SO₄ + NaCl solutions differing in Ci^? ion concentration, have shown that during pitting the anodic current I increases with time t:

I～t^b Depending on experimental conditions, b may vary from 2 to 6. At b = 2 all the pits nucleate simultaneously, so that their number does not change with time of anodic polarisation. At b > 2 the number of pits increases with time.

Galvanostatic polarisation of polycrystalline samples in solutions containing much fewer Cl_? ions than SO₄^2? ions does not lead to a steady potential. Under these conditions periodic oscillations of potential occur, several hundred millivolts in amplitude. This phenomenon is probably due to the inhibiting action of SO₄^2? ions on the nucleation of pits by Cl^? ions, and it occurs only at certain concentration ratios of these two ions in the electrolyte. Inhibition of pit nucleation is also revealed during potentio-static and potentiokinetic measurements at potential values several hundred millivolts more positive than the breakdown potential measured galvanostatically.

An interpretation of above phenomena is given for both single crystals and polycrystalline alloy samples.     

Anodisches Verhalten und Korrosion von Titan in methanolischen Lösungen

Anodic behaviour and corrosion of titanium in methanolic solutions The anodic behaviour of titanium in methanolic solutions containing halides or water in various concentrations has been investigated and the result were compared with the result obtained by corrosion tests performed on ?U”? bend specimens in similar solutions. Polarization curves can predict the susceptibility to titanium to stress corrosion cracking as in the case the metal surface is not passivable. These conditions can be obtained in the presence of low water content (i.e. 0.1% H₂O) and of activating ions as Cl^? and Br^? even in very small concentration (10^5?, 10^4? M). Presence of higher water contents and/or of F^? or I^? ions can to some extent produce passivation of the metal surface and cracking does not occur. A lower water amount in the solution (i.e. 130 ppm) eliminates any possibility of passivation of the metal surface, so that cracking can occur even in the absence of chlorides or bromides. High Cl^? concentration in the solution. (i.e. 0.1 M NaCl + 0.1% H₂O) can produce intergranular attack even in the absence of applied stress.     

The anodic dissolution of beryllium in non-aqueous solutions

The anodic dissolution of Be was studied in Cl^? and Cl0₄^? solutions of methanol, ethanol and N,N-dimethylformamide with water contents < 0.1 g/l at 25°C. The apparent valences of Be ions going into solution ranged from 0.37 to 1.8. The lower values were obtained in alcohol solutions with Cl^?. Considerable gas evolution was noted from the Be surface. The low and anomalous valences are attributed mainly to a chemical dissolution of the metal by reaction with the solution. This reaction is reported to be catalysed by Cl^?. Theeffect of the low watercontent is to hinder the reforming of an oxide or hydroxide film that protects the Be from chemical attack. The numerical value of the valence is mainly dependent on the rate that the Be will chemically react with the media once a current flows that disrupts the surface film.     

Anodic oxidation of Al–Ag alloys

The anodic oxidation of solution-treated and quenched Al–Ag alloys containing 0.3, 0.6, 0.9 and 1.2 at.%Ag, is examined in ammonium pentaborate electrolyte, which leads to growth of barrier-type anodic films. Enrichments of silver, 3.1×10¹⁵ Ag atoms cm⁻², are developed in the alloys immediately beneath the amorphous alumina films, with the level of enrichment not depending significantly upon the composition of the bulk alloy. The enrichment is relatively low due to clustering of silver atoms in the bulk alloy, which reduces the concentration of silver that is available to enrich from solid solution. Silver species are incorporated into the anodic film, where they migrate outward faster than Al³⁺ ions.     

Surface characteristics, corrosion behavior, and antibacterial property of Ag-implanted NiTi alloy

NiTi shape memory alloy was modified by Ag ion implantation with different incident doses to improve its antibacterial property. The atomic force microscopy, auger electron spectroscopy, and X-ray photoelectron spectroscopy show that the surface of NiTi alloy is covered by TiO₂ nano-film with embedded pure Ag with a peak concentration of 5.0 at% at the incident dose of 1.5 × 10¹⁷ ions·cm^?2, and Ni concentration is reduced in the superficial surface layer. The surface roughness reaches the maximum value nearly twice higher than the control sample at the incident dose of 1.5 × 10¹⁷ ions·cm^?2. The potentiodynamic anodic polarization curves show that the Ag-implanted NiTi samples possess higher self-corrosion potential (E _corr) and lower self-corrosion current density (i _corr) but lower breakdown potential (E _br). Therefore, the corrosion resistance of the Ag–NiTi is comparable to, if not better than, the untreated NiTi. The antibacterial tests reveal that there is a distinct reduction of the germ numbers on the Ag–NiTi, which is due to the direct contact between Ag and germ, and enhanced by the leaching Ag ions.     

