Estudo das propriedades do molibdato de estrôncio (SrMoO4) dopado com gadolínio e de seu uso como sensor
Data
2022-02-23
Autores
Braga, José Luiz Sousa 
Orientadores
Vieira, Rogério de Almeida
Tipo
Dissertação de mestrado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
Os molibdatos são materiais cerâmicos amplamente estudados na atualidade devido às suas aplicações industriais. A dopagem de materiais cerâmicos com terras raras é aplicada para modificar propriedades estruturais e morfológicas. No presente trabalho foram estudadas as propriedades do molibdato de estrôncio (SrMoO4) obtido por método de coprecipitação dopado com gadolínio assim como seu uso como sensor de umidade. Foi estudada a dopagem com nitrato de gadolínio (Gd(NO3)3.6H2O) durante o processo de coprecipitação e a dopagem via reação em estado sólido. São apresentados também resultados relacionados à caracterização do SrMoO4 obtido por diferentes métodos de síntese, aplicação de tratamentos hidrotermais e variação da temperatura no processo de sinterização. As técnicas de caracterização utilizadas neste trabalho foram: difração de raios-X (DRX), microscopia eletrônica de varredura (MEV), espectroscopia Raman, espectrometria por energia dispersiva (EDS), espectroscopia de absorção na região do infravermelho (FT-IR) e espectroscopia óptica nas regiões do ultravioleta e visível (UV-VIS). Foi desenvolvido um sistema eletrônico e sistema de câmaras para viabilizar as medidas de capacitância em função da umidade relativa. Os materiais apresentados no estudo das propriedades sensoras à umidade foram compactados, sinterizados a 1000°C e submetidos às medidas de capacitância em função da umidade relativa, tendo sensores modelos DHT11 e DHT22 como referências. As propriedades estruturais e morfológicas dos materiais foram elucidadas. Foram detectadas estruturas semelhantes a nanobarras de Gd2O3 após o processo de sinterização nas cerâmicas dopadas, assim como formação de Gd(OH)3 nas dopagens via coprecipitação. Houve decréscimo da cristalinidade de todos os materiais após o processo de sinterização. Os valores de banda de energia proibida (band gap ou Egap) dos materiais dopados mostraram-se superiores em relação ao SrMoO4 não dopado. O SrMoO4 não dopado foi o material que apresentou maior fator de sensibilidade (Sf = 99,9), sendo de 10 a 35 vezes maior que os demais fatores de sensibilidade calculados. As dopagens com gadolínio promoveram modificações morfológicas e estruturais nos materiais que contribuíram negativamente à interação entre as moléculas de água com a superfície dos elementos sensores. Tendo os resultados obtidos em vista, temos que o SrMoO4 não dopado com gadolínio é material promissor para uso como sensor de umidade.
Molybdates are widely studied materials nowadays due to their industrial applications. The doping process of ceramic materials with rare earths is applied in order to modify structural and morphological properties. In this work, the properties of strontium molybdate (SrMoO4) obtained by co-precipitation method doped with gadolinium were studied, as well as its use as a humidity sensor. Doping with gadolinium nitrate (Gd(NO3)3.6H2O) during the coprecipitation process and doping route via solid state reaction were studied. Results related to the characterization of SrMoO4 obtained by different synthesis methods, application of hydrothermal treatments and temperature variation in the sintering process are also presented, checking the morphological and structural differences of these materials. The characterization techniques used during the work were: X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, energy dispersive spectrometry (EDS), infrared absorption spectroscopy (FT-IR) and optical spectroscopy in the ultraviolet and visible regions (UV-VIS). An electronic system and humidity camera system was developed to enable capacitance measurements as a function of relative humidity. The materials presented in the study of humidity sensing properties were compacted, sintered at 1000°C and subjected to capacitance measurements as a function of relative humidity, with a DHT11 and DHT22 sensors as references. The structural and morphological properties of the materials were elucidated and the influence of gadolinium doping was verified. The formation of structures similar to Gd2O3 nanorods was observed after the sintering process in the doped ceramics and Gd(OH)3 formation in the coprecipitation doping method. There was a decrease in the crystallinity of all materials after the sintering process. The band gap values of doped materials were higher in relation to undoped SrMoO4. The undoped SrMoO4 was the material that presented the highest sensitivity factor (Sf = 99.9), being 10 to 35 times higher than the other calculated sensitivity factors. The gadolinium-doping promoted morphological and structural changes in the materials that contributed negatively to the interaction between water molecules and the surface of the sensor elements. Considering the results shown before, undoped SrMoO4 is a promising material for use as a humidity sensor.
Molybdates are widely studied materials nowadays due to their industrial applications. The doping process of ceramic materials with rare earths is applied in order to modify structural and morphological properties. In this work, the properties of strontium molybdate (SrMoO4) obtained by co-precipitation method doped with gadolinium were studied, as well as its use as a humidity sensor. Doping with gadolinium nitrate (Gd(NO3)3.6H2O) during the coprecipitation process and doping route via solid state reaction were studied. Results related to the characterization of SrMoO4 obtained by different synthesis methods, application of hydrothermal treatments and temperature variation in the sintering process are also presented, checking the morphological and structural differences of these materials. The characterization techniques used during the work were: X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, energy dispersive spectrometry (EDS), infrared absorption spectroscopy (FT-IR) and optical spectroscopy in the ultraviolet and visible regions (UV-VIS). An electronic system and humidity camera system was developed to enable capacitance measurements as a function of relative humidity. The materials presented in the study of humidity sensing properties were compacted, sintered at 1000°C and subjected to capacitance measurements as a function of relative humidity, with a DHT11 and DHT22 sensors as references. The structural and morphological properties of the materials were elucidated and the influence of gadolinium doping was verified. The formation of structures similar to Gd2O3 nanorods was observed after the sintering process in the doped ceramics and Gd(OH)3 formation in the coprecipitation doping method. There was a decrease in the crystallinity of all materials after the sintering process. The band gap values of doped materials were higher in relation to undoped SrMoO4. The undoped SrMoO4 was the material that presented the highest sensitivity factor (Sf = 99.9), being 10 to 35 times higher than the other calculated sensitivity factors. The gadolinium-doping promoted morphological and structural changes in the materials that contributed negatively to the interaction between water molecules and the surface of the sensor elements. Considering the results shown before, undoped SrMoO4 is a promising material for use as a humidity sensor.