substances, and ceramics. Only around five to six have been commercialized,
including niobium-titanium (Nb–Ti) and niobium-tin (Nb–Sn) alloys. This owes to
fact that superconductivity occurs only at extremely low temperatures, which
requires the use of expensive liquid helium (4 K/−276 °C) for refrigeration. Also,
because the helium gas needed to make liquid helium is light and tends not to
remain in the atmosphere, cooling costs are prohibitively expensive, and the
technology cannot be used except for purposes other than advanced precision
machinery.
After superconductivity was discovered, few believed in the existence of a
substance that would exhibit it when cooled to 77 K (−200 °C), a temperature
achievable with highly inexpensive liquid nitrogen. In 1986, however,
lanthanum-based LBCO developed by Bednorz and Müller was reported to become
a superconductor at the relatively high temperature of 30 K. In 1987, the discovery
of oxide-based superconductors developed by Paul Chu of the University of
Houston that exhibited superconductivity at 77 K drew attention to the area of
high-temperature superconductors. Examples of high-temperature superconductors
that are currently the focus of attention include rare earth oxides that are
titanium-based (critical temperature 30 K) and yttrium-based (»90 K), bismuth
oxides, and mercury-based forms (134 K) (Burns 1992).
D. Commercializing High-Temperature Superconductors
For high-temperature superconductors to be used commercially, they must be
fashioned into thin, rodlike wires that allow for easy passage of current. Recent
rapid strides in thin film technology have resulted in the production of outstanding
forms of film.
High-temperature superconducting ceramic are not only difficult to make but
also fragile. New forms of wire production are currently being explored to address
these issues. The most typical way of fashioning a wire from high-temperature
superconducting ceramic is powder sintering. In this method, ceramic powder is
joined to a pipe made of copper, silver, or another metal and pulled until it is
slender. Another approach currently being researched involves mixed an organic
binding agent into the ceramic powder to produce a wire form, which is then burned
into a wire.
Wires produced in this way have roughly the same critical temperature as a
regular block of superconducting ceramic. They differ, however, in having a critical
current density (the maximum current capable of flowing in the superconductor) of
10
7 A/cm
2 and over twice the utility level. This can be attributed to the sintered
wire materials containing remaining particles of the ceramic powder used as an
ingredient; the presence of many gaps between particles prevents a current from
flowing easily. When the crystalline particles in the material are arranged in a
disordered way, critical current density is constrained by the particles’ direction
relative to the current flow, preventing the superconducting ceramics from
achieving maximum performance. This problem is not something that can be solved
simply by shaping powder into wire form and sintering it.
256
8 Developing Functional Materials with Marine Organisms
including niobium-titanium (Nb–Ti) and niobium-tin (Nb–Sn) alloys. This owes to
fact that superconductivity occurs only at extremely low temperatures, which
requires the use of expensive liquid helium (4 K/−276 °C) for refrigeration. Also,
because the helium gas needed to make liquid helium is light and tends not to
remain in the atmosphere, cooling costs are prohibitively expensive, and the
technology cannot be used except for purposes other than advanced precision
machinery.
After superconductivity was discovered, few believed in the existence of a
substance that would exhibit it when cooled to 77 K (−200 °C), a temperature
achievable with highly inexpensive liquid nitrogen. In 1986, however,
lanthanum-based LBCO developed by Bednorz and Müller was reported to become
a superconductor at the relatively high temperature of 30 K. In 1987, the discovery
of oxide-based superconductors developed by Paul Chu of the University of
Houston that exhibited superconductivity at 77 K drew attention to the area of
high-temperature superconductors. Examples of high-temperature superconductors
that are currently the focus of attention include rare earth oxides that are
titanium-based (critical temperature 30 K) and yttrium-based (»90 K), bismuth
oxides, and mercury-based forms (134 K) (Burns 1992).
D. Commercializing High-Temperature Superconductors
For high-temperature superconductors to be used commercially, they must be
fashioned into thin, rodlike wires that allow for easy passage of current. Recent
rapid strides in thin film technology have resulted in the production of outstanding
forms of film.
High-temperature superconducting ceramic are not only difficult to make but
also fragile. New forms of wire production are currently being explored to address
these issues. The most typical way of fashioning a wire from high-temperature
superconducting ceramic is powder sintering. In this method, ceramic powder is
joined to a pipe made of copper, silver, or another metal and pulled until it is
slender. Another approach currently being researched involves mixed an organic
binding agent into the ceramic powder to produce a wire form, which is then burned
into a wire.
Wires produced in this way have roughly the same critical temperature as a
regular block of superconducting ceramic. They differ, however, in having a critical
current density (the maximum current capable of flowing in the superconductor) of
10
7 A/cm
2 and over twice the utility level. This can be attributed to the sintered
wire materials containing remaining particles of the ceramic powder used as an
ingredient; the presence of many gaps between particles prevents a current from
flowing easily. When the crystalline particles in the material are arranged in a
disordered way, critical current density is constrained by the particles’ direction
relative to the current flow, preventing the superconducting ceramics from
achieving maximum performance. This problem is not something that can be solved
simply by shaping powder into wire form and sintering it.
256
8 Developing Functional Materials with Marine Organisms