JP2022156925A - Mullite sintered body with excellent thermal resistance and durability and production method thereof - Google Patents

Abstract

To provide a mullite sintered body having an excellent thermal resistance and durability.SOLUTION: Provided is a mullite sintered body that satisfies the following requirements (1)-(6). (1) A mass ratio of Al2O3:SiO2 ranges from 73:27 to 77:23. (2) The sintered body consists of a single phase of mullite. (3) The relative density to the theoretical density is more than 95%. (4) The mean grain size is 7-15 μm. (5) The content of crystal grains whose size is 6 μm or less is 20% or less. (6) Deflection is 5 mm or less after holding for 5 hours at 1,650°C under applied stress of 3 MPa.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a mullite sintered body having high heat resistance and durability and a method for producing the same.

Conventional mullite sintered compacts are produced by mixing natural raw materials such as kaolin and alumina raw materials by reaction sintering. However, since many impurities are mixed, a large amount of glass phase is formed inside the sintered compact by reacting with silica, etc. Therefore, the high-temperature characteristics were poor, such as a decrease in strength and large deformation under load at high temperatures. After that, mullite sintered bodies were developed as high-temperature structural materials, and the Al ₂ O ₃ /SiO ₂ mass ratio of Al ₂ O ₃ and SiO ₂ constituting the mullite phase was defined as the theoretical composition of the mullite phase (3Al ₂ O 3.2 SiO ₂ ), a sintered body (Japanese Patent Application Laid-Open No. _61-286264 ) is proposed in which a raw material powder is prepared with less impurities by a chemical process such as a sol-gel method, and the raw material powder is used. and the high-temperature properties were greatly improved compared to sintered bodies made from natural raw materials and alumina raw materials. However, since the creep resistance decreases when the service temperature reaches 1500° C. or higher, there is a demand for a mullite sintered body that is stable at higher temperatures. Therefore, a mullite sintered body that can be used at a high temperature of 1600 ° C. was developed by controlling the Al ₂ O ₃ /SiO ₂ mass ratio, crystal grain size, crystal phase, etc. in order to further improve high-temperature characteristics (Japanese Patent Application Laid-Open No. 6-227859). However, when the load stress is low, it can be used stably, but as the load stress increases even within the range of load stress in use, deformation increases at an accelerated rate, cracking due to deformation is likely to occur, and stability against load stress At the same time, repeated heating and cooling causes residual strain to occur inside the sintered body due to the difference in thermal expansion coefficient between the mullite phase and the alumina phase due to the crystal phase change in which the alumina phase precipitates when held at high temperature for a long time. , there were problems such as destruction.

JP-A-61-286264 JP-A-6-227859

An object of the present invention is to provide a mullite sintered body with high heat resistance and durability.

The present inventors have found that compared to conventional mullite sintered bodies, they have excellent creep resistance even when used under high temperature and high load for a long period of time, are stable without cracks due to deformation, and further change in crystal phase ( Since there is no deterioration due to mullite phase → mullite phase + alumina phase), the development of mullite sintered bodies with high heat resistance and durability, with little deterioration in mechanical properties such as strength, has been started. In the course of development, in the mullite sintered body, we not only control the mass ratio of _Al2O3 and _{SiO2 ,} the crystal phase, the relative density above a certain level, and the crystal grain size, but also the inclusion of crystal grains of a specific size. It was found that by setting the modulus to a specific value or less, a mullite sintered body having excellent heat resistance, durability, and stability and having less load stress dependence of deformation such as bending can be obtained. That is, the amount of pores (porosity), which is the starting point of fracture at high temperature, is controlled to a specific value or higher relative density, and not only the mass ratio of Al ₂ O ₃ and SiO ₂ in the sintered body is specified, but also the crystal Stable against load stress for a long period of time even at high temperatures of 1500°C or higher or 1600°C or higher by keeping the grain size within a specific range and the content of crystal grains of a specific size below a specific value. As a result, it was found that a mullite sintered body can be obtained which has almost no deformation such as bending and exhibits excellent creep resistance against changes in load stress. The present invention is thus completed. The mullite sintered body of the present invention can be used, for example, as a furnace material or jig for a heat treatment furnace, particularly as a roller for a roller hearth kiln, enabling stable heat treatment for a long period of time even under conditions of high temperature and high load. It was something. In the present invention, heat resistance means that there is no deformation or cracking due to deformation at the use temperature and that it has high thermal shock resistance, and durability means that the crystal phase changes due to long-term storage at high temperature. It means that there is little deterioration of mechanical properties such as deterioration of strength and strength.

