JP4997433B2 - Method for producing zirconium tungstate-magnesium tungstate composite - Google Patents

Description

The present invention, zirconium tungstate - relates to the manufacture how tungstate magnesium complex. More specifically, it is possible to control the thermal expansion, the optical field, thermal energy field, useful zirconium tungstate in the field of electronic materials - relates to the production how tungstate magnesium complex.

  The thermal expansion behavior of the structural material causes deformation due to an increase in volume due to heating, which is a major cause of separation or breakage at the bonding interface of foreign substances. Especially for precision mechanical parts and optical parts that require high accuracy, how to suppress such thermal expansion is a major issue, and there is a desire to control thermal expansion and make it as low as possible. .

On the other hand, the behavior in which the volume continuously decreases as the temperature rises is called “negative thermal expansion (negative expansion)”. Tungsten has recently attracted attention as a material exhibiting such negative expansion (negative expansion material). Zirconate (ZrW ₂ O ₈ ). Zirconate tungstate is a ceramic that exhibits isotropic negative thermal expansion over a wide range of temperatures. Since thermal expansion can be suppressed and controlled, optical components, optical elements, precision mechanical components, thermoelectric conversion materials, and various precision devices In addition, it is used in various fields where control of thermal expansion is an important issue, such as optical filters such as ferrules, optical fibers and gratings.

  In addition, such a zirconium tungstate can control the coefficient of thermal expansion by combining it with a material exhibiting positive thermal expansion (positive expansion material), and changes in dimensions are difficult to appear due to changes in temperature. Therefore, a material having excellent dimensional stability can be obtained. And, as a means for obtaining such a composite containing zirconium tungstate, when obtaining a sintered body of a composition containing zirconium tungstate, the rate of temperature rise during sintering is set to 20 to 1000 ° C./minute, Means for setting the sintering temperature to 777 ° C. or lower (for example, see Patent Document 1), and means for compressing and solidifying a composite containing zirconium tungstate using a shock wave of 2 to 50 GPa are provided (for example, (See Patent Document 2).

JP 2003-129149 A ([Claim 1], [0022]) JP 2003-201502 A ([Claim 1], [0029])

  However, the composite containing zirconium tungstate obtained by the above means did not become a dense sintered body, and the actual condition was that a satisfactory product was not obtained. In addition, the manufacturing method is not efficient, and improvement has been demanded.

The present invention has been made in view of the above problems, is capable of thermal expansion controlled in a dense structure, and zirconium tungstate can be produced in a simple way - provide a manufacturing how tungstate magnesium complex There is to do.

  According to the method for producing a zirconium tungstate-magnesium tungstate composite of the present invention, an amorphous powder of zirconium tungstate is obtained by a sol-gel method using a first starting material containing tungsten and a second starting material containing zirconium. A second step of obtaining a magnesium tungstate powder by a sol-gel method using a third starting material containing tungsten and a fourth starting material containing magnesium, and the amorphous powder of zirconium tungstate, A third step is included, in which the magnesium tungstate powder is mixed and crystallized by discharge plasma sintering.

  In the method for producing a zirconium tungstate-magnesium tungstate composite according to the present invention, the magnesium tungstate crystal obtained by sintering the magnesium tungstate amorphous powder to the magnesium tungstate powder obtained in the second step. A powder is preferred.

  In the method for producing a zirconium tungstate-magnesium tungstate composite according to the present invention, the first starting material containing tungsten and the third material containing tungsten are tungsten hexachloride, and the second starting material containing zirconium. Preferably, the material is chlorinated zirconium oxide octahydrate, and the fourth starting material containing magnesium is magnesium chloride.

  According to the method for producing a zirconium tungstate-magnesium tungstate composite of the present invention, an amorphous powder of zirconium tungstate is obtained by a sol-gel method using a first starting material containing tungsten and a second starting material containing zirconium. A second step of obtaining a magnesium tungstate powder by a sol-gel method using a third starting material containing tungsten and a fourth starting material containing magnesium, and the amorphous powder of zirconium tungstate, This comprises a third step in which the magnesium tungstate powder is mixed and crystallized by spark plasma sintering. In the present invention, by using a sol-gel method, zirconium tungstate as a composite precursor can be easily produced at a low temperature as compared with other general methods. Since it is made into a composite by sintering and crystallization by spark plasma sintering, it is possible to efficiently prevent the occurrence of cracks due to the difference in thermal expansion coefficient between the two, improving the density of the composite and making it dense It becomes possible to obtain a complex of structure. In addition, the combined use of the sol-gel method and discharge plasma sintering reduces the load of holding time and heating time in the subsequent discharge plasma sintering, and the composite having the above-described effects can be obtained at low temperature and in a short time. It can be easily obtained.

