Negative thermal expansion materials and composite materials

Abstract

To provide a negative thermal expansion material further improved in negative thermal expansion characteristics of a copper-vanadium composite oxide of Cu2 V2O7.SOLUTION: The negative thermal expansion material comprises a copper-vanadium composite oxide represented by general formula (1): CuxMgyVzOt (1) (where 1.70≤x≤2.15, 0<y≤0.25, 1.90≤z≤2.10, and 6.00≤t≤8.00, provided that 1.80≤x+y≤2.20).SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a negative thermal expansion material that contracts in response to temperature rise, a method for producing the same, and a composite material containing the negative thermal expansion material. [Background technology]

[0002] Many materials increase in length or volume due to thermal expansion when their temperature rises. In contrast, there are also materials that exhibit negative thermal expansion, where their volume decreases when heated (hereinafter sometimes referred to as "negative thermal expansion materials").

[0003] It is known that materials exhibiting negative thermal expansion can be used in conjunction with other materials to suppress changes in the thermal expansion of the material due to temperature changes.

[0004] Examples of materials exhibiting negative thermal expansion include β-eucryptite, zirconium tungstate (ZrW2O8), zirconium tungstate phosphate (Zr2WO4(PO4)2), and Zn. x CD 1-x (CN)2, manganese nitride, bismuth nickel iron oxide, etc. are known examples.

[0005] The linear thermal expansion coefficient of zirconium tungstate is -3.4 to -3.0 ppm / °C in the temperature range of 0 to 400°C, and it is known to have high negative thermal expansion. By using zirconium tungstate in combination with a material that exhibits positive thermal expansion (hereinafter sometimes referred to as "positive thermal expansion material"), it is possible to produce a material with low thermal expansion (see Patent Documents 1-2, etc.). It has also been proposed to use a combination of a polymer compound such as a resin, which is a positive thermal expansion material, and a negative thermal expansion material (see Patent Document 3, etc.).

[0006] Furthermore, Non-Patent Document 1 discloses that the copper-vanadium composite oxide α-Cu2V2O7 has a linear thermal expansion coefficient of -5 to -6 ppm / °C in the temperature range from room temperature to 200°C. Furthermore, Non-Patent Document 2 below contains Cu 1.5 Mg 0.5The copper vanadium composite oxide of V2O7 is disclosed to have a linear thermal expansion coefficient of -8.72×10 -6 / K in the temperature range of 153 to 673K.

[0007] Also, in Patent Document 4 below, a negative thermal expansion material represented by the general formula: Cu 2―x R x V 2―y M y O7 (R is at least one element selected from Zn, Ga, Fe, Sn, Mn; M is at least one element selected from Mg, Si, Al, Ti, Cr, Mn, Fe, Co, Ni, Sn; 0≦x<2, 0<y<2) is disclosed.

[0008] However, what is actually implemented as a negative thermal expansion material containing the M element in Patent Document 4 is β-Cu 1.8 Zn 0.2 V 1.9 Si 0.1 O7, β-Cu 1.8 Zn 0.2 V 1.9 Mn 0.1 O7, where the M element is only Si and Mn, and the element substituting for pentavalent V is basically a pentavalent metal. Therefore, in Patent Document 4, although there is an exemplification of the M element as Mg, there is no technical basis for it.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0010]

Non-Patent Document 1

Non - Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0011] In examining a method for further improving the negative thermal expansion characteristics of the copper - vanadium composite oxide of α - Cu2V2O7, the inventors have found that when a part of Cu in the copper - vanadium composite oxide is substituted with Mg within a specific range, the negative thermal expansion characteristics are improved compared to the negative thermal expansion material of the copper - vanadium composite oxide of α - Cu2V2O7, and thus the present invention has been completed.

[0012] Therefore, an object of the present invention is to provide a negative thermal expansion material with further improved negative thermal expansion characteristics of the copper - vanadium composite oxide of Cu2V2O7.

