A method for producing a doped metal oxide ingot

Abstract

The present application relates to the field of optical coating material preparation, and discloses a preparation method of a doped metal oxide ingot. Indium oxide powder, tantalum oxide powder, and cerium oxide powder are mixed to obtain a mixture one; the mixture one is mixed with an additive A and then granulated for the first time to obtain a granulated powder one; the mixture one is pre-sintered to obtain a clinker; the granulated powder one is pre-sintered to obtain a skeleton support particle; the pre-sintering temperature is 1200-1350 DEG C; the skeleton support particle and the clinker are mixed with an additive B and then granulated for the second time; the granulated powder two is successively pressed and formed and sintered to obtain the doped metal oxide ingot. The present application can prepare a doped metal oxide ingot with large size and stable size, uniform distribution of forming density, and no cracking after sintering.

Description

Technical Field

[0001] This invention relates to the field of optical coating material preparation, specifically a method for preparing doped metal oxide ingots. Background Technology

[0002] In the field of optical coating, the demand for metal oxides is increasing year by year. They play a crucial role in high-performance optical thin film materials for reflection, transmission, and antireflection of visible, infrared, and ultraviolet light. Meanwhile, doped metal oxide ingots, such as ITO, ICO, and IGZO, exhibit their own differences in various application fields due to their unique optical properties.

[0003] Currently, the size of doped metal oxide ingots is mainly concentrated in the range of 4 to 10 mm in height and 10 to 15 mm in diameter. However, large-sized doped metal oxide ingots with diameters exceeding 25 mm and heights exceeding 40 mm are prone to uneven size and density distribution due to instability in the production process, which in turn leads to cracking of the ingots after sintering, making it difficult to achieve stable and large-scale production. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing doped metal oxide ingots, so as to solve at least one technical problem existing in the background art.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a doped metal oxide ingot includes the following steps:

[0007] (1) Indium oxide powder, tantalum oxide powder and cerium oxide powder are mixed in a mass ratio of 85~99:0.5~15:0.5~15 to obtain mixture one;

[0008] (2) Mix the mixture with additive A and then granulate for the first time to obtain granulated powder.

[0009] (3) The mixture obtained in step (1) is pre-sintered to obtain clinker; the granulated powder obtained in step (2) is pre-sintered to obtain skeleton support particles; the pre-sintering temperature is 1200~1350℃.

[0010] (4) Mix the skeleton support particles, clinker and additive B obtained in step (3) and then granulate them for the second time to obtain granulated powder II.

[0011] (5) The granulated powder is pressed and sintered in sequence to obtain a doped metal oxide ingot.

[0012] This invention creatively achieves synergistic optimization of material properties through doping metals and preparation processes. It limits the type and composition of the doping metals, and pre-sintering induces initial bonding between particles, forming a stable and uniform skeletal structure that provides support for subsequent molding and sintering. The resulting clinker, after sintering, is used as a filler material and undergoes a second granulation process with the skeletal support particles to further improve material properties. Finally, the granulated powder is pressed into a blank of the desired shape in a mold; molding and sintering then completes the bonding between particles in the blank, forming a dense and stable doped metal oxide ingot.

[0013] Furthermore, in step (1), the D50 of the indium oxide powder, tantalum oxide powder, and cerium oxide powder is 1~5 μm.

[0014] Furthermore, the purity of indium oxide powder is ≥4N; the purity of tantalum oxide powder is ≥3N; and the purity of cerium oxide powder is ≥3N.

[0015] Further, in step (1), indium oxide powder, tantalum oxide powder and cerium oxide powder are added to a three-dimensional mixer in proportion and mixed for 10-20 hours to obtain mixture one.

[0016] Further, in step (2), the additive A is at least one of PEG9000 and PEG6000.

[0017] Further preferably, the amount of additive A added is 3-5% of the mass of the mixture.

[0018] Further, step (2) specifically involves: taking the mixture into a rotary granulator, adjusting the chopper speed to 1000~1100r / min, adjusting the nozzle speed of additive A to 10mL / min, and after spraying, rotating and granulating in the rotary granulator for 1~5min. After granulation, the granulated powder is taken out and dried to obtain granulated powder one.

