Estudo da viabilidade técnica para obtenção de superfície duplex em aço inoxidável martensítico AISI 410 através do processo de deposição a plasma por gaiola catódica

The technique of plasma nitriding by the cathode cage mainly stands out for its ability to produce uniform layers, even on parts with complex geometries. In this study, it was investigated the efficiency of this technique for obtaining duplex surface, when used, simultaneously, to nitriding treatment and thin film deposition at temperatures below 500°C. For this, were used samples of AISI 41 0 Martensitic Stainless Steel and performed plasma treatment, combining nitriding and deposition of thin films of Ti and/or TiN in a plasma atmosphere containing N2-H2. It was used a cathodic cage of titanium pure grade II, cylindrical with 70 mm diameter and 34 mm height. Samples were treated at temperature 420ºC for 2 and 12 hours in different working pressures. Optical Microscopy (OM), Scanning Electron Microscopy (SEM) with micro-analysis by Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM) and analysis of Vickers Microhardness were used to investigate coating properties such as homogeneity and surface topography, chemical composition, layer thickness, crystalline phase, roughness and surface microhardness. The results showed there is a direct proportionality between the presence of H2 in plasma atmosphere and the quantity of titanium in surface chemical composition. It was also observed that the plasma treatment at lowpressure is more effective in formation of TiN thin film

Raman and photoluminescence of Er3+-doped SnO2 obtained via the sol-gel technique from solutions with distinct pH

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influence of processing parameters on nanomaterials synthesis efficiency by a carbothermal reduction process

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Dependence of the nonlinear electrical behavior of SnO2-based varistors on Cr2O3 addition

Tin dioxide varistors doped with Coo, ZnO, Ta2O5 and Cr2O3 were prepared by the mixed oxide method. Temperature dependent impedance spectroscopy revealed two different activation energies, one at low frequencies and the other at high frequencies. These activation energies were associated with the adsorption and reaction of O-2 species at the grain boundary interface. We show that Cr2O3 improves the varistor properties, generating sites for the adsorption of O' and O at the grain boundary region. The O' and O defects are truly responsible for the barrier formation at the grain boundary interface. (c) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Surface equilibrium angle for anisotropic grain growth in SnO2 systems

Usually, the kinetic models used in the study of sintered ceramic are performed by means of indirect physical tests, such as, results obtained from data of linear shrinkage and mass loss. This fact is justified by the difficulty in the determinations of intrinsic parameters of ceramic materials along every sintering process. In this way, the technique of atomic force microscopy (AFM) was used in order to determine the importance and the evolution of the dihedral angle in the sintering of 0.5 mol% MnO2-doped tin dioxide obtained by the polymeric precursor method.

Analysis of Er3+ incorporation in SnO2 by optical investigation

Er3+ emission in the wide bandgap matrix SnO2 is observed either through a direct Er ion excitation process as well as by an indirect process, through energy transfer in samples codoped with Yb3+ ions. Electron-hole generation in the tin dioxide matrix is also used to promote rare-earth ion excitation. Photoluminescence spectra as function of temperature indicate a slight decrease in the emission intensity with temperature increase, yielding low activation energy, about 3.8meV, since the emission even at room temperature is rather considerable.

Electronic ceramics based on polycrystalline SnO2, TiO2 and (Sn xTi1-x)O2 solid solution

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Evaluation of rare earth oxides doping SnO2.(Co1/4,Mn3/4)O-based varistor system

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Grain size effect on the electrical response of SnO2 thin and thick film gas sensors

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nonlinear electrical behaviour of the Cr2O3, ZnO, CoO and Ta2O5-doped SnO2 varistors

The effects of Cr2O3 on the properties of (Zn, Co, Ta)-doped SnO2 varistors were investigated in this study. The samples with different Cr2O3 concentrations were sintered at 1400 degrees C for 2 h. The properties of (Zn, Co, Ta, Cr)-doped SnO2 varistors were evaluated by XRD. dilatornetry, SEM, I-V and impedance spectroscopy. DC electrical characterization showed a dramatic increase ill the breakdown electrical field and in the nonlinear coefficient with the increase in Cr2O3 concentration. The grain size was found to decrease from 13 to 5 mu m with increasing the Cr2O3 content. The impedance data, represented by means of Nyquist diagrams, show two time constants, one at low frequencies and the other at high frequencies. (c) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

