Development and characterization of gas sensors using thin films of polyaniline as active layer

This work aimed at the development and characterization of gas sensing devices using thin films ofpolyaniline (PAni) as active layer, deposited by in situ polymerization. The polyaniline, an intrinsicallyconductive polymer, was used due to its high sensitivity to gases, low response time and stability, ease ofsynthesis and low cost. The sensor was built on a glass fiber reinforced substrate with interdigitated goldelectrodes coated with a PAni film layer whose thickness variation was fixed as a function of deposition time.The PAni characterization by Infrared Spectroscopy (FTIR) showed that the exposure to ethanol does notchange the chemical structure of PAni. The thickness (3.5 μm) and morphology of PAni films throughScanning Electron Microscopy (SEM) were compatible to those found in the literature. The electricalresistance of the sensors was evaluated as function of ethanol concentration and varied between 60 kohms forlower ethanol concentrations and 140 kohms for higher concentrations. Nevertheless, a statistical analysis ofthe measurements in five sensors with different ethanol concentrations demonstrated that the sensors have notbeen able to differentiate ethanol concentrations to the level of significance of 5%.Keywords: gas sensor, ethanol, polyaniline, electrical conductivit

CARACTERIZAÇÃO DAS PROPRIEDADES MAGNÉTICAS DE MATERIAIS COMPÓSITOS MAGNÉTICOS MACIOS

Este trabalho apresenta os resultados parciais de um projeto cujo objetivo é produzir materiais compósitos magnéticos macios (Soft Magnetic Composites - SMC) e obter suas características magnéticas e elétricas. Os materiais compósitos magnéticos macios são produzidos a partir de pequenas partículas de pó de ferro recobertas com uma fina camada de dielétrico. Eles possuem alta resistividade e isotropia magnética tridimensional. Essas características fazem dos SMC um tipo de material ferromagnético adequado à construção de núcleos de dispositivos eletromagnéticos submetidos a campo magnéticos variáveis e com distribuição tridimensional. As amostras de SMC foram produzidas com diferentes teores de dielétrico e compactadas com pressões de 400 MPa e 600 MPa. Os compósitos magnéticos macios produzidos com pó de ferro e baquelita apresentaram resistividades entre 0,0048 Ωm e 0,0145 Ωm. A permeabilidade magnética relativa máxima das amostras variou de 88 a 223