JP2018002556A - Ceramic composite, radome for missile, method for producing ceramic composite, and method for producing radome for missile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ceramic composite excellent in both of thermal impact resistance and electric wave directivity and used for a radome for a missile.SOLUTION: Provided is a ceramic composite 10 used for a radome for a missile. The ceramic composite 10 contains: a ceramic sintered compact 20 essentially consisting of SiN; and a metal oxide layer 30 formed on at least either surface 20a of the ceramic sintered compact 20. The thickness of the metal oxide layer 30 is 10-500 μm. The metal oxide layer 30 includes an amorphous phase.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ceramic composite used for a flying object flying toward a set target, a radome for a flying object, a method for manufacturing a ceramic composite, and a method for manufacturing a radome for a flying object.

  A flying object that flies toward a set target is equipped with an antenna, which is an electronic device that measures the distance and direction to the target, and a radome at the tip to protect the electronic device from air resistance during flight. Is installed. Since the flying object flies at supersonic speed, it undergoes rapid heating, so-called aerodynamic heating, due to friction with air during the flight. In particular, the radome installed at the tip of the flying object is heated to a temperature of 1000 ° C. or more by aerodynamic heating and receives thermal stress. Therefore, the material used for the radome is required to have heat resistance and thermal shock resistance. In addition, the flying object needs to transmit and receive radio waves via the radome in order to measure the distance and direction to the target during flight. Therefore, the material used for the radome is also required to have radio wave transparency.

As a material satisfying the required performance of such a radome, cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ), which is an oxide ceramic, is generally used. However, in recent years, the flying speed of the flying object has increased with the improvement of the flying object's performance, and when a conventional oxide ceramic is used for the radome of the flying object flying at a higher speed than before, the thermal shock However, there is a problem that cracking occurs due to thermal stress generated by aerodynamic heating.

Therefore, a ceramic material containing silicon nitride (Si ₃ N ₄ ) has been proposed as a ceramic material that is more excellent in thermal shock resistance than conventional oxide ceramics (see Patent Document 1).

International Publication No. 2013/124871

  However, the ceramic material containing silicon nitride proposed in Patent Document 1 is oxidized from the surface of the ceramic material containing silicon nitride when the flying object is heated by aerodynamic heating during flight. When such oxidation occurs during flight, the dielectric constant of the radome changes, so the refractive index when radio waves pass through the radome changes, and radio wave directivity, that is, the position accuracy of the target to be detected deteriorates. There is a problem of end.

  This invention is made | formed in view of the above, Comprising: It aims at obtaining the ceramic composite body which can be used for the radome for flying bodies which is excellent in both a thermal shock resistance and radio wave directivity.

In order to solve the above-described problems and achieve the object, the present invention is a ceramic composite used for a radome for a flying object, and a ceramic sintered body mainly composed of Si ₃ N ₄ , and ceramic sintering A metal oxide layer formed on at least one surface of the body, the thickness of the metal oxide layer is not less than 10 μm and not more than 500 μm, and the metal oxide layer contains an amorphous phase It is characterized by doing.

  According to the present invention, there is an effect that both thermal shock resistance and radio wave directivity are excellent.

1 is a perspective view of a ceramic composite according to Embodiment 1 of the present invention. Sectional schematic diagram of the flying object provided with the radome for flying object which concerns on Embodiment 2 of this invention

  Hereinafter, a ceramic composite according to an embodiment of the present invention, a flying radome, a method for manufacturing a ceramic composite, and a manufacturing method for a flying radome will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a perspective view of a ceramic composite according to Embodiment 1 of the present invention. In general, the thermal shock resistance of a ceramic material is mainly related to the bending strength and elastic modulus among the thermal expansion coefficient, thermal conductivity, and mechanical strength of the ceramic material. The lower the modulus and the elastic modulus, the better. Radio wave directivity is related to the refractive index due to the dielectric constant of the ceramic material that transmits radio waves. When the ceramic composite is oxidized by aerodynamic heating during flight, the dielectric constant changes and the refractive index changes. Changes, the directivity of the radio wave is deteriorated.

Thus, as a result of intensive studies to solve the above problems, the present inventors have found a ceramic sintered body mainly composed of silicon nitride (Si ₃ N ₄ ) having a low coefficient of thermal expansion and high mechanical strength. It has been found that by forming a metal oxide layer having an antioxidant effect on the surface of a ceramic sintered body in a specific thickness range, it is possible to achieve both improved thermal shock resistance and improved radio wave directivity. Invented.

