José Martins

New single-step electrosynthesis process of homogeneous and strongly adherent polypyrrole films on iron electrodes in aqueous medium

Homogeneous and strongly adherent polypyrrole (PPy) films were electrochemically synthesized on iron electrodes in sodium tartrate (Na2C4O6H4 0.2 M) aqueous solution. This one step pyrrole electropolymerization process has been successfully achieved under different electrochemical techniques, such as potentiodynamic, galvanostatic and potentiostatic modes. During the first stage of the electrochemical process the tartrate counterion slows down the iron dissolution by leading to the formation of a passivation layer on the working electrode surface, and the pyrrole electropolymerization takes place. The electrosynthesized polymer deposit has been characterized by several microscopic and spectroscopic techniques. Any iron traces have been detected by X-ray photoelectron spectroscopy (XPS) on the outer side of the PPy films, which confirms the compactness and the homogeneity of the polymeric coating. Scanning electronic microscopy (SEM) imaging showed uniform and compact PPy coatings with cauliflower-like structure. Infra-red (IR) and Raman spectroscopies proved that the obtained PPy films have the same vibrational properties as those electrodeposited on noble Pt plates.

Electrosynthesis of homogeneous and adherent polypyrrole coatings on iron and steel electrodes by using a new electrochemical procedure

Abstract A single-step electropolymerization of pyrrole (Py) on iron and steel surfaces has been performed in aqueous medium in the presence of malate (C 4 H 4 O 5 2− ) as supporting electrolyte. The malate counter-ion slows down the iron dissolution by leading to the formation of a passivation layer on the working electrode surface, and the Py electropolymerization starts on. The polypyrrole (PPy) films electrosynthesized under different electrochemical techniques are uniform and adherent. The polymer coatings performed galvanostatically have a cauliflower-like structure and are thicker than those obtained by potentiodynamic mode. The adherence of PPy layers to the iron electrodes was estimated at 100% according to the standard sellotape test. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) analysis showed that the obtained coatings have the same structure and morphological properties as those electrodeposited on Pt electrodes.

TwitterEcho: a distributed focused crawler to support open research with twitter data

Modern social network analysis relies on vast quantities of data to infer new knowledge about human relations and communication. In this paper we describe TwitterEcho, an open source Twitter crawler for supporting this kind of research, which is characterized by a modular distributed architecture. Our crawler enables researchers to continuously collect data from particular user communities, while respecting Twitters imposed limits. We present the core modules of the crawling server, some of which were specifically designed to focus the crawl on the Portuguese Twittosphere. Additional modules can be easily implemented, thus changing the focus to a different community. Our evaluation of the system shows high crawling performance and coverage.

Pyrrole electropolymerization on copper and brass in a single-step process from aqueous solution

The electrosynthesis of polypyrrole (PPy) on copper and brass (Cu–Zn alloy) electrodes was performed by anodic oxidation of pyrrole in a sodium tartrate (C4H4Na2O6 0.2 M) aqueous solution. The tartrate counter-ions slow the dissolution of the working electrode by leading to formation of a passivation layer on its surface, and pyrrole electropolymerization takes place. Strongly adherent and homogeneous polypyrrole films were electrodeposited on Cu and Cu–Zn alloy electrodes using different electrochemical techniques, such as potentiodynamic, galvanostatic and potentiostatic modes. The current densities of electropolymerization on brass are generally greater than those observed on copper. The corrosion behaviour of copper-coated electrodes, electrochemically modified by PPy films, was estimated by DC polarization and weight loss at different current densities in 0.1 M HCl solution. The synthesized polypyrrole films were characterised by several microscopic and spectroscopic techniques such as scanning electron microscopy, X-ray photo electron spectroscopy, Fourier transform infrared and Raman analysis. Galvanostatically deposited PPy films are shown to be an alternative to common black-nickel or black-chromium as a decorative top-coating.

Electrochemical synthesis of adherent polypyrrole films on zinc electrodes in acidic and neutral organic media

The electrodeposition of polypyrrole on zinc electrodes has been performed by anodic oxidation of pyrrole in acetonitrile, nitrobenzene and propylene carbonate media in the presence of para-toluene sulfonate counter-ions. When the zinc electrode has preferably undergone a chemical treatment by aqueous sodium sulfide solution, homogeneous and adherent PPy films are obtained. While, no PPy film grows (in the case of C6H5NO2 and PC) or a non-homogeneous and poorly adherent PPy–zinc oxide composite forms (in the case of CH3CN) when the zinc surface is simply polished. Among the electrochemical techniques used in these experiments, the galvanostatic mode was proved to be better adapted to perform the electropolymerization of pyrrole on the pretreated zinc electrodes using low applied current densities. The polypyrrole films synthesized by this technique has been characterized by several microscopic and spectroscopic techniques. In particular, SEM, XPS, FT-IR and Raman analyses showed that the obtained coatings have the same structure and morphological properties as those electrodeposited on Pt electrodes.

