JP4766852B2 - Method for producing zirconium tungstate - Google Patents

Description

  The present invention relates to a method for producing zirconium tungstate having a negative coefficient of thermal expansion.

Zirconate tungstate (ZrW ₂ O ₈ ) having a negative coefficient of thermal expansion is expected to be applied to devices for which thermal expansion control is an issue. Specifically, it is very useful in the fields of optical components (ferrules, optical fiber clothing, fiber gratings), thermoelectric conversion materials, and the like.

As a method for producing such zirconium tungstate, a rapid cooling method and a liquid phase reaction method are conventionally known.
As a rapid cooling method, in Patent Document 1 described later, an oxide (WO ₃ and ZrO ₂ ) is used as a starting material, and the raw material is melted and reacted at a high temperature, followed by ultra-quenching zirconium tungstate (ZrW ₂ O _8). ) Has been proposed.

On the other hand, as a liquid phase reaction method, a compound (A ⁴⁺ M ₂ ⁶⁺ O ₈ ) in which two types of metal elements are chemically bonded via oxygen is disclosed in Patent Document 2 described later, zirconium oxide chloride, Starting with tungstate containing no Na ions, hydrolyzing with H ₂ O for 10 hours, adding HCl, refluxing for 48 hours, filtering the solids and aging for 7 days, then at normal pressure 600 It has been proposed to produce zirconium tungstate (ZrW ₂ O ₈ ) by firing at 10 ° C. for 10 hours.

JP 2003-342075 A US Patent No. 6.183.713

However, first, it is difficult to obtain a large amount of single-phase zirconium tungstate (ZrW ₂ O ₈ ) in the ultra-quenching method after high-temperature melting of the oxide powder disclosed in Patent Document 1 described above. There was a problem to say.
Further, in the method of atmospheric pressure sintering of the powder raw material prepared by the liquid phase method disclosed in Patent Document 2, the tungsten (W) component is unstable, and it is difficult to ensure a stable process, There was a problem that a long time was required for firing and the mass productivity was poor.

  The present invention has been made in view of the various problems of the background art described above, and its purpose is to stably produce a large, high-purity single-phase zirconium tungstate in a short time. It is to provide a way that can be done.

The above-described problem is that an amorphous powder raw material is prepared by reacting a first starting material containing tungsten and a second starting material containing zirconium so that the molar ratio of tungsten to zirconium is 2: 1 and in a liquid phase. In the method for producing zirconium tungstate (ZrW ₂ O ₈ ) , comprising a liquid phase reaction process, a process of drying the obtained reaction product, and a crystallization process of crystallizing the amorphous powder raw material. The process includes a first firing process in which the amorphous powder raw material is fired between 500 ° C. and 700 ° C. in an air atmosphere using an electric furnace, and the amorphous powder raw material fired in the first firing process is energized and pressurized. It has been solved by a method for producing zirconium tungstate comprising a second firing step of sintering.

Here, the liquid phase reaction process includes a process of weighing the first starting material and the second starting material so that the molar ratio of tungsten to zirconium is 2: 1, and the first starting material is not mixed. It is preferable to include a process of dissolving in alcohol in an active gas atmosphere, a process of dissolving the second starting material in alcohol and acid, and a process of mixing and reacting the two solutions .
In the above current pressure sintering process, it is preferable to use a discharge plasma sintering (SPS) method, in the discharge plasma sintering method, the raw material powder was filled in a graphite die, 50 MPa from the press pressure 30 MPa, It is preferable to sinter by heating up to 600 ° C. at a rate of temperature increase of 100 ° C./min, holding for 2 to 5 minutes, and allowing to cool.
Furthermore, it is preferable to use tungsten hexachloride and zirconium chloride oxide octahydrate as the starting material.

According to the present invention described above, a large and highly pure single-phase zirconium tungstate (ZrW ₂ O ₈ ) can be produced stably and in a short time.
This is because an amorphous powder prepared by a liquid phase method (sol-gel method) has a chemical bond of the target product before crystallization and is in a chemically active state. On the other hand, an electric current pressure sintering method using a discharge plasma sintering (SPS) method or the like is a method suitable for producing a high-density sintered body in a short time. In the present invention, by using these features in combination, large-sized and high-purity single-phase zirconium tungstate (ZrW ₂ O ₈ ), which has been difficult to realize until now, can be stably and in a short time. It was realized to produce with.

  Hereinafter, the method for producing zirconium tungstate according to the present invention will be described in detail with reference to examples.

Example 1
FIG. 1 is a flowchart showing an embodiment of a method for producing zirconium tungstate according to the present invention.

  As shown in this flow chart, first, zirconium chloride oxide octahydrate (manufactured by Kishida Chemical Co., Ltd., purity 99%) and tungsten hexachloride (manufactured by Kishida Chemical Co., Ltd., purity 99%) are converted into a molar ratio of zirconium and tungsten. (1: 1614 g of chlorinated zirconium oxide octahydrate, 25.0444 g of tungsten hexachloride).

