39 research outputs found
Studio elettrochimico e XPS su film nanometrici formatisi sulla superficie di acciai inossidabili in ambiente alcalino
No full textAn XPS investigation on glucose oxidase and Ni/Al Hydrotalcite interaction”
No full textIn this work, a Ni/Al hydrotalcite (HT) was used as glucose oxidase (GOx) immobilizer. Small-area and angle-resolved X-ray
photoelectron spectra were recorded on HTs electrosynthesised on Pt in the absence and in the presence of GOx, and compared
with those obtained for a Pt surface,modified with the electrosynthesized HT, on which a drop of GOx solution was deposited.
The simultaneous electrodeposition of HT+GOx resulted in a compact deposit, thicker than the XPS sampling depth (>10 nm),
that is not homogeneous in the lateral and indepth composition. The presence of GOx can be deduced comparing the N1s
spectra of HT and HT + GOx: in the latter, the N1s component at 400 eV binding energy (BE) is predominant whilst, depending
on the analyzed point, a small or no contribution from the component at 407.2 eV, due to nitrate, is revealed. Angle-resolved
XPS provides evidence on the indepth composition of anions, cations and GOx. The results highlight the crucial role played by
nickel in GOx immobilization. On the basis of the results, it can be suggested that enzyme activity is unevenly distributed and
is localized in small areas, where Ni concentration is higher
An XPS investigation on glucose oxidase and Ni/Al hydrotalcite interaction
No full textIn this work, a Ni/Al hydrotalcite (HT) was used as glucose oxidase (GOx) immobilizer. Small-area and angle-resolved X-ray photoelectron spectra were recorded on HTs electrosynthesized on Pt in the absence and in the presence of GOx, and compared with those obtained for a Pt surface, modified with the electrosynthesized HT, on which a drop of GOx solution was deposited. The simultaneous electrodeposition of HT + GOx resulted in a compact deposit, thicker than the XPS sampling depth (>10 nm), that is not homogeneous in the lateral and in-depth composition. The presence of GOx can be deduced comparing the N1s spectra of HT and HT + GOx: in the latter, the N1s component at 400 eV binding energy (BE) is predominant whilst, depending on the analyzed point, a small or no contribution from the component at 407.2 eV, due to nitrate, is revealed. Angle-resolved XPS provides evidence on the in-depth composition of anions, cations and GOx. The results highlight the crucial role played by nickel in GOx immobilization. On the basis of the results, it can be suggested that enzyme activity is unevenly distributed and is localized in small areas, where Ni concentration is higher
Nickel-free manganese bearing stainless steel in alkaline media - electrochemistry and surface chemistry
No full textThe use of austenitic nickel-containing stainless steels as concrete reinforcement offers excellent corrosion protection for concrete structures in harsh chloride bearing environments but is often limited due to the very high costs of these materials. Manganese bearing nickel-free stainless steels can be a cost-effective alternative for corrosion resistant reinforcements. Little, however, is known about the electrochemistry and even less on surface chemistry of these materials in alkaline media simulating concrete pore solutions. In this work a combined electrochemical (ocp = open circuit potential) and XPS (X-ray photoelectron spectroscopy) surface analytical investigation on the austenitic manganese bearing DIN 1.4456 (X8CrMnMoN18-18-2) stainless steel immersed into 0.1 M NaOH and more complex alkaline concrete pore solutions was performed. The results show that the passive film composition changes with immersion time, being progressively enriched in chromium oxy-hydroxide becoming similar to the conventional nickel-containing stainless steels. The composition of the metal interface beneath the passive film is strongly depleted in manganese and enriched in iron; chromium has nearly the nominal composition. The results are discussed regarding the film growth mechanism (ageing) of the new nickel-free stainless steel in alkaline solutions compared to traditional austenitic steels. Combining the results from pitting potential measurements with the composition of the passive film and the underlying metal interface, it can be concluded that the resistance against localized corrosion of the new nickel-free stainless steel relies on the strong chromium(III) and molybdenum (VI) oxy-hydroxide enrichment in the passive film
Prediction of mortality for congestive heart failure patients: results from different wards of an italian teaching hospital
