Patent Application
20090134039
1. Field of the Invention
This invention relates to chemical reactions. In particular, the invention relates to the use of isotope effects to provide selectivity in chemical reactions.
2. Description of Related Art
The transport and reaction of chemical species may be influenced by isotope effects. For example, the classical mass isotope effect (CIE) provides the basis for uranium enrichment by diffusion and by centrifuge. Similarly, isotope effects may be found in electrochemical processes (e.g., the tritium effect), and in photochemical processes (e.g., photoexcitation/photodissociation). The magnetic isotope effect (MIE) may be used to alter the reaction pathways available to chemical reactants, as demonstrated in the photolysis of dibenzyl ketone.
Although there are a variety of isotope effects that may be harnessed for isotope enrichment and isotope selective reactions, the prior art methods for isotope separation and isotope selective chemical reactions have generally relied upon chemically stable species and focused on the use of a single isotope effect. For example, uranium hexafluoride has been the mainstay for the diffusion and centrifuge uranium enrichment techniques.
There are many chemical reactant combinations that may used to provide isotope selective chemical reactions; however, many of these reactions cannot be used in conventional separation processes due to long process timescales. Transport distances on the order of meters and process durations on the order of minutes make it difficult to make use of unstable intermediate complexes or recover unstable products. For example, many photolytic and photoexcitation processes can provide considerable initial differentiation between isotopologues in a gas or liquid, but the differentiation may be quickly lost through environmental interaction (e.g., exchange with neighboring species) or photoemission (e.g., fluorescence).
Conventional isotope separation processes that are based upon the difference in mass transport of isotopologues (e.g., diffusion and centrifuge) typically have a path length scale on the order of a meter or more, and thus have a relatively large minimum size for a functional unit. For many applications it would be desirable to have a small low-cost functional unit that could be used in a scalable array.
The differences in spin behavior between magnetic and nonmagnetic nuclei provides a basis for isotope separation and selective chemical reactions. For example, the behavior of a radical pair may be controlled by selective spin conversion and spin locking (e.g., manipulation of the Zeeman and hyperfine interactions by applied DC and RF magnetic fields). Microwave pumping has typically been done using microwave tubes as sources and beaming the microwave energy into the working material through waveguides. The combination of a tube and waveguide has the disadvantage of low efficiency, particularly if the dimensions of a working cell are below the cutoff frequency of the waveguide. The prior art of spin conversion does not provide efficient means for producing RF magnetic fields in highly localized regions.
Thus, there is a need for an isotope selective chemical reactor that uses a combination of isotope effects. There is also a need for a small chemical reactor that can take advantage of short-lived intermediates and products. It is also desirable that a small chemical reactor serve as the basic unit for a scalable array.
Accordingly, a system for isotope selective chemical reactions is described herein. Two or more isotope effects are combined within a reaction cell to produce transient differentiation of isotopologues through excitation or chemical reaction followed by rapid separation or conversion.
In an embodiment of the present invention, a current conductor adjacent to a fluid carries an excitation current produced by a switching source. The excitation current produces an alternating magnetic field adjacent to the conductor that interacts with a population of isotopologues within the adjacent layer to produce a population of reaction intermediates or products that have an isotopic composition different from the initial isotopologues.
In a further embodiment, an electrolytic power supply is also connected to the conductor and provides a voltage that may be used to selectively attract and electrolyze a portion of the reaction intermediates or products within an adjacent fluid electrolyte layer.
In another embodiment, the adjacent layer is subjected to electromagnetic radiation to provide excitation or dissociation. The electromagnetic radiation my be tuned for selective absorption by a particular isotopologue, or it may be from broadband source.
In an alternative embodiment the system is coupled to the input of a centrifuge or other mass separation device. The application of electromagnetic radiation and/or magnetic fields to a gas flowing through the reactor provides for a transient enhancement of the mass difference between chemical species bearing two distinct isotopes. The transient enhancement of the mass difference has a lifetime that may be greater than the time required for passage through the mass separation device.
The waveform generator 115 is coupled to a driver 120 by a signal bus 112. The bus 112 may couple two nodes and carry a single waveform as the output of the waveform generator 115, or it may carry a number of distinct signals between more than two nodes. In a preferred embodiment the driver 120 is driven by an input signal in the range of 1-10 volts and has output rise and fall times of less than 50 nanoseconds. The driver 120 is coupled to the control module 110 by a bus 125 that allows the control module 110 to monitor the driver output and/or control the supply voltage for the driver 120.
The driver 120 is coupled to a redox power module 130 that is essentially a switched current supply that provides current to an electrode assembly 140 via a transmission line 135. The power module may include N-channel and/or P-channel MOSFETs (metal-oxide semiconductor field-effect transistors). In a preferred embodiment the power module includes multiple selectively switched MOSFETs coupled to three or more supply voltages. The power module 130 is coupled to the control module 110 by bus 125, allowing for control of the supply voltages to the MOSFETs. A bus 127 may be used to provide feedback to the control module 110 from the electrode assembly 140.
In addition to MOSFETs, JFETs (junction field effect transistors), BJTs (bipolar junction transistors), and IGBTs (insulated-gate bipolar transistors) may be used as switches in the power module 130. Generally, the turn-off speed of silicon BJTs and IGBTs is inferior to that of silicon MOSFETs. However, BJTs using materials such as gallium arsenide and indium phosphide and employing heterojunction structures can provide considerable improvements over silicon BJTs. JFETs may be preferred for low voltage applications.
The transmission line 135 is preferably a coaxial transmission line or a parallel plate transmission line, or may be a combination of the two. In a preferred embodiment, the gap between conductors in the transmission line is substantially filled with a solid dielectric. It is desirable that the two conductors be restrained from moving under the influence of the magnetic fields generated by the current flowing through them. If the two conductors are able to respond to the magnetic fields that are generated, they may act as an electromechanical transducer that presents a variable load to the power module 130, thus altering the waveform at the electrode surface. For coaxial conductors, a displacement of the axis of the center conductor with respect to the axis of the outer conductor does not affect the DC inductance; however, it can affect the inductance at high frequencies.
For purposes of this disclosure, a statically configured transmission line is defined as a restrained pair of conductors configured as a transmission line with a sufficiently small spacing between them such that if they were not restrained, one or both conductors would experience a displacement as a result of the electromagnetic force generated by an operational current flowing through the pair of conductors. Operational current is defined as a current that would flow through the conductors during normal operation.