  Moreover, the manufacturing method of the zirconium tungstate-magnesium tungstate composite of the present invention is made of magnesium tungstate obtained by sintering an amorphous powder of magnesium tungstate as the magnesium tungstate powder obtained in the second step. Since the crystal powder is used, the sintered density of the composite to be manufactured can be further improved.

  The method for producing a zirconium tungstate-magnesium tungstate composite of the present invention includes tungsten hexachloride as a first starting material containing tungsten and tungsten hexachloride as a third material containing tungsten, and chlorination oxidation as a second starting material containing zirconium. Zirconium octahydrate and magnesium chloride are employed as the fourth starting material containing magnesium, respectively, so that the starting material is stable and the manufactured zirconium tungstate-magnesium tungstate complex has a more precise structure. can do.

The present invention will be described below. The zirconium tungstate-magnesium tungstate composite (hereinafter, simply referred to as “composite”) obtained in the present invention is composed of zirconium tungstate as a negative expansion material and magnesium tungstate powder as a positive expansion material. Therefore, the functional ceramic material is a functional ceramic material that is offset by the thermal expansion behavior and has good dimensional stability against temperature rise.

It is known that zirconium tungstate, which is a negative expansion material, transitions into two phases due to a change in temperature. In general, the α phase is stable at room temperature, but transitions from the α phase to the β phase at a temperature of 120 to 160 ° C. Since the α phase and the β phase have different crystal structures and lattice spacings, their thermal expansion coefficients are different. The α phase is cubic and has a thermal expansion coefficient of about −5.0 × 10 ⁻⁶ to −9.0 × 10 ⁻⁶ / ° C. in a temperature range of −273 to 120 ° C. The β phase is also cubic and has a thermal expansion coefficient of about −3.0 × 10 ⁻⁶ to −7.0 × 10 ⁻⁶ / ° C. in the temperature range of 170 to 400 ° C.

Magnesium tungstate has no phase transition due to temperature change, and the thermal expansion coefficient is about 5.0 × 10 ^{−6 to} 7.5 × 10 ⁻⁶ / ° C.

The thermal expansion coefficient in the composite obtained by the present invention depends on the composition balance of zirconium tungstate, which is a negative expansion material, and magnesium tungstate, which is a positive expansion material, although it depends on the sintering conditions and the crystalline state. Table 1 shows the relationship between the composition ratio of zirconium tungstate (ZrW ₂ O ₈ ) and magnesium tungstate (MgWO ₄ ) (zirconium tungstate / magnesium tungstate) and the thermal expansion coefficient.

(Relationship between composition ratio and thermal expansion coefficient)

In the zirconium tungstate-magnesium tungstate composite obtained by the present invention , the coefficient of thermal expansion is −6.0 × 10 ^{−6 to} 6.0 × 10 ⁻⁶ / ° C. (in Table 1, zirconium tungstate / If the magnesium tungstate is about 90/10 to 10/90), the change in the temperature is less likely to occur due to the change in temperature, so that the material is excellent in dimensional stability against a temperature rise. In particular, if the thermal expansion coefficient is −1.0 × 10 ^{−7 to} 1.0 × 10 ⁻⁷ / ° C. (in Table 1, zirconium tungstate / magnesium tungstate is approximately 70/30 to 50/50), It becomes a so-called substantially zero-expansion material, and the material hardly changes in dimensions due to a change in temperature, and is extremely excellent in dimensional stability against temperature rise.

  The composite includes, for example, a first step of obtaining a zirconium tungstate powder by a sol-gel method using a first starting material containing tungsten and a second starting material containing zirconium, and a third containing tungsten. A second step of obtaining a magnesium tungstate powder by a sol-gel method, and mixing the zirconium tungstate and magnesium tungstate, and crystallizing by discharge plasma sintering It can obtain efficiently by the manufacturing method including the 3rd process to make.

