Cerâmicas refratárias macroporosas derivadas de espumas ultraestáveis estabilizadas com partículas cerâmicas
Abstract
Innovation on materials for heat conservation in high-temperature industrial
processes is seen as an important strategy for Energy Efficiency. Fundamental
studies can support the development of these materials and the adoption of
processing routes resulting in lower environmental impact should be considered
to produce them. This thesis presents the development of Al2O3-based refractory
macroporous ceramics prepared by direct foaming with the help of mechanoquantum
simulations. Liquid foams stabilised with Al2O3 particles were developed
after partial hydrophobisation of their surfaces with nontoxic amino acids. These
foams attained extended lifetime and were stable for more than 100 hours. To
produce solid samples derived from them, a binder based on calcium aluminate
cement was developed based on mechano-quantum simulations. This binder is
comprised of an aqueous suspension of calcium aluminate particles stabilised by
gluconate, a non-toxic molecule. The hydration reactions of calcium aluminates
were reactivated with a weak organic acid and allowed the production of solid
samples with elevated porosity (≥ 70%) and cold crushing strength reaching 30
MPa after thermal treatment. Also, the in situ formation of a phase with lower
volumetric density was studied to counteract the volumetric shrinkage of solid
samples after firing. Calcium carbonate was used and, after processing at 1600°C
for 5 hours, calcium hexaluminate (CA6) was identified. The formation of this
phase helped to reduce the linear shrinkage from values close to 19% down to
4% maintaining the total porosity above 80%. The results presented in this thesis
pointed out that the combination of computational techniques on quantum level
and experimental routes can favour the development of new materials and
advanced technologies combining superior performance and a higher
commitment to the environment.
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