The pitting corrosion of supermartensitic stainless steel (SMSS) was studied in an aqueous solution of 0.1 mol/L NaCl using the scanning vibrating electrode technique (SVET) and cyclic voltammetry. The SMSS showed 0.9% of retained austenite, as verified by Mössbauer spectroscopy. Cuboidal TiN particles were identified on the steel surfaces, by using optical, scanning electron, and transmission microscopy, associated to Mg-Ca-Al rich precipitates. Pit nucleation was slow and only verified after 24 h, associated to TiN/CaO·MgO·Al2O3 complex inclusions, thus on original interdendritic spaces, where lower Cr content and the presence of inclusions are expected.

ABSTRACT This work examined the pitting corrosion resistance of two types of duplex stainless steels: UNS S31803, with molybdenum, and UNS S32304, without molybdenum. Cyclic potentiodynamic polarization and critical pitting temperature (CPT) tests were performed in 3.5 wt% NaCl solution. Scanning electron microscopy (SEM) was used for analysis of the pits on the surface of samples. The two steels studied presented susceptible to pitting corrosion in 3.5 wt% NaCl solution. UNS S31803 steel showed a higher corrosion potential (Ecorr), pitting potential (Epit), and polarization resistance (Rp) compared to UNS S32304 steel. It was also observed that the UNS S31803 steel showed higher capacity to repassivation and CPT than the UNS S32304 steel.

The effect of the increase in crystalline defects in the structure generated by high-pressure torsion (HPT) on the corrosion behavior of metallic materials is not well understood. This report evaluates the influence of HPT on the corrosion behavior of a solution treated Al-3wt% Mg-0.2wt% Sc alloy in a 3.5 wt./v.% NaCl solution. The electrochemical behavior of the alloy was evaluated using cyclic polarization, electrochemical impedance spectroscopy (EIS), Mott Schottky, X-ray photoelectron spectroscopy, and chronoamperometry testing. The passive current density decreased after HPT processing, indicating a more protective oxide layer was formed on the surface of the HPT-processed alloy. Mott Schottky analysis confirmed the higher protection efficiency of the passive layer on the HPT-processed alloy. The film formed in the solution-treated alloy was a p-type and an n-type semiconductor while the alloy processed by HPT exhibited only an n-type semiconductor behavior. EIS showed that corrosion resistance in a saline medium increased with HPT processing.

ABSTRACT Deposition of interference film is an alternative way for the formation of colored protective layers on the surface of stainless steels for decorative applications. The process involves growth of a chromium oxide film by electrochemical methods using in general sulphochromic solutions. However, it is well known that chromic acid contains Cr(VI), which is highly toxic, demanding special effluent treatments in order to avoid environmental pollution. The aim of the present work is to evaluate alternative chromium free solutions for coloration of stainless steel by an electrochemical method as a trial to avoid the Cr(VI) presence to achieve an environmentally friendly process. The morphology and corrosion resistance of the conversion coatings obtained from sodium vanadate solution were comparatively evaluated with a sample coloured in a sodium molybdate solution containing chromium and in a sulfochromic solution currently used in industrial coloration process. The corrosion behaviour of the colored samples was evaluated by using anodic potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The steel colored in a solution containing chromium and molybdenum ions showed the lowest corrosion resistance and a more porous and heterogeneous film than the other steel samples colored using vanadate and sulfochromic solutions. An electrochemical processing using a sodium vanadate solution can be a chromium free alternative for industrial application.

RESUMO A contaminação de corpos hídricos por petróleo e seus derivados tem sido um dos principais problemas ambientais da atualidade e causa prejuízos diversos, como o desequilíbrio ecológico pelos danos à fauna e flora e a redução da disponibilidade de luz solar no meio aquático. Diante desse contexto, este trabalho propôs o emprego de casca de eucalipto para a eliminação de hidrocarbonetos leves de petróleo (gasolina comercial do tipo C) contaminantes em ambientes simulados de água doce e água salgada. Para tanto, foi verificada a capacidade de a casca adsorver compostos orgânicos quando submetida ao contato com os corantes amarelo tartrazina, rodamina B e azul de metileno, tendo os dois últimos confirmado a afinidade química do biomaterial com compostos de carbono. Em seguida, na adsorção de hidrocarbonetos leves da solução contaminante simulada, foram avaliadas as influências: da granulometria da biomassa, pela qual se observou a tendência de melhor adsorção com o menor tamanho de partícula do material, a temperatura do corpo hídrico, que não afetou consideravelmente a capacidade de adsorção, e o tempo de reação, que beneficiou a biossorção em ambiente de água doce e desfavoreceu quando a biomassa esteve em contato com água salgada. Além disso, numa comparação da casca de eucalipto com outros adsorventes comerciais (carvão ativo, vermiculita e terra diatomácea), essa teve capacidade de adsorção superior aos demais, mostrando-se ser um material promissor para a descontaminação de águas contendo hidrocarbonetos de petróleo.

