Method for preparing high-fluidity spherical tungsten-copper composite powder by adopting spray drying method

Abstract

The invention discloses a method for preparing high-fluidity spherical tungsten-copper composite powder by adopting a spray drying method, and belongs to the technical field of tungsten-copper composite material preparation. The invention aims to provide an innovative spherical tungsten copper powder preparation technology, and the problem that the fluidity of superfine tungsten copper powder is insufficient is solved through spray granulation. Spray drying is combined with the hydrogen pre-sintering technology, and the tungsten-copper granulation powder with the uniform particle size is prepared. Copper is used as a binding phase to bind and wrap a tungsten phase to form large-particle-size spherical particles, and the powder fluidity can be effectively improved. Meanwhile, the apparent density (increased by 70%) and the tap density (increased by 95%) of the powder can be greatly improved, the relative tap density of the granulated powder is 36.3% of the theoretical density, and the powder is suitable for metal powder injection molding and other applications.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of tungsten copper composite material preparation, and particularly relates to a method for preparing high-fluidity spherical tungsten copper composite powder by adopting a spray drying method. BACKGROUND

[0002] Metal powder injection molding (MIM) technology, as a mature processing technology, has been widely used in many industries. In this technology, commonly used metal powders include iron powder, titanium powder, stainless steel powder, and tungsten copper powder, etc. In particular, tungsten copper powder is highly regarded due to its excellent application performance. The immiscibility between tungsten and copper makes W-Cu-based composite material be called "pseudo-alloy". Such composite material combines the advantages of high melting point and low thermal expansion coefficient of tungsten, and high thermal conductivity and electrical conductivity of copper, etc., and exhibits high hardness, high strength, excellent electrical conductivity, thermal conductivity and arc ablation resistance. In addition, W-Cu composite material also has excellent mechanical properties, free radical arc erosion resistance, and high efficiency of electrical conductivity and thermal conductivity, so it is widely used in thermal and electrical applications such as voltage electrical contact materials, electronic packaging materials and heat sink materials. However, the complex preparation process, low material utilization rate and difficulty in forming complex structures limit the further application of the material.

[0003] In recent years, the progress of injection molding technology makes it possible to prepare tungsten copper parts with complex structure. The traditional preparation method of tungsten copper powder adopts sol-spray drying-reduction method, and the prepared powder has the characteristics of uniform composition distribution, high sintering activity, etc. However, the tungsten copper powder prepared by this method has small particle size, irregular shape and poor fluidity, which cannot meet the demand of injection molding for high loading and high fluidity tungsten copper feedstock. Although granulation treatment can effectively improve the particle size and fluidity of tungsten copper powder, existing granulation technologies such as gas atomization, plasma sphericalization and plasma rotating electrode process are difficult to be applied to large-scale preparation of W-Cu composite powder, and the cost is high.

[0004] Therefore, it is urgent to develop a low-cost powder granulation method. Spray drying technology can effectively prepare large-size solid particles, and combined with sintering densification technology, spherical particles with ideal strength can be prepared, thereby optimizing the application performance in injection molding process. SUMMARY

[0005] The present application aims to provide an innovative spherical tungsten copper powder preparation technology, which solves the problem of poor fluidity of ultra-fine tungsten copper powder by spray granulation. Based on this, the present application adopts spray drying combined with hydrogen pre-sintering technology to prepare tungsten copper granulated powder with uniform particle size, which significantly improves the particle size and tap density of tungsten copper powder. After granulation treatment, the bulk density and tap density of tungsten copper powder are significantly enhanced, thereby greatly improving the fluidity of the powder.

