JPH0840765A - Production of sintered alumina - Google Patents

Abstract

PURPOSE:To produce a high-purity and high-density alumina ceramic excellent in uniformity and useful especially for a member of a semiconductor production apparatus. CONSTITUTION:This is a method for production of sintered alumina. This production method is composed of (1) a molding process for molding a powdery alumina raw material, (2) a primary calcination process for calcining the resultant alumina molding prepared by the molding process while removing the organic binder therefrom without reducing the open pores, (3) a heat treatment process for heat treating the obtained primary calcined material in an atmosphere of a hydrogen chloride-containing gas and (4) a sintering process for sintering it by further firing it after the heat treatment process.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an alumina sintered body,
More specifically, the present invention relates to a method for producing an alumina sintered body excellent in high purity, high density and homogeneity, which is suitable for a member for semiconductor manufacturing equipment, a metal vapor laser, etc., which is required to have high purity, high density and high homogeneity. .

[0002]

2. Description of the Related Art Alumina sintered bodies have excellent properties such as mechanical strength, heat resistance and chemical resistance, and are widely used for various purposes. However, it may contain impurities such as alkali metals and alkaline earth metals from its raw material and manufacturing process, and its use may be restricted. For example, in semiconductor manufacturing apparatuses, which have made remarkable progress in recent years, ceramics are widely used for various members by utilizing the heat resistance, chemical stability, high elastic modulus, electrical characteristics, etc. of ceramics. For example, a heat-resistant synthetic resin such as Teflon or a metal that is likely to cause troubles, such as an etching device, an ashing device, or CVD, which is exposed to plasma directly, or a portion such as a transfer fork or chuck that directly contacts the wafer. Used in place. It is well known that semiconductor wafers are strictly controlled from various types of contamination, and it is also necessary to strictly limit the contamination from the manufacturing equipment members. Impurities such as alkali metals in the ceramics forming the member are also sources of contamination, so it is desired that the content be ppm or less.

Conventionally, an alumina sintered body is manufactured by a series of steps such as crushing, granulating, molding, debinding and sintering of alumina raw material powder. In order to obtain a high-purity alumina sintered body, impurities are prevented from being mixed in each of the above steps as much as possible. First, the purity of the raw material powder is strictly checked. That is, after all, the purity of the sintered body basically depends largely on the purity of the raw material powder, and the production of high-purity alumina ceramics is usually carried out using the highest-purity alumina powder possible. High-purity alumina raw material powder is produced by the Bayer method, dawsonite method, ammonium alum pyrolysis method, spark discharge method, ethylene chlorohydrin method, organometallic hydrolysis method, etc. The content ratio varies depending on the above manufacturing method. But,
The purity of the high-purity alumina raw material powder obtained by the above-mentioned production method is generally 9 (Pho) (4) nine.
About 9.99% by weight, or even higher purity of about 5 (5) nine, Fe, Si, alkali metal,
It is unavoidable that impurities such as oxides of alkaline earth metals are contained in several ppm or more. Further, the organic material of the molding binder added during the molding for obtaining the alumina sintered body usually contains impurities such as alkali metal, and the impurities in the alumina sintered body are more likely to pass through the manufacturing process. It can be said that the impurity content gradually increases.

[0004]

As described above, the conventional high-purity alumina sintered body uses the high-purity raw material alumina, and even if careful attention is paid to the inclusion of impurities in each manufacturing process, the impurities are not removed. It is impossible to completely prevent contamination. Therefore, even if the alumina sintered body obtained by the conventional method has high purity, it contains impurities of several ppm to several tens of ppm, and it is difficult to use it for a semiconductor manufacturing apparatus member requiring high purity of ppm or less, Quartz and SiC-based materials are used exclusively. Further, since the alumina ceramics conventionally used for metal vapor laser tubes are used at a high temperature of 1500 to 1600 ° C. for a long time, it is desired that the deformation rate at a high temperature is slow. The characteristic against this deformation, that is, the creep characteristic depends on the impurities contained in the ceramics, and the higher the purity, the better. Further, the impurities contained in the alumina ceramics are vaporized to contaminate the atmosphere inside the laser tube and reduce the laser output. As described above, alumina ceramics for metal vapor laser tubes are not required to have a high level of purity for semiconductor manufacturing equipment, but an alumina sintered body that is highly purified to a content of each impurity of about 10 ppm is desired. . Furthermore, in the conventional sintered body, the density of the sintered body is not uniform due to the non-uniformity of the behavior of the raw material powder during forming and the distribution of pores, the behavior of the pores during firing and the generation of new pores. Are not homogeneous, which results in defects in the product, and even when internal presence does not lead to defects, these parts may be exposed during product processing, which is a problem. Was there.

