Method for preparing magnesium aluminate spinel transparent ceramic through hot pressed sintering

Abstract

The invention discloses a method for preparing magnesium aluminate spinel transparent ceramic through hot pressed sintering, which belongs to the technical field of ceramics, and specifically comprises the following steps: (1) putting magnesium aluminate spinel spherical powder into a graphite mold, and carrying out first vacuum hot pressed sintering to obtain a flat blank; (2) performing mold-free second-time vacuum hot pressed sintering on the flat-plate-shaped blank to obtain a compact blank; and (3) carrying out annealing and hot isostatic pressing on the compact blank to obtain the magnesium aluminate spinel transparent ceramic. The compact ceramic with the diameter larger than that of an original mold is prepared in a two-time hot pressing sintering mode, through the technology, preparation of the magnesium aluminate spinel transparent ceramic plate with the larger size under the original equipment and mold conditions is achieved, and the restriction of the mold and equipment size on preparation of the large-size ceramic is effectively solved to a certain degree.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramics, and particularly relates to a method for preparing magnesium aluminate spinel transparent ceramics by hot pressing sintering. Background Art

[0002] Magnesium aluminate spinel (MgAl2O4) transparent ceramics have excellent properties such as high melting point, high transmittance, wide transmission band, high hardness, high strength, high thermal conductivity, good thermal shock resistance, corrosion resistance and high temperature resistance, and can be widely used in infrared guidance windows, fairings of high Mach aircraft, transparent armor, observation windows of reaction vessels, and windows of optoelectronic devices in extreme environments, etc. With the development of equipment / devices, it is required that magnesium aluminate spinel transparent ceramics have larger sizes.

[0003] At present, the commonly used preparation methods for magnesium aluminate spinel transparent ceramics mainly include vacuum hot pressing / hot isostatic pressing and pressureless sintering / hot isostatic pressing. Among them, vacuum hot pressing is a forming and sintering method in which the forming and densification processes are carried out simultaneously. By applying axial pressure while heating up, it promotes particle rearrangement and pore elimination, and has the characteristics of low sintering temperature, short time, and effective control of green body deformation. It is more suitable for the preparation of large-size magnesium aluminate spinel transparent ceramics. However, since a larger mold is required when preparing large-size transparent ceramics, a larger available working size of the equipment is needed to place the large mold. At present, the commonly used hot pressing mold is a high-purity isostatic pressing graphite mold. The size of the graphite mold in the prior art is limited. When the size reaches a certain specification, a more expensive carbon-carbon material needs to be used, which greatly increases the manufacturing cost. And the size of the material and equipment is always limited, thus restricting the size of the hot-pressed sintered transparent ceramics.

[0004] Therefore, it is an urgent problem for those skilled in the art to provide a method for preparing large-size magnesium aluminate spinel transparent ceramics with simple process, high quality and low cost. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing large-size magnesium aluminate spinel transparent ceramics by hot pressing sintering. By adopting the method of two-stage hot pressing sintering, a denser ceramic with a diameter larger than that of the original mold is prepared. Through the above technology, the preparation of a larger-size magnesium aluminate spinel transparent ceramic plate under the conditions of the original equipment and mold is realized, and to a certain extent, the restriction of the mold and equipment size on the preparation of large-size ceramics is effectively solved.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] A method for preparing magnesium aluminate spinel transparent ceramics by hot pressing sintering specifically includes the following steps:

[0008] (1) Put the spherical powder of magnesium aluminate spinel into a graphite mold and conduct the first vacuum hot pressing sintering to obtain a flat blank;

[0009] (2) Subject the flat blank to a second vacuum hot pressing sintering without a mold to obtain a dense blank;

[0010] (3) Subject the dense blank to annealing and hot isostatic pressing to obtain the magnesium aluminate spinel transparent ceramic.

[0011] In the present invention, first, spherical powder is placed in a graphite mold for the first vacuum hot pressing. A small-sized graphite mold is used at a relatively low temperature stage to hot press a flat blank that is formed but not completely dense; then, the flat blank is subjected to a second hot pressing without using a mold, and a dense blank with a reduced thickness but a larger planar size than the flat blank is hot pressed. Since the second hot pressing does not use a mold, the space occupied by the mold is reduced, and the working size space of the hot pressing sintering furnace can be saved.