The electrode assembly 140 is preferably a transmission line structure, with the anode and cathode serving as the two conductors in the transmission line in contact with electrolyte 145. In one embodiment, the gap between the anode and cathode is substantially filled with a solid dielectric. In another embodiment, the gap between the anode and cathode is substantially filled with electrolyte 345. Frequent reference will be made in this specification to an “electrode assembly” or an “anode/cathode assembly” with two electrodes. Unless specifically stated otherwise, either of the two electrodes may serve as anode or cathode, with a reference to one designation implying the substitution of the other as an alternative embodiment.
For purposes of this disclosure, an “electrode” is a conductor that is intended to be used in contact with an electrolyte, and may be either an anode or a cathode. A “bus” is a conductor that may be used to couple an electrode to a power source or signal source, but is itself not intended to be used in contact with an electrolyte. A “transmission line” may refer to either a parallel plate transmission line or a coaxial transmission line.
For purposes of this disclosure, in reference to a parallel plate transmission line, a preferred but not exclusive embodiment thereof is a pair of substantially flat rectangular conductors that have a spacing s and a width w such that the inductance per unit length L in Henries/meter is approximated by the equation:
In general, there are a number of spatial arrangements of conductors that can be used for transmission lines, such as parallel wires, parallel plates, and coaxial conductors. For purposes of this disclosure, in reference to a transmission line, a preferred but not exclusive embodiment thereof includes a spatial arrangement of conductors that is mechanically fixed to maintain the spatial arrangement under load.
Electrolyte 145 may be an aqueous or nonaqueous solvent containing dissolved ions. A nonaqueous solvent may be an aprotic solvent. The electrolyte 145 may include one or more molten salts such as an alkali metal fluoride or chloride. Electrolyte 145 may also include an ionic material that is a liquid at room temperature. In contrast to electrochemical energy storage devices, which may have closely spaced planar electrodes, the volume of electrolyte 145 in contact with the electrode assembly 140 is typically larger than the volume between the electrodes. An electrolytic cell that is used for a manufacturing process requires access to reactant species to replace those converted to product species.
Electrolyte 145 may contain isotopically enhanced reactant species. For example, an aqueous electrolyte may use heavy water (D2O) or an organic acid may include 13C at a concentration that is above that found in nature. The selection of electrolyte species enhanced with magnetic or nonmagnetic isotopes provides for additional control of reactions in the interphase through spin locking or spin conversion.
For purposes of this disclosure, the term “accessible electrolyte volume” refers to the volume of electrolyte in an electrolytic cell that is in electrical contact with the anode and cathode. In a preferred embodiment for parallel plate or coaxial transmission line electrode assemblies, the accessible electrolyte volume is at least ten times greater than the volume swept out by the projection of one electrode onto the other.
A sensor 150 is in contact with the electrolyte 145 and coupled to the Control Module 110 by bus 126. Sensor 150 may be a reference electrode, temperature sensor or resistance measurement cell. Sensor 150 provides information feedback for process control by the Control Module 110. Sensor 150 may provide information concurrent with the output of power module 130, or the output of power Module 130 may be suspended while Sensor 150 is operational.
A high frequency current source 155 is coupled to the transmission line 135 and is also coupled to the control module 110 by a bus 128. The high frequency current source produces a magnetic field that permeates a portion of the electrolyte 145 and thus may be used to alter the spin evolution of species within the electrolyte 145. The current from the high frequency current source may flow in one or both electrodes of the electrode assembly 140.
In an embodiment the control module 110 is used to control an array of electrode assemblies 140 with each electrode assembly coupled to a dedicated high frequency current source 155. Each electrode assembly may also be coupled to a dedicated redox power module 130. The array of electrode assemblies 140 may be integrated on a single substrate (e.g., silicon). For spin locking or spin conversion of reactant species, the high frequency current source may operate at microwave frequencies (e.g., >1 GHz). In order to minimize losses and reduce switching transients, an array of individually driven small area electrode assemblies (e.g., <1 cm2) is preferred.
The delay module 122 provides a tunable delay1 between driver1 and switch1 and a tunable delay2 between driver2 and switch2. For switches with logic level inputs (e.g., logic level input MOSFETs) a monostable multivibrator such as the 74VHC221A device manufactured by the Fairchild Semiconductor Corporation may be used. For switches requiring a high drive voltage, the MM74C221 monostable multivibrator from the Fairchild Semiconductor Corporation may be used. The delay may be tuned once during manufacturing, or it may be tuned periodically during operation. For operational tuning, a digital potentiometer such as the AD5222 manufactured by Analog Devices, Inc. may be used to set the RC time constant for a monostable multivibrator.
Delay1 and/or delay2 may be adjusted to minimize the distortion in the output waveform. Although only two driver/delay/switch combinations are shown, several may be used in an electrolytic cell interphase control system. In general, the greater the number of switches (e.g., transistors) configured in parallel, the greater the benefit of tunable delays. In a preferred embodiment the output rise and fall times of the power module 130a are less than 100 nanoseconds.
Electrodes 325 and 315 are separated by a dielectric 320. The dielectric 320. Copper is a preferred material for electrodes 325, which may be coated with other metals (e.g., platinum) to provide a working surface with different properties. If a high permeability material such as nickel is used as a coating, it is desirable that the coating be kept thin to avoid an undue increase in inductance. The dielectric 320 may be a ceramic, a polymer, or a composite material. It may also be a sheet form that is bonded to electrodes 325 and 315. Alternatively, it may be a dielectric adhesive that is applied to electrode 325 and/or electrode 315.
Switched coaxial transmission line 445 is similar to switched coaxial transmission line 205 shown in
A first dielectric wall 625 and a second dielectric wall are sandwiched between the anode wall 615 and the cathode wall 630, and their height determine the height of the duct channel 635. Dielectric wall 625 and 630 are preferably fabricated from a dielectric material that is inert with respect to the electrolyte contemplated for use. For very short walls, a stiff, creep resistant material such as silica, alumina, beryllia, or other ceramic is preferred to maintain dimensional stability. Non-oxide ceramics such as silicon nitride, boron nitride, silicon nitride, and aluminum nitride may be used. The dielectric and conductive structures may also be integrated on a semiconductor substrate.
Top backup plate 605 and bottom backup plate 610 are not required, but are preferred when the anode wall 615 and cathode wall 620 are thin and additional mechanical support is desired. The anode wall 610 and the cathode wall 615 may be fabricated on the top backup plate 605 and the bottom backup plate 610, respectively, using thin-film or thick film techniques such as those used for fabricating electronic circuits on ceramic or semiconductor substrates. Patterning may be done using photolithographic techniques. Single crystal and polycrystalline ceramic materials may be lapped and polished to provide backup plates with high dimensional accuracy. Thin gold metallization may be applied along with appropriate adhesion layers to provide diffusion bondable surfaces. Opaque and/or transparent ceramic materials may be used for backup plate 605 and/or backup plate 610.
