Preparation method of nano WN powder material

Abstract

The invention discloses a preparation method of a nano tungsten nitride powder material, and belongs to the technical field of preparation of transition metal nitride materials. The preparation method comprises the following steps: by taking tungsten powder as a tungsten source and sodium azide and melamine as nitrogen sources, grinding and mixing the tungsten powder and the sodium azide according to a mass ratio of 5: 1, and tabletting the mixture and the melamine by using a hydraulic machine respectively, so as to obtain the composite material. The method comprises the following steps: preparing a cylindrical shape by wrapping a cylindrical sheet formed by pressing a mixture of tungsten powder and sodium azide with two pieces of melamine according to the size of a synthesis cavity, putting the cylindrical raw material into a heating container, putting the heating container into the synthesis cavity, keeping the temperature and pressure for 10 minutes at the pressure of 3.0-5.0 GPa and the temperature of 1500-1800 DEG C, cooling and relieving the pressure, and finally putting a sample into diluted hydrochloric acid for cleaning, and preparing the nano tungsten nitride powdery material. The technological process is simple, and the preparation period and the sintering time are shortened; air pollution and resource waste are avoided; the prepared nano powdery material has the characteristics of high purity, easiness in impurity removal and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of transition metal nitrides, and relates to a high-temperature and high-pressure preparation method of nano tungsten nitride (WN). Background Art

[0002] Transition metal nitrides are widely used in protective coatings, diffusion barriers in microelectronic systems, optical decorative coatings, catalytic materials, and multifunctional hard materials due to their high hardness, high thermal stability, wear resistance, corrosion resistance, and good catalytic properties. Among transition metal nitrides, tungsten nitride is considered to have higher hardness and better catalytic properties. However, the synthesis of pure-phase tungsten nitride is very difficult. It is difficult to synthesize pure-phase tungsten nitride by conventional methods. Commonly used methods for synthesizing tungsten nitride include high-temperature nitridation (reacting highly reactive nitrogen sources such as NH3, N2H4, etc. with tungsten or tungsten oxides), magnetron sputtering, and chemical vapor deposition. Transition metal nitrides prepared by these methods have disadvantages such as long reaction time, harsh conditions, high cost, generation of waste gas pollution, and impurities in the synthesized samples. Currently reported tungsten nitrides include: r-W2N3, h-W2N3, W2N, W3N4, c-WN, and h-WN. Most of the synthesized tungsten nitride materials are non-pure-phase materials with impurities. Pure-phase tungsten nitride can be synthesized by using sodium tungstate and boron nitride as raw materials through a high-temperature and high-pressure method (Wang S, et al. Synthesis, Crystal Structure, and Elastic Properties of Novel Tungsten Nitrides

[0003] [J]. Chemistry of Materials, 2012, 24, 15: 3023–3028. DOI: 10.1021 / cm301516w.), but the synthesis process is complex, and there is unreacted boron nitride in the synthesized samples, which needs to be removed by boiling with acid solution and alkali solution at high temperature. It is very difficult to remove boron nitride completely. In the high-temperature and high-pressure method, we have tried to synthesize tungsten nitride by sandwiching a piece of W2N3 between two pieces of melamine, and successfully synthesized pure-phase bulk tungsten nitride, but the synthesis process is complex. It is necessary to first synthesize W2N3 and then use W2N3 as a raw material to synthesize bulk WN. In addition, the amount of WN synthesized each time is too small, and it can only be used to study the properties of WN from a scientific research perspective, which is not conducive to industrial applications. When tungsten nitride is applied, it often needs to be in powder form, and nanostructured materials can exhibit excellent properties in fields such as catalysis. Therefore, if nano-powder pure-phase tungsten nitride can be synthesized, it has important value for the industrial application of tungsten nitride.

