Orientador: Nilson Cristino da Cruz / Resumo: O alumínio é um dos materiais mais utilizados em vários setores da indústria. Devido ao baixo custo, se comparado ao cobre, e considerando sua abundância de oferta, o interesse nas propriedades térmicas do alumínio tem aumentado. Neste contexto, a proposta desta pesquisa é avaliar as propriedades térmicas de amostras de alumínio tratadas por oxidação eletrolítica plasmática (PEO), em eletrólitos de silicato de sódio, utilizando espectroscopia fotoacústica. A rugosidade, morfologia e a composição química dos revestimentos foram analisados, respectivamente, por perfilometria, Microscopia Eletrônica de Varredura (MEV) e Espectroscopia de Energia Dispersiva (EDS). A porosidade da camada superficial do revestimento foi estimada pelo software de processamento de imagem digital, utilizando imagens da análise de MEV, enquanto difração de Raios X (DRX) foi utilizada para determinar a estrutura cristalina das superfícies tratadas. Os resultados das análises demonstraram que os revestimentos, predominantemente constituídos por γ-Al2O3, são rugosos, com superfícies porosas e apresentam boa resistência mecânica. A espectroscopia de absorção de UV-VIS demonstrou que a amostra tratada absorveu em média 18% mais radiação na região infravermelha quando comparada com amostras sem tratamento. Em consequência, como revelado pela espectroscopia fotoacústica a difusividade térmica das amostras tratadas é pelo menos 30% maior se comparada ao alumínio não tratado e 700% maior do que a alumina conven... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Aluminum is one of the most widely used materials in several areas of the industry. Owing to lower cost, if compared to copper, and considering its abundance, the interest on the thermal properties of aluminum has increased. In this context, the proposal of this research is to evaluate the thermal properties of aluminum samples treated by Plasma electrolytic oxidation (PEO), in sodium silicate electrolytes, using photoacoustic spectroscopy. Roughness, morphology and chemical composition of the coatings have been analyzed, respectively, by profilometry, scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). The porosity of the surface layer was estimated by digital image processing using SEM micrographs while X-ray diffraction (XRD) was used for determining the crystalline structure of the treated surfaces. The results of the analyses have shown that the coatings, predominantly constituted by γ-Al2O3, are rough, with porous surfaces and present good mechanical resistance. UV-Vis absorption spectroscopy has shown that the treated sample absorbed on average 18% more radiation in the infrared region than the pristine samples. In consequence, as revealed by photoacoustic spectroscopy the thermal diffusivity of the treated samples is at least 30% larger if compared to untreated aluminum and 700% larger than that of conventional Alumina / Mestre

Orientador: Antonio Manoel Mansanares / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-09-26T13:53:30Z (GMT). No. of bitstreams: 1 Mesquita_RicksonCoelho_M.pdf: 13672557 bytes, checksum: bbf3df05cb82c513d1c69aa2b28b84da (MD5) Previous issue date: 2005 / Resumo: O nível de iluminação das plantas é determinante da estrutura das folhas, em particular no tocante à quantidade e distribuição dos cloroplastos. O objetivo deste projeto é utilizar a técnica fotoacústica para demonstrar as diferenças fisiológicas entre plantas adaptadas a diferentes condições de irradiância. Plantas de tabaco foram cultivadas em dois níveis distintos de irradiância. Plantas congenéricas, provenientes de habitats diferentes (cerrado e mata atlântica), crescidas sob o mesmo nível de exposição à luz, também foram estudadas. Como a técnica fotoacústica é sensível ao O2 produzido na fotossíntese, a resposta dos sistemas fotossintéticos das plantas de diferentes condições foi avaliada por meio de medidas fotoacústicas de indução fotossintética. A quantidade de energia armazenada também foi determinada nessas plantas. A partir da contribuição da evolução de O2 para o sinal fotoacústico, obtivemos espectros de ação para as diferentes amostras. Os resultados mostraram que plantas adaptadas a ambientes de sol são menos eficientes em armazenar energia para as