Induced nuclear reactions: processes – systems – and elements – Nuclear transmutation – By neutron bombardment
Reexamination Certificate
1996-10-01
2002-12-10
Behrend, Harvey E. (Department: 3641)
Induced nuclear reactions: processes, systems, and elements
Nuclear transmutation
By neutron bombardment
C376S183000, C376S185000, C148S097000, C505S320000
Reexamination Certificate
active
06493411
ABSTRACT:
BACKGROUND OF THE INVENTION
The most distinctive property of a superconductive material is its absence of electrical resistance when it is at or below a critical temperature. This critical temperature (Tc) is an intrinsic property of the material.
Research into the ability of specific materials to superconduct began in 1911 with the discovery that mercury superconducts at a Tc of about 40° K. Since then, many applications for superconducting materials have been conceived, but such applications could not be commercialized because of the extreme low Tc of the superconducting materials then available.
Although many materials have since been examined in an effort to find compositions which superconduct at higher temperatures—temperatures at which the more economical and practical coolant of liquid nitrogen could be used—until about 1986 the highest temperature superconductor known was Nb
3
Ge having a critical temperature, Tc, of approximately 23.2K. Before 1987, superconducting devices, even those which employed the Nb
3
Ge superconductor, required the use of liquid helium as the refrigerant-coolant.
In late 1986 Bednorz and Muller disclosed that certain mixed phase compositions of La—Ba—Cu—O appeared to exhibit superconductivity being at an onset temperature, T
co
, of about 30K. Bednorz et al.,
Z. Phys. B., Condensed Matter,
Vol. 64, pp. 189-198 (1986). Investigation of that La—Ba—Cu—O mixed phase system established that the crystalline phase therein responsible for superconductivity had a crystal structure like that of K
2
NiF
4
(214). Since then it has been determined that whatever might be the rare earth metal or the alkaline earth metal constituent of a 214 system, the upper temperature limit of superconducting onset, T
co
, of superconductors of a 214 type crystalline structure is no greater than about 38K. Liquid helium was still required as the coolant for such a 214 type of material.
Following the discovery of superconductivity in a rare earth-alkaline earth-Cu oxide system of a 214 crystalline structure, a new class of rare earth-alkaline earth-copper oxides was discovered which are superconductive at temperatures above the boiling point of liquid nitrogen, 77K. These new rare earth-alkaline earth-copper oxides are of the formula L
1
M
2
Cu
3
O
7
wherein L is a rare earth metal and M is an alkaline earth metal. The L
1
M
2
Cu
3
O
7
compositions are commonly referred to as “123” high-temperature superconductors in reference to the stoichiometry in which the rare earth, alkaline earth, and copper metal atoms are present, namely a ratio of 1:2:3. Subsequent to the discovery of the 123 high temperature superconductors, another form of high temperature superconductor was discovered having the formula T
2
M′
2
Ca
n
Cu
n+1
O
6+2n
wherein T is bismuth and M′ is strontium or T is thallium and M′ is barium, and “n” is 1, 2, or 3. Both types of “high temperature superconducting” (HTS) compositions are ceramics materials.
