KR101319157B1 - High density wire arrays in a glassy matrix - Google Patents

Abstract

The present invention seals one end of the glass tube 14 such that the glass tube 14 has one open end and one closed end, introduces the thermoelectric active material 22 into the glass tube 14, and opens the glass tube. The thermoelectric material to be used in the first drawing operation by evacuating the glass tube 14 by attaching the end to the vacuum pump and heating the part of the glass tube 14 so that the glass partially melts and collapses under vacuum. Providing an ampoule 54 containing 22, introducing an ampoule 54 containing a thermoelectric material 22 into the heating device 10, and heating the glass tube 14 such that the glass tube 14 is melted just enough to be drawn out thereof. There is provided a method of withdrawing a thermoelectric active material 22 in a glass coating comprising increasing the temperature in (10) and withdrawing the fibers 24 of the glass coated thermoelectric active material.

Thermoelectric active materials, glass cladding, high density nanowires

Description

High Density Wire Array in Glass Substrate {HIGH DENSITY WIRE ARRAYS IN A GLASSY MATRIX}

The present invention relates to arrays of high density nanowires in glass substrates, and methods of drawing them.

Thermoelectric materials generate electricity when there is a thermal gradient and produce a thermal gradient when an electric current passes through it. Practical thermoelectrics can, inter alia, replace (1) the fluorocarbons used in existing cooling systems such as refrigerators or air conditioners, and (2) convert some or most of the waste heat into electricity to reduce harmful emissions during thermal power generation. Scientists have been trying to use utility thermoelectrics for decades. However, the prospect of utility thermoelectrics has not been realized yet. One problem is that, due to its low efficiency, industry standards of thermoelectric technology cannot be functionally integrated into everyday heating and cooling products and systems.

Bulk thermoelectric devices such as thermoelectric generators (TEGs), thermoelectric refrigerators (TER) and thermoelectric heat pumps are used to convert heat directly into electricity or directly into electricity. However, the energy conversion efficiency and / or coefficient of performance of these bulk thermoelectric devices is significantly lower than conventional reciprocating or rotary heat engines and vapor compression systems. Because of these shortcomings and the general incompleteness of the technology, bulk thermoelectric devices have not gained enormous popularity.

Early thermoelectric contacts were formed from two different metals or alloys that could produce small currents when there was a thermal gradient. Differential voltages are generated when heat is transported across the contacts, thereby converting some of the heat to electricity. Several contacts may be connected in series to provide greater voltages, or connected in parallel to provide increased current, or both. Modern thermoelectric generators can include many contacts in series, thus providing higher voltages. Such thermoelectric generators can be manufactured in modular form to provide parallel connectivity that increases the amount of generated current.

In 1821, Thomas Johann Seebeck discovered the first thermoelectric effect called the Seebeck effect. Seebeck found that the compass needle deflects when the compass is placed near a closed loop made of two different materials when one of the two contacts is maintained at a higher temperature than the other. This established that a voltage difference occurs when there is a temperature difference between the two contacts, and the voltage difference depends on the properties of the metal involved. The voltage (or EMF) generated per 1 ° C. of the thermal gradient is known as the Seebeck coefficient.

In 1833, Peltier discovered a second thermoelectric effect known as the Peltier Effect. Peltier found that temperature changes occur at different metal contacts whenever current flows through them. Depending on the direction of current flow, heat is absorbed or released at the contacts.

William Thomson, later known as Sir Kelvin, discovered a third thermoelectric effect called the Thomson effect, which is related to the heating or cooling of a single homogeneous current-carrying conductor with a temperature gradient. Sir Kelvin also established four equations (Kelvin relations) that correlate Seebeck coefficients, Peltier coefficients, and Thompson's coefficients. In 1911, Altenkirch proposed using the thermoelectric principle to convert heat directly into electricity and vice versa. He invented the thermoelectric theory of power generation and cooling, which required the Seebeck coefficient (thermal power) to be as high as possible for best performance. This theory also required that the electrical conductivity be as high as possible with the minimum thermal conductivity.

Altenkire established a measure for determining the thermal power conversion efficiency of a material, which he called power factor (PF). The latter is represented by the equation PF = S ² * σ = S ² / ρ, where S is Seebeck coefficient or thermal power, σ is electrical conductivity, and ρ (1 / σ) is the electrical resistivity. Thus, Altenkire established the following equation: Z = S ² * σ / κ = S ² / ρ * κ = PF / κ, where Z is a thermoelectric figure of merit with a dimension of K ⁻¹ . This equation can be rendered dimensionless by multiplying it by the absolute temperature T, where measurements of S, ρ and κ are performed such that the dimensionless thermoelectric figure of merit or ZT coefficient is equal to (S ² * σ / κ) T . In order to improve the performance of thermoelectric devices, it is concluded that the power factor should be increased as much as possible, while κ (thermal conductivity) should be reduced as much as possible.

