https://repositorio.ufpb.br/jspui/handle/tede/440 PPGCEM 2026-05-23T23:24:46Z https://repositorio.ufpb.br/jspui/handle/123456789/38082 Título: Influência da adição de Nb e Cr nas propriedades microestruturais e mecânicas de uma liga CuAlMn Autor(es): Caluête, José de Queiroz Orientador: Oliveira, Danniel Ferreira de Abstract: This work investigates the effects of chromium (Cr) and niobium (Nb) additions on the microstructural, mechanical, electrochemical, and functional properties of Cu–Al–Mn shape memory alloys. The alloys were produced by induction furnace melting, followed by homogenization heat treatment and quenching, and characterized using techniques such as optical microscopy, scanning electron microscopy, corrosion resistance testing, and microhardness measurements. The results demonstrate that Cr and Nb promote significant grain refinement, the formation of Al–Cr- and Al–Nb-rich precipitates, an increase in the fraction of 18R martensite, and improvements in the structural stability of martensite. Microhardness tests and X-ray diffraction (XRD) confirmed hardening and changes in phase equilibrium, while energy-dispersive spectroscopy (EDS) validated the incorporation of the alloying elements. Electrochemical analyses showed that the isolated additions of Cr and Nb increase corrosive activity; however, when combined, these elements exhibit a synergistic effect, strengthening the passive film and improving corrosion resistance. The observed increase in electrical resistivity and in the e/a value reinforces the influence of these elements on the electronic behavior and martensitic stability. Thus, Cr and Nb demonstrate strong potential to enhance mechanical reliability, structural and chemical integrity, and to ensure the stability of the functional properties of the alloy. Editor: Universidade Federal da Paraíba Tipo: Tese 2025-12-15T00:00:00Z https://repositorio.ufpb.br/jspui/handle/123456789/38036 Título: Efeito de fibras de sisal em compósitos cimentícios impressos em 3D submetidos a elevadas temperaturas Autor(es): Medeiros, Fernanda Karolline de Orientador: Anjos, Marcos Alyssandro Soares dos Abstract: When exposed to high temperatures, 3D-printed cementitious composites (3DP-CC) often exhibit delamination and poor interlayer bonding. This study aims to develop a 3D-printable cementitious composite reinforced with sisal fibers (3DP-SFCC) and to experimentally evaluate the impact of elevated temperatures on the mechanical, physical, and microstructural behavior of both printed and cast specimens. The 3DP-SFCC mixtures were developed with appropriate buildability for extrusion-based printing systems, incorporating sisal fibers of 6 mm and 12 mm in length at volumetric contents of 0,5% and 1,0%. The mixes also included limestone filler and metakaolin. Extrudability, rheological properties, and green strength were evaluated, and physical, mechanical, and microstructural properties were assessed before and after exposure to 200, 400, 600, and 800 °C. The heat propagation through the printed composites was evaluated using thermocouples installed at eight different points of blocks heated to 400 and 600 °C. Incorporating sisal fibers improved green strength but reduced the mechanical performance of unheated 3DP-SFCC in the hardened state. However, at high temperatures, tests demonstrated that sisal fibers prevented interlayer adhesion loss up to 400 °C, while fiber-free mixtures showed a ~37% reduction in interlayer adhesion at the same temperature. Sisal fibers significantly reduced the losses in compressive strength with heating. Between room temperature and 600 °C, the compressive strength decreased by 34% in REF-C and by only 0.3% in SF05%12 in the Y direction. The damage caused by heating was mitigated, especially with the use of 12 mm fibers, and the impact of heating on the anisotropy induced by the 3D printing process was reduced, reinforcing that 3DP-SFCC exhibits improved performance in environments prone to elevated temperatures. The incorporation of sisal fibers altered the heat propagation through the printed composites, modifying the preferential heat transfer path from the interlayer region to the intralayer region, thereby reducing the thermal gradient across the material and minimizing its effects. Editor: Universidade Federal da Paraíba Tipo: Tese 2025-10-31T00:00:00Z https://repositorio.ufpb.br/jspui/handle/123456789/37896 Título: Caracterização e estudo do potencial de uso do residuo de gesso para a fabricação de gesso acartonado (drywall) Autor(es): Diniz, Rayane Karoline Melo Orientador: Lima Filho, Marçal Rosas Florentino Abstract: Gypsum is an industrial mineral produced worldwide. It is estimated that the generation of gypsum waste exceeds the amount of 15 million tons, which are dumped in landfills; furthermore, there are many other environmental impacts related to its production, usage and dumping. In view of the growing inclusion and influence of sustainability in the civil industries, the National Environment Council - CONAMA Resolution 307/2002), reclassified the plaster waste to Class B - waste that can be recycled to other destinations. In this way, this work proposes