New electrochemical procedure for elaborating homogeneous and strongly adherent PPy films on zinc electrodes

Electropolymerization of pyrrole on zinc was investigated in sodium tartrate aqueous solution in order to obtain homogeneous and adherent polypyrrole films. The tartrate counter-anions inhibit the working electrode dissolution by leading to the formation of a passivation layer on its surface. Consequently, homogeneous and strongly adherent polypyrrole coating has been successfully achieved with different electrochemical techniques, such as potentiodynamic, galvanostatic and potentiostatic modes. Polypyrrole coatings electrosynthesized on zinc electrodes have been characterized by several microscopic and spectroscopic techniques. Particularly, scanning electron microscopy (SEM) analysis has revealed a compact, homogeneous and thick polypyrrole film. X-ray photoelectron spectroscopy (XPS), IR and Raman analyses proved that the coatings obtained have globally the same structural features and elementary composition as those electrosynthesized on noble metals.

Leaching of synthetic scheelite by hydrochloric acid without the formation of tungstic acid

Abstract The kinetics of the leaching reaction of synthetic scheelite with hydrochloric acid was studied to determine the effect of pH and temperature in the formation of tungstic acid. Conversion data obtained from leaching in a temperature range of 28–100 °C and pH between 1.5 and 3.0 are interpreted in terms of the predominating tungsten species present in the leaching liquors. The results show that it is possible to digest the synthetic scheelite in the acidic hydrochloric medium without the formation of tungstic acid by monitoring and controlling the pH, and controlling the temperature in the domain of metatungstates. In this case, the experimental results match with the shrinking core model, and show that the solids leaching is kinetically under both chemical and mass transfer control.

Thin and flexible bio-batteries made of electrospun cellulose-based membranes

The present work proposes the development of a bio-battery composed by an ultrathin monolithic structure of an electrospun cellulose acetate membrane, over which was deposited metallic thin film electrodes by thermal evaporation on both surfaces. The electrochemical characterization of the bio-batteries was performed under simulated body fluids like sweat and blood plasma [salt solution--0.9% (w/w) NaCl]. Reversible electrochemical reactions were detected through the cellulose acetate structure. Thus, a stable electrochemical behavior was achieved for a bio-battery with silver and aluminum thin films as electrodes. This device exhibits the ability to supply a power density higher than 3 μW cm(-2). Finally, a bio-battery prototype was tested on a sweated skin, demonstrating the potential of applicability of this bio-device as a micropower source.

Electropolymerization of pyrrole on zinc–lead–silver alloys electrodes in acidic and neutral organic media

Abstract Electropolymerization of pyrrole on zinc–lead–silver (Zn–Pb–Ag) alloys was carried out in acetonitrile, nitrobenzene and propylene carbonate (PC) organic media in the presence of para -toluene sulfonate counter ions. Adherent and homogeneous PPy films have been obtained on zinc alloy electrodes (65% Zn, 10% Pb and 25% Ag) prealably treated with aqueous sodium sulfide solution. Among the electrochemical techniques used in these experiments, the galvanostatic mode was proved to be better adapted to perform the electrosynthesis of polypyrrole using low applied current densities. The PPy coatings have been characterized by different microscopic and spectroscopic techniques. Scanning electron microscopy (SEM) showed that PC (DN=15.1) is the most suitable solvent for elaborating high-quality and thick PPy films. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) analysis proved that the obtained coatings have the same structure properties as those electrodeposited on noble Pt plates.

Accessibility levels of Portuguese enterprise websites: equal opportunities for all?

Web accessibility is growing in importance. We may also find an increasing need for access to web resources by those with some sort of disability. The Web is very important for spreading information and for promoting interaction between the various elements in society. Given this, it is essential that the Web presents itself as a totally accessible resource, so that it can help citizens with disabilities and their integration in society. This obligation should be even greater for enterprises as primarily the Web is used as a marketing and business platform. With this document, we present indicators regarding the [lack of] accessibility levels of Portuguese enterprise websites. This article contains theoretical and background considerations as well as the results of two different studies that the research team undertook. First of all, the research team made a comparison between the 1000 largest Portuguese enterprises (annual sales volume) and the 1000 best Portuguese small and medium enterprises (sales growth and profit) using a specialised software tool and according to Web Content Accessibility Guidelines (WCAG) 1.0; the research team then also considered WCAG 2.0 and its impact on enterprise Web accessibility. In the second study (qualitative in nature), focus group interactions led to a set of recommendations towards greater accessibility.