Desenvolvimento e caracterização de compósitos piezoelétricos de PZT com matriz cimentícia e borracha natural
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Data
2018-03-22
Autores
Santos, Josiane Alexandrino dos
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Universidade Estadual Paulista (Unesp)
Resumo
O uso de materiais inteligentes tem sido cada vez mais utilizado pelo ramo de engenharia civil, devido à crescente demanda por construções que têm como função não só atenderem ao crescente aumento populacional, como agirem também como facilitadores da vida humana. Dentro dos estudos em desenvolvimento nesta área, o que vem ganhando destaque é o desenvolvimento de sensores compósitos de materiais piezoelétricos à base de cimento, que sejam capazes de atuar no monitoramento e detecção de possíveis falhas nas estruturas civis em tempo real e contínuo. Alguns dos grandes problemas encontrados no desenvolvimento de sensores piezoelétricos baseados em matrizes cimentícias, encontram se na degradação das propriedades dos sensores frente às condições ambientais em tempo contínuo a que estes são submetidos, bem como, a possibilidades de as fases de preenchimento interferirem diretamente no processo de cura da matriz, reduzindo suas propriedades mecânicas desejáveis. Buscando resolver tais problemas, o presente trabalho teve como objetivo a obtenção e caracterização de compósitos piezoelétricos utilizando como matriz o cimento modificado com borracha natural (BN) e titanato zirconato de chumbo (PZT) como fase piezoelétrica. O PZT foi escolhido como fase piezoelétrica devido seu alto valor do coeficiente piezoelétrico enquanto a inserção da BN buscou garantir aos compósitos, resistência à passagem de água, umidade e a resistência a soluções nocivas ao cimento, atuando no aumento da durabilidade bem como das propriedades piezoelétricas do sensor. Os compósitos foram caracterizados por meio de microscopia eletrônica de Varredura (MEV), medidas de condutividade elétrica em regime DC, espectroscopia de impedância e por meio do coeficiente piezoelétrico (d33). Foi verificada não apenas as propriedades piezoelétricas dos compósitos, mas também, a influência do PZT e BN no processo de cura da pasta de cimento. Os resultados mostraram uma influência direta do PZT e da BN no processo de cura da pasta de cimento aumentando o tempo de cura do material. Medidas de espectroscopia de impedância indicaram a existência de reações tardias de cura da pasta de cimento interferindo diretamente nos valores da constante dielétrica dos compósitos e matriz. Por fim, os resultados do coeficiente piezoelétrico apresentaram grande instabilidade nos valores de d33 nos períodos iniciais pós-polarização para todas as composições, atribuído à existência de dipolos instáveis nas amostras decorrentes do processo de cura do cimento. Polarizações em função do período de cura da matriz evidenciaram aumento dos valores do d33 quando as amostras foram polarizadas mais tardiamente apresentando um máximo para o período de polarização de 130 h para os compósitos bifásicos de cimento/PZT para períodos de medidas iguais a 105 dias e sofrendo redução para polarizações realizadas em 30 dias de cura. Tal comportamento foi atribuído ao processo de cura do cimento e aos valores de εr em tais períodos. Por sua vez, as amostras de cimento/BN/PZT apresentaram comportamento inverso das amostras de cimento/PZT decorrente da presença de borracha natural e sua capacidade de reduzir tensões mecânicas aplicadas ao sistema.
