Ronald BOURGOIN
Ambient
Temperature Bismuth Superconductor
Process for Forming Ambient Temperature Superconducting Filaments
US Patent # 4325795; Process for Forming Ambient Temperature Superconducting Filaments
Ambient Temperature Superconducting Filaments (Conference Presentation)
China's Innova Superconductor Technology Co. Bismuth HTS Wire
Process for Forming Ambient Temperature Superconducting Filaments
Bulletin of the
Bismuth Institute (4th Quarter, 1983)
47 Rue de Ligna, 1000
Brussels, Belgium
Some metals, metalloids, alloys and metallic compounds, when placed in near Absolute Zero thermal environments, undergo significant decreases in ohmic resistance; at a certain temperature, or within a narrow range of temperatures -- termed a material's "transition temperature" or "transition temperature range" -- the ohmic resistance falls abruptly to practically zero. For a conductor of a given length and cross-sectional area with a measured R ohms of resistance at 25º C., the resistivity is determined to be a certain magnitude. As the ambient temperature of teh conductor is decreased, it has been found that there occurs a linear decrease in resistivity with temperature. Such linear behavior, however, is not the phenomenon of superconductivity. Superconductivity is the term applied to the sudden departure from linear behavior and the abrupt attainment of near zero ohmic resistance. At this point, it is said that the conductor has entered the "superconducting state", and it has been found that said conductors in said state are capable of passing very large magnitudes of current with a minimum of applied voltage.
Although it has been theorized that ambient or room temperature superconductivity might be possible, until now this has remained theory only although such diverse uses as high voltage long distance transmission lines, heat transfer means for heat pumps, and by-passes of damaged nerves in the spinal colum have been envisioned.
To investigate Carroll's prediction of elctrical superconductivity at normal ambient temperatures in thin filaments of bismuth metal, a technique was developed to create filamentary conductors from metal colloids suspended in a thermosetting resin. The application of an electrical field across the colloidal suspension as found to force migration of metal particulates parallel to electric field lines. The application of heat to the molten mixture was found necessary to ensure uniform distribution of suspended particles.
In order to bypass the very high voltage requirements to obtain filaments of at least one centimeter length, a technique of electrode extension was developed whichinvolved the application of about 1 kv potential and slow retraction of one of the electrodes through the colloidal suspension. the retractile electrode was usually a thin metal strip. As the pin electrode was drawn fron the metal strip, molten particulates migrated toestablish a filament between the pin tip and a point on the metal strip. Exptended filament lengths were easily obtained withno increase in applied voltage. It was also found that multiplicities of such filaments could be formed simultaneously if several pin electrodes were used. Formation curent was about 1 mA for each filament.
The time required for the prodcution of filmanets depends on the length desired. For filaments of one centimeter length, formation time ws found to be about 30 minutes.
It was determined that a 10 to 15% by volume mixture of bismuth to resin was sufficient for this procedure. Since molten particulates were desired, the mixture was heated to well beyond the melting point of the metal, typicaly 300º C.
In the early stage of experimentation, electrical tests revealed abrupt drops in resistance to extremely low values once a tansition volage was attained, which was usually 3 volts dc or less. Reversing direction of current resulted in equal behavior. Subsequent improvement in separation tecnique resulted in filaments with no measurable resistance.
It wa found that curent as high as 0.5 A could be passed comfortably by teh Bi filament and ohmic contacts at its ends. Excessive Joule heat generated in the ohmic contacts resulted in system failure at higher currents, but it was found that a filament could pass as high as 10 A prior ro loss of continuity.
This patnet (US 4,325,795) does not claim that a complete transition to the superconducting state has been achieved at room temperature. On the basis of the Carroll theory, the experimental findings indicate that large superconducting components of current have been obtained in thin filaments of the metal made by this process. The theory predicts that filaments of about 10 atomic diameters cross-section will provide complete superconductivity, but such filament uniformity has not been obtained by this technique.
US Patent # 4,325,795
April 20, 1982
Process for Forming Ambient Temperature Superconducting Filaments
Abstract --- This invention is a process for forming electrical conductors in the form of filaments which exhibit properties of electrical superconductivity at ambient or normal room temperature. The process includes the preparation of a molten mixture of conducting and insulator materials, the introduction of the nearly homogeneous mixture between electrodes across which a voltage is applied causing fine filaments to be formed having a diameter within the range of 10 to 1,000 A. The filaments thus formed give almost no resistance to the passage of the electricity therethrough at room temperature thus effectively forming an ambient temperature superconductor.
Inventors: Bourgoin;
Ronald C. (18 Woodfern Cir., Greenville, SC 29615)
Appl. No.: 202680
~ Filed: October 31, 1980
Current U.S. Class: 204/483;
174/125.1; 204/471; 264/441; 427/58; 427/62; 427/63; 505/816
Intern'l Class: C25B
007/00
Field of Search:
204/180 R,181 R,181 F,299 R,300 R 427/58,62,63 174/126 S
264/24,26,27
References Cited [Referenced
By]:
U.S. Patent Documents
3449227 Jun., 1969 Heron et
al. 204/180.
3449230 Jun., 1969 Heron et
al. 204/180.
3556969 Jan., 1971 Mizuguchi
et al. 204/180.
3626041 Dec., 1971 Fields et
al. 264/24.
3664938 May., 1972 Thomas et
al. 204/180.
3668096 Jun., 1972 Cook
204/180.
4048037 Sep., 1977 Chronberg
204/180.
Description
FIELD OF INVENTION:
This invention relates to electrical conductors and a method of forming the same and more particularly to electrically conducting filaments of submicron diameter for superconducting of electricity therethrough.
BACKGROUND OF INVENTION:
Some metals, metalloids, alloys and metallic compounds, when placed in near Absolute Zero thermal environments, undergo significant decreases in ohmic resistance; at a certain temperature, or within a narrow range of temperatures--termed a materials's "transition temperature" or "transition temperature range"--the ohmic resistance falls abruptly to practically zero. For a conductor of a given length and cross-sectional area with a measured R ohms of resistance at 25.degree. C., the resistivity is determined to be a certain magnitude. As the ambient temperature of the conductor is decreased, it has been found that there occurs a linear decrease in resistivity with temperature. Such linear behavior, however, is not the phenomenon of superconductivity. Superconductivity is the term applied to the sudden departure from linear behavior and the abrupt attainment of near zero ohmic resistance. At this point, it is said that the conductor has entered the "superconducting state", and it has been found that said conductors in said state are capable of passing very large magnitudes of current with a minimum of applied voltage.
