Negative thermal expansion material, method for producing same, and composite material

Abstract

The present invention provides a negative thermal expansion material which has excellent negative thermal expansion properties and exhibits a gentle volume reduction with temperature rise as compared with a conventional zinc phosphorus composite oxide such as Zn2P2O7.　The present invention specifically provides a negative thermal expansion material which is characterized by being a composite of a zinc phosphorus composite oxide represented by general formula (1): ZnxMyPz1Ot1(1) and a metal pyrophosphate salt represented by general formula (2): AwPz2Ot2 (2), wherein the composite has a core-shell structure. It is preferable that a core contains the zinc phosphorus composite oxide represented by the general formula (1), and a shell contains the metal pyrophosphate salt represented by the general formula (2).

Description

Negative thermal expansion material, its manufacturing method and composite material

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

[0002] Many substances increase in length and volume due to thermal expansion when the temperature rises. However, there are also known materials that exhibit negative thermal expansion, meaning that their volume decreases when heated (hereinafter referred to as "negative thermal expansion materials").

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

[0004] Materials that exhibit negative thermal expansion include, for example, β-eucryptite, zirconium tungstate (ZrW2O8), zirconium tungstate phosphate (Zr2WO4(PO4)2), Zn x Cd 1-x (CN)2, manganese nitride, bismuth-nickel-iron oxide, etc. are known.

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

[0006] Patent Document 3 proposes a zinc phosphorus composite oxide of Zn2P2O7 and a negative thermal expansion material in which part of the Zn in the zinc phosphorus composite oxide is substituted with at least one element selected from Mg, Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, La, Ta, W, and Bi, or part of the P is substituted with at least one element selected from Al, Si, V, Ge, and Sn.

[0007] JP 2005-35840 A JP 2015-10006 A International Publication No. 2022 / 114004 Pamphlet

[0008] The zinc-phosphorus composite oxide of Patent Document 3, in which ZnP0 and part of the zinc are substituted with another metal, has a smaller linear expansion coefficient than zirconium tungstate phosphate, and further has advantages such as being able to be produced from cheaper raw materials, being industrially advantageous, and having excellent water resistance.

[0009] However, zinc-phosphorus composite oxides such as Zn2P2O7 undergo a rapid volume reduction with increasing temperature. ２ P ２ O ７ A sudden volume decrease occurs with a temperature rise in the temperature range of 100 to 150° C. Therefore, in a composite material containing a negative thermal expansion material and a positive thermal expansion material, the positive thermal expansion material cannot keep up with the sudden volume decrease of the negative thermal expansion material, and as a result, it becomes difficult to achieve a zero or low thermal expansion coefficient in a composite material containing a negative thermal expansion material.

[0010] Therefore, an object of the present invention is to provide a negative thermal expansion material that has excellent negative thermal expansion properties and exhibits a gradual volume decrease with increasing temperature compared to conventional zinc-phosphorus composite oxides such as Zn2P2O7.

[0011] While investigating various methods for improving the negative thermal expansion properties of zinc phosphorus composite oxides such as Zn2P2O7, the present inventors discovered that a composite of the zinc phosphorus composite oxide and a specific metal pyrophosphate salt has excellent negative thermal expansion properties and serves as a negative thermal expansion material that exhibits a more gradual volume decrease with increasing temperature than conventional zinc phosphorus composite oxides such as Zn2P2O7, thereby completing the present invention.

[0012] That is, the present invention (1) is a composite of a zinc-phosphorus composite oxide and a metal pyrophosphate, and the zinc-phosphorus composite oxide is represented by the following general formula (1): Zn x M y P z1 O t1(1) (wherein M represents one or more elements selected from Mg, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Na, K, F, Cl, Br, I, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho; x represents 0.0<x≦2.0; y represents 0.0≦y<2.0; z1 represents 1.7≦z1≦2.3; and t1 represents 6.0≦t1≦8.0, with the proviso that 1.7≦x+y≦2.3), The metal pyrophosphate is represented by the following general formula (2): w P z2 O t2 (2) (wherein A represents one or more metal elements selected from Mg, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho; w represents 1.7≦w≦2.3; z2 represents 1.7≦z2≦2.3; and t2 represents 6.0≦t2≦8.0.)

[0013] The present invention (2) also provides a negative thermal expansion material according to (1), characterized in that the composite has a core-shell structure, the core contains the zinc-phosphorus composite oxide represented by the general formula (1), and the shell contains the metal pyrophosphate represented by the general formula (2).

[0014] The present invention (3) also provides the negative thermal expansion material according to (1) or (2), characterized in that the zinc-phosphorus composite oxide represented by the general formula (1) is Zn2P2O7.

[0015] The present invention (4) provides a negative thermal expansion material according to any one of (1) to (3), characterized in that the metal pyrophosphate represented by the general formula (2) is MnP2O7 or CuP2O7.

[0016] In addition, the present invention (5) has a thermal expansion coefficient of −23×10 between 80 and 200°C. -6 The present invention provides a negative thermal expansion material according to any one of (1) to (4), characterized in that the thermal expansion coefficient is 0.1 / K or less.

[0017] The present invention (6) provides a negative thermal expansion material according to any one of (1) to (5), characterized in that the ratio (α2 / α1) of the thermal expansion coefficient (α2) between 100 and 150°C to the thermal expansion coefficient (α1) between 100 and 130°C is 2.5 or less.

[0018] The present invention (7) provides a negative thermal expansion material according to any one of (1) to (6), characterized in that when X-ray diffraction measurement is performed using Cu-Kα as an X-ray source, the peak top of the main peak is observed at 2θ = 29.66 to 29.73° between 2θ = 29 and 30°.

[0019] The present invention (8) also provides a negative thermal expansion material according to any one of (1) to (7), characterized in that the average particle size is 0.1 to 100 μm.

[0020] In addition, the present invention (9) is a method for producing a granular material having a BET specific surface area of ​​0.05 to 50 m 2 The present invention provides a negative thermal expansion material according to any one of (1) to (8), characterized in that the thermal expansion coefficient is / g.

[0021] The present invention (10) also provides a compound represented by the following general formula (1): Zn x M y P z1 O t1 (1) (wherein M represents one or more elements selected from Mg, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Na, K, F, Cl, Br, I, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho; x represents 0<x≦2.0, y represents 0≦y<2.0, z1 represents 1.7≦z1≦2.3, and t1 represents 6.0≦t1≦8.0, provided that 1.7≦x+y≦2.3) and zinc-phosphorus composite oxide particles represented by the following general formula (2): w P z2 Ot2 (2) A method for producing a negative thermal expansion material, comprising firing a mixture containing an A source and a P source, which are raw materials for producing a metal pyrophosphate represented by the formula (wherein A represents one or more metal elements selected from Mg, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho; w represents 1.7≦w≦2.3; z2 represents 1.7≦z2≦2.3; and t2 represents 6.0≦t2≦8.0).

