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Desenvolvimento e caracterização de pigmentos inovadores a partir de nanomateriais inorgânicos e de biopolímeros : Aplicação à energia solar térmica
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Este trabalho consistiu na pesquisa e estudo de materiais já existentes, tanto na Natureza como produzidos industrialmente, com possível aplicação na conversão da energia solar térmica, de modo a aumentar a eficiência dos coletores existentes no mercado a baixo custo. Atualmente, o principal requisito das empresas é manter a eficiência dos coletores com um custo de produção menor, tendo sempre em conta o fim de vida dos materiais, a sua reciclagem e reutilização e o tratamento eficiente dos desperdícios gerados.
O estudo dos materiais dividiu-se em 4 áreas principais: o estudo ótico de pigmentos a partir de resíduos da indústria pesqueira e de bagas de plantas invasoras; o estudo de nanotubos de carbono aplicados a uma tinta aquosa desenvolvida numa empresa alemã, a caracterização mecânica e ótica dos revestimentos por pintura e a aplicação de uma tinta a um painel de cerâmica; a introdução de grafeno num fluido base de transferência térmica comum no mercado (água/etilenoglicol) e a introdução de nanotubos de carbono em etilenoglicol; e a produção de sensores de filme fino de temperatura a partir da técnica de deposição física em fase de vapor.
Os pigmentos a partir de bagas de plantas invasoras foram estudados por espectroscopia UV-Vis, o pigmento a partir de resíduos da indústria pesqueira foi estudado por espectroscopia UV-Vis-NIR, Raios-X, calorimetria, tratamento térmico, SEMEDS e TEM. As tintas produzidas foram caracterizadas por determinação da massa volúmica, viscosidade, reologia, resistência ao escorrimento, espessura do escorrimento, nivelamento, resistência ao empilhamento, dureza pendular, resistência à tração, alongamento de rutura, sensibilidade à água, brilho, cor e espectroscopia UV-Vis-NIR. O painel de cerâmica com uma das tintas produzidas foi colocado ao Sol e a variação da temperatura do fluido foi medida ao longo do tempo de exposição. O nanofluido de transferência térmica constituído por 0,05% (m/m) de grafeno em água/etilenoglicol foi posto a circular num coletor solar de bancada exposto a luz artificial e a variação da temperatura do fluido foi medida ao longo do tempo. A condutibilidade térmica de um nanofluido com 0,337% (m/m) de nanotubos de carbono em etilenoglicol foi determinada com 2 aparelhos comerciais. Os sensores de platina em diferentes ce râmicas foram caracterizados por SEM-EDS.
Verificou-se que os extratos das bagas da erva-dos-cachos-da-Índia são promissoras enquanto pigmentos para tintas aquosas e que a “tinta” a partir de resíduos da indústria pesqueira é um material espectralmente seletivo com capacidade de retenção de calor o que a torna desejável em aplicações para a conversão térmica da energia solar. Uma tinta comercial desenvolvida na BASF com nanotubos de carbono como pigmento apresenta boas características mecânicas e aumenta a eficiência da conversão da energia solar em calor de um protótipo de painel solar térmico de cerâmica. O nanofluido 0,05% (m/m) de grafeno em água/etilenoglicol é mais eficiente em trocas de calor num coletor solar de bancada. A condutibilidade térmica do nanofluido 0,337% (m/m) de nanotubos de carbono em etilenoglicol aumenta em relação ao fluido base a partir de 50 ºC tornando este um fluido prometedor em trocas térmicas. Os sensores de platina obtidos reproduzem as características iniciais, desde o seu desenho até à deposição do metal, e têm uma sensibilidade elevada a variações de potencial.