  Here, the sol-gel method is generally a solution in which a starting material is dissolved in a solvent, and a sol solution precipitated through a chemical reaction such as hydrolysis or polycondensation is aggregated to form a gelled product. This is a means for obtaining glass or ceramics by removing the solvent left inside by heat treatment, and further promoting densification by sintering treatment or the like if necessary. In the present invention, by using such a sol-gel method to produce zirconium tungstate and magnesium tungstate as precursors, the load of heating time and holding temperature in discharge plasma sintering applied in the subsequent process Can be reduced efficiently.

(1) Production of zirconium tungstate by sol-gel method (first step):
The first step constituting the production method of the present invention is a step of producing an amorphous powder of zirconium tungstate by using a first starting material containing tungsten and a second starting material containing zirconium using a sol-gel method. It is.

In the first step, the first starting material containing tungsten is dissolved in alcohol in an inert gas and hydrolyzed as a solution (hereinafter sometimes referred to as “first solution”). To advance. Examples of the first starting material containing tungsten include tungsten hexachloride (WCl ₆ ), tungsten alkoxides W (OC ₂ H ₅ ) ₅ , W (Oi-C ₃ H ₇ ) _{5, and the} like. However, it is preferable to use tungsten hexachloride in terms of material stability.

  As the alcohol for dissolving the first starting material, various compounds such as monohydric alcohol compounds such as methanol, ethanol, propanol, and butanol, and polyhydric alcohol compounds can be used. These alcohols may be used alone or in combination of two or more thereof. In the present invention, the first starting material may be dissolved in the alcohol in an inert gas such as argon gas or nitrogen gas to form the first solution.

The second starting material containing zirconium is dissolved in an alcohol and an acid to cause hydrolysis to proceed as a solution (hereinafter sometimes referred to as “second solution”). Examples of the second starting material containing zirconium include zirconium chloride oxide octahydrate (ZrOCl ₂ .8H ₂ O), ZrCl ₄ , ZrO (NO ₃ ) ₂ .2H ₂ O, Zr (OC ₂ H ₅ ), and the like. _{4 and the} like. Among them, it is preferable to use zirconium chloride oxide octahydrate (ZrOCl ₂ .8H ₂ O) in terms of material stability.

  As the alcohol for dissolving the second starting material, various compounds such as monohydric alcohol compounds such as methanol, ethanol, propanol and butanol, and polyhydric alcohol compounds as in the case of the alcohol dissolving the first starting material. Can be used. One of these alcohols may be used alone, or two or more thereof may be used in combination. As the acid, hydrochloric acid, sulfuric acid, nitric acid, acetic acid and the like can be used. These acids may be used alone or in combination of two or more. May be.

  Next, the first solution containing the first starting material and the second solution containing the second starting material dissolved are mixed, stirred, and allowed to stand, thereby allowing the first starting material containing tungsten to A sol solution of a second starting material containing zirconium is prepared. In preparing the sol solution, the first solution and the second solution are mixed and stirred at room temperature, preferably for 24 to 72 hours, more preferably for 30 to 72 hours, to obtain a mixed solution. The mixed solution is allowed to stand at room temperature, preferably for 12 to 48 hours, more preferably for 24 to 48 hours, so that the first starting material containing tungsten and the second starting material containing zirconium in the solution are mixed. Polycondensation occurs and a sol solution is formed.

  By subjecting such a sol solution to heat treatment, polycondensation of the first starting material containing tungsten and the second starting material containing zirconium in the solution further proceeds, and the solvent is removed, whereby tungstic acid is removed. A gelled product of zirconium is formed. In the formation of the gelated product by heat treatment, the heating temperature is preferably 80 to 100 ° C., more preferably 90 to 100 ° C., using a known heating means such as an oil bath or a hot plate. . The heating time is preferably 5 to 12 hours, and more preferably 8 to 12 hours.