[0012] Preferably, the parameters of the first vacuum hot pressing sintering in step (1) are:

[0013] The vacuum degree is 10 -1 -10 -3 Pa, the sintering temperature is 1000 - 1400 °C, and the pressure is 20 - 80 MPa;

[0014] Keep warm for 30 min - 5 h, then release the pressure and cool down. Then, cool down at a rate of 0.5 - 15 °C / min to 200 - 600 °C, and finally cool down naturally to room temperature.

[0015] The graphite mold has good high-temperature creep resistance and relatively low cost, and is easy to process. Using the graphite mold in the first hot pressing can ensure the stability of the forming process;

[0016] The temperature of the first hot pressing is relatively low, mainly to initially form the powder, obtain a moderate density and thickness. This is because at a lower temperature, the bonding between powder particles is relatively weak, which can better control the thickness of the blank and avoid structural defects caused by over-sintering;

[0017] During the hot pressing process, the powder will deform under the action of pressure, and the distance between particles decreases, resulting in a change in height (blank thickness), while the diameter remains unchanged because the inner diameter of the mold limits the expansion of the powder in the horizontal direction, so that the powder can only be compressed in the vertical direction.

[0018] Preferably, the particle size of the magnesium aluminate spinel spherical powder in step (1) is 20 - 150 μm.

[0019] Preferably, the preparation method of the magnesium aluminate spinel spherical powder is: adding a sintering aid and a grinding medium to the magnesium aluminate spinel powder with a purity ≥ 99.9%, and then performing ball milling and granulation to obtain the magnesium aluminate spinel spherical powder.

[0020] Preferably, the addition amount of the sintering aid is 0-4 wt% of the magnesium aluminate spinel powder, and the sintering aid is any one or more of CaO, LiF+NaF, LiF+CaCO3, AlCl3, AlF3, Na3AlF6, B2O3, ZrO2, LiF, Y2O3, and La2O3;

[0021] The addition amount of the grinding medium is 15-80 wt% of the magnesium aluminate spinel powder, and the grinding medium is anhydrous ethanol or deionized water.

[0022] Preferably, the ball milling time is 0.5-20 h, and the rotation speed is 100-400 rpm.

[0023] Preferably, the parameters of the second vacuum hot pressing sintering in step (2) are:

[0024] The vacuum degree is 10 -1 -10 -3 Pa, the sintering temperature is 1150-1700 °C, and the pressure is 20-80 MPa;

[0025] After heat preservation and pressure holding for 30 min-5 h, the pressure is released and the temperature is reduced (heat preservation and pressure holding may not be completely synchronous), then the temperature is reduced to 200-600 °C at a rate of 0.3-15 °C / min, and finally the temperature is naturally reduced to room temperature.

[0026] The purpose of the second hot pressing is to further improve the density of the blank, and by adjusting the pressure and temperature, the thickness of the blank is reduced while the size is increased, so as to prepare a denser ceramic sintered body with a larger size.

[0027] In the second hot pressing of the present invention, a graphite mold is not used, and the thickness and size of the blank change simultaneously during the hot pressing process. At the same pressure, the pressure applied to the blank is different, and the pressure to be applied needs to be calculated according to the pressure at different sizes to press out a transparent ceramic sintered body with high density.

[0028] Preferably, the annealing temperature in step (3) is 800-1400 °C.

[0029] Preferably, the parameters of the hot isostatic pressing in step (3) are: in an Ar atmosphere, the temperature is 1200-1950 °C, the pressure is 150-200 MPa, heat preservation and pressure holding are 1-5 h, then the temperature is reduced to 200-600 °C at a rate of 0.5-5 °C / min, and then the temperature is naturally reduced to room temperature.

[0030] After two hot pressings, the blank is annealed and hot isostatically pressed to obtain high-quality transparent spinel ceramics.