[0006] To achieve the above object, the technical scheme adopted by the present application is:

[0007] A method for preparing high-flowability spherical tungsten-copper composite powder by spray drying method, comprising the following steps:

[0008] Step 1: spray drying and hydrogen reduction

[0009] Dissolve ammonium paratungstate, copper nitrate trihydrate and oxalic acid dihydrate in deionized water, heat and stir to make the mixed solution react; then send the mixed solution through the feed pipe to the spray drying tower, spray dry into tungsten-copper precursor under hot air; then put the obtained tungsten-copper precursor into a ceramic boat, push it into a push rod reduction furnace for hydrogen reduction, to prepare ultra-fine tungsten-copper powder;

[0010] Step 2: preparation of tungsten-copper slurry and spray granulation

[0011] Add dispersant and binder to the solvent, and after complete dissolution, disperse the ultra-fine tungsten-copper powder prepared in step 1 therein to obtain tungsten-copper slurry, and send the tungsten-copper slurry through the feed pipe to the spray drying tower, dry into spherical tungsten-copper powder under nitrogen;

[0012] Step 3: debinding and hydrogen pre-sintering

[0013] Put the spherical tungsten-copper powder obtained by granulation into a tube furnace, and carry out debinding and pre-sintering process under hydrogen atmosphere, and after cooling, crush to prepare large-particle-size spherical tungsten-copper composite powder.

[0014] As a preferred technical scheme of the present application, in step 1, the mass of copper nitrate trihydrate and oxalic acid dihydrate is 32%~120% and 30%~45% of the mass of ammonium paratungstate, respectively. The temperature during the reaction of the mixed solution is controlled at 110~130 ℃, and the reaction time is 5~10 h; the inlet air temperature during spray drying is 240~260 ℃, the feed rate of the peristaltic pump is 2~4 L / h, and the rotation speed of the atomizer is 24000 r / min; the reduction temperature during hydrogen reduction is 880~920 ℃, and the reduction time is 8~12 h.

[0015] As a preferred technical scheme of the present application, in step 2, polyethylene glycol is used as a dispersant, hydroxypropyl methyl cellulose is used as a binder, and an alcohol aqueous solution is used as a solvent; the mass ratio between polyethylene glycol and hydroxypropyl methyl cellulose is 2-4:1, the total mass of polyethylene glycol and hydroxypropyl methyl cellulose is 1%-5% of the mass of the superfine tungsten-copper powder; the concentration of the alcohol aqueous solution is 60%-70%, and the usage amount is 100%-200% of the mass of the superfine tungsten-copper powder. In the stirring process, the stirring speed is 300-350 r / min, the stirring time is 2-4 h, and the stirring temperature is 50-70 DEG C; in the spray granulation process, the air inlet temperature is 170-190 DEG C, the air outlet temperature is 80-100 DEG C, and the atomizer speed is 20,000 r / min.

[0016] As a preferred technical scheme of the present application, in step 3, the temperature in the degreasing stage is 480-520 DEG C, the heating rate is 2-4 DEG C / min, the holding time is 1-2 h, so as to ensure that the binder and the dispersant are completely removed; then the temperature is raised to 980-1020 DEG C at a heating rate of 8-12 DEG C / min, and then the temperature is raised to 1100-1200 DEG C at a heating rate of 2-4 DEG C / min, and the holding time is 1-1.5 h; in the cooling stage, the temperature is first lowered to 480-520 DEG C at a cooling rate of 2-4 DEG C / min, and then the temperature is naturally cooled to room temperature.

[0017] The high-flowability spherical tungsten-copper composite powder prepared by the present application has a regular spherical micro-morphology, a particle size range of 10-20 mu m, and a tap density of more than 30% of the theoretical density, and is suitable for applications such as metal powder injection molding.

[0018] In order to solve the problem of poor flowability of the existing superfine tungsten-copper powder, the present application adopts an improved spray granulation method and a hydrogen pre-sintering method to prepare a high-sphericity tungsten-copper composite powder. The copper is used as a binder to bind and wrap the tungsten phase to form spherical particles with a large particle size, which can greatly improve the bulk density and tap density of the powder and effectively improve the flowability of the powder, and is suitable for applications such as injection molding. Compared with the prior art, the present application has the following advantages:

[0019] (1) The present application uses a spray drying method to prepare spherical granulated powder, which can prepare superfine powder with poor flowability into spherical powder with large particle size, significantly improve the flowability of the powder, reduce the agglomeration of the powder and improve the dispersion performance, thereby expanding the application range of the superfine tungsten-copper powder in the field of injection molding and other industries.