Means for Solving the Problems

[0013] The first invention provided by the present invention is the following general formula (1): Cu x Mg y V z O t (1) (In the formula, x represents 1.70 ≤ x ≤ 2.15, y represents 0 < y ≤ 0.25, z represents 1.90 ≤ z ≤ 2.10, and t represents 6.00 ≤ t ≤ 8.00. However, 1.80 ≤ x + y ≤ 2.20.) A negative thermal expansion material characterized by being composed of a copper - vanadium composite oxide represented by the formula.

[0014] The second invention provided by the present invention is a composite material characterized by including the negative thermal expansion material of the first invention and a positive thermal expansion material.

Effects of the Invention

[0015] According to the present invention, it is possible to provide a novel negative thermal expansion material in which the negative thermal expansion property of the copper vanadium composite oxide of Cu2V2O7 is further improved.

Brief Description of the Drawings

[0016] [Figure 1] X-ray diffraction pattern of the negative thermal expansion material sample obtained in Example 1. [Figure 2] X-ray diffraction pattern of the negative thermal expansion material sample obtained in Example 2. [Figure 3] X-ray diffraction pattern of the negative thermal expansion material sample obtained in Comparative Example 1. [Figure 4] X-ray diffraction pattern of the negative thermal expansion material sample obtained in Comparative Example 2.

Mode for Carrying Out the Invention

[0017] Hereinafter, the present invention will be described based on preferred embodiments. The negative thermal expansion material of the present invention has the following general formula (1): Cu x Mg y V z O t (1) (In the formula, x represents 1.70 ≦ x ≦ 2.15, y represents 0 < y ≦ 0.25, z represents 1.90 ≦ z ≦ 2.10, and t represents 6.00 ≦ t ≦ 8.00. However, 1.80 ≦ x + y ≦ 2.20.) It is composed of a copper vanadium composite oxide represented by

[0018] In the general formula (1), x is 1.70 ≦ x ≦ 2.15. x is preferably 1.75 ≦ x ≦ 2.10, particularly preferably 1.80 ≦ x ≦ 2.05, in terms of higher negative thermal expansion property. In the formula of the general formula (1), y is 0 < y ≦ 0.25. From the viewpoint of further improving the negative thermal expansion property, y is 0.01 ≦ y ≦ 0.25, particularly preferably 0.02 ≦ y ≦ 0.20, and even more preferably 0.12 ≦ y ≦ 0.20. In general formula (1), z is 1.9 ≤ z ≤ 2.10. z is preferably 1.85 ≤ z ≤ 2.05, as this provides a higher negative thermal expansion characteristic. In general formula (1), t is 6.00 ≤ t ≤ 8.00. Preferably, t is 6.50 ≤ t ≤ 7.50, where the negative thermal expansion characteristics are higher. However, in general formula (1), x+y is 1.80 ≤ x+y ≤ 2.20. Preferably, x+y is 1.90 ≤ x+y ≤ 2.10, as this provides better negative thermal expansion characteristics.

[0019] Furthermore, copper vanadium composite oxides represented by general formula (1) basically contain a Ziesite phase (β phase) and a Blossite phase (α phase), and also exist as a mixture of these phases. The negative thermal expansion material of the present invention may be a Ziesite phase (β phase), a Blossite phase (α phase), or a mixture of Ziesite phase (β phase) and Blossite phase (α phase). However, when the obtained copper vanadium composite oxide is subjected to X-ray diffraction analysis, a single-phase Ziesite phase (β phase) or a mixture containing more Ziesite phase (β phase), where the main peak around 2θ=25° caused by the Ziesite phase (β phase) is higher than the main peak around 2θ=27° caused by the Blossite phase (α phase), is preferred from the viewpoint of having excellent negative thermal expansion properties.