[0031] As can be seen from the above technical solutions, compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] The present invention adopts a two - stage hot - pressing method. In the first hot - pressing stage, a graphite mold is required, and the hot - pressing temperature is lower than that in the second hot - pressing stage. During the hot - pressing process, the height of the powder material (the thickness of the blank) changes while the diameter remains unchanged (equal to the inner diameter of the mold). After the first hot - pressing, the blank is initially formed, with a moderate density and sufficient thickness. In the second hot - pressing stage, no graphite mold is used, and the hot - pressing temperature is higher than that in the first hot - pressing stage. This further reduces the thickness of the blank and increases the size of the blank, enabling the preparation of a denser ceramic sintered body with a larger size than that obtained by using a graphite mold in the first hot - pressing. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention, and for those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to the provided drawings.

[0034] Figure 1 It is the product drawing of Embodiment 1 of the present invention;

[0035] Figure 2 It is the transmittance curve graph of the product of Embodiment 1 of the present invention in the range of 0.2 - 2.5 μm;

[0036] Figure 3 It is the transmittance curve graph of the product of Embodiment 1 of the present invention in the range of 2.5 - 8 μm. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0038] Embodiment 1

[0039] The present invention provides a method for preparing magnesium aluminate spinel transparent ceramics by hot - pressing sintering, and the specific steps are as follows:

[0040] (1) Raw material pretreatment: First, magnesium aluminate spinel powder with a purity of ≥99.99% is added with 1.5 wt% of sintering aid LiF and 80% by mass of deionized water, and then ball - milled at a ball - mill rotation speed of 240 rpm for 8 h. The mixed slurry is granulated by a spray granulator to obtain magnesium aluminate spinel spherical granulated powder with a particle size of 100 - 150 μm;

[0041] (2) First vacuum hot pressing: Load the spherical granulated magnesium aluminate spinel powder into a graphite mold with an inner diameter of Φ67 mm, place it in a vacuum hot pressing sintering furnace for hot pressing sintering. The vacuum degree of vacuum sintering is 10 -1 -10 -3 Pa, the sintering temperature is 1200 °C, the pressure is 40 MPa, after heat preservation for 1.5 h, relieve the pressure and cool down, then cool down to 300 °C at a cooling rate of 0.5 - 15 °C / min, and finally cool down to room temperature naturally to obtain a preliminarily formed Φ67 mm magnesium aluminate spinel flat blank;

[0042] (3) Second vacuum hot pressing: Put the above-mentioned preliminarily formed Φ67 mm magnesium aluminate spinel flat blank into a vacuum hot pressing sintering furnace for the second hot pressing sintering. The vacuum degree of sintering is 10 -1 -10 -3 Pa, the sintering temperature is 1550 °C, the pressure is 40 MPa, after heat preservation and pressure holding for 1.5 h, relieve the pressure and cool down, then cool down to 200 °C at a cooling rate of 2 - 15 °C / min, and finally cool down to room temperature naturally to obtain a dense Φ97 mm magnesium aluminate spinel flat blank;

[0043] (4) Annealing and hot isostatic pressing: Anneal the above-mentioned dense Φ97 mm magnesium aluminate spinel flat blank. The annealing temperature is 900 °C. After annealing, put the flat blank into a hot isostatic pressing furnace. Under the atmosphere of Ar, the temperature is 1750 °C, the pressure is 180 MPa. After heat preservation and pressure holding for 2 h, first cool down to 200 °C at a rate of 1 - 5 °C / min, and then cool down to room temperature naturally to obtain magnesium aluminate spinel transparent ceramic (product such as Figure 1 ). According to the use requirements, remove the spinel ceramic at the edge that does not fully meet the requirements, and process the remaining part by cutting, grinding, polishing, etc. according to the drawing to obtain a Φ85 mm transparent ceramic, that is, a transparent ceramic with a mold diameter of 1.268 times;

[0044] Among them, Figure 2 is the transmittance curve of 0.2 - 2.5 μm of the product of the present invention, Figure 3 is the transmittance curve of 2.5 - 8 μm. As can be seen from the figure, by using the two - step vacuum hot pressing process and a φ67 mm mold, a transparent ceramic with a usable size of φ85 mm is prepared. The transmittance of the transparent ceramic is equivalent to that of the conventional vacuum - hot - pressed spinel transparent ceramic, and the grid lines under the sample are clearly visible, meeting the requirements of the transmittance for general windows.