reações fotoquímicas. As curvas de indução indicaram que essas plantas demoram um tempo maior para atingir um estado estacionário de produção de O2. Experimentos de fotoinibição mostraram que plantas adaptadas a baixas irradiâncias são mais sensíveis ao excesso de luz saturante. Foi observada uma absorção de O2 após a saturação fotossintética em plantas de tabaco de sol, associada a uma provável competição entre fotossíntese e fotorrespiração. Os espectros de ação, obtidos pela primeira vez a partir de medidas fotoacústicas de produção de O2, mostraram uma boa concordância com a literatura (valores obtidos por outras técnicas) / Abstract: Ilumination level of plants during its growth is determinant for structure of leaves, specially refering to quantity and distribution of chloroplasts. The aim of this project is to use the photoacoustic technique to show physiological differences among plants adapted to different light intensity conditions. Tobacco plants were grown up under two distint irradiance levels. Congeneric plants, coming from different habitats (cerrado and florest), grown up under the same light level, were also studied. Since photoacoustic technique is sensitive to O2 produced by photosynthesis, photosynthetic response of plants from different light conditions were studied through PA measurements of photosynthetic induction. The energy storage was also determined in these plants. From the oxygen component of the photoacoustic signal it was possible to obtain action spectra for all the samples. Results showed that plants adapted to sunlight present lower efficiency in storing energy to photochemical reactions. The induction curves indicated these plants also take a longer time to reach a steady state of O2 production, after remaining a period in the dark. Photoinhibition experiments showed that plants grown up under lower light are more susceptible to excess of saturating light. It was also observed O2 uptake after photoinhibition in plants grown under full sunlight, which was associated to a competition between photosynthesis and photorespiration. The action spectra, obtained for the first time with photoacoustic measurements of O2 production, showed a good agreement with literature / Mestrado / Física da Matéria Condensada / Mestre em Física

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-10-16T16:03:48Z No. of bitstreams: 1 FAUSTO VAZ DE OLIVEIRA – DISSERTAÇÃO (PPGFísica) 2014.pdf: 2950759 bytes, checksum: f75675457b33950244dae94b86657cac (MD5) / Made available in DSpace on 2018-10-16T16:03:48Z (GMT). No. of bitstreams: 1 FAUSTO VAZ DE OLIVEIRA – DISSERTAÇÃO (PPGFísica) 2014.pdf: 2950759 bytes, checksum: f75675457b33950244dae94b86657cac (MD5) Previous issue date: 2014-03-13 / CNPq / Neste trabalho usamos a técnica de Espectroscopia Fotoacústica na identificação de Biomoléculas Funcionais, presentes em várias frutas e vegetais. Essas biomoléculas, em geral compostos polifenólicos, formam grupos de substâncias amplamente distribuídos em plantas, frutas e legumes, componentes comuns da alimentação humana, especialmente flavonóides e taninos que possuem diversas propriedades terapêuticas e farmacológicas. Dentre as espécies de frutas e cereais investigadas, cientificamente estabelecidas como depositárias de moléculas bioativas, algumas se destacam por suas excelentes propriedades funcionais, tendo, por este motivo, recebido o nome pomposo de “superfrutas”. São elas caracterizadas por apresentarem altas concentrações de polifenóis tais como as antocianinas, os flavonóis (quercetinas, kaempferol, catequinas, resveratrol e taninos), os ácidos fenólicos como o gálico, o ascórbico, o elágico, o clorogênico, o benzóico, o felúrico, etc e os carotenóides, onde se destacam o β–caroteno, licopeno, violaxantina, zeaxantina, luteína, neoaxantina, dentre outras. As superfrutas são assim classificadas por exibirem extraordinário valor funcional. Os resultados experimentais obtidos por espectroscopia fotoacústica para os comprimentos de onda λmax que representa os picos de absorção em cada amostra de frutas e vegetais investigados evidenciam a existência de Biomoléculas Funcionais, que fazem bem a saúde humana. Nossos resultados, obtidos pela técnica de Espectroscopia Fotoacústica, confirmam esta como uma ferramenta experimental de grande