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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4 resultados
Resultados da Pesquisa
Item Thermal analysis and infrared emission spectroscopy of the borate mineral colemanite (CaB3O4(OH)3H2O) : implications for thermal stability.(2016) Frost, Ray Leslie; Cipriano, Ricardo Augusto Scholz; Ruan, Xiuxiu; Lima, Rosa Malena FernandesColemanite CaB3O4(OH)3H2O is a secondary borate mineral formed from borax and ulexite in evaporate deposits of alkaline lacustrine sediments. The basic structure of colemanite contains endless chains of interlocking BO2(OH) triangles and BO3(OH) tetrahedrons with the calcium, water and extra hydroxide units interspersed between these chains. We have studied the thermal decomposition of colemanite by using a combination of thermal analysis (TG/DTG) and infrared emission spectroscopy (IES). Thermogravimetric analysis of the colemanite mineral was obtained by using TA Instruments Inc. Q50 high-resolution TGA operating at a 10 C min-1 ramp with data sample interval of 0.50 s pt-1 from room temperature to 1000 C in a high-purity flowing nitrogen atmosphere (100 cm3 min-1 ). Thermogravimetric analysis shows a sharp mass loss at 400.9 C. Only a single mass loss is observed. IES shows a sharp band at 3610 cm-1 assigned to the stretching vibration of hydroxyl units. Intensity in this band is lost by 350 C. A broad spectral feature is observed at 3274 cm-1 attributed to water stretching vibrations. Intensity in this band is lost by 300 C. A combination of thermogravimetry and IES is used to study the thermal stability of the borate mineral colemanite. It is important to characterize the very wide range of borate minerals including colemanite because of the very wide range of applications of boron-containing minerals.Item Vibrational spectroscopy of the mineral meyerhofferite CaB3O3(OH)5 H2O - an assessment of the molecular structure.(2013) Frost, Ray Leslie; López, Andrés; Xi, Yunfei; Cipriano, Ricardo Augusto Scholz; Costa, Geraldo Magela da; Belotti, Fernanda Maria; Lima, Rosa Malena FernandesMeyerhofferite is a calcium hydrated borate mineral with ideal formula: CaB3O3(OH)5_H2O and occurs as white complex acicular to crude crystals with length up to _4 cm, in fibrous divergent, radiating aggregates or reticulated and is often found in sedimentary or lake-bed borate deposits. The Raman spectrum of meyerhofferite is dominated by intense sharp band at 880 cm_1 assigned to the symmetric stretching mode of trigonal boron. Broad Raman bands at 1046, 1110, 1135 and 1201 cm_1 are attributed to BOH in-plane bending modes. Raman bands in the 900–1000 cm_1 spectral region are assigned to the antisymmetric stretching of tetrahedral boron. Distinct OH stretching Raman bands are observed at 3400, 3483 and 3608 cm_1. The mineral meyerhofferite has a distinct Raman spectrum which is different from the spectrum of other borate minerals, making Raman spectroscopy a very useful tool for the detection of meyerhofferite in sedimentary and lake bed deposits.Item The molecular structure of the borate mineral inderite Mg(H4B3O7)(OH)-5H2O - a vibrational spectroscopic study.(2013) Frost, Ray Leslie; López, Andrés; Xi, Yunfei; Lima, Rosa Malena Fernandes; Cipriano, Ricardo Augusto Scholz; Granja, AmandaWe have undertaken a study of the mineral inderite Mg(H4B3O7)(OH)_5H2O a hydrated hydroxy borate mineral of magnesium using scanning electron microscopy, thermogravimetry and vibrational spectroscopic techniques. The structure consists of ½B3O3ðOHÞ5_2_ soroborate groups and Mg(OH)2(H2O)4 octahedra interconnected into discrete molecules by the sharing of two OH groups. Thermogravimetry shows a mass loss of 47.2% at 137.5 _C, proving the mineral is thermally unstable. Raman bands at 954, 1047 and 1116 cm_1 are assigned to the trigonal symmetric stretching mode. The two bands at 880 and 916 cm_1 are attributed to the symmetric stretching mode of the tetrahedral boron. Both the Raman and infrared spectra of inderite show complexity. Raman bands are observed at 3052, 3233, 3330, 3392 attributed to water stretching vibrations and 3459 cm_1 with sharper bands at 3459, 3530 and 3562 cm_1 assigned to OH stretching vibrations. Vibrational spectroscopy is used to assess the molecular structure of inderite.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.