KR101897432B1 - Method for producing transparent magnesium aluminate spinel and transparent magnesium aluminate spinel - Google Patents

Abstract

The present invention relates to a method for producing a magnesium aluminate spinel transparent ceramic and a magnesium aluminate spinel transparent ceramic produced using the same, the method comprising the steps of: preparing an aqueous slurry of raw nano powder; Dispersing the raw nano powder in the aqueous slurry to form a uniformly monodispersed aqueous slurry; And spraying the homogeneously monodispersed aqueous slurry into liquid nitrogen to obtain spherical granules by rapid freezing and lyophilization; Molding the granules to form a formed body; And sintering the molded body, and a magnesium aluminate spinel transparent ceramic produced by the method.

Description

TECHNICAL FIELD The present invention relates to a method for producing a magnesium aluminate spinel transparent ceramic and a magnesium aluminate spinel transparent ceramic produced using the same,

The present invention relates to a process for producing magnesium aluminate spinel transparent ceramics and a magnesium aluminate spinel transparent ceramics produced using the same.

Transparent ceramics with excellent light transmission properties are attracting attention as laser oscillation, bulletproof windows, luminous fluxes, and IR transmission window materials.

The core properties required by the IR transmission window are high transmittance, resistance to erosion and thermal shock in the IR range. Magnesium Aluminate (MgAl ₂ O ₄ ) Spinel is a solid compound (or solid solution) of magnesia (MgO) and alumina (Al ₂ O ₃ ) and has a crystal structure of cubic (cubic) It belongs to a substance which can have transparency. The refractive index in the visible light region is about 1.72 and the theoretical light transmittance is about 86.9%. Mechanical properties such as bending strength in the range of 150 MPa to 200 MPa, and Vickers hardness of 13 GPa to 15 GPa.

The MgAl ₂ O ₄ spinel has relatively high hardness, moderate strength and relatively high transmittance in the infrared region compared to Sapphire and AlON, and is considered to be a promising material for the above-mentioned IR transmission window material. In order to be applied to this application field, it is necessary to obtain a MgAl ₂ O ₄ sintered body having a high light transmittance of 80% or more in the visible light region. To this end, it is necessary to minimize the defects such as pores in the sintered body, .

The primary particle size of the raw material powder is directly related to the internal pore size when the raw material powder is molded. That is, the smaller the primary particles, the smaller the size of the pores in the formed body. The smaller the size of the internal pores, the easier it is to remove through the grain boundary diffusion during the sintering process. Therefore, the smaller the size of the primary particles, the more advantageous to make transparent ceramics. For this reason, nano powder is used as a raw material when preparing translucent MgAl ₂ O ₄ spinel.

When the primary particles are used as the raw material, the agglomerates of the primary particles are not nano-sized. The smaller the primary particles, the more the Van der Waals force, which depends on the specific surface area, The cohesive force between them becomes stronger. Therefore, when particle size analysis is performed on a conventional nano powder, a large amount of agglomerates having a size of several to several tens of micrometers is detected. In non-patent document 001, J. Binner et al. Have reported that when the powder containing such aggregates is molded without any additional treatment, the shape of the aggregate remains intact inside the compact to cause microcracks therein. In addition, since such a microcrack acts as a passage through which light is scattered, it is a factor that greatly hinders the translucency. Dericioglu et al.

Therefore, it is indispensable to manufacture defoamers such as pores / microcracks in the production of translucent ceramics. To solve this problem, a high-level treatment process is required for the raw nano powder.

 J. Binner, Journal of the European Ceramic Society, Vol. 28, 2008, pp 1329-1339.  A.F. Dericioglu, Journal of the European ceramic society, Vol. 23, 2003, pp 951-959.

It is possible to improve the transmittance in the visible light / ultraviolet ray region by suppressing the re-agglomeration of the nano powder by dispersion and rapid freezing treatment of the raw material nano powder, and at the same time to improve the mechanical strength through suppression of defects, A method for producing a transparent ceramic, and a magnesium aluminate spinel transparent ceramic produced by the above method.

