https://ri.ufs.br/jspui/handle/riufs/2493 Fri, 24 Apr 2026 15:39:41 GMT 2026-04-24T15:39:41Z http://ri.ufs.br:80/retrieve/c465059d-3ea6-46db-98bd-aac44634e42e/P2cem.png https://ri.ufs.br/jspui/handle/riufs/2493 https://ri.ufs.br/jspui/handle/riufs/23933 Título: Efeito da microestrutura e temperatura na resistência à corrosão de aços inoxidáveis em fluido a base de iminodiacetato dissódico Autor(es): Silva, Paulo Roberto Rego Abstract: The corrosion of stainless steels in alkaline solutions containing organic complexing agents represents a challenge in various industrial applications. In this thesis, the effect of microstructure and temperature on the corrosion resistance of AISI 316L, 2205, and 430 stainless steels in a medium containing disodium iminodiacetate was evaluated. Electrochemical tests were carried out to investigate the stability of the passive film, complemented by microstructural analyses for phase identification and morphological changes. The results indicate that the duplex stainless steel 2205 exhibits superior behavior, with greater passive film stability even at temperatures of 80 °C and 100 °C. On the other hand, 316L and 430 showed higher susceptibility to localized corrosion and the formation of microcracks and porosity. This study deepens the understanding of the role of microstructure and temperature in corrosion mechanisms and provides relevant information for material selection and mitigation of corrosion in alkaline media. Fri, 29 Aug 2025 00:00:00 GMT https://ri.ufs.br/jspui/handle/riufs/23933 2025-08-29T00:00:00Z https://ri.ufs.br/jspui/handle/riufs/22145 Título: Síntese verde de nanopartículas de MnO2 utilizando extrato de folha da acerola e aplicação em fotocatálise para remoção do corante azul de metileno Autor(es): Silva, Jefferson David Oliveira da Abstract: Liquid effluents containing organic dyes are pollutants that pose a high environmental risk. Photocatalysis has been reported as an effective method for the degradation of these contaminants. In this work, green synthesis of MnO2 nanoparticles was carried out using an aqueous extract of acerola leaves. The effect of pH and plant extract concentration on the material properties was investigated, and its efficiency in removing methylene blue dye was evaluated. The doping of nanoparticles with praseodymium was also studied. Structural, compositional, and morphological characterizations were conducted using various techniques. The discoloration experiments were performed under UV light radiation. The results showed that for 30 g·L-1 of extract, an increase in pH decreased the particle diameter, while with 60 g.L -1, the opposite effect was observed. The crystalline phase was identified as α-MnO2 with a mesoporous structure. Doping with 1% Pr3+ increased the Mn3+/Mn4+ ratio, promoting the generation of surface defects that induced morphological changes, leading to the growth of nanoneedles in the structure and increasing the available surface area (180.8 m2 .g-1). These factors improved the separation of photogenerated charges, reduced the bandgap, and optimized the photocatalytic activity of the nanoparticles, which removed about 85.3% of the dye (50 mg.L-1) after 60 minutes of contact, showing superior performance compared to undoped samples. The green-synthesized MnO2 demonstrates excellent potential for technological applications in the remediation of organic pollutants, such as dyes, in aqueous solutions. Wed, 26 Feb 2025 00:00:00 GMT https://ri.ufs.br/jspui/handle/riufs/22145 2025-02-26T00:00:00Z https://ri.ufs.br/jspui/handle/riufs/20747 Título: Fadiga, corrosão-fadiga e corrosão sob tensão em parafusos prisioneiros fabricados em aço inoxidável AISI 304 e o desenvolvimento de um software educacional para as 3 solicitações nestes materiais Autor(es): Nery, Macclarck Pessoa Abstract: The thesis addresses three major loading conditions to which industrial equipment is subjected: fatigue, corrosion-fatigue, and stress corrosion cracking (SCC). When frequent assembly and disassembly are expected, bolts emerge as a solution. It is common for them to be subjected to fatigue due to cyclic external loads. When the application involves aggressive environments, such as coastal areas, oil platforms, and nuclear power plants, the AISI 304 austenitic stainless steel becomes one of the most popular choices