That is, the present invention is specified by the matters shown below.
[1] A mullite sintered body that satisfies the following requirements (1) to (6).
(1) Al ₂ O ₃ : SiO ₂ is 73:27 to 77:23 in mass ratio
(2) Made of mullite single phase (3) Relative density to theoretical density is 95% or more (4) Average crystal grain size is 7 to 15 μm
(5) The content of crystal grains of 6 μm or less is 20% or less (6) The amount of deflection after holding for 5 hours at 1650° C. and a load stress of 3 MPa is 5 mm or less [2] Requirements (a) to (c) A method of manufacturing a mullite sintered body by molding mullite powder that satisfies the above conditions and firing at 1600 to 1780° C. in the air.
(a) Al ₂ O ₃ : SiO ₂ is 73:27 to 77:23 in mass ratio
(b) The total amount of Al ₂ O ₃ and SiO ₂ is 99.9% by mass or more (c) The specific surface area is 8 to 15 m ² /g

The mullite sintered body of the present invention has high heat resistance and durability, particularly high heat resistance and durability even under high load. The method for producing a mullite sintered body according to the present invention can produce a mullite sintered body having high heat resistance and durability, particularly high heat resistance and durability even under high load.

1 is an SEM photograph of the mullite sintered body obtained in Example 1. FIG. 2 is an SEM photograph of the mullite sintered body obtained in Comparative Example 3. FIG. 3 is an SEM photograph of the mullite sintered body obtained in Comparative Example 5. FIG.

The mullite sintered body of the present invention has (1) a mass ratio of Al ₂ O ₃ : SiO ₂ of 73:27 to 77:23, (2) a single mullite phase, and (3) a relative density to the theoretical density of 95% or more, (4) an average crystal grain size of 7 to 15 μm, (5) a content of 6 μm or less crystal grains of 20% or less, and (6) after holding for 5 hours at 1650 ° C. and a load stress of 3 MPa. The mullite sintered body satisfies the requirement that the amount of deflection is 5 mm or less. The requirements (1) to (6) of the mullite sintered body of the present invention are described below.

(1) Al ₂ O ₃ : SiO ₂ is 73:27 to 77:23 in mass ratio
When the total mass of Al ₂ O ₃ and SiO ₂ contained in the mullite sintered body of the present invention is 100, the mass ratio of Al ₂ O ₃ and SiO ₂ is 73: Al ₂ O ₃ : SiO ₂ :27-77:23. When the ratio of Al ₂ O ₃ in the sum of Al ₂ O ₃ and SiO ₂ is less than 73% by mass, the SiO ₂ content increases, and the glass phase and second phase formed by reacting with trace impurities are sintered. Many of them are formed at the crystal grain boundaries inside the body, and these serve as starting points at which the crystal grain boundaries become slippery at high temperatures, resulting in poor creep resistance, heat resistance, and durability. On the other hand, when the ratio of Al ₂ O ₃ exceeds 77% by mass, the content of Al ₂ O ₃ increases, and alumina particles tend to precipitate inside the sintered body. It leads to deterioration of creep resistance. In particular, long-term retention at high temperature accelerates the precipitation of alumina crystals, which is not preferable. Moreover, when the ratio of Al ₂ O ₃ and SiO ₂ is out of the above range, thermal shock resistance and thermal fatigue resistance are lowered. From the viewpoint of further improving heat resistance and durability, Al ₂ O ₃ :SiO ₂ preferably has a mass ratio of 74:26 to 76:24. The contents of Al ₂ O ₃ and SiO ₂ in the mullite sintered body can be measured by fluorescent X-ray analysis.

