Navegando por CNPq "CNPQ::ENGENHARIAS::ENGENHARIA DE MATERIAIS E METALURGICA"

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Acesso aberto (Open Access)
Amido termoplástico: obtenção de nanocompósitos de amido de araruta termoplastificado com nanopartículas de óxido de zinco
(Universidade Federal do Pará, 2024-02-07) PINTO, Bianca Corrêa; PAULA, Marcos Vinícius da Silva; http://lattes.cnpq.br/7538211324097974; MAIA, Ana Áurea Barreto; http://lattes.cnpq.br/0820112425394964; https://orcid.org/0000-0002-1880-1442
The search for new materials with comparable performance to synthetics has driven the development of sustainable and biodegradable materials. The growing demand has stimulated the creation of innovative materials, such as starch-based films, biopolymers, and others, which offer excellent mechanical and barrier properties while being environmentally friendly. To achieve higher levels of sustainability, starch-based films, enriched with new components, gain prominence as possible candidates for food packaging applications. In this context, the present study aims to obtain and characterize thermoplasticized nanocomposites with arrowroot starch (TPA) and zinc oxide nanoparticles (ZnO NPs) in different proportions (1%, 3% and 5%). Films without ZnO NPs were used as controls. The thermoplasticized starch films were made using the casting solution technique (solvent evaporation). They were evaluated for the concentration of ZnO NPs, and were also submitted to laboratory techniques, such as moisture, solubility and swelling tests. In addition, they were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and tensile, strain at break and modulus of elasticity tests. For the moisture test, the results revealed that the addition of 1, 3 and 5% of ZnO NPs to the polymeric matrix provided a gradual decrease in the percentage of moisture when compared to the control TPA film. This fact is attributed to the interfacial interaction between the ZnO NPs and the arrowroot starch matrix, which in turn hinders the interaction of water molecules with the nanocomposite film. For the percentage of solubility of the films, a small change was observed after the addition of the NPs ZnO to the starch matrix, which becomes important for the maintenance of products stored in food packaging as well as the stability of the polymeric films. As for the swelling test, for the 1% TPA, 3% TPA and 5% TPA films, it was verified that when the SPL was added, they presented smaller variations compared to the TPA film containing only arrowroot starch in the polymeric matrix. In view of the above, the micrographs obtained by SEM revealed the presence of randomly dispersed aggregates of ZnO NPs in the polymeric matrix of arrowroot starch. The stress properties tests were conducted in 5 replicates, with a speed of 5 mm/min. The TPA film showed an average of 0.34 MPa and 59.80% for tensile strength and deformation at break, respectively. The incorporation of ZnO nanoparticles into the arrowroot starch matrix resulted in an increase in the tensile strength and deformation of TPA 1%, TPA 3% and TPA 5% films compared to TPA film. The mean strength for the films TPA 1%, TPA 3% and TPA 5% were 0.42 MPa, 0.45 MPa and 0.60 MPa, respectively. In addition, the mean strain at break for TPA 1%, TPA 3% and TPA 5% films were 77.14%, 86.34% and 86.05%, respectively. The FTIR spectra exhibited the same spectral behavior. This phenomenon is due to the presence of high starch content in the polymeric matrix of the films. The thermal stability for TPA, TPA1%, TPA 3% and TPA 5% films was investigated by thermogravimetric analysis (TGA). The results obtained for the TPA1%, TPA 3% and TPA 5% films presented similar data to the thermal stability of the TPA film and showed that the addition of ZnO NPs to the polymeric matrix did not cause a significant decrease in them. The results showed that it is possible to use the films produced in this work in the packaging sector.
Acesso aberto (Open Access)
Análise do comportamento mecânico de tubos de concreto com fibras de aço produzidos com materiais da região metropolitana de Belém do Pará
(Universidade Federal do Pará, 2015-09-25) OLIVEIRA, Marco Antonio Barbosa de; POMPEU NETO, Bernardo Borges; http://lattes.cnpq.br/6564259204591721; MACEDO, Alcebíades Negrão; http://lattes.cnpq.br/8313864897400179
The steel fibers in the concrete pipes have provided better mechanical performance levels. In the northern region, uniquely in Belem, no studies on the technical feasibility of this technological resource, although there is considerable deficiency of urban infrastructure. Thus become relevant conduct studies on alternative technology. This study seeks to analyze the mechanical behavior of concrete pipes with steel fibers, aiming at the technical feasibility of replacing the concrete pipe with conventional armor. The research methodology we used steel fibers in loose state and glued comb DRAMIX® 3D type 65/35 and 80/60 DRAMIX® 3D type. For each fiber type were adopted contents of 20 kg / m³ (0.25%), 30 kg / m³ (0.38%) and 40 kg / m³ (0.50%) by weight and volume fraction, respectively. The size of all concrete pipes was 600 mm diameter, wall thickness of 60 mm and effective length 1000 mm, and the cylindrical bodies of the test piece of 100x200mm and prismatic of 150x150x500mm and 150x150x550mm, which were subjected to the tests for mechanical behavior evaluation and durability. In the production of concrete with the fibers was reviewed in the fresh state with frustoconical rebate between 0 and 10 mm. The dosage of concrete with fibers was routinely employed by the company for concrete without fibers, and the strength of the fibers takes place under the rule of the mixture. The results obtained that the concrete pipe with fiber type 80/60 loose at all levels and pasted comb the levels of 0.38% and 0.50%, reached the minimum breaking load and post-cracking set by the NBR 8900 (ABNT, 2007), thus would be technically feasible as the replacement of reinforced concrete pipes conventionally, under the conditions and specifications of this study.
