JPH0248513B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a high-density composite sintered body containing aluminum nitride and boron nitride. (Prior art and problems to be solved by the invention) So-called non-oxide ceramics such as silicon nitride and silicon carbide are ceramics that have recently attracted particular attention as high-temperature, high-strength materials. Once sintered, it becomes extremely difficult to give it a desired shape through post-processing, and this problem is considered to be one of the major practical difficulties. For this reason, in the field of oxides, glass ceramics in which many fine mica crystals are precipitated in glass, and so-called mica ceramics obtained by hot-pressing natural or synthetic mica powder have recently been developed. These ceramics are machinable ceramics that can be cut and ground with ordinary tools, and are useful as ceramics with improved workability.
Furthermore, among non-oxidizing ceramics, hexagonal boron nitride has a layered graphite structure, so its sintered body can be cut and ground with ordinary tools, and has been in practical use for a long time. However, although the above-mentioned various machinable ceramics have the advantage of being easy to process, they also have fundamental drawbacks such as being "soft" and "weak", so they cannot be widely used as ceramics. I'm not used to it. As a result of intensive research on non-oxide-based machinable ceramics, the present inventors discovered a novel material consisting of aluminum nitride, boron nitride, and at least one metal compound selected from Group A metals or Group A metals of the periodic table. We have already developed and proposed a composite sintered body. (Japanese Unexamined Patent Publication No. 195059/1983) The composite sintered body is tightly packed with crystal grains whose mechanical fracture surfaces are polygonal, and thin layered crystals are formed on part or all of the grain interface of the packed particles. It is a sintered body composed of grains, which can be cut at high speed with ordinary tools, and has a bending strength of 35 kg/mm ² or more depending on the composition, which is comparable to high-strength ceramics. It is a revolutionary ceramic with As a result of intensive research into the manufacturing method of the composite sintered body, the present inventors found that aluminum nitride powder, boron nitride powder, and at least one metal compound selected from Group A metals or Group A metals of the periodic table. When firing a mixed powder to obtain a composite sintered body, adjusting the average heating rate in a specific temperature range depending on the shape of the composite sintered body can significantly improve the homogeneity of the composite sintered body. The present invention was completed based on the findings that (Means for solving the problem) That is, the present invention provides a mixed powder containing aluminum nitride powder, boron nitride powder, and at least one metal or metal compound selected from Group A metals or Group A metals of the periodic table. When obtaining a composite sintered body by firing, the average speed R (unit: °C/min) in the temperature range of at least 1400 to 1750 °C is determined by the following formula 0.1
S/V≦R≦2.0×S/V (where, S is the surface area of the composite sintered body (unit: cm ² ), and V is the volume of the composite sintered body (unit: cm ³ ). This is a method for producing a composite sintered body, which is characterized by In order to obtain a composite sintered body, the average particle size of the raw material aluminum nitride powder (mean particle size of aggregated particles measured with a centrifugal particle size distribution analyzer, such as Horiba's CAPA500) must be 5 μm or less. Preferably, the powder is 3 μm or less, most preferably 2 μm or less. Particularly suitable is a powder containing 70% by volume or more of particles of 3 μm or less. AlN if you want to get the body
Aluminum nitride powder with a nitrogen content (calculated from the nitrogen content of the AlN powder) of 90% by weight or more is preferably used, more preferably 94% by weight or more, and even more preferably 97% by weight or more. will be adopted. In addition, when obtaining a composite sintered body with high thermal conductivity, the oxygen content is 3% by weight or less, preferably 1.5% by weight.
