KR100812952B1 - Zirconia added neutron absorbing pellets and their fabrication methods - Google Patents

Abstract

The present invention relates to a neutron-absorbing sintered body to which zirconia is added and a method for manufacturing the same. The dilution material according to the present invention adds zirconia to the raw material powder of the neutron-absorbing material and performs powder treatment. By controlling the density, a sintered body that satisfies a given concentration of the neutron absorbing material, homogeneous microstructure, and a geologically stable sintered body can be prepared and can be used as a neutron absorbent having excellent performance in a reactor.

Zirconia, Neutron Absorber, Sintered Body

Description

Zirconia added neutron absorbing sintered body and its manufacturing method {Zirconia added neutron absorbing pellets and their fabrication methods}

1 is a graph of the final density of the sintered body with respect to the addition amount of the pore-forming agent and the neutron absorbing material according to an embodiment of the present invention;

Figure 2 is a photograph of the sintered body when the pore-forming agent is added at least 0.5% by weight after the spherical treatment of the milled powder according to the conventional method;

3 is a sintered body picture according to an embodiment of the present invention;

Figure 4 is a photograph of the sintered body produced by adjusting the density of the sintered body by insufficient powder treatment or lowering the sintering temperature according to the conventional method;

Figure 5 is a photograph of the sintered body when 1% by weight of the pore-forming agent according to an embodiment of the present invention; And

Figure 6 is a sintered body picture when 3% by weight of the pore-forming agent according to an embodiment of the present invention.

Figure 7 is a graph comparing the thermal diffusivity of the neutron absorbing sintered compact according to an embodiment of the present invention.

The present invention relates to a neutron absorbing sintered body in which zirconia is added to a neutron absorbing material as a diluent material and its density and concentration are controlled using a pore-forming agent, and a method of manufacturing the same.

In order to maintain a constant output or increase or decrease the output of the reactor, it is necessary to adjust the amount of neutrons generated in the reactor. At this time, the adjustment is the control rod. The control rod is made of a material mainly composed of a neutron absorbent that absorbs neutrons such as cadmium or boron, and the output of the control rod is adjusted by adding or subtracting the number of neutrons to or from the core. Therefore, the role of the neutron absorber used in the control rod is important.

Neutron absorbers are substances that control the density of the neutrons in the reactor to control the output of the reactor or to offset the excess reactivity of the fuel. These neutron absorbers should be free of unnecessary nuclear reactions, have adequate strength, and have good stability and thermal conductivity in the reactor.

Neutron absorbers used in control rods are currently used in commercial reactors such as silver-indium-cadnium alloys, hafnium, and boron. However, these metal absorbents have a disadvantage of low melting point and gold instability, and in the case of boron, swelling is caused by helium generated in the reaction of B-10 isotope (neutron absorption, α particle emission). have. To solve this swelling problem, dysprosium oxide (Dy ₂ O ₃ ), which does not emit α particles but causes a reaction (neutron absorption, γ-ray emission), is used as a reactor control material. At this time, in order to achieve the concentration (Dy g / cm ³ ) of dysprosium (Dy) required for the control rod sintered body, the sintered body is added to the dysprosium oxide powder by adding titania (TiO ₂ ) or alumina (Al ₂ O ₃ ) powder as a diluent material. Manufacture.

On the other hand, extra reactivity is required to compensate for the loss of reactivity due to combustion of fuel, temperature change, fission material generation, etc., and gadolinium (Gd), erbium (Er), Europium (Eu), samarium (Sm) oxides, and the like are used. Combustible absorbent homogeneous and gadolinium oxide (Gd ₂ O ₃ ) made of U-Gd (Er, Eu, Sm) -O sintered body by directly mixing with uranium oxide (UO ₂ ) powder Alternatively, the dilution oxide is added to the dysprosium oxide, and is divided into a heterogeneous type made of a sintered body.

Homogeneous type is a method of manufacturing a sintered body by uniformly mixing a flammable absorbent with UO ₂ powder, which is a raw material of nuclear fuel. The homogeneous type has the advantage that the output distribution is uniform. Has a problem.

Heterogeneous type is a method of producing a sintered body with a neutron absorbent and a diluent without containing fissile material. However, Gd ₂ O ₃ -TiO ₂ or Dy ₂ O ₃ -TiO ₂ using Titania as a diluent The sintered body may be melted by a process reaction at about 1545 ° C. or about 1620 ° C., respectively. Particularly, the sintered body reacts with the alumina plate, which is used as a pellet support, at a relatively low temperature in the sintering process. have.