The ceramic composite 10 according to Embodiment 1 is a ceramic composite used for a flying object radome. As shown in FIG. 1, the ceramic composite 10 includes a ceramic sintered body 20 containing Si ₃ N ₄ as a main component. Further, the ceramic composite 10 includes a metal oxide layer 30 formed on at least one surface 20 a of the ceramic sintered body 20.

The ceramic sintered body 20 mainly composed of Si ₃ N ₄ in the ceramic composite 10 according to the first embodiment has characteristics of low thermal expansion coefficient and high mechanical strength, and is known as a heat-resistant impact ceramic. Compared with silica or cordierite which is an oxide ceramic, the thermal conductivity is also high. Therefore, the ceramic sintered body 20 has excellent thermal shock resistance. Furthermore, the ceramic sintered body 20 mainly composed of Si ₃ N ₄ of Embodiment 1 preferably contains boron nitride (BN). The ceramic sintered body 20 is composed of boron nitride, which has a low elastic modulus and high thermal conductivity, combined with Si ₃ N ₄ to form a composite, thereby reducing the elastic modulus and maintaining the thermal conductivity while keeping the thermal expansion coefficient low. The rate can be increased. Thereby, the ceramic sintered body 20 can further improve the thermal shock resistance of the ceramic composite 10.

On the other hand, the oxidation of the ceramic sintered body 20 containing Si ₃ N ₄ as a main component at a high temperature proceeds mainly due to oxygen diffusing from the surface 20a into the ceramic. Therefore, if the diffusion of oxygen from the surface 20a of the ceramic sintered body 20 can be prevented, the oxidation can be suppressed. The ceramic composite 10 of the first embodiment includes the metal oxide layer 30 formed on the surface 20a of the ceramic sintered body 20 as an antioxidant film having a function of preventing the diffusion of oxygen. Even if the temperature is increased due to aerodynamic heating, the ceramic sintered body 20 is not oxidized, and variation in the dielectric constant can be suppressed. Thereby, the directivity of the radio wave passing through the radome is improved. Furthermore, since the ceramic composite 10 contains an amorphous phase in the metal oxide layer 30, the dense metal oxide layer 30 is formed, so that the oxidation suppression effect is improved. In addition, since the metal oxide layer 30 formed on the surface 20a of the ceramic sintered body 20 is mainly composed of a metal oxide having a high insulation resistance, the dielectric loss that is a factor that deteriorates radio wave transmission is small. . Therefore, the metal oxide layer 30 formed on the surface 20a of the ceramic sintered body 20 does not hinder radio wave permeability of radio waves that pass through the radome.

  In the ceramic composite 10 of the first embodiment, the thickness of the metal oxide layer 30 formed on the surface 20a of the ceramic sintered body 20 is not less than 10 μm and not more than 500 μm. When the thickness of the metal oxide layer 30 is less than 10 μm, a pinhole which is a defect is easily generated in the metal oxide layer 30 and oxygen is diffused through the defect, so that the effect of preventing oxidation is small. That is, when the thickness of the metal oxide layer 30 is less than 10 μm, the radio wave directivity of the ceramic composite 10 is lowered.

On the other hand, when the thickness of the metal oxide layer 30 exceeds 500 μm, it becomes easy to peel off at the interface between the ceramic sintered body 20 mainly composed of Si ₃ N ₄ and the metal oxide layer 30, and a crack occurs at the interface. It becomes easy. Furthermore, when the metal oxide layer 30 is made of a material having low thermal conductivity, if the thickness of the metal oxide layer 30 exceeds 500 μm, the temperature difference between the surface and the inside of the ceramic composite 10 increases, Cracks due to stress are likely to occur. That is, when the thickness of the metal oxide layer 30 exceeds 500 μm, the thermal shock resistance of the ceramic composite 10 is lowered.

In the ceramic composite 10 according to the first embodiment, the metal oxide layer 30 on the surface 20a of the ceramic sintered body 20 includes R ₂ Si ₂ O ₇ which is a kind of rare earth silicate and boron, where R is a rare earth element. It preferably contains an amorphous phase. Since the amorphous phase containing R ₂ Si ₂ O ₇ (R = rare earth element) and boron has the same thermal expansion coefficient as silicon nitride, the interface between the ceramic sintered body 20 and the metal oxide layer 30. It is difficult to generate thermal stress at the point, and the occurrence of peeling and cracking when a thermal shock is applied is suppressed. Here, the R ₂ Si ₂ O ₇ (R = rare earth element) is not particularly limited, but Y ₂ Si ₂ O ₇ , Lu ₂ Si ₂ O ₇ , or Yb ₂ Si ₂ O ₇ is used. be able to. Further, the amorphous phase containing boron is not particularly limited, but borosilicate glass, aluminoborosilicate glass, or Pyrex (registered trademark) can be used.