The use of intelligent materials has been increasingly used by the civil engineering industry, in response to the increasing demand for constructions that serve, not only to attend to the increasing population, but also to act as facilitators of human life. Within the studies under development in this area, the one that has being gaining prominence is the development of composite sensors of cement-based piezoelectric materials, that can act in the monitoring and detection of possible failures in civil structures in real and continuous time. Some of the major problems encountered in the development of piezoelectric sensors based on cementitious matrices lie in the degradation of the properties of the sensors, both as against the environmental conditions in continuous time to which they are subjected, as well as the possibility that filling phases interfere directly in the process of curing the matrix, reducing its desirable mechanical properties. In order to solve such problems, the present study aimed to obtain and characterize of a composite piezoelectric array of modified cement with natural rubber (NR) and lead zirconate titanate (PZT) as the piezoelectric layer. The PZT was chosen as the piezoelectric phase because of its high piezoelectric coefficient, while the BN insertion sought to guarantee the resistance of the composites to the passage of water, moisture and noxious solutions to the cement, in order to increase not only the durability, as well the piezoeletric properties of the sensors. The composites were characterized by scanning electron microscopy (SEM), electrical conductivity measurements in DC, impedance spectroscopy and by means of the piezoelectric coefficient (d33). It was verified not only the piezoelectric properties of the composites, but also the influence of PZT and BN on the cement paste curing process. The results demonstrated a direct influence of PZT and BN on the cement paste curing process by shifting it for longer curing times. Impedance spectroscopy measurements indicated late cure reactions of the cement paste directly interfered in the values of the dielectric constant of the composites and matrix. Finally, the results of the piezoelectric coefficient showed great instability in the values of d33 in the initial post-polarization periods for all the compositions, being this fact attributed the existence of unstable dipoles in the samples resulting from the cement cure process. Polarizations as a function of the curing period of the matrix showed an increase in d33 values when the samples were later polarized, presenting a maximum for the polarization period of 130h for biphasic cement/PZT composites for periods of measurements equal to 105 days and reducing to polarizations carried out in 30 days of curing. Such behavior was attributed to the cement cure process and the εr values at such moments. In turn, cement/BN/PZT samples showed an inverse behavior of cement/PZT samples due to the presence of natural rubber and its ability to reduce mechanical stresses applied to the system.
The use of intelligent materials has been increasingly used by the civil engineering industry, in response to the increasing demand for constructions that serve, not only to attend to the increasing population, but also to act as facilitators of human life. Within the studies under development in this area, the one that has being gaining prominence is the development of composite sensors of cement-based piezoelectric materials, that can act in the monitoring and detection of possible failures in civil structures in real and continuous time. Some of the major problems encountered in the development of piezoelectric sensors based on cementitious matrices lie in the degradation of the properties of the sensors, both as against the environmental conditions in continuous time to which they are subjected, as well as the possibility that filling phases interfere directly in the process of curing the matrix, reducing its desirable mechanical properties. In order to solve such problems, the present study aimed to obtain and characterize of a composite piezoelectric array of modified cement with natural rubber (NR) and lead zirconate titanate (PZT) as the piezoelectric layer. The PZT was chosen as the piezoelectric phase because of its high piezoelectric coefficient, while the BN insertion sought to guarantee the resistance of the composites to the passage of water, moisture and noxious solutions to the cement, in order to increase not only the durability, as well the piezoeletric properties of the sensors. The composites were characterized by scanning electron microscopy (SEM), electrical conductivity measurements in DC, impedance spectroscopy and by means of the piezoelectric coefficient (d33). It was verified not only the piezoelectric properties of the composites, but also the influence of PZT and BN on the cement paste curing process. The results demonstrated a direct influence of PZT and BN on the cement paste curing process by shifting it for longer curing times. Impedance spectroscopy measurements indicated late cure reactions of the cement paste directly interfered in the values of the dielectric constant of the composites and matrix. Finally, the results of the piezoelectric coefficient showed great instability in the values of d33 in the initial post-polarization periods for all the compositions, being this fact attributed the existence of unstable dipoles in the samples resulting from the cement cure process. Polarizations as a function of the curing period of the matrix showed an increase in d33 values when the samples were later polarized, presenting a maximum for the polarization period of 130h for biphasic cement/PZT composites for periods of measurements equal to 105 days and reducing to polarizations carried out in 30 days of curing. Such behavior was attributed to the cement cure process and the εr values at such moments. In turn, cement/BN/PZT samples showed an inverse behavior of cement/PZT samples due to the presence of natural rubber and its ability to reduce mechanical stresses applied to the system.
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Palavras-chave
Piezoeletricidade, Pasta de cimento, Borracha natural, Coeficiente piezoelétrico, Piezoelectricity, Cement paste, Natural rubber, Piezoelectric coefficient