[0045] Example 2

[0046] The present invention provides a method for preparing magnesium aluminate spinel transparent ceramic by hot pressing sintering, and the specific steps are as follows:

[0047] (1) Raw material pretreatment: First, magnesia-alumina spinel powder with a purity ≥ 99.99% is added with 1.0 wt% of sintering aid LiF, and 70% by mass of absolute ethanol is added for ball milling. The ball milling speed is 260 revolutions per minute, and the ball milling time is 8 h. The mixed slurry is granulated by a spray granulator to obtain magnesia-alumina spinel spherical granulated powder with a particle size of 100 - 150 μm;

[0048] (2) First vacuum hot pressing: The magnesia-alumina spinel spherical granulated powder is loaded into a graphite mold with an inner diameter of Φ155 mm and placed in a vacuum hot pressing sintering furnace for hot pressing sintering. The vacuum degree of vacuum sintering is 10 -1 -10 -3 Pa, the sintering temperature is 1250 °C, the pressure is 35 MPa, after holding for 2 h, the pressure is released and the temperature is lowered. Then, it is cooled to 600 °C at a cooling rate of 0.5 - 15 °C / min, and finally naturally cooled to room temperature to obtain a preliminarily formed magnesia-alumina spinel flat blank with a diameter of Φ155 mm;

[0049] (3) Second vacuum hot pressing: The above preliminarily formed magnesia-alumina spinel flat blank with a diameter of Φ155 mm is placed in a vacuum hot pressing sintering furnace for the second hot pressing sintering. The vacuum degree of sintering is 10 -1 -10 -3 Pa, the sintering temperature is 1600 °C, the pressure is 40 MPa, after holding and maintaining pressure for 2 h, the pressure is released and the temperature is lowered. Then, it is cooled to 300 °C at a cooling rate of 2 - 15 °C / min, and finally naturally cooled to room temperature to obtain a dense magnesia-alumina spinel flat blank with a diameter of Φ240 mm;

[0050] (4) Annealing and hot isostatic pressing: The above dense magnesia-alumina spinel flat blank with a diameter of Φ240 mm is annealed at an annealing temperature of 1000 °C. After annealing, the flat blank is placed in a hot isostatic pressing furnace. Under an Ar atmosphere, the temperature is 1750 °C and the pressure is 190 MPa. After holding and maintaining pressure for 2 h, it is first cooled to 300 °C at a rate of 0.5 - 5 °C / min, and then naturally cooled to room temperature to obtain magnesia-alumina spinel transparent ceramic. According to the usage requirements, the spinel ceramic at the edge that does not fully meet the requirements is removed, and the remaining part is processed by cutting, grinding, polishing, etc. according to the drawing to obtain a transparent ceramic with a diameter of Φ220 mm, that is, a transparent ceramic with a diameter 1.419 times that of the mold.

[0051] Example 3

[0052] The present invention provides a method for preparing magnesia-alumina spinel transparent ceramic by hot pressing sintering, and the specific steps are as follows:

[0053] (1) Raw material pretreatment: First, magnesia-alumina spinel powder with a purity ≥ 99.99% is added with 1.5 wt% of sintering aids and deionized water with a mass content of 75% for ball milling. The ball milling speed is 260 revolutions per minute, and the ball milling time is 8 h. The mixed slurry is granulated by a spray granulator to obtain magnesia-alumina spinel spherical granulated powder with a particle size of 80 - 150 μm;

[0054] (2) First vacuum hot pressing: The magnesia-alumina spinel spherical granulated powder is loaded into a graphite mold with an inner diameter of Φ400 mm and placed in a vacuum hot pressing sintering furnace for hot pressing sintering. The vacuum degree of vacuum sintering is 10 -1 -10 -3 Pa, the sintering temperature is 1300 °C, the pressure is 32 MPa, after holding for 3 h, the pressure is released and the temperature is decreased. Then, it is cooled to 500 °C at a cooling rate of 0.5 - 15 °C / min, and finally naturally cooled to room temperature to obtain a preliminarily formed magnesia-alumina spinel flat blank with a diameter of Φ400 mm;

[0055] (3) Second vacuum hot pressing: The above preliminarily formed magnesia-alumina spinel flat blank with a diameter of Φ400 mm is placed in a vacuum hot pressing sintering furnace for the second hot pressing sintering. The vacuum degree of sintering is 10 -1 -10 -3 Pa, the sintering temperature is 1600 °C, the pressure is 40 MPa, after holding and maintaining pressure for 3 h, the pressure is released and the temperature is decreased. Then, it is cooled to 500 °C at a cooling rate of 1 - 5 °C / min, and finally naturally cooled to room temperature to obtain a dense magnesia-alumina spinel flat blank with a diameter of Φ565 mm;