[0019] More preferably, once the granulated powder is taken out, it is placed in a drying oven at 80~120℃ for drying. After the volatile matter has fully evaporated and the weight loss rate of the granulated powder no longer decreases significantly, the granulated powder can be taken out and sieved.

[0020] Furthermore, in step (3), granulated powder with a particle size greater than 40 mesh is pre-sintered. The particle size is screened after the first granulation process in this invention to ensure the uniformity of particle size.

[0021] In the further optimization step (2), the particle size of the particles obtained in the first granulation is 20~40 mesh.

[0022] Furthermore, in step (3) of the pre-sintering process, an alumina crucible is used as the pre-sintering container.

[0023] Further, in step (3), the mixture is pre-sintered, and the resulting material is passed through a 60-mesh sieve and then ball-milled for 10-20 hours to obtain clinker.

[0024] Furthermore, in step (4), the mass ratio of the skeleton support particles to the clinker is 1~5:9~5.

[0025] Further, in step (4), the additive B is at least one of PVA, liquid paraffin, and water.

[0026] Further preferably, the amount of additive B added is 1 to 3% of the total mass of the skeleton support particles and clinker.

[0027] Further, in step (4), the skeleton support particles, clinker and additive B are put into a three-dimensional mixer and mixed for 10~20 hours, and then granulation is carried out for the second time.

[0028] Furthermore, in step (4), the granulation pressure for the second granulation is 3~15MPa, and the holding time is 3~15s.

[0029] Furthermore, in step (5), granulated powder with a particle size greater than 35 mesh is screened and pressed into shape; screening ensures the uniformity of particle size and further meets the molding requirements.

[0030] In the further optimization step (4), the particle size of the particles obtained by the second granulation is 40~60 mesh.

[0031] Further, step (5) pressing and molding specifically involves: weighing out granulated powder II and adding it into the mold, then using a double-sided pressure molding machine to flatten the upper and lower pressure heads of the mold before demolding.

[0032] More preferably, the mass of the doped metal oxide ingot is calculated based on the theoretical density and size, and then the granulated powder is weighed and added to the mold.

[0033] Furthermore, the temperature for forming and sintering in step (5) is 1100~1250℃; the forming and sintering time is 1~5h.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] This invention utilizes the sintering characteristics of raw materials for a pre-sintering process without introducing impurities, significantly reducing the risk of shrinkage ingots after molding. The preparation of the framework support particles introduces a new granulation process, and the granulated powder is pre-sintered to achieve high particle strength, preventing cracking and pulverization due to insufficient particle strength during pressing, thus ensuring its supporting function. Simultaneously, mixing the framework support particles with the powder allows for mutual support and filling, resulting in a uniform overall strength distribution in the ingots and the preparation of stable, large-sized doped oxide ingots.

[0036] This invention creatively sets up a framework support particle, which does not introduce new impurities during the preparation of the particle, maintains the original purity, and greatly improves the stability of the finished product, producing large-sized doped metal oxide ingots with stable dimensions and no cracking after firing.

[0037] This invention involves thoroughly mixing the skeleton support particles with the clinker and adding additives. The resulting mixture is then placed into the mold cavity of a molding die for pressing and molding, allowing the skeleton particles to support each other and the clinker to fully fill the spaces between the particles. This controls the uniform distribution of molding strength and density throughout the product, preventing ingot cracking, uneven shrinkage causing deformities, and uneven density causing splashing during application after molding and sintering. Detailed Implementation

[0038] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0039] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0040] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0041] Example 1

[0042] (1) Weigh 1600g of indium oxide powder with D50 of 0.32μm and purity of 4N, 100g of tantalum oxide powder with D50 of 1.63μm and purity of 4N, and 300g of cerium oxide powder with D50 of 0.84μm and purity of 4N and add them into a 20L capacity three-dimensional mixer. Set the mixing frequency to 15Hz and the mixing time to 10h. Take out the uniformly mixed powder to obtain mixture one.

[0043] (2) Take 800g of mixture one and add it into the granulator. Add 32mL of PEG9000 into the nozzle measuring cylinder, start the granulator, set the chopper speed to 1000r / min, and set the nozzle speed to 10mL / min. After the PEG9000 is completely sprayed in, let the granulator run for another 120s to make the powder more uniform and granulated to obtain granulated powder one.

