Molybdenum powder and preparation method thereof

Abstract

The present invention belongs to the field of metal powder metallurgy and specifically relates to a molybdenum powder and its preparation method. Compared to existing molybdenum powders that are uneven and have low density, the molybdenum powder of the present invention contains uniform, porous, hard agglomerated particles with a high specific surface area. During the slurry sintering process, this molybdenum powder can enhance liquid phase migration and filling and coating during sintering, improve the bond strength between the substrate and the slurry after sintering, and increase the yield of high-quality products.

Description

Technical Field

[0001] The invention belongs to the field of metal powder metallurgy powder making, and particularly relates to molybdenum powder and a preparation method thereof. Background Art

[0002] Since its establishment as an independent discipline and specialized expertise in the 1940s, powder preparation technology has made significant progress over the past half century. Currently, powder preparation technology can be categorized into three broad categories, including vapor-phase methods (including evaporation-condensation and vapor-phase reaction methods), liquid-phase methods (including precipitation, sol-gel, and hydrothermal methods), and solid-phase methods (including mechanical and chemical methods), encompassing dozens of preparation processes. However, the molybdenum powder prepared using these conventional methods typically consists of solid, single-particle molybdenum powder with poor uniformity. Agglomerates may form, and most of these are soft aggregates. The few hard aggregates that do form lack a porous internal structure, resulting in poor sintering activity. Summary of the Invention

[0003] In view of the problems of poor sintering activity of molybdenum powder in the above-mentioned prior art, the present invention provides a molybdenum powder and a preparation method thereof.

[0004] To achieve the above objectives, the following technical solutions are specifically included:

[0005] Disclosed is molybdenum powder, comprising agglomerated particles formed by agglomeration of nano-scale molybdenum powder, wherein the interior of the agglomerated particles is a loose porous structure.

[0006] In one embodiment, the average particle size of the agglomerated particles is 1-8 μm.

[0007] When the particle size is between 1 and 8 μm, the particle size distribution is relatively concentrated, and the slurry produced has good uniformity, which can effectively improve the raw processing and sintering performance of the product.

[0008] In one embodiment, the surface structure of the agglomerated particles is dense.

[0009] In one embodiment, the pore size of the micropores inside the agglomerated particles is 1-20 nm; the pore size of the micropores on the surface of the agglomerated particles is 1-10 nm.

[0010] In one embodiment, the molybdenum powder further comprises agglomerated particle intermediates formed by agglomeration of nano-scale molybdenum powder.

[0011] In one embodiment, the surface porosity of the agglomerated particle intermediate is ≥10%.

[0012] Since the powder is broken during the plasma ball milling process, the particles undergo secondary sintering due to the action of plasma and voltage, which is the granulation process. The intermediate is the state where the granulation is not completed in this process, and the intermediate in this process is relatively loose.

[0013] When the pore size of the micropores inside the agglomerated molybdenum powder particles is less than 1nm, the slurry containing molybdenum powder is difficult to flow in the internal voids, and it indicates that the granulation has been over-granulated at this time, such as too long time, too high voltage, etc. In this case, the surface porosity and internal porosity of the particles will be very small, even close to solid sphericalization. The relative specific surface area of ​​such particles is small, the sintering liquid phase is difficult to migrate, and it is easy to sinter loosely, resulting in poor bonding between the two. When the pore size of the micropores inside the agglomerated particles is greater than 20nm, the particles are intermediates of the agglomerated particles, and the particles are relatively loose, indicating that the granulation process has not reached the best, such as insufficient time, too low voltage, etc. Such intermediate particles are easily broken up during the sintering process, resulting in excessive sintering of the slurry, affecting the surface porosity and roughness.