[0004] Due to the above problems in the prior art, it is very difficult to obtain pure-phase WN powder with a nanostructure. Therefore, there is an urgent need in the art for a method that can synthesize pure-phase WN powder with a nanostructure and has the characteristics of a short synthesis period and a simple impurity removal process. SUMMARY OF THE INVENTION

[0005] The object of the present invention is to provide a method for preparing pure-phase WN with a nanosheet structure to solve the above problems. In the present invention, tungsten powder, sodium azide, and melamine are used as reactants. A small amount of sodium azide and tungsten powder are mixed and pressed into a cylindrical sheet, which is sandwiched between cylindrical sheets made of melamine, and then placed in a six-sided top hydraulic press for high-temperature and high-pressure synthesis. There are fewer sodium ions in the synthesized product, which can be removed by washing with dilute hydrochloric acid. The synthesized tungsten nitride has a nanosheet structure and is a pure phase. The material synthesized by the present invention has the characteristics of a short synthesis time, pure samples, and a simple impurity removal process. This material can be used as a multifunctional material or a catalytic material in industrial production.

[0006] The specific technical solution of the present invention is described as follows.

[0007] A method for preparing pure-phase nanosheet tungsten nitride (WN) uses melamine with a purity of 99.99%, sodium azide with a purity of 99.99%, and tungsten powder with a purity of 99.99% as raw materials. Through the technological processes of raw material mixing, briquetting, assembly, high-temperature and high-pressure synthesis, cooling and pressure relief, and impurity removal, tungsten nitride nanopowder materials are obtained; the so-called raw material mixing refers to grinding and mixing tungsten powder and sodium azide powder in an agate mortar for one hour according to a mass ratio of 5:1. The so-called raw material briquetting refers to using a hydraulic press to press the mixture powder (tungsten and sodium azide powder) and melamine into circular sheets with a diameter of 4 mm and a thickness of 1 mm and circular sheets with a diameter of 4 mm and a thickness of 0.75 mm respectively according to the size of the synthesis cavity. Two circular sheets pressed with melamine wrap one circular sheet pressed with the mixture powder to form a sandwich structure as the reaction raw material; the so-called assembly is to load the sandwich-structured cylindrical raw material into a heating container and place it in the synthesis cavity; the so-called high-temperature and high-pressure synthesis is to keep the pressure at 3.0 - 5.0 GPa and the temperature at 1500 - 1800 °C for heat preservation and pressure holding for 10 minutes; the so-called cooling and pressure relief is to stop power supply for heating and let the assembled block cool naturally to room temperature, and then relieve the pressure; the so-called impurity removal is to soak and mix the generated tungsten nitride powder in dilute hydrochloric acid, centrifuge and separate it in a centrifuge, and then wash it by centrifugation with deionized water. There are only a small amount of sodium impurities in this reaction product, and after the decomposition reaction of melamine, it naturally separates from the generated tungsten nitride.

[0008] The experiments of the present invention can be completed on a domestic SPD-6×600 type cubic press. The experimental results show that a pressure of 5 GPa and a temperature of 1600 °C are the optimal synthesis conditions for pure-phase tungsten nitride. The optimal synthesis temperature of tungsten nitride is lower than that of other nitrides. This is because sodium azide and melamine as nitrogen sources can provide highly active nitrogen ions, reducing the reaction temperature. It can be seen from Examples 1 to 2 that when the temperature increases, the tungsten nitride samples produced show grain growth. The thickness of the nanosheets grows from about 93 nm to about 280 nm. Continuing to increase the temperature will result in the growth of grains into large grains. Therefore, at a pressure of 5 GPa, 1600 °C is the optimal condition for synthesizing nano-tungsten nitride. By comparing Example 1 and Example 3, it can be seen that tungsten nitride can also be synthesized at a pressure of 3 GPa and a temperature of 1500 °C. However, under these conditions, there is grain boundary adhesion between the grains of the synthesized tungsten nitride, and the grains are relatively large. Since pressure can inhibit grain growth, the lower the pressure, the larger the grains of the synthesized sample. And at lower pressures, nitrogen ions are more likely to diffuse into tungsten elements, the nitrogen ions are released rapidly, the reaction is rapid, and there are defects between the grain boundaries. Therefore, 5 GPa is a relatively superior synthesis condition. Therefore, the optimal synthesis pressure for pure-phase tungsten nitride is 5.0 GPa, and the optimal synthesis temperature is 1600 °C. Description of the Drawings

