CN109019604B - Nano lamellar polycrystalline tungsten carbide powder and preparation method thereof - Google Patents
Nano lamellar polycrystalline tungsten carbide powder and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of tungsten carbide design, and particularly provides a nano lamellar sheet-shaped polycrystalline tungsten carbide powder and a preparation method thereof. The nano-layered polycrystalline tungsten carbide powder is formed by mutually stacking and/or penetrating and/or inlaying tungsten carbide nano-sheets. The preparation method comprises the following steps of; and uniformly mixing the soluble tungsten source, the nano carbon black and the molten salt a according to a set proportion, adding the mixture into the molten salt b, reacting, dissolving out the molten salt, and cleaning to obtain the product. The nano tungsten carbide prepared by the method is of a lamellar polycrystalline structure and has the advantages of uniform granularity, thin thickness, high specific surface area, strong chemical activity and sintering activity and the like; the preparation process has simple process, short period and low cost, and can realize continuous large-scale production.
Description
Technical Field
The invention belongs to the technical field of tungsten carbide design, and particularly provides a nano lamellar sheet-shaped polycrystalline tungsten carbide powder and a preparation method thereof.
Background
Tungsten carbide (WC), which is a major component of cemented carbides due to its high melting point, high hardness, high wear resistance, and excellent thermal stability, is also the most used hard compound in the cemented carbide industry; meanwhile, the nano WC also has the platinum-like catalytic activity, higher electric and thermal conductivity and stronger acid and alkali corrosion resistance, and has wide application prospect in the field of catalysis.
Conventional WC-based cemented carbides are brittle materials, the main phase WC provides high hardness and wear resistance, the plastic binder phase provides the necessary toughness, and there is an inherent contradiction between hardness and strength that is long-term. With the rapid development of industries such as cutting and machining, the performance of the traditional WC-based hard alloy is difficult to meet the requirements. The three-dimensional space of WC crystal grains in the hard alloy is generally triangular prism-shaped, and because WC belongs to an anisotropic hexagonal system, the mechanical properties of the crystal grains on different crystal planes and crystal directions are greatly different, and the hardness of the WC crystal (0001) basal plane is approximately 2 times of the hardness of the (1-100) prism plane. Therefore, when the (0001) basal plane with higher WC grain ductility hardness preferentially grows in the hard alloy, the trigonal prism-shaped WC grains are promoted to be converted into the dish-shaped WC grains, and the overall hardness of the alloy is obviously improved. Research shows that the lamellar crystal strengthening is a better way for alleviating the contradiction between hardness and strength and effectively combining the hardness and the strength, and the lamellar crystal WC-based hard alloy has high hardness, high toughness, high wear resistance, excellent plastic deformation resistance and better high-temperature creep resistance and thermal shock resistance, thereby showing good market prospect in the processing fields of turning, drilling, milling and the like, and the aspects of being used as a die, a coating hard alloy matrix and the like.
The nano WC has Pt-like catalytic performance and shows stronger resistance to CO and H in the catalytic action process2S poisoning ability, and is expected to be a catalytic material for replacing Pt group noble metals; meanwhile, the nanometer WC also has higher electric and thermal conductivity and excellent acid and alkali corrosion resistance, and can be used as an electrode in the fields of electrochemical catalysis, fuel cells and the like. At present, nano WC shows certain catalytic activity in the aspects of methanol electrochemical oxidation, hydrogen anodic oxidation, aromatic nitro compound electro-reduction and the like, but the catalytic activity of WC particles is far lower than that of noble metal catalysts such as Pt and the like because WC particles are easy to agglomerate and grow up and have small specific surface area. Therefore, it is the key to the practical application of WC materials to improve their own catalytic activity. The structure of the catalyst has obvious influence on the catalytic performance of the catalyst, and the modification and regulation of the structural morphology of the nano WC are important ways for increasing the catalytic activity of the nano WC. Researches show that the two-dimensional structure of the nano lamellar crystal has higher specific surface area than the particle crystal, can provide a large number of surface atoms and more reactive active centers, and is an ideal catalyst structure. The ultrathin multilayer geometrical characteristics of the nano lamellar crystals are beneficial to quickly transmitting load from the inside to the surface in the catalytic reaction process, so that the reaction process is accelerated.
