Preparation method of nano tungsten-nickel-iron composite powder

Abstract

The invention discloses a preparation method of nano tungsten-nickel-iron composite powder, which comprises the following steps: 1, dissolving ammonium metatungstate, nickel chloride hexahydrate and ferric chloride hexahydrate in water, and stirring to obtain a solution; step 2, atomizing the solution and spraying the atomized solution into liquid nitrogen for pre-freezing to obtain frozen particles; 3, freeze-drying the frozen particles to obtain precursor composite powder; and 4, the precursor composite powder is subjected to roasting and reduction in the hydrogen atmosphere in sequence, and the nano tungsten-nickel-iron composite powder is obtained. According to the preparation method, frozen particles containing tungsten, nickel and iron are obtained through pre-freezing, then solid ice of the frozen particles is directly sublimated into gas to be separated through a freeze-drying process, nanoscale precursor composite powder is obtained, and the nano tungsten-nickel-iron composite powder is prepared through roasting and reduction in the hydrogen atmosphere. The method is suitable for the technical field of powder preparation engineering.

Description

Technical Field

[0001] The present invention belongs to the technical field of powder preparation engineering, and in particular relates to a method for preparing nano tungsten-nickel-iron composite powder. Background Art

[0002] Tungsten-nickel-iron alloy is a two-phase composite material formed by using tungsten grains with a BCC crystal structure as the matrix and introducing iron and nickel, a metal with an FCC crystal structure of low melting point in the transition group, as the binder phase. With excellent mechanical properties, this material has important application value in the fields of aerospace, electronic information, national defense and military industry, etc. With the development of science and technology and the upgrading of social demands, the tungsten alloy system and its preparation technology have been continuously innovated. In the coarse-grained tungsten alloy prepared by the traditional high-temperature liquid-phase sintering method, the tungsten grain size usually reaches 40μm - 50μm. Due to defects such as large grains and non-uniform structures in the material, it is difficult to meet the strict requirements for high-performance tungsten alloys in the front-line fields.

[0003] According to the Hall-Petch relationship, grain refinement can significantly improve the mechanical properties of materials. For this reason, global researchers have made a series of breakthroughs by means of adjusting alloy components, introducing grain inhibitors, new sintering and forming processes, etc. However, due to insufficient research on the front-end powder preparation process, no breakthrough has been achieved from the source of the material, resulting in the fact that the current tungsten alloy grain refinement level has not reached the ideal state. At present, there are still technical barriers in the low-cost industrial production of nano tungsten-nickel-iron composite powder, which has become a bottleneck restricting the industrial application of fine-grained / ultrafine-grained tungsten alloys.

[0004] At present, mechanical alloying and spray drying-hydrogen reduction are mainly used to prepare ultrafine / nano tungsten-nickel-iron composite powder. Among them, mechanical alloying realizes the nano-level mixing of W, Ni, and Fe element powders through high-energy ball milling. Although this technology is suitable for large-scale industrial production, long-term grinding is likely to cause equipment wear and lead to impurity pollution, affecting the powder purity, and further affecting the mechanical properties of the subsequent alloy materials. The spray drying method obtains the precursor composite powder by means of solution atomization. However, in the subsequent hydrogen reduction stage, the chemical vapor transport mechanism promotes the formation of WO2(OH)2 gas hydrate, and coupled with the effect of the material layer stacking, the number of nucleation points is insufficient, and the particle size of the final product is generally in the micron level, making it difficult to obtain ultrafine or even nano tungsten-nickel-iron composite powder.

[0005] Therefore, how to achieve particle size control on the basis of improving the purity of nano tungsten-nickel-iron composite powder is an urgent problem to be solved. Summary of the Invention

[0006] The object of the present invention is to overcome the deficiencies in the above-mentioned prior art and provide a method for preparing nano tungsten-nickel-iron composite powder. This preparation method obtains frozen particles containing tungsten, nickel, and iron through pre-freezing, and then uses the freeze-drying process to directly sublime the solid ice of the frozen particles into gas and separate it, obtaining a nano-scale precursor composite powder. The nano tungsten-nickel-iron composite powder is prepared through roasting and reduction in a hydrogen atmosphere, solving the problem that the prior art cannot prepare high-purity nano tungsten-nickel-iron composite powder.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing nano tungsten-nickel-iron composite powder, characterized in that the preparation method includes the following steps:

[0008] Step 1: Dissolve ammonium metatungstate, nickel chloride hexahydrate, and iron chloride hexahydrate in water and stir to obtain a solution;

[0009] Step 2: Atomize and spray the solution obtained in Step 1 into liquid nitrogen for pre-freezing to obtain frozen particles;

[0010] Step 3: Freeze-dry the frozen particles obtained in Step 2 to obtain a precursor composite powder;

[0011] Step 4: Roast and reduce the precursor composite powder obtained in Step 3 in a hydrogen atmosphere in sequence to obtain nano tungsten-nickel-iron composite powder.