In the ceramic composite 10 of the first embodiment, the content of Si ₃ N ₄ and boron nitride in the ceramic sintered body 20 is 80% by mass or more and 98% by mass in total of Si ₃ N ₄ and boron nitride. Hereinafter, it is preferably 81% by mass or more and 97% by mass or less, more preferably 82% by mass or more and 96% by mass or less, and further preferably 83% by mass or more and 95% by mass or less. When the total content of Si ₃ N ₄ and boron nitride is less than 80% by mass or exceeds 98% by mass, the thermal shock resistance of the ceramic composite 10 is not sufficiently improved. Further, if the total content of Si ₃ N ₄ and boron nitride exceeds 98 mass%, the ceramic composite 10 is not sufficiently densified, and the mechanical strength of the ceramic composite 10 is reduced.

In the ceramic composite 10 of the first embodiment, the mass ratio of Si ₃ N ₄ and boron nitride in the ceramic sintered body 20 is in the range of 95: 5 to 70:30, preferably 90:10 to 70:30. Within the range of 88:12 to 72:28, more preferably within the range of 86:14 to 74:26, and even more preferably within the range of 85:15 to 75:25. If the proportion of boron nitride is too small, the ceramic composite 10 cannot sufficiently increase the thermal conductivity of the ceramic composite 10. As a result, when the ceramic composite 10 is used for a flying object radome, the temperature difference between the surface and the inside of the flying object radome becomes large, and cracks or cracks occur due to thermal stress. That is, the thermal shock resistance of the ceramic composite 10 is not sufficiently improved. On the other hand, when the proportion of boron nitride is too large, the ceramic composite 10 has a markedly reduced mechanical strength and does not sufficiently improve the thermal shock resistance. When the metal oxide layer 30 is not provided on the surface 20a of the ceramic sintered body 20, since the ceramic sintered body 20 is easily oxidized to the inside, the proportion of boron nitride is increased in order to prevent a decrease in thermal conductivity. There is a need to. However, since the ceramic composite 10 of the first embodiment includes the metal oxide layer 30 formed on the surface 20a of the ceramic sintered body 20, heat conduction caused by oxidation of the ceramic sintered body 20 to the inside. The effect | action which suppresses a rate fall is produced. Therefore, even in a composition with a small proportion of boron nitride, both impact resistance and radio wave directivity can be excellent.

The ceramic sintered body 20 in the ceramic composite 10 of the first embodiment can contain a sintering aid for densification in addition to Si ₃ N ₄ and boron nitride. The sintering aid is not particularly limited, and those known in the technical field can be used. As the sintering aid, one or a combination of two or more of rare earths yttrium, aluminum, titanium, magnesium oxide, silicon oxide, aluminum nitride, and titanium nitride can be used. . In addition, the sintering aid is preferably a rare earth oxide from the viewpoint of the thermal shock resistance and mechanical strength of the ceramic composite 10.

The content of the sintering aid of the ceramic sintered body 20 in the ceramic composite 10 of the embodiment is not particularly limited, but is preferably 2% by mass or more and 20% by mass or less, more preferably 3% by mass or more. And 19% by mass or less, more preferably 4% by mass or more and 18% by mass or less, and most preferably 5% by mass or more and 17% by mass or less. When the content of the sintering aid is less than 2% by mass, the ceramic composite 10 may not be sufficiently densified. On the other hand, when the content of the sintering aid exceeds 20% by mass, the content of Si ₃ N ₄ and boron nitride decreases, so that the thermal shock resistance of the ceramic composite 10 may not be sufficiently improved.

  The ceramic composite 10 according to the embodiment can contain various components known in the art in order to obtain a desired effect set in advance in addition to the above components. The content of the component in the ceramic composite 10 of the embodiment is not particularly limited as long as it does not inhibit the effects of the present invention.

  The porosity of the ceramic composite 10 is related to the mechanical strength and thermal shock resistance of the ceramic composite 10. That is, when the porosity of the ceramic composite 10 is too high, the voids are connected inside the ceramic composite 10, resulting in a decrease in the mechanical strength of the ceramic composite 10. In addition, when the porosity of the ceramic composite is too low, the elastic modulus of the ceramic composite 10 increases, and as a result, the thermal shock resistance of the ceramic composite 10 decreases. Therefore, the porosity of the ceramic composite 10 of the first embodiment is preferably 30% or less, more preferably 5% or more and 29% or less, from the viewpoint of obtaining desired mechanical strength and thermal shock resistance set in advance. More preferably, it is 7% or more and 28% or less.

