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The sensitivity of four-terminal devices like Hall and piezoresistive sensors is very dependent on its geometric parameters. This dependence is modeled by the Geometrical Correction Factor (G). The majority of these studies take very time-consumption analytical calculations for the analysis of G. In order to simplify this analysis, we present numerical analyses using FEM (Finite Element Method) for the most common geometrical forms of four-terminal devices. This result is general for any fourterminal-shaped sensors and can be used to optimize the sensor aspect ratio leading the maximization of G. In addition, FEM was also used to evaluate the membrane´s thickness influence over the sensor sensitivity by analyzing the in-plane mechanical stress behavior on the sensor active area. Experimental result of a new topology of pressure sensor is also presented, which maximizes G in comparison with conventional four-terminal devices and also improves its sensitivity. A special designed anisotropic wet etching system was used to post-process the sensor membrane. This anisotropic wet etching system allows the fabrication of well-defined membranes with thickness of 20 μm ± 3 μm and roughness as low as 90 nm rms.

This study aims to analyze the efficiency of additional carbides in the high-energy milling of duplex stainless steel chips. At the end of the life of a mechanical component, it is discarded in deposits or recast. Chips originating from machining processes are raw materials for products obtained through powder metallurgy. To obtain the duplex structure for a stainless steel, rolled and annealing are necessary subsequent steps, making this cycle costly for the industry, and its disposal leads to environmental problems. Components produced by powder metallurgy from corrosion-resistant alloys are considered advantageous. The addition of carbides aims to increase the efficiency of the milling process and improve the mechanical properties of the steels produced by powder metallurgy. The granulometric analysis and the scanning electron microscopy were used in the characterization and identification of the particle size. Results indicated that the milling with the addition of carbides showed a higher efficiency in the milling process. The particle size obtained with the addition of TiC and NbC in the milling of UNS S 31803 steel chips was 98 and 85 times smaller than the original chip.

Duplex stainless steel presents an attractive combination of mechanical properties and resistance to corrosion. These properties rely on a two-phase mixture compound to produce a microstructure that is approximately equal for the ferritic and austenitic phases. The samples used in this study were cold rolled to degrees of deformation of 20%, 40%, 60% and 80% according to their thickness. The vibrating sample magnetometer (VSM), X-ray diffraction (XRD), and optical microscopy were used to characterize the rolled samples. It was observed that the cold rolled samples of 40%, 60% and 80% showed an increase in saturation magnetization compared to the samples of as received and cold rolled of 20%, and this probably occurred because of the formation of strain-induced martensite. It can be seen that the amount of the ferromagnetic phase calculated by ferritoscope tends to decrease with an increasing degree of deformation. The deformation caused by cold rolling resulted in a significant change in diffraction peaks and the mechanical and magnetic properties.

Resumo Os objetivos deste trabalho foram a obtenção de uma ferrita de chumbo e cobre com a estrutura do espinélio, a caracterização da sua microestrutura e a determinação das suas propriedades magnéticas. A ferrita de cobre e chumbo é um material com baixa coercividade magnética, alta resistividade elétrica e alta permeabilidade magnética. Amostras com estequiometria PbxCu1-xFe2O4, com (x= 0, 0,1 e 0,2), foram produzidas pelo processo de metalurgia do pó e sinterizadas a 800 °C por 6 h em atmosfera ambiente. As caracterizações estrutural, microestrutural e magnética foram realizadas utilizando as técnicas de difração de raios X, microscopia eletrônica de varredura, magnetômetro de amostra vibrante e análise termogravimétrica magnética. Os resultados mostram que as amostras são formadas exclusivamente pela estrutura do espinélio tetragonal. As curvas de histerese mostram características de materiais magnéticos moles e sua magnetização de saturação aumentou com a concentração de chumbo. O valor da temperatura de Curie diminuiu com o aumento da concentração de chumbo. Abstract The objectives of this work were to obtain a lead and copper ferrite with spinel structure, characterizing the microstructure and the determination of their magnetic properties. The copper and lead ferrite is a material with low magnetic coercivity, high electrical resistivity and high magnetic permeability. Samples with stoichiometry PbxCu1-xFe2O4 with (x = 0, 0.1, and 0.2) were prepared by powder metallurgy process and sintered at 800 ºC for 6 h in air. The structural, microstructural and magnetic characterizations were performed using the techniques of X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer, and magnetic thermal gravimetric analysis. The results showed that samples are formed exclusively by the tetragonal spinel structure. Hysteresis loops show the characteristics of a soft magnetic material and the saturation magnetization increased with the lead concentration. The value of the Curie temperature decreased with increasing lead concentration.