The anode wall 610 and/or the cathode wall 615 may be fabricated by depositing transparent conductive materials on the top backup plate 605 and the bottom backup plate 610, respectively. Examples of suitable transparent conductive materials are antimony doped tin oxide and tin doped indium oxide. Transparent conductive materials may be deposited alone or in combination with a fine-line metal pattern for enhanced conductivity. Examples of materials that are suitable for use as top backup plate 605 and bottom backup plate 610 are sapphire and fused silica. For greater transmission in the IR region, sulfides, selenides and halides may be used. The use of transparent materials for the backup wall and anode/cathode walls enables the illumination of the electrode surfaces.
The flat surface surrounding the duct channel 635 provides an area against which a seal may be made to enable a forced fluid flow through the channel duct 935.
Additional backup plates may be added to increase the seal surface area around the channel duct 635. A temporary seal may be made using gaskets or o-rings, and a more permanent seal may be made using adhesives. The use of ceramic materials and thin film techniques enables the construction of ducts with a height on the order of 0.001 inches or smaller and a width on the order of an inch or larger. For low profile transmission line ducts, adapters may be attached to facilitate plumbing connections. The transmission line duct 691 is an embodiment of a fundamental element of the present invention: an electrolytic cell with inherently low inductance that is achieved through closely spaced and substantially parallel electrodes with a separation that is small compared to the width of parallel plate electrodes. A transmission line duct with coaxial electrodes will have an electrode separation that is small in comparison to the cross-section perimeter of the center conductor. In a preferred embodiment of transmission line duct 691, the width to separation ratio of the anode wall 610 and the cathode wall 615 is at least 100.
The detachable switch module 694 has a lower conductor plate 613b and an upper conductor plate 618b that are separated by and coupled to a transmission line dielectric 631c. The transmission line dielectric 631c is also coupled to a switch plate 619 and separates switch plate 619 from the lower conductor plate 613b. The switch plate 619 is coupled to upper conductor plate 618b by switches 640 (e.g., transistors).
In an electrolytic cell with an aqueous electrolyte, a nominal double-layer capacitance of 20 microfarads per square centimeter and an electrode area of 25 square centimeters, the average current required to charge the capacitance to one volt in one microsecond is on the order of 500 amperes. Faster charging times will require proportionally larger currents, with peak currents on the order of thousands of amperes.
For an electrolytic manufacturing process that requires large total electrode areas in order to obtain a reasonable throughput, driving a single large electrolytic cell (e.g., plating bath) will be very difficult. Thus, it is an aspect of the present invention to provide a compact module that combines an electrolytic cell with a local power supply.
Another aspect of the invention is the combination of an array of compact modules to provide a large total electrode area.
The inductance of a circuit element increases with length. It is thus desirable to minimize the circuit path between the switch and the anode/cathode of a high-speed electrolytic cell. Instead of increasing the size of a power supply and the electrolytic cell it serves, the electrolytic cell can be divided into a plurality of smaller cells, each with a dedicated power supply. To reduce the overall load capacitance and thus reduce the peak current, an array of electrolytic cells may be configured in series. The smaller capacitance will reduce the charging current that is required; however, the overall applied voltage will be increased.
Control circuit board 715 provides a number of control functions for the switch transistors 720a, 720b, and 720c. Bypass capacitors 725a, 725b, and 725c are in close proximity to switch transistors 725a, 725b, and 725c, and serve to minimize voltage drops at turn-on. Bypass capacitors 725a, 725b, and 720c preferably have a low equivalent series resistance. Multiple capacitors may be used in parallel for each transistor. Transistor driver 735 provides the drive signal to switch transistors 720a, 720b, and 720c. Transistor driver 735 may be a MOSFET driver, and more than one may be used to drive the switch transistors 720a, 720b, and 720c. Waveform generator 740 provides the waveform that is amplified by transistor driver(s) 735. Voltage regulators 730a, 730b, and 730c provide the supply voltages to switch transistors 720a, 720b, and 720c.
Microcontroller 745 controls the output voltages of voltage regulators 730a, 730b, and 730c. Microcontroller 745 may have a built-in Analog-to-digital conversion capability that provides for adjustment of the voltage regulators in response to measured I-V characteristics of the anode and cathode. Microcontroller 745 may also have a communications capability that allows it to be networked with a master controller, thus allowing a central master controller to control an array of electrolytic modules 790. Examples of devices suitable for use as microcontroller 745 are the Z8 Encore!®8K Series of 8-bit microcontrollers manufactured by Zilog, Inc.
The functions described in relation to circuit board 715 may be provided by different configurations of integrated circuits and discrete devices. Field programmable gate arrays (FPGAs) or application specific integrated circuits (ASICs) may also be used. Additional switch transistors, bypass capacitors, and voltage regulators may be added to provide more complex output waveforms and high frequency excitation.
Illumination module 780 may be provided as a photon source for use with transparent backup plate/electrode assemblies to provide radiation at an electrode surface to assist redox reactions. The illumination module may be a continuous source or it may be a pulsed source. The illumination module may be controlled by the circuit board 715. As a pulsed source, the illumination module may be synchronized with a switch driver waveform output by the circuit board 715.
The illumination module 780 may be a monochromatic light source or a filtered light source for providing a limited spectrum. Light emitting diodes (LEDs) and/or laser diodes may be used as elements in the illumination module 780. The illumination module 780 may include fiber optics or other transmission means to couple the electrolytic module 792 to a remote photon source (e.g., a tunable dye laser).
Due to a large resistance or a large capacitance, or both, the RC time constant of an electrolytic cell may prevent the voltage across the double-layer capacitance in the cell from rising quickly enough to suit a particular process. In this instance, a voltage greater than the desired working cell voltage may be applied for a short duration to accelerate charging or discharging of the double-layer capacitance.
For example, if the intended electrolytic process is a reduction reaction at the cathode, the application of V0 to the electrode serving as the anode will produce a positive charge at the cathode. This positive charge will lower the cation concentration within the interphase at the cathode surface and increase the anion concentration in the interphase at the cathode surface. The mean distance between the cathode surface and the cations within the interphase will be increased.
Subsequent to period t0, a voltage V1 is applied for a period t1. V1 is a voltage that is greater in magnitude than the voltage V2 at which the intended reaction will occur. For systems including a solvent and a dissolved electrolyte, V1 may be equal to or greater than the cell potential at which the solvent is oxidized and/or reduced. For embodiments in which the electrolyte has a low conductivity, it is preferred that V1 be greater than the voltage at which solvent electrolysis occurs.
