阅读说明：本技术 一种碳热还原燃烧前驱物合成纳米wc粉末的方法 (Method for synthesizing nano WC powder by using carbon thermal reduction combustion precursor ) 是由 秦明礼 吴昊阳 王倩玉 丁旺旺 贾宝瑞 曲选辉 于 2019-12-04 设计创作，主要内容包括：一种碳热还原燃烧前驱物合成纳米WC粉末的方法,属于粉末冶金纳米粉末制备技术领域。具体制备方法为：以钨酸铵、氧化剂、燃料为原料,在保护气氛中通过溶液燃烧合成反应制备出纳米针状紫钨,然后将紫钨粉末置于炉中保温,紫钨被氧化成WO<Sub>3</Sub>。将制得的WO<Sub>3</Sub>与碳黑按照一定配比在球磨机中机械混合得到均匀的混合前驱体粉末。最后,将混合粉末在真空炉中进行原位还原和碳化反应,成功制得纳米WC粉末。本方法设计出一种特殊形貌的WO<Sub>3</Sub>—纳米棒状WO<Sub>3</Sub>,解决了颗粒状WO<Sub>3</Sub>在球磨过程中容易发生团聚的问题。本方法制备的纳米WC粉末性能优异,粒径小、粒度均匀、分散性好、成分和粒径能够精确控制,并且本方法工艺简单、耗能低、效率高、成本低,适合大规模生产。(A method for synthesizing nano WC powder by using a carbon thermal reduction combustion precursor belongs to the technical field of powder metallurgy nano powder preparation. The preparation method comprises the following steps: preparing nano needle-shaped purple tungsten by using ammonium tungstate, oxidant and fuel as raw materials through solution combustion synthesis reaction in protective atmosphere, then placing the purple tungsten powder in a furnace for heat preservation, and oxidizing the purple tungsten into WO 3 . The obtained WO 3 Mechanically mixing the precursor powder with carbon black in a ball mill according to a certain proportion to obtain uniform mixed precursor powder. And finally, carrying out in-situ reduction and carbonization reaction on the mixed powder in a vacuum furnace to successfully prepare the nano WC powder. The method designs WO with special appearance 3 -nanorod shaped WO 3 Solve the problem of granular WO 3 The problem of agglomeration easily occurs during the ball milling process. Prepared by the methodThe nanometer WC powder has the advantages of excellent performance, small particle size, uniform particle size, good dispersibility, accurate control of components and particle size, simple process, low energy consumption, high efficiency and low cost, and is suitable for large-scale production.)

1. A method for synthesizing nano WC powder by using a carbon thermal reduction combustion precursor is characterized by comprising the following preparation steps:

(1) method for preparing nano needle-like purple tungsten by solution combustion synthesis method

The preparation process takes a tungsten source, a fuel and an oxidant as raw materials, and the raw materials are mixed according to a molar ratio of 1: (30-40): (10-15) mixing, dissolving in deionized water, fully dissolving to prepare an aqueous solution, heating the solution on a resistance furnace until a combustion reaction occurs, carrying out the whole combustion process in a protective atmosphere, and finally grinding to obtain the nano needle-like purple tungsten with the diameter of 50-100 nm and the length of 1-2 microns;

(2) preparation of nano rod-like yellow tungsten by oxidation of purple tungsten

Placing the nano acicular purple tungsten powder prepared in the step (1) in a furnace tube in a constant temperature area for oxidation, wherein the heating rate is 5-10 ℃/min, introducing Ar in the heating process, heating to 500-650 ℃, preserving heat for 0.5-3 h, stopping introducing Ar in the heat preservation process, starting oxidizing the purple tungsten in the air, and cooling along with the furnace after the heat preservation is finished to obtain single-phase nano rodlike yellow tungsten with the diameter of 100-200 nm and the length of 200-600 nm;

(3) preparation of precursor by ball milling and mixing powder

Taking the nano-rod-shaped yellow tungsten prepared in the step (2) and carbon black with the particle size of 30-40 nm as raw materials, and carrying out carbon blending according to the carbon blending amount of 16.5-17.5 wt.%; uniformly mixing the raw materials by using a low-energy ball mill, taking deionized water as a grinding medium, and simultaneously adding a surfactant, wherein the mass ratio of grinding balls to powder is 10: 1-12: 1, the diameter of the grinding balls is 2-5 mm, the rotating speed of the ball mill is 100-200 r/min, the ball milling time is 2-5 h, and the powder is uniformly mixed at a nanometer level after ball milling;

(4) carbothermic reduction

Putting the mixed precursor powder obtained in the step (3) into a vacuum furnace for reduction and carbonization reaction, and introducing N firstly₂Raising the temperature to 750 ℃ at a heating rate of 7-9 ℃/min, and preserving the heat for 1-2 h; and vacuumizing, raising the temperature to 850-1000 ℃ at the heating rate of 10-15 ℃/min, and keeping the temperature for 1-3 h, wherein the vacuum degree is below 10 Pa.