Acesso aberto (Open Access)
Avaliação probabilística do impacto da recarga rápida de veículos elétricos nos sistemas de distribuição de energia elétrica
(Universidade Federal do Pará, 2024-11-13) HERNÁNDEZ GÓMEZ, Oscar Maurício; VIEIRA, João Paulo Abreu; http://lattes.cnpq.br/8188999223769913
The mass adoption of electric vehicles (EVs) is transforming the automotive sector, driven by environmental concerns and technological advancements. Governments and companies are investing in the expansion of charging networks, focusing on fast charging to meet the growing demand. Developing a robust infrastructure of charging stations is essential to eliminate “range anxiety” and encourage the transition to EVs. Fast charging is crucial for the success of vehicle electrification. It allows batteries to be charged much more quickly than conventional charging, increasing convenience for users and improving the overall user experience. As more fast-charging stations are installed, consumer confidence in EVs grows, paving the way for a more sustainable future. With a well-distributed fast-charging network, EVs become a practical alternative to fossil fuel-powered vehicles, accelerating the transition to greener mobility. However, fast charging of EVs can cause technical impacts on medium voltage networks. The high current demand can result in voltage drops, especially in areas with weaker distribution infrastructure. Transformers can be overloaded, reducing their lifespan and increasing the risk of failures. Excessive heating of conductors due to high current can also cause losses and damage cables. These challenges highlight the need for proper planning and investments in electrical infrastructure to support the increase in fast charging. A probabilistic analysis of the impact of fast charging on medium voltage networks is crucial. Energy demand varies throughout the year due to seasonal factors, such as the use of air conditioning in summer and heaters in winter. Fast charging adds a considerable load to the network, which can coincide with these demand peaks, exacerbating management challenges. The installation of multiple charging points can cause voltage fluctuations and overloads. Probabilistic analysis helps predict these impacts and develop mitigation strategies by simulating charging scenarios and user behaviors. This allows for more precise infrastructure planning, including network reinforcements and improvements to ensure supply reliability. This thesis proposes a probabilistic methodology to evaluate the impact of fast charging of electric vehicles on medium voltage distribution networks, considering voltage drops, network element loading, and regulator tap changes. Using the Power Factory software by DIgSILENT©, a real feeder in Brazil is simulated, analyzing different case studies. Three fast charging stations (FCS) are connected, each with six charging points of 100 kVA, totaling 600 kVA per EP. The charging profile of the EPs is programmed with stochastic variables. Finally, a Volt/Var control strategy is presented to mitigate the impact on voltage drops and regulator tap changes, allowing reactive power injection without the need for communication between charging points.