According to the present invention, in the method for producing an alumina sintered body as described above, the fine powder of the raw material and the careful treatment such as the prevention of the mixing of impurities in the manufacturing process are carried out, while finally allowing the mixing of some impurities. In view of the fact that it is unavoidable, an alumina sintered body that applies the same raw material powder as that in the past and measures to prevent the inclusion of impurities in each step, and is of higher purity and superior in homogeneity obtained by the conventional method Earnestly studied for the purpose of obtaining. Further, generally, the price of the alumina raw material powder becomes high in proportion to the degree of refining, that is, the purity, and when a high-purity raw material is used, the product price rises accordingly. Therefore, using a relatively low-purity raw material powder, a product with low impurity content, in particular, even if the iron content of the alumina powder raw material is several hundreds of ppm, a few p
If it can be made pm, its economic and industrial effects are remarkable. In view of this, the present invention also aims to develop a method of obtaining a high-purity alumina sintered body which is equivalent to the conventional one, without making the raw material purity higher than a predetermined level. Furthermore,
The purpose is to obtain a high-density, high-homogeneity alumina sintered body in addition to high purity.

In order to achieve the above-mentioned object, the inventors have studied to positively incorporate a purification treatment step. As a method for purifying quartz glass or silicon-impregnated SiC ceramics, treatment with hydrogen chloride gas is already known, but the purification step in this case is a high-purification treatment of raw material powder at the beginning of the process or a purification treatment of a product. Was incorporated into the final stage of the manufacturing process. In addition, for carbon materials, a technique of removing alkali metals and the like with chlorine gas to make them highly purified has been used for a long time. However, conventionally, not only alumina ceramics, but generally, industrially produced oxide ceramics, for example, zirconia,
There is no one that incorporates a purification treatment step in the manufacturing process of magnesia, spinel, etc., and increasing the number of steps in the production of sintered compacts rather increases impurities, as described above, so it is possible to omit the step. Was there. The inventors have reversed the idea from the conventional method for producing oxide ceramics, and by actively incorporating a purification step together with a predetermined firing process as an intermediate step in the production of alumina ceramics, semiconductor manufacturing equipment members and metal The present inventors have found that a high-purity, high-density, and homogeneous alumina sintered body applicable to a vapor laser tube can be obtained, and arrived at the present invention.

[0007]

According to the present invention, there is provided a method for producing an alumina sintered body, comprising: (1) a molding step of molding using alumina raw material powder; and (2) an alumina obtained in the molding step. After the organic binder is removed from the molded body and the firing is performed while leaving open pores, (3) a heat treatment step of heat treating the primary fired body in a hydrogen chloride gas-containing atmosphere, and (4) after the heat treatment step Further, there is provided a method for producing an alumina sintered body, which comprises a sintering step of further firing and sintering.

In the method for producing an alumina sintered body according to the present invention, it is preferable to use submicron fine powder as the alumina raw material powder and perform primary firing at 800 to 1000 ° C.
If the alumina raw material powder is micron fine powder,
It is preferable to perform the primary firing at 1000 to 1200 ° C. Furthermore, the hydrogen chloride gas heat treatment step is performed at 700 to 1400.
It is preferable to carry out at ° C.

