Development of Bulk Bi2+xSr3-yCa yCu 2O8+delta Superconductors by Partial-Melting Route for Fault Current Limiters Application

Abstract

The production of bulk Bi 2+x Sr 3-y Ca y Cu 2 O 8+∆ (Bi-2212) superconductors for fault current limiter application was developed via a partial-melting route. Aiming high I c (critical current), which is the essential superconducting characteristic for application of this material in the construction of Fault Current Limiters (FCL), the produced blocks have predominance of Bi-2212 phase (83 wt%), which characterizes with high values of zero and onset transport critical temperature of 92 K and 97.5 K, respectively. A relatively low transition width, ∆T, from the superconducting to the normal state of 5.5 K, revealed a good intergrain connectivity. Consequently, current measurements on the blocks of Bi-2212 show promising I c values of 230 A and 850 A for direct and alternate current, respectively. It is expected that further increases in the I c values will depend on the elimination of an observed amorphous phase and further reduction of amount and grain sizes of secondary phases, still present in the blocks obtained by the proposed partial-melting route. This may be achieved by a further optimization of the partial-melting processing parameters.

PROCESSAMENTO DO SUPERCONDUTOR CERÂMICO Bi-2212 POR FUSÃO PARCIAL

“…Em trabalhos anteriores foi observado que a fusão parcial, a cerca de 900°C, leva à formação de uma microestrutura aparentemente inadequada. (6,7) Contudo, nos referidos estudos, as amostras aquecidas a T > 895°C apresentaram valores de corrente crítica maiores do que os das amostras aquecidas a temperaturas inferiores. O precursor empregado na ocasião fora obtido por reação no estado sólido, nas mesmas condições e com a mesma composição do precursor CEPEL utilizado no presente trabalho.…”

“…(4,7) O controle do teor de oxigênio também influencia fortemente no valor da temperatura crítica de transição (T c ) desta fase e, por conseguinte, no valor de I c à temperatura do nitrogênio líquido. (6,7) Deste modo, é necessário o uso de atmosfera rica em oxigênio, com uma etapa final de tratamento em atmosfera rica em nitrogênio, para otimização do teor de oxigênio da fase 2212.…”

“…A taxa de resfriamento lento (5°C/h) e a temperatura de recozimento (850°C) empregadas no presente estudo correspondem a valores ótimos da literatura. (3,6) O estágio de recozimento a 850°C tem por objetivo a continuidade do processo de formação e crescimento da Bi-2212, iniciado durante o resfriamento lento. No entanto, pode ocorrer coalescência de partículas de fases secundárias durante o recozimento, o que pode ter influído na formação de precipitados grosseiros observados, principalmente no bloco A.…”

Improvement in granularity of NdFeAsO0.8F0.2 superconductor through Agx doping (x = 0.0–0.3)

“…As far as the improving of grain boundaries connectivity is concerned, a lot of work has already been done in case of cuprate superconductors and the addition of Ag has proven to be very effective [22][23][24][25][26]. Infact, to draw wires/tapes of high T c cuprates for their practical applications, researchers have drawn silver sheathed wires and tapes of them for their high current applications [27][28][29].…”

“…Infact, to draw wires/tapes of high T c cuprates for their practical applications, researchers have drawn silver sheathed wires and tapes of them for their high current applications [27][28][29]. It is known that Ag does not have any deteriorating effect on superconductivity of HTSc cuprates, primarily because Ag gets distributed at the grain boundaries instead of being substituted in the parent superconducting unit cell of these compounds [22][23][24][25][26][27][28][29]. This way Silver addition has resulted in improving the critical current of high Tc cuprates in a big way.…”