2. The method for synthesizing nano WC powder by carbothermic reduction of the combustion precursor according to claim 1, wherein the tungsten source in step (1) is any one of ammonium metatungstate and ammonium paratungstate.

3. The method for synthesizing nano WC powder according to claim 1, wherein the oxidizing agent in step (1) is any one of ammonium nitrate and nitric acid.

4. The method for synthesizing nano WC powder by using the carbothermic combustion precursor as claimed in claim 1, wherein the fuel in step (1) is either one or both of glycine and citric acid, and the molar ratio of the two is (10-12): 1.

5. the method for synthesizing nano WC powder by carbothermic reduction of the precursor according to claim 1, wherein the combustion reaction in step (1) is performed in a protective atmosphere by introducing Ar or N with a gas flow rate of 0.2L/min to 0.5L/min from top to bottom₂Air in the beaker is fully discharged, additional consumption of fuel is avoided, and accurate proportioning of the raw materials is realized.

6. The method for synthesizing nano WC powder by carbothermic combustion precursor according to claim 1, wherein the surfactant is added in an amount of 0.2 wt.% to 2 wt.% in step (3), and the surfactant is any one of high molecular polymer, high molecular weight block copolymer, stearyl alcohol, polyurethane, ammonium polyacrylate salt, and sodium polyacrylate.

Technical Field

The invention belongs to the technical field of powder metallurgy nano powder preparation, and particularly relates to WO with a special appearance₃Powder, a novel process for the preparation of nano WC powder.

Background

The nanocrystalline WC-Co hard alloy can effectively overcome the problems of mutual contradiction between hardness and strength, large brittleness, processing softening and the like in the traditional hard alloy, has the performances of high hardness, high strength, high wear resistance, high toughness, high thermal conductivity, excellent thermal shock resistance, oxidation resistance and the like, is widely applied to the fields of aerospace, automobile industry, precision manufacturing, electronic information, national defense and military industry and the like, and becomes a tool and a structural material which cannot be replaced in high and new technology industry.

The preparation of high-performance nano WC powder is the basis and key of the development of nanocrystalline WC-Co hard alloy. At present, due to the difficult technical problem of preparation, only individual enterprises in several countries such as the United states, Japan, Sweden and the like in the world can realize large-scale industrial production of the nanometer WC powder, and the requirements of the international market can not be met. In recent decades, many countries including China need to import nano WC powder from these enterprises in high quantities every year. Therefore, the situation that few foreign manufacturers control the international nanometer tungsten carbide powder market is broken through, and research and development of the preparation technology of the nanometer WC powder with the independent intellectual property rights are extremely important research and development directions and hot subjects.

The traditional industrial preparation method of WC powder is to directly carburize tungsten powder and carbon in a hydrogen atmosphere for 2-10 hours, and the method is complex in process, long in time consumption and high in carbonization temperature (1400-1600 ℃), so that the preparation of nano WC powder is restricted. In recent years, some effective methods for preparing nano WC powder have been reported, including carbothermic method, mechanical alloying method, sol-gel method, plasma method, and spray conversion method. Wherein the carbothermic method has the advantages of convenient operation, low cost and heavy weightGood renaturation and the like, no water vapor is generated in the reduction process, the growth phenomenon of W particles is avoided, and the method is considered to be an ideal method for preparing the nano WC powder. According to literature reports, one carbothermic process that is most efficient typically involves two steps: firstly, tungsten oxide and carbon are mixed by ball milling, and then furnace heat treatment is carried out. However, since tungsten oxide particles are highly likely to agglomerate during ball milling, WO cannot be obtained₃Precursor powder uniformly mixed with C causes insufficient carbonization in the subsequent carbothermic reduction process to generate carbon-deficient phase W₂C; and the existence of the aggregate easily causes the phenomenon of abnormal growth of particles in the subsequent heat treatment process, thereby influencing the performance of the prepared nano WC powder. Therefore, aiming at the limitation of the current technology for preparing nano WC powder by a carbothermic method, the improvement is carried out, and the finding of a novel method for preparing high-performance nano WC powder has important theoretical value and practical application significance.

Disclosure of Invention

The invention aims to design a WO with a special appearance according to the problems of insufficient carbonization and easy abnormal growth of powder particles in the existing technology for preparing nano WC powder by a carbothermic method₃-nanorod shaped WO₃And the ball milling process is improved to obtain nanometer precursor mixed powder with good uniformity, so that a method for quickly preparing nanometer WC powder in a large scale at low cost is developed, and the prepared nanometer WC powder has excellent performance, small particle size, uniform granularity, high purity and good dispersibility, and is suitable for large-scale production.

