Superfine tungsten carbide as well as preparation method and application thereof

Abstract

The invention provides superfine tungsten carbide and a preparation method and application thereof, and belongs to the technical field of nanomaterials, and the preparation method comprises the following steps: mixing WO3 and carbon black powder to obtain mixed powder, and carrying out primary thermal reduction on the mixed powder in a vacuum atmosphere at the temperature of 900-1050 DEG C to obtain a primary reduction product; and the primary reduction product is subjected to secondary thermal reduction in a vacuum atmosphere, superfine tungsten carbide is obtained, and the secondary reduction temperature is 1100-1300 DEG C. Through two times of reduction reactions, on one hand, carbon black powder and WO3 can fully react, and a carbon-deficient phase is prevented from appearing in a product; on the other hand, WO3 is reduced into elementary substance W at a relatively low temperature, so that abnormal increase of W particles can be avoided, and subsequent preparation of superfine tungsten carbide with high specific surface area and small average particle size is facilitated.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, specifically to an ultrafine tungsten carbide, its preparation method, and its applications. Background Technology

[0002] Ultrafine-grained cemented carbide is an advanced alloy that improves the overall performance of materials by controlling the tungsten carbide (WC) grain size to below 0.5 μm and optimizing the cobalt (Co) content to 9%–15%. Its highly uniform dispersion structure of hard and binder phases enables the material to maintain high hardness (up to HRA93) while achieving a bending strength of 2.5–3.5 GPa, thus realizing a synergistic gain in hardness and strength.

[0003] Currently, the traditional method used for mass production of tungsten carbide both domestically and internationally is the hydrogen reduction-carburization method for tungsten oxide. This method primarily uses tungsten dioxide as a raw material, reducing it to ultrafine tungsten powder with hydrogen. The ultrafine tungsten powder is then mixed with carbon black and carbonized to obtain ultrafine tungsten carbide powder. However, in the first step of hydrogen reduction, the gaseous product water vapor generated by the combination of hydrogen and oxygen atoms reacts with tungsten oxide, allowing the tungsten source to migrate in the gas phase via WO2(OH)2 and deposit on the W core. This results in an abnormal increase in W particle size, leading to a larger WC particle size after reduction. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides an ultrafine tungsten carbide, its preparation method and application, aiming to solve the technical problem of the easy formation of abnormal coarse grains in the existing tungsten carbide preparation process.

[0005] In a first aspect, embodiments of this application provide a method for preparing ultrafine tungsten carbide, comprising the following steps: S1. Mix WO3 and carbon black powder to obtain a mixed powder. Perform a thermal reduction on the mixed powder under vacuum to obtain a primary reduction product. The primary thermal reduction temperature is 900~1050℃. S2. The product from the first reduction is subjected to a second thermal reduction under a vacuum atmosphere to obtain ultrafine tungsten carbide. The second reduction temperature is 1100~1300℃.

[0006] Secondly, embodiments of this application provide an ultrafine tungsten carbide, which is prepared using the above-described method.

[0007] Thirdly, embodiments of this application provide an application of ultrafine tungsten carbide in ultrafine grain cemented carbide.

[0008] The advantages of this application, which differ from existing technical solutions, include: This invention first reduces WO3 to elemental W using carbon black powder at a lower temperature, and then raises the temperature to a higher temperature to allow elemental W to undergo a second reduction with carbon black powder, thus obtaining ultrafine tungsten carbide. Through the two reduction reactions, on the one hand, the carbon black powder and WO3 can react fully, avoiding the appearance of carbon-deficient phases in the product; on the other hand, reducing WO3 to elemental W at a lower temperature can prevent abnormal growth of W particles, which is beneficial for the subsequent production of ultrafine tungsten carbide with high specific surface area and small average particle size.

[0009] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Detailed Implementation

[0010] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0011] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0012] Currently, the traditional method used for mass production of tungsten carbide both domestically and internationally is the hydrogen reduction-carburization method for tungsten oxide. This method primarily uses tungsten dioxide as a raw material, reducing it to ultrafine tungsten powder with hydrogen. The ultrafine tungsten powder is then mixed with carbon black and carbonized to obtain ultrafine tungsten carbide powder. However, in the first step of hydrogen reduction, the gaseous product water vapor generated by the combination of hydrogen and oxygen atoms reacts with tungsten oxide, allowing the tungsten source to migrate in the gas phase via WO2(OH)2 and deposit on the W core. This results in an abnormal increase in W particle size, leading to a larger WC particle size after reduction.