[0020] (2) The solvent used in the granulation process is an alcohol aqueous solution, and the dispersant and binder system is a compound system of polyethylene glycol and hydroxypropyl methyl cellulose; the solvent, dispersant and binder can be completely removed in the subsequent spray granulation and pre-sintering processes, and the granulation process has the characteristics of environmental friendliness, no pollutant residues and controllable raw material cost, thereby forming a low-cost and high-efficiency green granulation process.

[0021] (3) The spherical particles prepared by the granulation process have a particle size increased by 80-90% compared with ungranulated ultrafine tungsten copper powder, a bulk density increased by 70%, and a tap density increased by 95%; according to the performance requirements of the powder for injection molding process, the relative tap density of the powder suitable for injection molding needs to reach 30%-80% of the theoretical density, and the relative tap density of the powder after the granulation process is 36.3% of the theoretical density, which meets the above application requirements, and therefore the applicability of the powder in the injection molding process is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is the SEM morphology of the ultrafine W 17 Cu composite powder before granulation.

[0023] Figure 2 is the SEM morphology of the W 17 Cu spherical powder prepared by spray granulation of Example 1, Comparative Examples 1 and 2.

[0024] Figure 3 is the SEM morphology of the spherical tungsten copper composite powder after pre-sintering of Example 1 (a and b are low and high magnification SEM images, respectively, c is an EDS test selected dark field image, and d and e are W and Cu element mapping images of the corresponding regions, respectively). DETAILED DESCRIPTION

[0025] The application will be further described in detail below in combination with the embodiments and the drawings.

[0026] Example 1

[0027] A preparation method of a high-flowability spherical tungsten copper composite powder, comprising the following steps:

[0028] Step 1: spray drying and powder preparation and hydrogen reduction

[0029] Ammonium metatungstate (AMT, Aladdin, purity≥99.95%) was selected as the tungsten source, copper nitrate trihydrate (Aladdin, purity≥99.95%) as the copper source, and oxalic acid dihydrate (C2H2O4·2H2O, analytical pure) as the complexing agent. The three were mixed and dissolved in a reaction kettle in a mass ratio of copper nitrate trihydrate to oxalic acid dihydrate to ammonium metatungstate (50%, 40%, and 50% by mass, respectively). Four times the mass of deionized water was added to the mixture. The oil bath heating temperature was controlled at 120°C, the stirring speed was 220 r / min, and the reaction time was 6 h.

[0030] The mixed solution after the reaction was transported to the spray drying tower at a rate of 2 L / h through the feed pipe. The inlet air temperature was set to 250°C, the outlet air temperature was 100°C, the atomizer speed was 24000 r / min, and the tungsten-copper precursor was obtained after drying.

[0031] The obtained tungsten-copper precursor was loaded into a ceramic boat, with a loading amount of 1 kg / boat. The boat was sent to a push rod reduction furnace at a push rate of 0.5 h / boat. The target product, ultra-fine tungsten-copper powder, was prepared under the process conditions of a maximum reduction temperature of 880°C and a hydrogen flow rate of 8 m 3 / h for 10 h.

[0032] Step 2: Preparation of tungsten-copper slurry and spray granulation

[0033] According to 2wt% of the mass of the ultra-fine tungsten-copper powder, polyethylene glycol and hydroxypropyl methylcellulose composite powder (mass ratio of 3:1) were accurately weighed as the binder system for granulation and uniformly dispersed in an alcohol aqueous solution (concentration of 65wt%, usage amount of 140% of the mass of the ultra-fine tungsten-copper powder). Then, the mixture was stirred at 60°C and 350 r / min for 30 min to promote the dissolution of the powders. After complete dissolution, the ultra-fine tungsten-copper powder prepared in step 1 was slowly added to the solution, and continuous stirring was performed for 2 h to prepare a uniformly dispersed tungsten-copper slurry.

[0034] The obtained uniformly dispersed tungsten-copper slurry was introduced into the spray drying tower at a rate of 2 L / h through the feed pipe, and spray drying granulation was performed in a nitrogen atmosphere. The inlet air temperature was set to 180°C, the outlet air temperature was 90°C, and the atomizer speed was 20000 r / min.