The ZT coefficient of a material indicates its thermoelectric power conversion efficiency. Forty years ago, the best ZT coefficient that existed at that time was about 0.6. After 40 years of research, commercially available systems are still limited to ZT values close to one. It is widely recognized that ZT coefficients greater than 1 will open the door where thermoelectric power begins to replace existing power generation technologies, traditional household refrigerators, air conditioners, and the like. In fact, it is likely that practical thermoelectric technologies with ZT coefficients of even 2.0 or higher will produce the next generation of heating and cooling systems. In light of the above, there is a need for a method of creating a practical thermoelectric technique that achieves an increased ZT coefficient of about 2.0 or greater.

Recently, it has been found that nanostructured solid state thermoelectric coolers and thermoelectric generators can exhibit improved thermoelectric performance over corresponding bulk thermoelectric devices. It has been demonstrated that the ZT coefficient increases dramatically when the size of some thermoelectrically active materials (eg, PbTe, Bi ₂ Te ₃ and SiGe) is reduced to the nanometer scale (typically about 4-100 nm). This increase in ZT prompted the expectation that quantum confinement could be used to develop utility thermoelectric generators and coolers [refrigerators]. Various promising approaches have been recently studied, such as transport and confinement in nanowires and quantum dots, reduction in thermal conductivity in a direction perpendicular to the superlattice plane, and optimization of ternary or quaternary chalcogenides and squaterites. . However, these approaches are too expensive and many of them cannot be manufactured in significant amounts.

The ability to efficiently convert energy into different forms is one of the most recognizable symbols of science and engineering. The conversion of thermal energy into electricity is a proof of energy economy, where even minor improvements in efficiency and conversion methods can have a huge impact on monetary savings, energy reserves and environmental effects. Likewise, electromechanical energy conversion is of interest to many modern machines. In light of the continuing exploration of the miniaturization of electronic circuits, nanoscale devices can play a role in energy conversion, and can also play a role in the development of cooling technology for microelectronic circuits that generate large amounts of heat. Thus, there is a need for a wide range of high performance energy conversion and thermoelectric devices based on one-dimensional inorganic nanostructures or nanowires.

Summary of the Invention

The present invention relates to nanostructures formed from fibers of a substantially one-dimensional thermoelectric active material having a diameter significantly smaller than the length. Such nanostructured fibers have a diameter of about 200 nm or less. The nanostructures of the invention described herein are referred to as "nanowires", "cables", "arrays", "heterostructures" or "composites" containing a plurality of one-dimensional fibers. The cable preferably comprises at least one thermoelectric active material and a glass material which acts as an electrical insulator for the thermoelectric active material, which is also referred to herein as a "thermoelectric material."

According to another aspect of the invention, the thermoelectric material comprises a high concentration of nanoscale wire (eg, 10 ^{6-10 10} / cm 2) embedded in a suitable glass to form a cable, in which case the thermoelectric material Is in the form of glass-covered nanowires comprising a number of one-dimensional fibers that extend over a long distance along the length of the cable without contacting other fibers. The thermoelectric active material may include any suitable metal, alloy or semiconductor material that maintains the integrity of the interface between the thermoelectric material and the glass material without any appreciable soaking and / or diffusion of the thermoelectric material.

According to a further aspect of the present invention, a cable manufacturing method includes increasing the density of thermoelectric fibers above 10 ⁹ / cm 2 (cable cross section). Each cable includes an array of fibers having a certain distribution of diameters, in which case the variation in fiber diameter can be reduced by using an automatic drawer tower, which is commonly used for fiber drawing in the fiber industry.

Preferred cables made in accordance with the principles of the present invention preferably comprise one or more thermoelectric fibers embedded in an electrically insulating material, said thermoelectric material exhibiting quantum confinement. Preferred cables include multiple fibers such that there is electrical connectivity between the ends of all the fibers. Alternatively, electrical connectivity is not between all fibers of the cable but between some fibers. The glass cladding of the cable preferably comprises an electrical insulating material such as pyrex, borosilicate, aluminosilicate, quartz or glass having lead oxide, tellurium dioxide and silicon dioxide as the main component. The thermoelectric material may be selected from the group consisting of metals, semimetals, alloys and semiconductors so that the thermoelectric material exhibits electrical connectivity and quantum confinement.

