J.C.S. Fernandes

Corrosion resistance of a composite polymeric coating applied on biodegradable AZ31 magnesium alloy

The high corrosion rate of magnesium alloys is the main drawback to their widespread use, especially in biomedical applications. There is a need for developing new coatings that provide simultaneously corrosion resistance and enhanced biocompatibility. In this work, a composite coating containing polyether imide, with several diethylene triamine and hydroxyapatite contents, was applied on AZ31 magnesium alloys pre-treated with hydrofluoric acid by dip coating. The coated samples were immersed in Hanks solution and the coating performance was studied by electrochemical impedance spectroscopy and scanning electron microscopy. In addition, the behavior of MG63 osteoblastic cells on coated samples was investigated. The results confirmed that the new coatings not only slow down the corrosion rate of AZ31 magnesium alloys in Hanks solution, but also enhance the adhesion and proliferation of MG63 osteoblastic cells, especially when hydroxyapatite nanoparticles were introduced in the coating formulation.

Anodising of Al 2024-T3 in a modified sulphuric acid/boric acid bath for aeronautical applications

A novel borate/boric/sulphuric acid anodising process is studied. The results show that the physical structure of the films is influenced not only by the bath used, but also and mainly by the substrate, i.e., Al 2024-T3 or Al. The corrosion resistance of the anodised specimens is satisfactory for practical applications and the fatigue resistance is not significantly different from that obtained with the traditional chromic acid anodising.

EIS on plasma-polymerised coatings used as pre-treatment for aluminium alloys

Plasma coatings from hexamethyldisiloxane (HMDSO) have proven to be effective primer coatings for adhesion promotion to aluminium but the corrosion properties of these coatings have not been thoroughly assessed. In the present work, electrochemical impedance spectroscopy (EIS) was used to evaluate the corrosion behaviour of Alclad AA2024-T3 covered with a polymer film prepared by plasma polymerisation, using HMDSO as monomer. The present results indicate that, although the polymer film was mainly intended to provide a strong coupling between the metal substrate and the organic coating, the film in itself confers protection against corrosion. Equivalent circuits are proposed for the immersion behaviour of uncoated and plasma-coated material, allowing the determination of the parameters relative to natural aluminium oxide, coating layer and pitting. An estimation of the water uptake during the immersion time from the values obtained for the coating capacitance was carried out. The evaluation of the corrosion performance of these plasma-coated materials by means of their water uptake behaviour may be useful, as the water volume fraction seems to be much more sensitive to the changes in the system due to delamination than the values obtained from the fitting of EIS data to an equivalent circuit.

Impedance spectra for aluminum 7075 during the early stages of immersion in sodium chloride

Abstract The impedance spectra obtained at short exposure times for Al 7075-T6 immersed in 0.5 N NaCl do not agree with the pitting model proposed by Mansfeld and co-workers. Instead of a transmission line impedance, an inductive loop is observed at low frequencies. This result is due to the non-linearity of the system at short exposure times, when E corr is close to E pit . The application of the anodic portion of the ac signal causes this non-linear behavior. The observed impedance is therefore a system response and not a true impedance. For longer exposure times agreement with the pitting model is observed.

SmartSantander: Internet of Things Research and Innovation through Citizen Participation

The Smart City concept relates to improving efficiency of city services and facilitating a more sustainable development of cities. However, it is important to highlight that, in order to effectively progress towards such smart urban environments, the people living in these cities must be tightly engaged in this endeavour. This paper presents two novel services that have been implemented in order to bring the Smart City closer to the citizen. The Participatory Sensing service we are proposing exploits the advanced features of smartphones to make the user part of the ubiquitous sensing infrastructure over which the Smart City concept is built. The Augmented Reality service is connected to the smart city platform in order to create an advanced visualization tool where the plethora of available information is presented to citizens embedded in their natural surroundings. A brief description of the smart city platform on top of which these services are built is also presented.

