Phosphonium iodine as nickel corrosion inhibitor in 1 M sulfuric acid medium

The inhibiting action of alkyltriphenylphosphonium iodine salt ((C₈H₁₇)Ph₃P⁺,I⁻) towards the corrosion behaviour of nickel in 1 M H₂SO₄ solution has been studied. This compound was found to retard both anodic and cathodic reactions of nickel corrosion. At constant temperature, the corrosion rate decreases with increasing inhibitor concentration. On the other hand, the increase in temperature leads to an increase in the corrosion rate. The activation energy, ΔE _a, were calculated. They were found 19.3 kJ mol⁻¹ and 71.1 kJ mol⁻¹, respectively for the uninhibited solution and in the presence of 10⁻³ M of phosphonium salt. The inhibitor adsorption was identified to occur according to Langmuir isotherm. The equilibrium constant, k, as well as the free energy of adsorption, Δ_ads G°, for inhibitor process were then calculated. Phosphonium iodine exhibited a singular behaviour for T ≥ 318 K where inhibitor desorption increases.     

Corrosion Potential oscillations

The corrosion potentials of stainless steels in chloride solutions for conditions significantly removed from those leading to pitting and crevice corrosion are constant and to a first approximation largely independent of temperature and chloride ion concentration. With increasing temperature and/or chloride ion concentration or with decreasing corrosion resistance there comes a situation when the corrosion potential begins to oscillate, between two and values roughly corresponding to E_p and E_pp. These potential oscillations are often associated with pitting and crevice corrosion, although there are clear cases when no corrosion attack was visible even after prolonged exposure. The oscillations are attributed to unstable passivity.     

Combined effect of staining substances on the discoloration of esthetic Class V dental restorative materials

The purpose of this study was to determine the combined effect of an organic substance (mucin as a substitute for salivary organic substances), chlorhexidine, and an iron compound/tea solution on the changes in the color of esthetic Class V dental restorative materials. Color of a glass ionomer, resin-modified glass ionomer, compomer and flowable resin composite of A2 shade, respectively, was determined according to the CIELAB color scale relative to the standard illuminant D65. Color was measured at baseline, and after sequential immersion in the following substances: Step-1, mucin in PBS (MCP) for 48 h; Step-2, chlorhexidine (CHX) for 24 h; Step-3, iron compound (IRN) or tea solution (TEA) up to 7 days; and Step-4, ultrasonic cleaning for 1 h. Color change (ΔE _ab *) was calculated by the equation: Δ E _ab* = [(Δ L*)² + (Δ a*)² + (Δ b*)²]^1/2, of which ΔL ^∗ indicates changes in value, Δa ^∗ indicates changes in red-green parameter and Δb ^∗ indicates changes in yellow-blue parameter. Δ E _ab* values after immersion in MCP and CHX were compared, and Δ E _ab* values after immersion in IRN or TEA, and subsequent ultrasonic cleaning were compared with respect to the restorative material and immersion substance. Δ E _ab* and changes in the color parameters (ΔL ^∗, ΔC _ab* and ΔH _ab*) were analyzed by repeated measures, analysis of variance and a post-hoc test at the 0.05 level of significance. Color changes after immersion in MCP were acceptable (Δ E _ab* < 3.3), and those after immersion in CHX were generally acceptable. The range of Δ E _ab* values after immersion in IRN was 3.1–19.6, and that after ultrasonic cleaning was 2.4–9.6. The range of Δ E _ab* values after immersion in TEA was 10.7–21.1, and that after ultrasonic cleaning was 11.9–14.5. Color changes of four Class V restorative materials after combined treatment with mucin, chlorhexidine and an iron compound/tea solution were not acceptable. Colors did not recover to their original values after ultrasonic cleaning. Modifications on the surface of a restoration should be considered to reduce stain accumulation.     

