The most widely recognized method for producing ceramic wire is the sol-gel
method. This method involves gelling an organic sol containing a metal ion into
wire form, then heating it into ceramic form. Since this method involves mixing the
constituent atoms in ceramic at the atomic level without a powdered process, it is
less uniform than the powder sintering method, and the ability to produce precise
wire forms is uncertain. For this reason, research is under way on an approach
involving use of the sol-gel method on several organic metal salt gels to produce
superconducting ceramic wire. The resulting wires are not precise and long like the
wires currently produced; they are typically hollow like tubes and contain numerous
gas bubbles (McGinn 1998).
E. Producing High-Temperature Superconducting Wires with Alginic Acid
As sodium alginate, alginic acid [(C 5 H 7 O 4 COOH)X Á (YH 2 O)] becomes a viscous
liquid when dissolved in water. The resulting solution acquires gelling properties
when the sodium ions are replaced with hydrogen or multivalent metal ions. For
this reason, research is currently focusing on the fashioning of high-temperature
superconducting materials into wire through the sol-gel method using alginic acid, a
polysaccharide present in algae such as sea mustard and kelp. The principle
involves using taking advantage of the gelling properties of alginic acid by binding
the metal ions needed for high-temperature superconducting ceramics to an alginic
acid gel in wire form and then heating the surface to produce a high-temperature
superconducting ceramic wire (Crow et al. 1991).
An example of the alginic acid method of producing high-temperature ceramic
wire is the use of YBa 2 Cu 3 O x as a high-temperature superconducting ceramic and
creation of an alginic acid precursor which is then shaped. For the alginic acid
precursor, a 5% sodium alginate solution is carefully directed from a nozzle toward
1 N hydrochloric acid. The sodium ions in the sodium alginate solution are replaced
with hydrogen ions from the HCl and gel in the same form produced as they
emerged from the nozzle. The gelled alginic acid precursor is washed with distilled
water and placed in a sodium acetate/barium acetate/copper (I/II) acetate solution.
As the hydrogen ions in the alginic acid precursor are replaced by Y Á Ba Á Cu ions,
an alginic acid wire is produced. The stoichiometric ratio of Y Á Ba Á Cu bonding
with hydrogen ions in the alginic acid wire is 1:2:3; more copper than yttrium or
barium is also found when an acetate solution is used. This is a result of selectivity
in alginic acid’s ion exchange capacity.
This alginic acid wire is then washed again with distilled water and subjected to
a load as it dries at room temperature to produce the final wire. Magnification with a
scanning electron microscope showed a smooth, evenly surface wire with no gas
bubbles or evidence of metal salt deposition.
The alginic acid wire exhibits a tensile strength of 146 MPa and 5.7% expansion. A firing temperature of 900 °C is inadequate, but firing proceeds when the
temperature is raised to 950 °C. The empty spaces are removed, and the
cross-section assumes a continuous, smooth, nearly cylindrical surface.
8.3 Bio Materials
257
method. This method involves gelling an organic sol containing a metal ion into
wire form, then heating it into ceramic form. Since this method involves mixing the
constituent atoms in ceramic at the atomic level without a powdered process, it is
less uniform than the powder sintering method, and the ability to produce precise
wire forms is uncertain. For this reason, research is under way on an approach
involving use of the sol-gel method on several organic metal salt gels to produce
superconducting ceramic wire. The resulting wires are not precise and long like the
wires currently produced; they are typically hollow like tubes and contain numerous
gas bubbles (McGinn 1998).
E. Producing High-Temperature Superconducting Wires with Alginic Acid
As sodium alginate, alginic acid [(C 5 H 7 O 4 COOH)X Á (YH 2 O)] becomes a viscous
liquid when dissolved in water. The resulting solution acquires gelling properties
when the sodium ions are replaced with hydrogen or multivalent metal ions. For
this reason, research is currently focusing on the fashioning of high-temperature
superconducting materials into wire through the sol-gel method using alginic acid, a
polysaccharide present in algae such as sea mustard and kelp. The principle
involves using taking advantage of the gelling properties of alginic acid by binding
the metal ions needed for high-temperature superconducting ceramics to an alginic
acid gel in wire form and then heating the surface to produce a high-temperature
superconducting ceramic wire (Crow et al. 1991).
An example of the alginic acid method of producing high-temperature ceramic
wire is the use of YBa 2 Cu 3 O x as a high-temperature superconducting ceramic and
creation of an alginic acid precursor which is then shaped. For the alginic acid
precursor, a 5% sodium alginate solution is carefully directed from a nozzle toward
1 N hydrochloric acid. The sodium ions in the sodium alginate solution are replaced
with hydrogen ions from the HCl and gel in the same form produced as they
emerged from the nozzle. The gelled alginic acid precursor is washed with distilled
water and placed in a sodium acetate/barium acetate/copper (I/II) acetate solution.
As the hydrogen ions in the alginic acid precursor are replaced by Y Á Ba Á Cu ions,
an alginic acid wire is produced. The stoichiometric ratio of Y Á Ba Á Cu bonding
with hydrogen ions in the alginic acid wire is 1:2:3; more copper than yttrium or
barium is also found when an acetate solution is used. This is a result of selectivity
in alginic acid’s ion exchange capacity.
This alginic acid wire is then washed again with distilled water and subjected to
a load as it dries at room temperature to produce the final wire. Magnification with a
scanning electron microscope showed a smooth, evenly surface wire with no gas
bubbles or evidence of metal salt deposition.
The alginic acid wire exhibits a tensile strength of 146 MPa and 5.7% expansion. A firing temperature of 900 °C is inadequate, but firing proceeds when the
temperature is raised to 950 °C. The empty spaces are removed, and the
cross-section assumes a continuous, smooth, nearly cylindrical surface.
8.3 Bio Materials
257