Acesso aberto (Open Access)
Caracterização de tintas industriais aplicadas na região amazônica a partir de análises físico-químicas, mecânicas e de durabilidade
(Universidade Federal do Pará, 2024-02-28) LUCAS, Mathaus Moraes; SILVA, Alisson Clay Rios da; http://lattes.cnpq.br/7389345867032737; https://orcid.org/0000-0001-9186-2287
In Brazil, the industrial sector of paints and varnishes is among the five largest in the market. The manufacture of paints for various applications, with technology and technical responsibility, equals the most advanced global production centers. The durability of a paint refers to its resistance to weathering. For weathering, a weather-resistant paint is necessary so that fading does not occur on the substrate where it will be used, which can occur among some factors, due to the incidence of sunlight and heavy rains. The North region, with high rainfall, influenced by instability lines, presents significant spatial and seasonal heterogeneity of rainfall and has the highest annual rainfall total. Given this reality, a paint commercially applied in the Amazon region was developed. In the standard formulation, variations of mineral loads (Kaolin, Dolomite and Precipitated Calcium Carbonate) were made and subsequently analyses and tests were carried out to evaluate the performance of this paint, compared with the original formulation, such as abrasion resistance and weathering resistance. The paint production methodology will be according to Castro (2009) using Hare’s technique (1974). The characterization of the paints in the fresh state was carried out through the Viscosity, pH and specific weight tests, while the characterization of the paints in the hardened state was carried out through the abrasion resistance tests, weathering resistance test and Scanning Electron Microscopy. The physico-chemical tests revealed that, in relation to Stormer viscosity, all formulations exceeded the standard (130 KU), with the exception of the paints containing 30% Dolomite, 15% PCC, 15% Dolomite and the ternary combination of 5% Kaolin, 5% Dolomite and 20% PCC. As for the specific weight, the formulation that came closest to the standard was the binary paint with 15% Kaolin and 15% PCC, presenting an average value of 1.43 g/cm³. In terms of pH, all formulations showed alkalinity, with values ranging between 7.5 and 9.6. After a period of exposure of 180 days, none of the mixtures, including the standard formulation, showed the formation of pathologies, demonstrating resistance to weathering. The formulations with 30% Dolomite; 15% PCC and 15% Dolomite; 5% PCC, 5% Kaolin and 20% Dolomite; 10% Kaolin, 10% PCC and 10% Dolomite, exhibited respectively 300, 290, 240, 270 cycles of abrasion resistance, indicating the potential of these paints for a variety of applications, such as floor paints, external paints and road paints.
Acesso aberto (Open Access)
Código de resposta rápida nanoestruturado impresso em 3D
(Universidade Federal do Pará, 2023-07-12) OLIVEIRA, Dhonata Sebastião Caldas; REIS, Marcos Allan Leite dos; http://lattes.cnpq.br/8252507933374637; https://orcid.org/0000-0003-2226-2653
Due to the Fourth Industrial Revolution, also known as Industry 4.0, factories increasingly have systems dependent on the Internet and communication technologies, which guarantees them unprecedented efficiency, but makes them vulnerable to cyber attacks. For this reason, cybersecurity it is an increasingly relevant topic, with technologies such as blockchain and quantum cryptography based on physically unclonable functions (PUFs) presenting themselves as alternatives in this area. In this sense, this work presents the synthesis of poly(acrylonitrile-butadiene-styrene) (ABS) nanocomposites with respectively 1 and 2 % by mass of carbon nanotubes (CNTs) for the 3D printing of the so-called NanoCodecs, which present Raman spectral signatures, classified as PUFs, which can be used as cryptographic keys generated by a code built in the Python programming language. For this, two solutions were prepared, the first with multi-walled CNTs functionalized with carboxylic acid in acetone, and the other with pure ABS pellets in this same solvent. After mixing these solutions and ultrasonic baths, the acetone was evaporated and ABS/NTC1%m/m and ABS/NTC2%m/m pellets were produced, which were used for the production of nanostructured filaments in an extruder. Then NanoCodecs as quick response code (QR code) and as round/square stamps were 3D printed. The electrical characterization of samples printed with nanostructured filaments showed a reduction in electrical resistance with an increase in the percentage by mass of CNTs. Despite this, the morphological characterization by Scanning Electron Microscopy showed that there is a low concentration of nanotubes on the surface of the samples, which indicates that they are dispersed throughout the volume of the samples. The vibrational characterization by Raman spectroscopy was used to identify the characteristics of pure materials, both ABS and NTCs, and compare with the Raman spectrum of the ABS/NTCs nanocomposite. As a result, there was an overlap of the vibrational modes of both materials, with emphasis on the shift to the right of the sub-band 𝐺𝑒𝑥𝑡 in 8 𝑐𝑚−1, which indicates that the nanotubes are compressed in the polymeric matrix. Finally, using nanocomposites as PUFs, it was possible to generate keys from the main vibrational modes of these materials: the D, G and 2D bands of nanotubes and the bands named as 1001-PS and 2239-PAN of ABS. Therefore, the results obtained indicate that NanoCodecs can be used as elements of ybersecurity in Industry 4.0, through cryptographic keys generated by the spectral analisys of the nanocoposite used for produtction of the NanoCodecs.
