Alessio Giorgio Settimi

In this work, the possibility of incorporating TiO₂ titanium dioxide particles derived from the recycling process of photovoltaic panels into PEO coatings was investigated. These particles constitute the main filler of the polymer constituting the rear part of the panels, and are characterized by possessing photocatalytic properties. The particles were added in different quantities to the electrolyte (a basic solution containing sodium silicate). The incorporation into the PEO coating produced on an aluminum alloy 1050, and the possibility of conferring photocatalytic properties to the surface of the samples were studied. The different samples were first characterized by optical microscope analysis, SEM and XRD and from the point of view of corrosion resistance by means of potentiodynamic tests. The photocatalytic properties of the samples were evaluated by monitoring the degradation of aqueous solutions of methylene blue exposed to a UV lamp. The particles have been successfully incorporated into the coating, and their presence does not alter the corrosion properties, which are improved compared to the uncoated sample. The particles, initially composed of a mixture of rutile and anatase, are instead transformed into rutile after incorporation due to the locally very high temperatures that can occur during the PEO process. In the samples obtained with higher quantities of titanium dioxide particles (60 and 80 g/L), a significant photocatalytic effect is observed with a significant reduction of methylene blue.

In the present work, Plasma Electrolytic Oxidation (PEO) coatings were produced on zinc-aluminized carbon steels (Galvalume commercial treatment). In addition, copper particles of various sizes were introduced into the coating in order to produce samples with antifouling properties. The particles were successfully embedded into the coating. A higher number of embedded particles was observed when these are in sub-micrometric size and obtained in pulsed current. The presence of particles produces significant antifouling properties on the sample’s surfaces during the first 20 days of immersion. The presence of the particles reduces the corrosion resistance in comparison to the samples PEO coated without the particles; however, the corrosion resistance remain higher than the one of the untreated sample.

Non-thermal plasma technology is increasingly being applied in the plant biology field. Despite the variety of beneficial effects of plasma-activated water (PAW) on plants, information about the mechanisms of PAW sensing by plants is still limited. In this study, in order to link PAW perception to the positive downstream responses of plants, transgenic Arabidopsis thaliana seedlings expressing the Ca²⁺-sensitive photoprotein aequorin in the cytosol were challenged with water activated by low-power non-thermal plasma generated by a dielectric barrier discharge (DBD) source. PAW sensing by plants resulted in the occurrence of cytosolic Ca²⁺ signals, whose kinetic parameters were found to strictly depend on the operational conditions of the plasma device and thus on the corresponding mixture of chemical species contained in the PAW. In particular, we highlighted the effect on the intracellular Ca²⁺ signals of low doses of DBD-PAW chemicals and also presented the effects of consecutive plant treatments. The results were discussed in terms of the possibility of using PAW-triggered Ca²⁺ signatures as benchmarks to accurately modulate the chemical composition of PAW in order to induce environmental stress resilience in plants, thus paving the way for further applications in agriculture.

Increasing evidence indicates that water activated by plasma discharge, termed as plasma-activated water (PAW), can promote plant growth and enhance plant defence responses. Nevertheless, the signalling pathways activated in plants in response to PAW are still largely unknown. In this work, we analysed the potential involvement of calcium as an intracellular messenger in the transduction of PAW by plants. To this aim, Arabidopsis thaliana (Arabidopsis) seedlings stably expressing the bioluminescent Ca²⁺ reporter aequorin in the cytosol were challenged with PAW generated by a plasma torch. Ca²⁺ measurement assays demonstrated the induction by PAW of rapid and sustained cytosolic Ca²⁺ elevations in Arabidopsis seedlings. The dynamics of the recorded Ca²⁺ signals were found to depend upon different parameters, such as the operational conditions of the torch, PAW storage, and dilution. The separate administration of nitrate, nitrite, and hydrogen peroxide at the same doses as those measured in the PAW did not trigger any detectable Ca²⁺ changes, suggesting that the unique mixture of different reactive chemical species contained in the PAW is responsible for the specific Ca²⁺ signatures. Unveiling the signalling mechanisms underlying plant perception of PAW may allow to finely tune its generation for applications in agriculture, with potential advantages in the perspective of a more sustainable agriculture.

New generations of green concretes are often consuming large amounts of industrial waste, as recycled or manufactured aggregates and alternative binders substituting ordinary Portland cement. Among the recycled materials that may be used in civil engineering works, construction and demolition waste (C&DW), fly ashes, slags and municipal solid waste incinerator bottom ashes (MSWI BA) are those most diffused, but at the same, they suffer due to a large variability of their properties. However, the market increasingly asks for new materials capable of adding some specific features to construction materials, and one of the most interesting is the pozzolanic activity. Hence, this work deals with an experimental study aimed at assessing the technical feasibility of using an industrial waste comprised largely of MSWI BA, with small quantities of C&DW and electric arc furnace slag (EAFS), in green cement-based mixtures (cement paste and mortars). The aim of the work is to achieve the goal of upcycling such waste and avoiding its disposal and landfilling. Particularly, the test methods for assessing the pozzolanic activity of this waste are discussed, analyzing the efficacy of indirect methods such as the strength activity index (SAI), the conductivity test and the efficiency factor (k), together with a direct method based on lime consumption.

A process for producing a black oxide coating on aluminum alloy was investigated in the present work. The blackening process is widely used in industrial applications, but it was not deeply studied for aluminum alloys. The aim of this work is to study the black coating obtained on AA6060 surfaces employing two different solutions, both containing potassium permanganate, copper nitrate and nitric acid. The first solution carried out the coloring treatment at 50 °C, whereas the second one was done at room temperature. Different immersion times were investigated. The morphology of the coating was investigated by means of optical and electron microscopy to evaluate the color of the layer and the presence of defects, porosities, and cracks. X-ray diffraction analysis was performed to evaluate the protective layer composition. The corrosion properties were studied with potentiodynamic polarization tests and electrochemical impedance spectroscopy tests. The results showed that the blackening process performed at room temperature, besides the clear advantages in term of costs and safety, obtained more uniform coatings with increased corrosion performance in comparison with the ones obtained at higher temperatures.

A novel high silicon austempered (AHS) steel has been studied in this work. The effect of different austenitizing temperatures, in full austenitic and biphasic regime, on the final microstructure was investigated. Specimens were austenitized at 780 °C, 830 °C, 850 °C and 900 °C for 30 min and held isothermally at 350 °C for 30 min. A second heat treatment route was performed which consisted of austenitizing at 900 °C for 30 min and austempering at 300 °C, 350 °C and 400 °C for 30 min. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) have been used to evaluate the microstructural evolution. These techniques revealed that the microstructures were composed of carbide-free bainite, ferrite, martensite and retained austenite (RA) in different volume fractions (Vγ). An aqueous borate buffer solution with 0.3 M H₃BO₃ and 0.075 M Na₂B₄O₇∂10H₂O (pH = 8.4) was used for corrosion tests in order to evaluate the influence of the different volume fractions of retained austenite on the corrosion properties of the specimens. The results showed that when increasing the austenitization temperatures, the volume fractions of retained austenite reached a maximum value at 850 °C, and decrease at higher temperatures. The corrosion properties were investigated after 30 min and 24 h immersion by means of potentiodynamic polarization (after 30 min) and electrochemical impedance spectroscopy (after both 30 min and 24 h) tests. The corrosion resistance of the samples increased with increases in the volume fraction of retained austenite due to lower amounts of residual stresses.