Although it has been theorized that ambient or room temperature superconductivity might be possible, until now this has remained theory only although such diverse uses as high voltage long distance transmission lines, heat transfer means for heat pumps, and by-passes of damaged nerves in the spinal column have been envisioned.
BRIEF DESCRIPTION OF INVENTION:
After much research and study into the phenomenon of superconductivity and the problems associated therewith in obtaining the same at ambient temperature, the present invention has been developed which accomplishes this condition at 25 to 30 degrees Centigrade. This is done through the use of extremely fine filaments having a diameter of between 10 and 1,000 A formed from elements which normally have a high resistance to current flow. Through practice of the method taught by the present invention, it is now practical to consider not only building electrical transmission long lines, spinal cord by-passes and improved heat transfer means for heat pumps, but also many other applications in such fields as microelectronics and computer technology.
In view of the above, it is an object of the present invention to provide a method of producing a filament which will superconduct at temperatures substantially above zero K.
Another object of the present invention is to provide a superconducting filament which does not lose its superconductivity at temperatures even above zero degrees Centigrade.
Another object of the present invention is to provide a method for producing filaments having a diameter of between 10 and 1,000 A which exhibit characteristics of superconductivity at room temperature.
Another object of the present invention is to provide a practical method for producing fine filament conductors which have superconducting qualities.
Other objects and advantages of the present invention will become apparent and obvious from a study of the following description and the accompanying drawings which are merely illustrative of such invention.
BRIEF DESCRIPTION OF DRAWINGS:
FIG. 1 is a graph illustrating observed increase in current as voltage increases.
FIG. 2 illustrates how voltage drops as current increases.
FIG. 3 is a graph illustrating that as current is increased, resistance decreases.
FIG. 4 is a graph showing the tendency of the filaments to pass currents instantly and the voltage to drop toward zero.
FIG. 5 is a graph illustrating observations made of filaments reaction to current and voltage variations.
FIG. 6 is a basic filament forming circuit.
FIG. 7 is a graph showing negative resistance behavior of resistanceless bismuth filament; and
FIG. 8 is a schematic of a basic filament forming apparatus.
DETAILED DESCRIPTION OF INVENTION
If a DC voltage V volts is applied across the ends of a conducting material of uniform length L centimeters and cross-sectional area A square centimeters in an ambient temperature environment of T .degree.C. by means of an ammeter it is found that a current of I amperes is passed by the conductor. By means of Ohm's Law, the resistance R ohms offered to the passage of electric current is found by
R=V/1. (1)
If a constant DC voltage V volts is applied across the ends of various materials of equal uniform lengths and cross-sectional areas at constant temperature, it is found that each material passes a different current I. By the use of equation (1), the resistance offered to current flow can be determind for each material. This leads to the conclusion that resistance is determined by the conducting property of each material. For the purpose of comparison of conducting properties of various materials at constant temperature, a coefficient of resistance, .rho.--termed the "resistivity"--is calculated by the use of
.rho.=(R.times.L)/A. (2)
If R is in units of ohms, L in centimeters, and A in square centimeters, .rho. is in units of ohm-centimeter.
The resistivities of several
metals at 20.degree. C. as taken from "Properties of Metals as
Conductors", Handbook of Physics and Chemistry, CRC Press,
1979-80, are given below:
______________________________________
METAL
RESISTIVITY (.times. 10.sup.-6 ohm - cm)
______________________________________
Aluminum 2.824
Bismuth 120.0
Copper;
Annealed
1.7241
Gold
2.44
Iron,
99.98% pure
10.0
Lead
22.0
Mercury 95.783
Monel
metal 42.0
*Nichrome 100.0
Nickel 7.8
Silver 1.59
Tin
11.5
Tungsten,
drawn
5.6
Zinc 5.8
______________________________________
*Trademark
According to the conventional view of the nature of resistivity, examination of the above table reveals that silver is the best conductor of electricity. Bismuth has nearly 751/2 times the resistivity of silver and is hence considered that much poorer a conductor.
The chief cause of resistance in a metal crystal is thought to be due to the collisions of electrons in a current flow with the vibrating lattice. From the Boltzmann form equating mechanical energy to thermal energy,
1/2 MV.sup.2 =KT (3)
Where M=mass of a particle in the lattice structure, in grams; V=velocity of the particle, in cm/sec; K=Boltzmann's constant, 1.38.times.10.sup.-16 erg/.degree.K, and T=absolute temperature, .degree.K. A lattice electron of mass 9.11.times.10.sup.-28 gram at room temperature, 300.degree. K., will vibrate at a rate of ##EQU1## This is commonly referred to as the thermal agitation velocity.
The current flow velocity, or the drift velocity, is found by the use of the current equation
I=ANeV (5)
where
I=magnitude of current, in amperes
A=conductor cross-sectional area, in square centimeters
N=conduction electron density: electrons/cm.sup.3
E=charge of one electron: 1.6.times.10.sup.-19 coulomb/electron
V=drift velocity
Using copper as an example, where N=8.42.times.10.sup.22 conduction electrons per cm.sup.3 : if a current of one ampere is passed in a wire of cross-sectional area 0.01 cm.sup.2, ##EQU2## This is about nine orders of magnitude below the velocity of thermal agitation at room temperature.
It has been found that by cooling materials, the resistivity is decreased. The reduction in resistivity is attributed to the reduced rates of lattice vibrations resulting in increased drift velocity. For many materials, a plot of resistivity versus temperature as the material is cooled to very low temperatures reveals a linear relationship. Some materials, however, on approaching absolute zero (0.degree. K.), suddenly lose nearly all trace of electrical resistance. It is said that the materials have then entered the "superconducting state". The temperature at which, or the range of temperature within which this practically resistanceless condition is attained is called the material's "transition temperature(s)". Most metals which have been found to exhibit this behavior do so below 10.degree. K.; many of the alloys and metallic compounds do so below 20.degree. K.
Tin, for example, has been found to enter the superconducting state at 3.69.degree. K. Although a sudden drop in resistance is observed at that temperature, it is found that some ohmic resistance exists in the metal. By the use of equation (3), the thermal agitation velocity at 3.69.degree. K. is found to be ##EQU3##
Attempts have been made to completely eliminate the ohmic resistance in conductors, but at the lowest temperatures yet attained--about 10.sup.-8 .degree.K.--traces of electrical resistance can still be found. By the use of equation (3), the thermal agitation velocity at 10.sup.-8 .degree.K. is ##EQU4## Not until the absolute zero of temperature is attained, it is expected, will a completely resistanceless conductor be obtained.
