Favorite places of adolescents in the Federal District

Explorou-se neste estudo quais os lugares preferidos e não preferidos por 562 jovens (292 F e 270 M), com idades entre 13 e 19 anos (média = 15 anos e 7 meses e desvio padrão = 1 ano e 1 mês), freqüentando a primeira série do ensino médio, sendo 274 de escolas públicas e 288 de escolas particulares. Dentre os participantes 39,5% moram no Plano Piloto de Brasília e 60,5% em Cidades Satélites do DF. Em casas, moram 341, em apartamento, 215. Os resultados mostram que o lugar favorito mais freqüentemente mencionado foi a própria casa, indicado por 195 (35,3%) dos respondentes, seguido por Shopping (n = 108; 19,6%) e bar/boate/festa (n = 103; 18,7%). O lugar que obteve maior freqüência como não sendo preferido foi bar, boate, festa, indicado por 108 (21,3%) dos participantes, seguido por escola (n = 90; 17,7%) e lugares que provocam sentimentos ruins (n = 32; 6,3%). As diferenças encontradas são discutidas em termos de gênero, tipo de escola (pública ou privada) e tipo de moradia (casa ou apartamento).This study explored which are the most and least favorite places among 562 adolescents (292 F e 270 M), with ages between 13 and 19 (mean age 15 yr 7 mo, s.d. 1 yr 1 mo), attending 9th grade, with 274 respondents in public and 288 in private schools. Some 39.5% live in the central area of Brasília, 60.5% in the surrounding cities. Some 215 live in apartments, 314 in single occupancy houses. Results indicate that the most frequently mentioned favorite place was the home (n = 195, 35.3%), followed by Shopping Malls (n = 108, 19.6%) and bar/disco/parties (n = 103, 18.7%). The least favorite places were bar/disco/parties (n = 108, 21.3%), school (n = 90, 17.7%) and places that provoke negative feelings (n = 32, 6.3%). Differences are discussed in terms of gender, type of school and type of residence

An assessment of pitting corrosion in anodized aluminum alloys: It might not be what it seems

In this study, special attention was given to the characterization of pits on the anodized aluminum alloy (Al–Zn–Mg–Cu) with an anodic aluminum oxide formed in tartaric sulfuric acid. Anodic polarization in 0.1 mol L−1 NaCl solution was used to initiate pitting corrosion in the anodized alloy. Pit characteristics, such as morphology and depth, were evaluated by using optical microscopy and optical profilometry, and scanning electron microscopy. The methodology adopted in this study revealed severe under-film pitting due to highly occluded conditions and showed that the extent of the under-film pitting is significantly greater than the size of pit mouth observed from the surface.<br/

Corrosion and anodizing behavior of dissimilar AA5052-H32 and AA6061-T6 alloys joined by metal inert gas welding

peer reviewedEnormous efforts have been made to reduce fossil fuel consumption and greenhouse gas emissions in several sectors, such as the transport and agricultural sectors. Weight reduction is an efficient way to reduce fuel consumption. In this context, Aluminum alloys are excellent choices due to their properties of lightweight and high strength. However, corrosion is a major concern when using dissimilar alloys joined by welding. This might result in galvanic corrosion. Also, thermal effects during welding might affect the microstructure and the material corrosion resistance. Consequently, the study of dissimilar materials joined by welding is of great importance. In order to decrease corrosion susceptibility, surface protection of aluminum alloys against corrosion is a core issue in these applications. In this work, the corrosion resistance of the AA5052-H32 and AA6061-T6 alloys welded by metal inert gas (MIG) welding, with or without TSA anodizing, was investigated. The corrosion resistance was evaluated by immersion tests in sodium chloride solution and monitored by electrochemical impedance spectroscopy (EIS) and as scanning vibrating electrode technique (SVET). The anodic layers formed by TSA anodizing were analyzed and characterized by Scanning Electron Microscopy with Energy-Dispersive Spectroscopy (SEM-EDS) and Transmission Electron Microscopy (TEM). The results present the correlation between corrosion resistance, microstructure and surface film characteristics

evaluation of Zn-Cr(III)-organic coating by electrochemical impedance spectroscopy