[0022] The present invention (11) also provides a method for producing a negative thermal expansion material according to (10), characterized in that the zinc-phosphorus composite oxide represented by the general formula (1) is obtained by firing a reaction precursor containing at least zinc pyrophosphate.

[0023] The present invention (12) also provides a composite material characterized by containing a negative thermal expansion material according to any one of (1) to (9) and a positive thermal expansion material.

[0024] The present invention (13) also provides the composite material according to (12), characterized in that the positive thermal expansion material is at least one selected from metals, alloys, glass, ceramics, rubber, and resins.

[0025] According to the present invention, it is possible to provide a negative thermal expansion material that has excellent negative thermal expansion properties and exhibits a gradual volume decrease with increasing temperature compared to conventional zinc-phosphorus composite oxides such as Zn2P2O7.

[0026] 1 shows an X-ray diffraction diagram of a negative thermal expansion material sample of Example 1. 2 shows an X-ray diffraction diagram of a negative thermal expansion material sample of Comparative Example 1. 3 shows an SEM photograph of a negative thermal expansion material sample of Example 1. 4 shows an SEM photograph of a negative thermal expansion material sample of Reference Example 1. 5 shows an X-ray diffraction diagram of a negative thermal expansion material sample of Example 1 when 2θ is between 29 and 30°. 6 shows an X-ray diffraction diagram of a negative thermal expansion material sample of Reference Example 1 when 2θ is between 29 and 30°. 7 shows a relationship between the thermal shrinkage (%) and temperature (°C) of ceramic molded bodies (prepared by heating to 700°C in 3 hours and firing for 4 hours) using the negative thermal expansion material samples of Examples 1 to 3 and Comparative Example 1. 8 shows a relationship between the thermal shrinkage (%) and temperature (°C) of ceramic molded bodies (prepared by heating to 750°C in 3 hours and firing for 4 hours) using the negative thermal expansion material samples of Examples 1 to 3 and Comparative Example 1.

[0027] The present invention will be described below based on preferred embodiments thereof. The negative thermal expansion material of the present invention is a composite of zinc-phosphorus composite oxide and metal pyrophosphate, and the zinc-phosphorus composite oxide is represented by the following general formula (1): Zn x M y P z1 O t1 (1) (wherein M represents one or more elements selected from Mg, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Na, K, F, Cl, Br, I, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho; x represents 0.0<x≦2.0; y represents 0.0≦y<2.0; z1 represents 1.7≦z1≦2.3; and t1 represents 6.0≦t1≦8.0, with the proviso that 1.7≦x+y≦2.3), The metal pyrophosphate is represented by the following general formula (2): w P z2 O t2 (2) (wherein A represents one or more metal elements selected from Mg, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho; w represents 1.7≦w≦2.3; z2 represents 1.7≦z2≦2.3; and t2 represents 6.0≦t2≦8.0).

[0028] The negative thermal expansion material of the present invention is a composite of a zinc-phosphorus composite oxide and a metal pyrophosphate. The negative thermal expansion material of the present invention is a composite of a zinc-phosphorus composite oxide mainly containing a zinc-phosphorus composite oxide represented by general formula (1) and a metal pyrophosphate mainly containing a metal pyrophosphate represented by general formula (2).

[0029] In the general formula (1), M represents an element optionally contained for the purpose of further adjusting the negative thermal expansion. M represents one or more elements selected from Mg, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Na, K, F, Cl, Br, I, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho. In the present invention, among these, M is preferably Mg, Mn, or Cu, in view of the excellent negative thermal expansion and the gradual volume reduction with increasing temperature.

[0030] In the general formula (1), x satisfies 0.0<x≦2.0, and from the viewpoint of excellent negative thermal expansion characteristics, x is preferably 1.5≦x≦2.0, and particularly preferably 1.6≦x≦2.0.

[0031] In the general formula (1), y satisfies 0.0≦y<2.0, and from the viewpoint of excellent negative thermal expansion characteristics, y is preferably 0≦y≦1.9, and particularly preferably 0≦y≦1.8.

[0032] In the general formula (1), z1 satisfies 1.7≦z1≦2.3. From the viewpoint of excellent negative thermal expansion characteristics, z1 is preferably 1.8≦z1≦2.2, and particularly preferably 1.9≦z1≦2.1.

[0033] In the general formula (1), t1 satisfies 6.0≦t1≦8.0, and from the viewpoint of excellent negative thermal expansion characteristics, t1 is preferably 6.5≦t1≦7.5, and particularly preferably 6.2≦t1≦7.2.

[0034] However, x+y in the general formula (1) satisfies 1.7≦x+y≦2.3, and preferably satisfies 1.8≦x+y≦2.2 in order to further enhance the negative thermal expansion characteristics.

[0035] In general formula (2), A represents one or more metal elements selected from Mg, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho. Of these, Mn and Cu are particularly preferred from the viewpoint of being excellent in negative thermal expansion properties and exhibiting a gradual volume decrease with increasing temperature.

[0036] In the general formula (2), w satisfies 1.7≦w≦2.3, and is preferably 1.8≦w≦2.2, particularly preferably 1.9≦w≦2.1, from the viewpoint of exhibiting a gradual volume decrease with increasing temperature and excellent negative thermal expansion properties.

[0037] In the general formula (2), z2 satisfies 1.7≦z2≦2.3. From the viewpoint of exhibiting a gradual volume decrease with increasing temperature and excellent negative thermal expansion properties, z2 is preferably 1.8≦z2≦2.2, and particularly preferably 1.9≦z2≦2.1.

[0038] In the general formula (2), t2 satisfies 6.0≦t2≦8.0. From the viewpoint of exhibiting a gradual volume decrease with increasing temperature and excellent negative thermal expansion characteristics, t2 is preferably 6.5≦t2≦7.5, and particularly preferably 6.2≦t2≦7.2.

[0039] The metal pyrophosphate represented by general formula (2) has a lower phase transition temperature than the zinc phosphorus composite oxide represented by general formula (1). In the negative thermal expansion material of the present invention, by combining the zinc phosphorus composite oxide represented by general formula (1) with the metal pyrophosphate represented by general formula (2) which has a lower phase transition temperature than the zinc phosphorus composite oxide represented by general formula (1), the negative thermal expansion material has excellent negative thermal expansion properties and exhibits a gradual volume decrease with increasing temperature compared to conventional zinc phosphorus composite oxides such as Zn2P2O7.