ABSTRACT The contamination of water bodies by petroleum and its derivatives has been one of the main environmental problems nowadays and it causes many losses, such as ecological imbalance by damage to fauna and flora, and the reduction of the sunlight availability in the aquatic environment. Given this context, this paper proposed the employing of eucalyptus bark for the removal of petroleum light hydrocarbons (commercial gasoline type C) contaminant in simulated freshwater and saltwater environments. Therefore, it was verified the bark ability in adsorbing organic compounds when it was submitted to the contact with tartrazine, rhodamine B and methylene blue dyes, and the latter two had confirmed the chemical affinity of the biomaterial with carbon compounds. Then, in the adsorption of the simulated contaminant solution, it was evaluated the influences of: the biomass particle size, observing a trend toward better adsorption with the smallest particle size of the material, the water body temperature, that did not appreciably affect the adsorption capacity, and the reaction time, which benefited the adsorption in freshwater environment and reduced when the biomass was in contact with the saltwater. Furthermore, in a comparison among eucalyptus bark and other commercial adsorbents (activated charcoal, vermiculite and diatomaceous earth), it had higher adsorption capacity than all of them, proving to be a promising material for the decontamination of water containing petroleum hydrocarbons

RESUMO Na produção de soros antiofídicos e antitóxicos, comumente se utiliza a terra diatomácea, que é um mineral leve, de baixa massa específica e com alto potencial de adsorção, sendo este comumente empregado em processos de filtração. A fim de se reutilizar a terra residual dos processos de filtração de soros antiodíficos e antitóxicos da Fundação Ezequiel Dias, este trabalho propôs sua recuperação via tratamento térmico. Após Análise Termogravimétrica da terra diatomácea residual, concluiu-se que a partir de 600°C todas as impurezas presentes neste material haviam sofrido degradação. Assim, uma amostra do mineral saturado foi aquecido em forno mufla até a temperatura de 700°C. Em seguida, a influência do tratamento térmica nas propriedades do mineral foi avaliada por meio da determinação dos parâmetros físico-químicos como pH, densidade aparente, teor de umidade base seca e seu potencial de adsorção em plasma equino hiperimune, principal característica para sua aplicação no processo de filtração para obtenção dos soros. Foi verificado que as propriedades físico-químicas do material recuperado estiveram próximas àquelas da terra nova, sendo obtidas diferenças percentuais de 6,1% para o pH, 12,8% para densidade aparente, 3,6% para o teor de umidade base seca e 1,4% em relação ao potencial de adsorção relativo. Desta forma, foi possível inferir que o tratamento térmico proposto não alterou consideravelmente a capacidade de adsorção da terra diatomácea, tornando-a reutilizável como agente filtrante no processo de produção dos soros.

ABSTRACT In the production of antiophidic and antitoxic sera, it is common to use diatomaceous earth, which is a light mineral, with low specific mass and high adsorption potential, commonly employed in filtration processes. In order to reuse the residual earth from filtration processes of antiophidic and antitoxic sera of Fundação Ezequiel Dias, this work purposed its recuperation by thermal treatment. After Thermogravimetric Analysis of the residual diatomaceous earth, it was concluded that from 600°C all the impurities present in this material suffered degradation Thus, a sample of saturated mineral was heated in a muffle oven up to temperature of 700°C. Then, the influence of the thermal treatment in the mineral properties was evaluated by means of the determination of the physicochemical parameters pH, apparent density, dry basis moisture content and its adsorption potential in hiperimune horse plasma, the main characteristic for its application in the filtration process to obtain the sera. It was verified that the physicochemical properties of the recuperated material were very close to them of the new earth, being obtained percentage variations of 6.1% for pH, 12.8% for apparent density, 3.6% for basis moisture content and 1.4% in relation to relative adsorption percentage. Therefore, it was possible to infer that that the purposed thermal treatment did not vary its adsorption capability considerably, making possible to reuse it as a filtration agent in the sera production process.

ABSTRACT In the oil and gas industry, super matensitic steels have been used primarily in the manufacture of seamless steel pipe for use in drilling oil and gas. The objective of this work is to evaluate the corrosion resistance of rolled and rerolled super martensitic steels in electrolytes of aqueous solution of NaCl 35 g/L, and aqueous solution of NaCl 120 g/L, sodium acetate 0.4 g/L, with pH 4.5 (standard solution), saturated and unsaturated with H2S, simulating the service conditions of petroleum industry in the pre-salt operation. For this evaluation, the electrochemical tests used are electrochemical impedance spectroscopy (EIS) and cyclic polarization test. The characterization techniques used are optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The effect of H2S saturation of the solutions studied on the corrosion resistance of steels was detrimental. The super martensitic steel in the rerolled condition showed a higher corrosion resistance than the rolled steel in an aqueous solution of 35 g/L NaCl and in a standard solution saturated with H2S. In the 35 g/L NaCl aqueous solution saturated with H2S and in the standard solution, the rolled steel showed a higher corrosion resistance than the rerolled steel. In an aqueous solution of 35 g/L NaCl, the rolled and rerolled steels showed pitting diameter of 140μm and 100μm, respectively.

Stainless steel (SS) is successfully used in food industries due to the characteristics of its surface, which is essential for the maintenance of the properties of food. Tanks and stainless steel pipes, which come into direct contact with food and drink, undergo a process of cleaning and disinfecting called CIP (Clean-in-Place). This method consists of automatic recirculation of a detergent solution for a controlled time followed by a rinsing with water, and finally a cleaning and sanitizing solution immersion. This work consists of investigating the corrosion resistance of stainless steels used in the food industry using sanitizing solutions employed in the CIP procedure, and using electrochemical techniques such as potentiodynamic anodic polarization and electrochemical impedance spectroscopy.