In addition, when alumina is used as a diluent material, the melting point of Dy (Gd) _x Al _y O _z solid solution is higher and the thermal conductivity is better than that of Dy (Gd) _x Al _y O _z solid solution using titania, but the sintering temperature must be high. There is a problem that swelling is large in a nuclear reactor because of the presence of a mixed phase.

On the other hand, zirconia (ZrO ₂ ) is stable to high temperature, has a wide chemical stability from acidic to alkaline region, and has excellent material properties such as low thermal expansion, high strength and high hardness (Mos hardness of 7.0 or higher), and friction resistance. Neutron absorption cross section has the advantage of low.

Thus, the present inventors, in order to solve the problem of a neutron absorber in which a titania or alumina is added as a dilution material of a neutron absorbent in a conventional reactor, a neutron that prevents swelling of the sintered body in the reactor and forms a gold phase stable solid solution During the research to develop the absorbent, when neutron absorbent is manufactured using zirconia as the diluent material, it is possible to form a solid solution in the form of gold, so that the microstructure of the sintered body is homogeneous, the thermal conductivity is excellent, and the pore forming agent is used. By controlling the density to confirm that the swelling can be prevented and completed the present invention.

An object of the present invention is to provide a neutron absorbing sintered body to which zirconia is added.

Another object of the present invention is to provide a method for producing the neutron absorbing sintered compact.

In order to achieve the above object, the present invention provides a neutron absorbing sintered body to which zirconia is added.

In addition, the present invention provides a method for producing a neutron absorbing sintered body to which the zirconia is added.

Hereinafter, the present invention will be described in detail.

In the present invention, zirconia is uniformly dispersed in the neutron absorbing element oxide selected from Dy or Gd, and the concentration of the neutron absorbing element is controlled to be in the range of 1.5 to 6.4 g / cm 3. To provide.

In the neutron absorbing sintered body according to the present invention, the neutron absorbing element is preferably Dy when used in a control rod, and Gd when used in a flammable absorbing rod. The concentration of the neutron absorbing element is different depending on the type of reactor and the core design criteria, but can be produced in the range of 1.5 to 6.4 g / cm 3, the diameter and length are based on the design criteria.

The zirconia has a molecular weight of 123.22, has a melting point of about 2,700 ° C., is stable at high temperatures, has a low thermal conductivity, has a wide chemical resistance from an acidic to alkaline region, and has low thermal expansion, high strength, and high hardness (more than 7.0 MOS hardness). ), Has excellent material properties such as friction resistance. In addition, the zirconia monoclinic crystal structure has excellent dielectric properties, tack and ion conductivity, and is useful for oxygen sensors, complexing devices, and sound wave detectors. However, no zirconia has been reported as a diluent of neutron absorbents.

Since the concentration of Dy or Gd given in the neutron absorbing sintered body changes not only in the mixing ratio but also in the density of the sintered compact, the mixing ratio of the raw powder is determined by reflecting the percentage of the actual sintered compact density with respect to the theoretical density of the solid solution having the corresponding composition. The density of the actual sintered body produced should satisfy the density value given in the design specification.

In the present invention, the neutron absorbing sintered body has a sintered density of 85 to 95% of the theoretical density of 5 to 15% of pores and satisfies a given concentration of neutron absorbing element in order to prevent minimal swelling in the reactor. Do. The final density of the sintered body can be controlled by the amount and the sintering process conditions of the pore-forming as shown in Fig.

In addition, the present invention

Based on the concentration of the neutron absorbing element, it is corrected by calculating the mixing ratio of the neutron absorbing material Dy ₂ O ₃ or Gd ₂ O ₃ powder and zirconia powder and applying the percentage of the actual sinter density to the theoretical density of the solid solution of the composition Mixing at a mixing ratio (step 1);

Wet milling the mixed powder mixed in step 1 and then drying (step 2);

Adding a pore-forming agent to the powder dried in step 2 and mixing the mixture, and then sphering the powder (step 3);

Further mixing the pore former or lubricant with the spherical powder prepared in step 3 (step 4);

Compacting the spherical powder prepared in step 4 (step 5); And

It provides a method for producing a homogeneous sintered compact used as a zirconia-added neutron absorbent comprising the step (step 6) of sintering the green compact prepared in step 5.