[0040] Examples of the form of the composite related to the negative thermal expansion material of the present invention include: a) a simple mixture of zinc phosphorus composite oxide particles represented by general formula (1) and metal pyrophosphate particles represented by general formula (2); b) a composite having a core-shell structure, comprising a core containing zinc phosphorus composite oxide represented by general formula (1) and a shell covering all or part of the surface of the core and comprising metal pyrophosphate represented by general formula (2); c) a composite having a core-shell structure, comprising a core containing metal pyrophosphate represented by general formula (2) and a shell covering all or part of the surface of the core and comprising zinc phosphorus composite oxide represented by general formula (1); and d) a composite in which particles containing zinc phosphorus composite oxide represented by general formula (1) and particles containing metal pyrophosphate represented by general formula (2) are bonded together.

[0041] In the embodiment b), the core is formed mainly of a zinc phosphorus composite oxide containing the zinc phosphorus composite oxide represented by general formula (1). That is, in the embodiment b), the core may be formed only of the zinc phosphorus composite oxide represented by general formula (1), or may be formed of a zinc phosphorus composite oxide represented by general formula (1) containing the A element and / or other impurity elements in an amount not exceeding 0.5 mass% relative to the zinc phosphorus composite oxide represented by general formula (1) to a degree that does not produce the effects of the present invention. In the embodiment b), the shell is formed mainly of a metal pyrophosphate containing the metal pyrophosphate represented by general formula (2). That is, in the embodiment b), the shell may be formed only of the metal pyrophosphate represented by general formula (2), or may be formed of a metal pyrophosphate represented by general formula (2) containing the Zn element, the M element, and / or other impurity elements in an amount not exceeding 0.5 mass% relative to the metal pyrophosphate represented by general formula (2) to a degree that does not produce the effects of the present invention.

[0042] In the embodiment c), the core is formed mainly from a metal pyrophosphate containing the metal pyrophosphate represented by general formula (2). That is, in the embodiment c), the core may be formed only from the metal pyrophosphate represented by general formula (2), or may be formed from a metal pyrophosphate represented by general formula (2) containing Zn, M, and / or other impurity elements in an amount that does not achieve the effects of the present invention, for example, in an amount of 0.5 mass% or less relative to the metal pyrophosphate represented by general formula (2). Furthermore, in the embodiment c), the shell is formed mainly from a zinc phosphorus composite oxide containing the zinc phosphorus composite oxide represented by general formula (1). That is, in the embodiment c), the shell may be formed only from the zinc phosphorus composite oxide represented by general formula (1), or may be formed from a zinc phosphorus composite oxide represented by general formula (1) containing A and / or other impurity elements in an amount that does not achieve the effects of the present invention, for example, in an amount of 0.5 mass% or less relative to the zinc phosphorus composite oxide represented by general formula (1).

[0043] Examples of d) include core particles consisting of only the zinc-phosphorus composite oxide represented by general formula (1), or core particles consisting of the zinc-phosphorus composite oxide represented by general formula (1) containing the A element and / or impurity elements in an amount not exceeding 0.5% by mass relative to the zinc-phosphorus composite oxide represented by general formula (1), and coated particles consisting of only the metal pyrophosphate represented by general formula (2) adhering to and coating a part or all of the surface of the core particles, or composite particles consisting of the metal pyrophosphate represented by general formula (2) containing the Zn element, the M element and / or other impurity elements in an amount not exceeding 0.5% by mass relative to the pyrophosphate represented by general formula (2), ...). Examples of d) include core particles consisting solely of metal pyrophosphate represented by general formula (2), or core particles consisting of metal pyrophosphate represented by general formula (2) containing Zn, M and / or other impurity elements in an amount not exceeding 0.5% by mass relative to the metal pyrophosphate represented by general formula (2), and coated particles consisting solely of zinc-phosphorus composite oxide represented by general formula (1) that coats and adheres to part or all of the surface of the core particles, or composite particles consisting of zinc-phosphorus composite oxide represented by general formula (1) containing A and / or other impurity elements in an amount not exceeding 0.5% by mass relative to the zinc-phosphorus composite oxide represented by general formula (1), in an amount not exceeding 0.5% by mass relative to the zinc-phosphorus composite oxide represented by general formula (1), that does not exhibit the effects of the present invention.

[0044] Among the above-mentioned forms, a composite having a core-shell structure (b) and a shell containing a zinc-phosphorus composite oxide represented by general formula (1) and a metal pyrophosphate represented by general formula (2) covering all or part of the surface of the core is preferred, from the viewpoint of being particularly excellent in negative thermal expansion property and exhibiting a gradual volume reduction with increasing temperature.

[0045] In the negative thermal expansion material of the present invention, it is preferable that the zinc phosphorus composite oxide represented by the general formula (1) is Zn2P2O7 and the metal pyrophosphate represented by the general formula (2) is Mn2P2O7 and / or Cu2P2O7, from the viewpoint of particularly excellent negative thermal expansion and exhibiting a gradual volume decrease with increasing temperature. For example, when the zinc phosphorus composite oxide represented by the general formula (1) is Zn２ P ２ O ７ In this case, the negative thermal expansion material of the present invention preferably exhibits a gradual volume reduction with increasing temperature, particularly in the temperature range of 100 to 150°C.

[0046] The content ratio of the zinc phosphorus composite oxide represented by the general formula (1) and the metal pyrophosphate represented by the general formula (2) in the composite of the negative thermal expansion material according to the present invention is preferably 0.002 to 0.50, particularly preferably 0.005 to 0.30, in terms of the molar ratio of the metal pyrophosphate represented by the general formula (2) to the zinc phosphorus composite oxide represented by the general formula (1) (metal pyrophosphate represented by the general formula (2) / zinc phosphorus composite oxide represented by the general formula (1)). When the molar ratio of the metal pyrophosphate represented by the general formula (2) / zinc phosphorus composite oxide represented by the general formula (1) is in the above range, the negative thermal expansion property is excellent, and the effect of exhibiting a gradual volume decrease with increasing temperature is further enhanced.

[0047] When the negative thermal expansion material of the present invention is subjected to X-ray diffraction measurement using Cu-Kα as an X-ray source, the main peak preferably has a peak top at 2θ = 29.66 to 29.73° between 2θ = 29 to 30°. When conventional negative thermal expansion materials made of Zn2P2O7 or zinc-phosphorus composite oxides in which part of the zinc in Zn2P2O7 is replaced with another metal element is subjected to X-ray diffraction measurement using Cu-Kα as an X-ray source, the main peak has a peak top at 2θ = 29.65°, which is smaller than 29.66°, between 2θ = 29 to 30° (see Figure 6). In contrast, the negative thermal expansion material of the present invention has a main peak at 2θ = 29.66 to 29.73° between 2θ = 29 to 30° (see Figure 5).