Acesso aberto (Open Access)
Desenvolvimento de sensor piezorresistivo nanoestruturado impresso em 3D
(Universidade Federal do Pará, 2023-07-05) QUARESMA, Luciano José Barbosa; REIS, Marcos Allan Leite dos; http://lattes.cnpq.br/8252507933374637; https://orcid.org/0000-0003-2226-2653; FEIO, Waldeci Paraguassu; http://lattes.cnpq.br/3512689932467320; https://orcid.org/0000-0003-4980-4694
The emergence of smart factories based on Industry 4.0 increases the automation and optimization of industrial processes in production chains. In this context, the integration between physical and digital systems depends on intelligent sensors, with greater sensitivity and integrated by the Internet of Things (IoT). The literature indicates that piezoresistive sensors can be produced by additive manufacturing (AM) and nanostructured with carbon nanotubes (NTCs), which generate a nanoelectromechanical system (NEMS) after its dispersion in the material. Thus, this work presents the development of a low-cost piezoresistive nanoelectromechanical sensor, produced by applying layers of NTCs on poly(acrylonitrile-butadiene-styrene) (ABS) parts printed by fused deposition modeling (FDM), integrable to the Industry 4.0 via IoT through ESP32 microcontrollers. For this, a diaphragm-type sensor device with dimensions 17.8, 17.8 and 5.5 𝑚𝑚 was developed, whose sensor element deformation occurs by pressing a button. After MA printing of the device parts, carboxylic acid functionalized multi-walled CNTs (MWCNT-COOH) were dispersed by ultrasonic bath in a solution with a concentration of 1 𝑚𝑔/𝑚𝑙 of acetone and dimethylformamide, in a ratio of 1 ∶ 1 in volume, for coating the sensor elements in successive layers with an aerograph. After the deposition of five layers of CNTs on the polymeric substrate, measurements of electrical resistance obtained with a picoammeter showed the percolation of the material in the second layer, with initial values above 10 𝑇 Ω and final values below 100 𝑘 𝑂𝑚𝑒𝑔𝑎 after the fifth layer, which occurs by the formation of conduction channels originating from the random arrangement of CNTs on the ABS surface, as observed by Field Emission Scanning Electron Microscopy (FEG-SEM). After that, the electrical resistance was measured during pressure cycles with progressive load and with maximum load, in which the sensor elements presented an operating range of 139.97 ± 0.46 to 363.25 ± 0.39 𝑘𝑃 𝑎. In the first test, the minimum sensitivity of 0.1 % and maximum sensitivity of 1.16 %. In the second, the highest average sensitivity was 0.63 ± 0.04 % and the lowest average response and recovery times were 0.55 ± 0.29 𝑠 and 12.29 ± 1.44 𝑠, respectively. Raman spectroscopy showed the overlapping of the signals of each material, in particular the ABS band at 1447 𝑐𝑚−1 which appears prominently between the NTCs 𝐷 and 𝐺 bands. Based on the piezoresistive response that the material presented from the NEMS generated by the deposition of NTCs on ABS, this concept of a load cell can be integrated into an ESP32 microcontroller board, making it an intelligent device with potential application in industrial systems. 4.0.
Acesso aberto (Open Access)
Desenvolvimento e caracterização de bioplásticos de fécula de mandioca com extrato alcoólico de Vismia Guianensis
(Universidade Federal do Pará, 2024-08-27) SANTOS, Josiel Ferreira; PASCA, Gabriel Adolfo Cabrera; http://lattes.cnpq.br/5642784995274060; https://orcid.org/0000-0002-9411-0889
This work investigates the incorporation of the alcoholic extract of Vismia Guianensis (EAVG) cassava starch, aiming to improve its bioplastic properties. Cassava starch was dissolved in distilled water at the following concentrations with 0.2%, 0.5% and 1.0% EAVG under controlled temperature at the gelatinization point (~70 °C) and then molded to form bioplastics. The prepared samples were characterized by Attenuated Total Reflectance/Fourier Transform Infrared Spectroscopy (ATR/FTIR), Thermogravimetric and Thermal Differential Analysis (TGA-DTA), X-ray Diffraction (XRD), Scanning Electron Microscopy/Energy Spectroscopy Dispersive (SEM/EDS), Atomic Force Microscopy (AFM) and mechanical assays, providing insights into chemical composition, thermal stability, crystallinity, surface morphology and mechanical properties. These techniques comprehensively characterized cassava starch bioplastics with EAVG addition, highlighting their enhanced mechanical properties. The results demonstrated that EAVG played an effective role as a plasticizer, increasing the flexibility, resistance and stability of the biofilm that has a thickness of 0.8 mm, and supports a traction of 4.19 to 18.43 MPa. This study justifies EAVG as a promising additive for the production of biocompatible and sustainable materials, suitable for numerous applications in biodegradable plastics. EAVG presents a path forward for the advancement of bioplastics with improved mechanical, thermal and functional properties, with a promising future in terms of their contribution to new developments in these areas.