Electrochemical behaviour and stress-corrosion cracking of titanium in alcoholic solutions

The electrochemical behaviour of titanium in neutral methanolic and ethanolic solutions containing chlorides, and corrosion tests performed with U-bend specimens in similar solutions, indicate that stress-corrosion phenomena occur on titanium when particular anodic and cathodic conditions are settled.In neutral aerated ethanolic solutions the oxide film is stable and its electronic properties (ionic and electronic currents) are similar to the ones observed in aqueous solutions. Exception is made only for the breakdown potential. In ethanolic solutions, stress-corrosion occurs only in the presence of depolarizing species which can set mixed potentials more noble than the one characteristic of oxygen (i.e. FeCl₃).Breakdown potential weakly depends on the chloride concentration, but the adsorption of chlorides on the oxide surface, in ethanolic solutions shifts the steady state potential of the metal to more active potentials so that, from the electrochemical point of view the more concentrated NaCl solutions, appear to be less effective in promoting stress-corrosion, the corrosion potentials settled at the higher Cl^? concentrations, being less noble than the potentials settled at the lowest Cl^? concentrations. In this case the role of Cl^? in the dissolution of titanium in ethanolic solution seems to be restricted to the formation of complex ions. The stability of titanium oxide films in methanolic solutions is very weak and, in the anodic sense, is restricted to a very narrow range of potentials. Presence of oxygen can create mixed potentials more noble than the breakdown potentials and thus the stress-corrosion occurrence.The beneficial effect of cathodic polarization in neutral alcoholic environment can be due to the establishment of corrosion potential less noble than breakdown potential of the oxide film.     

SCC of X‐52 and X‐60 weldements in diluted NaHCO3 solutions with chloride and sulfate ions

Stress corrosion cracking tests were performed in both X‐52 and X‐60 weldments in sodium bicarbonate (NaHCO₃) solutions at 50°C using the Slow Strain Rate Testing (SSRT) technique. Solution concentrations varied between 0.1 to 0.0001 M, and to simulate the NS‐4 solution, chloride (Cl^?) and/or sulfate ( ) ions were added to the 0.01 M solution. Tests were complemented with hydrogen permeation measurements and polarization curves. It was found that the corrosion rate, taken as the corrosion current, I_corr, was maximum in 0.01 M NaHCO₃ and with additions of ions. Higher or lower solution concentrations or additions of Cl^? alone decreased the corrosion rate of the weldment. The SSC susceptibility, measured as the percentage reduction in area, was maximum in 0.01M NaHCO₃. Higher or lower solution concentrations of additions of Cl^? or decreased the SCC susceptibility of the weldment. The amount of hydrogen uptake for the weldment was also highest in 0.01 M NaHCO₃ solution, but it was minimum with the addition of Cl^? or ions. Thus, the most likely mechanism for the cracking susceptibility of X‐52 and X‐60 weldments in diluted NaHCO₃ solutions seems to be hydrogen‐assisted anodic dissolution.     

EQCN study of anodic dissolution and surface oxide film formation at Au in the presence of Cl or Br ions: A model process for corrosion studies

The anodic dissolution of an Au electrode and associated thin-layer oxide film formation in aq. H₂SO₄ in the presence of Cl⁻ or Br⁻ ions at various concentrations provides a model process for metal corrosion. In the present work such processes were investigated using cyclic voltammetry and chronoamperometry, with complementary nanogravimetry measurements using the EQCN. The results clearly indicate that in 0.5 M H₂SO₄ electrolyte, containing 1 mM Br⁻ or Cl⁻, Au dissolves over the potential range 1.0 - 1.45 V(RHE) through a 3e oxidation process involving Au complex-ion formation that can be followed in situ by means of UV spectroscopy. The linear relationship between mass changes and reciprocal square-root of sweep-rate and between anodic currents in cyclic voltammetry at ca. 1.20 V for Br⁻ (1.39 V for Cl⁻) and square-root of sweep-rate/or electrode rotation rate indicated quantitatively that the dissolution process is diffusion-controlled. It was interesting to find that electrode rotation in the presence of Cl⁻ ions has little effect on the anodic formation of surface oxide, while, on the contrary, with Br⁻ ions present, currents for oxide film reduction are not observed at rotation rates > ca. 400 rpm.     