[0048] 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 m 2 / g, particularly preferably 0.10 to 10m 2 / g, more preferably 0.20 to 8 m 2 / g. When the BET specific surface area of ​​the negative thermal expansion material is within the above range, the negative thermal expansion material is easy to handle when used as a filler for resin, glass, etc. In the present invention, the BET specific surface area of ​​the negative thermal expansion material is a value measured by the BET single-point method using a fully automatic specific surface area measuring device Macsorb (manufactured by Mountec Co., Ltd.).

[0049] The average particle size of the negative thermal expansion material of the present invention is not particularly limited, but is preferably 0.1 to 100 μm, particularly preferably 0.2 to 80 μm, and even more preferably 0.2 to 20 μm, as determined by scanning electron microscopy. Having the average particle size of the negative thermal expansion material within this range facilitates handling when used as a filler for resins, glass, etc. In the present invention, the average particle size of the negative thermal expansion material was determined by taking the arithmetic mean value of the particle sizes of 50 particles randomly selected at 1000x magnification during scanning electron microscopy. Here, the particle size of each particle refers to the longest length (maximum length) of the line segments intersecting the two-dimensional projection image of the particle.

[0050] The particle shape of the negative thermal expansion material of the present invention is not particularly limited, and may be, for example, spherical, granular, plate-like, scale-like, whisker-like, rod-like, filament-like, or crushed.

[0051] The thermal expansion coefficient of the negative thermal expansion material of the present invention between 80 and 200°C is not limited as long as it is less than 0. However, the thermal expansion coefficient of the negative thermal expansion material of the present invention between 80 and 200°C is -23×10 -6 / K or less, preferably -20×10 -6 / K or less, and the lower limit is not particularly limited, but is generally −100×10 -6 / K or more, preferably −70×10 -6 In the negative thermal expansion material of the present invention, when combined with a positive thermal expansion material, the thermal expansion coefficient is more likely to offset the positive expansion. Therefore, the thermal expansion coefficient between 80 and 200°C is particularly preferably -10 × 10 -6 ~-50 x 10 -6 / K.

[0052] In the present invention, the thermal expansion coefficient between 80 and 200°C is determined by the following procedure. First, 0.05 g of propylene carbonate is added to 1.00 g of sample and pulverized and mixed in a mortar for 3 minutes. Then, 0.15 g is weighed out and the entire amount is filled into a φ6 mm mold. Next, a powder compact is produced by molding at a pressure of 0.5 tons using a hand press. The obtained powder compact is heated to 700°C in an electric furnace over 3 hours and held there for 4 hours to produce a ceramic molded body. The thermal expansion coefficient of the produced ceramic molded body is then measured using a thermomechanical measuring device (e.g., TMA4000SE manufactured by NETZSCH JAPAN). The measurement conditions are a nitrogen atmosphere, a load of 10 g, and a temperature range of 50°C to 225°C. The measurement is repeated twice in the temperature range of 50°C to 225°C, and the thermal expansion coefficient between 80 and 200°C from the second measurement is taken as the thermal expansion coefficient of the negative thermal expansion material.

[0053] For example, in the case of a negative thermal expansion material according to the present invention, in the case of a negative thermal expansion material using Zn2P2O7 as the zinc-phosphorus composite oxide of general formula (1), the degree of volume reduction with temperature increase is gentler between 100 and 150°C than in the case of a conventional negative thermal expansion material using Zn2P2O7. Furthermore, the ratio (α2 / α1) of the thermal expansion coefficient between 100 and 150°C (α2) to the thermal expansion coefficient between 100 and 130°C (α1) is approximately 2.7 in the case of a conventional negative thermal expansion material using Zn2P2O7, whereas in the case of a negative thermal expansion material according to the present invention using Zn2P2O7 as the zinc-phosphorus composite oxide represented by general formula (1), the ratio is 2.5 or less, preferably 0.5 to 2.5.

[0054] A smaller ratio of α2 to α1 indicates a gradual volume decrease with increasing temperature in the temperature range of 100 to 150°C.

[0055] In the present invention, the degree of volume reduction with temperature increase between 100 and 150° C. is determined by the following procedure.

[0056] First, 0.05 g of propylene carbonate was added to 1.00 g of sample and pulverized and mixed 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 compact was produced by molding at a pressure of 0.5 ton using a hand press. The obtained powder compact was heated to 700 °C in an electric furnace over 3 hours and held there for 4 hours to produce a ceramic compact. The thermal expansion coefficient of the produced ceramic compact was then measured using a thermomechanical measuring device (TMA4000SE manufactured by NETZSCH JAPAN). The measurement conditions were a nitrogen atmosphere, a load of 10 g, and a temperature range of 50 °C to 225 °C. The degree of volume reduction associated with temperature increase was evaluated by calculating the ratio of the thermal expansion coefficient (α2) between 100 and 150 °C to the thermal expansion coefficient (α1) between 100 and 130 °C in the second repeat.

[0057] As a preferred method for producing a negative thermal expansion material in the present invention, the method for producing a composite having the core-shell structure b) and containing a core containing a zinc-phosphorus composite oxide represented by general formula (1) and a shell containing a metal pyrophosphate represented by general formula (2) covering all or part of the surface of the core will be described below. x M y P z1 O t1 (1) (wherein Mg, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Na, K, F, Cl, Br, I, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho; x represents 0<x≦2.0, y represents 0≦y<2.0, z1 represents 1.7≦z1≦2.3, and t1 represents 6.0≦t1≦8.0, provided that 1.7≦x+y≦2.3) and a zinc-phosphorus composite oxide represented by the following general formula (2): A w P z2 O t2 (2) (wherein A represents one or more metal elements selected from Mg, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho; w represents 1.7≦w≦2.3; z2 represents 1.7≦z2≦2.3; and t2 represents 6.0≦t2≦8.0), and the method is characterized by comprising calcining a mixture containing an A source and a P source necessary for producing a metal pyrophosphate represented by the formula (2):

[0058] That is, the negative thermal expansion material of the present invention is produced by a production method including the following steps A and B. Step A: A step of preparing a raw material mixture containing a zinc-phosphorus composite oxide represented by general formula (1) and an A source and a P source necessary for producing a metal pyrophosphate represented by general formula (2). Step B: A step of firing the raw material mixture to obtain a negative thermal expansion material.

