Abstract The objective of this work was to develop a chemical admixture to make concrete capable to heal its fissures autonomously and, consequently, mitigate the concrete’s reinforcement corrosion due to the ingress of aggressive agents. For that, polymeric microcapsules built by a shell of urea-formaldehyde-melamine (UFM) and a core of methylmethacrylate were developed and added to the concrete to further evaluation. The concrete specimens containing 0%, 3% and 6% of the proposed microcapsules (mass of microcapsules / mass of cement) were subjected to destructive and non-destructive tests. The water absorption and the mechanical tests i.e., compressive strength and indirect tensile strength (Brazilian test) were carried out to characterize concrete, while the electrochemical impedance spectroscopy (EIS) and the non-destructive ultrasonic pulse velocity (UPV) tests were conducted to evaluate the concrete self-healing ability. These tests showed that the proposed admixture was able to heal the concrete’s fissures partially. In addition, it was concluded that the samples with 3% of microcapsules presented higher self-repairing rates. Despite the microcapsules developed in this work have presented a satisfactory self-healing efficiency, their effectiveness looks to be affected by the mixing procedure once part of them is broken during the process.

Resumo O objetivo deste trabalho foi desenvolver um aditivo químico capaz de tornar o concreto auto reparável e, consequentemente, mitigar a corrosão da armadura em seu interior devido à entrada de agentes agressivos. Para isso, microcápsulas poliméricas compostas por uma casca de uréia-formaldeído-melamina (UFM) e um núcleo de metilmetacrilato foram desenvolvidas e adicionadas ao concreto para posterior avaliação. Os corpos de prova de concreto contendo 0%, 3% e 6% das microcápsulas propostas (massa de microcápsulas / massa de cimento) foram submetidos a ensaios destrutivos e não destrutivos. O ensaio de absorção de água e os mecânicos, ou seja, resistência à compressão e resistência à tração indireta (teste brasileiro) foram realizados para caracterizar o concreto, enquanto a espectroscopia de impedância eletroquímica (EIS) e os ensaios não destrutivos de velocidade de pulso ultrassônico (UPV) foram conduzidos para investigar a ocorrência de autorreparação. Esses testes mostraram que o aditivo proposto foi capaz de cicatrizar as fissuras do concreto parcialmente. Além disso, analisando os dados coletados com o programa de testes, concluiu-se que as amostras com 3% de microcápsulas apresentaram maiores taxas de autorreparação. Apesar das microcápsulas desenvolvidas neste trabalho terem apresentado uma eficiência de autorreparação satisfatória, sua eficácia parece ser afetada pelo procedimento de mistura, uma vez que parte delas é quebrada durante o processo.

The inhibition effect of the cocoa bean shell powder (CBSP) on SAE 1008 carbon steel was studied in acidic medium (HCl 0.5 mol L-1) by electrochemical techniques and gravimetric measurements. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were used to the chemical and morphological characterization. The gravimetric and EIS results showed that the corrosion rate decreases with increasing inhibitor concentration, reaching the maximum value of 97.92% in 1.77 g L-1 inhibitor (highest concentration studied). Even at the lowest concentration (0.44 g L-1) good corrosion inhibition efficiency (96.03%) was observed. The polarization curves indicated that the CBSP acts as a mixed type inhibitor. The inhibitory molecules adsorption followed the Langmuir isotherm model. The inhibitor economic evaluation showed that the use of CBSP is 48-616 times cheaper than traditional inhibitors. The results showed that CBSP is an efficient corrosion inhibitor for carbon steel and its production is financially attractive.

Abstract Objective The aim of this study is to test, in vitro, the anti-cariogenic effect of experimental hybrid coatings, with nano clays of halloysite or bentonite, loaded with sodium fluoride or with a combination of sodium fluoride and stannous chloride, respectively. Methodology The varnish Fluor Protector (1,000 ppm of F-) was used as positive control and no treatment was the negative control. Enamel specimens (5 mm × 5 mm) were obtained from bovine teeth. The specimens (n=10) had their surfaces divided into two halves (5 mm × 2.5 mm each), in which one half received one of the treatments (Hybrid; Hybrid + NaF; Hybrid + NaF + SnCl2; Hybrid + NaF Loaded; Hybrid + NaF + SnCl2 Loaded). The specimens were submitted to a cariogenic challenge using a biofilm model (S. mutans UA159, for 5 days). Enamel surfaces both under and adjacent to the treated area were analyzed for mineral loss and lesion depth, by transverse microradiography. The pH of the medium was measured twice a day, and the fluoride release was analyzed. Additional specimens were submitted to confocal analysis. Results Data were statistically analyzed by two-way ANOVA followed by Tukey test (α=0.05). None of hybrid groups were able to reduce the lesion depth; the Hybrid + NaF group, however, was able to reduce mineral loss differing from the negative control (p=0.008). The groups showed no significant difference in the pH measurement and fluoride release. Confocal analysis confirmed that for all groups the biofilm growth was similar. Conclusion None of the hybrid groups reduced lesion depth, but the Hybrid + NaF group was able to promote protection against mineral loss.

