A method for preparing sodium molybdenum ceramic targets by low-temperature and rapid sintering

Abstract

This invention discloses a low-temperature, rapid sintering method for preparing sodium molybdenum ceramic targets. Specifically, molybdenum trioxide powder and sodium molybdate dihydrate powder are first mixed using alcohol as a medium through ball milling to obtain a sodium molybdenum slurry. The slurry is then dried, filtered, ground, and sieved to obtain sodium molybdenum powder. The sodium molybdenum powder is then wetted with ammonium molybdate solution. The wetted sodium molybdenum powder is placed in a graphite mold for pre-pressing. The pre-pressed green body is then placed in a sintering furnace along with the graphite mold and subjected to spark plasma-assisted cold sintering at 200℃~400℃ and 50 MPa high pressure to obtain a sintered target body. The sintered body is then mechanically polished and ultrasonically vibrated to obtain a semi-finished target. The semi-finished target and a copper backing plate are brazed together, and after cleaning, drying, and vacuum sealing, the sodium molybdenum ceramic target is obtained. This invention enables the rapid (5 min) sintering of high-purity, high-density sodium molybdenum ceramic targets at low temperatures.

Description

Technical Field

[0001] This invention relates to the field of ceramic target preparation, specifically a method for preparing molybdenum-sodium ceramic targets by low-temperature and rapid sintering. Background Technology

[0002] Copper indium gallium selenide (CIGS) thin-film solar cells possess advantages such as good stability, high photoelectric conversion efficiency, low manufacturing cost, and long lifespan, making them one of the most promising thin-film solar cell materials. The conversion efficiency of CIGS thin-film solar cells is significantly affected by doping with alkali metal elements (Na, K, Rb, etc.). Adding 0.1 at.% (atomic percentage) of an alkali metal element can improve the performance of solar cells by 30-50%. Through optimized alkali metal doping, the efficiency of currently fabricated CIGS thin-film cells has reached 23.35%. For a long time, the conversion efficiency of CIGS thin-film cells on flexible substrates has not been able to match that of cells using rigid glass substrates. The low Na content in flexible substrates is the main reason for this difference in photoelectric conversion efficiency.

[0003] Adding a Mo-Na layer to the Mo back electrode provides Na to the CIGS absorber layer, enabling sodium-free flexible CIGS thin-film batteries to achieve efficiencies comparable to those of rigid substrate CIGS batteries. However, due to the significant difference in chemical reactivity between Na atoms and chemical stability between Mo atoms, as well as the difference in physical properties between the high melting point of Mo and the low melting point of Na, it is difficult to guarantee the recovery rate and stability of sodium during the preparation of the Mo-Na target.

[0004] For example, CN104073771A discloses a method for preparing a sodium-doped molybdenum sputtering target using pure molybdenum powder and sodium molybdate powder as raw materials. The target is first pre-formed using cold isostatic pressing, followed by multi-stage sintering in a quartz tube. The process involves holding the target at 500°C for 1-5 hours, then raising the temperature to 800-1100°C and holding it for 8-20 hours. CN111593305A discloses a method for preparing a sodium-doped molybdenum target using high-purity molybdenum powder and sodium hydroxide reagent as raw materials, employing hot-pressing sintering. The target is first held at 800°C and 20 MPa for 20 minutes, then raised to 1500°C and held at 30 MPa for 60 minutes. These two patents respectively employ cold isostatic pressing followed by sintering and hot-pressing sintering. Due to the chemical reactivity of Na ions, the loss rate of Na ions is high under the influence of high temperature and multi-stage sintering conditions, resulting in a sodium-doped molybdenum target that cannot provide sufficient and stable Na elements for CIGS flexible thin-film batteries.

[0005] CN115196964A discloses a method for preparing sodium-containing molybdenum oxide ceramic sputtering targets using molybdenum trioxide powder, aluminum powder, and sodium molybdate powder as raw materials, with aluminum powder acting as a binder. The targets are sintered for 4-6 minutes at a pressure of 30-35 MPa and a temperature of 500-510℃ using spark plasma sintering. While rapid spark plasma sintering effectively stores Na ions, the yield of the sodium molybdenum oxide ceramic target is low. Furthermore, while using aluminum powder as a binder increases the density of the sodium-containing molybdenum oxide ceramic target, it also increases the impurity content within the target, significantly negatively impacting its film-forming properties.

