Patent Application
20120074832
The present application claims priority to a corresponding patent application filed in India and having application number 2276/DEL/2010, filed on Sep. 23, 2010, the entire contents of which are herein incorporated by reference.
Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
In 1880 Thomas Edison invented the light bulb using a carbon filament. Edison's light bulb provided 40 hours of light in an oxygen-free environment ushering in the electric lighting era. The carbon filament, however, has low reliability at high operating temperatures. To replace the carbon filament, more than 40 elements have been tested as a filament material. In 1910, William D. Coolidge successfully substituted a tungsten filament in light bulbs for Edison's carbon filament.
Incandescent light bulbs, however, provide light via blackbody (thermal generated) radiation. The visible light of a typical vacuum tungsten light bulb is approximately 5% of the total radiation. Thus, a majority of electrical energy to operate the bulb is converted to heat. Increasing the operating temperature increases efficiency, however, this method of increasing the efficiency is limited by the melting temperature of tungsten.
Sodium lamps are more efficient than tungsten lamps, but their light is essentially monochromatic and not pleasing to the human eye. Light-emitting diodes are not widely used currently because of their complicated fabrication technique and high processing cost.
Some embodiments relate to a device configured, for example, to produce light. Some example devices include a filament having carbon nanotubes. These devices may be configured such that they produce light with a luminary characteristic having a value higher than a value of the luminary characteristic of a device having an uncoated filament at a same operating condition.
Some embodiments relate to a method including making a device with a filament having carbon nanotubes. These devices may be configured such that they produce light with a luminary characteristic having a value higher than a value of the luminary characteristic of a device having an uncoated filament at a same operating condition.
The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
Embodiments are shown in the drawings, in which like reference numerals designate like elements.
a-d show micrographs obtained using a scanning electron microscope (SEM) for electroless catalyst coatings performed for 5, 10, 15, and 20 minutes.
a-c depict embodiments of a device including a CNT-coated tungsten filament.
a shows various graphs depicting change in relative efficacy as a function of applied voltage for a CNT-coated filament device and an uncoated filament device.
b shows various graphs depicting change in relative efficacy as a function of applied power for a CNT-coated filament device and an uncoated filament device.
Multiwall carbon nanotube (CNT), single wall CNT, and mixtures of multiwall and single wall CNT-coated tungsten substrates have been developed for use as a filaments for incandescent light bulbs. Embodiments include a light bulb in which the conventional tungsten filament is replaced by a CNT-coated tungsten filament. Embodiments of CNT-coated tungsten filaments exhibited higher lighting efficiency, higher brightness and a lower threshold voltage for light emission as compared to conventional tungsten filaments. In an embodiment, CNTs were grown on transition metal catalyst-coated tungsten substrate by thermal chemical vapor deposition (CVD) method. In alternative embodiments, other methods of growing CNTs, may be used.
Various processing conditions including catalyst concentration, time, temperature, and pH of coating solution, flow rates of inert gas, carbon containing gas and reducing gas, etc. have been investigated. Luminescence properties like relative efficacy (lux/watt), irradiance, and the I-V characteristics of CNT-coated light bulbs have been measured and compared with light bulbs with uncoated tungsten filaments. Results show that the CNT-coated filament in an incandescent light bulb improves efficiency and energy saving and it can be a good candidate as incandescent light source.
Carbon nanotubes have been reported in the literature since 1991, and have been shown to have excellent electrical properties, including field emission, thermionic emission and work function. Additionally, CNTs are reported to be stable at certain temperatures in oxygen-free atmosphere. Use of straight, continuous single wall and double wall CNTs as filaments in light bulbs and electric lamps has also been reported.
An embodiment provides a filament which includes a support material coated with a carbon product(s). In an embodiment, the support material is tungsten. Other support materials include but are not limited to, platinum, carbon, tantalum, and other suitable filament materials.
The carbon product may include single wall carbon nanotubes, multiwall carbon nanotubes, or a mixture of single wall and multiwall carbon nanotubes.