[0044] (3) Place the granulated powder one in a drying oven, set the drying temperature to 95℃ and the drying time to 4.5h. After cooling, sieve the granulated powder one with a sieve mesh of 40 mesh and remove the powder that has not formed particles.

[0045] (4) Place 1200g of mixture 1 in a set of alumina crucibles, and place the screened granulated powder 1 in another set of alumina crucibles. Put them together into a bell furnace with tube heating for pre-sintering. Set the pre-sintering temperature to 1250℃, the heating rate to 5℃ / min, the holding time to 4h, and the cooling rate to 4℃ / min. After the furnace body is cooled, the screened granulated powder 1 is pre-sintered to obtain strong skeleton support particles. The mixture 1 is pre-sintered to obtain clinker 1, whose sintering activity is greatly reduced.

[0046] (5) Place clinker one in a ball mill jar, and mix zirconia balls at a ratio of 1:1.8 for ball milling. The ball milling frequency is 28.8 Hz and the ball milling time is 12 h. After the ball milling is completed, separate the zirconia balls and powder to obtain clinker two.

[0047] (6) Weigh 1000g of clinker II and 500g of skeleton support particles, add 15mL of PVA while stirring. After adding, pour it into the three-dimensional mixer for mixing. Set the mixing frequency to 15Hz and the mixing time to 10h. Take out the mixed material to obtain the mixed material II.

[0048] (7) Weigh 50g of the mixture 2 into a portion, and press each portion into granules separately. Take one portion of the mixture 2 and pour it into the mold cavity of the pressure granulator. Set the pressure to 20MPa and the pressing time to 10s. Repeat until all of the mixture 2 has been pressed into granules. Crush and screen the pressed mixture 2. Use a 35-mesh sieve to screen it to ensure that all powders can pass through the 35-mesh sieve. The powder that passes through the sieve is the granulation powder 2.

[0049] (8) Select and assemble the molding die according to the size requirement of D30*45mm, based on the sample pellet density of 4.2g·cm³. -3 As required, weigh 133.53g of granulated powder and add it to the mold cavity. After placing the upper pressure head, tighten the mold and place it flat in the double-sided hydraulic press. Press the upper and lower pressure heads flat against their side baffles to ensure that the internal space height of the mold is 40mm. Set the pressure to 15MPa and the holding time to 5s. After the holding time is completed, remove the mold and perform the demolding operation to remove the ingot blank.

[0050] (9) Place the ingot blanks on the sintering plate of the tubular heating bell furnace, arrange them neatly, set the sintering temperature to 1150℃, the heating rate to 3℃ / min, the holding time to 4h, and the cooling rate to 5℃ / min. After the cooling is completed, take out the sintered ingots, inspect them for compliance, and then package them to obtain the large-size doped metal oxide ingots.

[0051] Example 2

[0052] (1) Weigh 1700g of indium oxide powder with D50 of 0.32μm and purity of 4N, 50g of tantalum oxide powder with D50 of 1.63μm and purity of 4N, and 250g of cerium oxide powder with D50 of 0.84μm and purity of 4N and add them into a 20L capacity three-dimensional mixer. Set the mixing frequency to 15Hz and the mixing time to 10h. Take out the uniformly mixed powder to obtain mixture one.

[0053] (2) Take 1000g of mixture one and add it into the granulator. Add 45mL of PEG6000 into the nozzle measuring cylinder, start the granulator, set the chopper speed to 1020r / min, and set the nozzle speed to 10mL / min. After the PEG6000 is completely sprayed in, let the granulator run for another 145s to make the powder more uniform and granulated to obtain granulated powder one.

[0054] (3) Place the granulated powder one in a drying oven, set the drying temperature to 95℃ and the drying time to 4.5h. After cooling, sieve the granulated powder one with a sieve mesh of 40 mesh and remove the powder that has not formed particles.