Changes in surface characteristics of dental resin composites after polishing

The objectives of this study were (1) to determine in vitro changes in surface roughness and color of dental resin composites after application of three finishing and polishing systems; (2) to evaluate the difference in color stability after immersion in a dye solution after polishing; and (3) to evaluate the effects of surface condition, especially roughness, on measured color depending on the color measuring geometries of specular component excluded (SCE) and specular component included (SCI). Color and surface roughness (R_a) of resin composites of four brands of A2 shade and one brand of Yellow Enamel shade were measured after polymerization, after polishing with Enhance (Dentsply), Sof-Lex (3M ESPE), or Super-Snap (Shofu) composite finishing and polishing systems. Color was also measured after immersion in 2% methylene blue solution. Color was measured according to the CIELAB color scale. Color changes (E*_ab) after polishing/staining and by the measuring geometry were calculated by the equation; E*_ab = [(L*)² + (a*)² + (b*)²]^1/2. Ra value was measured with a surface roughness tester. E*_ab and L* values after polishing and after staining varied among polishing systems when measured with SCE geometry. Composites polished with Super-Snap and Sof-Lex systems showed higher E*_ab and L* values than those polished with Enhance polishing system with SCE geometry. E*_ab and L* values between specimens with different surface conditions measured with SCE geometry were significantly higher than those with SCI (p < 0.01). Changes in R_a value after polishing was insignificant in most cases.     

Corrosion study of single crystal Ni–Mn–Ga alloy and Tb<Subscript>0.27</Subscript>Dy<Subscript>0.73</Subscript>Fe<Subscript>1.95</Subscript> alloy for the design of new medical microdevices

Once placed in a magnetic field, smart magnetic materials (SMM) change their shape, which could be use for the development of smaller minimally invasive surgery devices activated by magnetic field. However, the potential degradation and release of cytotoxic ions by SMM corrosion has to be determined. This paper evaluates the corrosion resistance of two SMM: a single crystal Ni–Mn–Ga alloy and Tb_0.27Dy_0.73Fe_1.95 alloy. Ni–Mn–Ga alloy displayed a corrosion potential (E _corr) of −0.58 V/SCE and a corrosion current density (i _corr) of 0.43 μA/cm². During the corrosion assay, Ni–Mn–Ga sample surface was partially protected; local pits were formed on 20% of the surface and nickel ions were mainly found in the electrolyte. Tb_0.27Dy_0.73Fe_1.95 alloy exhibited poor corrosion properties such as E _corr of −0.87 V/SCE and i _corr of 5.90 μA/cm². During the corrosion test, this alloy was continuously degraded, its surface was impaired by pits and cracks extensively and a high amount of iron ions was measured in the electrolyte. These alloys exhibited low corrosion parameters and a selective degradation in the electrolyte. They could only be used for medical applications if they are coated with high strain biocompatible materials or embedded in composites to prevent direct contact with physiological fluids.     

Localized Corrosion Behavior of 6% Mo Super Austenitic & 316L Stainless Steels in Low pH 3% NaCl Solution

Electrochemical techniques were applied to study the crevice corrosion resistance of two types of stainless steel alloys namely, conventional 316L and 6% Mo super austenitic in acidified 3% NaCI solution at room temperature. Potentiodynamic results showed that 6% Mo alloy possessed a remarkable resistance to crevice corrosion compared with 316L alloy when they are tested in the same solution. The breakdown potential at which passivity broke down for 316L alloy was 0.00 mV (SCE). The corresponding value for 6% Mo alloy could not reach up to the potential value of 700 mV (SCE). 316L alloy suffered extremely from crevice corrosion at room temperature (about 25℃), which indicates that the critical crevice corrosion temperature, below which crevice corrosion does not occur, was lower than the test temperature. For 6% Mo alloy, the critical crevice corrosion temperature was higher than the testing temperature. Electrochemical parameters indicated that 6% Mo alloy exhibited higher crevice corrosion resistance than 316L alloy.     

Long-term assessment of the implant titanium material—artificial saliva interface

This paper studies the long-term (20,000 exposure hours) behavior of titanium and Ti–5Al–4V alloy—Carter–Brugirard saliva interface and the short-term (500 exposure hours) resistance of titanium and Ti–5Al–4V alloy—Tani&Zucchi saliva interface. Potentiodynamic polarization method was applied for the determination of the main electrochemical parameters. Linear polarization measurements for to obtain the corrosion rates were used. Monitoring of the open circuit potentials (E _oc) for long-term have permitted to calculate the potential gradients due to the pH, ΔE _oc(pH) and to the saliva composition ΔE _oc(c) changes which can appear “in vivo” conditions and can generate local corrosion. Atomic force microscopy (AFM) has analyzed the surface roughness. Ion release was studied by atomic absorption spectroscopy (AAS). In Carter–Brugirard saliva both titanium and Ti–5Al–4V alloy present very stable passive films, long-term stability, “very good” resistance, low values of the open circuit potential gradients, which cannot generate local corrosion. In Tani&Zucchi artificial saliva, pitting corrosion and noble pitting protection potentials (which cannot be reached in oral cavity) were registered; titanium ion release is very low; surface roughness increase in time and in the presence of the fluoride ions, denoting some increase in the anodic activity.     

