Flaky nano tungstic acid as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of tungsten metallurgy, and particularly relates to flaky nano tungstic acid and a preparation method and application thereof.The preparation method comprises the steps that S1, hydrochloric acid is added into a container, continuous stirring is conducted in the adding process, and the temperature in the container is made to be stable; s2, 8-10 mL of a sodium tungstate solution B is added into the container in a spraying mode, continuous stirring is conducted in the adding process, and the temperature in the container is made stable; s3, 0.5-1.0 L of a sodium tungstate solution A is added into the container in a spraying mode, stirring is continuously conducted in the adding process, and the temperature in the container is made to be stable; the amount of hydrochloric acid added in the step S1 is 2.5-4.0 times of the theoretical amount of hydrochloric acid required for preparing tungstic acid according to the concentration of tungstate radicals in the sodium tungstate solution A; s4, repeating the steps S1 and S3; and S5, the prepared tungstic acid is filtered, washed with hydrochloric acid and then dried, the flaky nano tungstic acid with completely developed crystals can be stably prepared, and the thickness of the flaky nano tungstic acid is smaller than 100 nm.

Description

Technical Field

[0001] The present invention belongs to the technical field of tungsten metallurgy, and particularly relates to a flaky nano tungstic acid, a preparation method thereof, and an application thereof. Background Art

[0002] Cesium tungsten bronze (Cs x WO 3 ) has great research value in aspects such as transparent heat-insulating coatings, photocatalysis, energy-saving materials, and sensor carriers due to its broad absorption spectrum. Due to the quantum confinement effect, 2D nanomaterials possess many physical, chemical, electrical, and optical properties that cannot be achieved in the original material structure. In recent years, cesium tungsten bronze nanosheets, as a candidate material for a new near-infrared absorbing material, have been deeply studied by a large number of researchers.

[0003] Tungstic acid is one of the raw materials for preparing cesium tungsten bronze. Its original particle size, morphology, and crystal development degree will affect the morphology and crystal development degree of cesium tungsten bronze, and thus affect the overall performance of cesium tungsten bronze. For example, if the original crystal development of tungstic acid is incomplete, cesium tungsten bronze will have problems such as uneven pores, increased thermal conductivity, decreased mechanical strength, and reduced durability. Summary of the Invention

[0004] To solve the problems existing in the prior art, the main object of the present invention is to propose a flaky nano tungstic acid, a preparation method thereof, and an application thereof.

[0005] According to one aspect of the present invention, the present invention provides the following technical solution: A preparation method of flaky nano tungstic acid, comprising the following steps: S1. Add hydrochloric acid to a container, continuously stir during the addition process, and keep the temperature in the container stable; S2. Spray 8 - 10 mL of sodium tungstate solution B into the container, continuously stir during the addition process, and keep the temperature in the container stable; S3. Spray 0.5 - 1.0 L of sodium tungstate solution A into the container, continuously stir during the addition process, and keep the temperature in the container stable; the amount of hydrochloric acid added in step S1 is 2.5 - 4.0 times the theoretical amount of hydrochloric acid required to prepare tungstic acid according to the concentration of tungstate in sodium tungstate solution A; S4. Repeat steps S1 and S3; S5. Filter the obtained tungstic acid, wash it with hydrochloric acid, and then dry it to obtain flaky nano tungstic acid.

[0006] According to another aspect of the present invention, the present invention provides the following technical solution: A flaky nano tungsten acid, prepared by the preparation method of the above-mentioned flaky nano tungsten acid, has a complete crystal development of the flaky nano tungsten acid, and its thickness is less than 100 nm.

[0007] According to another aspect of the present invention, the present invention provides the following technical solutions: Application of a flaky nano tungsten acid in the field of preparing cesium tungsten bronze.

