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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10 resultados
Resultados da Pesquisa
Item Conventional hammering of a Fe-7.2%Ni alloy sample from Itutinga meteorite : an evaluation of its formability and functionality.(2020) Nunes, Gilson Antônio; Silva, Gilberto Henrique Tavares Álvares da; Costa, Adilson Rodrigues daUsing a mechanical forming process used in the beginning of metallurgy, the samples from the iron meteorite Itutinga were heated and plastically deformed by hammering. Two sharp pieces, similar to small arrowheads, were produced and characterized microstructurally by optical microscopy and scanning electron microscopy (SEM/EDS/EBSD), complemented with Vickers hardness. As expected, the observations pointed to the presence of α2 phase, cracks, oxidation and deformed taenite lamellae. To assess the performance of the arrowheads a penetration test was done on a leather sample. The results demonstrated the possibility of making a useful rudimentary arrowhead from of iron meteorite.Item Defining the hematite topotaxial crystal growth in magnetite–hematite phase transformation.(2020) Oliveira, Flavia Braga de; Silva, Gilberto Henrique Tavares Álvares da; Graça, Leonardo MartinsMagnetite and hematite iron oxides are minerals of great economic and scientific importance. The oxidation of magnetite to hematite is characterized as a topotaxial reaction in which the crystallographic orientations of the hematite crystals are determined by the orientation of the magnetite crystals. Thus, the transformation between these minerals is described by specific orientation relationships, called topotaxial relationships. This study presents electronbackscatter diffraction analyses conducted on natural octahedral crystals of magnetite partially transformed into hematite. Inverse pole figure maps and pole figures were used to establish the topotaxial relationships between these phases. Transformation matrices were also applied to Euler angles to assess the diffraction patterns obtained and confirm the identified relationships. A new orientation condition resulting from the magnetite–hematite transformation was characterized, defined by the parallelism between the octahedral planes {111} of magnetite and rhombohedral planes f1011 g of hematite. Moreover, there was a coincidence between one of the octahedral planes of magnetite and the basal {0001} plane of hematite, and between dodecahedral planes {110} of magnetite and prismatic planes f1120 g of hematite. All these three orientation conditions are necessary and define a growth model for hematite crystals from a magnetite crystal. A new topotaxial relationship is also proposed: (111)Mag || (0001)Hem and ð111 ÞMag || ð1011 ÞHem.Item Case study : abrasive capacity of Limnoperna fortunei (golden mussel) shells on the wear of 3 different steel types.(2019) Castro, Ana Leticia Pilz de; Serrano, Rodrigo Otávio Peréa; Pinto, Maria Aparecida; Silva, Gilberto Henrique Tavares Álvares da; Ribeiro, Livia de Andrade; Viana, Edna Maria de Faria; Martinez, Carlos BarreiraThe impact of particles suspended in the water is responsible for the wear of mechanical surfaces in hydraulic systems. The characteristics and concentrations of these particles in the flow directly influence the intensity of the abrasion processes. Within this context, knowledge of the abrasive power of a particle is of great importance. It is known that an invasive species, known as golden mussel shell, has become embedded in several hydroelectric plants of the South and Southeast of Brazil, provoking an increase of the wear caused by shells that pass through the hydraulic system. In this context, the abrasive capacity of ground golden mussel shells on the three metallic materials used in the labyrinth component of the hydraulic turbines was analyzed. To determine the wear pattern and the relationship of the specific wear coefficient of the material (k), due to the increased concentration of golden mussel shell, micro-scale abrasive wear tests were performed on three different steel plates using abrasive suspensions at different concentrations of ground golden mussel shell in distilled water. The abrasivity of the golden mussel shell was also compared with the abrasivity of silicon carbide (SiC), commonly used as standard material in microabrasion tests. The analyses showed that the golden mussel shell is around 16 times less abrasive than the silicon carbide, taking into account the average obtained for the three different materials tested. In addition, the wear mechanisms acting on the SiC tests and those with the golden mussel shell were the same.Item Polycrystals of “imperial” topaz from Minas Gerais state, Brazil.