WC-Cu thermal barriers for fusion applications

ABSTRACT: WC-Cu cermets have been devised for thermal barriers between the plasma facing tungsten tiles and the copperbased heat sink in the first wall of nuclear fusion reactors. Composite materials with 50 and 75 v/v% WC have been prepared by hot pressing at 1333 and 1423 K with pressures of 37 and 47 MPa, respectively. Microstructural changes have been investigated by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction. The materials consolidated have also been evaluated in terms of Archimedes' density, thermal diffusivity, Vickers hardness and elastic modulus. Implantation was carried out at room temperature with Ar+ at 100 keV ion beam with a fluence of 4 · 1020 at/m2. The materials consisted of homogeneous dispersions of WC particles in a Cu matrix and presented densifications of about 90%. Incipient swelling in copper-rich regions have been observed on the implanted surfaces, however no significant changes have been detected by X-ray diffraction. Higher WC content in the cermet materials increased hardness and the elastic modulus. The cermets' thermal diffusivity was significantly lower than that of pure copper or tungsten, as desirable for a thermal barrier.info:eu-repo/semantics/acceptedVersio

New WC-Cu composites for the divertor in fusion reactors

ABSTRACT: The requirements for the divertor components of future fusion reactors are challenging and therefore a stimulus for the development of new materials. In this paper, WC-Cu composites are studied for use as thermal barrier between the plasma facing tungsten tiles and the copper-based heat sink of the divertor. Composite materials with 50% vol. WC were prepared by hot pressing and characterized in terms of microstructure, density, expansion coefficient, elastic modulus, Young's modulus and thermal diffusivity. The produced materials consisted of WC particles homogeneously dispersed in a Cu matrix with densifications between 88% and 98%. The sample with WC particles coated with Cu evidenced the highest densification. The thermal diffusivity was significantly lower than that of pure copper or tungsten. The sample with higher densification exhibits a low value of Young's modulus (however, it is higher compared to pure copper), and an average linear thermal expansion coefficient of 13.6 x 10(-6) degrees C-1 in a temperature range between 100 degrees C and 550 degrees C. To estimate the behaviour of this composite in actual conditions, a monoblock of the divertor in extreme conditions was modelled. The results predict that while the use of WC-Cu interlayer leads to an increase of 190 degrees C on the temperature of the upper part of the monoblock when compared to a pure Cu interlayer, the composite will improve and reduce significantly the cold-state stress between this interlayer and the tungsten.info:eu-repo/semantics/publishedVersio

On the measurement of the electrical conductivity of ionic liquids

Encontro realizado em Santiago de Compostela, Espanha, a 2 Julho de 201

O Produto Viscosidade Densidade em Misturas Nafta+Dióxido de Carbono em Condições Supercríticas.

11º Encontro da Sociedade Portuguesa de Química, Lisboa, 12-15 Dezembro 1988.Efectuou-se um estudo de viabilidade da medida do produto viscosidade (n) densidade (p) de misturas NAFTA+CO2 em condições supercríticas do dióxido de carbono com um viscosimetro de cristal de quartzo em vibração torsional, para uma gama de temperaturas entre (40º-60ºC) e pressões até 12MPa. Foram efectuadas medidas para o CO2 puro e a mistura NAFTA+CO2 a 40ºC e a pressões que atingiram os 9MPa. Foi assim possível tirar algumas conclusões acerca do sistema de trabalho, NAFTA+CO2, que sugerem modificações da célula de medida, tendo-se provado no entanto que o método de medida aplicado, sob a forma relativa, é um bom método para medir a viscosidade da mistura, desde que a viscosidade seja conhecida

Tungsten–nanodiamond composite powders produced by ball milling

The major challenge in producing tungsten–nanodiamond composites by ball milling lies in successfully dispersing carbon nanoparticles in the metallic matrix while keeping carbide formation at a minimum. Processing windows for carbide minimization have been established through systematic variation of the nanodiamond fraction, milling energy and milling time. Materials characterization has been carried out by X-ray diffraction, scanning and transmission electron microscopy and microhardness testing. Nanostructured matrices with homogeneously dispersed particles that preserved the diamond structure have been produced. Differential thermal analysis has been used to evaluate the composites thermal stability

Photocapacitance measurements in irradiated a-Si:H based detectors

Photocapacitance measurements were performed on amorphous silicon p–i–n detectors before and after particle irradiation with 1.5 MeV 4 He+ ions. The spatial resolution across a degraded spot is similar to the one obtained in photocurrent scans and is of the order of the diameter of the scanning laser beam. We monitored the transient capacitance after applying short laser pulses to deduce trap energies of 0.64 eV. Photocapacitance measurements as a function of the applied bias, the measurement frequency up to 1 MHz, and the wavelength of laser light are discussed. The reduction in photocapacitance signal and the shift of the cut-off frequency after ion bombardment are correlated with the change in transport properties

O Produto Viscosidade Densidade em Misturas Nafta+Dióxido de Carbono em Condições Supercríticas.

11º Encontro da Sociedade Portuguesa de Química, Lisboa, 12-15 Dezembro 1988.Efectuou-se um estudo de viabilidade da medida do produto viscosidade (n) densidade (p) de misturas NAFTA+CO2 em condições supercríticas do dióxido de carbono com um viscosimetro de cristal de quartzo em vibração torsional, para uma gama de temperaturas entre (40º-60ºC) e pressões até 12MPa. Foram efectuadas medidas para o CO2 puro e a mistura NAFTA+CO2 a 40ºC e a pressões que atingiram os 9MPa. Foi assim possível tirar algumas conclusões acerca do sistema de trabalho, NAFTA+CO2, que sugerem modificações da célula de medida, tendo-se provado no entanto que o método de medida aplicado, sob a forma relativa, é um bom método para medir a viscosidade da mistura, desde que a viscosidade seja conhecida