JP6765236B2 - Radomes for ceramic composites and flying objects - Google Patents

Description

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

The projectile that flies toward the 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 the air during flight. In particular, the radome installed at the tip of the flying object is heated to a temperature of 1000 ° C. or higher 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, since the flying object measures the distance and azimuth to the target at the time of flight, it is necessary to transmit and receive radio waves via the radome. Therefore, the material used for the radome is also required to have radio wave transmission.

As a material that satisfies the performance requirements of such radomes, cordierite _{(2MgO · 2Al 2 O 3 ·} 5SiO 2) is generally used is an oxide ceramic. However, in recent years, the flight speed of the projectile has increased along with the improvement of the performance of the projectile, and when the conventional oxide-based ceramic is used for the redome of the projectile that flies at a higher speed than the conventional one, heat-resistant impact is applied. There is a problem that the properties are not sufficient and cracks occur due to the thermal stress generated by aerodynamic heating.

Therefore, as a ceramic material having superior thermal shock resistance to conventional oxide-based ceramics, a ceramic material containing silicon nitride (Si ₃ N ₄ ) has been proposed (see Patent Document 1).

International Publication No. 2013/124871

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

The present invention has been made in view of the above, and an object of the present invention is to obtain a ceramic composite which is excellent in both thermal shock resistance and radio wave directivity and can be used for a radome for a flying object.

In order to solve the above-mentioned problems and achieve the object, the present invention is a ceramic composite used for a projectile radome, and is a ceramic sintered body containing Si ₃ N ₄ as a main component and a ceramic sintered body. A metal oxide layer formed on at least one surface of the body is provided, the thickness of the metal oxide layer is 10 μm or more and 500 μm or less, and the metal oxide layer is amorphous containing boron. It is characterized by containing a phase.

According to the present invention, it has the effect of being excellent in both thermal shock resistance and radio wave directivity.

Perspective view of the ceramic composite according to the first embodiment of the present invention. Schematic cross-sectional view of a flying object provided with a radome for the flying object according to the second embodiment of the present invention.

Hereinafter, a method for producing a ceramic composite, a radome for a flying object, a method for producing a ceramic composite, and a method for producing a radome for a flying object according to an embodiment of the present invention will be described in detail with reference to the drawings. The present invention is not limited to this embodiment.

Embodiment 1.
FIG. 1 is a perspective view of the ceramic composite according to the first embodiment of the present invention. In general, the thermal shock resistance of a ceramic material is mainly related to the bending strength and elastic modulus of the thermal expansion coefficient, thermal conductivity, and mechanical strength of the ceramic material, and the thermal conductivity and mechanical strength are high and thermal expansion. The lower the coefficient and elastic modulus, the better. In addition, radio wave directivity is related to the refractive index caused by 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. Will change, and the directivity of radio waves will deteriorate.

Therefore, as a result of diligent research to solve the above problems, the present inventors have found a ceramic sintered body containing silicon nitride (Si ₃ N ₄ ) as a main component, which has a small coefficient of thermal expansion and high mechanical strength. We have 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 improvement in thermal shock resistance and improvement in radio wave directivity. It led to the invention.

The ceramic composite 10 according to the first embodiment is a ceramic composite used for a radome for a flying object. 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 20a of the ceramic sintered body 20.