It is preferable to use the following aluminum nitride powder. The aluminum nitride powder preferably used in the present invention has an average particle diameter of 2 μm or less, contains 70% by volume or more of particles of 3 μm or less, has an oxygen content of 3.0% by weight or less, and has an aluminum nitride composition. When is AlN, the cationic impurity contained is
Aluminum nitride powder containing 0.5% by weight or less. When such aluminum nitride powder is used, it is preferably used in the present invention because it can improve the thermal conductivity of the resulting composite sintered body and suppress a decrease in mechanical strength at high temperatures. In particular, powders with an average particle diameter of 2 μm or less, and particles of 3 μm or less
Contains 70% by volume or more, oxygen content 1.5% by weight or less,
In addition, when using aluminum nitride powder containing cationic impurities of 0.3% by weight or less when the aluminum nitride composition is AlN, the thermal conductivity of the obtained composite sintered body is improved and the mechanical properties at high temperatures are improved. Since it has a remarkable effect of suppressing a decrease in strength, it is particularly preferably used in the present invention. The method for producing the aluminum nitride powder is not particularly limited, and any known method can be used. The boron nitride powder is not particularly limited, and any powder can be used. Typical examples that are generally suitably used are as follows. Generally, the boron nitride powder preferably used has a boron nitride purity of 99.0% by weight or more and an average particle size of 5 μm or less. Further, the method for producing the boron nitride powder is not particularly limited, and any known method can be employed. Further, at least one metal or metal compound selected from the group a metals and group a metals of the periodic table (hereinafter sometimes simply referred to as a sintering aid).
is not particularly limited, and any known material can be used. Typical examples that are particularly preferably used are as follows. Generally, beryllium, calcium, strontium, barium, etc. are suitable as the metal of Group a of the periodic table. Yttrium or lanthanum group metals are preferably used as metals belonging to group a of the periodic table. More specifically, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium,
Dysprosium, holmium, erbium, thulium, ytterbium, lutetium, etc., particularly yttrium, lanthanum, cerium, neodymium, etc. are suitable. These periodic table group a or group a
The metal compound of the group is not particularly limited, and the metal compounds known as sintering aids for aluminum nitride powder and/or boron nitride powder can be used. In general, compounds such as nitrates, carbonates, aluminates, halides, and oxides are preferably used. Further, the composition ratio of each component constituting the composite sintered body of the present invention can be selected from a wide range depending on the properties required of the composite sintered body. Generally, for example, 60 to 95 parts by weight of aluminum nitride powder, preferably 70 to 95 parts by weight,
Based on 90 parts by weight, the amount of boron nitride powder may be selected in the range of 5 to 40 parts by weight, preferably 10 to 30 parts by weight. In addition, the amount of at least one metal or metal compound selected from group a metals and group a metals of the periodic table may be selected in consideration of the temperature increase rate during firing, which will be described later, but it is usually nitrided. It is preferable to add the powder in an amount of 0.01 to 10% by weight, preferably 0.05 to 5% by weight, calculated as the highest valence oxide of the metal, based on the total amount of aluminum powder and boron nitride powder. It should be noted that the sintering aid does not necessarily have to be added to the aluminum nitride powder or boron nitride powder, and the raw materials for the production of the aluminum nitride powder or boron nitride powder should be prepared in advance so that the sintering aid is included in the production of the aluminum nitride powder or boron nitride powder. It may be mixed inside. Of course, in addition to the above-mentioned raw materials, binders, peptizers, plasticizers, and the like may be added and mixed as necessary. The mixing of the aluminum nitride powder, boron nitride powder, and sintering aid in the present invention is not particularly limited, and may be dry mixing or wet mixing. A particularly preferred embodiment is wet mixing, ie mixing in the wet state using a liquid dispersion medium. The liquid dispersion medium is not particularly limited, and commonly used water, alcohols, hydrocarbons, or mixtures thereof are preferably used. In particular, methanol, ethanol,
Lower alcohols having 4 or less carbon atoms, such as butanol. In addition, the wet mixing device used for the above mixing is not particularly limited and any known device may be used. However, when used for mixing particularly high purity aluminum nitride powder and boron nitride powder, It is preferable to choose one that does not produce any impurity components. For example, the material may be aluminum nitride itself, a plastic material such as polyethylene, polyurethane, nylon, or a material coated with these materials. Specific aspects of firing in the present invention include:
The mixed powder obtained by adding a sintering aid to the aluminum nitride powder and boron nitride powder is formed into the desired shape by an appropriate molding method, such as dry pressing, rubber pressing, extrusion, injection, doctor blade sheet molding, etc. After molding it into a suitable crucible,
Place it on top of pod wood, etc., under a non-oxidizing atmosphere of vacuum or atmospheric pressure, for example, under an atmosphere of nitrogen gas, helium gas, argon gas, etc.