Step 1 is to calculate the mixing ratio of the neutron absorbing material Dy ₂ O ₃ or Gd ₂ O ₃ powder and zirconia powder according to the concentration of the neutron absorbing element and the actual sintered body density of the theoretical density of the solid solution of the composition after sintering It is a step of weighing and mixing raw material powder by correcting the mixing ratio calculated by applying percentage.

In step 1, Dy ₂ O ₃ or Gd ₂ O ₃ powder and zirconia powder may be mixed as a raw material powder. Each of the raw powders may be synthesized or marketed by methods well known in the art, and should have a purity of 99% or more.

A method of correcting the mixing ratio is described in detail below. For example, when preparing a neutron absorbing sintered body having a concentration of 4.5 g / cm ³ , Gd _x Zr _y O _z , the calculated weight ratio of the raw material powder is Gd ₂ O ₃ / ZrO ₂ = 74.61 / 25.39. The sintered body manufactured by applying the mixing ratio satisfies the concentration of Gd 4.5 g / cm ³ when the theoretical density is 100% at which no pores exist. However, the neutron-absorbing sintered body should have pores inside the reactor in consideration of swelling. When the actual sintered body is manufactured to have 10% (volume percentage) of pores, the sintered density is 90% of the theoretical density, and the mixed ratio corrected by applying this is Gd ₂ O ₃ / ZrO ₂ = 81.51 / 18.49. When the raw powder is mixed at this ratio to produce a sintered compact having a sintered density of 90% of the theoretical density, the actual concentration of Gd, a neutron absorbing element, becomes 4.5 g / cm ³ .

According to the corrected mixing ratio, Dy ₂ O ₃ or Gd ₂ O ₃ powder and zirconia powder may be weighed, charged into a powder container, and mixed with a mixer such as a turbular mixer.

Step 2 is a step of wet milling the powder mixed in Step 1 and then drying.

The mixed powder is powdered through wet milling for homogenization. As the wet milling, for example, atrium milling, planetary milling and the like can be used.

The liquid medium used in the wet milling is preferably carbon tetrachloride or ethanol, and 70-100 ml of the liquid medium is added to 100 g of the mixed powder, mixed, and gelled into a milling vessel.

When performing attrition milling, the amount of zirconia balls, which are milling media, is usually higher than the volume of the powder, but preferably not more than 40% of the volume of the milling vessel, the rotation speed of the impeller is 200 to 300 rpm, and the milling time is 3 Powder treatment is preferably performed at about 5 hours. When the rotation speed of the impeller is less than 200 rpm, the kinetic energy of the medium is low to reduce the milling efficiency, and when it exceeds 300 rpm, the medium is separated from the powder so that the medium is concentrated toward the inner wall of the milling vessel and the milling effect. Decreases and excessive vortex occurs. In addition, when the milling time is less than 3 hours, there is insufficient mixing homogeneity and sintering property. When the milling time is more than 5 hours, the viscosity of the gel increases due to the volatilization of the solvent and the inflow of impurities increases.

In the case of planetary milling, when two sizes of zirconia balls are used as the milling medium, the powder is crushed by the kinetic energy of the large balls and the small balls are filled between the large balls, so that the contact area is relatively increased and the milling effect is increased. Increases. In this case, the zirconia ball is preferably used by mixing a ball having a diameter of 18 to 22 mm and a ball of 6 to 10 mm, and charged to the milling vessel at 25 to 35% and 10 to 20% of the gel volume, respectively. Most effective.

 In the planetary milling, the eccentric rotation speed of the powder container is 300 to 400 rpm, and the powder treatment is preferably performed for 3 to 5 hours. When the rotation speed of the impeller is less than 300 rpm, there is a problem in that the milling time is long, and when it exceeds 400 rpm, small zirconia balls may be damaged due to excessive kinetic energy of the medium.

The milled gel is separated from the ball, powder and liquid using a sieve or the like and then the separated powder is dried.

Next, step 3 is a step of spheroidizing the powder after mixing by adding a pore-forming agent to the powder dried in the step 2 above.

Since the neutron-absorbing sintered compact in the reactor can be swelled by various reactions, the sintered density must be controlled so that some pores exist in the sintered compact to prevent this phenomenon. If the density is controlled by lowering the sintering temperature, a homogeneous microstructure cannot be obtained, so the density is controlled using a pore-forming agent.