  And the amorphous powder of a zirconium tungstate can be obtained by carrying out temporary sintering processing (it agrees with what is called calcination. The following is the same) for the gelled product of the obtained zirconium tungstate. In the preliminary sintering treatment, the heating temperature is preferably 400 to 450 ° C., and particularly preferably 430 to 450 ° C., by a known heating means such as an electric furnace. The heating time is preferably 5 to 12 hours, particularly preferably 10 to 12 hours.

(2) Production of magnesium tungstate powder by sol-gel method (second step):
The second step constituting the production method of the present invention is a step of producing a zirconium tungstate powder by using a sol-gel method with a third starting material containing tungsten and a fourth starting material containing magnesium. .

Here, in the second step, as in the first step, a third starting material containing tungsten is dissolved in alcohol in an inert gas (hereinafter referred to as “third solution”). The hydrolysis is allowed to proceed. As the third starting material containing tungsten, for example, tungsten hexachloride (WCl ₆ ), tungsten alkoxide W (OC ₂ H ₅ ) ₅ , W (O-i-C) is the same as the first starting material. ₃ H ₇ ) _{5 and the} like, and tungsten hexachloride is preferably used in terms of material stability.

  As the alcohol for dissolving the third starting material, various compounds such as monohydric alcohol compounds such as methanol, ethanol, propanol and butanol, and polyhydric alcohol compounds may be used as in the first step. it can. These alcohols may be used alone or in combination of two or more thereof. In the present invention, the third starting material may be dissolved in the alcohol in an inert gas such as argon gas or nitrogen gas to form a third solution.

Similar to the third starting material containing zirconium in the first step, the fourth starting material containing magnesium is dissolved in alcohol and acid as a solution (hereinafter, sometimes referred to as “fourth solution”). , Proceed with hydrolysis. As the fourth starting material containing magnesium, magnesium such as magnesium chloride (MgCl ₂ ), Mg (C ₂ H ₃ O ₂ ) ₂ .4H ₂ O, MgCl ₂ .6H ₂ O, Mg (OC ₂ H5) _2, etc. Of the alkoxide. Among these, it is preferable to use magnesium chloride (MgCl ₂ ) in terms of material stability.

  As the alcohol for dissolving the fourth starting material, a monovalent alcohol compound such as methanol, ethanol, propanol, butanol or a polyhydric alcohol is used in the same manner as the alcohol for dissolving the first starting material and the third starting material. Various compounds such as a compound can be used. One of these alcohols may be used alone, or two or more thereof may be used in combination. As the acid, hydrochloric acid, sulfuric acid, nitric acid, acetic acid and the like can be used. These acids may be used alone or in combination of two or more. May be.

  Next, in the same manner as in the first step, the third solution in which the third starting material is dissolved and the fourth solution in which the fourth starting material is dissolved are mixed, stirred, and allowed to stand, thereby leaving tungsten. A sol solution of a third starting material containing and a fourth starting material containing magnesium is prepared. In preparing the sol solution, the third solution and the fourth solution are mixed and stirred at room temperature, preferably for 24 to 72 hours, more preferably for 30 to 72 hours, to obtain a mixed solution. The mixed solution is allowed to stand at room temperature, preferably for 12 to 48 hours, more preferably for 24 to 48 hours, so that the third starting material containing tungsten and the fourth starting material containing magnesium in the solution are mixed. Polycondensation occurs and a sol solution is formed.

As in the first step, the sol solution is subjected to a heat treatment, so that the polycondensation of the third starting material containing tungsten and the fourth starting material containing magnesium in the solution further proceeds, and the solvent is removed. By being removed, a gelled product of magnesium tungstate is formed. The formation of the gelled product by such heat treatment is performed at a heating temperature of preferably 80 to 100 ° C., more preferably 90 to 100 ° C., using a known heating means such as an oil bath or a hot plate, as in the first step. The heating time is preferably 5 to 12 hours, more preferably 8 to 12 hours.

  And the amorphous powder of zirconium tungstate can be obtained by pre-sintering the gelled product of the obtained magnesium tungstate. Such pre-sintering treatment is performed by a known heating means such as an electric furnace, preferably at a heating temperature of 400 to 450 ° C., more preferably 430 to 450 ° C., and a heating time of preferably 5 to 12 hours, more preferably 10 It should be ~ 12 hours.