[0009]

The present invention is configured as described above, and at the same time as incorporating the purification step into the ceramics firing process, open pores that sufficiently communicate with the compact obtained by compacting the raw material powder of submicron or micron order remain. Bake under the conditions. This keeps open pores in the porous molded body in a communicating state, and allows the hydrogen chloride gas of the purification treatment to quickly reach the inside of the porous molded body during sintering, and the chloride of the reaction product with impurities The discharge can be facilitated, and the sintered body can have a high purity. Further, in the method for producing an alumina sintered body of the present invention, in order to maintain the open pores in a communicating state in the firing process as described above,
In the pores and grain boundaries, the fine particle alumina reacts with hydrogen chloride in the purification process to become aluminum chloride, and at the same time, evaporates, and then is oxidized again and condensed, and alumina particles gradually grow with it, and then sintered. It is possible to obtain a high-density sintered body by densifying the inside of the body and making the whole uniform.

The present invention will be described in detail below. First, the alumina primary fired body of the present invention will be described. That is, in the present invention, the alumina compact to be primarily fired is formed by subjecting the alumina powder to slip casting, uniaxial pressure molding, press molding such as CIP (cold isostatic pressing), and the like as in the conventional case. There are various molding methods, but the method is not particularly limited, and a method generally used in conventional ceramics production can be used. The obtained molded body is then subjected to treatment steps such as drying, curing and binder removal as necessary, and then primary firing is performed. The primary firing of the present invention is generally carried out in the atmosphere under the condition that open pores that are sufficiently communicated with each other are left, and specifically, the firing temperature can be appropriately controlled to leave the open pores. In this case, the suitable primary firing temperature varies depending on the particle size of the alumina raw material powder, the molding method of the molded body, etc. Further, if the temperature of the primary firing is too low, the open porosity becomes sufficiently high, which is suitable for removing impurities. However, in the obtained primary fired body, the bond between the powders is insufficient and the strength is low, and the primary fired body is easily damaged during work such as transportation, and practical handling is difficult. On the other hand, if the primary firing temperature is too high, the sintering proceeds and the strength of the primary fired body becomes sufficiently high, but the grain growth of the sintered body proceeds at the same time, and impurities grow in the grown grains even in the open pore state. Even if it is taken in and subjected to the subsequent purification heat treatment, it becomes difficult to discharge it. Therefore, the primary firing temperature must be appropriately selected according to each condition. For example, a compact using submicron fine powder with high sintering activity as the raw material powder,
Even if the temperature is low, the strength of the fired body tends to be high, and it is preferable to set the primary firing temperature low in order to obtain a high purification effect. Usually, it is about 800 ° C to 1000 ° C. Further, in the case of alumina powder having a particle diameter of about several microns and low sintering activity, it is usually preferable to perform firing at about 1000 to 1200 ° C.

In the present invention, the primary sintered body obtained by the above-mentioned primary calcination and having a sufficient number of communicating open pores is then heat treated in an atmosphere containing hydrogen chloride (HCl) gas for purification treatment. The heat treatment for this purification is performed at a temperature of 700 ° C.
It is desirable to carry out at ˜1400 ° C. At a low temperature of less than 700 ° C., it takes a long time for the concentration of the impurity element to decrease, which is not practical. Further, when the heat treatment is performed at a temperature higher than 1400 ° C., the particles of alumina constituting the obtained primary fired body react with hydrogen chloride as described above to evaporate as aluminum chloride, and then again grow by condensation as alumina. Therefore, the particle size becomes large and the sintering activity is lost, so that a sufficiently dense ceramic cannot be formed in the subsequent sintering step. When the desired alumina ceramic may contain some pores, it can be heat-treated at a temperature higher than 1400 ° C. However, when the heat treatment temperature in the HC1 gas atmosphere is higher than 1400 ° C., the amount of alumina particles of the primary fired body scattered as aluminum chloride increases rapidly, and the amount of condensation and deposition in the purifier increases due to particle growth. The primary fired body is consumed, which is not industrially preferable. Therefore, after all, the heat treatment temperature is preferably 700 to 1400 ° C.