It is important that V1 and t1 are closely controlled, since overcharging of the double-layer capacitance may occur. In processes where V1 is greater than the voltage at which solvent electrolysis occurs, electrolysis is inevitable if t1 is not sufficiently limited. The purpose of the (V1, t1) pulse is to overcome the RC time constant of the electrolytic cell. Ideally, at the end of t1, the potential across the double-layer capacitance is equal to the desired process potential associated with the cell voltage V2, and has been reached in a time t1 that is less than the time it would have taken if V2 were applied directly.
The change in polarity from V0 to V1 and the magnitude of V1 may result in large currents during the initial charging of the double-layer capacitance. It is important that the power supply providing V1 have a low inductance and a low internal resistance so that current lag and limiting are minimized.
V2 is the cell voltage at which the desired reaction (e.g., reduction at the cathode) occurs. V2 may be the voltage associated with the onset of the reaction, but is preferably one hundred millivolts or more higher. Due to the small distances and short timescales involved with the interphase, it is desirable to carry out redox reactions with large overpotentials so that charge transfer kinetics are not a limiting factor. It is preferable that V2 provide a sufficiently large reaction overpotential so that the time required for migration of a cation to the electrode is large compared to the time required for its reduction.
During the application of (V1, t1) and (V2, t2), cations will migrate toward the cathode, and their velocity will be influenced by charge, mass, and solvation. Not all cations will have the same velocity under the influence of the applied voltage, thus there will be a degree of segregation between the cations. Segregation may occur between cations with the same mass and different charge, or between cations with the same charge and different mass. The first species to arrive at the cathode will tend to be those with the greatest mobility. The period t2 may be ended shortly after the first reduction reactions occur, thus limiting reaction participation to the initially closer and faster cations.
At the end of period t2 a voltage V3 is applied for a period t3. The purpose of V3 is to quickly remove the charge acquired by the double-layer capacitance during the application of V1 and V2. This charge removal helps to reset the electrolytic cell so that another pulse cycle can be applied. The application of V3 for the period t3 may be omitted from the waveform; however, the discharge of the double-layer capacitance may require a longer time. For processes involving the application of a series of pulses, the (V3, t3) segment may be used to increase the pulse rate, and thus the throughput of the process.
At the end of period t3 voltage V4 is applied for a period t4. In this instance, V4 is shown as being different from V0; however, V4 may be equal to V0. In the application of a series of pulses, the (V0, to) segment may be absent altogether (e.g., V0=0). In addition, V4 is shown as being of opposite polarity from V1 and V2; however, V4 may be of the same polarity as V1 and V2. V4 serves as a reference voltage at which the electrolytic cell is allowed to equilibrate before the next application of V1. In one embodiment, the period t4 is at least ten times greater than the sum of t1 and t2. In another embodiment, the period t4 is at least 100 times greater than the sum of t1 and t2. Since cation diffusion can be significantly slower than cation migration in a large electric field, a relatively long period may be required for the equilibrium concentration of the cationic species being reduced to be restored in the interphase and the adjacent region in the bulk electrolyte.
The output pulse of MMV5 provides a delay between the output pulses from MMV4 and MMV6 to avoid shootthrough in the NFETs. The output pulse of MMV6 drives a first high input and a first low input of H-bridge driver 2. The output pulse of MMV7 provides a delay between output pulse from MMV6 and MMV8 to avoid shootthrough in the NFETs. The output pulse of MMV8 drives a second high input and a second low input of H-bridge driver 1.
A first pair of outputs of H-bridge driver 1 drives high side NFET5 and low side NFET4. A second pair of outputs of H-bridge driver 1 drives high side NFET3, high side NFET7, and low side NFET4. A first pair of outputs of H-bridge driver 2 drives high side NFET8 and low side NFET1. A second pair of outputs of H-bridge driver 2 drives high side NFET6, high side NFET8, and low side NFET1.
The circuit of
H-bridge driver 1 and H-bridge driver 2 in
Low side NFETs M1 and M4 are driven by sources V3 and V5 respectively. High voltage NFETs M5 and M2 are driven by sources V7 and V9, respectively. Low voltage NFETs M7 and M3 are driven by source V10. NFETs M7 and M3 are configured back-to-back to prevent diode conduction when M5 is on. Similarly, Low voltage NFETs M6 and M8 are driven by source V10 and are configured back-to-back to prevent diode conduction when M2 is on. As an alternative, the back-to-back NFET combination could be replaced by a NFET in series with an external diode at the expense of the diode forward voltage drop.
A magnet 1322 may be used to provide a magnetic field in the electrolyte gap between the electrodes. The magnet 1322 may be a permanent magnet or it may be an electromagnet. For high frequency fields an electromagnet with a ferrite core is preferred. The application of a magnetic waveform may be synchronized with the application of the electrical waveform applied to the electrodes (1305, 1310) and may also be synchronized with the output of the photon source 1320. A static magnetic field may be combined with an alternating magnetic field, and more than one magnet 1322 may be used.
The magnetic field produced by magnet 1322 is essentially perpendicular to the electrode surface; however, other magnetic field orientations may be employed. For example, a magnet may be oriented so that the magnetic field it produces is parallel to the electrode surface. A static magnetic field may also be oriented from 0 to 90 degrees with respect to an alternating magnetic field produced by currents flowing in the electrodes, or applied independently.
The integrated electrode assembly 1306 may also serve as a coplanar waveguide or microstrip circuit. The integrated electrode assembly may be fabricated on a dielectric substrate or a semiconductor substrate. When fabricated on a semiconductor substrate, active components such as switches (e.g., a shunt switch) may also be incorporated. For low power systems, the pulse power supply 1315 may also be incorporated on the substrate.
The circulating coaxial transmission line assembly 1400 has a circular cross-section for which the inductance may be approximated by the equation:
With respect to the above equation, ro=inner radius of outer conductor 1405, ri=outer radius of inner conductor 1410, and L=inductance in henries/meter. Although the circulating coaxial transmission line assembly 1400 is shown with a circular cross-section, other geometries (e.g., rectangular) may also be used.
It is preferable that each electrolyte gap 1510 be served by an independent electrolyte fluid circuit; however, for high resistivity electrolytes a common circuit with a remote common connection may be used. The leakage current due to a common electrolyte connection may be reduced to an acceptable level by maintaining a large resistance between the electrolyte cells 1510 and their common electrolyte connection.
The liquid metal electrode 1625 may be a metal that is liquid at or near room temperature (e.g., mercury or gallium) and can be used with low melting point electrolytes. For low melting point electrolytes such as room temperature ionic liquids, aqueous electrolytes and organic solvents, polymer materials such as epoxy resins and fluorocarbons may be used in the fabrication of the circulating electrolytic coaxial transmission line assembly 1600. The preferred metals for use in the transmission line assembly are metals that are insoluble in the liquid metal 1625, or metals that form intermetallic compounds with a melting point that is higher than the operating temperature of the circulating electrolytic coaxial transmission line assembly 1600.