potencial e eficiência na identificação de biomoléculas em sistemas biológicos “in natura”, sem necessidade de utilização de processos exaustivos de extração molecular. / In this work we have used the technique of Photoacoustic Spectroscopy to identify Functional Biomolecules, present in various fruits and vegetables. These polyphenolic compounds constitute groups of substances widely distributed in plants, fruits and vegetables, common components of the human diet, especially anthocyanins, flavonols, tannins and carotenoids that have been found to exhibit several therapeutic and pharmacological properties. Among the fruits and vegetables species investigated and scientifically established as host for bioactive or functional biomolecules, some of them are detached by their excellent functional properties, then, have been nominates as “superfruits”. They are characterized by exhibit high concentrations of polyphenols compounds such as anthocyanins, flavonols (quercitins, kaempferol, catechins, tannins), the phenolic acids such as the gallic, ascorbic, ellagic, chlorogenic, benzoic, ferulic, etc, and the carotenoids β–carotene, lycopene, violaxanthin, zeaxanthin, lutein, neoaxanthin among others. The “superfruits” are classified in this way for exhibit functional extraordinary value. The experimental results obtained by photoacoustic spectroscopy λmax for the wave lengths representing the absorption peaks of each sample of fruits and vegetables investigated showed the existence of Functional Biomolecules, which are human health as well. Our results obtained by the technique Photoacoustic Spectroscopy confirm this as an experimental tool with great potential and efficiency in the detection of biomolecules in biological systems “in nature”, without the need of using exhaustive molecular extraction processes.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Amostras policristalinas de Sr(Ga1-xCrx)2O4 com x = 0,01 foram estequiometricamente preparadas pela mistura dos materiais em pó SrCO3, Ga2O3 e Cr2O3. A estrutura cristalina da amostra dopada foi analisada pelas medidas de difração de raios-X. O padrão de difração revelou uma única fase relacionada a fase monoclínica do SrGa2O4. Os dados foram ajustados usando o Método de Rietveld para refinamento de estruturas e os parâmetros da rede foram determinados. A luminescência do íon de Cr3+ na rede do SrGa2O4 foi investigada pelas espectroscopias de excitação e emissão a temperatura ambiente, através das quais verificamos que os íons de Cr3+ estão localizados em dois sítios diferentes. Os espectros de emissão apresentam bandas largas associadas à transição eletrônica 4T2(4F) → 4A2(4F) para ambos os sítios. Estes resultados são analisados pela teoria de campo cristalino e o parâmetro de campo cristalino Dq e os parâmetros de Racah B e C são determinados pelas posições das bandas de excitação. A partir destes parâmetros determinamos um campo cristalino forte para ambos os sítios. Além disto, foram realizadas medidas de espectroscopia fotoacústica que confirmaram as transições identificadas e estimadas nos espectros de excitação. / Polycrystalline samples of Sr(Ga1-xCrx)2O4, with x = 0.01, were stoichiometrically prepared by mixing powder materials SrCO3, Ga2O3 and Cr2O3. The crystalline structure of the doped sample was analyzed by X-ray diffraction measurements. The diffraction patterns showed a single phase, which corresponds to the SrGa2O4 monoclinic phase. The data were fitted by using the Rietveld Method for structural refinements and the lattice parameters were determined. The luminescence of Cr3+ ions in the lattice of SrGa2O4 was investigated by excitation and emission spectroscopies at room temperature and the results show that the emission of Cr3+ ions comes from two different sites. In the emission spectra, we can observe that they present broadbands associated with the electronic transition 4T2(4F) → 4A2(4F) for both sites. These results are analyzed by crystal field theory and the crystal-field parameter Dq and the Racah parameters B and C are determined by the excitation band positions. From these parameters we determined a strong crystal field for both sites. Moreover, photoacoustic spectroscopy measurements were performed and they confirmed the transitions identified and estimated in the excitation spectra.