Centro de Química Estrutural

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Publications

Electrochemical assessment of corrosion-fatigue degradation stages

Publication . Simões, Alda Maria Pereira; Canut, Felipe; Reis, Luis; Napoleão Bastos, Ivan; Mamiya, Edgar

ABSTRACT: The study is focussed on the joint effect of corrosion and mechanical cyclic stresses observed on mooring chains of Floating Production Storage and Offloading (FPSO) units. The tests were performed using grade R4 steel in artificial sea water, under stress-controlled and fully reversed loading. The corrosion-fatigue degradation was monitored using open circuit potential measurements simultaneously with the cyclic mechanical load. The open circuit potential response varies during the corrosion-fatigue test, depending on the stage of degradation of the material. This technique has proven to be capable of identifying important phenomena, such as crack initiation and crack propagation, on the material under corrosion-fatigue loading condition.

2022-11Conference object

Open access

Lipid and carotenoid production by a Rhodosporidium toruloides and Tetradesmus obliquus mixed culture using primary brewery wastewater supplemented with sugarcane molasses and urea

Publication . Dias, Carla; Nobre, B. P.; Santos, J. A. L.; Reis, Alberto; Silva, Teresa Lopes da

ABSTRACT: In this study, Rhodosporidium toruloides and Tetradesmus obliquus were used for lipid and carotenoid production in mixed cultures using primary brewery wastewater (PBWW) as a culture medium, supplemented with sugarcane molasses (SCM) as a carbon source and urea as a nitrogen source. To improve biomass, lipid, and carotenoid production by R. toruloides and T obliquus mixed cultures, initial SCM concentrations ranging from 10 to 280 g L-1 were tested. The medium that allowed higher lipid content (26.2% w/w dry cell weight (DCW)) and higher carotenoid productivity (10.47 mu g L-1 h(-1)) was the PBWW medium supplemented with 100 g L-1 of SCM and 2 g L-1 of urea, which was further used in the fed-batch mixed cultivation performed in a 7-L bioreactor. A maximum biomass concentration of 58.6 g L-1 and maximum lipid content of 31.2% w/w DCW were obtained in the fed-batch cultivation. PBWW supplemented with SCM was successfully used as a low-cost medium to produce lipids and carotenoids in a R. toruloides and T obliquus mixed culture, with higher productivities than in pure cultures, which can significantly reduce the cost of the biofuels obtained.

2022-07Journal article

Open access

Solid-gas reactors driven by concentrated solar energy with potential application to calcium looping: A comparative review

Publication . Rivero, Mayra Alvarez; Rodrigues, Diogo; Pinheiro, Carla I.C.; Cardoso, João P.; Mendes, Luís Filipe

ABSTRACT: The calcium looping process, based on the reversible calcination-carbonation reaction cycle of CaCO3-CaO, is an emerging and promising technology for thermochemical energy storage in concentrating solar power plants. In this process, concentrated solar energy is used to carry out the endothermic solar-driven calcination of CaCO3 with formation of CaO and CO2 as products in a solid-gas reactor. In this review, a number of experimental studies of solid-gas reactors driven by concentrated solar energy are discussed, with a particular focus on solar reactors for calcination of CaCO3 or with that potential application. The solid-gas reactors for solar-driven calcination of CaCO3 reported in the literature achieved a total efficiency of 16.6%-88% for a mass flow rate up to 25 kg h(-1) and a power up to 55 kW. Also, a detailed comparison of the different types of solid-gas reactors driven by concentrated solar energy is provided by outlining their advantages and disadvantages according to several relevant criteria. This review is intended to be a valuable tool for the selection of a reactor configuration for future studies related to solar-driven calcination of CaCO3.

2022-04Journal article

Open access

Naphthenic corrosion using electrochemical and analytical techniques

Publication . Simões, Alda Maria Pereira; Pereira Da Silva, Rejane Maria; Suffredini, Hugo; Santos, Luis; Bastos, Ivan Napoleão

ABSTRACT: Naphthenic acid corrosion of steel was studied in a stagnant, biphasic oil/aqueous phase system, by means of electrochemical measurements and surface analysis. Corrosion was restricted to the region of the aqueous phase, as crater-shaped pits that eventually coalesced, generating a nearly uniform attack in the vicinity of the oil phase. In-situ electrochemical impedance spectroscopy (EIS) reveals the processes occurring at the aqueous phase, which nevertheless increase with the fraction of oil phase and with degree of acidity of the oil.

2022-11Conference object

Open access

Banhos de anodização contendo aditivos sustentáveis utilizados para proteção contra corrosão na liga AA2024-T3

Publication . Proença, Carla Sofia; Serrano, B.; Cabral, A. M.; Correia, J. P.; Araujo, Maria Eduarda

RESUMO: A liga de alumínio 2024-T3 é uma das ligas mais utilizadas na indústria aeronáutica devido às suas boas propriedades mecânicas. No entanto, devido à presença de partículas intermetálicas de cobre na sua matriz, esta liga é muito suscetível à corrosão. O presente trabalho teve como principal objetivo avaliar a capacidade de inibição da corrosão, de camadas de conversão eletroquímica obtidas com banhos de anodização e posteriormente seladas. Os banhos continham aditivos orgânicos de origem natural. Foram estudados os aditivos orgânicos sorbitol (SSA) e xilitol (XSA), e feita uma comparação com os filmes obtidos no banho de anodização em que foi utilizado o ácido tartárico (TSA). A resistência à corrosão das amostras tratadas foi monitorizada por ensaios de espectroscopia de impedância eletroquímica. Recorreu-se à técnica de voltametria cíclica para obter informação sobre o mecanismo de inibição de cada um dos aditivos envolvidos neste estudo. Para determinar as possíveis interações químicas entre os aditivos com capacidade inibidora utilizados e o substrato, recorreu-se à técnica de Espectroscopia no Infravermelho por Transformada de Fourier (FTIR). A morfologia das amostras tratadas com estes compostos foi avaliada por microscopia eletrónica de varrimento acoplada com Espectroscopia de Energia Dispersiva de Raios-X.

2022-11Conference object

Open access