Evaluating electrochemical behaviour of recrystallized titanium alloys in Ringer's solution

By anodic potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques, the effect of recrystallization on the corrosion and electrochemical behaviour of Ti12Mo and Ti12Mo5Ta alloys was studied. Aerated Ringer's solution was employed as electrolyte solution at 37 °C. The pH was 6.9 and adjusted to 2.5 simulating the disease state. The results show excellent corrosion resistance for recrystallized Ti12Mo and Ti12Mo5Ta alloys, corroborated by high values of polarization resistance and low values of passive current density. Recrystallized structure rendered the Ti12Mo and Ti12Mo5Ta alloys extremely corrosion resistant.     

Highly luminescent europium and terbium complexes based on succinimide and N-hydroxysuccinimide

The preparation of two highly luminescent europium(III) and terbium(III) complexes with succinimide(SI) and N-hydroxysuccinimide(NHSI) were reported,which were further investigated through elemental chemical analysis,thermal analysis,FT-IR,powder X-ray diffraction,SEM and fluorescence spectroscopy.Data collected through these analysis revealed the formation of the Eu(III) and Tb(III) complexes with the above mentioned ligands at a metal to ligand(M:L) molar ratio of 1:3.Interesting conclusions regarding the efficient sensitization through the coordination site of the lanthanide luminescent centers were retained from the photoluminescent spectra investigation.Strong luminescence emission was observed in case of Eu(III)-SI and Tb(III)-NHSI complexes while the corresponding Eu(III)-NHSI and Tb(III)-SI complexes exhibited no photo luminescent properties.Newly obtained luminescent lanthanide complexes may be of particular interest for various applications in optoelectronics.     

The estimation of corrosion behaviour of ZrTi binary alloys for dental applications using electrochemical techniques

Titanium and zirconium are in the same group in the periodic table of elements and are known to have similar physical and chemical properties. Both Ti and Zr usually have their surfaces covered by a thin oxide film spontaneously formed in air. However, the cytotoxicity of ZrO₂ is lower than that of TiO₂ rutile. Treatments with fluoride are known as the main methods to prevent plaque formation and dental caries. The corrosion behaviour of ZrTi alloys with Ti contents of 5, 25 and 45 wt.% and cp-Ti was investigated for dental applications. All samples were tested by linear potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) performed in artificial saliva with different pH levels (5.6 and 3.4) and different fluoride (1000 ppm F⁻) and albumin protein (0.6%) contents. In addition, scanning electron microscopy (SEM) was employed to observe the surface morphology of the test materials after linear potentiodynamic polarisation. The corrosion current densities for the ZrTi alloys increased with the titanium content. The Zr5Ti and Zr25Ti alloys were susceptible to localised corrosion. The role that Ti plays as an alloying element is that of increasing the resistance of ZrTi alloy to localised corrosion. The presence of 0.6% albumin protein in fluoridated acidified artificial saliva with 1000 ppm F⁻ could protect the cp-Ti and ZrTi alloys from attack by fluoride ions.     

Electrochemical aspects of Ti–Ta alloys in HBSS

Corrosion behaviour of the studied Ti–Ta alloys with Ta contents of 30, 40 and 50 wt% together with the currently used metallic biomaterials commercial pure titanium (Cp–Ti) was investigated for biomedical applications. All the samples were tested by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in Hank's balanced salt solution (HBSS) with and without albumin protein at 25 °C. Very low corrosion current densities and passive current densities (in the order of 10^?6 A/cm²) were obtained from the polarization curves, indicating a typical passive behaviour for all the samples in HBSS with and without albumin. The EIS technique was applied to study the nature of the passive film formed on all the samples at various imposed potentials ?500 mV (SCE), 0 mV (SCE), 500 mV (SCE) and 1000 mV (SCE). The equivalent circuit (EC) used successfully to describe the behaviour of the samples suggests a single passive film present on the metals' surface in HBSS with and without albumin. The results showed that the presence of albumin in HBSS had an influence on the zero current potential (ZCP), polarization resistance (R_p) and capacitance (C). The presence of albumin protein in HBSS improved slightly the corrosion resistance of the entire sample. The experimental results confirm that the electrochemical behaviour of the studied Ti–Ta alloys is better to that of Cp–Ti, suggesting their promising potential for biomedical applications.     