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Amostras policristalinas de Sr(Ga1-xCrx)2O4 com x = 0,01 foram estequiometricamente preparadas pela mistura dos materiais em pó SrCO3, Ga2O3 e Cr2O3. A estrutura cristalina da amostra dopada foi analisada pelas medidas de difração de raios-X. O padrão de difração revelou uma única fase relacionada a fase monoclínica do SrGa2O4. Os dados foram ajustados usando o Método de Rietveld para refinamento de estruturas e os parâmetros da rede foram determinados. A luminescência do íon de Cr3+ na rede do SrGa2O4 foi investigada pelas espectroscopias de excitação e emissão a temperatura ambiente, através das quais verificamos que os íons de Cr3+ estão localizados em dois sítios diferentes. Os espectros de emissão apresentam bandas largas associadas à transição eletrônica 4T2(4F) → 4A2(4F) para ambos os sítios. Estes resultados são analisados pela teoria de campo cristalino e o parâmetro de campo cristalino Dq e os parâmetros de Racah B e C são determinados pelas posições das bandas de excitação. A partir destes parâmetros determinamos um campo cristalino forte para ambos os sítios. Além disto, foram realizadas medidas de espectroscopia fotoacústica que confirmaram as transições identificadas e estimadas nos espectros de excitação. / Polycrystalline samples of Sr(Ga1-xCrx)2O4, with x = 0.01, were stoichiometrically prepared by mixing powder materials SrCO3, Ga2O3 and Cr2O3. The crystalline structure of the doped sample was analyzed by X-ray diffraction measurements. The diffraction patterns showed a single phase, which corresponds to the SrGa2O4 monoclinic phase. The data were fitted by using the Rietveld Method for structural refinements and the lattice parameters were determined. The luminescence of Cr3+ ions in the lattice of SrGa2O4 was investigated by excitation and emission spectroscopies at room temperature and the results show that the emission of Cr3+ ions comes from two different sites. In the emission spectra, we can observe that they present broadbands associated with the electronic transition 4T2(4F) → 4A2(4F) for both sites. These results are analyzed by crystal field theory and the crystal-field parameter Dq and the Racah parameters B and C are determined by the excitation band positions. From these parameters we determined a strong crystal field for both sites. Moreover, photoacoustic spectroscopy measurements were performed and they confirmed the transitions identified and estimated in the excitation spectra.

Contamination of peanuts by secondary metabolites of certain fungi, namely aflatoxins present a great health hazard when exposed either at low levels for prolonged times (carcinogenic) or at high levels at once (poisonous). It is important to develop an accurate and rapid measurement technique to trace the aflatoxin and/or source fungi presence in peanuts. Thus, current research focused on development of vibrational spectroscopy based methods for detection and separation of contaminated peanut samples. Aflatoxin incidence, as a chemical contaminant in peanut paste samples, was investigated, in terms of spectral characteristics using FTIR-ATR. The effects of spectral pre-processing steps such as mean-centering, smoothing the 1st derivative and normalizing were studied. Logarithmic method was the best normalization technique describing the exponentially distributed spectral data. Spectral windows giving the best correlation with respect to increasing aflatoxin amount led to selection of fat associated spectral bands. Using the multivariate analysis tools, structural contributions of aflatoxins in peanut matrix were detected. The best region was decided as 3028-2752, 1800-1707, 1584-1424, and 1408-1127 cm-1 giving correlation coefficient for calibration (R2C), root mean square error for calibration (RMSEC) and root mean square error for prediction (RMSEP) of 98.6%, 7.66ppb and 19.5ppb, respectively. Applying the constructed partial least squares model, 95% of the samples were correctly classified while the percentage of false negative and false positive identifications were 16% and 0%, respectively. Aspergillus species of section Flavi and the black fungi, A. niger are the most common colonists of peanuts in nature and the majority of the aflatoxin