Here, in this specification, the “porosity” of the ceramic composite 10 is calculated from the following formula 1 using measured values of the weight and dimensions (vertical, horizontal, and height) of the ceramic composite cut into a rectangular parallelepiped shape. be able to.
Porosity = {1- [W _drying / (L × W × T) / ρ _theory ]} × 100 Formula 1

In Formula 1, W _drying is the weight (g) of the ceramic composite 10 dried at 150 ° C. for 2 hours, and L, W, and T are the vertical, horizontal, and height of the rectangular parallelepiped ceramic composite, respectively. The ρ _theory is the theoretical density (g / cm ³ ) of the ceramic composite 10.

In the ceramic composite 10 of Embodiment 1, Si ₃ N ₄ and boron nitride exist as particles. From the viewpoint of improving the thermal shock resistance and grinding processability of the ceramic composite 10, it is preferable that the boron nitride particles are uniformly dispersed among the Si ₃ N ₄ particles. From the viewpoint of ensuring uniform dispersibility of the boron nitride particles, the average particle size of the boron nitride particles is preferably 1 μm or less, more preferably 0.05 μm or more and 0.9 μm or less, and even more preferably 0.1 μm or more. And 0.8 μm or less, most preferably 0.2 μm or more and 0.5 μm or less. The average particle size of Si ₃ N ₄ is not particularly limited, but is preferably 2 μm or more and 30 μm or less, more preferably 5 μm or more and 20 μm or less.

  Here, the average particle diameter of each particle in the ceramic composite 10 is determined by cutting the ceramic composite 10 and enlarging the cross section with a scanning electron microscope (SEM) 15000 times, and then increasing the major diameter of at least 20 particles. It can be obtained by measuring and averaging the measured values.

When the average particle diameter of the boron nitride particles exceeds 1 μm, it may be difficult to obtain a state in which the boron nitride particles are uniformly dispersed among the Si ₃ N ₄ particles. As a result, in the ceramic composite 10, there are a portion with a lot of boron nitride (hereinafter referred to as “BN rich portion”) and a portion with a large amount of Si ₃ N ₄ (hereinafter referred to as “Si ₃ N ₄ rich portion”). It occurs unevenly. Since the porosity of the BN rich portion is increased, the mechanical strength is lowered and the thermal shock resistance is lowered. On the other hand, the Si ₃ N ₄ rich portion has a higher elastic modulus and lowers the grindability. Therefore, when the boron nitride particles are not uniformly dispersed between the Si ₃ N ₄ particles, the thermal shock resistance and the grindability as a whole of the ceramic composite 10 tend not to be sufficiently improved.

Since the ceramic composite 10 of the first embodiment contains Si ₃ N ₄ and boron nitride, which are low dielectric constant materials, the dielectric constant is low. Specifically, the ceramic composite 10 of Embodiment 1 has a dielectric constant of 8.0 or less. Therefore, the ceramic composite 10 of Embodiment 1 is excellent in radio wave transmission.

  The ceramic composite 10 according to the first embodiment can be manufactured using a method known in the art. The ceramic composite body 10 of Embodiment 1 can be manufactured as follows.

First, a slurry is prepared by mixing Si ₃ N ₄ powder, boron nitride powder, sintering aid, dispersant, binder and water. The average particle size of the Si ₃ N ₄ powder, boron nitride powder and sintering aid is not particularly limited, but is preferably 1 μm or less, more preferably 0.8 μm or less, and even more preferably 0.5 μm or less. In particular, when the average particle size of the boron nitride powder exceeds 1 μm, the surface smoothness of the ceramic composite 10 after grinding tends to be lowered.

  The dispersant is not particularly limited as long as it can be used for the aqueous slurry, and those known in the technical field can be used. Examples of dispersants include alkyl sulfates, polyoxyethylene alkyl ether sulfates, alkylbenzene sulfonates, reactive surfactants, fatty acid salts, anionic surfactants such as naphthalene sulfonate formalin condensate, Alkylamine salt, quaternary ammonium salt, amphoteric surfactant alkylbetaine, alkylamine oxide and other cationic surfactant polyoxyethylene alkyl ether, polyoxyalkylene derivative, sorbitan fatty acid ester, polyoxyethylene Sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene fatty acid castor oil, polyoxyethylene alkylamine, Can be used in combination of one or more of the alkyl alkanolamide is down surfactant.