Alternatively, the liquid metal electrode 1625 may be a metal with a higher melting point, thus making it suitable for use with molten halides and other molten salts. Examples of higher melting point metals are: Zn, In, Sn, Sb, Te, Pb, and Bi. The preferred materials for construction of the circulating electrolytic coaxial transmission line assembly 1600 are ceramics such as oxides and nitrides that may be metallized for bonding and providing conductive surfaces. Materials and techniques (e.g., moly-manganese metallized alumina) for metallizing and bonding ceramics that are used in the high power vacuum tube industry are well suited to fabrication of high temperature embodiments of the circulating electrolytic coaxial transmission line assembly 1600.
A high-melting point liquid metal 1625 may be chosen based on compatibility with a metal that is being reduced. For example, uranium may be reduced from a molten salt electrolyte into a liquid zinc electrode. Metals used in contact with liquid zinc or other liquid metals would preferably be insoluble in liquid metal 1625 or form an intermetallic compound with a melting point that is higher than the operating temperature of the liquid metal 1625.
Either the perforated cover 1725 or the container 1705 may be wholly or partly conductive to provide electrical contact to the liquid metal 1710. The cover 1725 may be a flat structure, or may have optional reinforcing features 1730 to provide rigidity. The cover 1725 may be a composite structure that is composed of both dielectric and electrically conductive materials. For example, a metallic base may be coated with a dielectric in those areas that are in contact with an electrolyte. Alternatively, a metallic honeycomb structure may be used to support a thin ceramic plate.
Forces that may act to destabilize the liquid metal surface include circulation currents in the liquid metal 1710, circulation currents in an electrolyte, and electromagnetic forces due to currents flowing through the electrolytic cell. The division of the metal electrode surface into a plurality of smaller surfaces 1735 increases the force that is necessary to achieve a given displacement of the surface 1735, thus allowing smaller electrolyte gaps to be used in the cell. The smaller electrolyte gaps contribute to lower cell resistance and faster charging of the double-layer capacitance. The viscosity of the electrolyte in contact with the liquid metal 1710 may also be adjusted to dampen oscillations that may arise due to electromagnetic effects.
Examples of materials that are preferred for the construction of high-temperature electrodes (1745a, 1745, 1740a) are tungsten/copper and silver/molybdenum composites. These materials have a low magnetic permeability, good electrical conductivity, and their composition can be adjusted to achieve a good thermal expansion match to a variety of ceramic materials. They can also be coated by a wide variety of other materials to optimize their performance as electrodes and liquid metal containers.
The outer conductor 1740 is separated from the center conductor elements by dielectric 1775. Each cell in the coaxial transmission line 1701 has an electrolyte intake port 1765a and an electrolyte exhaust port 1765b. Each cell in the coaxial transmission line 1701 also has a liquid metal intake port 1770a and a liquid metal exhaust port 1770b. Two different types of liquid metal electrode stabilizing covers are shown. Stabilizing cover 1755 has apertures whose sides are non-wetting with respect to the liquid metal 1760. Stabilizing cover 1755a has apertures that are wet by the liquid metal 1760.
Stabilizing cover 1755a is given mechanical support by electrolyte standoff 1780a and electrode standoff 1780b. For large area electrodes, standoffs 1780a and 1780b stiffen the stabilizing cover and enable the use of smaller electrolyte gaps. Stabilizing cover 1755a has aperture surfaces that are wet by the liquid metal 1760, thus providing a liquid metal surface 1756 that is closer to the opposing electrode 1745.
In one embodiment, the test controller causes the power supply to charge the load 1925 to a voltage value that is slightly greater than VH. When charged to a voltage greater than VH the outputs of comparators 1910 and 1920 are in the same state (e.g., high) since the voltage across the load 1925 is greater than both VH and VL. The outputs of comparators 1910 and 1920 are coupled to logic 1935 (e.g., an XOR gate). Clock 1940 is coupled to logic 1935 and a counter 1945 that is enabled to count pulses from clock 1940 when the logic 1935 is in the appropriate state (e.g., XOR high).
When the test controller 1950 causes the load 1925 to be shunted to ground or other potential that is less than or equal to VL, the discharge is initiated and the voltage across the load 1925 falls. When the voltage falls below VH the logic 1935 enables the counting of clock pulses by the counter 1945 until the voltage across the load falls below VL, at which time the logic disables the counting of pulses by the counter 1945. The test controller 1950 may be used to set VL and VH so that the RC time constant over a particular voltage range may be determined. The RC time constant thus determined might be used to establish the required pulse width of a fixed voltage pulse that is applied to charge the double-layer capacitance to a desired voltage.
For example, VH may be established as the voltage for which the onset of a desired redox reaction occurs in the load 1925. With respect to
A current sense resistor 2015 that is in series with the load 2010 is coupled to a switch network 2020 and to sampling capacitors C1 and C2. The switch network sequentially samples the potential across the current sense resistor 2015 at an interval controlled by the sampling control clock 2025. The current sense resistor may be a specific discrete resistor that is added to the circuit, or it may be a resistance that is intrinsic to the circuit.
At the beginning of a sampling cycle capacitor C1 may be switched by the switch network 2020 to a parallel connection with the current sense resistor 2015 for a short period of time (e.g., <10 nanoseconds) that allows C1 to track the potential across the current sense resistor 2015. C1 is then disconnected from the current sense resistor 2015 by the switch network 2020. The sampling process may then be repeated for C2. After voltage samples V1 and V2 have been acquired respectively on C1 and C2, the switch network 2020 subsequently couples C1 and C2 to comparator 2030.
When charging the capacitance associated with the load 2010 by a fixed voltage in the absence of redox reactions, the current through the current sense resistor 2015 will decrease over time. Since V2 is acquired after V1, it will normally be less than V2. However, the onset of a redox reaction may produce an increase in current that will result in V2 being greater than V1. When this happens, the comparator output changes state, causing the control logic to turn off the driver 2045 which in turn causes the power switch 2005 to shut off. Alternatively, the power switch may reduce the current to a preselected value for a period prior to shutting off.
RC measurement circuit shown in
A pulse power supply 2105, a radio frequency (RF) power supply 2110 and shunt 2120 are each coupled by a pair of switches 2106 to the transmission line duct 2115. Two switches generally provide better isolation between the switched components, and reduce parasitic elements (e.g., capacitance) seen by an active component. Alternatively, a single switch may be used with the other switch being replaced by a connection.