[0008] The beneficial effects of the present invention are as follows: The present invention provides a flaky nano tungsten acid, its preparation method and application. The preparation method includes: S1. Add hydrochloric acid to a container, and continuously stir during the addition process to keep the temperature in the container stable; S2. Add 8-10 mL of sodium tungstate solution B to the container in a spray manner, and continuously stir during the addition process to keep the temperature in the container stable; S3. Add 0.5-1.0 L of sodium tungstate solution A to the container in a spray manner, and continuously stir during the addition process to keep the temperature in the container stable; the amount of hydrochloric acid added in step S1 is 2.5-4.0 times the theoretical amount of hydrochloric acid required to prepare tungstic acid according to the tungstate ion concentration in sodium tungstate solution A; S4. Repeat steps S1 and S3; S5. Filter the prepared tungstic acid, wash it with hydrochloric acid, and then dry it to stably prepare flaky nano tungsten acid with complete crystal development and a thickness less than 100 nm. Description of the drawings

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the structures shown in these drawings.

[0010] Figure 1 It is the electron microscope image of the flaky nano tungsten acid prepared in Example 1 of the present invention; Figure 2 It is the electron microscope image of the flaky nano tungsten acid prepared in Example 2 of the present invention; Figure 3 It is the electron microscope image of the flaky nano tungsten acid prepared in Example 3 of the present invention; Figure 4 It is the electron microscope image of the tungstic acid prepared in Comparative Example 1 of the present invention; Figure 5 It is the electron microscope image of the tungstic acid prepared in Comparative Example 2 of the present invention; Figure 6 It is the electron microscope image of the tungstic acid prepared in Comparative Example 3 of the present invention; Figure 7 It is the electron microscope image of the tungstic acid prepared in Comparative Example 4 of the present invention.

[0011] The realization, functional features and advantages of the present invention will be further described in conjunction with the embodiments with reference to the accompanying drawings. Specific Embodiments

[0012] The technical solutions in the embodiments will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0013] The present invention provides a method for preparing flaky nano tungstic acid and its preparation method and application. At a certain temperature, by means of pre-preparing seeds and adding materials in segments, flaky nano tungstic acid with complete crystal development of tungstic acid crystals is prepared. Alternately adding hydrochloric acid and sodium tungstate solution A can keep the concentration of hydrochloric acid in the reaction system within a relatively stable range all the time, can control the reaction rate and the concentration of solutes in the solution, and make the particle size of the formed tungstic acid more uniform. If hydrochloric acid is not added alternately in batches, the concentration of hydrochloric acid will become lower and lower, resulting in tungstic acid with greatly different sizes and morphologies.

[0014] According to one aspect of the present invention, the present invention provides the following technical solutions: A method for preparing flaky nano tungstic acid, comprising the following steps: S1. Add hydrochloric acid to a container, continuously stir during the adding process and keep the temperature in the container stable; S2. Spray 8 - 10 mL of sodium tungstate solution B into the container, continuously stir during the adding process and keep the temperature in the container stable; S3. Spray 0.5 - 1.0 L of sodium tungstate solution A into the container, continuously stir during the adding process and keep the temperature in the container stable; the amount of hydrochloric acid added in step S1 is 2.5 - 4.0 times the theoretical amount of hydrochloric acid required for preparing tungstic acid according to the concentration of tungstate in sodium tungstate solution A; S4. Repeat steps S1 and S3; S5. Filter the obtained tungstic acid, wash it with hydrochloric acid and then dry it to obtain flaky nano tungstic acid.

[0015] Preferably, in the steps S1 - S3, the temperature inside the container is 80 - 95 °C, and the stirring speed is 150 - 250 r / min. Temperature has a great influence on nucleation and reaction rate. When the temperature is low, the morphology of the formed crystal nuclei is often irregular; when the temperature is high, the surface of the crystal nuclei is wrapped by high - density packed planes. Specifically, the temperature inside the container can be any one of, for example, 80 °C, 85 °C, 90 °C, 95 °C or the range between any two of them. If the stirring speed is too low, tungstic acid is prone to deposit and grow, with a low specific surface area; if the stirring speed is too high, tungstic acid is easily broken, with poor crystal form and uniformity. Specifically, the stirring speed can be any one of, for example, 150 r / min, 175 r / min, 200 r / min, 225 r / min, 250 r / min or the range between any two of them.