[0014] When the pore size of the micropores on the surface of the agglomerated particles is less than 1nm, it is difficult for the slurry containing molybdenum powder to flow into the interior of the particles from the surface voids, and it indicates that the granulation has been over-granulated at this time, such as too long time, too high voltage, etc. In this case, the internal porosity of the particles will be very small, even close to solid sphericalization. The relative specific surface area of ​​such particles is small, the sintering liquid phase is difficult to migrate, and it is easy to sinter loosely, resulting in poor bonding between the two. When the pore size of the micropores on the surface of the agglomerated particles is greater than 10nm, the particles are intermediates of the agglomerated particles, and the particles are relatively loose, indicating that the granulation process has not reached the best, such as insufficient time, too low voltage, etc. Such intermediate particles are easily broken up during the sintering process, resulting in excessive sintering of the slurry containing molybdenum powder, affecting the surface porosity and roughness.

[0015] In one embodiment, the average porosity of the agglomerated particles is ≥60%. Preferably, the average porosity of the agglomerated particles is 60%-85%.

[0016] In one embodiment, the surface porosity of the agglomerated particles is less than 10%. The average porosity and surface porosity of the agglomerated particles can be measured using conventional testing methods, such as FIB, Fisher particle size analyzer, and other measurement methods.

[0017] If the porosity is too low and the relative specific surface area is small, the sintering liquid phase is difficult to migrate during the sintering of molybdenum powder, and the sintering is easy to be loose, resulting in poor bonding between the ceramic phase and the metallization layer; if the porosity is too high and the relative specific surface area is also large, it is also easy to cause over-sintering.

[0018] In one embodiment, the agglomerated particles are spherical in shape.

[0019] In one embodiment, the specific surface area of ​​the agglomerated particles is 2-4 m 2 / g.

[0020] If the specific surface area of ​​the agglomerated particles is too large, the slurry containing molybdenum powder will easily be over-sintered, affecting the surface porosity and roughness; if the specific surface area of ​​the agglomerated particles is too small, the slurry containing molybdenum powder will be difficult to sinter, resulting in loose sintering.

[0021] In one embodiment, the micropores inside the agglomerated particles are interconnected and have irregular pore sizes; the micropores on the surface of the agglomerated particles are irregularly distributed and are not interconnected.

[0022] In one embodiment, the average particle size of the agglomerated particle intermediates is 1-8 μm.

[0023] In one embodiment, in the molybdenum powder, the agglomerated particles account for 90-100% of the total amount, and the agglomerated particle intermediates account for 0-10% of the total amount.

[0024] In one embodiment, the molybdenum powder further comprises unagglomerated nano-scale molybdenum powder, and the amount of the nano-scale molybdenum powder in the molybdenum powder is less than 5% of the total amount of the molybdenum powder.

[0025] In one embodiment, the average particle size of the nano-scale molybdenum powder is 50-500 nm, and the specific surface area of ​​the nano-scale molybdenum powder is 2-4 m 2 / g,

[0026] In one embodiment, the nano-scale molybdenum powder particles are spherical in shape.

[0027] In one embodiment, the specific surface area of ​​the nano-scale molybdenum powder is 2-4 m 2 / g.

[0028] The agglomerated particles in the molybdenum powder of the present invention have the characteristics of good overall uniformity, particle size distribution dispersion = (D90-D10) / D5 approaching zero, uniform porosity, and high specific surface area. During the sintering process of the slurry containing the molybdenum powder of the present invention, liquid phase migration and filling and coating can be improved, the bonding strength can be improved, and the product quality rate can be improved.

[0029] A method for preparing molybdenum powder comprises the following steps:

[0030] Under the protection of inert gas, large-particle molybdenum powder or molybdenum blocks and activators are subjected to three-stage electric ball milling;

[0031] The three-stage electric ball mill specifically comprises the following steps:

[0032] The first stage: ball milling for 0.5-3h at a pressure of 5-10MPa, a current of 5-35A, a voltage of 0.1-0.5KV, and a frequency of 2000-3000Hz;

[0033] The second stage: ball milling for 1-6 hours at a pressure of 5-10 MPa, a current of 5-35 A, a voltage of 3-5 KV, and a frequency of 2000-3000 Hz;

[0034] The third stage: continue ball milling at a pressure of 5-10 MPa, a current of 5-35 A, a voltage of 0.1-0.5 KV, and a frequency of 100-2000 Hz, while maintaining the system temperature below 100°C.

