Cordierite sintered body and method for producing same

Abstract

The present invention provides a novel cordierite sintered body. The present invention relates to a cordierite sintered body containing at least calcium, magnesium, aluminum, and silicon, among elements belonging to an element group M1 comprising calcium, magnesium, aluminum, yttrium, and silicon, wherein: the content of the silicon is 44.0-53.0 mass% in terms of oxides; the content of the calcium is no more than 2.0 mass% in terms of oxides; the content of the yttrium is no more than 7.0 mass% in terms of oxides; the content of an element M2, which is a metal element other than the elements belonging to the element group M1, is no more than 2.5 mass% in terms of oxides; and the dielectric loss tangent at 20 GHz is no more than 0.00100.

Description

Cordierite sintered body and method for producing the same

[0001] The present invention relates to a cordierite sintered body and a method for producing the same.

[0002] BACKGROUND ART Sintered bodies containing cordierite (cordierite-based sintered bodies) have been used, for example, as members exposed to plasma (Patent Document 1).

[0003] Japanese Patent Application Publication No. 9-295863

[0004] In recent years, cordierite sintered bodies have been considered for use in various fields, and there is a demand for the development of novel cordierite sintered bodies having properties different from conventional ones.

[0005] The present invention has been made in view of the above points, and an object of the present invention is to provide a novel cordierite sintered body and a method for producing the same.

[0006] As a result of extensive research, the present inventors have found that the above object can be achieved by employing the following configuration, and have thus completed the present invention. That is, the present invention provides the following [1] to

[15] . [1] A cordierite-based sintered body containing at least calcium, magnesium, aluminum, and silicon among elements belonging to an element group M1 consisting of calcium, magnesium, aluminum, yttrium, and silicon, wherein the silicon content is 44.0 to 53.0 mass% inclusive, calculated as oxide, the calcium content is 2.0 mass% or less, calculated as oxide, the yttrium content is 7.0 mass% or less, the content of element M2, which is a metal element other than an element belonging to the element group M1, is 2.5 mass% or less, calculated as oxide, and the dielectric loss tangent at 20 GHz is 0.00100 or less. [2] The cordierite-based sintered body according to [1] above, wherein the magnesium content is 15.0 mass% or less, calculated as oxide. [3] The cordierite-based sintered body according to [1] or [2] above, having a Weibull modulus of 9.0 or more. [4] The cordierite-based sintered body according to any one of [1] to [3] above, having an iron content of 2000 mass ppm or less, calculated as oxide. [5] The cordierite-based sintered body according to any one of [1] to [4] above, having a calcium content of 1.0 mass% or less, calculated as oxide. [6] The cordierite-based sintered body according to any one of [1] to [5] above, having an aluminum content of 33.0 mass% or more, calculated as oxide. [7] The cordierite-based sintered body according to any one of [1] to [6] above, having a relative dielectric constant of 4.80 or more at 20 GHz. [8] The cordierite-based sintered body according to any one of [1] to [7] above, wherein the total content of sodium, potassium, strontium, titanium, phosphorus, chromium, manganese, iron, nickel, lanthanum, gallium, zirconium, zinc, and niobium is 3000 ppm by mass or less, calculated as oxides. [9] The cordierite-based sintered body according to any one of [1] to [8] above, wherein the total content of chromium, manganese, iron, and nickel is 1000 ppm by mass or less, calculated as oxides.

[10] The cordierite sintered body according to any one of [1] to [9] above, having a thermal conductivity of 3.0 W / (m K) or more.

[11] The number of foreign particles containing the element M2 and having an equivalent circle diameter of 5 μm or more is 150 particles / cm. ２

[10] The cordierite-based sintered body according to any one of [1] to

[10] above, wherein the yttrium content is 0.2 mass% or more, calculated as oxide.

[12] The cordierite-based sintered body according to any one of [1] to

[11] above, wherein the yttrium content is 0.2 mass% or more, calculated as oxide.

[13] The cordierite-based sintered body according to any one of [1] to

[12] above, wherein the four-point bending strength is 170 MPa or more.

[14] A method for producing the cordierite-based sintered body according to any one of [1] to

[13] above, comprising: preparing a compact using raw material powders; heating the compact; and using, as the raw material powder, a mixed powder containing cordierite powder produced by an electric melting method, mullite powder, and magnesium oxide powder.

[15] A method for producing the cordierite-based sintered body according to

[14] above, wherein the cordierite powder is used after magnetic separation.