[0059] Regarding the physical properties of the zinc-phosphorus composite oxide represented by the general formula (1) in step A, from the viewpoint of easy handling when using the negative thermal expansion material as a filler for resin, glass, etc., the average particle size determined by scanning electron microscopy observation is preferably 0.1 to 100 μm, more preferably 0.2 to 80 μm.

[0060] The BET specific surface area of ​​the zinc-phosphorus composite oxide represented by the general formula (1) is 0.05 to 50 m 2 / g, preferably 0.1 to 10 m 2 / g is preferable from the viewpoint of ease of handling when the negative thermal expansion material is used as a filler for resin, glass, etc.

[0061] In the method for producing a negative thermal expansion material of the present invention, the zinc phosphorus composite oxide represented by general formula (1) in step A is preferably obtained by the following steps, from the viewpoint of industrially advantageous production of a negative thermal expansion material: Step 1: A step of preparing a reaction precursor containing Zn, P, and an optionally added M element; Step 2: A step of calcining the reaction precursor to obtain the zinc phosphorus composite oxide represented by general formula (1).

[0062] The first step is to prepare a reaction precursor containing Zn, P, and an M element which is added as needed.

[0063] The reaction precursor can be produced by mixing a Zn compound, a phosphorus compound, and an M element-containing compound, which is added as needed.

[0064] The Zn compound is a compound containing a Zn atom, and examples of the Zn compound include zinc salts of organic carboxylic acids such as zinc gluconate, zinc citrate, zinc acetate, and zinc lactate, zinc salts of mineral acids, zinc oxide, zinc hydroxide, zinc phosphate, and zinc pyrophosphate.

[0065] The phosphorus compound is a compound having a phosphorus atom. Phosphorus compound is preferably phosphoric acid. Furthermore, a compound having a Zn source and a P source, such as zinc phosphate or zinc pyrophosphate, can serve as both a Zn compound and a phosphorus compound. The zinc phosphate and zinc pyrophosphate may be either hydrated or anhydrous.

[0066] The M element-containing compound added as needed is a compound having the element M. Examples of the M element-containing compound include carbonates of M, oxides of M, hydroxides of M, halides of M, and carboxylates of M. Examples of carboxylates of M include gluconates, citrates, oxalates, acetates, and lactates.

[0067] It is preferable that the reaction precursor in the first step contains at least zinc pyrophosphate hydrate, because this makes it easy to obtain a reaction precursor in which the raw materials are uniformly dispersed through an inexpensive and simple operation, and also because the obtained reaction precursor is easily calcined in the second step described below to obtain a zinc-phosphorus composite oxide represented by general formula (1) that is a single phase in terms of X-ray diffraction.

[0068] The reaction precursor containing at least zinc pyrophosphate contains only zinc pyrophosphate when ZnP0 in the general formula (1) where y is 0 is produced, whereas when a zinc-phosphorus composite oxide containing an M element and represented by the general formula (1) is produced, the reaction precursor contains zinc pyrophosphate, a phosphorus compound, and an M element compound.

[0069] In the first step, it is preferable to appropriately adjust the contents of the zinc compound, phosphorus compound, and M element-containing compound so that the atomic molar ratio of Zn, P, and M in the reaction precursor corresponds to the composition of a zinc-phosphorus composite oxide represented by general formula (1). When zinc phosphate or zinc pyrophosphate is used as the zinc compound, it is preferable to prepare the reaction precursor taking into consideration the amount of phosphorus atoms in the zinc compound.

[0070] In the first step, if necessary, a mixing treatment of the zinc compound, the phosphorus compound and the compound containing element M can be carried out. The mixing treatment can be carried out in a wet or dry manner.

[0071] When wet mixing is performed, the reaction precursor can be obtained by drying the entire amount to remove the solvent.

[0072] In the first step, the composition of the zinc-phosphorus composite oxide represented by general formula (1) obtained by removing the solvent after the wet mixing treatment and drying the entire amount of the oxide substantially coincides with the atomic molar ratio of Zn, P, and M at the time of charging the raw materials.

[0073] The second step is a step of calcining the reaction precursor prepared in the first step to obtain the zinc-phosphorus composite oxide represented by the general formula (1).

[0074] The firing temperature in the second step is preferably 300 to 900°C, more preferably 500 to 800°C. On the other hand, if the firing temperature in the second step is below the above range, the production of the zinc-phosphorus composite oxide represented by general formula (1) tends to be insufficient, and if it exceeds the above range, a solidified sintered body tends to result. The firing time in the second step is not particularly limited, and firing is carried out for a sufficient time until the zinc-phosphorus composite oxide represented by general formula (1) is produced.

[0075] The production of the zinc-phosphorus composite oxide represented by the general formula (1) can be confirmed, for example, by X-ray diffraction analysis to determine whether a single-phase zinc-phosphorus composite oxide represented by the general formula (1) is obtained.

[0076] In the second step, in many cases, the firing time is 0.5 hours or more, preferably 2 to 20 hours, and almost all of the reaction precursor can be converted into the zinc-phosphorus composite oxide represented by the general formula (1).

[0077] The firing atmosphere in the second step is not particularly limited, and may be any of an inert gas atmosphere, a vacuum atmosphere, an oxidizing gas atmosphere, and the air.

[0078] In the second step, the calcination may be carried out once or multiple times as desired. For example, in order to make the powder characteristics uniform, the calcined product may be pulverized and the pulverized product may be further calcined.

[0079] After firing, the mixture is cooled appropriately, and may be crushed, crushed, classified, etc., as required.

[0080] The A source in step A is a compound containing element A. Examples of the A source include carbonates of A, oxides of A, hydroxides of A, halides of A, and carboxylates of A. Examples of carboxylates of A include gluconic acid, citrates, oxalates, acetates, and lactates.

[0081] The P source in step A is a compound having a P atom. The P source is preferably phosphoric acid.

[0082] The A source and P source in step A may be a phosphate or pyrophosphate containing both an A element and a P atom. The phosphate or pyrophosphate may be either a hydrous or anhydrous salt.

[0083] In step A, it is preferable to appropriately adjust the amounts of the A source and the P source mixed so that the atomic molar ratio of A and P in the raw material mixture corresponds to the composition of the metal pyrophosphate represented by general formula (2).

[0084] In step A, it is preferable to adjust the mixing amounts of the zinc-phosphorus composite oxide represented by general formula (1), the A source, and the P source so that the metal pyrophosphate salt represented by general formula (2) produced is 0.1 to 20 parts by mass, preferably 0.2 to 15 parts by mass, per 100 parts by mass of the zinc-phosphorus composite oxide represented by general formula (1) in the negative thermal expansion material produced.

