阅读说明：本技术 一种碳化硼纳米粉末的制备方法 (Preparation method of boron carbide nano powder ) 是由 金利华 贾佳林 白利锋 刘国庆 冯建情 李成山 张平祥 于 2019-11-05 设计创作，主要内容包括：本发明公开了一种碳化硼纳米粉末的制备方法,该方法包括以下步骤：一、将氧化石墨烯和硼粉混合后加入乙醇并通入惰性气体,在机械搅拌下反应,再经静置分层后得到氧化石墨烯包覆硼粉；二、将氧化石墨烯包覆硼粉在惰性气体条件下进行低温热处理,随炉冷却后得到预成型的碳化硼；三、将预成型的碳化硼在还原性气氛的条件下或真空条件下进行高温热处理,得到碳化硼纳米粉末。本发明利用氧化石墨烯具有的高比表面积和高反应活性,使氧化石墨烯包覆在硼粉的周围形成B-O-C混合物,然后依次经低温和高温热处理的成相反应除去氧,得到碳化硼纳米粉末,有效避免了硼粉的氧化,降低了杂质含量,提高了碳化硼的纯度,同时减少了制备成本。(The invention discloses a preparation method of boron carbide nano powder, which comprises the following steps: firstly, mixing graphene oxide and boron powder, adding ethanol, introducing inert gas, reacting under mechanical stirring, and standing for layering to obtain graphene oxide-coated boron powder; secondly, carrying out low-temperature heat treatment on the boron powder coated with the graphene oxide under the condition of inert gas, and cooling along with the furnace to obtain preformed boron carbide; and thirdly, performing high-temperature heat treatment on the preformed boron carbide under the reducing atmosphere condition or the vacuum condition to obtain boron carbide nano powder. According to the invention, the graphene oxide is coated around the boron powder to form a B-O-C mixture by utilizing the high specific surface area and the high reaction activity of the graphene oxide, and then the boron carbide nano powder is obtained by removing oxygen through the resultant reaction of low-temperature and high-temperature heat treatment in sequence, so that the oxidation of the boron powder is effectively avoided, the impurity content is reduced, the purity of boron carbide is improved, and the preparation cost is reduced.)

1. A method for preparing boron carbide nanopowder, comprising the steps of:

step one, mixing graphene oxide and boron powder, placing the mixture in a three-neck round-bottom flask, adding ethanol, introducing inert gas, reacting under the condition of mechanical stirring, standing for layering, and removing a solvent to obtain graphene oxide-coated boron powder;

step two, placing the boron powder coated with the graphene oxide obtained in the step one in heating equipment, introducing inert gas for low-temperature heat treatment, and cooling along with a furnace to obtain preformed boron carbide; the temperature of the low-temperature heat treatment is 200-400 ℃, and the heat preservation time is 0.5-2 h;

step three, performing high-temperature heat treatment on the preformed boron carbide obtained in the step two under the condition of reducing atmosphere or vacuum to obtain boron carbide nano powder; the temperature of the high-temperature heat treatment is 800-1200 ℃, and the heat preservation time is 0.5-5 h.

2. The method for preparing boron carbide nanopowder according to claim 1, wherein in the first step, the atomic ratio of the graphene oxide to the boron powder is (1-2): 4.

3. the method according to claim 1, wherein the boron powder in the first step is a boron nanopowder, and the high temperature heat treatment in the third step is performed under a reducing atmosphere.

4. The method for preparing boron carbide nanopowder of claim 1, wherein in step three the reducing atmosphere is Ar, H₂And CH₄A mixed gas of composition wherein Ar, H₂And CH₄Is 50: (30-49): (1-20).

5. The method according to claim 1, wherein the boron powder in the first step is non-nano boron powder, the pre-formed boron carbide in the third step is firstly ball-milled at a speed of 200 rpm-400 rpm for 1 h-5 h, and carbon powder is supplemented in the ball-milling process,then placing the carbon tube in a carbon tube furnace with the vacuum degree of 10^-2Pa～10^-4Carrying out high-temperature heat treatment under the vacuum condition of Pa; the mass ratio of the carbon powder to the preformed boron carbide is 0.2: 1.

6. The method according to claim 1, wherein the inert gas in the first step is nitrogen.

7. The method according to claim 1, wherein the mechanical stirring speed in the first step is 500rpm to 20000rpm, and the reaction time is 5min to 60 min.

8. The method according to claim 1, wherein the inert gas in step two is nitrogen or argon.

9. The method for preparing boron carbide nanopowder of claim 1, wherein the heating rate for the low temperature heat treatment in step two is 1-5 ℃/min.

Technical Field

The invention belongs to the technical field of ceramic materials, and particularly relates to a preparation method of boron carbide nano powder.