[0056] (4) Annealing and hot isostatic pressing: The above dense magnesia-alumina spinel flat blank with a diameter of Φ565 mm is annealed at an annealing temperature of 1100 °C. After annealing, the flat blank is placed in a hot isostatic pressing furnace. Under the atmosphere of Ar, the temperature is 1800 °C, the pressure is 190 MPa. After holding and maintaining pressure for 3 h, it is first cooled to 300 °C at a speed of 0.5 - 5 °C / min, and then naturally cooled to room temperature to obtain magnesia-alumina spinel transparent ceramic. According to the usage requirements, the spinel ceramic at the edge that does not fully meet the requirements is removed, and the remaining part is processed by cutting, grinding, polishing, etc. according to the drawing to obtain a transparent ceramic with a diameter of Φ540 mm, that is, a transparent ceramic with a mold diameter of 1.350 times.

[0057] Example 4

[0058] The present invention provides a method for preparing magnesia-alumina spinel transparent ceramic by hot pressing sintering, and the specific steps are as follows:

[0059] (1) Raw material pretreatment: First, magnesia-alumina spinel powder with a purity ≥ 99.99% is added with 2 wt% of sintering aid LiF and 70% by mass of deionized water, and then ball-milled at a rotation speed of 260 revolutions per minute for 7 h. The mixed slurry is granulated by a spray granulator to obtain magnesia-alumina spinel spherical granulated powder with a particle size of 80 - 150 μm;

[0060] (2) First vacuum hot pressing: The magnesia-alumina spinel spherical granulated powder is loaded into a graphite mold with an inner diameter of Φ580 mm and placed in a vacuum hot pressing sintering furnace for hot pressing sintering. The vacuum degree of vacuum sintering is 10 -1 -10 -3 Pa, the sintering temperature is 1300 °C, the pressure is 35 MPa, after holding for 5 h, the pressure is released and the temperature is lowered. Then, it is cooled to 600 °C at a cooling rate of 0.5 - 5 °C / min, and finally naturally cooled to room temperature to obtain a preliminarily formed magnesia-alumina spinel flat blank with a diameter of Φ580 mm;

[0061] (3) Second vacuum hot pressing: The above-mentioned preliminarily formed magnesia-alumina spinel flat blank with a diameter of Φ580 mm is placed in a vacuum hot pressing sintering furnace for the second hot pressing sintering. The vacuum degree of sintering is 10 -1 -10 -3 Pa, the sintering temperature is 1550 °C, the pressure is 35 MPa, after holding and maintaining the pressure for 4 h, the pressure is released and the temperature is lowered. Then, it is cooled to 600 °C at a cooling rate of 0.5 - 5 °C / min, and finally naturally cooled to room temperature to obtain a dense magnesia-alumina spinel flat blank with a diameter of Φ778 mm;

[0062] (4) Annealing and hot isostatic pressing: The above-mentioned dense magnesia-alumina spinel flat blank with a diameter of Φ778 mm is annealed at an annealing temperature of 1000 °C. After annealing, the flat blank is placed in a hot isostatic pressing furnace. Under the atmosphere of Ar, the temperature is 1750 °C and the pressure is 200 MPa. After holding and maintaining the pressure for 4 h, it is first cooled to 200 °C at a rate of 0.5 - 5 °C / min, and then naturally cooled to room temperature to obtain magnesia-alumina spinel transparent ceramics. According to the usage requirements, the spinel ceramics at the edge that do not fully meet the requirements are removed, and the remaining part is processed by cutting, grinding, polishing, etc., according to the drawing, to obtain transparent ceramics with a diameter of Φ750 mm, that is, transparent ceramics with a diameter 1.293 times that of the mold.