[0055] (4) Place 1000g of mixture 1 in a set of alumina crucibles, and place the screened granulated powder 1 in another set of alumina crucibles. Put them together into a bell furnace with tube heating for pre-sintering. Set the pre-sintering temperature to 1350℃, the heating rate to 5℃ / min, the holding time to 4h, and the cooling rate to 4℃ / min. After the furnace body is cooled, the screened granulated powder 1 is pre-sintered to obtain strong skeleton support particles. The mixture 1 is pre-sintered to obtain clinker 1, whose sintering activity is greatly reduced.

[0056] (5) Place clinker one in a ball mill jar, and mix zirconia balls at a ratio of 1:1.8 for ball milling. The ball milling frequency is 28.8 Hz and the ball milling time is 12 h. After the ball milling is completed, separate the zirconia balls and powder to obtain clinker two.

[0057] (6) Weigh 900g of clinker II and 400g of skeleton support particles, add 12mL of PVA while stirring. After adding, pour it into the three-dimensional mixer and mix. Set the mixing frequency to 15Hz and the mixing time to 10h. Take out the mixed material to obtain the mixed material II.

[0058] (7) Weigh 50g of the mixture 2 into a portion, and press each portion into granules separately. Take one portion of the mixture 2 and pour it into the mold cavity of the pressure granulator. Set the pressure to 20MPa and the pressing time to 10s. Repeat until all of the mixture 2 has been pressed into granules. Crush and screen the pressed mixture 2. Use a 35-mesh sieve to screen it to ensure that all powders can pass through the 35-mesh sieve. The powder that passes through the sieve is the granulation powder 2.

[0059] (8) Select and assemble the molding die according to the size requirement of D35*60mm, based on the sample pellet density of 3.6g·cm³. -3 As required, weigh 207.7g of granulated powder and add it to the mold cavity of the molding die. After placing the upper pressure head, tighten the die and place it flat in the double-sided hydraulic press. Press the upper and lower pressure heads flat against their side baffles to ensure that the internal space height of the die is 60mm. Set the pressure to 10MPa and the holding time to 5s. After the holding time is completed, remove the die and demold the pellet blank.

[0060] (9) Place the ingot blanks on the firing plate of the tubular heating bell furnace, arrange them neatly, set the sintering temperature to 1175℃, the heating rate to 3℃ / min, the holding time to 4.2h, and the cooling rate to 5℃ / min. After the cooling is completed, take out the sintered ingots, inspect them for compliance, and then package them to obtain the large-size doped metal oxide ingots.

[0061] Example 3

[0062] (1) Weigh 1700g of indium oxide powder with D50 of 0.32μm and purity of 4N, 50g of tantalum oxide powder with D50 of 1.63μm and purity of 4N, and 250g of cerium oxide powder with D50 of 0.84μm and purity of 4N and add them into a 20L capacity three-dimensional mixer. Set the mixing frequency to 15Hz and the mixing time to 10h. Take out the uniformly mixed powder to obtain mixture one.

[0063] (2) Take 1000g of mixture one and add it into the granulator. Add 45mL of PEG6000 into the nozzle measuring cylinder, start the granulator, set the chopper speed to 1020r / min, and set the nozzle speed to 10mL / min. After the PEG6000 is completely sprayed in, let the granulator run for another 145s to make the powder more uniform and granulated to obtain granulated powder one.

[0064] (3) Place the granulated powder one in a drying oven, set the drying temperature to 95℃ and the drying time to 4.5h. After cooling, sieve the granulated powder one with a sieve mesh of 40 mesh and remove the powder that has not formed particles.

[0065] (4) Place 1000g of mixture 1 in a set of alumina crucibles, and place the screened granulated powder 1 in another set of alumina crucibles. Put them together into a bell furnace with tube heating for pre-sintering. Set the pre-sintering temperature to 1200℃, the heating rate to 5℃ / min, the holding time to 4h, and the cooling rate to 4℃ / min. After the furnace body is cooled, the screened granulated powder 1 is pre-sintered to obtain strong skeleton support particles. The mixture 1 is pre-sintered to obtain clinker 1, whose sintering activity is greatly reduced.

[0066] (5) Place clinker one in a ball mill jar, and mix zirconia balls at a ratio of 1:1.8 for ball milling. The ball milling frequency is 28.8 Hz and the ball milling time is 12 h. After the ball milling is completed, separate the zirconia balls and powder to obtain clinker two.

