JPH0676216B2 - Method for producing tungsten bronze and composite thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sodium tungsten bronze and a method for producing an inorganic composite body obtained by coating the same.

[0002]

_2. Description of the Related Art Na ₂ WO ₄ -WO ₃ -using a reducing action of tungsten metal, which is known as a general method for producing powdery sodium tungsten bronze (Na _x WO ₃ , 0.4 ≤ x ≤ 1). In the W-based reaction method, metal tungsten, which is difficult to separate and remove, is inevitable despite the long reaction time. Furthermore, the x in the formula to obtain a tungsten bronze of 0.8 or more compositions, in order to over-addition reaction Na ₂ WO ₄ and WO ₃ with respect to metallic tungsten, sodium hydroxide for removal of the WO _3, etc. It is necessary to perform a washing operation with an aqueous solution of the above, which deteriorates the quality of the product tungsten bronze. Also, high composition x
As a special method to obtain powdery tungsten bronze having (0.7 to 1), explosive sodium azide and W
O ₃ in high pressure reactor (under 65 kbar), 700-1000 ℃
Although a method of reacting under the temperature condition of 1 has been reported, it is difficult to call it a simple method, and it is considered that there is a problem in the occurrence of side reactions. In addition, the electrolytic reduction method of Na ₂ WO ₄ -WO ₃ eutectic which is often used as a method for producing a single crystal is as follows.
There is a problem in setting electrolysis conditions for obtaining a tungsten bronze having a target composition x, and a high composition x (0.85 or more) is hardly obtained. On the other hand, there is almost no example of a method for producing a coated inorganic composite of sodium tungsten bronze, and Na ₂ WO ₄ -WO is slightly present.
Methods for _3-based interpolymer Torubutsu electrolytic reduction to thereby coat the medium composition x tungsten bronze (Na _0.65 WO ₃₎ to the wire of platinum and gold have been reported.

[0003]

DISCLOSURE OF THE INVENTION The present invention overcomes the problems found in the conventional methods and provides a method for easily producing a sodium tungsten bronze having a desired composition x, and a tungsten bronze-coated inorganic composite. A method of manufacturing a body is provided.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems of the prior art, and as a result,
It has been found that the above problems can be solved by utilizing the disproportionation reaction caused by hydrogen reduction of sodium ditungstate, and the present invention has been completed.

That is, according to the present invention, (1) powder crystals of sodium ditungstate (chemical formula Na ₂ W ₂ O ₇ ) are reduced in a hydrogen atmosphere to produce sodium tungsten bronze (Na _x WO ₃ , 0.60 < x <1) and sodium monotungstate (Na ₂ WO ₄ ) are produced, and sodium monotungstate is separated and removed by washing with water, (2) A sodium tungstate aqueous solution (Na / W molar ratio is 1 to 1.1
) Is applied to a support material by a method such as dipping and then dried to form a hydrous amorphous film of sodium tungstate (Na / W molar ratio of 1 to 1.1) on the surface of the support, and then hydrogen. A method for producing a tungsten bronze-coated composite, which comprises reducing and forming a coating containing sodium monotungstate on the same sodium tungsten bronze as in (1) above, (3) the support according to (2) above. It is characterized by being selected from carbon materials including carbon fibers whose surface is modified with carbide (for example, WC and Mo ₂ C), zirconia-based materials, magnesia-based materials, carbide materials, alumina-based materials or corrosion-resistant / heat-resistant metal materials. The method for producing a tungsten bronze-coated composite according to (4), and (4) hydrogen reduction followed by washing with water to remove sodium monotungstate. Method of manufacturing a ring stent bronze coated composite is provided.

In the present invention, a powder crystal of sodium ditungstate (chemical formula Na ₂ W ₂ O ₇ ) which is a known substance is reduced with hydrogen under heating, which is preferably about 500-.
It is carried out by controlling and supplying the hydrogen concentration in the inert gas with respect to the heating temperature of 690 ° C., and sodium tungsten bronze (Na _x WO ₃ , 0.60 <x <1) and sodium monotungstate (Na ₂ WO ₄ ) is generated. The reaction in this reduction is represented by the following disproportionation reaction formula. Na ₂ W ₂ O _{7 ^{(solid) + (2/2-x}} -1) H 2 ( _{^{gas) → (2/2-x}} ) Na x WO 3 ( _{^{solid) + (2 - 2/2}} -x) Na ₂ WO ₄ (solid) + ( ² / _2-x -1) H ₂ O (gas) The fineness of sodium ditungstate as a raw material is
It only needs to be crushed in a mortar or the like. Further, as the heating temperature condition, the reaction is slow at less than 500 ° C, and the melting of sodium monotungstate (melting point 698 ° C) occurs at 700 ° C or more, which is not preferable in the reaction operation. Therefore, the temperature is preferably 500 to 690 ° C, and more preferably 520 to 680 ° C.

