JPS61281065A - Manufacture of high temperature strength alumina silica baseceramic sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a sintered body of alumina-silica-based high-strength ceramics containing mullite, in particular, whose high-temperature strength up to 1300°C does not drop below the room-temperature strength, or where the room-temperature strength This paper provides a method for producing a high-strength alumina-silica ceramic sintered body that is superior in strength.

Mullite is 3Al2O3 and SiO203 ・2Si
It is an alumina-silica-based oxide with a composition represented by 0.2 oz, and has a low thermal expansion coefficient among oxide ceramics and a low density, and has creep resistance at temperature B compared to alumina, a typical oxide ceramic. It has characteristics such as excellent heat resistance and has the potential to be applied as a heat-resistant structural material, so research and development is becoming more active both in Japan and abroad.

Conventionally, the raw material for this mullite sintered body was '! 13& methods include: (1) adding alumina to clay (kaolin) raw materials; (2) mixing alumina sol and silica sol to form a gel;
(3) A method of mixing and heating silicate powder and aluminum salt. However, (1) is a method of mixing glass phase in the sintered body due to the influence of impurities caused by natural raw materials. is generated.

(2) creates a strong virtual image during gelation, and local compositional inhomogeneity occurs due to the difference in gelation speed between alumina gel and silica gel, resulting in a decrease in sinterability and a sintered body. A glass phase is likely to form inside. (3) is N
Due to the use of a-salt, there are disadvantages such as the tendency to form a liquid phase (glass phase) in the sintered body, and in any of the above cases, the viscosity of the glass phase decreases due to the presence of impurities, especially alkaline earths, especially Na+. Therefore, there was a drawback that the strength of the sintered body, especially the high-temperature strength at 800° C. or higher, was significantly lowered.

Recently, in addition to the above methods, (4) Co-precipitation method of alkoxide and aluminum salt, (5)
A method of hydrolyzing a mixed solution of alkoxides, (6) a method of spray pyrolysis of alkoxides and aluminum salts, etc. have been proposed.

However, no consideration is usually given to the influence of impurities, particularly Na2O and K2O, on high-temperature strength and strict control of composition.

The strength of the sintered body obtained by the method (6) (patent application has been filed by the applicant of the present invention) slightly increased from room temperature to 13
Although it only showed a bending strength of approximately 400 MPa up to 00°C, the strength generally tends to decrease as the temperature rises.
High temperature strength exceeding normal temperature strength has not been obtained.

The reasons for the low high-temperature strength of conventional mullite-based ceramics are: (a) Impurities, especially alkaline earth elements, form a glass layer with a low melting point and low viscosity at the grain boundaries of the mullite crystal phase, resulting in a decrease in the high-temperature strength of the sintered body. decreases.

(b) If there is a large local compositional deviation during the mullite synthesis process, more glass phase than estimated from the chemical composition is formed in the sintered body during sintering, resulting in a decrease in strength.

There are two points, and cause (a) in particular is the main cause of a significant decrease in high-temperature strength at 800°C or higher.

1. What to do - - The purpose of this invention is to solve the above-mentioned problems by using i!, which has a strong covalent bond among oxide ceramics. A synthetic powder that eliminates the heterogeneity of the raw material powder, which is considered a conventional drawback, when synthesizing an alumina-silica-based raw material powder containing mullite that has strong creep resistance at 1iU and excellent heat resistance and Width impact resistance. An object of the present invention is to provide a method for manufacturing alumina-silica ceramics containing mullite, which has higher high-temperature strength than room-temperature strength and can control the degree of deformation up to fracture. Such objects of the present invention are achieved by using homogeneous raw material powder, strictly controlling the alumina/silica composition ratio, and reducing the concentration of impurities in the raw material to a predetermined value or less.

1X S and = In the method of the present invention, the alumina-silica raw material powder containing mullite! ! ! ! The structure is an aluminum salt and the general formula SiO
(OR>(n>1゜n n-12n42 R: alkyl group) alkoxide is dissolved in a water-soluble solvent and this solution is spray pyrolyzed, or from a non-aqueous mixed solution of aluminum alkoxide and silicon alkoxide. A Si source and an An source are mixed in a solution state in a pre-stage of raw material powder synthesis such as in a hydrolysis method, in other words, synthesis is performed from a mixture obtained by homogeneously mixing at an atomic (molecule) level. In other words, since a method is used in which mullite powder is directly produced by heating a mixture of alumina-based raw materials and silica-based raw materials, raw material powder with an extremely homogeneous composition can be obtained, and unlike conventional methods, mullite can be produced by heating a raw material mixture. The problem of compositional heterogeneity that occurs during the oxidation process is eliminated.