[0020] In this invention, "around 2θ = 25°" refers to 2θ = 23.5 to 26.5°. Also, "around 2θ = 27°" refers to 2θ = 26.8 to 27.8°. In the negative thermal expansion material of the present invention, when the negative thermal expansion material is subjected to X-ray diffraction analysis using CuKα rays as the radiation source, the diffraction peak around 2θ=25° originates from the Ziesite phase (β phase), and the diffraction peak around 2θ=27° originates from the Blossite phase (α phase).

[0021] The BET specific surface area of ​​the negative thermal expansion material of the present invention is not particularly limited, but is preferably 0.05 to 50 m². 2 / g, particularly preferably 0.1 to 10m 2 / g, more preferably 0.2~8m2 The value is / g. Because the BET specific surface area of ​​the negative thermal expansion material falls within the above range, handling becomes easier when using the negative thermal expansion material as a filler for resins, glass, etc.

[0022] The average particle diameter of the negative thermal expansion material of the present invention is not particularly limited, but is preferably 0.1 to 100 μm, and particularly preferably 0.2 to 80 μm, as determined by scanning electron microscopy. Having the average particle diameter of the negative thermal expansion material within the above range makes it easier to handle when using the negative thermal expansion material as a filler for resins, glass, etc. In this invention, the average particle diameter of the negative thermal expansion material was determined by the arithmetic mean of the particle diameters of 50 particles arbitrarily extracted at a magnification of 1000x using scanning electron microscopy. In this case, the particle diameter of each particle refers to the largest length (maximum length) of the line segment that crosses the two-dimensional projection image of the particle.

[0023] The particle shape of the negative thermal expansion material of the present invention is not particularly limited and may be spherical, granular, plate-like, flaky, whisker-like, rod-like, filamentous, or crushed.

[0024] The negative thermal expansion material of the present invention exhibits improved negative thermal expansion characteristics compared to the α-Cu2V2O7 copper-vanadium composite oxide. Specifically, its linear thermal expansion coefficient is smaller than that of the α-Cu2V2O7 copper-vanadium composite oxide.

[0025] In this invention, the linear thermal expansion coefficient is determined by the following procedure. First, 1.0 g of negative thermal expansion material sample and 0.05 g of binder resin are mixed and the entire mixture is filled into a φ6 mm mold. Then, a molded body is created by molding it with a band press at a pressure of 0.5 t. This molded body is fired in an electric furnace at 700°C for 4 hours in an atmospheric environment to obtain a ceramic molded body. The obtained ceramic molded body is measured twice repeatedly using a thermomechanical measuring device in a nitrogen atmosphere with a load of 10 g and a temperature of 50 to 425°C, and the measurement value between 50 and 400°C in the second repeated measurement is taken as the linear thermal expansion coefficient. For example, a NETZSCH JAPAN TMA400SE can be used as the thermomechanical measuring device.

[0026] The linear thermal expansion coefficient of the negative thermal expansion material of the present invention is not limited as long as it is smaller than that of the copper-vanadium composite oxide α-Cu2V2O7, but the linear thermal expansion coefficient of the negative thermal expansion material of the present invention is -11 × 10 -6 / K or less, preferably -12 × 10 -6 / K or less, more preferably -13 × 10 -6 It is less than or equal to / K, and there are no particular restrictions on the lower limit, but it is approximately -40 × 10 -6 / K or higher, preferably -30×10 -6 It is 10 / K or higher. In the negative thermal expansion material of the present invention, when combined with a positive thermal expansion material, the linear thermal expansion coefficient is particularly preferably -25 × 10 when it cancels out the positive expansion. -6 ~―11×10 -6 It is / K.

[0027] The negative thermal expansion material of the present invention can be manufactured industrially advantageously by the manufacturing method described below.

[0028] The negative thermal expansion material of the present invention can be manufactured industrially advantageously by performing the following first and second steps. Step 1: A step of preparing a raw material mixture by mixing a Cu source, an Mg source, and a V source. Second step: The next step is to calcine the raw material mixture.