One example is a method of firing at high temperature under nitrogen gas pressure of about 100 atmospheres. Alternatively, the mixed powder may be directly applied in a non-oxidizing atmosphere at vacuum or atmospheric pressure while applying mechanical pressure of about 20 to 500 kg/ ^cm2 , or
The method used is firing at high temperatures under nitrogen gas pressure of about 100 atmospheres. In the case of a non-oxidizing atmosphere of vacuum or atmospheric pressure, the firing temperature is preferably 1750 to 2100°C, preferably 1800 to 2050°C.
Under nitrogen gas pressure of ~100 atmospheres, a temperature of 1750 to 2400°C, preferably 1800 to 2300°C is suitably employed. The temperature in the present invention is determined by measuring the surface of the graphite crucible containing the mixed powder using a radiation thermometer.
This is a value compensated to indicate the gas temperature inside the graphite crucible. The most important firing condition during the firing is the temperature increase rate, especially when the average temperature increase rate R (unit: °C/min) in the temperature range of 1400 to 1750 °C is 0.1 × S / V ≦ R ≦ 2.0 ×S/V preferably 0.2×S/V≦R≦1.5×S/
V (However, S is the surface area of the composite sintered body (unit: cm ² ), V
It is important to raise the temperature so as to satisfy the volume of the composite sintered body (unit: cm ³ ). Particularly, when the S/V of the composite sintered body is 4 or less, performing firing to satisfy the above conditions brings about very good results. Here, the surface area S and volume V of the composite sintered body are values determined for the shape assuming that the composite sintered body having the target composition is completely densified to the theoretical density. The actual density of a sintered body is usually smaller than the theoretical density, so when determining the average temperature increase rate, assume in advance the final shape of the composite sintered body when the theoretical density is reached, and It is better to calculate S and V based on . If the above average temperature increase rate is too fast, the balance between the rate at which pores escape through grain boundaries while grains grow during sintering and the rate at which pores are confined within the grains due to grain growth will be affected. It is difficult to form a dense and uniform sintered body. In addition, if the average temperature increase rate is too fast, the temperature difference between the surface and the inside of the object to be fired will increase, and oxides added as sintering aids will tend to be unevenly distributed inside the composite sintered body. This is not preferable in obtaining a uniform sintered body. This kind of negative impact is
Generally, the smaller the S/V of the composite sintered body, the larger the S/V becomes, especially when the S/V is 4 or less. On the other hand, if the average temperature increase rate is too slow, the sintering aid will volatilize before densification has sufficiently progressed.
There is a tendency that a dense sintered body cannot be obtained. Note that the above-mentioned average temperature increase rate has an optimum range depending on the type and amount of the sintering aid added, so it is desirable to appropriately determine it depending on the sintering aid. Furthermore, when the type and amount of sintering aids are the same, the above average temperature increase rate is generally set higher for normal pressure sintering or gas pressure sintering than for hot press sintering. It's good to do that. In determining the temperature increase rate, it is important to ensure that the temperature is raised so that there is no excessive volatilization of the sintering aid during the temperature increase process, and that the sintering aid component is not unevenly distributed after sintering. It is about selecting the conditions. As for the above heating method, it is industrially preferable to set a single heating rate in the temperature range of 1,400 to 1,750°C, but there are also other methods such as multiple speed gradients or continuously changing speeds. It is also possible to set up a heating program with a gradient. Further, the rate of temperature increase until reaching 1400°C is not particularly limited, and any rate of temperature increase may be used. However, from the standpoint of industrial productivity, it is generally preferable to shorten the overall firing time by increasing the temperature increase rate faster than the above-mentioned average rate. On the other hand, when it is necessary to further raise the temperature from 1750° C. to the firing temperature, the rate of temperature increase is not particularly limited, but it is generally desirable to maintain the above-mentioned average rate of temperature increase. Now, after raising the temperature in this manner, firing is then preferably performed at a firing temperature of 1750 to 2400°C. Firing time varies depending on firing temperature, type and amount of sintering aid, and average heating rate, but usually
