EM - Escola de Minas
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6
Notícias
A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.
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9 resultados
Resultados da Pesquisa
Item Evaluation of the microstructure and micromechanics properties of structural mortars with addition of iron ore tailings.(2023) Almada, Bruna Silva; Silva Neto, Gilberto Alves da; Prado, Dyala Fraga do; Aguilar, Maria Teresa Paulino de; Garcia, Dayana Cristina Silva; Silva, Guilherme Jorge Brigolini; Santos, White José dosThe Interfacial Transition Zone (ITZ) between the cement paste and aggregates is a region of great interest for concretes because it is the composites’ weakest region. ITZ presents a great amount of large calcium hydroxide and ettringite crystals, with the porosity being able to be up to 2.5 greater than that the rest of the paste. The microstructure, and consequently the ITZ, can be improved by mineral addition. These materials fill the pores in the composite, influence the hydration process and densify the matrix. Therefore, mineral additions, such as iron ore tailings (IOT), can modify microstructure of composites. There are few studies on the assessment of IOT heterogeneity on the microstructure and hardness of structural mortar. Thus, the present study analyzes the properties influences of four IOT types on the microstructure, porosity, and thickness of the structural mortars’ Interfacial Transition Zone (ITZ) with IOT addition, by different evaluation methods. The composites were characterized through the Scanning Electron Microscope by backscattered electrons (SEM-BSE), line scan by Energy Dispersive Spectroscopy and nanoindentation. Results presented that IOT improved particle packing and tended to reduce the ITZ. The IOT improved nucleation since it reduces the amount of anhydrous cement particles and increases the amount of calcium hydroxide particles in the cement matrix. The nanoindentation showed that IOT-added matrix presented greater hardness and indentation module. It can be concluded that the IOT heterogeneity may affect microstructural properties and that the methods presented can be good ways to evaluate the parameters.Item Study of mechanical, durability and microstructural properties of cementitious composite with addition of different iron ore tailings from Brazil.(2022) Almada, Bruna Silva; Melo, Henrique da Silva Silveira; Duarte, Marlo Souza; Aguilar, Maria Teresa Paulino de; Garcia, Dayana Cristina Silva; Silva, Guilherme Jorge Brigolini; Santos, White José dosBrazil is the second-largest global iron ore producer in the world. Consequently, a large volume of iron ore tailings (IOTs) is generated, which is associated with environmental impacts. IOTs present potential to be used as an addition in cementitious compounds, however, few studies assess how the heterogeneity of this waste can limit its utilization as a building material. Thus, the present study aims to assess whether the heterogeneity of IOTs influences mechanical, durability, and microstructural properties when added to the cementitious composite. Four IOTs samples from different origins were collected and added to cementitious composite at 40% addition content. Composites’ mechanical (compressive strength and modulus of elasticity) and durability properties (water absorption, porosity, electrical resistivity, carbonation, and pH pore solution) were correlated to the microstructure of the IOTs. Results showed that the IOTs from different mines exhibited different physical properties and chemical/mineralogical compositions. Moreover, the higher the degree of ore processing, the lower the heterogeneity, iron content, and specific gravity. Although the IOT samples are heterogeneous, this type of tailing can be used as a filler addition in structural mortars. IOT addition tends to improve the mechanical and durability properties. Heterogeneity most significantly influenced the properties in the fresh state, durability, and microstructural properties. The microstructure of the cement matrix tends to be denser in the IOT-added with higher SSA and silica content. Was observed higher-porosity in regions close to the interfacial transition zone in the samples with coarser IOT.Item Thermal stability of copper processed by multidirectional forging : effect of deformation amplitude and cumulative strain.