WO3 and ZnO-doped SnO2 ceramics as insulating material

SnO2 ceramics doped with ZnO and WO3 were prepared by mixed oxide method. The effect of ZnO and WO3 additives could be explained by the substitution of Sn4+ by Zn2+ and W6+. The addition of WO3 inhibits the grain growth due to the segregation of SnZnWO8 and ZnWO6 at the grain boundaries without strong influence on the densification process. The electrical characterization (log E x log J) shows that the ternary system SnO2-ZnO-WO3 exhibits a very high resistivity of around 10(14) Omega M. Independently of the WO3 concentration, the electrical conductivity of the Sn02-ZnO-WO3 system is always lower than that of the undoped tin dioxide. (C) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Electrical and micro structural properties of (Zn, Nb, Fe)-doped SnO2 varistor systems

The electrical and microstructural properties of SnO2-based varistors with the addition of 0.025 and 0.050 mol% of Fe2O3 have been characterised. Electric field (E) versus current density (J) curves showed that the effect of Fe2O3 addition is to increase both the non-linear coefficient and the breakdown voltage. Variations in the potential barrier height were inferred from impedance spectroscopy (IS) analysis. Through transmission electron microscopy (TEM), the presence of precipitates of secondary phases was confirmed. Samples with precipitates displayed poor electrical properties. (c) 2004 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Densification and coarsening of SnO2-based materials containing manganese oxide

The present work presents results on natural sintering of tin dioxide ceramics, prepared by a chemical route or by conventional mixing and containing manganese (X-Mn = Mn/(Mn + Sn)(atomic) with 0 less than or equal to X(Mn)less than or equal to 0.15). This cation, which is practically insoluble in SnO2 network, stays at the grain surface. During thermal treatment (500 degrees C less than or equal to T-s less than or equal to 1400 degrees C), as long as the manganese surface concentration is lower than a critical value, equal to 5.10(-6) mol m(-2), no densification takes place. As soon as this value is reached, densification and grain growth occur simultaneously. The shrinkage kinetics is fast and high rho/rho(t) values can be obtained (for example. rho/rho(t)=0.95 for T-s=1300 degrees C and X-Mn=0.004). The dependence between manganese content, manganese distribution, grain size and sintering behaviour is also discussed. (C) 1998 Published by Elsevier B.V. Limited.

Structural and microstructural behaviour of SnO2 dense ceramics doped with ZnO and WO3

SnO2-based varistors doped with ZnO and WO3 were prepared by mixed oxide method. Experimental evidence shows that the increase in ZnO amount increases the volume and microstrain of unit cell while the WO3 promotes a decrease. The effect of ZnO and WO3 additives could be explained by the substitution of Sn4+ by Zn2+ and W6+. The addition of WO3 inhibits the grain growth due to the segregation in the grain boundary without influence in the densification of the samples. Besides that, an increase in the electrical resistance of the SnO2-ZnO-WO3 system was observed independent of the WO3 concentration. (c) 2005 Elsevier B.V. All rights reserved.

Influence of the rare-earths oxides doped on the SnO2CoOMnO2Ta2O5 varistor system

The tin dioxide is an n-type semiconductor, which exhibits varistor behavior with high capacity of absorption of energy, whose function is to restrict transitory over-voltages without being destroyed, when it is doped with some oxides. Varistors are used in alternated current fields as well as in continuous current, and it can be applied in great interval of voltages or in great interval of currents. The electric properties of the varistor depend on the defects that happen at the grain boundaries and the adsorption of oxygen. The (98.90-x)%SnO2.0.25%CoO+0.75%MnO2+0.05%Ta2O5+0.05%Tr2O3 systems, in which Tr=La or Nd. Current-voltage measurements were accomplished for determination of the non-linear coefficient were studied. SEM microstructure analysis was made to evaluate the microstructural characteristics of the systems. The results showed that the rare-earth oxides have influenced the electrical behavior presented by the system. (C) 2002 Kluwer Academic Publishers.