[0012] By using ammonium metatungstate, nickel chloride hexahydrate, and iron chloride hexahydrate powders that are easily soluble in water as raw materials and fully stirring the solution, the present invention can effectively disperse the solute, avoid component segregation, obtain a solution with uniform composition and no obvious color segregation, and improve the composition uniformity of the subsequent precursor composite powder; by atomizing the solution and spraying it into liquid nitrogen for low-temperature pre-freezing and freeze-drying, the expansion effect generated by ice crystal growth is used to force adjacent particles to separate, and the solid ice of the frozen particles is directly sublimated into gas and separated. The solid matrix can effectively inhibit solute reaggregation, obtaining a precursor composite powder with an average particle size of 300 nm to 500 nm; subsequently, the precursor composite powder is converted into a composite oxide with an average particle size of 200 nm to 300 nm through roasting, and a nano tungsten-nickel-iron composite powder with uniform particle size and high dispersibility is obtained after hydrogen atmosphere reduction treatment.

[0013] Since the cooling rate of the traditional cold well is slower than the movement speed of the solute, a part of deionized water will first solidify into ice crystals uniformly in the solution, resulting in incomplete separation of the solute and ultimately affecting the powder uniformity; by using liquid nitrogen that can quickly freeze for pre-freezing, the present invention is more conducive to the uniform distribution of precursor elements.

[0014] The preparation method of the above-mentioned nano tungsten-nickel-iron composite powder is characterized in that the mass ratio of tungsten element in ammonium metatungstate, nickel element in nickel chloride hexahydrate, and iron element in iron chloride hexahydrate in step one is 90:7:3 or 93:4.9:2.1.

[0015] The preparation method of the above-mentioned nano tungsten-nickel-iron composite powder is characterized in that the pre-freezing temperature in step two is -190°C to -180°C.

[0016] The preparation method of the above-mentioned nano tungsten-nickel-iron composite powder is characterized in that the freeze-drying method in step three is as follows: in an environment with a vacuum degree of 1 Pa to 20 Pa, use a freeze dryer to dry the frozen particles at a temperature of -80°C to -50°C for 12 h to 72 h.

[0017] The present invention can effectively improve the drying efficiency by performing freeze-drying in a high-vacuum environment and controlling the temperature of freeze-drying, and obtain a precursor composite powder with uniform particle size distribution, good dispersibility, and small particle size; compared with vacuum drying in the prior art, the freeze-drying process can make ice crystals sublime to form a three-dimensional pore structure, effectively avoiding macroscopic collapse of the material, and the obtained precursor composite powder presents a loose and porous morphology, with significantly reduced agglomeration between particles and improved dispersibility.

[0018] The preparation method of the above-mentioned nano tungsten-nickel-iron composite powder is characterized in that the thickness of the frozen particles laid in the freeze dryer is 10 mm to 20 mm.

[0019] The present invention controls the thickness of the frozen particles laid in the freeze dryer to avoid that if the thickness is too thick, it is difficult to convert the ice crystals of the internal frozen particles into gaseous sublimation, prolonging the freeze-drying time; and avoiding that if the thickness is too thin, the drying efficiency is reduced.

[0020] The preparation method of the above-mentioned nano tungsten-nickel-iron composite powder is characterized in that the roasting temperature in step four is 300°C to 500°C, and the roasting duration is 1 h to 2 h.

[0021] The present invention can improve the reaction efficiency by controlling the temperature to 300°C to 500°C, and further obtain a composite oxide with uniform particle size distribution and good dispersibility.

[0022] The preparation method of the above-mentioned nano tungsten-nickel-iron composite powder is characterized in that the reduction temperature in a hydrogen atmosphere in step four is 700°C to 800°C, and the reduction time in a hydrogen atmosphere is 1 h to 2 h.

