A presente invenção descreve composições varistoras de baixa e média tensão a base de SnO2, as quais poderão ser utilizadas em aplicações eletroeletrônicas de baixa tensão, tais como circuitos de entrada de residências, telefones, televisores e produtos eletrônicos em geral. As referidas composições apresentam nanofitas de SnO2 incorporadas em sua estrutura, sendo estas as responsáveis pela diminuição do campo elétrico de ruptura.

This work has focused on the electrical and microstructural properties of Nb2O5-doped SnO2-MnO2 ceramics. The pellets were prepared by solid-state reaction method according to the system (99.5-x) SnO2 - 0.5 MnO2 - x Nb2O5, on the following molar ratio x = 0.05; 0.10; 0.15; 0.20 and 0.25. Scanning electron microscopy and electrical measurements (ac and dc) were used to study the materials properties. The results showed that the increase of Nb2O5 content in the SnO2-MnO2 matrix has led to an increase in the varistor properties. A detailed study of the electrical properties of materials was conducted using impedance spectroscopy and the results indicated that Nb2O5 has a tendency to form an electron trapping level near the conduction band. In order to explain these findings, a parallel equivalent circuit model was used to simulate the values of the grain boundary resistance. A close relationship was found between the value of the nonlinear coefficient and the grain boundary resistance for the studied varistors, where both values increased with increasing the amount of Nb2O5, which is important for practical applications.

Morphological characteristics analysis before and after tensile tests were studied using scanning electron microscopy (SEM) technique to follow the failure evolution on carbon fiber reinforced polymer (CFRP) and epoxy resins. Micrograph analysis of CFRP plate before tensile test shows some intrinsic manufacturing defects, which can influence the mechanical properties of the material. Micrograph analysis after tensile test shows that cracks propagation start in manufacturing defects, which lead the carbon fiber to be pulled out instead of breaking. Thus, cracks propagate through interfacial zones affecting the sharing force between matrix and carbon fiber. For the epoxies materials, the microscopy analysis showed that although epoxies adhesive have different phase distribution before tensile test, failure surfaces are described by fine granular particles covalent bonded with matrix, and the material fails in a brittle manner when the strength outstripped these bonds. Failure process for each material correlating the mechanical properties with the morphological characteristics of materials was discussed.

A systematic study about synthesis of In1-xSnxO2 (ITO) nanostructured crystals by microwave-assisted solvothermal method is reported. Different solutions using InCl3.4H2O and SnCl4.5H2O precursors in ethylene glycol solvent were prepared in distinct pHs (acid and basic ones). The syntheses were performed at 200 ºC using a heating rate of 50 ºC min-1 and soaking time of 30 minutes. All the synthesized powders were characterized by X-ray Diffraction (XRD) and Rietveld refinement to study the phase evolution as a function of pH. The materials synthesized in the pH ranging between 11.5 and 11.9 were further studied by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) techniques. As ITO materials have many practical applications due to their transparency in the visible spectrum, UV-Vis spectroscopy analysis was performed to obtain the optical band gap and the respective optical window.

Many techniques for structural health monitoring (SHM) have been studied with the objective of ensuring the structural integrity of aeronautical structures. One of the most recent solutions for this problem is the use of continuous sensors, constituted by thin films made of nanocomposites. Since the nanocomposites, as any other composite material, can be tailored according to the application needs, there is a vast range of material that has the properties needed to detect damage. The work in this paper proposes the use of a new kind of sensor with nanowires or nanobelts of ITO (indium tin oxide) inserted in a polymeric matrix, such as PMMA (poly(methyl methacrylate) or acrylic). PMMA is transparent and it gives a very nice appearance to the monitored surface. In order to evaluate the effectiveness of this method, several tests are proposed. These tests consist of monitoring the behavior of the nanocomposites when affected by some kind of damage, which can be a mass addition, excessive strains or a crack. The resistivity of the nanocomposite was measured using a two point conventional conductivity test and showed promising results, where the sensors form a net, similar to a neural network capable of sensing structural variations.

Oxide ceramics find large application in several segments of the human life, as functional materials are used as components in several devices such as sensors of chemical species for improved environment, surge protectors for electronic appliances, and electrochemical transducers for sustainable alternative energy production. Other applications involve detectors in medical appliances, components of mobiles and computers, etc. One of the most important features deals with the electrical behavior of the oxide ceramics, which span from superconductors to insulators, including ionic/electronic/mixed conductors and semiconductors. This chapter reports a brief overview of ceramic oxide semiconductors and ionic conductors, taking into account the role of surfaces and interfaces (mainly grain boundaries) on their performance as components in surge protectors-varistors, in chemical sensors and solid electrolytes in solid oxide fuel cells.