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Metal oxide composites have attracted much consideration due to their promising applications in humidity sensors in response to the physical and chemical property modifications of the resulting materials. This work focused on the preparation, microstructural characterization and analysis of humidity-dependent electrical properties of undoped and vanadium oxide (V2O5)-doped titanium oxide/tungsten oxide (TiO2/WO3) sintered ceramic films obtained by electrospinning. The electrical properties were investigated by impedance spectroscopy (400 Hz–40 MHz) as a function of relative humidity (RH). The results revealed a typical transition in the transport mechanisms controlled by the appropriated doping level of V2O5, which introduces important advantages to RH detection due to the atomic substitution of titanium by vanadium atoms in highly doped structures. These aspects are directly related to the microstructure modification and structure fabrication procedure.

The performance of metal oxide-based devices for humidity impedimetric sensors depends on different conduction mechanisms during water molecules adsorption. As consequence, new strategies for development of hierarchical and doped structures of mixed metal oxides play a critical role in the production of more efficient humidity sensors. It is reported an alternative method for synthesis of hexagonal ZnO nanocrystals on TiO2-decorated electrospun fibers, allowing the production of ordered arrays of hierarchical TiO2/ZnO nanostructures. Polymeric matrix supporting fibers were removed after annealing (500 °C), providing nanostructures with promising application as low-cost humidity sensors. The structure of resulting materials was explored in addition to the influence of relative humidity (RH) (measured in the range 400 Hz–40 MHz) on complex impedance spectra.

Nowadays, semiconducting metal oxides humidity sensors are applied in many areas: regarding Relative Humidity (RH) measurement, the electronic/ionic charge transfer reactions that take place at the semiconductor surface and inside the pores, for which the overall conduction mechanisms are highly influenced by the sensing material physical/chemical properties. In a previous paper, the influence of different contents of V 2 O 5 , 3, 5 and 7% in weight in sensors based on the T i O 2 : W O 3 pair sintered at 700 °C was investigated. Since V 2 O 5 as a low melting point (∼690 °C), authors decided to alter the fabrication procedure: mechanical alloying was applied to the as received starting powders, allowing the reduction of the sintering temperature to 500 °C, and sensors based on the T i O 2 : W O 3 pair, with 3, 5 and 7% in weight content of V 2 O 5 , were prepared. The present paper describes the influence that the change of fabrication steps had on the new sensors response to moisture: some of the sensors present a conduction type transition, and were investigated concerning microstructural characterization and their electrical response was measured in the range 400 Hz–40 MHz, at the operating temperature of 20 °C and on the relative humidity (RH) range between 10 and 100%. Besides, a model of the sensors electrical behaviour is depicted, which permits to better comprehend the phenomena’s present in our sensors that contribute to the overall electrical response.

TiO2/ZnO hierarchical heteronanostructures were produced following a two-step procedure in which the hydrothermal growth of nanorods takes place on the surface of decorated electrospun fibers. The reaction product was a 3D-nanorod arrangement of a single-phase hexagonal wurtzite deposited onto the surface of a TiO2-decorated 1D-polymer nanoporous structure. The resulting composite was characterized as a potential candidate for photocatalytic applications, due to the available surface area and the high concentration of charge carriers, which minimizes the recombination of electrons and holes during photocatalytic processes. Photodegradation tests using rhodamine B (under visible-light irradiation) were performed to explore the photocatalytic activity of the nanostructures. Dye photodegradation ratio was determined to be 90% after 70 min, which indicates that TiO2/ZnO hierarchical heteronanostructures are potential photocatalysts.

Actually, humidity sensors have got multiplying applications from the industrial processing to the environmental control, mainly those based on semiconducting metal oxides. Certain ceramic oxides or composite oxides are wide-bandgap semiconductors and the overall conduction mechanisms are highly influenced by the sensing material physical/chemical properties. For the humidity measurement (relative humidity (RH)), the electronic/ionic charge transfer reactions that take place at the semiconductor surface can be used for this purpose. It is well recognized that water molecules are observed to increase the conductivity of n-type ceramics and to decrease the conductivity of p-type ceramics. Nevertheless several mechanisms have been proposed to explain electrical response variations of oxide metals of with humidity. The present paper describes part of the work that is being carried out to investigate the effect of doping metals oxides on TiO 2 :WO 3 bulk sensors humidity response. For that the V 2 O 5 ceramic was selected. The influence of different contents, 3, 5 and 7 percentage in weight, were investigated concerning microstructural characterization and their electrical response was measured in the range 400 Hz–40 MHz, at operating temperatures of 20 and 30 °C and on the relative humidity (RH) range between 10 and 100%. For all doped sensors a p- to n-conduction transition was found, and the best humidity response was observed for the sensor containing 3 percentage in weight of oxide doping. Besides a new non-classical model for the doped sensors electrical behaviour with moisture is depicted, which allow to better comprehend the diverse phenomena present in our sensors contributing to the overall electrical response.

