JP2009263198A - METHOD FOR PRODUCING MgO-BASED CERAMIC - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing MgO-based ceramics suitable for an optical material by a simple process. <P>SOLUTION: The method for producing MgO-based ceramics comprises: a first stage S1 where the powder of MgO as the first component and the powder of at least one kind of oxide selected from the group consisting of the oxides of Fe, Ni, Co, Cu, Mn and Zn as the second component are mixed to form solid solution powder in which the second component is solid-solubilized in the first component; a second stage S2 where the solid solution powder is molded to obtain a molded body; and a third stage S3 where the molded body is sintered to obtain a sintered compact. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing MgO-based ceramics suitably used for optical materials and the like.

  Since MgO (magnesium oxide or magnesia) has a cubic crystal structure and no birefringence, it is possible to obtain a sintered body having excellent translucency by removing segregation of vacancies and impurities. . Such MgO is known to be an excellent material having a very high melting point of 2800 ° C. and having heat resistance, alkali resistance and high thermal conductivity. However, since MgO has an extremely high melting point, it has been difficult to synthesize large crystals that are optically superior with existing single crystal synthesis techniques.

  On the other hand, ceramics (polycrystals) can be synthesized at a relatively low temperature below the melting point. Therefore, high-temperature infrared window materials and discharge lamps are used for high-melting yttrium oxide (yttria) and other rare earth oxides like MgO. Many studies have been made to apply it to envelopes and corrosion-resistant members.

As a report example regarding the polycrystalline translucent MgO sintered body, there is a method of improving the sinterability by dispersing MgO powder in an organic solvent and re-calcining (see, for example, Patent Document 1). As a method for adding the sintering aid, a method of adding a solution-like aluminum compound (see, for example, Patent Document 2), a method of adding SiO ₂ and a small amount of B ₂ O ₃ (for example, see Patent Document 3). ), Scandium oxide, ytterbium oxide, and germanium oxide in an amount of 0.01 to 0.5 wt%, and firing in an inert atmosphere (see, for example, Patent Document 4).
JP 51-80313 A JP 59-50068 JP 2000-281428 A JP-A-48-2883

However, MgO has a big problem in water resistance, and MgO easily reacts with moisture in the atmosphere at room temperature (for example, 25 ° C.) and is converted to Mg (OH) ₂ having a lower density than MgO. When such Mg (OH) ₂ powder is press-molded and sintered, Mg (OH) ₂ is converted again to MgO at 300 ° C. or higher. During the conversion, the particles in the molded body cause a large volume shrinkage. Therefore, the molded body heated to 300 ° C. or more has voids and its relative density is lower than that at room temperature (for example, 25 ° C.). To do. Therefore, in order to remove such voids, the molded body is densified by processing at a higher temperature. During such densification, the molded body undergoes significant shrinkage and cracks are generated in the sintered body, or the relative density of the molded body (the percentage of the density of the molded body with respect to the theoretical density of MgO; the same applies hereinafter). Therefore, there is a problem that the densification is insufficient and pores remain, and the sintered body is not optically transparent.

  In order to solve the above problems, an object of the present invention is to provide a method for producing an MgO ceramic suitable for an optical material by a simple method.

  The present invention mixes MgO powder as the first component and at least one oxide powder selected from the group consisting of oxides of Fe, Ni, Co, Cu, Mn and Zn as the second component. Then, a first step of forming a solid solution powder in which the second component is dissolved in the first component, a second step of forming the solid solution powder to obtain a molded body, and sintering and sintering the molded body And a third step of obtaining a body.

  Here, the second component is preferably any one of ZnO, NiO and CuO. The ratio of the second component metal element to the total amount of the first component and the second component metal element is preferably 20 mol% or more and 40 mol% or less.

  In the first step, the mixing is preferably performed by a mechanical alloying method. Furthermore, this mechanical alloying method preferably uses a planetary ball mill. Moreover, it is preferable that the grinding | pulverization acceleration by this planetary ball mill is 10G or more. Further, it is preferable to use an Fe-based ball as a ball of the planetary ball mill, and the Fe-based ball is preferably a stainless ball.

