1,721,056 research outputs found
The anodic oxidation of titanium and its alloys
No full textTitanium is naturally covered with a nanometric oxide film (TiO2) that accounts for most of its industrial applications, where corrosion resistance is the key property. In functional applications, like biomedical devices, photocatalytic reactors, water splitting, and more, focus is set on the TiO2 film characteristics. Anodic oxidation allows obtaining a variety of oxide features-amorphous or crystalline, nanometers micrometers thick, doped with other elements or ions, with surface texturing at the micro or nanoscale. Controlling TiO2 surface properties can not only drastically improve the material efficiency in existing applications but also broaden its fields of use; therefore, an increasing control on production methods is necessary. This article is intended to provide an overview of the anodic oxidation techniques with specific reference to titanium anodizing, and to describe the mechanisms of widely diffused anodic processes, focusing on the resulting oxide features
Towards a better preservation of current and future outdoor architectural heritage; maximum suppression of discolouration in anodized and non-anodized titanium sheets
No full textOutdoor atmospheric corrosion has been exerting continuous deteriorating effects on the cultural heritage, both in the matter of structural resistance and aesthetic quality. To this point, titanium as a modern metal with excellent mechano-physical properties, especially high strength, light weight, superior corrosion resistance has already gained many attentions in different engineering and design fields. In addition to its high atmospheric corrosion resistance, titanium sheets ability to provide a wide range of tasteful colours with high aesthetic quality have paved their way towards the field of modern art and architecture, to the point that its use for monuments and especially as faÁade material for exterior cladding design has been continuously increasing. On the other hand, the undesired growth of this titanium dioxide layer due to long-term exposure in harsh atmospheric conditions leads to the appearance of interference colours and spoils the building from the viewpoint of aesthetic appearance. In particular, acidity of the rainwater falls and its reaction with the impurities present on the surface of titanium sheets to eventually alter the thickness of the oxide film is the main cause of discolouration. This review provides a conceptual framework on different manufacturing issues which have to be precisely taken into consideration in order to minimize the presence of impurities on both anodized and non-anodized end-products, as well as principles of anodizing process to increase the thickness of the oxide layer in order to eventually limit the access of acid rains to the remaining impurities
Evaluation of the Environmental and Economic Impact Deriving from the Adoption of a Reuse Strategy for Disposable FFP2
No full textThe COVID-19 pandemic has exposed the vulnerability of emergency response systems to personal protective equipment shortages, particularly FFP2 masks. In that context the Milan Fire and Rescue Service has developed a novel method for regenerating and reusing disposable FFP2 masks, evaluating its safety and effectiveness through comprehensive biological, mechanical, and stress tests, guaranteeing this way up to 10 safe reuses per mask. The method not only ensures personnel safety and uninterrupted emergency service but also yields significant environmental and economic benefits, minimizing the environmental footprint associated with masks life cycle and leading to substantial financial savings to the entities willing to adopt it, through reduced procurement and disposal costs. Benefits linked to the regeneration method are validated in this work by three distinct case studies, conducted within the Milan province and encompassing three distinct entities. This study provides evidence that through regeneration it is possible to achieve environmental and economic impact reductions of up to 90% across various operational settings and presents a groundbreaking and sustainable approach to FFP2 mask reuse, offering a viable solution to address potential shortages during future pandemics
A green vanadium-based formulation for the conversion of steel
No full textThe electroless deposition of a novel vanadium-based conversion coating (VCC) on carbon steel was investigated varying parameters as vanadium salt concentration, immersion time, bath pH and temperature. The novelty resides on the deposition of a protective layer from a V4+ solution comprising green reducing agents like ascorbic and citric acids. The VCC was found to be amorphous, composed by closely packed particles rich in vanadium oxides/hydroxides. Corrosion resistance was evaluated by linear polarization resistance, Tafel extrapolation and electrochemical impedance spectroscopy. Such conversion coating provided an optimum corrosion performance for steel substrates immersed in sulphates and chlorides rich solutions. An optimum was achieved with a 0.1 M KVO3 solution held at 45 & DEG;C, at pH = 3 and a deposition time of 10 min. Higher values of the latter parameters did not provide any further improvements: the formation of cracks during the dehydration process compromised the coating integrity