[0023] In the present invention, by maintaining a relatively low reduction temperature during the reduction process, the rate of reduction of the oxide to the elemental form is slowed down, which is beneficial to enhancing the migration of the tungsten source during the reduction of tungsten oxide, increasing the nucleation rate and controlling the growth process. At the same time, the relatively low temperature can also effectively prevent the coalescence growth between particles and refine the particle size of the reduced powder product.

[0024] In the above method for preparing a nano tungsten-nickel-iron composite powder, it is characterized in that the average particle size of the nano tungsten-nickel-iron composite powder described in step four is 30 nm to 50 nm.

[0025] The present invention has the following advantages compared with the prior art:

[0026] 1. In the preparation method of the present invention, by using pre-freezing to obtain frozen particles containing tungsten, nickel, and iron, and then using the freeze-drying process to directly sublime the solid ice of the frozen particles into gas and separate it, a nano-scale precursor composite powder is obtained. The low-temperature treatment process of pre-freezing + freeze-drying can completely retain the chemical composition and physical properties of the raw materials. The particle size of the obtained precursor composite powder can reach the sub-micron level and the distribution is highly concentrated. Furthermore, it can reduce the reduction temperature, shorten the preparation time, and is beneficial to reducing the production cost. At the same time, it can avoid the mixing of impurity elements and simplify the preparation process. Through the roasting and reduction processes in a hydrogen atmosphere, the nucleation and growth processes of the tungsten-nickel-iron composite powder are regulated to obtain a nano tungsten-nickel-iron composite powder with uniform particle size distribution and high dispersion.

[0027] 2. The present invention uses ammonium metatungstate, nickel chloride hexahydrate, and iron chloride hexahydrate powders that are easily soluble in water as raw materials. After stirring, the solutes can be evenly dispersed, avoiding composition segregation and improving the mixing uniformity of the subsequent precursor composite powder.

[0028] 3. In the preparation method of the present invention, by using the freeze-drying process, it is possible to avoid the capillary force problem caused by the gas-liquid interface in the spray-drying process in the prior art. The freeze-drying process can completely eliminate the liquid phase stage, fundamentally avoiding the formation of particle skeleton collapse and dense agglomeration.

[0029] 4. The nano tungsten-nickel-iron composite powder of the present invention is suitable for sintering to prepare fine-grained / ultrafine-grained tungsten-nickel-iron alloys, has a wide application range, and can effectively improve the density and mechanical properties of the tungsten-nickel-iron alloy.

[0030] Next, through the drawings and embodiments, the technical solutions of the present invention will be further described in detail. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the SEM diagram of the nano tungsten-nickel-iron composite powder prepared in Example 1 of the present invention.

[0032] Figure 2XRD pattern of the nano tungsten-nickel-iron composite powder prepared in Example 1 of the present invention. Detailed implementation mode

[0033] Example 1

[0034] The preparation method of this example includes the following steps:

[0035] Step 1: Dissolve ammonium metatungstate, nickel chloride hexahydrate and ferric chloride hexahydrate in deionized water and then carry out magnetic stirring at a speed of 700 rpm for 2 h to obtain a solution; the average particle sizes of ammonium metatungstate, nickel chloride hexahydrate and ferric chloride hexahydrate are all 10 μm, and the mass purities are all not less than 99%; the mass ratio of tungsten element in ammonium metatungstate, nickel element in nickel chloride hexahydrate and iron element in ferric chloride hexahydrate is 90:7:3;

[0036] Step 2: Atomize and spray the solution obtained in Step 1 into liquid nitrogen at -190 °C for pre-freezing to obtain frozen particles;

[0037] Step 3: Place the frozen particles obtained in Step 2 in a freeze dryer, and carry out drying at -80 °C for 72 h in an environment with a vacuum degree of 20 Pa to obtain a precursor composite powder; the thickness of the frozen particles laid in the freeze dryer is 10 mm;

[0038] Step 4: Place the precursor composite powder obtained in Step 3 in a tubular furnace, calcine at 500 °C for 2 h in an argon atmosphere to obtain a composite oxide powder, and then raise the temperature to 700 °C and reduce it in a hydrogen atmosphere for 1 h to obtain a nano tungsten-nickel-iron composite powder; the mass purity of the hydrogen is greater than 99.99%.

