AEROSOL-ASSISTED SYNTHESIS OF CRYSTALLINE TUNGSTEN BRONZE PARTICLES

Abstract

Provided herein are methods for producing crystalline tungsten bronze oxide particles. The method may include atomizing a liquid solution comprising an alkali metal precursor and a tungsten precursor to produce droplets; mixing the droplets with one or more gaseous flows to produce a combined flow; flowing the combined flow through a heated reactor to provide crystalline tungsten bronze oxide particles having the formula M.sub.xWO.sub.3, wherein M is the alkali metal; and collecting the particles.

Claims

1. A method for producing crystalline tungsten bronze oxide particles, comprising atomizing a liquid solution comprising an alkali metal precursor and a tungsten precursor to produce droplets; mixing the droplets with one or more gaseous flows to produce a combined flow; flowing the combined flow through a heated reactor to provide crystalline tungsten bronze oxide particles having the formula M.sub.xWO.sub.3, wherein M is the alkali metal and x is a number from zero to 1; and collecting the particles.

2. The method of claim 1, wherein the particles are collected using baghouse filter sampling, a cyclone, an impactor, a thermo-precipitator, or electrostatic sampling.

3. The method of claim 1, wherein the tungsten precursor is ammonium tungstate or tungsten chloride.

4. The method of claim 1, wherein the alkali metal is selected from sodium, potassium, and cesium.

5. The method of claim 1, wherein the ratio of alkali metal precursor to tungsten precursor is from 0.4:1 to 1:1.

6. The method of claim 1, wherein the one or more gaseous flows comprise nitrogen and hydrogen.

7. The method of claim 1, wherein a flow rate through the reactor is 0.1-15 SLPM.

8. The method of claim 1, wherein the reactor comprises a plurality of tube reactors.

9. The method of claim 1, wherein the reactor comprises a spiral flow channel.

10. The method of claim 1, wherein the reactor is heated to a temperature of 600-1000° C.

11. The method of claim 1, wherein the particles are in the cubic phase or tetragonal phase.

12. The method of claim 1, further comprising recirclating a gaseous flow after the particles are collected.

13. The method of claim 1, wherein the liquid solution is an aqueous solution and does not contain an organic solvent.

14. The method of claim 1, wherein the method does not include an annealing step.

15. The method of claim 1, further comprising introducing a dilution flow to the combined flow flowing through the reactor.

16. The method of claim 15, wherein a ratio of a flow rate of the dilution flow to a flow rate of the combined flow is from 2:1 to 10:1.

17. The method of claim 15, wherein the dilution flow is heated.

18. The method of claim 15, wherein the dilution flow is unheated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1. Diagram of an aerosol-assisted reactor with a Collison atomizer according to some embodiments of the disclosure.

[0014] FIG. 2. Diagram of an aerosol-assisted reactor with a Collison atomizer and dilution flow according to some embodiments of the disclosure.

[0015] FIG. 3. Diagram of an aerosol-assisted reactor with an ultrasonic nebulizer and dilution flow according to some embodiments of the disclosure.

[0016] FIG. 4. Diagram of a recycle synthesis setup according to some embodiments of the disclosure.

[0017] FIG. 5. XRD pattern of Produced Na.sub.0.3WO.sub.3 Particles.

[0018] FIG. 6. XRD pattern of Produced Na.sub.0.7WO.sub.3 Particles.

[0019] FIG. 7. SEM image of Produced Na.sub.0.7WO.sub.3 Particles.

[0020] FIG. 8. XRD pattern of Produced Cs.sub.0.3WO.sub.3 Particles.

[0021] FIG. 9. SEM image of Produced Cs.sub.0.3WO.sub.3 Particles.

[0022] FIG. 10. XRD pattern of Produced K.sub.0.3WO.sub.3 Particles.

[0023] FIGS. 11A-C. Produced particle number size distribution on dilution ratio (A) 2/1, (B) 6/1 and (C) 10/1.

[0024] FIG. 12. Produced particle number (1.sup.st row) and mass (2.sup.nd row) size distribution on precursor solution concentration at 0.01 M, 0.0075 M 0.0050 M and 0.0025 M (on the mole concentration of W element).

