CN115229189A - A kind of preparation method of uniform porous tungsten product - Google Patents

Abstract

A preparation method of a uniform porous tungsten product belongs to the field of preparation of porous metal materials. The problems of the porous tungsten product prepared by the existing method, such as coarse grains, densification of the sintered body, low porosity, uneven pore structure and poor mechanical properties, are solved. In the invention, tungsten powder is used as tungsten source, metal nitrate is used as oxidant and pore-forming agent, and a large amount of gas is generated by low-temperature combustion synthesis to form metal-loaded porous tungsten composite precursor. Finally, the corrosion characteristics of the metal are used to remove the metal particles, and a large number of pores are formed in the tungsten matrix to increase the porosity. The invention has the advantages of simple process, good repeatability, low cost, low energy consumption, short cycle and the like, and can prepare crystal grains whose size can be controlled within a range of less than 1 μm, a pore size can be controlled within a range of 0.1-2 μm, and a porosity of 15 μm. ～45%, the porous tungsten products that meet various usage requirements have broad application prospects.

Description

A kind of preparation method of uniform porous tungsten product

technical field

The invention belongs to the technical field of porous metal material preparation, and in particular relates to a preparation method of a uniform porous tungsten product.

Background technique

Due to its high melting point (3420°C), low density, low thermal expansion coefficient and high strength, porous tungsten is widely used in aerospace, national defense engineering, construction engineering, power electronics and metallurgical industries, and can be used as a reserve type It can be used as the base material of diffused tungsten hot cathode, or as the skeleton of W-Cu composite material prepared by infiltration method, and can also be used as high-temperature fluid filter material, etc. In various applications of porous tungsten, its pore size and porosity play a vital role in its own performance and the performance of its components. Powder metallurgy (PM) is a process in which metal powder (or a mixture of metal powder and non-metal powder) is used as raw material to prepare porous metal materials, composite materials and various types of products through molding and sintering. It has been widely used in the synthesis of porous materials. Tungsten products. However, the sintering temperature of this method is above 1600°C, which will inevitably lead to coarse grains, densification of the sintered body, weakening of mechanical properties, and reduction of porosity. In addition, expensive pressurization equipment and molds are required when preparing large-sized workpieces.

The low-temperature combustion synthesis method has the advantages of self-sustaining reaction, low energy consumption, mixing of reactants at the molecular level, fast speed, simple process and equipment, low economic cost, industrial scale production, high product purity, small size and easy control of structure and morphology, etc. Advantages, it has been widely used in the preparation of porous materials. However, there are few reports on the preparation of porous tungsten materials directly by combustion synthesis, and they mainly stay in the preparation stage of porous tungsten powder. Due to the limitation of processing technology, there has been no report on the synthesis of porous tungsten products with complex shapes in situ by combustion synthesis.

Contents of the invention

Aiming at the difficulties faced by the current powder metallurgy method for preparing porous tungsten products, the present invention proposes a solution technology for preparing uniform porous tungsten products by combining low-temperature combustion synthesis method with SPS low-temperature sintering and pickling treatment.

A preparation method of a uniform porous tungsten product, comprising the following specific steps:

(1) Mix tungsten powder, fuel, nitrate and deionized water according to a certain ratio, and stir with a magnetic stirrer while heating in a water bath to form a homogeneous aqueous solution, and then put it on an electric heating plate and heat it at a certain temperature to Form a sol, continue to heat for a period of time until the volume of the sol expands, and a large amount of smoke is generated, and a low-temperature combustion synthesis reaction occurs. After the reaction, the precursor powder is obtained;

(2) Place the precursor powder prepared in step (1) in a spark plasma sintering furnace for SPS low-temperature sintering reaction molding;

(3) The product prepared in step (2) is placed in an acidic solution and pickled and dissolved under heating conditions. Then, the sample is cleaned with deionized water and ethanol and dried completely to obtain a porous material with uniform pores and high porosity. Tungsten products.