In order to control the final sintering density, it is preferable to use acroax or dicarbonamide as a pore-forming agent added to the dried powder, and the addition amount is 1 to 5% by weight to obtain the required sintering density. desirable.

After the pore-forming agent is added, the mixture may be mixed in a mixer for about 1 hour, and then pre-divided at a pressure lower than 50 MPa, and spherical powder may be spheronized by crushing and sieving.

Next, step 4 is a step of further mixing the pore-forming agent or lubricant to the spherical powder prepared in step 3.

0.3 to 0.5% by weight of acrowax or stearic acid powder is added to the spherical powder as a pore-forming agent or a lubricant. In addition, when oil can be supplied to the mold of the mill, molybdenum disulfide (MoS ₂ ) may be added to apply a high pressure oil having a high viscosity to the mold inner wall to be used as a lubricant.

When the pore-forming agent is added to 0.5 wt% or more in step 4 after spheroidizing the powder, as shown in FIG. 2 , the shape of powder grains remains on the sintered body and a heterogeneous microstructure in which pores are distributed is shown. In addition, when added in less than 0.3% by weight there is a problem that the lubricating effect is inferior. Therefore, in step 3, 1 to 5% by weight of the pore-forming agent is added to the milled powder, and after spherical treatment, the lubricant is divided into 0.5% by weight or less in step 4, and 5 to 15% of the pores are uniformly distributed. The sintered compact of can be manufactured.

Next step 5 is to compact the spherical powder prepared in step 4.

At this time, the compaction pressure is preferably 200 ~ 400 MPa. If the compaction pressure is too low, less than 200 MPa, the sintered body is nonuniform and severely contracted at the intermediate part, which makes it difficult to obtain a final diameter, and if it exceeds 400 MPa, capping or layer cracking is likely to occur. There is. The compaction may be performed using hydraulic or mechanical compactors.

Next, step 6 is a step of sintering the green compact prepared in step 5.

The prepared green compact is arranged on an alumina plate, charged to a sintering furnace, and sintered in air. The sintering is preferably carried out for 2 to 6 hours at 1600 ~ 1680 ℃ after removing the pore-forming agent by heating for 1 to 2 hours at 600 ~ 800 ℃, which is a uniform neutron absorber used according to the present invention A sintered compact can be manufactured. The sintering temperature is slightly different depending on the mixing ratio of the two raw material powders or the addition amount of the pore-forming agent, but the sintering density required when sintering in the above temperature range can be obtained.

The present invention will be described in more detail with reference to the following Examples. However, the following Examples are only for illustrating the present invention, the present invention is not limited to these.

< Example  1> Dy _x Zr _y O _z  Production of sintered bodies 1

Dy _x Zr _y O _{z with} Dy concentration of 4.0 g / cm 3 To prepare the sintered body, the mixing ratio was calculated by correcting the sintered density to 93% of the theoretical density, and Dy ₂ O ₃ And The raw material powder of ZrO ₂ (Aldrich, purity> 99.9%) was weighed into a turbula mixer and mixed for 30 minutes. 200 g of ethanol was mixed with 200 g of the mixed powder to prepare a gel, and the powder was treated for 5 hours at an rotation speed of the impeller at 250 rpm using an atrium mill. Thereafter, the milled gel was separated from a ball, powder and a liquid using a vibrating body, and then the powder was dried. In order to control the final sintered density, the dried powder was added to a turbula mixer, acro wax was added at 1.2 wt%, mixed for 1 hour, pre-crushed at 50 MPa, crushed and sieved to prepare powder granules. 0.3% by weight of acro wax was further mixed into the powder granules.

The powder granules were put into a mill to prepare a green compact at a pressure of 300 MPa. The green compacts were arranged on an alumina sheet, charged into a sintering furnace, heated at 700 ° C. for 1 hour to remove acro wax, and then sintered at 1650 ° C. for 4 hours to obtain Dy _x Zr _y O having the required density and homogeneous structure. _z sintered body was manufactured.

< Example  2> Dy _x Zr _y O _z  Preparation of Sintered Body 2

The same procedure as in Example 1 was carried out except that dicarbonamide was used instead of acro wax as a pore-forming agent.