The processing time in the above heat treatment step, including the heating time up to the processing temperature and the cooling time after the processing, is industrially preferably several days at the longest as a processing cycle. The heat treatment time may be appropriately selected depending on the thickness and size of the primary fired body to be heat treated and the heat capacity of the heat treatment furnace, but generally, the time required for heating or cooling is several hours to about one day, The heat treatment at the temperature may be several hours to several tens hours, for example, 1 to 10 hours.

In the purification by heat treatment of the present invention, the impurity reduction is presumed to be due to the following transition.
That is, (1) The hydrogen chloride gas molecules diffuse and reach the impurity element through the pores communicating with each other. In this case, it depends on the thickness of the object to be treated, the size of the communicating pores, the concentration of HC1, and the temperature, but it is considered that it will take almost no time. (2) The impurity element diffuses solidly from the inside of the alumina fine particles of the primary fired body to the surface. After the impurities on the surface of the alumina fine particles constituting the ceramics primary fired body are removed, the diffusion of internal impurities to the surface is controlled by the size of the alumina particles in the primary fired body, and the smaller the particles, the shorter the diffusion distance. It will be a short time. When the particle size of alumina is large, industrial removal of impurities solid-dissolved in the particles is practically impossible. (3) HCl reacts with the impurity element to form chloride and evaporate. In this case, the reaction equilibrium constant of the impurity element and HCl and the equilibrium vapor pressure of the produced chloride are rate-determining.

(4) The produced chloride flows through the continuous ventilation holes of the primary fired body and flows out of the primary fired body. For example, if the diameter of the alumina particles forming the primary fired body is 0.5 μm, the diameter of the communication holes between the particles is about 0.2 μm. On the other hand, when the vapor pressure of the purified gas HCl is about 1 atm and the heat treatment temperature is 1000 ° C., the mean free path of the average distance of collision of gas molecules is about 0.4 μm, and the pore diameter is 0.2.
It becomes larger than μm. That is, the chloride of the reaction product flows out of the primary fired body ceramic by so-called Knudsen diffusion. The outflow rate of the produced chloride from the primary sintered body depends on the alumina particle diameter of the primary fired body as described above, and is also related to the wall thickness of the primary fired body, but impurities are particles of the primary fired body. It is considered to be the rate-determining factor when there are many on the surface. (5) The chloride vapor generated from impurities on the surface of the primary fired body is removed. A small amount of impurities on the order of ppm can be removed even at a low flow rate, but the removal rate becomes faster as the temperature rises. According to the knowledge of the inventors, 7
Temperatures below 00 ° C are not sufficient.

The purification heat treatment of the present invention is performed in an atmosphere containing HCl gas. The HCl gas-containing atmosphere can be formed by supplying hydrogen chloride gas alone or a mixed gas of hydrogen chloride gas and diluent gas to the heat treatment furnace. As the diluting gas, an inert gas such as helium, argon or nitrogen may be used alone or in combination of two or more. The ratio of hydrogen chloride gas and diluent gas is the rate of purification by heat treatment,
It can be appropriately set based on the alteration behavior of the alumina primary fired body and the processing cost. For example, the weight of the primary fired body is 1 kg
At that time, the impurity weight of 1 ppm is 1 mg, and the HC1 gas necessary for purification of the heat treatment is about 1 mg, that is, about 20 cc. Therefore, the content rate of the HCl gas may be a low content content corresponding thereto. Further, when the concentration of HCl gas in the heat treatment furnace is low, the reaction rate between the alumina particles constituting the sintered body and HCl becomes slow, which is preferable from the viewpoint of preventing alumina consumption.

The HCl-containing gas is supplied to a reaction chamber such as a heat treatment furnace by a gas flow system, a gas circulation system in which the gas is circulated in a predetermined temperature range, a gas is enclosed in the processing furnace and heat-treated for a predetermined time, and then exhausted. However, any method such as a batch gas exchange method in which gas is introduced again may be used. In the gas exchange system, when changing the pressure of the reaction container, it is necessary to make the container pressure resistant. Generally, the flow system is preferable, and the gas exchange system is not preferable because the chloride concentration generated by the reaction between impurities and hydrogen chloride becomes high and the impurity removal rate becomes slow, but it may be appropriately selected according to various conditions. Regarding the gas flow rate in the gas flow system, by increasing the dilution gas ratio and increasing the overall flow rate, the impurity chloride that has diffused and moved to the surface of the primary fired body and is exposed can be easily removed to the downstream side. preferable. In addition, in consideration of the cost and the effect of cooling the gas, the impurities and HC may be different depending on the shape and volume of the heat treatment furnace, the shape of the heat-treated primary sintered body, and the like.
It is possible to appropriately select and set the minimum gas flow rate necessary for the removal of the chloride generated in the above-mentioned process.