[0039] Perform microscopic analysis on the nano tungsten-nickel-iron composite powder prepared in this example, as Figure 1 shown, the nano tungsten-nickel-iron composite powder has uniform particle size and good dispersibility, and the average particle diameter is 30 nm; perform XRD analysis on the nano tungsten-nickel-iron composite powder, and the results are as Figure 2 shown, the nano tungsten-nickel-iron composite powder is composed of W and γ-(Ni,Fe,W) phases, indicating that the composition of the nano tungsten-nickel-iron composite powder prepared in this example meets the requirements of tungsten-nickel-iron powder.

[0040] Example 2

[0041] The preparation method of this example includes the following steps:

[0042] Step 1: Dissolve ammonium metatungstate, nickel chloride hexahydrate and ferric chloride hexahydrate in deionized water and then perform magnetic stirring at a speed of 500 rpm for 1 h to obtain a solution; the mass purities of ammonium metatungstate, nickel chloride hexahydrate and ferric chloride hexahydrate are all not less than 99%, the average particle size of ammonium metatungstate is 20 μm, and the average particle sizes of nickel chloride hexahydrate and ferric chloride hexahydrate are both 15 μm; the mass ratio of tungsten element in ammonium metatungstate, nickel element in nickel chloride hexahydrate and iron element in ferric chloride hexahydrate is 90:7:3;

[0043] Step 2: Atomize and spray the solution obtained in Step 1 into liquid nitrogen at -180 °C for pre-freezing to obtain frozen particles;

[0044] Step 3: Place the frozen particles obtained in Step 2 in a freeze dryer and dry the frozen particles at -50 °C for 12 h in an environment with a vacuum degree of 1 Pa to obtain a precursor composite powder; the thickness of the frozen particles laid in the freeze dryer is 20 mm;

[0045] Step 4: Place the precursor composite powder obtained in Step 3 in a tube furnace, calcine it at 300 °C for 1 h in an argon atmosphere to obtain a composite oxide powder, and then heat it up to 800 °C and reduce it in a hydrogen atmosphere for 2 h to obtain a nano tungsten-nickel-iron composite powder; the mass purity of the hydrogen is greater than 99.99%.

[0046] After detection, the average particle size of the nano tungsten-nickel-iron composite powder prepared in this example is 50 nm.

[0047] Example 3

[0048] The preparation method of this example includes the following steps:

[0049] Step 1: Dissolve ammonium metatungstate, nickel chloride hexahydrate and ferric chloride hexahydrate in distilled water and then perform magnetic stirring at a speed of 600 rpm for 1 h to obtain a solution; the mass purities of ammonium metatungstate, nickel chloride hexahydrate and ferric chloride hexahydrate are all not less than 99%, the average particle size of ammonium metatungstate is 15 μm, and the average particle sizes of nickel chloride hexahydrate and ferric chloride hexahydrate are both 10 μm; the mass ratio of tungsten element in ammonium metatungstate, nickel element in nickel chloride hexahydrate and iron element in ferric chloride hexahydrate is 90:7:3;

[0050] Step 2: Atomize and spray the solution obtained in Step 1 into liquid nitrogen at -180 °C for pre-freezing to obtain frozen particles;

[0051] Step 3: Place the frozen particles obtained in Step 2 into a freeze dryer. Under an environment with a vacuum degree of 10 Pa, dry the frozen particles at -60°C for 24 h to obtain a precursor composite powder; the thickness of the frozen particles laid in the freeze dryer is 15 mm;

[0052] Step 4: Place the precursor composite powder obtained in Step 3 into a tubular furnace, calcine it at 400°C for 2 h under an argon atmosphere to obtain a composite oxide powder, and then raise the temperature to 700°C and reduce it for 1 h under a hydrogen atmosphere to obtain a nano tungsten-nickel-iron composite powder; the mass purity of the hydrogen is greater than 99.99%.

[0053] After testing, the average particle size of the nano tungsten-nickel-iron composite powder prepared in this example is 40 nm.