Acesso aberto (Open Access)
Desevolvimento de dispositivos eletrônicos orgânicos nano e micro-estruturados: memória volátil, sesores e fotocélulas
(Universidade Federal do Pará, 2011-02-14) REIS, Marcos Allan Leite dos; DEL NERO, Jordan; http://lattes.cnpq.br/5168545718455899
In this work, several nano and microstructured organic devices were developed based on molecules of 4-dimethyl amino azobenzene-2-carboxylic acid (Methyl Red – VM), C60 Fullerene, nanocomposite of Aluminum/Carbon Nanotubes (Al/NC) and polymers: Poly(3, 4- dioxithiophene ethylene)-poly(sulfonate stireno) – PEDOT-PSS and poly(3-hexiltiofeno) – P3HT. These devices are volatile memory, fuel sensors, thermal-piezoresisitive sensor and photocells, which were manufactured by spin-coating, drop casting and chemical vapor deposition, resulting in devices with planar or layer by layer geometry. Morphological, optical, electrical and thermal characterizations were performed on devices, resulting: (a) volatile memory with a bit retention time of 4.5 s, the characteristic curves of current vs. voltage with peak-valley ratios of 8: under a 10:1 voltage positive and negative electrical energized with electrical conductivity of 10-4 S / m (OFF state) to 3.10 S / m (ON) at room temperature, (b) fuel sensors like chemiresistor sensors characteristics with sensitivity to ethanol and gasohol in concentrations of 26.25 ppm, (c) thermal-piezoresistive sensor with polynomial relationship between temperature and electrical resistance, linear relationship between pressure and electrical resistance, more accurate than a K type thermocouple when compared to a mercury thermometer at room temperature, (d) photocells with better performance when doped by Methyl Red showed quantum efficiencies up to 0.04%, real power at 0.27 and power conversion efficiency of 2.0%. These results indicate that electronic devices developed showed a better performance in comparison to similar organics.
Acesso aberto (Open Access)
Efeitos do tipo, tamanho e teor de agregado graudo na resistencia e energia de fratura do concreto
(Universidade Estadual de Campinas, 2004-09-28) POMPEU NETO, Bernardo Borges; DUCATTI, Vitor Antonio; http://lattes.cnpq.br/4679656185466685; FERREIRA, Itamar; http://lattes.cnpq.br/9135346053526486
This thesis presents the results of the experimental study carried out for considering the effects of the type, size and amount of coarse aggregate on the behavior of normal and high strength concretes, and on relationship among the fracture energy and typical mechanical strength of concrete. The experimental concrete mixtures were made with basalt and granite coarse aggregates having maximum size particle 9.5 mm e 19 mm and volumetrically fraction in the mixture ranging from 0.65 to 0.75. The water to cementation materiais ratio ranged from 0.35 to 0.50. The high strength concrete mixtures contained a fixed amount of 10 percent of silica fume in relation to the weight Portland cement used and a proper addition of superplasticizing agent. Sixteen (16) concrete batching, and one hundred and ninety two tests were carried out to measure the mechanical resistance of concrete (compressive strength, flexure strength, spittling tensile strength, modulus of elasticity) and fracture energy. The fracture properties measured in agreement of the RILEM test methods. The concrete compressive strength ranged from 40 to 60 MPa, and from 70 to 110 MPa, for moderate and high strength concretes, respectively, depending on the type of coarse aggregate utilized. The results showed that the concrete resistance (compressive, flexure, spittling tensile) and fracture energy, at given water to binder ratio, depend on type, particle dimension and content of coarse aggregate. The characteristic length of Hülerborg^ fictitions cracks model increases with the variation in the particle dimension of coarse aggregate.
Acesso aberto (Open Access)
Emprego de resíduo de silício metálico na produção de cimento portland composto
(Universidade Federal do Pará, 2017-12-19) CUNHA, Rodrigo Rodrigues da; MACEDO, Alcebíades Negrão; http://lattes.cnpq.br/8313864897400179
The reuse of industrial waste and alternative raw materials in construction is fundamental to sustainable development with reduced consumption of natural resources and CO2 emissions. In this line, the present study contemplates the use of a powdered waste, originating from the production of metallic silicon, which is designated as pre-separator residue. In this way, the objective of this research is to produce and evaluate properties of Portland cement composite CP II-E with the addition, during its manufacture, of metallic silicon industrial residue after calcination. For this purpose, the residue was used in partial replacement to blast furnace slag, in mass contents of 30%, 50% and 70%, in addition to the reference situation, in which no silicon residue was added to the cement (0%). Cement properties, produced with residues, were evaluated for their chemical composition, mineralogical, physical parameters (fineness, picking times, fire loss and insoluble residue), compressive strength, water absorption, absorption by capillarity, microscopic techniques and analytical techniques (DR-X, chemical composition and thermal analyzes of TG / DTG). As results, there were no significant differences in the physical parameters of the cements produced. Cement mortars produced with higher residue contents (70% and 50%) had the highest values of compressive strength and lower values of capillary water absorption, voids index and water absorption by capillarity than mortars produced with standard cement ( without siliceous residue). The same was not observed for cement mortars with 30% silicon residue. Analytical techniques of scanning electron microscopy images indicated a more closed porosity for cement mortars in the contents of 70% and 50% of cement with residue. Thus, as a conclusion, the utilization of the residue studied as partial replacement material of granulated slag in composite cement type "E" is technically and environmentally feasible.
