Banca de DEFESA: EVERSON JUNIO DA CRUZ FERREIRA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : EVERSON JUNIO DA CRUZ FERREIRA
DATA : 21/08/2019
HORA: 14:00
LOCAL: Auditório - Campus Itabira, UNIFEI
TÍTULO:

CARACTERIZAÇÃO MORFOLÓGICA E ESTRUTURAL DO COBALATO DE CÁLCIO DOPADO COM MOLIBDÊNIO.

PALAVRAS-CHAVES:

Thermoelectricity, thermal conductivity, electrical conductivity, calcium cobalate.

PÁGINAS: 78
GRANDE ÁREA: Engenharias
ÁREA: Engenharia de Materiais e Metalúrgica
RESUMO:

ince the 1990s, ceramic materials have demonstrated their potential in the generation of
electric energy through the application of a temperature gradient due to its good chemical and
dimensional stability. These materials have aroused the interest of the literature as a candidate
for the substitution of classical thermoelectric materials based on metallic alloys as they exhibit
thermoelectric behavior in upper temperature ranges (500ºC or more). This characteristic is not
well established in the classic thermoelectric. In the present work, we propose to investigate the
influence of the structure and morphology of the thermoelectric ceramics of calcium cobalate,
in addition to the addition of dopant (molybdenum), in the properties of thermal and electrical
conductivity of the material, at room temperature. For these reasons, in this project, Ca3Co4(1-
x)MoxO9 ceramic powders were obtained by the traditional oxide mixture method, and
concentrations of 0.5, 1, 2 and 2.5% molybdenum were added to the material to replace cobalt.
The thermogravimetry revealed a slight thermostability between the temperatures of 800ºC and
900ºC which were then defined as the temperatures of the calcination of the material. The Xray diffraction analysis showed a long-range structural ordering of Ca3Co4(1-x)MoxO9,
identifying the desired phase (Ca3Co4O9) and the presence of secondary phases (CaO and
Co3O4) at temperatures of 800 and 900ºC. The presence of the incorporated molybdenum in the
material structure can be observed in a slight left angular displacement of the diffraction peaks.
Infrared spectroscopy revealed a short-range structural organization in which the vibrational
modes of stretching belonging to Ca3Co4O9 and the second phases vibrational modes were
identified. The results of the dilatometry suggested the sintering of the Ca3Co4(1-x)MoxO9 pellets
at temperatures of 1050ºC and 1250ºC. They were also submitted to density and green density
analysis by the Archimedes principle, showing high densification in samples treated at 1250ºC
(97%), while the samples treated at 1050°C reached intermediate densities (70%). The images
obtained by scanning electron microscopy evidenced the presence of more defined and
homogeneous grains and larger average grain sizes compared to the samples treated at 1250ºC.
This samples in turn presented grains with heterogeneous appearance. The values of electrical
conductivity were higher in the sintered samples at 1050ºC and, generally, lower with the
molybdenum concentration increase. Finally, the values obtained in the thermal conductivities
were higher in pellets treated at 1250ºC than in samples treated at 1050ºC.

MEMBROS DA BANCA:
Presidente - 1765329 - FRANCISCO MOURA FILHO
Externo ao Programa - 2380440 - HAROLDO LHOU HASEGAWA
Interno - 1315678 - RERO MARQUES RUBINGER
Externo à Instituição - RODOLFO FOSTER KLEIN GUNNEWIEK - UNIFAL-MG