[0025] FIGS. 13A-C. Particle size distribution when Flow #1 of reactor shown in FIG. 3 has a rate of (A) 0.2 SLPM, (B) 1 SLPM, or (C) 4 SLPM.

[0026] FIG. 14. UV-VIS of different aerodynamic diameter sample of sodium tungsten bronze particles. Note: aerodynamic diameter is equal to d.sub.a=d.sub.p(ρ.sub.p/ρ.sub.0).sup.1/2[ρ.sub.0=1000 kg .Math.m.sub.−3, ρ.sub.p is particle density, for bulk Na.sub.xWO.sub.3 crystal, ρ.sub.p≤7.4 g.Math.cm.sup.−3].

[0027] FIG. 15. Diagram of an aerosol-assisted reactor having a plurality of tubes according to some embodiments of the disclosure.

[0028] FIG. 16. Diagram of an aerosol-assisted reactor having a spiral tube according to some embodiments of the disclosure.

[0029] FIG. 17. Alternate view of an aerosol-assisted reactor having a spiral tube according to some embodiments of the disclosure.

DETAILED DESCRIPTION

[0030] Embodiments of the disclosure provide methods of aerosol-assisted synthesis to produce crystalline tungsten bronze oxide (M.sub.xWO.sub.3) particles, where M is an alkali metal. The production process is in one step, continuous, and without any aftertreatment. The sizes of as-produced M.sub.xWO.sub.3 particles may be controlled by adjusting the dilution and quenching of reaction agents. Due to the high transmittance in visible range (VLT) and excellent absorption in NIR range, the synthesized M.sub.xWO.sub.3 particles may be used as a near infrared (NIR) shielding material which could be applied to transparent media such as glass as disclosed in U.S. Patent Application 2020/0002220 incorporated herein by reference.

[0031] Tungsten bronze particles as described herein are tungsten oxide (WO.sub.3) lattice based, with alkali metal atoms inserted into the voids in the WO.sub.3 lattices forming nano- or micro-crystals. Tungsten bronze particles are capable of shielding near infrared light to reduce the thermal effect of the solar light. The material in the powder form can be easily applied to any surface.

[0032] Various aerosol synthesis routes are known e.g. as described in Charitidis et al. (Manufacturing Rev., 2014) and Gurav et al. (Aerosol Science and Technology, 1993). An aerosol can be defined as a system of solid or liquid particles suspended in air or other gaseous environment. Particles can range from molecules up to 100 μm in size. Spraying is used either for drying wet materials or for applying coatings. When the precursor chemicals are sprayed onto a heated surface or into a hot atmosphere, a precursor pyrolysis occurs and particles are formatted.

[0033] Synthesis methods as described herein may include steps of atomizing a liquid solution comprising an alkali metal precursor and a tungsten precursor to produce droplets; mixing the droplets with one or more gaseous flows to produce a combined flow; flowing the combined flow through a heated reactor to provide crystalline tungsten bronze oxide particles having the formula M.sub.xWO.sub.3, wherein M is the alkali metal; and collecting the particles. In some embodiments, the methods described herein do not include flame-assisted spray pyrolysis and thus do not require an annealing step.

[0034] The alkali metal may be lithium, sodium, potassium, rubidium, cesium, or francium. In some embodiments, x is a number from zero to 1, e.g. 0.3-0.7. In some embodiments, the tungsten precursor is ammonium tungstate or tungsten chloride. In some embodiments, the ratio of alkali metal precursor to tungsten precursor is from 0.2:1 to 1.5:1, e.g. from 0.4:1 to 1:1. The alkali metal and tungsten precursors may be dissolved in water or an alcohol such as methanol. In some embodiments, the aqueous solution does not contain an organic solvent. In some embodiments, the alkali metal precursor may be present at a concentration of 1-40 mmol/L, e.g. about 10-30 mmol/L. In some embodiments, the tungsten precursor may be present at a concentration of 1-50 mmol/L, e.g. 3-10 mmol/L.