Effect of sintering process on electrical properties and ageing behavior of ZnO–V2O5–MnO2–Nb2O5 varistor ceramics

The effect of sintering process on microstructure, electrical properties, and ageing behavior of ZnO–V₂O₅–MnO₂–Nb₂O₅ (ZVMN) varistor ceramics was investigated at 875–950 °C. The sintered density decreased from 5.52 to 5.44 g/cm³ and the average grain size increased from 4.4 to 9.6 μm with the increase of sintering temperature. The breakdown field (E_{1 mA}) decreased from 6991 to 943 V/cm with the increase of sintering temperature. The ZVMN varistor ceramics sintered at 900 °C led to surprisingly high nonlinear coefficient (α = 50). The donor concentration (N_d) increased from 3.33 × 10¹⁷ cm⁻³ to 7.64 × 10¹⁷ cm⁻³ with the increase of sintering temperature and the barrier height (Φ_b) exhibited the maximum value (1.07 eV) at 900 °C. Concerning stability, the varistors sintered at 925 °C exhibited the most stable accelerated ageing characteristics, with %ΔE_{1 mA} = 1.5% and %Δα = 13.3% for DC accelerated ageing stress of 0.85 E_{1 mA}/85 °C/24 h.     

Corrosion behavior of surface-modified titanium in a simulated body fluid

We investigate the influence of micro-sandblasting and electrochemical passivation on properties such as corrosion rate and surface roughness, which are important to the biocompatibility of titanium (Ti), using surface analysis techniques and electrochemical measurements. Results of microscopy and surface profilometry experiments reveal roughened but uniform surface topography with an average surface roughness in the 0.87–1.06 μm range, depending on the alternating current passivation voltage applied to the micro-sandblasted samples. Open circuit potential versus time measurements in Hank’s Balanced Salt Solution (HBSS, a simulated body fluid) allow determination of the corrosion potential (E _corr) and reveal a shift of E _corr toward higher values upon passivation, thus pointing to increased corrosion stability. Corrosion rates in HBSS range between 0.049 and 0.288 μm year⁻¹ for micro-sandblasted and passivated Ti, as compared to that for the micro-sandblasted and non-passivated surface that is 0.785 μm year⁻¹. Results from this study demonstrate that micro-sandblasting coupled with electrochemical passivation provides a roughened surface with increased corrosion stability and a low corrosion rate in HBSS. Application of this technique to Ti in medical and dental applications may be expected to result in an improvement of biocompatibility.     

Electrochemical repairing of pitted 18-8 stainless steel

In order to clarify the reaction essential of electrochemical repairing method, which was developed to repair the passive film on pits and suppress pitting corrosion on passive 18-8 stainless steel (18-8ss) after occurrence of pitting, the electrochemical characteristics, morphology and composition of passive film after different treatments were investigated by electrochemical impedance spectroscopy (EIS), Cyclic Voltammogram (CV), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The dynamic behavior of reactions occurred at lower potential (E _L = −200 mV) and higher potential (E _H = 1000 mV) of alternating electric filed was discussed respectively and the correlation between those reactions was analyzed. Based on above results, reaction essence of electrochemical repairing for pitted 18-8ss electrode was proposed: during the periodic action of alternating current, recycle reactions take place on the surface and the pit area of pitted electrode, i.e., metal dissolves into cations (occurs at E _L and form hydrous hydroxide, the hydrous hydroxide turns into metal oxide (occurs at E _H), a ‘bipolar mode’ passive film forms and Cr content is increased in repaired passive film. At the pit area, enclosed state of the pit is destroyed by the perturbing effect of alternating current in 1.0 M H₂S0₄ solution, thus the pit area will be repaired through above-mentioned process.     