Further, the molar ratio of tungsten powder, glycine and nitrate in step (1) is (4.5-7): (1.5-3): (1-2).

Further, the particle size of the tungsten powder in step (1) is 50-200 nm, and the purity is 99.9%.

Further, the nitrate in step (1) is at least one of calcium nitrate, copper nitrate, zinc nitrate, manganese nitrate, nickel nitrate, and chromium nitrate.

Further, the water bath heating and magnetic stirring treatment conditions in step (1) are: the water bath temperature is 60-90° C., and the stirring time is 20-40 min.

Further, the heating condition of the combustion synthesis in step (1) is 250-400°C.

Further, the SPS low-temperature sintering conditions in step (2) are as follows: the temperature is 800-1200°C, the time is 2-5min, the heating rate is 50-120°C/min, the pressure is 10-40MPa, and the sintering vacuum is 1×10 ^-4 ~ 1×10 ^-2 Pa.

Further, the heating condition in step (3) is 80-120° C. for 1-4 hours.

Further, the acidic solution described in step (3) is at least one of sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid, with a concentration of 5-15 wt%.

Further, the grain size of the porous tungsten product produced in step (3) is less than 1 μm, the porosity is 15-45%, and the pore size is 0.1-2 μm.

The invention combines the characteristics of low-temperature combustion synthesis and porous materials, and combines the combustion synthesis product with the preparation method of the porous material to successfully prepare porous tungsten products with high porosity, uniform pores, small pore diameter and high strength, which has certain practical significance and innovation. significance. Porous tungsten products with porosity and pore size that meet the requirements of use can be obtained by reasonably customizing process parameters such as low-temperature combustion synthesis, spark plasma (SPS) low-temperature sintering and pickling. It can be adjusted in the range of 0.1-2 μm, the porosity is increased by more than 20%, and the performance of the porous tungsten material prepared by powder metallurgy can be significantly optimized.

Technology of the present invention has following advantage:

(1) The low-temperature combustion synthesis method of the present invention utilizes the advantages of simple solution raw materials and easy to achieve uniform mixing to prepare molecular-level mixed precursors, which overcomes the problem of uneven mixing of raw materials in traditional powder metallurgy methods.

(2) The preparation method of a kind of uniform porous tungsten product provided by the present invention, with tungsten powder as tungsten source, nitrate as pore-forming agent and dispersant, utilize the self-exothermic combustion reaction of combustion reaction to carry out combustion synthesis, prepare porous tungsten/ Other metal oxide precursors. The burning time is only 2 to 3 minutes and other metal oxides in the precursor can effectively reduce the reaction thermodynamic temperature in the subsequent sintering process, and there is no need to use a sintering furnace for high temperature and long-term heat preservation sintering in the prior art, so the process is simple and repeatable. It has the advantages of good performance, low cost, low energy consumption, and short cycle time, and overcomes the shortcomings of traditional methods such as long cycle time and low production efficiency for preparing porous tungsten.

(3) The present invention can freely change the size and quantity of pore-forming metal oxide particles by controlling the type and proportion of nitrate, combustion synthesis and sintering conditions, thereby precisely controlling the pore size, distribution and porosity, and overcoming the traditional method to prepare porous The disadvantage that the tungsten hole structure is difficult to control.

(4) The metal oxide particles that act as pore-forming agents in the early stage combustion synthesis and SPS low-temperature sintering process of the present invention always exist, the heat treatment deformation is small, and the size of the metal oxide particles increases with the increase of temperature, which can effectively avoid the preparation of traditional porous tungsten In the method, the excessive shrinkage of the tungsten matrix and the reduction of the porosity caused by the too high sintering temperature can improve the performance and service life of the porous tungsten product.

(5) The porous tungsten product prepared by the present invention has regular shape, good surface quality, uniform and connected pores, low impurity content, grain size of 200-900 nm, pore diameter of 0.1-2 μm, and porosity of 15-45%. The preparation process is simple and easy to operate, and the cost is low, which is suitable for industrialized mass production, and has a very broad application prospect.

