Lately the electrical and dielectric properties of cork and some cork-based materials (commercial and non-commercial) have been studied in order to understand their ability to store electrical charge. The main problem found so far is related to the water content in cork, only of a few % weight. but large enough to influence greatly the conductivity of cork and, consequently, the charge storage capability. To overcome this problem cork has been combined with hydrophobic materials. In this work a commercial wax (paraffin wax) was used to produce a cork/paraffin composite by hot pressing. After milled and mixed natural cork. TetraPak (R) containers waste and paraffin were pressed to make plaques of a new composite. Different concentrations of cork. TetraPak (R) and paraffin, different granules sire, different temperature and pressure were used to produce the samples. The electrical properties of the new composite were measured by the isothermal charging and discharging current method and the results compared to previously ones obtained for natural cork and other derivative products. The new composite has shown to have lower conductivity than the commercial agglomerate. which makes it a better material for charge storage.

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The thermally stimulated discharge current (TSDC.) method is a very sensitive and a very selective technique to analyze dipole disorientation and the movement of de-trapped space charge (SC). We have proposed a variant of the TSDC method, namely the final thermally stimulated discharge current (FTSDC) technique. flee experimental conditions can be selected so that the FTSDC is mainly determined by the SC de-trapping. The temperatures of the maximum intensity of the fractional polarization peaks obtained at low temperature, in the range of the local (secondary) relaxation, are in general about 10 to 20 K above the poling temperature. Measurements of the FTSDC in a wide temperature range demonstrate the existence of an apparent peak at a temperature T-ma shifted with about 10 to 30 K above the charging temperature T-c. The shift of T-ma with respect to T-c depends on the experimental conditions. The peak width at the half maximum intensity decreases as T-c increases and the thermal apparent activation energy increases. The variations are not monotonous revealing the temperature range where the molecular motion is stronger and consequently the charge trapping and de-trapping processes are affected. Our results demonstrate that there is a strong similarity between the elementary peaks obtained by the two methods, and the current is mainly determined by SC de-trapping. Even the best elementary peaks are not fitted very well by the analytical equation, indicating that the hypothesis behind this equation have to be reconsidered.

The thermally stimulated discharge current (TSDC.) method is a very sensitive and a very selective technique to analyze dipole disorientation and the movement of de-trapped space charge (SC). We have proposed a variant of the TSDC method, namely the final thermally stimulated discharge current (FTSDC) technique. flee experimental conditions can be selected so that the FTSDC is mainly determined by the SC de-trapping. The temperatures of the maximum intensity of the fractional polarization peaks obtained at low temperature, in the range of the local (secondary) relaxation, are in general about 10 to 20 K above the poling temperature. Measurements of the FTSDC in a wide temperature range demonstrate the existence of an apparent peak at a temperature T-ma shifted with about 10 to 30 K above the charging temperature T-c. The shift of T-ma with respect to T-c depends on the experimental conditions. The peak width at the half maximum intensity decreases as T-c increases and the thermal apparent activation energy increases. The variations are not monotonous revealing the temperature range where the molecular motion is stronger and consequently the charge trapping and de-trapping processes are affected. Our results demonstrate that there is a strong similarity between the elementary peaks obtained by the two methods, and the current is mainly determined by SC de-trapping. Even the best elementary peaks are not fitted very well by the analytical equation, indicating that the hypothesis behind this equation have to be reconsidered.

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Power electronics (PE) plays a major role in electrical devices and systems, namely in electromechanical drives, in motor and generator controllers, and in power grids, including high-voltage DC (HVDC) power transmission. PE is also used in devices for the protection against grid disturbances, like voltage sags or power breakdowns. To cope with these disturbances, back-up energy storage devices are used, like uninterruptible power supplies (UPS) and flywheels. Some of these devices may use superconductivity. Commercial PE semiconductor devices (power diodes, power MOSFETs, IGBTs, power Darlington transistors and others) are rarely (or never) experimented for cryogenic temperatures, even when designed for military applications. This means that its integration with HTS power devices is usually done in the hot environment, raising several implementation restrictions. These reasons led to the natural desire of characterising PE under extreme conditions, e. g. at liquid nitrogen temperatures, for use in HTS devices. Some researchers expect that cryogenic temperatures may increase power electronics' performance when compared with room-temperature operation, namely reducing conduction losses and switching time. Also the overall system efficiency may increase due to improved properties of semiconductor materials at low temperatures, reduced losses, and removal of dissipation elements. In this work, steady state operation of commercial PE semiconductors and devices were investigated at liquid nitrogen and room temperatures. Performances in cryogenic and room temperatures are compared. Results help to decide which environment is to be used for different power HTS applications.