[0016] Preferably, in the step S1, the concentration of hydrochloric acid is 16 - 22 wt%; there is no special requirement for the addition speed of hydrochloric acid, and it can be added as soon as possible; for example, each time hydrochloric acid is added, it can be added within 5 - 10 s. As a reactant for preparing tungstic acid, the concentration of hydrochloric acid also has an impact on both nucleation and growth. If the concentration of hydrochloric acid is too high, the probability of hydrogen ions combining with tungstate ions becomes larger, the local reaction is too fast, and a small number of large crystal seeds are obtained, ultimately causing excessive crystal development and too large crystal size; if the concentration of hydrochloric acid is too low, the supersaturation is low, numerous small and uneven crystal nuclei will be formed, and the growth and development are slow, ultimately obtaining crystals with great differences in both morphology and size. Specifically, the concentration of hydrochloric acid can be any one of, for example, 16 wt%, 16.5 wt%, 17 wt%, 17.5 wt%, 18 wt%, 18.5 wt%, 19 wt%, 19.5 wt%, 20 wt%, 20.5 wt%, 21 wt%, 21.5 wt%, 22 wt% or the range between any two of them.

[0017] Preferably, in the step S2, based on WO 3 calculation, the concentration of sodium tungstate solution B is 150 - 200 g / L; in the step S3, based on WO 3 calculation, the concentration of sodium tungstate solution A is 150 - 200 g / L. Specifically, the concentration of sodium tungstate solution B and the concentration of sodium tungstate solution A can be the same or different. The tungsten concentration of the reactants has an impact on both the nucleation and growth and development of the crystals. Too low a concentration will cause a large number of nuclei to form, with slow growth and development, resulting in incomplete crystal development; too high a concentration will lead to too fast a growth rate, less nucleation of the product and rapid development, forming thick particles. Specifically, based on WO 3 calculation, the concentration of sodium tungstate solution A can be any one of, for example, 150 g / L, 155 g / L, 160 g / L, 165 g / L, 170 g / L, 175 g / L, 180 g / L, 185 g / L, 190 g / L, 195 g / L, 200 g / L or the range between any two of them; based on WO3 For example, the concentration of sodium tungstate solution B can be any one of 150 g / L, 155 g / L, 160 g / L, 165 g / L, 170 g / L, 175 g / L, 180 g / L, 185 g / L, 190 g / L, 195 g / L, 200 g / L or within the range between any two of them.

[0018] Preferably, in step S2, 8 - 10 mL of sodium tungstate solution B is added to the container by spraying and then stirred for 8 - 12 min. Spray feeding can make the materials evenly distributed in the reaction system, avoid excessive local concentration, and improve the uniformity of the product; it can also increase the reaction area and accelerate the reaction rate. Specifically, the amount of sodium tungstate solution B can be any one of 8 mL, 9 mL, 10 mL or within the range between any two of them. At the same time, the spraying rate of 8 - 10 mL of sodium tungstate solution B is controlled to be 50 - 80 mL / min. Specifically, the spraying rate of 8 - 10 mL of sodium tungstate solution B can be any one of 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min or within the range between any two of them.

[0019] Preferably, in step S3, sodium tungstate solution A is added using a peristaltic pump; the adding rate of sodium tungstate solution A is 50 - 120 mL / min; after the addition of sodium tungstate solution A is completed, it is stirred for 2 - 3 min and then step S4 is carried out. Specifically, the adding rate of sodium tungstate solution A can be any one of 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min, 90 mL / min, 100 mL / min, 110 mL / min, 120 mL / min or within the range between any two of them; the stirring time after the addition of sodium tungstate solution A is completed can be any one of 2 min, 2.5 min, 3 min or within the range between any two of them. The volume of sodium tungstate solution A can be any one of 0.5 L, 0.55 L, 0.6 L, 0.65 L, 0.7 L, 0.75 L, 0.8 L, 0.85 L, 0.9 L, 0.95 L, 1.0 L or within the range between any two of them; the amount of hydrochloric acid used can be any one of 2.5 times, 2.6 times, 2.7 times, 2.8 times, 2.9 times, 3.0 times, 3.1 times, 3.2 times, 3.3 times, 3.4 times, 3.5 times, 3.6 times, 3.7 times, 3.8 times, 3.9 times, 4.0 times the theoretical amount of dilute hydrochloric acid required to prepare tungstic acid according to the tungstate ion concentration in sodium tungstate solution A or within the range between any two of them.