(2) Mullite Single Phase The crystal phase of the mullite sintered body of the present invention is a mullite single phase. If the mullite sintered body contains a second phase such as a glass phase or an alumina phase formed with impurities at the grain boundaries, the heat resistance and durability are lowered. The second phase such as the glass phase and the alumina phase in the mullite sintered body can be measured by the following method.
(glass phase)
After immersing the sample with a mirror-finished sintered surface in a 1% HF aqueous solution at 0 to 5°C for 24 hours, thoroughly wash and dry, and observe the sample before and after the HF treatment with a scanning electron microscope at a magnification of 1000 to 5000. do. In the sample after the HF treatment, where the glass phase existed, the traces of the glass phase are observed as wedge-shaped voids due to the HF treatment. Let S be the area of the observed sample, GB be the area occupied by the pores and voids observed in the sample before HF treatment, and GA be the area occupied by the pores, voids and traces of the glass phase observed in the sample after HF treatment. , the glass phase content is determined by the following formula.
Glass phase content (%) = [(GA-GB) / S] × 100
Although the glass phase is formed at the grain boundaries, it softens at high temperatures, making the grain boundaries slippery, resulting in a decrease in creep resistance.
(Alumina phase and other phases)
To identify whether or not the mullite sintered body contains an alumina phase, the sintered body is pulverized to a level that cannot be felt by fingers, and the pulverized powder is subjected to X-ray diffraction. X-ray diffraction conditions are: X-ray source CuKα, output 40 kV/40 mA, divergence slit 1/2°, scattering slit 1/2°, receiving slit 0.15 mm, scan speed: 0.5°/min. The axis is 2θ/θ, the monochrome receiving slit is 0.8 mm, the counter is a scintillation counter, and the monochromator is an automatic monochromator. A sintered body with a qualitative alumina phase does not show a large drop in creep resistance at high temperatures under low load conditions, but it shows a drop in creep resistance as the load increases. This is because the size of precipitated alumina crystal grains is smaller than that of mullite crystal grains, and small crystals greatly affect the deterioration of high-temperature properties. In addition, when kept in a certain temperature range for a long period of time, alumina crystals precipitate and the amount of alumina phase increases, resulting in deterioration of properties. When cooled to room temperature, cracks occur due to the difference in thermal expansion between the mullite phase and the alumina phase. may occur. The amount of alumina phase is calculated by the following formula using the obtained diffraction pattern. In the following equations, I _A (113) is the diffraction intensity of the alumina phase (113) plane, and I _M (210) is the diffraction intensity of the mullite phase (210) plane.
Alumina phase amount (volume %) = I _A (113) / [I _M (210) + I _A (113)] x 100
The identification and quantification of whether or not the mullite sintered body contains a second phase other than the glass phase and the alumina phase is performed by X-ray diffraction as in the case of the alumina phase. When the second phase other than the alumina phase is qualitatively determined by X-ray diffraction, the temperature range in which the characteristics can be stably maintained for a long period of time becomes low.
(mullite single phase)
In the present invention, it is necessary that the obtained X-ray diffraction pattern shows no diffraction peaks other than those of the mullite phase. However, in the mullite sintered body of the present invention, it is permissible to contain up to 3% by volume of the alumina phase. Preferably, the amount of alumina phase is up to 2% by volume. In the mullite sintered body of the present invention, the amount of the second phase other than the glass phase and the alumina phase is below the detection limit. Further, in the mullite sintered body of the present invention, it is permissible to contain up to 3% of the glass phase. Preferably the glass phase is up to 2%. As described above, the mullite single phase in the mullite sintered body of the present invention is an alumina phase and a glass phase as the second phase, the glass phase content is 3% or less, and the alumina phase content is 3% by volume. or less, and the other second phase is a mullite phase below the detectable amount limit.

(3) Relative density to theoretical density is 95% or more The relative density to theoretical density of the mullite sintered body of the present invention is 95% or more. The relative density in the present invention can be measured according to JIS1634. When the relative density is low, the number of pores inside the sintered body increases, and when the relative density is less than 95%, even at high temperatures and under low load conditions, the creep resistance is greatly affected. However, when the load is high, the pores become the starting point, and the crack progresses remarkably, making it easy to break in a short time. Although the upper limit of the relative density is not particularly limited, the upper limit of the relative density is about 98% from the viewpoint of actual production. The relative density of the mullite sintered body of the present invention is preferably 95-98%, more preferably 95-97%.

(4) Average crystal grain size is 7 to 15 μm
The average crystal grain size of the mullite sintered body of the present invention is 7 to 15 μm. If the average crystal grain size is less than 7 μm, the creep resistance and corrosion resistance are lowered, and if it exceeds 15 μm, the strength is lowered and the thermal shock resistance is lowered. From the viewpoint of further improving creep resistance and thermal shock resistance, the mullite sintered body of the present invention preferably has an average crystal grain size of 8 to 13 μm. In the present invention, a mirror-finished sintered body is thermally etched, and the sample is observed with an electron microscope to measure the major axis and minor axis of one crystal grain. do. The average crystal grain size in the present invention is the average value of the grain sizes of arbitrary 100 crystal grains measured as described above.