< Example  3> Dy _x Zr _y O _z  Preparation of Sintered Body 3

After mixing 100 ml of carbon tetrachloride to 100 g of the mixed powder to prepare a gel, powder processing was performed for 5 hours at a rotational speed of 350 rpm using planetary milling instead of attrition milling. The milled gel was separated from the ball, powder and liquid using a vibrating body, and then the powder was dried. 2.5% by weight of acro wax was added thereto, mixed for 1 hour, preliminarily pressed at a pressure of 50 MPa, crushed and sieved to prepare a powder granule. 0.5% by weight of acro wax was further mixed into the powder granules. After the compacting and sintering step was carried out in the same manner as in Example 1.

< Example  4> Dy _x Zr _y O _z  Preparation of Sintered Body 4

As pore former The same procedure as in Example 3 was conducted except that dicarbonamide was used instead of acrowax.

< Example  5 to 8> Gd _x Zr _y O _z  Preparation of Sintered Body 1-4

To prepare a Gd _x Zr _y O _z sintered body having a Gd concentration of 4.2 g / cm 3, the mixing ratio was calculated by correcting the sintered density to 93% of the theoretical density, and Gd ₂ O ₃ And Except that the raw material powder of ZrO ₂ (Aldrich product, purity> 99.9%) was used in the same manner as in Examples 1 to 4.

< Experimental Example  1> Comparison of microstructure of sintered body according to powder treatment or sintering temperature

In the present invention, the following experiment was performed to determine the effect of the sintered microstructure according to the powder treatment or the sintering temperature.

One type of zirconia ball (19 mm in diameter) when the powder was treated by dry method using attrition milling and sintered at 1650 ° C or in wet planetary milling. The microstructure of the sintered body prepared by the powder treatment using only) was observed with an optical microscope and the results are shown in FIGS . 3 and 4 .

3 is a photograph showing a sintered body produced by the method according to the present invention. As shown in FIG . 3 , it can be seen that when the mixture is prepared under optimum sintering conditions using the homogeneous mixed powder according to the present invention, the distribution of the pores and the microstructures form a homogeneous and geologically stable solid solution. However, when sintering by applying a conventional powder treatment technique or lowering the sintering temperature to a temperature lower than 1600 ℃ to obtain 5% or more pores, as shown in Figure 4 , Dy ₂ O ₃ and zirconia or Gd ₂ O ₃ and No homogeneous solid solution is formed between zirconia, It was confirmed that there was a density difference between the outside and the inside of the sintered body, and a heterogeneous microstructure appeared.

< Experimental Example  2> Comparison of Sintered Body Structure According to Addition of Pore Forming Agent

In the present invention, the following experiment was carried out to determine the effect of the sintered body structure according to the addition amount of the pore-forming agent.

In the sintered body prepared according to the method of Example 3, the structure of the sintered body prepared by adding 1% by weight of acrowax or dicarbonamide as the pore-forming agent and the sintered body prepared by adding 3% by weight of the pore-forming agent was observed under an optical microscope. The results are shown in FIGS . 5 and 6 .

As shown in FIG . 5 , the sintered body manufactured using 1% by weight of the pore-forming agent can be seen that the distribution of the pores and the microstructure is homogeneous . As shown in FIG . 6 , 3.0% by weight of the pore-forming agent is used. Even if the sintered body is prepared by adding a pore-forming agent by the method according to the invention it can be seen that the distribution of pores and the microstructure is homogeneous.

< Experimental Example  3> As a diluent ZrO ₂  or TiO ₂ Of the neutron absorbing sintered body manufactured using Thermal diffusivity  compare

In order to control the concentration of neutron absorbing material, ZrO ₂ or TiO ₂ , which is used as a diluent material, is added to prepare a sintered body, and then a specimen is manufactured to produce a thermal diffusivity using a laser flash apparatus (Netzsch LFA-427). Was measured.

In the sintered body so that the concentration of Dy and Gd, respectively ^{4.0g / cm 3, 4.2g / cm} 3 Dy 2 O 3 and Gd ₂ O ₃ weighed ZrO ₂ or TiO ₂ in each raw material powder, the method of Example 3 was added According to Dy _x Zr _y O _z , Dy _x Ti _y O _z , Gd _x Zr _y O _z , Gd _x Ti _y O _z After preparing the sintered bodies, the specimens were processed, and thermal diffusivity was measured, and the results are shown in FIG. 7 .