[0006] Patent CN116444269A uses molybdenum trioxide powder and sodium molybdate dihydrate powder as raw materials, adding polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and bismuth oxide (BOD) as a flux to improve the density of the target material. It employs spark plasma sintering at 300℃~600℃ for 3~6 hours. The addition of the binder, dispersant, and flux in this patent results in excessively high impurity content in the target material, significantly impacting its performance. Furthermore, spark plasma sintering technology achieves target densification by applying a high-intensity pulsed current to activate the powder particle surface and rapidly sinter, typically with a sintering time of less than 60 minutes. Excessively long sintering times cause severe damage to the equipment. Simultaneously, it leads to significant loss of Na ions in the molybdenum-sodium target material, further reducing its film-forming properties.

[0007] Therefore, designing a novel preparation method for sodium molybdenum ceramic targets to avoid the loss of Na ions, limit the introduction of impurity elements, and ensure the yield of sodium molybdenum ceramic targets is one of the key research focuses for engineers in the field of target materials. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a low-temperature, rapid sintering method for preparing molybdenum-sodium ceramic targets. This method not only enables the preparation of high-purity, high-density, fine-grained molybdenum-sodium ceramic targets with low energy consumption, but also eliminates impurity elements in the targets, significantly improving the yield of molybdenum-sodium target products.

[0009] To achieve the above objectives, the specific solution adopted by the present invention is as follows:

[0010] A method for preparing molybdenum-sodium ceramic targets by low-temperature and rapid sintering mainly includes the following steps:

[0011] Step 1: Using molybdenum trioxide powder and sodium molybdate dihydrate powder as raw materials and alcohol as the medium, ball mill them evenly to obtain a molybdenum-sodium slurry;

[0012] Step 2: The molybdenum-sodium slurry is dried, filtered, ground, and sieved to obtain three groups of powders with particle sizes of 1~10μm, 20~50μm, and 50~100μm; then the three groups of powders are thoroughly mixed in a ratio of 3:6:1 to obtain molybdenum-sodium mixed powder.

[0013] Step 3: Thoroughly wet the surface of the sodium molybdate mixed powder with a 0.05 mol / L ammonium molybdate solution;

[0014] Step 4: Place the moistened molybdenum-sodium mixed powder into a graphite mold for pre-pressing.

[0015] Step 5: Place the pre-pressed green blank together with the graphite mold into a sintering furnace, and perform spark plasma-assisted cold sintering at a sintering temperature of 200~400℃ and a sintering pressure of 50MPa, and hold for 5 minutes to obtain the sintered body.

[0016] Step 6: The sintered body is mechanically polished and ultrasonically cleaned to remove surface impurities, resulting in a semi-finished target material;

[0017] Step 7: The semi-finished target material and copper backing plate are brazed together, and then cleaned, dried and vacuum-sealed to obtain the molybdenum-sodium ceramic target material.

[0018] Furthermore, in step one, the purity of the molybdenum trioxide powder is greater than 99.95%, and the particle size is 50~100 μm.

[0019] Furthermore, in step one, the sodium molybdate dihydrate powder has a purity greater than 99.9% and a particle size of 70~120 μm.

[0020] Furthermore, in step two, the drying temperature is 80℃, and the drying time is 24 hours.

[0021] Furthermore, in step four, the pre-compression pressure is 10 MPa.

[0022] Furthermore, in step five, the sodium content in the sintered body is 3 at.%.

[0023] Furthermore, in step six, the diameter of the semi-finished target material is 50 mm and the thickness is 4 mm.

[0024] Beneficial effects:

[0025] 1) In this invention, ammonium molybdate solution is used to wet the surface of the molybdenum-sodium mixed powder. This not only allows the molybdenum-sodium mixed powder to partially dissolve in the solution, but also ensures that ammonium molybdate will decompose into molybdenum trioxide, ammonia and water during the sintering process of the target material, without introducing impurity elements into the molybdenum-sodium target material.

[0026] 2) The electrical conductivity of the molybdenum-sodium mixed powder in the wetted state is significantly improved, while the surface activity of the powder sintering is also enhanced. Under the action of high-intensity pulsed current, the interaction between the transient liquid phase and plasma greatly improves the activity of the molybdenum-sodium ceramic sintered body. At the same time, under high pressure, the wetted molybdenum-sodium mixed powder undergoes rearrangement, and the surface liquid fills the pores between the particles; in addition, under spark plasma sintering, the transient liquid phase volatilizes, and molybdenum-sodium particles precipitate and fill the voids in the target material; under heat preservation conditions, grain growth further eliminates the porosity in the sintered body, resulting in a significant increase in the density of the molybdenum-sodium target material under cold sintering conditions.