[0067] (6) Weigh 900g of clinker II and 400g of skeleton support particles, add 12mL of PVA binder while stirring. After adding, pour it into the three-dimensional mixer for mixing. Set the mixing frequency to 15Hz and the mixing time to 10h. Take out the mixed material to obtain the mixed material II.

[0068] (7) Weigh 50g of the mixture 2 into a portion, and press each portion into granules separately. Take one portion of the mixture 2 and pour it into the mold cavity of the pressure granulator. Set the pressure to 20MPa and the pressing time to 10s. Repeat until all of the mixture 2 has been pressed into granules. Crush and screen the pressed mixture 2. Use a 35-mesh sieve to screen it to ensure that all powders can pass through the 35-mesh sieve. The powder that passes through the sieve is the granulation powder 2.

[0069] (8) Select and assemble the molding die according to the size requirement of D35*60mm, based on the sample pellet density of 3.6g·cm³. -3 As required, weigh 207.7g of granulated powder and add it to the mold cavity of the molding die. After placing the upper pressure head, tighten the die and place it flat in the double-sided hydraulic press. Press the upper and lower pressure heads flat against their side baffles to ensure that the internal space height of the die is 60mm. Set the pressure to 10MPa and the holding time to 5s. After the holding time is completed, remove the die and demold the pellet blank.

[0070] (9) Place the ingot blanks on the firing plate of the tubular heating bell furnace, arrange them neatly, set the sintering temperature to 1175℃, the heating rate to 3℃ / min, the holding time to 4.2h, and the cooling rate to 5℃ / min. After the cooling is completed, take out the sintered ingots, inspect them for compliance, and then package them to obtain the large-size doped metal oxide ingots.

[0071] Comparative Example 1

[0072] This comparative example is basically the same as Example 2, except that the pre-sintering temperature in step (4) is 1100℃.

[0073] Comparative Example 2

[0074] This comparative example is basically the same as Example 2, except that the pre-sintering temperature in step (4) is 1400℃.

[0075] Comparative Example 3

[0076] This comparative example is basically the same as Example 2, except that the molding and sintering temperature in step (9) is 1000℃.

[0077] Comparative Example 4

[0078] This comparative example is basically the same as Example 2, except that the molding and sintering temperature in step (9) is 1300℃.

[0079] Comparative Example 5

[0080] This comparative example is basically the same as Example 1, except that the mass ratio of indium oxide powder, tantalum oxide powder and cerium oxide powder is different in step (1).

[0081] Specifically, 1700g of indium oxide powder with a D50 of 0.32μm and a purity of 4N, 5g of tantalum oxide powder with a D50 of 1.63μm and a purity of 4N, and 295g of cerium oxide powder with a D50 of 0.84μm and a purity of 4N are weighed and added to a 20L three-dimensional mixer.

[0082] Comparative Example 6

[0083] This comparative example is basically the same as Example 1, except that the mass ratio of indium oxide powder, tantalum oxide powder and cerium oxide powder is different in step (1).

[0084] Specifically, 1700g of indium oxide powder with a D50 of 0.32μm and a purity of 4N, 295g of tantalum oxide powder with a D50 of 1.63μm and a purity of 4N, and 5g of cerium oxide powder with a D50 of 0.84μm and a purity of 4N are weighed and added to a 20L three-dimensional mixer.

[0085] Comparative Example 7

[0086] This comparative example is basically the same as Example 1, except for step (6).

[0087] Specifically:

[0088] (6) Weigh 950g of clinker II and 50g of skeleton support particles, add 12mL of PVA binder while stirring. After adding, pour it into the three-dimensional mixer for mixing. Set the mixing frequency to 15Hz and the mixing time to 10h. Take out the mixed material to obtain the mixed material II.

[0089] Comparative Example 8

[0090] This comparative example is basically the same as Example 1, except for step (6).

[0091] Specifically:

[0092] (6) Weigh 450g of clinker II and 550g of skeleton support particles, add 12mL of PVA binder while stirring. After adding, pour it into the three-dimensional mixer for mixing. Set the mixing frequency to 15Hz and the mixing time to 10h. Take out the mixed material to obtain the mixed material II.