[0035] In the preparation method of the present invention, electric ball milling is divided into three stages. The first stage is a low-pressure and high-frequency stage, the purpose of which is to form soft agglomerates and nuclei; the second stage is a high-pressure and stable-frequency stage, which is mainly to grow hard agglomerates at the nuclear sites of soft agglomerates; the third stage is a low-pressure and low-frequency stage. Since the energy released in the second stage is very high, the entire tank is in a high-temperature state and the surface energy of the internal powder is very high. At this time, it is necessary to cool it down in the dynamic process to prevent the accumulation of high-energy powder from causing excessive sintering and reducing the uniformity of the powder. Therefore, it is necessary to keep the tank body below 100°C. The ball milling time in this stage starts when the tank body is reduced to below 100°C.

[0036] In the methods of the prior art, the core of the preparation of molybdenum powder molding is to granulate by nucleation and growth. According to the principle of entropy increase and minimum energy, it is generally only based on the original solid particles, infinite nucleation and growth, and finally dense large spherical particles are obtained (molybdenum powder spheroidization process). In order to prepare solid and dense molybdenum particles, the conventional method is only to allow the nanoparticles to grow into micron particles, and it is impossible to control the formation of agglomerated particles with a porous structure. The main reason is that the entire preparation process of the current prior art is a static process (no electric field is applied). The present invention combines dynamic ball milling with an external electric field. In the ball mill, the synergistic effect of high-energy non-equilibrium ionization formed by gas at near normal pressure under high voltage and mechanical ball milling is utilized. Under the action of non-thermal plasma formed in the sealed ball mill system, molybdenum molecules are easily converted into atomic states and excited states for recombination, promoting the refinement, alloying, activation, chemical reaction and acceleration of in-situ gas-solid phase reaction of the molybdenum powder, forming a unique molybdenum powder structure, thereby significantly improving the performance of the molybdenum powder.

[0037] The large-particle molybdenum powder has an average particle size greater than 8 μm and can be homemade or commercially available. The molybdenum block can also be homemade or commercially available.

[0038] In one embodiment, the ball mill includes grinding media, and the grinding media are steel balls. In the electric ball mill, the mass ratio of the balls to the materials is 1:(1-5000).

[0039] In one embodiment, the active agent includes at least one of ethanol and oleic acid.

[0040] In one embodiment, the active agent accounts for 0-5% of the mass of the large-particle molybdenum powder or molybdenum block. Adding a small amount of active agent can control the porosity and pore size of the agglomerated particles, but excessive active agent will hinder the granulation and agglomerated particle process.

[0041] In one embodiment, in the first stage to the third stage, the gas pressure of the ball milling is each selected from 8-10 MPa.

[0042] In one embodiment, in the first stage to the third stage, the current of the ball milling is each selected from 30-35A.

[0043] In one embodiment, in the first stage, the ball milling voltage is 0.3-0.5 KV.

[0044] In one embodiment, in the second stage, the ball milling frequency is 2000 Hz.

[0045] In one embodiment, in the second stage, the ball milling time is 4-5 hours.

[0046] In one embodiment, in the third stage, the ball milling frequency is 700-1000 Hz.

[0047] In one embodiment, in the third stage, the ball milling time is 0.5-3 hours.

[0048] In one embodiment, the inert gas includes at least one of nitrogen, argon, and helium.

[0049] A conductive paste comprises the following components in percentage by mass: 68-78% of molybdenum powder, 5-10% of non-metallic phase, 14-19% of solvent, and 1-3% of adhesive.

[0050] In one embodiment, the non-metallic phase comprises aluminum oxide.

[0051] In one embodiment, the solvent includes diethylene glycol monobutyl ether acetate.

[0052] In one embodiment, the binder comprises a cellulosic polymer.

[0053] Compared with the prior art, the present invention has the following beneficial effects: compared with the existing uneven and low-density molybdenum powder, the molybdenum powder of the present invention contains uniform, porous, hard agglomerated particles with a high specific surface area. During the slurry sintering process, the molybdenum powder can improve the liquid phase migration and filling coating during the sintering process, improve the bonding strength between the substrate and the slurry after sintering, and improve the product quality rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 Schematic diagram of the metal ring, metal layer welding and ceramic substrate structure.