In addition, in the manufacturing method of this invention, it is preferable to further sinter and crystallize the obtained amorphous powder of magnesium tungstate. By using magnesium tungstate as crystal powder, the sintered density of the composite to be produced can be further improved. The means for sintering the magnesium tungstate is not particularly limited. For example, in addition to heat sintering at normal pressure, heat sintering in a pressurized state, discharge plasma sintering, which will be described later, is used for sintering / crystallization. You may make it make it. According to the following conditions, the thermal expansion coefficient of the obtained magnesium tungstate crystal powder is approximately 6.0 × 10 ^{−6 to} 7.5 × 10 ⁻⁶ / ° C. in the temperature range of 50 to 400 ° C. Can be controlled.

In obtaining the crystal powder of magnesium tungstate, the holding temperature is 600 to
It is preferable to set it as 850 degreeC, and it is still more preferable to set it as 750-850 degreeC. In addition, the temperature holding time is preferably 30 minutes or more, and more preferably 60 minutes or more. The rate of temperature rise is preferably 50 to 200 ° C./hour, 50 to 1
More preferably, the temperature is set to 00 ° C./hour.

  The press pressure in heat sintering or discharge plasma sintering in a pressurized state is preferably 20 to 100 MPa, and more preferably 50 to 100 MPa. In addition, it is preferable to perform these in inert gas atmosphere, such as argon gas and nitrogen gas.

(3) Production of zirconium tungstate-magnesium tungstate composite by spark plasma sintering (third step):
In the third step constituting the production method of the present invention, the zirconium tungstate amorphous powder obtained in the first step and the magnesium tungstate powder obtained in the second step are mixed, and discharge plasma sintering is performed. This is a process of sintering and crystallization by crystallization.

  In addition, in order to mix the amorphous powder of zirconium tungstate obtained in the first step and the magnesium tungstate powder obtained in the second step, a known mixing means such as wet mixing or dry mixing is employed. can do. Among these, as a solvent in wet mixing, non-aqueous solvents, for example, alcohol solvents such as methanol and ethanol, aromatic solvents such as benzene, toluene and xylene, ketone solvents such as methyl ethyl ketone, and the like should be used. Is preferred. The amount of solvent used may be, for example, about 5 Pa · s as the slurry viscosity. In addition, in the case of wet mixing or dry mixing, mixing may be performed using a known mill device such as a ball mill, a vibration mill, or a planetary mill, in addition to a normal stirring process.

  In the third step of the present invention, the mixture of zirconium tungstate and magnesium tungstate mixed as described above is sintered and crystallized by spark plasma sintering. In spark plasma sintering (also referred to as SPS method), a DC pulse voltage is applied to a compacted powder compact at a low voltage, and several thousand to one instantaneously generated in a gap between powders due to a spark discharge phenomenon. This is a method of sintering powder by effectively applying high energy of discharge plasma of about 10,000 ° C. to thermal diffusion, electric field diffusion and the like.

  In the present invention, rapid Joule heating of the powder surface by passing a large pulse current between the powders is performed by applying a pulse current in a compressed and compressed state when compositing zirconium tungstate and magnesium tungstate. By virtue of surface activation by the discharge plasma generated in the gap between the raw material alloy fine powders, cleaning action, movement of the discharge point and Joule heating point, only the vicinity of the surface of the raw material alloy fine powder is rapidly heated and heated. By adopting spark plasma sintering as the production method of the present invention, it is possible to raise the temperature much more rapidly than general sintering, and the sintering density of the composite can be significantly improved. When sintering and crystallizing negatively-expanded material zirconium tungstate and positively-expanded material magnesium tungstate to form a composite, it effectively prevents cracks due to the difference in thermal expansion coefficient between the two. be able to. As an apparatus for performing heat radiation plasma sintering, for example, a discharge plasma sintering apparatus (Doctor Sinter SPS-1050: manufactured by SPS Syntex Corporation) or the like can be used.

  The discharge plasma sintering is preferably performed in an inert gas atmosphere such as argon gas or nitrogen gas. Moreover, as a press pressure in discharge plasma sintering, it is preferable to set it as 10-200 Mpa, and it is still more preferable to set it as 50-100 Mpa.