The ceramic sintered body 20 containing Si ₃ N ₄ as a main component in the ceramic composite 10 of the first embodiment has characteristics of low thermal expansion coefficient and high mechanical strength, and is known as a heat-resistant impact ceramic. The thermal conductivity is also higher than that of silica or cordierite, which is an oxide ceramic. Therefore, the ceramic sintered body 20 has excellent thermal shock resistance. Further, the ceramic sintered body 20 containing Si ₃ N ₄ as a main component of the first embodiment preferably contains boron nitride (BN). In the ceramic sintered body 20, boron nitride having a low elastic modulus and a high thermal conductivity is combined with Si ₃ N ₄ and composited to reduce the elastic modulus and conduct the heat while maintaining a low coefficient of thermal expansion. The rate can be increased. As a result, the ceramic sintered body 20 can further improve the thermal shock resistance of the ceramic composite body 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 diffused from the surface 20a into the inside of the ceramic. Therefore, if the diffusion of oxygen from the surface 20a of the ceramic sintered body 20 can be prevented, oxidation can be suppressed. The ceramic composite 10 of the first embodiment is provided with a 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, so that the ceramic composite 10 can be used during flight. Even if the temperature rises due to aerodynamic heating, the ceramic sintered body 20 does not oxidize, and fluctuations in the dielectric constant can be suppressed. As a result, the directivity of the radio wave transmitted through the radome is improved. Further, in the ceramic composite 10, since the metal oxide layer 30 contains an amorphous phase, a dense metal oxide layer 30 is formed, so that the oxidation suppressing effect is improved. Further, 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 high insulation resistance, the dielectric loss which is a factor of deteriorating radio wave transmission is small. .. Therefore, the metal oxide layer 30 formed on the surface 20a of the ceramic sintered body 20 does not interfere with the radio wave transmission of the radio waves transmitted 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 10 μm or more and 500 μm or less. When the thickness of the metal oxide layer 30 is less than 10 μm, pinholes, which are defects, are likely to occur in the metal oxide layer 30, and oxygen is diffused through the defects, 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 is easily peeled off at the interface between the ceramic sintered body 20 containing Si ₃ N ₄ as a main component and the metal oxide layer 30, and cracks occur at the interface. It will be easier. Further, when the metal oxide layer 30 is composed of a substance having a 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 becomes large, resulting in heat. 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 of the first embodiment, the metal oxide layer 30 on the surface 20a of the ceramic sintered body 20 contains R ₂ Si ₂ O ₇ and boron, which are a kind of rare earth silicate, when 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 a coefficient of thermal expansion similar to that of silicon nitride, the interface between the ceramic sintered body 20 and the metal oxide layer 30 It is difficult to generate thermal stress in silicon, and it suppresses peeling and cracking when a thermal shock is applied. 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. The amorphous phase containing boron is not particularly limited, but borosilicate glass, aluminoborosilicate glass, or Pyrex (registered trademark) can be used.

The contents of Si ₃ N ₄ and boron nitride in the ceramic sintered body 20 in the ceramic composite 10 of the first embodiment are 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. If the total content of Si ₃ N ₄ and boron nitride exceeds 80% by mass or 98% by mass, the thermal impact 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% by mass, the ceramic composite 10 is not sufficiently densified, and the mechanical strength of the ceramic composite 10 is lowered.

The mass ratio of Si ₃ N ₄ of the ceramic sintered body 20 to boron nitride in the ceramic composite 10 of the first embodiment is in the range of 95: 5 to 70:30, preferably 90:10 to 70:30. Is more preferably in the range of 88:12 to 72:28, even more preferably in the range of 86:14 to 74:26, and even more preferably in 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 radome, the temperature difference between the surface and the inside of the flying radome becomes large, and cracks or cracks occur due to thermal stress. That is, the thermal impact resistance of the ceramic composite 10 is not sufficiently improved. On the other hand, if the proportion of boron nitride is too large, the mechanical strength of the ceramic composite 10 is significantly reduced, and the thermal shock resistance is not sufficiently improved. When the metal oxide layer 30 is not provided on the surface 20a of the ceramic sintered body 20, the ceramic sintered body 20 is easily oxidized to the inside, so that 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 due to the ceramic sintered body 20 being oxidized to the inside. It has the effect of suppressing the decrease in rate. Therefore, even in a composition having a small proportion of boron nitride, both impact resistance and radio wave directivity can be made excellent.

In the ceramic composite 10 of the first embodiment, the ceramic sintered body 20 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 art can be used. As the sintering aid, one or more of the rare earth elements yttrium, aluminum, titanium, magnesium oxide, silicon oxide, aluminum nitride and titanium nitride can be used in combination. .. The sintering aid is preferably a rare earth oxide from the viewpoint of thermal shock resistance and mechanical strength of the ceramic composite 10.