to investigate a new alternative for the reuse of gypsum residues, from the production of a drywall sealing element, without calcination, evaluating physical, mechanical, and microstructural properties. The raw materials used were kraft paper, plaster glue, commercial gypsum, and gypsum waste. The residue was comminuted and processed in a disc mill. The powders were characterized by XRF, XRD and laser granulometer. The XRF revealed the percentage of SO3 and CaO, which have limits determined by the standard. The XRD revealed to us the phases both qualitatively and quantitatively, indicating the quality of the material that resulted in the waste as well as the hydration process. The granulometry helped to determine the water/gypsum ratio for making the boards, which had the following variables: thickness of 9.5 and 15.0 mm, weight of 0 and 70 kg during molding, and curing temperature at 25° C and 50°C. The different boards were analyzed according to their geometric and visual characteristics, surface density, flexural strength, and SEM/EDS. The geometric and visual characteristics exposed the character of shrinkage, which was associated with the appearance of defects and influence on the boards interface. The surface density indicated to us how much the grain size of the gypsum residue (7,98 μm) can influence this characteristic, as well as the flexural strength. In the SEM/EDS analysis, it was observed the interface and its adhesion, the microstructure of the plaster residue resembling that of the commercial plaster, and also indicated the concentration of the components along the boards, mainly sulfur (S) and calcium (Ca), which are the main elements of the composition of plaster and gypsum. All these results indicate the possibility of reusing plaster waste with low energy expenditure. Editor: Universidade Federal da Paraíba Tipo: Dissertação 2020-12-15T00:00:00Z https://repositorio.ufpb.br/jspui/handle/123456789/37811 Título: Produção, caracterização e estudo catalítico de nanofibras cerâmicas produzidas por Solution Blow Spinning, aplicadas como catalisadores heterogêneos a base de níquel nos processos de reforma do metano para produção de hidrogênio Autor(es): Silva, Thamyscira Herminio Santos da Orientador: Macedo, Daniel Araújo de Abstract: The production of hydrogen and synthesis gas through catalytic methane reforming processes was carried out using fibrous catalysts prepared by the Solution Blow Spinning technique. Nickel-based catalyst nanofibers were produced with different types of supports, characterized, and compared with their counterparts prepared by conventional synthesis techniques. The influence of the preparation method was studied under methane reforming reaction conditions, and the experimental results were separated into three chapters, according to the type of support used. The Ni- CeO2 fibrous catalyst produced by SBS showed good catalytic activity and stability of 30 hours in the dry reforming reaction of methane when compared to a conventional catalyst prepared by wet impregnation of the same composition. Characterizations by XRD, SEM, and XPS evidenced that the good performance of the nanofiber catalyst is due to the good metal-support interaction, high thermal stability, and good oxygen mobility associated with the use of CeO2, which prevent the formation of deposits and growth of metal particles. In the second study, Ni/Co-MgAl2O4 bimetallic catalysts prepared by SBS were compared with catalysts of the same composition prepared by thermal decomposition of hydrotalcites synthesized by co-precipitation. The preparation method influenced the performance of the catalysts in both steam reforming and dry methane reforming reactions. The nanofibers presented good surface and reduction properties, and a mixture of oxides with strong interaction that ensured good catalytic performance compared to the other samples, as well as greater resistance to deactivation by deposition of crystalline carbon. Finally, calcium aluminate nanofiber supports were obtained at a lower calcination temperature than supports produced by solid-state reaction. An industrial waste from the shellfish sector was used as a source of CaCO3 for solid-state synthesis, with the aim of adding value to the waste. The supports were wet impregnated to produce nickel-based catalysts for applications in steam reforming of methane. Regardless of the type of support preparation, the catalysts showed methane conversion above 80% and remained stable throughout the 8-hour tests. Thus, based on the results obtained from XRD, SEM, TPR, XPS, N2 adsorption, and thermal analysis characterization tests, the viability of producing ceramic nanofibers prepared by SBS and the positive impact of their use as fibrous catalysts in heterogeneous methane catalysis was verified. When compared to conventional preparation methods under different methane reforming reaction conditions, the nanofibers showed good catalytic activity, high thermal resistance to prevent particle sintering, and little impact of crystalline carbon deposits that could result in catalyst deactivation. Editor: Universidade Federal da Paraíba Tipo: Tese 2022-12-14T00:00:00Z