  The binder is not particularly limited, and those known in the technical field can be used. Examples of the binder may be one or a combination of two or more of acrylic, cellulose, polyvinyl alcohol, polyvinyl acetal, urethane, and vinyl acetate resins. The water is not particularly limited, and pure water, RO water, or deionized water can be used. The mixing at the time of preparing the slurry is not particularly limited, and can be performed using a method known in the technical field. As a mixing method, a method using a kneader, a ball mill, a planetary ball mill, a kneading mixer, or a bead mill is used.

  Next, the slurry is granulated to prepare granulated powder. It does not specifically limit as a granulation method, It can carry out according to a well-known method in the said technical field. Granulated powder can be obtained by spray drying using a spray dryer or the like. The conditions for spray drying may be adjusted as appropriate according to the equipment to be used, and are not particularly limited.

  Next, the granulated powder is filled into a mold having a radome shape which is a desired shape, and pressure-molded to produce a molded body. The pressure molding method is not particularly limited, and can be performed according to a method known in the technical field. As the pressure molding method, a CIP (Cold Isostatic Pressing) molding method, a WIP (Warm Isostatic Press) molding method, or a uniaxial pressure molding method is used. The pressing force at the time of pressure molding may be appropriately adjusted according to the type of granulated powder, the apparatus to be used, etc., and is not particularly limited, but is generally 30 MPa or more and 500 MPa or less.

  Next, the molded body is degreased. The method of degreasing is not particularly limited, and can be performed according to a method known in the technical field. A degreasing process can be performed by heat-processing a molded object in an air atmosphere. The heating temperature is not particularly limited as long as the binder can be thermally decomposed, and is generally 300 ° C. or higher and 800 ° C. or lower.

Next, the molded body after the degreasing treatment is fired. The firing method is not particularly limited, and can be performed according to a method known in the technical field. A molded body consisting mainly of Si ₃ N ₄ after degreasing, was fired in a nitrogen atmosphere is an inert gas, may be creating a ceramic sintered body 20. Although the pressure of the nitrogen gas at the time of baking may be a normal pressure, it is preferably 0.2 MPa or more and 1.0 MPa or less from the viewpoint of suppressing thermal decomposition of Si ₃ N ₄ . The firing temperature is not particularly limited, but is generally 1700 ° C. or higher and 2100 ° C. or lower, preferably 1750 ° C. or higher and 2050 ° C. or lower, more preferably 1800 ° C. or higher and 2000 ° C. or lower.

  Next, the surface of the ceramic sintered body 20 which is a formed body after firing is ground in order to adjust the shape. It does not specifically limit as a grinding method, It can carry out according to a well-known method in the said technical field. As a grinding method, grinding using a diamond tool is used.

  The metal oxide layer 30 on the surface 20a of the ceramic sintered body 20 of the first embodiment is heat-treated at a temperature of 1000 ° C. or higher and 1700 ° C. or lower for an arbitrary time in the air atmosphere. Then, by oxidizing the surface 20a of the ceramic sintered body 20, it can be formed on the surface of the ceramic sintered body 20. At this time, the thickness of the metal oxide layer 30 formed on the surface 20a of the ceramic sintered body 20 can be controlled by arbitrarily changing the heat treatment temperature and the heat treatment time.

As described above, the ceramic composite 10 includes a step of sintering a molded body mainly composed of Si ₃ N ₄ in an inert gas atmosphere to produce a ceramic sintered body 20 that is a sintered body, and a ceramic firing. Forming the metal oxide layer 30 on the surface 20a of the ceramic sintered body 20 by heat-treating the bonded body 20 in air and oxidizing the surface of the ceramic sintered body 20. Manufactured by a manufacturing method. The ceramic composite 10 of the first embodiment manufactured as described above has an antioxidant on the surface 20a of the ceramic sintered body 20 whose main component is Si ₃ N ₄ having a low elastic modulus and a high thermal conductivity. Since the metal oxide layer 30 having the effect is combined, it is excellent in both thermal shock resistance and oxidation resistance.

In the ceramic composite 10 of the first embodiment, the thermal shock resistance is improved by applying the ceramic sintered body 20 mainly composed of Si ₃ N ₄ to the material of the radome. Further, the ceramic composite 10 includes the metal oxide layer 30 on the surface 20a of the ceramic sintered body 20, so that the ceramic sintered body 20 does not oxidize even when subjected to aerodynamic heating during flight and becomes high temperature. In addition, fluctuations in dielectric constant can be suppressed. Thereby, the ceramic composite body 10 improves the directivity of the radio wave passing through the radome. As a result, the ceramic composite 10 can be used for a flying object radome that is excellent in both thermal shock resistance and radio wave directivity.