[0013] To address the technical problem of abnormally coarse grains forming during existing tungsten carbide preparation processes, this application provides an ultrafine tungsten carbide, its preparation method, and its application. This invention utilizes a two-stage reduction reaction. On one hand, this allows carbon black powder to fully react with WO3, preventing the formation of carbon-deficient phases in the product. On the other hand, reducing WO3 to elemental W at a lower temperature prevents abnormal growth of W particles, which is beneficial for subsequently obtaining ultrafine tungsten carbide with high specific surface area and small average particle size.

[0014] In a first aspect, embodiments of this application provide a method for preparing ultrafine tungsten carbide, comprising the following steps: S1. Mix WO3 and carbon black powder to obtain a mixed powder. Perform a thermal reduction on the mixed powder under vacuum to obtain a primary reduction product. The primary thermal reduction temperature is 900~1050℃. S2. The product from the first reduction is subjected to a second thermal reduction under a vacuum atmosphere to obtain ultrafine tungsten carbide. The second reduction temperature is 1100~1300℃.

[0015] In the technical solution of this application embodiment, the temperature is relatively low during the first thermal reduction process, and the conditions for directly reducing WO3 to WC are not met. WO3 and carbon black powder react to generate elemental W at a temperature of 900~1050℃. Furthermore, the elemental W generated at this temperature has finer grains, which avoids the abnormal increase in grain size of elemental W at high temperatures during the direct one-time reduction preparation of WC at higher temperatures. This lays a good foundation for the subsequent preparation of ultrafine tungsten carbide.

[0016] The secondary thermal reduction temperature is 1100~1300℃. Elemental W reacts with carbon black powder at high temperature to generate WC. Compared with the direct reduction of WO3 to WC, this allows WO3 to react more completely, avoids the appearance of carbon-deficient phases in the product, and improves the purity of ultrafine tungsten carbide.

[0017] Furthermore, in some embodiments, the holding time for the first heat reduction is 100-150 min, and the holding time for the second heat reduction is 100-200 min.

[0018] In the technical solution of this application embodiment, the time for the first thermal reduction and the second thermal reduction are set within the above range. This ensures that WO3 is completely reduced to WC while avoiding excessive reaction time that could lead to grain size growth.

[0019] Furthermore, in some embodiments, the molar ratio of carbon black powder to WO3 is 3.5 to 4.

[0020] Furthermore, in some embodiments, the carbon content of the carbon black is 97% to 99%.

[0021] In the technical solution of this application embodiment, the use of high-purity carbon black is beneficial for accurately controlling the amount of C added during the thermal reduction reaction process, and can also avoid introducing impurities.

[0022] Furthermore, in some embodiments, the particle size of WO3 is 20~100μm, and the particle size of the carbon black powder is 20~60nm.

[0023] Furthermore, in some embodiments, the vacuum degree is 5 to 20 Pa during both the primary and secondary thermal reduction processes.

[0024] In the technical solution of this application embodiment, thermal reduction under vacuum conditions can reduce the temperature at which the reaction occurs, increase the reaction rate, and shorten the reaction time.

[0025] Furthermore, in some embodiments, WO3 and carbon black powder are mixed by ball milling at a speed of 200-300 r / min for a time of 3-8 h.

[0026] In the technical solution of this application embodiment, WO3 and carbon black powder are ball-milled before the reaction, which can make WO3 and carbon black powder fully mixed and reduce the particle size.

[0027] Furthermore, in some embodiments, the primary and secondary thermal reductions are carried out in a rotary kiln with a rotation speed of 1.5~3 r / min.

[0028] In the technical solution of this application embodiment, the reduction reaction is carried out in a rotary kiln, which enables the reaction to proceed more uniformly.

[0029] Secondly, embodiments of this application provide an ultrafine tungsten carbide, which is prepared using the above-described method.

[0030] Thirdly, embodiments of this application provide an application of ultrafine tungsten carbide in ultrafine grain cemented carbide.

[0031] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0032] I. Preparation Method Example 1 A method for preparing ultrafine tungsten carbide includes the following steps: S1. 232g of WO3 and 48g of carbon black powder were ball-milled at a speed of 200r / min for 8h to obtain a mixed powder. The average particle size of WO3 was 20~100μm and the average particle size of carbon black powder was 20~60nm.