(5) The Content of Crystal Grains with a Diameter of 6 μm or Less is 20% or Less The content of crystal grains with a diameter of 6 μm or less in the mullite sintered body of the present invention is 20% or less. The content of crystal grains of 6 μm or less in the present invention means the ratio of the number of crystal grains having a grain size of 6 μm or less in 100 crystal grains measured for calculating the average crystal grain size (the number of crystal grains of 6 μm or less number/100) in %. The grain size has a great effect on creep resistance. result in a decline in If the content of crystal grains of 6 μm or less exceeds 20%, the creep resistance is lowered. From the viewpoint of further improving creep resistance, the content of crystal grains of 6 μm or less in the mullite sintered body of the present invention is preferably 15% or less.

(6) The mullite sintered body of the present invention has a deflection amount of 5 mm or less after being held at 1650 ° C. and 3 MPa for 5 hours under a load stress of 1650 ° C. and 3 MPa for 5 hours. and preferably 3 mm or less. The amount of deflection of the mullite sintered body in the present invention is obtained by processing the mullite sintered body to 5 × 2 × 150 mm, bending at four points with an upper span of 31.3 mm and a lower span of 100 mm, and applying a stress of 3 MPa at 1650 ° C. and 5 It is the amount of deflection measured at the position of the lower span of 50 mm of the sample after time holding.

The method for producing the mullite sintered body of the present invention is not particularly limited. In the method for producing a mullite sintered body of the present invention, (a) the mass ratio of Al ₂ O ₃ : SiO ₂ is 73:27 to 77:23, and (b) the total amount of Al ₂ O ₃ and SiO ₂ is 99. 9% by mass or more and (c) a specific surface area of 8 to 15 m ² /g is molded and fired at 1600 to 1780° C. in air. _The method for producing mullite powder that satisfies the above requirements ₍ a) to ( _c ) is not particularly limited. A mixed solution obtained by stirring and mixing alumina sol and silica sol is dried and then heated in the atmosphere at 1000 to 1500° C. to synthesize mullite and obtain mullite powder. The mullite powder is not limited to the sol-gel method, and high-purity mullite powder prepared by a method such as a coprecipitation method using an aluminum salt aqueous solution and a silicon alkoxide or a hydrolysis method using an alkoxide mixed solution can be used. . In order to prevent the impurities described later from being mixed as much as possible, it is necessary to employ high-purity aluminum compounds and silicon compounds that serve as sources of alumina and silica, such as alumina sol and silica sol. In addition, the mixing of solutions reduces the uniformity of alumina and silica in the synthesized mullite powder, and increases the variation in the mass ratio of Al ₂ O ₃ and SiO ₂ in individual mullite crystals when sintered. In order to prevent deterioration in heat resistance and durability, it is preferable to uniformly mix the solution by using a high-speed mixer or the like. The produced mullite powder is pulverized to have a specific surface area of 8 to 15 m ² /g, preferably 9 to 13 m ² /g. If the specific surface area is less than 8 m ² /g, the sinterability will be low, and if it exceeds 15 m ² /g, abnormal grain growth will occur during sintering, and the average crystal grain size will exceed the range of the average crystal grain size in the present invention. In addition, the particle size distribution tends to be widened, resulting in a decrease in strength and a decrease in thermal shock resistance.

The method of pulverizing the mullite powder is not particularly limited, but it is necessary to pulverize it so as not to mix impurities as much as possible. Examples of the pulverization method include a wet pulverization method and the like. In order to pulverize without contamination with impurities, pulverization is performed using a pot lined with high-purity alumina with an alumina purity of 99.9% or more or a resin-lined pot and high-purity alumina balls. It is important to control such conditions to prevent impurities from being mixed as much as possible. The use of balls with low alumina purity is not preferable because abrasion powder containing a large amount of impurities is mixed into the pulverized powder. In the case of pulverization with zirconia balls, zirconia wear powder that has been worn by pulverization is mixed in with the pulverized powder. Impurities such as TiO ₂ , Fe ₂ O ₃ , CaO, Na ₂ O, K ₂ O, MgO and ZrO ₂ in the produced mullite powder are 0.1% by mass or less, preferably 0.05% by mass or less. That is, the total amount of Al ₂ O ₃ and SiO ₂ is 99.9% by mass or more, preferably 99.95% by mass or more. When the content of impurities exceeds 0.1% by mass, that is, when the total amount of Al ₂ O ₃ and SiO ₂ is less than 99.9% by mass, a second phase or glass phase is formed at the grain boundaries, resulting in poor high-temperature properties. cause a decline.