Hybrid ZnO/TiO2nanoparticles were applied as potential photocatalyst agents incorporated into electrospun fibers of enteric block copolymers. The resistance of fibers avoids aggregation and contributes to prolonged action of semiconductor nanoparticles under continuous light irradiation. Such behavior is attributed to the minimal aggregation degree and elevated efficiency of photodegradation of modified nanoparticles in comparison with pristine ones. Hybrid ZnO/TiO2in nanofibers contributes to the association of different mechanisms such as N-deethylation and cleavage of dye molecules applied in the overall process of photodegradation.

The study of selective metal oxide-based binary/ternary systems has received increasing interest in recent years due to the possibility of producing efficient new ceramic materials for relative humidity (RH) detection, given the superior properties of the mixed compounds in comparison with pristine ones. The aim of this work was focused on preparation and characterization of non-doped and Nb2O5-doped TiO2 : WO3 pair (in the pellet form) and evaluation of corresponding humidity-dependent electrical properties. The microstructure of the samples was analyzed from scanning electron microscopy, X-ray diffraction patterns, Raman spectra, BET surface area analysis, and porosimetry. The electrical characterization was obtained from impedance spectroscopy (100 Hz to 40 MHz) in the 10–100% RH range. The results showed that adequate doping levels of Nb2O5 introduce important advantages due to the atomic substitution of Ti by Nb atoms in highly doped structures with different levels of porosity and grain sizes. These aspects introduced a key role in the excursion (one order of magnitude) in the bulk resistance and grain boundary resistance, which characterizes these composite ceramics as a promising platform for RH identification.

This work aims to determine the diffusion coefficient of the plasticizers dibutyl phthalate (DBP), dioctyl phthalate (DOP) and dioctyl azelate (DOZ) on the internal insulating layer of solid rocket motors. These plasticizers are originally present in the layers of rubber, liner and propellant, respectively. This species are not chemically bonded and tend to diffuse from propellant to insulating and vice versa. A computer program based on the mathematical model of Fick's second Law of diffusion was developed to perform the calculus from the concentration data obtained by gas chromatographic (GC) analyses. The samples were prepared with two different adhesive liners; one conventional (LHNA) and the other with barrier properties (LHNT). A common feature of both liners was that they were synthesized by the reaction of hydroxyl-terminated polybutadiene (HTPB) and diisocyanates. However, a bond promoter was used to increase the crosslink density of the LHNT liner and to improve its performance as barrier against the diffusion. The effects of the diffusion of the plasticizers were also investigated by hardness analyses, which were executed on samples aged at room temperature and at 80oC. The results showed an increase trend for the samples aged at room temperature and an opposite behavior for the tests carried out at 80oC.

The aim of this work was to determine the dioctyl azelate (DOZ) plasticizer diffusion coefficient (D) for samples containing the interfaces of rubber, liner and solid composite propellant based on hydroxyl-terminated polybutadiene (HTPB). The samples used in the diffusion study were aged up to 31 days after the cure period at 80 °C. A computer program implementing a mathematical model of Fick's second Law of diffusion was developed to calculate the diffusion coefficient based on concentration data obtained from gas chromatographic analyses. The effects of the diffusion phenomenon were also investigated by Shore A hardness and scanning electron microscope (SEM) techniques. These analyses were carried out using samples aged at room temperature and at 80 °C. The hardness results showed an increasing trend for the samples aged at room temperature; however in the tests carried out at 80 °C they showed the opposite trend. The SEM analyses detected meaningful changes in the surface morphology of the propellant for both aging temperatures.