producing strains are from section Flavi. Seed colonization by selected Aspergillus spp. was investigated by following the chemical alterations as a function of fungal growth by means of spectral readouts. FTIR-ATR was utilized to correlate spectral characteristics to mold density, and to separate Aspergillus at section, species and strain levels, threshold mold density values were established. Even far before the organoleptic quality changes became visually observable (~10,000 mold counts), FTIR distinguished the species of same section. Besides, the analogous secondary metabolites produced increased the similarity within the spectra even their spectral contributions were mostly masked by bulk peanut medium; and led to grouping of species producing the same mycotoxins together. Aflatoxigenic and non-aflatoxigenic strains of A. flavus and A. parasiticus were further studied for measurement capability of FTIR-ATR system in discriminating the toxic streams from just moldy and clean samples. Owing to increased similarity within the collected spectral data due to aflatoxin presence, clean samples (having aflatoxin level lower than 20 ppb, n=44), only moldy samples (having aflatoxin level lower than 300 ppb, n=28) and toxic samples (having aflatoxin level between 300-1200 ppb, n=23) were separated into appropriate classes (with a 100% classification accuracy). Photoacoustic spectroscopy (PAS) is a non-invasive technique and offers many advantages over more traditional ATR system, specifically, for in-field measurements. Even though the sample throughput time is longer compared to ATR measurements, intact seeds can be directly loaded into sample compartment for analysis. Compared to ATR, PAS is more sensitive to high moisture in samples, which in our case was not a problem since peanuts have water content less than 10%. The spectral ranges between: 3600-2750, 1800-1480, 1200-900 cm-1 were assigned as the key bands and full separation between Aspergillus spp. infected and healthy peanuts was obtained. However, PAS was not sensitive as ATR either in species level classification of Aspergillus invasion or toxic-moldy level separation. When run for separation of aflatoxigenic versus non-aflatoxigenic batches of samples, 7 out of 54 contaminated samples were misclassified but all healthy peanuts were correctly identified (15 healthy/ 69 total peanut pods). This study explored the possibility of using vibrational spectroscopy as a tool to understand chemical changes in peanuts and peanut products to Aspergillus invasion or aflatoxin contamination. The overall results of current study proved the potential of FTIR, equipped with either ATR or PAS, in identification, quantification and classification at varying levels of mold density and aflatoxin concentration. These results can be used to develop quality control laboratory methods or in field sorting devices. / Ph. D.

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / O objetivo deste trabalho é a síntese e investigação estrutural e óptica de amostras SrGa2O4 dopados com 1% de íons Ni2+. Estas amostras foram sintetizados por reação do estado sólido convencional, utilizando como materiais de partida de alta pureza Ga2O3, SrCO3 e NiO em quantidades estequiométricas. As amostras foram caracterizadas estruturalmente pelo método de difração de raios - X( XRD ) e as medições de difração mostraram que as amostras têm uma única fase monoclínica. Os padrões de XRD também foram refinados pelo método de Rietveld, que permitiu a determinação dos parâmetros de célula unitária. A Caracterização óptica das amostras puras e dopadas SrGa2O4 foram realizadas as medições a partir de fotoluminescência, de excitação e de absorção fotoacústica, à temperatura ambiente. Os espectros de emissão mostraram três bandas de emissão localizadas em 557 nm, 661 nm e 844 nm e foram identificadas essas bandas, respectivamente, com as seguintes transições eletrônicas :1T2 (1D) → 3A2 (3F), 3T1 (3F)→ 3A2 (3F) e 1T2 (1D) → 3T2 (3F). Os espectros de excitação mostraram seis bandas de absorção associadas às transições electrônicas do nível 3A2 (3F) para o 3T1 (3P) , T1 (3P), 1A1 (1G), 1T2 (1D), 3T1 (3F), 1E (1D) e 1T2, 1E (1G). Medidas de absorção fotoacústica também foram realizados com o fim de verificar as transições ópticas observadas