CN114906851A - Preparation method of nano tungsten carbide with high specific surface area - Google Patents
Preparation method of nano tungsten carbide with high specific surface area Download PDFInfo
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Abstract
The invention relates to a preparation method of nano tungsten carbide with high specific surface area. In order to further improve the BET specific surface area of the nano tungsten carbide, the invention provides a preparation method capable of further improving the specific surface area of the nano tungsten carbide powder. The invention takes nano tungsten powder as a raw material, and prepares the nano tungsten carbide powder with high specific surface area through the steps of carbon preparation, carbonization, airflow crushing and the like. According to the invention, a plurality of boats are stacked to replace a single boat, and the specific surface area of the nano tungsten carbide powder can be increased by 8-25% by combining a carbonization process. The invention is matched with a carbonization process, further reduces the bulk density of the powder and effectively improves the specific surface area of the tungsten carbide powder. The nano tungsten carbide with high specific surface area prepared by the method has very wide application market prospect in the field of nano ultra-fine structure hard alloy.
Description
Technical Field
The invention belongs to the field of powder metallurgy, and particularly relates to a preparation method of nano tungsten carbide with a high specific surface area.
Background
Cemented carbide is widely used as a material for various machining tools, called "industrial teeth" due to its high hardness and wear resistance, among which WC — Co type cemented carbide is the most productive and consumable cemented carbide material at present. After decades of development, in the engineering application of hard alloy, the hardness and the wear resistance can basically meet the requirement of service performance, and the fracture strength and the impact toughness are the bottlenecks of the expansion application, especially the high-end application of the current hard alloy.
The nanometer superfine structure hard alloy has the characteristics of high wear resistance and high toughness, and is widely applied to manufacturing tools and dies which are applicable to high load and high stress wear, sharp and good in rigidity, such as Printed Circuit Board (PCB) micro-drills, V-CUT cutters, milling cutters and the like. At present, the methods for producing ultrafine or nanocrystalline WC/WC-Co powder which are widely used in industry mainly comprise a high-energy ball milling method, a spray conversion method and a chemical vapor synthesis method. In addition, the production process of WC — Co based cemented carbide generally includes the steps of reduction of tungsten oxide, carbonization of W, wet grinding of mixed powder, drying and granulation of mixed powder, green pressing, degreasing, sintering, and the like. Obviously, the production process is complicated, the production period is long, two high-temperature processes of carbonization and sintering are needed, and the energy consumption is high.
At present, the scientific problem of common basic research from engineering application in the field of cemented carbide can be summarized in the following aspects: 1. in the industrial preparation process of ultra-fine grain and nano-grain hard alloy, the grain growth in the sintering process must be controlled by adding a grain growth inhibitor. However, inhibitors generally have an adverse effect on the toughness and strength of cemented carbides, and a thorough understanding of the stability control factors of inhibitor-derived structures and the effect on the structural and mechanical properties of cemented carbides is required. 2. As the grain size of the hard phase decreases below submicron scale, the internal interface becomes the dominant factor affecting the toughness and strength of the cemented carbide. However, the factors and stabilizing regulation mechanism for stabilizing the WC/Co phase boundary and the WC/WC grain boundary are lack of accurate knowledge, and the formation of the low-energy interface and the evolution mechanism thereof are not known. 3. The understanding of the strengthening and toughening mechanism in the service process can be deepened through the research on the mechanical behavior and the microscopic mechanism of the hard alloy at room temperature and high temperature, so as to guide the design and preparation of the high-performance hard alloy. Currently there is a lack of systematic knowledge about the micro-deformation mechanism, the source of plasticity, and the high temperature mechanical behavior of cemented carbides.
The performance of the nanometer ultrafine structure hard alloy depends on the performance of the nanometer ultrafine tungsten carbide powder. The method for preparing superfine or nano WC powder in recent years mainly comprises the following steps: mechanical alloying, direct reduction carbonization, sol-gel, gas phase carbonization, fixed bed chemical vapor, plasma, etc.
