Efeitos da adição de resíduos de cinza da casca de café na microestrutura e propriedades de cerâmicas à base de cordierita
Cordierite is one of the compounds of the MgO-Al2O3-SiO2 system that presents the lowest thermal expansion coefficient among the inorganic oxides. Despite this advantage, which results in high thermal shock resistance, monophasic cordierite is difficult to prepare due to its narrow sintering rang...
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| مؤلفون آخرون: | |
| التنسيق: | doctoralThesis |
| اللغة: | pt_BR |
| منشور في: |
Universidade Federal do Rio Grande do Norte
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| الموضوعات: | |
| الوصول للمادة أونلاين: | https://repositorio.ufrn.br/handle/123456789/47201 |
| الوسوم: |
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| الملخص: | Cordierite is one of the compounds of the MgO-Al2O3-SiO2 system that presents the
lowest thermal expansion coefficient among the inorganic oxides. Despite this advantage,
which results in high thermal shock resistance, monophasic cordierite is difficult to
prepare due to its narrow sintering range and the existence of secondary phases that raises
its thermal expansion coefficient. Fluxes are generally used to stimulate the sintering of
cordierite precursor powders and to modify the microstructures and properties of these
ceramics. In this context, this paper proposes to study the effects of adding different levels
of Coffee Husk Ash Residue (CHAR), as fluxing agent, on the elimination of secondary
phases, analyzing the behavior during sintering processes and the effects on the
microstructures obtained and the properties of cordierite-based ceramics. A standard
formulation was prepared using kaolinitic clay, talc and alumina as a source of the
elements: aluminum, silicon and magnesium. Samples of the pure standard formulation
and of the formulation containing different content of CHAR were prepared by reactive
sintering (in conventional kiln) in the temperature range between 1250 and 1450 °C. The
quantitative phase analysis of sintered samples was determined by Rietveld refinement of
XRD (X-Ray Diffraction) data. Physical properties were estimated by Archimedes
methodology, microstructure was inspected by Scanning Electron Microscopy (SEM).
The coefficient of thermal expansion was determined using a thermal dilatometer and the
dielectric properties were determined by impedance spectroscopy. The addition of up to
1% of CHAR stimulated the reaction between cristobalite and spinel to form cordierite,
contributing to the decrease of apparent density and increase of apparent porosity, but
with the addition of more than 1% of CHAR, the content of the cordierite phase reduces
and there is an increase of spinel in nearly the same proportion, contributing to the
increase of the thermal expansion coefficient. The samples with 2% and 4% of CHAR
content by weight presented an unprecedented discontinuity of electrical behavior for
aluminosilicate based materials. |
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