The content of the sintering aid in 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. It is 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. If 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 contents of Si ₃ N ₄ and boron nitride are reduced, so that the thermal impact resistance of the ceramic composite 10 may not be sufficiently improved.

In addition to the above components, the ceramic composite 10 of the embodiment may contain various components known in the art in order to obtain a preset desired effect. The content of the components in the ceramic composite 10 of the embodiment is not particularly limited as long as it does not interfere with the effects of the present invention.

The void ratio of the ceramic composite 10 is related to the mechanical strength and thermal shock resistance of the ceramic composite 10. That is, if the void ratio of the ceramic composite 10 is too high, the voids are connected to each other inside the ceramic composite 10, and as a result, the mechanical strength of the ceramic composite 10 decreases. If the void ratio 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 void ratio 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 preset desired mechanical strength and thermal shock resistance. More preferably, it is 7% or more and 28% or less.

Here, in the present specification, the "void ratio" of the ceramic composite 10 is calculated from the following formula 1 using the measured values of the weight and dimensions (length, width, height) of the ceramic composite cut out into a rectangular parallelepiped shape. be able to.
Void ratio = {1- [W _drying / (L × W × T) / ρ _theory ]} × 100 ・ ・ ・ Equation 1

W _drying in the formula 1 is the weight (g) of the ceramic composite 10 dried at 150 ° C. for 2 hours, and L, W and T are the length, width 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 the first embodiment, Si ₃ N ₄ and boron nitride are present as particles. From the viewpoint of improving the thermal shock resistance and grinding workability of the ceramic composite 10, the boron nitride particles are preferably 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, still 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, and more preferably 5 μm or more and 20 μm or less.

Here, the average particle size of each particle in the ceramic composite 10 is the major axis of at least 20 particles after cutting the ceramic composite 10 and magnifying the cross section of the ceramic composite 10 by 15,000 times with an SEM (scanning electron microscope). It can be obtained by measuring and averaging the measured values.

When the average particle size 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, inside the ceramic composite 10, a portion rich in boron nitride (hereinafter referred to as “BN rich portion”) and a portion rich in Si ₃ N ₄ (hereinafter referred to as “Si ₃ N ₄ rich portion”) are formed. Occurs unevenly. Since the void ratio is large in the BN-rich portion, the mechanical strength is lowered and the thermal shock resistance is lowered. On the contrary, the Si ₃ N ₄ rich portion has a high elastic modulus and a low grindability. Therefore, if the boron nitride particles are not uniformly dispersed among the Si ₃ N ₄ particles, the thermal impact resistance and grinding workability of the ceramic composite 10 as a whole tend not to be sufficiently improved.

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

The ceramic composite 10 of the first embodiment can be produced by a method known in the art. The ceramic composite 10 of the first embodiment can be produced as follows.

First, Si ₃ N ₄ powder, boron nitride powder, sintering aid, dispersant, by mixing a binder and water to prepare a slurry. Si ₃ N ₄ powder, the average particle diameter of boron nitride powder and sintering aid is not particularly limited, but is preferably 1μm or less, more preferably 0.8μm or less, more preferably 0.5μm 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 decrease.

The dispersant is not particularly limited as long as it can be used for an aqueous slurry, and those known in the art can be used. Examples of dispersants include alkyl sulphates, polyoxyethylene alkyl ether sulphates, alkylbenzene sulphonates, reactive surfactants, fatty acids, anionic surfactants such as sodium naphthalenphate formalin condensates, Polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, sorbitan fatty acid esters, polyoxyethylene, which are cationic surfactants such as alkylamine salts, quaternary ammonium salts, amphoteric surfactants alkylbetaine, and alkylamine oxides. One of sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene fatty acid castor oil, polyoxyethylene alkylamine, and alkylalkanolamide which is a nonionic surfactant. Alternatively, two or more types can be used in combination.