In addition, the present invention seals one end of the glass tube so that the glass tube has one open end and one closed end, introduces a thermoelectric active material into the glass tube, and exhausts the glass tube by attaching the open end of the glass tube to the vacuum pump. And heating a portion of the glass tube such that the glass is partially melted and collapsed under vacuum to provide an ampoule in which the partially molten glass tube contains a thermoelectric material to be used in the first drawing operation, and an ampoule containing the thermoelectric material is introduced into a heating apparatus and And increasing the temperature in the heating apparatus such that the glass tube is melted sufficiently to be drawn out, and withdrawing the fiber of the glass coated thermoelectric active material. The method may further comprise bundleting the fibers of the glass clad thermoelectric active material together and redrawing them one or more times in succession to produce a multi-core cable having a plurality of individual thermoelectric fibers insulated from each other by the glass cladding.

In addition, the method includes breaking the glass coated fiber into shorter pieces, introducing a piece of glass coated fiber into another glass tube having one sealing end and one open end, and attaching the open end to the vacuum pump. Evacuating the substrate, heating the portion of the glass tube so that the glass is partially melted and collapsed under vacuum to provide an ampoule in which the partially molten glass tube contains a piece of glass-coated fiber, introducing the ampoule into a heating device, the glass tube being Increasing the temperature in the heating apparatus such that it melts only enough to be withdrawn, and withdrawing fibers of the glass-coated thermoelectric active material to produce a cable having a plurality of multicore fibers.

All of these embodiments are intended to fall within the scope of the invention as disclosed herein. These and other embodiments of the invention will be apparent to those skilled in the art from the following detailed description of the preferred embodiments which refer to the accompanying drawings, and the invention is not limited to any particular preferred embodiment disclosed.

1 is a cross-sectional view of a tubular furnace for drawing thermoelectrically active material embedded in a glass cladding in accordance with the principles of the present invention.

2 shows an x-ray diffraction pattern of a PbTe based cable made in accordance with the principles of the present invention.

3 is a side view of a glass sheathed PbTe based cable made in accordance with the principles of the present invention.

4 is an enlarged cross sectional view of the glass sheathed PbTe based cable of FIG. 3 taken along lines 3A-3A.

FIG. 5 is a cross-sectional view of the glass sheathed PbTe based cable of FIG. 3 after a second extraction of PbTe fibers. FIG.

FIG. 6 is a cross sectional view of the glass sheathed PbTe based cable of FIG. 3 after a third extraction of PbTe fibers. FIG.

FIG. 7 is a table showing the DC resistance of the PbTe cable (after the first extraction of PbTe fibers) of FIG. 4.

FIG. 8 is a table showing the DC resistance of the PbTe cable (after the second withdrawal of PbTe fibers) of FIG. 5.

FIG. 9 is a table showing the DC resistance of the PbTe cable (after the third withdrawal of PbTe fibers) of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following paragraphs the invention will be described in detail with reference to the accompanying drawings by way of example. Throughout this description, the preferred embodiments and examples shown are to be regarded as illustrative rather than limiting to the invention. As used herein, "invention" refers to any of the embodiments and equivalents of the invention described herein. In addition, reference throughout this specification to various feature (s) of "the invention" does not imply that all claimed embodiments or methods must include the feature (s) mentioned.

Before beginning the description of the drawings, we will now define some terms.

Bulk material: A thermoelectric material of gross size, typically all three dimensions greater than 1 micron or 1 μm.

Chalcogenide: A group VI element of the periodic table.

Chemical Vapor Deposition: Depositing a thin film (usually a dielectric / insulator) on a wafer substrate by placing the wafer in a reactant gas mixture at the wafer surface. This can be done at medium to high temperatures in which the wafer is heated in the furnace or reactor but the walls of the reactor are not heated. Plasma chemical vapor deposition does not require high temperatures by exciting the reactive gases into the plasma.

Doping: Intentionally adding a very small amount of foreign material to a very pure semiconductor crystal. These added impurities provide the semiconductor with excess conductive electrons or excess conductive holes (in the absence of conductive electrons).

 Efficiency: The power generated by a system divided by the power supplied to the system and is a measure of how well a material converts one form of energy into another. The efficiency of bulk thermoelectric devices currently available or available in the near future is only 8-12%.

The figure of merit: The thermoelectric figure of merit ZT is given by ZT = (S ² * σ / κ) * T, where S is the Seebeck coefficient, T is the absolute temperature, σ is the electrical resistivity, and κ is the thermal conductivity. .

Lead Telluride: PbTe is one of the most commonly used thermoelectric materials other than Bi ₂ Te ₃ . PbTe is typically used for power generation because it exhibits the highest ZT at temperatures of 400-500 ° C. and has an effective working range of about 200 ° C. to about 500 ° C.

NANO: Prefix that means one billionth or 0.000000001. For example, the wavelength of ultraviolet light used to etch silicon chips is hundreds of nanometers. The symbol for nanometer is nm.

