Tungsten Oxide-Based Material

Abstract

A material of Formula (I)

M.sub.yA.sub.xWO.sub.z(I)

where M represents one or more monoatomic species, A represents one or more polyatomic cationic species, each having an ionic radius of no more than 2 , W is tungsten, O is oxygen, y is non-zero and is up to and including 0.32, x is non-zero and up to and including 0.32, and z is from 2.5 to 4.0, provided that x+y0.33.

Claims

1. A material of Formula (I)
MyAxWOz(I) where M represents one or more monoatomic species A represents one or more polyatomic ionic species, each having an ionic radius of no more than 2 , W is tungsten, O is oxygen, y is non-zero and up to and including 0.32, x is non-zero and up to and including 0.32, and z is from 2.5 to 4.0, provided that x+y0.33.

2. A material according to claim 1 wherein x+y0.30.

3. A material according to claim 2 wherein x+y=0.33.

4. A material according to claim 1 wherein A represents one or more polyatomic cationic species.

5. A material according to claim 4 wherein A represents one or more of NH4+, H3O+, VO2+, H2F+ and H3S+.

6. A material according to claim 5 wherein A represents NH4+.

7. A material according to claim 1 wherein M represents one or more metal.

8. A material according to claim 1 wherein M represents one or more of an alkali metal, an alkaline earth metal, a rare earth species, Zr, Cu, Ag, Zn, Al, Ga, In, Tl, Ge, Sn, Pb, Sb, Ti, Nb, V, Mo, Ta, Re, Be, Hf, and Bi.

9. A material according to claim 8 wherein M represent one or more of an alkali metal, an alkaline earth metal, Ti, Zr, Hf, Ge, Sn, Pb, Nb, Mo and Ta.

10-11. (canceled)

12. A material according to claim 9 wherein M represents one alkali metal and either Sn or Pb.

13. A material according to claim 1, wherein A represents n polyatomic species, A1, A2, . . . An, where n is two or more, and A represents A1x1, A2x2, . . . Anxn, where x= (x1, x2, . . . xn).

14-17. (canceled)

18. A material according to claim 1 wherein M comprises one or more alkali metal and Sn.

19. A material according to claim 1 wherein x is at least 0.02.

20-28. (canceled)

29. A material according to claim 1 wherein x is from 0.10 to 0.20, y is from 0.10 to 0.20, where A represents ammonium and M represents one or more of an alkali metal, Ti, Zr, Hf, Ge, Sn, Pb, Nb, Mo and Ta.

30. A material according to claim 1 wherein x is from 0.02 to 0.10, y is from 0.20 to 0.31, x+y0.30, A represents ammonium, and M represents one or more of Na, K and Cs, and one or more of Sn, Pb, Nb, Mo and Ta.

31. A composition comprising a material of claim 1 dispersed in a carrier.

32. (canceled)

33. A method of making a material according to claim 1, the method comprising providing in admixture monoatomic species M (or source thereof), polyatomic species A (or source thereof) and a source of WO.sub.z.

34. A method according to claim 33, wherein the source of WO.sub.z comprises a Tungsten (VI) species and a reducing agent.

35-38. (canceled)

39. A method of providing infrared absorbing capability to an object, the method comprising providing said object with a material of claim 1.

40. (canceled)

Description

DESCRIPTION OF THE DRAWINGS

[0054] Embodiments of the present invention will now be described by way of example only with reference to the accompanying FIGURE, FIG. 1, which shows x-ray diffraction data for an exemplary embodiment of a tungsten oxide in accordance with the present invention and comparative examples.

DETAILED DESCRIPTION

[0055] The synthesis of exemplary embodiments of various materials of formula (I) in accordance with the present invention will now be described.