[0085] In the step A, the zinc-phosphorus composite oxide represented by the general formula (1), the A source, and the P source can be mixed by a wet method or a dry method.

[0086] When wet mixing is performed, it is preferable to obtain a raw material mixture by drying the entire amount to remove the solvent.

[0087] Step B is a step of firing the raw material mixture prepared in Step A to obtain a composite of the zinc-phosphorus composite oxide represented by general formula (1) and the metal pyrophosphate represented by general formula (2), i.e., the negative thermal expansion material of the present invention.

[0088] The firing temperature in Step B is preferably 300 to 850°C, more preferably 350 to 800°C. On the other hand, if the firing temperature in Step B is below the above range, the production of the metal pyrophosphate represented by general formula (2) tends to be insufficient, and if it exceeds the above range, the product tends to become solidified by sintering. The firing time in Step B is not particularly limited, and firing is carried out for a sufficient time until the metal pyrophosphate represented by general formula (2) is produced.

[0089] The production of the metal pyrophosphate represented by general formula (2) can be confirmed, for example, by whether or not a peak top of the main peak is observed at 2θ=29.66° to 29.73° between 29° and 30° in X-ray diffraction analysis.

[0090] In Step B, in most cases, the firing time is 0.5 hours or more, preferably 1 to 10 hours, and the negative thermal expansion material of the present invention can be obtained.

[0091] The firing atmosphere in the step B is not particularly limited, and may be any of an inert gas atmosphere, a vacuum atmosphere, an oxidizing gas atmosphere, and the air.

[0092] In step B, firing may be performed once or may be performed multiple times as desired. For example, in order to uniformize the powder properties, the fired product may be pulverized and the pulverized product may be further fired.

[0093] After firing, the material is cooled appropriately, and if necessary, crushed, disintegrated, classified, etc., to obtain a negative thermal expansion material that is a composite having a core-shell structure and including a core containing a zinc-phosphorus composite oxide represented by general formula (1) and a shell containing a metal pyrophosphate represented by general formula (2) that covers all or part of the surface of the core.

[0094] In addition, as a method for obtaining a simple mixture of zinc phosphorus composite oxide particles represented by general formula (1) and metal pyrophosphate particles represented by general formula (2) described above as a composite, there is a method of mixing the zinc phosphorus composite oxide represented by general formula (1) and the metal pyrophosphate represented by general formula (2) by a mechanical means in which a strong shear force is applied in a dry or wet manner. In addition, as a method for producing a composite described above as c) having a core-shell structure and having a core containing a metal pyrophosphate represented by general formula (2) and a shell containing a zinc phosphorus composite oxide represented by general formula (1) covering all or part of the surface of the core, there is a method of firing a mixture containing the metal pyrophosphate represented by general formula (2) as the core and the reaction precursor of the zinc phosphorus composite oxide represented by general formula (1) obtained in the first step described above at 300 to 850°C. As a method for producing the composite d) in which particles containing a zinc-phosphorus composite oxide represented by the general formula (1) and particles containing a metal pyrophosphate represented by the general formula (2) are bonded together, a method of heat-treating a uniform mixture of particles of the zinc-phosphorus composite oxide represented by the general formula (1) and particles of the metal pyrophosphate represented by the general formula (2) at 300 to 850°C can be mentioned.

[0095] The negative thermal expansion material obtained by the method for producing a negative thermal expansion material of the present invention preferably has an average particle size of 0.1 to 100 μm, particularly preferably 0.2 to 80 μm, and even more preferably 0.2 to 20 μm, and the BET specific surface area is 0.05 to 50 m 2 / g, particularly preferably 0.10 to 10m 2 / g, more preferably 0.20 to 8 m 2 It is preferable that the average particle size and / or BET specific surface area of ​​the negative thermal expansion material be within the above ranges, since this makes the negative thermal expansion material easy to handle when used as a filler for resin, glass, etc.

[0096] Furthermore, the particle surfaces of the negative thermal expansion material according to the present invention may be subjected to a surface treatment if necessary in order to improve the resin dispersibility and moisture resistance of the negative thermal expansion material. Furthermore, in the method for producing a negative thermal expansion material according to the present invention, the negative thermal expansion material obtained by carrying out step B may be subjected to a surface treatment if necessary in order to improve the resin dispersibility and moisture resistance of the negative thermal expansion material.

[0097] Examples of surface treatments include methods of coating particle surfaces with inorganic compounds containing one or more elements selected from silane coupling agents, titanate coupling agents, fatty acids or derivatives thereof, Zn, Si, Al, Ba, Ca, Mg, Ti, V, Sn, Co, Fe, and Zr (see, for example, WO2020 / 095837, WO2020 / 261976, WO2019 / 087722, and JP-A-2020-147486). Surface treatments may also be performed by appropriately combining these.

[0098] The thermal expansion coefficient of the negative thermal expansion material obtained by the method for producing a negative thermal expansion material of the present invention between 80 and 200°C is -23 × 10 -6 / K or less, preferably -20×10 -6 / K or less, and the lower limit is not particularly limited, but is generally −100×10 -6 / K or more, preferably −70×10 -6 When the negative thermal expansion material of the present invention is combined with a positive thermal expansion material, the thermal expansion coefficient is particularly preferably −10×10 -6 ~-50 x 10 -6 / K.

[0099] In addition, in the negative thermal expansion material obtained by the method for producing a negative thermal expansion material of the present invention, the zinc-phosphorus composite oxide of general formula (1) is Zn ２ P ２ O ７When using a thermoplastic elastomer, the ratio (α2 / α1) of the thermal expansion coefficient (α2) between 100 and 150°C to the thermal expansion coefficient (α1) between 100 and 130°C, which indicates the degree of volume reduction with temperature increase between 100 and 150°C, is preferably 2.5 or less, more preferably 0.5 to 2.5.

[0100] The negative thermal expansion material of the present invention is used as a powder or paste. When the negative thermal expansion material of the present invention is used as a paste, the negative thermal expansion material of the present invention is mixed and dispersed in a solvent and / or a low-viscosity liquid resin and used in the form of a paste. Alternatively, the negative thermal expansion material of the present invention may be dispersed in a solvent and / or a low-viscosity liquid resin, and if necessary, a binder, a flux material, a dispersant, etc. may be added to use in the form of a paste.

[0101] The negative thermal expansion material of the present invention is used in combination with various organic or inorganic compounds as a positive thermal expansion material to form a composite material. The composite material of the present invention contains the negative thermal expansion material of the present invention and a positive thermal expansion material.