[0035] Atomization/neubulization refers to converting a bulk substance to minute parts/pieces in gas phase. Atomization may be accomplished, for example, using an ultrasonic nebulizer which atomizes the solution into aerosol droplets by using ultrasonic vibrations passed through the solution to generate an aerosol. Other atomizers/nebulizers such as a Collison or jet nebulizer which uses compressed air or a mesh nebulizer which uses high frequencies to vibrate a mesh may also be utilized to generate an aerosol.

[0036] With reference to FIG. 1, two inlet flows may enter the reactor. In this exemplary embodiment, Flow 1 passes through a water container which maintains the water at a specific temperature, e.g. 20-80° C., e.g. about 30-70° C. Flow 1 carries the moisture from the water container and mixes with Flow 2, which comes from the atomizer The precursor solution is fed in and sprayed by Flow 2 into the Collison atomizer to create the aerosol droplets. The mixture of Flow 1 and Flow 2 then enters the tube furnace. The aerosol droplets carried within the flow are converted into nanocrystalline particles in the heating process. Then, the particles are collected by the filter. A vent, e.g. one-way valve, is incorporated for safety. A portion of the aerosol particles may be utilized for measurement and characterization. Flow 1 and/or Flow 2 may contain one or more of nitrogen and hydrogen. In some embodiments, a flow rate of Flow 1 and/or Flow 2 may be 0.1-20 SLPM, e.g. 0.1-15 SLPM, 0.5-3 SLPM, or 0.5-1 SLPM.

[0037] With reference to FIG. 2, a dilution flow may be introduced into the reactor along with Flows 1 and 2. The dilution flow may be introduced, for example, at a position near the tail end of the heating zone to quench the produced particles. In this way, the particle size can be tuned by the dilution ratio. The dilution flow may have a flow rate that is about 1-15 times (i.e. a ratio of 1:1 to 15:1), e.g. about 2-10 times, the combined flow rate of Flows 1 and 2.

[0038] With reference to FIG. 3, the precursor solution may be driven by a device with cooling effect to circulate between ultrasonic nebulizer and solution container. The solution in container is kept stirring to maintain homogeneity. The ultrasonic nebulizer atomizes the solution into aerosol droplets. Then, the aerosol is carried by the gas flow controlled by #1 mass flow controller. The aerosol flow is mixed with another flow which is controlled by the #2 mass flow controller. The flow rate of the #1 and #2 flow determines the aerosol velocity passing through the furnace, which provides for the residence time in the high temperature. The combined flow enters into a tube furnace and then, mixes with the third flow (dilution flow) which is controlled by the #3 mass controller and does not contain any precursor. The dilution flow may be heated or unheated. The #3 flow also pass through the furnace and the mixing occurs at the end of the heating zone of the furnace to impose a dilution effect.

[0039] The flows described herein, including the dilution flow, may come from a fresh flow input, which is a gas source containing one or both of hydrogen and nitrogen. In some embodiments, the gas source contains 1-10% hydrogen, e.g. about 4% hydrogen and 90-99% nitrogen, e.g. about 96% nitrogen.

[0040] The tube furnace reactor utilized in the methods described herein may have a diameter of about 0.5-2 inches, e.g. about 1 inch. In some embodiments, the heating zone length is about 1-3 feet, e.g. about 2 feet. In some embodiments, the reactor is heated to a temperature of 400-1000° C., e.g. about 500-900° C. The reactor can be made of any material that can sustain a high temperature (e.g. up to 1000 ° C.) and is chemically inert such as stainless steel. The reactor may comprise a single tube (FIG. 1) or a bundle of multiple tubes (FIG. 15). In some embodiments, the reactor includes one or more tubes having a spiral flow channel (FIGS. 16 and 17).

[0041] After the aerosol flow exits the furnace and cools down, the products are collected. Before collection, one outlet may introduce the sample aerosol to be measured by TSI SMPS to get the size distribution of particles. In some embodiments, the particles are collected using baghouse filter sampling, a cyclone, a cascade impactor, a thermo-precipitator, or electrostatic sampling. For the particle collection, a vacuum pump or injector provides the driving force for moving the particle stream through the collection devices. In some embodiments, the collected particles are in the cubic phase or tetragonal phase.

