JP5982058B2 - Zirconium tungstate - Google Patents

Description

The present invention relates to a material having a negative expansion coefficient (volume decreases with increasing temperature) used when adjusting the expansion coefficient of glass or the like.

In recent years, in precision machine parts, optical parts, and electronic material packages that are required to have higher precision, measures are required to avoid the occurrence of distortion due to temperature changes caused by the external environment. In addition, some sensors are required to have a material design that avoids deterioration of the element due to such stress and has a long life in order to ensure that it can be operated in an emergency.

The expansion strain is caused by the difference in volume change at the bonding interface of different materials, and sometimes causes a large amount of peeling or breaking.
Negative expansion materials that shrink in volume with increasing temperature can be combined with materials with positive thermal expansion commonly found in most substances to control the coefficient of thermal expansion of the composite material. Because of it. In particular, zirconium tungstate (ZrW ₂ O ₈ ) has a large thermal contraction coefficient and has a characteristic of exhibiting isotropic negative thermal expansion uniformly over a wide temperature range. Furthermore, as environmental regulation standards become stricter, it is a highly anticipated material because it is a lead-free material that does not use lead.

However, various studies have been made on ZrW ₂ O ₈ after its negative thermal expansion was reported in the 1960s. However, a production method that shows a high crystal ratio of perovskite and can be mass-produced has not yet been established.

In the prior art, Patent Document 1 listed below proposes a method that is capable of stably producing a large and highly pure single-phase zirconium tungstate (ZrW ₂ O ₈ ). In the method of Document 1, first, an amorphous powder in which the element of the target substance has an accurate stoichiometric ratio is made by using a liquid phase method (sol-gel method), and then it is used for discharge plasma sintering or the like. The method is energization and pressure sintering. Preferably, the amorphous powder is fired at a temperature of 500 ° C. to 700 ° C. at normal pressure to prepare a seed crystal in advance, and this is energized and pressure sintered by a method such as discharge plasma sintering. .

By doing so, it has been proposed that a single-phase zirconium tungstate (ZrW ₂ O ₈ ) having better crystallinity can be obtained. However, this method also requires a long time in the liquid phase reaction process of the amorphous powder, and it is a batch type process in which a graphite mold (jig diameter 20 mmΦ) is filled and pressed. Is not suitable for mass production (production line of several tons or more per month).

As another prior art, in Patent Document 2, oxide (WO ₃ and ZrO ₂ ) is used as a starting material, the material is made into a bipolar particle size distribution, and this raw material powder is put into a desired mold and sintered. Proposed manufacturing methods have been proposed. However, the oxide powder sintering method disclosed in Patent Document 2 requires long-time mixing and long-time sintering, and cannot be manufactured in a short time, resulting in high manufacturing costs. is there.

Further, in Patent Document 3, a compound (A ⁴⁺ M ₂ ⁶⁺ O ₈ ) in which two kinds of metal elements are chemically bonded through oxygen, zirconium oxide chloride and tungstate containing no Na ions are used as starting materials. , Hydrolyzed with H ₂ O for 10 hours, added HCl, refluxed for 48 hours, filtered solids, aged for 7 days, calcined at 600 ° C. for 10 hours at atmospheric pressure, and zirconium tungstate (ZrW It has been proposed to produce ₂ O ₈ ).
However, in the method of atmospheric pressure sintering of powder raw materials prepared by such a liquid phase method, the tungsten component is unstable, stable production cannot be performed, and firing requires a long time, resulting in inferior mass productivity. There is.

JP 2006-44953 A JP 2003-342075 A US Pat. No. 6,183,713

As described above, there is a problem that it takes a long time to synthesize the crystallization, and the application to the product has not progressed so far. At the laboratory level, although there was a report of using a platinum crucible, it was not suitable for mass production. In addition, tungsten oxide easily volatilizes (there is a 0.3% weight loss at 950 ° C.-2 h), and there is a problem that it is difficult to control the composition. An object of the present invention is to reduce manufacturing costs by reducing composition fluctuations, improving quality and yield, and performing synthesis for crystallization in a very short time.

In order to solve the above problems, the following inventions are provided.
1) When the intensity of a diffraction peak located at 2θ = 21.4-21.8 ° in X-ray diffraction is 100%, the diffraction peak intensity located at 2θ = 23.5-23.9 ° is 92- Zirconate tungstate characterized by being 115%.

2) Zirconate tungstate according to 1) above, wherein the half width of the diffraction peak located at 2θ = 21.4 to 21.8 ° is 0.05 ° or more and 0.2 ° or less.