  Next, tungsten hexachloride was dissolved in alcohols (250 ml of ethanol) with stirring in a glove box in an inert gas (Ar gas) atmosphere. On the other hand, zirconium chloride oxide octahydrate was placed in alcohols (2-butanol 100 ml) in the atmosphere, and acid (4N acetic acid 50 ml) was added and stirred and dissolved.

  The obtained raw material solution was mixed, stirred at room temperature for 30 hours, then allowed to stand for another 42 hours, dried at 80 ° C. for 9 hours, calcined at 450 ° C. for 12 hours using an electric furnace, and raw material powder Got.

The X-ray diffraction spectrum of the obtained raw material powder is shown in FIG.
This X-ray diffraction spectrum shows a halo pattern. That is, it was confirmed that the obtained raw material powder was amorphous.
The horizontal axis of the X-ray diffraction spectrum is the diffraction angle when CuKα is used as the X-ray source, and the vertical axis indicates the intensity (dimensionless) of the diffracted X-ray. The same applies to other X-ray diffraction spectra described later.

The raw material powder prepared as described above was subjected to spark plasma sintering (SPS) to obtain a sintered body. Here, the discharge plasma sintering (SPS) is a method in which a DC pulse voltage is applied while pressing a raw material powder filled in a mold made of graphite or the like in a vacuum or an inert gas atmosphere. This is a known method of causing plasma discharge to occur in the raw material powder in the mold by voltage to bring the raw material powder to a high temperature locally and sintering the raw material powder.
In this example, a graphite mold (jig diameter 20 mmφ) is filled with the above raw material powder, heated to 600 ° C. at a press pressure of 50 MPa and a heating rate of 100 ° C./min, held for 2 minutes and allowed to cool. Was sintered.

FIG. 2B shows an X-ray diffraction spectrum of the sintered body sample thus obtained.
From this X-ray diffraction spectrum, it was confirmed that the obtained sample was single-phase zirconium tungstate (ZrW ₂ O ₈ ).
Similar results were obtained at a press pressure of 30 MPa. Furthermore, the retention time was 2 to 5 minutes, and similar results were obtained.

-Example 2-
FIG. 3 is a flowchart showing another embodiment of the method for producing zirconium tungstate according to the present invention.

As shown in this flowchart, first, the same conditions as in Example 1 above, that is, the preliminary raw material firing in FIG.
The X-ray diffraction spectrum of the obtained raw material powder is shown in FIG.
This X-ray diffraction spectrum showed a halo pattern, and it was confirmed that the obtained raw material powder was amorphous.

Next, in the case of the method according to this example, a part of the raw material powder prepared as described above is crystallized and then sintered by discharge plasma to obtain a sintered body.
That is, in order to crystallize a part of the prepared raw material powder, in this example, the raw material powder prepared as described above is press-molded, and the electric furnace is used in an air atmosphere at 600 ° C. for 12 hours. Atmospheric pressure firing was performed.
In addition, it is preferable to perform this normal-pressure baking temperature between 500 degreeC and 700 degreeC when the thermal decomposition of tungsten (W) is considered.

An X-ray diffraction spectrum of the sample thus fired is shown in FIG.
From this X-ray diffraction spectrum, it can be seen that a part of the obtained sample is crystallized. That is, a part is a seed crystal.

The raw material powder partially crystallized in this way and used as seed crystals was subjected to discharge plasma sintering under the same conditions as in the method of Example 1 to obtain a sintered body.
That is, a graphite mold (jig diameter 20 mmφ) is filled with the above raw material powder, heated to 600 ° C. at a pressing pressure of 50 MPa and a heating rate of 100 ° C./min, held for 2 minutes and allowed to cool for sintering. I let you.

FIG. 4C shows an X-ray diffraction spectrum of the sintered body sample thus obtained.
From this X-ray diffraction spectrum, it was confirmed that the obtained sample was single-phase zirconium tungstate (ZrW ₂ O ₈ ) excellent in crystallinity.
Similar results were obtained at a press pressure of 30 MPa. Furthermore, the retention time was 2 to 5 minutes, and similar results were obtained.

Moreover, the thermal expansion coefficient of 50 to 300 degreeC about the obtained sintered compact is shown in FIG.
From this figure, it was confirmed that the obtained sintered body had a negative thermal expansion coefficient in the range of at least 50 ° C to 300 ° C.

-Comparative example-
In order to contrast with the method for producing zirconium tungstate according to the present invention, spark plasma sintering was performed using a simple mixed powder of zirconium oxide and tungsten oxide powder as a starting material powder.
FIG. 6 shows a flowchart of the specific procedure.

  As shown in this flowchart, first, zirconium oxide (manufactured by Kishida Chemical Co., Ltd., purity 99.9%) and tungsten oxide (manufactured by Kishida Chemical Co., Ltd., purity 99.9%) are mixed at a molar ratio of zirconium to tungsten of one pair. 2 (zirconium oxide 42.0224 g, tungsten oxide 158.1324 g) were weighed and mixed with a V mixer for 3 hours. Next, this mixed powder was calcined at 450 ° C. for 12 hours in an air atmosphere using an electric furnace to obtain a raw material powder.