Mechanical alloying method: willow and the like adopt a mechanical alloying method, and W powder and C powder are firstly mixed according to an atomic ratio of 1: 1, putting the mixture into a steel pipe, introducing argon, selecting a WC grinding ball with the diameter of 12mm, and mixing the mixture according to a ball-material ratio of 18: finally, high-energy ball milling was carried out in a planetary ball mill, by which method WC powder with an average grain size of 7.2nm was obtained. Malachi singing and the like utilize a mechanical alloying technology to mix W powder and C powder with the granularity of about 75 mu m according to the atomic ratio of 1: 1, mixing, wherein the selected ball material ratio is 30: 1, ball milling is carried out on a QM-1F planetary high-energy ball mill, and WC powder with the average grain size of 11.3nm is obtained after ball milling for 100 hours.
Direct reduction carbonization: reduction carbonization methods for preparing ultrafine WC powder can be divided into two major categories: (1) a reduction carbonization two-step method: the first step is to prepare W powder by decomposing and reducing a precursor containing W; and the second step is to mix W powder with C-containing material and heat to high temperature, and carbonize by chemical reaction to produce WC powder. The method is characterized in that the W powder and the C powder are mixed and then react and combine at high temperature (1400 ℃ C. and 1600 ℃ C.) to generate WC powder. (2) The reduction carbonization one-step method, namely a direct reduction carbonization method: and mixing the precursor containing W and the substance containing C, and directly reducing and carbonizing at high temperature to generate WC powder. By adopting the method, the production efficiency of the WC powder is improved, and the obtained WC powder is more uniformly distributed and has finer grains.
Sol-gel method: the preparation method of the nano tungsten carbide powder comprises the following steps: first hydrogen peroxide (H) 2 O 2 30%) into W powder (200 mesh), adding glacial acetic acid andpreparing yellow tungsten sol as stabilizer, evaporating to remove excessive water, adding absolute ethanol dissolved with phenolic resin, ultrasonic mixing to obtain sol containing W source and C source, aging to obtain gel, and adding H to obtain gel 2 And AR as protective gas, and carbonizing at 900 ℃ to prepare WC powder with the grain size of 10.2 nm.
Gas phase carbonization method, namely Japanese light well utilizes gas phase carbonization method to obtain nano tungsten carbide powder, which is WCl 6 Is a source of W, with CH 4 WC powder with the grain size of 20-30nm is prepared by chemical reaction at high temperature (1300-1400 ℃) as a gas phase C source, and the grain size relation between reactant-product systems and the reaction temperature are discussed in more detail. WO was applied to Tokyo tungsten Co Ltd 3 The patent of the direct carbonization method which is used as a W source and uses CO as a carbonization gas to prepare the superfine WC powder can control the granularity and the content of C of the prepared WC powder.
The fixed bed chemical vapor method is used for successfully preparing WC powder with the particle size of about 15nm by the fixed bed chemical vapor method, such as Lichenggai and the like. By nano WO 3 As W source, acetylene was used as C source, and the preparation steps were as follows: mixing the nano WO 3 Putting the quartz reaction boat into a high-temperature stainless steel tubular reactor; vacuumizing and introducing H 2 After heat preservation for 1.5h at 660 ℃, the nano WO 3 The powder is completely reduced into nanometer W powder, and then H is reduced 2 And introducing acetylene, heating to 800 ℃, and keeping the temperature for 4 hours to convert the nano W powder into WC powder.
Plasma method there is also a common method for preparing ultra-fine/nano WC powder: the plasma method utilizes plasma as a heat source, the temperature of the plasma can reach 4000-5000 ℃, and at the high temperature, the powder raw materials are decomposed and reacted to generate the required products. The method generally adopts WO 3 WC or W as W source, with CH 4 As C source, WC or W is mainly generated after the reaction 2 C, Japanese Mount Tortoise's philosophy et al, showed: when CH is present 4 When the molar ratio of the beta-WC to WC is more than 15, the mass fraction of the beta-WC is 90-95%, and the powder particle size is about 10 nm. TEM observation of betaThe WC crystal grain size is 5-20nm, and the fractional property is good.
In recent years, the research on WC has obvious two-stage differentiation at home and abroad, and the research direction mainly includes the preparation research of ultra-coarse WC powder and the research of nano tungsten carbide powder. At present, the preparation of nanometer ultrafine tungsten carbide is mainly carried out in the industrial production through a molybdenum wire furnace. However, with the continuous development of the technology, the requirements of rear-end products on tungsten carbide raw materials are higher and higher, and higher requirements on the specific surface area of the nanometer ultrafine tungsten carbide are inevitably provided in the future. Therefore, how to further increase the BET specific surface area of tungsten carbide on the basis of the prior art is worth further research.