[0055] Figure 2 Schematic diagram of metal ring peeling after welding.

[0056] Figure 3 This is an SEM image of the agglomerated particles in the molybdenum powder prepared in Example 1.

[0057] Figure 4 This is an SEM image of the agglomerated particle intermediate in the molybdenum powder prepared in Example 1.

[0058] Figure 5 This is an SEM image of the agglomerated particle intermediate in the molybdenum powder prepared in Example 1.

[0059] Figure 6 This is a cross-sectional SEM image of the agglomerated particles in the molybdenum powder prepared in Example 1, showing that the agglomerated particles have a loose and porous internal structure. DETAILED DESCRIPTION

[0060] To better illustrate the objectives, technical solutions, and advantages of the present invention, the present invention will be further described below with reference to specific examples. The experimental methods used in the examples and / or comparative examples are conventional methods unless otherwise specified; the materials and reagents used are commercially available unless otherwise specified.

[0061] Example 1

[0062] 1. Prepare raw materials and select commercially available large-particle molybdenum powder. The raw material molybdenum powder particles can be selected according to different processes each time. This time, the original molybdenum powder with D50 of 30μm is selected.

[0063] 2. The molybdenum powder was loaded into a ball mill (using XYZ axis three-dimensional vibration ball milling equipment), and ethanol was added at the same time. The addition amount was 5wt% of the total molybdenum powder. The grinding medium was steel balls. The mass ratio of balls to materials was 1:500. The tank was evacuated and filled with inert gas (Ar gas) for protection. The vacuum degree was maintained at ≥1×10 -3 Pa.

[0064] 3. Control the gas pressure in the ball mill at 8MPa, and pass current and voltage into the ball mill for ball milling. The current is 30A. The whole process needs to be divided into three stages:

[0065] The first stage: low-voltage and high-frequency ball milling. The voltage in this stage is set at 0.3KV, the grinding frequency is set at 2000Hz, and the holding time is 2h. This frequency is the vibration frequency of the ball mill in an unfixed direction.

[0066] The second stage: high voltage and stable frequency ball milling, in which the voltage is increased to 5KV and the grinding frequency is stabilized at 2000Hz for 4 hours;

[0067] The third stage: low-voltage and low-frequency ball milling. In this stage, the voltage is reduced to 0.5KV, the grinding frequency is 800Hz, and the time is 1h. At the same time, air cooling is used in this stage to keep the system temperature between 80-99℃.

[0068] Example 2

[0069] The difference between this embodiment and embodiment 1 is that the raw material in step 1 is commercially available molybdenum block.

[0070] Example 3

[0071] The difference between this embodiment and embodiment 1 is that the mass ratio of the ball material in step 2 is 1:5000.

[0072] Example 4

[0073] The difference between this embodiment and embodiment 1 is that in step 2, the amount of ethanol added is 3 wt% of the total amount of molybdenum powder, and the mass ratio of the ball material is 1:5000.

[0074] Example 5

[0075] The difference between this embodiment and embodiment 1 is that in step 2, the amount of ethanol added is 3 wt% of the total amount of molybdenum powder, and the mass ratio of the ball material is 1:1000.

[0076] Example 6

[0077] The difference between this embodiment and embodiment 1 is that in step 2, the amount of ethanol added is 3 wt% of the total amount of molybdenum powder, and the mass ratio of the ball material is 1:1.

[0078] Examples 7-11

[0079] The difference between Examples 7-11 and Example 1 lies in the voltage, frequency and time in step 3. The specific voltage, frequency and time are shown in Table 1.

[0080] Comparative Examples 1-8

[0081] The differences between Comparative Examples 1-8 and Example 1 are the ball-to-material ratio and the amount of ethanol added in step 2, and the voltage, frequency and time in step 3, as shown in Table 1.