Low cost adsorbents obtained from ash for copper removal

We investigated the utilization of ash and modified ash as a low-cost adsorbent to remove copper ions from aqueous solutions such as wastewater. Batch experiments were conducted to determine the factors affecting adsorption of copper. The influence of pH, adsorbent dose, initial Cu²⁺ concentration, type of adsorbent and contact time on the adsorption capacity of Cu²⁺ from aqueous solution by the batch adsorption technique using ash and modified ash as a low-cost adsorbent were investigated. The optimum pH required for maximum adsorption was found to be 5. The results from the sorption process showed that the maximum adsorption rate was obtained at 300 mg/L when a different dosage of fly ash was added into the solution, and it can be concluded that decreasing the initial concentration of copper ion is beneficial to the adsorption capacity of the adsorbent. With the increase of pH value, the removal rate increased. When the pH was 5, the removal rate reached the maximum of over 99%. When initial copper content was 300 mg/L and the pH value was 5, the adsorption capacity of the zeolite Z 4 sample reached 27.904 mg/g. The main removal mechanisms were assumed to be the adsorption at the surface of the fly ash together with the precipitation from the solution. The adsorption equilibrium was achieved at pH 5 between 1 and 4 hours in function of type of adsorbent. A dose of 1: 25 g/mL of adsorbent was sufficient for the optimum removal of copper ions. For all synthesized adsorbents the predominant mechanism can be described by pseudo-second order kinetics.     

Electrochemical determination of the corrosion resistance of NiCr dental casting alloys

Based on the polarization curves and electrochemical impedance spectroscopy (EIS) in the case of four commercial dental alloys (Wirolloy, Heraenium, NicromalSoft and VeraSoft) maintained in 0.1 M NaCl solution, it was established the type and the intensity of the corrosion process by means of the corrosion currents value. The passivation of all the samples occurred spontaneously at the open circuit potential. The corrosion currents value decrease after the alloys maintenance in the corrosive medium due their passivation. The corrosion currents have values of nA order for all the samples and decrease with the increase of the immersion time. The alloys Heraenium and Wirolloy are in the optimum corrosion resistant condition. The VeraSoft and NicromalSoft alloys presented a dangerous breakdown potential (about 200–300 mV). The EIS results show that all NiCr-based alloys exhibits passivity at open circuit potential. The Heraenium and Wirolloy alloys with dendritic microstructure show the best electrochemical behaviour in 0.1 M NaCl solutions     

The Estimation of Localized Corrosion Behavior of Ni-Based Dental Alloys Using Electrochemical Techniques

The aim of this study is to investigate the electrochemical behavior of the five non-precious Ni-based dental casting alloys in acidified artificial saliva. For comparison, nickel was also investigated. In order to study the localized corrosion resistance, the cyclic potentiodynamic polarization (CCP) and electrochemical impedance spectroscopy were performed. Scanning electron microscopy (SEM) observations were made after the CCP tests. The Ni-Cr alloys with chromium (14-18%) contents were susceptible to localized corrosion. The Ni-Cr-Mo alloy with contents of chromium (??13%) and molybdenum (9%) presents a dangerous breakdown, but have a zero corrosion potential so that the difference between them is around 650?mV. The Ni-Cr-Mo alloys with higher chromium (22-25%) and molybdenum (9-11%) contents had a much larger passive range in the polarization curve and were immune to pitting corrosion. Pitting resistance equivalent (PRE) of about ??54 could provide the Ni-based alloy with a good pitting corrosion resistance.     

