T. Bellezze

Electrochemical study on the corrosion resistance of Cr III-based conversion layers on zinc coatings

Abstract Zinc coatings submitted to a Cr III-based passivation treatment, with and without a sealing treatment, were studied. For comparison, similar coatings with a Cr VI-based passivation treatment were also examined. The corrosion behaviour was studied by polarization resistance (Rp) measurements, anodic polarization and mainly by electrochemical impedance spectroscopy (EIS) in aerated 0.85 M NaCl solution. Salt spray tests and morphological observations on the coating surface were also performed. The results indicate that the Cr III passivated coatings with sealing treatments have a corrosion resistance comparable with that of coatings with a Cr VI passivation treatment without a sealant; therefore, they could be a less polluting alternative to the traditional chromated coatings.

Contemporary use of Ni and Bi in hot-dip galvanizing

Abstract Five series of commercially hot-rolled mild steels, with different silicon and phosphorus content, were tested in four industrial hot-dip galvanizing plants with different bath compositions: two innovative alloys containing low percentages of Ni and Bi (Ni≈0.04% and Bi≈0.1%), one alloy containing Ni (≈0.05%) and a traditional Zn–Pb (Pb≈1.1%) alloy. The coatings obtained were studied by chemical analysis, thickness measurements and by metallographic technique observation. The Zn–Ni–Bi alloy gave very interesting results with all the steels tested. Indeed, the steel reactivity and the coating thickness in the two innovative baths were always lower than those obtained by the traditional Zn–Pb bath and similar to those obtained with the bath containing Ni (Technigalva). These results have been attributed to a synergistic effect of Ni and Bi on the reactivity control of the reactive steels; in fact, even a low Ni content gives the same or even better results than the classical Zn–Ni bath, except for high phosphorus steels. Furthermore, Bi is not detrimental to human health and the environment and can be considered a very good alternative to Pb to improve bath fluidity.

Localised corrosion and cathodic protection of 17 4PH propeller shafts

Abstract Some 17 4PH propeller shafts showed severe localised corrosion after a long period of time in Ancona harbour. The shaft is concentrically mounted in an AISI 304 stern tube through two rubber bearings. Both 17 4PH and AISI 304 stainless steels were characterised by anodic polarisation in natural sea water, in order to obtain the necessary corrosion parameters for designing a suitable cathodic protection of the propeller system. The cathodic protection effectiveness was tested on a portion (about 1 m long) of this system. Two cathodic protection methods were tested: an impressed current cathodic protection at −0·3 V(SCE) and a galvanic cathodic protection. The tests were performed both in stagnant and in moving sea water and the results showed that these cathodic protection solutions were able to protect the propeller system; in particular some guidelines are suggested for both old and new ships.

Solutions for critical raw materials under extreme conditions: A review

In Europe, many technologies with high socio-economic benefits face materials requirements that are often affected by demand-supply disruption. This paper offers an overview of critical raw materials in high value alloys and metal-matrix composites used in critical applications, such as energy, transportation and machinery manufacturing associated with extreme working conditions in terms of temperature, loading, friction, wear and corrosion. The goal is to provide perspectives about the reduction and/or substitution of selected critical raw materials: Co, W, Cr, Nb and Mg.

Binders alternative to Portland cement and waste management for sustainable construction—part 1:

This review presents “a state of the art” report on sustainability in construction materials. The authors propose different solutions to make the concrete industry more environmentally friendly in order to reduce greenhouse gases emissions and consumption of non-renewable resources. Part 1—the present paper—focuses on the use of binders alternative to Portland cement, including sulfoaluminate cements, alkali-activated materials, and geopolymers. Part 2 will be dedicated to traditional Portland-free binders and waste management and recycling in mortar and concrete production.