The pulse power supply 2105 provides current for charging/discharging the double layer capacitance Cdl and/or carrying out redox reactions. For example, the circuit shown in
The RF power supply 2110 may be used to provide a high frequency current at one or more frequencies. The RF power supply 2110 may include one or more oscillators, which may be either tunable or fixed frequency. The RF power supply 2110 is typically used in conjunction with the shunt 2120. The shunt 2120 provides a switchable path that reduces the voltage developed across the electrolytic cell (Rct, Cdl, Lshunt, and Rel), while providing a current through the transmission line conductors. The shunt 2120 may act as a short circuit in a lumped circuit, or may provide a matched termination to minimize reflections in a distributed circuit.
Depending upon the physical dimensions associated with the transmission line duct 2115, the nature of the dielectric used in construction, and the operating frequency of the RF power supply 2110, the transmission line duct 2115 may be treated as either a lumped circuit or a distributed circuit. In general, it is desirable that size of the electrolytic isotope separation circuit 2100 be chosen so that it may be treated as a lumped circuit; however, at high frequencies (e.g., above about 100 MHz), the difficulty associated with physical miniaturization must be balanced with the complexity of dealing with a distributed circuit.
An array of small circuits that can be treated individually as lumped circuits is preferred to a single large system that has a dimension on the order of the excitation wavelength. Nuclear magnetic resonance (NMR) frequencies in low static magnetic fields are generally below 100 MHz, whereas electron paramagnetic resonance (EPR) frequencies may be orders of magnitude higher (e.g., greater than 10 GHz). Due to skin depth effects, a large system will have resistive losses associated with conductor lengths that cannot be simply offset by a proportional increase in conductor cross-section. In a preferred embodiment, the length of the electrode/electrolyte interface, measured in the direction of the current flow, is less than 1/100 of the wavelength of the magnetic excitation frequency.
The combination of the RF power supply 2110 and transmission line duct 2115 may be a resonant structure with capacitance being largely provided by the RF power supply 2110, and inductance being largely provided by the transmission line duct 2115 series inductance Lseries. The resonant frequency of the structure may be tuned to a frequency for producing a microwave-induced magnetic isotope effect (MIMIE) in species present in the electrolyte within the transmission line electrode unit 2115b.
In the following description of an operational embodiment it is assumed that switches 2106(a, b, c, d) are initially open. Excitation is enabled by closing switches 2106a and 2106b so that shunt 2120 effectively shorts the end of the transmission line duct 2125. Switch 2106d is closed to charge Cpulse. Once Cpulse is charged, switch 2106d may be opened. Switch 2106c is closed to charge Cres. Switch 2106e may then be closed to connect pulsed excitation source 2130 to the transmission line duct 2125. Upon the closure of switch 2106e, the energy stored in Cres will oscillate between Cres and the inductance Lseries of transmission line 2125. Rseries and other lossy elements will damp the oscillation, which may be regenerated by further discharges from Cpulse. It should be noted that a single capacitor may be used for single shot excitation.
In one embodiment, switch 2106e is kept in a closed state while switch 2106c is operated to produce a sequence of resonance regeneration pulses. Each pulse produced by switch 2106c produces a damped resonant response that decays after a number of cycles at the resonant frequency. For example, transmission line duct system 2101 may be excited at a resonant frequency of 80 MHz and switch 2106c may be operated at a frequency of 10 MHz. In the process of excitation, a precise amplitude may not be critical, but it may be desirable to maintain the current above a threshold value required for a desired magnetic field intensity within the electrolyte gap. The number of resonant cycles between pulses applied by switch 2106c may be determined by the threshold current value and the amount of energy delivered in each pulse. Thus, an excitation frequency that is considerably higher than the power switching frequency may be obtained.
Selection of the value for Cres may be done by characterizing the transmission line 2125 and then selecting the value of Cres that corresponds to a desired resonant frequency. The characteristics of electrolytic cell 2135 may vary with frequency, particularly at high frequencies (e.g., the Debye-Falkenhagen effect). Thus, the criteria for selection of solvents and/or electrolytes may extend beyond electrochemical concerns and may involve solvent and/or ionic species behavior at RF and microwave frequencies.
Typically, the required excitation voltage will rise with frequency due to the increasing inductive reactance. However, the increase in applied frequency will offset the enhanced charging of Cdl due to the increased voltage since the charging time will be reduced. It is generally desired that redox reactions in the electrolytic cell be avoidable during RF or microwave excitation. The area of the electrode/electrolyte interface may be selected to provide a desired Cdl. Rel may also be tailored to provide an RC time constant that allows RF excitation to be achieved while minimizing unwanted redox reactions in the electrolytic cell during excitation. An intentional DC bias may be applied to induce redox reactions during excitation.
Preferred materials for the top conductor 2210 and bottom conductor 2240 are copper and silver, particularly at high frequencies where the skin depth is small. The top conductor 2210 and bottom conductor 2240 may have portions that are coated to provide compatibility with an electrolyte or liquid metal. For example, the top conductor 2210 may have a platinum coating. It is generally desirable to maintain thin (e.g., less than one micron) coatings of uniform thickness with abrupt transitions to the base metal, particularly at higher frequencies. A liquid metal stabilizer 2245 and an electrode chamber 2250 provide containment for a liquid metal electrode. In an alternative embodiment, the liquid metal stabilizer is a narrow slit with a length that is at least ten times greater than its width. The electrode chamber 2250 may have one or more ports 2255.
Ideally, most of the magnetic flux produced by excitation current flowing in the parallel plate transmission line duct 2200 would pass through the electrolyte chamber 2206; however, for a structure with a uniform magnetic permeability the magnetic field will be distributed over a region of space that will be significantly larger than the volume of the electrolyte chamber 2206. Thus, it may be desirable to introduce elements that can shape the magnetic field and increase the magnetic flux that is produced by a given excitation current.
A magnetic field enhancer 2260 intensifies the magnetic field in the electrolyte chamber 2250 that is produced by the RF current flowing through the parallel plate transmission line duct 2200. The magnetic field enhancer is fabricated from a material that has a relative permeability greater than one. In general, structures with a high initial permeability and a low saturation inductance are preferred. In a particular embodiment the magnetic field enhancer 2260 is saturated at current levels that exceed the desired operating excitation current amplitude by 10% or more.