An embodiment of a process of making a carbon nanotube-coated filament includes steps of activating the surface of the support material and growing carbon nanotubes on the activated surface.
In an embodiment, the filament may be etched 104 by dipping into an etching solution. The etching solution may include, for example, about 1 ml of about 30% solution of hydrogen peroxide (H2O2) in about 100 ml deionized water. In an embodiment, etching is performed for about 1 to about 5 minutes in a temperature range of about 25 to 90° C. Other times and temperatures may also be used. In an embodiment, the etched filament may be rinsed 106 in de-ionized water and ultrasonicated for about 1 to about 10 minutes. Other times may also be used. In an embodiment, the filament may be dried at about 60 to about 90° C. for about 1 to about 3 hours. Alternatively, the filament by be dried at higher or lower temperatures and/or for more or less time.
An example process of coating the activated surface with carbon nanotubes 200, illustrated in
Mixing reaction and carrier gases 208 may be performed in a separate mixing chamber prior to introducing the gases into a reaction chamber. Alternatively, mixing reaction and carrier gases 208 may be performed in a manifold. In an embodiment, the method includes a step of removing moisture and de-oxidizing the mixed gases 210. Alternatively, the gases may have the moisture removed and be de-oxidized prior to mixing. Growing the carbon nanotubes 212 may be performed under different conditions (temperature, gas mixtures, etc.) as discussed in more detail below.
Filaments according to one or more embodiments include: continuous monofilaments, continuous flat multifilaments, continuous twisted multifilaments, continuous textured multifilaments and coiled filaments. Discontinuous filaments may be filaments that are less than 10 mm in length. Continuous filaments may be filaments that are 10 mm or more in length. In an embodiment, the diameter of the filament varies from about 0.0030 cm to about 0.0102 cm. In other embodiments, the filament may have larger diameters.
In an embodiment, the catalyst includes one or more Group VIII metals such as Ni (Nickel), Ru (Ruthenum), Rh (Rhodium), Pd (Palladium), Ir (Iridium) and Pt (Platinum) and/or mixtures or alloys thereof. Alternatively, the catalyst includes one or more Group VIb metals such as Cr (Chromium), Mo (Molybdenum) and W (Tungsten) and/or mixtures or alloys thereof. Alternatively, the catalyst includes mixtures and/or alloys of group VIII metals and group Vlb metals. The catalyst may be in a ratio of one part of group VIb metal to at least 2 or more part of metal from group VIII.
Coating Filaments with Catalyst
The catalyst(s) may be coated on the filament via a number of different methods. For example, the catalyst may be coated using an electroless dip coating process. In an embodiment using a dip coating process, the oxidizing agents used in dip coating include metals, metal sulfides, metal disulifides, metal halides and metal sulphates. In this embodiment, the metals may include group VIII metals such as Ni, Ru, Rh, Pd, Ir, and group VIb metals such as of Cr, Mo, W and as well as mixtures and alloys of these metals. Reducing agents in this embodiment may include metals such as Na, Mg, Al, Zn, Cu and mixtures thereof, metal hydrides of Na, Mg, Al, Zn, Cu and mixtures thereof, and metal hypophosphites of Na, Mg, Al, Zn, Cu and mixtures thereof. Chelating agents in this embodiment may include water, carbohydrates, including polysaccharides, organic acids with more than one coordination group lipids, steroids, amino acids and related compounds, peptides, phosphate, nucleotides, tetrapyrrois, ferrioxamines, ionophores, such as gramicidin, monensin, valinomycin, phenolics, 2,2′-bipyridyldimercaptopropanol, ethylenedioxydiethylene-dinitrilo-tetraacetic acid, ethylene,glycol-bis(2-aminoethyl)-N,N,N′,N″-tetraacetic acid, lonophores-nitrilotrriacetic acid, NTA ortho-Phenanthroline, salicylic acid, triethanolamine, sodium succinate, sodium acetate, ethylene diamine, ethylenediaminetetraacetic acid, dethylenetriaminepentaacetic acid, ethylenedinitrilotetraatic acid, and mixture thereof.