[0007] According to the present invention, a novel cordierite sintered body and a method for producing the same can be provided.

[0008] The meanings of terms used in this specification are as follows: A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0009] [Cordierite-based sintered body] The cordierite-based sintered body of this embodiment contains at least calcium, magnesium, aluminum, and silicon among elements belonging to an element group M1 consisting of calcium, magnesium, aluminum, yttrium, and silicon. The silicon content is 44.0 mass% or more and 53.0 mass% or less, calculated as oxide. The calcium content is 2.0 mass% or less, calculated as oxide. The yttrium content is 7.0 mass% or less, calculated as oxide. The content of element M2, which is a metal element other than elements belonging to the element group M1, is 2.5 mass% or less, calculated as oxide. The dielectric loss tangent at 20 GHz is 0.00100 or less.

[0010] Hereinafter, the cordierite sintered body will also be referred to simply as "sintered body", and the cordierite sintered body of this embodiment will also be referred to as "the present sintered body".

[0011] The present sintered body is a sintered body of a metal oxide containing cordierite. Cordierite is represented by the chemical formula, for example, 2MgO.2Al ２ O ３ 5SiO ２ The present sintered body is made of cordierite (2MgO.2Al ２ O ３ 5SiO ２ ), it also contains calcium (Ca), but in a small amount. Furthermore, the present sintered body has a small amount of metal elements (element M2, described below) other than Ca and magnesium (Mg). Such a present sintered body has a small dielectric loss tangent at 20 GHz. The present sintered body will be described in more detail below. Note that, hereinafter, the dielectric loss tangent at 20 GHz and the dielectric loss tangent at 10 GHz will also be collectively referred to simply as the "dielectric loss tangent."

[0012] <Element Group M1> The element group consisting of calcium (Ca), magnesium (Mg), aluminum (Al), yttrium (Y), and silicon (Si) is referred to as "element group M1." As described above, the present sintered body is composed of cordierite (2MgO.2Al ２ O ３ 5SiO ２), further contains Ca. Therefore, the present sintered body contains at least Ca, Mg, Al, and Si among the elements belonging to the element group M1.

[0013] <<Ca>> Because the dielectric loss tangent of the present sintered body is small, the Ca content is 2.0% by mass or less, preferably 1.0% by mass or less, more preferably 0.7% by mass or less, even more preferably 0.4% by mass or less, even more preferably 0.2% by mass or less, particularly preferably 0.15% by mass or less, more particularly preferably 0.1% by mass or less, very preferably 0.05% by mass or less, and most preferably 0.01% by mass or less. On the other hand, from the viewpoint of mass production costs and raw material procurement, the Ca content, calculated as oxide, is more than 0% by mass, preferably 0.02% by mass or more, and more preferably 0.05% by mass or more. The Ca content calculated as oxide specifically means the content of CaO.

[0014] <<Mg>> Because the dielectric loss tangent of the present sintered body becomes small, the Mg content, calculated as oxide, is preferably 15.0 mass% or less, more preferably 14.5 mass% or less, even more preferably 14.0 mass% or less, particularly preferably 13.5 mass% or less, and most preferably 13.0 mass% or less. On the other hand, the Mg content, calculated as oxide, is preferably 11.0 mass% or more, more preferably 12.0 mass% or more, and even more preferably 12.5 mass% or more. The Mg content calculated as oxide specifically means the content of MgO.

[0015] <<Al>> Because the present sintered body has an excellent balance between the dielectric loss tangent and the strength, the Al content, calculated as oxide, is preferably 33.0 mass% or more, more preferably 34.0 mass% or more, even more preferably 35.0 mass% or more, and particularly preferably 36.0 mass% or more. For the same reason, the Al content, calculated as oxide, is preferably 40.0 mass% or less, more preferably 39.0 mass% or less, and even more preferably 38.0 mass% or less. The Al content calculated as oxide specifically means Al ２ O ３ means the content of

[0016] <<Si>> In the present sintered body, the Si content, calculated as oxide, is 44.0 mass% or more and 53.0 mass% or less. Because the dielectric loss tangent of the present sintered body becomes small, the Si content, calculated as oxide, is 53.0 mass% or less, preferably 51.0 mass% or less, more preferably 50.0 mass% or less, even more preferably 49.0 mass% or less, particularly preferably 48.5 mass% or less, and most preferably 48.0 mass% or less. On the other hand, the Si content, calculated as oxide, is 44.0 mass% or more, preferably 45.0 mass% or more, and more preferably 46.0 mass% or more. The Si content calculated as oxide specifically refers to SiO ２ means the content of