The conducting behavior of a material below its transition temperature is described on the basis of the "two-fluid" model of superconductivity: one "fluid" consists of electrons in a normal conduction process expected at the particular ambient temperature of the conductor; the other consists of high speed electrons whose passage along the conductor is apparently unimpeded.
From the work of J. Bardeen, L. N. Cooper, and J. R. Schrieffer Physical Review, 108, 1175 (1957), the high speed electron flow component consists of paired electrons with oppositely directed spins. These pairs can pass along the conductor with velocities in excess of the thermal agitation velocity tending to disrupt their flow. It has been postulated that the fast electron component has a flow velocity of the order of 10.sup.7 cm/sec.
It appears reasonable to treat conduction electron flow as a fluid flow. Considering the conduction electron density of copper found in (6), the particle density is within range of particle densities in fluid media.
All fluids exhibit viscosity, or internal friction (resistance). Just as a coefficient of viscosity (fluid resistivity) can be determined for a material fluid, R. L. Carroll The Eternity Equation (1976) derived an expression for a coefficient of electronic viscosity (electrical resistivity). The form is ##EQU5## Where N=number of electrons paired with like spins per cm.sup.3
h=Planck's constant: 6.625.times.10.sup.-27 erg-sec.
.mu.=coefficient of electronic viscosity, spin/cm.sup.3
It can be deduced from (9) that if paired electrons with opposite spins can be formed, N can be reduced, and, subsequently, .mu.(electrical resistivity). The attractiveness of Carroll's development is that resistivity reduction is not temperature dependent: pairing of electrons with opposite spins should be possible at any temperature.
Carroll (ibid.) suggested that the desired pairing could be effected if electrons were forced into proximity upon entry into an extremely narrow conductor: said conductor would have to be of a material wherein electron flow velocities under normal conditions of conduction were quite high. If extremely narrow conductors could be created of such a material, the thermal agitation velocity at ambient temperatures would have little effect on the electron pairs. Carroll further expected that forced proximity would cause the electron to pair in an orientation of least potential; i.e., with spins annulling.
Since the attainment of superconductivity, or a close approximation to it, at normal temperatures is very desirable, laboratory investigations of Carroll's theories were performed. The material selected for the thin conductors were bismuth since the metal is known to contribute only one conduction electron per 10.sup.5 to 10.sup.6 atoms. This places a restricton on N in equation (9). The atomic density of bismuth is 2.82.times.10.sup.22 atoms/cm.sup.3. If the mid-range of conduction electron contribution is taken to be one per 5.times.10.sup.5 atoms, then the conduction electron density in bismuth is ##EQU6##
From equation (5), if one microampere (10.sup.-6 ampere) is passed along a bismuth conductor of cross-sectional area 10.sup.-10 cm.sup.2, the drift velocity is found to be ##EQU7##
Comparison of (11) with (4) reveals that the drift velocity in bismuth is quite high and that a thin wire of the order of 10.sup.-6 cm diameter or less can be expected to provide a drift velocity of the order of 10.sup.8 cm/sec, or higher; if a current flow velocity of this magnitude could be attained, a large fast-electron component should be attainable at normal temperatures.
The literature of solid state physics was found to contain a few references to resistivity anomalies discovered in thin bismuth wires of 10.sup.-4 cm diameter: Eucken and Forster, "Gottinger Nachrichten", Math. Phys. Klasse, Fachgruppe 2, 1, 43 (1934); and 10.sup.-5 cm diameter: Gurvitch, Journal of Low Temperature Physics, 38, 5/6, 777 (1980). Suppositions have been made to explain the anomalous behavior in these thin bismuth wires but there is no general acceptance of any one reason. If Carroll's spin interaction theory is applied to interpret the observed behavior: due to the high speed current flow in a contracted space, some electrons--by virtue of their proximity--are forced to pair in an orientation of least resistance; the increase in the number of pairs with annulled spins results in a decrease of resistivity. In view of the experimental evidence, it appeared that Carroll might be correct, and it was expected that significant resistivity anomalies would occur in bismuth wires of diameters less than 10.sup.-5 cm.
The thinnest bismuth wires that have been produced by mechanical techniques are claimed by Gurvitch (ibid). The employment of his techniques to form wires of 10.sup.-6 cm diameter, however, would require the application of approximately 22,000 pounds per square inch of pressure.
No practical procedure existed prior to this invention to form wires, or thin conducting filaments, with diameters less than 10.sup.-5 cm.
Filaments were formed with diameters within the range of 10-1000A; following their formation, tests were performed at room temperature by applying various magnitudes of low DC voltage across the ends of the filaments, and graphs were made of the recorded current flow through them and the effective resistance offered to current flow by them.
From equation (2), and taking the value of the resistivity of bismuth at 20.degree. C. given in the herein table of resistivities of various metals, the resistance expected from the filaments ranged from 10.sup.5 to 10.sup.6 ohms. In addition, extrapolation of well-known tables of maximum allowable current carrying capacities of conductors of various cross-section led to the expectation that current of the order of picoamperes (10.sup.-12 ampere) should be the maximum order of magnitude of current passed by the filaments. It was found, however, that the filaments were capable of passing much higher currents, and most electrical tests were performed by passing currents through each filament within a range of 100-500 milliamps. In some cases, as much as 2 amperes were passed through single filaments.
A typical graph of the increase in current flow with an increase in voltage for many of the samples is provided in FIG. 1. It is observed that at some threshold voltage, the current appears to increase without bound.
In many samples it was observed that, once the threshold voltage was attained, the current flow suddenly increased, as shown in FIG. 1, but the voltage drop across the filaments decreased as the current approached a maximum allowed by power supply. This behavior is illustrated in FIG. 2.
As the threshold voltage was attained, the increase in current flow toward the maximum was sudden. If 100 milliamps were passing through a filament just prior to reaching the threshold voltage, for example, current rose from that value to the maximum available from the power supply within a fraction of a second as the threshold voltage was reached.
If the graph is made of the apparent resistance offered to the current flow as said current is increased in most of the samples, it is seen that the resistance is decreased to near zero, as shown in FIG. 3.
For most samples, the threshold voltage was found to be between one and five volts. If a voltage exceeding the threshold was applied to the filaments, and if the power supply was capable of delivering high current, it was found that the filaments passed the permitted currents instantly and the voltage drops across the conductors instantly tended toward zero as illustrated in FIG. 4.
A few samples exhibited extremely low resistance during the testing. For them, it was found that the application of only a few millivolts was sufficient to render them to behave in a fashion illustrated in FIG. 1, except that the threshold voltage was much lower, as shown in FIG. 5.
Some samples exhibited no apparent resistance to current flow. The application of a voltmeter across the ends of these filaments as 500 milliamps was passed through them indicated zero voltage drop at an accuracy of 10.sup.-6 volt.