Preparing an aqueous slurry of the raw nano powder according to one embodiment; Dispersing the raw nano powder in the aqueous slurry to form a uniformly monodispersed aqueous slurry; And spraying the homogeneously monodispersed aqueous slurry into liquid nitrogen to obtain spherical granules by rapid freezing and lyophilization; Molding the granules to form a formed body; And sintering the shaped body; To a process for producing magnesium aluminate spinel transparent ceramics.

According to one embodiment, the step of forming the homogeneously monodisperse aqueous slurry may be performed by applying a high pressure shear force to the aqueous slurry.

According to one embodiment, the high pressure shear force may be at least 50 MPa.

According to one embodiment, the particle size of the raw nano powder may be 40 nm to 300 nm.

According to one embodiment, the volume fraction of solid particles in the aqueous slurry of the raw nano powder may be 20% or less.

According to one embodiment, the size of the aggregate in the homogeneously monodispersed aqueous slurry may be less than 300 nm.

According to one embodiment, the obtaining of the spherical granules may be performed by spraying the uniformly monodisperse aqueous slurry using at least one of ultrasonic atomization, pressurized atomization, and indirect atomization by high pressure gas.

According to one embodiment, the spherical granules may have a diameter of 300 mu m or less.

According to one embodiment, the step of sintering the shaped body includes: a first sintering of the formed body; And a second high pressure heat treatment after the first sintering step; . ≪ / RTI >

According to one embodiment, the first sintering step may be performed at 1,300 ° C to 1,550 ° C.

According to one embodiment, the first sintering step may be to obtain a sintered body having a density of at least 3.35 g / cm < ³ >.

According to one embodiment, the second high pressure heat treatment step may be performed at a pressure of 1,400 ° C to 1,650 ° C and a pressure of 50 MPa or more.

According to one embodiment, a magnesium aluminate spinel transparent ceramic is produced by the process according to the invention and has a transmittance of at least 50% in the ultraviolet and visible light regions.

According to one embodiment, the magnesium aluminate spinel transparent ceramic may have a strength of at least 250 MPa.

According to one embodiment, the raw material nano powder is subjected to rapid freezing by using liquid nitrogen to uniformly monodisperse an aqueous slurry with a high shear force to suppress the re-agglomeration of the nano powder, and transmittance in the visible ray / ultraviolet ray region And at the same time, it is possible to provide magnesium aluminate spinel ceramics having improved mechanical strength through suppression of defects.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow diagram of a method of making a magnesium aluminate spinel transparent ceramic, in accordance with one embodiment.
2 is a graph showing the particle size distribution in the magnesium aluminate spinel aqueous slurry prepared in Examples and Comparative Examples.
3 is a scanning electron microscope (SEM) image of the spherical granules prepared in the examples.
4 is a graph showing the densities of the primary sintered bodies produced in Examples and Comparative Examples.
Fig. 5 is an image of the secondary sintered body (magnesium aluminate spinel transparent ceramic) produced in Examples and Comparative Examples.
6 is a graph showing the light transmittance by the UV-Vis-NIR spectrum of the secondary sintered body manufactured in Examples and Comparative Examples.
Fig. 7 is a scanning electron microscope (SEM) image of the fractured surface of the molded article produced in Examples and Comparative Examples.
8 is a scanning electron microscope (SEM) image of the fracture section of the primary sintered body manufactured in Examples and Comparative Examples.
9 is a scanning electron microscope (SEM) image of the fracture surface of the secondary sintered body manufactured in Examples and Comparative Examples.

In the following, embodiments will be described in detail with reference to the accompanying drawings. However, various modifications may be made in the embodiments, and the scope of the patent application is not limited or limited by these embodiments. It is to be understood that all changes, equivalents, and alternatives to the embodiments are included in the scope of the right.

The terms used in the examples are used for descriptive purposes only and are not to be construed as limiting. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises" or "having" and the like refer to the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this embodiment belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

In the following description of the present invention with reference to the accompanying drawings, the same components are denoted by the same reference numerals regardless of the reference numerals, and redundant explanations thereof will be omitted. In the following description of the embodiments, a detailed description of related arts will be omitted if it is determined that the gist of the embodiments may be unnecessarily blurred.

According to one embodiment, a method of making a magnesium aluminate spinel transparent ceramic is disclosed.