The binder is not particularly limited, and those known in the art can be used. As an example of the binder, one or more of acrylic-based, cellulosic-based, polyvinyl alcohol-based, polyvinyl acetal-based, urethane-based, and vinyl acetate-based resins can be used in combination. The water is not particularly limited, and pure water, RO water, or deionized water can be used. The mixing when preparing the slurry is not particularly limited, and can be carried out by using a method known in the art. 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. The granulation method is not particularly limited, and can be performed according to a method known in the art. Granulated powder can be obtained by spray drying using a spray dryer or the like. The conditions for spray drying may be appropriately adjusted according to the equipment to be used, and are not particularly limited.

Next, a mold having a radome shape, which is a desired shape, is filled with granulated powder and pressure-molded to prepare a molded product. The pressure molding method is not particularly limited, and can be performed according to a method known in the art. 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 used, and the like, and is not particularly limited, but is generally 30 MPa or more and 500 MPa or less.

Next, the molded product is degreased. The method of degreasing treatment is not particularly limited, and can be performed according to a method known in the art. The degreasing treatment can be performed by heat-treating the molded product 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 product after the degreasing treatment is fired. The firing method is not particularly limited, and can be performed according to a method known in the art. The degreased molded product containing Si ₃ N ₄ as a main component may be fired in a nitrogen atmosphere which is an inert gas to prepare a ceramic sintered body 20. The pressure of the nitrogen gas at the time of firing may be normal pressure, but from the viewpoint of suppressing the thermal decomposition of Si ₃ N ₄ , it is preferably 0.2 MPa or more and 1.0 MPa or less. 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, and more preferably 1800 ° C. or higher and 2000 ° C. or lower.

Next, the surface of the ceramic sintered body 20, which is a molded body after firing, is ground in order to adjust the shape. The grinding method is not particularly limited, and can be performed according to a method known in the art. As the grinding method, a grinding process using a diamond bite is used.

The metal oxide layer 30 on the surface 20a of the ceramic sintered body 20 of the first embodiment heat-treats the ceramic sintered body 20 after grinding at a temperature of 1000 ° C. or higher and 1700 ° C. or lower in an air atmosphere for an arbitrary time. 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 containing Si ₃ N ₄ as a main component in an inert gas atmosphere to prepare a ceramic sintered body 20 which is a sintered body, and ceramic firing. The ceramic composite 10 has a step of forming a metal oxide layer 30 on the surface 20a of the ceramic sintered body 20 by heat-treating the 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 resistance on the surface 20a of the ceramic sintered body 20 containing Si ₃ N ₄ as a main component, which has a low elastic modulus and a high thermal conductivity. Since the metal oxide layer 30 having an effect is combined, it is excellent in both thermal impact 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 containing Si ₃ N ₄ as a main component to the material of the radome. Further, since the ceramic composite 10 is provided with the metal oxide layer 30 on the surface 20a of the ceramic sintered body 20, the ceramic sintered body 20 is not oxidized even if the temperature rises due to aerodynamic heating during flight. , Fluctuation of dielectric constant can be suppressed. As a result, the ceramic composite 10 improves the directivity of the radio waves transmitted through the radome. As a result, the ceramic composite 10 can be used for a radome for a flying object, which is excellent in both thermal shock resistance and radio wave directivity.

Further, the method for producing the ceramic composite 10 of the first embodiment is to heat-treat the ceramic sintered body 20 in the air and oxidize the surface 20a of the ceramic sintered body 20 to form the metal oxide layer 30. As a result, the manufacturing process is simplified and productivity is improved. Further, in the method for producing the ceramic composite 10 of the first embodiment, the surface 20a of the ceramic sintered body 20 is oxidized to form a metal oxide layer 30 which is an oxide layer, whereby the ceramic sintered body 20 is formed. The adhesion strength between the surface 20a and the metal oxide layer 30 can be strengthened.

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

As shown in FIG. 2, the flying 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 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. Further, the radome ring 3 is made of CFRP (Carbon Fiber Reinforced Plastics) and is joined to the flying object main body 4 by using a metal bolt to form the flying object 5. The radome ring 3 and the flying object main body 4 are not particularly limited, and those known in the art can be used.