The main focus of this work was on the research and study of existing materials, in Nature and those produced industrially, with potential application in the conversion of solar thermal energy in order to increase the efficiency of solar collectors available commercially, at a lower cost. Nowadays, the companies’ main requisite is to maintain the efficiency of collectors with a lower production cost, taking into account the end of life of materials, their recycling and reuse and the efficient treatment of the generated waste. The materials’ study was divided in 4 main areas: the optical study of pigments from fishing industry residues and berries from invasive plants; the study of carbon nanotubes added to waterborne paints developed in a German company, the mechanical and optical characterization of paint coatings and the application of a paint on ceramic panel; the addition of graphene in a base heat transfer fluid (water/ethylene glycol) and the addition of carbon nanotubes to ethylene glycol; the production of thin film temperature sensors with the Physical Vapor Deposition technique. Pigments from berries from invasive plants were studied by UV-Vis spectroscopy, the pigment from the fishing industry residues was studied by UV-Vis-NIR spectroscopy, Xrays, calorimetry, heat treatment, SEM, TEM and EDS. The paints produced were characterized by the determination of density, viscosity, rheology, sag resistance, thickness of sag resistance, levelling, stacking resistance, pendulum hardness, tensile strength, elongation at break, water uptake, gloss, color and UV-Vis-NIR spectroscopy. The ceramic panel painted with one of the paints produced was placed under the Sun and the temperature variation of the fluid was measured over the time of exposure. The heat transfer nanofluid consisting of 0,05% (m/m) of graphene in water/ethylene glycol was circulated in a bench-scale solar collector exposed to artificial light and the temperature variation of the fluid was measured over the time of exposure. The thermal conductivity of a nanofluid with 0,337% (m/m) of carbon nanotubes in ethylene glycol was determined with 2 commercial equipments. The thin film platinum sensors in different ceramics were characterized by SEM-EDS. It was determined that the extracts from the berries of the pokeweed are promising as pigments for waterborne paints and that the “ink” from the fishing industry residues is a spectrally selective material with a capacity to conserve heat which makes it desirable in applications for the thermal conversion of solar energy. A commercial paint developed at BASF with carbon nanotubes as a pigment demonstrates good mechanical characteristics and increases the efficiency of solar energy conversion into heat of a ceramic solar thermal panel prototype. The nanofluid 0,05% (m/m) of graphene in water/ethylene glycol is more efficient in the heat exchange process of a bench-scale solar collector. The thermal conductivity of the nanofluid 0,337% (m/m) of carbon nanotubes in ethylene glycol increases when compared to the base fluid when the working temperature is higher than 50 °C, making this a promising fluid in heat exchange. The platinum sensors produced present a good reproducibility of the initial characteristics, from its design up to the metal deposition, and have a high sensitivity to variations of potential.
The main focus of this work was on the research and study of existing materials, in Nature and those produced industrially, with potential application in the conversion of solar thermal energy in order to increase the efficiency of solar collectors available commercially, at a lower cost. Nowadays, the companies’ main requisite is to maintain the efficiency of collectors with a lower production cost, taking into account the end of life of materials, their recycling and reuse and the efficient treatment of the generated waste. The materials’ study was divided in 4 main areas: the optical study of pigments from fishing industry residues and berries from invasive plants; the study of carbon nanotubes added to waterborne paints developed in a German company, the mechanical and optical characterization of paint coatings and the application of a paint on ceramic panel; the addition of graphene in a base heat transfer fluid (water/ethylene glycol) and the addition of carbon nanotubes to ethylene glycol; the production of thin film temperature sensors with the Physical Vapor Deposition technique. Pigments from berries from invasive plants were studied by UV-Vis spectroscopy, the pigment from the fishing industry residues was studied by UV-Vis-NIR spectroscopy, Xrays, calorimetry, heat treatment, SEM, TEM and EDS. The paints produced were characterized by the determination of density, viscosity, rheology, sag resistance, thickness of sag resistance, levelling, stacking resistance, pendulum hardness, tensile strength, elongation at break, water uptake, gloss, color and UV-Vis-NIR spectroscopy. The ceramic panel painted with one of the paints produced was placed under the Sun and the temperature variation of the fluid was measured over the time of exposure. The heat transfer nanofluid consisting of 0,05% (m/m) of graphene in water/ethylene glycol was circulated in a bench-scale solar collector exposed to artificial light and the temperature variation of the fluid was measured over the time of exposure. The thermal conductivity of a nanofluid with 0,337% (m/m) of carbon nanotubes in ethylene glycol was determined with 2 commercial equipments. The thin film platinum sensors in different ceramics were characterized by SEM-EDS. It was determined that the extracts from the berries of the pokeweed are promising as pigments for waterborne paints and that the “ink” from the fishing industry residues is a spectrally selective material with a capacity to conserve heat which makes it desirable in applications for the thermal conversion of solar energy. A commercial paint developed at BASF with carbon nanotubes as a pigment demonstrates good mechanical characteristics and increases the efficiency of solar energy conversion into heat of a ceramic solar thermal panel prototype. The nanofluid 0,05% (m/m) of graphene in water/ethylene glycol is more efficient in the heat exchange process of a bench-scale solar collector. The thermal conductivity of the nanofluid 0,337% (m/m) of carbon nanotubes in ethylene glycol increases when compared to the base fluid when the working temperature is higher than 50 °C, making this a promising fluid in heat exchange. The platinum sensors produced present a good reproducibility of the initial characteristics, from its design up to the metal deposition, and have a high sensitivity to variations of potential.
Descrição
Palavras-chave
Energia solar térmica pigmentos espectralmente seletivos tinta solar com nanotubos de carbono nanofluido sensor de filme fino de platina Solar thermal energy spectrally selective pigments solar paint with carbon nanotubes nanofluid platinum thin film sensor