nos espectros de excitação e de identificar novas bandas de absorção óptica. Os resultados demonstraram que os íons de Ni2+ ocupam dois locais octaédricos diferentes na amostra SrGa2O4 dopado. A partir das transições ópticas observadas nos espectros de excitação e fotoacústica, determinou-se o parâmetro de cristal de campo, dq, e parâmetros Racah, B e C. A proporção Dq / B ≈ 1.2 para ambos os locais são típicos para Ni2+ íons inseridos em redes de óxido e em coordenação octaédrica. / The aim of this work is the synthesis and structural and optical investigation of SrGa2O4 samples doped with 1% of Ni2+ ions. These samples were synthesized by conventional solid-state reaction using as starting materials high purity SrCO3, Ga2O3 and NiO in stoichiometric quantities. Samples were structurally characterized by X-ray diffraction (XRD) method and the diffraction measurements showed that the samples have a single monoclinic phase. The XRD patterns were also refined by the Rietveld method which allowed the determination of the unit cell parameters. Optical characterization of the pure and doped SrGa2O4 samples were performed from photoluminescence, excitation and photoacoustic absorption measurements at room temperature. Emission spectra showed three emission bands localized at 557 nm, 661 nm and 844 nm and these bands were identified, respectively, with the following electronic transitions: 1T2 (1D) → 3A2 (3F), 3T1 (3F)→ 3A2 (3F) e 1T2 (1D) → 3T1 (3F). Excitation spectra showed six absorption bands associated to the electronic transitions from the level 3A2 (3F) to the 3T1 (3P), 1A1 (1G), 1T2 (1D), 3T1 (3F), 1E (1D) e 1T2, 1E (1G) levels. Photoacoustic absorption measurements were also carried out in order to verify the optical transitions observed in the excitation spectra and to identify new optical absorption bands. The results showed that Ni2+ ions occupy two different octahedral sites in the SrGa2O4 doped sample. From the optical transitions observed in the excitation and photoacoustic spectra, we determined the crystal-field parameter, Dq, and Racah parameters, B and C. The ratio Dq/B ≈ 1.2 for both sites are typical for Ni2+ ions inserted in oxide lattices and in octahedral coordination.

Aerosols contribute the largest uncertainty to estimates of radiative forcing of the Earth’s atmosphere, which are thought to exert a net negative radiative forcing, offsetting a potentially significant but poorly constrained fraction of the positive radiative forcing associated with greenhouse gases. Aerosols perturb the Earth’s radiative balance directly by absorbing and scattering radiation and indirectly by acting as cloud condensation nuclei, altering cloud albedo and potentially cloud lifetime. One of the major factors governing the uncertainty in estimates of aerosol direct radiative forcing is the poorly constrained aerosol single scattering albedo, which is the ratio of the aerosol scattering to extinction. In this thesis, I describe a new instrument for the measurement of aerosol optical properties using photoacoustic and cavity ring-down spectroscopy. Characterisation is performed by assessing the instrument minimum sensitivity and accuracy as well as verifying the accuracy of its calibration procedure. The instrument and calibration accuracies are assessed by comparing modelled to measured optical properties of well-characterised laboratory-generated aerosol. I then examine biases in traditional, filter-based absorption measurements by comparing to photoacoustic spectrometer absorption measurements for a range of aerosol sources at multiple wavelengths. Filter-based measurements consistently overestimate absorption although the bias magnitude is strongly source-dependent. Biases are consistently lowest when an advanced correction scheme is applied, irrespective of wavelength or aerosol source. Lastly, I assess the sensitivity of the direct radiative effect of biomass burning aerosols to aerosol and cloud optical properties over the Southeast Atlantic Ocean using a combination of offline radiative transfer modelling, satellite observations and global climate model simulations. Although the direct radiative effect depends on aerosol and cloud optical properties in a non-linear way, it appears to be only weakly dependent on sub-grid variability.