Effect of Mo content on electrochemical behaviour of TiMo alloys for dental applications

Corrosion behaviour of the new TiMo alloys together with the currently used metallic biomaterials commercial pure titanium (Cp‐Ti) was investigated for dental applications. Ingots of composition Ti12Mo, Ti20Mo and Ti40Mo were synthesized by the cold crucible levitation melting (CCLM) technique. All the samples were examined using electrochemical techniques: open circuit potential, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in two electrochemical media: artificial saliva and in commercial mouthwash solution with 450 ppm F^? (Astera^©, EU), at 25 °C. The passive behaviour for all the Ti samples is observed for artificial saliva and for commercial mouthwash solution. The results suggest a non‐predominant fluoride effect on the passive behaviours of titanium samples. The EIS technique was applied to study the nature of the passive film formed on all the samples at various potentials in artificial saliva and in commercial mouthwash solution. Equivalent circuits (EC) were used to modelling EIS data, in order to characterize samples surface and better understanding the effect of Mo addition on the Cp‐Ti. The TiMo alloys, with a dendritic arrangement, appear to possess superior corrosion resistance than the Cp‐Ti in both electrochemical media.     

Electrochemical characterization of Ni47.7Ti37.8Nb14.5 shape memory alloy in artificial saliva

Electrochemical corrosion behaviour of the studied Ni_47.7Ti_37.8Nb_14.5 (NiTiNb) shape memory alloy was investigated for dental applications. An equiatomic NiTi alloy was used in some tests as reference material. Electrochemical techniques such as anodic potentiodynamic polarization, open circuit potential and electrochemical impedance spectroscopy (EIS) were employed. Experiments were carried out using artificial saliva. Very low passive current densities were obtained from the anodic polarization curve, indicating a typical passive behaviour for NiTiNb alloy. Over the surface of the NiTiNb alloy uniform corrosion appears, while in case of the NiTi alloy surface pitting corrosion is developed. The role that Nb plays as an alloying element is by increasing the resistance of NiTi alloy to localized corrosion. The EIS results exhibited high impedance values (order of 10⁶ Ω cm²) obtained from medium to low frequencies which are indicative of the formation of a highly stable passive film on NiTiNb alloy in the artificial saliva.     

Comparative corrosion study of Ag-Pd and Co-Cr alloys used in dental applications

The electrochemical behaviour of two Ag-Pd alloys (Unique White and Paliag) used in dental prosthetics construction for crowns and bridges and one Co-Cr alloy (Vitallium 2000) was studied in artificial saliva using the polarization curves and electrochemical impedance spectroscopy (EIS). The corrosion resistance was evaluated by means of the corrosion currents value and by coulometric analysis. The open circuit potential of Ag-Pd are attributed to dealloying followed by surface enrichment with Ag and the possible formation of an insoluble AgCl surface film on the respective alloy surfaces. Our results have shown that these alloys have a somewhat good corrosion resistance in artificial saliva. The corrosion current densities of Unique White and Vitallium 2000 alloys were very low (∼100 nA/cm²). For Ag-Pd alloys, when increasing the content of Cu, corrosion resistance decreases. The passivation of all samples occurred spontaneously at the open circuit potential. The electrochemical properties of the spontaneously passivated electrodes at the open circuit potential were studied by EIS. The polarization resistance (R _p) and the electrode capacitance (C _dl) were determined. The polarization resistance of all the samples increases with the immersion time. The polarization resistances are largest for Unique White (Ag-Pd) and Vitallium 2000 (Co-Cr) alloys. Because the electrochemical behaviour of the Co-Cr alloy was compared with that of Ag-Pd alloy, this type of alloy may be a suitable alternative for use in the manufacture of fixed dental prostheses. The present study, though limited, has shown that electrochemical characteristics can be used to identify such alloys. Knowledge of the in vitro corrosion behaviour of these alloys may lead to better understanding of any biologically adverse effects in vitro.