  Moreover, it is preferable to further include a fourth step of obtaining a HIP body by subjecting the sintered body to a hot isostatic pressing (HIP) treatment. The relative density of the molded body, which is a percentage of the density of the molded body with respect to the theoretical density of MgO, is preferably 54% or more.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of MgO type | system | group ceramics suitable for an optical material can be provided with a simple method.

<Embodiment 1>
Referring to FIG. 1, an embodiment of a method for producing an MgO-based ceramic according to the present invention includes MgO powder as a first component and Fe, Ni, Co, Cu, Mn, and Zn as a second component. First step S1 of mixing at least one oxide powder selected from the group consisting of oxides to form a solid solution powder in which the second component is dissolved in the first component, and forming the solid solution powder The second step S2 for obtaining a molded body and the third step S3 for obtaining a sintered body by sintering the molded body.

(First component)
In the manufacturing method of the MgO-based ceramic of the present embodiment, MgO is used as the first component. MgO has a cubic crystal structure and no birefringence. For this reason, a sintered body with high translucency can be obtained by removing vacancies and segregation of impurities. MgO is a material having high heat resistance, alkali resistance, and thermal conductivity.

However, since MgO has a very high melting point of 2800 ° C., it is difficult to grow a single crystal by the chocolate ski (CZ) method or the Bernoulli method, and it is necessary to use an extremely expensive electrofusion method. Further, when producing ceramics by sintering raw material powder, a high sintering temperature is required, and it is necessary to forcibly densify using pressure sintering such as hot pressing. In particular, MgO has low water resistance, and easily reacts with moisture in the atmosphere at room temperature (for example, 25 ° C.) to be converted into Mg (OH) ₂ having a lower density than MgO.

When such MgO powder is press-molded and sintered, Mg (OH) ₂ is converted again to MgO at 300 ° C. or higher. During the conversion, the particles in the molded body cause a large volume shrinkage. Therefore, the molded body heated to 300 ° C. or more has voids and its relative density is lower than that at room temperature (for example, 25 ° C.). To do. Therefore, in order to remove such voids, the molded body is densified by processing at a higher temperature. During such densification, the compact may shrink significantly and cracks may occur in the sintered body, or the compact may not be sufficiently densified due to the low relative density of the compact, and voids may not be removed.

(Second component)
Therefore, in the method for manufacturing the MgO-based ceramic according to the present embodiment, Fe, Ni, Co, Cu, Mn, and Zn oxides are used as the second component.

  Referring to FIG. 2, when, for example, ZnO is added as the second component to MgO as the first component, a solid solution is formed in which the second component (ZnO) is dissolved in a wide composition region in the first component (MgO). The Such a solid solution does not form a second phase and maintains a cubic crystal, so that optical isotropy is secured, and since the second phase does not exist at grain boundaries, it tends to be transparent. In addition, since the melting point and the liquid phase appearance temperature are lowered together with the solid solution of the second component (ZnO) in the first component (MgO), the production of MgO-based ceramics is facilitated. Further, when the ionic radii of the metal element (Mg) ion in the first component (MgO) and the metal element (Zn) ion in the second component (ZnO) are close, the degree of lattice distortion of the solid solution is small, and MgO The decrease in thermal conductivity is small.

  Here, the solid solution (MgO solid solution) in which the second component (ZnO) is dissolved in the first component (MgO) has the same crystal structure as the first component (MgO), and its powder X-ray diffraction pattern is It is substantially the same as the first component (MgO) and does not show the diffraction pattern of any other chemical substance. It is defined that the diffraction angle slightly shifts depending on the ionic radius and solid solution amount of the metal element contained in the second component that is in solid solution. For example, a MgO solid solution in which ions smaller than the Mg ion radius are dissolved in MgO has a small lattice constant of MgO, so that the diffraction pattern shifts to the high angle side.