(2022) Flausino, Paula Cibely Alves; Corrêa, Elaine Carballo Siqueira; Pereira, Pedro Henrique Rodrigues; Aguilar, Maria Teresa Paulino de; Cetlin, Paulo RobertoExperiments were performed in order to evaluate the effect of deformation amplitude (Δε) and cumulative strain (ε) on the thermal stability of Copper 99.8% pure, after processing with 8 and 48 Multidirectional forging (MDF) cycles at room temperature with Δε ≈ 0.075 (MDF0.075) or 2 and 12 MDF cycles with Δε ≈ 0.30 (MDF0.30), leading to cumulative deformations of ε ≈ 1.8 and 10.8. The microstructural stability at elevated temperatures was evaluated through Differential Scanning Calorimetry (DSC) and heat treatments, combined with Vickers microhardness measurements and Electron Backscattered Diffraction (EBSD). Further analyses were carried out through thermodynamic considerations about the stored energy and driving pressures for boundary migration. The results showed that the thermal stability associated with static recrystallization decreases as ε and Δε in MDF increase, due to the presence of finer grain structures and higher dislocation density in the as-deformed material. In addition, the MDF-processed specimens deformed with high ε and Δε exhibited finer recrystallized grains than those processed with low ε and Δε as a result of their increased number of nucleation sites. Thermal stability increases in the following order: 12C-MDF0.30, 2C-MDF0.30, 48C-MDF0.075 and 8C-MDF0.075.Item Influence of strain amplitude on the microstructural evolution and flow properties of copper processed by multidirectional forging.(2020) Flausino, Paula Cibely Alves; Nassif, Maria Elisa Landim; Bubani, Franco de Castro; Pereira, Pedro Henrique Rodrigues; Aguilar, Maria Teresa Paulino de; Cetlin, Paulo RobertoCommercial-purity copper (99.8%) is processed by multidirectional forging (MDF) using strain amplitudes per compression (Δε) of 0.15 and 0.30, leading to accumulated strains (ε) of up to 10.8. It is shown that increasing the accumulated strain causes continuous reactions at the substructural level, involving the progressive evolution of dislocation arrangements toward structures having high misorientation angles. This evolution depends upon the strain amplitude in MDF processing and is characterized by the fragmentation of the original grains due to formation and intersection of micro shear bands (MSBs) assisted by dynamic recovery processes. Higher Δε enhances the “monotonic” character of processing, resulting in a higher fraction of MSBs and band intersections, increased work hardening, flow stresses, and dislocation density, lower cell/subgrain and grain sizes, and faster grain refinement kinetics, compared with MDF under lower Δε. The yield strength of copper, measured along a direction orthogonal to that of the previous compression step, is lower than the flow stress at the end of this compression step, and this behavior becomes more prominent with increasing ε and Δε.Item Influence of the heterogeneity of waste from wet processing of ornamental stones on the performance of Portland cement composites.(2020) Almada, Bruna Silva; Melo, Luciane de Souza; Dutra, Julia Baptistella; Bubani, Larissa Cardoso; Silva, Guilherme Jorge Brigolini; Santos, White José dos; Aguilar, Maria Teresa Paulino deOne of the difficulties of using some residues, such as those from stones beneficiation (cutting and polishing), is their heterogeneity. This study analyzes the influence of the heterogeneity of waste from wet processing of ornamental stones (marble, granite, slate, among others) on the performance of Portland cement composites when used at a 20% replacement of cement. The mechanical behavior (compressive strength, flexural strength, and elastic modulus) and durability parameters (porosity, water absorption, carbonation, and electrical resistivity) are analyzed. Results indicate that the waste can present considerable heterogeneity while maintaining composites properties, indicating little influence on their physicochemical properties. It can be inferred that the filler effect of the waste compensated to a certain extent the negative effects (the increase in w/c ratio and the reduction of important hydrates) due to reduced cement content, showing its viability as mineral addition, despite its heterogeneity.Item Microstructural evolution and mechanical behavior of copper processed by low strain amplitude multi-directional forging.