Power electronics (PE) plays a major role in electrical devices and systems, namely in electromechanical drives, in motor and generator controllers, and in power grids, including high-voltage DC (HVDC) power transmission. PE is also used in devices for the protection against grid disturbances, like voltage sags or power breakdowns. To cope with these disturbances, back-up energy storage devices are used, like uninterruptible power supplies (UPS) and flywheels. Some of these devices may use superconductivity. Commercial PE semiconductor devices (power diodes, power MOSFETs, IGBTs, power Darlington transistors and others) are rarely (or never) experimented for cryogenic temperatures, even when designed for military applications. This means that its integration with HTS power devices is usually done in the hot environment, raising several implementation restrictions. These reasons led to the natural desire of characterising PE under extreme conditions, e. g. at liquid nitrogen temperatures, for use in HTS devices. Some researchers expect that cryogenic temperatures may increase power electronics' performance when compared with room-temperature operation, namely reducing conduction losses and switching time. Also the overall system efficiency may increase due to improved properties of semiconductor materials at low temperatures, reduced losses, and removal of dissipation elements. In this work, steady state operation of commercial PE semiconductors and devices were investigated at liquid nitrogen and room temperatures. Performances in cryogenic and room temperatures are compared. Results help to decide which environment is to be used for different power HTS applications.

Power electronics (PE) plays a major role in electrical devices and systems, namely in electromechanical drives, in motor and generator controllers, and in power grids, including high-voltage DC (HVDC) power transmission. PE is also used in devices for the protection against grid disturbances, like voltage sags or power breakdowns. To cope with these disturbances, back-up energy storage devices are used, like uninterruptible power supplies (UPS) and flywheels. Some of these devices may use superconductivity. Commercial PE semiconductor devices (power diodes, power MOSFETs, IGBTs, power Darlington transistors and others) are rarely (or never) experimented for cryogenic temperatures, even when designed for military applications. This means that its integration with HTS power devices is usually done in the hot environment, raising several implementation restrictions. These reasons led to the natural desire of characterising PE under extreme conditions, e. g. at liquid nitrogen temperatures, for use in HTS devices. Some researchers expect that cryogenic temperatures may increase power electronics' performance when compared with room-temperature operation, namely reducing conduction losses and switching time. Also the overall system efficiency may increase due to improved properties of semiconductor materials at low temperatures, reduced losses, and removal of dissipation elements. In this work, steady state operation of commercial PE semiconductors and devices were investigated at liquid nitrogen and room temperatures. Performances in cryogenic and room temperatures are compared. Results help to decide which environment is to be used for different power HTS applications.

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This paper presents the design of a test rig for an all HTS linear synchronous motor. Although this motor showed to have several unattractive characteristics, its design raised a number of problems which must be considered in future HTS machines design. HTS electromagnetic properties led to the development of new paradigms in electrical machines and power systems, as e. g. in some cases iron removal and consequent assembly of lighter devices. This is due to superconductor's ability to carry high currents with minimum losses and consequent generation in the surrounding air of flux densities much higher than the allowed by ferromagnetic saturation. However, severe restrictions in HTS power devices design that goes further beyond cryogenic considerations must be accounted in. This is usually the case when BSCCO tapes are used as conductors. Its bending limitations and the presence of flux components perpendicular to tape surface, due to the absence of iron, have to be considered for it may turn some possible applications not so attractive or even practically unfeasible. An all HTS linear synchronous motor built by BSCCO tapes as armature conductors and two trapped-flux YBCO bulks in the mover was constructed and thrust force measurements are starting to be performed. Although the device presents severe restrictions due to the exposed and other reasons, it allowed systematising its design. A pulsed-field magnetiser to generate opposite fluxes for both YBCO bulks is also detailed. Thrust force numerical predictions were already derived and presented.