  The second component used in the manufacturing method of the present embodiment is at least one oxide selected from the group consisting of oxides of Fe, Ni, Co, Cu, and Zn. The second component is dissolved in MgO as the first component to form a solid solution of MgO, thereby lowering its melting point and reducing the surface activity of MgO to suppress the reactivity with moisture in the atmosphere. To do. For this reason, the solid solution powder of the first component (MgO) suppresses the reaction with moisture in the atmosphere and suppresses the conversion to a low-density hydroxide as compared with the MgO powder. Therefore, when the solid solution powder is press-molded and sintered, large volume shrinkage of the particles of the molded body does not occur, so that a decrease in the relative density of the molded body is suppressed. When the compact is densified by processing at a higher temperature, the compact is not significantly contracted and cracks are suppressed from occurring in the sintered compact, and the densification proceeds sufficiently and the removal of pores proceeds. Therefore, an optically transparent ceramic is easily obtained.

Such a second component is preferably either ZnO, NiO, or CuO, and particularly preferably ZnO. ZnO has a high thermal conductivity of about 56 W · m ⁻¹ · K ⁻¹ itself, and Zn and Mg have similar ionic radii as shown in Table 1 below, and ZnO is dissolved in MgO. This is because the degree of lattice distortion is small in some cases, and the thermal conductivity of MgO is not greatly reduced.

Even if FeO, NiO, CoO, CuO or MnO is used, the melting point of MgO is lowered and the effect of forming a solid solution can be obtained as in the case of ZnO. However, it is necessary to consider the ionic radius of these metal elements to determine whether or not the high thermal conductivity of MgO is greatly reduced. The crystal structure of MgO is a sodium chloride (NaCl) structure, and the metal element atom is a hexacoordinate divalent ion. Table 1 below shows the ion radius (Å) of various metal elements and the ion radius consistency Δr (%) with Mg ions. Δr is expressed by the following equation (i):
Δr = (ion radius of the metal element−ion radius of Mg) / ion radius of Mg × 100 (%) (i)
In formula (i), the smaller the absolute value, the closer to the ionic radius of Mg ions.

  As is clear from Table 1, Cu has the highest matching Δr. However, since CuO has a small optical band gap (Eg = 1.4 eV), when 60 mol% or more is dissolved, the optical band gap of MgCuO Becomes 400 nm or more, and some visible light may be absorbed. On the other hand, Ni having relatively high ionic radius consistency following ZnO is preferable because the optical band gap (Eg = 3.7 eV) of NiO is large and the optical band gap of MgNiO exists in the ultraviolet region regardless of the composition. .

  On the other hand, Co has the same band gap as that of ZnO (Eg = 3.2 eV), and MgCoO is optically transparent, as in the case of Ni. Even in solid solution, the thermal conductivity tends to decrease. In addition, Fe and Mn have the lowest ionic radius matching, and therefore the thermal conductivity tends to decrease greatly.

  Empirically, the absolute value of the consistency Δr is preferably 5% or less, and Zn, Ni, and Cu satisfying this condition are preferable. In particular, any one of ZnO, NiO, or CuO is adopted as described above. Is preferred.

  The ratio of the metal element of the second component to the total amount of the metal elements of the first component and the second component is within a range where a solid solution in which the second component is dissolved in the first component is obtained when the second component is ZnO. Although there is no particular limitation, a range in which a single-phase solid solution in which the second component is dissolved in the first component is obtained (region indicated by MgO (SS) in FIG. 2) is preferably 20 mol% or more and 40 mol% or less. Is particularly preferred. If it exceeds 40 mol%, MgO (cubic) and hexagonal ZnO (second component) having a different refractive index co-deposit (region shown by MgO (SS) + ZnO (SS) in FIG. 2). Therefore, it becomes difficult to be transparent and birefringence is likely to occur. Moreover, since the fall degree of melting | fusing point will become small if it is less than 20 mol%, high sintering temperature is needed.

  When the second component is NiO, CoO, CuO or FeO, the second component is dissolved in the first component (MgO) in the entire ratio range regardless of the ratio of the second component, and the second component in the entire composition range. A solid solution is formed with no phase formation.

(First step)
Referring to FIG. 1, the first step S1 in the method for producing an MgO-based ceramic according to the present embodiment includes MgO powder as a first component and Fe, Ni, Co, Cu, Mn and the like as a second component. This is a step (solid solution powder forming step) in which at least one oxide powder selected from the group consisting of oxides of Zn is mixed to form a solid solution powder in which the second component is dissolved in the first component.