[0020] Preferably, in step S4, it is repeated 3 - 6 times and then step S5 is carried out. Specifically, the number of repetitions can be 3, 4, 5, 6.

[0021] Preferably, in step S5, the concentration of hydrochloric acid is 2 wt%, and it is washed 2 to 4 times, and the drying temperature is 100 to 120 °C. With a relatively high drying temperature, at this drying temperature, it is beneficial to the volatilization of the residual hydrochloric acid in tungstic acid, but if the temperature is too high, the water evaporates too quickly and it is not easy to obtain loose tungstic acid. Specifically, the drying temperature can be any one of, for example, 100 °C, 105 °C, 110 °C, 115 °C, 120 °C or the range between any two of them.

[0022] According to another aspect of the present invention, the present invention provides the following technical solution: A flaky nano-tungstic acid is prepared by using the above-mentioned preparation method of flaky nano-tungstic acid. The flaky nano-tungstic acid has complete crystal development and is a two-dimensional nano material, and its thickness is less than 100 nm.

[0023] According to another aspect of the present invention, the present invention provides the following technical solution: An application of a flaky nano-tungstic acid in the field of preparing cesium tungsten bronze.

[0024] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0025] Example 1 A preparation method of a flaky nano-tungstic acid includes the following steps: S1. Add hydrochloric acid to a container, and continuously stir during the addition process to keep the temperature in the container stable; S2. Add 10 mL of sodium tungstate solution B to the container in a spray manner, and continuously stir during the addition process to keep the temperature in the container stable; S3. Add 0.8 L of sodium tungstate solution A to the container in a spray manner, and continuously stir during the addition process to keep the temperature in the container stable; the amount of hydrochloric acid added in step S1 is 3.0 times the theoretical amount of hydrochloric acid required to prepare tungstic acid according to the concentration of tungstate in sodium tungstate solution A; S4. Repeat steps S1 and S3; S5. Filter the prepared tungstic acid, wash it with hydrochloric acid, and then dry it to obtain flaky nano-tungstic acid.

[0026] In steps S1 - S3, the temperature in the container is 90 °C, and the stirring speed is 200 r / min. The concentration of hydrochloric acid is 20 wt%. In step S2, based on WO 3 calculated, the concentration of sodium tungstate solution B is 200 g / L; in step S3, based on WO 3In the calculation, the concentration of sodium tungstate solution A is 200 g / L. In step S2, 10 mL of sodium tungstate solution B is added to the container by spraying and then stirred for 10 min; the spraying speed of sodium tungstate solution B is 60 mL / min. In step S3, sodium tungstate solution A is added by a peristaltic pump; the adding speed of sodium tungstate solution A is 66.67 mL / min; after the addition of sodium tungstate solution A is completed, it is stirred for 2 min and then step S4 is carried out. In step S4, it is repeated 5 times and then step S5 is carried out. In step S5, the concentration of hydrochloric acid is 2 wt%, it is washed 3 times, and the drying temperature is 110 °C.

[0027] The electron microscope image of the flaky nano tungsten acid obtained in this example is as Figure 1 shown. Its thickness is less than 100 nm, it is a two-dimensional nano material, the crystal grains are completely developed, and the surface is smooth.

[0028] Example 2 A preparation method of flaky nano tungsten acid includes the following steps: S1. Add hydrochloric acid to the container, and keep stirring during the addition process to make the temperature in the container stable; S2. Add 8 mL of sodium tungstate solution B to the container by spraying, and keep stirring during the addition process to make the temperature in the container stable; S3. Add 1.0 L of sodium tungstate solution A to the container by spraying, and keep stirring during the addition process to make the temperature in the container stable; the amount of hydrochloric acid added in step S1 is 4.0 times the theoretical amount of hydrochloric acid required to prepare tungstic acid according to the concentration of tungstate in sodium tungstate solution A; S4. Repeat steps S1 and S3; S5. Filter the prepared tungstic acid, wash it with hydrochloric acid, and then dry it to obtain flaky nano tungsten acid.