In the present invention, in order to remove impurities from the primary fired body as described above, heat treatment is performed in an atmosphere containing HCl gas. In this case, magnesium ions (Mg ²⁺ ), which is well known as an abnormal grain growth inhibitor, may be removed at the same time during the sintering of alumina ceramics. In such a case, Mg ²⁺ may be removed after heat treatment. It is preferable to add it. The addition of Mg ²⁺ can be preferably carried out by immersing the heat-treated primary fired body in an aqueous solution of magnesium salt and then drying. This method is effective because it can replenish the required amount of Mg ²⁺ . The amount of magnesium required for sintering varies depending on the final sintering temperature, the content of other impurities, etc., but in general, it is several 1
0 ppm or more is necessary.

In the present invention, after the heat treatment in the above-mentioned HCl gas-containing atmosphere, it is further fired to obtain an alumina sintered body. In the present invention, the firing method in the sintering step is not particularly limited, but contamination of the purified primary fired body in the subsequent main firing does not mean purification, and contamination in the main firing is purified. It is necessary to make the content of impurities sufficiently small. In this case, electric heating firing in a hydrogen atmosphere or in a vacuum is desirable as a firing method after purification and homogenization treatments because contamination can be reduced and density can be increased. Further, when a burner with a large atmosphere substitution rate is used, firing in air is also possible in consideration of refractory and contaminants in the atmosphere. The firing in the sintering step of the present invention is not particularly different from the firing of the conventional high-purity alumina sintered body, and can usually be performed at 1600 to 1850 ° C., although it depends on the raw material powder particles and the molding method.

When γ-alumina is contained in the method for producing an alumina sintered body of the present invention, γ-alumina is α
-The specific surface area is larger than that of alumina, and for example, impurities such as iron oxide existing in the roasting atmosphere in the alumina raw material powder manufacturing process may be selectively adsorbed. in this case,
Although impurities other than alkali metal and alkaline earth metal-based impurities will be contained, the primary fired body of the formed body using alumina raw material powder containing γ-alumina is used for purification.
When heat treatment is performed in an atmosphere containing 1 gas, γ-alumina is likely to be attacked by HC1, which contributes to rapid removal of impurities. Therefore, the inclusion of impurities is not preferable, but it is not necessary to positively prevent the inclusion of impurities.

When the alumina raw material powder contains silicon, the silicon is not removed even by the above-mentioned purification treatment of the present invention, that is, the heat treatment in the gas atmosphere containing HC1. for that reason,
When silicon is contained as an impurity and the presence of silicon in the alumina sintered body poses a problem, it is necessary to perform some sort of silicon removal treatment. As described above, the present invention, in the production of the same alumina sintered body as in the prior art, by subjecting the primary sintered body after calcination to heat treatment in an atmosphere containing hydrogen chloride gas, alkali metal, alkaline earth Impurities such as group metals and iron oxides can be efficiently removed, and thereafter, by firing at a higher temperature and sintering, it is possible to obtain a highly purified alumina sintered body that is highly densified and has excellent homogeneity.

[0021]

EXAMPLES The present invention will be described in more detail based on the following examples. However, the present invention is not limited to the following examples. In the following examples, the porosity state of the primary fired body was observed using a mercury porosimeter to confirm whether or not it communicated with the open pores. The porosity was calculated based on the values measured using the mercury porosimeter and Archimedes method. The impurity content of the molded body, the primary fired body, and the sintered body is a value obtained by crushing about 0.5 g of the sample and performing chemical analysis using a flameless atomic absorption spectrophotometer. The relative density of the sintered body was measured using the Archimedes method.