Le besoin d'analyse de gaz à l'état de traces s'est accentué ces dernières années en raison des préoccupations du public et de l'industrie sur des questions telles que le contrôle des émissions de polluants atmosphériques, la surveillance de l'environnement au sens large, la santé et la sécurité au travail. Il est donc nécessaire de posséder des instruments de détection sélectifs, sensibles et capables d'effectuer une mesure directe en temps réel. La fiabilité des systèmes de mesure est également un critère important et, selon l'application envisagée, s'ajoute aussi le besoin de miniaturisation pour aller vers des microsystèmes permettant le développement de dispositifs portables pour des opérations sur site.Le travail de thèse présenté dans ce manuscrit est situé dans ce contexte et porte sur l'étude et la mise au point d'un système sensible, efficace et assez simple à mettre en œuvre permettant de réaliser des mesures de traces de gaz sélectives, en temps réel et in-situ. Ce système est basé sur la spectroscopie d'absorption par quartz (QEPAS, Quartz Enhanced PhotoAcoustic Spectrocopy) qui consiste en la mesure d'une onde acoustique générée après la relaxation non-radiative des molécules excitées par l'absorption de la lumière modulée émise par des diodes lasers accordables, à l'aide d'un diapason à quartz (QTF). Le fonctionnement des sources lasers accordables et du QTF ainsi que différentes configurations du spectrophone (association du micro-résonateur et du QTF) utilisés dans cette technique QEPAS sont détaillés. Une modélisation de l'onde acoustique et de la réponse du capteur est également proposée. Deux dispositifs ont été réalisés. Le premier, nommé banc QEPAS prototype, est dédié à la mesure de l'éthylène avec une diode laser DFB émettant à 3,32 µm. Le second dispositif est une nouvelle version de capteur QEPAS, plus compacte que des dispositifs existant actuellement, dans laquelle il est possible de placer tout type de diode laser commerciale montée dans des supports de type T0xx. Ce banc compact est utilisé pour la mesure de méthane avec notamment une diode laser DFB émettant à 3,26 µm. / The need for trace gas analysis has increased in recent years due to an important concern of the public and industry on issues such as the control of emissions of air pollutants, environmental monitoring, health and security. It is therefore necessary to have the trace gas sensors able of high selectivity, sensitivity and a direct measurement in real time. The reliability of the measurement systems is also an important criterion, depending on the intended application, the need to move towards miniaturization of microsystems for the development of portable devices for on-site operations is also interesting.This thesis is in this context and focuses on the study and development of a sensitive, efficient and simple setup to make selective, in-situ and in real time measurements of trace gases. This system is based on quartz enhanced photoacoustic spectrocopy (QEPAS) which consists on the measurement of an acoustic wave generated by the non-radiative relaxation of the excited molecules after light absorption, with a quartz tuning fork (QTF). The operation of tunable laser sources, of QTF and different spectrophone configurations (combination of the micro-resonator and QTF) used in QEPAS technique are detailed. A model of the acoustic wave and the response of the sensor are also proposed. Two devices have been designed. The first one is a QEPAS prototype bench, dedicated to the measurement of ethylene with a DFB laser diode emitting at 3.32 µm. The second device is a new version of QEPAS sensor that is more compact than the currently existing devices and where it is possible to place any type of commercial laser diode. This compact bench is used for methane measurement with a DFB laser diode emitting at 3.26 µm.