  Here, the solid solution powder in which the second component is dissolved in the first component is not particularly limited as long as it contains a solid solution in which the second component is dissolved in the first component, but the second component is included in the first component. It is a powder of a solid solution having a solid solution (solid solution in a region indicated by MgO (SS) in FIG. 2), that is, a powder formed only by a solid solution phase in which the second component is dissolved in the first component. Is preferred. When the solid solution powder is formed of a solid solution having a plurality of phases, it is difficult to be optically transparent and birefringence is likely to occur.

  In order to produce a solid solution powder in which the second component is dissolved in the first component, usually, the first component powder and the second component powder that forms the solid solution with the first component are mixed. The solid solution powder is prepared by calcining at an appropriate temperature, and the solid solution powder is molded and sintered.

  However, since the solid solution powder obtained by the above calcining has grain growth or agglomeration of fine powder, it needs to be pulverized or pulverized before forming and sintering after calcining.

  The manufacturing method of the MgO-based ceramics according to the present embodiment includes a solid solution powder in which the first component powder and the second component powder are mixed in the first step, and the second component is dissolved in the first component. Therefore, heat treatment (calcination) of the raw material powder for forming a solid solution and subsequent pulverization or pulverization treatment are unnecessary, and the MgO-based ceramic can be efficiently produced in a short time.

  In the first step, the mixing of the first component powder and the second component powder is not particularly limited as long as it is a method in which a solid solution powder in which the second component is dissolved in the first component is formed. In this case, it is preferable to perform the mechanical alloying method in which a large energy can be applied. Here, the mechanical alloying method refers to a method in which solid powder is mechanically finely mixed. The mechanical alloying method uses, for example, a ball mill to repeatedly fold and roll the first component powder and the second component powder using the collision energy of the ball, and finely mix both powders. can do.

  Although there is no restriction | limiting in particular in a mechanical alloying method, From a viewpoint which can add big energy at the time of powder mixing, it is preferable to use a planetary ball mill. By using a planetary ball mill, the powder of the first component and the powder of the second component can be mixed at the atomic level. The pulverization acceleration (also referred to as synthetic acceleration, hereinafter the same) by the planetary ball mill is preferably 10G or more. By mixing the first component powder and the second component powder with a planetary ball mill at a grinding acceleration of 10 G or more, a uniform solid solution powder can be obtained in a short time. The ball of the planetary ball mill is not particularly limited, but an Fe-based ball is preferable from the viewpoint that Fe dissolves in MgO in a wide composition range. Furthermore, stainless steel balls are more preferable as the Fe balls. This is because the stainless balls have high hardness and are not easily rusted, and Ni and Cr contained in the stainless balls are dissolved in MgO in a wide range of composition.

  In the first step, a mixed powder of the solid solution powder and the sintering aid can be formed by adding and mixing the sintering aid to the powder of the first component and the second component.

(Second step)
Referring to FIG. 1, the second step S2 of the method for producing an MgO-based ceramic according to the present embodiment is a step (forming step) of forming the solid solution powder obtained in the first step to obtain a formed body. . In such a molding process, not only the solid solution powder but also a mixed powder of the solid solution powder and the sintering aid may be molded to obtain a molded body. There is no restriction | limiting in particular in the method of shape | molding solid solution powder, Any method can be employ | adopted if it is a method which can obtain such a molded object. For example, a molding method using each mold, a press molding method, or the like can be employed. Moreover, you may add the binder for shaping | molding.

  The relative density of the molded body, which is a percentage of the density of the molded body with respect to the theoretical density of MgO, is preferably 54% or more. When the relative density of the molded body is less than 54%, the sintered body obtained by sintering the molded body is insufficiently densified, and the properties as a ceramic are lowered. From this viewpoint, the relative density of the molded body is more preferably 55% or more, and further preferably 60% or more.

(Third step)
Referring to FIG. 1, the third step S3 of the method for producing an MgO-based ceramic according to the present embodiment is a step of sintering the formed body obtained in the second step to obtain a sintered body (sintering). Process). The sintering temperature of the molded body may be changed depending on the melting point of the solid solution forming the solid solution powder. If the sintering is performed at a temperature at which a liquid phase appears in part, it becomes liquid phase sintering and tends to be densified. Of course, even solid-phase sintering tends to be densified as the sintering temperature approaches the melting point. When liquid phase sintering is performed, even if pressure sintering such as hot pressing is not performed, it can be easily densified by atmospheric pressure sintering which is inexpensive in terms of equipment. Of course, hot pressing may be performed even in such liquid phase sintering.