The precondition and the key point are that the lamellar nanometer WC with excellent performance is prepared no matter the flaky crystal WC-based hard alloy is manufactured or the catalytic activity of the nanometer WC is improved. At present, the industrial preparation method of WC is that high-purity tungsten powder and a proper amount of carbon black are uniformly mixed, then the mixture is put into a graphite carbon tube furnace or a molybdenum wire furnace to be carbonized for 2 to 10 hours at 1200 to 2200 ℃ in hydrogen atmosphere, and then the product is obtained after ball milling and sieving. The WC powder prepared by the process is usually granular, the structural morphology is difficult to control, and the WC crystal grains grow seriously due to high carbonization temperature and long period. The preparation methods of nano WC powder reported at home and abroad include a spray conversion method, a plasma method, a carbothermic reduction carbonization method, a high-energy ball milling method, a mechanical-chemical synthesis method and the like, but the preparation techniques usually need special tool equipment, and have the problems of complex process flow, high production cost, low efficiency, easy introduction of impurities and the like, so that the industrial application is difficult to realize.
Disclosure of Invention
The invention aims to provide a nano lamellar polycrystalline tungsten carbide powder and a preparation method thereof, aiming at the defects of the existing nano tungsten carbide.
The invention relates to a nano lamellar polycrystalline tungsten carbide powder; the nano-layered polycrystalline tungsten carbide powder is formed by mutually stacking and/or penetrating and/or inlaying tungsten carbide nano-sheets.
The invention relates to a preparation method of nano lamellar polycrystalline tungsten carbide powder, which comprises the following steps:
step one
According to the molar ratio, tungsten: nano carbon black: adding a soluble tungsten source, nano carbon black and molten salt a into a solvent at a ratio of 10: 35-50: 0.2, uniformly mixing, and performing spray drying or evaporation drying at a temperature of more than 120 ℃ to obtain precursor powder; the molten salt a is selected from at least one of sodium chloride and potassium chloride, preferably sodium chloride;
step two
Placing the fused salt b in a reaction crucible, heating to a molten state by high-frequency induction, then pouring the precursor powder prepared in the step one into the reaction crucible, covering a layer of carbon powder on the surface of the fused salt, heating to a reaction temperature, carrying out heat preservation reaction, and cooling to obtain a reaction product; the reaction temperature is 750-1250 ℃, preferably 850-1250 ℃; the molten salt b is sodium chloride and/or potassium chloride;
step three
And D, dissolving the reaction product obtained in the step two by using water, pouring out supernatant, repeatedly washing the precipitate by using deionized water and absolute ethyl alcohol, and drying to obtain the nano lamellar polycrystalline tungsten carbide powder.
The invention adopts a solution chemical method to prepare uniformly mixed precursor powder, and then prepares lamellar nano tungsten carbide through low-temperature reaction in an induction heating molten salt medium.
The invention relates to a preparation method of nano lamellar polycrystalline tungsten carbide powder.
The invention relates to a preparation method of nano lamellar polycrystalline tungsten carbide powder. Preferably, the alcohol in the alcohol aqueous solution is 40% by volume.
In industrial application, the soluble tungsten source, the nano carbon black and the flux are uniformly mixed by mechanical stirring.
The invention relates to a preparation method of nano lamellar polycrystalline tungsten carbide powder, wherein in the first step, the granularity of nano carbon black is less than or equal to 200 nm.
In the second step, the fused salt b is prepared by mixing sodium chloride and potassium chloride according to the molar ratio; potassium chloride 1: 4-4: 1.
Preferably, in the preparation method of the nano lamellar polycrystalline tungsten carbide powder, the mass of the molten salt b is 0.7-1.3 times of that of the precursor powder.
Preferably, in the method for producing a nanoplatelet-shaped polycrystalline tungsten carbide powder according to the present invention, the mass of the molten salt b is 100 times or more the mass of the molten salt a. Preferably 200 times or more, and more preferably 220 times and 350 times.
Preferably, in the method for preparing the nano lamellar polycrystalline tungsten carbide powder, the carbonaceous powder in the second step is graphite powder.
In a preferable scheme, in the second step of the preparation method of the nano lamellar polycrystalline tungsten carbide powder, the heat preservation reaction time is 10-40 min.