Structure and electrochemical reactivity of new sulphur–silicon podands adsorbed on silver or gold surfaces

By the self-assembly monolayer (SAM) organization, three new podands belonging to silylpropanethiols have been tested as to their ability to form nanolayers protecting the noble metal surface (gold or silver) and to form complexes with monovalent metal cations on the metal surfaces. The stable self-assembled chemisorbed layers, providing protection to metal surface against electrooxidation and capable of blocking propylene carbonate (PC) electroreduction and Li electrodeposition were produced. Reflection-absorption infrared spectroscopy (RAIRS) indicated cleavage of the S–H bond upon adsorption of species 1–3 with the formation of S–Ag bonds on the metal surface. By cyclic voltammetry, it was found that the primary adsorbate formed on a Au electrode at E _ad (between −0.2 and −1.2 V vs. SCE) underwent reductive desorption at E < −1.3 V vs. SCE. The structures of 1–3 and their complexes with Na⁺ cations on the Ag surfaces were calculated and visualized by the AM1d semi-empirical method.     

Effect of temperature, chloride ion and pH on the crevice corrosion behavior of SAF 2205 duplex stainless steel in chloride solutions

An investigation was conducted to examine the crevice corrosion behaviors for SAF 2205 duplex stainless steel in NaCl solutions by using potentiostatic critical crevice temperature measurement. Potentiodynamic polarization technique was comparably used to study the electrochemical behavior. The influence of temperature, chloride concentration and pH on the critical crevice temperature and electrochemical behavior in NaCl solutions was studied. The critical crevice temperature of SAF 2205 DSS in 4% NaCl solution was about 28 °C. The critical crevice temperature decreased linearly with an increase in log [Cl⁻]. A maximum critical crevice temperature was found in 4% NaCl solutions at pH 8.5. The influence of the duplex microstructure on attack development and morphology was analyzed by scanning electron microscope.     

Corrosion resistance evaluation of a Ca- and P-based bioceramic thin coating in Ti-6Al-4V

The objective of this study was to physico/chemically characterize and determine the corrosion resistance of a Calcium–Phosphate (Ca–P) based bioceramic thin coating processed by a sputtering process on titanium alloy (Ti-6Al-4V). The samples utilized in this study were uncoated and coated disks of 10 mm diameter by 3 mm thickness. The coating was characterized by SEM, XPS + ion beam milling (IBM), thin-film mode XRD, and atomic force microscope (AFM) (n = 3). Coated and uncoated Ti-6Al-4V disk surfaces were tested in Phosphate Buffered Saline (PBS) at 25°C through an area of 0.79 cm². A three-electrode cell set-up was used with a saturated calomel electrode (SCE) and a platinum wire as reference and counter electrodes. After 3, 17, and 25 days of immersion, electrochemical impedance spectroscopy (EIS) experiments were performed (n = 3). The EIS tests were carried out in potentiostatic mode at the open circuit potential (OCP). The frequency range considered was from 100 kHz to 10 mHz, using 10 mV root mean square as the amplitude of the perturbation signal. A potentiodynamic polarization scan using a frequency response analyzer potentiostat, was acquired following 3 days of immersion in PBS. The potentiodynamic polarization scans (n = 3) were carried out with a scan rate of 1 mV/s ranging from −0.8V(SCE) to 3.0V(SCE). Results: The physico/chemical characterization showed an amorphous Ca- and P-based coating of ~400–700 nm thickness with Ca–P nanometer size particles embedded in a Ca–P matrix. The Bode phase angle diagrams showed highly capacitive results at low and medium frequencies for both surfaces tested. The polarization curves showed low current densities at the corrosion potential (E _corr), in the order of 10⁻⁸A/cm², typical of passive materials with protective surface films. Coated sample current densities were comparable to the uncoated samples. Conclusion: Coated and uncoated samples were stable in the test solution with a protective film maintained throughout the 25 day immersion test period.     