[0029] In steps S1 - S3, the temperature in the container is 85 °C, and the stirring speed is 200 r / min. The concentration of hydrochloric acid is 16 wt%. In step S2, calculated by WO 3 the concentration of sodium tungstate solution B is 180 g / L; in step S3, calculated by WO 3 the concentration of sodium tungstate solution A is 180 g / L. In step S2, 8 mL of sodium tungstate solution B is added to the container by spraying and then stirred for 10 min; the spraying speed of sodium tungstate solution B is 80 mL / min. In step S3, sodium tungstate solution A is added by a peristaltic pump; the adding speed of sodium tungstate solution A is 83.33 mL / min; after the addition of sodium tungstate solution A is completed, it is stirred for 2 min and then step S4 is carried out. In step S4, it is repeated 4 times and then step S5 is carried out. In step S5, the concentration of hydrochloric acid is 2 wt%, it is washed 3 times, and the drying temperature is 120 °C.

[0030] The electron micrograph of the flaky nano tungstic acid obtained in this example is as follows Figure 2 shown. Its thickness is less than 100 nm. It is a two-dimensional nano material with complete grain development and a smooth surface.

[0031] Example 3 A preparation method of flaky nano tungstic acid includes the following steps: S1. Add hydrochloric acid to a container, and continuously stir during the addition process to keep the temperature in the container stable. S2. Add 10 mL of sodium tungstate solution B to the container in a spray manner, and continuously stir during the addition process to keep the temperature in the container stable. S3. Add 0.6 L of sodium tungstate solution A to the container in a spray manner, and continuously stir during the addition process to keep the temperature in the container stable. The amount of hydrochloric acid added in step S1 is 2.5 times the theoretical amount of hydrochloric acid required to prepare tungstic acid according to the concentration of tungstate in sodium tungstate solution A. S4. Repeat steps S1 and S3. S5. Filter the obtained tungstic acid, wash it with hydrochloric acid, and then dry it to obtain flaky nano tungstic acid.

[0032] In steps S1 - S3, the temperature in the container is 95 °C, the stirring speed is 200 r / min, and the concentration of hydrochloric acid is 22 wt%. In step S2, based on WO 3 calculated, the concentration of sodium tungstate solution B is 190 g / L; in step S3, based on WO 3 calculated, the concentration of sodium tungstate solution A is 190 g / L. In step S2, after adding 10 mL of sodium tungstate solution B to the container in a spray manner, stir for 10 min; the spray speed of sodium tungstate solution B is 50 mL / min. In step S3, sodium tungstate solution A is added using a peristaltic pump; the addition speed of sodium tungstate solution A is 55.56 mL / min; after the addition of sodium tungstate solution A is completed, stir for 2 min and then proceed to step S4. In step S4, repeat 4 times and then proceed to step S5. In step S5, the concentration of hydrochloric acid is 2 wt%, wash 3 times, and the drying temperature is 120 °C.

[0033] The electron micrograph of the flaky nano tungstic acid obtained in this example is as follows Figure 3 shown. Its thickness is less than 100 nm. It is a two-dimensional nano material with complete grain development and a smooth surface.

[0034] Comparative Example 1 The difference from Example 1 is that in steps S1 - S3, the temperature in the container is 105 °C.

[0035] The electron micrograph of the tungstic acid obtained in this comparative example is as follows Figure 4As shown, its thickness significantly exceeds 100 nm, which has exceeded the grain size of two-dimensional nanomaterials. The grains are completely developed and the surface is smooth.

[0036] Comparative Example 2 The difference from Example 1 is that in steps S1 - S3, the temperature in the container is 45°C.

[0037] The electron micrograph of the tungstic acid obtained in this comparative example is as Figure 5 shown. The tungstic acid is in the form of stacked flakes. The grains are not completely developed and have irregular edges and complex surface morphologies.

[0038] Comparative Example 3 The difference from Example 1 is that hydrochloric acid and sodium tungstate solution A are not added in a segmented and alternating manner: that is, all hydrochloric acid is added first, and then sodium tungstate solution B is added followed by all sodium tungstate solution A.