Examples 1 to 11 and Comparative Example 1 (α-alumina raw material powder) 100 parts by weight of an α-alumina raw material powder (trade name: AKP-20) manufactured by Sumitomo Chemical Co., Ltd. and having an average particle size of 0.4 μm, A slurry was prepared by mixing 80 parts by weight of ion-exchanged water, 0.2 parts by weight of polyacrylic acid ammonium as a dispersant, and 0.2 parts by weight of high-purity polyvinyl alcohol as a binder in a pot mill overnight. The obtained slurry was poured onto a porous alumina ceramics plate and then left to dry to obtain a molded body. The obtained molded body was fired in the atmosphere at 1000 ° C. for 2 hours to obtain a primary fired body. As a result of inspecting the pore state of the primary fired body, it was confirmed that the pores communicate with each other. The porosity was 56%. Further, impurities in the primary fired body were found to contain 10 ppm of iron (Fe), 6 ppm of sodium (Na), and 10 ppm of silicon (Si) based on the elemental analysis by chemical analysis. Using a milling machine, the thickness of the primary sintered body is 2m.
Two types, m and 8 mm, were processed into a 20 × 20 (mm) plate-shaped body. The work-formed primary fired slope was heat-treated in an atmosphere containing hydrogen chloride gas under the conditions shown in Table 1. In addition, nitrogen gas and H were used as the atmosphere gas of Examples 6 to 11.
A gas mixed with Cl at the N ₂ / HCl ratio shown in Table 1 was used. After the heat treatment, the purified primary fired body obtained was chemically analyzed to confirm the effect of removing impurities. The results are shown in Table 1.

[0023]

[Table 1]

From the results of the above Examples and Comparative Examples, at 600 ° C., where the heat treatment in the hydrogen chloride gas-containing atmosphere of the purification treatment is less than 700 ° C., the purification does not proceed even if the HC1 concentration is increased and the time is increased. I understand. It can be seen that purification proceeds at 700 ° C. or higher, and the flow rate at least progresses even when the HC1 concentration is low. Further, it can be seen that at 1200 ° C., the purification is remarkable, but at the same time, the amount of alumina is greatly reduced.
It can be seen that Si contained in alumina is not removed by heat treatment in an atmosphere containing HC1.

Examples 12 to 20 and Comparative Examples 2 to 4 Average particle size of 0.10 made by Baikowski Co. containing γ-alumina.
05 μm high-purity alumina raw material powder (trade name: CR-3
0) 100 parts by weight, 150 parts by weight of ion-exchanged water, a small amount of ammonium polyacrylate as a dispersant, and 1.5 parts by weight of polyvinyl alcohol as a binder were mixed in a pot mill all day and night to prepare a slurry. The obtained slurry is granulated using a spray dryer, and the obtained granulated powder is used with CIP at a pressure of 1 ton / cm ² and a diameter of 25 m.
It was molded into a cylinder with a length of m and a length of 110 mm. The columnar formed body was fired at 1000 ° C. in the atmosphere to obtain a primary fired body. The obtained primary fired body contained 8 ppm of Fe as an impurity on an elemental basis. Further, all the pores were open pores with a porosity of 61%. Processing the primary fired body, diameter 20mm, length 10
It was a 0 mm cylinder. The primary fired body after processing was subjected to heat treatment in a hydrogen chloride atmosphere while changing the treatment temperature as shown in Table 2 to be purified and homogenized. The result of measuring the iron content of the primary fired body after the heat treatment was 3 ppm, which is shown in Table 2 as Example 12. Then, Mg ions were impregnated with an aqueous solution of magnesium salt so that the Mg content was 100 ppm, followed by firing at 1800 ° C. for 2 hours in a hydrogen atmosphere and sintering. The Fe density of each of the obtained sintered bodies was measured by chemical analysis, and the relative density was measured. The results are shown in Table 2. Table 2 also shows the results of a sintered body that was sintered without heat treatment as Comparative Example 2.