Kinetics of hydrogen evolution reaction on Zr0.5Ti0.5V0.6Cr0.2Ni1.2 alloy in KOH electrolyte

A hydrogen-storage alloy of the composition Zr_0.5Ti_0.5V_0.6Cr_0.2Ni_1.2 has been investigated for corrosion resistance and hydrogen-evolution reaction (HER) in KOH electrolyte of varying concentrations. Activation of the electrode by absorption of hydrogen takes place after prolonged cathodic polarization in the potential range of HER. Prior to activation, the open-circuit potential is about −0.4 V vs Hg/HgO, OH⁻, at which the alloy electrode tends to undergo corrosion with oxygen-reduction reaction (ORR) as the conjugate reaction. The corrosion-current density measured from Tafel polarization of ORR is found to be independent of KOH concentration and has an average value of about 30 μA cm⁻². Subsequent to activation, the open circuit potential of the electrode is shifted to about −0.93 V vs Hg/HgO, OH⁻, which is equal to the reversible potential of HER. The exchange current density values measured from Tafel polarization of HER are marginally higher in relation to the values obtained before the electrode is activated. Alternating-current impedance spectra in the Nyquist form contain two overlapped semicircles. The high-frequency semicircle is attributed to the electrode geometry, while the low-frequency semicircle is due to the charge-transfer reaction and double-layer capacitance. The impedance data are analyzed by a non-linear least square curve fitting technique and impedance parameters are evaluated.     

PZT-36/NiCo0.02Cu0.02Mn0.1Fe1.8O4 − δ magnetoelectric rod composites with 1-3, 3-1, and 1-1 connectivity

We have developed a technique for the fabrication of piezoelectric/ferrite rod composites with 1-3, 3-1, and 1-1 connectivity, which has the advantage of employing piezoelectric ceramics poled under optimal conditions. All types of rod composites produced by this technique have better piezoelectric and magnetoelectric properties in comparison with 2-2 layered structures produced in the same way. The magnetoelectric coefficient of the composites has a maximum at equal volume fractions of the components (0.5PZT-36/0.5NiCo_0.02Cu_0.02Mn_0.1Fe_1.8O_{4 − δ}), independent of the connectivity type of the composites. The best piezo- and magnetoelectric properties are offered by the 1-1 composites, which have ΔE/ΔH = 140 mV/(cm Oe) at 1 kHz. The ΔE/ΔH of the composites correlates with their |d ₃₃/d ₃₁| ratio: with a decrease in this ratio, the magnetoelectric coefficient increases.     

Methods for the construction of the diagrams of fatigue crack-growth rate of materials

We study different parameters used for the construction of the diagrams of fatigue crack-growth rate of materials in the force, deformation, and energy approaches and tested for 08kp low-strength steel and 60 high-strength steel. The applicability of the dependences known from the literature for the evaluation of the crack-tip opening displacement and local strain energy at the crack tip is analyzed. It is shown that the range of local strains Δε* and the total range of dissipation of local energy in a loading cycle ΔW _t * specify the fatigue crack-growth rate in the material and that the da / dN−Δε* and da / dN−ΔW _t * diagrams are more sensitive to the structural and mechanical characteristics of the materials than the ordinary da / dN−ΔK diagrams. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 4, pp. 31–41, July–August, 2007.     

Tunneling conductance of break junction with the (100) plane fracture surface of Bi2Sr2CaCu2O8

Using the new method of breaking, the tunnel junctions with the (100) plane fracture surface could be obtained. The observed singularities in conductivity can be explained by tunneling between the different layers (CuO₂→CuO₂, sharp peaks at 2Δ _p−p =64±2mV;CuO ₂→BiO, peaks at 100–140 mV; BiO→BiO, wide maxima at about 250 mV). The tunneling spectra measured at T=4.2–100 K show that a shift of the 2Δ _p−p peak to lower biases is much stronger (from 64 to 37 mV) than the BCS prediction at T/T_c≤0.7. At higher T (up to T_c≈87K) the changes of the spectra look like those expected for gapless superconductivity in agreement with the ARPES data for a-direction.     