This paper presents the design of a test rig for an all HTS linear synchronous motor. Although this motor showed to have several unattractive characteristics, its design raised a number of problems which must be considered in future HTS machines design. HTS electromagnetic properties led to the development of new paradigms in electrical machines and power systems, as e. g. in some cases iron removal and consequent assembly of lighter devices. This is due to superconductor's ability to carry high currents with minimum losses and consequent generation in the surrounding air of flux densities much higher than the allowed by ferromagnetic saturation. However, severe restrictions in HTS power devices design that goes further beyond cryogenic considerations must be accounted in. This is usually the case when BSCCO tapes are used as conductors. Its bending limitations and the presence of flux components perpendicular to tape surface, due to the absence of iron, have to be considered for it may turn some possible applications not so attractive or even practically unfeasible. An all HTS linear synchronous motor built by BSCCO tapes as armature conductors and two trapped-flux YBCO bulks in the mover was constructed and thrust force measurements are starting to be performed. Although the device presents severe restrictions due to the exposed and other reasons, it allowed systematising its design. A pulsed-field magnetiser to generate opposite fluxes for both YBCO bulks is also detailed. Thrust force numerical predictions were already derived and presented.

This paper presents the design of a test rig for an all HTS linear synchronous motor. Although this motor showed to have several unattractive characteristics, its design raised a number of problems which must be considered in future HTS machines design. HTS electromagnetic properties led to the development of new paradigms in electrical machines and power systems, as e. g. in some cases iron removal and consequent assembly of lighter devices. This is due to superconductor's ability to carry high currents with minimum losses and consequent generation in the surrounding air of flux densities much higher than the allowed by ferromagnetic saturation. However, severe restrictions in HTS power devices design that goes further beyond cryogenic considerations must be accounted in. This is usually the case when BSCCO tapes are used as conductors. Its bending limitations and the presence of flux components perpendicular to tape surface, due to the absence of iron, have to be considered for it may turn some possible applications not so attractive or even practically unfeasible. An all HTS linear synchronous motor built by BSCCO tapes as armature conductors and two trapped-flux YBCO bulks in the mover was constructed and thrust force measurements are starting to be performed. Although the device presents severe restrictions due to the exposed and other reasons, it allowed systematising its design. A pulsed-field magnetiser to generate opposite fluxes for both YBCO bulks is also detailed. Thrust force numerical predictions were already derived and presented.

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The decolorization of aqueous solutions methylene blue (C.I. Basic Blue 9), due to the presence of nanocrystalline Bi2S3, supported on SiO2 submicron particles, was investigated here. For this decolorization process, two distinct characteristics, though related, associated to the role of SiO2/Bi2S3 were identified: (i) high methylene blue adsorption capability and (ii) photocatalytic activity to methylene blue photodecolorization. Effects of experimental parameters on the decolorization process, such as methylene blue and nanocomposite concentrations, pH and Bi2S3 particle size were investigated. The maximum adsorption ability of the SiO2/Bi2S3 was approximately 15.6 mg methylene blue per gram. The complete decolorization of a 16 ppm organic dye solution can be achieved, by an adsorption process, in an extremely short time (less than 5 min), using 1.6 g/L of SiO2/Bi2S3 nanocomposite. The study of the decolorization of the dye by an adsorption-photoassisted decolorization process was carried out by irradiation of a suspension prepared with 100 mL of methylene blue solution (8 ppm) and 50 mg of SiO2/Bi2S3. In these conditions the complete decolorization of the dye, adsorbed and in the solution, was achieved in 40 min. © 2008 Elsevier B.V. All rights reserved.