The produced mullite powder satisfying the above requirements (a) to (c) is molded. The molding method is not particularly limited, and examples thereof include press molding, rubber press molding, extrusion molding, casting molding, and the like. When press molding such as press molding or rubber press molding is employed, a known molding aid such as wax emulsion, PVA, or acrylic resin is added to the slurry after pulverization, and dried by a known method such as a spray dryer. The obtained powder can be molded into a predetermined shape. When extrusion molding is employed, the pulverized slurry is dried and granulated, water and a binder such as methyl cellulose are added and mixed in a mixer to prepare a clay, which is then extruded. When cast molding is employed, slurry obtained by dispersing powder obtained by drying pulverized slurry is cast using a gypsum mold or a resin mold to obtain a compact. By firing the formed body at 1600 to 1780° C., preferably at 1650 to 1780° C., a sintered body having a predetermined shape can be obtained. In the production method of the present invention, by using mullite powder that satisfies the above requirements (a) to (c), the firing temperature in the range of 1600 to 1780 ° C., the particle size of the powder, etc. can be appropriately adjusted. , the mullite sintered body of the present invention can be obtained.

EXAMPLES The present invention will be specifically described below with reference to examples, but the technical scope of the present invention is not limited to these examples.

Alumina sol and silica sol are mixed so that the mass ratio of alumina sol and silica sol is the mass ratio shown in Table 1, the mixed solution is dried, and the resulting dried product is heated at 1450 ° C. in the atmosphere. Then, mullite was synthesized and mullite powder was produced. The prepared mullite powder is wet-ground for a predetermined time using a high-purity alumina pot with high-purity alumina balls having a diameter of 10 mm (SSA-999W manufactured by Nikkato Co., Ltd.), and the ratio shown in Table 1. Mullite powder with a surface area was used. In Comparative Example 3, an alumina ball (HD manufactured by Nikkato Co., Ltd.) with an alumina purity of 92% and a diameter of 10 mm was used, and in Comparative Example 6, a zirconia ball (YTZ manufactured by Nikkato Co., Ltd.) with a diameter of 10 mm was used. Mullite powders of Examples 1 to 7 and Comparative Examples 1 to 7 were thus produced. The slurry after pulverization was dried and granulated to prepare molding powder. A plate-shaped sample was press-molded using the prepared molding powder, and fired under each temperature condition of 1590 to 1800° C. shown in Table 1 to obtain a sintered body. Table 1 shows the properties of the obtained sintered body. SEM (scanning electron microscope) photographs of the microstructures of Example 1 and Comparative Example 3 are shown in FIGS. 1 and 2, respectively. FIG. 3 shows a SEM photograph of the microstructure of Comparative Example 5 in which alumina crystal grains are present in addition to mullite crystals. Alumina crystals are indicated by arrows. The mullite sintered body of Example 1 was subjected to SEM-EDX analysis of each crystal grain (energy dispersive X-ray analysis: acceleration voltage: 20 kV, magnification: 2000 times, irradiation time: 5 seconds, EMAX Evolution Model: X _- Max80 (manufactured by HORIBA), the mass ratio of Al ₂ O ₃ and SiO _{2 (} mass ratio when the _total amount of Al ₂ O ₃ and SiO ₂ is 100) is 74. It was in the range of 7:25.6 to 76.1:23.9, and consisted of crystal grains with a uniform mass ratio of Al ₂ O ₃ and SiO ₂ with very little variation.

(Evaluation of creep resistance)
The resulting sintered body was cut and processed into strips of 5×2×150 mm as samples for evaluation of creep resistance. Creep resistance is measured by four-point bending with an upper span of 31.3 mm and a lower span of 100 mm at 1650 ° C. and a load (P) of 3 MPa. ) was evaluated. The evaluation sample was heated from room temperature to 1,650° C. at a temperature elevation rate of 100° C./h in an electric furnace, held for 5 hours, taken out from the electric furnace, and naturally cooled to room temperature. Table 1 shows the results.
(Evaluation of Thermal Shock)
The obtained sintered body was processed into a square bar of 10×10×50 mm as a sample for thermal shock test, and subjected to a thermal shock test. The test method was to put the sample into an electric furnace heated to 1450° C., hold it for 1 hour, and immediately take it out of the furnace. Table 1 shows the results.

