Biblioteca Digital do IPB
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Soldadura do aço SAE 1020 com processo MAG: influência do recozimento e otimização pelo método Taguchi
Publication . Turone, Renato Augusto do Carmo; Ribeiro, J.E.; Francisco , Júlio César de Souza
O processo de soldadura MIG/MAG é amplamente utilizado na indústria devido à sua alta eficiência na união de materiais por fusão com arco elétrico. A definição adequada
dos parâmetros operacionais impacta diretamente na qualidade do cordão de solda. Com o ajuste correto desses parâmetros, é possível reduzir o consumo de material de adição, otimizar propriedades mecânicas e, por consequência, elevar a produtividade do processo. Este estudo teve como finalidade selecionar um conjunto de variáveis de soldadura e otimizá-las por meio da metodologia de Taguchi, além de analisar sua influência com base na Análise de Variância (ANOVA). Foi utilizado um arranjo ortogonal L9, envolvendo três fatores (tensão de soldadura, velocidade de avanço e ângulo da tocha), cada um em três níveis distintos. Após a realização das nove combinações experimentais, foram efetuadas análises macrográficas e ensaios de flexão, tanto para amostras submetidas ao recozimento quanto para aquelas sem tratamento térmico, de modo a determinar características geométricas e mecânicas.
A otimização foi conduzida com o auxílio das razões sinal-ruído, enquanto a ANOVA permitiu identificar a relevância de cada parâmetro de entrada sobre os resultados obtidos,
como largura, reforço, penetração e limite de resistência à flexão do cordão de solda. Observou-se que a velocidade de soldadura teve maior impacto sobre o reforço nas amostras sem recozimento (33,08%), ao passo que nas recozidas, a tensão foi predominante (53,05%). Em relação à largura, a tensão demonstrou maior influência em ambos os casos, com 36,94% e 34,89% para amostras sem e com recozimento, respectivamente. Para a penetração, o ângulo da tocha foi o fator de maior relevância, contribuindo com 59,47% nas amostras sem recozimento e 48,24% nas recozidas. Quanto à resistência à flexão, a velocidade foi dominante nas amostras não recozidas (27,59%), enquanto o ângulo da tocha prevaleceu nas recozidas (26,54%). As combinações otimizadas encontradas para os diferentes parâmetros foram: para o reforço, 25 , 23,7 V e 400 mm/min nas amostras sem recozimento, e 0 , 24,1 V e 250 mm/min nas recozidas; para a largura, 0 , 24,1 V e 400 mm/min nas não recozidas, e 25 , 23,7 V e 325 mm/min nas recozidas; para a penetração, 0 , 24,1 V e 400 mm/min nas amostras sem recozimento, e 15 , 22,4 V e 325 mm/min nas recozidas; e, por fim, para o limite de resistência à flexão, as melhores condições foram 25 , 23,7 V e 250 mm/min sem recozimento, e 0 , 23,7 V e 250 mm/min com recozimento.
Use of generative AI by PHD students: impact on productivity and skills development
Publication . Gonçalves, Bruno F.
Higher education is constantly changing, especially with the growing use of generative artificial intelligence by doctoral students. This reality has led to significant changes in the way research activities are planned, organized, and executed, directly influencing productivity and skills development. This article aims to analyze the impact of the use of generative AI on productivity and the acquisition of skills by doctoral students at a university in Mozambique. The research, exploratory and descriptive, was based on the application of a questionnaire to all students on two postgraduate courses at a higher education institution. Sixty-two responses were validated, allowing for a robust analysis of the data. The results indicate that the use of AI has significantly changed the way students plan and carry out their research tasks, facilitating productivity. However, concerns were also identified about a possible over-reliance on these tools. In addition, participants recognized that certain skills were particularly impacted by the use of AI. Despite the risks, students reported a balance between productivity gains and skills development, highlighting the importance of conscious and strategic use of AI in the academic context.
Retting of natural fibers for the manufacturing of filaments
Publication . Ferreira, Luana Francisca Novais; Rocha, João; Ribeiro, J.E.
Nos últimos anos, a necessidade imperiosa de mitigar a dependência de polímeros derivados do petróleo, aliada à crescente exigência por materiais ambientalmente sustentáveis, tem fomentado de forma significativa a investigação no domínio dos compósitos biodegradáveis. Entre os biopolímeros disponíveis, o ácido poliláctico (PLA) evidencia-se pela sua proveniência renovável, biodegradabilidade e propriedades mecânicas superiores face a outros polímeros sustentáveis. Contudo, o PLA apresenta limitações intrínsecas, nomeadamente fragilidade e reduzida resistência ao impacto, características que podem ser atenuadas mediante a incorporação de fibras naturais como elementos de reforço.
As fibras lignocelulósicas naturais têm vindo a assumir uma preponderância crescente no setor industrial, devido à sua relação otimizada entre resistência e massa volúmica, elevada biodegradabilidade e impacto ambiental quando comparadas com as fibras sintéticas. Alguns exemplos de fibras naturais muito utilizadas são as do cânhamo e do linho O cânhamo, em particular, distingue-se pela sua robustez estrutural e elevada rigidez, sendo amplamente utilizado nas indústrias automóvel e da construção. O linho, por outro lado, estingue-se pela sua flexibilidade e notável capacidade de absorção a impactos.
O presente estudo visa a investigação, caracterização e otimização da produção de fibras naturais de cânhamo, linho e castanha para a formulação de filamentos destinados à manufatura aditiva, com particular foco na impressão tridimensional. Será realizada uma análise holística das propriedades físicas, químicas e mecânicas dos compósitos obtidos, com o intuito de aferir a viabilidade da substituição de reforços convencionais por fibras naturais. Os resultados do trabalho desta tese contribuirão para o desenvolvimento de soluções compósitas inovadoras, sustentáveis e de elevado desempenho, promovendo alternativas tecnologicamente avançadas e ambientalmente responsáveis em setores industriais estratégicos.