O controle da corrosão de aço eletrogalvanizado empregando soluções à base de sais de Cr VI é amplamente conhecido e estudado. No entanto, pesquisadores vêm buscando alternativas para substituir estes sais já que diretrizes ambientais e industriais exigem que sejam banidos. Os revestimentos de conversão à base de Cr III têm mostrado um desempenho compatível aos baseados em Cr VI. Neste trabalho são utilizadas medidas de espectroscopia de impedância eletroquímica (EIE) em NaCl 0,05 mol/L e em Na2 SO4 0,1 mol/L, durante o tempo de imersão, para avaliar a resistência à corrosão de aço eletrogalvanizado revestido com tratamento à base de Cr III e pintado com três diferentes revestimentos orgânicos. Os revestimentos orgânicos sãocaracterizados por sua adesão. Os resultados mostram um comportamento semelhante para os três revestimentos e, apesar de uma segunda constante de tempo ter sido observada nos ajustes de EIE, os valores de R2 indicam uma baixa velocidade de corrosão. O sistema Zn – Cr III – revestimento orgânico é compatível ao sistema Zn – Cr VI – revestimento orgânico, para o período de imersão considerado.Corrosion control of electrogalvanized steel employing Cr VI based treatments is widely known and studied. However, researchers have been trying to find out alternatives to replace these salts once they must be banned in accord to environmental and industrial guidelines. Cr III – based conversion coatings have shown performance compatible to Cr VI – based treatments. In this work, EIS measurements are performed in NaCl 0,05 mol/L and Na2 SO4 0,1 mol/L, during the immersion time, to evaluate the corrosion resistance of electrogalvanized steel passivated with Cr III – based conversion treatment and painted with three different organic coatings. The organic coatings are characterized by their adherence. The results show a similar behavior for the three coatings and, despite a second constant time has been pointed by the EIS fitting, the R2 values indicate a low corrosion rate. The system Zn – Cr III – organic coating is compatible to the system Zn – Cr VI – organic coating, for the immersion period considered.Fil: Queiroz, Fernanda Martins. Centro de Ciências e Tecnologia de Materiais; BrasilFil: Elsner, Cecilia Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Centro de Investigación y Desarrollo En Tecnología de Pinturas (i); Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; ArgentinaFil: Tomachuk, Celia Regina. Centro de Ciências e Tecnologia de Materiais; BrasilFil: Di Sarli, Alejandro Ramón. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Costa, Isolda. Centro de Ciências e Tecnologia de Materiais; Brasi

The protection of electrogalvanised steel by passivation treatment with trivalent chromium and cobalt ions

Electroplated zinc coatings have been largely employed as active galvanic protection for steel substrates. However, as zinc is highly electrochemically active, its corrosion rate may be very high. For this reason, a post treatment to increase the lifetime of the coatings is necessary, which, in industrial practice, consists of immersion in a chemical bath that forms a conversion layer on plated zinc. This layer must be a dielectric passive coating with high corrosion resistance that also offers good adherence to paints. The main problem of conventionally used post treatments is the presence of Cr6+ salts which are carcinogenic substances whose usage was forbidden by European regulations. In this work the effect of trivalent chromium and Co ions in solution of passivation treatments on the corrosion resistance of electrogalvanised steel has been investigated in 0.1 M Na2SO4 solution by electrochemical impedance spectroscopy (EIS) and polarization curves. Prior and after the corrosion tests, the chemical composition and morphology of the electrogalvanised surface was characterized by SEM and XPS. The EIS results showed that impedance values associated to the surface with Cr3+ + Co treatments were inferior to those exhibited by the Cr6+ treated ones. The higher impedances related to the Cr6+ samples could be explained by the self-healing effect of this type of coating. The SEM analyses revealed coating cracks associated to the surface of the Cr6+ treated samples whereas for those treated in the Cr3+ + Co solution, elongated fissures were seen. These last samples presented inferior corrosion resistance to that of the Cr6+ passivated ones. The cobalt addition to the trivalent chromium containing solution was not sufficient to increase the corrosion resistance to acceptable levels in comparison to the Cr6+ conversion coating.Fil: Tomachuk, C. R.. Universidade de Sao Paulo; BrasilFil: Culcasi, José Daniel. Universidad Nacional de La Plata. Facultad de Ingeniería. Departamento de Mecánica. Laboratorio de Investigación de Metalurgia Física; ArgentinaFil: Elsner, Cecilia Ines. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; ArgentinaFil: Costa, Isolda. Universidade de Sao Paulo; BrasilFil: Di Sarli, Alejandro Ramón. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; Argentina65th Annual Meeting of the International Society of ElectrochemistryLausanneSuizaInternational Society of Electrochemistr

Multiscale electrochemical study of welded al alloys joined by friction stir welding

Friction stir welding (FSW) is an efficient way to join high strength aluminum alloys. However, FSW generates different microstructural areas in contact that may give rise to galvanic couplings, affecting the corrosion resistance of the assembly. In the present work, a multiscale electrochemical study of the 7475-T651 and 2024-T3 aluminum alloys butt-joined by FSW was carried out.Much lower impedances were associated with the FSW affected zones compared to the two aluminum base metals tested individually. Corrosion of the welded system resulted in the establishment of galvanic coupling, shown by local electrochemical impedance spectroscopy (LEIS) measurements, at which the AA7475 behaves anodically with respect to the AA2024. A Zn deposit was observed on the intermetallic particles of the AA2024 after 24 h of immersion in the electrolyte resulting from the galvanic coupling, which seems to reduce the galvanic coupling effects. Such a behavior in combination with LEIS results allowed a description of the galvanic coupling development between two different aluminum alloys (AA2024-T3 and AA7475-T761) butt-welded by FSW as a function of time from the early stage of immersion

A Conversion Layer Based on Trivalent Chromium and Cobalt for the Corrosion Protection of Electrogalvanized Steel