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Os materiais ferroelétricos têm sido utilizados em muitas áreas da tecnologia e da ciência, pois possuem um grande número de aplicações, como: sensores; transdutores; capacitores; dispositivos ópticos; dentre outras. A busca por novos materiais cerâmicos ferroelétricos tem sido grande. Um dos materiais cerâmicos ferroelétricos mais estudados é o titanato de bário (BT). São vários os métodos de produção e caracterização do titanato de bário. Neste trabalho, pós cerâmicos de titanato de bário foram obtidos por reação do estado sólido a partir de misturas reacionais calcinadas em diferentes temperaturas entre 400C e 900C. Foram três as misturas reacionais: não dopadas; dopadas com 1%; e dopadas com 5% de dióxido de cério (CeO2). A identificação da formação do BT, nos pós cerâmicos produzidos, foi feita a partir de três técnicas de caracterização: difração de raios X (DRX); espectroscopia fotoacústica (PAS); e técnicas de análise térmica. Com a técnica DRX, difratogramas mostraram que a plena formação do titanato de bário ocorreu a partir da temperatura de calcinação de 700C. Para a amostra não dopada com cério e calcinada a 800C, houve deslocamento de todos os picos de difração. Nas amostras dopadas com dióxido de cério houve deslocamento de todos os picos de difração, em relação as amostras não dopadas. Observou-se também que nas amostras dopadas com 5% de CeO2, e calcinadas a 700C e 800C, resíduos de dióxido de cério foram observados nos difratogramas. Com a técnica PAS, espectros de absorção foram obtidos. Foi possível observar uma grande diferença de absorção da amostra calcinada a 600 e 630C, indicando a formação do titanato de bário a partir da temperatura de 630C, nas amostras sem a dopagem dióxido de cério. Houve um alargamento nas bandas de absorção a partir da temperatura de 600C, quando o dióxido de cério entrou na matriz. Foi também possível determinar as energias de band-gap das amostras utilizando o método de Tauc. Com as técnicas de análise térmica, em especial através da técnica termogravimétrica (TG/DTG), foi comprovado que até 400C não havia formação de titanato de bário. Visto que nesta temperatura de calcinação houve a maior perda de massa durante a rampa de aquecimento. O início da formação do titanato de bário foi observado a partir da temperatura de calcinação de 500C, assim como nas técnicas DRX e PAS. Portanto, com os resultados apresentados, foi demonstrada a identificação da formação do titanato de bário nas misturas reacionais calcinadas, com auxílio das potencialidades das três técnicas utilizadas. / Ferroelectric materials have been used in many areas of technology and science, because they have a large number of applications, such as sensors; transducers; capacitors; optical devices; among others. The search for new ferroelectric ceramics has been great. One of the most studied ferroelectric ceramic material is barium titanate (BT). There are several methods for production and characterization of barium titanate. In this work, ceramic powders of barium titanate were obtained by solid state reaction from reaction mixtures calcined at different temperatures between 400C and 900C. Three reaction mixtures were used: undoped; doped with 1%; and 5% doped with cerium dioxide (CeO2). The identification of the formation of BT, for the ceramic powders produced, was taken from three characterization techniques: X-ray diffraction (XRD); photoacoustic spectroscopy (PAS); and thermal analysis techniques. With the technique XRD diffraction patterns showed that complete formation of the barium titanate occurred after the calcination temperature of 700C. For the sample not doped with cerium and calcined at 800C, there was displacement of all diffraction peaks. In samples doped with cerium dioxide was no displacement of all diffraction peaks, comparing to undoped samples. It was also observed that the samples doped with 5% CeO2 and calcined at 700C and 800C, cerium dioxide residues were observed in the diffraction pattern. The absorption spectra were obtained with the technique PAS. It was possible to observe a large difference in absorption spectra in the samples calcined at 600C and 630C, indicating the formation of barium titanate at temperature of 630C in the samples without doping of cerium dioxide. There was an enlargement in the absorption band above temperature of 600C when the cerium dioxide was introduced into the matrix. It was also possible to determine the band-gap energy of the samples using the method of TAUC. With thermal analysis techniques, in particular by thermogravimetric technique (TG/DTG), has been proven that up to 400C there was no formation of barium titanate. Once, in this calcination temperature there was the largest mass loss during the heating ramp. The onset of formation of barium titanate was observed from the calcination temperature of 500C, as it has been found by the XRD and PAS techniques. Therefore, with the results presented, the identification of the formation of barium titanate calcined in reaction mixtures with the aid of the potentialities of the three techniques was demonstrated.