Stainless steels: passive film composition, pitting potentials and critical chloride content in concrete

Stainless steel reinforcing bars show excellent corrosion resistance in concrete structures exposed to harsh environments. Only little information on the surface chemistry of these materials in alkaline media is available. This work reports XPS surface analytical results (thickness, composition of the passive film and of the interface beneath the film) obtained on black steel, FeCr alloys, DIN 1.4301, DIN 1.4462 and the nickel-free DIN 1.4456 after exposure to alkaline solutions simulating concrete. The pitting potentials of the steels could be related to the Cr(III)oxy-hydroxide and Mo(VI) content in the passive film. Ccrit, the critical chloride content for corrosion initiation in concrete, necessary for life-time predictions can be determined only with time consuming tests, especially for high-alloyed stainless steels. This work reports a correlation between Ccrit in concrete (made with CEM II A/LL and CEM I) and the pitting potential for carbon steel, Fe12%Cr alloy, DIN 1.4301 and DIN 1.4571 stainless steels. This could allow for the first time a quantitative estimation of Ccrit for stainless steels in concrete based on short-term solution tests

Enargite by XPS

X-ray photoelectron spectroscopy was used for characterizing the enargite surface. Freshly cleaved samples were analyzed at liquid nitrogen temperature. Enargite is a copper arsenic sulfide of formula Cu3AsS4; it is used as a minor ore of copper. Enargite is a potential source of arsenic and may create environmental problems through the release of toxic elements upon oxidatio

Breathing New Life into Historical Instruments. How to Monitor Corrosion

‘To play or to display’ is the dilemma that museums have to face, given the increasing trend towards historically informed performance. Brass instruments can suffer corrosion both during and after playing due to the high humidity inside them. To forestall or at least reduce corrosion, drying with a fan has been chosen as a preventive measure. The state of corrosion inside the tuning slides of the instruments was determined with a specially developed electrochemical sensor. The results of the project show that drying with a fan indeed reduces ongoing corrosion, when compared to a group of instruments played without preventive measures that showed an increasing corrosion rate over time

Nanostructured spinel cobalt ferrites: Fe and Co chemical state, cation distribution and size effects by X-ray photoelectron spectroscopy

Nanostructured spinel cobalt ferrite samples having crystallite size ranging between 5.6 and 14.1 nm were characterized by X-ray photoelectron spectroscopy and X-ray induced Auger electron spectroscopy in order to determine the chemical state of the elements, the iron/cobalt ratio and the cation distribution within tetrahedral and octahedral sites. The presence of size-dependent trends in the binding energy of the main photoelectron peaks and in the kinetic energy of the X-ray induced O KLL signal was also investigated. The results showed that iron is present as FeIII and cobalt is present as CoII. The iron/cobalt ratio determined by XPS ranges between 1.8 and 1.9 and it is in very good agreement, within experimental uncertainty, with the expected 2 : 1 ratio. The percentage of Fe in octahedral sites ranges between 62% and 64% for all samples. The kinetic energy of the O KLL signals increases with crystallite size. These results are explained in terms of changes in the ionicity of the metal–oxygen bonds. The results of this investigation highlight how the XPS technique represents a powerful tool to investigate the composition, the chemical state and inversion degree of cobalt spinel ferrites, contributing to the comprehension of their properties

Influence of Water on Tribolayer Growth When Lubricating Steel with a Fluorinated Phosphonium Dicyanamide Ionic Liquid

This work aims to elucidate the role of environmental humidity on the tribological behavior of steel surfaces lubricated with an ionic liquid comprised of a fluorinated phosphonium cation—tributyl-3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-octyl-phosphonium—and a dicyanamide anion (i.e. N(CN)2−). Ball-on-disk tribotests were carried out at room temperature and at various levels of relative humidity (RH). Water was found to be required to promote the formation of a tribofilm over the contact area. The reaction layer exhibited a patchy morphology, which resembles that observed formed with conventional antiwear additives such as ZnDTP. A surface-chemical analysis of the tribofilm indicated that the tribofilm is composed of fluorides, oxides, and phosphates, pointing to a stress-induced degradation of the ions and corrosion of the sliding counterparts, which is enabled by the presence of water at the sliding interface

Selecting molecular or surface centers in carbon dots-silica hybrids to tune the optical emission: A photo-physics study down to the atomistic level