  In consideration of using a general sintering furnace in such a sintering process, it is preferable to sinter at about 1200 to 2000 ° C., so that the liquid phase appears at this temperature so that the liquid phase appears. It is preferable to adjust the solid solution species and the solid solution amount.

  In order to facilitate the sintering, in the step of forming the solid solution powder, a mixed powder can be prepared by adding a sintering aid to the solid solution powder. In this case, the sintering temperature and the hot isostatic press (hereinafter referred to as HIP), which will be described later, may be determined depending on the temperature at which the sintering aid changes to the liquid phase. As a sintering aid, for example, means such as adding an oxide of Sc and Al at an appropriate ratio can be employed. When such a sintering aid is used, the finally obtained MgO-based ceramic will contain a second phase other than the solid solution, so if such a second phase is not desired to be sintered, It is preferred not to use a binder.

  Since the sintered body obtained in this way is formed of a solid solution of MgO, it is a ceramic having high translucency, heat resistance, water resistance and thermal conductivity and no birefringence, and is preferably used for optical materials and the like. It is done.

Note that MgO is a ceramic that is very easy to react with moisture, and not only reacts with moisture in the air to form Mg (OH) ₂ to devitrify, but also eventually collapses. When such MgO is used as an optical material, the surface devitrifies over time. This phenomenon is particularly remarkable in the sintered body of MgO.
The MgO-based ceramic (sintered body) of this embodiment is a sintered body of a solid solution of MgO in which a second component such as ZnO is solid-solved in MgO that is the first component, and the surface of MgO that is the first component Since the activity is reduced and the reaction with moisture is suppressed, the material is chemically stable even in the long term.

<Embodiment 2>
Referring to FIG. 1, in another embodiment of the method for producing an MgO-based ceramic according to the present invention, a sintered body obtained in the third step of Embodiment 1 is subjected to hot isostatic pressing (HIP). A fourth step S4 for obtaining a HIP body by processing is further provided.

(Fourth process)
The 4th process of the manufacturing method of MgO type ceramics of this embodiment is a process (HIP processing process) which carries out HIP processing of the sintered compact obtained at the 3rd process of Embodiment 1, and obtains a HIP body. By such a HIP treatment step, pores in the sintered body are sufficiently removed, and a HIP body having high translucency can be obtained.

  In this HIP treatment step, the pressure medium is not particularly limited, but it is preferable to use an industrially available inert gas. The HIP processing temperature is preferably about 1200 ° C. or higher. When the temperature is lower than 1200 ° C., vacancies cannot be completely removed, and when the sintering temperature is exceeded, grain growth proceeds and residual vacancies tend to occur. For this reason, it is preferable that the upper limit of the HIP processing temperature does not exceed the sintering temperature. On the other hand, the HIP treatment pressure is preferably 500 atm (50.7 MPa) or more and 2000 atm (202.7 MPa) or less. If the pressure is less than 500 atm (50.7 MPa), a sufficient effect cannot be obtained, and even if it exceeds 2000 atm (202.7 MPa), the translucency is not further improved, and the apparatus becomes large. Therefore, it is not preferable. Further, it is sufficient that the HIP treatment time is 0.5 hours or longer, for example, 0.5 hours or longer and 2 hours or shorter, and various times may be changed depending on the thickness of the obtained MgO ceramics. Such HIP processing time varies depending on the holding time at the maximum temperature.

  The MgO-based ceramics (HIP body) of the present embodiment obtained in this way is a ceramic having higher translucency and no birefringence compared to the MgO-based ceramics (sintered body) of the first embodiment. It is preferably used for optical materials such as lenses.

  The MgO-based ceramics (sintered body and HIP body) obtained in Embodiments 1 and 2 above have high translucency, heat resistance and water resistance and no birefringence, and therefore satisfy the physical properties required for ordinary optical lenses. In particular, it is preferably used as an optical element for a color liquid crystal projector.