[0029] The first step is to prepare a raw material mixture by mixing a Cu source, an Mg source, and a V source.

[0030] Examples of Cu sources for the first step include copper salts of organic carboxylic acids such as copper gluconate, copper citrate, copper acetate, and copper lactate, copper salts of mineral acids, copper oxides, and copper hydroxides.

[0031] Examples of magnesium sources for the first step include magnesium carbonates, oxides, hydroxides, halides, and carboxylates. Examples of magnesium carboxylates include magnesium gluconates, citrates, oxalates, acetates, and lactates.

[0032] Examples of V sources for the first step include vanadic acid and its sodium salt, potassium salt, ammonium salt, carboxylate salt, vanadium oxide such as vanadium pentoxide, etc.

[0033] Examples of vanadium salts of carboxylic acids include monocarboxylic acid salts such as formic acid, acetic acid, glycolic acid, lactic acid, and gluconic acid; dicarboxylic acids such as oxalic acid, maleic acid, malonic acid, malic acid, tartaric acid, and succinic acid; and carboxylate salts such as citric acid, which has three carboxyl groups.

[0034] The amounts of Cu, Mg, and V added are preferably adjusted as appropriate so that the molar ratios of Cu, Mg, and V in the raw material mixture match the composition of the copper-vanadium composite oxide represented by the general formula (1).

[0035] The mixing of the Cu, Mg, and V sources can be carried out wet or dry, but it is preferable to perform the mixing process wet from the viewpoint that a homogeneous raw material mixture can be easily obtained. From the viewpoint of industrially advantageously obtaining the desired product, the following two methods are preferable for wet mixing.

[0036] The first method involves preparing a raw material mixture using a solvent that is insoluble or sparingly soluble in the Cu source, Mg source, and V source.

[0037] The solvent that can be used in the first method varies depending on the type of Cu source, Mg source, and V source, but water, methanol, ethanol, etc. can be used. Furthermore, in order to enhance reactivity, it is preferable to use Cu sources, Mg sources, and V sources with an average particle size of 50 μm or less, preferably 0.1 to 40 μm, as determined by laser diffraction.

[0038] Furthermore, while there are no particular limitations on the apparatus used for wet mixing in the first method, examples include wet mixing using media mills such as bead mills, ball mills, paint shakers, attritors, and sand mills. However, for small quantities at the laboratory level, wet mixing may be performed using a mortar and pestle or similar.

[0039] The raw material mixture can be obtained by drying the entire volume after the wet mixing process to remove the solvent.

[0040] The second method involves dissolving a Cu source, an Mg source, and a V source in an aqueous solvent, and then removing the aqueous solvent to prepare a raw material mixture.

[0041] In the second method, a solution in which the Cu source, Mg source, and V source are dissolved in an aqueous solvent may be used.

[0042] For the second method, it is preferable to use, for example, a copper salt of an organic carboxylic acid or a copper salt of a mineral acid as the Cu source.

[0043] Furthermore, as the Mg source for the second method, for example, calcium salts, carbonates, hydroxides, etc. of organic carboxylic acids can be used. In addition, if the Mg source is sparingly soluble or insoluble, the Mg source can be dissolved in the aqueous solvent by adding a carboxylic acid that forms a chelate with Mg, such as citric acid, oxalic acid, or lactic acid, to the aqueous solvent and then used.

[0044] For the V source in the second method, for example, vanadic acid and its sodium salt, potassium salt, ammonium salt, carboxylate salt, etc., can be used.

[0045] Furthermore, when using a vanadium salt of a carboxylic acid as the V source, vanadium pentoxide, a reducing agent, and a carboxylic acid may be added to an aqueous solvent, and the mixture may be heated at 60-100°C to produce a vanadium salt of the carboxylic acid. This reaction solution can then be used directly to prepare the raw material mixture.

