doctoralThesis
Estudo de métodos de dopagem para obtenção e caracterização de óxido e carbeto de nióbio com cobre e sua aplicação em compósitos sinterizados (Cu-NbC)
Fecha
2017-12-22Registro en:
SOUTO, Maria Veronilda Macêdo. Estudo de métodos de dopagem para obtenção e caracterização de óxido e carbeto de nióbio com cobre e sua aplicação em compósitos sinterizados (Cu-NbC). 2017. 131f. Tese (Doutorado em Ciência e Engenharia de Materiais) - Centro de Ciências Exatas e da Terra, Universidade Federal do Rio Grande do Norte, Natal, 2017.
Autor
Souto, Maria Veronilda Macêdo
Resumen
The study of wet doped and solid path doping methods to obtain niobium oxides and niobium
carbides with copper (5% Cu and 10% Cu mol / mol) from the hydrated ammonium trioxalate
oxyniobate precursor, as well as, an evaluation of the properties of copper-doped niobium
(Cu-NbC) composite sintered through SPS (Spark Plasma Sintering) was performed in this
work. Niobium and copper oxide (CuNb2O6) was obtained by solid-solid reaction at 1000 ° C
and duration of 120min. The niobium carbide was synthesized at low temperature (980ºC)
and in short reaction time (60min), in a tubular oven, and in a gas atmosphere of methane
(CH4) and hydrogen (H2). For the liquid phase sintering of the Cu-NbC composite, the
following parameters were adopted: iqual temperature at 1200 ° C, compaction pressure iqual
at 30Mpa, reaction time of 10min. The powders were characterized by X-ray diffraction,
scanning electron microscopy, X-ray fluorescence (FRX), particle size analysis and nitrogen
adsorption by BET technique, as well as crystallite size measurements. The crystallite size
was calculated by the Scherrer method using the X-ray diffraction data. The reaction powders
were obtained with nanometric particle sizes, ranging from approximately 20nm to 28nm, and
in the desired proportions with the desired purity. The specific surface area ranged from
approximately 38.0 m²/g to 48.0 m²/g. The moforlogy of both presented agglomerated
particles of varied sizes and forms, predominating, however, the spherical shape. The lowest
compositional deviations of the powders were obtained by the solid route method, however by
wet method the properties were improved, presenting smaller particle sizes and larger specific
surface areas. The sintered composite was evaluated by XRD, Vickers hardness and density.
Also, measurements were made of Vickers hardness, density by Archimedes, SEM, and EDS
with mapping, in which good dispersion and homogenization of the phases were identified.
The wet doped powders with 10% Cu, after sintering, presented the best results, showing
Vickers hardness (84.1 HV) and density (79.3%).