<Example 1>
(A) Raw material powder As the first component powder, MgO powder having an average particle diameter of 5 μm and a purity of 99.99 wt% was used. As the second component powder, ZnO powder having an average particle diameter of 3 μm and a purity of 99.99 wt%, FeO powder having an average particle diameter of 10 μm and a purity of 99.99 wt%, CoO powder having an average particle diameter of 3 μm and a purity of 99.99 wt%, average NiO powder having a particle size of 3.8 μm and a purity of 99.99 wt% or CuO powder having an average particle size of 4.5 μm and a purity of 99.99 wt% was used.

(B) Step of forming solid solution powder (first step)
Referring to Table 2, sample no. For 1-3, 7-9, the powder of the first component (MgO) and the powder of the second component are blended so as to have a predetermined composition ratio, and a stainless steel (SUS304) ball having a diameter of 3 mm, SiC (SC360) A ball or alumina (Al ₂ O ₃ ) ball is added and mixed for a predetermined time at a predetermined crushing acceleration using a planetary ball mill using a stainless steel pot to obtain a solid solution powder by mechanical alloying (MA). It was.

Sample No. For 4 and 5, the powder of the first component (MgO) and the powder of the second component were blended so as to have a predetermined composition ratio, a stainless steel (SUS304) ball having a diameter of 3 mm was added, and a normal ball mill (BM ) To obtain a solid solution powder. For sample No. 6, without adding the second component powder to the first component (MgO) powder, a stainless steel (SUS304) ball with a diameter of 3 mm was added, and a normal ball mill (BM) was used for a predetermined time. Mixed. Furthermore, sample no. The powder obtained in 4-6 is put in a crucible made of aluminum oxide (Al ₂ O ₃ ), calcined in the atmosphere at 1360 ° C. for 13 hours, and then crushed for 1 hour using a normal ball mill (BM). did.

  In addition, the production | generation phase of the solid solution powder obtained above was identified by powder X-ray diffraction. The results are summarized in Table 2. “MgO” in the “Formation phase” column of Table 2 indicates that the production phase is cubic MgO. “ZnO” indicates that the product phase is a hexagonal crystal of ZnO. Further, the true density of the solid solution powder is measured with a pycnometer, and the composition of the first component and the second component in the solid solution powder is determined from the theoretical true density (theoretical density) of the first component (MgO) and the second component. As a result of calculating (mol%), the composition (mol%) of the powder of the first component (MgO) and the powder of the second component was the same. Here, the composition of each component means the composition of the metal element of each component with respect to the whole of the metal elements of all components.

(C) Step of obtaining a molded body (second step)
To 50 g of each solid solution powder formed above, 0.22 g of PVB-BL1 (trade name) manufactured by Sekisui Chemical Co., Ltd. was added as a binder, 20 g of ethanol was added, and the mixture was collected after mixing for 24 hours using a nylon pot and nylon balls. .

  The solid solution powder after collection was loaded into a mold to produce a disk-shaped molded body having a diameter of 20 mm and a thickness of 2 mm. The relative density of the molded body thus obtained (percentage of the density of the molded body with respect to the theoretical density of MgO) was measured by the Archimedes method. The results are summarized in Table 2.

(D) Step of obtaining a sintered body (third step)
Each molded body obtained above was heated to a predetermined temperature (sintering temperature described in Table 2) at 100 ° C./hr in a vacuum furnace, held at that temperature for 1 hour, and then naturally cooled in the furnace. A sintered body was obtained. The degree of vacuum during firing was set to 10 ⁻² Pa or less. The relative density of the sintered body (percentage of the density of the sintered body with respect to the theoretical density of MgO) was measured by the Archimedes method. The product phase was confirmed by powder X-ray diffraction. The results are summarized in Table 2. “MgO” in the “Formation phase” column of Table 2 indicates that the production phase is cubic MgO. “ZnO” indicates that the product phase is a hexagonal crystal of ZnO.