The 123 high temperature superconducting compounds have a perovskite related crystalline structure. The unit cell of such 123 compounds consists of three sub-cells in alignment along the crystallographic C-axis wherein the center of the middle subcell is occupied by a rare earth metal atom, the center of each end subcell is occupied by an alkaline earth metal atom, and copper atoms occupy the corner positions in each subcell. X-ray and neutron powder diffraction studies indicate the structure of superconductive 123 compounds to be oxygen deficient and that the ordering of oxygen in the basal planes is critical to the existence of superconducting properties in such compounds. See C. Poole et al,
Copper Oxide Superconductors
(John Wiley & Sons 1988). The unit cell formula of a 123 compound is L
1
M
2
Cu
3
O
6+&dgr;
(&dgr;=0.1 to 1.0, preferably about 1.0) wherein the rare earth metal constituent, L, is yttrium, lanthanum, neodymium, samarium, europium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, or lutetium, or mixtures thereof including mixtures with scandium, cerium, praseodymium, terbium and the alkaline earth constituent, M, is barium, strontium or mixtures thereof. Studies indicate that when &dgr; is between about 0.1 to about 0.6, the resulting 123 compound assumes a tetragonal unit cell crystallographic symmetry and is non-superconductive. In the tetragonal unit cell symmetry, the lattice dimension of the C-axis is approximately 11.94 angstroms and that of the A and B axis is approximately 3.9 angstroms. When &dgr; is between about 0.7 and 1.0, the resulting 123 compound has an orthorhombic unit cell crystallographic symmetry and is superconductive. The orientation of the oxygen atoms in the unit cell causes, the unit cell to compress slightly along the A crystallographic axis and thus the lattice dimension of the A axis is less than that of the B axis. Lattice constants in the orthorhombic symmetry are about A=3.82, B=3.89 and C=11.55 angstroms.
With the discovery of the new “high temperature superconducting” (HTS) compounds—HTS compounds are those which superconduct at a Tc above the temperature at which liquid N
2
can be used as a refrigerant—it has become economically possible to pursue many previously conceived applications of the superconductivity phenomena which before were commercially difficult wherein cooling by liquid helium was required. Since they superconduct at temperatures greater than 77K, the new high temperature superconductors may in practical applications be cooled with liquid nitrogen—a more economically feasible refrigerant. The HTS compounds, both the 123 compositions and those containing bismuth or thallium, simplify and enhance the reliability of commercial applications of superconductors. Recent studies also show that the HTS compounds have better performance at 4K than the prior materials.
Nevertheless, the ceramic HTS compounds have been economically and technologically impractical for use in some applications due to the inability of bodies thereof (1) to carry high current loads (J
c
(0)) (2) to carry high current loads in intense magnetic fields (J
c
(H)) (3) and to entrap strong magnetic fields (B
t
). As a result, significant commercial and technological barriers against use of the ceramic HTS compounds as a superconductor body in a variety of practical applications, such as in magnets, magnetic separators, transmission lines, trapped field magnets, levitation bearing and magnetically levitating trains (meglav), still exist.
In magnetic separators, for example, the body of a superconducting material is required, as a practical constraint, to have a critical current density (J
c
) between about 10
3
to 10
5
amps/cm
2
in a magnetic field between 0 to 10 T. To be practical for some magnet applications, bodies of a ceramic HTS compound must be capable of entrapping within its crystalline structure a high magnetic field. The critical current (J
c
) which a body of a HTS compound is capable of carrying is strongly affected by the granular alignment and homogeneity of the polycrystals HTS compound comprising the body and by the distribution and force with which lattice defects within the HTS material can pin magnetic flux lines. Accordingly, one approach to improve the J
c
of a ceramic HTS body has been directed to methods of processing the HTS composition into shaped bodies wherein the number and content of “weak links” due to its granular ceramic nature is reduced. Another approach has examined techniques whereby strong flux pinning centers may be homogeneously introduced into the HTS composition of which a body article is composed.
The Jc and ability to entrap a magnetic field of a HTS compound body, particularly a 123 HTS compound, is dramatically influenced by several factors which introduces “weak links” into the HTS material of the body. “Weak links” exist in the forms of (1) grain boundaries; (2) micro-cracks; (3) impurity content—i.e., the wt. % content of the body of nonsuperconducting phases (i.e., L
2
BaCuO
5
, BaCuO
2
, CuO, etc.
Chu Wei-Kan
Liu Jiarui
Akin Gump Strauss Hauer & Feld & LLP
Behrend Harvey E.
University of Houston-University Park
LandOfFree
Method for producing formed bodies of high temperature... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing formed bodies of high temperature..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing formed bodies of high temperature... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2974214