3) In the range of diffraction angle 2θ = 15-60 °, the intensity of the diffraction peak at the 2θ position not registered in JCPDS card code 00-050-1868 is located at 2θ = 21.4-21.8 °. The zirconium tungstate according to 1) or 2) above, wherein the peak intensity is 2% or less when the peak intensity is 100%.
4) The half width of the three diffraction peaks at 2θ = 22-24 ° is 0.25 ° or more, or the peak at 2θ = 33-37 ° is single, or 2θ = 49 °- A method for producing zirconium tungstate, wherein WO ₃ powder having a single peak of 51 ° or 53 ° to 57 ° is used as a raw material.
5) The above-mentioned WO ₃ powder is sufficiently mixed with ZrO ₂ powder, then held at 1190 ° C. or higher for 30 seconds or longer, and rapidly cooled to 200 ° C. or lower within 3 minutes. The manufacturing method of the zirconium tungstate of description.

Conventionally, there is a problem that it takes a long time to synthesize the crystallization, and the application to the product has not progressed so far. At the laboratory level, although there was a report of using a platinum crucible, it was not suitable for mass production. In addition, tungsten oxide easily volatilizes (there is a 0.3% weight loss at 950 ° C.-2 h), and there is a problem that it is difficult to control the composition.
The present invention makes it possible to solve these problems, reduce composition fluctuations, improve quality and yield, and reduce production costs by synthesizing to crystallization in a relatively short time. It has a remarkable effect that can be achieved.

Is a diagram showing the results of XRD of WO ₃ powder. Is a diagram showing the results of XRD of standard ZrO ₂ powder. It is a figure which shows the result of XRD of Examples 1-3. It is a figure which shows the result of XRD of Examples 4-6. It is a figure which shows the result of XRD of Comparative Examples 1-2. It is a figure which shows the result of XRD of Comparative Examples 3-5.

The zirconium tungstate of the present invention has a peak located at 2θ = 23.5-23.9 ° when the diffraction peak intensity located at 2θ = 21.4-21.8 ° in X-ray diffraction is taken as 100%. Is 92 to 115%.
There are four types of zirconium tungstate registered in X-ray diffraction (JCPDS: Joint Committee for Powder Diffraction Standards) as shown in Table 1 below. That is, there are four types of card codes 00-013-0557, 00-050-1868, 01-083-1005, and 01-087-1528.
In any case, the diffraction peak intensity at 2θ = 21.552 to 21.690 ° is larger than the diffraction peak intensity at 2θ = 23.643 to 23.789 °.
On the other hand, in the present invention, the latter diffraction peak is characterized by being larger than the conventional relative intensity ratio, and conventionally, there is no “zirconium tungstate” exhibiting this characteristic.

Taking advantage of this feature, as shown below, zirconium tungstate can be used effectively. When the thermal expansion coefficient of the zirconium tungstate of the present invention was measured by TMA (thermomechanical analysis), it was −9.6 × 10 ⁻⁶ / K, indicating a large negative thermal expansion characteristic equal to or higher than that of the conventional one. Since this zirconium tungstate has a very large negative expansion coefficient, by adding it to the main positive expansion material, it is possible to more effectively produce a zero expansion material whose expansion coefficient is almost zero. It becomes possible.
In addition, in elements to which different materials are joined, by adding a negative expansion material, measures can be taken to reduce the occurrence of expansion strain by bringing the expansion coefficients of both materials closer to each other. Since the same effect can be obtained with an addition amount equal to or less than that, it is very effective.

In addition, in producing the zirconium tungstate of the present invention, unlike the standard crystal structure of WO ₃ (card code 01-083-0950), the half width of three diffraction peaks at 2θ = 22-24 ° is different. Each is 0.25 ° or more, or diffraction peaks of 2θ = 33 to 37 ° are almost integrated and single, or peaks of 2θ = 49 ° to 51 ° or 53 ° to 57 ° are broad. Prepare and prepare raw material before heat synthesis with an average particle size of 2 μm or less by mixing and grinding WO ₃ powder (FIG. 1.a) with insufficient crystallization and standard ZrO ₂ powder (FIG. 2). did.

The WO ₃ powder in an insufficiently crystallized state can be determined (evaluated) by a diffraction peak. That is, the half width of each diffraction peak is 0.25 ° or more, or the diffraction peaks of 2θ = 33 to 37 ° are almost integrated and single, or 2θ = 49 ° to 51 ° or 53 It can be said that any of those having a broad peak at from -57 ° is a WO ₃ powder in a state of insufficient crystallization.
And after maintaining at a high temperature of 1190 ° C or higher for 30 seconds or more to crystallize to zirconium tungstate (ZrW ₂ O ₈ ), it is cooled instantly to avoid re-decomposition into WO ₃ or ZrO ₂ when the temperature is lowered. This can be achieved. The cooling rate at that time is desirably within 3 minutes, more preferably within 1 minute, until the temperature reaches 200 ° C. or lower.