[0046] As a reducing agent, reducing sugars are preferred, and examples of reducing sugars include glucose, fructose, lactose, maltose, and sucrose. Of these, lactose and sucrose are particularly preferred from the viewpoint of having excellent reactivity. The amount of reducing sugar added is preferably such that the molar ratio of C in the reducing sugar to V in the vanadium pentoxide (C / V) is 0.7 to 3.0, and more preferably 0.8 to 2.0 from the viewpoint of efficiently carrying out the reduction reaction. The amount of carboxylic acid added is preferably such that the molar ratio to vanadium pentoxide is 0.1 to 4.0, and more preferably 0.2 to 3.0 from the viewpoint of efficiently obtaining a clear vanadium solution.

[0047] In the second method, a raw material mixture can be obtained by removing the aqueous solvent from a raw material mixture obtained by dissolving the Cu source, Mg source, and V source in an aqueous solvent. One method for removing the aqueous solvent from the raw material mixture is to heat the mixture while stirring it until the aqueous solvent is removed and the mixture becomes a paste or solid, thereby obtaining the raw material mixture. In this case, it is not necessary to remove all the aqueous solvent and obtain the raw material mixture as a solid; it may be in the form of a paste containing a small amount of aqueous solvent. Note that "paste-like" refers to a state with considerable viscosity.

[0048] The heating temperature for removing the aqueous solvent from the raw material mixture is not particularly limited as long as it is a temperature at which the aqueous solvent can be removed, but a temperature at which a boiling state can be maintained is preferred, usually 90 to 120°C, and more preferably 100 to 120°C.

[0049] In the present invention, the raw material mixture obtained by the method described in 2 above is preferred because it yields a more uniform raw material mixture and makes it easier to obtain a single-phase copper-vanadium composite oxide represented by general formula (1) in X-ray diffraction analysis. In this invention, "single phase" means that the Ziesite phase (β phase) of the copper vanadium composite oxide represented by general formula (1) exists alone, the Blossite phase (α phase) exists alone, or it may exist as a mixed phase of the Ziesite phase (β phase) and the Blossite phase (α phase), and no diffraction peaks other than those of the copper vanadium composite oxide represented by general formula (1) are detected by X-ray diffraction.

[0050] The second step is to calcine the raw material mixture prepared in the first step to produce the negative thermal expansion material that is the target of the present invention.

[0051] The firing temperature in the second step is preferably 580 to 780°C, more preferably 600 to 770°C, and even more preferably 600 to 760°C. This is because if the firing temperature is lower than 580°C, the formation of the vanadium compound represented by the general formula (1) tends to be insufficient, and if it is higher than 780°C, it tends to be difficult to recover the product due to fusion to the crucible, etc. The firing time in the second step is not particularly limited, and the reaction is carried out for a sufficient amount of time until the negative thermal expansion material according to the present invention is formed. The formation of the negative thermal expansion material can be confirmed, for example, by checking whether a single-phase copper-vanadium composite oxide represented by general formula (1) has been obtained by X-ray diffraction analysis.

[0052] In most cases, the firing time is 1 hour or more, preferably 2 to 20 hours, and the negative thermal expansion material consists of almost all of the raw material mixture being a copper-vanadium composite oxide represented by the general formula (1).

[0053] Furthermore, the firing atmosphere is not particularly limited and may be an inert gas atmosphere, a vacuum atmosphere, an oxidizing gas atmosphere, or air.

[0054] In the second step, firing may be performed once or multiple times as desired. For example, to ensure uniform powder properties, the material may be fired once, then ground, and the ground material may be fired again.

[0055] After firing, the material is cooled as needed, and crushing, pulverizing, classifying, etc., is performed as necessary to obtain the desired negative thermal expansion material.

