Inorganic–organic hybrid materials with zirconium oxoclusters as protective coatings on aluminium alloys

Inorganic–organic hybrid materials are attracting a strong scientific interest mainly for their outstanding inherent mechanical and thermal properties, which can be traced back to the intimate coupling of both inorganic and organic components. By carefully choosing the experimental parameters used for their synthesis, chemically and thermally stable acrylate-based hybrid material embedding the zirconium oxocluster Zr₄O₄(OMc)₁₂, where OMcCH₂C(CH₃)C(O)O, can be deposited as UV-cured films on aluminium alloys.

In particular, the molar ratios between the oxocluster and the monomer, the polymerisation time, the amount of photo-initiator and the deposition conditions, by using an home-made spray-coating equipment, were optimised in order to obtain the best performing layers in terms of transparency and hardness to coat aluminium alloy (AA1050, AA6060 and AA2024) sheets. Furthermore, it was also evaluated whether the hybrid coatings behave as barrier to corrosion.

Several coated samples were prepared and characterised. Environmental scanning electronic microscopy (ESEM) and scratch test were used to investigate the morphology of the films and to evaluate their scratch resistance, respectively. Electrochemical impedance spectroscopy (EIS) was performed in order to evaluate if the coatings actually protect the metallic substrate from corrosion.

In order to measure shear storage modulus (G′) and loss modulus (G″) of the materials used for coatings, bulk samples were also obtained by UV-curing of the precursors solution. Dynamical mechanical thermal analysis (DMTA) was performed in shear mode on cured disks of both the hybrid materials and pristine polymer for comparison. The values of T_g were read off as the temperatures of peak of loss modulus. The length and mass of all the samples were measured before and after the DMTA analysis, so that the shrinkage of the materials in that temperature range was exactly evaluated.     

Effect of powder painting procedures on the filiform corrosion of aluminium profiles

In this work, the filiform corrosion behaviour of powder painted aluminium profiles was studied, and the coating barrier properties together with adhesion to the substrate were analysed. Samples coated with a traditional painting procedure (one powder layer application followed by curing), and other samples coated using a special cycle to obtain wood grain effect were compared using accelerated filiform corrosion tests. Moreover, in order to better understand the degradation mechanisms of painted metal substrates, thermal stresses were applied to accelerate the natural weathering. The effects of the thermal aging were analysed by electrochemical impedance spectroscopy.     

Modelling group processes and effort estimation in project management using the Choquet integral: An MCDM approach

We investigate the group processes involved in effort estimation in the context of project management. The groups considered are formed by “experts” (people with specific technical competence) and “non-experts” (people with less specific technical competence, usually experts in related fields), because the typically complementary bias of the two classes contribute to a more balanced estimate. In this paper we exploit further the synergies between experts and non-experts in an MCDM framework, aggregating the individual estimates by means of non-additive Choquet integration, and representing the complementary bias by the multiagent interaction structure underlying the capacity. We present some examples and computer simulations whose aggregation results outperform those of the classical weighted mean (additive case), showing lower MMRE (mean magnitude of the relative error between the central estimate and the actual value) and higher HitRate (at which the interval estimate contains the actual value).     

Electrochemical behaviour of ZrO2 sol-gel pre-treatments on AA6060 aluminium alloy

ZrO₂ pre-treatments applied with the sol-gel technique are a possible replacement of chromium based pre-treatments on aluminium alloys. The thickness and homogeneity of the films deposited on AA6060 alloy are strongly related to the process parameters like preparation of the surface, number of dips and thermal treatment of the film.ZrO₂ films were prepared using the dip-coating technique in sol obtained from metal-organic precursors in an organic solvent (0.1 M Zr(OBuⁿ)₄ in anhydrous n-butanol with addition of acetic acid as complexing agent). Different layers were applied on AA6060 changing number of dips and thermal treatment (150 °C for 1 h or 250 °C for 4 min). The typical thickness of the deposited layers was in the range 70-180 nm depending on process parameters. The electrochemical behaviour of the pre-treated alloy in diluted Harrison solution (0.05 wt% NaCl + 0.35 wt% (NH₄)₂SO₄) was investigated by means of potentiodynamic polarization, open circuit potential measurements, and electrochemical impedance spectroscopy. In addition, the electrochemical behaviour of ZrO₂ sol-gel films was compared with that of chromatized AA6060 and fluotitanated/fluozirconated AA6060. In order to evaluate the adhesion properties of the films, ZrO₂ pre-treated AA6060, chromatized AA6060 and fluotitanated/fluozirconated AA6060 were painted with a polyester resin and subjected to thermal cycles in 0.05 wt% NaCl. Each thermal cycle consisted of heating the samples at 90 °C, permanence at 90 °C for 6 h, cooling at room temperature and permanence at room temperature for 18 h. Impedance measurements were performed at the end of each cycle.Potentiodynamic polarization curves and impedance spectra indicate that ZrO₂ pre-treatments have similar barrier properties to those of chromatized AA6060. However, no self-healing ability is observed for ZrO₂ films.The barrier properties of ZrO₂ films are strongly dependent on process parameters. In particular, the number of dips determines the amount of defects in the film and its homogeneity. The electrochemical behaviour strongly improves increasing the number of dips in the deposition bath. Thermal aging cycles evidence good adhesion properties for ZrO₂ pre-treatments.     