Background

Boron carbide (B)₄C) Is an extremely hard material, has excellent physicochemical properties such as high melting point, extremely high hardness, low density, high Young's modulus, high chemical stability, good wear resistance and the like, and has wide applications in many fields such as polishing materials in polishing and grinding media, nozzles, ceramic bearings and wire drawing dies. In addition, B₄C is an ideal control and shielding material in the nuclear industry.

B₄The synthesis of the C powder has a plurality of processes, and the production characteristics and the processing cost of each process are different. Direct synthesis of B from boron and carbon in traditional method₄C powder, difficult to react, requires high temperatures and is time consuming and costly, making the process less attractive. Carbothermic reduction of boron oxide (B) in electric arc or resistance furnaces₂O₃) Boric acid (H)₃BO₃) Iso-boron oxide compounds, and also B₄C. In the process, Mg or Na is usually introduced as a reducing agent, and other metal ion impurities are easily introduced; and the product obtained by the method is in a block shape and coarse particles, and needs subsequent crushing, grinding and acid washing purification.

In recent years, people have been exploring B₄And C, a novel method for preparing the powder, such as laser irradiation chemical vapor deposition and sol-gel. However, the limitations of these preparation methods prevent their mass production, such as laser processing requiring expensive equipment and low productivity, while sol-gel methods have disadvantages of requiring the introduction of strong metal reducing agents, low productivity, and the like.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a method for preparing boron carbide nanopowder, aiming at the deficiencies of the prior art. According to the method, the graphene oxide is coated around the boron powder to form a B-O-C mixture by utilizing the high specific surface area and the high reaction activity of the graphene oxide, and then the boron carbide nano powder is obtained by removing oxygen through the resultant reaction of low-temperature and high-temperature heat treatment in sequence, so that the oxidation of the boron powder is effectively avoided, the impurity content is reduced, the purity of boron carbide is improved, and the preparation cost is reduced.

The invention utilizes the high specific surface area and the high reaction activity of the graphene oxide to lead the graphene oxide to be coated around the boron powder to form a B-O-C mixture,

in order to solve the technical problems, the invention adopts the technical scheme that: a method for preparing boron carbide nanopowder, comprising the steps of:

step one, mixing graphene oxide and boron powder, placing the mixture in a three-neck round-bottom flask, adding ethanol, introducing inert gas, reacting under the condition of mechanical stirring, standing for layering, and removing a solvent to obtain graphene oxide-coated boron powder;

step two, placing the boron powder coated with the graphene oxide obtained in the step one in heating equipment, introducing inert gas for low-temperature heat treatment, and cooling along with a furnace to obtain preformed boron carbide; the temperature of the low-temperature heat treatment is 200-400 ℃, and the heat preservation time is 0.5-2 h;

step three, performing high-temperature heat treatment on the preformed boron carbide obtained in the step two under the condition of reducing atmosphere or vacuum to obtain boron carbide nano powder; the temperature of the high-temperature heat treatment is 800-1200 ℃, and the heat preservation time is 0.5-5 h.

Firstly, graphene oxide and boron powder are coated and combined, the graphene oxide is dispersed by adding ethanol, inert gas is introduced to prevent further oxidation of the boron powder, the graphene oxide is coated around the boron powder by utilizing the high specific surface area and high reaction activity of the graphene oxide to form a B-O-C mixture, then the resultant reaction of low-temperature heat treatment is carried out under the protection of the inert gas, most of oxygen in the graphene oxide is released and removed to form graphene, meanwhile, the oxidation of the boron powder is avoided, preformed boron carbide is obtained, then high-temperature heat treatment is carried out under the condition of reducing atmosphere or vacuum, the residual oxygen is further removed, and B is generated₄C, nano powder. The method does not need to adopt metals such as magnesium or sodium and the like in the traditional method as reducing agents, avoids introducing metal impurities, reduces the impurity content, improves the purity of boron carbide, realizes the phase reaction of the boron carbide at lower temperature in shorter time, reduces the process difficulty and reduces the preparation cost.

The preparation method of the boron carbide nanopowder is characterized in that in the first step, the atomic ratio of the graphene oxide to the boron powder is (1-2): 4. the target product of the invention is boron carbide B₄And C, controlling the atomic ratio of the graphene oxide to the boron powder within the range, effectively avoiding the phenomenon of uneven reaction caused by uneven mixing and stirring of the graphene oxide and the boron powder, and ensuring the generation of boron carbide nano powder.

The preparation method of the boron carbide nanopowder is characterized in that in the first step, the boron powder is nano boron powder, and in the third step, the high-temperature heat treatment is performed under the condition of a reducing atmosphere. The particle size of the nano boron powder is smaller, the surface area is larger, and the contact area with the graphene oxide is larger, so that smooth reaction is facilitated, the graphene oxide coated boron powder with more uniform coating is obtained, after most of oxygen is removed through low-temperature phase formation, residual oxygen can be directly reduced and removed under the reducing atmosphere condition, and finally the boron carbide nano powder is directly obtained.