Since the above-described “zirconium tungstate” of the present invention can be converted into a material having a crystal structure of zirconium tungstate in a very short time when heated, it suppresses volatilization of WO ₃ having a high vapor pressure, Variations in composition can be reduced, and quality and yield can be improved. In addition, this short-time synthesis is possible even for mass production and reduction of manufacturing costs.
Further, the zirconium tungstate of the present invention has a half-width of the X-ray diffraction peak located at 2θ = 21.4 to 21.8 ° of 0.05 ° or more and 0.2 ° or less and JCPDS. The characteristic that the intensity of the diffraction peak at the 2θ position not registered in the card 00-050-1868 is 2% or less when the peak intensity at 2θ = 21.4 to 21.8 ° is defined as 100%. I have.

The present invention will be described based on examples and comparative examples. In addition, a present Example is an example to the last, and is not restrict | limited only to this example. That is, other aspects or modifications included in the present invention are included.

(Example 1-3)
WO ₃ powder (FIG. 1.a) that does not have a complete WO ₃ crystal structure, which is an intermediate product when APT (ammonium paratungstate) is reduced to metallic tungsten, and addition of Ca, Y or the like zirconia The pure ZrO ₂ powder that has not been stabilized is weighed so as to have a molar ratio of 2: 1, and is mixed and pulverized to an average particle size of 0.3 μm by a pulverizer.

This raw material was put in a container in which a platinum foil was pasted on the lining of a quartz crucible and held in the atmosphere at 1200 ° C. for 10 hours (Example 1), 1 hour (Example 2), and 10 minutes (Example 3), and then the furnace The crucible was taken out from the state where the temperature remained at 1200 ° C., and the raw material was charged by quickly inverting the crucible into 20 ° C. water with a sufficient amount of water. The result of X-ray diffraction obtained under these conditions is shown in FIG.

Further, it is a specific 2θ of a peak located at 2θ = 21.4 to 21.8 ° and having a diffraction peak intensity ratio of 100, a half width value thereof, and another main peak of zirconium tungstate. It is not registered in JCPDS card 00-050-1868 in the range of specific 2θ of the diffraction peak located at 2θ = 23.5-23.9 ° and its intensity ratio, and further in the range of 2θ = 15-60 ° Table 2 shows values obtained by comparing the diffraction peak at the 2θ position with the peak at 2θ = 21.4 to 21.8.

Examples 1 to 3 were all made of zirconium tungstate having a high purity, and the strength ratios were 102%, 106%, and 115%, which did not exist in the conventional JCPDS card. This is because the WO ₃ used as a raw material has an unstable crystal structure, and thus crystallization to zirconium tungstate may have progressed more rapidly than a material having a complete WO ₃ crystal structure. Further, it is considered that rapid cooling from 1200 ° C. was sufficiently appropriate and the temperature could be lowered without greatly changing the crystal structure formed at a high temperature. Further, it is also found that the crystallinity is high because the diffraction peak half-width is as narrow as 0.05 ° to 0.2 ° at 2θ = 21.4 to 21.8 °.

(Example 4-6)
A mixed raw material of WO ₃ and ZrO ₂ prepared in the same manner as in Example 1-3 was put into a shell, heated in the atmosphere at 1200 ° C. for 1 hour in a continuous furnace (roller hearth furnace), and then the liquid nitrogen was cooled in the cooling zone. A shower was introduced and cooled rapidly.
Example 4-6 is the material located above in the upper (Example 4), the material located on the side of the upper (Example 5), and the material located inside (Example 6). The X-ray diffraction results are shown in FIG. 4 and the analysis results of the peaks are shown in Table 2.

Examples 4 to 6 were all made of zirconium tungstate with high purity, and the X-ray diffraction intensity ratio was 94%, 95%, and 92%, which did not exist in the conventional JCPDS card.
The strength ratio was lower than in Examples 1 to 3, which may be due to the fact that the cooling rate was somewhat slower due to the heat capacity than that in the water, but the crystallinity that has not existed in the past. It was possible to obtain zirconium tungstate.