Detailed ways

Example 1

Weigh 3.27g of glycine, 4.83g of copper nitrate and 1.79g of manganese nitrate, put them in a 500ml beaker, add an appropriate amount of deionized water and stir evenly with a glass rod to prepare a solution. Then add 22.08g of tungsten powder with a particle size of 50nm to the beaker, place it on a magnetic stirrer and stir for 30min under the condition of heating in a water bath at 80°C to form a homogeneous aqueous solution. Then, put the beaker on the electric heating plate and heat it at 300°C to form a sol, and continue heating for a period of time until the volume of the sol expands, accompanied by the generation of a large amount of smoke, and a low-temperature combustion synthesis reaction occurs to obtain the precursor powder. The precursor was placed in a spark plasma sintering furnace for SPS sintering reaction in an environment with a vacuum degree of 1×10 ^-2 Pa. The heating rate was 80°C/min, the pressure was 30MPa, the reaction temperature was 1000°C, and the time was 3min. Furnace cools. Finally, the sample was placed in 8wt% sulfuric acid solution, pickled and dissolved under heating at 80°C for 4 hours, and then washed with deionized water and ethanol and dried completely to obtain a grain size of 420nm, a porosity of 38%, and a pore size of Porous tungsten products with a size of 0.37 μm.

Example 2

Weigh 4.35g of glycine, 3.28g of calcium nitrate and 4.76g of chromium nitrate, place them in a 500ml beaker, add appropriate amount of deionized water and stir evenly with a glass rod to prepare a solution. Add 25.76g of tungsten powder with a particle size of 100nm to the beaker, place it on a magnetic stirrer and stir for 40min under the condition of heating in a water bath at 60°C to form a homogeneous aqueous solution. Then, put the beaker on the electric heating plate and heat it at 350°C to form a sol, and continue heating for a period of time until the volume of the sol expands, accompanied by the generation of a large amount of smoke, and a low-temperature combustion synthesis reaction occurs to obtain the precursor powder. The precursor was placed in a spark plasma sintering furnace for SPS sintering reaction in an environment with a vacuum degree of 5×10 ^-3 Pa. The heating rate was 100°C/min, the pressure was 20MPa, the reaction temperature was 1200°C, and the time was 2min. Furnace cools. Finally, the sample was placed in 10wt% hydrochloric acid solution, pickled and dissolved under the condition of heating at 100°C for 2 hours, and the sample was washed with deionized water and ethanol and dried completely to obtain a grain size of 977nm, a porosity of 16%, and a pore size of A porous tungsten product with a size of 1.22 μm.

Example 3

Weigh 7.53g of glycine and 17.84g of zinc nitrate, place them in a 1000ml beaker, add an appropriate amount of deionized water and stir evenly with a glass rod to prepare a solution. Then add 46.37g of tungsten powder with a particle size of 150nm to the beaker, place it on a magnetic stirrer and stir for 30min under the condition of heating in a water bath at 70°C to form a homogeneous aqueous solution. Then, put the beaker on the electric heating plate and heat it at 250°C to form a sol, and continue heating for a period of time until the volume of the sol expands, accompanied by the generation of a large amount of smoke, and a low-temperature combustion synthesis reaction occurs to obtain the precursor powder. The precursor was placed in a spark plasma sintering furnace for SPS sintering reaction in an environment with a vacuum degree of 8×10 ^{- 3} Pa. The heating rate was 90°C/min, the pressure was 40MPa, the reaction temperature was 1100°C, and the time was 4min. Furnace cools. Finally, the sample was placed in a 15wt% sulfuric acid solution, pickled and dissolved under heating at 90°C for 3 hours, washed with deionized water and ethanol, and dried completely to obtain a grain size of 610nm, a porosity of 26%, and a pore size of Porous tungsten products with a size of 0.51 μm.