Quantum confinement: Quantum confinement occurs when an electrical carrier (electron or hole) is confined in space by reducing the size of the conductor. Very thin conductive films, for example, reduce the freedom of the carrier by limiting the freedom of the carrier to propagate in a direction perpendicular to the plane of the film. The film is said to be a 2-d structure, and the carrier of this film is said to be both constrained in one direction. It can move around in two different directions, ie in the plane of the film.

Seebeck coefficient: The electromotive force generated when there is a thermal gradient in a substance. This is usually expressed in μV / Kelvin. The thermal power or Seebeck coefficient of a material plays a large role in determining its ZT coefficient.

Thermal Conductivity: Thermal conductivity is an inherent property of a substance that specifies the amount of heat transported through a unit of cross-section and unit thickness for a unit temperature gradient. Although thermal conductivity is inherent in a medium, it depends on the temperature measured. The thermal conductivity of air is about 50% greater than the thermal conductivity of water vapor, while the thermal conductivity of liquid water is about 25 times that of air. The thermal conductivity of solids, especially metals, is thousands of times greater than the thermal conductivity of air.

The present invention relates to nanostructures referred to herein as "nanowires", "cables", "arrays", "heterostructures", "composites" containing a plurality of one-dimensional fibers. Nanowires according to the present invention comprise heterostructures of one or more thermoelectrically active materials and other materials of different composition and structure, such as glass, with interfaces or contacts formed therebetween. Thermoelectrically active materials are reduced in thickness or diameter to nanodimensions to take advantage of quantum confinement. By doing in this way, the thermoelectric efficiency of a thermoelectric active material improves. Thermoelectrically active materials are also referred to as "thermoelectric materials". The coating preferably comprises suitable glass, such as glass comprising an amorphous material that is free of long-range order of constituent atoms.

One aspect of the present invention includes a method for generating utility thermoelectrics by developing quantum constrained nanowires that can exhibit high ZT values. As explained above, the equation of the thermoelectric figure of merit Z can be made dimensionless by multiplying it by an absolute temperature T, for example the temperature of the hot contact of the thermoelectric device. It is concluded that the dimensionless thermoelectric figure of merit ZT = (S ² * σ / κ) * T can be used to evaluate the performance and energy conversion efficiency of a thermoelectric material or device.

For PbTe nanowires, taking into account the bulk thermal conductivity (κ) of PbTe, the ZT coefficient at 750 K is still very high when using ZT = (S ² * σ / κ) * T (ie ZT is greater than about 2.0). being). At about 300 K to 750 K the ZT coefficient increases with temperature. In the case of PbTe-based thermoelectric nanowires, the S ² * σ value tends to increase from a certain level to the highest value, increasing the ZT coefficient as the nanowire width decreases. However, after reaching a certain nanowire width, the ZT coefficients begin to decrease as the nanowire width decreases. The PbTe based nanowires described herein can be easily tailored to exhibit n-type or p-type conduction by changing the stoichiometry of Pb and Te or by adding some trace components / impurities.

Many thermoelectric materials, including PbTe, are sensitive to oxygen, which can degrade thermoelectric performance. For this reason, it is advantageous to ensure that these thermoelectric materials are sealed and protected from oxygen contamination within the target environmental range. Of course, thermoelectric devices are not commercially viable unless they can withstand the elements and environments in which they will be used.

Although PbTe Thermoelectric materials are preferred although other materials such as thermally without departing from the scope of the present invention, _{Bi 2 Te 3, SiGe, ZnSb} , Zn 2 S and Cd _{0 .8} Sb ₃ may be used. The thermoelectric material may initially be in any convenient form, such as granules or powders.

Once the fiber drawn nanowire cable is produced using this method, the electrical conductivity (σ) and thermal power (S) are measured and the variation of the parameter S ² * σ is determined. The parameter S ² * σ is determined by experiment, multiplied by the measured temperature (K) and divided by the known thermal conductivity (κ) to give the ZT value of the nanowires produced by the present invention.

 Testing conducted with a van der Pauw 4-probe instrument on glass coatings without nanowires showed that the sample was very resistant and the instrument did not measure conductivity at all. Likewise, thermal power measurements using conventional methods (e.g., using the Seebeck coefficient determination system sold by MMR Technologies (Mountain, Calif.)) Do not yield any results due to the high resistivity of the glass cladding. I couldn't. However, the electrical conductivity and thermal power of the PbTe embedded cable could easily be measured, indicating that the electrical conductivity and thermal power measurements are due to continuous nanowires along the length of the cable.