In order for the parallel plate transmission line duct 2200 to provide a sufficiently strong RF magnetic field within the electrolyte chamber 2206, a certain amount of inductance is required. However, too much inductance in the electrolytic current path may degrade the electrolytic pulse waveform. Since the peak electrolytic current may be much larger than the current used to produce the RF magnetic field, a low saturation inductance in the magnetic field enhancer 2260 minimizes the impact on the electrolytic pulse waveform that is applied. Application and synchronization of the electrolytic pulse and magnetic excitation may be controlled by components similar to those disclosed with respect to
A magnetic field enhancer 2260 may be disposed between the upper conductor 2210 and the lower conductor 2240. Since a magnetic field enhancer 2260 that is disposed between the upper conductor 2210 and the lower conductor 2240 will have a greater impact on the capacitance of the parallel plate transmission line duct 2200, a material with a lower dielectric constant may be used. Although the dielectric constants of the materials of construction are not critical with respect to the electrolytic pulse, it can make the difference as to whether the parallel plate transmission line duct 2200 may be treated as a lumped circuit or a distributed circuit, as the excitation wavelength in the transmission line duct 2515 will decrease with increasing dielectric constant of the dielectric 2205.
In a particular embodiment, a portion of a parallel plate transmission line duct 2200 that includes a magnetic field enhancer 2260 and an electrolyte chamber 2206, forms a magnetic circuit in which more than 75% of the shortest magnetic flux path length lies within the magnetic field enhancer 2260 and less than 25% of the magnetic flux path lies within the electrolyte chamber 2206.
In one embodiment the magnetic field enhancer 2260 is fabricated from a homogeneous soft ferrite. In another embodiments, thin film laminate and/or composite structures may be used. More than one magnetic field enhancer 2260 may be used to enhance and/or shape the RF magnetic field. Since the RF current path differs from the electrolytic current path, the magnetic field enhancer may not be placed to simply maximize the RF magnetic field intensity, but may be placed to optimize the tradeoff between the increase in the RF magnetic field and the degradation of the electrolytic pulse.
A window insert 2211 provides for the transmission of electromagnetic radiation to the electrolyte chamber 2206. The window insert is preferably a high transmittance material that is chemically inert with respect to the electrolyte that is used. The window insert may have a transparent conductive coating such as indium tin oxide, or it may have a metal pattern disposed on the surface to form an electrode. In a preferred embodiment, a metal pattern having parallel metal traces with a width of less than 20 microns is used. Diffraction of incident electromagnetic radiation should be taken into account when a metal pattern is used, particularly for monochromatic sources.
The exclusion pulse creates a depletion region through which the species of interest may subsequently be transported to the electrode surface under the influence of an applied potential of opposite potential to that of the exclusion pulse. The products of reactions involving the species of interest may also be subsequently transported to the electrode surface under the influence of an applied potential. The increased separation between the electrode surface and the species of interest provides a greater distance over which mass-dependent transport processes (e.g., electromigration and diffusion) may provide isotope separation.
Conventional centrifuge and diffusion techniques for isotope separation typically rely on the gaseous state and thus have a relatively limited number of compounds that can be used as a working material. In contrast, there are an enormous number of anionic and cationic species that can be prepared using a wide variety of solvents and solutes. Water, aprotic solvents, molten halides, and room temperature ionic liquids are examples of solvents that may be used. Given the wide variety of organic and inorganic liquids, and supercritical fluids that are available for use, a mixture of isotopes of any of the following elements may be prepared as a dissolved ionic species, organometallic compound, or a soluble complex for use in embodiments of the present invention: Li, B, C, Mg, Si, K, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Ga, Ge, Se, Rb, Sr, Zr, Mo, Ru, Pd, Ag, Cd, In, Sn, Sb, Te, Ba, La, Ce, Nd, Sm, Eu, Gd, Dy, Er, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Hg, TI, Pb, Bi, Po, Th, U, Np, Pu, Am, and Cm.
Room temperature ionic liquids (RTILs) are of particular interest since there are many possible compounds that can be prepared. The selection of cation and anion for a RTIL can take into account the properties desired in an ionic species (e.g., a transition metal or actinide complex). For example, quaternary ammonium salts of the bis(trifluoromethanesulfonyl)imide anion (N(SO2CF3)2 (i.e., —NTf2) have been shown to be useful vehicles for redox reactions involving uranium and uranium complexes. A room temperature ionic liquid may be used in combination with salts (e.g., chlorides) that provide additional complexing agents or ligands.
In one embodiment, the exclusion pulse appears across the electrode surfaces as a fixed voltage square wave with a rise time of less than one microsecond and a fall time of less than microsecond, and the applied voltage is a voltage at which no redox reactions occur that involve species other than impurities. In another embodiment, the exclusion pulse appears across the electrode surfaces as a fixed voltage square wave with a rise time of less than 500 nanoseconds and a fall time of less than 500 nanoseconds, and the applied voltage is a voltage at which no redox reactions occur that involve species other than impurities. Further, in each of the aforementioned embodiments the RC time constant of the electrolytic cell associated with the electrodes is greater than 10 microseconds and less than 1000 microseconds.
Cationic or anionic species may be excluded at an electrode. For example, a UO22+ cationic complex may be excluded at an electrode by applying a positive potential prior to reversing the electrode polarity and carrying out a reduction of the UO22+ cationic complex. Similarly an anionic trivalent actinide (e.g., U3+) complex may be excluded at an electrode by applying a negative potential prior to reversing the potential and carrying out an oxidation of the anionic trivalent actinide complex.
At step 2410, the species of interest is dissociated by the application of an energy pulse. The pulse of energy may be electromagnetic radiation (e.g., with a wavelength between 0.2 microns and 20 microns). The species of interest may be an electrically neutral species such as an organometallic compound, a solvated ion, or a charged complex (e.g., transition metal or actinide complex). The dissociation of the species of interest may result in a radical pair or a radical-ion pair, which may be spin-correlated. The radical pair or radical-ion pair may be a triplet pair or may be a singlet pair.
For gaseous atoms or free ions, distinct differences in optical absorption may exist between isotopes. However, in solutions the differences are less distinct due to the effects of the solution environment. A monochromatic or narrow-band light source may be used to produce a small preferential dissociation for a species containing a particular isotope. This preferential dissociation may contribute to an overall isotope separation process that employs the mass isotope effect or the magnetic isotope effect.
The use of liquid electrolytes also allows for exploitation of the field shift effect in which a heavy isotope has a preference for the chemical species with the smaller number of s electrons in the bonding or valence orbital. With the proper selection of photonic and magnetic excitations and reactant species, the magnetic isotope effect and the field shift effect can be exercised in concert to provide an enhanced overall isotope separation.
An anionic complex may be dissociated to produce an anion-cation pair or a neutral-anion pair. Similarly, a cationic complex may be dissociated to produce an anion-cation pair or a neutral-cation pair. A pair produced by dissociation may also be further dissociated to form another pair through multi-photon absorption. Pair formation may involve electron transfer with other adjacent species (e.g., photoreduction).
