Scielo RSS http://scielo.pt/rss.php?pid=0872-190420080005&lang=pt vol. 26 num. 5 lang. pt http://scielo.pt/img/en/fbpelogp.gif http://scielo.pt http://scielo.pt/scielo.php?script=sci_arttext&pid=S0872-19042008000500001&lng=pt&nrm=iso&tlng=pt Kinetic parameters and stability constants of [Mn - sulfonamides - cephalothin] system were reported at pH = 7.30 ± 0.01 in 1.0 M NaCO4 at 25 ºC. The sulfonamides were sulfadiazine, sulfisoxazoe, sulfamethaxyzoe, sulfamethazine, sulfathiazoe, sulfacetamide and sulfaniamide as primary ligands, and cephalothin as secondary ligand. Values of transfer coefficient (α) varied from (0.41 to 0.59), showing that transition state behaves between oxidant and reductant response to applied potential and it adjusts itself in such a way that the transition state is located midway between dropping mercury electrode and solution interface. The rate constants (k) varied from 3.61 x 10-3 cm.sec.-1 to 9.93 x 10-3 cm.sec.-1, confirming that the electrode processes were quasi reversible. Small changes in potential not only affect the rate of the electrochemical reaction, but also strongly affect the rate constant. Values of stability constants (log β) varied from 1.75 to 9.13, showing that these drugs or their complexes could be used against Mn toxicity. http://scielo.pt/scielo.php?script=sci_arttext&pid=S0872-19042008000500002&lng=pt&nrm=iso&tlng=pt Diffusion models capable of describing the ionic diffusion inside host materials, e.g. oxides, during intercalation processes, have been reported in the literature. However, the majority of the models do not succeed in establishing a good correlation between diffusion and structural environment. What is frequently described is the influence of an addition solid state reaction. In this paper we discuss about such additional reaction and its influence on the diffusion. The responses were evaluated by means of impedance patterns analyzed in (Sn x,Ti1-x)O2 binary systems whose structural disorder control provides a way to evaluate how such structural disorder influences the global diffusion. http://scielo.pt/scielo.php?script=sci_arttext&pid=S0872-19042008000500003&lng=pt&nrm=iso&tlng=pt The performance of two resin combinations, such as acrylic polyol - aromatic isocyanate and polyester polyol - aromatic isocyanate as durable and effective rebar coatings for steel in concrete has been examined by studying their mechanical properties and by using accelerated tests such as salt spray test and electrochemical impedance spectroscopy. It is found that polyester polyol-aromatic isocyanate combination performs better than acrylic polyol-aromatic isocyanate combination. Incorporation of fly ash in the coating is found to influence the performance of the coating. http://scielo.pt/scielo.php?script=sci_arttext&pid=S0872-19042008000500004&lng=pt&nrm=iso&tlng=pt Repair and rehabilitation of deteriorated concrete structures are essential not only to utilize them for their intended service life, but also to assure the safety and serviceability of the associated components. A good repair improves the function and performance of the structure, thus prevents ingress of aggressive species to the steel/concrete interface and improves its durability. It is important to evaluate the performance of repair materials available for repairing the deteriorated concrete structures. This investigation was carried out to evaluate the durability characteristics of five types of modified cement based repair mortars. The corrosion resistance of the repair materials was evaluated by conducting various tests such as water absorption, rapid chloride ion penetration test, impressed voltage, 90 days ponding test, macro cell corrosion test, weight loss measurement, etc. Details of the test and their results were discussed. It is concluded that the modified cement based repair mortars formulated with different mineral admixtures (fly ash and/or silica fume) showed improved corrosion resistance. http://scielo.pt/scielo.php?script=sci_arttext&pid=S0872-19042008000500005&lng=pt&nrm=iso&tlng=pt Acid catalyzed reactions of three proton pump inhibitors (PPIs), namely omeprazole, lansoprazole and pantoprazole, have been investigated and monitored by direct current polarography at dropping mercury electrode (D.M.E) in phosphate buffer (0.1 M) of pH 3-7.5. This gives well defined current-time profiles of individual electroactive degradation products along with their starting materials. The investigation shows that the order of stability of three PPIs can be written as: pantoprazole > omeprazole > lansoprazole. The rate of degradation of PPIs decreases with decreasing the basicity of the corresponding benzimidazole nitrogen of PPIs, as predicted by the effect of individual substituents on each of the benzimidazole rings. At pH 7.5 all three PPIs are almost stable and the observed half wave potentials (E1/2 ) are -1.07 V for omeprazole, -1.25 V for lansoprazole and -1.32 V for pantoprazole. On decreasing the pH from 7.5 to 3.0 the anodic shift in E1/2 values were observed along with degradation of the PPIs and simultaneous appearance of degradation products. The present study may provide an insight for designing more potent new proton pump inhibitors. http://scielo.pt/scielo.php?script=sci_arttext&pid=S0872-19042008000500006&lng=pt&nrm=iso&tlng=pt The work presented in this paper deals with the investigations on the effect of Cu and Ni on the corrosion behavior of carbon steel under different experimental conditions. Electrochemical techniques like potentiodynamic polarization, linear polarization resistance and AC impedance have been used to investigate the effect of Cu and Ni on the corrosion behavior of carbon steel. The important experimental conditions which include the nature of aqueous medium, metal ion concentration and pH have been taken into account. The instantaneous corrosion parameters as computed by potentiodynamic polarization, linear polarization resistance and AC impedance show an increase in corrosion rates of carbon steel with increasing Cu and Ni concentrations. However, the corrosion parameter as computed by AC impedance for an extended period of one month follows an interesting trend. The presence of Cu and Ni in the aqueous medium produces almost identical effect on the corrosion behavior of carbon steel. The microscopic examination of the test samples, under controlled laboratory conditions, did not show the evidence of localized attack on carbon steel in presence of different concentrations of Cu and Ni. http://scielo.pt/scielo.php?script=sci_arttext&pid=S0872-19042008000500007&lng=pt&nrm=iso&tlng=pt The work presented in this paper deals with the investigations on the effect of Cu and Ni on the corrosion behavior of carbon steel under different experimental conditions. Electrochemical techniques like potentiodynamic polarization, linear polarization resistance and AC impedance have been used to investigate the effect of Cu and Ni on the corrosion behavior of carbon steel. The important experimental conditions which include the nature of aqueous medium, metal ion concentration and pH have been taken into account. The instantaneous corrosion parameters as computed by potentiodynamic polarization, linear polarization resistance and AC impedance show an increase in corrosion rates of carbon steel with increasing Cu and Ni concentrations. However, the corrosion parameter as computed by AC impedance for an extended period of one month follows an interesting trend. The presence of Cu and Ni in the aqueous medium produces almost identical effect on the corrosion behavior of carbon steel. The microscopic examination of the test samples, under controlled laboratory conditions, did not show the evidence of localized attack on carbon steel in presence of different concentrations of Cu and Ni.