Acesso aberto (Open Access)
Ensaios mecânico e aplicação da lógica fuzzy para avaliação do canote do garfo
(Universidade Federal do Pará, 2010-09-04) SANTOS, Ruy Sidney Nascimento dos; FARIA, Marlene Araújo de; http://lattes.cnpq.br/1906265701265000
Technological innovation has been one of the fundamental factors that drive major companies to stay atop the world ranking of global market, according to the technological advance the engineering sector has sought solutions that provide positive results for growth of your company or organization. Simulation methods for evaluating the mechanical behavior of products subjected to static loads and dynamic loads are extremely necessary to reduce the costs of manufacturing products. The use of mechanical and virtual is vital in evaluating the product. This study aimed to use fuzzy logic in a product called seatpost of the bicycle fork, where it was considered beyond the degree of membership varied between 0 and 1, the degree of accuracy also varied between 0 and 1, with the main focus of the behavior of the fork and seatpost product validation.
Acesso aberto (Open Access)
Estudo da potencialidade da cinza da casca do murumuru, um resíduo agro industrial amazônico como filler ao concreto estrutural
(Universidade Federal do Pará, 2022-11-17) SOUZA, Milleno Ramos de; CORDEIRO, Luciana de Nazaré Pinheiro; http://lattes.cnpq.br/9126233381230999; https://orcid.org/0000-0001-7931-4042; TEIXEIRA, Marcelo Rassy; http://lattes.cnpq.br/8912916360456192
The use of agro-industrial waste in the partial replacement of cement in concrete has been the subject of research that analyzes the possible improvements in mechanical and physical properties and durability of the concrete, in addition to providing the use of mineral additions of natural origin or partial replacement in relation to the constituent materials of the composite, waste that would have inappropriate disposal, such as open-air landfills and burning. With this scenario, the study aims to research the use of murumuru husk ash (MHA), an agro-industrial waste generated specifically in the Amazon region as partial replacement of cement in structural concrete and evaluate the physical, chemical and mineralogical characteristics of the ash to act as filler in concrete, and its properties in the fresh and hardened state in concrete. With this purpose, the MHA underwent the physical-mechanical characterization tests such as specific mass, pozzolanic activity with Portland cement, pozzolanic activity with lime and BET test, also performing the mineralogical and chemical analysis of the ash. For concreting, a mix 1:1.6:2.4 (by mass) with water/cement ratio of 0.43 was considered, with replacement levels of 0%, 6%, 9% and 13% of the cement mass by MHA. After the dosage, the tests were performed on the concrete in its fresh and hardened state: slump test, specific mass, compressive strength (28 days), tensile strength in diametrical compression, water absorption by capillarities, specific mass in the hardened state, modulus of elasticity and morphological evaluation, through the Scanning Electron Microscope (SEM). Checking first the properties of concrete in the fresh state, it is evaluated that the insertion of the waste decreased the consistency and decreases the specific mass, except the concrete for the content of 6% that there was a 10% increase in the specific mass in relation to the concrete reference. Regarding the properties in the hardened state, the replacement by CCM showed an increase specifically in compressive and tensile strength in the 6% content at 28 days around 1% and 9% respectively, occurring a decrease in the contents of 9% and 13%. The results showed that there is a technical feasibility with partial replacement of 6% of MHA in cement, using plasticizer additive to improve workability
Acesso aberto (Open Access)
Estudo da resistência à corrosão de soldas de ferro fundido branco alto cromo na presença de NaOH (30% p.p)
(Universidade Federal do Pará, 2024-10-03) SANTOS, Renata Soraia Guimarães dos; BRAGA, Eduardo de Magalhães; http://lattes.cnpq.br/4783553888547500; https://orcid.org/0000-0003-0739-7592
In the mining industry, specifically in bauxite beneficiation, adverse working conditions are encountered, requiring high mechanical and chemical resistance. For these conditions, it is necessary to choose potentially resistant materials, such as high Cr white cast iron (FFBA-Cr). However, currently, there is no effective recovery of equipment manufactured with FFBA-Cr, mainly due to the difficulty of machinability generated in the repair process. An alternative recovery has been developed by the Laboratory of Characterization of Metallic Materials of UFPA - LCAM, through electric arc welding, using two filler metals, the electric wire ER307L and the wire with high Mn value. In this context, this work proposes to investigate the corrosion resistance of the welded joint, obtained with these two filler metals. The base metal (FFBA-Cr) as a reference and the metals generated by the welded joints, ER307L and with high Mn value, were analyzed. The samples underwent optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and electrochemical tests of corrosion potential, polarization and impedance. It was observed that the samples presented a similar structure of carbide matrix, but with different organization and volumes. However, the electrochemical behavior of corrosion potential, polarization and impedance were similar, with their resulting values very close, variations: 50 V; 3.53 µA; 0.18 ohm, respectively, which was corroborated by the corrosion rate, 0.4 mmpy, and explained by the calculations of Cr and Ni volume, which present inverse values of concentration magnitude between the samples. Raman analyses performed after polarization of the samples indicated the formation of important oxides on this surface and possibly the formation of a passivating layer, which is corroborated by the mass loss analysis that showed the possibility of passivation of the welded joints, despite corrosion processes in the anodic phase of this exposure process over the exposure time.