In the second step, after reaction and heat preservation, the nano lamellar polycrystalline tungsten carbide powder is naturally cooled.
Preferably, the preparation method of the nano lamellar polycrystalline tungsten carbide powder comprises the third step of dissolving the reaction product obtained in the second step with deionized water, pouring out supernatant, taking precipitate, alternately cleaning with deionized water and absolute ethyl alcohol for 3 times, and drying to obtain the nano lamellar polycrystalline tungsten carbide powder.
The invention relates to a preparation method of nano lamellar polycrystalline tungsten carbide powder, wherein the total thickness of the obtained nano lamellar polycrystalline tungsten carbide powder is less than or equal to 500nm, and the number of layers is 2-35; the monolayer thickness is less than or equal to 80 nm.
Compared with the prior art, the invention has the advantages that:
1. compared with the prior superfine/nano tungsten carbide preparation technology, the method combines a solution chemical method and a molten salt medium reaction method, quickly reacts at a lower temperature to prepare lamellar nano tungsten carbide, and can effectively avoid the rapid growth and abnormal growth of tungsten carbide particles caused by high-temperature long-time carbonization.
2. The nano tungsten carbide prepared by the method is of a lamellar polycrystalline structure and has the advantages of uniform granularity, thin thickness, high specific surface area, strong chemical activity and sintering activity and the like.
3. The morphology and the particle size of the tungsten carbide are controllable: the thickness, the grain diameter and the layer number of the polycrystalline tungsten carbide can be effectively controlled by adjusting the carbon-mixing ratio of the precursor, the reaction temperature and the heat preservation time.
4. High-frequency induction heating is used as a reaction heat source, the heating speed is high, and the preparation period is short.
5. The raw materials such as ammonium metatungstate and sodium chloride are common industrial raw materials, the preparation process has no special equipment and tool requirements, inert gas protection is not needed, the cost is low, the process is simple, and continuous large-scale production can be rapidly realized.
Drawings
FIG. 1 is an X-ray diffraction pattern of a nano-layered flaky polycrystalline tungsten carbide powder prepared in example 1.
FIG. 2 is an SEM photograph of the nano-layered flaky polycrystalline tungsten carbide powder prepared in example 1.
Detailed Description
The invention will be further illustrated by the following examples, without limiting the scope of the invention thereto.
Example 1:
according to the weight ratio of tungsten: nano carbon black: sodium chloride 10: 45: 0.2, weighing 500g of ammonium metatungstate, 108.9g of nano carbon black and 2.34g of sodium chloride, adding the materials into an aqueous solution containing 40% ethanol, mechanically stirring the materials to be uniformly mixed, and then carrying out spray drying at 135 ℃ to obtain precursor powder; according to the following steps of 1: weighing 250g of sodium chloride and 319g of potassium chloride according to the molar ratio of 1, uniformly mixing, placing in a graphite reaction crucible, performing high-frequency induction heating to a molten state, then pouring precursor powder into the reaction crucible, paving a layer of graphite powder on the surface of molten salt, continuing induction heating to 1180 ℃, performing heat preservation reaction for 25min, and then naturally cooling. Dissolving the cooled reaction product with deionized water, pouring out supernatant, taking precipitate, alternately cleaning with deionized water and absolute ethyl alcohol for 3 times, and drying to obtain the nano-lamellar polycrystalline tungsten carbide powder. The X-ray diffraction and Scanning Electron Microscope (SEM) results show that the tungsten carbide powder particles prepared by the process are triangular or hexagonal, have a lamellar polycrystalline structure, the side length is 0.6-2.5 mu m, the thickness is 200-500 nm, the single-layer thickness is 20-80 nm, and the number of layers is 5-20.
Example 2:
according to the weight ratio of tungsten: nano carbon black: sodium chloride 10: 35: weighing 250g of sodium tungstate, 31.8g of nano carbon black and 0.88g of sodium chloride according to a molar ratio of 0.2, adding the sodium tungstate, the nano carbon black and the sodium chloride into an aqueous solution containing 40% ethanol, mechanically stirring the mixture to uniformly mix the mixture, and drying the mixture at 140 ℃ to obtain precursor powder; according to the following steps of 4: weighing 200g of sodium chloride and 64g of potassium chloride according to the molar ratio of 1, uniformly mixing, placing in a graphite reaction crucible, performing high-frequency induction heating to a molten state, then pouring precursor powder into the reaction crucible, paving a layer of graphite powder on the surface of molten salt, continuing induction heating to 850 ℃, performing heat preservation reaction for 40min, and naturally cooling. And dissolving the cooled reaction product with deionized water, pouring out supernatant, taking precipitate, alternately cleaning with deionized water and absolute ethyl alcohol for 3 times, and drying to obtain the nano lamellar polycrystalline tungsten carbide powder with the side length of 2-4 mu m, the thickness of 100-400 nm, the single layer thickness of 40-80 nm and the number of layers of 3-5.