[0017] <<Y>> In the present sintered body, the Y content may be 0% by mass. However, it is preferable that the present sintered body contains Y because the four-point bending strength is increased. Specifically, the Y content, calculated as oxide, is preferably 0.2% by mass or more, more preferably 1.0% by mass or more, even more preferably 1.5% by mass or more, particularly preferably 2.0% by mass or more, very preferably 2.5% by mass or more, and most preferably 3.0% by mass or more. However, if the Y content is too high, the four-point bending strength will actually decrease. For this reason, the Y content, calculated as oxide, is 7.0% by mass or less. Because the four-point bending strength of the present sintered body is increased, the Y content, calculated as oxide, is preferably 6.0% by mass or less, more preferably 5.0% by mass or less, and even more preferably 4.0% by mass or less. The Y content calculated as oxide specifically refers to the amount of Y ２ O ３ means the content of

[0018] <Element M2> In the present sintered body, the content of element M2, which is a metal element other than the above-mentioned element group M1, is low. As a result, the present sintered body has a small dielectric loss tangent. Specifically, the content of element M2, calculated as oxide, is 2.5% by mass or less, preferably 2.0% by mass or less, more preferably 1.0% by mass or less, even more preferably 0.5% by mass or less, even more preferably 0.3% by mass or less, particularly preferably 0.2% by mass or less, very preferably 0.15% by mass or less, and most preferably 0.1% by mass or less. The lower limit is preferably zero.

[0019] Examples of the element M2 include at least one element selected from the group consisting of sodium (Na), potassium (K), strontium (Sr), titanium (Ti), phosphorus (P), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), lanthanum (La), gallium (Ga), zirconium (Zr), zinc (Zn), and niobium (Nb).

[0020] Because the dielectric loss tangent of the present sintered body becomes small, the total content of Na, K, Sr, Ti, P, Cr, Mn, Fe, Ni, La, Ga, Zr, Zn, and Nb is preferably 3000 ppm by mass or less (0.3% by mass or less), more preferably 2100 ppm by mass or less, even more preferably 1600 ppm by mass or less, still more preferably 1200 ppm by mass or less, particularly preferably 800 ppm by mass or less, and most preferably 400 ppm by mass or less, calculated as oxides.

[0021] Although P is not a metal element, when it is treated as element M2, it is regarded as a metal element.

[0022] The content of Na converted into oxide is specifically Na ２ The content of K in terms of oxide specifically means the content of K. ２ The Sr content calculated as an oxide specifically means the content of SrO. The Ti content calculated as an oxide specifically means the content of TiO. ２ The oxide-equivalent P content specifically means P ２ O ５The Cr content calculated as an oxide specifically means the Cr content. ２ O ３ The content of Mn calculated as an oxide specifically means the content of MnO. The content of Fe calculated as an oxide specifically means the content of Fe ２ O ３ The Ni content calculated as an oxide specifically means the NiO content. The La content calculated as an oxide specifically means the La content. ２ O ３ The Ga content calculated as an oxide specifically means the Ga content. ２ O ３ The oxide-equivalent Zr content specifically refers to ZrO ２ The Zn content calculated as an oxide specifically means the ZnO content. The Nb content calculated as an oxide specifically means the Nb content. ２ O ５ means the content of

[0023] <<Fe>> Because the dielectric dissipation factor of the present sintered body is small and the amount of heterophase is reduced, the content of Fe is preferably 2000 ppm by mass (0.2% by mass) or less, more preferably 1000 ppm by mass or less, even more preferably 500 ppm by mass or less, still more preferably 300 ppm by mass or less, particularly preferably 200 ppm by mass or less, very preferably 150 ppm by mass or less, and most preferably 100 ppm by mass or less, calculated as an oxide.

[0024] <Cr, Mn, Fe, and Ni> Because the amount of heterogeneous phases in the present sintered body is reduced, the total content of Cr, Mn, Fe, and Ni, calculated as oxides, is preferably 1,000 ppm by mass or less (0.1% by mass or less), more preferably 800 ppm by mass or less, even more preferably 600 ppm by mass or less, still more preferably 400 ppm by mass or less, very preferably 350 ppm by mass or less, particularly preferably 200 ppm by mass or less, and most preferably 100 ppm by mass or less.