Acesso aberto (Open Access)
Formação de heteroestruturas compostas por microtubos de Cu/Cu2O/CuO decorados com nanocristais de CoO
(Universidade Federal do Pará, 2024-08-21) SANTOS, Suzilene Vasconcelos dos; PASCA, Gabriel Adolfo Cabrera; http://lattes.cnpq.br/5642784995274060; https://orcid.org/0000-0002-9411-0889
A particularly important class of micro/nanostructured materials is that of transition metal oxides. In this work, copper and cobalt oxides are used to obtain micro/nanostructures. Copper (II) oxide (CuO) and copper (I) oxide (Cu2O) are p-type semiconductors, widely studied due to their peculiar characteristics and potential technological applications. Specifically, copper (Cu) microwires with approximately 50 μm in diameter and 4 cm in length, extracted from discarded cellphone earphones, were subjected to thermal treatments at 600°C with different synthesis parameters to obtain CuO microtubes. On the other hand, cobalt acetate was used in the synthesis of nanoparticles through the chemical method called thermal decomposition, which uses organometallic salts in organic solvents, being a suitable method for the synthesis of CoO nanostructures. Metallic cobalt and its oxides have been intensively studied due to numerous applications enhanced by their properties. CoO nanoparticles exhibit instability in the hexagonal close-packed Wurtzite structure (hcp - space group P63mc). This implies that, depending on the synthesis parameters, phase transition can occur, that is, from CoO-hcp to CoO-fcc (face-centered cubic phase - space group Fm3m), which is considered the most stable phase for CoO. However, in order to obtain a hierarchical structure of CuO microtubes decorated with CoO nanoparticles, this work uses different synthesis methodologies to produce a micro-nano-hierarchical structure. In this study, X-ray diffraction was used to identify the crystalline structures present in the microwires and nanoparticles, highlighting the influence of the time parameter on the phase transition of both structures. The morphological characterization of the samples was performed using scanning electron microscopy (for the microwires) and transmission electron microscopy (for the nanoparticles). Raman spectroscopy was also employed to obtain information about the sample surfaces. With these characterization techniques, it was possible to determine the elemental and structural composition of the microtubes and nanoparticles composed of copper and cobalt oxides, as well as to evaluate the influence of the laser on the nanoparticle samples. Thus, a Cu/Cu2O/CuO heterostructure with CoO monocrystals on the surface was developed, presenting potential sensory properties.
Acesso aberto (Open Access)
Influência no comportamento mecânico do concreto com a utilização de microfibras de polipropileno para redução do efeito de retração: um estudo realizado em Belém do Pará
(Universidade Federal do Pará, 2022-10-27) CUNHA, Wictor Alencar; SOUZA, Paulo Sérgio Lima; http://lattes.cnpq.br/4933212993218783
Seeking to mitigate the effect of concrete shrinkage, the influence on the mechanical behavior of concrete reinforced with polypropylene microfibers was studied in this study. In the experimental program, 15 (fifteen) study series were produced: one reference without the addition of polypropylene microfiber for each w/c ratio studied, totaling 3 series; and another 12 (twelve) series with the following characteristics: addition of 0.6% and 1.0% of microfiber content varying the length in 12 mm and 25 mm, the w/c ratios being studied with values of 0.45 ; 0.55 and 0.65. Tests were carried out in the fresh state of the concrete to evaluate consistency and workability; and in the hardened state to evaluate compressive strength, flexural traction and modulus of elasticity with age of the specimens at 7 and 28 days; and dimensional variation with age of 48h, 7 and 28 days. The results obtained were studied through analysis of variance (ANOVA) and the Tukey test to determine the statistical significance of the responses found. It was concluded that the optimum content of addition of polypropylene microfiber to concrete was 1.0% with fibers of 12 mm length and w/c ratio=0.55.