[0027] 3) This invention belongs to the low-temperature densification sintering process of ceramics by discharge plasma assisted liquid phase particles undergoing "dissolution-precipitation". The evolution process of the liquid phase on the surface of molybdenum and sodium particles during discharge plasma assisted cold sintering is: dissolution → rearrangement → precipitation → sintering into ceramics.

[0028] 4) The advantages of this invention are low-temperature densification, low energy consumption, short sintering time, and easy acquisition of nanocrystalline ceramic targets. High-purity, high-density sintered bodies with a diameter of 50 mm and a thickness of 4 mm can be rapidly prepared (5 min) at a low temperature of only 400 ℃.

[0029] 5) The low-temperature and rapid sintering characteristics of discharge plasma-assisted cold sintering effectively ensure the recovery rate of sodium in molybdenum-sodium ceramic targets; using only high-purity molybdenum trioxide powder and sodium molybdate powder as raw materials, without the addition of binders, dispersants and fluxes, impurity elements in molybdenum-sodium targets can be effectively eliminated, ensuring the purity of molybdenum-sodium targets; at the same time, the use of discharge plasma-assisted cold sintering of wetted molybdenum-sodium powder can significantly improve the yield of molybdenum-sodium targets.

[0030] 6) Low-temperature rapid cold sintering significantly reduces the energy consumed in ceramic densification. Attached Figure Description

[0031] Figure 1 This is a physical image of the molybdenum-sodium ceramic target material prepared in Example 3 of the present invention.

[0032] Figure 2 This is a cross-sectional microstructure diagram of the semi-finished target material prepared in Example 3 of the present invention.

[0033] Figure 3 This is a physical image of the sintered body prepared in Comparative Example 1 of the present invention. Detailed Implementation

[0034] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0035] This invention provides a method for preparing molybdenum-sodium ceramic targets by low-temperature and rapid sintering, which mainly includes the following steps:

[0036] Step 1: Using molybdenum trioxide powder (purity greater than 99.95%, particle size 50~100 μm) and sodium molybdate dihydrate powder (purity greater than 99.9%, particle size 70~120 μm) as raw materials and alcohol as medium, ball mill them evenly to obtain a molybdenum-sodium slurry.

[0037] Step 2: The molybdenum-sodium slurry is dried, filtered, ground, and sieved to obtain three groups of powders with particle sizes of 1~10μm, 20~50μm, and 50~100μm; then the three groups of powders are thoroughly mixed in a ratio of 3:6:1 to obtain molybdenum-sodium mixed powder.

[0038] Step 3: Thoroughly wet the surface of the sodium molybdate mixed powder with a 0.05 mol / L ammonium molybdate solution;

[0039] Step 4: Place the moistened molybdenum-sodium mixed powder into a graphite mold for pre-pressing.

[0040] Step 5: Place the pre-pressed green blank together with the graphite mold into a sintering furnace, and perform spark plasma-assisted cold sintering at a sintering temperature of 200~400℃ and a sintering pressure of 50MPa, and hold for 5 minutes to obtain the sintered body.

[0041] Step 6: The sintered body is mechanically polished and ultrasonically cleaned to remove surface impurities, resulting in a semi-finished target material;

[0042] Step 7: The semi-finished target material and copper backing plate are brazed together, and then cleaned, dried and vacuum-sealed to obtain the molybdenum-sodium ceramic target material.

[0043] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the molybdenum trioxide powder has a purity greater than 99.95% and a particle size of 50-100 μm; the sodium molybdate dihydrate powder has a purity greater than 99.9% and a particle size of 70-120 μm.

[0044] Example 1

[0045] A method for preparing molybdenum-sodium ceramic targets by low-temperature and rapid sintering mainly includes the following steps:

[0046] 1) Mixing: Using 52.50g of molybdenum trioxide powder and 6.12g of sodium molybdate dihydrate powder as raw materials, and with alcohol as the medium, the mixture was mixed in a planetary ball mill for 12 hours at a ball mill speed of 250 r / min to obtain a molybdenum-sodium slurry.

[0047] 2) Powdering: The sodium molybdenum slurry was placed in a drying oven and dried for 24 hours at a temperature of 80℃ to obtain dried powder;

[0048] 3) Refinement: After filtering, grinding and sieving the dried powder, three groups of powders with particle sizes of 1~10 μm, 20~50 μm and 50~100 μm are obtained respectively. Then, the three groups of powders with particle sizes of 1~10 μm, 20~50 μm and 50~100 μm are thoroughly mixed in a mixer at a ratio of 3:6:1 to obtain molybdenum-sodium mixed powder.