1 is a flow chart of a method of manufacturing a magnesium aluminate spinel transparent ceramic according to an embodiment of the present invention, in accordance with one embodiment. 1, the method comprises: preparing an aqueous slurry of raw nano powder; Forming a homogeneously monodispersed aqueous slurry; And rapidly freezing and drying to obtain spherical granules; Forming a formed body; And sintering the shaped body.

According to one embodiment, preparing the aqueous slurry of the raw nano powder is a step of preparing an aqueous slurry in which an aqueous solvent and a magnesium aluminate raw nano powder are mixed.

The primary particle size of the magnesium aluminate raw nano powder is 40 nm to 300 nm; Or from 100 nm to 200 nm. A first sintered body having a high sintered density at a low temperature when the size of the sintered body is within the above range; For example, it is possible to obtain a primary sintered body of 3.35 g / cm ³ or more at a temperature of 1600 ^° C or less, and to easily obtain an aqueous slurry having a volume fraction of 5% or more.

The volume fraction of solid particles in the aqueous slurry of the starting nano powder is 20% or less; 0.01% to 20%; 1% to 15%; Or from 5% to 10%. When the volume fraction is within the above range, the nano powder can be well dispersed, and it may be advantageous to obtain frozen granules having a uniform shape and size.

The aqueous solvent may be water (e.g., tertiary distilled water); Alternatively, the organic solvent may further include an organic solvent. For example, the organic solvent may be an alcohol having 1 to 5 carbon atoms.

The preparation of the aqueous slurry of the raw nano powder may be performed by ball milling, stirred ball milling, vibration milling, ultrasonic milling or the like.

The aqueous slurry of the raw nano powder may further include an additive for obtaining a dispersion of the nano powder and an aqueous slurry of the stable raw nano powder, and may include, for example, a surfactant. The surfactant may include at least one selected from the group consisting of a binder, a lubricant, a plasticizer, and a dispersant. 1 to 3 parts by weight of the surfactant is added to 100 parts by weight of the aqueous slurry of the raw nano powder; Or 1.5 to 2.4 parts by weight.

According to one embodiment, the step of forming the homogeneously monodisperse aqueous slurry comprises: applying a high pressure shear force to the aqueous slurry to destroy (or remove) the aggregates of the particles in the aqueous slurry, Thereby forming a slurry.

A high pressure shearing force is applied to the slurry to disperse agglomerates of several to several tens of micrometers contained in the aqueous slurry, and the shear force is preferably at least 50 MPa. The high-pressure shear force is 50 MPa or higher; 100 MPa or more; Or 200 MPa or more. When included in the high pressure shear force range, large particle aggregates in the aqueous slurry, for example, agglomerates of 300 nm or more and agglomerates of several to several tens of micrometers in size can be removed and dispersed to provide a monodisperse aqueous slurry.

The high-pressure shear force may be determined by using a high-hardness ceramic medium such as planetary milling, attrition milling, beads milling or the like; High - speed rotation of high - hardness rotor; A method of passing a narrow passage through the Bernoulli principle; , And the like.

The size of the agglomerates in the homogeneously monodispersed aqueous slurry is less than 300 nm, which leads to uniform droplet spraying of the slurry in obtaining the next step of spherical granules, Can be reduced.

According to one embodiment, the step of rapidly freezing and drying to obtain spherical granules comprises spraying the uniformly monodispersed aqueous slurry into liquid nitrogen, rapidly freezing it, and lyophilizing it to obtain spherical granules. That is, by spraying the uniformly monodispersed aqueous slurry into a spherical droplet in a water tank containing liquid nitrogen and rapidly freezing, and sublimating the residual solvent, for example, water, through freeze drying before the frozen spherical droplet is melted, Thereby obtaining a spherical granule composed of particles.

The step of acquiring the spherical granules may spray the uniformly dispersed aqueous slurry using at least one of ultrasonic spraying, pressurized spraying and indirect spraying with high-pressure gas.

The lyophilization may be performed in a freeze dryer in which the rapidly frozen spherical droplets are dissolved in the liquid nitrogen for 1 hour or more; 20 hours or more; Or lyophilized for at least 30 hours to obtain spherical granules, preferably at least 30 hours to remove moisture at less than 0.1 wt% and prevent agglomeration between granules due to melting of unsintered ice; It can be lyophilized for more than 36 hours.