Disclosure of Invention
In order to further increase the specific surface area of the nano tungsten carbide powder, the invention provides a preparation method capable of further increasing the specific surface area of the nano tungsten carbide powder, so that the nano tungsten carbide powder with higher specific surface area is prepared.
In one aspect of the invention, the invention provides a method for preparing nano tungsten carbide powder by taking nano tungsten powder as a raw material through the steps of carbon preparation, carbonization, airflow crushing and the like.
In one aspect of the present invention, the present invention provides a method for preparing nano tungsten carbide powder, which is characterized by comprising the following steps:
(1) uniformly mixing nano tungsten powder and carbon black in proportion to obtain W + C;
(2) putting the uniformly mixed W + C into a reaction boat, ensuring the total height of the boat to be unchanged, stacking a plurality of boats for placing materials, and putting the materials into a molybdenum wire furnace for carbonization;
(3) and (3) performing gas breaking and grading treatment on the carbonized tungsten carbide block.
In addition, the preparation method of the high-purity silicon tungsten powder can also have the following additional technical characteristics:
further, the average particle size of the nano tungsten powder in the step (1) is 30-52 nm.
Further, the BET specific surface area of the nano tungsten powder in the step (1) is 6.0m 2 /g～10m 2 /g。
Further, the boat in the step (2) is a carbon-based coating boat and Y 2 O 3 Spray coating boat and Al 2 O 3 One of a boat and a graphite boat.
Further, the number of the boat layers stacked in the step (2) is 2-5.
Further, the bulk density of the materials in the step (2) is controlled to be 1.48-1.96 g/cm 3 。
Further, in the step (2), the carbonization temperature is 1050-1150 ℃, and the carbonization time is 2-4 h.
Further, in the step (3), the gas breaking pressure is 8-10 bar, and the rotating speed of the grading wheel is 4000-5000 r/min.
Further, in one aspect of the invention, the invention also provides a nano tungsten carbide powder product, wherein the nano tungsten carbide powder is prepared by the method.
Further, in one aspect of the invention, the invention also provides a nano ultrafine structure hard alloy product, wherein the nano ultrafine structure hard alloy is prepared by adopting the nano tungsten carbide powder prepared by the method.
The invention has the beneficial effects that:
1. under the condition of ensuring that the total height of the boat is not changed, the specific surface area of the nano tungsten carbide powder can be improved by 8-25% by adopting a plurality of boats to be stacked to replace a single boat and combining the carbonization process. Under the same boat height, the more the number of the layers of the boat, the less W + C can be contained in the single-layer boat, the thinner the material layer is, the smaller the extrusion force of the W + C by gravity and the material layer is, the larger the gap between W and W particles is, the smaller the sintering growth probability in the carbonization process is, so that the specific surface area of the prepared WC is larger; and the W + C in the single-layer boat has large loading capacity, high material layer thickness, large extrusion force by gravity and the material layer, tight contact between W and W particles, and high sintering and growing probability in the carbonization process, so that the prepared WC has smaller specific surface area. However, the number of the boat layers is not suitable to be too large, and the inventor researches that when the number of the boat layers is 6 or more, the boat loading amount of a single-layer boat is greatly reduced, and meanwhile, the overall boat loading amount is reduced, so that the yield is reduced, and the production cost is increased.
2. The bulk density of the powder is reduced by matching with a carbonization process, and the specific surface area of the tungsten carbide powder is further effectively increased.
Drawings
In order to facilitate understanding for those skilled in the art, the invention is further described below with reference to the accompanying drawings.
FIG. 1 is a process flow chart of the preparation method of the nano tungsten carbide with high specific surface area.
Detailed Description
The present invention will be further described in order to more clearly understand the objects, technical solutions and advantages of the present invention, but the scope of the present invention is not limited to the following examples, which are only used for describing the present invention in detail and are not limited in any way. The instruments and devices referred to in the following examples are conventional instruments and devices unless otherwise specified; the raw materials are all conventional commercial industrial raw materials if not specifically indicated; the processing and manufacturing methods are conventional methods unless otherwise specified. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
In order to further increase the specific surface area of the nano tungsten carbide powder, the invention provides a preparation method capable of further increasing the specific surface area of the nano tungsten carbide powder, so that the nano tungsten carbide powder with higher specific surface area is prepared.