Orientadores : Sergio Persio Ravagnani, Choyu Otani Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica Resumo: Os propelentes compósitos à base de polibutadieno líquido hidroxilado (PBLH) utilizados na produção dos motores foguete a propelente sólido (MFPS), desenvolvidos no Instituto de Aeronáutica e Espaço (IAE), podem sofrer alterações em suas propriedades físicas devido ao processo de difusão de plastificantes entre as interfaces das camadas de propelente e de proteção térmica, que reveste a parede interna deste motor. A ocorrência deste fenômeno afeta diretamente a integridade estrutural dos motores e conseqüentemente seu desempenho. O objetivo deste trabalho foi desenvolver um programa computacional, em linguagem FORTRAN, para calcular os coeficientes de difusão a partir das concentrações dos plastificantes dioctilazelato (DOZ), dibutilftalato (DBF) e dioctilftalato (DOP) presentes nas camadas do propelente sólido, liner e borracha isolante, respectivamente. Para a realização dos cálculos computacionais foi adotado o modelo matemático proposto pela segunda Lei de difusão de Fick. O coeficiente de difusão foi obtido por meio da solução da equação não linear deste modelo com auxílio de métodos numéricos iterativos. Os dados de concentração utilizados no software foram obtidos em amostras contendo as interfaces de propelente/liner/borracha envelhecidas a 50°C e a 80°C. Na primeira condição, foi adotado o período de envelhecimento entre 30 a 125 dias após a cura do propelente. As amostras utilizadas nesta etapa foram preparadas com o liner LHNA que é produzido à base do polímero polibutadieno líquido hidroxilado e curado com o tolueno diisocianato. Foi verificado, por meio dos resultados obtidos, que houve pouca variação nos valores das concentrações dos plastificantes ao longo do envelhecimento, indicando que neste período a difusão entre as interfaces estudadas apresentou um estado próximo ao equilíbrio. Neste caso, os coeficientes não foram calculados devido ao modelo adotado executar os cálculos com base nas diferenças de concentração do plastificante na região estudada ao longo do tempo. Na segunda condição pesquisada as amostras foram envelhecidas a 80°C por um período entre 0 e 31 dias após o término da cura do propelente. Neste caso, os corpos de prova foram preparados com dois tipos diferentes de liner: LHNA e LHNT, este último também é produzido à base do polímero PBLH, no entanto, o LHNT é curado com o isoforona diisocianato que promove maior do reticulação do liner. O programa realizou os cálculos com sucesso e os coeficientes obtidos revelaram que a aplicação de um "liner" com maior densidade de ligações cruzadas reduz, como esperado, o processo de difusão dos plastificantes. Os dados experimentais e os simulados pelo programa exibiram bom ajuste entre si, revelando que o modelo aplicado é válido. Para verificar o efeito da difusão dos plastificantes sobre a dureza do propelente foram realizados testes de dureza Shore A em diferentes regiões dos corpos de prova. Alterações nesta propriedade, ao longo do envelhecimento, podem comprometer a integridade estrutural do motor foguete. Os testes foram executados em amostras de propelente envelhecidas a 80°C e a temperatura ambiente por um período máximo de 54 dias após a cura. Para as amostras mantidas à temperatura ambiente foi verificado o aumento dos valores de dureza ao longo de tempo de envelhecimento e para as amostras armazenadas a 80°C os valores diminuíram no mesmo período de análise. Abstract: The hydroxyl-terminated (HTPB) based solid composite propellant used in the production of solid rocket motors, developed in the Institute of Aeronautics and Space (IAE), can suffer changes of physical properties due to the diffusion process of plasticizers between the interfaces layers of propellant and thermal insulation. The occurrence of this phenomenon affects directly the structural integrity of the rocket motor and consequently its performance. The aim of this work was to develop a computational program, in FORTRAN language, to calculate the diffusion coefficient, from the concentration data, of plasticizers dioctyl azelate (DOZ), dibutyl phthalate (DBF) and dioctyl phthalate (DOP) contained into layers of propellant, liner and insulation rubber, respectively. The mathematical model proposed by Fick's second law of diffusion was used in computational calculus. The diffusion coefficient was obtained by solution of non liner equation of this model which is solved with assistance of iterative numeric methods. The concentration data used by the software were obtained from samples containing the interfaces of propellant/liner/rubber aged at 50°C and 80°C. In the first condition, the aging was executed between 30 and 125 days after the end of cure. From these results was verified that diffusion process practically reached the equilibrium state. In this case, the diffusion coefficients were not calculated once the mathematical model is based on concentration differences of plasticizers over aging. In the second condition, the samples were aged at 80°C between 0 and 31 days after the end of cure. In this case, the samples were prepared with two different types of liners: LHNA and LHNT, which has higher crosslinking density and is also hydroxyl-terminated polybutadiene based, however, the LHNT is cured with isophorone diisocyanate which is responsible for higher crosslinking. The program executed the calculus with success and the results obtained revealed that the diffusion process is reduced by the application of the liner with higher crosslinking density. It was observed good agreement between the experimental and simulated results showing that the model applied is valid. The Shore A tests was achieved to verify the effects of diffusion on hardness of propellant in different regions of the sample. Changes in propellant hardness over the aging may compromise the structural integrity of the rocket motor. In this study, the analyses were executed in samples aged up to 54 days after the end of cure and submitted to 80°C and room temperature conditions. To samples stored at room temperature the hardness values increased with time while it decreased for samples at 80°C at the same period. Doutorado Ciência e Tecnologia de Materiais Doutor em Engenharia Química