[0102] Organic compounds used as positive thermal expansion materials include, but are not limited to, 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), polyvinyl chloride resin, etc. Inorganic compounds used as positive thermal expansion materials include silicon dioxide, silicates, graphite, sapphire, various glass materials, concrete materials, various ceramic materials, etc.

[0103] Since the composite material of the present invention contains the negative thermal expansion material of the present invention, which has excellent negative thermal expansion properties, it is possible to achieve a negative thermal expansion coefficient, zero thermal expansion coefficient, or low thermal expansion coefficient depending on the blending ratio with other compounds.

[0104] The present invention will be described below with reference to examples, but is not limited to these. (X-ray Diffraction Apparatus) In the examples, measurements were carried out using an X-ray diffractometer (Ultima IV manufactured by Rigaku Corporation) under the following measurement conditions: Radiation source: Cu-Kα Tube voltage: 40 kV Tube current: 40 mA Scanning speed: 1° / sec Smoothing: Weighted averaging method Kα2 elimination: Intensity ratio 0.5

[0105] <Zn2P2O7 sample preparation> Zinc pyrophosphate trihydrate (Zn2P2O7.3H2O, average particle size 1.2 μm) was calcined at 700°C for 4 hours. X-ray diffraction analysis of the calcined powder revealed that it was single-phase α-Zn2P2O7. The average particle size of the obtained Zn2P2O7 sample was 1.1 μm and the BET specific surface area was 0.6 m 2 The average particle size of the Zn2P2O7 sample was determined by averaging the values ​​of 50 particles randomly selected at a magnification of 1000 times under a scanning electron microscope.

[0106] (Example 1) <Step A> 5.000 g of the Zn2P2O7 sample prepared above, 0.0943 g of manganese carbonate (average particle size 1.6 μm), 0.0946 g of 85% phosphoric acid, and 10 mL of pure water were thoroughly ground and mixed in a mortar. The entire mixture was then dried at 130°C. <Step B> The resulting dried powder was fired at 700°C for 4 hours. X-ray diffraction analysis of the fired powder revealed peaks derived from α-Zn2P2O7 (Figure 1). This was used as a negative thermal expansion material sample.

[0107] (Example 2) <Step A> 5.000 g of the Zn2P2O7 sample prepared above, 0.0472 g of manganese carbonate (average particle size 1.6 μm), 0.0473 g of 85% phosphoric acid, and 10 mL of pure water were thoroughly ground and mixed in a mortar. The entire mixture was then dried at 130°C. <Step B> The resulting dried powder was fired at 700°C for 4 hours. X-ray diffraction analysis of the fired powder revealed peaks derived from α-Zn2P2O7. This was used as a negative thermal expansion material sample.

[0108] Comparative Example 1 The Zn2P2O7 sample prepared above was used as a negative thermal expansion material sample (Zn2P2O7). The X-ray diffraction pattern is shown in Figure 2.

[0109] (Reference Example 1) 3.5516 g of zinc pyrophosphate trihydrate (Zn2P2O7.3H2O, average particle size 1.2 μm), 0.1198 g of manganese carbonate (average particle size 1.6 μm), 0.1201 g of 85% phosphoric acid, and 10 mL of pure water were thoroughly ground and mixed in a mortar. The entire mixture was then dried at 130°C. The resulting dried powder was fired at 700°C for 4 hours. When the fired powder was subjected to X-ray diffraction analysis, a peak derived from α-Zn2P2O7 was observed. This was used as a reference sample (Zn 1.90 Mn 0.10 P2O7).

[0110] (Physical Property Evaluation) The samples obtained in the Examples, Comparative Examples, and Reference Examples were measured for average particle size, BET specific surface area, main peak at 2θ = 29 to 30° using an X-ray diffractometer, and thermal expansion coefficient. The average particle size and thermal expansion coefficient were measured as follows. The results are shown in Tables 1 and 2. SEM photographs of the negative thermal expansion material samples obtained in Example 1 and Reference Example 1 are shown in Figures 3 and 4, respectively. X-ray diffraction patterns between 2θ = 29 to 30° when the samples of Example 1 and Reference Example 1 were measured using an X-ray diffractometer are shown in Figures 5 and 6, respectively.

[0111] (Average Particle Diameter) The average particle diameter of the negative thermal expansion material sample was determined by averaging the diameters of 50 particles randomly selected at a magnification of 1000 times under a scanning electron microscope.

[0112] [Measurement of Thermal Expansion Coefficient] (Preparation of Molded Body) 0.05 g of propylene carbonate was added to 1.00 g of sample and pulverized and mixed in a mortar for 3 minutes. Then, 0.15 g was weighed out and the entire amount was filled into a φ6 mm mold. A powder molded body was then produced by molding at a pressure of 0.5 ton using a hand press. The obtained powder molded body was heated to 700°C in an electric furnace over 3 hours and maintained at this temperature for 4 hours to produce a ceramic molded body. The produced ceramic molded body was evaluated for its thermal expansion coefficient between 80 and 200°C and the degree of linear expansion with increasing temperature between 100 and 150°C, as described below.

[0113] (Measurement of thermal expansion coefficient between 80 and 200°C) The thermal expansion coefficient of the prepared ceramic molded body was measured using a thermomechanical measuring device (TMA4000SE manufactured by NETZSCH JAPAN). The measurement conditions were a nitrogen atmosphere, a load of 10 g, and a temperature range of 50°C to 225°C. The measurement was repeated twice. The thermal expansion coefficient between 80 and 200°C from the second repeated measurement was used as the thermal expansion coefficient of the negative thermal expansion material sample. Figure 7 shows the relationship between the thermal shrinkage rate (%) and temperature (°C) of the negative thermal expansion material sample. The thermal expansion coefficient was also measured for a ceramic molded body (prepared by heating to 700°C in 3 hours and holding for 4 hours) obtained by further sintering the above ceramic molded body (prepared by heating to 750°C in 3 hours and holding for 4 hours). Figure 8 shows the relationship between the thermal shrinkage rate (%) and temperature (°C) of the negative thermal expansion material sample.

[0114] (Evaluation of the degree of volume reduction with temperature increase between 100 and 150°C) The thermal expansion coefficient of the produced ceramic molded body was measured using a thermomechanical measuring device (TMA4000SE manufactured by NETZSCH JAPAN). The measurement conditions were a nitrogen atmosphere, a load of 10 g, and a temperature range of 50°C to 225°C, and the measurement was repeated twice. The degree of volume reduction with temperature increase was evaluated by comparing the thermal expansion coefficient (α1) between 100 and 130°C in the second repeat with the thermal expansion coefficient (α2) between 100 and 150°C. A smaller ratio of α2 to α1 indicates a gradual volume reduction with temperature increase.

