Superconducting wire
Encyclopedia
Superconducting wire is wire made of superconductors. Most commonly, conventional superconductors such as niobium-titanium
are used, but high-Tc superconductors such as YBCO are entering the market. Superconducting wire's advantages over copper or aluminum include higher maximum current densities and zero power dissipation. Its disadvantages include the cost of refrigeration
of the wires to superconducting temperatures (often requiring cryogens such as liquid helium
or liquid nitrogen
), the danger of the wire quenching (a sudden loss of superconductivity), the inferior mechanical properties of some superconductors, and the cost of wire materials and construction. One important application is in superconducting magnets, which are used in scientific and medical equipment where high magnetic fields are necessary.
Often the superconductor is in filament form in a copper or aluminium matrix which carries the current should the superconductor quench for any reason. The superconductor filaments can form a third of the total volume of the wire.
process can be used for malleable alloys such as niobium-titanium.
(V3) can be prepared by surface diffusion where the high temperature component as a solid is bathed in the other element as liquid or gas. When all components remain in the solid state during high temperature diffusion this is known as the Bronze Process
The powder-in-tube (PIT, or oxide powder in tube, OPIT) process is often used for making electrical conductors from brittle superconducting materials such as niobium-tin
or magnesium diboride
, and ceramic cuprate superconductors such as BSCCO. It has been used to form wires of the iron pnictides. (PIT is not used for YBCO (Yttrium barium copper oxide) as it does not have the weak layers required to generate adequate 'texture
' (alignment) in the PIT process.)
This process is used because the high-temperature superconductors are too brittle for normal wire forming process
es. The tubes are metal, often silver
. Often the tubes are heated to react the mix of powders. Once reacted the tubes are sometimes flattened to form a tape-like conductor. The resulting wire is not as flexible as conventional metal wire, but is sufficient for many applications.
There are 'in situ' and 'ex situ' variants of the process, as well a 'double core' method that combines both.
Niobium-titanium
Niobium-titanium is an alloy of niobium and titanium, used industrially as a type II superconductor wire for superconducting magnets...
are used, but high-Tc superconductors such as YBCO are entering the market. Superconducting wire's advantages over copper or aluminum include higher maximum current densities and zero power dissipation. Its disadvantages include the cost of refrigeration
Refrigeration
Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...
of the wires to superconducting temperatures (often requiring cryogens such as liquid helium
Liquid helium
Helium exists in liquid form only at extremely low temperatures. The boiling point and critical point depend on the isotope of the helium; see the table below for values. The density of liquid helium-4 at its boiling point and 1 atmosphere is approximately 0.125 g/mL Helium-4 was first liquefied...
or liquid nitrogen
Liquid nitrogen
Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4...
), the danger of the wire quenching (a sudden loss of superconductivity), the inferior mechanical properties of some superconductors, and the cost of wire materials and construction. One important application is in superconducting magnets, which are used in scientific and medical equipment where high magnetic fields are necessary.
Often the superconductor is in filament form in a copper or aluminium matrix which carries the current should the superconductor quench for any reason. The superconductor filaments can form a third of the total volume of the wire.
Important parameters of SC wires/tapes/conductors
The construction and operating temperature will typically be chosen to maximise :- Current density (see images below for examples).
Wire drawing
The normal wire drawingWire drawing
Wire drawing is a metalworking process used to reduce the cross-section of a wire by pulling the wire through a single, or series of, drawing die. There are many applications for wire drawing, including electrical wiring, cables, tension-loaded structural components, springs, paper clips, spokes...
process can be used for malleable alloys such as niobium-titanium.
Surface diffusion
Vanadium-galliumVanadium-gallium
Vanadium-gallium a superconducting alloy of vanadium and gallium often used for the high field insert coils of superconducting electromagnets.Vanadium-gallium tape is used in superconducting magnets...
(V3) can be prepared by surface diffusion where the high temperature component as a solid is bathed in the other element as liquid or gas. When all components remain in the solid state during high temperature diffusion this is known as the Bronze Process
Powder-in-tube
Niobium-tin
Niobium-tin or triniobium-tin is a metallic chemical compound of niobium and tin , used industrially as a type II superconductor. This intermetallic compoundis a A15 phases superconductor...
or magnesium diboride
Magnesium diboride
Magnesium diboride is a simple ionic binary compound that has proven to be an inexpensive and useful superconducting material.Its superconductivity was announced in the journal Nature in March 2001. Its critical temperature of is the highest amongst conventional superconductors...
, and ceramic cuprate superconductors such as BSCCO. It has been used to form wires of the iron pnictides. (PIT is not used for YBCO (Yttrium barium copper oxide) as it does not have the weak layers required to generate adequate 'texture
Texture (crystalline)
In materials science, texture is the distribution of crystallographic orientations of a polycrystalline sample. A sample in which these orientations are fully random is said to have no texture. If the crystallographic orientations are not random, but have some preferred orientation, then the...
' (alignment) in the PIT process.)
This process is used because the high-temperature superconductors are too brittle for normal wire forming process
Wire drawing
Wire drawing is a metalworking process used to reduce the cross-section of a wire by pulling the wire through a single, or series of, drawing die. There are many applications for wire drawing, including electrical wiring, cables, tension-loaded structural components, springs, paper clips, spokes...
es. The tubes are metal, often silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
. Often the tubes are heated to react the mix of powders. Once reacted the tubes are sometimes flattened to form a tape-like conductor. The resulting wire is not as flexible as conventional metal wire, but is sufficient for many applications.
There are 'in situ' and 'ex situ' variants of the process, as well a 'double core' method that combines both.
See also
- Niobium-titaniumNiobium-titaniumNiobium-titanium is an alloy of niobium and titanium, used industrially as a type II superconductor wire for superconducting magnets...
easier to handle - Niobium-tinNiobium-tinNiobium-tin or triniobium-tin is a metallic chemical compound of niobium and tin , used industrially as a type II superconductor. This intermetallic compoundis a A15 phases superconductor...
difficult to handle - YBCO
- BSCCO