The effect of Cl− ions on the passivation of Fe26Cr alloy

Anodic oxide films formed on Fe26Cr in pH 2.0 H₂SO₄ solution in the presence and absence of Cl⁻ ions have been investigated using electrochemical techniques and Auger electron spectroscopy (AES) combined with ion sputtering. It is possible to incorporate Cl⁻ ions into passive oxide films formed over the entire passive potential range only when Cl⁻ is present in the solution from the very beginning of film formation. Cl⁻ ion incorporation does not cause any change in film thickness or Fe/Cr ratio, or any film thinning or film breakdown. A relatively short anodization in Cl⁻-free solution is sufficient to prevent any subsequent Cl⁻ ion incorporation. The susceptibility of the passive film to Cl⁻ attack appears to depend on the presence of small amounts of impurity in the alloy. A 99.97% pure alloy does not pit, whereas a 99.93% pure alloy, with larger concentrations of C, S, Mn, Co and Ni, does suffer intergranular attack in Cl⁻ solution.     

Nature of passive films on Fe26Cr alloy

Anodic oxide films formed on Fe26Cr alloy in pH 2.0 H₂SO₄ solution have been investigated using electrochemical techniques, and Auger electron spectroscopy (AES) combined with ion sputtering and subsequent quantitative thin film analysis. Films formed on electropolished (EP) and cathodically reduced (CR) surfaces have been examined in terms of their thickness, composition and open-circuit stability as a function of potential and time of anodization. Passive films on CR surfaces appear to be composed of either a (Fe,Cr)₂O₃ type of oxide, or an inner layer of FeCr₂O₄ and an outer layer of (Fe,Cr)₂O₃ depending on the anodizing potential. The Cr/Fe ratio in the films varied with both potential and time of anodization, but all films were enriched in Cr relative to the underlying alloy. Oxide thicknesses were $\text{≈17}\text{A}\text{?}\text{(±5?10\%)}$ irrespective of the conditions of formation. The somewhat thicker EP prior oxide contained Cl^? which was removed by CR. If no CR was performed, subsequent passive films on EP surfaces contained various amounts of incorporated Cl^? depending on the anodizing potential. The Cl^?-containing films were also Cr rich, and their composition and thickness were potential dependent. Open-circuit decay profiles and surface reactivity measurements demonstrated that the Cl^?-containing films break down faster than Cl^?-free anodic films with preferential removal of Fe and Cl^? occurring from the outer part of the film. The stability of both types of film increased with time of anodization.     

Slow strain rate stress corrosion testing at elevated temperatures and high pressures

Slow strain rate stress corrosion cracking experiments have been performed on single phase and duplex phase 304 stainless steels at 290°C. Environmental variables included chloride concentrations (0–1000 ppm), oxygen concentration (0–2 ppm) and potential (?_corr to + 500 mV vs Ag/AgCl). These experiments have shown that s.c.c. resistance is relatively unaffected by Cl^? if O₂ concentrations approach zero. However, at 2 ppm O₂ concentration, there is a large decrease in resistance with increasing Cl^? concentrations. Anodic polarization of the steels during straining in solutions containing 100 ppm Cl^? and 0 ppm O₂ showed a threshold potential for s.c.c. at ～ 500 mV more noble than the corrosion potential (? 650 ± 60 mV vs Ag/AgCl at temperature).     

Breakdown of cadmium passivity in alkaline solution

The electrochemical behaviour of a Cd anode was investigated in 0.05–2 M NaOH solutions by the potentiodynamic technique. The polarization curves exhibit active to passive transition prior to oxygen evolution. The threshold potential of the active dissolution is very close to the reversible potential of the system Cd/Cd(OH)₂. X-Ray diffraction and XPS measurements reveal that the passive layer is composed of both Cd(OH)₂ and CdO. The influence of increasing amounts of Cl^?, Br^? or I^? ions on the anodic behaviour of Cd in NaOH solution has been investigated. The halides stimulate the anodic dissolution in the active region and tend to break-down the passive layer in the passive region, leading to pitting attack. The pitting potential shifts to more negative values with increasing halide ion concentration but to the reverse direction with increasing alkali concentration.     

The electrochemical behaviour of dental amalgam alloys

The anodic and cathodic behaviour of a dental amalgam alloy in artificial saliva has been studied using galvanostatic techniques. The different intermetallic compounds as well as separate metals are indicated by steps or breaks in the anodic polarization or cathodic polarization curves or both.