The length of alginic acid wire is constrained by the size of the furnace, but is
typically around 150 mm. Theoretically, there is no limit to the possible length,
which means that longer wire could be produced. The wire shrinks in diameter by
around one-third when fired at 950 °C. The minimum diameter of alginic acid wire
currently being produced is around 70 lm, although even smaller wires could be
made.
F. Characteristics of Wires Produced with the Alginic Acid Method
YBa 2 Cu 3 O x wire produced with the alginic acid method has a maximum tensile
strength of 192 MPa, or five times higher than YBa 2 Cu 3 O x wire produced with the
powder sintering method. The alginic acid method’s YBa 2 Cu 3 O x precursor is also
more precisely designed. The cross-section of a wire fired at 950 °C after hardening
a YBa 2 Cu 3 O x powder with the powder sintering method contains remaining particles from the source powder, resulting in many gaps between particles. This is a
significant difference from wires produced with the alginic acid method (Poncelet
et al. 1992).
In YBa 2 Cu 3 O x wires produced with the alginic acid method, electrical resistance
depends on temperature: as the temperature falls, it slowly declines until the temperature reaches around 90 K, at which point it begins dropping sharply from 85 K
all the way to zero. 85 K is the maximum critical temperature for YBa 2 Cu 3 O x wires
made with the sol-gel method. Currently, the critical current density at a critical
temperature of 77 K is 10
5 A/m
2 , which decreases as the wire’s critical temperature
is increased above 90 K.
Critical current density does not readily decline when crystalline particles within
the wire are directionally disordered and not arrayed in a particular direction. This
phenomenon also appears in wires produced through other methods besides the
alginic acid approach and is a fundamental issue encountered in the making of
high-temperature superconducting ceramics. Attempts are currently being made to
solve this problem by raising critical current density through increased orientation
of crystalline particles in wines made with the powder sintering approach. Research
should also be conducted to increase the alignment of crystalline particles in
high-temperature superconducting ceramic wires made with the alginic acid
method.
G. What Happens to the Alginic Acid When the Wires Are Fired?
When high-temperature superconducting ceramic wires made with the alginic acid
method are fired, the alginic acid is ultimately converted into water and carbon
dioxide that evaporate into the air. This fact can be ascertained from thermogravimetric analysis (TGA) and differential thermal analysis (DTA) of the alginic
acid wire firing process. Weight decreases slowly as the temperature rises from
room temperature to 180 °C, and the DTA curve similarly slows a slow rate of heat
absorption before reaching this temperature, at which point the water in the alginic
acid evaporates. As it continues heating from 180 to 340 °C, most of the water and
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8 Developing Functional Materials with Marine Organisms
typically around 150 mm. Theoretically, there is no limit to the possible length,
which means that longer wire could be produced. The wire shrinks in diameter by
around one-third when fired at 950 °C. The minimum diameter of alginic acid wire
currently being produced is around 70 lm, although even smaller wires could be
made.
F. Characteristics of Wires Produced with the Alginic Acid Method
YBa 2 Cu 3 O x wire produced with the alginic acid method has a maximum tensile
strength of 192 MPa, or five times higher than YBa 2 Cu 3 O x wire produced with the
powder sintering method. The alginic acid method’s YBa 2 Cu 3 O x precursor is also
more precisely designed. The cross-section of a wire fired at 950 °C after hardening
a YBa 2 Cu 3 O x powder with the powder sintering method contains remaining particles from the source powder, resulting in many gaps between particles. This is a
significant difference from wires produced with the alginic acid method (Poncelet
et al. 1992).
In YBa 2 Cu 3 O x wires produced with the alginic acid method, electrical resistance
depends on temperature: as the temperature falls, it slowly declines until the temperature reaches around 90 K, at which point it begins dropping sharply from 85 K
all the way to zero. 85 K is the maximum critical temperature for YBa 2 Cu 3 O x wires
made with the sol-gel method. Currently, the critical current density at a critical
temperature of 77 K is 10
5 A/m
2 , which decreases as the wire’s critical temperature
is increased above 90 K.
Critical current density does not readily decline when crystalline particles within
the wire are directionally disordered and not arrayed in a particular direction. This
phenomenon also appears in wires produced through other methods besides the
alginic acid approach and is a fundamental issue encountered in the making of
high-temperature superconducting ceramics. Attempts are currently being made to
solve this problem by raising critical current density through increased orientation
of crystalline particles in wines made with the powder sintering approach. Research
should also be conducted to increase the alignment of crystalline particles in
high-temperature superconducting ceramic wires made with the alginic acid
method.
G. What Happens to the Alginic Acid When the Wires Are Fired?
When high-temperature superconducting ceramic wires made with the alginic acid
method are fired, the alginic acid is ultimately converted into water and carbon
dioxide that evaporate into the air. This fact can be ascertained from thermogravimetric analysis (TGA) and differential thermal analysis (DTA) of the alginic
acid wire firing process. Weight decreases slowly as the temperature rises from
room temperature to 180 °C, and the DTA curve similarly slows a slow rate of heat
absorption before reaching this temperature, at which point the water in the alginic
acid evaporates. As it continues heating from 180 to 340 °C, most of the water and
258
8 Developing Functional Materials with Marine Organisms