[0025] The content of metal elements (element group M1 and element M2, excluding Si) in the sintered body is measured by inductively coupled plasma mass spectrometry (ICP-MS). ３ The sample is immersed in an extractant with a mass ratio of 4:1 for 2 days, and then heated at 80°C for 1 hour. The sample is then removed using tweezers to obtain an extractant containing the metal elements extracted from the sample. The extractant is then dried and solidified, followed by immersion in HNO ３ The solution is adjusted to a volume of 10 mL and analyzed using an apparatus manufactured by Agilent Technologies (Agilent 8800).

[0026] The Si content in a sintered body is determined as follows. First, a powder sample is taken from the center of the sintered body by polishing, and the total oxygen content Z1 in the sintered body is determined by infrared absorption using an oxygen / hydrogen analyzer (ROH-600 manufactured by LECO Corporation). The oxygen content Z2, which is stoichiometrically bonded to elements contained in the sintered body (excluding silicon atoms), is subtracted from the total oxygen content Z1 in the sintered body to calculate the oxygen content Z3 (oxygen content Z3 = total oxygen content Z1 - oxygen content Z2). Assuming that the entire amount of oxygen Z3 is used to bond with silicon atoms, the oxygen content Z3 is calculated by subtracting the amount of oxygen Z2 from the total oxygen content Z1 in the sintered body (oxygen content Z3 = total oxygen content Z1 - oxygen content Z2). ２ The SiO thus obtained is converted into an amount. ２ The converted amount is the oxide-converted Si content (SiO ２ (content of

[0027] <Dielectric loss tangent> The dielectric loss tangent of the present sintered body at 20 GHz is 0.00100 or less, preferably 0.00080 or less, more preferably 0.00060 or less, even more preferably 0.00050 or less, particularly preferably 0.00040 or less, and most preferably 0.00035 or less. Similarly, the dielectric loss tangent of the present sintered body at 10 GHz is preferably 0.00100 or less, more preferably 0.00080 or less, even more preferably 0.00060 or less, even more preferably 0.00050 or less, particularly preferably 0.00040 or less, and most preferably 0.00035 or less. The lower limit is not particularly limited, and both the dielectric loss tangent at 20 GHz and the dielectric loss tangent at 10 GHz are, for example, 0.00010, and preferably 0.00020. The dielectric loss tangent is a value measured by the SPDR (split post dielectric resonator) method at a frequency of 20 GHz or 10 GHz in an environment within the range of 23°C ± 2°C and 50 ± 5% RH. When measuring the dielectric loss tangent by applying an AC electric field to a dielectric, the energy loss tends to increase as the measurement frequency increases. Therefore, generally, the dielectric loss tangent increases as the frequency increases, and conversely, the dielectric loss tangent decreases as the frequency decreases.

[0028] <Dielectric Constant> The dielectric constant at 20 GHz of the present sintered body (hereinafter also simply referred to as "dielectric constant") is preferably 4.80 or more, more preferably 4.82 or more, more preferably 4.85 or more, and even more preferably 4.90 or more. The upper limit is not particularly limited, and is, for example, 5.20, preferably 5.10. The dielectric constant is a value measured at a frequency of 20 GHz by the SPDR (split post dielectric resonator) method in an environment within the range of 23°C ± 2°C and 50 ± 5% RH.

[0029] <Porosity> The porosity of the present sintered body is preferably 3.0 vol% or less, more preferably 1.5 vol% or less, even more preferably 0.5 vol% or less, particularly preferably 0.2 vol% or less, very preferably 0.15 vol% or less, and most preferably 0.1 vol% or less. The lower limit is preferably zero.

[0030] The porosity is determined in accordance with the calculation method for open porosity described in JIS R 1634:1998 "Method for measuring density and open porosity of sintered fine ceramics."

[0031] In order to achieve the porosity within the above range, it is preferable to adjust the contents of each component to the above-described ranges and to produce a sintered body by the method (the present production method) described below. In particular, it is preferable to use cordierite powder produced by an electric melting method as the raw material powder.

[0032] <Four-point bending strength> The four-point bending strength of the present sintered body is preferably 170 MPa or more, more preferably 180 MPa or more, even more preferably 190 MPa or more, and particularly preferably 200 MPa or more. There is no particular upper limit, and the four-point bending strength of the present sintered body may be, for example, 300 MPa or less, or 250 MPa or less.