[0026]

[Table 2]

From the results of the above Examples and Comparative Examples, after the porous primary fired body was heat treated in an atmosphere containing HC1 to be purified, even after firing for sintering again, the purification after heat treatment was performed. It was confirmed that the effect was maintained. Also,
When using alumina powder containing γ-alumina as a raw material,
It can be seen that the purification effect is improved as compared with the raw materials containing only the α-alumina raw material of Examples 1 to 11. Further, it can be seen that, along with the heat treatment for purification, the sintered body density improves in the heat treatment temperature range of about 900 to 1100 ° C., but conversely the sintered body relative density decreases at 1200 ° C. or higher.

Examples 21 to 32 Sintered bodies were obtained in exactly the same manner as in Example 12 except that the heat treatment was performed in the HCl atmosphere under the conditions shown in Table 3. The evaporation loss of each of the obtained sintered bodies was measured, and further, each sintered body was cut into three parts near the surface, the middle part and the central part, and the relative density of each part was measured and shown in Table 3. It was Also,
The relative density of each of the sintered bodies obtained in Comparative Example 2 without heat treatment was measured in the same manner, and the results are shown in Table 3.

Also from these results, the primary fired body was treated with HCl.
It is apparent that the heat treatment at 700 ° C. or higher in the atmosphere improves the relative density and homogeneity of the finally obtained sintered body, and can achieve densification and homogenization. Also,
Although heat treatment in an HCl-containing atmosphere at a high temperature of 1100 ° C. or higher improves the homogeneity of the sintered body, the above-mentioned Examples 12 to
As is clear even with 0, the density decreases.

[0030]

[Table 3]

Examples 33 to 50 and Comparative Examples 6 to 7 (low-purity raw material) To 100 parts by weight of easily-sinterable alumina powder (trade name: AES-11E) manufactured by Sumitomo Chemical Co., Ltd. and having an average particle size of 1.0 μm. Then, 2 parts by weight of polyvinyl alcohol and 60 parts by weight of deionized water were added to prepare a slurry. The obtained slurry was spray-dried using a spray dryer to obtain granulated powder. The granulated powder was pressure-molded using CIP at a pressure of 1 ton / cm ² , and was then lathe processed to produce a circular tube having an outer diameter of 30 mm, a wall thickness of 2 mm and a length of 100 mm. This processed circular tube is 1250
The binder was burned off by heating in air at 0 ° C. for 2 hours to obtain a primary fired body. The obtained primary fired body has a porosity of 60%,
It was confirmed that the pores were communicating. In addition, the content of impurities was measured and shown in Table 4 as Comparative Example 7. Next, the primary fired body was heat-treated under the conditions shown in Table 4 in a gas atmosphere in which nitrogen gas and HCl were mixed at the N ₂ / HCl ratio shown in Table 4. The impurity content and the weight loss of the obtained primary fired body after the heat treatment were measured in the same manner as in Example 1. The results are shown in Table 4.

[0032]

[Table 4]

From the results of the above-mentioned Examples and Comparative Examples, the primary calcined body made of the easily sintered low-purity alumina raw material powder can be substantially purified only at a higher temperature than the primary calcined body of the high-purity alumina powder. I understand. Therefore, it is necessary to select the purity of the raw material powder in consideration of the evaporation amount of alumina at high temperature. Further, even if the HC1 gas concentration in the heat treatment atmosphere is low, it is effective for purification, and alumina evaporation is suppressed in a dilute atmosphere containing HCl gas, and it is suitable when high-temperature heat treatment is required using a low-purity raw material powder. I understand.