In one aspect of the invention, the invention provides a method for preparing nano tungsten carbide powder by taking nano tungsten powder as a raw material through the steps of carbon preparation, carbonization, airflow crushing and the like.
In one aspect of the present invention, the present invention provides a method for preparing nano tungsten carbide powder, which is characterized by comprising the following steps:
(1) uniformly mixing nano tungsten powder and carbon black in proportion to obtain W + C;
(2) putting the uniformly mixed W + C into a reaction boat, ensuring the total height of the boat to be unchanged, stacking a plurality of boats for placing materials, and putting the materials into a molybdenum wire furnace for carbonization;
(3) and carrying out gas breaking and grading treatment on the carbonized tungsten carbide block.
In addition, the preparation method of the high-purity silicon tungsten powder can also have the following additional technical characteristics:
further, in the embodiment of the present invention, the average particle size of the nano tungsten powder in the step (1) is 30 to 52 nm; the average particle size of the nano tungsten powder is further preferably 30-40 nm; the average particle size of the nano tungsten powder is more preferably 30 nm.
Further, in the example of the present invention, the BET specific surface area of the nano tungsten powder in the step (1) is 6.0m 2 /g～10m 2 (ii)/g; the BET specific surface area of the nano tungsten powder is more preferably 7.0m 2 /g～10m 2 (ii)/g; the BET specific surface area of the nano tungsten powder is more preferably 8.0m 2 /g～10m 2 /g。
Further, in the embodiments of the present invention, tungsten, which is a high-specific gravity strategic non-ferrous metal, has properties such as high melting point, high elastic modulus, high hardness, good thermal conductivity, and excellent fracture toughness, and thus the product thereof is widely used in many industrial fields, and nano tungsten powder is widely used to manufacture high-performance tungsten products and process nano tungsten wires, and the excellent performance of nano tungsten wires is utilized to manufacture high-performance ultra-fine nano crystalline alloys and high-specific gravity alloys, which have become indispensable functional materials in many high-tech fields.
The nano tungsten powder refers to powder with particles of which the size is as small as nano level in tungsten powder. The preparation of the nano tungsten powder adopts a nano technology. Industrial production of tungsten powder ammonium tungstate is first converted to APT, which is then calcined to obtain tungsten oxide, and tungsten powder is then produced by hydrogen reduction of tungsten oxide. The tungsten powder prepared by the traditional powder metallurgy method is micron-sized, the relative density is very low after the tungsten powder is pressed into a compact, and the prepared tungsten wire, tungsten block and tungsten plate can be very easily broken, so that the service life of the tungsten material is influenced. Moreover, the tungsten powder with micron size is difficult to densify and sinter, and usually needs high sintering temperature and long sintering time. After the tungsten powder is subjected to nanocrystallization, the small-size effect can obviously reduce the sintering temperature and improve the sintering density, and high-density tungsten alloy and tungsten target materials can be obtained at a lower temperature, so that the mechanical properties such as strength, ductility and hardness of a tungsten product are obviously improved.
With the development of the preparation technology of the nano-grade tungsten powder and the development of advanced materials, the nano-grade tungsten powder has great advantages in improving the performance of tungsten products. When the granularity of the tungsten powder is less than 100 nanometers, the surface activity of the tungsten powder is obviously increased, and the solid-phase sintering temperature of the blank can be obviously reduced; the crystal grain of the nano tungsten powder is very fine, and the tungsten product prepared from the nano tungsten powder is also finer than the crystal grain of the product prepared from the coarse tungsten powder, so that the sintered tungsten product has finer structure and lower porosity, and the comprehensive mechanical property of the product is obviously improved. The nano tungsten powder is packaged in an inert gas antistatic way, should be sealed and stored in a dry and cool environment, is not suitable for being exposed in the air for a long time, and is prevented from being agglomerated due to moisture so as to influence the dispersing performance and the using effect. However, the present invention does not have any other specific limitation on the nano tungsten powder, and a commercially available or self-made nano tungsten powder satisfying the above average particle size and BET specific surface area, which is well known to those skilled in the art, may be used.