In this study, we investigate the diffusion of carbon (C) and other elements into steel substrates (Impax Supreme™) during diamond chemical vapour deposition (CVD). The substrate temperature varied from 700 to 850ºC by plasma power manipulations to enable the correlation of substrate temperature with diffusion length and depth of the above mentioned critical elements into steel during film growth conditions. Methane concentration is also a parameter which has been considered during the parametric analysis. The crystalline compounds formed during the diamond growth process were studied using XRD analysis. In addition, SIMS technique is used with depth profiling to monitor the diffusion of elements induced by the process. The results obtained enabled to improve traditional understanding about the mechanisms relating to diamond deposition on steel substrates using CVD processes.

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Hysteresis motors are very attractive in a wide range of fractional power applications, due to its torque-speed characteristics and simplicity of construction. This motor's performance is expected to improve when HTS rotors are used, and in fact, hysteresis motors have shown to be probably the most viable electrical machines using HTS materials. While these motors, either conventional or HTS, are both hysteresis motors, they base their operation on different physical phenomena: hysteretic behaviour in conventional ferromagnetic materials is due to the material's non-linear magnetic properties, while in HTS materials the hysteresis has an ohmic nature and is related with vortices' dynamics. In this paper, theoretical aspects of both conventional and HTS hysteresis motors are discussed, its operation principles are highlighted, and the characteristics of both motors are presented. The characteristics, obtained both by experimental tests and numerical simulation (made with commercial software), are compared, in order to evaluate not only the motor's electromechanical performances but also the overall systems efficiency, including cryogenics for the HTS device.

Power electronics (PE) plays a major role in electrical devices and systems, namely in electromechanical drives, in motor and generator controllers, and in power grids, including high-voltage DC (HVDC) power transmission. PE is also used in devices for the protection against grid disturbances, like voltage sags or power breakdowns. To cope with these disturbances, back-up energy storage devices are used, like uninterruptible power supplies (UPS) and flywheels. Some of these devices may use superconductivity. Commercial PE semiconductor devices (power diodes, power MOSFETs, IGBTs, power Darlington transistors and others) are rarely (or never) experimented for cryogenic temperatures, even when designed for military applications. This means that its integration with HTS power devices is usually done in the hot environment, raising several implementation restrictions. These reasons led to the natural desire of characterising PE under extreme conditions, e. g. at liquid nitrogen temperatures, for use in HTS devices. Some researchers expect that cryogenic temperatures may increase power electronics' performance when compared with room-temperature operation, namely reducing conduction losses and switching time. Also the overall system efficiency may increase due to improved properties of semiconductor materials at low temperatures, reduced losses, and removal of dissipation elements. In this work, steady state operation of commercial PE semiconductors and devices were investigated at liquid nitrogen and room temperatures. Performances in cryogenic and room temperatures are compared. Results help to decide which environment is to be used for different power HTS applications

Power electronics (PE) plays a major role in electrical devices and systems, namely in electromechanical drives, in motor and generator controllers, and in power grids, including high-voltage DC (HVDC) power transmission. PE is also used in devices for the protection against grid disturbances, like voltage sags or power breakdowns. To cope with these disturbances, back-up energy storage devices are used, like uninterruptible power supplies (UPS) and flywheels. Some of these devices may use superconductivity. Commercial PE semiconductor devices (power diodes, power MOSFETs, IGBTs, power Darlington transistors and others) are rarely (or never) experimented for cryogenic temperatures, even when designed for military applications. This means that its integration with HTS power devices is usually done in the hot environment, raising several implementation restrictions. These reasons led to the natural desire of characterising PE under extreme conditions, e. g. at liquid nitrogen temperatures, for use in HTS devices. Some researchers expect that cryogenic temperatures may increase power electronics' performance when compared with room-temperature operation, namely reducing conduction losses and switching time. Also the overall system efficiency may increase due to improved properties of semiconductor materials at low temperatures, reduced losses, and removal of dissipation elements. In this work, steady state operation of commercial PE semiconductors and devices were investigated at liquid nitrogen and room temperatures. Performances in cryogenic and room temperatures are compared. Results help to decide which environment is to be used for different power HTS applications

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