(2019) Araújo, Teodoro Gauzzi Rodrigues de; Silva, Gilberto Henrique Tavares Álvares da; Diniz, Rafael Silva; Graça, Leonardo Martins“Imperial” topaz is a gemstone variety that occurs in the Ouro Preto region (Minas Gerais state, Brazil). Polygonal sectors within the core and rims of topaz crystals, were optically observed but without consensual explanations about them. With the aid of optical microscopy, scanning electron microscopy-cathodoluminescence (SEM-CL), backscattered electrons (BSE) imaging, electron probe micro-analyser (EPMA) chemical analyses and electron backscatter diffraction (EBSD) maps, the present study intended to demonstrate the distinct crystallographic orientations within “imperial” topaz and relate the polygonal sectors with the compositional data. Cross-polarised transmitted-light photomicrographs show a well delimited and optically heterogeneous central rhombic area at (21 l) in the cores, and quadrant-like and alternated extinction areas at (200, (010) and (110) in the rims. Scanning electron microscopy-cathodoluminescence images show a central rhombic area heterogeneously luminescent in the core, and dark and homogeneous rims. Grey and completely homogeneous BSE images and EPMA results corroborate constant and homogeneous major composition of “imperial” topaz. Electron backscatter diffraction maps collected in the rim region show different areas and microstructural features instead of a uniform microstructure. The respective pole figures of orthorhombic system yielded multiple (001) poles disoriented in higher than 15° from each other. These results display numerous c-axes, suggesting distinct crystallographic orientations, and no reduction in the orthorhombic symmetry. Therefore, the presumed monocrystal of “imperial” topaz actually is a polycrystal.Item Toward the influence of iron oxide morphology on the grinding and filtration processes and on the cold crushing strength (CCS) of heat-treated iron ore pellets.(2020) Graça, Leonardo Martins; Silva, Gilberto Henrique Tavares Álvares da; Machado, Marcos Meyer; Silva, Josué Bortolini Sette da; Ávila, Carlos Fernando; Cipriano, Ricardo Augusto Scholz; Lagoeiro, Leonardo EvangelistaThe present study demonstrates the effect of the different morphological types on the cold crushing strength (CCS) of heat-treated iron ore pellets. Blends with different iron ore oxides morphologies were subjected to grinding, filtering and pot grate tests on industrial scale trials. Results of grinding tests showed the hematite-goethite aggregates the most influent one on energy consumption. The martitichematite content was straightly related to the final moisture and filtration productivity. The hematitegoethite aggregates, therefore the goethite content, influences CCS, being the lower the goethite content, the higher the values of CCS.Item Designing NiTiAg shape memory alloys by vacuum arc remelting : first practical insights on melting and casting.(2018) Silva, Gilberto Henrique Tavares Álvares da; Otubo, JorgeNiTi-based shape memory alloys are successful owing to its capacity to cover specific applications unreachable by binary NiTi. The additions of ternary, and even quaternary, elements are intended to change specific properties. Known for its antibacterial activity, Ag became an alloying element in a search for a functional biomaterial; however, the melting appears to hampering the system exploration. A special melting procedure by vacuum arc remelting was developed based on chemical and thermal analysis, via EDS, XRF, and DSC, assessing the element loss and ingot homogeneity, respectively. By alloy design, different Ag content NiTiAg SMA were produced and analyzed on as-cast condition. The melting procedure developed involves specific feedstock cares and preparation, melting, and some remelting steps. The measured chemical composition slightly differs from the nominal due to alloying element loss and the melting reaction thermodynamics. Being the lower the possible, the remelting steps were optimized to maintain the compromise between chemical composition and compositional homogeneity through the ingot, since the Ag content stabilizes along them, also indicating a limited content possible to be alloyed. Ag-yields are content-dependent, while the Ni:Ti relation is stable, being therefore the melting of NiTiAg SMA better performed by VAR than other melting routes under high vacuum conditions.Item Geological sample preparation evaluations by EBSD pattern quality.(2011) Silva, Gilberto Henrique Tavares Álvares da; Lagoeiro, Leonardo Evangelista; Barbosa, Paola FerreiraItem Electron Backscattering Diffraction (EBSD) as a tool to evaluate the topotactic and epitactic growth of minerals : the example of the magnetite and hematite.(2011) Barbosa, Paola Ferreira; Lagoeiro, Leonardo Evangelista; Cipriano, Ricardo Augusto Scholz; Graça, Leonardo Martins; Silva, Gilberto Henrique Tavares Álvares daItem Techniques for preparation geological samples for EBSD analysis : an example of Iron oxide – quartz aggregates.(2010) Silva, Gilberto Henrique Tavares Álvares da; Lagoeiro, Leonardo EvangelistaItem Characterization of iron ore via combining optical and EBSD technique.(2010) Mendes, Mônica de Cássia Oliveira; Lagoeiro, Leonardo Evangelista; Silva, Gilberto Henrique Tavares Álvares da