  In addition, in the method for manufacturing the ceramic composite body 10 according to the first embodiment, the ceramic sintered body 20 is heat-treated in the air, and the surface 20a of the ceramic sintered body 20 is oxidized to form the metal oxide layer 30. This simplifies the manufacturing process and improves productivity. In addition, in the method for manufacturing the ceramic composite body 10 according to the first embodiment, the ceramic sintered body 20 is formed by oxidizing the surface 20a of the ceramic sintered body 20 to form the metal oxide layer 30 that is an oxide layer. The adhesion strength between the surface 20a and the metal oxide layer 30 can be made strong.

Embodiment 2. FIG.
A flying object radome 1 according to a second embodiment will be described with reference to the drawings. FIG. 2 is a schematic cross-sectional view of a flying object including a flying object radome according to Embodiment 2 of the present invention.

  As shown in FIG. 2, the flying object radome 1 according to the second embodiment includes a radome 2 composed of the ceramic composite 10 according to the first embodiment and a radome ring 3. That is, the flying object radome 1 includes the ceramic composite 10 according to the first embodiment. The radome 2 and the radome ring 3 are joined using a resin adhesive. The radome ring 3 is made of CFRP (Carbon Fiber Reinforced Plastics), and is joined to the flying object body 4 using a metal bolt to constitute the flying object 5. The radome ring 3 and the flying body main body 4 are not particularly limited, and those known in the technical field can be used.

In the radome 2 of the flying object radome 1 according to the second embodiment, the metal oxide layer 30 is formed on the surface 20 a exposed to the outside of the flying object 5 of the ceramic sintered body 20. As in the first embodiment, the radome 2 of the flying object radome 1 according to the second embodiment is obtained by sintering a molded body containing Si ₃ N ₄ and boron nitride in an inert gas atmosphere. A step of producing a certain ceramic sintered body 20, and heat treatment of the ceramic sintered body 20 in the air to oxidize the surface 20 a of the ceramic sintered body 20, thereby forming a metal oxide on the surface 20 a of the ceramic sintered body 20. And a step of forming the layer 30.

  The flying object radome 1 of the second embodiment includes the radome 2 composed of the ceramic composite 10 of the first embodiment with improved thermal shock resistance and radio wave directivity. Excellent in properties. Moreover, since the ceramic composite 10 of Embodiment 1 is excellent in grinding workability, the productivity of the flying radome 1 can be improved.

  Next, the inventors of the present invention confirmed the effects of the ceramic composite 10 of the first embodiment by manufacturing the following Examples 1 to 9 and Comparative Examples 1 to 4. In addition, Example 1 to Example 9 and Comparative Example 1 to Comparative Example 4 do not limit the present invention.

Example 1
78 parts by mass of Si ₃ N ₄ powder having an average particle diameter of 0.1 μm, 20 parts by mass of boron nitride powder having an average particle diameter of 0.1 μm, and Y ₂ O ₃ powder 1 having an average particle diameter of 1 μm as a sintering aid 4 parts by mass of polyoxyethylene lauryl ether as a dispersant and 1 mass of polyvinyl alcohol as a binder in a mixed powder of 1 part by mass of Al ₂ O ₃ powder having an average particle diameter of 1 μm as a mass part and a sintering aid And 50 parts by mass of water were added and mixed for about 5 hours with a ball mill to prepare a slurry.

  Next, the obtained slurry was spray-dried with a spray dryer to obtain granulated powder. Next, the obtained granulated powder was filled in a mold having the shape of the radome 2, and a molded body was obtained by performing CIP molding using a cold isostatic press. The applied pressure was 98 MPa.

  Next, the obtained molded body was degreased by heat treatment at 600 ° C. for 2 hours in an air atmosphere. Next, the degreased compact was fired at 1900 ° C. for 2 hours in a nitrogen atmosphere. The pressure of nitrogen gas during firing was 0.9 MPa.

  Next, the fired molded body was ground with a diamond tool. Next, the sintered ceramic sintered body 20 was heat-treated at 1400 ° C. for 10 hours in an air atmosphere to oxidize the surface 20a of the ceramic sintered body 20 and deposit the metal oxide layer 30.

(Example 2)
Example 1 except that the ground ceramic sintered body 20 was heat-treated at 1400 ° C. for 1 hour in an air atmosphere to oxidize the surface 20a of the ceramic sintered body 20 and precipitate the metal oxide layer 30. And so on.