Examples 51 to 62 and Comparative Example 8 100 parts by weight of the alumina powder used in Example 1, 80 parts by weight of deionized water, 1 part by weight of polyethylene oxide as a slip agent, and 2 parts by weight of polyvinyl alcohol as a binder were pot-milled. At that time, the mixture was dispersed for one day to prepare a slurry. The obtained slurry was granulated using a spray dryer, and the resulting granulated powder was molded into a cylinder having a diameter of 60 mm and a length of 110 mm at a pressure of 1 ton / cm ² using a rubber press. The columnar formed body was fired in the atmosphere at 1000 ° C. for 2 hours to obtain a primary fired body. The porosity of the obtained primary fired body was continuous, and the porosity was 50%. The primary fired body was processed into a cylinder having a diameter of 50 mm and a length of 100 mm. The primary fired body after processing was subjected to heat treatment in a hydrogen chloride atmosphere while changing the treatment temperature as shown in Table 5, to be purified and homogenized. Then
Impregnate Mg ions with an aqueous solution of magnesium salt so that the Mg content will be 100 ppm, and in a hydrogen atmosphere at 1850 ° C
And baked for 2 hours to sinter. Each of the obtained sintered bodies was cut into three parts, near the surface, in the middle and in the center, and the relative density of each part was measured and shown in Table 5. Further, a sintered body obtained by impregnating and sintering magnesium ion without heat treatment of the primary fired body was similarly divided into three and the relative densities thereof were measured, and the results are shown in Table 5.

From these results, the primary fired body made of only the raw material powder of α-alumina was 700 times in the HCl atmosphere.
It is clear that the heat treatment at a temperature of not less than 0 ° C. improves the relative density and homogeneity of the finally obtained sintered body, and can achieve densification and homogenization. Further, it can be seen that heat treatment in an HCl-containing atmosphere at a high temperature of 1100 ° C. or higher improves the homogeneity of the sintered body but decreases the density.

[0036]

[Table 5]

Example 63 and Comparative Example 9 The acid resistance of the alumina ceramics, which is the alumina sintered body obtained in Example 25 and Comparative Example 2, was evaluated. That is, 3
Each of the divided alumina ceramic pieces was processed with a diamond grinder and then immersed in a molten sodium borate salt kept at 1000 ° C. in a platinum crucible to remove the damage tank formed by the processing. Then, it was taken out from the molten salt of sodium borate and left to dry at room temperature. After drying, the solidified product of sodium borate on the surface of the ceramic was immersed in warm dilute hydrochloric acid and removed to obtain a sample ceramic piece. Each sample ceramic piece produced as described above was immersed in hydrofluoric acid at 30 ° C. for a predetermined time, and the elution amount was measured. Table 6 shows the results.

[0038]

[Table 6]

As is clear from the above-mentioned Examples and Comparative Examples, the alumina ceramics obtained by heat-treating the primary fired body in an atmosphere containing HCl gas and firing and sintering the same were compared with the ceramics sintered without heat treatment. However, it can be seen that the acid resistance is remarkably improved.

[0040]

The method for producing an alumina sintered body of the present invention comprises:
By incorporating a simple purification operation, it is possible to reduce the content of impurities such as alkali metals and to make it highly purified, and to obtain a high-density alumina sintered body that is densified as a whole and has excellent homogeneity. It is possible to manufacture aluminous ceramics suitable for a semiconductor manufacturing apparatus member that is strict in the generation of metal and a metal vapor laser tube that is exposed to a high temperature for a long time, which is extremely useful industrially. Furthermore, the alumina-based ceramics produced by the present invention is highly densified and has excellent acid resistance, and is versatile and highly industrial as a material for parts such as devices that are treated under various severe conditions.

Claims (4)

[Claims] 1. A method of manufacturing an alumina sintered body, comprising:
(1) A molding step of molding using alumina raw material powder,
(2) A primary baking step of removing the organic binder from the alumina molded body obtained in the molding step and baking while leaving open pores, (3) a heat treatment of heat-treating the primary baked body in an atmosphere containing hydrogen chloride gas A method of manufacturing an alumina sintered body, which comprises a step, and (4) a heat treatment step, followed by a sintering step of further firing and sintering. 2. The method for producing an alumina sintered body according to claim 1, wherein the alumina raw material powder is submicron fine powder, and the primary firing step is performed at 800 to 1000 ° C. 3. The method for producing an alumina sintered body according to claim 1, wherein the alumina raw material powder is micronized fine powder, and the primary firing step is performed at 1000 to 1200 ° C. 4. The method for producing an alumina sintered body according to claim 1, wherein the heat treatment step is performed at 700 to 1400 ° C.