Generality and legibility in mobile manipulation

This article investigates methods for achieving more general manipulation capabilities for mobile manipulation platforms, which produce legible behavior in human living environments. To achieve generality and legibility, we combine two control mechanisms. First of all, experience- and observation-based learning of skills is applied to routine tasks, so that the repetitive and stereotypical character of everyday activity is exploited. Second, we use planning, reasoning, and search for novel tasks which have no stereotypical solution. We apply these ideas to the learning and use of action-related places, to the model-based visual recognition and localization of objects, and the learning and application of reaching strategies and motions from humans. We demonstrate the integration of these mechanisms into a single low-level control system for autonomous manipulation platforms.     

Advanced testing procedures for high performance coatings

In the first part of this work, an integrated approach incorporating electrochemical (electrochemical impedance spectroscopy), calorimetric (differential scanning calorimetry), mechanical (dynamic mechanical thermal analysis), and infrared spectroscopy (Fourier transform infrared spectroscopy) techniques was used to characterize some organic coatings from the automotive industry. Comparison of the results obtained with different techniques allows not only a higher precision in the evaluation of natural or artificial degradation, which is very difficult to obtain using traditional techniques, but also better data interpretation and, therefore, the possibility of understanding the different degradation mechanisms. In the second part, some preliminary results concerning the comparison of salt spray exposure and EIS measurements are discussed. The statistical analysis of the results showed that the degradation mechanism in the two cases is completely different and, therefore, the information which is obtained with the two testing approaches is also different. With EIS measurements obtained in immersion, it is possible to monitor, in particular, the barrier properties of the coatings, which are dominated by the presence of defects. In the case of salt spray (without scratch), the main property to be measured is the loss of adhesion which causes blister formation. Presented at the 77th Annual Meeting of the Federation of Societies for Coatings Technology, on October 18–22, 1999, in Dallas, TX. Dept. of Materials Engineering, Via Mesiano 77, Trento, Italy. e-mail: Flavio.Deflorian@ing.unitn.it; Stefano.Rossi@ing.unitn.it; Bonora@ing.unitn.it. Dept. ICMMPM, Via Eudossiana, Rome, Italy. e-mail: Lorenzo.Fedrizzi@ing.unitn.it.     

A multi-expert system for ranking patents: An approach based on fuzzy pay-off distributions and a TOPSIS–AHP framework

The aim of this paper is to introduce a decision support system that ranks patents based on multiple expert evaluations. The presented approach starts with the creation of three value scenarios for each considered patent by each expert. These are used for the construction of individual fuzzy pay-off distribution functions for the patent value; a consensual fuzzy pay-off distribution is then determined starting from the individual distributions. Possibilistic moments are calculated from the consensus pay-off distribution for each patent and used in ranking them with TOPSIS. It is further showed how the analytic hierarchy process (AHP) can be used to include additional decision variables into the patent selection, thus allowing for a two-tier decision making process. The system is illustrated with a numerical example and the usability of the system and the combination of methods it includes for patent portfolio selection in the real world context is discussed.     

Corrosion mechanisms of an AISI type 316L sintered stainless steel in sodium chloride solution

The electrochemical behaviour of a sintered stainless steel and of a wrought AISI type stainless steel of the same composition were compared. The electrochemical measurements used were the evolution of the corrosion potential vs time, the anodic and cathodic polarizations and the current-time transients. Comparisons were also performed for the sintered alloy before and after stabilization of the corrosion potential. The low corrosion resistance of the sintered stainless steel is due to the formation of a galvanic couple between the free surface and the inside of the interconnected pores. Hence the free surface is cathodically protected by the pores, but reciprocally the corrosion increases inside the pores where the reactive area is very large.     

Study of chromate coatings obtained on phosphatized steels: a characterization by AES and XPS techniques

Electrogalvanized and phosphatized steel sheets were passivated in chromate baths, and both the composition and temperature of these were varied in order to study the effects of such parameters on the chromate film formation. Scanning electron microscopy (SEM) together with microanalytical electronic spectroscopy techniques such as Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were chosen as the most useful methods for a suitable and careful study of the chromate presence, distribution and thickness. The chromium presence on the treated surfaces is easily detectable by XPS. Moreover it is possible to compare the surface chromium content of differently produced specimens. The detection of chromium is more difficult using AES, due to charging problemS. Nevertheless, by this technique we found that the passive film is not homogeneously distributed on the whole phosphatized surface, but it is localized on randomly distributed areas, the chromate passive layer being very thin (about 4 nm). With respect to corrosion resistance of electrogalvanized steel, it seems that passivation in baths containing only Cr³⁺ is more effective than passivation in baths containing Cr⁶⁺.