Preferred thermoelectric materials for the nanowire cables of the present invention are PbTe because of favorable thermoelectric properties and reasonable costs. Using the known bulk thermal conductivity of PbTe, the calculated ZT ((S ² * σ / κ) * T) coefficient at 750 K is> 2.5. S ² σ of PbTe shows a clear trend of increasing to a maximum at any given nanowire width. Given that the best known ZT coefficient of bulk PbTe is about 0.5, it is believed that the ZT coefficient of about 2.0 or greater is significantly improved by quantum confinement. The ZT coefficient increases as the nanowire width decreases until this maximum is reached, and then the ZT coefficient begins to decrease as the nanowire width further decreases. As will be appreciated by those skilled in the art, other thermoelectric materials having suitable thermoelectric properties (eg, Bi ₂ Te ₃ ) can be used without departing from the scope of the present invention.

According to the invention, the maximum diameter of the nanowires is preferably less than about 200 nm, most preferably from about 5 nm to about 100 nm. If the cross section of the nanowire is not a circle, in this situation the term "diameter" means the average of the lengths of the major and minor axes of the cross section of the nanowire perpendicular to the longitudinal axis of the nanowire. Nanowires having a diameter of about 50 nm to about 100 nm can be prepared using a method of withdrawing a thermoelectric material in a glass coating as described below.

The cable of the invention is preferably made to exhibit a high degree of diameter uniformity from one end to the other. According to some embodiments of the present invention, the maximum diameter of the glass cladding may vary in the range of less than about 10% over the cable length. For less precise applications, the diameter of the nanowires can vary in larger ranges (eg 5-500 nm depending on the application). Electrically, the glass is 10 times higher in resistance than the thermoelectric material it coats with it. Cables are generally based on semiconducting wires and mainly control the doping and composition of the wires by varying the composition of the thermoelectric material to produce wires exhibiting p-type or n-type thermoelectric behavior. Advantageously, the cable can be used cost-effectively in developing superior thermoelectric devices.

According to the invention, the method of drawing out the thermoelectric material in the glass coating material comprises drawing out the glass coating thermoelectric material to form individual fibers (or monofibers) of the thermoelectric material, preferably individual fibers having a diameter of about 500 μm or less. . As will be appreciated by one of ordinary skill in the art, monofibers may have a diameter of greater than 500 μm without departing from the scope of the invention. The cable diameter can be reduced to at least 5-100 nm by repeatedly drawing the fiber bundles of monofibers, and the concentration of the wire in the cross section of the cable can be increased to ˜10 ⁹ / cm 2. Advantageously, these cables exhibit quantum confinement to provide improved thermal power generation efficiency.

The method of drawing the thermoelectric material in the glass cladding may further comprise bundleing the cables together and redrawing several times in succession to produce a multicore cable comprising the glass clad thermoelectric fiber. For example, the material that forms the fibers of the cable may include PbTe or Bi ₂ Te ₃ . The resulting cable includes a multicore cable having a plurality of individual fibers insulated from each other by a glass cladding. Particular glass coatings may be selected to contain specific compositions that match the physical, chemical, thermal and mechanical properties of the selected thermoelectric material. The glass cladding preferably has an electrical resistivity of several orders of magnitude higher than the metal, alloy or semiconductor material forming the thermoelectric fiber. Suitable commercial glass for most applications include, but are not limited to, Pyrex, Vico and Quartz glass.

According to one further aspect of the present invention, individual cables can be used as n-type and p-type components of thermoelectric devices by varying the metal, alloy or semiconductor material forming the fiber to make the cable n-type or p-type. The cable can exhibit quantum confinement by reducing the thickness or diameter of the fiber to a predetermined range, thereby increasing the efficiency of thermoelectric power generation.

Method of drawing out the thermoelectric material in the glass coating material

1, a vertical tubular furnace 10 is used to provide heat for drawing glass-covered thermoelectric fibers. In particular, the vertical tubular furnace 10 is sealed in an area with a reduced cross section 18 so as to form a preform comprising a glass tube 14 which forms a vacuum space 20 at least partially filled with a thermoelectric material 22. central lumen (11) for receiving a preform (12). A furnace is used to melt the thermoelectric material 22 and the glass tube 14 in preparation for one or more withdrawal operations to produce the glass coated thermoelectric fiber 24.

Further referring to FIG. 1, the vertical tubular furnace 10 includes a furnace cover 26, a thermal insulator 28 and a muffler tube 30. Suitable materials for the muffler tube 30 include a conductive metal such as aluminum. The vertical tubular furnace 10 further includes one or more heating coils 34 embedded therein. More precisely, the heating coil 34 is disposed between the muffler tube 30 and the thermal insulator 28, and the refractory cement 38 is disposed between the heating coil 34 and the thermal insulator to the heating coil 34. The heat generated thereby is directed inward to form the hot zone 40 in the muffler tube 30. The heating coil 34 is provided with a conductive wire 44 which can be insulated using the ceramic insulator 48. In addition, a thermocouple probe 50 is provided to measure the temperature in the hot zone 40, which may include a length of about 1 inch.