FIG. 6 illustrates the basic filament forming apparatus. A voltage is applied across the pin points 11 and 12, and as the filament material is introduced between the points, the intense electrical field forces particles of filament material to migrate between points. Sufficient current is passed through the aligned particles to cause them to fuse into a solid wire.
The attached leads and pins are of ohmic materials, so they will offer some resistance to current flow. Ohmmeter measurements made of the pins and connected leads yielded a total least resistance of one-tenth (0.1) ohm. Following the formation of the practically zero-resistance bismuth filaments, ohmmeter measurements yielded total resistance values of less than one-tenth ohm. When placed in test circuits, graphs made of the applied voltage to the recorded current passed by the filaments and their associated pins and leads resulted in the discovery that the effective resistance was of the order of one-hundreth (0.01) ohm.
If R.sub.o is the measured resistance of a filament and its attached leads and pins prior to its placement in a test circuit, a graph of resistance versus current yielded the typical behavior shown in FIG. 7 when the filament and its associated leads and pins were placed in test circuits.
The least resistance expected was that offered by the pins and the leads, but the discovery that the effective resistance was reduced by a factor of ten lead to the conclusion that the superconducting component was extracting energy from the conductor. The most obvious energy that could be extracted was thermal energy since its extraction would result in decreased resistance to current flow. If this were in fact occurring, it should be possible to detect a higher temperature at one pin than the other. Currents of up to two amperes were passed through the filaments and attached leads, and it was found that significant heat transfer did in fact occur. The hotter junction was found to be that of the electrode of positive potential. Considering that the electrons enter the filament at the point of negative potential and are accelerated upon entry into the filament toward the positive electrode, and considering that the electrons absorb thermal energy from the filament and negative electrode as they pass through them, the electrons' sudden entry into the ohmically resistive positive electrode and subsequent decelerations would cause them to radiate the thermal energy that they had absorbed from the filament and negative electrode. As the thermal energy is radiated into the positive electrode and dissipated into the ambient environment, the overall effect is that of cooling the conducting path to provide decreased resistance to current flow. This leads to the conclusion that if heat could be removed from the hot junction at a greater rate than is possible in a static air environment of 20.degree. C. temperature, the thermal agitation at the hot junction would be decreased to provide an even lower negative resistance effect.
The basic components of the filament forming apparatus are schematically presented in FIG. 8.
The component indicated at 14 represents a container within which filaments are formed; it may also represent a surface onto which filaments are formed. The container or substrate material should possess the properties of an electrical insulator for reasons hereinafter set forth.
A mixture of molten conductor, which can be rendered superconducting, or nearly so, at normal ambient temperatures, and insulator is introduced between the points 11 and 12 within or onto component 14.
An appropriate DC voltage from a source 15 is applied across electrodes 11' and 12' to create an electric field between points 11 and 12. Particles of conducting material align between these termination points 11 and 12 of electrodes 11' and 12' respectively due to the electric field existing between said termination points. The voltage is maintained across the electrode ends until such time as the entire, once-molten mixture becomes completely solidified. What results are thin conducting filaments formed within and supported by a completely solid insulator.
The function of ammeter 16 is to indicate when continuity is established in the filament forming circuit and to record the magnitude of current passing through the circuit. Resistor 17 is a current-limiting component which serves to restrict the magnitude of charge transfer along the newly forming filaments. The passage of between one and two milliamps through each filament has been found to result in the formation of excellent filaments; this suggestion, however, is not intended to exclude other possibilities. What is important is that sufficient current be passed along newly-forming filaments to cause them to become thin solid wires threading through a solid insulating and supporting material.
The terminals designated 18 and 19 are components by which voltage from source 20 is supplied to electrodes 11' and 12' respectively. If 11' and 12' represent single electrodes, terminals 18 and 19 would simply be the points to which leads of opposite potential from the basic electrical energy supply circuit--consisting of voltage source 20, a current-limiting resistor 17, an ammeter 16, and associated component connecting conductors--are attached.
If 11' and 12' represent a multiplicity of electrodes providing for the formation of numerous filaments between opposite electrode points simultaneously, then terminals 18 and 19 can represent conducting plates to which the electrodes are attached, or it can represent the point at which each electrode is connected to the energy supply. What is important for the formation of a multiplicity of filaments is to provide a potential at point or points 11 that is opposite to the potential at point or points 12. The creation of fields of sufficient intensity will result in the simultaneous formation of numerous filaments as the conductor particles migrate between electrode termination points.
Should it be desirable to form filaments of lengths beyond those that can be produced by the action of the electric field, or fields, alone, one electrode can be retracted with respect to another, or both can be retracted, under the continued application of voltage. It has been found that increase in filament length by a process of electrode retraction is a function of increased applied voltage. What is important is to maintain the continued migration of conductor particles as the distance of separation between electrode termination points 11 and 12 is increased.
The molten mixture of conductor and insulator is prepared by either of the following methods. The conductor can be melted within a molten insulator, such as amorphous glass, although this choice of insulator is not intended to exclude other insulator materials. A ten to fifteen percent by volume mixture of conductor to insulator has been found to be adequate for filament formation, although other ratios are not excluded. The introduction of the well-stirred, nearly homogeneous molten mixture between electrode points 11 and 12, across which voltage is applied, will result in the formation of thin filaments, as above described.
The mixture may also be prepared by heating a fine powder form of conductor material within a molten insulator to high temperatures until the particles have been reduced to the desired cross-sections. Certain epoxy resin melting compounds have been used as insulator material for this method with excellent results, although this suggestion is not meant to exclude the employment of other insulator materials. Introduction of this mixture between points 11 and 12 under applied voltage will also result in permanent solid filaments within a solid insulator.
The choice of conductor materials for the filaments is restricted to those materials that can be rendered superconducting, or nearly so, at normal ambient temperatures. It has been found that conducting materials that contribute very few electrons to the conduction process per unit volume, and that do not possess a resistivity to correspond to the low conduction electron contribution, are those that will exhibit superconducting behavior as current is passed along very thin filaments made of the materials. In bismuth, for example, the conduction electron contribution is of the order of one per hundred thousand atoms, yet the metal's resistivity at normal temperatures is about 10.sup.-4 ohm-cm. For comparison, copper contributes one conduction electron per atom, and its resistivity at normal temperatures is about 10.sup.-6 ohm-cm. The conduction electron contribution of bismuth is of the order of one-hundred-thousandths that of copper, yet bismuth's resistance to current flow is only one hundred times greater than that of copper's. Based on its conduction electron contribution, it would be reasonable to expect that bismuth ought to be of the order of 100,000 times more resistive than copper, but the fact that it is only 100 times more resistive than copper places it in the category of normal ambient temperature superconductive materials. If n is the ratio of conduction electrons contributed per quantity of atoms, an order of magnitude for bismuth yields ##EQU8## If n is multiplied by the material's resistivity, .rho., at normal ambient temperatures, we have an order of magnitude for bismuth of ##EQU9## It appears that the elements possessing desirable products are those designated the metalloids, although some alloys and metallic compounds can also be used as filament materials. The use of bismuth for the filament material is attractive due to its low melting point (271.3.degree. C.), its nonhazardous property, and its 31/3% expansion on solidification. Bismuth's expansion on cooling assures that the ends of the formed filaments will not become disengaged from the electrode termination points 11 and 12 of FIG. 8.