The spherical granules have a particle size of 300 mu m or less; 200 탆 or less; 100 탆 or less; And may have a diameter of 50 mu m. If it is within the above range, the shape of the sintered body can be stably maintained after freeze-drying of spherical granules, and the sintered density, strength, hardness and transparency of the sintered body can be improved.

According to one embodiment, the step of forming the molded body is a step of dry-molding the spherical granules to form a predetermined shaped body. The dry molding is a dry molding method in which the powder is charged into a certain mold and a certain pressure is applied to the molded body. The dry molding method applied in the technical field of the present invention can be used, for example, Warm molding, and the like.

According to one embodiment, the step of sintering the molded body is a step of obtaining a magnesium aluminate spinel transparent ceramic by sintering the molded body obtained in the step of forming the molded body.

The step of sintering the formed body may include: a first sintering the formed body; And a second high pressure heat treatment after the first sintering step; . ≪ / RTI >

In the first sintering step, the first sintered body can be obtained by performing sintering heat treatment at a temperature of 1,300 ° C to 1,550 ° C for 2 hours to 15 hours. The sintered body having a sintered density of at least 90% when the temperature and time are within the above range is obtained, and a sintered body having high strength and transparency after the second high pressure heat treatment is obtained. The mechanical strength Can be prevented from being lowered.

The first sintering may be performed in an atmosphere containing at least one selected from the group consisting of air, oxygen, vacuum, Ar, and N ₂ .

The second high pressure heat treatment step can increase the sintered density of the primary sintered body obtained in the primary sintering step to improve the mechanical strength and obtain the sintered body having improved transparency.

The second high-pressure heat treatment may be performed by introducing the primary sintered body into a hot-isostatic press (HIP) apparatus and heating at a temperature of 1,400 to 1,650 DEG C to 50 MPa or more; 150 MPa or more; Or from 150 MPa to 200 MPa for 3 hours to 10 hours. When the amount is within the above range, sufficient pores are removed, high transmittance is achieved, and mechanical strength deterioration due to grain growth due to high temperature can be prevented.

The second high pressure heat treatment step may be performed in an atmosphere containing Ar, N _2, or both.

The density of the second sintered body obtained in the second high pressure heat treatment step is preferably 3.35 g / cm ³ or more. If the density is less than 3.35 g / cm ³ , complete densification (3.578 g / cm ³ ) by the HIP process is not achieved.

According to one embodiment, there is provided a magnesium aluminate spinel transparent ceramic produced by the process according to the present invention. The magnesium aluminate spinel transparent ceramics is obtained by rapidly freezing the aqueous slurry which is homogeneously monodispersed by applying a high shear force to the raw nano powder and liquid nitrogen to inhibit the re-agglomeration of the nano powder thereby to improve the transmittance in the visible ray / It is possible to improve the mechanical strength through improvement of the defect while suppressing the defect.

The magnesium aluminate spinel transparent ceramic has a transmittance of at least 50% in the ultraviolet and visible regions, for example at least 50% in the ultraviolet region, for example at a wavelength of 300 nm; 55% or more; 60% or more, visible light region, for example, 70% or more at 550 nm to 800 nm; 80% or more; It can be more than 90%.

According to one embodiment, the magnesium aluminate spinel transparent ceramic has a melting point of at least 250 MPa; Or a four point bending strength of 250 to 300 MPa.

< Example  1>

(1) Manufacture of spherical granules

The raw material MgAl ₂ O ₄ spinel powder is S30CR powder from Baikowski of France. It is a high-purity nano powder having a mean particle size D ₅₀ of 55 to 60 nm, and has an equiaxed shape with a polygonal shape.

The raw material powder was mixed with third distilled water (18.5 M?) So as to have a final solid particle volume fraction of 10.0 vol.%. To obtain a stable slurry, 2.5 wt% of a surfactant (ammonium polyacrylic acid, NH ₄ PAA) was added. The mixed slurry was first dispersed for 24 hours in a ball milling process, and then a high pressure shear force of 100 MPa was applied to uniformly disperse the spinel nanoparticles in a second order to prepare a monodispersed slurry. The particles in the slurry were analyzed and shown in Fig.