Example 4

Weigh 6.90g of glycine and 12.79g of nickel nitrate, place them in a 1000ml beaker, add an appropriate amount of deionized water and stir evenly with a glass rod to prepare a solution. Then add 38.64g of tungsten powder with a particle size of 80nm to the beaker, place it on a magnetic stirrer and stir for 20min under the condition of heating in a water bath at 90°C to form a homogeneous aqueous solution. Then, put the beaker on the electric heating plate and heat it at 400°C to form a sol, and continue heating for a period of time until the volume of the sol expands, accompanied by the generation of a large amount of smoke, and a low-temperature combustion synthesis reaction occurs to obtain the precursor powder. The precursor was placed in a spark plasma sintering furnace for SPS sintering reaction in an environment with a vacuum degree of 1×10 ^{- 4} Pa. The heating rate was 120°C/min, the pressure was 10MPa, the reaction temperature was 800°C, and the time was 5min. Furnace cools. Finally, the sample was placed in 12wt% sulfuric acid solution, pickled and dissolved under the condition of heating at 120°C for 1 hour, and the sample was washed with deionized water and ethanol and dried completely to obtain a grain size of 230nm, a porosity of 43%, and a pore size of Porous tungsten products with a size of 0.14 μm.

Claims (10)

1. The preparation method of the uniform porous tungsten product is characterized by comprising the following preparation steps:

(1) Mixing tungsten powder, fuel, nitrate and deionized water according to a certain proportion, heating with a magnetic stirrer in a water bath and stirring to form a homogeneous aqueous solution, then placing the homogeneous aqueous solution on an electric heating plate, heating at a certain temperature to form sol, continuously heating for a period of time until the volume of the sol expands, generating low-temperature combustion synthesis reaction along with generation of a large amount of dense smoke, and obtaining precursor powder after the reaction is finished;

(2) Placing the precursor powder prepared in the step (1) in a spark plasma sintering furnace to perform SPS low-temperature sintering reaction and forming;

(3) And (3) placing the product prepared in the step (2) in an acid solution, carrying out acid washing dissolution under a heating condition, then washing the sample with deionized water and ethanol, and completely drying to obtain the porous tungsten product with uniform pores and high porosity.

2. The method for preparing a uniform porous tungsten product according to claim 1, wherein the molar ratio of the tungsten powder to the glycine to the nitrate in the step (1) is (4.5-7): (1.5-3): (1-2).

3. The method for preparing a uniform porous tungsten product according to claim 1 or 2, wherein the tungsten powder has a particle size of 50 to 200nm and a purity of 99.9%.

4. The method of claim 1 or 2, wherein the nitrate is at least one of calcium nitrate, copper nitrate, zinc nitrate, manganese nitrate, nickel nitrate, and chromium nitrate.

5. The method for preparing a uniform porous tungsten article according to claim 1, wherein the conditions of the water bath heating and magnetic stirring treatment in step (1) are as follows: the water bath temperature is 60-90 ℃, and the stirring time is 20-40 min.

6. The method for preparing a uniform porous tungsten product according to claim 1, wherein the combustion synthesis heating condition in step (1) is 250-400 ℃.

7. The method of claim 1, wherein the SPS low temperature sintering conditions in step (2) are: the temperature is 800-1200 ℃, the time is 2-5 min, the heating rate is 50-120 ℃/min, the pressure is 10-40 MPa, the sintering vacuum degree is 1 multiplied by 10 ^-4 ～1×10 ^-2 Pa。

8. The method for preparing a uniform porous tungsten product according to claim 1, wherein the heating condition in step (3) is 80-120 ℃ for 1-4 hours.

9. The method according to claim 1, wherein the acidic solution in step (3) is at least one of sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid, and has a concentration of 5-15 wt%.

10. The method of claim 1, wherein the porous tungsten article obtained in step (3) has a grain size of less than 1 μm, a porosity of 15 to 45%, and a pore size of 0.1 to 2 μm.