Furthermore, in the method of the present invention, an example in which the concentration of impurities at temperature B, which will be described later, was investigated (see the curve displacement diagram in Figure 3)
As can be seen from the figure, there are impurities other than A2O3 and SiO2 in the synthetic powder, namely Fe203, CaO, M(IO
, Na20, K2O, Li20, TiO2, etc., the total amount must be less than 2500 ppm, especially N.
The total amount of a2O and K2O is adjusted to be 1,000,0011 or less, preferably 5,001)I)11 or less.

In addition, the A1203/Si02 composition ratio of the above powder is Δ120373 to 60% in weight% (61.4 to 61.4 in mole%).
46.9%), 5i0237-40% (38 in mol%,
Powder adjusted to a range of 6 to 53.1%) is used.

These composition ranges preferably include Al2O3 of γ0 to 65
The weight R%, 5102, is preferably 30 to 35% by weight.

The powder thus obtained was then molded at 150
Normal pressure sintering in air or pressure sintering in air, vacuum or an inert atmosphere is carried out at a temperature of 0 to 1700°C, preferably 1600 to 1650°C.

Control of impurities as described above is essential to obtain particularly high temperature strength, and the reason for limiting the A1203/5iOz composition as described above is A! When the m ratio of L203 is in the range from 60% to 73%, a high temperature strength of 1300°C which does not lower than the room temperature strength can be obtained, and especially Δu20
This is because high high temperature strength can be obtained in the range of a65 to 70%.

When the Al2O3 content becomes less than 60m%, the presence of the glass phase increases relatively, the number of contact points between mullite particles decreases, and the high temperature strength gradually decreases as the Si0 content increases. Hem length 203 in the above composition range
The lower limit of the content m was set to 60%.

In conventional methods, compositional heterogeneity tends to occur at the stage of synthesizing an alumina-silica-based raw material containing mullite from a mixture of an alumina source and a silica source, and impurities, particularly Na20. If K2O is present in excess, Na2O and K2O will dissolve into the SiO2 glass phase that exists in addition to the mullite crystal phase in a composition with excess silica, and the viscosity of the SiO2 glass will decrease with temperature n. There was a tendency for the strength of the sintered body to decrease at the 14th temperature.

According to the findings of the present inventors, the method of the present invention aims to homogenize the composition, suppress the presence of the SiO2 glass phase in the sintered body to the minimum in the composition, and reduce the amount of impurities. Especially Na 20. By minimizing the amount of K2O and preparing it as described above, the SiO2 glass phase is prevented from becoming low in viscosity at high temperatures. By allowing the sintered body to absorb stress from the outside and exhibit behavior close to plastic deformation, the sintered body exhibits normal-temperature strength at high temperatures up to 1300°C, contrary to conventional wisdom. By selecting a more preferable composition range, a sintered body with a bending strength of 1.5 to 2 times the normal temperature strength was obtained.

x1 Aluminum pentaunitrate [A text (NO3)3 ・91-R0]
and ethyl orthosilicate (Si (OC2F+5)4)
A mixed aqueous solution of J3 to the composition of A1203/Si02
The ratio of Al2O3 was adjusted to 60 to 78%, and an alumina-silica powder was synthesized by a spray pyrolysis method at 600°C. This synthetic powder was calcined at 950°C for 1rR, then pulverized, molded, and sintered at 1650°C in air for 4 hours under normal pressure to produce a sintered body. Next, a 3 x 4 x 40 m test piece was prepared from this sintered body, and its three-point bending strength at room temperature and 1300°C was measured. The results are shown in Figure 1.

In Figure 1, the ○ mark indicates the bending strength at room temperature, and the mu mark indicates 1300
The dotted line shows the bending strength at °C, and the dotted line is mullite (3Au2
03 ・2Si 02 ) (7) Chemical seedling theory composition (A!1
203 71.8 heavy ff1%, 3 i 0228.2
We accept the position of No. 4%). As can be seen from this figure, the room temperature strength and 13
The trend lines of 00℃ high temperature strength intersect, 8020365-7
In the range of 0%, strength 1.5 to 2.0 times the room temperature strength is obtained.