Influence of noble metals alloying additions on the corrosion behaviour of titanium in a fluoride-containing environment

Titanium alloys exhibit excellent corrosion resistance in most aqueous media due to the formation of a stable oxide film, and some of these alloys (particularly Ti-6Al-7Nb) have been chosen for surgical and odontological implants for their resistance and biocompatibility. Treatment with fluorides (F⁻) is known to be the main method for preventing plaque formation and dental caries. Toothpastes, mouthwashes, and prophylactic gels can contain from 200 to 20,000 ppm F⁻ and can affect the corrosion behaviour of titanium alloy devices present in the oral cavity. In this work, the electrochemical corrosion behaviour of Ti-1M alloys (M = Ag, Au, Pd, Pt) was assessed in artificial saliva of pH = 3.0 containing 910 ppm F⁻ (0.05 M NaF) through open circuit potential, E_OC, and electrochemical impedance spectroscopy (EIS) measurements. The corrosion behaviour of the Ti-6Al-7Nb commercial alloy was also evaluated for comparison. E _OC measurements show an active behaviour for all the titanium alloys in fluoridated acidified saliva due to the presence of significant concentrations of HF and HF₂ ⁻ species that dissolve the spontaneous air-formed oxide film giving rise to surface activation. However, an increase in stability of the passive oxide layer and consequently a decrease in surface activation is observed for the Ti-1M alloys. This behaviour is confirmed by EIS measurements. In fact, the Ti-6Al-7Nb alloy exhibits lower impedance values as compared with Ti-1M alloys, the highest values being measured for the Ti-1Au alloy. The experimental results show that the corrosion resistance of the studied Ti-1M alloys is similar to or better than that of Ti-6Al-7Nb alloy currently used as biomaterial, suggesting their potential for dental applications.     

Combined effects of staining substances on resin composites before and after surface sealant application

The objective was to measure the combined effect of mucin, chlorhexidine and tea solution on the staining of four dental resin composites, and to determine the effect of surface sealant on staining. One side of cured resin composite specimens of 10 mm in diameter and 2 mm in thickness were polished with 600-grit silicon carbide paper. One group of specimens (n = 5) was treated with a surface sealant [BisCover, Bisco, USA; SS (surface sealant) group], and the other group was not (NO group; control). Specimens were sequentially immersed in the following substances: Mucin in phosphate buffered saline (PBS); chlorhexidine; tea solution; and ultrasonic cleaning and then immersion in PBS. Color was measured on a reflection spectrophotometer. Changes in color (ΔE ^* _ab ) and color parameters, such as hue, chroma and value, after immersion in tea solution and subsequent cleaning were analyzed by repeated measures, analysis of variance at the 0.05 level of significance. The range of ΔE ^* _ab values after immersion in tea solution was 11.4–21.1 for NO group and 10.5–19.6 for SS group, and that after cleaning was 2.4–10.0 for NO group and 2.7–8.3 for SS group. After staining, CIE L ^* value (lightness) decreased, and CIE a ^* and b ^* values increased. Color changes of resin composites were not acceptable after sequential immersion treatment (ΔE ^* _ab > 3.3). The changes in color and color parameters of sealant applied group were not significantly different from those of control group except for a few combinations of color parameters and resin composites.     

Spatial organization of peptide nanotubes for electrochemical devices

A novel biosensor for hydrogen peroxide was developed by combining the known properties of microperoxidase-11 (MP11) as an oxidation catalyst, and the interesting properties of diphenylalanine peptide nanotubes (PNTs) as a supporting matrix to allow a good bioelectrochemical interface. In this case, the synthesized MP11/PNTs were immobilized onto the ITO electrode surface via layer-by-layer (LBL) deposition, using poly(allylamine hydrochloride) (PAH) as positively charged polyelectrolyte layers. The PNTs provide a favorable microenvironment for MP11 to perform direct electron transfer to the electrode surface. The resulting electrodes showed a pair of well-defined redox peaks with formal potential at about −343 mV (versus SCE) in phosphate buffer solution (pH 7). The experimental results also demonstrated that the resulting biosensor exhibited good electrocatalytic activity to the reduction of H₂O₂ with a sensitivity of 9.43 μA cm⁻² mmol⁻¹ L, and a detection limit of 6 μmol L⁻¹ at the signal-to-noise ratio of 3. Moreover, we also observed that the peptides self-assembly can be influenced upon changing the pH of the solution. Alkaline solution appears to favor the packing of diphenylalanine nanotubes being closer than acidic or neutral conditions. The study proved that the combination of PNTs with MP11 is able to open new opportunities for the design of enzymatic biosensors with potential applications in practice.