[0056] Furthermore, as a method for producing a negative thermal expansion material having a spherical particle shape, for example, it can be produced by drying the entire amount after the wet mixing process in the first step using a spray dryer, and then performing the second step. In the spray drying method, the size of the atomized droplets is not particularly limited, but is preferably 1 to 40 μm, and particularly preferably 5 to 30 μm. The amount of slurry supplied to the spray dryer is preferably determined with this in mind. Furthermore, the temperature of the hot air used for drying in the spray dryer is preferably 100 to 270°C, more preferably 150 to 230°C, as this prevents moisture absorption of the powder and facilitates powder recovery.

[0057] The average particle size of the negative thermal expansion material obtained by the method for producing the negative thermal expansion material of the present invention, which consists of a copper-vanadium composite oxide represented by general formula (1), is preferably 0.1 to 100 μm, particularly preferably 0.2 to 80 μm, and the BET specific surface area is 0.05 to 50 m². 2 / g, particularly preferably 0.1 to 10m 2 The value is / g. The average particle size and BET specific surface area of ​​the negative thermal expansion material being within the above range is preferable because it makes handling easier when using the negative thermal expansion material as a filler in resins, glass, etc.

[0058] Furthermore, the negative thermal expansion material according to the present invention may be subjected to surface treatment on the particle surface of the negative thermal expansion material as necessary, in order to improve resin dispersibility and moisture resistance of the negative thermal expansion material.

[0059] Examples of surface treatments include coating the particle surface with a silane coupling agent, a titanate coupling agent, a fatty acid or its derivative, or an inorganic compound containing one or more elements selected from Zn, Si, Al, Ba, Ca, Mg, Ti, V, Sn, Co, Fe, and Zr (see, for example, WO2020 / 095837, WO2020 / 261976, WO2019 / 087722, and Japanese Patent Publication No. 2020-147486). Alternatively, these methods may be combined as appropriate for surface treatment.

[0060] The linear thermal expansion coefficient of the negative thermal expansion material obtained by this manufacturing method is -11 × 10⁻¹⁰ -6 / K or less, preferably -12 × 10 -6 It is less than or equal to / K, and the lower limit is approximately -30 × 10 -6 / K or higher, preferably -40×10 -6 It is 10 / K or higher. In the negative thermal expansion material of the present invention, when combined with a positive thermal expansion material, the linear thermal expansion coefficient is particularly preferably -25 × 10 when it cancels out the positive expansion. -6 ~-11×10 -6 It is / K.

[0061] The negative thermal expansion material of the present invention is used as a powder or a paste. When the negative thermal expansion material of the present invention is used as a paste, it can be used in the form of a paste with a solvent and / or a low-viscosity liquid resin. Alternatively, the obtained negative thermal expansion material may be dispersed in a solvent and / or a low-viscosity liquid resin, and if necessary, a binder, flux, dispersant, etc., may be added to form a paste for use.

[0062] The negative thermal expansion material of the present invention can be used as a composite material in combination with various organic or inorganic compounds. Examples of organic compounds, though not particularly limited, include rubber, polyolefin, polycycloolefin, polystyrene, ABS, polyacrylate, polyphenylene sulfide, phenolic resin, polyamide resin, polyimide resin, epoxy resin, silicone resin, polycarbonate resin, polyethylene resin, polypropylene resin, polyethylene terephthalate resin (PET resin), and polyvinyl chloride resin. Examples of inorganic compounds include silicon dioxide, silicates, graphite, sapphire, various glass materials, concrete materials, and various ceramic materials.