A method for synthesizing nano WC powder by using a carbon thermal reduction combustion precursor comprises the following specific steps:

(1) preparing nano needle-shaped purple tungsten by a solution combustion synthesis method: the preparation process takes a tungsten source, a fuel and an oxidant as raw materials, and the raw materials are mixed according to a molar ratio of 1: (30-40): (10-15) mixing, dissolving in deionized water, fully dissolving to prepare aqueous solution, heating the solution on a resistance furnace until combustion reaction occurs, carrying out the whole combustion process in a protective atmosphere, and finally grinding to obtain the nano needle-like purple tungsten with the diameter of 50-100 nm and the length of 1-2 microns.

(2) Preparing nano rod-shaped yellow tungsten by oxidizing purple tungsten: and (2) placing the nano acicular purple tungsten powder prepared in the step (1) in a constant temperature area of a furnace tube for oxidation, wherein the heating rate is 5-10 ℃/min, introducing Ar in the heating process, heating to 500-650 ℃, preserving heat for 0.5-3 h, stopping introducing Ar in the heat preservation process, starting oxidizing the purple tungsten in the air, and cooling along with the furnace after heat preservation is finished to obtain the single-phase nano rodlike yellow tungsten with the diameter of about 100-200 nm and the length of about 200-600 nm.

(3) Preparing a precursor by ball milling and mixing powder: taking the nano-rod-shaped yellow tungsten prepared in the step (2) and carbon black with the particle size of 30-40 nm as raw materials, and carrying out carbon blending according to the carbon blending amount of 16.5-17.5 wt.%; uniformly mixing the raw materials by using a low-energy ball mill, taking deionized water as a grinding medium, and simultaneously adding a surfactant, wherein the mass ratio of grinding balls to powder is 10: 1-12: 1, the diameter of the grinding balls is 2-5 mm, the rotating speed of the ball mill is 100-200 r/min, the ball milling time is 2-5 h, and the powder is uniformly mixed at a nanometer level after ball milling.

(4) C, carbothermic reduction: placing the mixed precursor powder obtained in the step (3) in a vacuum furnace for reduction and carbonization, introducing N2, raising the temperature to 750 ℃ at the heating rate of 7-9 ℃/min, and keeping the temperature for 1-2 h; and vacuumizing, raising the temperature to 850-1000 ℃ at the heating rate of 10-15 ℃/min, and keeping the temperature for 1-3 h, wherein the vacuum degree is below 10 Pa.

Further, the tungsten source in the step (1) is any one of ammonium metatungstate and ammonium paratungstate.

Further, the oxidant in the step (1) is any one of ammonium nitrate and nitric acid.

Further, the fuel in the step (1) is one or two of glycine and citric acid, and the molar ratio of the glycine to the citric acid is (10-12): 1.

further, the combustion reaction process in the step (1) is carried out in a protective atmosphere by introducing Ar or N with the airflow velocity of 0.2L/min-0.5L/min from top to bottom₂Air in the beaker is fully discharged, additional consumption of fuel is avoided, and accurate proportioning of the raw materials is realized.

Further, the addition amount of the surfactant in the step (3) is 0.2 wt.% to 2 wt.%, and the surfactant is any one of a high molecular polymer, a high molecular weight block copolymer, stearyl alcohol, polyurethane, an ammonium polyacrylate salt, sodium polyacrylate, and the like.

The technique of the invention has the following advantages:

(1) solves the problem of easy agglomeration of powder in the ball milling process. By adopting the designed nano-rod-shaped WO₃The powder is used as a tungsten source and added with a surfactant, thereby effectively avoiding WO₃The particles are easy to agglomerate in the ball milling process, and WO is obtained₃The precursor powder uniformly mixed with C provides a precondition for the preparation of high-performance nano WC powder.

(2) Nanorod-shaped WO₃And the carbon black belong to nanoscale powder, and uniform nanometer precursor powder can be obtained through low-energy and short-time ball milling, so that the diffusion distance of atoms is favorably shortened, the carbothermic reduction reaction temperature is obviously reduced, the heat preservation time is shortened, and the reaction efficiency is improved.

(3) The nano WC powder prepared by the method has the advantages of high purity, small particle size, uniform particle size distribution, good dispersibility and the like. And the morphology, the particle size and the carbon content of the powder can be freely and accurately regulated and controlled by designing the reaction temperature, the reaction time and the carbon distribution amount.

(4) The preparation process of the precursor powder is pollution-free, and the protective atmosphere and vacuum are adopted in the carbothermic reduction process, so that the introduction of impurities is effectively avoided, and the contents of impurities such as Fe, Mo, NVR (chlorinated residues) and the like in the powder are effectively controlled.

(5) The raw materials of ammonium tungstate, oxidant, fuel and the like are common industrial raw materials, the preparation process has no special equipment requirement, the cost is low, the process flow is short, and the large-scale production can be rapidly realized.

Drawings

FIG. 1a is a prepared nano-rod shaped WO₃The SEM image of the powder is shown,

FIG. 1b is a prepared nanorod-like WO₃XRD pattern of the powder;

figure 2a is an SEM image of the nano WC powder prepared,

fig. 2b is an XRD pattern of the prepared nano WC powder.

Detailed Description