[0054] Example 4

[0055] The preparation method of this example includes the following steps:

[0056] Step 1: Dissolve ammonium metatungstate, nickel chloride hexahydrate and iron chloride hexahydrate in deionized water, and then perform magnetic stirring at a rotation speed of 600 rpm for 2 h to obtain a solution; the mass purities of ammonium metatungstate, nickel chloride hexahydrate and iron chloride hexahydrate are all not less than 99%, the average particle size of ammonium metatungstate is 20 μm, the average particle size of nickel chloride hexahydrate is 15 μm, and the average particle size of iron chloride hexahydrate is 10 μm; the mass ratio of tungsten element in ammonium metatungstate, nickel element in nickel chloride hexahydrate and iron element in iron chloride hexahydrate is 90:7:3;

[0057] Step 2: Atomize and spray the solution obtained in Step 1 into liquid nitrogen at -180°C for pre-freezing to obtain frozen particles;

[0058] Step 3: Place the frozen particles obtained in Step 2 into a freeze dryer. Under an environment with a vacuum degree of 15 Pa, dry the frozen particles at -60°C for 48 h to obtain a precursor composite powder; the thickness of the frozen particles laid in the freeze dryer is 20 mm;

[0059] Step 4: Place the precursor composite powder obtained in Step 3 into a tubular furnace, calcine it at 450°C for 2 h under an argon atmosphere to obtain a composite oxide powder, and then raise the temperature to 800°C and reduce it for 2 h under a hydrogen atmosphere to obtain a nano tungsten-nickel-iron composite powder; the mass purity of the hydrogen is greater than 99.99%.

[0060] After testing, the average particle size of the nano tungsten-nickel-iron composite powder prepared in this example is 45 nm.

[0061] Example 5

[0062] The difference between this embodiment and Embodiment 1 lies in that: the mass ratio of tungsten element in ammonium metatungstate, nickel element in nickel chloride hexahydrate, and iron element in iron chloride hexahydrate described in Step 1 is 93:4.9:2.1.

[0063] After testing, the average particle size of the nano tungsten-nickel-iron composite powder prepared in this embodiment is 45 nm.

[0064] Embodiment 6

[0065] The difference between this embodiment and Embodiment 5 lies in that: the temperature of pre-freezing described in Step 2 is -185 °C; the temperature of low-temperature reduction of pre-freezing described in Step 3 is 750 °C.

[0066] After testing, the average particle size of the nano tungsten-nickel-iron composite powder prepared in this embodiment is 45 nm.

[0067] The above are only the preferred embodiments of the present invention, and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent structural transformations made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A preparation method of nano tungsten-nickel-iron composite powder, characterized in that, The preparation method comprises the following steps: Step 1: Dissolve ammonium metatungstate, nickel chloride hexahydrate, and iron chloride hexahydrate in water and stir to obtain a solution; Step 2: Atomize and spray the solution obtained in Step 1 into liquid nitrogen for pre-freezing to obtain frozen particles; Step 3: Freeze-dry the frozen particles obtained in Step 2 to obtain a precursor composite powder; Step 4: Calcinate and then reduce the precursor composite powder obtained in Step 3 under a hydrogen atmosphere to obtain a nano tungsten-nickel-iron composite powder.

2. The preparation method of a nano tungsten-nickel-iron composite powder according to claim 1, characterized in that, In Step 1, the mass ratio of tungsten element in ammonium metatungstate, nickel element in nickel chloride hexahydrate, and iron element in iron chloride hexahydrate is 90:7:3 or 93:4.9:2.

1.

3. The preparation method of a nano tungsten-nickel-iron composite powder according to claim 1, characterized in that, In Step 2, the temperature of the pre-freezing is -190°C to -180°C.

4. The preparation method of a nano tungsten-nickel-iron composite powder according to claim 1, characterized in that, In Step 3, the method of freeze-drying is as follows: Under an environment with a vacuum degree of 1 Pa to 20 Pa, use a freeze-dryer to dry the frozen particles at a temperature of -80°C to -50°C for 12 h to 72 h.

5. The preparation method of a nano tungsten-nickel-iron composite powder according to claim 4, characterized in that, The thickness of the laid frozen particles in the freeze-dryer is 10 mm to 20 mm.

6. The preparation method of a nano tungsten-nickel-iron composite powder according to claim 1, wherein, In Step 4, the temperature of the calcination is 300°C to 500°C, and the duration of the calcination is 1 h to 2 h.

7. The preparation method of a nano tungsten-nickel-iron composite powder according to claim 1, characterized in that, In Step 4, the temperature of the reduction under a hydrogen atmosphere is 700°C to 800°C, and the time of the reduction under a hydrogen atmosphere is 1 h to 2 h.

8. The preparation method of a nano tungsten-nickel-iron composite powder according to claim 1, characterized in that, In Step 4, the average particle size of the nano tungsten-nickel-iron composite powder is 30 nm to 50 nm.

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