Now, a method of withdrawing a thermoelectric active material 22 comprising an array of metal, alloy or semiconductor rods embedded in a glass cladding will be described. Initially, a suitable thermoelectric material 22 is selected. Preferred thermoelectric materials of the invention include PbTe, which is initially in granular form. Further suitable thermoelectric materials include, but are not limited to, Bi ₂ Te ₃ , SiGe, and ZnSb. The next step involves selecting a suitable material to form the glass tube 14. The glass material is preferably selected to have a slightly higher fiber pull-out temperature than the melting temperature of the thermoelectric material (eg ≥ 920 ° C. for PbTe). Next, one end of the glass tube 14 is sealed using the vertical tubular furnace 10. Alternatively, a blowtorch or other heating device may be used to seal the glass tube 14 and create a vacuum space 20.

After sealing one end of the glass tube 14, the next step includes introducing the thermoelectric granules into the vacuum space 20 and evacuating the glass tube by attaching the open end of the glass tube to the vacuum pump. During operation of the vacuum pump, the middle of the glass tube 14 is heated so that the glass partially melts and collapses under vacuum. The partially molten glass tube provides an ampoule 54 containing a thermoelectric material 22 to be used in the first drawing operation. The next step involves introducing the end of the ampoule 54 containing the thermoelectric material 22 into the vertical tubular furnace 10. In the illustrated embodiment, the tubular furnace 10 is configured such that the ampoule 54 is introduced vertically, in which case the ends of the ampoule 54 containing thermoelectric granules are connected to the heating coil 34 in the hot zone 40. Are arranged adjacently.

Once the ampoule 54 is properly placed in the vertical tubular furnace 10, the temperature is increased so that the glass surrounding the thermoelectric granules melts only enough to be withdrawn, as occurs in conventional glass withdrawal towers known in the art. As discussed above, the composition of the glass is preferably selected such that the fiber withdrawal temperature range is slightly above the melting point of the thermoelectric granules. For example, if PbTe is selected as the thermoelectric material, a suitable material for withdrawing glass containing PbTe fibers is pyrex glass. The physical, mechanical and chemical properties of glass tube 14 and thermoelectric material 22 will be somewhat related to the properties of the resulting cable. Preferably, glass is selected as the coating material in which these properties exhibit a minimum deviation with respect to the properties of the thermoelectric material 22.

The glass tube 14 may comprise a commercially available Pyrex tube having an outer diameter of 7 mm and an inner diameter of 2.75 mm, wherein the glass tube is filled with PbTe granules over a length of about 3.5 inches. The evacuation of the glass tube 14 can be achieved overnight under a vacuum of about 30 mtorr. After evacuation, the zone of the glass tube 14 containing the thermoelectric material 22 is gently heated with a torch for several minutes to remove residual gas, and then the glass tube 14 is sealed above the height of the thermoelectric material 22 under vacuum.

In operation, a vertical tubular furnace 10 is used to draw glass-covered thermoelectric fibers. The vertical tubular furnace 10 includes a short hot zone 40 of about 1 inch and places the preform 12 into the vertical tubular furnace 10 so that the lower tube end is slightly below the hot zone 40. When the furnace is about 1030 ° C., the weight from the bottom tube end is sufficient to allow the glass tube 14 to extend under its own weight. When the lower end of the glass tube 14 appears in the lower opening of the furnace, it can be grabbed by forceps and pulled by hand. The preform 10 can be manually advanced periodically to replenish the preform material consumed during the fiber takeout process. Fiber 24 preferably comprises a diameter of about 70 μm to about 200 μm. According to a further embodiment of the invention, the withdrawal operation can be carried out using an automatic withdrawal tower which exhibits little change in diameter.

According to a further embodiment of the present invention, short fiber segments can be formed by drawing the heterostructure and then breaking the heterostructure into shorter fragments. For example, these short pieces can be machined to be about 3 inches long. The fragments are then bunched in another pyrex tube sealed at one end using a vertical tubular furnace or a blowtorch as described above. When the appropriate number of monofibers are filled in the tube, the open end is attached to the vacuum pump and the middle zone is heated. This heating causes the glass tube to collapse, thus sealing the tube and forming an ampoule for the second drawing operation, which produces a cable having a plurality of multicore fibers. After the second withdrawal operation, the fibers are collected and placed in the holes of another sealed tube. When the hole is filled with the appropriate number of monofibers, the preform is evacuated and sealed under vacuum. Subsequently, fiber withdrawal is performed on the fibers withdrawn twice. This process is repeated as necessary to obtain a final thermoelectric material diameter of about 100 nm.