[0082] Table 1

[0083]

[0084]

[0085]

[0086] The symbols in Table 1 are as follows:

[0087] The added amount is the mass percentage of ethanol to the total amount of molybdenum powder;

[0088] First stage voltage: V1, first stage frequency: H1, first stage holding time: T1;

[0089] Second stage voltage: V2, second stage frequency: H2, second stage holding time: T2;

[0090] The third stage voltage: V3, the third stage frequency: H3, the third stage holding time: T3.

[0091] Effect Examples

[0092] The molybdenum powder of the above-mentioned Examples 1-11 and Comparative Examples 1-8 was prepared into a conductive paste, which included the following components in percentage by weight: 78% molybdenum powder, 5% non-metallic phase, 14% solvent, and 3% binder, wherein the non-metallic phase was aluminum oxide, the solvent was diethylene glycol monobutyl ether acetate, and the binder was a cellulose polymer.

[0093] Performance testing methods and qualification standards of molybdenum powders obtained in the examples and comparative examples:

[0094] 1. Particle size test method: First use SEM to photograph the molybdenum powder particle size, and statistically analyze the particle size distribution of the powder; standard: particle size is 1-8μm.

[0095] 2. Porosity test: FIB slices were used for 3D reconstruction. The average porosity of the agglomerated particles and the average porosity of the surface layer were calculated using this method.

[0096] 3. Specific surface area: Use a specific surface area analyzer to analyze the specific surface area of ​​the prepared molybdenum powder. The specific surface area of ​​the molybdenum powder is required to be between 2-4m 2 / g range.

[0097] 4. Morphology: (1) Use SEM to observe molybdenum powder; (2) Use secondary electron mode to photograph the powder morphology; (3) Use secondary electron mode to confirm the pore situation after slurry sintering; (4) Use backscattering mode to distinguish between metal phase and non-metal phase, and observe the distribution form and uniformity of metal phase and non-metal phase. If the molybdenum powder itself is distributed more evenly, then the metal phase and non-metal phase will also be distributed more evenly.

[0098] 5. Purity: Use XRF pellets to test the chemical composition of molybdenum powder, and the purity of molybdenum powder is required to be ≥99.9%.

[0099] 6. Oxygen content: Oxygen content affects the sintering temperature and densification degree. Use an oxygen and nitrogen analyzer to test the oxygen content in molybdenum powder.

[0100] 7. Test of bonding strength between conductive paste containing molybdenum powder and ceramic substrate: The molybdenum powder of the present invention is applied to the ceramic package base. Specifically, the conductive paste containing molybdenum powder is coated on the ceramic package base, the metal ring is covered with solder, and the metal ring is sintered in a brazing furnace at 800-900°C. The metal layer formed by sintering the conductive paste containing molybdenum powder is welded together, as shown in the attached figure. Figure 1As shown, the metal ring is peeled off and the peeling force of the metal ring is tested. Figure 2 As shown, the peel force can reflect the bonding strength between the ceramic substrate and the metal layer after sintering the molybdenum powder-containing slurry, thereby reflecting the bonding strength and product qualification rate of the products prepared using the molybdenum powder of the present invention. A greater peel force indicates a higher bonding strength between the metal layer and the ceramic layer. The product is required to meet the required standard with a peel force of ≥40N. The molybdenum powder used in the molybdenum powder-containing conductive slurry is the molybdenum powder prepared in the corresponding Examples and Comparative Examples, and the remaining non-metallic phase, solvent, binder, and other conditions are the same.

[0101] Table 2

[0102]

[0103] Compared with the existing uneven and low-density molybdenum powder, the molybdenum powder of the present invention contains uniform, porous, hard agglomerated particles with a high specific surface area. During the slurry sintering process, the molybdenum powder can improve the liquid phase migration and filling coating during the sintering process, improve the bonding strength between the substrate and the slurry after sintering, and improve the product quality rate.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A molybdenum powder, characterized in that The molybdenum powder comprises agglomerated particles formed by agglomeration of nano-scale molybdenum powder, and the interior of the agglomerated particles is a loose porous structure; The preparation method of the molybdenum powder comprises the following steps: Under the protection of inert gas, large-particle molybdenum powder or molybdenum blocks and activators are subjected to three-stage electric ball milling; The three-stage electric ball mill specifically comprises the following steps: The first stage: ball milling for 0.5-3h at a pressure of 5-10MPa, a current of 5-35A, a voltage of 0.1-0.5KV, and a frequency of 2000-3000Hz; The second stage: ball milling for 1-6 hours at a pressure of 5-10 MPa, a current of 5-35 A, a voltage of 3-5 KV, and a frequency of 2000-3000 Hz; The third stage: continue ball milling at a pressure of 5-10 MPa, a current of 5-35 A, a voltage of 0.1-0.5 KV, and a frequency of 100-2000 Hz, while maintaining the system temperature below 100°C.