The radome 2 of the flying object radome 1 according to the second embodiment forms a metal oxide layer 30 on the surface 20a exposed to the outside of the flying object 5 of the ceramic sintered body 20. In the redome 2 of the flying object redome 1 according to the second embodiment, similarly to the first embodiment, a molded body containing Si ₃ N ₄ and boron nitride is sintered in an inert gas atmosphere, and the sintered body is used. A metal oxide is formed on the surface 20a of the ceramic sintered body 20 by the process of producing a certain ceramic sintered body 20 and the heat treatment of the ceramic sintered body 20 in the air to oxidize the surface 20a of the ceramic sintered body 20. It is manufactured by a method for manufacturing a flying object radome 1 having a step of forming a 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 having improved thermal shock resistance and radio wave directivity, and thus has thermal shock resistance and radio wave directivity. Excellent in sex. Further, since the ceramic composite 10 of the first embodiment is excellent in grinding workability, the productivity of the flying radome 1 can be improved.

Next, the inventors of the present invention confirmed the effect of the ceramic composite 10 of the first embodiment by producing the following Examples 1 to 9 and Comparative Examples 1 to 4. It should be noted that Examples 1 to 9 and Comparative Examples 1 to 4 do not limit the present invention.

(Example 1)
78 parts by mass of Si ₃ N ₄ powder with an average particle size of 0.1 μm, 20 parts by mass of boron nitride powder with an average particle size of 0.1 μm, and Y ₂ O ₃ powder 1 with an average particle size of 1 μm, which is a sintering aid. A mixed powder of 1 part by mass and 1 part by mass of Al ₂ O ₃ powder having an average particle size of 1 μm as a sintering aid, 4 parts by mass of polyoxyethylene lauryl ether as a dispersant, and 1 part by mass of polyvinyl alcohol as a binder. A part and 50 parts by mass of water were added and mixed with a ball mill for about 5 hours 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 a radome 2, and CIP molding was performed using a cold isotropic press to obtain a molded product. The pressing force was 98 MPa.

Next, the obtained molded product was degreased by heat-treating it at 600 ° C. for 2 hours in an air atmosphere. Next, the degreased molded product was calcined at 1900 ° C. for 2 hours in a nitrogen atmosphere. The pressure of nitrogen gas during firing was 0.9 MPa.

Next, the fired compact was ground with a diamond bite. Next, the ground 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 precipitate 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. I did the same.

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

(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. I did the same.

(Example 5)
Example 1 except that the ground ceramic sintered body 20 was heat-treated at 1400 ° C. for 30 hours in an air atmosphere to oxidize the surface 20a of the ceramic sintered body 20 and precipitate the metal oxide layer 30. I did the same.

(Example 6)
The amount of Si ₃ N ₄ powder is 86 parts by mass, the amount of boron nitride powder is 10 parts by mass, the amount of Y ₂ O ₃ powder is 3 parts by mass, and the amount of Al ₂ O ₃ powder is 2 parts by mass. The same procedure as in Example 1 was carried out except that the powder was changed to a mixed powder.

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

(Example 8)
The amount of Si ₃ N ₄ powder is 95 parts by mass, the amount of boron nitride powder is 0 parts by mass, the amount of Y ₂ O ₃ powder is 3 parts by mass, and the amount of Al ₂ O ₃ powder is 2 parts by mass. The same procedure as in Example 1 was carried out except that the powder was changed to a mixed powder.

(Example 9)
The amount of Si ₃ N ₄ powder is 90 parts by mass, the amount of boron nitride powder is 5 parts by mass, the amount of Y ₂ O ₃ powder is 3 parts by mass, and the amount of Al ₂ O ₃ powder is 2 parts by mass. The procedure was the same as in Example 1 except that the powder was changed to a mixed powder.

(Comparative Example 1)
The same as in Example 1 was carried out except that the heat treatment in the air after the grinding process 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 precipitate the metal oxide layer 30. I did the same.

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

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

The radome 2 made of the ceramic composite 10 obtained in the above Examples and Comparative Examples was evaluated as follows.