[0033] The four-point bending strength is measured in accordance with JIS R 1601 (2008) on a test piece of the sintered body (flat plate, length 50 mm, width 4 mm, thickness 3 mm) at 25°C.

[0034] In order to achieve a four-point bending strength within the above range, it is preferable to set the contents of each component as described above and to produce the sintered body by the method (the present production method) described below.

[0035] <Weibull Coefficient> The Weibull coefficient of the present sintered body is preferably 9.0 or more, more preferably 10.0 or more, more preferably 10.5 or more, even more preferably 11.0 or more, even more preferably 11.5 or more, particularly preferably 12.0 or more, more particularly preferably 12.2 or more, and most preferably 12.5 or more. The upper limit is not particularly limited, and the Weibull coefficient of the present sintered body may be, for example, 14.0 or less, or 13.0 or less.

[0036] The Weibull coefficient (Weibull coefficient of four-point bending strength) is an index showing the degree of variation in four-point bending strength, and a larger value means a smaller variation in four-point bending strength. The Weibull coefficient is determined as follows: First, the four-point bending strength of 30 test pieces is measured using the method described above. Next, the Weibull coefficient is calculated in accordance with JIS R 1625 (2010) using the bending strength data of the 30 measured pieces.

[0037] In order to set the Weibull coefficient within the above range, it is preferable to set the contents of each component as described above and to produce the sintered body by the method (the present production method) described below.

[0038] <Thermal Conductivity> The thermal conductivity of the present sintered body is preferably 3.0 W / (m K) or more, more preferably 3.4 W / (m K) or more, even more preferably 3.5 W / (m K) or more, even more preferably 3.8 W / (m K) or more, and particularly preferably 4.0 W / (m K) or more. There is no particular upper limit, and the thermal conductivity of the present sintered body may be, for example, 6.0 W / (m K) or less, or 5.5 W / (m K) or less.

[0039] The thermal conductivity is measured for a test piece of the sintered body (12 mm x 12 mm plate, 6.0 mm thick) using a laser flash method thermal property measuring device "Xenon Flash Analyzer LFA 467 HyperFlash" manufactured by NETZSCH under the condition of 21°C.

[0040] In order to achieve a thermal conductivity within the above range, it is preferable to adjust the contents of each component to the above-mentioned ranges and to produce the sintered body by the method (the present production method) described below.

[0041] <Amount of Heterogeneous Phases (Number of Foreign Particles)> Using a scanning electron microscope (SEM), the sintered body is observed at a magnification of 1,000 times, and SEM images of 50 random fields of view are obtained. From the obtained SEM images, foreign particles containing element M2 (particles composed of element M2) are identified using an EDX (energy dispersive X-ray spectroscopy) device attached to the SEM. Of the identified foreign particles, the number of foreign particles having a circle equivalent diameter of 5 μm or more (unit: particles / cm ２) is measured and the average value of 50 fields of view is calculated. The circle equivalent diameter is calculated by importing each captured SEM image into image processing software (WinROOF: manufactured by Mitani Shoji Co., Ltd.) and performing binarization processing to calculate the circle equivalent diameter of each pre-specified foreign particle. The average value of the calculated number of foreign particles is used as the number of foreign particles in the sintered body (this is conveniently referred to as the "amount of foreign phase").

[0042] The amount of heterogeneous phases in this sintered body is 150 pieces / cm ２ Preferably, 100 or less per cm ２ More preferably, 50 or less particles / cm ２ More preferably, 30 or less per cm ２ Particularly preferred is 10 particles / cm ２ The following are most preferred: The lower limit is preferably zero.

[0043] In order to set the amount of different phases within the above range, it is preferable to set the contents of each component as described above and to produce the sintered body by the method (the present production method) described below.

[0044] <Shape and Use> The shape of the present sintered body may be plate-like (for example, disc-like or flat), spherical, or spheroidal, and may be appropriately selected depending on the use.

[0045] Since the sintered body has a small dielectric loss tangent, it is suitable for use as a dielectric material with small energy loss in technical fields where high frequency electromagnetic waves are used, for example.

[0046] [Method for manufacturing cordierite-based sintered body] Next, a method for manufacturing the present sintered body (hereinafter also referred to as "the present manufacturing method") will be described. The present manufacturing method is, in outline, a method for producing a compact using raw material powder and heating this compact. The present manufacturing method will be described in detail below.

[0047] <Raw Material Powder> A mixed powder containing cordierite powder produced by an electric melting method, mullite powder, and magnesium oxide powder is used as the raw material powder. Commercially available raw material powders can be used as appropriate.