[0033] The mixed powder was subjected to a single thermal reduction in a rotary kiln under a vacuum atmosphere to obtain a single reduction product. The single thermal reduction temperature was 900℃, the thermal reduction time was 150min, the vacuum degree in the rotary kiln was 5Pa, and the rotation speed of the rotary kiln was 3r / min. S2. The product from the first reduction is subjected to a second thermal reduction in a rotary furnace under a vacuum atmosphere to obtain ultrafine tungsten carbide. The second reduction temperature is 1100℃, the thermal reduction time is 200min, the vacuum degree in the rotary furnace is 5Pa, and the rotation speed of the rotary furnace is 3r / min.

[0034] XRD and BET surface area measurements showed that the powder prepared in this embodiment was a single WC phase with a specific surface area of ​​5.72 m². 2 / g, with an average particle size of 62 nm.

[0035] Example 2 A method for preparing ultrafine tungsten carbide includes the following steps: S1. 232g of WO3 and 42g of carbon black powder were ball-milled together at a speed of 300r / min for 3h to obtain a mixed powder. The average particle size of WO3 was 20~100μm and the average particle size of carbon black powder was 20~60nm.

[0036] The mixed powder was subjected to a single thermal reduction in a rotary kiln under a vacuum atmosphere to obtain a single reduction product. The single thermal reduction temperature was 1050℃, the thermal reduction time was 100min, the vacuum degree in the rotary kiln was 20Pa, and the rotation speed of the rotary kiln was 1.5r / min. S2. The primary reduction product is subjected to secondary thermal reduction in a rotary kiln under vacuum to obtain ultrafine tungsten carbide. The secondary reduction temperature is 1300℃, the thermal reduction time is 100min, the vacuum degree in the rotary kiln is 20Pa, and the rotation speed of the rotary kiln is 1.5r / min.

[0037] XRD and BET surface area measurements showed that the powder prepared in this embodiment was a single WC phase with a specific surface area of ​​5.68 m². 2 / g, with an average particle size of 65 nm.

[0038] Comparative Example 1 A method for preparing ultrafine tungsten carbide includes the following steps: S1. 232g of WO3 and 48g of carbon black powder were ball-milled at a speed of 200r / min for 8h to obtain a mixed powder. The average particle size of WO3 was 20~100μm and the average particle size of carbon black powder was 20~60nm.

[0039] The mixed powder was thermally reduced in a rotary kiln under a vacuum atmosphere to obtain ultrafine tungsten carbide. The secondary reduction temperature was 1100℃, the thermal reduction time was 200 min, the vacuum degree in the rotary kiln was 5 Pa, and the rotation speed of the rotary kiln was 3 r / min.

[0040] XRD and BET surface area measurements showed that the powder prepared in this embodiment was a single WC phase with a specific surface area of ​​5.26 m². 2 / g, with an average particle size of 73 nm.

[0041] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and function as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing ultrafine tungsten carbide, characterized in that, Includes the following steps: S1. Mix WO3 and carbon black powder to obtain a mixed powder. Perform a thermal reduction on the mixed powder under vacuum to obtain a primary reduction product. The primary thermal reduction temperature is 900~1050℃. S2. The primary reduction product is subjected to a secondary thermal reduction under a vacuum atmosphere to obtain ultrafine tungsten carbide. The secondary reduction temperature is 1100~1300℃.

2. The method for preparing ultrafine tungsten carbide according to claim 1, characterized in that, The holding time for the first heat reduction is 100-150 min, and the holding time for the second heat reduction is 100-200 min.

3. The method for preparing ultrafine tungsten carbide according to claim 1, characterized in that, The molar ratio of carbon black powder to WO3 is 3.5 to 4.

4. The method for preparing ultrafine tungsten carbide according to claim 1, characterized in that, The carbon black has a carbon content of 97% to 99%.

5. The method for preparing ultrafine tungsten carbide according to claim 1, characterized in that, The particle size of the WO3 is 20~100μm, and the particle size of the carbon black powder is 20~60nm.

6. The method for preparing ultrafine tungsten carbide according to claim 1, characterized in that, The vacuum level is 5–20 Pa during both the primary and secondary thermal reduction processes.

7. The method for preparing ultrafine tungsten carbide according to claim 1, characterized in that, The WO3 and carbon black powder were mixed by ball milling at a speed of 200-300 r / min for 3-8 h.

8. The method for preparing ultrafine tungsten carbide according to claim 1, characterized in that, The primary and secondary thermal reductions are carried out in a rotary kiln with a rotation speed of 1.5~3 r / min.

9. An ultrafine tungsten carbide, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 8.

10. The application of the ultrafine tungsten carbide as described in claim 9 in ultrafine grain cemented carbide.