[0035] After granulation, the powder was sieved to obtain granulated powder with uniform particle size.

[0036] Step 3: Degreasing and hydrogen pre-sintering

[0037] The spray granulation powder obtained in step 2 is subjected to a pre-sintering treatment, and is kept at a predetermined temperature to complete the debinding process (2-4 ℃ / min to 500 ℃, and then kept for 2 h), so as to ensure that the polyethylene glycol and hydroxypropyl methyl cellulose in the powder are fully removed; then the debound powder is subjected to sintering (first 10 ℃ / min to 1000 ℃, then 3 ℃ / min to 1150 ℃, and kept for 1.5 h; then 3 ℃ / min to 500 ℃, and then naturally cooled), so as to make the copper phase melt and flow out and form spherical tungsten-copper composite particles with a preset strength with the tungsten phase; after the sintering process is completed, the sintered product is taken out and crushed into a powder by a crushing device.

[0038] Comparative Example 1

[0039] The preparation method is basically the same as that of Example 1, except that no hydroxypropyl methyl cellulose is added during granulation, and only 2 wt% of polyethylene glycol based on the mass of the ultra-fine tungsten-copper powder is used as a binder.

[0040] Comparative Example 2

[0041] The preparation method is basically the same as that of Example 1, except that the dispersant and binder used during granulation are polyethylene glycol and polyvinyl butyral, respectively, and the total mass of the polyethylene glycol and polyvinyl butyral is 2 wt% based on the mass of the ultra-fine tungsten-copper powder.

[0042] Test result analysis:

[0043] Figure 1 is the SEM morphology of the ultra-fine W 17 Cu composite powder before granulation. From the figure, it can be seen that the tungsten-copper powder has a particle size of 1-2 μm, and the morphology is irregular, and the agglomeration between the powders is serious.

[0044] Figure 2 is the SEM morphology of the W 17 Cu spherical powder obtained by spray granulation in Example 1, Comparative Example 1 and 2. From the figure, it can be seen that the tungsten-copper powder after granulation in Example 1 has a regular spherical shape, and the particle size range is 10-20 μm Figure 2 a); compared with the ungranulated powder, the granulated powder prepared by the present application has a more regular geometric shape and a significantly increased particle size; as shown in the marked area in Figure 2 b, the binder can be seen to bond the ultra-fine tungsten-copper powder particles to form a dense spherical structure. Compared with Comparative Example 1 Figure 2 c, d), the spherical particles have smaller gaps and are more dense. Comparative Example 2 does not form spherical particles Figure 2 e, f) relative to Example 1 and Comparative Example 1. Therefore, the complex system of polyethylene glycol + hydroxypropyl methyl cellulose in Example 1 can better prepare high-flowability spherical tungsten-copper composite powder.

[0045] Figure 3 Figure 1 is a SEM image of the spherical tungsten-copper composite powder after pre-sintering according to Example 1. As can be seen from the figure, the spherical tungsten-copper powder after sintering can basically maintain the shape unchanged, and the particle size is still maintained at 10-20 μm Figure 3 a, b). After pre-sintering, the binder between the tungsten-copper powder is removed, and the copper liquid flows out from the inside to act as a new binder to bond the tungsten skeleton together. As shown in Figure 3 c, d, e, it can be seen from the element analysis that the red tungsten skeleton is distributed on the outside, and the green copper phase is distributed between the internal tungsten skeleton as an adhesive phase to ensure the strength of the sintered sphere

[0046] Table 1 Comparison of bulk and tap densities of tungsten-copper powder (pre-sintered) before and after granulation

[0047] Powder Loose bulk density / g-cm -1 ]]> Tap density / g-cm -1 ]] % of theoretical density [WCu granulation 17 Cu before granulation 1.40 3.01 18.6 W 17 Cu after granulation (pre-sintering) 2.38 5.87 36.3 Table 1 is a comparison of the bulk and tap densities of the tungsten-copper powder (pre-sintered) before and after granulation. As can be seen from the table, the bulk and tap densities of the tungsten-copper powder are greatly improved by granulation and pre-sintering, and the tap density reaches more than 30% of the theoretical density, indicating that the flowability of the powder is also greatly improved compared to the ungranulated powder.