An X-ray diffraction spectrum of the obtained raw material powder is shown in FIG.
From this X-ray diffraction spectrum, it is understood that the raw material powder is a mixture of crystalline zirconium oxide and tungsten oxide.

The raw material powder thus prepared was subjected to discharge plasma sintering under the same conditions as in the method of the above-described embodiment of the present invention to obtain a sintered body.
That is, a graphite mold (jig diameter 20 mmφ) is filled with the above raw material powder, heated to 600 ° C. at a pressing pressure of 50 MPa and a heating rate of 100 ° C./min, held for 2 minutes and allowed to cool for sintering. I let you.

FIG. 7B shows an X-ray diffraction spectrum of the obtained sintered body sample.
From this X-ray diffraction spectrum, it was revealed that the obtained sample was simply a mixture of zirconium oxide and tungsten oxide, and the intended zirconium tungstate (ZrW ₂ O ₈ ) was not obtained.

Furthermore, a sample fired under the same conditions as described above was prepared except that the holding temperature and time were set at 850 ° C. for 2 minutes.
The X diffraction spectrum of this sample is shown in FIG.
From this X-ray diffraction spectrum, it is clear that the sample thus obtained is also a mixture of zirconium oxide and tungsten oxide, and the target zirconium tungstate (ZrW ₂ O ₈ ) has not been obtained. It was.

As is clear from the above-described Examples and Comparative Examples of the present invention, according to the method for producing zirconium tungstate according to the present invention, the starting materials are, for example, zirconium chloride oxide octahydrate (ZrOCl ₂ .8H ₂ O) and hexa It is clear that the target single-phase zirconium tungstate (ZrW ₂ O ₈ ) can be obtained only when amorphous powder prepared by liquid phase method (sol-gel method) is used with tungsten chloride (WCl ₆ ). Became.

The amorphous powder prepared by this liquid phase method (sol-gel method) is considered to have a chemical bond of the target product before crystallization, and is in a chemically active state. On the other hand, an electric pressure sintering method using a discharge plasma sintering (SPS) method or the like is a method suitable for manufacturing a high-density sintered body at a low temperature and in a short time.
The method for producing zirconium tungstate according to the present invention uses large and pure single-phase zirconium tungstate (ZrW ₂ O ₈ ), which has been difficult to realize by combining these features. Thus, it can be manufactured stably and in a short time.

  As mentioned above, although the Example of the manufacturing method of the zirconium tungstate based on this invention was described with the comparative example, the said Example is only one illustration of embodiment of this invention, and this invention is what said Example above. Of course, various modifications and changes are possible within the scope of the technical idea of the present invention.

It is the flowchart which showed one Example of the manufacturing method of the zirconium tungstate based on this invention. It is the figure which showed the X-ray-diffraction spectrum in various steps at the time of producing zirconium tungstate by the method shown in FIG. It is the flowchart which showed the other Example of the manufacturing method of the zirconium tungstate based on this invention. It is the figure which showed the X-ray-diffraction spectrum in various steps at the time of producing zirconium tungstate by the method shown in FIG. It is the figure which showed the thermal expansion coefficient of the sintered compact of the zirconium tungstate produced by the method shown in FIG. It is the flowchart which showed the procedure of the comparative example. FIG. 7 is a diagram showing X-ray diffraction spectra at various stages in the method shown in FIG. 6.

Claims (5)

A liquid phase reaction process in which a first starting material containing tungsten and a second starting material containing zirconium are reacted in a liquid phase such that the molar ratio of tungsten to zirconium is 2: 1 to produce an amorphous powder raw material; In the method for producing zirconium tungstate (ZrW ₂ O ₈ ) , including a process of drying the obtained reaction product and a crystallization process of crystallizing the amorphous powder raw material, the crystallization process includes an electric furnace A first firing process in which the amorphous powder raw material is fired between 500 ° C. and 700 ° C. in an air atmosphere, and a second current in which the amorphous powder raw material fired in the first firing process is pressure-sintered. A process for producing zirconium tungstate, comprising: The liquid phase reaction process includes a process of weighing the first starting material and the second starting material so that the molar ratio of tungsten to zirconium is 2: 1, and the first starting material is placed in an inert gas atmosphere. 2. The zirconium tungstate according to claim 1, comprising a step of dissolving in alcohol, a step of dissolving the second starting material in alcohol and acid, and a step of mixing and reacting the two solutions. Manufacturing method.   2. The method for producing zirconium tungstate according to claim 1, wherein the electric current pressure sintering process uses a discharge plasma sintering method.   Fill the graphite mold with the raw material powder by the above discharge plasma sintering method, raise the pressure to 600 ° C. at a press pressure of 30 MPa to 50 MPa and a temperature increase rate of 100 ° C./min, hold for 2 to 5 minutes, and allow to cool. The method for producing zirconium tungstate according to claim 3, wherein the sintering is performed by:   The method for producing zirconium tungstate according to claim 1, wherein the first starting material is tungsten hexachloride and the second starting material is zirconium chloride oxide octahydrate.

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