[0063] Since the above composite material contains the negative thermal expansion material according to the present invention, it is possible to achieve a negative thermal expansion coefficient, zero thermal expansion coefficient, or low thermal expansion coefficient by adjusting the blending ratio with other compounds. [Examples]

[0064] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0065] (X-ray diffractometer) In this example, measurements were performed using an X-ray diffractometer (Ultima IV, manufactured by Rigaku Corporation) under the following measurement conditions. Source: Cu-Kα Tube voltage: 40kV Tube current: 40mA Scanning speed: 4° / sec

[0066] {Example 1} (1st step) 3.00 g of ammonium vanadate (NH4VO3), 6 ml of aqueous ammonia, and 80 ml of pure water were placed in a beaker and heated to 60°C while stirring to obtain solution A. Next, 10.77 g of copper gluconate (manufactured by Fuso Chemical Industry Co., Ltd.) was added to 50 ml of pure water and stirred to obtain solution B. Next, 0.11 g of magnesium hydroxide was added to 10 ml of pure water and 0.50 g of lactic acid and stirred to obtain solution C. Solution B and then C were added to solution A in that order to obtain a homogeneous raw material mixture. (2nd process) The aforementioned raw material mixture was heated to a boiling point while being stirred to remove water and obtain a paste-like reaction precursor. (3rd step) The paste-like reaction precursor was calcined in a crucible under air at 650°C for 4 hours to obtain a calcined product. The X-ray diffraction pattern of the calcined product is shown in Figure 1. Next, the fired product was crushed in a mortar and pestle to obtain a negative thermal expansion material sample. X-ray diffraction analysis of the obtained calcined product revealed a single phase of Cu2V2O7, with a Ziesite phase of Cu2V2O7 having its main diffraction peak around 2θ=25° and a Blossite phase having its main diffraction peak around 2θ=27°, indicating that the copper vanadium composite oxide ((Cu 1.85 Mg 0.15 )V 2.00 O 7.00 ) was.

[0067] {Example 2} (1st step) 3.00 g of ammonium vanadate (NH4VO3), 6 ml of aqueous ammonia, and 80 ml of pure water were placed in a beaker and heated to 60°C while stirring to obtain solution A. Next, 10.94 g of copper gluconate (manufactured by Fuso Chemical Industry Co., Ltd.) was added to 50 ml of pure water and stirred to obtain solution B. Next, 0.09 g of magnesium hydroxide was added to 10 ml of pure water and 0.50 g of lactic acid and stirred to obtain solution C. Solution B and then Solution C were added to Solution A in that order to obtain a homogeneous raw material mixture. (2nd process) The aforementioned raw material mixture was heated to a boiling point while being stirred to remove water and obtain a paste-like reaction precursor. (3rd step) The paste-like reaction precursor was calcined in a crucible under air at 700°C for 4 hours to obtain a calcined product. The X-ray diffraction pattern of the calcined product is shown in Figure 2. Next, the fired product was crushed in a mortar and pestle to obtain a negative thermal expansion material sample. X-ray diffraction analysis of the obtained calcined product revealed a single phase of Cu2V2O7, with a Ziesite phase of Cu2V2O7 having its main diffraction peak around 2θ=25° and a Blossite phase having its main diffraction peak around 2θ=27°, indicating that the copper vanadium composite oxide ((Cu 1.88 Mg 0.12 )V 2.00 O 7.00 ) was.

[0068] {Comparative Example 1} (1st step) 3.00 g of ammonium vanadate (NH4VO3), 6 ml of aqueous ammonia, and 80 ml of pure water were placed in a beaker and heated to 60°C while stirring to obtain solution A. Next, 8.73 g of copper gluconate (manufactured by Fuso Chemical Industry Co., Ltd.) was added to 50 ml of pure water and stirred to obtain solution B. Next, 0.37 g of magnesium hydroxide was added to 10 ml of pure water and 1.7 g of lactic acid and stirred to obtain solution C. Solution B and then C were added to solution A in that order to obtain a homogeneous raw material mixture. (2nd process) The aforementioned raw material mixture was heated to a boiling point while being stirred to remove water and obtain a paste-like reaction precursor. (3rd step) The paste-like reaction precursor was calcined in a crucible under air at 650°C for 4 hours to obtain a calcined product. The X-ray diffraction pattern of the calcined product is shown in Figure 3. Next, the fired product was crushed in a mortar and pestle to obtain a negative thermal expansion material sample. X-ray diffraction analysis of the obtained calcined product revealed a single phase of Cu2V2O7, with a Ziesite phase of Cu2V2O7 having its main diffraction peak around 2θ=25° and a Blossite phase having its main diffraction peak around 2θ=27°, indicating that the copper vanadium composite oxide ((Cu 1.50 Mg 0.50)V 2.00 O 7.00 ) was.