Fruit J1”2 Aluminum isopropoxide [A1 (OC31-17
)3) and ethyl orthosilicate (Si (OC2H5)
4) containing Al2O3 @' Fi 68~781j a
% (7) K were each dissolved in bempine and mixed. The solution obtained by mixing was diluted with ammonia at pl+11
The mixture was hydrolyzed with distilled water adjusted to 100% and dried to synthesize a powder. This synthetic powder was calcined at 1200° C. for 1 hour to form mullite, pulverized, molded at a pressure of 2000 kg/ci, and then fired at 1650° C. for 4 hours under atmospheric pressure to produce a sintered body. The results of the three-point bending strength test of the sintered body at room temperature and 1300°C are shown in Figure 2. In the figure, the marks Δ and Mu indicate the strength at room temperature and the high temperature strong electric current at 1300°C, respectively.The test results are shown in Figure 1. It showed almost the same tendency as the case shown in the figure.

As seen in the test results in Figures 1 and 2 above,
In the powder synthesis method, if the raw material powder is homogeneous and the amount of impurities in the raw material is strictly controlled, a sintered body with the same mechanical properties can be obtained even if the synthesis method is different. I understand.

Using the raw materials of Example 1, A (containing 1203 70% by weight)
When a sintered body was produced from the sample prepared in Example 1 under the same conditions as in Example 1, and the alkali content in the sample was changed, 1
The stress-displacement relationship at 300°C was tested. The test results are shown in Figure 3. In FIG. 3, the curve 1 is the case where the Na2O content in the sample is 500 ppm, and the curve 2 is the case where the Na2O content is 2500 ppm. As seen in this figure, it can be seen that the sintered body prepared by the method of the present invention has an excellent yield strength that can be tolerated before breaking.

As mentioned above, in the method of manufacturing an alumina-silica ceramic sintered body of the present invention, the impurity concentration is controlled and a homogeneously synthesized powder is used, so that an extremely homogeneous alumina-silica ceramic containing mullite can be produced. In addition to obtaining a sintered body, breaking the conventional wisdom, the bending strength at 1300°C is not lower than the strength at room temperature, and its Δ! L20
3/Si02 If you choose the composition range, the room temperature strength is 1.5~
The method of the present invention is an extremely useful method industrially, as it is possible to obtain a sintered body with a high-temperature strength that is twice as high.

[Brief explanation of the drawing]