Next, regarding the hydrogen concentration conditions for hydrogen reduction, if the hydrogen concentration in the inert gas is 40 to 50 vol% or more, the reduction rate is too high, so even if the heating temperature is lowered and the reaction time is shortened. Along with the tungsten bronze, metallic tungsten and oxides such as W ₃ O and WO _{2 which} are difficult to separate and remove are produced. Further, if the concentration is lower than 0.1 vol%, long-time reaction is required, which is not preferable. Therefore 0.1 ~
An appropriate hydrogen concentration is 40 vol%, preferably 0.5 to 30 vol%. Sodium tungsten bronze Na _x WO ₃ for the purpose of the present invention obtained under the above reaction conditions is usually 0.60.
<X <1, preferably 0.70 <x <0.95. A few examples of the composition x of the sodium tungsten bronze obtained according to the present invention and the heating temperature and hydrogen concentration conditions are shown below,
635 ℃, 20% x = 0.93, 590 ℃, 20% x = 0.74, 65
X = 0.82 at 0 ° C. and 5%. Details will be shown in Examples.
In the present method, as described above, a small amount of sodium monotungstate (Na _0.9 WO) accompanies the tungsten bronze.
_In case of ₃ , about 10 wt% is generated), but it can be easily separated and removed by washing with water. After this washing operation, powdery tungsten bronze is obtained.

Next, a description will be given of the production of a coating composite of sodium tungsten bronze. The hydrated tungsten trioxide (H ₂ WO ₄ ) was dissolved in advance in an aqueous solution of sodium monotungstate or sodium di / tungstotrinate (Na ₆ W ₂ O ₉ ) to prepare an aqueous solution having a Na / W molar ratio of 1 to 1.1. After being prepared and applied to a support material by a method such as dipping, it is dried at 100 to 300 ° C., more preferably 150 to 200 ° C., and the surface of the support is uniformly coated with water-free sodium tungstate. After forming the crystalline film, the same hydrogen reduction treatment as in the case of the above-described sodium ditungstate powder crystal may be performed. That is, the amorphous coating film of water-containing sodium tungstate (water content 1 to 3 wt%) formed on the surface of the support crystallized with dehydration at about 400 ° C or higher, and crystallized with sodium ditungstate or this compound and sodium monotungstate. Of the above mixture (when the Na / W molar ratio of the raw material aqueous solution is 1 or more), it becomes a microcrystalline substance. Therefore, a reducing operation similar to that of sodium ditungstate described above is carried out, and then a complex coated with tungsten bronze is treated after washing with water. It can be manufactured. In the case of a composite, mixing a small amount of Na ₂ WO ₄ (which has stronger resistance to oxidation and reduction than that of bronze) is not a problem in use in many cases. Therefore, the washing operation does not necessarily have to be performed.

When the Na / W molar ratio of the raw material sodium tungstate aqueous solution is smaller than 1, sodium tetratungstate (Na ₂ W) is present in addition to sodium ditungstate crystals.
₄ O ₁₃ ) is mixed, which is not preferable. Further, the sodium monotungstate mixed at a molar ratio of 1 or more shows a positive effect when a tungsten bronze of high composition x is to be obtained. That is, since this sodium monotungstate appropriately suppresses the disproportionation reaction rate of sodium ditungstate by hydrogen reduction,
A tungsten bronze having a composition x of about 0.85 or more can be stably formed on the support. The molar ratio is 1.
If it exceeds 1, it is unsuitable because it becomes a region where a Na ₂ O-WO ₃ system glass phase is formed. The concentration of the raw material sodium tungstate aqueous solution is about 0.01 mmol / ml to about 2 mmol / m.
It can be changed arbitrarily within the range of l. To describe the coating amount of this sodium tungstate after water-soluble, when the support is a plate material, for example, per unit cm ² , preferably 0.001 ~
0.006 ml, more preferably 0.002-0.004 ml, is applied.
Further, in the case of carbon fiber cloth, for example, 0.005 to 0.06 ml, more preferably 0.01 to 0.04 ml, is applied per unit cm ² . The material used as the support of the tungsten bronze-coated composite of the present invention is not limited to plate materials and bar materials as long as it has heat resistance, hydrogen reduction resistance and alkali resistance at a temperature of at least 700 ° C. Even a woven fabric or porous material having a structure does not cause any inconvenience.

[0010]

【Example】

Example 1 Sodium ditungstate crystals synthesized by a fusion method using anhydrous sodium monotungstate and tungsten trioxide were crushed in a mortar, and about 1 g was placed in a platinum boat and heated under heating to a quartz reaction tube (diameter 25 mm). The intermediate hydrogen concentration was diluted with argon gas and supplied (flow rate of about 300 ml / min) for reduction treatment, and the obtained product was identified by X-ray analysis.
The composition x of the tungsten bronze (Na _x WO ₃ ) produced by this reaction was determined from the relationship with the lattice constant. The results are shown in Table 1.