Nanowire  Property

In order to characterize the electronic properties of bulk and heterostructured nanowires, it is important to determine the x-ray diffraction properties of the glass coated thermoelectric material. 2 shows an x-ray diffraction pattern of a PbTe based cable made according to the principles of the present invention, where the characteristic spectrum of PbTe overlaps the x-ray diffraction pattern of glass. In particular, the x-ray diffraction pattern clearly indicates that PbTe peaks are present and no other peaks, thus exemplifying that the glass material neither reacts nor devitrifies during fiber withdrawal. These peaks are the proprietary properties of the peaks of the PbTe crystals.

FIG. 3 shows a glass coated PbTe based cable 60 fabricated using the method of withdrawing the thermoelectric active material embedded in the glass coating described above. Specifically speaking, the cable 60 comprises a number of multiple monofibers 64 that are bundled and fused to form a cable (or button) that can have virtually any length. The buttons can be split, cut or otherwise split to produce a number of short cables having a predetermined length. 4 is an enlarged cross sectional view of the glass sheathed PbTe based cable 60 of FIG. 3 taken along lines 3A-3A. The cable 60 comprises a plurality of monofibers 64, has a width of about 5.2 mm and is made using a single pull of PbTe fibers at a temperature of about 300 K.

According to a preferred embodiment of the present invention, the cables 60 are bundled together and redrawn several times in succession to produce a multicore cable having a plurality of individual thermoelectric fibers insulated from one another by a glass cladding. FIG. 5 is a cross sectional view of the glass sheathed PbTe based cable 60 after the second withdrawal of PbTe fibers. The twice drawn cable has a width of about 2.78 mm. FIG. 6 is a cross sectional view of the glass sheathed PbTe based cable 60 after the third extraction of the PbTe fibers, where the cable has a width of about 2.09 mm.

3-6 show that microstructures develop when the concentration of wire in the cable increases to ˜10 ⁹ / cm 2. These microstructures can be observed using optical and scanning electron microscopy. For example, energy dispersive spectroscopy can be used to clearly see the presence of PbTe wire in the glass substrate.

Thermoelectric Characterization

Another aspect of the invention includes the continuity and electrical connectivity of fibers embedded in glass along the entire length of the cable. Electrical connectivity is easily demonstrated by determining the resistance of the cable at different thicknesses. According to one preferred embodiment of the present invention, if no thermoelectric wire is embedded in the glass coating material, the resistance of the glass coating material is about 10 ⁷ to 10 ⁸ times higher than that of the continuous thermoelectric fiber.

The sample used to determine the electrical connectivity of the thermoelectric wire is in the form of a "button" of PbTe made from the preform after following one of the fiber drawing steps. 7-9, the resistance of thermoelectric wires embedded in glass is about 1 kΩ or less. On the other hand, the resistance of the glass coating material without the thermal wire is 10 and greater than ⁸ Ω, which is about 10 ⁸ times higher than the resistance of the cable embedded in the PbTe. This difference in electrical resistance indicates that the glass coated thermoelectric wire drawn using the method described herein exhibits electrical connectivity from one end to the other end.

FIG. 7 is a table showing the DC resistance of the PbTe cable 60 after the first extraction of the PbTe fiber, where the resistance of the cable is plotted against the current A. FIG. In particular, the DC resistance of the cable 60 decreases steadily with increasing current. FIG. 8 is a table showing the DC resistance of the cable 60 after the second withdrawal of PbTe fiber, while FIG. 9 is a table showing the DC resistance of the PbTe cable 60 after the third withdrawal of PbTe fiber.

Preferred cables made in accordance with the principles of the present invention preferably comprise one or more thermoelectric fibers embedded in an electrically insulating material, wherein the thermoelectric material exhibits quantum confinement. According to a preferred embodiment of the present invention, the width of each fiber is substantially equal to the width of the single crystal of the thermoelectric material, where each fiber has a substantially identical crystal orientation. Preferred cables include a plurality of fibers that are fused or sintered together to have electrical connectivity between all the fibers. Alternatively, there is electrical connectivity between some but not all of the fibers in the cable.

The glass cladding of the cable preferably comprises an electrically insulating material comprising a bicomponent, ternary or higher component glass structure such as pyrex, borosilicate, aluminosilicate, quartz and lead telluride-silicate. The thermoelectric material may be selected from the group consisting of metals, semimetals, alloys and semiconductors such that the thermoelectric material exhibits electrical connectivity and quantum confinement along a predetermined length of cable ranging from several nanometers to several miles. The ZT coefficient of the cable is preferably at least 0.5, more preferably at least 1.5 and most preferably at least 2.5.