Example 1

[0056] Sodium tungstate solution (6.6 g in 100 ml water) was passed through an ion exchange column to form tungstic acid. Lactic acid (90%, 6.03 g, Alfa Aesar) was added, followed by ammonium bicarbonate (0.57 g, VWR International), and tin powder (0.36 g, Royal Metal Powders). The mixture was heated in an autoclave to 150 C. for about 48 hours to afford the product, which is separated by filtration, dried under vacuum and heated under a flow of nitrogen at 500 C. for 1 hour to provide a material of expected formula (NH.sub.4).sub.0.18Sn.sub.0.15WO.sub.3. XPS data indicate that the oxygen content is from 2.7 to 3.1. XRF showed that the tin content is 0.15. Kjeldahl analysis showed the presence of ammonium in the material at a level of at least 0.04. It is noted that the material is defined as having a minimum content of ammonium due to the insolubility of the material. It is well-known in the field that for Kjeldahl analysis where a product is not fully soluble this can lead to a result showing lower ammonium content than expected, or shown in other methods of analysis. This the amount of ammonium measured in the sample is defined as ammonium content. For the material of Example 1, the ammonium dopant was added in excess and the applicant has no reason to believe that the interstitial sites in the tungsten oxide are not completely filled. Furthermore, the IR absorbance performance which is described below for the material of Example 1 is consistent with a high level of doping. Thus it is expected that the level of ammonium is from 0.04 to 0.15; and more particularly, it is expected that the level of ammonium is 0.15.

[0057] All reagents were used as supplied.

Example 2

[0058] A further method may be used to prepare exemplary embodiments of materials in accordance with the first aspect of the present invention. A metal tungstate (such as sodium tungstate [3.34 g]), ammonium metatungstate [2.25 g, Alfa Aesar], and lactic acid (90%, 6.03 g) are dissolved to a clear solution, tin (0.36 g) and then sulfuric acid is added to a pH of 1.1. The mixture is then heated in an autoclave at 190 C. for 40 hours. The solid product is separated by filtration, dried under vacuum, then heated under a nitrogen flow at 500 C. for 1 hour. The resulting tungsten oxide was of formula Na.sub.0.19(NH.sub.4).sub.0.03 Sn.sub.0.11WO.sub.3. The tin and sodium content were measured using XRF. It is expected that the sodium content here is a maximum content, and may be slightly lower than measured using XRF. Kjeldahl analysis showed a minimum ammonium content of 0.03, and may be slightly higher, given that the material of Example 2 was not completely soluble in the solvent used which would tend to produce a lower than expected measurement in the Kjeldahl analysis. The total content of sodium, ammonium and tin is expected to be about 0.33.

Example 3

[0059] Sodium tungstate dihydrate (6.6 g, 0.02 mol, Alfa Aesar) was dissolved in DI water to a volume of 100 ml. This solution was passed through a column of acid form cation exchange resin to form tungstic acid. 90% Lactic acid (6.0 g) was added to give a clear, colourless solution. Ammonium bicarbonate (0.61 g, 7.7210.sup.3 mol, VWR) and sodium carbonate (0.37 g, 3.4910.sup.3 mol, Solvay) were added to form a clear colourless solution. This solution was transferred to a hydrothermal reactor (volume 200 ml), which was heated to 190 C. for 72 hours. The blue product was separated by filtration, washed with water, then dried under vacuum at 40 C. The afforded solid was then annealed at 500 C. for 1 hour under a flow of N.sub.2. The product is expected to have formula Na.sub.0.165 (NH.sub.4).sub.0.165 WO.sub.3.

Example 4

[0060] Sodium tungstate solution (6.6 g in 100 ml water) was passed through an ion exchange column to form tungstic acid. Lactic acid (80%, 6.6 g) was added, followed by ammonium bicarbonate (0.54 g) and lead nitrate (1.13 g, VWR). The mixture was heated in an autoclave to 190 C. for about 72 hours to afford the product, which is separated by filtration, dried under vacuum and heated under a flow of nitrogen at 500 C. for 1 hour to provide a material of expected formula (NH.sub.4).sub.0.165Pb.sub.0.165WO.sub.3.

Example 5

[0061] Sodium tungstate solution (6.6 g in 100 ml water) was passed through an ion exchange column to form tungstic acid. Lactic acid (80%, 6.6 g) was added, followed by ammonium bicarbonate (0.54 g) and potassium carbonate (0.23 g, VWR). The mixture was heated in an autoclave to 190 C. for about 72 hours to afford the product, which is separated by filtration, dried under vacuum and heated under a flow of nitrogen at 500 C. for 1 hour to provide a material of expected formula (NH.sub.4).sub.0.165K.sub.0.165WO.sub.3.