(2019) Flausino, Paula Cibely Alves; Nassif, Maria Elisa Landim; Bubani, Franco de Castro; Pereira, Pedro Henrique Rodrigues; Aguilar, Maria Teresa Paulino de; Cetlin, Paulo RobertoExperiments were performed to analyze the microstructural evolution and mechanical behavior of commercial-purity copper (99.8%) processed by up to 48 cycles of multi-directional forging (MDF) using a low strain amplitude of ∼0.075 (total accumulated strain ε ≈ 10.8). Parabolic work-hardening concomitantly with increasing dislocation densities was observed up to ε ≈ 2, followed by a practically constant flow stress due to dynamic recovery. The average grain size was reduced from 30.5 μm in the annealed metal down to 4.1 μm for ε ≈ 7.2; the fraction of sub-micrometric grains reached ∼12% for ε ≈ 10.8. The microstructural changes were attributed to the fragmentation of the original grains by dislocation structures having low misorientation angles which gradually evolved into arrays of high-angle grain boundaries with increasing numbers of MDF cycles. The Cu samples subjected to 48 cycles of MDF displayed limited dynamic recrystallization, exhibiting basically dislocation cells and sub-grains with an average size of ∼0.6 μm. It is demonstrated that low strain amplitude MDF delays the kinetics of grain refinement in copper compared with MDF using higher strain amplitudes.Item Mechanical behavior and microstructures of aluminum in the MultiAxial Compression (MAC) with and without specimen re-machining.(2019) Stemler, Pedro Malaquias Araujo; Flausino, Paula Cibely Alves; Pereira, Pedro Henrique Rodrigues; Faria, Cleber Granato de; Almeida, Natanael Geraldo e Silva; Aguilar, Maria Teresa Paulino de; Cetlin, Paulo RobertoSevere Plastic Deformation (SPD) leads to grain refinement and strengthening of metals. The most utilized SPD techniques are Equal Channel Angular Pressing (ECAP), High Pressure Torsion (HPT) and Multi-Axial Compression (MAC). Only MAC allows the determination of the stress–strain curves of the material during processing. Although ECAP and HPT processing has been analyzed in detail, there are few studies of MAC procedures and their consequences. It is shown that only specimens re-machined after each compression lead to adequate MAC stress–strain curves of the material, whose microstructures are not affected by re-machining.Item Eucalyptus chip ashes in cementitious composites.(2014) Resende, Domingos Sávio de; Radispiel Filho, Herbet; Keles, José Genário; Bezerra, Augusto Cesar da Silva; Aguilar, Maria Teresa Paulino de; Gouveia, Antônio Maria Claret deThe Alto Paranaiba and Triângulo Mineiro mesoregion in the state of Minas Gerais and the State of São Paulo have a number of industries with eucalyptus chip fired boilers that produce great amounts of ash. Since thermoelectric ashes generally have good pozzolanic activity, this paper studied the mechanical behavior of cementitious composites made with raw eucalyptus chip ash as a partial replacement for Portland cement and processed under two different conditions. The mechanical behavior of the composites was measured from tests on specimens for their compressive strength, tensile strength to diametral stress and to bending. Results show ashes could be used as mineral additives.Item Sterile clay pozzolans from phosphate mining.(2015) Matos Neto, José Afonso de; Resende, Domingos Sávio de; Silva Neto, João Trajano da; Gouveia, Antônio Maria Claret de; Aguilar, Maria Teresa Paulino de; Bezerra, Augusto Cesar da SilvaThe work presents the characterization of clays from sterile mining of the concentrated phosphatic materials of Araxá in Minas Gerais as pozzolanic materials. Three clays of distinct tones, namely, yellow (YC), red (RC), and intermediate (IC) clays, were used at different levels of excavation depth. The clays were calcined at three temperatures (680, 760, and 840 °C) in a muffle-type electric oven. The pozzolanic activity levels of the calcined clays was measured through the conductivity change in saturated Ca(OH)2 solutions and also from the result of the compressive failure load achieved by mortars with 35% of the Portland cement replaced with the calcined material. The results indicated that the calcined clays showed a high level of pozzolanic activity and can be used as a partial substitute for Portland cement, thus suggesting the possibility of recovering this sterile material.