Estrogen removal through adsorption using carbon materials prepared from biomass waste
Publication . Exposto, Bruno Marques; Queiroz, A.M.; Ribeiro, António E.; Brito, Paulo
Endocrine disruptors are class of micropollutants that can influence and deregulate the endocrine system in humans and animals. Endocrine disruptors can consist of natural estrogenic hormones, such as E1 and E2, and synthetic estrogenic hormones, such as EE2, that are not easily removed by conventional treatment processes in water and sewage treatment plants, becoming dangerous emerging pollutants. This work addresses the removal of such compounds from aqueous matrices through adsorption processes onto activated carbon produced from biomass waste.
The materials selected were almond shell in natura (ASiN) and cork in natura (CiN). These were activated through carbonization at 550ºC for 1 h, obtaining carbonized almond shell (CAS) and carbonized cork (CC). These materials were characterized by carbonization yield, moisture and ash content, PZC value, quantification of acidic and basic sites and FTIR analysis.
For the adsorption assays, the impact of conditions such as adsorbent type, temperature and medium pH was assessed in relation to removal performance. Kinetic and isotherm assays were also performed in batch mode, together with the assessment of the thermodynamic data.
The results show that equilibrium time was 16 h for ASiN, 4 h for CAS, 6 h for CiN and 24 h for CC. The adsorption process was regulated through the Elovich model for all adsorbents except for CiN, where the best model was PSO. Moreover, cork-based adsorbents presented higher adsorption capacities and activation through carbonization did not contribute to an increase in estrogen removal. Therefore, CiN was selected as the best material for estrogen removal to the posterior assays.
A temperature increase did not affect CiN’s adsorption capacity, and Ea was determined to be 136.15, 80.84 and 146.81 kJ/mol for E2, EE2 and E1, respectively. Moreover, pH change only negatively affects adsorption when in extreme basic media.
CiN’s adsorption process has been characterized by the Sheindorf-Rebuhn-Sheintuch multicomponent isotherm for all estrogens, with maximum adsorption capacities of 3.75, 7.23 and 3.82 mg/g achieved for estrogens E2, EE2 and E1, respectively, at 25ºC. Average removal percentage increased with the adsorbent’s dosage until it reached a maximum of 66.1% at 1 g/L. Both the adsorption capacity and removal percentage decreased with the increase in temperature.
Thermodynamic data was determined and negative values for ΔGº and ΔHº and positive values for ΔSº were obtained, meaning that adsorption was characterized as spontaneous, exothermic and entropically favourable. It was verified that estrogen adsorption occurred through a combination of
chemisorption and physisorption phenomena. Chemisorption occurred mainly through pEDA interactions and hydrogen bridges between estrogen and CiN’s functional groups and aromatic rings, while physisorption occurred mainly through pore filling. pEDA bonding assisted by hydrophobic interactions could be an explanation for the higher adsorption rates verified for EE2 in CiN.
Green extraction of artemisinin from Artemisia annua L. and evaluation of the antimalarial activity
Publication . Corso, Luan Barichello; Martins, Mónia; Pinho, Simão; Ferreira, Olga; Zuber, André
Malaria remains one of the greatest global public health challenges, affecting millions of people, especially in tropical and subtropical regions. One of the main obstacles to treating the disease is the low water solubility of antimalarial compounds, which compromises their bioavailability. In this work, terpenes are proposed as alternative solvents and pharmaceutical excipients for processing and formulating these drugs, aiming for higher sustainability and safety in line with green chemistry principles. First, the COSMO-RS model was used to investigate approximately 8000 systems that combine solvents from different classes with antimalarial drugs (artemisinin, quinine, quinidine, tetracycline, artemether, dapsone, and pyrimethamine). Focusing on artemisinin and the evaluated terpene candidates, thymol and its mixtures with α-pinene, β-pinene, γ-terpinene, and p-cymene showed the greatest potential, and were selected as solvents to extract artemisinin from the plant Artemisia annua L. Heat extractions with magnetic stirring were performed using a carousel system under the conditions: 50 °C, 600 rpm, 1 hour, and 1:10 solid-liquid ratio. Besides artemisinin (ART), dihydroartemisinic acid (DHAA) was also identified in significant amounts. The extraction yields using conventional solvents were 1.15 mg ART/gplant and 5.53 mg DHAA/gplant for water and 7.11 mg ART/gplant and 9.42 mg DHAA/gplant for ethanol. Higher global yields were obtained using pure terpenes (α-pinene and β-pinene), and all the equimolar thymol mixtures. The highest values were 10.43 mg ART/gplant for the thymol:α-pinene mixture and 11.86 mg DHAA/gplant for α-pinene. These values are consistent with the maximum amount available in the plant (11.2 ± 0.8 mg ART/gplant, 13.4 ± 1.0 mg DHAA/gplant), obtained by performing five consecutive extraction cycles with an Accelerated Solvent Extractor (100 °C, 5 min, 1:10 S/L ratio). A selected set of extracts (water, dichloromethane, ethanol, p-cymene, γ-terpinene, α-pinene, β-pinene) was subject to in vitro antimalarial activity assays against Plasmodium falciparum (strain 3D7-GFP). All extracts obtained with terpenes were proven to be significant inhibitors, with IC50 values ranging from 5.19 nM (γ-terpinene) to 8.17 nM (α-pinene), close to the value of the standard artemisinin (IC50 = 4.20 nM). Terpenes maintained high activity, highlighting them and reinforcing their predictions as a green alternative for the extraction and formulation of antimalarial compounds.