[0048] <Cordierite powder> Cordierite (2MgO 2Al ２ O ３5SiO ２ The cordierite powder is a raw material for Mg, Al, and Si that constitute the present sintered body. Furthermore, the cordierite powder may contain Ca as an impurity, and in this case, the cordierite powder supplies the Ca that constitutes the present sintered body. By using a highly pure cordierite powder, the Ca content in the sintered body can be reduced.

[0049] (Fused Cordierite Powder) In the present manufacturing method, cordierite powder manufactured by an electric melting method (for convenience, also referred to as "fused cordierite powder") is used. The method for obtaining the fused cordierite powder is roughly as follows, for example. First, raw materials for the fused cordierite powder are placed in a crucible. Examples of raw materials for the fused cordierite powder include magnesium oxide (MgO), aluminum oxide (AlO), and the like. ２ O ３ ), silica (SiO ２ ) and other materials. These raw materials may contain impurities such as Ca. Next, for example, plasma is generated using carbon electrodes to melt the raw materials in the crucible. The molten raw materials are then air-shattered and rapidly cooled. This results in electrofused cordierite powder. Electrofused cordierite powder is a primarily amorphous substance (powder) containing some crystals. The particles that make up electrofused cordierite powder are spherical and have a uniform particle size. In other words, it is homogeneous. For this reason, electrofused cordierite powder is easily sintered in the presence of mullite powder, a sintering aid described below. In other words, it has good sinterability. As a result, a dense sintered body can be obtained, and porosity can be reduced. Furthermore, impurities can also be reduced by manufacturing it using the electric melting method.

[0050] Mullite powder: Mullite is, for example, 3Al ２ O ３ 2SiO ２ , 2Al ２ O ３ SiO ２Mullite powder is used as a sintering aid. By using mullite powder as a sintering aid, a dense sintered body can be obtained. Mullite powder is the raw material for Al and Si that make up this sintered body.

[0051] <Magnesium Oxide Powder> Magnesium oxide (MgO) powder is the raw material of Mg that constitutes the present sintered body.

[0052] <<Yttrium Oxide Powder>> When the present sintered body contains Y, yttrium oxide (Y ２ O ３ The yttrium oxide powder is the raw material for Y that constitutes the present sintered body.

[0053] <<Magnetic Separation>> Each powder used as a raw material powder is preferably magnetically separated before use. This allows the content of element M2 (Fe, etc.), which is a metal element other than element group M1 (Ca, Mg, Al, Y, and Si), to be reduced in the present sintered body that is finally obtained. A suitable example of a magnetic separation method is a method using a wet magnetic filter. The conditions for magnetic separation are not particularly limited, and may be appropriately adjusted, for example, so that the desired content of element M2 is achieved in the present sintered body that is obtained.

[0054] <<Preparation of Raw Powder>> The above-mentioned powders are mixed after magnetic separation if necessary. This produces a raw powder which is a mixed powder of the powders. The mixing method is not particularly limited, and a conventionally known method can be used. The content of each powder in the raw powder (mixed powder) is adjusted appropriately so that the content of each component in the final sintered body is the desired amount. The mixed powder is preferably pulverized to reduce the particle size in order to improve the sinterability during heating, which will be described later. Specifically, the particle size of the pulverized mixed powder is preferably 10 μm or less, more preferably 2 μm or less. The particle size is determined by the particle size at 50% of the integrated value in the particle size distribution (D ５０ ) (the same applies hereinafter). The pulverization method is not particularly limited, and pulverization can be performed using a ball mill, an attritor, a bead mill, a jet mill, or the like. When wet pulverization is performed, the mixed powder after pulverization is dried.

[0055] <Preparation of Molded Body> Next, a molded body is prepared using the raw material powder (mixed powder). That is, it is molded. The molding method is not particularly limited, and a general molding method can be used. For example, molding is performed using an isostatic press at a pressure of 100 MPa or more and 200 MPa or less. As an alternative method, a mixture of the mixed powder and an organic binder may be molded into a predetermined shape by press molding, extrusion molding, sheet molding, or the like. The shape obtained by molding is appropriately selected depending on the application of the sintered body to be obtained, etc.