The time period is selected from the range of 30 minutes to 72 hours, preferably 3 hours to 24 hours. In addition, the smaller the S/V of the composite sintered body mentioned above, the longer the firing time is generally preferable. If the S/V of the composite sintered body is extremely small, the firing time is longer than the above range. Sometimes it takes. (Effects) The composite sintered body obtained by the method of the present invention exhibits high density and high thermal conductivity, and also has excellent mechanical strength and can be cut with ordinary tools. There is. As mentioned above, the heating rate conditions for producing a composite sintered body with high density and high thermal conductivity are determined by the system in which a specific sintering aid is added to the aluminum nitride powder and boron nitride powder. The fact that the surface area of a solid body is related to the value divided by its volume by an extremely simple formula was only revealed by the present inventors after a detailed study of numerous experimental results, and it was not previously known. This was something that could not have been predicted from the current technology. Conventionally, when the size, shape, etc. of a composite sintered body changes, the only way to determine the heating rate conditions for firing it is through trial and error. Being able to set the heating rate conditions is revolutionary, and its industrial value is truly enormous. The composite sintered body obtained by the manufacturing method of the present invention can be used without particular limitation in fields of application in which hexagonal boron nitride sintered bodies have conventionally been used. In addition, the composite sintered body obtained by the present invention is not only suitable for use in the field of conventionally known machinable ceramics, but also has excellent mechanical strength as described above. For,
It can also be used in completely new fields of application where conventional machinable ceramics could not be used, particularly in mechanical parts that require strength. Specific uses of the above composite sintered bodies include semiconductor substrates and heat sinks that take advantage of their electrical insulation and thermal conductivity properties; crucibles, boats, pipes, and valves that take advantage of their corrosion resistance, heat resistance, and strength properties. , jigs, etc. In addition, machinability, strength,
Utilizing its lubricity and other properties, it is suitably used for bearings, guide surfaces, etc., and is also used as molds for injection molding of plastics and the like. EXAMPLES The present invention will be specifically illustrated below with reference to Examples, but the present invention is not limited to these Examples. Example 1 Particles with an average particle size of 1.31 μm and 3 μm or less accounted for 90% by volume, and 80 parts by weight of aluminum nitride powder had the composition shown in Table 1, and the ratio of particles with an average particle size of 2.5 μm and 5 μm or less was 95% by weight. 20 parts by weight of hexagonal boron nitride powder with a purity of 99.5% by volume and 0.2 parts by weight of calcium aluminate (3CaO Al ₂ O ₃ ),
Using a nylon pot and a nylon-coated ball, the mixture was uniformly mixed in a ball mill using ethanol as a dispersion medium. After drying the obtained mixed powder, about 1000g
Hexagonal boron nitride powder was placed in a graphite mold with an inner diameter of 100 mm and coated on the inner wall, and the mold was fired at a temperature of 2000°C for 18 hours in nitrogen gas at about 1 atm while being uniaxially pressurized at 200 Kg/cm ² . The theoretical density of the obtained composite sintered body is 3.00 g/cm 3 using the theoretical densities of 3.26 g/cm ³ and 2.27 g/cm ³ of aluminum nitride and hexagonal boron nitride, respectively.
It is calculated as cm ³ . If the composite sintered body reaches its theoretical density, its outer dimensions will be 100mmφ x 42mm, so
The value of S/V is 0.88. Therefore, we set the temperature increase rate from 1400℃ to 2000℃ to 1℃/min, and
The temperature was raised at a rate of 5°C/min. The temperature decreasing rate was 2° C./min, and the sintered body was taken out after cooling to room temperature. The external dimensions of the sintered body are 100mmφ×
It was 43mm. Table 1 Analysis of aluminum nitride powder AlN content 97.8% Element Content Mg <5 (ppm) Cr 21 ( ) Si 125 ( ) Zn 9 ( ) Fe 20 ( ) Cu <5 ( ) Mn 5 ( ) Ni 27 ( ) Ti <5 ( ) Co <5 ( ) Al 64.8 (wt%) N 33.4 ( ) O 1.1 ( ) C 0.11 ( ) The obtained sintered body is white. , the density was 2.96 g/cm ³ . When this sintered body was cut, it was found that the inside was white and even. Further, when the amount of oxygen was measured by charged particle activation analysis, it was found to be 0.4% by weight. A columnar test piece of approximately 3 mm square was cut out from this sintered body so that the span could be taken in the direction perpendicular and parallel to the hot press axis.
After finishing with 1500 grit sandpaper, the three-point bending strength was measured at a crosshead speed of 0.5 mm/min and a span of 20 mm. As a result, the average strength when the span is taken perpendicular to the hot press axis is 38
Kg/mm ² , and the average strength when the span was taken in the direction parallel to the hot press axis was 18 Kg/mm ² . Also, from the same sintered body, the diameter is about 10 mm and the thickness is 2.5 mm.