In this embodiment, the electroless dip solution may include a buffer. The buffer may include a weak acid, its salt and mixture thereof. Example weak acids include but are not limited to succinic acid, formic acid, acetic acid, tricholoroacetic acid, hydrofluoric acid, hydrocynic acid, hydrogen sulphide, and water. The buffer may also include sodium and/or potassium salts of succinic acid, formic acid, acetic, trichoroacetic acid, hydrofluoric acid, and hydrocynic acid. The buffer may also include hydrogen sulphide.
In an embodiment, electroless dip coating is carried out in an atmosphere that includes nitrogen, argon, helium or mixtures of these gases. Further, electroless dip coating may be carried out, for example, at a temperature of about 10-90° C. for a time period of about 10-3600 seconds. Under these process conditions, a catalyst layer may be with a thickness of about 50-200 nm may be obtained.
In an embodiment, the filament is dipped in an acidic/basic bath prepared by dissolving an oxidizing agent in de-ionized water having a ratio of about 1:100 to about 9:100 to which is added a reducing agent (ratio range of about 1:1 to 1:5, by weight), a chelating agent (ratio range of about 1:1 to 1:10) and a buffer (ratio range of about 1:0.10 to 1:1) followed by stirring of the mixture to obtain the acidic/basic bath. An example spraying solution is provided in Table 1 below.
In another embodiment, coating of the catalyst on the filament may be carried out by spray coating a solution on the filament. A method 300 of making the spray solution is illustrated in
The solution may be prepared by a method 300 that includes the steps of: dissolving a metal nitrate, magnesium oxide and citric acid 302, stirring the solution to form a semi-solid mass (i.e., a matter having a rigidity and viscosity intermediate between a solid and a liquid) 304, a first heat treating of the semi-solid mass 306, a second heat treating of the semi-solid mass 308, cooling to form oxide powder 310, adding methyl alcohol to powder form solution 312. In an embodiment, the metal nitrate, magnesium oxide and citric acid are provide in a ratio of about 1:1:4 by weight, and dissolved in 100 ml of de-ionized water. Other ratios may also be used. Stirring the solution to form a semi-solid mass 304 may be performed, for example, at a temperature of about 80° C. for about 6 hours. Other times and temperatures may be used. Typically, when stirring at a lower temperature, stirring is performed for a longer time while stirring at a higher temperature is performed for a shorter time.
The first heating treating of the semi-solid mass 306 may be performed, for example, in an oven at a temperature of about 120° C. for a period of about 2 hours. Other temperatures and times may be used. The second heat treating of the semi-solid mass 308 may be performed, for example, in a furnace at a temperature of about 300° C. to 700° C. for a period of about 5 hours in air. The time may be longer or shorter than 5 hours. Generally, heat treating at higher temperatures allows for shorter heat treatment times. The product of this step is a powder of mixed nickel and magnesium oxides. The cooling step 310 may be performed at any rate. Cooling may be accomplished by air cooling, forced air cooling, or any other cooling technique. The addition of methyl alcohol to the powder may be accompanied with stirring to form the solution 312.
An example dip coating specifications is provided in Table 2 below.
A method 400 of making the spray solution for a solution coating embodiment is illustrated in
The first heat treating of the semi-solid mass 406 may be performed, for example, at a temperature of about 100° C. for a period of about 24 hours. Other times and temperatures may be used. The second heat treating of the semisolid mass 408 may be performed in a furnace at a temperature of 300 to 600° C. for a period of 5 hours. In example embodiments, heat treating at higher temperatures allows for shorter heat treatment times. The product of this step is a powder of mixed nickel and silicon oxides. The cooling step 410 may be performed at any rate. Cooling may be accomplished by air cooling, forced air cooling, or any other cooling technique. The addition of methyl alcohol to the powder may be accompanied with stirring to form the solution 412.