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0010] Figure 1 Assembly diagram for synthesizing samples;

[0011] Figure 2 XRD pattern of the nano-tungsten nitride prepared in Example 1;

[0012] Figure 3 Scanning electron microscope image of the nano-tungsten nitride prepared in Example 1;

[0013] Figure 4 XRD pattern of the tungsten nitride prepared in Example 2;

[0014] Figure 5 Scanning electron microscope image of the tungsten nitride prepared in Example 2;

[0015] Figure 6 XRD pattern of the tungsten nitride prepared in Example 2;

[0016] Figure 7 Scanning electron microscope image of the tungsten nitride prepared in Example 2; Specific Embodiment

[0017] An embodiment of the present invention provides a method for preparing nano-powder tungsten nitride. Using tungsten powder, sodium azide and melamine as raw materials, nano-tungsten nitride powder materials are prepared through a process of raw material grinding and mixing, briquetting, assembly, high-temperature and high-pressure synthesis, and cooling and pressure relief. Among them, the raw material grinding and mixing is to grind and mix tungsten powder and sodium azide powder in an agate mortar; the briquetting is to use a cold press to press melamine into a cylindrical raw material with a diameter of 4 mm and a thickness of 0.75 mm, and use a cold press to press the mixed tungsten powder and sodium azide into a cylindrical raw material with a diameter of 4 mm and a thickness of 1 mm, and place it in a synthesis tool as a reaction raw material; the assembly is to load the cylindrical raw material into a heating container and place it in a synthesis cavity; the high-temperature and high-pressure synthesis is to put the sample into a six-sided top hydraulic press and keep it at a pressure of 3.0 GPa to 5.0 GPa and a temperature of 1500 °C to 1800 °C for heat preservation and pressure holding for 10 minutes; the cooling and pressure relief is to stop the power-on heating and let the assembled block cool naturally to room temperature, and then reduce the pressure to atmospheric pressure. Figure 1 It is a schematic assembly diagram of the present invention.

[0018] The room temperature in the present invention refers to 25 ± 2 °C.

[0019] The embodiments of the present invention are all completed on a domestic SPD-6×600 type six-sided top press.

[0020] In order to ensure the uniformity of the temperature in the synthesis cavity during the synthesis of the sample, the heating method adopted in the present invention is the side heating of an electrically heated graphite tube. In order to ensure that the sample does not react with the graphite tube that generates heat, the cavity for synthesizing the sample is protected by hexagonal boron nitride.

[0021] Example 1

[0022] Using melamine with a purity of 99.99%, sodium azide with a purity of 99.99% and tungsten with a purity of 99.99% as raw materials. The tungsten powder and sodium azide powder are ground and mixed in an agate mortar according to a mass ratio of 5:1 to form a mixture. The mixture of tungsten powder and sodium azide and melamine are respectively pressed into a disc with a diameter of 4 mm and a thickness of 1 mm and a disc with a diameter of 4 mm and a thickness of 0.75 mm by a cold press according to the size of the synthesis cavity. Two discs pressed with melamine are used to wrap a disc pressed with the mixture powder to form a sandwich-structured sample and loaded into the synthesis cavity. Graphite tube heating is used in the assembled cavity, pyrophyllite is used as a heat-insulating material, and the cavity is protected by hexagonal boron nitride. (The schematic assembly diagram is as Figure 1As shown in the figure, the synthesis pressure was 5.0 GPa, the synthesis temperature was 1600 °C, the heat preservation and pressure holding time was 10 minutes. After stopping heating, the sample was naturally cooled to room temperature and then depressurized. The specific X-ray diffraction (XRD) results of tungsten nitride prepared under this condition are shown in Figure 2 , and the scanning electron microscope (SEM) image of tungsten nitride prepared under this condition is as shown in Figure 3 . It can be seen from the two figures that the synthesized sample is a pure-phase sample, and the sample is a nano-sheet structure with a thickness of about 93 nm.