The slurry was sprayed into a water tank containing liquid nitrogen using a pressure type atomizer and rapidly frozen, and spherical granules were obtained through freeze-drying. An image of the spherical granules is shown in Fig.

(2) Production of transparent ceramics

And then subjected to uniaxial molding using a steel mold, followed by hydrostatic molding at 200 MPa to obtain a molded article. The molded article was degreased at 850 DEG C to completely remove the surfactant. Thereafter, the density was measured by sintering (primary sintering) at 1450 ° C., 1500 ° C., 1550 ° C., and 1600 ° C. for 2 hours under an air atmosphere, and the density of the sintered body was measured by Archimedes method (ASTM C373). The results are shown in Fig.

The density of the sintered body of Figure 4 3.35 g / cm ³ The sintered body was pressurized in a hot isostatic press at 1,450 ° C and 180 MPa in an Ar atmosphere for 5 hours to obtain a magnesium aluminate spinel transparent ceramic.

< Example  2>

A high pressure shear force of 100 MPa was applied in the same manner as in Example 1 except that the final solid particle volume fraction was 10.0 vol.%, And the spinel nanoparticles were uniformly quadratically dispersed to prepare a monodisperse slurry. After obtaining the granules, sintered bodies were prepared. The particles in the slurry were analyzed and shown in Fig.

< Comparative Example  1>

A slurry having a final solid particle volume fraction of 20.0 vol.% Was prepared by a ball-milling process in the same manner as in Example 1 without applying a high-pressure shear force of 100 MPa, and after obtaining spherical granules, . The particles in the slurry were analyzed and shown in Fig.

In FIG. 2, the particle distributions of the slurries prepared in Examples and Comparative Examples are shown using a laser analyzer. 2, there was no agglomerate having a size of 300 nm or more in the case of applying a high pressure shear force. On the contrary, in the case of the ball-milling-only slurry (Comparative Example 1) .

FIG. 3 shows the image of the spherical granules obtained in Example 1, and the average size of the granules is about 50 μm.

In Fig. 4, when the formed body was sintered at 1,450 ° C to 1,600 ° C, the density of the sintered body was the highest in the case of Example 1. When the volume fraction of the solid phase particle is low, the effect of increasing the sintering property can be confirmed.

< Test Example  1> Solid particle Volume fraction  Evaluation of permeability according to dispersion method 1

Fig. 5 shows images of a second sintered ceramic specimen at 1550 DEG C manufactured in Examples and Comparative Examples. As shown in Fig. 5, It can be seen that the translucency of the specimen of Comparative Example 1 on the left side is lower than that of the other two specimens on the left side.

< Test Example  2> Solid particle Volume fraction  Evaluation of permeability according to dispersion method 2

The light transmittance was measured using a spectroscope to more accurately evaluate the transmittance evaluation of Test Example 1 above.

The light transmittance of the three specimens (1550 ° C) and the sintered specimen of 1600 ° C used in Test Example 1 were measured. The light transmittance was measured using a UV-Vis-NIR spectrophotometer (Cary 5000, Agilent Technologies, Santa Clara, CA, USA) using a 4 mm diameter slit in the wavelength range of 0.3 to 0.8 μm. The results are shown in Fig. As shown in FIG. 6, as shown in FIG. 5, the difference in transmittance between the visible light and the UV / Vis / NIR spectroscope clearly shows the difference in transmittance. It can be seen that the specimen of Example 1 has the highest transmittance, the case of Example 2 has the lowest visible light transmittance, and the case of Comparative Example 3 has the lowest visible light transmittance.

In order to analyze the reason why the transmittance is different, a molded body, a first sintered body and a second high-pressure heat-treated specimen for each specimen were respectively measured by a scanning electron microscope (SEM) and shown in FIGS. 7 to 9.

In FIG. 7, it can be seen that the form of the fracture surface of the formed body largely differs according to the preparation conditions of the aqueous slurry. In the case of Comparative Example 1, a step-like fracture surface appears, which reflects the non-uniformity of the slurry dispersion. In Example 1 and Example 2, a step-like fracture section is not shown, which is due to uniform dispersion. However, in Example 2, some agglomerates were observed. As the solid fraction increased, the distance between particles became closer to each other, and local aggregates were formed by Van der Waals attraction.

