Corrosione atmosferica in area urbana-costiera di un acciaio Cor-Ten: studio del rilascio in ambiente dei metalli di lega

Cor-Ten is a particular kind of steel, belonging to low-alloyed steel; thanks to his aesthetic features and resistance to atmospheric corrosion, this material is largely used in architectural, artistic and infrastructural applications. After environmental exposure, Cor-Ten steel exhibits the characteristic ability to self-protect from corrosion, by the development of a stable and adherent protective layer. However, some environmental factors can influence the formation and stability of the patina. In particular, exposure of Cor-Ten to polluted atmosphere (NOx, SOx, O3) or coastal areas (marine spray) may cause problems to the protective layer and, as a consequence, a release of alloying metals, which can accumulate near the structures. Some of these metals, such as Cr and Ni, could be very dangerous for soils and water because of their large toxicity. The aim of this work was to study the corrosion behavior of Cor-Ten exposed to an urban-coastal site (Rimini, Italy). Three different kinds of commercial surface finish (bare and pre-patinated, with or without a beeswax covering) were examined, both in sheltered and unsheltered exposure conditions. Wet deposition brushing the specimens surface (leaching solutions) are monthly collected and analyzed to evaluate the extent of metal release and the form in which they leave the surface, for example, as water-soluble compounds or non-adherent corrosion products. Five alloying metals (Fe, Cu, Cr, Mn and Ni) and nine ions (Cl-, NO3-, NO2-, SO42-, Na+, Ca2+, K+, Mg2+, NH4+) are determined through Atomic Absorption Spectroscopy and Ion Chromatography, respectively. Furthermore, the evolution and the behaviour of the patina are periodically followed by surface investigations (SEM-EDS and Raman Spectroscopy). After two years of exposure, the results show that Bare Cor-Ten, cheaper than the other analyzed specimens, even though undergoes the greater mass variation, his metal release is comparable to the release of the pre-patinated samples. The behavior of pre-patinated steel, with or without beeswax covering, do not show particular difference. This exposure environment doesn’t allow a completely stabilization of the patina; nevertheless an estimate of metal release after 10 years of exposure points out that the environmental impact of Cor-Ten is very low: for example, the release of chromium in the soluble fraction is less than 10 mg if we consider an exposed wall of 10 m2.

Studio retrospettico sul ruolo della strumentazione nei fallimenti meccanici a seguito di Trattamento Chirurgico nelle Scoliosi dell'adulto

The spinal column performs important functions in the body, including the support of the entire weight of the human body, the ability to orientate the head in space, bending, flexing and rotating the body. Diseases affecting the spine are manifold: the most frequent is scoliosis, which often affects the female population. It is often treated surgically with a very high percentage of failures. The aim of the thesis is to study the role of instrumentation in mechanical failures encountered 12 months after surgery in the treatment of scoliosis. For the purposes of the study, we analyzed specific biomechanical parameters. The pelvic angles determine the position of the pelvis, while the imbalance parameters the structure of the body. We infer other parameters by analyzing the characteristics of the implanted instrumentation. Initially, the anatomy is described of the spine and vertebrae, the equipment used and the possible failures that may occur after surgery. Subsequently, the materials and methods used for the analysis of the above-mentioned parameters for the 61 patients are reported. All data are obtained by the observation of pre and post-operative x-rays with a special program, by reading reports from operators and by medical records. In the fourth chapter, we report the results: the overall failure rate is 60.9%; the types of failures that occurred are rupture of bars and rupture of bars simultaneously to PJK. The most influential parameters on results of the progress of the surgery are the type of material used and the BMI. It is estimated a high percentage of failures in patients treated with implants of cobalt chromium alloys (90.0%). According to the results obtained, it is possible to understand the aspects that in the future should be studied, in order to find a solution to the most frequent surgical failures.

Distribution of metals in several vineyards of North Italy: from soil to wine

Nowadays we live in densely populated regions and this leads to many environmental issues. Among all pollutants that human activities originate, metals are relevant because they can be potentially toxic for most of living beings. We studied the fate of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in a vineyard environment analysing samples of plant, wine and soil. Sites were chosen considering the type of wine produced, the type of cultivation (both organic and conventional agriculture) and the geographic location. We took vineyards that cultivate the same grape variety, the Trebbiano). We investigated 5 vineyards located in the Ravenna district (Italy): two on the Lamone Valley slopes, one in the area of river-bank deposits near Ravenna city, then a farm near Lugo and one near Bagnacavallo in interfluve regions. We carried out a very detailed characterization of soils in the sites, including the analysis of: pH, electric conductivity, texture, total carbonate and extimated content of dolomite, active carbonate, iron from ammonium oxalate, Iron Deficiency Chlorosis Index (IDCI), total nitrogen and organic carbon, available phosphorous, available potassium and Cation Exchange Capacity (CEC). Then we made the analysis of the bulk chemical composition and a DTPA extraction to determine the available fraction of elements in soils. All the sites have proper ground to cultivate, with already a good amount of nutrients, such as not needing strong fertilisations, but a vineyard on hills suffers from iron deficiency chlorosis due to the high level of active carbonate. We found some soils with much silica and little calcium oxide that confirm the marly sandstone substratum, while other soils have more calcium oxide and more aluminium oxide that confirm the argillaceous marlstone substratum. We found some critical situations, such as high concentrations of Chromium, especially in the farm near Lugo, and we noticed differences between organic vineyards and conventional ones: the conventional ones have a higher enrichment in soils of some metals (Copper and Zinc). Each metal accumulates differently in every single part of grapevines. We found differences between hill plants and lowland ones: behaviors of plants in metal accumulations seems to have patterns. Metals are more abundant in barks, then in leaves or sometimes in roots. Plants seem trying to remove excesses of metal storing them in bark. Two wines have excess of acetic acid and one conventional farm produces wine with content of Zinc over the Italian law limit. We already found evidence of high values relating them with uncontaminated environments, but more investigations are suggested to link those values to their anthropogenic supplies.