Thus, it can be seen that a thermoelectric device manufactured by quantum confinement in nanowires is provided. Those skilled in the art will understand that the present invention may be practiced differently from the various and preferred embodiments presented herein for purposes of illustration and not limitation, and the invention is limited only by the following claims. It is noted that equivalents of the particular embodiments discussed herein may also practice the present invention.

Claims (24)

An electrically insulating glass material, and at least one semiconductor wire embedded in the electrically insulating glass material, at least one semiconductor wire comprising a thermoelectric material, wherein the at least one semiconductor wire is between 73 mm (3 inches) and 588 mm (2 ft) A cable having a length of Z and a ZT coefficient of semiconductor wire of 1.5 or more. The cable of claim 1 wherein each semiconductor wire is substantially a single crystal of thermoelectric material. 3. The cable of claim 2, wherein each semiconductor wire has a substantially identical crystal orientation. The cable of claim 1 wherein each semiconductor wire has a diameter of 1 nm to 500 nm. The cable of claim 1, wherein the one or more semiconductor wires comprise a plurality of wires, the electrical connections being between some but not all of the wires. The cable of claim 1 wherein the electrically insulating glass material is selected from the group consisting of pyrex, borosilicates, aluminosilicates, quartz, lead telluride-silicates, and combinations thereof. 7. The cable of claim 6, wherein the electrically insulating glass material comprises a bicomponent, ternary or higher component glass structure. The cable of claim 1, wherein the semiconductor wire is automatically drawn out using a wire drawing tower. The cable of claim 1 wherein the semiconductor wire is manually drawn. The cable of claim 1, wherein the one or more semiconductor wires comprise a plurality of glass clad semiconductor wires. The cable of claim 1 wherein the thermoelectric material comprises PbTe. The cable of claim 1 wherein the thermoelectric material is selected from the group consisting of Bi ₂ Te ₃ , SiGe and ZnSb. Sealing one end of the glass tube so that the glass tube has one open end and one closed end, Introducing a thermoelectric active material into the glass tube, Heating a portion of the glass tube to partially melt the glass to form an ampoule containing a thermoelectric material to be used in the first drawing operation, Introducing an ampoule containing a thermoelectric active material into a heating device, Increasing the temperature in the heating device such that the glass tube melts to a sufficient extent that it is drawn out, and Drawing out the wire of the glass clad thermoelectric active material Method for extracting the thermoelectric active material in the glass coating material comprising a. 14. The method of claim 13, Bunching together wires of glass clad thermoelectric active material, and Redrawing one or more times in succession to produce a multi-core cable having a plurality of individual thermoelectric wires insulated from each other by a glass cladding ≪ / RTI > 14. The method of claim 13, Splitting the glass sheathed wire into shorter pieces, Introducing a piece of glass sheathed wire into another glass tube having one sealing end and one open end, Evacuating the glass tube by attaching the open end to a vacuum pump, Heating a portion of the glass tube such that the glass is partially melted and collapsed under vacuum to provide an ampoule in which the partially molten glass tube contains a piece of glass sheathed wire, Introducing an ampoule into a heating device, Increasing the temperature in the heating device such that the glass tube melts only enough to be drawn out, and Drawing a cable having a plurality of multi-core wires by drawing a wire of glass-covered thermoelectric active material ≪ / RTI > The method of claim 13, wherein the heating device comprises a vertical tubular furnace comprising a central lumen for receiving the glass tube, and the central lumen includes a high temperature zone for melting the glass tube. The method of claim 13, wherein the thermoelectrically active material comprises an array of metal, alloy, or semiconductor rods embedded in a glass cladding. The method of claim 13, wherein the thermoelectrically active material comprises PbTe initially in granular form. The method of claim 13, wherein the thermoelectrically active material comprises Bi ₂ Te ₃ , SiGe or ZnSb. The method of claim 13, wherein the glass coating comprises an electrically insulating material selected from the group consisting of pyrex, borosilicate, aluminosilicate, quartz, and lead telluride-silicate. The method of claim 13 wherein the electrical resistance of the thermoelectric wires embedded in the glass is less than 1 kPa, and the electrical resistance of the glass cladding without thermoelectric wires is greater than 10 ⁸ kPa. The method of claim 13, wherein the width of each wire is substantially equal to the width of the single crystal of the thermoelectric active material. The method of claim 13, wherein the glass sheathed wires are fused or sintered together such that the wires are electrically connected from one end to the other end but there are no lateral electrical connections between the wires. 14. The method of claim 13, wherein the individual wires are fused or sintered together such that they are electrically connected from one end to the other, not between all of the wires.

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