Further, in the embodiment of the present invention, the boat in the step (2) is a carbon-based paint boat, Y 2 O 3 Spray coating boat and Al 2 O 3 One of a boat and a graphite boat; the boat described in the step (2) is more preferably a graphite boat. However, the present invention is not limited to any particular type of boat apparatus, and any commercially available or homemade boat apparatus known to those skilled in the art that can meet the temperature requirements of the present invention may be used.
Further, in the embodiment of the present invention, the number of stacked boats in step (2) is 2 to 5, and the number of stacked boats in step (2) is more preferably 3 to 4. Under the condition of ensuring that the total height of the boat is not changed, the specific surface area of the nano tungsten carbide powder can be improved by 8-25% by adopting a plurality of boats to be stacked to replace a single boat and combining the carbonization process. The reason is as follows: under the same boat height, the more the number of the layers of the boat, the less W + C can be contained in the single-layer boat, the thinner the material layer is, the smaller the extrusion force of the W + C by gravity and the material layer is, the larger the gap between W and W particles is, the smaller the sintering growth probability in the carbonization process is, so that the specific surface area of the prepared WC is larger; and the W + C in the single-layer boat has large loading capacity, high material layer thickness, large extrusion force by gravity and the material layer, tight contact between W and W particles, and high sintering and growing probability in the carbonization process, so that the prepared WC has smaller specific surface area. However, when the number of the boat layers is 6 or more, the boat loading amount of the single-layer boat is greatly reduced, and the overall boat loading amount is reduced, so that the yield is reduced, and the production cost is increased. In addition, when the number of layers of the boat is increased to a certain degree, the improvement effect on the specific surface area of the tungsten carbide is limited, and the specific surface area of the tungsten carbide is difficult to be further improved.
Further, in the embodiment of the invention, the bulk density of the material in the step (2) is controlled to be 1.48-1.96 g/cm 3 The bulk density of the material in the step (2) is further preferably controlled to be 1.58-1.76 g/cm 3 . If the stacking density is too large, the clearance between W and W particles is small, the sintering growth probability is high in the carbonization process, and the specific surface area of the prepared WC is smaller; if the bulk density is too low, the productivity is seriously reduced and the production cost is increased.
Further, in the embodiment of the invention, the carbonization temperature in the step (2) is 1050-1150 ℃, and the carbonization time is 2-4 h; the carbonization temperature in the step (2) is more preferably 1080 to 1120 ℃, and the carbonization time is more preferably 3 hours. The inventor researches and finds that the tungsten carbide product with high specific surface area is easier to prepare in the reasonable temperature and time range. If the carbonization temperature is too low, the sintering effect is poor, the situation of insufficient carbonization and incomplete carbonization is easy to occur, and the free carbon of the product is high; when the carbonization temperature is too high, solid-phase agglomeration is easily formed seriously, so that the specific surface area of the powder is reduced. In addition, the excessive carbonization temperature has higher requirements on equipment and higher cost, and is not beneficial to large-scale industrial production. The carbonization time is too short, the effect of complete carbonization cannot be realized, and the free carbon of the product is higher; and if the carbonization time is too long, the tungsten carbide product is easy to sinter and grow up, the productivity is reduced, the production cost is increased, and the large-scale industrial production is not facilitated. Therefore, the optimum carbonization effect can be ensured by using the carbonization temperature and the carbonization time within the above-described ranges of the present invention.
Further, in the embodiment of the invention, the gas burst pressure in the step (3) is 8-10 bar, the rotation speed of the classifier wheel is 4000-5000 r/min, the gas burst pressure in the step (3) is further preferably 10bar, and the rotation speed of the classifier wheel is further preferably 5000 r/min. The gas breaking pressure is too high, the rotating speed of the grading wheel is too high, the tungsten carbide product is thinner, the specific surface area is larger, but the requirement on the pressure resistance of equipment is high, the loss of the grading wheel is large, the production cost is increased, and the industrial production is not facilitated. If the gas burst pressure is too low and the rotating speed of the grading wheel is slow, the thicker the tungsten carbide product is, the smaller the specific surface area is, and the product quality requirement is difficult to meet.