[0062] Comparative examples were also synthesised so that their properties could be compared to those of the Examples.

Comparative Example 1

[0063] A material of formula (NH.sub.4).sub.0.33WO.sub.3 was made using a method substantially the same as that described in relation to Example 1, but without any tin. The reaction time was 72 hours as in Example 1, and the reaction temperature was 150 C.

Comparative Example 2

[0064] A material of formula Sn.sub.0.2WO.sub.3 was made using a method substantially the same as that described in relation to Example 1, but without any ammonium bicarbonate and without heating in nitrogen. The mass of tin used was 0.48 g.

Comparative Example 3

[0065] Sodium tungstate solution (6.6 g in 100 ml water) was passed through an ion exchange column to form tungstic acid. Lactic acid (90%, 6.03 g, Alfa Aesar) was added, followed by caesium carbonate (1.5 g, Alfa Aesar). The mixture was heated in an autoclave to 190 C. for about 48 hours to afford the product, which is separated by filtration, dried under vacuum and heated under a flow of nitrogen at 500 C. for 1 hour to provide a material of formula Cs.sub.0.33WO.sub.3.

Comparative Example 4

[0066] Sodium tungstate dihydrate (6.6 g, 0.02 mol) was dissolved in DI water to a volume of 100 ml. This solution was passed through a column of acid form cation exchange resin to form tungstic acid. 90% Lactic acid (6.0 g) was added to give a clear, colourless solution. Sodium carbonate (0.7 g, 6.610.sup.3 mol) was added to form a clear colourless solution. This solution was transferred to a hydrothermal reactor (volume 200 ml), which was heated to 190 C. for 48 hours. The blue product was separated by filtration, washed with water, then dried under vacuum at 40 C. The afforded solid was then annealed at 500 C. for 1 hour under a flow of N.sub.2. A material of expected formula Na.sub.0.33WO.sub.3 was provided.

Comparative Example 5

[0067] Sodium tungstate solution (6.6 g in 100 ml water) was passed through an ion exchange column to form tungstic acid. Lactic acid (80%, 6.6 g) was added, followed by lead nitrate (2.25 g). The mixture was heated in an autoclave to 190 C. for about 72 hours to afford the product, which is separated by filtration, dried under vacuum and heated under a flow of nitrogen at 500 C. for 1 hour to provide a material of expected formula Pb.sub.0.33WO.sub.3.

Comparative Example 6

[0068] Sodium tungstate dihydrate (6.6 g, 0.02 mol) was dissolved in deionised water to a total volume of 100 ml. This solution was passed through an acid form ion exchange resin to produce tungstic acid solution. To this, 6.0 g 90% lactic acid solution was added, followed by potassium sulfate (5.0 g, 0.0287 mol). The suspension was transferred to a 200 ml hydrothermal reaction bomb. This was heated to 190 C. for 72 hours to afford the product which is separated by filtration, dried under vacuum and heated under a flow of nitrogen at 500 C. for 1 hour to provide a material of formula K.sub.0.33WO.sub.3.

Comparative Example 7

[0069] Sodium tungstate dihydrate (6.7 g, 0.02 mol) was dissolved in DI water to a volume of 100 ml and 90% lactic acid (6 g) added. 20% sulfuric acid was added to a pH of 1.1, then tin (0.36 g, 3.03*10.sup.3 mol) added. This mixture was transferred to a hydrothermal reactor (volume 200 ml), which was heated to 190 C. for 48 hours. The blue product was separated by filtration, washed with water, then dried under vacuum at 40 C. The afforded solid was then annealed at 500 C. for 1 hour under a flow of N.sub.2 to yield a material of expected formula Na.sub.0.18Sn.sub.0.15WO.sub.3.

[0070] The materials of Example 1 and Comparative Examples 1 and 2 were characterised by x-ray diffraction.

[0071] X-ray diffraction measurements were performed on powder samples at room temperature (about 25 C.) using a Bruker D8 Advance diffractometer (Cu K, radiation, 1.54 wavelength, tube operated at 40 kV, 40 mA) over a 2-theta range of 5 to 85 degrees. Diffraction patterns are shown in FIG. 1, the darker continuous line being from Example 1, the lighter continuous line being from Comparative Example 2 and the vertical lines showing peak position being from Comparative Example 1.