[0056] <Heating> Next, the obtained molded body is heated. This results in a sintered body. From the viewpoint of improving sinterability, the heating temperature (maximum temperature during heating) is preferably 1400°C or higher, more preferably 1410°C or higher, and even more preferably 1430°C or higher. On the other hand, if the heating temperature is too high, a portion of the obtained sintered body may melt and be damaged, or a sintered body of the desired dimensions may not be obtained. Therefore, the heating temperature is preferably 1450°C or lower, more preferably 1440°C or lower. The heating time (holding time at the maximum temperature) is preferably 1 hour or longer, more preferably 2 hours or longer, and even more preferably 5 hours or longer. On the other hand, the heating time is preferably 48 hours or shorter, more preferably 12 hours or shorter, and even more preferably 8 hours or shorter. The atmosphere during heating (heating atmosphere) is not particularly limited, and examples thereof include air atmosphere; inert atmospheres such as nitrogen and argon atmospheres; and reducing atmospheres such as hydrogen atmospheres and mixed atmospheres of hydrogen and nitrogen.

[0057] The obtained sintered body is preferably densified. Densification is performed, for example, using a hot isostatic press. Specifically, for example, the sintered body is heated at a temperature of 1000°C to 1350°C while applying a pressure of 100 MPa to 200 MPa using a hot isostatic press.

[0058] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples described below.

[0059] Below, Examples 1 to 18 are working examples, and Examples 19 to 23 are comparative examples.

[0060] Examples 1 to 23 The sintered bodies of the respective examples were obtained as follows.

[0061] Raw material powder: Electrofused cordierite (2MgO 2Al ２ O ３ 5SiO ２ ) powder and mullite (3Al ２ O ３ 2SiO ２ ) powder and magnesium oxide (MgO) powder were mixed. Optionally, yttrium oxide (Y ２ O ３ ) powder, silica (SiO ２ Powders of other metal oxides, such as ZnO, NiO, and CuO, were also mixed.

[0062] As the electrofused cordierite powder, powder A and / or powder B, which is purer than powder A, were used. Powder A was "ELP-150FINE" manufactured by AGC Ceramics Co., Ltd. Powder B was prepared as follows. First, high-purity magnesia ("Kyowamag MF30" manufactured by Kyowa Chemical Industry Co., Ltd.), high-purity alumina ("AKP-30" manufactured by Sumitomo Chemical Co., Ltd.), and high-purity silica ("Admafine SO-E5" manufactured by Admatechs Co., Ltd.) were placed in a crucible as raw materials. Next, plasma was generated using a carbon electrode to melt the raw materials in the crucible. The molten raw materials were then air-crushed and quenched to obtain powder B. As the mullite powder, "KM101" manufactured by Kyoritsu Material Co., Ltd. was used.

[0063] Specifically, the powders were mixed so that the contents of element group M1 and element M2 in the resulting sintered body would be the values ​​shown in Table 1 below, to obtain a raw material powder that was a mixed powder.

[0064] Each powder was magnetically separated before mixing. Specifically, a wet magnetic filter ("Wet High Magnetic Flux Tester FG Type" manufactured by Japan Magnetic Separation Co., Ltd.) was used to magnetically separate a slurry prepared by dispersing each powder in water. The magnetic separation conditions were basically a slurry concentration of 15% by volume, a magnetic flux density of 2.8 tesla, and three magnetic separation runs, although the conditions were appropriately changed as necessary.

[0065] The raw material powder (mixed powder) was wet mixed and pulverized using a ball mill with high-purity alumina balls and ethanol as a dispersion medium. ５０ ) was 2.0 μm.

[0066] <<Preparation and Heating of Compacted Body>> The obtained raw material powder (mixed powder) was pressed at room temperature using an isostatic press at a pressure of 180 MPa to produce a compact. The produced compact was then heated in the atmosphere to obtain a sintered body. The heating temperature was 1430°C and the heating time was 5 hours. The obtained sintered body was then densified. Specifically, the compact was heated at 1300°C while applying a pressure of 145 MPa using a hot isostatic press.

[0067] <Contents of element group M1 and element M2> For each sintered body of the example, the contents of element group M1 and element M2 calculated as oxides were determined by the method described above. The results are shown in Table 1 below. The "other" elements in Table 1 below are Sr, P, Ga, Zr, Zn, and Nb.

[0068] <Dielectric loss tangent, etc.> For each sintered body, the porosity, four-point bending strength, Weibull coefficient, thermal conductivity, heterogeneous phase amount, dielectric loss tangent, and relative dielectric constant were determined by the methods described above. The results are shown in Table 1 below. Note that when measurements were not taken, "-" is entered in Table 1 below.