2. molybdenum powder as claimed in claim 1, is characterized in that, The average particle size of the agglomerated particles is 1-8 μm.

3. molybdenum powder as claimed in claim 1, is characterized in that, The pore size of the micropores inside the agglomerated particles is 1-20 nm; the pore size of the micropores on the surface of the agglomerated particles is 1-10 nm.

4. molybdenum powder as claimed in claim 1, is characterized in that, The agglomerated particles are spherical in shape.

5. molybdenum powder as claimed in claim 1, is characterized in that, The average porosity of the agglomerated particles is ≥60%.

6. molybdenum powder as claimed in claim 1, is characterized in that, Include at least one of the following (1)-(3): (1) The porosity of the surface layer of the agglomerated particles is less than 10%; (2) The molybdenum powder also includes agglomerated particle intermediates formed by agglomeration of nano-scale molybdenum powder, and the surface porosity of the agglomerated particle intermediates is ≥10%; in the molybdenum powder, the number of the agglomerated particles accounts for 90-100%, and the number of the agglomerated particle intermediates accounts for 0-10%; (3) The molybdenum powder further includes unagglomerated nano-scale molybdenum powder; in the molybdenum powder, the amount of the unagglomerated nano-scale molybdenum powder is less than 5% of the total amount of the molybdenum powder.

7. A method for preparing molybdenum powder according to any one of claims 1 to 6, characterized in that: The steps include: Under the protection of inert gas, large-particle molybdenum powder or molybdenum blocks and activators are subjected to three-stage electric ball milling; The three-stage electric ball mill specifically comprises the following steps: The first stage: ball milling for 0.5-3h at a pressure of 5-10MPa, a current of 5-35A, a voltage of 0.1-0.5KV, and a frequency of 2000-3000Hz; The second stage: ball milling for 1-6 hours at a pressure of 5-10 MPa, a current of 5-35 A, a voltage of 3-5 KV, and a frequency of 2000-3000 Hz; The third stage: continue ball milling at a pressure of 5-10 MPa, a current of 5-35 A, a voltage of 0.1-0.5 KV, and a frequency of 100-2000 Hz, while maintaining the system temperature below 100°C.

8. The method for preparing molybdenum powder as claimed in claim 7, wherein The active agent includes at least one of ethanol and oleic acid; the active agent accounts for 0-5% of the mass of the large-particle molybdenum powder or molybdenum block.

9. The method for preparing molybdenum powder as claimed in claim 7, wherein Include at least one of the following (1)-(9): (1) In the first to third stages, the gas pressure of the ball mill is selected from 8-10 MPa; (2) In the first to third stages, the current of the ball milling is selected from 30-35A; (3) In the first stage, the ball milling voltage is 0.3-0.5 kV; (4) In the second stage, the ball milling frequency is 2000 Hz; (5) In the second stage, the ball milling time is 4-5 hours; (6) In the third stage, the ball milling frequency is 700-1000 Hz; (7) In the third stage, the ball milling time is 0.5-3 hours; (8) The inert gas includes at least one of nitrogen, argon, and helium; (9) In the electric ball mill, the mass ratio of the ball to the material is 1:1-5000.

10. A conductive paste, characterized in that: The invention comprises the following components in percentage by mass: 68-78% of the molybdenum powder according to any one of claims 1 to 6, 5-10% of aluminum oxide, 14-19% of a solvent, and 1-3% of a binder.

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