[0072] The x-ray diffraction data of FIG. 1 show that the material of Example 1 generates a different diffraction pattern from each of Comparative Examples 1 and 2, and that the diffraction pattern of Example 1 is not merely a combination of the diffraction patterns of Comparative Examples 1 and 2 which may be expected, for example, for a mixture of Comparative Examples 1 and 2.

[0073] The infra-red absorption characteristics of the materials of the Examples and the Comparative Examples were examined as described below. The material was dispersed at a concentration of 0.01% w/v in deionised water. Those skilled in the art will realise that % w/v is calculated based on the weight of the infra-red absorbing material in grams per 100 ml of deionised water. The IR absorbance characteristics of the suspensions were measured at a nominal wavelength of 1039 nm using a Hach DR2000 or a Hach DR3900 spectrometer, a cell of 10 mm path length and a reference sample provided with deionised water. The absorbance measurements are shown in Table 1 below.

TABLE-US-00001 TABLE 1 absorbance measurements Material IR absorbance (arbitrary units) Example 1 1.86 Example 2 2.01 Example 3 0.64 Example 4 1.13 Example 5 0.70 Comparative Example 1 0.56 Comparative Example 2 1.43 Comparative Example 3 1.40 Comparative Example 4 0.31 Comparative Example 5 0.90 Comparative Example 6 0.60 Comparative Example 7 1.43

[0074] It can be observed that the absorbance shown by the material of Example 1 (containing ammonium and tin) is far greater (and unexpectedly so) than the absorbance values demonstrated by Comparative Example 1 (containing ammonium only) and Comparative Example 2 (containing tin only).

[0075] Example 2 (containing ammonium, tin and sodium) also shows an unexpectedly high IR absorbance (2.01) compared to Comparative Example 1 (ammonium only, absorbance of 0.56), Comparative Example 2 (tin only, absorbance of 1.43), Comparative Example 4 (sodium only, absorbance of 0.31) and Comparative Example 7 (sodium and tin, absorbance of 1.43).

[0076] Furthermore, the material of Example 3 (Na.sub.0.165(NH.sub.4).sub.0.165WO.sub.3) unexpectedly shows a higher absorbance (0.64) than the material which contains solely sodium (Comparative Example 4, absorbance of 0.31) and the material which contains solely ammonium (Comparative Example 1, absorbance of 0.56).

[0077] Similarly, unexpectedly high absorbance values are observed from Examples 4 and 5. Example 4 containing ammonium and lead shows an unexpectedly high absorbance value of 1.13, given the absorbance values of Comparative Example 1 (ammonium only, absorbance of 0.56) and Comparative Example 5 (lead only, absorbance of 0.90). It is worth noting that the absorbance at 600 nm (yellow-orange) for Example 4 (0.43) was very similar to that measured for Comparative Example 5 (0.38), indicating that an appreciable increase in IR absorbance can be achieved without an appreciable increase in absorbance at visible wavelengths. Example 5 containing ammonium and potassium shows an unexpectedly high absorbance value of 0.70, given the absorbance values of Comparative Example 1 (ammonium only, absorbance of 0.56) and Comparative Example 6 (potassium only, absorbance of 0.60).

[0078] It has therefore been found that if ammonium is incorporated into tungsten oxide in combination with other species (such as metals, such tin, lead and/or Group I metals), then the IR absorbance properties of the resulting material is higher than expected.

[0079] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0080] The examples above illustrate the use of ammonium as the single polyatomic cation. Those skilled in the art will realise that it would be possible to use more than one polyatomic cation, for example, ammonium and H.sub.2F.sup.+. Furthermore, if only a single polyatomic cation were to be used, then this need not be ammonium. For example, H.sub.2F.sup.+ may be used.

[0081] The examples above illustrate the use of particular stoichiometric amounts of polyatomic cation and metal. Those skilled in the art will realise that alternative amounts may be used.

[0082] The examples above illustrate the use of various metals with ammonium. Those skilled in the art will realise that other metals and combinations of metals may be used.

[0083] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.