Influence of aeration cycles on mechanical characteristics of elastomeric diffusers in biological intermittent processes: Accelerated tests in real environment

The paper deals with the evaluation of the effect of on/off switching of diffuser membranes, in the intermittent aeration process of the urban wastewater treatments. Accelerated tests were done using two types of commercial EPDM diffusers, which were submitted to several consecutive cycles up to the simulation of more than 8 years of real working conditions. The effect of this switching on the mechanical characteristics of the membranes was evaluated in terms of pressure increment of the air operating at different flow rates (2, 3.5 and 6 m3/h/diff): during accelerated tests, such increment ranged from 2% to 18%. The intermittent phases emphasized the loss both of the original mechanical proprieties of the diffusers and of the initial pore shapes. The main cause of pressure increment was attributed to the fouling of the internal channels of the pores. Further analyses performed by scanning electron microscopy and by mechanical tests on EPDM membrane, using a traditional tensile test and a non destructive optical method, from which the Youngs Modulus was obtained, supported previous conclusions. Any changes in terms of oxygen transfer parameters (KLa and SOTE%) were specifically founded by causing to the repeated on/off switching.

Bond Behavior of FRCM Carbon Yarns Embedded in a Cementitious Matrix: Experimental and Numerical Results

The use of inorganic cement based composite systems, known as Fiber Reinforced Cementitious Matrix (FRCM), is a very promising technique for retrofitting and strengthening the existing masonry or concrete structures. The effectiveness of FRCM systems is strongly related to the interface bond between inorganic matrix and fabric reinforcement, and, since the major weakness is often located on this interface, the study of stress-transfer mechanisms between fibers and matrix becomes of fundamental importance.FRCM are usually reinforced with uni-directional or bi-directional fabrics consisting of multifilament yarns made of carbon, glass, basalt or PBO fibers, disposed along two orthogonal directions. The difficulty of the mortar to penetrate within the filaments that constitute the fabric yarns and the consequent non-homogeneous stress distribution through the yarn cross section makes difficult to access the characterization of the composite material. The use of polymer coatings on the fibers surface showed to enhance the bond strength of the interface between fibers and mortar and, as a consequence, to improve the mechanical performance of the composite. The coating does not allow the mortar to penetrate within the filaments while is able to improve the bond between the two materials and to increase the shear stress transfer capacity at the interface.An experimental session of several pull out tests on carbon yarns embedded in a cementitious matrix was carried out. Different embedded lengths have been analyzed, equal to 20, 30 and 50 mm. The carbon yarns object of this study were pre-impregnated with a flexible epoxy resin enhanced with a thin layer of quartz sand applied on the surface.A variational model was proposed to evaluate the pull-out behaviour and failure mechanisms of the system and to compare numerical results to the experimental outcomes. Evolution of fracture in the yarn-matrix system is determined by solving an incremental energy minimization problem, acting on an energy functional which account for brittle failure of matrix and yarn, and for debonding at the yarn-matrix interface. The model was able to accurately describe the three phases of the pull-out mechanism, depending on the embedded length.

The Effect of Fly Ash on the Corrosion Behaviour of Galvanised Steel Rebarsin Concrete

The effect of fly ash on the corrosion behaviour of galvanised steel rebars in cracked concrete specimens exposed to wet-dry cycles in a chloride solution has been investigated. The obtained results show that the use of fly ash, replacing either cement or aggregate, always improves the corrosion behaviour of galvanised steel reinforcements. In particular, the addition of fly ash, even in the presence of concrete cracks, decreases the corrosion rate monitored in very porous concretes, as those with w/c = 0.80, to values comparable with those obtained in good quality concretes, as those with w/c = 0.45. Therefore, fly ash cancels the negative effect, at least from the corrosion point of view, of a great porosity of the cement matrix.

Effect of the Type of Surface Treatment and Cement on the Chloride Induced Corrosion of Galvanized Reinforcements

The effect of a new passivation treatment, obtained by immersion of the galvanized reinforcements in a trivalent chromium salts based solution, on the chlorides induced corrosion has been investigated. To investigate also the effect of cement alkalinity on corrosion behaviour of reinforcements, concretes manufactured with three different European cements were compared. The obtained results show that the alternative treatment based on hexavalent chromium-free baths forms effective protection layers on the galvanized rebar surfaces. The higher corrosion rates of zinc coating in concrete manufactured with Portland cement compared to those recorded for bars in concrete manufactured with pozzolanic cement depends strongly on the higher chloride content at the steel concrete interface.