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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3 resultados
Resultados da Pesquisa
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 The application of high-temperature X-ray diffraction and infrared emission spectroscopy to the thermal decomposition of krohnkite.(2016) Testasicca, Leonardo Pena; Frost, Ray Leslie; Ruan, Xiuxiu; Lim, Jéssica; Belotti, Fernanda Maria; Cipriano, Ricardo Augusto ScholzHigh-temperature X-ray diffraction and infrared emission spectroscopy have been applied to measure the thermal stability of the sulphate mineral kro¨hnkite Na2Cu(SO4)2 2H2O. Kro¨hnkite shows a low thermal stability. The mineral decomposes into a complex mixture of sulphates below 500 C and sulphides below 650 C, before melting. Broad emission infrared bands at 3350 and 3105 cm-1 are assigned to the stretching vibration of the water units. The intensity of these two bands decreases as the temperature is raised. The intensity of these bands is lost by 250 C. The sharp IES band at 992 cm-1 is assigned to the m1 SO4 2- symmetric stretching vibration. Intensity in this band is lost by 200 C. New IES bands are noted. The important aspect of this work is the use of hightemperature X-ray diffraction to determine the thermal decomposition of a mineral, in this case krohnkite.Item Thermal analysis and vibrational spectroscopic characterization of the boro silicate mineral datolite - CaBSiO4(OH).(2013) Frost, Ray Leslie; Xi, Yunfei; Cipriano, Ricardo Augusto Scholz; Lima, Rosa Malena Fernandes; Horta, Laura Frota Campos; López, AndrésThe objective of this work is to determine the thermal stability and vibrational spectra of datolite CaBSiO4(OH) and relate these properties to the structure of the mineral. The thermal analysis of datolite shows a mass loss of 5.83% over a 700–775 °C temperature range. This mass loss corresponds to 1 water (H2O) molecules pfu. A quantitative chemical analysis using electron probe was undertaken. The Raman spectrum of datolite is characterized by bands at 917 and 1077 cm^-1 assigned to the symmetric stretching modes of BO and SiO tetrahedra. A very intense Raman band is observed at 3498 cm^-1 assigned to the stretching vibration of the OH units in the structure of datolite. BOH out-of-plane vibrations are characterized by the infrared band at 782 cm^-1. The vibrational spectra are based upon the structure of datolite based on sheets of four- and eight-membered rings of alternating SiO4 and BO3(OH) tetrahedra with the sheets bonded together by calcium atoms.