The following is an example of the method of producing one specific type of fiber which exhibits properties of electrical superconductivity at ambient room temperature.
An insulating material such as epoxy resin is heated to approximately 280.degree. Centigrade for at least fifteen minutes. Depending on the application and use of the product being formed, a hardening catalyst can be added at this time. Next a conducting material is added to the liquid insulator. When Bismuth is used as the conductor, this is added at 10 to 15 percent by volume to the insulator. The insulator and conductor are well mixed to an almost homogeneous solution and the mixture is then heated to a temperature of between 280.degree. and 310.degree. Centigrade for a period of from one to three hours. This heating reduces the size of the conductor particles to colloidal dimensions having diameters of less than 10,000 A.
Preferably a flat plate type electrode corresponding to 11 in FIG. 8 is provided within the insulator/conductor solution. Once this solution has been heated as described above, one or more pin type electrodes corresponding to 12 of FIG. 8 are placed in the solution near electrode 11 while a voltage of between 800 and 1100 volts at between 0.5 and 2 milliamps is being applied. When the electrodes approach to within 0.15 to 3 millimeters of each other, they will generate an intense field to cause the conductor material to align between such electrodes thus forming a filament. A voltmeter can be provided within the voltage circuit to tell when continuity is established which takes only a few seconds.
By the above process, the filaments formed are only between 1.5 and 3 millimeters in length. The voltage required to establish longer filaments very quickly becomes impractical as compared to the small increased length obtainable.
To overcome the above length limitation and to form filaments of lengths greater than that which can be produced by the electrical field alone, the electrodes are moved apart from each other in a linear motion. It has been determined that a rate of approximately 0.5 millimeter per minute allows filaments up to 1 centimeter to be produced while still maintaining applied voltage in the 800 to 1100 volt range.
Although filaments of up to 1 centimeter have been produced by the method hereinabove described, greater lengths can, of course, be produced with the real limiting factor being determined largely by the solidifying properties of the surrounding fluid insulator material.
The applied voltage is maintained throughout the forming period which, using epoxy resin, ordinarily ranges between 30 and 45 minutes. As indicated above, a harden catalyst can be used as determined appropriate although in many instances is not necessary because of the heat applied during the process.
Due to random distribution of impurities within the conductor powder, some filaments have been found not to initially exhibit the desired conductivity after formation. It has been determined that through the application of between 200 and 600 volts with a current of up to 100 milliamps across such filaments will order the lattice structure of the same and sufficiently decrease its resistivity to provide the desired conductivity approaching that of superconductivity.
It is obvious from the above that an advantage of the present invention is that the conducting behaviors which have until this invention been obtained only at extremes of low temperatures can now be obtained at normal temperatures. A further advantage is the elimination of the need of expensive and high-energy consuming refrigeration devices to obtain low resistive high velocity electron flows. Since power dissipation by electrical conductors is the product of current squared and resistance (I.sup.2 R), a still further advantage is to provide for large charge transfer with low power dissipation. An even further advantage is to provide means by which changes in electron flow velocities can be effected at normal temperatures to transfer heat.
The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.
Figure 1:Figure 2:
Ambient Temperature Superconducting Filaments
by Ron Bourgoin
Proceedings of the Second International Symposium on Non-Conventional Energy Technology (1983)
What I should like to do is to review with you the field of superconductivity. As you know, superconductivity at this time is a phenomenon that is found to occur at the extremes of low temperature. For those of you who are comfortable with the Fahrenheit scale, we are talking about electrical behavior which occurs at around 400 degrees below zero on the Fahrenheit scale. We're talking about 0 degrees, or something close to 0 Kelvin, or about minus 273 Celsius.
Kammerlingh Onnes is attributed with the discovery of superconductivity in 1911. Now there were a few things that occurred prior to this discovery. In 1908, Kammerlingh Onnes was the first, as far as I have been able to determine, to liquefy helium. In 1908! And he was able thereby to obtain temperatures near 1 degree Kelvin, which had never been attained before.
Of course, there was considerable theory at the time of how metals might behave as the ambient thermal environment was reduced, and so his first work, as far as I am able to determine, was with platinum. He took platinum, cooled it down to his new found temperature, and found, essentially, a linear decrease in resistivity with reduction in temperature. When he made tests specifically with pure platinum and impure platinum, he found that the resistivity reduction was a function of purity of material.
Now, the point that I want to emphasize is this; the reduction in resistivity with temperature was no surprise. That had been expected. The near-zero resistance which was measured at these extremes of low temperature was low because he was already close to zero resistance anyway. So there was not a significant finding in that particular case.
Now when he used mercury, he wanted to use a material with extremely high purity, and mercury, at the time, was the metal known with the highest purity. He cooled it down and he found the resistivity reduction essentially as he had found in the platinum, except that when he got down to about 40 Kelvin, he got a little surprise. The material dropped abruptly in resistance to measurably zero value. (I emphasize the measurably zero value because what it actually is we really don't know, but measurably it has a zero value.) He conducted some tests with impure mercury and found exactly the same behavior.
That's quite an important point. In the case of platinum, he found that resistivity reduction was a function of temperature; in the case of mercury he found that it really didn't matter whether the material was pure or impure - it dropped in resistivity exactly the same way. So it didn't appear to matter to the mercury whether it was pure or impure.
You're already close to zero anyway when you get down to these extremes of low temperature, so I have often questioned the gain [of the measuring instruments - ed.) measuring the drop in resistance to a measurably zero value, especially when you consider the expense of cooling the materials to that degree of temperature.
Let's have a general review of the types of superconductors that are presently in existence. One is the Type One superconductor, which is essentially a metallic superconductor. Those materials have been found to enter the superconducting state at temperatures typically below 10 degrees Kelvin. We find that the superconductivity is a surface effect. The current wants to travel on the surface. The electron drift velocities have been determined to be something of the order of 10 to the 5th cm/sec. The thickness of the conducting sheath has been found to be something of the order of 10 to the -5th cm.