Figure 1 shows three points at room temperature and 1300°C of sintered bodies synthesized from powders synthesized by spray pyrolysis from solutions of aluminum nitrate and ethyl orthosilicate mixed at various A1203/Si02 ratios. These are the bending strength test results. Figure 2 shows sintered bodies obtained from powders synthesized by hydrolyzing solutions of aluminum isopropoxide and ethyl orthosilicate mixed at various Al2O:+/SiO2 ratios at room temperature and 1300°C. These are the results of a point bending strength test. Figure 3 shows the I2O3-containing film 7 of the sample shown in Figure 1.
FIG. 3 is a stress-displacement diagram showing the influence of Na2O content at 1300° C. in the case of 0% by weight. (Other 8 people) Alzθ3 * Amount Z change A Amendment to the procedure dated July 7, 1985 1, Case description 1985 Patent Application No. 123127 2, Name of the invention Alumina-silica ceramics with excellent high-temperature strength Manufacturing method for sintered bodies 3, relationship with the amended case Patent applicant address name (114) Director of the Agency of Industrial Science and Technology Tatsu Todoroki (3 others) 4. Sub-agent address 2-2 Otemachi, Chiyoda-ku, Tokyo Number 1 Akira
Specification 1, Title of the invention] Method for producing an alumina-silica ceramic sintered body with excellent high-temperature strength 2, Claims] (1) Alumina-silica raw material powder is synthesized, and this raw material powder is temporarily In a method for producing an alumina-silica ceramic sintered body by firing, crushing, molding, and sintering: A raw material powder is obtained from a homogeneous mixture obtained by mixing a Si source and a ΔSilicon source in a solution state. Synthesis, Al2O3 relative to the total amount of Al2O3 and SiO2 in the synthesized raw material powder
The ratio of A 1203 and S i of the raw material powder is adjusted to a range of 60 to 73%
A method for producing an alumina-silica ceramic sintered body with excellent high-temperature strength, characterized in that the content of other than 02 (r) K"rjlJffiNa 20 and K2O is adjusted to less than 2500 ppm. (2) The raw material mentioned above The powder is mixed with aluminum salt in the solvent and the general formula 5in (OR> (n≧1.R:n n-1
2. The method according to claim 1, wherein the silicon alkoxide having a 2n+2 alkyl group is dissolved and the resulting blue solution is subjected to spray pyrolysis. (3) The manufacturing method according to claim 1, wherein the impurities in the raw material powder include Na2O and KzO(7)mffi 1000 pl) III). (4) The manufacturing method according to claim 1, wherein #8 of Na2O and K2O as the impurities in the raw material powder is adjusted to below 50 (lppmj). (5) The manufacturing method of the raw material powder The manufacturing method according to claim 1, wherein the ratio of Al2O3 to the combination of Ag2O3 and SiO2 is adjusted to a range of 65 to 10%. 3. Detailed description of the invention] The present invention provides a method for producing an alumina-silica ceramic sintered body, particularly a high-strength alumina-silica ceramic sintered body whose high-temperature strength up to 1300°C is superior to room-temperature strength and whose absolute value is high. Concerning this, mullite is an alumina-silica-based oxide with a composition expressed by 3A1203 2Sio2, and has a coefficient of thermal expansion that is small among oxide ceramics and a low density, making it the most suitable for alumina, which is a typical oxide ceramic. Comparatively, it has characteristics such as superior creep resistance at high temperatures, and as it has the potential to be applied as a heat-resistant structural material, research and development is becoming more active both in Japan and abroad. The compact is obtained by calcining, crushing, molding, and sintering the raw material powder, but the methods for synthesizing the raw material powder are: (1) A method of adding alumina to clay (kaolin) raw material. Typical methods are (2) a method of forming alumina sol and heating it, and (3) a method of mixing sodium silicate and aluminum salt and heating. However, (1) is difficult to sinter due to the influence of impurities contained in natural raw materials. Many glass phases are generated in the compact. (2) causes local compositional inhomogeneity due to the creation of strong temporary transport during gelation and the difference in gelation speed between alumina gel and silica gel. Therefore, the sinterability decreases and a glass phase is generated in the sintered body. (3)
Since the method uses Na salt, it has drawbacks such as a tendency to form a glass phase in the sintered body. In all of the above cases, impurities, especially Na20. Since the viscosity of the glass phase decreases due to the presence of K2O, there is a drawback that the strength of the sintered body, especially the high temperature strength at 800° C. or higher, is significantly lowered. Recently, in addition to the above method, three methods have been developed to synthesize raw material powder using alkoxide, namely (4) Co-precipitation method of silicon alkoxide and aluminum salt, (5) Co-precipitation method of silicon alkoxide and aluminum aluminum salt] A method of hydrolyzing a mixed solution, (6) a method of spray pyrolysis of silicon alkoxide and aluminum salt, etc. have been proposed. However, in all of the above methods, no consideration was given to the contamination of impurities, particularly minute amounts of Na20 or Na20. Method (6) (Japanese Patent Application Laid-open No. 161371-1983)
) The strength of the sintered body obtained only at room temperature was 130
Although they exhibit a bending strength of approximately 400 MPa up to 0° C., all of them show a tendency for the strength to decrease as the temperature rises, and high-temperature strength exceeding room-temperature strength has not been obtained. The reasons for the low high-temperature strength of conventional mullite-based sintered bodies are: (a) Impurities, especially alkali metal oxides, form a glass with a low melting point and low viscosity at the powder boundaries of mullite crystals; (b) during the mullite synthesis process. If there is a large local compositional deviation, there are two reasons: a glass phase of the seedlings will be formed in the sintered body during sintering, compared to what is estimated from the chemical composition.In particular, causes (a) IL; This is the main cause of a significant decrease in high temperature strength at temperatures above 800°C. The purpose of the present invention is to eliminate the heterogeneity of the raw material powder, which is considered a drawback of the conventional method, and to produce alumina, which has higher high-temperature strength than room temperature strength and has a high absolute value of strength. It is an object of the present invention to provide a method for manufacturing a silica-based ceramic sintered body.The purpose of the present invention is to adjust the composition ratio of alumina and silica using homogeneous raw material powder, and to adjust the composition ratio of alumina and silica in the raw material powder. This is achieved by reducing the concentration of impurities to an extremely small value on the ppm order. %: A method of dissolving silicon alkoxide ((R) group) in a solvent and spraying and pyrolyzing this solution, or a method of hydrolysis from a non-aqueous mixed solution of aluminum alkoxide and silicon alkoxide, etc. The Si source and the A1 source are mixed, in other words, atoms (molecules)
It is synthesized from a homogeneously mixed mixture at an order of magnitude. Therefore, a raw material powder with an extremely homogeneous composition is obtained, and the problem of compositional heterogeneity that occurs in the process of heating the raw material powder to form mullite as in the conventional method is eliminated. In addition, the ratio of Al2O3 to the total amount of Al2O3 and SiO2 in the raw material powder was 60 to 13% by weight (46% by mole).
