Metallurgical and Materials Data

Corrosion Behavior of Dental Metallic Alloys

Karlo Raić — 2025-06-30

Dental metallic alloys undergo electrochemical degradation in the oral environment, which compromises structural integrity and surface functionality. Ionic dissolution can activate hypersensitivity and potential cytotoxic or genotoxic effects; therefore, released ion levels must remain within defined safety limits. Corrosion also accelerates fatigue, fretting fatigue, and tribocorrosion, increasing the risk of deformation and fracture.

This review consolidates methodologies for immersion and galvanic corrosion testing, presents the electrochemical background required for study design and data interpretation, and identifies the physiological variables that govern intraoral degradation, including saliva composition and pH cycling, proteins and biofilms, mechanical loading, temperature fluctuations, and fluoride exposure. Evidence on the corrosion behavior of dental alloys is summarized across in vitro, in situ, and in vivo contexts. In addition, surface engineering approaches are examined, including passivation strategies, surface modification, and protective coatings, with the aim of reducing ion release, improving corrosion resistance, and extending clinical service life.

Electrochemical Evaluation of 304 Stainless-Steel in Aqueous Curry-Leaf Extract: Effect of NaCl on Passivity and Food-Contact Safety

T. Umamathi — 2025-06-30

Stainless-steel drinkware and food containers must withstand complex, plant-based beverages that may include dissolved salts. This study quantifies the corrosion behaviour of 304 stainless steel (commercially “Ever Silver”) in three media at 25 °C: de-ionised water, an aqueous extract of shade-dried curry leaves (CLE), and CLE containing 5 000 ppm NaCl. Potentiodynamic polarisation was carried out in a three-electrode cell (Ever Silver working electrode, SCE reference, Pt counter). Key parameters—including corrosion potential (E_corr), Tafel slopes, linear polarisation resistance (LPR), and corrosion current density (i_corr)—were extracted from the Tafel plots.

Relative to water (LPR ≈ 6.2 × 10⁴ Ω cm²; i_corr ≈ 0.86 µA cm⁻²), exposure to CLE alone reduced passivity markedly (LPR ≈ 4.0 × 10⁴ Ω cm²; i_corr ≈ 1.11 µA cm⁻²), indicating enhanced anodic dissolution driven by phytochemicals that adsorb on the surface. Incorporating 5 000 ppm NaCl partially restored passivity (LPR ≈ 4.4 × 10⁴ Ω cm²; i_corr ≈ 1.05 µA cm⁻²): chloride ions appear to promote a more compact, adsorbate-assisted film, offsetting some of the extract’s aggressiveness, though the alloy remains less resistant than in pure water.

The hierarchy of corrosion resistance derived from LPR and i_corr is: water > CLE + NaCl > CLE. Practically, 304 stainless vessels can safely accommodate curry-leaf infusions, and moderate chloride contents (typical of culinary use) mitigate rather than exacerbate deterioration compared with salt-free extracts. These findings support the suitability of “Ever Silver” containers for flavoured beverages while providing quantitative guidance for food-contact applications involving herbal ingredients.

Influence of Colgate mouthwash on corrosion resistance of orthodontic wire made of Ni-Ti alloy immersed in artificial saliva

Thangarajan Umamathi — 2025-06-30

This study investigates the corrosion resistance of orthodontic wire made of Ni-Ti alloy when immersed in artificial saliva, both in the absence and presence of Colgate mouthwash. The evaluation was carried out using potentiodynamic polarization techniques and electrochemical impedance spectroscopy (EIS). Polarization results show that the presence of Colgate mouthwash reduces the corrosion resistance of the Ni-Ti alloy, as indicated by a decrease in linear polarization resistance and an increase in corrosion current. EIS analysis confirms this trend, revealing reductions in charge transfer resistance, impedance magnitude, and phase angle, along with an increase in double-layer capacitance. These findings suggest that the aggressive components in Colgate mouthwash accelerate corrosion processes. Therefore, individuals wearing orthodontic appliances composed of Ni-Ti alloy are advised to avoid using Colgate mouthwash to prevent potential degradation of their dental wires.

An Examination of the Effect of Listerine Mouthwash on the Corrosion Characteristics of Orthodontic Wire Composed of Ss316l Alloy in Simulated Saliva by Electrochemical Impedance Spectra

Thangarajan Umamathi — 2025-06-30

Orthodontic appliances are frequently fabricated from corrosion-resistant alloys such as stainless steel. However, the complex oral environment, which includes exposure to various mouthwashes, can influence the electrochemical stability of these materials. This study investigates the corrosion behavior of orthodontic wire composed of SS 316L alloy in artificial saliva, both in the absence and presence of Listerine mouthwash, using Electrochemical Impedance Spectroscopy (EIS). The electrochemical parameters—including charge transfer resistance (Rt), impedance, phase angle, and double layer capacitance (Cdl)—were systematically analyzed. The results indicate that Listerine mouthwash enhances the corrosion resistance of SS 316L alloy, as evidenced by increased Rt, impedance, and phase angle, along with reduced Cdl. These findings support the safe use of Listerine mouthwash by individuals with orthodontic wires made of SS 316L alloy.

Fabrication and Characterization of Tungsten-Based Hard Materials by Novel Mechanical Alloying and Spark Plasma Sintering Methods

Muddassar Hussain — 2025-06-30

The influence of Ir and Y₂O₃ on the densification, microstructure, and wear characteristics of pure W-based alloy/composite was examined. The precursor powders, including W, Ir, and Y₂O₃, underwent mechanical alloying for 30 hours, resulting in two compositions: W–1.5 wt.% Ir and W–1.5 wt.% Ir–2 wt.% Y₂O₃. Subsequently, the prepared mixtures were subjected to spark plasma sintering at a temperature of 1650 °C for 5 minutes, with a simultaneous application of 50 MPa pressure. X-ray diffraction, scanning electron microscopy combined with energy dispersive spectroscopy, a micro-Vickers hardness tester, and two-dimensional optical profilometry were employed to analyze the synthesized powders, along with the consolidated and worn samples. Results indicated that the W–1.5 wt. % Ir-2 wt. % Y₂O₃ composite produced a highly dense sample characterized by the smallest grain size, superior micro-hardness, and enhanced wear resistance. The composite achieved values of up to 98% density, 3.6 µm grain size, 4.9 GPa HV₀.₅ hardness, and 2.5 × 10⁻⁵ mm³/Nm wear resistance, in contrast to pure tungsten, which exhibited 83.1% density, 6.6 µm grain size, 1.9 GPa HV₀.₅ hardness, and 6.2 × 10⁻⁵ mm³/Nm wear resistance. Thus, both Ir and Y₂O₃ have been recognized as effective additives that can enhance the consolidation and refinement of tungsten's microstructure under current mild processing conditions. This advancement not only makes these materials commercially viable but also enhances their performance in a range of demanding applications, such as fusion, military, tooling, electrode manufacturing, and coatings.