At one time it was thought that if you took a highly pure crystalline solid and, as you attained the absolute zero of temperature, the thermal vibrations would reduce in such a way that the mean free pass of the conduction electrons would be practically infinite, and so it was thought, you see, that the metal would provide almost perfect conductivity through the material - through the crystalline solid.
However, this is not what occurs. It you take a pure metal of the highest purity you can obtain, ninety nine point nine nine out to the tenth decimal place somewhere, you find that the superconduction, that is this almost perfect conductivity, does not occur through the material.
And yet the thermal vibrations at something of the order of a few degrees Kelvin is supposed to be significantly reduced, but when you crank the values of temperature through the equation, you find that the thermal agitation of electrons in the conduction band is still something of the order of 10 to the 6th cm/sec. Now, you see, you've got a surface velocity of 10 to the 5th.
So, apparently, you have a higher agitation in the structure, and that might be one of the reasons why the electrons are forced to the surface. As far as the theory was concerned at the time, what I want to emphasize is that a pure crystalline structure was expected to provide near infinite or near perfect conductivity at near absolute zero temperatures, which we have not found.
Another type of superconductor is called Type Two superconductor. Type Two superconductors are essentially alloys and metallic compounds. Can you think of any conducting structure less ordered than an alloy or metallic compound?
These materials have been found to enter the superconducting state at as high as 23 degrees Kelvin. In these highly disordered structures we find that the superconductivity is through the material, and when we examine what's going on we find that there are naturally forming thin current filaments is something of the order of 10 to the -6ths cm. This is all in the literature. It also has been determined that the superconduction speed is of the order of 10 to the 6th cm/sec.
So, the highly disordered structures that were supposed to provide all of this resistance, these imperfect structures which were supposed to contain all sorts of defects and impurities were never expected to provide the superconductivity that they do, yet we find that they superconduct at higher temperatures than the metals, and that the conducting speed of the superconduction current is increased by a factor of at least 10 times.
So you see that, when I saw all of that coming out in the literature years ago, I began to question. What is resistance? Wouldn't you? You're told for years and years and years that resistance is a function of thermal agitation of metal ions in the lattice. Resistance is a function of collisions of conduction electrons between each other.
Resistance is a function of crystal defects. I could go on and on, but you know this as well as I. And yet we find that when we cool the imperfect materials down to as high as 23 degrees Kelvin, resistance goes to zero, or measurably so. So what happened to all of this resistance that's supposed to be provided by the defects in the structure, and the impurities, and the thermal vibration?
Because, as I told you a while ago, the thermal agitation velocities occurring in the conduction band in the metals near 1 degree Kelvin or below is found to be something of the order of 10 to the 6th cm/sec. What I didn't tell you is that, at room temperature those vibrations are of something of the order of 10 to the 7th. So we find a reduction in thermal agitation velocity of only a factor of 10. And yet we get all of this high conductivity in the alloys.
Apparently, you see, when the material enters the superconducting stage the defects don't evaporate, the impurities don't evaporate, everything is still right there. They have found no changes whatsoever in the structure of the material. So what caused the resistance in the first place? You say, 'Well, the thermal agitation in the structure has reduced significantly.'
Really? You call reduction by a factor of 10 significant? You're going from 10,000,000 cm/sec thermal agitation in the conduction band down to 1,000,000 - that's a significant reduction?
So what's happened? Well, it appears the key to a high temperature superconductor might be in that thin filament existing in the Type Two superconductor. We'll explore that a little bit later.
Let's talk about some of the general properties of superconductors. This is very important. The first general property is extremely high current, something of the order of 10 to the 5th amps per cm squared. 10 to the 6th amps per cm squared is no surprise. As a matter of fact, they get up much higher than that, but you're talking about current densities that are truly anomalous.
The superconductors have extremely long electron mean free path, which means they can go for a long, long way without colliding into anything, whatever that means. I never have understood how twolike charged particles like electrons could collide anyway, but it's in the literature, and those of you who have read the textbooks on electrical theory know it's there. You've seen the word 'collision' all over the place, and yet you know that chance collisions can't possibly happen.
The electrons have high electron drift. Obviously we're talking about something to the order of 10 to the 5th cm/sec in a Type One and 10 to the 6th cm/sec in a Type Two. When you calculate the electron drift velocity in a copper wire, say 20 gauge, at room temperature, you find something of the order of 1/100th of a cm/sec. Even that's pretty liberal; I think it's quite less than that, depending on how much current we're passing through, of course. So you can see a significant increase in order of magnitude.
Next point is the generation of extremely high magnetic fields - in the Type One material, something of the order of 600 gauss; in the Type Two material, something of the order of 200,000 gauss. That's in the literature, Niobium-Tin, for instance, has a field of 200,000 gauss.
The next point is extremely enhanced diamagnetism, and we've heard diamagnetism mentioned frequently here. What is it? You approach a diamagnetic material with a magnet, it has a tendency to run away from you. So, extremely high diamagnetism. It repels any incoming magnetic field.
The next point is extremely poor thermal conductivity.
The next point is that if you make thin film 'chips' with this material, you find that when they enter the superconducting state, they do so at a particular temperature and they measure certain current magnitude and they also measure certain magnitude of magnetic field. Then, as you probably know, if you increase the current to a value that is called the 'critical current', then you lose the superconductivity, or, if you apply a magnetic field in excess of its particular value, you find that you lose the superconductivity. But they have found - the sides (tapered edges - ed.) of the chip continue superconducting.
The fields required to lose the superconductivity in the edges are significantly higher than in the rest of the chip. The current drift along the edges is much higher than it is in the remainder of the chip. But you know what they do; they feel that the sides are causing them all kinds of difficulty, so what they do is they clip them off.
That is a fact. Because, you see, those darn sides are causing them to get erroneous measurements. The blasted things just won't go out of superconductivity. It just destroys the magnetic effects on the chip so when they want to force re-entry of the chip into the normal conducting state, they have to cut the things off.
What they ought to do is keep the edges and throw the rest away.
What I want to discuss, basically, is a field called 'superfluidity.' I'm not going to go over all the details of superfluidity, except to say this. When you take helium and you cool it and you get down to about 4 degrees Kelvin, about 4.2 degrees, to be exact, it enters the liquid state, which is no surprise.
But then, if you keep cooling and cooling and cooling, you get to a point at 2.17 degrees Kelvin where you have a completely inviscid fluid. Zero viscosity.