No full textCongestive heart failure (CHF) constitutes an important public health problem in Italy, evidenced by the high number of hospital admissions each year. Significant inter-hospital as well as interward differences in mortality rates for CHF patients that have been described may, in part, be explained by the differences in the severity of the illness of admitted patients. The goal of this study was to predict 30-day severity-adjusted mortality risk in patients with CHF admitted to wards of a teaching hospital in Siena, Italy, in 1997. A 30-day mortality was determined by linking hospital discharge files with the Tuscany Mortality Registry database. The 3M all patient refined diagnosis related group (APR-DRG) software was used as a risk assessment method. The relationships between death and the following variables were studied by univariate analyses: APR-severity risk, APR-mortality risk, age, sex, length of stay and, discharge ward. Multivariate analysis was also performed to verify the associations between death and those parameters found to be significant by univariate analysis. Unadjusted mortality proportions ranged from 4.3 to 44.0%. Logistic regression analysis demonstrated that APR-mortality risk, length of stay, and discharge ward were significantly and independently associated with 30-day mortality risk in patients with CHF. In summary, 30-day mortality risk varied significantly according to the ward of discharge in an Italian teaching hospital, even after adjustment for severity of illness
The solvation Structure of Ca (II), Pb (II), Cd (II) in dilute aqueous solution: A first principles study
No full textWhen an ion is inserted into a network of water molecules, the structure of the hydrogen bonds changes. Water is a polar molecule. It tends to orientate so to face its opposite charge to the ion. The group of water molecules bound to the ion is called “first hydration shell”. The orientation of the molecules in the hydration shell results in a net charge on the outside of this shell, a charge of the same sign as that of the ion in the center. The charge on the outside of the hydration shell tends to orient water molecules in the vicinity, leading to a second hydration shell.
The purpose of this work is to conduct a systematic study of ion solvation, comparing positive ions of different size, namely the divalent Ca2+, Pb2+ and Cd2+. In particular, the analysis focuses on the characterization of the structural reorganization of the solvent due to the presence of the ion. To this aim, we use first principles calculations within the framework of the Density Functional Theory (DFT), i.e. an investigation at an electronic and atomistic scale, accounting for electronic polarization as well as geometrical conformations. A metal ion in aqueous solution (aqua-ion) is a cation, dissolved in water, of chemical formula [M(H2O)n]z+. The n water molecules directly bonded to the metal ion are meant to belong to the first coordination sphere.
The sistems considered are small clusters, from one water molecule to the cluster containing a number of molecules equal to the coordination number. This stepwise analysis allows for an accurate detection of the structural and energy changes due to each additional water in the first hydration shell. There are many experimental and theoretical reports on the hydration of ions. More specifically, calcium raises great interest due to its role in many biological fuctions, several industrial applications (paper, rubber, plastics, paint production, and the wide occurrence in works of art)
Stainless steel reinforcing bars – reason for their high pitting corrosion resistance
No full textIn harsh chloride bearing environments stainless steel reinforcing bars offer excellent corrosion resistance and very long service life for concrete structures, but the high costs limit a more widespread use. Manganese bearing nickel-free stainless steels could be a cost-effective alternative. Whereas the corrosion behavior of stainless steels in alkaline solutions, mortar and concrete is quite well established, only few information on the reasons for the high pitting resistance are available. This work reports the results of pitting potential measurements in solutions simulating alkaline and carbonated concrete on black steel, stainless steel DIN 1.4301, duplex steel DIN 1.4462 and nickel-free stainless steel DIN 1.4456. Duplex and nickel-free stainless steels are fully resistant even in 5 M NaCl solutions with pH 13 or higher, the lower grade DIN 1.4301 shows a wide scatter between fully resistant and pitting potentials as low as +0.2 V SCE. In carbonated solutions with pH 9 the nickel-free DIN 1.4456 shows pitting corrosion at chloride concentrations ≥ 3 M. This ranking of the pitting resistance can be rationalized based on XPS surface analysis results: both the increase of the Cr(III)oxy-hydroxide and Mo(VI) contents in the passive film and a marked nickel enrichment beneath the film improve the pitting resistance. The duplex DIN 1.4464 shows the highest pitting resistance, which can be attributed to the very high Cr(III)oxy-hydroxide, to a medium Mo(VI) content in the film and to a nickel enrichment beneath the film. Upon time, the protective properties of the surface film improve. This beneficial effect of ageing (transformation of the passive film to a less Fe2+ containing, more hydrated film) will lead to higher pitting potentials. It can be concluded that short-term solution experiments give conservative results in terms of resistance to chloride-induced corrosion in reinforced concrete structures
Crescita e caratterizzazione del film passivo su acciai inossidabili in NaOH 0.1M mediante misure elettrochimiche e XPS
No full textAnalisi di superficie e studio elettrochimico di acciai inossidabili in soluzioni alcaline
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