[0115]

[0116] Note: "-" in the table indicates that the data was not measured. In Comparative Example 1, the ceramic molded body was prepared by heating the dry powder to 750°C over 3 hours and holding the temperature for 4 hours. The linear expansion coefficient at 80-200°C was -53 ppm / K, the linear expansion coefficient (α1') at 100-130°C was -32 ppm / K, and the linear expansion coefficient (α2') at 100-150°C was -119 ppm / K, with the α2' / α1' ratio being 3.7.

[0117] (Example 3) <Step A> The Zn prepared above ２ P ２ O ７5.000 g of sample, 0.1457 g of copper pyrophosphate trihydrate (average particle size: 0.5 μm), and 10 mL of pure water were thoroughly ground and mixed in a mortar. The entire mixture was then dried at 130°C. <Step B> The resulting dried powder was fired at 700°C for 4 hours. X-ray diffraction analysis of the fired powder revealed that α-Zn ２ P ２ O ７ A peak due to the above was observed. This was used as a negative thermal expansion material sample. Furthermore, the average particle size, BET specific surface area, the main peak at 2θ = 29 to 30° using an X-ray diffractometer, and the thermal expansion coefficient were measured in the same manner as in Examples 1 and 2. Furthermore, a ceramic molded body was prepared by heating to 700°C in 3 hours and then maintaining it for 4 hours, and the evaluation molded body was used as a negative thermal expansion material sample. The relationship between the thermal shrinkage (%) and temperature (°C) of the negative thermal expansion material sample was also shown in Figure 7. Furthermore, a ceramic molded body was prepared by heating to 750°C in 3 hours and then maintaining it for 4 hours, and the evaluation molded body was used as a negative thermal expansion material sample. The relationship between the thermal shrinkage (%) and temperature (°C) of the negative thermal expansion material sample was also shown in Figure 8.

[0118] 7, it can be seen that the negative thermal expansion material samples obtained in the examples have excellent negative thermal expansion properties, and the ratio of the thermal expansion coefficient (α2) between 100 and 150°C to the thermal expansion coefficient (α1) between 100 and 130°C is smaller than that of the negative thermal expansion material sample of Comparative Example 1, and that there is a gradual decrease in volume with increasing temperature in the temperature range of 100 to 150°C. Also, from FIG. 8, it can be seen that for the ceramic molded bodies produced by heating to 750°C in 3 hours and holding for 4 hours, the examples show a gradual decrease in volume with increasing temperature in the temperature range of 100 to 150°C compared to the negative thermal expansion material sample of Comparative Example.

Claims

1. A complex of zinc-phosphorus composite oxide and metal pyrophosphate, wherein the zinc-phosphorus composite oxide is represented by the following general formula (1): Zn x M y P z1 O t1 (1) (wherein M represents one or more elements selected from Mg, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Na, K, F, Cl, Br, I, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho; x represents 0.0<x≦2.0, y represents 0.0≦y<2.0, z1 represents 1.7≦z1≦2.3, and t1 represents 6.00≦t1≦8.00, with the proviso that 1.7≦x+y≦2.3; The metal pyrophosphate is represented by the following general formula (2): w P z2 O t2 (2) A negative thermal expansion material comprising a metal pyrophosphate salt represented by the formula: (wherein A represents one or more metal elements selected from Mg, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho; w represents 1.7≦w≦2.3; z2 represents 1.7≦z2≦2.3; and t2 represents 6.00≦t2≦8.00).

2. The negative thermal expansion material according to claim 1, characterized in that the composite has a core-shell structure, the core containing the zinc phosphorus composite oxide represented by the general formula (1), and the shell containing the metal pyrophosphate represented by the general formula (2).

3. A negative thermal expansion material according to claim 1 or 2, characterized in that the zinc-phosphorus composite oxide represented by the general formula (1) is Zn2P2O7.

4. A negative thermal expansion material according to claim 1 or 2, characterized in that the metal pyrophosphate represented by the general formula (2) is Mn2P2O7 or Cu2P2O7.

5. The thermal expansion coefficient between 80 and 200°C is -23 x 10 -6 3. The negative thermal expansion material according to claim 1, wherein the thermal expansion coefficient is 0.1 to 0.5 K.

6. A negative thermal expansion material as described in claim 3, characterized in that the ratio (α2 / α1) of the thermal expansion coefficient (α2) between 100 and 150°C to the thermal expansion coefficient (α1) between 100 and 130°C is 2.5 or less.

7. The negative thermal expansion material according to claim 1 or 2, characterized in that, when X-ray diffraction measurement is performed using Cu-Kα as an X-ray source, the peak top of the main peak is observed at 2θ = 29.66 to 29.73° with 2θ between 29 and 30°.

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

9. BET specific surface area: 0.05 to 50 m 2 3. The negative thermal expansion material according to claim 1, wherein the thermal expansion coefficient is 0.01 to 0.

5.

10. The following general formula (1): Zn x M y P z1 O t1 (1) (wherein M represents one or more elements selected from Mg, Ca, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Na, K, F, Cl, Br, I, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, S, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho. x represents 0<x≦2.0, y represents 0≦y≦2.0, z1 represents 1.7≦z1≦2.3, and t1 represents 6.0≦t1≦8.0, with the proviso that 1.7≦x+y≦2.3 is satisfied.) and a zinc-phosphorus composite oxide particle represented by the following general formula (2): A w P z2 O t2 (2) A method for producing a negative thermal expansion material, comprising firing a mixture containing an A source and a P source serving as raw materials for producing a metal pyrophosphate represented by the formula: (wherein A represents one or more metal elements selected from Mg, Cu, Fe, Cr, Mn, Ni, V, Li, Al, B, Sr, Ba, Ti, Zr, Hf, Nb, Ta, Y, Yb, Si, W, Mo, Co, Bi, Te, Pb, Ag, Cd, In, Sn, Sb, Te, Ga, Ge, La, Ce, Nd, Sm, Eu, Tb, Dy, and Ho; w represents 1.7≦w≦2.3; z2 represents 1.7≦z2≦2.3; and t2 represents 6.0≦t2≦8.0).

11. The method for producing a negative thermal expansion material according to claim 10, characterized in that the zinc-phosphorus composite oxide represented by the general formula (1) is obtained by firing a reaction precursor containing at least zinc pyrophosphate.

12. A composite material comprising the negative thermal expansion material according to claim 1 or 2 and a positive thermal expansion material.

13. The composite material according to claim 12, wherein the positive thermal expansion material is at least one material selected from the group consisting of metals, alloys, glasses, ceramics, rubbers and resins.

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