As shown in Table 1, the sintered bodies obtained in Examples 1 to 7, which are the mullite sintered bodies of the present invention, have a deflection amount of 3 mm or less even under the severe conditions of holding at 1650 ° C., 3 MPa, and 5 hours. It had stable heat resistance and durability for a long period of time. Furthermore, the sintered bodies obtained in Examples 1 to 7 did not develop cracks in the thermal shock test.

On the other hand, the sintered bodies obtained in Comparative Examples 1 to 7 failed to satisfy both creep resistance and thermal shock resistance, and lacked heat resistance and durability. In Comparative Example 1, since the specific surface area and firing temperature of the mullite powder were less than the lower limit values of the range in the present invention, sintering did not progress easily, and as a result, the average crystal grain size was less than the lower limit value of the range in the present invention. , the amount of deflection was large, and the heat resistance and durability were poor. In Comparative Example 2, since the specific surface area and firing temperature of the mullite powder exceeded the upper limit of the range in the present invention, the average grain size exceeded the upper limit of the range in the present invention, and the deflection amount was the same as the sintered body of the present invention. However, since the crystal grain size increased, the strength decreased, the thermal shock resistance decreased, cracks occurred, and the heat resistance and durability were inferior. In Comparative Example 3, since balls with a purity of alumina of 92% were used for pulverizing the raw material powder, the balls were worn by the pulverization, and components other than alumina mixed in the abrasion powder were mixed as impurities, and the amount of impurities was reduced. Since the upper limit of the range in the present invention was exceeded, the mass ratio of Al ₂ O ₃ and SiO ₂ was within the range in the present invention, but a large amount of glass phase was formed at the grain boundaries, and the obtained sintered body The amount of deflection increased, and the heat resistance and durability were poor. In Comparative Example 4, since the mass ratio of Al ₂ O ₃ and SiO ₂ was outside the range of the present invention (because alumina was less than the lower limit), a large amount of glass phase was formed at the grain boundaries and the amount of deflection was large. , the thermal shock resistance was low, cracks occurred, and the heat resistance and durability were poor. In Comparative Example 5, since the relative density was less than the lower limit of the range in the present invention, the crystal grains did not grow sufficiently due to insufficient sintering, so that the variation in the crystal grain size distribution increased, and the crystal grains of 6 μm or less were formed. Since the content exceeded the upper limit of the range in the present invention, the amount of deflection was large, the thermal shock resistance was low, cracks occurred, and the heat resistance and durability were poor. In Comparative Example 6, since zirconia balls were used for pulverizing the raw material powder, the balls were worn by the pulverization, and the abrasion powder was mixed as impurities, and the deflection amount of the obtained sintered body was increased, and heat resistance and durability were increased. It was of poor quality. In Comparative Example 7, the mass ratio of Al ₂ O ₃ and SiO ₂ was outside the range of the present invention (because alumina exceeded the upper limit), so the alumina phase was present in the sintered body exceeding the specified range. , the amount of deflection was large, the thermal shock resistance was low, cracks occurred, and the heat resistance and durability were poor.

The mullite sintered body of the present invention has higher heat resistance and durability than conventional mullite sintered bodies. Because it exhibits excellent heat resistance and durability even under high temperature and high load conditions, it is used as a furnace material and jig for heat treatment furnaces such as roller hearth kilns used for firing advanced materials such as electronic parts. It can be used stably for a long time. In addition, since the mullite sintered body of the present invention has high heat resistance and durability even in a high temperature and high load environment, for example, when used as a roller for a roller hearth kiln, the size of the roller can be reduced Since the thickness can be reduced, it also has the advantage of reducing the weight of the member.

Claims (2)

A mullite sintered body that satisfies the following requirements (1) to (6).
(1) Al ₂ O ₃ : SiO ₂ is 73:27 to 77:23 in mass ratio
(2) Made of mullite single phase (3) Relative density to theoretical density is 95% or more (4) Average crystal grain size is 7 to 15 μm
(5) The content of crystal grains of 6 μm or less is 20% or less (6) The amount of deflection after holding for 5 hours under a load stress of 3 MPa at 1650° C. is 5 mm or less A method for producing a mullite sintered body, comprising molding mullite powder satisfying the following requirements (a) to (c) and firing at 1600 to 1780° C. in air.
(a) Al ₂ O ₃ : SiO ₂ is 73:27 to 77:23 in mass ratio
(b) The total amount of Al ₂ O ₃ and SiO ₂ is 99.9% by mass or more (c) The specific surface area is 8 to 15 m ² /g

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