In this work, we unveil the fluorescence features of citric acid and urea-based Carbon Dots (CDs) through a photo-physical characterization of nanoparticles synthesized, under solvent-free and open-air condi-tions, within silica-ordered mesoporous silica, as a potential host for solid-state emitting hybrids. Compared to CDs synthesized without silica matrices and dispersed in water, silica-CD hybrids display a broader emission in the green range whose contribution can be increased by UV and blue laser irradi-ation. The analysis of hybrids synthesized within different silica (MCM-48 and SBA-15) calls for an active role of the matrix in directing the synthesis toward the formation of CDs with a larger content of graphitic N and imidic groups at the expense of N-pyridinic molecules. As a result, CDs tuned in size and with a larger green emission are obtained in the hybrids and are retained once extracted from the silica matrix and dispersed in water. The kinetics of the photo-physics under UV and blue irradiation of hybrid samples show a photo-assisted formation process leading to a further increase of the relative contribution of the green emission, not observed in the water-dispersed reference samples, suggesting that the porous matrix is involved also in the photo-activated process. Finally, we carried out DFT and TD-DFT calcula-tions on the interaction of silica with selected models of CD emitting centers, like surface functional groups (OH and COOH), dopants (graphitic N), and citric acid-based molecules. The combined experimen-tal and theoretical results clearly indicate the presence of molecular species and surface centers both emitting in the blue and green spectral range, whose relative contribution is tuned by the interaction with the surrounding media

Indirect daylight oxidative degradation of polyethylene microplastics by a bio-waste modified TiO2-based material

Microplastics are recognized as an emerging critical issue for the environment. Here an innovative chemical approach for the treatment of microplastics is proposed, based on an oxidative process that does not require any direct energy source (irradiation or heat). Linear low-density polyethylene (LLDPE) was selected as target commodity polymer, due to its widespread use, chemical inertness and inefficient recycling. This route is based on a hybrid material coupling titanium oxide with a bio-waste, rosin, mainly constituted by abietic acid, through a simple sol-gel synthesis procedure. The ligand-to-metal charge transfer complexes formed between rosin and Ti4+ allow the generation of reactive oxygen species without UV irradiation for its activation. In agreement with theorical calculations, superoxide radical ions are stabilized at ambient conditions on the surface of the hybrid TiO2. Consequently, an impressive degradation of LLDPE is observed after 1 month exposure in a batch configuration under indirect daylight, as evidenced by the products revealed by gas chromatography-mass spectrometry analysis and by chemical and structural modifications of the polymer surface. In a context of waste exploitation, this innovative and sustainable approach represents a promising cost-effective strategy for the oxidative degradation of microplastics, without producing any toxic by-products

Modelling the Fenton reaction of amphibole asbestos

In this work a sample of UICC crocidolite and a sample of fibrous tremolite were leached up to 1 week both in a simplified Gamble’s solution at acidic pH and in a phosphate buffered medium at neutral pH, in presence of H2O2. Surface chemical modifications were monitored by XPS spectroscopy. Subsequently, the generation of HO• radicals following reaction of both pristine and leached fibres with H2O2 (Fenton reaction) was investigated by spin trapping/EPR spectroscopy, with the aim of better clarifying the relationships between possible surface alteration occurring in vivo and chemical reactivity of amphibole asbestos. Moreover, the generation of HO• radicals was monitored on thermally treated fibres after leaching in phosphate buffered medium at neutral pH and in presence of H2O2 to investigate how chemical reactivity may be modulated by Fe oxidation state. Results showed that, for both amphibole asbestos, the surface alteration following incubation in the modified Gamble’s solution does not alter HO• radical generation. Interestingly, leaching in phosphate buffered solution in presence of H2O2 induced a progressive increase in HO• release for crocidolite fibres, whereas a strong reduction was observed for asbestos tremolite. This behaviour is likely due to the quicker alteration of the crocidolite surface due to the interaction with H2O2, as indicated by XPS analysis. In particular, the oxidation induced by H2O2 promotes the dissolution of the first atomic layer of the crocidolite structure and the following occurrence on its surface of new reactive Fe centres, particularly under the form of Fe(II), of which the bulk is richer than the oxidized surface. Accordingly, the heated samples showed a reduced, but not suppressed by thermal oxidation, chemical reactivity, with no significant evolution following incubation in phosphate buffered medium at neutral pH and in presence of H2O2

From field analysis to nanostructural investigation. A multidisciplinary approach to describe natural occurrence of asbestos in view of hazard assessment

The environmental impact of natural occurrences of asbestos (NOA) and asbestos-like minerals is a growing concern for environmental protection agencies. The lack of shared sampling and analytical procedures hinders effectively addressing this issue. To investigate the hazard posed by NOA, a multidisciplinary approach that encompasses geology, mineralogy, chemistry, and toxicology is proposed and demonstrated here, on a natural occurrence of antigorite from a site in Varenna Valley, Italy. Antigorite is, together with chrysotile asbestos, one of the serpentine polymorphs and its toxicological profile is still under debate. We described field and petrographic analyses required to sample a vein and to evaluate the NOA-hazard. A combination of standardized mechanical stress and automated morphometrical analyses on milled samples allowed to quantify the asbestoslike morphology. The low congruent solubility in acidic simulated body fluid, together with the toxicity-relevant surface reactivity due to iron speciation, signalled a bio-activity similar or even greater to that of chrysotile. Structural information on the genetic mechanism of antigorite asbestos-like fibres in nature were provided. Overall, the NOA site was reported to contain veins of asbestos-like antigorite and should be regarded as source of potentially toxic fibres during hazard assessment procedure