  The holding temperature is preferably 500 to 750 ° C. and more preferably 600 to 650 ° C. in consideration of the decomposition temperature of tungsten (777 ° C.). In addition, the temperature holding time is preferably 10 minutes or more, and more preferably 30 minutes or more. Moreover, it is preferable to set it as 50-200 degreeC / min as a temperature increase rate, and it is still more preferable to set it as 50-100 degreeC / min.

  In the method for producing the zirconium tungstate-magnesium tungstate composite of the present invention, the zirconium tungstate powder and the magnesium tungstate powder are prepared by the sol-gel method. Zirconate and the like can be easily produced at a low temperature compared to other general methods. In addition, zirconium tungstate, which is a negative expansion material, and magnesium tungstate, which is a positive expansion material, are subjected to discharge plasma sintering. Because it is sintered and crystallized into a composite by sintering, cracks due to the difference in thermal expansion coefficient between them are effectively prevented, the density of the composite is improved, and a composite with a dense structure is formed. Obtainable. Furthermore, by combining the sol-gel method and the discharge plasma sintering, the burden of holding time and heating time in the subsequent discharge plasma sintering is reduced, and the composite having the above-described effects can be reduced at a low temperature and in a short time. Can be obtained.

The zirconium tungstate-magnesium tungstate composite obtained by the present invention can be used as a functional ceramic material, and the molded body prepared by molding or sintering the powder composite is used for heating. In the optical, thermal energy, and electronic materials fields where control of thermal expansion is an important issue due to excellent dimensional stability, optical filters such as optical fiber ferrules, optical fibers and gratings, optical fiber coatings, and semiconductors It can be used for parts, precision electronic parts, precision devices such as optical waveguides, thermoelectric conversion materials such as fuel cell separators, precision optical parts, optical elements, and the like.

  The aspect described above shows one aspect of the present invention, and the present invention is not limited to the above-described embodiment, and has the configuration of the present invention and can achieve the objects and effects. It goes without saying that modifications and improvements within the scope are included in the content of the present invention. Further, the specific structure, shape, and the like in carrying out the present invention are not problematic as other structures, shapes, and the like as long as the objects and effects of the present invention can be achieved. The present invention is not limited to the above-described embodiments, and modifications and improvements within the scope that can achieve the object of the present invention are included in the present invention.

  For example, the sol-gel method as a means for obtaining an amorphous powder of zirconium tungstate or a magnesium tungstate powder in the method for producing a composite of the present invention is not limited to the above-described contents, and the first containing tungsten. To obtain an amorphous zirconium tungstate powder from a second starting material containing zirconium and a second starting material containing zirconium, or obtaining a magnesium tungstate powder from a third starting material containing tungsten and a fourth starting material containing magnesium. If a sol-gel method that can be used is adopted, there is no particular limitation.

In addition, in producing the zirconium tungstate-magnesium tungstate composite body obtained in the present invention, a sintering aid, a binder (binder), etc. are appropriately added within a range not hindering the object and effect of the present invention. can do.
In addition, the specific structure, shape, and the like in the implementation of the present invention may be other structures as long as the object of the present invention can be achieved.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these.

[Example 1]
Production of zirconium tungstate-magnesium tungstate composite:
The following (1) to (3), data tungsten zirconium - was prepared tungsten magnesium complex.

(1) Production of amorphous powder of zirconium tungstate:
10.15 g of chlorinated zirconium oxide octahydrate (manufactured by Kishida Chemical Co., Ltd., purity 99%) and tungsten hexachloride (Kishida Chemical) so that the molar ratio of zirconium to tungsten is 1/2. 25.00 g each (manufactured by Co., Ltd., purity 99%) were weighed. After weighing, tungsten hexachloride was dissolved in 250 ml of ethanol with stirring in a glove box under an argon gas atmosphere to obtain a first solution. On the other hand, zirconium chloride octahydrate was mixed with 100 ml of 2-butanol in the atmosphere, and further 50 ml of 4N acetic acid was added and dissolved by stirring to obtain a second solution.