A disk-shaped sample was cut out, and the thermal conductivity at room temperature was determined by the laser flash method.The thermal conductivity in the direction perpendicular to the hot press axis was 100 W/mK, and in the direction parallel to the hot press axis was 85 W/mK. Furthermore, when the workability of the obtained composite sintered body was investigated, it was found that it was easy to perform both drilling with a carbide drill and high-speed cutting with a carbide bit, and was found to be free-cutting. Comparative Example 1 A test was carried out in the same manner as in Example 1 except that the temperature increase rate from 1400°C to 2000°C was changed to 5°C/min. The appearance of the obtained sintered body was similar to that of the sintered body obtained in Example 1, but when it was cut and the inside was examined, it was found that the outer part of about 5 mm was white, but the inner part was black. I found out what happened. As a result of analysis using an X-ray microanalyzer, the black part of the composite sintered body was
It was found that there was a large amount of Ca, and it was assumed that the black color was caused by the sintering aid being unevenly distributed inside the sintered body. Furthermore, when the amount of oxygen was measured by charged particle activation analysis, it was found to be 0.5% by weight in the white part, while it was 1.5% by weight in the black part, which was considerably higher. Further, when the three-point bending strength was measured in the same manner as in Example 1, it was 23 Kg/mm ² when the span was taken in the direction perpendicular to the hot press axis. Furthermore, as a result of measuring the thermal conductivity, the white part was 82W/mK, while the black part was 82W/mK.
It was found that the black part of the composite sintered body was not only colored but also had poor physical properties due to unevenly distributed sintering aid and oxygen. Example 2 After drying the mixed powder obtained in Example 1,
Approximately 250g was placed in the same graphite mold as in Example 1, and 200g
In nitrogen gas at about 1 atm while uniaxially pressurizing at Kg/cm ²
It was baked at a temperature of 1900°C for 6 hours. If the obtained composite sintered body reaches the theoretical density, its outer dimensions will be 100 mmφ x 11 mm, so the value of S/V will be 2.2. Therefore, the temperature increase rate from room temperature to 1400°C was set to 10°C/min, and various values shown in Table 2 were adopted as the temperature increase rate from 1400°C to 1900°C. After firing, the sintered body was taken out in the same manner as in Example 1, and the outer dimensions were 100 mmφ×11 mm. The properties of the obtained composite sintered body are also shown in Table 2. still,
No. 4 is a comparative example.

[Table] ** For the inner black part, the values in the direction perpendicular to the hot press axis are shown.
*** Measured in the same manner as in Example 1.
Example 3 85 parts by weight of the same aluminum nitride powder used in Example 1 and 15 parts by weight of boron nitride powder,
1 part by weight of yttrium oxide was mixed in the same manner as in Example 1. After drying the obtained mixed powder, about 290 g was filled into a rubber mold and hydrostatically pressed at a pressure of 2000 Kg/cm ² to form a cylindrical molded body with an outer diameter of 60 mm and a length of 60 mm. This compact was placed in a graphite crucible whose inner wall was coated with hexagonal boron nitride powder, and fired at a temperature of 1900° C. for 12 hours in nitrogen gas at about 1 atm. The theoretical density of the obtained composite sintered body is calculated as 3.06 g/cm ³ in the same manner as in Example 1. If the composite sintered body reaches its theoretical density, its external dimensions are 49
Since mmφ×50mm, the value of S/V is 1.2. Therefore, the temperature increase rate from 1400℃ to 1900℃ was set at 1.5℃/min.
The temperature was raised from room temperature to 1400°C at a rate of 10°C/min. The temperature decreasing rate was 2° C./min, and the sintered body was taken out after cooling to room temperature. The external dimensions of the sintered body are 50mmφ x 51mm
It was hot. This sintered body is white and has a density of 2.90g/
It was warm at ^cm3 . Furthermore, when this sintered body was cut, it was found that the inside was white and even.
