The effect of the volume expansion on the total linear magnetostriction of , , and mold-cast bulk alloys was investigated by measuring the change in length with applied field longitudinal and perpendicular to the temperature gradient during solidification. In the magnetically saturated state, due to the contribution of the volume expansion, the saturation magnetostriction for all three alloys was about 66 % of the total linear magnetostriction. The magnetostriction is strongly dependent on the direction of the temperature gradient, being larger in this direction. The substitution of Fe by Ga atoms increases the lattice constant and causes a change to the crystal structure, which was confirmed by Mössbauer spectroscopy. The thermal-expansion coefficient increases with Ga content at temperatures between 4.2 and .
1 April 2005 in Journal of Magnetism and Magnetic Materials
The diffusion between Nb–20%Ta (wt %) and pure Ti is studied at temperatures of 973, 1023, and , for duration times among 25 and in an artificial pinning center (APC) wire composed of a Ti core surrounded by a Nb–20%Ta layer. The produced diffusion layer is a ternary alloy with superconducting properties, such as critical field and critical current density , which intrinsically depend on the layer composition. Measurements of layer morphology and composition were performed, and the results show a preferential diffusion of Nb and Ta into Ti. There is a slight diffusion of Ti into Nb through grain boundaries. The presence of Ta also slows down the diffusion of Nb in Ti if compared to the couple formed by pure Nb and Ti. Regarding the mechanical properties of the composite wire, the use of lower temperatures to form the ternary phase is desirable in order to avoid a larger portion of the diffusion layer rich in Ti that favorites precipitations that are detrimental to the wire ductility. The best value was obtained for the sample heat treated at . The improvement of the flux-line pinning was associated with a sharp change of the diffusion layer composition rather than pinning by normal layer interfaces, suggesting a new source of pinning in this kind of material. Nb–Ti–Ta ternary alloys have the potential to be used in superconducting magnets when fields above are required.
19 March 2003 in Superconductor Science and Technology
O correto gerenciamento da Segurança e Saúde no Trabalho (SST) reduz riscos de acidentes, promove a saúde e a satisfação dos trabalhadores, além de melhorar os resultados operacionais e a imagem das empresas. As alterações nas Normas regulamentadoras vieram para intensificar a melhoria das condições de segurança, exigindo dos empregadores a implantação do Gerenciamento de Riscos Ocupacionais (GRO). Baseado na Norma Regulamentadora NR-22, o Programa de Gerenciamento de Riscos (PGR) contido agora na NR-1 foi definido como artifício utilizado pelas empresas que ainda não possuam um Sistema de Gestão em Segurança e Saúde Ocupacional (SGSSO) ou uma certificação ISO 45.001. A nova NR-9 trará novas diretrizes quando a identificação e avaliação de riscos que servirá de eixo guia para o PGR rumo ao GRO. Este trabalho apresentou uma visão prática e objetiva do GRO e PGR frente às mudanças da atualidade, evidenciando a conexão entre as NR 1, 9 e 22. Além disso, o artigo teve o intuito de mostrar a abrangência do GRO, propondo um novo modelo de segurança do trabalho. Este trabalho apresentou uma análise dos três pilares do GRO, a NR-1, ISO 45.001 o Sistema de Gestão de Segurança e Saúde Ocupacional, com o intuito de mostrar uma sinergia entre esses três eles. Sendo assim, o PGR é a “ponte necessária” para se chegar ao GRO.
31 August 2004 in Physica C: Superconductivity and its Applications