The corrosion resistance of pure zinc coatings can be improved through the application of suitable chemical passivation treatments. Hexavalent chromium (Cr6+) compounds have widely been used to formulate conversion layers providing better anticorrosive protection as well as anchorage properties to painting systems. However, taking into account that they are produced using hazardous chemical compounds, the development of alternative and “green” technologies with equivalent protective performance is a paramount purpose of many R&amp;D laboratories working around the world. In the present paper, the corrosion behavior of industrially electrogalvanized steel subjected to a Cr3+ + Co2+-based passivation treatment was studied. The experimental work involved electrochemical impedance spectroscopy (EIS)measurements and polarization curves in a 0.1 mol/L Na2SO4 solution, surface microstructural and morphological characterization by electronic microscopy as well as chemical analysis by EDXS and XPS. The most commonly observed failures on the Cr6+ treated sampleswere attributed to microstructural features of the substrate that were not adequately healed by the Cr6+ passivation treatment.Centro de Investigación y Desarrollo en Tecnología de Pintura

A study on corrosion resistance of ISO 5832-1 austenitic stainless steel used as orthopedic implant

The ISO 5832-1 austenitic stainless steel used as biomaterial is largely applied in the area of orthopedics, especially in the manufacture of implants, such as temporary or permanent replacement of bone structures. The objective of this study was to evaluate the localized corrosion resistance of the ISO 5832-1 stainless steel used in orthopedic implants by electrochemical tests in two different solutions. The results of this study are of great interest to evaluate the corrosion of metallic implants that can result in the release of corrosion products into bodily fluids causing possible adverse biological reactions. The determination of the chemical elements in the composition of the ISO 5832-1 stainless steel was performed by neutron activation analysis (NAA). The samples for electrochemical tests were grinded with silicon carbide paper up to #4000 finishing, followed by mechanical polishing with diamond paste. The open circuit potential measurements and anodic polarization curves were obtained in solution of 0.90 wt.&nbsp;% of NaCl and of simulated body fluid (SBF). The results indicated that the ISO 5832-1 stainless steel presented a high resistance to crevice corrosion in simulated body fluid solution but high susceptibility to this form of corrosion in the chloride solution. &nbsp

On the corrosion mechanism of Mg investigated by electrochemical impedance spectroscopy

This work reported a detailed analysis of the electrochemical impedance spectra obtained for the Mg electrode during immersion in a sodium sulfate solution. A model was proposed which took into account the presence of: (i) a thin oxide film (MgO) which progressively covered the Mg electrode surface, (ii) film-free areas where the Mg dissolution occurs in two consecutive steps, (iii) a thick layer of corrosion products (Mg(OH)2), (iv) an adsorbed intermediate (Mg+ads) which is responsible for the chemical reaction allowing the negative difference effect to be explained. From the impedance data analysis, various parameters were extracted such as the thin oxide film thickness, the resistivity at the metal/oxide film interface and at the oxide film/electrolyte interface, the active surface area as a function of the exposure time to the electrolyte, the thickness of the thick Mg(OH)2 layer and the kinetic constants of the electrochemical reaction

Evaluation of Zn-Cr III-organic coating by electrochemical impedance spectroscopy

Corrosion control of electrogalvanized steel employing Cr VI based treatments is widely known and studied. However, researchers have been trying to find out alternatives to replace these salts once they must be banned in accord to environmental and industrial guidelines. Cr III – based conversion coatings have shown performance compatible to Cr VI – based treatments. In this work, EIS measurements are performed in NaCl 0,05 mol/L and Na2SO4 0,1 mol/L, during the immersion time, to evaluate the corrosion resistance of electrogalvanized steel passivated with Cr III – based conversion treatment and painted with three different organic coatings. The organic coatings are characterized by their adherence. The results show a similar behavior for the three coatings and, despite a second constant time has been pointed by the EIS fitting, the R2 values indicate a low corrosion rate. The system Zn – Cr III – organic coating is compatible to the system Zn – Cr VI – organic coating, for the immersion period considered.O controle da corrosão de aço eletrogalvanizado empregando soluções à base de sais de Cr VI é amplamente conhecido e estudado. No entanto, pesquisadores vêm buscando alternativas para substituir estes sais já que diretrizes ambientais e industriais exigem que sejam banidos. Os revestimentos de conversão à base de Cr III têm mostrado um desempenho compatível aos baseados em Cr VI. Neste trabalho são utilizadas medidas de espectroscopia de impedância eletroquímica (EIE) em NaCl 0,05 mol/L e em Na2 SO4 0,1 mol/L, durante o tempo de imersão, para avaliar a resistência à corrosão de aço eletrogalvanizado revestido com tratamento à base de Cr III e pintado com três diferentes revestimentos orgânicos. Os revestimentos orgânicos sãocaracterizados por sua adesão. Os resultados mostram um comportamento semelhante para os três revestimentos e, apesar de uma segunda constante de tempo ter sido observada nos ajustes de EIE, os valores de R2 indicam uma baixa velocidade de corrosão. O sistema Zn – Cr III – revestimento orgânico é compatível ao sistema Zn – Cr VI – revestimento orgânico, para o período de imersão consideradoCentro de Investigación y Desarrollo en Tecnología de Pintura