ABSTRACT In this work, the wettability of the galvannealed surface pretreated with the hybrid silane APTES/GPTMS film was measured by sessile drop method. The coatings were applied on the substrate from dip-coating method and dried in an oven. The study followed an experimental factorial design, 3³, with contact angle as response. The corrosion resistance was evaluated by electrochemical techniques and the surface morphology was characterized by scanning electron microscopy. The wettability results showed the best condition for galvannealed steel pretreated with the hybrid silane film for 2:1 APTES:GPTMS ratio, 2% silane concentration and 150 min of hydrolysis time, because the result may be related to a higher rate of hydrolysis of the silanes that is influenced by both the functional group present and by the type and number of hydrolyzed groups, resulting consequently in a higher availability of silanol groups in solution, promoting a greater crosslinking of the film on the metallic substrate.

RESUMO Silanos são compostos organo funcionais utilizados como agentes de acoplamentos entre interfaces orgânicoinorgânicas, com boas propriedades de adesão. Por esta razão, o uso de silanos como pré-tratamento para aços, vem ganhando espaço já que também são geradores de resíduos de menor toxidade ao meio ambiente e à saúde humana. Para melhorar a barreira de proteção do filme de silano e conferir propriedades de autorreparação, esses filmes podem ser modificados com íons cério. Assim, esse trabalho tem como objetivo avaliar a resistência à corrosão do filme de silanoviniltrimetoxisilano (VTMOS) modificado com íons Ce(III) ou íons Ce(IV) aplicado em aço carbono, utilizando a espectroscopia de impedância eletroquímica (EIE), técnica de varredura por eletrodo vibratório (Scanning Vibrating Electrode Technique -SVET), microscopia eletrônica de varredura (MEV) e transformada de Fourier de espectroscopia na região do infravermelho (Fourier Transform Infrared Spectroscopy -FTIR). Os resultados mostraram que os filmes com adição de íons Ce(IV) apresentaram uma melhor resistência à corrosão se comparados aos filmes com íons Ce(III), isto porque o filme formado com a adição de íons Ce(IV) mostrou um melhor efeito barreira devido à uma maior reticulação do filme.

ABSTRACT Silanes are organo functional compounds used as coupling agents between organic-inorganic interfaces, with good adhesion properties. For this reason, the use of silanes as pre-treatment for carbon steel is becoming more and more applicable , since they are also generators of less toxicity residues to the environmental and human health. In order to improve the barrier protection of the silane film and confer self-healing properties, these films can be modified by addition of cerium ions. Thus, these work aims to evaluate the corrosion resistance of vinythrimethoxysilane (VTMOS) film modified with Ce(III) ions or Ce(IV) ions for carbon steel, using the electrochemical impedance spectroscopy (EIS), scanning vibrating electrode technique (SVET), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results show that Ce(IV) ions addition improved better corrosion resistance than the films with Ce(III) ions. The higher barrier effect is since the film formed in the presence of Ce(IV) ions is better reticulated.

The inhibition effect of castor bark powder obtained from Ricinus communis on AISI 1020 carbon steel in acidic media (HCl 0.5 mol.L-1) has been studied by electrochemical impedance spectroscopy (EIS), polarization curves, scanning vibrating electrode technique (SVET) and weight loss measurements. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were employed as characterization techniques. The EIS and gravimetric results showed that the inhibitory efficiency increases with inhibitor concentration achieving 83%. Polarization curves indicated that the castor bark powder acts as mixed inhibitor. The adsorption of the powder components on the metal surface follows the Langmuir isotherm. The FTIR analyses indicate the presence of C, N and O heteroatoms, incorporated in functional groups mainly related to the presence of carboxylic acids as ricinoleic acid, which could be responsible for the inhibitory properties of the powder. SEM analyses showed that the corrosion process was retarded in the presence of inhibitor in the electrolyte, which was confirmed by SVET measurements. Therefore, the results indicate that castor bark powder has potential to be a corrosion inhibitor for carbon steel in acidic media.

