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Paraffin‐based fuels have received attention in hybrid propulsion studies towards their regression rate assessment, although little efforts have been dedicated to a consistent selection of their formulations. This work deals with melting enthalpy, dynamic viscosity, and linear thermal expansion characterization of novel low‐density polyethylene‐macrocrystalline paraffin‐ammonium nitrate composite fuels, followed by model fitting under mixture modeling principles and subsequent optimization through the desirability method. This approach allowed a better understanding of the raw materials’ roles and provided a trade‐off formulation, which was satisfactorily produced and characterized in a confirmatory experiment, thus making it a suitable candidate for further regression rate measurements.

A geopolymer with high specific surface area was synthesized from metakaolin, amorphous silica and KOH, in the absence of foaming or saponification agents. The mixture modelling technique was selected for this study among the Design of Experiments tools, using surface area and total pores volume as response variables. The Si/K = 2.46 and Si/Al = 1.37 ratios lead to the optimal experimental conditions, allowing the formation of a geopolymer having a specific surface area of 75 m 2 /g and total pores volume of 0.28 cm 3 /g. The pores had a bimodal pore size distribution (7 and 20 nm). In spite of its amorphous nature, this structure is similar to zeolites in terms of ion exchange and metal ions accommodation. Therefore, this study envisages its application as a catalyst support.

Agradeço à minha família, particularmente aos meus avós Hélio (in memoriam)e Clara e à minha tia Lasthenia (in memoriam), cujo apoio, dedicação e exemplos foram e continuam a ser fundamentais em minha vida.Agradeço ao meu orientador, Dr. Ricardo Vieira, pela disponibilidade, pelo estímulo à criatividade e à independência intelectual e pela confiança em mim depositada.Agradeço ao meu co-orientador, Dr. Leonardo Henrique Gouvêa, por me apresentar ao mundo instigante da propulsão híbrida e pelas sugestões pertinentes. Agradeço ao Dr. Leandro José Maschio por todo o apoio prestado ao longo deste trabalho, pelas discussões produtivas e, sobretudo, pela amizade com que me honrou. Agradeço a todos os profissionais do Laboratório Associado de Combustão e Propulsão do Instituto Nacional de Pesquisas Espaciais (LABCP-INPE), cuja colaboração foi essencial para a realização desta Tese, especialmente à Dra.

This work presents the application of a cobalt and manganese mixed oxides-based catalyst with spinel structure to the decomposition of the storable green monopropellant H 2 O 2 90 wt%. The 5.4 % Co 0.5 Mn 2.5 O 4 /Al 2 O 3 catalyst was tested in a series of continuous and pulsed 2 N thruster firings, yielding a fast and repetitive performance, spontaneously and completely decomposing H 2 O 2 90 wt% without undergoing deactivation or fragmentation during the tests. A specific impulse of 104 s and a characteristic velocity of 881 m/s were reached, so that the characteristic velocity efficiency amounted to 93.7 %. The adiabatic decomposition temperature of the monopropellant (756°C) was also reached, thus evidencing the effectiveness of the 5.4 % Co 0.5 Mn 2.5 O 4 /Al 2 O 3 catalyst. Its excellent activity in the decomposition of H 2 O 2 90 wt% was attributed to the presence of the redox pairs Mn 2 + /Mn 3 + and Co 2 + /Co 3 + , therefore making it a feasible material for low and medium thrust propulsive systems.