Further, in one aspect of the invention, the invention also provides a nano tungsten carbide powder product, wherein the nano tungsten carbide powder is prepared by the method. Tungsten carbide (WC) is an important raw material for cemented carbide and cermet, and the particle size of WC powder substantially determines the mechanical properties of cemented carbide and cermet. With the reduction of the grain size of WC powder, the performance of the hard alloy and the metal ceramic is obviously improved; particularly, when the particle size of the WC powder is reduced to a nano level, the strength, elastic modulus, wear resistance, etc. of the material are remarkably improved, and the toughness thereof is improved. The nano tungsten carbide powder is a product with high technical content and high performance, and is mainly used for producing hard alloy and various hard surface materials. The nano tungsten carbide is an important raw material for manufacturing the ultra-fine grain hard alloy, and the performance of the nano tungsten carbide has important influence on the performance of the ultra-fine grain hard alloy. The nano tungsten carbide prepared by the preparation method has the advantages of high purity, uniform granularity, good dispersibility, high specific surface area and the like.
Further, in one aspect of the invention, the invention also provides a nano ultrafine structure hard alloy product, wherein the nano ultrafine structure hard alloy is prepared by adopting the nano tungsten carbide powder prepared by the method. The hard alloy is mainly applied to the aspects of cutting tools, mining tools, dies, high-pressure and high-temperature resistant throwing cavities and the like, wherein the proportion of the cutting tools to the mining tools accounts for 33 percent and 25 percent of that of the hard alloy respectively. In cutting tools, cemented carbide is mainly used as a tool material, such as turning tools, milling cutters, planing tools, drill bits, boring tools and the like, and is used for cutting cast iron, nonferrous metals, plastics, chemical fibers, graphite, glass, stones, common steel, difficult-to-machine materials and the like, and cutting machining is mainly realized by a machine tool. In the aspect of mining tools, the hard alloy is mainly used as a rock drilling tool, a mining tool and a drilling tool and plays an important role in the aspects of mineral production, oil exploitation, infrastructure construction and the like.
The invention will now be described with reference to specific examples, which are intended to be illustrative only and not to be limiting in any way.
Example 1:
1. BET of 6.0m 2 Uniformly mixing the per gram of nano tungsten powder and carbon black in proportion to obtain W + C;
2. placing the uniformly mixed W + C in a graphite boat to ensure that the total height of the boat is constant, and placing the two boats in a superposition manner to control the stacking density to be 1.48g/cm 3 And putting the mixture into a molybdenum wire furnace to carbonize for 4 hours at 1050 ℃.
3. Carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 8bar, and the rotating speed of a grading wheel is 4000 r/min;
4. the specific surface area of the obtained WC is 3.0m 2 /g。
Example two:
1. BET of 6.0m 2 Uniformly mixing the per gram of nano tungsten powder and carbon black in proportion to obtain W + C;
2. placing the uniformly mixed W + C in a graphite boat to ensure that the total height of the boat is constant, and placing the two boats in a superposition manner to control the stacking density to be 1.75g/cm 3 And putting the mixture into a molybdenum wire furnace to carbonize for 4 hours at 1050 ℃.
3. Carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 8bar, and the rotating speed of a grading wheel is 4000 r/min;
4. the specific surface area of the obtained WC is 2.95m 2 /g。
Example three:
1. uniformly mixing nano tungsten powder with BET of 6.0m2/g and carbon black in proportion to obtain W + C;
2. placing the uniformly mixed W + C in a graphite boat to ensure that the total height of the boat is constant, and placing the two boats in a superposition manner to control the stacking density to be 1.96g/cm 3 And putting the mixture into a molybdenum wire furnace to carbonize for 4 hours at 1050 ℃.
3. Carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 8bar, and the rotating speed of a grading wheel is 4000 r/min;
4. the specific surface area of the obtained WC is 2.9m 2 /g。
Example four:
1. BET of 6.0m 2 Uniformly mixing the per gram of nano tungsten powder and carbon black in proportion to obtain W + C;
2. putting the uniformly mixed W + C into a graphite boat, ensuring the total height of the boat to be constant, adopting four boats to be stacked, and controlling the stacking density to be 1.8g/cm 3 And carbonizing the mixture in a molybdenum wire furnace at 1100 ℃ for 2.5 hours.
3. Carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 9bar, and the rotating speed of a grading wheel is 4600 r/min;
4. the specific surface area of the prepared WC is 3.1m 2 /g。
Example five:
1. BET is 8.0m 2 Uniformly mixing the per gram of nano tungsten powder and carbon black in proportion to obtain W + C;
2. putting the uniformly mixed W + C into a graphite boat, ensuring the total height of the boat to be constant, adopting four boats to be stacked, and controlling the stacking density to be 1.75g/cm 3 And putting the mixture into a molybdenum wire furnace to carbonize for 3 hours at 1100 ℃.
3. And (3) carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 10bar, and the rotating speed of the grading wheel is 4800 r/min.
4. The specific surface area of the obtained WC is 3.2m 2 /g。
Example six:
1. BET of 10.0m 2 Uniformly mixing the per gram of nano tungsten powder and carbon black in proportion to obtain W + C;
2. putting the uniformly mixed W + C into a graphite boat, ensuring the total height of the boat to be constant, adopting four boats to be stacked, and controlling the stacking density to be 1.52g/cm 3 And putting the mixture into a molybdenum wire furnace to carbonize for 4 hours at 1050 ℃.
3. Carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 10bar, and the rotating speed of a grading wheel is 5000 r/min;
4. the specific surface area of the obtained WC is 3.5m 2 /g。
Example seven:
1. BET of 10.0m 2 Uniformly mixing the per gram of nano tungsten powder and carbon black in proportion to obtain W + C;
2. putting the uniformly mixed W + C into a graphite boat, ensuring the total height of the boat to be constant, adopting three boats to be stacked, and controlling the stacking density to be 1.52g/cm 3 And putting the mixture into a molybdenum wire furnace to carbonize for 4 hours at 1050 ℃.
3. Carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 10bar, and the rotating speed of a grading wheel is 5000 r/min;
4. the specific surface area of the obtained WC is 3.38m 2 /g。
Example eight:
1. BET of 10.0m 2 Uniformly mixing the per gram of nano tungsten powder and carbon black in proportion to obtain W + C;
2. placing the uniformly mixed W + C in a graphite boat to ensure that the total height of the boat is constant, and placing the two boats in a superposition manner to control the stacking density to be 1.52g/cm 3 And putting the mixture into a molybdenum wire furnace to carbonize for 4 hours at 1050 ℃.
3. And (3) carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 10bar, and the rotating speed of the grading wheel is 5000 r/min.
4. The specific surface area of the obtained WC is 3.3m 2 /g。
Example nine:
1. BET of 10.0m 2 Uniformly mixing the per gram of nano tungsten powder and carbon black in proportion to obtain W + C;
2. putting the uniformly mixed W + C into a graphite boat, ensuring the total height of the boat to be constant, and adopting three boats to be stacked and controlledThe bulk density is 1.52g/cm 3 And putting the mixture into a molybdenum wire furnace to carbonize for 3 hours at 1100 ℃.
3. And (3) carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 9bar, and the rotating speed of the grading wheel is 4500 r/min.
4. The specific surface area of the obtained WC is 3.05m 2 /g。
Comparative example one:
1. BET of 10.0m 2 Uniformly mixing the per gram of nano tungsten powder and carbon black in proportion to obtain W + C;
2. placing the uniformly mixed W + C in a graphite boat, ensuring the total height of the boat to be constant, adopting a single boat, and controlling the stacking density to be 1.52g/cm 3 And putting the mixture into a molybdenum wire furnace to carbonize for 4 hours at 1050 ℃.
3. And (3) carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 10bar, and the rotating speed of the grading wheel is 5000 r/min.
4. The specific surface area of the obtained WC is 3.1m 2 /g。
Comparative example two:
1. BET of 10.0m 2 Uniformly mixing the per gram of nano tungsten powder and carbon black in proportion to obtain W + C;
2. placing the uniformly mixed W + C in a graphite boat, ensuring the total height of the boat to be constant, adopting a single boat, and controlling the stacking density to be 1.96g/cm 3 And putting the mixture into a molybdenum wire furnace to carbonize for 4 hours at 1050 ℃.
3. And (3) carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 10bar, and the rotating speed of the grading wheel is 5000 r/min.