  The obtained first solution and second solution were mixed and stirred at room temperature for 30 hours to obtain a sol solution. The sol solution was allowed to stand for 42 hours and then heated for 9 hours with stirring in an oil bath at 80 ° C. to evaporate the water and gelled. The obtained gelled product was pre-sintered (pre-fired) at 450 ° C. for 12 hours using an electric furnace to obtain about 8.0 g of zirconium tungstate amorphous powder having an average particle size of about 0.1 μm. Obtained.

  The X-ray diffraction spectrum of the obtained amorphous powder of zirconium tungstate is shown in FIG. As shown in FIG. 1, the X-ray diffraction spectrum of the powder showed a so-called halo pattern, and it was confirmed that the obtained powder was an amorphous powder. In the X-ray diffraction spectrum, the horizontal axis represents the diffraction angle when CuKα rays are used as the X-ray source, while the vertical axis represents the intensity of the diffracted X-rays. The same applies to the X-ray diffraction spectra of FIGS. 2, 3 and 5 described later.

(2) Production of magnesium tungstate crystal powder:
6.01 g of magnesium chloride (manufactured by Kishida Chemical Co., Ltd., purity 99%), tungsten hexachloride (manufactured by Kishida Chemical Co., Ltd., purity) so that the molar ratio of magnesium to tungsten is 1/1. 99%) was weighed 25.00 g each. After weighing, tungsten hexachloride was dissolved in 250 ml of ethanol with stirring in a glove box under an argon gas atmosphere to obtain a third solution. On the other hand, zirconium chloride octahydrate was mixed with 100 ml of 2-butanol in the atmosphere, and further 50 ml of 4N acetic acid was added and stirred to dissolve to form a fourth solution.

  The obtained third solution and fourth solution were mixed and stirred at room temperature for 30 hours to obtain a sol solution. The sol solution was allowed to stand for 42 hours and then heated for 9 hours with stirring in an oil bath at 80 ° C. to evaporate the water and gelled. The obtained gelled product was pre-sintered at 450 ° C. for 12 hours using an electric furnace to obtain about 5.0 g of zirconium tungstate amorphous powder having an average particle size of about 0.1 μm.

  The obtained amorphous powder of magnesium tungstate was uniaxially pressed in an argon gas atmosphere at 1 atm and sintered under the following conditions. In addition, as holding temperature, it implemented by seven types of temperatures, 450 degreeC, 600 degreeC, 650 degreeC, 700 degreeC, 750 degreeC, 800 degreeC, and 850 degreeC, respectively.

(Sintering conditions)
Press pressure: 50 MPa
Holding temperature: 450 ° C, 600 ° C, 650 ° C, 700 ° C, 750 ° C,
800 ° C and 850 ° C
Holding time: 60 minutes Heating rate: 100 ° C / hour

  The X-ray diffraction spectrum of the obtained magnesium tungstate crystal powder is shown in FIG. 2 (result when the holding temperature is 450 ° C.) and FIG. 3 (result when the holding temperature is 600 to 850 ° C.). As shown in FIG. 2, what was processed at a holding temperature of 450 ° C. was an amorphous powder with no clear peak, but as shown in FIG. 3, when the holding temperature was 600 ° C., the amorphous powder A peak due to the crystallization was confirmed, and as the sintering temperature was raised, crystallization progressed and the peak became clear. On the other hand, there is almost no difference in peak between 800 ° C. and 850 ° C., and the amorphous powder of magnesium tungstate prepared by the sol-gel method is sintered at least at 600 ° C., preferably at 800 ° C. or higher. Thus, it was confirmed that a crystalline powder of magnesium tungstate could be prepared.

FIG. 4 is a diagram showing the thermal expansion behavior of the magnesium tungstate crystal powder sintered at a holding temperature of 800.degree. From FIG. 4, it was found that the thermal expansion coefficient of the powder was 6.92 × 10 ⁻⁶ / ° C. in the temperature range of 50 to 300 ° C.

(3) Production of zirconium tungstate-magnesium tungstate composite:
The zirconium tungstate amorphous powder obtained in (1) and the magnesium tungstate crystal powder obtained in (2) (with a holding temperature of 700 ° C.) were dry mixed. This mixed powder is filled in a graphite mold (jig diameter φ20 mm), and a discharge plasma discharge sintering apparatus (Doctor Sinter SPS-1050: manufactured by SPS Syntex Co., Ltd.) is used in an argon gas atmosphere of 1 atm. Then, discharge plasma sintering was performed under the following conditions to obtain a crystal powder of a zirconium tungstate-magnesium tungstate composite.