[0039] The electron micrograph of the tungstic acid obtained in this comparative example is as Figure 6 shown. The tungstic acid is in the form of flakes. There is tungstic acid with a thickness exceeding 200 nm and a smooth surface, as well as tungstic acid with a thickness within 100 nm. At the same time, there are a large number of incompletely developed and complex-shaped nano-tungstic acids.

[0040] Comparative Example 4 The difference from Example 1 is that sodium tungstate solution A and sodium tungstate solution B are added in a dropping manner.

[0041] The electron micrograph of the tungstic acid obtained in this comparative example is as Figure 7 shown. The tungstic acid is in the form of completely developed flakes and agglomerated fine particles, and there is a large difference in thickness between the flaky grains.

[0042] The tungstic acids prepared in Example 1 and Comparative Example 4, and the cesium source were respectively used to prepare cesium tungsten bronze in the same proportion and their full infrared barrier and light transmittance properties were detected. The results are as follows: The full infrared barrier rate of the cesium tungsten bronze film prepared with the tungstic acid prepared in Example 1 is 94.2%, and the light transmittance is 71.8%.

[0043] The full infrared barrier rate of the cesium tungsten bronze film prepared with the tungstic acid prepared in Comparative Example 4 is 78.5%, and the light transmittance is 53.6%.

[0044] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made using the content of the specification of the present invention under the inventive concept of the present invention, or direct / indirect application in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A method for preparing flaky nano-tungstic acid, characterized in that: The steps include: S1. Add hydrochloric acid to the container, stirring continuously during the addition process and keeping the temperature in the container stable; S2. Add 8-10 mL of sodium tungstate solution B into the container by spraying, stirring continuously during the addition process and keeping the temperature in the container stable; S3, add 0.5-1.0L of sodium tungstate solution A into the container by spraying, keep stirring during the adding process and keep the temperature in the container stable; the amount of hydrochloric acid added in step S1 is 2.5-4.0 times the theoretical amount of hydrochloric acid required for preparing tungstic acid according to the tungstate concentration in the sodium tungstate solution A; S4, repeat steps S1 and S3; S5. Filter the prepared tungstic acid, wash it with hydrochloric acid, and then dry it to obtain flaky nano tungstic acid.

2. The method for preparing flaky nano-tungstic acid according to claim 1, characterized in that: In the steps S1-S3, the temperature in the container is 80-95° C., and the stirring speed is 150-250 r / min.

3. The method for preparing flaky nano-tungstic acid according to claim 1, characterized in that: In step S1, the concentration of hydrochloric acid is 16-22 wt %.

4. The method for preparing flaky nano-tungstic acid according to claim 1, characterized in that: In the step S2, the concentration of the sodium tungstate solution B is 150-200 g / L in terms of WO3; in the step S3, the concentration of the sodium tungstate solution A is 150-200 g / L in terms of WO3.

5. The method for preparing flaky nano-tungstic acid according to claim 1, characterized in that: In the step S2, 8-10 mL of sodium tungstate solution B is added to the container by spraying and then stirred for 8-12 min; the spraying speed of sodium tungstate solution B is 50-80 mL / min.

6. The method for preparing flaky nano-tungstic acid according to claim 1, characterized in that: In step S3, the sodium tungstate solution A is added at a rate of 50-120 mL / min; after the sodium tungstate solution A is added, it is stirred for 2-3 min before proceeding to step S4.

7. The method for preparing flaky nano-tungstic acid according to claim 1, characterized in that: In the step S4, step S5 is performed after repeating 3 to 6 times.

8. The method for preparing flaky nano-tungstic acid according to claim 1, characterized in that: In step S5, the concentration of hydrochloric acid is 2 wt %, washing is performed 2 to 4 times, and the drying temperature is 100 to 120° C.

9. A sheet-like nano-tungstic acid, characterized in that: The flaky nano-tungstic acid is prepared by the preparation method of any one of claims 1 to 8. The flaky nano-tungstic acid crystals are fully developed and are two-dimensional nanomaterials with a thickness of less than 100 nm.

10. Use of the flaky nano-tungstic acid according to claim 9 in the preparation of cesium tungsten bronze.

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