Example 3:
according to the weight ratio of tungsten: nano carbon black: sodium chloride 10: 50: weighing 500g of ammonium metatungstate, 121g of nano carbon black and 2.34g of sodium chloride according to the molar ratio of 0.2, adding the materials into an aqueous solution containing 40% ethanol, mechanically stirring the materials to uniformly mix the materials, and then carrying out spray drying at 130 ℃ to obtain precursor powder; according to the following steps: weighing 350g of sodium chloride and 223g of potassium chloride according to the molar ratio of 1, uniformly mixing, placing in a graphite reaction crucible, performing high-frequency induction heating to a molten state, then pouring precursor powder into the reaction crucible, paving a layer of graphite powder on the surface of molten salt, continuing induction heating to 1250 ℃, performing heat preservation reaction for 15min, and then naturally cooling. And dissolving the cooled reaction product with deionized water, pouring out supernatant, taking precipitate, alternately cleaning with deionized water and absolute ethyl alcohol for 3 times, and drying to obtain the nano lamellar polycrystalline tungsten carbide powder with the side length of 0.5-2 mu m, the thickness of 150-400 nm, the single layer thickness of 15-60 nm and the number of layers of 4-10.
Example 4:
according to the weight ratio of tungsten: nano carbon black: sodium chloride 10: 40: weighing 800g of tungstic acid, 154g of nano carbon black and 3.71g of sodium chloride according to the molar ratio of 0.2, adding the tungstic acid, the nano carbon black and the sodium chloride into an aqueous solution containing 40% ethanol, mechanically stirring the mixture to uniformly mix the mixture, and drying the mixture at 145 ℃ to obtain precursor powder; according to the following steps of 1: 2, weighing 196g of sodium chloride and 500g of potassium chloride, uniformly mixing, placing in a graphite reaction crucible, performing high-frequency induction heating to a molten state, then pouring precursor powder into the reaction crucible, paving a layer of graphite powder on the surface of molten salt, continuing induction heating to 1000 ℃, performing heat preservation reaction for 30min, and then naturally cooling. And dissolving the cooled reaction product with deionized water, pouring out supernatant, taking precipitate, alternately cleaning with deionized water and absolute ethyl alcohol for 3 times, and drying to obtain the nano lamellar polycrystalline tungsten carbide powder with the side length of 0.4-2.5 mu m, the thickness of 100-400 nm, the single layer thickness of 20-80 nm and the number of layers of 5-10.
Comparative example 1:
according to the weight ratio of tungsten: nano carbon black: sodium chloride 10:25: 0.2, weighing 500g of ammonium metatungstate, 60.5g of nano carbon black and 2.34g of sodium chloride, adding the materials into an aqueous solution containing 40% ethanol, mechanically stirring the materials to be uniformly mixed, and then carrying out spray drying at 135 ℃ to obtain precursor powder; according to the following steps of 1: weighing 250g of sodium chloride and 319g of potassium chloride according to the molar ratio of 1, uniformly mixing, placing in a graphite reaction crucible, performing high-frequency induction heating to a molten state, then pouring precursor powder into the reaction crucible, paving a layer of graphite powder on the surface of molten salt, continuing induction heating to 1180 ℃, performing heat preservation reaction for 25min, and then naturally cooling. Dissolving the cooled reaction product with deionized water, pouring out supernatant, taking precipitate, alternately cleaning with deionized water and absolute ethyl alcohol for 3 times, and drying. The product powder is detected as WO by X-ray diffraction2And W.