  The composition ratio between the amorphous powder of zirconium tungstate and the crystalline powder of magnesium tungstate is zirconium tungstate / magnesium tungstate = 20/80 (Example 1-a), 40/60 (Example 1-b). ), 50/50 (Example 1 / c), 60/40 (Example 1-d), and 80/20 (Example 1-e). In addition, as a blank, the magnesium tungstate crystal powder obtained in (2) and the zirconium tungstate amorphous powder obtained in (1) were also sintered by discharge plasma under the same conditions, respectively, and Reference Example 1, Reference Example 2 was adopted.

(Discharge plasma sintering conditions)
Press pressure: 50 MPa
Holding temperature: 600 ° C
Holding time: 10 minutes Heating rate: 100 ° C / min

  FIG. 5 shows X-ray diffraction spectra of the sintered powders of Example 1-a to Example 1-e and Reference Examples 1 and 2. From the results of FIG. 5, for the composites of Example 1-a to Example 1-e, the peaks of zirconium tungstate and magnesium tungstate, which are reactants, were not confirmed, and composite peaks corresponding to the respective blending ratios. It was observed. Therefore, it was confirmed that zirconium tungstate and magnesium tungstate were made into a composite in a crystallized state.

  Moreover, although the density of the composites of Example 1-a to Example 1-e was measured by the Archimedes method, all the composites have a relative density that is not substantially different from the theoretical density, and the sintering is satisfactorily performed. It was confirmed that the structure was dense.

  Furthermore, the thermal expansion behavior of the zirconium tungstate-magnesium tungstate composite is shown in FIG. The thermal expansion behavior of the composite changed from positive to negative as the compounding ratio of zirconium tungstate was increased, and it became clear that the thermal expansion can be controlled.

  In addition, it is thought that the change of the thermal expansion coefficient in the vicinity of 160 ° C. seen in Reference Example 1 is due to the α-β phase transition of zirconium tungstate. Table 2 shows the results of the thermal expansion coefficient obtained from FIG.

(Coefficient of thermal expansion)

The present invention requires the control of thermal expansion, the optical field, thermal energy field, useful zirconium tungstate in an electronic material field, etc. - and can provide a manufacturing method of tungstate magnesium complex.

It is a figure which shows the X-ray-diffraction spectrum of the amorphous powder of zirconium tungstate. It is a figure which shows the X-ray-diffraction spectrum of the magnesium tungstate powder sintered by 450 degreeC. It is a figure which shows the X-ray-diffraction spectrum of the magnesium tungstate powder sintered at 600-850 degreeC. It is a figure which shows the thermal expansion behavior of the crystal powder of magnesium tungstate. It is a figure which shows the X-ray-diffraction spectrum of a zirconium tungstate-magnesium tungstate complex. It is a figure which shows the thermal expansion behavior of a zirconium tungstate-magnesium tungstate composite.

Claims (3)

  A first step of obtaining an amorphous powder of zirconium tungstate by a sol-gel method using a first starting material containing tungsten and a second starting material containing zirconium;
  A second step of obtaining a magnesium tungstate powder by a sol-gel method using a third starting material containing tungsten and a fourth starting material containing magnesium;
  A method of producing a zirconium tungstate-magnesium tungstate composite, comprising a third step of mixing the amorphous powder of zirconium tungstate and the magnesium tungstate powder and crystallizing by discharge plasma sintering. .   The tungstic acid according to claim 1, wherein the magnesium tungstate powder obtained in the second step is a magnesium tungstate crystal powder obtained by sintering an amorphous powder of magnesium tungstate. A method for producing a zirconium-magnesium tungstate composite.   The first starting material containing tungsten and the third material containing tungsten are tungsten hexachloride;
  The second starting material containing zirconium is chlorinated zirconium oxide octahydrate,
  The method for producing a zirconium tungstate-magnesium tungstate composite according to claim 1 or 2, wherein the fourth starting material containing magnesium is magnesium chloride.

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