Acesso aberto (Open Access)
Resistência ao fendilhamento de elementos estruturais de concreto simples e armado com agregados reciclados de concreto
(Universidade Federal do Pará, 2018-07-06) PAMPLONA, Matheus Kenji Yoshikawa; FERREIRA, Maurício de Pina; http://lattes.cnpq.br/4242041552985485
Recycling of solid construction waste is presented as a sustainable and economically viable alternative, especially when applied in an industrial context, such as the production of precast concrete structures. However, the use of recycled concrete aggregates (RCA) for the production of structures still generates many uncertainties due to the variables related to the origin of the material itself. In this context, this work seeks to analyze the behavior and the strength to splitting failure of RCA structural elements. An experimental program was developed with 36 local prismatic specimens to evaluate the influence of parameters such as the rate of replacement of natural aggregates by recycled aggregates (0%, 30% and 100%), loading concentration and the performance of transverse reinforcement. All specimens failed by splitting, and the strength, rupture, displacements and strains in concrete and reinforcement were analyzed. The results were compared with other studies in the literature and with standard codes of ACI 318 (2014), fib Model Code 2010 (2013), Eurocode 2 (2004) and ABNT NBR 6118 (2014). No evidence was found of an influence on behavior and strength to splitting failure of structural elements using RCA at different replacement levels. However, it was found that factors such as loading concentration and use of transverse reinforcement interfere in the way the strains are distributed in the structure, which can increase or reduce the ductility and splitting strength, despite being parameters that could be neglected by normative recommendations for concrete structures projects.
Acesso aberto (Open Access)
Substituição parcial do cimento portland por cinzas de Bambu (Bambusa Vulgaris)
(Universidade Federal do Pará, 2018-06-28) MENDONÇA, Marcelly de Figueiredo; MACEDO, Alcebíades Negrão; http://lattes.cnpq.br/8313864897400179
The partial replacement of Portland cement for industrial waste or materials of natural origin with renewable source is a way that has already been used to minimize the environmental impacts generated during its manufacture, such as CO2 emission, high energy expenditure and exploitation of the limestone deposits. The partial replacement of this binder can further improve certain properties of concrete and mortars and reduce the cost of their production. In this context, bamboo appears as a material with potential to use its ashes in partial replacement to the Portland cement, because it’s a natural material with renewable source and fast growth. Therefore, the objective of this paper is to evaluate the use of bamboo stem ashes (Bambusa Vulgaris) as partial replacement of Portland cement. For that, bamboo stem ashes were produced at three calcination temperatures: 500°C, 600°C and 700°C. The ashes produced at 600ºC obtained a performance index with Portland cement at 28 days higher than that established by NBR 12653 (ABNT, 2014). It was evaluated the hydration of the Portland cement partially substituted by this ash, in proportions of 0, 6, 10 and 14% and it was verified the decrease of the concentration of calcium hydroxide, being more expressive with the incorporation of 10% of ashes. Mortars with the same replacement proportions were evaluated in the fresh and hardened state. The consistency in the fresh state remained constant, while the compressive strength, in the hardened state, increased between 10 and 15% with the addition of the ashes. Therefore, it was concluded that the partial replacement of the Portland cement by bamboo stem ashes calcined at 600ºC presented benefits to the studied samples, characteristic of pozzolanic materials.
Acesso aberto (Open Access)
Utilização de dutos descartados do gasoduto Coari-Manaus para confecção de ponte provisória sobre o Igarapé do Cedro segundo a norma API5LX70
(Universidade Federal do Pará, 2010-09-03) SANTOS, Doriel Andrade dos; FARIA, Marlene Araújo de; http://lattes.cnpq.br/1906265701265000
This paper aims to present an alternative construction of an engineering project, with the use of API 5L X70 pipeline discarded the Coari-Manaus, in the process of building a temporary bridge over the Cedro affluent of the Amazon rainforest, to enable transport workers and materials for industrial production of construction Compression Station - ECOMP in Juaruna. To verify the behavior of an element of the bridge, we used the ANSYS 8.0 program that applies the method to numerical analysis of stresses and deformations of structural elements subjected to stresses. It also presents a proposal for mitigation of environmental impacts caused by the equipment at the crossing of the affluent of Cedro and the logistical challenges faced by transportation companies in the Amazon region.