[0049] 4) Wetting: The surface of the sodium molybdenum mixed powder was uniformly wetted with 6.33g of 0.05mol / L ammonium molybdate solution;

[0050] 5) Pre-compression molding: The wetted molybdenum-sodium mixed powder is placed into a graphite mold and pre-compressed under a pressure of 10 MPa;

[0051] 6) Sintering: The pre-pressed green blank, along with the graphite mold, is placed into the sintering furnace. The temperature inside the furnace is increased to 200℃ at a rate of 20℃ / min; simultaneously, the pressure is increased to 50 MPa at a rate of 10 MPa / min. Sintering is performed at 50 MPa and 200℃ for 5 minutes. The sintering vacuum degree is (1-10)×10 -2 Pa. After sintering, the furnace is cooled to room temperature. During cooling, the pressure is gradually released to obtain the sintered body.

[0052] 7) Machining: The surface of the sintered body is mechanically polished and ultrasonically cleaned to remove surface impurities, and finally a semi-finished target material with a diameter of about 50 mm and a thickness of 4 mm is obtained.

[0053] 8) Brazing: The molybdenum sodium target and the copper backing plate are brazed together, and then the finished product is cleaned, dried and vacuum-sealed.

[0054] Example 2

[0055] A method for preparing molybdenum-sodium ceramic targets by low-temperature and rapid sintering mainly includes the following steps:

[0056] 1) Mixing: Using 52.50g of molybdenum trioxide powder and 6.12g of sodium molybdate dihydrate powder as raw materials, and with alcohol as the medium, the mixture was mixed in a planetary ball mill for 12 hours at a ball mill speed of 250 r / min to obtain a molybdenum-sodium slurry.

[0057] 2) Powdering: The sodium molybdenum slurry was placed in a drying oven and dried for 24 hours at a temperature of 80 ℃ to obtain dried powder;

[0058] 3) Refinement: After filtering, grinding and sieving the dry powder raw material, three groups of powders with particle sizes of 1 μm~10 μm, 20 μm~50 μm and 50 μm~100 μm are obtained respectively. Then, the three groups of powders with particle sizes of 1 μm~10 μm, 20 μm~50 μm and 50 μm~100 μm are thoroughly mixed in a mixer at a ratio of 3:6:1 to obtain molybdenum-sodium mixed powder.

[0059] 4) Wetting: The surface of the sodium molybdenum mixed powder was uniformly wetted with 6.33g of 0.05mol / L ammonium molybdate solution;

[0060] 5) Pre-compression molding: The wetted molybdenum-sodium mixed powder is placed into a graphite mold and pre-compressed under a pressure of 10 MPa;

[0061] 6) Sintering: The pre-pressed green blank is placed into the sintering furnace along with the mold. The temperature inside the furnace is increased to 300 ℃ at a rate of 20 ℃ / min; simultaneously, the pressure is increased to 50 MPa at a rate of 10 MPa / min; sintering is performed at 300 ℃ and 50 MPa pressure for 5 min, with a sintering vacuum degree of (1-10)×10 -2 Pa, after sintering, is cooled to room temperature in the furnace, and the pressure is gradually released during the cooling process to obtain the sintered body;

[0062] 7) Machining: The surface of the sintered body is mechanically polished and ultrasonically cleaned to remove surface impurities, and finally a semi-finished target material with a diameter of about 50 mm and a thickness of 4 mm is obtained.

[0063] 8) Brazing: The semi-finished target material and copper backing plate are brazed together, and then the finished product is cleaned, dried and vacuum-sealed.

[0064] Example 3

[0065] A method for preparing molybdenum-sodium ceramic targets by low-temperature and rapid sintering mainly includes the following steps:

[0066] 1) Mixing: Using 52.50g of molybdenum trioxide powder and 6.12g of sodium molybdate dihydrate powder as raw materials, and using alcohol as a medium, the mixture is mixed in a planetary ball mill for 12 hours at a ball mill speed of 250 r / min to obtain a molybdenum-sodium slurry.

[0067] 2) Powdering: The sodium molybdenum slurry was placed in a drying oven and dried for 24 hours at a temperature of 80 ℃ to obtain dried powder;

[0068] 3) Refinement: After filtering, grinding and sieving the dry powder raw material, three groups of powders with particle sizes of 1~10 μm, 20~50 μm and 50~100 μm are obtained respectively. Then, the three groups of powders with particle sizes of 1~10 μm, 20~50 μm and 50~100 μm are thoroughly mixed in a mixer at a ratio of 3:6:1 to obtain molybdenum-sodium mixed powder.