That means that it has no internal friction and, once you get it going, it won't stop. They have passed liquid helium through extremely fine apertures, something of the order of a few Angstroms diameter. A few Angstroms - an atomic diameter is an Angstrom or a couple of Angstroms, or three, or something like that, and we're talking about a capillary of five to ten Angstroms through which you are passing liquid helium!
And you measure no reduction in pressure from the point of input to the point of output. No loss in pressure. What does that mean? That means that there was no friction between the capillary walls and the liquid. There was also no viscosity - no internal friction in the liquid. There was nothing to slow it down. No dissipation of energy whatsoever.
They have determined that the superfluid state is due to the pairing of helium atoms in an orientation of antiparallel spin. What that means, basically, is that one rotates clockwise, adjacent to another that is rotating counterclockwise.
Now, if you look at Bernoullis' theorem, what does he say ought to happen when you have parallel flow lines? Think of two ships out at sea that get too close to each other. You get parallel flow lines. What happens to the water in between? Parallel flow lines, in essence in an antiparallel configuration. What happens? You get attraction. Those of you who have ever sailed know exactly what I'm talking about.
Now, these gentlemen here, Tilly and Tilly, have written a wonderful textbook called 'Superfluidity and Superconductivity', and they have found some interesting parallels between electrical superconductivity and the field of superfluidity. What they're talking about is essentially this: Isn't it interesting that in the field of superconductivity three men, Bardeen, Shriefer and Cooper, in 1957 generated an acceptable theory for a phenomenon that was discovered in 1911, and, I believe, were awarded the Nobel Prize in 1972.
What did they find? They found that the basic superconducting unit is antiparallel spinning electron pairs. So these gentlemen here, you see, said, 'Look! You've got antiparallel spins leading to attraction of conduction electrons. You have essentially the same kind of thing happening at extremes of low temperature in liquid helium.'
And so what they have done is to apply equations from superconductivity to superfluids, and some of the predictions they were able to make are wonderful. That is about a 250 page to 300 page book, and it's absolutely delightful for those of you who might be interested.
I'm just giving you a background now, some of the things that I was seeing over the years, which eventually led to the research that I performed.
In the fields of whiskers and filaments, Howard L. Cobb, in 1946, reported finding some whiskers growing off of capacitors that were able to short out radio units. Sydney Arnold, at Bell Laboratories, in 1956, was talking about 'tin whiskers' that were able to short out large capacitors.
He conducted resistance measurements and found drops in resistance, very anomalous drops in resistance from what is expected from the standard law of resistivity. And he made this statement: 'The current magnitudes exceeded those expected by a factor of 100.'
Those of you in the electrical and electronics fields know that we try not to pass any more than 100 amps/cm squared through a wire. You just don't pass more than that; otherwise it's going to evaporate. Arnold found 200,000 amps/cm squared. And that was found about 1951 and the man, I'm sure, had to think a long time before he published his results. But he published them in 1956.
There was a book by Bogenschultz in 1974 that talked about all of the problems that were being provided by metallic whiskers and thin filaments. These things were just shorting everything out. Well, why didn't somebody look at those fibers at the time and say, 'Might it be that we have something that' trying to superconduct at normal ambient temperatures and higher temperatures?' - because these capacitors are at quite high temperatures, as you know.
What they should have done is stopped all of this work that was going on at the extremes of low temperatures and the helium refrigeration devices and so on and so forth, and gone to work on these thin whiskers and filaments. Stanford R. Ovshinsky, in 1966, received a United States patent for a symmetrical current controlling device and what the man found was this; he was able to make a chip which offered resistance in the several millions of Ohms.
When he got to a certain threshold voltage, he found that the resistance went down to something far less than one Ohm, and the only way that he could explain what was going on was to hypothesize the creation of very thin current filaments inside his chip. The drop in resistance from several million Ohms down to less than one occurred instantaneously and there was no excessive generation of heat in te devices. So much for i square r heating.
Article by Marcus and Rottersmann in 1967. They found that in making chips they were making thin stripe conductors going all over the chip - and they were being shorted out. They examined the situation and found extremely thin filaments that had grown inside the thin film conductors themselves.
Now, those thin film conductors were something of the order of 200 to 1,000 Angstroms in diameter. If there were thin filaments forming inside that, how big were they? They had to be significantly less than 1,000 Angstroms in diameter. That's in the literature. A.K. Jonscher, in 1969, found thin filaments in glassy insulator substrate material. It seems that nature is going to find a path of least resistance whether we provide it or not.
D.E. Thomson in 1980, in 'Science News,' reported work with Saran wrap. Those of you who have ever seen Saran wrap under an electron microscope know that there are fibrils going all over the place. If you put an Ohmmeter across the thing, you'll measure several millions of Ohms. But take it and stretch it; align those fibrils inside the material and you find that the resistance drops down by several orders of magnitude, like 10 to the 5th or 10 to the 6th, resistance drops by a factor of about 1,000,000. What's the size of them? Roughly 500 Angstroms in diameter.
IBM at the present time is doing some work on nanobridges, extremely fine line conductors on chips. These things are about 20 to 200 Angstroms in cross-sectional diameter. That is one particular method at this time of making very thin film strips. Bell Labs is presently working with quantum well wires. It's a rectangular thin film conductor that has a thickness of 200 Angstroms and a width of about 200 Angstroms. The length is as long as you want to make it. M.I.T. is making what it calls 'narrow lines'. All of these people are making narrow lines of essentially the same dimensions. My question is why are they making them but they are not reporting resistance?
My method of making thin filaments is to prepare a chemical colloidal suspension. I take extremely fine metallic particulates and I suspend them in high dielectric mediums such as an epoxy resin.
I heat the mixture to the melting point of the metal, which in the case of bismuth is something of the order of 271 degrees Kelvin. The only reason for doing that is to bring the particle into the molten or semi-molten state.
Then you apply the voltage, which in some cases can be several thousand volts, wait awhile, and you'll get conductivity in just a matter of a minute or so.
Then you retract one set of electrodes as far as you want to go. If you'll take cross sections of your mixture, you'll find little thin fibers going all over the place.
It's a very easy way to make filaments. As far as controlling the diameters and the lengths, I'm still working on that. I'm trying to get into the Ph.D. program in Materials Science at North Carolina State University, and hope that if I'm invited back next year that I will have some good reports for you. But this is presently what I'm doing.
I do have a United States patent for the process. What it's doing at the present time is nothing, but there is a publication next month, the Bismuth Institute, which is headquartered in La Paz, Bolivia, has gotten very interested in my findings, and has decided to publish a very long abstract of the patent. The publication center for the Bismuth Institute is in Brussells, Belgium.