(Example 3)
Example 1 except that the ground ceramic sintered body 20 was heat-treated at 1400 ° C. in an air atmosphere for 3 hours to oxidize the surface 20a of the ceramic sintered body 20 and deposit the metal oxide layer 30. And so on.

Example 4
Example 1 except that the ground ceramic sintered body 20 was heat-treated at 1400 ° C. for 20 hours in an air atmosphere to oxidize the surface 20a of the ceramic sintered body 20 and precipitate the metal oxide layer 30. And so on.

(Example 5)
Example 1 except that the ground ceramic sintered body 20 was heat-treated in air at 1400 ° C. for 30 hours to oxidize the surface 20a of the ceramic sintered body 20 and deposit the metal oxide layer 30. And so on.

(Example 6)
86 parts by mass of Si ₃ N ₄ powder, 10 parts by mass of boron nitride powder, ₃ parts by mass of Y ₂ O ₃ powder, ₂ parts by mass of Al ₂ O ₃ powder The procedure was the same as Example 1 except that the mixed powder was used.

(Example 7)
63 parts by mass of Si ₃ N ₄ powder, 27 parts by mass of boron nitride powder, 8 parts by mass of Y ₂ O ₃ powder, ₂ parts by mass of Al ₂ O ₃ powder The procedure was the same as Example 1 except that the mixed powder was used.

(Example 8)
95 parts by mass of Si ₃ N ₄ powder, 0 parts by mass of boron nitride powder, ₃ parts by mass of Y ₂ O ₃ powder, ₂ parts by mass of Al ₂ O ₃ powder The procedure was the same as Example 1 except that the mixed powder was used.

Example 9
90 parts by mass of Si ₃ N ₄ powder, 5 parts by mass of boron nitride powder, ₃ parts by mass of Y ₂ O ₃ powder, ₂ parts by mass of Al ₂ O ₃ powder The procedure was the same as Example 1 except that the mixed powder was used.

(Comparative Example 1)
Example 1 was performed except that heat treatment in air after grinding was not performed.

(Comparative Example 2)
Example 1 except that the ground ceramic sintered body 20 was heat treated at 1400 ° C. for 10 minutes in an air atmosphere to oxidize the surface 20a of the ceramic sintered body 20 and deposit the metal oxide layer 30. And so on.

(Comparative Example 3)
Example 1 except that the ground ceramic sintered body 20 was heat-treated at 1400 ° C. in an air atmosphere for 45 hours to oxidize the surface 20a of the ceramic sintered body 20 and precipitate the metal oxide layer 30. And so on.

(Comparative Example 4)
A slurry obtained by dispersing Y ₂ Si ₂ O ₇ powder in an organic solvent is applied to the ground surface 20a of the ceramic sintered body 20 that has been ground, dried at 80 ° C. for 30 minutes, and then at 1400 ° C. in an air atmosphere. Example 1 was performed except that the metal oxide layer 30 was formed by heat treatment for 1 hour.

  The following evaluation was performed on the radome 2 made of the ceramic composite body 10 obtained in the above examples and comparative examples.

(1) Thermal shock resistance First, the high temperature arc exposure test which simulated the aerodynamic heating at the time of flight was implemented with respect to the radome 2 which consists of the ceramic composite bodies 10. FIG. For the high temperature arc exposure test, a high temperature arc exposure test apparatus that supplies energy to the air by arc discharge to generate a high temperature and high speed air flow was used. The flying object 5 attached with the radome 2 made of the ceramic composite 10 was placed at a position 50 mm away from the nozzle that generates a high-temperature and high-speed air current, and was exposed to the high-temperature and high-speed air current for 10 seconds. At this time, the test was performed with the current value, which is an output for generating an arc, set to 150A.

  The impact resistance was evaluated by measuring the three-point bending strength of the ceramic composite 10 at the tip of the radome 2 before the high-temperature arc exposure test and the three-point bending strength after the high-temperature arc exposure test. This was done by calculating the three-point bending strength ratio before and after the arc test. The three-point bending strength was measured according to JIS (Japanese Industrial Standard) R1601.

  Thermal shock resistance = (3-point bending strength of ceramic composite 10 after high-temperature arc exposure test) / (3-point bending strength of ceramic composite 10 before high-temperature arc exposure test) Equation 2

(2) Rate of change of dielectric constant The dielectric constant of the radome 2 made of the ceramic composite 10 at a room temperature frequency of 10 GHz was measured. Next, the radome 2 made of the ceramic composite 10 was heat-treated in air at 1400 ° C. for 30 minutes, and the dielectric constant having a frequency of 10 GHz at room temperature was measured again. Using the dielectric constant before and after the heat treatment, the change rate of the dielectric constant was determined from the following formula 3.