At step 2415, magnetic excitation is applied. The excitation may be applied by a DC magnetic field, an alternating magnetic field, or a combination of a DC magnetic field and an alternating magnetic field. A DC magnetic field may be applied to modify the spin evolution of species formed in step 2410. The Δg mechanism (ΔgM), hyperfine coupling mechanism (HFCM), and the level crossing mechanism (LCM) are examples of mechanisms that can be modified by a DC magnetic field to control differential spin conversion of isotope containing radical pairs or radical-ion pairs. An alternating magnetic field may also be used to induce differential level transitions in the electron and nuclear spins of isotope containing species. The alternating magnetic field may have a frequency in the range of 100 kHz to 100 GHz. Although the energy differences involved in spin conversion may be small in comparison to the thermodynamic energies associated with chemical reactions, they may have a significant impact on chemical reaction rates.
Excitation by an alternating magnetic field or a combination of an alternating magnetic field and a DC magnetic field may be used to alter the relative recombination or reaction rates of magnetic and nonmagnetic isotope containing pairs. The alteration of recombination or reaction rates may include accelerating or retarding a reaction rate. The excitation may be used to produce a transient population of cationic or anionic species having an enhanced concentration of a magnetic or nonmagnetic isotope. Although not as great as the differences between magnetic and nonmagnetic isotopes, the difference in magnetic moment between magnetic isotopes of the same element (e.g., 63Cu and 65Cu) may also be used as a basis for transient fractionation through magnetic excitation.
Transient fractionation produced by managed differences in nuclear spin and magnetic moment may be used to produce an isotopically enhanced population near the surface of an electrode that may be converted to stable species through redox reactions at the electrode surface. In addition to the enhancement of the recombination and/or reaction of magnetic isotopic species to produce such a population, magnetic excitation (e.g., spin inversion) may be used to provide a relative enhancement of recombination and/or reaction of nonmagnetic isotopic species with respect to magnetic isotopic species to create the population.
Reversible photoreduction of uranyl (UO22+) to uranoyl (UO2+) in the presence of an appropriate electron donor provides a method for transient fractionation that relies on magnetically enhanced reoxidation of 235UO2+ to 235UO22+ to provide a 235U enhanced population of UO22+ that may be attracted to an electrode with a greater velocity than the 238U enriched UO2+. As with other photolytic transient fractionation processes that rely on differential recombination to reproduce a starting species, it is desirable to have a high quantum yield for the initial reaction.
At step 2420, a potential is applied to the electrolytic cell to extract cationic or anionic species. The population of cationic or anionic species attracted to the electrode may or may not have been produced by step 2405 and/or step 2410. In the absence of step 2405 and 2410, the mass isotope effect will be the primary effect in providing isotope separation. As the ionic species migrate toward the electrode, the lighter isotope will do so with a greater velocity, causing the initial contact population on the electrode surface to be enriched in the lighter isotope.
The applied potential waveform may correspond to the (V1, t1) and/or (V2, t2) segments shown in
Transient isotope fractionation provided by step 2405 and/or step 2410 may be used to produce a population of cation/neutral pairs from a cationic complex, with the difference in mass between the cationic complex and the cation pair component being considerably greater than the isotope mass difference. For example, accelerated recombination of a 235U containing pair will produce a population of lighter unrecombined cations that is enriched in 238U. Since most neutral species (e.g., solvent molecules) will have a mass that is considerably greater than the 3 atomic mass unit difference between 235U and 238U, the total isotope fractionation at the electrode surface will be a combination of initial population isotope fractionation through the magnetic isotope effect combined with an enhanced mass isotope effect during migration. Although all cationic species will respond to the electrode potential, the 238U containing species will be greater in number and faster than the 235U containing species.
In another embodiment, transient isotope fractionation between magnetic and nonmagnetic isotopes is provided by step 2405 and/or step 2410 to produce a population of cation/anion pairs from an anionic complex. Due to enhanced recombination and/or reaction of magnetic cations (e.g., 235U containing cations) to form anionic complexes, the unrecombined cation population will be rich in nonmagnetic (e.g., 238U containing cations). Under the influence of a negative potential at the electrode surface, the 235U rich population of anionic complexes will tend to be excluded from the electrode surface as the 238U rich cation complexes are attracted to the electrode surface.
Upon application of an extraction pulse, both diffusion and migration within the applied electric field may drive mass transport to the electrode. It is desirable that the transport time to the electrode surface be shorter than the lifetime of transient species of interest. The mean distance to the electrode may be decreased by increasing the concentration of ionic species, and the transport velocity may be increased by reducing the electrolyte viscosity. The magnitude of the exclusion potential applied in step 2405 may be reduced to decrease the mean distance to the electrode.
At step 2425, charge transfer between the electrode and species attracted to the electrode surface during step 2420 occurs and an oxidation or a reduction is carried out. The oxidation or reduction reaction may be partial or complete. For example, a Cu2+ cation may be reduced to Cu+ or it may be reduced to Cu metal. Reduction may be carried out at a solid or liquid electrode surface. The charge involved in the reaction may be provided by the attraction pulse applied in step 2420.
A redox power supply 2605 is coupled to working electrode 2625 and alternate electrode 2635 by a transmission line 2620. Redox power supply 2605 may be similar to the power supplies shown in
The impedance of redox power supply 2605, electrolyte 2630, and C2shunt is such that the current produced by magnetic excitation source 2610 is essentially limited to a single loop through working electrode 2625 without flowing through the electrolyte 2630 and the alternate electrode 2635. This configuration reduces the damping effect of REL during resonant excitation.
In an embodiment, transmission line 2615 has a capacitance in excess of 400 pF per meter and an inductance of less than 50 nH per meter. Similarly, it may also be desirable that transmission line 2115a of
For configurations in which the electrolyte 3530 is flowing, a magnetic excitation current is established between electrode 3510 and ground plane 3515 and a redox potential is established between electrode 3520 and electrode 5325. For configurations in which the electrolyte 3530 is essentially static, electrode 3510 is omitted and the magnetic excitation current is applied between the ground plane 3515 and either electrode 3520 or electrode 3525. Substrate 3505 may be a dielectric (e.g., sapphire) or a semiconductor (e.g., silicon). For semiconductor substrates, the electrodes 3510, 3520, 3525, and ground plane 3505 are isolated from the substrate 3505 by thin dielectric films.
While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. Various embodiments of power supplies, transmission line structures, fluid circuits, and electrode assemblies have been disclosed using a variety of components. Within the scope of the invention, combinations of the aforementioned disclosed components other than those combinations explicitly disclosed may be used in a system for isotope selective chemical reactions.
This application claims priority of U.S. Provisional Application No. 60/990,913, filed Nov. 28, 2007.
| Number | Date | Country | |
|---|---|---|---|
| 60990913 | Nov 2007 | US |