[0042] With reference to FIG. 4, a recirculation process may be provided to reuse the carry gas and to decrease the usage of nitrogen and hydrogen at the same total volume. The condenser and dryer are provided to remove the moisture in the flow. Using this setup, the producing rate can be increased by at least 10 times, e.g. the total flow rate may be increased from ˜25 SLPM to ˜200 SLPM.

[0043] The crystalline tungsten bronze oxide particles synthesized by the methods described herein may be utilized in various NIR shielding applications. Tungsten bronze is capable of absorbing NIR (780 ˜3000 nm) while having good transmission for visible light. Because ˜50% energy in solar radiation is in the infrared (IR) range, having transparent medium, e.g., window glasses, with the NIR (near Infrared) shielding function will save energy and operational costs of air conditioning of a building/vehicle, e.g. by coating the particles onto automobile windshields or building windows. The particles in the powder form can be easily applied to surfaces of any shape, e.g. flat or curved surfaces. In some embodiments, the particles are mixed with resins, such as a PVB resin used in the inner layer of automobile windshields. For window applications, crystalline tungsten bronze particles can be embedded in hot glasses prior to the cooling or mixed with resin and coated on glass surfaces for the production of window glasses with permanent NIR shielding (offering a more cost-effective option as compared to smart windows). Due to hydrolysis reactions, tungsten bronze particles should not be exposed to a high humidity environment. However, this issue can be resolved by coating the tungsten bronze particles with a thin layer of refractory material, such as, TiO2.

[0044] Unless stated otherwise, all the ratios of reactants or products described herein are mole ratios.

[0045] Before exemplary embodiments of the present invention are described in greater detail, it is to be understood that this invention is not limited to particular embodiments described, as such may, 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, since the scope of the present invention will be limited only by the appended claims.

[0046] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

[0047] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, representative illustrative methods and materials are now described.

[0048] All publications and patents cited in this specification are herein incorporated by reference as if each individual publication or patent were specifically and individually indicated to be incorporated by reference and are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.

[0049] It is noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation.

[0050] As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. Any recited method can be carried out in the order of events recited or in any other order which is logically possible.

[0051] The invention is further described by the following non-limiting examples which further illustrate the invention, and are not intended, nor should they be interpreted to, limit the scope of the invention.

EXAMPLE 1

[0052] Dissolve sodium chloride (NaCl, 12 and 35 mmol/L) and tungsten chloride (WCl.sub.6, 50 mmol/L) into methanol (MeOH, 95 vol %) & ethylene glycol (EG, 5 vol %) to form the precursor solution. The precursor feed-in rate is 0.3 mL/min An aerosol-assisted reactor as shown in FIG. 1 was used as the synthesis device. Flow 1 is 0.5 SLPM. Flow 2 is 1.5 SLPM. The flow gas composition is nitrogen (N.sub.2, 100 vol %). The as-produced Na.sub.0.3WO.sub.3 and Na.sub.0.7WO.sub.3 particle XRD (X-ray powder Diffraction) pattern is shown in FIGS. 5 and FIG. 6. FIG. 7 shows the SEM (Scanning Electron Microscope) image of as-produced Na.sub.0.7WO.sub.3 particles.

EXAMPLE 2

[0053] Dissolve cesium chloride (CsCl, 0.15 mol/L) and tungsten chloride (WCl.sub.6, 0.5 mol/L) into methanol and ethylene glycol (EG, 100 vol %) to form the precursor solution. The precursor feed-in rate is 0.050 mL/min. An aerosol-assisted reactor as shown in FIG. 1 was used as the synthesis device. Flow 1 is 1 SLPM. Flow 2 is 3 SLPM. The flow gas composition is nitrogen & hydrogen (N.sub.2, 75 vol %; H2 25 vol %). The as-produced Cs.sub.0.3WO.sub.3 particle XRD (X-ray powder Diffraction) pattern is shown in FIG. 8. FIG. 9 shows the SEM (Scanning Electron Microscope) image of as-produced Na.sub.0.7WO.sub.3 particles.

