RESUMO O trabalho apresenta avaliação do extrato alcoólico do chá branco como potencial inibidor de corrosão para o aço carbono P110 na presença de ácido clorídrico 1 mol.L-1. Os inibidores de corrosão destacam-se na proteção de peças metálicas em ambientes ácidos, sendo que muitas das substâncias presentes na composição de inibidores comerciais apresentam caráter danoso ao meio ambiente. Por este motivo, extratos de plantas passaram a ser avaliados como potenciais inibidores de corrosão pela sua natureza não tóxica ao meio ambiente, além de seu caráter renovável, constituindo-se nos chamados inibidores verde de corrosão. O chá branco é proveniente da Camellia sinensis, sendo utilizadas folhas e galhos secos na preparação do extrato em etanol. Foram realizados ensaios de perda de massa para diferentes concentrações do extrato (100, 200 e 300 ppm), com a concentração de 300 ppm apresentando o melhor resultado, com uma eficiência de inibição de 90,2%. Ensaios de polarização e impedância eletroquímica foram realizados com redução nas correntes anódicas e catódicas, aumento na resistência a transferência de carga e redução na capacitância da dupla camada elétrica, indicando um processo de adsorção do extrato sobre as áreas ativas do metal. Os resultados apontam para o potencial uso de extrato alcoólico do chá branco como matéria ativa na formulação de inibidor de corrosão ambientalmente seguro.

ABSTRACT This research work presents an evaluation of the alcoholic extract of the white tea as potential corrosion inhibitor for the carbon steel P110 in the presence of 1 mol.L-1 hydrochloric acid. Corrosion Inhibitors stand out in the protection of metallic parts in acid environments, and many of the substances present in the composition of the commercial inhibitors are harmful to the environment. For this reason, plant extracts began to be evaluated as potential corrosion inhibitors because of their non toxic nature, as well as their renewable character, constituting the so called green corrosion inhibitors. The white tea comes from the Camellia sinensis, leaves and dry branches are used in the preparation of the extract in ethanol. Mass loss tests were performed for different concentrations of the extract (100, 200, 300 ppm) with the concentration of 300 ppm showing the best result, with an inhibition efficiency of 90,2%. Polarization and electrochemical impedance tests were carried out with reduction in the anodic and cathodic currents, increase in the resistance to charge transfer and reduction in the capacitance of the electric double layer, indicating a process of adsorption of the extract over the active areas of the metal. The results indicate the potential use of the alcoholic extract of white tea as an active material in the formulation of an environmentally safe corrosion inhibitor.

Very often hydrochloric acid is employed in acidification operations aiming to dissolve the mineral matrix in petroleum wheel operations, which always require intense use of corrosion inhibitors. This work presents an evaluation of common indicators, phenolfthaleine, fluorescein, methylene blue, alizarine S and methyl orange, as corrosion inhibitors for carbon steel in HCl 15% w/v at temperatures of 26, 40 and 60 ºC. Fluorescein and methyl orange show excelent corrosion inhibition efficiencies at 26 ºC; however at 60 ºC only fluorescein shows good corrosion inhibition when employed with alcohol and/or formaldehyde. For the fluorescein 1% w/v + formaldehyde 0.6% w/v mixture we present polarization and impedance curves and adsorption isotherms.

Aromatic nitration is one of the most relevant class of reactions in organic chemistry. It has been intensively studied by both experimental, including works in the condensed as well as in the gas phase, and theoretical procedures. However, the published results do not seem to converge to an unique mechanism. Electrophilic substitution and electron transfer, in an exclusive way, are both proposed as the main mechanism for the reaction. We review these proposals and discuss the most recent findings.

This work intends to identify the reasons why people either like or dislike chemistry classes, based on a written questionnaire answered by 157 students of private and public schools. It has a main question - "Do you like to study chemistry? Why?" - and along with others that complement it, we attempt to explore both pupils' school and personal experiences which help them to increase their learning capacities. The answers have given us a very rich piece of discussing material about the like-and-dislike on the study of chemistry mainly about the social interactions in teaching not only this but all other subjects.

We analyse vibrational frequencies of 168 compounds with the AM1 model concerning its experimentally observed gaseous frequencies. Stretching of CH, NH, OH and CO bonds, its related bending frequencies, and the CC frame movements are the studied vibrations. The results show problems with the AM1 vibrational splittings. Often symmetric stretching frequencies, like in CH3, CH2 and NH3, appear switched with the corresponding antisymmetrical ones. Among the studied vibrations many stretchings are overestimated, while bendings oscillate around experimental values. Fluorine stretchings, NN, OO, CH, double and triples CC bonds and cyclic hydrocarbon breathing modes are always overestimated while torsions, umbrella modes and OH/SH stretching are, in average, underestimated. Graphical analysis show that compounds with the lowest molecular masses are the ones with the largest difference to the experimental values. From our results it is not possible to fit confortably the calculated frequencies by a simple linear relationship of the type, n(obs)=a*n(AM1). Better aggreement is obtained when different curves are adjusted for the stretching and bending modes, and when a complete linear function is used. Among our studies the best obtained statistical results are for CH, NH and OH. The conclusions obtained in this work will improve the AM1 calculated frequencies leading to accurate results for these properties.