(E) Step of obtaining a HIP body (fourth step)
Each sintered body obtained above was heated to a predetermined temperature (HIP temperature shown in Table 2) at 800 ° C./hr in Ar gas, and held at a pressure of 1000 atm (101.3 MPa) for 1 hour. A HIP body (thickness 1 mm) was obtained by performing a HIP (hot isostatic pressing) process. The relative density of HIP bodies thus obtained (percentage of density of HIP bodies relative to the theoretical density of MgO) was measured by the Archimedes method. The results are summarized in Table 2. In Table 2, sample No. 1 to 5 and 7 to 9 are examples of the present invention. 6 is a comparative example.

(F) Evaluation (f-1) Linear transmittance The MgO-based ceramics (HIP body) obtained above is mirror-polished using a diamond slurry, and the linear transmittance (thickness 1 mm) is measured with a spectrophotometer. It was measured. As a result, the linear transmittance at a wavelength of 420 nm to 680 nm was lowest at 420 nm, and thus the linear transmittance at 420 nm was measured in the samples of the examples and comparative examples. The results are summarized in Table 2.

(F-2) Water resistance Water resistance was evaluated by conducting a water resistance acceleration test of the MgO-based ceramics (HIP body) obtained above. That is, each MgO-based ceramic was pulverized with a planetary ball mill at an acceleration of 150 G for 10 minutes to form a powder until the BET specific surface area value was about 0.3 m ² / g, which was immersed in boiling water at 98 ° C. for 5 hours. The weight increase ratio after immersion was measured. It shows that it is inferior to water resistance, so that a weight increase becomes large. The results are summarized in the column of “weight increase rate during water resistance test (wt%)” in Table 2.

(F-3) Thermal conductivity A test piece having a diameter of 10 mm is cut out from the MgO-based ceramics (HIP body) (thickness 1 mm) obtained above, and the thermal conductivity at room temperature (for example, 25 ° C.) is measured by a laser flash method. It was measured. The results are summarized in Table 2.

  As is apparent from Table 2, the MgO-based ceramics of the examples of the present invention (sample Nos. 1 to 5 and 7 to 9) are optical materials and the like as compared with the MgO-based ceramics of the comparative example (sample No. 6). It is possible to manufacture ceramics having translucency, water resistance and thermal conductivity suitable for the above in a short time and efficiently at a low cost. Sample No. In No. 1, the linear transmittance was low, but this was probably due to insufficient mixing and the formation of a plurality of MgO and ZnO phases in the solid solution.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a flowchart which shows the manufacturing method of the MgO type | system | group ceramic concerning this invention. It is a phase diagram of a MgO-ZnO type solid solution.

Explanation of symbols

  S1 1st process, S2 2nd process, S3 3rd process, S4 4th process.

Claims (10)

Mixing the powder of MgO as the first component and the powder of at least one oxide selected from the group consisting of oxides of Fe, Ni, Co, Cu, Mn and Zn as the second component, A first step of forming a solid solution powder in which the second component is dissolved in the first component;
A second step of forming the solid solution powder to obtain a molded body;
And a third step of obtaining the sintered body by sintering the molded body.   The method for producing an MgO-based ceramic according to claim 1, wherein the second component is any one of ZnO, NiO, and CuO.   The method for producing an MgO-based ceramic according to claim 1 or 2, wherein a ratio of the metal element of the second component to a total amount of the metal elements of the first component and the second component is 20 mol% or more and 40 mol% or less. .   The method for producing an MgO-based ceramic according to any one of claims 1 to 3, wherein the mixing is performed by a mechanical alloying method in the first step.   The said mechanical alloying method is a manufacturing method of the MgO type | system | group ceramics of Claim 4 using a planetary ball mill.   The method for producing an MgO-based ceramic according to claim 5, wherein a grinding acceleration by the planetary ball mill is 10 G or more.   The method for producing an MgO-based ceramic according to claim 5 or 6, wherein an Fe-based ball is used as a ball of the planetary ball mill.   The method for producing an MgO ceramic according to claim 7, wherein the Fe ball is a stainless ball.   The method for producing an MgO-based ceramic according to any one of claims 1 to 8, further comprising a fourth step of obtaining a HIP body by subjecting the sintered body to hot isostatic pressing.   The method for producing an MgO-based ceramic according to any one of claims 1 to 9, wherein a relative density of the compact, which is a percentage of the density of the compact relative to a theoretical density of MgO, is 54% or more.

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