Properties and photocatalytic applications of black TiO2 produced by thermal or plasma hydrogenation
Full text linkMulti-angle color prediction of glossy anodized titanium samples through the determination of the oxide layer structural parameters
No full textThe purpose of the present study is to predict the whole chromatic path traveled by the colors of glossy anodized titanium samples in every specular geometry. It is based on measurements of the samples’ reflectance spectra in a limited number of specular geometries, which allow us to obtain the oxide layer structural parameters (thickness, refractive index), which are then put into an optical model to predict the samples’ reflectance spectra in every specular geometry. A good color prediction performance is obtained, with an average 1E94 color distance over all samples and geometries of 1.9. The oxide layer structural parameters are also in good agreement with refractive index values extracted from the literature and thicknesses measured on electron microscopy images of sample sections
Corrosion resistance enhancement of chemically oxidized titanium through NaOH and H2O2 exposure
Full text linkTitanium owes its astounding corrosion resistance to a thin, compact oxide layer that is formed spontaneously when the metal is exposed to the environment. However, even titanium can be subject to corrosion in very aggressive environments. To enhance its corrosion resistance, it is possible to exploit the same mechanism that leads to the formation of the protective oxide layer and force its growth with an external contribution. Oxidation can be easily stimulated with the use of an electrochemical cell. However, when part geometry or dimensions do not allow the immersion in an anodizing bath, chemical oxidation can be used. This study compares corrosion resistance enhancement after NaOH and H2O2 treatment. Treatment duration and temperature, solution concentration, and quantity are optimized to achieve the best corrosion resistance with the least time and chemicals consumption, by maintaining the process easy to perform and safe for the operator
Pitting corrosion on anodized titanium: Effect of halides
Full text linkTitanium corrosion resistance is high in the majority of environments. However, titanium is susceptible to different forms of corrosion, if exposed to high concentrated halides containing solutions. To face this corrosion problem, expensive titanium alloys are used. An alternative method, consisting of electrochemical anodizing treatment, which promote the formation of a compact titanium oxide on the surface, could be applied to increase titanium corrosion resistance. In this work, titanium samples anodized at 20V in H2SO4 0.5M have been tested in sodium fluorides, chlorides, bromides, and iodides at 0.5 and 2.0M in order to define halides aggressiveness
Big milestones in the study of steel corrosion in concrete
No full textRebar corrosion in concrete has been neglected for a long time in the scientific and technical literature, as reinforced concrete was considered an "eternal" material. Only during the 60s, and more during the 70s and the 80s, several research groups and many corrosion schools gave important contributions. An important impact was also achieved by Italian researchers thanks to the Universities of Roma, Napoli, Ancona, Ferrara, Bergamo, and Politecnico di Milano, where professor Pietro Pedeferri and his school contributed to the study of stainless steel reinforcement, corrosion inhibitors, service life modeling, cathodic protection and cathodic prevention, the latter proposed by Pedeferri in the early 90s. The paper is dedicated to the memory of Pietro Pedeferri (1938-2008) and Luca Bertolini (1966-2017)
Unipolar plasma electrolytic oxidation: Waveform optimisation for corrosion resistance of commercially pure titanium
No full textThis study deals with the anodisation of titanium grade 2 in 0.5-M sulphuric acid using a pulsed signal in a unipolar regime. The electrical parameters investigated are voltage, frequency and duty cycle. The use of duty cycles with a high percentage of anodic polarisation (90%), combined with high frequencies (1000 Hz) and the higher voltage tested (220 V), favoured the establishment of a plasma regime involving strong dielectric discharges, allowing the growth of thicker oxides but with rough architecture. The corrosion resistance of the formed film has been characterised by potentiodynamic tests in 0.5-M NaBr for localised corrosion resistance and by immersion tests in 10% v/v sulphuric acid solution for a uniform corrosion assessment. Current–time curves, visual observations and electron microscope analysis (scanning electron microscopy, energy-dispersive X-ray spectroscopy) were the tools selected to provide a correlation between technological parameters and oxide growth mechanism. For localised and uniform corrosion, anodisation at 220 V with a high level of anodic polarisation (90%) and frequency (1000 Hz) was verified to be particularly advantageous
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