The preparation method of the boron carbide nanopowder is characterized in that in the third step, the reducing atmosphere is Ar and H₂And CH₄A mixed gas of composition wherein Ar, H₂And CH₄Is 50: (30-49): (1-20). The mixed gas with the composition further promotes the deoxidation of the preformed boron carbide into B₄C, nano powder; meanwhile, in the high-temperature heat treatment process, CH in the mixed gas₄The carbon is generated by cracking, the shortage of carbon source caused by graphene consumption is made up, the removal of residual oxygen in preformed boron carbide is promoted, the boron carbide is formed by carbon deposited on the B, and the B is further ensured₄And C, generating nano powder.

Preparation method of boron carbide nanopowderThe method is characterized in that the boron powder in the step one is non-nano boron powder, the preformed boron carbide in the step three is firstly subjected to ball milling treatment for 1-5 h under the condition that the speed is 200-400 rpm, carbon powder is supplemented in the ball milling treatment process, and then the boron powder is placed in a carbon tube furnace with the vacuum degree of 10^-2Pa～10^-4Carrying out high-temperature heat treatment under the vacuum condition of Pa; the mass ratio of the carbon powder to the preformed boron carbide is 0.2: 1. The common non-nano boron powder is adopted, so that the preparation cost is reduced, the preparation efficiency is improved, meanwhile, as the particles of the non-nano boron powder (mainly micron-sized boron powder) are larger, the size of the preformed boron carbide is reduced through ball milling, carbon powder is supplemented in the ball milling, then the carbon is used for reduction in the vacuum heat treatment process, the residual oxygen in the preformed boron carbide after the ball milling is further consumed, and the boron carbide nano powder is obtained.

The preparation method of the boron carbide nanopowder is characterized in that in the step one, the inert gas is nitrogen. The most common nitrogen is used as inert gas, so that the method is convenient and efficient, is easy to realize, and simultaneously reduces the preparation cost.

The preparation method of the boron carbide nanopowder is characterized in that in the step one, the mechanical stirring speed is 500-20000 rpm, and the reaction time is 5-60 min. Stirring in the early stage of the reaction to promote the graphene oxide and the boron powder to be uniformly mixed, and stirring in the later stage to improve the single-layer rate of the graphene oxide and enable the graphene oxide to be uniformly coated around the boron powder, so that the mechanical stirring of the process parameters promotes the graphene oxide and the boron powder to be fully contacted, and the graphene oxide is favorably coated around the boron powder to form a B-O-C mixture.

The preparation method of the boron carbide nanopowder is characterized in that in the second step, the inert gas is nitrogen or argon. The preferred inert gas is readily available.

The preparation method of the boron carbide nanopowder is characterized in that the heating rate adopted by the low-temperature heat treatment in the second step is 1-5 ℃/min. The optimized low-temperature heat treatment temperature rise rate effectively avoids severe separation of graphene oxideExplaining the oxygen release and causing the separation of the boron powder coated by the graphene oxide in the B-O-C mixture, the subsequent B is ensured₄And C, smoothly generating the nano powder.

Compared with the prior art, the invention has the following advantages:

1. according to the invention, the graphene oxide is coated around the boron powder by utilizing the high specific surface area and the high reaction activity of the graphene oxide to form a B-O-C mixture, then the resultant reaction of low-temperature and high-temperature heat treatment is carried out in sequence, and oxygen is removed in sequence to prepare the boron carbide nano powder, so that the oxidation of the boron powder is effectively avoided, the introduction of metal impurities is avoided, the impurity content is reduced, the purity of the boron carbide is improved, meanwhile, the resultant reaction of the boron carbide is realized at a lower temperature in a shorter time, the process difficulty is reduced, and the preparation cost is reduced.

2. According to the invention, the nano boron powder is used as a raw material, so that the graphene oxide is promoted to be fully contacted with the boron powder, and the boron carbide powder with good and uniform appearance is obtained.

3. According to the invention, the boron carbide powder is directly obtained through the phase reaction of low-temperature and high-temperature heat treatment, post-treatment processes such as crushing, grinding, acid washing, separation and purification and the like are not needed, the process flow is greatly shortened, the environmental pollution is avoided, and all the used devices are general devices and are easy to realize industrialization.

4. The invention adopts methane-containing gas as reducing atmosphere for high-temperature heat treatment, and utilizes CH₄The carbon is generated by cracking, the shortage of carbon source caused by graphene consumption is made up, the removal of residual oxygen in preformed boron carbide is promoted, and the condition that B is generated is further ensured₄And C, generating nano powder.

The technical solution of the present invention is further described in detail by the accompanying drawings and examples.

Drawings

FIG. 1 is a scanning electron micrograph of boron carbide nanopowder prepared in example 1 of the present invention.

FIG. 2 is an X-ray diffraction pattern of the boron carbide nanopowder prepared in example 1 of the present invention.

Detailed Description