, 9 to 61.4%), preferably 65 to 70i 1%. Furthermore, in the method of the present invention, impurities other than A203 and SiO2 in the raw material powder, that is, Fe203, are present in the raw material powder, as can be seen from an example in which the influence of impurities at high temperatures was investigated (Fig. 3). , Ca O, fvlgo
, Na 20. K20°Li 20. It is necessary to reduce the total amount of Ti 02 etc. to less than 2500 ppm,
In particular, the total amount of Na2O and K2O is 11,000 pp or less,
The raw material powder is preferably synthesized to have a content of 500 ppm or less. Next, the raw material powder synthesized in this way is calcined,
After crushing and shaping, it is sintered at a temperature of 1500 to 1700°C, preferably 1600 to 1650°C, under normal pressure in air, or under pressure in air, vacuum, or an inert atmosphere. Control of impurities as described above is especially essential for improving high temperature strength, and the reason why the ratio of AJ+203 to the content of A1203 and SiO2 is limited as described above is that the ratio of Al2O3 is 60% to 73% by weight. This is because a high temperature strength of 1300° C. higher than the room temperature strength can be obtained in the range up to 1,300° C., and a particularly high high temperature strength can be obtained when the proportion of the heel 203 is in the range of 65 to 70 ffi ffi%. If the proportion of Heai 203 is lower than that of 60 Shigekawa, the glass phase increases, the number of contact points between mullite particles decreases, and the high temperature strength decreases, which is not preferable. In the conventional method, compositional heterogeneity tends to occur at the stage of synthesizing alumina-silica raw material powder from a mixture of an alumina source and a silica source, and impurities, especially Na, tend to occur.
20. When K2O is present in excess, Na20. Since the viscosity of the K20-filled SiO2 glass decreases with increasing temperature, the strength of the sintered body at high temperatures of 800° C. or higher tends to become extremely low. According to the findings of the present inventors, in the method of the present invention, by homogenizing the composition, the suspension of the SiO2 glass phase in the sintered body can be suppressed to a minimum depending on the composition. Remove impurities, especially the total amount of Na2O and K2O (7)
By reducing pI11 to an extremely small amount, the SiO2 glass phase is prevented from becoming less viscous at high temperatures. It is possible to absorb the stress from
Strength exceeding room temperature strength was obtained at high temperatures up to 300°C, and by selecting a more preferable composition range, a sintered viscous material with bending strength about 1.5 times the room temperature strength was obtained. - Aluminum nitrate (Al(NO3)3 90) and L-thyl orthosilicate (St (OC2H5>4)) are added to the raw material powder so that the proportion of Al203 in the raw material powder is 60 to 78%. Alumina-silica raw material powder was synthesized from the mixed aqueous solution prepared in the above manner at 600°C by spray pyrolysis.This raw material powder was calcined in an electric furnace at 950°C for 1 iri!, then pulverized and molded. A sintered body was obtained by sintering at normal pressure in air for 4 hours at ℃.Then, from this sintered body, 3 x 4
A test piece of X4O was prepared, and its three-point bending strength at room temperature and 1300°C was measured. The results are shown in FIG. The total amount of Na2O and K2O in the raw material powder is 30
There was 0 ppm'c. In Figure 1, for J3, the O mark indicates room temperature bending strength, and the Mu mark indicates 130
The bending strength at 0°C is shown, and the dotted line is mullite (3A1
203 ・2Si 02 ) (7) Chemically identical composition (A addition 20371.8%, Si 0228.2 %)
It shows the position of As you can see from this figure, Al
When the proportion of 2O3 is 13% by weight, the room temperature strength and 1300
The trend lines of ℃ high temperature strength intersect, and the proportion of A1203 is 65.
In the range of ~70 wt β%, the strength is about 1.5 times the room temperature strength.
4. Point t2 Aluminum isopropoxide (A-(OC3H7)3) and ethyl orthosilicate (S
i (OC2H5)4 ) in the raw material powder
They were each dissolved in benzene and mixed so that the ratio of 68 to 78% was obtained. The solution obtained by mixing was hydrolyzed with distilled water adjusted to pH 11 with ammonia,
The raw material powder was synthesized by drying. This raw material powder is 1200
℃, calcined for 1 hour, after grinding, 200ONgf/cp
After molding at a pressure of s2, 1650℃4 under atmospheric pressure.
A sintered body was obtained by sintering for a period of time. A test piece having the same dimensions as in Example 1 was prepared from the sintered body, and the three-point bending strength at room temperature and 1300°C was measured. The results are shown in FIG. The total amount of Na2O and K2O in the raw material powder is 800ppIIlt''.
This shows high temperature strength at 300°C. The test results showed almost the same tendency as in Figure 1. As seen in the test results in Figures 1 and 2 above,
In the raw material powder synthesis method, the raw material powder is homogeneous and
By strictly controlling the amount of impurities in the raw material powder,
It can be seen that sintered bodies with similar physical properties can be obtained even if the synthesis methods are different. The raw material powder used in Example 1, in which the proportion of A-2O3 was adjusted to 70% by weight, was treated under the same conditions as in Example 1 to obtain a sintered body. At that time, the stress-displacement relationship at 1300°C was tested while changing the alkali content in the raw material powder. The test results are shown in Figure 3. In Figure 3, the curve (
Curve r) is for the case where the alkali content in the raw material powder is 5 ooppm, and curve (0) is for the case where the alkali content is 2500 ppm. As seen in this figure, it can be seen that the sintered body manufactured by the method of the present invention has an excellent allowable yield strength before breaking. 1 group 5 momme I As mentioned above, in the method for producing an alumina-silica ceramic sintered body of the present invention, the impurity concentration is reduced to a predetermined value or less, and since homogeneously synthesized raw material powder is used, extremely homogeneous alumina and silica ceramics can be produced. In addition to obtaining a silica-based ceramic sintered body, its Al2
By selecting the proportion of O3, it is possible to obtain a sintered body that has a high-temperature strength that is about 1.5 times the strength at room temperature and has a high absolute value of the strength, and the method of the present invention is extremely useful industrially. This is a great method. 4. Brief explanation of the drawings Figure 1 shows a sintered body manufactured by WIJ from raw material powder synthesized by spray pyrolysis of a solution containing aluminum nitrate and ethyl orthosilicate in various ratios of A1203 at room temperature and 1.
These are the results of a three-point bending strength test at 300°C. Figure 2 shows the three-point bending strength at room temperature and 1300°C of sintered bodies synthesized from raw material powders synthesized by hydrolyzing solutions of aluminum isopropoxide and ethyl orthosilicate mixed in various A12 (1+ ratios). The test results are shown. Figure 3 shows that the ratio of 8ρ203 of the sample shown in Figure 1 is 7.
FIG. 3 is a stress-displacement diagram showing the influence of alkali content at 1300° C. in the case of 0% by weight.