[0069] {Comparative Example 2} 1.71 g of vanadium pentoxide (V2O5: average particle size 1.0 μm), 1.50 g of copper oxide (CuO: average particle size 1.5 μm), and 30 ml of ethanol were ground and mixed in a mortar for 20 minutes as a dispersion medium, and then dried to obtain a raw material mixture. This powder was calcined in air at 700°C for 4 hours to obtain a calcined product. X-ray diffraction analysis of the obtained calcined product revealed a single phase of Cu2V2O7, with a Ziesite phase of Cu2V2O7 having its main diffraction peak around 2θ=25° and a Blossite phase having its main diffraction peak around 2θ=27°. A copper-vanadium composite oxide mainly composed of a Blossite phase was obtained. The X-ray diffraction pattern of the calcined product is shown in Figure 4. Next, the calcined product was ground in a mortar and used as a negative thermal expansion material sample.

[0070] (Evaluation of physical properties) The average particle size, BET specific surface area, and linear thermal expansion coefficient were measured for the negative thermal expansion material samples obtained in the examples and comparative examples. The average particle size and linear thermal expansion coefficient were measured as described below. The results are shown in Table 1.

[0071] (Average particle size) The average particle size of the negative thermal expansion material sample was determined by the average value of 50 particles arbitrarily extracted at a magnification of 1000x using a scanning electron microscope.

[0072] [Measurement of linear thermal expansion coefficient] (Manufacturing of molded bodies) 1.00 g of the sample was mixed with 0.05 g of propylene carbonate in a mortar for 3 minutes, then 0.15 g was weighed out and the entire amount was filled into a φ6 mm mold. Next, a powder molded body was produced by molding with a pressure of 0.5 t using a hand press. The obtained powder molded body was heated to 700°C in an electric furnace over 3 hours and held for 4 hours to produce a ceramic molded body. (Measurement of linear thermal expansion coefficient) The linear thermal expansion coefficient of the fabricated ceramic molded body was measured using a thermomechanical thermometer (NETZSCH JAPAN TMA4000SE). The measurement conditions were a nitrogen atmosphere, a load of 10g, and a temperature range of 50°C to 425°C, with two repeated measurements. The linear thermal expansion coefficients in the second repeated measurement between 50°C and 400°C were compared.

[0073] [Table 1] Note) The linear thermal expansion coefficient of the negative thermal expansion material sample in Comparative Example 2 between 50 and 300°C is -4.4 × 10⁻⁶ -6 It was / K

Claims

1. The following general formula (1): Cổ ｘ Mẽ ｙ V ｚ O ｔ (1) (In the equation, x represents 1.70 ≤ x ≤ 2.15, y represents 0 < y ≤ 0.25, z represents 1.90 ≤ z ≤ 2.10, and t represents 6.00 ≤ t ≤ 8.00, where 1.80 ≤ x + y ≤ 2.20.) A negative thermal expansion material characterized by being composed of a copper-vanadium composite oxide represented by [formula].

2. The coefficient of linear thermal expansion is -11 × 10⁻⁶ －６ The negative thermal expansion material according to claim 1, characterized in that it is less than or equal to / K.

3. The negative thermal expansion material according to claim 1 or 2, characterized in that the average particle size is 0.1 to 100 μm.

4. BET specific surface area is 0.05 to 50 m². ２ The negative thermal expansion material according to claim 1 or 2, characterized in that it is / g.

5. A composite material characterized by comprising a negative thermal expansion material and a positive thermal expansion material according to any one of claims 1 to 4.

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