(Comparative Example 1)
In a container in which WO ₃ powder having a sufficient WO ₃ crystal structure (FIG. 1.b) and the ZrO ₂ powder used in Examples 1 to 6 were mixed and pulverized, and a platinum foil was attached to the quartz crucible lining. And heated at 1200 ° C. for 10 hours in the atmosphere and put into water in the same manner as in Examples 1 to 3. The X-ray diffraction results are shown in FIG. The crystal structure of zirconium tungstate was not obtained.

(Comparative Example 2)
The raw material was prepared and heated under the same conditions as in Example 1, and the temperature was lowered to room temperature over 8 hours only for the cooling method. The X-ray diffraction result of the obtained material is shown in FIG. The crystal structure of zirconium tungstate was not obtained.

(Comparative Example 3)
Raw materials were prepared in the same manner as in Examples 1 to 3, and heat treatment was performed under the conditions that the rate of temperature increase to 1200 ° C. was as slow as 8 hours and the holding time at 1200 ° C. was 60 hours. It was cooled by charging in water. The X-ray diffraction result of the obtained material is shown in FIG. The analysis results of the peak are shown in Table 2.
The crystal structure showed that it was mainly zirconium tungstate, but a peak different from ZrW ₂ O ₈ appeared around 2θ = 21.3 °, and the intensity ratio was 29%. This is presumably because WO ₃ was evaporated during the heat treatment and a ZrO ₂ rich phase was formed.

(Comparative Example 4-5)
In consideration of volatilization during the heat treatment of WO ₃ , WO ₃ and ZrO ₂ powder are mixed and pulverized at a molar ratio of 2.1: 1, put in a container in which a platinum foil is pasted on a quartz crucible lining, and 1200 ° C. in the air Then, heat treatment was performed for 1 hour (Comparative Example 4) and 30 hours (Comparative Example 5), and the mixture was put into water in the same manner as in Examples 1 to 3. The X-ray diffraction result of the obtained material is shown in FIG. 6, and the analysis result of the peak is shown in Table 2.

The crystal structure showed that it was mainly zirconium tungstate, but peaks different from ZrW ₂ O ₈ appeared around 2θ = 23.7 °, and the intensity ratio was 37% and 7%. . This is a peak related to WO ₃ , which is considered to be because the WO ₃ remained excessively than evaporated.
When heat treating for a long time, it is necessary to consider the evaporation of WO ₃ and it is difficult to obtain stable quality. On the other hand, when it can be crystallized in a very short time as in the examples, it has the advantage that it can be stably produced with the targeted formulation.

As described above, there is a problem that it takes a long time to synthesize the crystallization, and the application to the product has not progressed so far. At the laboratory level, although there was a report of using a platinum crucible, it was not suitable for mass production. In addition, tungsten oxide easily volatilizes (there is a 0.3% weight loss at 950 ° C.-2 h), and there is a problem that it is difficult to control the composition. In the present invention, when the intensity of a diffraction peak located at 2θ = 21.4 to 21.8 ° in X-ray diffraction is 100%, the diffraction peak intensity located at 2θ = 23.5 to 23.9 ° is Provide zirconium tungstate that is 92-115%.

As a result, the composition variation is reduced, the yield is improved by improving the quality, and the production cost can be reduced by performing the synthesis for crystallization in a relatively short time. As described above, since a material having a negative expansion coefficient (the volume decreases as the temperature rises) and excellent quality can be provided, it can greatly contribute to the industry used when adjusting the expansion coefficient of glass or the like.

Claims (3)

   In X-ray diffraction, when the intensity of a diffraction peak located at 2θ = 21.4-21.8 ° is 100%, the diffraction peak intensity located at 2θ = 23.5-23.9 ° is 102% -115. In the range of diffraction angle 2θ = 15-60 °, the intensity of the diffraction peak at the 2θ position not registered in JCPDS card code 00-050-1868 is 2θ = 21.4-21.8 °. Zirconate tungstate characterized by being 2% or less when the peak intensity located at 100 is 100%.   2. The zirconium tungstate according to claim 1, wherein the half width of a diffraction peak located at 2θ = 21.4 to 21.8 ° is 0.05 ° or more and 0.2 ° or less. The half-value width of three diffraction peaks at 2θ = 22-24 ° is 0.25 ° or more, or the peak at 2θ = 33-37 ° is single, or 2θ = 49 ° -51 ° Alternatively, WO ₃ powder having a single peak at 53 ° to 57 ° is used as a raw material, and after mixing the WO ₃ powder and ZrO ₂ powder, heating and holding at 1190 ° C. to 1200 ° C. for 30 seconds to 10 hours And then rapidly cooling to 200 ° C. or less within 3 minutes to produce zirconium tungstate.