  Percent change in dielectric constant before and after heat treatment (%) = (1400 ° C.−dielectric constant at room temperature after 30 minutes) / (dielectric constant at room temperature before heat treatment) × 100 Equation 3

(3) Mechanical strength (3-point bending strength)
Three-point bending strength was measured as mechanical strength. This three-point bending strength corresponds to the three-point bending strength before the high-temperature arc exposure test in the evaluation of thermal shock resistance.

(4) Elastic modulus The elastic modulus was calculated from the slope of the stress-strain diagram measured in the evaluation of (3) mechanical strength (three-point bending strength).

(5) Thermal conductivity The thermal conductivity was measured by cutting out a test piece having a diameter of 10 mm and a thickness of 1 mm from the ceramic composite 10 and using the laser flash method for the test piece.

  Table 1 shows the evaluation results and the like.

  As shown in Table 1, the ceramic composites 10 of Examples 1 to 9 are excellent in impact resistance, have a small change rate of dielectric constant before and after heat treatment, and have improved oxidation resistance. It was.

  Compared with Example 1 to Example 9, the ceramic composite 10 of Comparative Example 1 was not provided with the metal oxide layer 30 and thus had poor oxidation resistance and a large change in dielectric constant before and after heat treatment. In the ceramic composite 10 of Comparative Example 2, since the thickness of the metal oxide layer 30 was too thin, the antioxidant effect was not sufficient, and the change in the dielectric constant before and after the heat treatment was large. On the other hand, in the ceramic composite 10 of Comparative Example 3, since the metal oxide layer 30 was too thick, when the thermal shock was applied, cracks occurred in the metal oxide layer 30 and the thermal shock resistance was reduced. Since the ceramic composite 10 of Comparative Example 4 does not contain an amorphous phase in the metal oxide layer 30, the dense metal oxide layer 30 is not formed. For this reason, the antioxidant effect is insufficient, and the change in the dielectric constant before and after the heat treatment is large.

  As can be seen from the above results, it is apparent that according to the present invention, it is possible to provide a ceramic composite 10 that is excellent in both thermal shock resistance and radio wave directivity and can be used for the radome 1 for a flying object. became. Moreover, according to this invention, it became clear that the radome 1 for flying bodies which was excellent in the thermal shock resistance and radio wave directivity, and whose productivity was high can be provided.

  The configuration described in the above embodiment shows an example of the contents of the present invention, and can be combined with another known technique, and can be combined with other configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

  1 radome for flying object, 10 ceramic composite, 20 ceramic sintered body, 20a surface, 30 metal oxide layer.

Claims (6)

A ceramic composite used for a flying object radome,
A ceramic sintered body mainly composed of Si ₃ N ₄ ;
A metal oxide layer formed on at least one surface of the ceramic sintered body,
The thickness of the said metal oxide layer is 10 micrometers or more and 500 micrometers or less, and the said metal oxide layer contains an amorphous phase. The ceramic composite body characterized by the above-mentioned. The ceramic sintered body containing Si ₃ N ₄ as a main component contains Si ₃ N ₄ and boron nitride in a total amount of 80 mass% or more and 98 mass% or less, and the Si ₃ N ₄ and the nitride The mass ratio with boron is in the range of 95: 5 to 70:30,
The ceramic composite according to claim 1. The metal oxide layer includes an amorphous phase including R ₂ Si ₂ O ₇ and boron, where R is a rare earth element,
The ceramic composite according to claim 1 or 2.   A flying object radome comprising the ceramic composite according to any one of claims 1 to 3. A method for producing a ceramic composite according to any one of claims 1 to 3,
A step of sintering a molded body mainly composed of Si ₃ N ₄ in an inert gas atmosphere to produce a ceramic sintered body;
Forming a metal oxide layer on the surface of the ceramic sintered body by heat-treating the ceramic sintered body in air and oxidizing the surface of the ceramic sintered body;
A method for producing a ceramic composite, comprising: It is a manufacturing method of the radome for flying objects according to claim 4,
Sintering a molded body containing Si ₃ N ₄ and boron nitride in an inert gas atmosphere to produce a sintered body;
Forming a metal oxide layer on the surface of the sintered body by heat-treating the sintered body in air and oxidizing the surface of the sintered body;
A method for producing a radome for a flying object, comprising:

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