Further, the oxygen content was 0.6% by weight. A columnar test piece approximately 3 mm square was cut out from this sintered body, and its three-point bending strength was measured in the same manner as in Example 1, and the average strength was 32 Kg/mm ² . Further, the thermal conductivity measured in the same manner as in Example 1 was 92 W/mK. Furthermore, when the workability of this sintered body was examined, it was found that it had free machinability similar to that obtained in Example 1. Example 4 80 parts by weight of the same aluminum nitride powder used in Example 1, 20 parts by weight of boron nitride, and 2 parts by weight of calcium oxide were mixed in the same manner as in Example 1. After drying the obtained mixed powder, about 2 g was placed in a graphite mold with an inner diameter of 20 mm whose inner wall was coated with hexagonal boron nitride powder, and heated at 1850°C in nitrogen gas at about 1 atm while pressurizing at 150 Kg/cm ² . It was baked at a temperature of 4 hours. Furthermore, if the obtained composite sintered body reaches the theoretical density, its outer dimensions will be 20 mmφ x 2.1 mm, so
The value of S/V is 12. Therefore, the temperature increase rate from 1400℃ to 1850℃ is set to 15℃/min, and the temperature rises from room temperature to 1400℃.
Until then, the temperature was raised at 20°C/min. After firing, the sintered body was taken out in the same manner as in Example 1, and the outer dimensions were 20 mmφ×2.1 mm. The sintered body was white and had a density of 2.99 g/cm ³ . Furthermore, when this sintered body was cut, it was found that the interior was white and even. Further, the physical properties of this sintered body were similar to those of the sintered body obtained in Example 1. Example 5 80 parts by weight of the same aluminum nitride used in Example 1, 20 parts by weight of boron nitride, and 3 parts by weight of strontium oxide were mixed in the same manner as in Example 1. After drying the obtained mixed powder, approx.
1.9 g was filled into a mold and uniaxially pressed at a pressure of 1500 Kg/cm ² to form a plate-shaped molded product of 31 mm x 31 mm x 1.2 mm. This compact was sandwiched between graphite plates coated with hexagonal boron nitride powder and fired at a temperature of 1900° C. for 12 hours in nitrogen gas at about 8 atmospheres. If the obtained composite sintered body reaches the theoretical density, its outer dimensions will be 25 mm x 25 mm x 1 mm, so
The value of S/V is 22. Therefore, the temperature was raised at a rate of 15°C/min from 1400°C to 1900°C, and at 25°C/min from room temperature to 1400°C. After firing, the sintered body was taken out in the same manner as in Example 1 and had external dimensions of 25 mm x 25 mm x 1 mm. The sintered body was white and had a density of 2.96 g/cm ² . When this sintered body was cut, it was found that the inside was white and even. A test piece approximately 3 mm wide was cut out from this sintered body.
When finished with 1500 grit sandpaper and measured for three-point bending strength with a crosshead bead of 0.5 mm/min and a span of 10 mm, the average strength was 35 Kg/mm ² . In addition, a disk-shaped sample with a diameter of 10 mm was cut from the same sintered body, and its thermal conductivity at room temperature was determined by the laser flash method, and it was 88 W/mK. The oxygen content of the obtained composite sintered body was measured by charged particle activation analysis and was found to be 0.35%.
Furthermore, when the workability of the composite sintered body was examined, it was found that it was free-cutting, similar to that obtained in Example 1. Example 6 In Example 5, strontium oxide was changed to lanthanum oxide, and the same procedure as in Example 5 was carried out except for that. The obtained sintered body is white inside, and the outer dimensions and
The density was also similar to that obtained in Example 5. Further, when the physical properties were measured in the same manner as in Example 5, the bending strength was 37 Kg/mm ² and the thermal conductivity was 8 W/mK. The oxygen content determined in the same manner as in Example 5 was 0.42%. Furthermore, when the workability of the composite sintered body was examined, it was found that it had free machinability similar to that obtained in Example 1.

Claims (1)

[Claims] 1. Composite sintering by sintering a mixed powder containing aluminum nitride powder, boron nitride powder, and at least one metal or metal compound selected from Group A metals or Group A metals of the periodic table. When obtaining solids, the average temperature increase rate R (unit: °C/min) in the temperature range of at least 1400 to 1750 °C is determined by the following formula: 0.1×S/V≦R≦2.0×S/V (however, S is the surface area (unit: cm ² ) of the composite sintered body, and V is the volume (unit: cm ³ ) of the composite sintered body. How the body is manufactured.