(1) Heat-resistant impact resistance First, a high-temperature arc exposure test simulating aerodynamic heating during flight was carried out on a radome 2 made of a ceramic composite 10. For the high-temperature arc exposure test, a high-temperature arc exposure test device was used, which supplies energy to the air by arc discharge to generate a high-temperature, high-speed air flow. A flying object 5 to which a radome 2 made of a ceramic composite 10 was attached was installed at a position 50 mm away from a nozzle in which a high temperature and high speed air flow was generated, and was exposed to a high temperature and high speed air flow for 10 seconds. At this time, the test was conducted with the current value, which is the output for generating an arc, set to 150 A.

The impact resistance is 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, and using the following formula 2 to evaluate the high temperature. This was done by calculating the 3-point bending strength ratio before and after the arc test. The 3-point bending strength was measured according to JIS (Japanese Industrial Standards) R1601.

Thermal impact 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) Permittivity Change Rate The dielectric constant of the radome 2 made of the ceramic composite 10 having a frequency of 10 GHz at room temperature 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 at room temperature having a frequency of 10 GHz was measured again. Using the dielectric constant before and after the heat treatment, the rate of change of the dielectric constant was determined from the following formula 3.

Permittivity change rate (%) before and after heat treatment = (dielectric constant at room temperature after heat treatment for -30 minutes at 1400 ° C) / (dielectric constant at room temperature before heat treatment) x 100 ... Equation 3

(3) Mechanical strength (3-point bending strength)
The three-point bending strength was measured as the 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 (3) evaluation of 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 a laser flash method for the test piece.

Table 1 shows the results of each of the above evaluations.

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

Since the ceramic composite 10 of Comparative Example 1 did not have the metal oxide layer 30 as compared with Examples 1 to 9, the oxidation resistance was poor and the change in the dielectric constant before and after the heat treatment was large. 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, cracks were generated in the metal oxide layer 30 when a thermal shock was applied, and the thermal shock resistance was lowered. In the ceramic composite 10 of Comparative Example 4, since the metal oxide layer 30 does not contain an amorphous phase, a dense metal oxide layer 30 is not formed. Therefore, the antioxidant effect became insufficient, and the change in the dielectric constant before and after the heat treatment was large.

As can be seen from the above results, it is clear 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 flying object radome 1. became. Further, according to the present invention, it has been clarified that it is possible to provide a radome 1 for a flying object, which is excellent in heat resistance and radio wave directivity and has high productivity.

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

1 Radome for flying objects, 10 ceramic composites, 20 ceramic sintered bodies, 20a surface, 30 metal oxide layers.

Claims (7)

A ceramic composite used for radomes for flying objects.
A ceramic sintered body containing Si ₃ N ₄ as the main component,
A metal oxide layer formed on at least one surface of the ceramic sintered body is provided.
A ceramic composite having a thickness of 10 μm or more and 500 μm or less, and the metal oxide layer containing an amorphous phase containing boron . The ceramic sintered body composed mainly of the _Si 3 _{N 4} contains the Si ₃ N ₄ and by summing the boron nitride and 80 wt% or more 98 wt% or less, and with the _Si 3 _{N 4} The mass ratio with the boron nitride is in the range of 95: 5 to 70:30.
The ceramic composite according to claim 1. The metal oxide layer, when the R a rare earth element, the amorphous phase is characterized by the early days including the R ₂ Si ₂ O ₇ and boron,
The ceramic composite according to claim 1 or 2. The boron nitride particles are the Si. ₃ N ₄ The ceramic composite according to claim 2, wherein the boron nitride particles are dispersed between the particles, and the average particle size of the boron nitride particles is 1 μm or less. The ceramic composite according to claim 1, wherein the void ratio is 30% or less. The ceramic sintered body containing Si3N4 as a main component is the Si. ₃ N ₄ The ceramic composite according to claim 1, further comprising boron nitride and a sintering aid, and the content of the sintering aid is 2% by mass or more and 20% by mass or less. A radome for a flying object, comprising the ceramic composite according to any one of claims 1 to 6 .

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