[0063] In this embodiment, a graphite mold with a diameter of Φ580mm, an inner diameter of 580mm, and an outer diameter of 740mm, leaving a 20mm operating space, requires a working area of more than φ760mm. Using the secondary hot pressing process, a transparent ceramic with a diameter of φ750mm can be obtained; the original process for preparing a ceramic with a diameter of φ750mm requires a graphite mold with an inner diameter of 750mm and an outer diameter of 950mm, and the required working area is more than 970mm in diameter; the process of the present invention reduces the size requirements for both the mold and the equipment, directly reducing the mold cost, and a relatively small equipment can be used. For larger-sized products, when a mold with an outer diameter of more than 1000mm is required, a more expensive carbon-carbon material needs to be replaced, the mold cost increases sharply, and a larger hot pressing sintering equipment is required.

[0064] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing magnesium aluminate spinel transparent ceramics by hot pressing sintering, characterized in that, Specifically, it includes the following steps: (1) Put the spherical magnesium aluminate spinel powder into a graphite mold and conduct the first vacuum hot pressing sintering to obtain a flat blank; (2) Conduct the second vacuum hot pressing sintering without a mold on the flat blank to obtain a dense blank; (3) Anneal and hot isostatically press the dense blank to obtain the magnesium aluminate spinel transparent ceramic.

2. The method for preparing magnesium aluminate spinel transparent ceramics by hot pressing sintering according to claim 1, characterized in that, The parameters of the first vacuum hot pressing sintering in step (1) are: The vacuum degree is 10 -1 -10 -3 Pa, the sintering temperature is 1000 - 1400 °C, and the pressure is 20 - 80 MPa; Keep the temperature for 30 min - 5 h and then relieve the pressure and cool down. Then, cool down at a rate of 0.5 - 15 °C / min to 200 - 600 °C, and finally cool down to room temperature naturally.

3. The method for preparing magnesium aluminate spinel transparent ceramics by hot pressing sintering according to claim 1, characterized in that, The particle size of the spherical magnesium aluminate spinel powder in step (1) is 20 - 150 μm.

4. A method for preparing magnesium aluminate spinel transparent ceramics by hot pressing sintering according to claim 3, characterized in that, The preparation method of the spherical magnesium aluminate spinel powder is: add a sintering aid and a grinding medium to the magnesium aluminate spinel powder with a purity ≥ 99.9%, and then conduct ball milling and granulation to obtain the spherical magnesium aluminate spinel powder.

5. A method for preparing magnesium aluminate spinel transparent ceramics by hot pressing sintering according to claim 4, characterized in that, The addition amount of the sintering aid is 0 - 4 wt% of the magnesium aluminate spinel powder, and the sintering aid is any one or several of CaO, LiF + NaF, LiF + CaCO3, AlCl3, AlF3, Na3AlF6, B2O3, ZrO2, LiF, Y2O3, and La2O3; The addition amount of the grinding medium is 15 - 80 wt% of the magnesium aluminate spinel powder, and the grinding medium is anhydrous ethanol or deionized water.

6. A method for preparing magnesium aluminate spinel transparent ceramics by hot pressing sintering according to claim 4, characterized in that, The time of the ball milling is 0.5 - 20 h, and the rotation speed is 100 - 400 rpm.

7. A method for preparing magnesium aluminate spinel transparent ceramics by hot pressing sintering according to claim 1, characterized in that, The parameters of the second vacuum hot pressing sintering in step (2) are: The vacuum degree is 10 -1 -10 -3 Pa, the sintering temperature is 1150 - 1700 °C, and the pressure is 20 - 80 MPa; Keep the temperature and pressure for 30 min - 5 h and then relieve the pressure and cool down. Then, cool down at a rate of 0.3 - 15 °C / min to 200 - 600 °C, and finally cool down to room temperature naturally.

8. The preparation method of a method for preparing magnesium aluminate spinel transparent ceramics by hot pressing sintering according to claim 1, characterized in that, The annealing temperature in step (3) is 800 - 1400 °C.

9. The preparation method of a method for preparing magnesium aluminate spinel transparent ceramics by hot pressing sintering according to claim 1, characterized in that, The parameters of the hot isostatic pressing in step (3) are: in an Ar atmosphere, the temperature is 1200 - 1950 °C, the pressure is 150 - 200 MPa, keep the temperature and pressure for 1 - 5 h, then cool down at a rate of 0.5 - 5 °C / min to 200 - 600 °C, and then cool down to room temperature naturally.

Images