EXAMPLE 3

[0054] Dissolve cesium chloride (KCl, 0.15 mol/L) and tungsten chloride (WCl.sub.6, 0.5 mol/L) into methanol and ethylene glycol (EG, 100 vol %) to form the precursor solution. The precursor feed-in rate is 0.050 mL/min. An aerosol-assisted reactor as shown in FIG. 2 was used as the synthesis device. Flow 1 is 1 SLPM. Flow 2 is 1 SLPM. Dilution flow is 3 SLPM. The flow gas composition is nitrogen & hydrogen (N.sub.2, 75 vol %; H.sub.2 25 vol %). The as-produced K.sub.0.3WO.sub.3 particle XRD (X-ray powder Diffraction) pattern is shown in FIG. 10.

EXAMPLE 4

[0055] Dissolve sodium chloride (NaCl, 28 mmol/L) and Ammonium tungsten oxide hydrate ((NH.sub.4).sub.10W.sub.12O.sub.41.Math.xH.sub.2O, 3.33 mmol/L) into water (H.sub.2O, 100 vol %) to form the precursor solution. An aerosol-assisted reactor as shown in FIG. 3 was used as the synthesis device. Flow #1 is 0.5 SLPM. Flow #2 is 0.5 SLPM. Flow #3 is 3˜5 SLPM. The flow gas composition is nitrogen & hydrogen (N.sub.2, 75 vol % and H.sub.2 25 vol %). By adjusting the dilution flow ratio (Flow #3 to the sum of Flow #1 and Flow #2) and precursor solution concentration, the size of the particles was adjusted. The size distribution of produced particles are shown in FIGS. 11 and FIG. 12.

EXAMPLE 5

[0056] According to the precursor solution composition and final products, Table 1 provides example recipes for different tungsten bronze products. This table encompasses all aerosol-assisted reactor types.

TABLE-US-00001 TABLE 1 Configuration for different tungsten bronze products. Precursor Precursor solution salt Flow gas Major solution solvent Alkali metal halide Tungsten salt composition product MeOH 95 vol %,   35 mmol/L NaCl   50 mmol/L WCl.sub.6 N.sub.2 100 vol % Na.sub.0.7WO.sub.3 EG 5 vol %   15 mmol/L NaCl Na.sub.0.3WO.sub.3   15 mmol/L KCl K.sub.0.3WO.sub.3   15 mmol/L CsCl Cs.sub.0.3WO.sub.3 EG 100 vol % 0.35 mol/L NaCl  0.5 mol/L WCl.sub.6 N.sub.2 75 vol %, Na.sub.0.7WO.sub.3 0.15 mol/L NaCl H.sub.2 25 vol % Na.sub.0.3WO.sub.3 0.15 mol/L KCl K.sub.0.3WO.sub.3 0.15 mol/L CsCl Cs.sub.0.3WO.sub.3 Water 100 vol %   28 mmol/L NaCl, 3.33 mmol/L Na.sub.0.7WO.sub.3   12 mmol/L NaCl (NH.sub.4).sub.10W.sub.12O.sub.41•XH.sub.2O Na.sub.0.3WO.sub.3   12 mmol/L KCl K.sub.0.3WO.sub.3   12 mmol/L CsCl Cs.sub.0.3WO.sub.3

EXAMPLE 6

[0057] The size distribution of particles produced by the reactor shown in FIG. 3 can be tuned in the range below 1000 nm. For example, if the setup parameters are set as in Table 2, the size distribution of particle products are shown in FIG. 13. A key factor relating particle size is the dilution ratio for the aerosol flow before cool down from high temperature, which is controlled by #1 #2 and #3 flow rate.

TABLE-US-00002 TABLE 2 Setup parameters Parameter name (in FIG. 1) Value Mass flow controller #1 0.2 SLPM (FIG. 13A),   1 SLPM (FIG. 13B),   4 SLPM (FIG. 13C) Mass flow controller #2   1 SLPM Mass flow controller #3   5 SLPM

EXAMPLE 7

[0058] FIG. 14 shows the UV-Vis of Na.sub.xWO.sub.3 (x=˜0.7) dispersed in IPA solution. It shows different particle size products have different performance on UV and NIR light shielding. When the mean aerodynamic diameter of particles is below 0.5 μm, the shielding effect is enhanced.

[0059] While the invention has been described in terms of its preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims. Accordingly, the present invention should not be limited to the embodiments as described above, but should further include all modifications and equivalents thereof within the spirit and scope of the description provided herein.