[0011]

[Table 1]

Each reaction product of the above Experiment Nos. 1 to 7 was fractionated (about 0.3 g) and the glass filter-attached funnel (NO4 type) was used.
X-ray analysis of a sample which was washed twice with 5 ml of warm water and dried at 150 ° C. showed that sodium monotungstate was not detected at all and the desired sodium tungsten bronze was obtained.

Example 2 Na / W molar ratios 1.0 and 1. prepared by adding hydrated tungsten trioxide to an aqueous solution of sodium monotungstate.
Sodium tungstate aqueous solution of 07 (Na ⁺ concentration of about 0.
Graphite fiber cloth (thickness 0.4 ^mm , 8 mmol / ml)
3 pieces (15 ^mm long, 40 ^{mm wide} ) are dipped and dried at 150 ° C, then heated at 650 ° C, hydrogen concentration in argon is 20 vol%, reaction time is 1
The hydrogen reduction treatment similar to that in Example 1 was performed under the condition of h. When the obtained sample was analyzed in the same manner, it was _confirmed that Na _0.92 WO ₃ and Na ₂ were obtained in the case of a sample having a Na / W molar ratio of 1.0 as a product.
WO _{4 is} also Na _{0.94 in} the sample having the same molar ratio of 1.07.
WO ₃ and Na ₂ WO ₄ were obtained. Further, when yttria-stabilized zirconia plates and Hastelloy-based corrosion-resistant and heat-resistant alloy plates having almost the same size as the support instead of the graphite fiber cloth were subjected to the same operation to analyze the products after the hydrogen reduction treatment, Similar results were obtained. Then, the above sample is placed in a flat glass container containing 30 ml of warm water, washed with water for about 10 minutes with occasional shaking, then the attached water is removed with filter paper, etc., and dried at 150 ° C. A bronze coating was obtained.

[0014]

INDUSTRIAL APPLICABILITY The present invention uses sodium ditungstate crystals as a raw material, and after supplying hydrogen at a temperature of 690 ° C. or lower while appropriately controlling the hydrogen concentration, sodium tungsten bronze (Na _x WO ₃ , 0.60 <x <1)
A high composition x (0.85%) can be obtained by simply adding a washing operation to remove the sodium monotungstate produced in a small amount.
It is possible to manufacture a tungsten bronze powder crystal which is free of impurities such as metallic tungsten. INDUSTRIAL APPLICABILITY The present invention facilitates the production of high-composition x tungsten bronze, which has been reported to be successful as an electrode catalyst for fuel cells and the like. In the present invention, instead of the above-mentioned sodium ditungstate crystal, N
By using an aqueous sodium tungstate solution with an a / W molar ratio of 1 to 1.1 as a raw material, a tungsten bronze film with a high composition x can be formed on the surface of woven fabrics and porous materials that have fine structures as well as plates and rods. Can be formed. The composite thus obtained is suitable for manufacturing an electrode material for an electrolytic device or a fuel cell using sodium tungsten bronze.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Shindo 1-1 Higashi Tsukuba City, Ibaraki Prefectural Institute of Industrial Science and Technology (72) Inventor Susumu Mizuta 1-1 Higashi Tsukuba City, Ibaraki Industrial Research Institute of Chemical Technology In-house

Claims (4)

[Claims] 1. Sodium ditungstate (chemical formula N
a ₂ W ₂ O ₇ ) powder crystals are reduced in a hydrogen atmosphere to produce sodium tungsten bronze and sodium monotungstate (Na ₂ WO ₃ ) represented by the chemical formula Na _x WO ₃ (where 0.60 <x <1). ₄ ) and is produced, and sodium monotungstate is separated and removed by washing with water. 2. A sodium tungstate water-containing amorphous coating film on the surface of a support, which is coated with an aqueous solution of sodium tungstate (wherein the Na / W molar ratio is 1 to 1.1) and then dried. (However, if the Na / W molar ratio is
1 to 1.1. ) Is formed and then reduced with hydrogen to give Na _x
A method for producing a tungsten bronze-coated composite, comprising forming a coating containing sodium monotungstate on sodium tungsten bronze represented by WO ₃ (wherein 0.60 <x <1). 3. A carbon material containing a carbon fiber whose surface is modified with carbide, a zirconia material, a magnesia material, a carbide material, an alumina material and a corrosion resistant material.
The method for producing a tungsten bronze-coated composite body according to claim 2, wherein the composite material is selected from heat-resistant metal materials. 4. The method for producing a tungsten bronze-coated composite according to claim 2, wherein sodium monotungstate is removed by washing with water after hydrogen reduction.