Plasma-polymerised coatings used as pre-treatment for aluminium alloys

The pre-treatment of aluminium alloys prior to painting or adhesive bonding is an essential technology in many industrial sectors (e.g. aerospace industry). However, the pre-treatments used on the substrates, which are vital to ensure reliable long-term performance, often comprise a range of environmentally objectionable chemicals, such as solvents and chromates, some of which are carcinogenic. The plasma deposition of thin coatings on aluminium, which exhibit strong interfacial bonding, could be an alternative to the traditional chromate-based treatments. It is envisaged that in a single plasma reactor, plasma cleaning, etching and deposition could provide a complete preparation cycle before painting, avoiding the use, handling and disposal of hazardous materials. In the present work, the corrosion behaviour and adhesive joint performance of plasma-coated Alclad AA2024-T3 alloy were investigated. The coatings were deposited from hexamethyldisiloxane monomer (HMDSO) in a capacitively coupled RF plasma reactor. The same evaluations were carried out on specimens painted with an epoxy primer after coating deposition. The coatings conferred protection against corrosion and provided a good interface for strong, durable adhesive bonds.

Spin valve heads with a corrosion resistant MnRh exchange layer

A new exchange material, Mn/sub 78/Rh/sub 22/, is described, requiring no post-deposition anneal to obtain the antiferromagnetic phase and leading to spin valve sensors with good corrosion resistance, thermal stability up to 225/spl deg/C, and good exchange coupling characteristics. Potentiodynamic polarization scans performed in a sodium sulfate electrolyte show that Mn/sub 78/Rh/sub 22/ films exhibit a good corrosion resistance, comparable to that of Ni/sub 81/Fe/sub 19/, Mn/sub 80/Ir/sub 20/, and Mn/sub 50/Ni/sub 50/ films but with higher corrosion potential. Spin valve structures prepared with this exchange material show an exchange coupling strength (J/sub ex/) of 0.19 erg/cm/sup 2/. The blocking temperature (T/sub B/) of the as-deposited spin valve coupon samples is 235/spl deg/C. Unshielded sensors with trackwidths W=4-6 /spl mu/m and height h=1-2 /spl mu/m were fabricated. The sensors show well-linearized magnetoresistance (MR) transfer curves, without hysteresis or Barkhausen noise and are thermally stable under consecutive 5 h anneals in vacuum up to 225/spl deg/C. A shielded tape head device was fabricated showing a maximum output of 1.8 mV/sub pp///spl mu/m, with potential for operating at linear densities near 100 kfci, at which a 580 /spl mu/V/sub pp///spl mu/m output is measured.

Biofunctional composite coating architectures based on polycaprolactone and nanohydroxyapatite for controlled corrosion activity and enhanced biocompatibility of magnesium AZ31 alloy

In this work a biofunctional composite coating architecture for controlled corrosion activity and enhanced cellular adhesion of AZ31 Mg alloys is proposed. The composite coating consists of a polycaprolactone (PCL) matrix modified with nanohydroxyapatite (HA) applied over a nanometric layer of polyetherimide (PEI). The protective properties of the coating were studied by electrochemical impedance spectroscopy (EIS), a non-disturbing technique, and the coating morphology was investigated by field emission scanning electron microscopy (FE-SEM). The results show that the composite coating protects the AZ31 substrate. The barrier properties of the coating can be optimized by changing the PCL concentration. The presence of nanohydroxyapatite particles influences the coating morphology and decreases the corrosion resistance. The biocompatibility was assessed by studying the response of osteoblastic cells on coated samples through resazurin assay, confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The results show that the polycaprolactone to hydroxyapatite ratio affects the cell behavior and that the presence of hydroxyapatite induces high osteoblastic differentiation.

Mycobacterium parascrofulaceum in Acidic Hot Springs in Yellowstone National Park

ABSTRACT Mycobacterium parascrofulaceum was found in Norris Geyser Basin, Yellowstone National Park, in a system composed of two acidic (pH 3.0) springs with temperatures between 56°C at the source and 40°C at the confluence of both springs. Growth and survival assays at 56°C for 60 days were performed, confirming the origin of the strain.

Toxicological Assessment of Coated versus Uncoated Rubber Granulates Obtained from Used Tires for Use in Sport Facilities

Abstract Reuse of tire crumb in sport facilities is currently a very cost-effective waste management measure. Considering that incorporation of the waste materials in artificial turf would be facilitated if the rubber materials were already colored green, coatings were specifically developed for this purpose. This paper presents an experimental toxico-logical and environmental assessment aimed at comparing the obtained emissions to the environment in terms of polycyclic aromatic hydrocarbons (PAHs), heavy metals, and ecotoxicity for coated and noncoated rubber granulates. This study is a comprehensive evaluation of the major potential critical factors related with the release of all of these classes of pollutants because previous studies were not systematically performed. It was concluded that between the two types of coatings tested, one is particularly effective in reducing emissions to the environment, simultaneously meeting the requirements of adherence and color stability.