[0023] Example 2

[0024] Using the same raw materials as in Example 1, after pressing the powder sample into shape, the same assembly as in Example 1 was used. The synthesis pressure was 5.0 GPa, the synthesis temperature was 1800 °C, the pressure holding and heat preservation time was 10 minutes. After stopping heating, the sample was naturally cooled to room temperature and then depressurized. From the XRD results ( Figure 4 ), it can be seen that a pure-phase tungsten nitride material can still be prepared under this condition. However, from the SEM pictures ( Figure 5 ), it can be seen that the synthesized sample shows the situation of grain adhesion and growth. Combining the above Example 1, it can be known that increasing the temperature is beneficial to the growth of grains and is not conducive to synthesizing nano-structured tungsten nitride.

[0025] Example 3

[0026] Using the same raw materials as in Example 1, after pressing the powder sample into shape, the same assembly as in Example 1 was used. The synthesis pressure was 3.0 GPa, the synthesis temperature was 1500 °C, the pressure holding and heat preservation time was 10 minutes. After stopping heating, the sample was naturally cooled to room temperature and then depressurized. The sample synthesized under this condition is also a pure-phase material, but it can be seen from the XRD pattern that there are defects. The specific XRD results are shown in Figure 6 . Figure 7 This is the SEM image of the synthesized sample. It can be seen from the figure that the sample grains grow and there are grain boundary adhesions between the grains. Therefore, the optimal synthesis pressure for synthesizing pure-phase tungsten nitride is 5.0 GPa, and the optimal synthesis temperature is 1600 °C.

[0027] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should fall within the protection scope determined by the claims of the present invention.

Claims

1. A tungsten nitride nanopowder material, characterized in that, The material has a nano-sheet structure, and the thickness of the nano-sheets is about 93 nm. There is no growth relationship between the nano-sheets.

2. The preparation method of the tungsten nitride nanomaterial according to claim 1, characterized in that, Using tungsten powder as a nitrogen source, and melamine and sodium azide as nitrogen sources, a nano-sheet tungsten nitride powder material is prepared through a process of raw material mixing, briquetting, assembly, high-temperature and high-pressure synthesis, cooling and pressure relief, and impurity removal; the raw material mixing refers to grinding and mixing tungsten powder and sodium azide in an agate mortar according to a mass ratio of 5:1; the raw material briquetting refers to using a hydraulic press to make the raw materials into a cylindrical shape with a sandwich structure (two pieces of melamine wrapping a cylindrical sheet made of a mixture of tungsten powder and sodium azide mixed powder) according to the size of the synthesis cavity; the assembly is to load the pressed cylindrical raw materials into a heating container and place it in the synthesis cavity; the high-temperature and high-pressure synthesis is to keep the pressure at 3.0 - 5.0 GPa and the temperature at 1500 - 1800 °C for heat preservation and pressure holding for 10 minutes; the cooling and pressure relief is to stop the power supply for heating and let the assembled block cool naturally to room temperature, and then relieve the pressure; the impurity removal is to soak and dissolve the synthesized powder sample with dilute hydrochloric acid and centrifuge and wash it.

3. The preparation method of the tungsten nitride nanomaterial according to claim 2, characterized in that, Using sodium azide, which is relatively easy to remove impurities, as an auxiliary nitrogen source and melamine as the main nitrogen source, the carbon powder generated by the reacted melamine is naturally separated from the generated tungsten nitride, without carbon pollution.

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