[0069] 4) Wetting: The surface of the sodium molybdenum mixed powder was uniformly wetted with 6.33g of 0.05mol / L ammonium molybdate solution;

[0070] 5) Pre-compression molding: The wetted molybdenum-sodium mixed powder is placed into a graphite mold and pre-compressed under a pressure of 10 MPa;

[0071] 6) Sintering: The pre-pressed green blank is placed into the sintering furnace along with the mold. The temperature inside the furnace is increased to 400 ℃ at a heating rate of 20 ℃ / min. At the same time, the pressure is increased to 50 MPa at a pressure of 10 MPa / min. Sintering is carried out at 400 ℃ and 50 MPa pressure for 5 min. The sintering vacuum degree is (1-10)×10 -2 Pa, after sintering, is cooled to room temperature in the furnace. During cooling, the pressure is gradually released to obtain the sintered body;

[0072] 7) Machining: The surface of the sintered body is mechanically polished and ultrasonically cleaned to remove surface impurities, and finally a semi-finished target material with a diameter of about 50 mm and a thickness of 4 mm is obtained.

[0073] 8) Brazing: The semi-finished target material and copper backing plate are brazed together, and then the finished product is cleaned, dried and vacuum-sealed.

[0074] Please refer to Figure 1 , Figure 1 The image shown is a physical picture of the molybdenum-sodium target material prepared in this embodiment. Figure 2 This is a cross-sectional microstructure diagram of a semi-finished target material, from... Figure 2 It can be seen that the semi-finished target material prepared by the method of the present invention has good density.

[0075] Comparative Example 1

[0076] The only difference between Comparative Example 1 and Example 3 is that the wetting treatment in step 4) is not performed.

[0077] Experiments revealed that, under the same experimental parameters, the sintering effect of unwetting molybdenum-sodium powder was poor, failing to form a sintered target and resulting in target preparation failure (please refer to...). Figure 3 ).

[0078] The density of the semi-finished target materials prepared in Examples 1-3 was tested, and the results are shown in Table 1.

[0079] Table 1. Density of the semi-finished target materials prepared in Examples 1-3

[0080]

[0081] As shown in Table 1, the target material prepared by the preparation method of the present invention has high density.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention in any way. All equivalent transformations or modifications made in accordance with the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing molybdenum-sodium ceramic targets by low-temperature and rapid sintering, characterized in that, Includes the following steps: Step 1: Using molybdenum trioxide powder and sodium molybdate dihydrate powder as raw materials and alcohol as the medium, ball mill them evenly to obtain a molybdenum-sodium slurry; Step 2: The molybdenum-sodium slurry is dried, filtered, ground, and sieved to obtain three groups of powders with particle sizes of 1~10μm, 20~50μm, and 50~100μm; then the three groups of powders are thoroughly mixed in a ratio of 3:6:1 to obtain molybdenum-sodium mixed powder. Step 3: Thoroughly wet the surface of the sodium molybdate mixed powder with a 0.05 mol / L ammonium molybdate solution; Step 4: Place the moistened molybdenum-sodium mixed powder into a graphite mold for pre-pressing. Step 5: Place the pre-pressed green blank along with the graphite mold into a sintering furnace and perform spark plasma-assisted cold sintering at a sintering temperature of 200~400℃ and a sintering pressure of 50MPa for 5 minutes to obtain the sintered body; the sodium content in the sintered body is 3 at.% Step 6: The sintered body is mechanically polished and ultrasonically cleaned to remove surface impurities, resulting in a semi-finished target material; Step 7: The semi-finished target material and copper backing plate are brazed together, and then cleaned, dried and vacuum-sealed to obtain the molybdenum-sodium ceramic target material.

2. The method for preparing a molybdenum-sodium ceramic target material by low-temperature and rapid sintering according to claim 1, characterized in that, In step one, the purity of the molybdenum trioxide powder is greater than 99.95%, and the particle size is 50~100 μm.

3. The method for preparing a molybdenum-sodium ceramic target material by low-temperature and rapid sintering according to claim 1, characterized in that, In step one, the purity of sodium molybdate dihydrate powder is greater than 99.9%, and the particle size is 70~120 μm.

4. The method for preparing a molybdenum-sodium ceramic target material by low-temperature and rapid sintering according to claim 1, characterized in that, In step two, the drying temperature is 80℃, and the drying time is 24 hours.

5. The method for preparing a molybdenum-sodium ceramic target material by low-temperature and rapid sintering according to claim 1, characterized in that, In step four, the pre-compression pressure is 10 MPa.

6. The method for preparing a molybdenum-sodium ceramic target material by low-temperature and rapid sintering according to claim 1, characterized in that, In step six, the diameter of the semi-finished target material is 50 mm and the thickness is 4 mm.

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