[0069]

[0070]

[0071] <Summary of Evaluation Results> As shown in Table 1 above, the sintered bodies of Examples 1 to 18 had a dielectric dissipation factor of 0.00100 or less at 20 GHz. In contrast, Example 19, in which the Ca content (oxide equivalent) was greater than 2.0 mass%, had a dielectric dissipation factor of greater than 0.00100 at 20 GHz. Example 20, in which the element M2 content (oxide equivalent) was greater than 2.5 mass%, had a dielectric dissipation factor of greater than 0.00100 at 20 GHz. Example 21, in which the Si content (oxide equivalent) was greater than 53.0 mass%, had a dielectric dissipation factor of greater than 0.00100 at 20 GHz. Example 22, in which the yttrium content (oxide equivalent) was greater than 7.0 mass%, had a dielectric dissipation factor of greater than 0.00100 at 20 GHz. Furthermore, in Example 23 in which the content of element M2 (in terms of oxide) was more than 2.5 mass %, the dielectric loss tangent at 20 GHz was more than 0.00100.

[0072] As mentioned above, the dielectric loss tangent decreases as the frequency decreases. That is, the dielectric loss tangent at 10 GHz is smaller than the dielectric loss tangent at 20 GHz. Therefore, since the dielectric loss tangent at 20 GHz in all of Examples 1 to 18 is 0.00100 or less, it can be inferred that the dielectric loss tangent at 10 GHz is 0.00100 or less.

[0073] According to the present invention, a novel cordierite sintered body and a method for producing the same can be provided.

[0074] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2023-117542) filed on July 19, 2023, the contents of which are incorporated herein by reference.

Claims

1. A cordierite sintered body containing at least calcium, magnesium, aluminum and silicon among elements belonging to an element group M1 consisting of calcium, magnesium, aluminum, yttrium and silicon, the silicon content being 44.0 mass% or more and 53.0 mass% or less, calculated as an oxide, the calcium content being 2.0 mass% or less, calculated as an oxide, the yttrium content being 7.0 mass% or less, calculated as an oxide, the content of element M2 which is a metal element other than elements belonging to the element group M1 being 2.5 mass% or less, calculated as an oxide, and a dielectric tangent at 20 GHz being 0.00100 or less.

2. The cordierite sintered body according to claim 1, wherein the magnesium content is 15.0 mass % or less, calculated as oxide.

3. The cordierite sintered body according to claim 1 or 2, having a Weibull coefficient of 9.0 or more.

4. A cordierite sintered body according to claim 1 or 2, having an iron content of 2000 mass ppm or less calculated as oxide.

5. A cordierite sintered body according to claim 1 or 2, wherein the calcium content is 1.0 mass % or less, calculated as oxide.

6. A cordierite sintered body according to claim 1 or 2, wherein the aluminum content is 33.0 mass % or more, calculated as oxide.

7. A cordierite sintered body according to claim 1 or 2, having a relative dielectric constant of 4.80 or more at 20 GHz.

8. The cordierite sintered body according to claim 1 or 2, wherein the total content of sodium, potassium, strontium, titanium, phosphorus, chromium, manganese, iron, nickel, lanthanum, gallium, zirconium, zinc and niobium is 3,000 mass ppm or less in terms of oxide.

9. The cordierite sintered body according to claim 1 or 2, wherein the total content of chromium, manganese, iron and nickel is 1000 mass ppm or less in terms of oxides.

10. The cordierite sintered body according to claim 1 or 2, having a thermal conductivity of 3.0 W / (m·K) or more.

11. The number of foreign particles having a circle equivalent diameter of 5 μm or more and containing the element M2 is 150 particles / cm ２ 3. The cordierite sintered body according to claim 1 or 2, wherein:

12. A cordierite sintered body according to claim 1 or 2, wherein the yttrium content is 0.2 mass % or more calculated as oxide.

13. The cordierite sintered body according to claim 1 or 2, having a four-point bending strength of 170 MPa or more.

14. A method for producing a cordierite sintered body as defined in claim 1 or 2, comprising the steps of: preparing a molded body using raw material powder; heating the molded body; and using, as the raw material powder, a mixed powder containing cordierite powder produced by an electric melting method, mullite powder, and magnesium oxide powder.

15. The method for producing a cordierite sintered body according to claim 14, wherein the cordierite powder is magnetically separated before use.

Images