4. The specific surface area of the obtained WC is 2.8m 2 /g。
Comparative example three:
1. BET of 10.0m 2 Uniformly mixing the per gram of nano tungsten powder and carbon black in proportion to obtain W + C;
2. putting the uniformly mixed W + C into a graphite boat, ensuring the total height of the boat to be constant, adopting six boats to be stacked, and controlling the stacking density to be 1.52g/cm 3 And putting the mixture into a molybdenum wire furnace to carbonize for 4 hours at 1050 ℃.
3. And (3) carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 10bar, and the rotating speed of the grading wheel is 5000 r/min.
4. The specific surface area of the obtained WC is 3.5m 2 /g。
Comparative example four:
1. BET of 10.0m 2 Uniformly mixing the per gram of nano tungsten powder and carbon black in proportion to obtain W + C;
2. putting the uniformly mixed W + C into a graphite boat, ensuring the total height of the boat to be constant, adopting four boats to be stacked, and controlling the stacking density to be 1.32g/cm 3 And putting the mixture into a molybdenum wire furnace to carbonize for 1h at 950 ℃.
3. And (3) carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 10bar, and the rotating speed of the grading wheel is 5000 r/min.
4. Experimental results show that the prepared WC is not carbonized completely, the product phase is more (tungsten carbide, ditungsten carbide, tungsten powder, carbon black and the like), and the specific surface area of the tungsten carbide cannot be reflected.
Comparative example five:
1. BET of 10.0m 2 Uniformly mixing the per gram of nano tungsten powder and carbon black in proportion to obtain W + C;
2. putting the uniformly mixed W + C into a graphite boat, ensuring the total height of the boat to be constant, adopting four boats to be stacked, and controlling the stacking density to be 2.12g/cm 3 And putting the mixture into a molybdenum wire furnace to carbonize for 5 hours at 1250 ℃.
3. And (3) carrying out gas breaking on the carbonized tungsten carbide block, wherein the gas breaking pressure is 10bar, and the rotating speed of the grading wheel is 5000 r/min.
4. The specific surface area of the obtained WC is 2.8m 2 /g。
The specific surface area nano tungsten carbide measurements obtained in the examples and comparative examples are shown in table 1 below:
TABLE 1
Therefore, the nano tungsten carbide prepared by the preparation method has relatively higher specific surface area.
The foregoing examples are merely illustrative of and explain the present invention and are not to be construed as limiting the scope of the invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
Claims (10)
1. A preparation method of nano tungsten carbide powder is characterized by comprising the following steps:
(1) uniformly mixing nano tungsten powder and carbon black in proportion to obtain W + C;
(2) putting the uniformly mixed W + C into a reaction boat, ensuring the total height of the boat to be unchanged, stacking a plurality of boats for placing materials, and putting the materials into a molybdenum wire furnace for carbonization;
(3) and carrying out gas-breaking classification treatment on the carbonized tungsten carbide block.
2. The method according to claim 1, wherein the average particle size of the nano tungsten powder in the step (1) is 30 to 52 nm.
3. The method according to claim 1, wherein the BET specific surface area of the nano tungsten powder in the step (1) is 6.0m 2 /g～10m 2 /g。
4. The method as claimed in any one of claims 1 to 3, wherein the boat in the step (2) is a carbon-based paint boat, Y 2 O 3 Spray coating boat and Al 2 O 3 One of a boat and a graphite boat.
5. The method of any of claims 1-3, wherein the number of boats placed one on top of the other in step (2) is 2-5.
6. The method according to any one of claims 1 to 3, wherein the bulk density of the material in the step (2) is controlled to be 1.48 to 1.96g/cm 3 。
7. The method according to any one of claims 1 to 3, wherein the carbonization temperature in the step (2) is 1050 ℃ to 1150 ℃ and the carbonization time is 2 to 4 hours.
8. The method according to any one of claims 1 to 3, wherein the gas burst pressure in step (3) is 8 to 10bar and the rotation speed of the classifier wheel is 4000 to 5000 r/min.
9. Nano tungsten carbide powder, characterized in that it is prepared by the method according to any one of claims 1 to 8.
10. The nanometer ultrafine structure hard alloy is characterized in that the nanometer ultrafine structure hard alloy is prepared from the nanometer tungsten carbide powder prepared by the method of any one of claims 1 to 8 or the nanometer tungsten carbide powder of claim 9.
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