Cerium conversion layers and silane films are among the potential substitutes for the carcinogenic chromate conversion layers used to protect high-strength Al alloys. In the present work the adhesion of a cerium conversion layer and of a silane film to an aluminium alloy (AA) 2024-T3 substrate was investigated using mechanical and electrochemical tests. Scanning electron microscopy (SEM)- X ray energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR) and X ray photoelectron spectroscopy (XPS) were used to characterize the layers prior and after the mechanical test consisting of ultrasonic rinse in deionized water during 30 minutes. Mechanically tested and untested layers were also submitted to electrochemical impedance spectroscopy (EIS) and anodic polarization measurements in 0.1 M NaCl solution. The results of the characterization tests have pointed to a stronger adhesion of the Ce layer to the substrate in comparison with the silane film, which was confirmed by the electrochemical tests. The adhesion between the silane film and the Ce conversion layer was also tested, to evaluate the possibility of using the system as a protective bi-layer in accordance with the new trends being developed to substitute chromate conversion layers.

Um climatograma é um diagrama das condições climáticas de uma região e é definido pela severidade característica dessas condições. A severidade característica de um parâmetro climático é determinada pelos valores extremos desse parâmetro que são obtidos a partir de uma distribuição estatística da temperatura do ar medida (T) e da humidade relativa do ar (RH) num local específico durante um período de monitorização longo. É apresentado aqui o climatograma de Lisboa, em Portugal. Lisboa é classificada como uma região de clima temperado, com uma estação curta de Inverno e período longo e temperado do Verão. Lisboa está situada a uma latitude de 38º 43' N e 9º 11' W de longitude e tem uma pressão atmosférica média de 1,0043 bar. A humidade relativa é geralmente muito elevada o que torna o seu clima muito especial e um tanto similar ao das regiões tropicais. Neste trabalho foram utilizados na construção do climatograma 8519 valores de T e de RH, adquiridos num período de cinco anos, com uma frequência de tempo de quatro horas de intervalo, num total de seis valores por dia. Para cada valor de RH está associada uma pressão parcial da água (pA). Além disso, para cada valor de RH medido pode ser determinada uma humidade absoluta (AH). Então, conhecendo a T, a RH e a AH, os valores máximos e mínimos com probabilidade de 1% e de 10% de ocorrência podem ser determinados a partir da distribuição estatística dos parâmetros observados ou calculados usando o software estatístico Minitab. Deste modo, podem ser obtidos os valores limite (valores extremos de T e de RH) do diagrama do quadrado do climatograma. De forma a completar o diagrama, traçou-se uma curva determinada pela equação que relaciona T e RH. Há um diagrama para cada percentil [1% (exterior) ou 10% (interior)] na probabilidade do lote de ocorrência. Foram efectuadas comparações entre o climatograma de Lisboa e outros obtidos em regiões de clima tropical, no âmbito do Projecto Tropicorr, ao abrigo do programa Cyted que tem como objectivo caracterizar a corrosividade de climas Ibero-Americanos específicos nos materiais usados em dispositivos electro-eletrónicos com vista a melhorar o seu desempenho e fiabilidade.

A climatogram is an envelope of climatic conditions defined by the characteristic severity of these conditions. A characteristic severity of a climatic parameter is determined by the extreme values of the parameter obtained from a statistical distribution of the measured air temperature (T) and the relative air humidity (RH) in a specified location for a long monitoring period. The climatogram of Lisbon, in Portugal, is presented. Lisbon is classified as a temperate climate region, with short winter season and long and warm summer period. Lisbon is located at 38º 43’ N of latitude and 9º 11’ W of longitude and an average atmospheric pressure of 1.0043 bar. The relative humidity is commonly very high which makes its climate very special and somewhat similar to those of the tropical regions. In this work 8519 paired T and RH values acquired for five years, in a time frequency of four hours intervals starting from 2:00a.m, summing up a total of six recordings per day that were used for constructing the climatogram. For every RH value there is an associated water partial pressure (pA). Moreover, for each RH values an absolute humidity (AH) can be determined. So, with the known quantities T, RH and AH, the maximum and the minimum values with 1% and 10% probability of occurrence can be determined from the statistical distribution of the observed or calculated parameters using Minitab statistical software. Thus, the boundary values (extreme values of T and RH) of the climatogram square envelope can be obtained. In order to complete the envelope, a curve determined by the equation relating T and RH was drawn. There is an envelope for each percentile [1% (outer) or 10% (inner)] in the probability of occurrence plot. Comparisons between Lisbon climatogram and others obtained for regions of tropical climate are made, under the scope of the Tropicorr project, beneath the Cyted Programme in order to characterise the corrosivity of specific Ibero-American climates on materials used in electro-electronic devices to improve their reliability.