Comparative example 2:
according to the weight ratio of tungsten: nano carbon black: sodium chloride ═ 1: 45: 0.2, weighing 500g of ammonium metatungstate, 108.9g of nano carbon black and 2.34g of sodium chloride, adding the materials into an aqueous solution containing 40% ethanol, mechanically stirring the materials to be uniformly mixed, and then carrying out spray drying at 135 ℃ to obtain precursor powder; according to the following steps of 1: weighing 250g of sodium chloride and 319g of potassium chloride according to the molar ratio of 1, uniformly mixing, placing in a graphite reaction crucible, performing high-frequency induction heating to a molten state, then pouring precursor powder into the reaction crucible, paving a layer of graphite powder on the surface of molten salt, continuing induction heating to 700 ℃, performing heat preservation reaction for 80min, and then naturally cooling. Dissolving the cooled reaction product with deionized water, pouring out supernatant, taking precipitate, alternately cleaning with deionized water and anhydrous ethanol for 3 times, and detecting the dried product powder as W and W by X-ray diffraction2C, mixtures thereof. (As can be seen from comparative example 2 and examples; when the reaction temperature is too low, carbonization is incomplete even with a prolonged period of time, and pure phase WC is difficult to obtain.)
Comparative example 3:
according to the weight ratio of tungsten: nano carbon black: sodium chloride ═ 1: 45: 0.2, weighing 500g of ammonium metatungstate, 108.9g of nano carbon black and 2.34g of sodium chloride, adding the materials into an aqueous solution containing 40% ethanol, mechanically stirring the materials to be uniformly mixed, and then carrying out spray drying at 135 ℃ to obtain precursor powder; according to the following steps of 1: weighing 250g of sodium chloride and 319g of potassium chloride according to the molar ratio of 1, uniformly mixing, placing in a graphite reaction crucible, performing high-frequency induction heating to a molten state, then pouring precursor powder into the reaction crucible, paving a layer of graphite powder on the surface of molten salt, continuously performing induction heating to 1320 ℃, performing heat preservation reaction for 10min, and then naturally cooling. Dissolving the cooled reaction product with deionized water, pouring out supernatant, taking precipitate, alternately cleaning with deionized water and absolute ethyl alcohol for 3 times, and drying. The product powder is detected as pure WC phase by X-ray diffraction, but SEM result shows that the WC powder is coarse triangular prism-shaped single crystal particles with the average particle size of 3-5 mu m (from comparative example 3 and the example, when the reaction temperature is too high, lamellar polycrystalline WC can generate crystal grains which are combined and grow to form coarse single crystal WC.)
Comparative example 4:
according to the weight ratio of tungsten: nano carbon black: sodium chloride 10: 50: weighing 500g of sodium tungstate, 90.9g of graphite powder and 1.76g of sodium chloride according to a molar ratio of 0.2, adding the weighed materials into an aqueous solution containing 40% ethanol, mechanically stirring the materials to uniformly mix the materials, and then carrying out spray drying at 130 ℃ to obtain precursor powder; according to the following steps: weighing 350g of sodium chloride and 223g of potassium chloride according to the molar ratio of 1, uniformly mixing, placing in a graphite reaction crucible, performing high-frequency induction heating to a molten state, then pouring precursor powder into the reaction crucible, paving a layer of graphite powder on the surface of molten salt, continuing induction heating to 1250 ℃, performing heat preservation reaction for 90min, and then naturally cooling. Dissolving the cooled reaction product with deionized water, pouring out supernatant, taking precipitate, alternately cleaning with deionized water and absolute ethyl alcohol for 3 times, and drying. The product powder was detected by X-ray diffraction as W2C and a small amount of WC, the SEM results showed that the powder particles were irregularly granular, (it can be seen from comparative example 4 and examples that graphite as a carbon source had low reactivity and was not completely carbonized within the claimed temperature range, and that increasing the temperature resulted in grain coalescence of lamellar polycrystalline WC)
Comparative example 5:
according to the weight ratio of tungsten: nano carbon black: sodium chloride ═ 1: 50: weighing 500g of ammonium metatungstate according to the molar ratio of 0.2; 121g of ordinary carbon black having an average particle diameter of 0.8 μm and 2.34g of sodium chloride were added to a solution containing 40% of ethyleneMechanically stirring in an alcohol aqueous solution to uniformly mix, and then spray-drying at 130 ℃ to obtain precursor powder; according to the following steps: weighing 350g of sodium chloride and 223g of potassium chloride according to the molar ratio of 1, uniformly mixing, placing in a graphite reaction crucible, performing high-frequency induction heating to a molten state, then pouring precursor powder into the reaction crucible, paving a layer of graphite powder on the surface of molten salt, continuing induction heating to 1250 ℃, performing heat preservation reaction for 25min, and then naturally cooling. Dissolving the cooled reaction product with deionized water, pouring out supernatant, taking precipitate, alternately cleaning with deionized water and absolute ethyl alcohol for 3 times, and drying. The product powder is detected as WC and trace W by X-ray diffraction2C, SEM result shows that the powder particles have a triangular prism-shaped or flaky single crystal structure and the average particle size is 0.8-2.5 μm (from comparative example 5 and the example, it can be seen that the particle size of the carbon black also influences the structure and the particle size of WC.)