due to its corrosion resistance, good mechanical properties, machinability, formability, and weldability. For stainless steels, higher mean stress reduces the alternating stress in the fatigue life; however, frequency has distinct effects. In corrosion-fatigue, the performance of these materials in chloride environments is deteriorated, and stress corrosion cracking is more common in seawater or chloride solutions. In particular, the study investigated such conditions on studs made of AISI 304 stainless steel and developed educational software about these for stainless steels in general. The objective was to identify and rank among the three requests which one is the most aggressive to the component. The results indicated a deleterious effect of mean stress on fatigue, the reduction in frequency produced an increase in the stress amplitude at the endurance limit of fatigue by up to 160%. The corrosion-fatigue tests conducted in chloride solution showed worse performance, with a reduction of up to 74.5% in stress level at N = 2x106 cycles. There were no SCC failures at room temperature in 278 hours even when exceeding the yield stress. In parallel, an educational software in JAVA was developed for the three themes with textual and infographic content, an endurance limit of fatigue calculator, and links to specific bibliographies. Finally, an usability analysis was conducted using the System Usability Scale among materials engineering and mechanical engineering students, achieving satisfactory rates. Tue, 29 Oct 2024 00:00:00 GMT https://ri.ufs.br/jspui/handle/riufs/20747 2024-10-29T00:00:00Z https://ri.ufs.br/jspui/handle/riufs/20217 Título: Produção e caracterização de arcabouços tridimensionais baseados em quitosana, polidopamina e hidroxiapatita para aplicações na engenharia tecidual óssea Autor(es): Andrade, Gabriela Santos Abstract: Three-dimensional scaffolds should serve as a temporary environment for cell growth, with biodegradability at controlled rates, as well as mechanical properties like the area where they are applied. Chitosan (CHI) has promising properties, and its characteristics can be improved with the addition of hydroxyapatite (HA) and polydopamine (PDA). HA is a bioactive ceramic whose composition corresponds to the mineral phase of bones. To the best of our knowledge, PDA has not yet been investigated in addition to CHI and HA to produce scaffolds. PDA coating can be promising, due to its biocompatibility, cell adhesion and relatively slow degradation. Therefore, this study aimed to prepare and characterize 3D chitosan (CHI) and hydroxyapatite (HA) scaffolds coated with polydopamine (PDA) and test aspects of their applicability in bone tissue engineering. The present research also studies different concentrations of dopamine polymerization and contact time for scaffolds coating. First, CHI scaffolds were prepared with different coatings (1, 2, 3 and 4 mg/mL) within periods of 0.5h, 1h, 3h, 6h, 12h and 24h. They were compared with the uncoated CHI scaffold FTIR, SEM and compression test. After the coating standardization, groups including HA were tested. The groups were produced with different formulations of the three materials, comparing the presence or absence of PDA coating. In addition to the above characterizations, EDS, porosity analysis, XRD, TGA, DSC, in vitro degradation and cell viability assay were performed. It was found the interaction between CHI and PDA and more uniform layer for the groups with the highest coating concentration. These also showed greater potential for resistance to compressive loads. The interaction of the polymers and HA was also suggested. They exhibited suitable resistance to compressive loads at areas that do not require high stress load. Its microstructure showed heterogeneous porosity patterns and its surface became rougher with the inclusion of HA and PDA. Also, CHI/HA/PDA (50/50) displayed interconnected pores with long channels microstructure. MTT cytotoxicity assay demonstrated the groups cell viability, the scaffolds similar behavior to negative control group (p > 0.05) reveals their biocompatible potential. This information appears to be favorable for the materials employment, under these conditions, for bone tissue engineering. Mon, 26 Feb 2024 00:00:00 GMT https://ri.ufs.br/jspui/handle/riufs/20217 2024-02-26T00:00:00Z