There are several theories of high temperature superconductivity. The Soviet theories say this: That if you make an extremely thin filament process, or film, and you encapsulate it by a polarizable medium, then the high current flow, assuming there will be one through the thin filament process, will induce positive charges all over the surface of the thin filament. And that extremely high positive fields will serve to reduce the repulsive effect between electrons, and let those natural spin forces take over. And they must be extremely short range. They are saying basically that you create a positive, attractive field for the electrons. So you can get pairing that way.
Another theory, as expressed by my old professor, Dr. Robert Carroll, says that if you take a thin film of material that normally contributes very few electrons to the conduction process, and yet presently contains high drift velocities, you ought to be able to confine the electrons into an extremely thin channel and force them to pair thereby. Just upon entry to an extremely thin channel.
And so, what I started doing was to look around for materials. All this seemed very exciting to me. It seemed there was a lot of theory saying that these things outght to superconduct at normal ambient temperatures. And also the findings with the edges on thin films and with the whiskers. If I could speak with Mr. Arnold of Bell Laboratories, I would ask him this: 'How come that first whisker that made contact with the ground did not evaporate?'
This man was talking about capacitors in the order of a hundred microfarad. What about the instantaneous current drain through the whisker? It must have been truly enormous. So you see, you look at all those things and then a picture begins emerging, and that is that if you can make extremely thin conductive filaments, they ought to superconduct, or you ought to see something akin to superconductivity at normal ambient temperatures, and possibly higher temperatures.
This is what I did. I started looking at bismuth, which has a resistivity that is about 100,000 tiems less than what it should be according to its conduction electron density. The resistance is high, but not as high as it ought to be..
Also, the electron mean free path, that is, the distance between collisions, to use the present vocabulary, is extremely long, so you have extremely long mean free paths in the bismuth. This is in bulk, at normal ambient temperatures.
Bismuth is the most diamagnetic of all of the metals. If you don't believe it, approach it with a magnet and see what happens, I did that on purpose. I made extremely thin filaments that I could see, put them on a tabletop, approached them with a magnet - and off the tabletop they went, instantaneously.
If that's not diamagnetism, I don't know what is. Also, bismuth, in the bulk form, has the next to the lowest thermal conductivity of all the metals.. And also, another of the things that I liked about bismuth is that it has extremely low wear resistance, or a very low coefficient of friction.
Remember the first list I gave you and compare it with what I've just given you. So then I thought that if I could make bismuth filaments down to a couple of hundred Angstroms in diameter, I ought to be able to observe superconductivity behavior at ambient temperatures. All of the details are in the patent.
I worked and I worked and I worked and I was down to a micron diameter of fibers. I noticed that I needed a certain voltage, and then suddenly, I got very rapid oscillations all over the place, tremendous instability, and then I would increase the current just by a little bit, and the needles would just go out of sight.
The voltage went down to practically zero, as far as I could measure; the current tended to rise to infinity. Now, I didn't like the idea of having a voltage drop - they tell you, you're not supposed to have a voltage drop in a superconductor. So I worked to eliminate the voltage drop.
So I learned to prepare a colloidal suspension having smaller particulates suspended, and worked at that and, my wife can tell you, I will never forget the day that this happened - I succeeded in making the suspension; I went ahead and formed the fibers as I had normally done; I took resistance measurements at the end of the trials, and they measured ZERO RESISTANCE.
That was one of the happiest days. I immediately ran out of that laboratory, took my wife out and we had some wonderful wine and a wonderful meal, and just had a great time. I have made hundreds of these, and I can tell you that it works as I say it does. I have not measured resistance. I am not exactly certain what's going on, and that's why I'm going on into this program and hopefully doing some additional work.
As far as the magnetic field is concerned, I don't need to get into details. You can surmise what they would be as well as I can. Potential applications include the obvious computer applications. One application which might not be so obvious is the possibility of developing a synthetic spinal cord bridge. That excites me more than anything. If we are able to find a way to make something that will not generate resistance and i square r heating in the body, insert a material that would be accepted by the body (and, by the way, bismuth is very nice) and bridge gaps in the spinal cord where fibers have not regenerated, wouldn't that be wonderful?
We've got a lot of work to do. There's a possibility of very thin microelectrodes for single neuron studies, which they desperately need. You have a zero resistance electrode - think of the activity that you could measure in the individual neurons. The extended lengths of fibers - think of the possibility of low loss cables. Think of the possibilities of the generation of high magnetic fields, without auxiliary refrigeration mechanisms. Think about windings for motors and generators. And I could go on and on, but I've got to quit at some point. Thank you all very much.
Question: In one of your comments you were surprised that the voltage dropped to zero. Why did you not want this? And second question, can you comment on 'frozen-in' fields in superconductors?
Answer: Are you talking about the so-called 'fluxoids'?
Questioners Answer: Yes.
Continued first answer: Regarding the first question - I wanted a voltage drop to zero. If I said that, I certainly didn't mean it. When I found initially a voltage drop I didn't want it because I knew that in order for a material to be superconducting, it would have to provide no potential drop. Regarding the second question, in superconductors you can have a persistent field which stays there and 'locks' the superconducting filament in place. In my case, we are talking about a single one of those filaments. So we are not talking about exactly the same thing.
http://www.nikkeibp.asiabiztech.com/wcs/frm/leaf?CID=onair/asabt/moren/158444
December 5, 2001 (BEIJING) -- China's first bismuth high-temperature superconductor wire production line has been put into operation in Beijing.
Innova Superconductor Technology Co. is China's first full-scale production company for the development and manufacture of HTS wire.
At the trial production phase, the company already has manufactured dozens of thousand-meter long high temperature wires. The newly installed production line can produce more than 200 kilometers of wire per year, and the company plans to set up a production base for manufacturing 1,000km of wire.
The production of superconductor wire helps China's superconductor development with its own intellectual property rights.
The superconductor industry also has great significance in the national economy and China's defense construction.
Superconductor material is expected to lead a new revolution in the electrical industry.
High-temperature superconductor material refers to that at liquid nitrogen temperature or at 196 degrees centigrade below zero with its electric resistance close to zero.
It has been widely used in the new generation of superconductor transformers, superconductor cables, superconductor machinery, superconductor magnetic trains and other products.
According to the World Bank's estimates, related HTS products will occupy US$100 billion worth of market share by 2010, while the needs for high-temperature superconductor wire, as the key material for superconductor technology research and applications, will reach 10,000km within one or two years.
Among the U.S. Energy Department's seven key superconductor technologies, six will use bismuth HTS wire.
(Xinhua News Agency)