In the process of technical development, a scheme without adding the molten salt a in the first step is also tried, and the performance of the obtained product is far worse than that of the invention.
Claims (9)
1. A nano-sheet-like polycrystalline tungsten carbide powder is characterized in that; the nano lamellar polycrystalline tungsten carbide powder is formed by mutually stacking and/or penetrating and/or inlaying tungsten carbide nanosheets, and the preparation method of the powder comprises the following steps:
step one
According to the molar ratio, tungsten: nano carbon black: adding a soluble tungsten source, nano carbon black and the molten salt a into an alcohol-water solution at a ratio of 10: 35-50: 0.2, uniformly mixing, and performing spray drying or evaporation drying at a temperature of more than 120 ℃ to obtain precursor powder; the molten salt a is selected from sodium chloride or potassium chloride; in the first step, the particle size of the nano carbon black is less than or equal to 200 nm;
step two
Placing the fused salt b in a reaction crucible, heating to a molten state by high-frequency induction, then pouring the precursor powder prepared in the step one into the reaction crucible, covering a layer of carbon powder on the surface of the fused salt, heating to a reaction temperature, carrying out heat preservation reaction, and cooling to obtain a reaction product; the reaction temperature is 750-1250 ℃; the molten salt b is sodium chloride and potassium chloride;
step three
Dissolving the reaction product obtained in the second step with water, pouring out supernatant, repeatedly cleaning the precipitate with deionized water and absolute ethyl alcohol, and drying to obtain nano lamellar polycrystalline tungsten carbide powder;
the total thickness of the obtained nano lamellar polycrystalline tungsten carbide powder is less than or equal to 500nm, and the number of layers is 2-35; the monolayer thickness is less than or equal to 80 nm.
2. The nanoplatelet polycrystalline tungsten carbide powder of claim 1, wherein: in the first step, the soluble tungsten source is selected from at least one of ammonium metatungstate, sodium tungstate and tungstic acid.
3. The nanoplatelet polycrystalline tungsten carbide powder of claim 1, wherein: in the first step, the molten salt a is sodium chloride.
4. The nanoplatelet polycrystalline tungsten carbide powder of claim 1, wherein: in the second step, the molten salt b is prepared from sodium chloride and potassium chloride according to the molar ratio of sodium chloride: potassium chloride 1: 4-4: 1.
5. The nanoplatelet polycrystalline tungsten carbide powder of claim 1, wherein: the reaction temperature in the second step is 850-1250 ℃.
6. The nanoplatelet polycrystalline tungsten carbide powder of claim 1, wherein: the mass of the fused salt b is 0.7-1.3 times of that of the precursor powder.
7. The nanoplatelet polycrystalline tungsten carbide powder of claim 1, wherein: the mass of the molten salt b is 100 times or more of that of the molten salt a.
8. The nanoplatelet polycrystalline tungsten carbide powder of claim 1 wherein the mass of the molten salt b is 220 to 350 times the mass of the molten salt a.
9. The nanoplatelet polycrystalline tungsten carbide powder of claim 1, wherein: in the second step, the time of the heat preservation reaction is 10-40 min.
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| CN105948052A (en) * | 2016-06-03 | 2016-09-21 | 宁波检验检疫科学技术研究院 | Flaky nano tungsten carbide and preparation method and application thereof |
| CN107352543A (en) * | 2017-07-13 | 2017-11-17 | 东莞理工学院 | A kind of preparation method of molybdenum carbide micro-nano powder |
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