In other embodiments, other coating techniques may used to coat transition metal catalyst(s) on tungsten filament. Examples include, but are not limited to, electroplating, dip coating through sol-gel, spin coating through sol-gel, radio frequency (RF) sputtering, magnetron sputtering, electron beam evaporation, physical vapor deposition, thermal evaporation, chemical vapor deposition, combustion, co-precipitation, impregnation, and langmuir blodgett.
In one or more embodiments, the catalyst-coated tungsten filament is characterized and analyzed using scanning electron microscope (SEM) (e.g., JSM-840 electron microscope) and energy dispersive X-ray (EDAX) analysis technique. Such analysis is used to analyze the transition metal(s), phosphorous and carbon content (e.g., in wt percentage) of the transition metal-coated tungsten filament. For EDAX analysis, the surface area of the filament may be magnified at least 100 times such that the entire area of the filament can be scanned. This magnified-area analysis enhances the reliability of the characterization results, unlike conventional techniques in which only a few randomly selected area spots are chosen for analysis. The results from EDAX analysis were quantified using the standard ZAF technique, where “Z” relates to the atomic number, “A” relates to the absorption, and “F” relates to the florescence correction factors used in X-ray analysis.
In example embodiments, it was also observed that the temperature in the coating process plays a role in determining the rate and quality of the coating process.
In addition to coating temperature and coating time, in example experiments, it was seen that the pH value of the coating solution at which the reaction in the coating process occurs plays a role in the coating process kinetics, as well as in the composition of the coating.
a-d show micrographs obtained using a scanning electron microscope (SEM) for electroless NiP (catalyst) coatings performed for 5, 10, 15, and 20 minutes, respectively. It was observed that phosphorous content in the coating increases with the increase in the coating time. Some transverse cracks were also seen in the SEM micrographs for 15 and 20 minutes coating time (
The SEM and EDAX analysis of Ni—Co catalyst-coated tungsten substrates for a fixed coating time equal to 10 minutes and a fixed coating temperature equal to 70° C. are shown in
For growing or coating CNTs on a tungsten filament, any suitable technique may be used. In one embodiment, chemical vapor deposition (CVD) is used. The chemical vapor deposition technique makes use of the gases comprising of carbon containing gas such as group of saturated hydrocarbons, aliphatic hydrocarbons, oxygenated hydrocarbons, aromatic hydrocarbons, alcohols, carbon monoxide and mixture thereof; reducing gas such as group of gases hydrogen, chlorine and mixtures thereof; and diluent gas such as group of nitrogen, argon, helium and mixture thereof. In some embodiments, the ratio of reducing gas to diluent gas is about 0:100 to 50:50; the ratio of carbon containing gas to reducing gas to diluent gas is about 0:5:95 to 60:20:20; the ratio of carbon containing gas to diluent gas is about 0:100 to 60:40. Other ratios of these gases may be used.
An example system 1300 for coating carbon nanotubes on a catalyst-coated tungsten filament using the CVD technique is shown in
In one embodiment, after placing the catalyst-coated tungsten filament in the middle of reactor 1304, a vacuum is created in reactor 1304. Reactor 1304 may be connected to a vacuum line, the pressure in reactor 1304 may be reduced to less than about 200 mm Hg. This process may be repeated 10 or more times to completely remove oxygen from reactor 1304. Further, furnace 1302 may be activated to expose reactor 1304 to temperature in the range of about 400° C. to 600° C. in an inert atmosphere. Various precursor gases for the execution of the CVD process are then introduced into reactor 1304 from cylinders 1310, 1312 and 1314. For example, inert gas cylinder 1310 provides an inert gas such as nitrogen, helium, or argon; reducing gas cylinder 1312 provides a reducing gas such as hydrogen, or chlorine; and carbon-source gas cylinder 1314 provides a gas containing carbon such as acetylene, methane, ethylene, propane, carbon dioxide, or ethane. Before entering reactor 1304, one or more of these gases are first deoxygenated by passing through an alkaline pyrogallol solution in containers 1316, concentrated sulphuric acid and calcium chloride in containers 1318, and potassium hydroxide in containers 1320. Subsequently, moisture is removed from the gases by passing them through a silica gel bed in container 1322. The gases directed entered in the reactor through three different non-return valves. The flow rates of gases directed toward reactor 1304 are measured by rotameter 1324, and the gas flow is controlled by non-return valves 1326. The gases are then mixed in mixing chamber 1308 before entering into reactor 1304.