[0093] The sintered dimensions, appearance, and application tests of the doped metal oxide ingots obtained in Examples 1-3 and Comparative Examples 1-8 are shown in Table 1.

[0094] Table 1

[0095]

[0096] It can be seen that:

[0097] The preparation method of this application can prepare large-sized and dimensionally stable doped metal oxide ingots, which do not crack after sintering and exhibit minimal splashing and high utilization rate during application testing.

[0098] The pre-sintering temperature of Comparative Example 1 was too low, resulting in the skeleton particles not being sintered and forming poorly, essentially failing to form a solid shape. The pre-sintering temperature of Comparative Example 2 was too high, resulting in severe vitrification of the skeleton particles and excessive strength. This could easily lead to uneven heat dissipation and splashing during application, resulting in poor application performance and low utilization rate.

[0099] The molding and sintering temperature of Comparative Example 3 was too low, resulting in severe deformation and lack of significant strength in the sintered pellets, leading to failure to form a proper shape. The molding and sintering temperature of Comparative Example 4 was too high, resulting in severe vitrification of the pellets and excessive strength, which caused excessive stress and cracking, and severe splashing occurred during application testing.

[0100] In Comparative Example 5, the reduced proportion of tantalum oxide and increased proportion of cerium oxide in the formulation resulted in excessive energy absorption during the coating process, leading to excessive splattering. In Comparative Example 6, the increased proportion of tantalum oxide in the formulation caused the migration rate to fail to meet product requirements, resulting in substandard coated products.

[0101] In Comparative Example 7, the content of skeletal support particles was too low, failing to support the original shape of the particles and thus preventing molding. In Comparative Example 8, the content of skeletal support particles was too high, resulting in loose and porous pellets after molding, leading to cracking after sintering.

[0102] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the present invention.

Claims

1. A method for preparing a doped metal oxide ingot, characterized in that, Includes the following steps: (1) Indium oxide powder, tantalum oxide powder and cerium oxide powder are mixed in a mass ratio of 85~99:0.5~15:0.5~15 to obtain mixture one; (2) Mix the mixture with additive A and then granulate for the first time to obtain granulated powder. (3) The mixture obtained in step (1) is pre-sintered to obtain clinker; the granulated powder obtained in step (2) is pre-sintered to obtain skeleton support particles; the pre-sintering temperature is 1200~1350℃. (4) After mixing the skeleton support particles, clinker and additive B obtained in step (3), granulation is carried out for the second time to obtain granulated powder II. The mass ratio of the skeleton support particles to the clinker is 1~5:9~5. (5) The granulated powder is pressed and sintered in sequence to obtain a doped metal oxide ingot. The sintering temperature is 1100~1250℃.

2. The preparation method according to claim 1, characterized in that, In step (1), the D50 of indium oxide powder, tantalum oxide powder, and cerium oxide powder is 1~5μm; The purity of indium oxide powder is ≥4N; the purity of tantalum oxide powder is ≥3N; and the purity of cerium oxide powder is ≥3N.

3. The preparation method according to claim 1 or 2, characterized in that, In step (2), additive A is at least one of PEG9000 and PEG6000; The amount of additive A added is 3-5% of the mass of the mixture.

4. The preparation method according to claim 1, characterized in that, In step (3), granulated powder with a particle size greater than 40 mesh is pre-sintered.

5. The preparation method according to claim 1, characterized in that, In step (3), the pre-sintering time is 3~10h.

6. The preparation method according to claim 1, characterized in that, In step (3), after the mixture is pre-sintered, the resulting material is passed through a 60-mesh sieve and then ball-milled for 10-20 hours to obtain clinker.

7. The preparation method according to claim 1, characterized in that, In step (4), the additive B is at least one of PVA, liquid paraffin, and water; The amount of additive B added is 1-3% of the total mass of the skeleton support particles and clinker.

8. The preparation method according to claim 1, characterized in that, In step (5), granulated powder with a particle size greater than 35 mesh is screened and pressed into shape.

9. The preparation method according to claim 1, characterized in that, Step (4) The particle size of the particles obtained by the second granulation is 40~60 mesh.

10. The preparation method according to claim 1, characterized in that, The sintering time for step (5) is 1~5h.

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