Claims (5)

[Claims] (1) In a method of synthesizing alumina-silica powder, calcining this powder, shaping and sintering it to produce an alumina-silica high strength ceramic sintered body: Si source and Al in a solution state In the Al_2O_3/SiO_2 composition of the synthesized powder, Al_2O
High-temperature strength, characterized in that the weight ratio occupied by _3 is adjusted to a range of 73 to 60%, and the impurities other than Al_2O_3 and SiO_2 in the synthetic powder are adjusted to less than 2500 ppm, including Na_2O and K_2O. A method for producing an alumina-silica ceramic sintered body with excellent properties. (2) The above synthetic powder is combined with aluminum salt in a water-soluble solvent and the general formula Si_nO_n_-_1(OR)_2_n_+_
2 (n≧1, R: alkyl group), and the method is synthesized by spray pyrolysis of the resulting solution. (3) The manufacturing method according to claim 1, wherein the total amount of Na_2O and K_2O as the impurities in the synthetic powder is adjusted to 1000 ppm or less. (4) The manufacturing method according to claim 1, wherein the total amount of Na_2O and K_2O as the impurities in the synthetic powder is adjusted to 500 ppm or less. (5) The manufacturing method according to claim 1, wherein the polymerization ratio of Al_2O_3 in the composition of the synthetic powder is adjusted to a range of 70 to 65%.