As shown in FIG . 7 , Dy _x Zr _y O _z prepared by adding ZrO ₂ as a diluent Alternatively, the Gd _x Zr _y O _z sintered body may be a Dy _x Ti _y O _z or Gd _x Ti _y O _z in which TiO ₂ is used as a diluent Since thermal diffusivity is higher, it was confirmed that the thermal conductivity of the sintered compact to which ZrO ₂ was added is superior to that of TiO ₂ .

Therefore, the present invention controls the final density of the sintered body by using a pore-forming agent in the sintering temperature range to obtain a homogeneous microstructure to satisfy the concentration of Dy or Gd, and to prepare a neutron absorber homogeneous in the pore distribution and the microstructure. can do. As such, the microstructure is homogeneous, a complete solid solution is formed, and a pore forming agent is used to produce a sintered body having a density in the range of 85 to 95% of the theoretical density, thereby minimizing swelling due to neutron absorption in the reactor. Excellent thermal conductivity can lower the center temperature of the control rod or the flammable absorbent rods, thereby improving the performance and stability of the control rod or the flammable absorbent rods. Therefore, according to the present invention Dy _x Zr _y O _z or Gd _x Zr _y O _z The sintered body may be loaded and used in a reactor tube of a reactor control rod or a flammable absorption rod.

As described above, the neutron absorbing sintered body in which zirconia is added as a diluent material according to the present invention, a pore forming agent is added, and sintered at a temperature at which a solid solution is formed is homogeneous, has excellent thermal conductivity, and has suitable pores. Since the swelling phenomenon due to the neutron absorption reaction in the reactor is minimized, and the center temperature is lower than that of the conventional sintered body by good thermal conductivity, it is effective to further improve the performance and safety as a reactor control or a flammable absorbent material.

Claims (8)

A homogeneous porous neutron absorbing sintered body, wherein zirconia is uniformly dispersed in a neutron absorbing element oxide selected from Dy or Gd, and the concentration of the neutron absorbing element is controlled in a range of 1.5 to 6.4 g / cm 3. The neutron absorbing sintered compact according to claim 1, wherein the sintered density of the sintered compact is 85 to 95% of the theoretical density of a solid solution having a corresponding composition in order to minimize swelling in the reactor. Based on the concentration of the neutron absorbing element, it is corrected by calculating the mixing ratio of the neutron absorbing material Dy ₂ O ₃ or Gd ₂ O ₃ powder and zirconia powder and applying the percentage of the actual sinter density to the theoretical density of the solid solution of the composition Mixing at a mixing ratio (step 1); Wet milling the mixed powder mixed in step 1 and then drying (step 2); Adding a pore-forming agent to the powder dried in step 2 and mixing the mixture, and then sphering the powder (step 3); Further mixing the pore former or lubricant with the spherical powder prepared in step 3 (step 4); Compacting the spherical powder prepared in step 4 (step 5); And The sintered body manufacturing method of claim 1, comprising the step (step 6) of sintering the green compact prepared in the step 5. The method of claim 3, wherein in the wet milling of step 2, 70 to 100 ml of carbon tetrachloride or ethanol is added per 100 g of mixed powder as a liquid medium to make the gel, and milling is performed using atrium or planetary milling. The manufacturing method of the sintered compact of Claim 1. The method of claim 4, wherein the rotation speed of the impeller is 200 to 300 rpm and the milling time is 3 to 5 hours. The zirconia balls having a diameter of 18 to 22 mm and a diameter of 6 to 10 mm as milling media in the planetary milling are powdered so as to be 25 to 35% and 10 to 20% of the total gel volume, respectively. The method for manufacturing the sintered body according to claim 1, which is charged in a container and milled for 3 to 5 hours at a rotational speed of 300 to 400 rpm. The method according to claim 3, wherein the pore forming agent of step 3 is acrowax or dicarbonamide, and the amount thereof is 1 to 5% by weight, and in step 4, 0.3 to 0.5 acrowax or stearic acid as a pore forming agent or lubricant. A method for producing the sintered body according to claim 1, which is added by weight%. The sintered body of claim 3, wherein the sintering of step 6 is performed at 600 to 800 ° C. for 1 to 2 hours to remove the pore-forming agent, and then is performed at 1600 to 1680 ° C. for 2 to 6 hours. Manufacturing method.

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