Claims

1. A method for preparing high flowability spherical tungsten-copper composite powder by a spray drying method, characterized by, Comprising the following steps: Step 1: spray drying and hydrogen reduction Ammonium metatungstate, copper nitrate trihydrate and oxalic acid dihydrate are dissolved in deionized water, heated and stirred to react; then the mixed solution is sent to the spray drying tower through the feeding pipe, and the tungsten copper precursor is prepared by spray drying under hot air; then the obtained tungsten copper precursor is loaded into a ceramic boat and pushed into a push rod reduction furnace for hydrogen reduction to prepare ultra-fine tungsten copper powder; Step 2: preparation of tungsten copper slurry and spray granulation The dispersant and binder are added to the solvent, and after complete dissolution, the ultra-fine tungsten copper powder prepared in step 1 is dispersed and stirred to obtain a tungsten copper slurry, which is sent to the spray drying tower through the feeding pipe, and the spherical tungsten copper powder is dried under nitrogen; Step 3: debinding and hydrogen pre-sintering The spherical tungsten copper powder obtained by granulation is placed in a tube furnace and subjected to debinding and pre-sintering processes in a hydrogen atmosphere, and after cooling, it is crushed to prepare large-particle-size spherical tungsten copper composite powder.

2. The method of claim 1, wherein, In step 1, the mass of copper nitrate trihydrate and oxalic acid dihydrate is 32%~120% and 30%~45% of the mass of ammonium metatungstate, respectively.

3. The method of claim 1, wherein, In step 1, the temperature of the mixed solution reaction stage is controlled at 110~130 ℃, and the reaction time is 5~10 h; the inlet air temperature of the spray drying stage is 240~260 ℃, the outlet air temperature is 90~100 ℃, the feeding rate of the peristaltic pump is 2~4 L / h, and the rotation speed of the atomizer is 24000 r / min; the reduction temperature in the hydrogen reduction stage is 880~920 ℃, and the reduction time is 8~12 h.

4. The method of claim 1, wherein, In step 2, polyethylene glycol is used as a dispersant, hydroxypropyl methyl cellulose is used as a binder, and an alcohol aqueous solution is used as a solvent; the mass ratio between polyethylene glycol and hydroxypropyl methyl cellulose is 2~4:1, and the total mass of polyethylene glycol and hydroxypropyl methyl cellulose is 1%~5% of the mass of the ultra-fine tungsten copper powder; the concentration of the alcohol aqueous solution is 60%~70%, and the usage amount is 100%~200% of the mass of the ultra-fine tungsten copper powder.

5. The method of claim 1, wherein, In step 2, the stirring speed for obtaining the tungsten copper slurry is 300~350 r / min, the stirring time is 2~4 h, and the stirring temperature is 50~70 ℃; the inlet air temperature of the spray granulation stage is 170~190 ℃, the outlet air temperature is 80~100 ℃, the feeding rate of the peristaltic pump is 2~4 L / h, and the rotation speed of the atomizer is 20000 r / min.

6. The method of claim 1, wherein, In step 3, the debinding temperature is 480~520 ℃, the heating rate is 2~4 ℃ / min, the holding time is 1~2 h, and the binder and dispersant are completely removed; then the temperature is raised to 980~1020 ℃ at a rate of 8~12 ℃ / min, and then to 1100~1200 ℃ at a rate of 2~4 ℃ / min, and held for 1~1.5 h; in the cooling stage, the temperature is first lowered to 480~520 ℃ at a rate of 2~4 ℃ / min, and then naturally cooled to room temperature.

7. The high flowability spherical tungsten-copper composite powder prepared by the method according to any one of claims 1 to 6, characterized in that, The micro-morphology is regular spherical, the particle size range is 10~20 μm, and the tap density reaches more than 30% of the theoretical density.

8. Use of the high flowability spherical tungsten-copper composite powder according to claim 7 for the production of tungsten-copper composite materials by means of metal powder injection molding.

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