In FIG. 8, it can be seen that the shapes of the primary sintered body polishing surfaces are largely different depending on the preparation conditions of the aqueous slurry. In the case of BM20, large and long circular pores were observed, reflecting the stepped fracture profile observed in FIG. In Examples 1 and 2, circular pores were not observed but uniformly dispersed isolated pores were observed. The shape of the fracture surface was reflected in the sintered body as it is. However, a relatively large pore was observed in Example 2 as compared with Example 1.

It can be seen in FIG. 9 that the shapes of the sintered body polishing surfaces subjected to the secondary heat treatment differ greatly depending on the preparation conditions of the aqueous slurry. In the case of Comparative Example 1, pores having a large and long arc shape were observed, which was observed without removing the pores observed in FIG. In Examples 1 and 2, circular pores were not observed but uniformly dispersed isolated pores were observed. The shape of the primary sintered body polishing surface was directly reflected in the sintered body. However, the pores in Example 2 were relatively larger and larger than those in Example 1.

As a result, the shape and size of the pore defects in the specimen were significantly different according to the preparation conditions of the aqueous slurry, as a result of scanning electron microscopic observation of the molded body, the first sintered body and the second high pressure heat- This difference can be seen as reflected in the difference in transmittance in the ultraviolet / visible region. That is, it is advantageous to prepare a magnesium aluminate spinel transparent ceramic having a high permeability by using a slurry having a low solid fraction fraction in the aqueous slurry and uniformly dispersed by a high pressure shear force.

Although the embodiments have been described with reference to the drawings, various technical modifications and variations may be applied to those skilled in the art. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI &gt; or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (14)

Preparing an aqueous slurry of magnesium aluminate nano powder;
Dispersing the nanopowder in the aqueous slurry to form a uniformly monodispersed aqueous slurry; And
Spraying the homogeneously monodispersed aqueous slurry into liquid nitrogen to obtain spherical granules by rapid freezing and lyophilization;
Molding the granules to form a formed body; And
Sintering the shaped body;
/ RTI &gt;
Wherein the volume fraction of the solid particles in the aqueous slurry of the nano powder is greater than 0 and less than 20%
Method of manufacturing magnesium aluminate spinel transparent ceramic.
The method according to claim 1,
Wherein forming the homogeneously monodispersed aqueous slurry is performed by applying a high pressure shear force to the aqueous slurry.
Method of manufacturing magnesium aluminate spinel transparent ceramic.
3. The method of claim 2,
Wherein the high-pressure shearing force is at least 50 MPa.
The method according to claim 1,
Wherein the nano powder has a particle size of 40 nm to 300 nm.
delete The method according to claim 1,
Wherein the size of the agglomerates in the homogeneously monodispersed aqueous slurry is less than 300 nm. &Lt; Desc / Clms Page number 20 &gt;
The method according to claim 1,
Wherein the step of obtaining the spherical granules comprises spraying the homogeneously monodisperse aqueous slurry using at least one of ultrasonic spraying, pressurized spraying and indirect spraying with a high-pressure gas to produce a magnesium aluminate spinel transparent ceramic .
The method according to claim 1,
Wherein the spherical granules have a diameter of 300 mu m or less.
The method according to claim 1,
The step of sintering the formed body may include: a first sintering the formed body; And a second high pressure heat treatment after the first sintering step; &Lt; / RTI &gt; wherein the magnesium aluminate spinel transparent ceramic has a thickness of at least 100 microns.
10. The method of claim 9,
Wherein the first sintering step is performed at a temperature of 1,300 ° C to 1,550 ° C.
10. The method of claim 9,
Wherein the first sintering step obtains a sintered body having a density of at least 3.35 g / cm &lt; ³ &gt;.
10. The method of claim 9,
Wherein the second high pressure heat treatment step is carried out at a pressure of 1,400 DEG C to 1,650 DEG C and a pressure of 50 MPa or more.
A process for the preparation of a compound according to any one of claims 1 to 4 and 6 to 12,
Magnesium aluminate spinel transparent ceramics having a transmittance of at least 50% in the ultraviolet and visible light regions.
14. The method of claim 13,
Wherein the magnesium aluminate spinel transparent ceramic has a strength of at least 250 MPa.

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