In this embodiment, first, only the inert gas from cylinder 1310 is released and allowed to enter reactor 1304. The rate of inert gas flow may be kept constant at about 120 ml/min. After about 5 to 10 minutes, the reducing gas from cylinder 1312 is allowed to flow into reactor at the rate of about 5 to 25 ml/min for about 10 to 30 minutes. About 5 to 10 minutes thereafter, furnace temperature is increased to about 500° C.-900° C. After reactor 1304 reaches the increased temperature, carbon-containing gas is allowed to pass out from cylinder 1314 at the rate of about 10 to 200 ml/min. This flow rate of the carbon-containing gas may be held for about 1 to 30 minutes. Accordingly, the product of the CVD process performed by system 1300 is a CNT-coated tungsten filament. In other embodiments, other temperatures, times and/or flow rates for the CVD process may be used.
Additionally, a water-circulation arrangement is operatively arranged with reactor 1304 such that water is circulated between an entrance and an exit of reactor 1304 to maintain the reactor temperature at a desired level. Water from this arrangement may also be used as a coolant in condenser 1328. Any condensable material flowing out of reactor 1304 is collected in liquid collector 1330, whereas any non-condensable material is sent to the exit flow of reactor 1304 to be eventually released into the atmosphere.
In other embodiments, other techniques for coating CNTs on a tungsten filament may be used. Examples, include, but are not limited to, electric arc discharge technique, laser ablation method, thermal chemical vapor deposition (CVD) technique, plasma enhanced CVD technique, microwave CVD technique, microwave plasma enhanced CVD method, radio frequency plasma enhanced CVD method, cold plasma enhanced CVD method, laser assisted thermal CVD technique, catalytic CVD technique, low pressure CVD method, aero-gel supported CVD technique, vapor phase growth CVD technique, high pressure carbon monoxide disproportionation process (HIPCO), water assisted CVD technique, flame synthesis method, hydrothermal synthesis, electrochemical deposition technique, and pyrolytic method.
In one or more embodiments, the CNT-coated tungsten filaments are characterized and analyzed using SEM images and current-voltage analysis.
For current-voltage (I-V) analysis, example CNT-coated tungsten filament devices prepared, for example, using systems and processes described above are shown in
Using system 1600, various indices that may be recorded to compare the performance of bulbs 1604, 1606 may include irradiance, relative efficacy, and current-voltage (I-V) characteristics curve. As discussed above, the intensity of irradiance (lux) for both the bulbs may be measured by their respective light meters 1608, 1610. Relative efficacy (lux/watt) may be calculated as irradiance-to-power ratio. Relative efficacy may be analyzed for various values of applied voltage and/or for various values of applied power. I-V characteristic curves may be are measured for bulbs 1604, 1606 using I-V meter 1612.
a shows graphs of relative efficacy as a function of applied voltage for CNT-coated filament bulb 1604 (graph 1802) and for uncoated filament bulb 1606 (graph 1804). As can be seen, the relative efficacy of bulb 1604 increases much faster than that of bulb 1606 as the applied voltage increases. It was also observed that the efficacy of bulb 1604 is greatly increased when a higher voltage is applied. For example, the efficacy of bulb 1604 was measured to about 18.26 lx/W at about 24.2V, while the efficacy of bulb 1606 was measured equal to about 8.13 lx/W at the same applied voltage. Further at higher voltages, say about 50V, relative efficacy for bulb 1604 was measured as about 123.31 lx/W, while for bulb 1606, it merely reached about 20.29 lx/W.
The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds compositions or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.
As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth.
While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2276/DEL/2010 | Sep 2010 | IN | national |
