A method for preparing a nano-WN powder material

Abstract

The application discloses a preparation method of nano tungsten nitride powder material and belongs to the technical field of transition metal nitride material preparation. The preparation process is as follows: taking tungsten powder as a tungsten source and taking 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; respectively pressing the mixture and the melamine into tablets by using a hydraulic machine; wrapping two melamine tablets around one cylindrical tablet pressed by the mixture of the tungsten powder and the sodium azide into a cylindrical shape according to the size of a synthesis cavity; loading the cylindrical raw material into a heating container and placing the cylindrical raw material into the synthesis cavity; keeping the pressure at 3.0-5.0 GPa and the temperature at 1500-1800 DEG C for 10 minutes; cooling and unloading the pressure; finally, cleaning the sample in dilute hydrochloric acid to obtain the nano tungsten nitride powder material. The application has the advantages of simple technological process, shortened preparation period and sintering time, no air pollution and resource waste, and the prepared nano powder material has the characteristics of high purity and easy impurity removal.

Description

TECHNICAL FIELD

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

[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 and corrosion resistance and good catalytic properties. Among transition metal nitrides, tungsten nitride is considered to have higher hardness and better catalytic properties, but the synthesis of pure-phase tungsten nitride is very difficult. Pure-phase tungsten nitride is difficult to synthesize by conventional methods. Common methods for synthesizing tungsten nitride include high-temperature nitriding (using highly active nitrogen sources such as NH3 and N2H4 to react with tungsten or tungsten oxides), magnetron sputtering and vapor deposition. Transition metal nitrides prepared by these methods have the disadvantages of long reaction time, harsh conditions, high cost, 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 high-temperature and high-pressure method using sodium tungstate and boron nitride as raw materials (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 the synthesized sample contains unreacted boron nitride which needs to be removed by high-temperature boiling with acid and alkali solutions. Boron nitride is difficult to remove completely. In the high-temperature and high-pressure method, we tried to synthesize tungsten nitride by using two pieces of melamine sandwiching one piece of W2N3, and successfully synthesized pure-phase bulk tungsten nitride, but the synthesis process is complex, and W2N3 needs to be synthesized first as raw material to synthesize bulk WN. In addition, the amount of WN synthesized each time is too small, which can only be used for research on the properties of WN from the perspective of scientific research, and is not conducive to industrial application. Tungsten nitride is often used in powder form in applications, and nanostructured materials can exhibit excellent properties in the field of catalysis. Therefore, if nano-powder pure-phase tungsten nitride can be synthesized, it will have important value for the industrial application of tungsten nitride.

[0004] Since the prior art has the above problems, it is difficult to prepare the nanostructured pure-phase WN powder, and therefore, there is an urgent need in the field for a method capable of synthesizing the nanostructured pure-phase WN powder and having the characteristics of short synthesis period and simple impurity removal process. SUMMARY

[0005] The present application aims to provide a preparation method of nano-sheet structured pure-phase WN to solve the above problems. The present application uses tungsten powder, sodium azide and melamine as reactants, mixes a small amount of sodium azide and tungsten powder, presses into a cylindrical sheet, clamps it in a cylindrical sheet made of melamine, and puts it into a six-surface hydraulic press for high-temperature and high-pressure synthesis. The synthesized product has a small amount of sodium ions, which can be removed by washing with dilute hydrochloric acid. The synthesized tungsten nitride has a nano-sheet structure and is a pure phase. The synthesized material has the characteristics of short synthesis time, sample purity and simple impurity removal process, and can be applied in industrial production as a multifunctional material or a catalytic material.

[0006] The specific technical solutions of the present application are as follows.

[0007] A preparation method of pure-phase nano-sheet tungsten nitride (WN), which uses 99.99% purity melamine, 99.99% purity sodium azide and 99.99% purity tungsten powder as raw materials. The tungsten nitride nano-powder material is prepared through the 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 powder in a ratio of 5:1 in a agate mortar for one hour. The raw material briquetting refers to using a hydraulic press to press the mixed powder (tungsten and sodium azide powder) and melamine into a circular sheet with a diameter of 4mm and a thickness of 1mm and a circular sheet with a diameter of 4mm and a thickness of 0.75mm according to the size of the synthesis cavity. The two circular sheets pressed with melamine wrap a circular sheet pressed with the mixed powder to form a sandwich structure as the reaction raw material. The assembly is to put the sandwich structure cylindrical raw material into a heating container and put it into the synthesis cavity. The high-temperature and high-pressure synthesis is to keep the temperature at 1500-1800℃ and the pressure at 3.0-5.0GPa for 10 minutes. The cooling and pressure relief is to naturally cool the assembly block to room temperature after stopping the electric heating, and then release the pressure. The impurity removal is to soak the generated tungsten nitride powder in dilute hydrochloric acid, centrifuge in a centrifuge, and then centrifugally wash with deionized water. There is only a small amount of sodium impurities in the reaction product, and the melamine is naturally separated from the generated tungsten nitride after decomposition reaction.

[0008] The experiment of the present application can be completed on a domestic SPD-6x600 type six-surface press. The experimental results show that the pressure of 5 GPa and the temperature of 1600 DEG C are the best synthesis conditions of pure-phase tungsten nitride, and the best synthesis temperature of tungsten nitride is lower than that of other nitrides, because sodium azide and melamine as the nitrogen source can provide high-activity nitrogen ions, thereby reducing the reaction temperature. As can be seen from examples 1-2, when the temperature is increased, the generated tungsten nitride sample appears grain growth phenomenon, and the thickness of the nanosheet is grown from about 93 nm to about 280 nm. If the temperature is continuously increased, the grains will grow into large grains. Therefore, when the pressure is 5 GPa, 1600 DEG C is the optimal condition for synthesizing nano tungsten nitride. As can be seen from the comparison between example 1 and example 3, when the pressure is 3 GPa and the temperature is 1500 DEG C, tungsten nitride can also be synthesized, but under this condition, the grain boundaries of the synthesized tungsten nitride appear to be adhered, and the grains are large. Because the pressure can inhibit the growth of the grains, the lower the pressure, the larger the grains of the synthesized sample, and when the pressure is low, the nitrogen ions are more likely to diffuse into the tungsten element, 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 best synthesis pressure of pure-phase tungsten nitride is 5.0 GPa, and the best synthesis temperature is 1600 DEG C. BRIEF DESCRIPTION OF DRAWINGS

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings described in the following are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0010] Figure 1 Assembled diagram for synthesizing samples;

[0011] Figure 2 XRD diagram of the nano tungsten nitride prepared in example 1;

[0012] Figure 3 Scanning electron microscope diagram of the nano tungsten nitride prepared in example 1;

[0013] Figure 4 XRD diagram of the tungsten nitride prepared in example 2;

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

[0015] Figure 6 XRD diagram of the tungsten nitride prepared in example 2;

[0016] Figure 7 Scanning electron microscope diagram of the tungsten nitride prepared in example 2; DETAILED DESCRIPTION

[0017] The embodiment of the present application provides a preparation method of nano-powdered tungsten nitride, taking tungsten powder, sodium azide and melamine as raw materials, and performing the process of raw material grinding and mixing, briquetting, assembling, high-temperature and high-pressure synthesis and cooling and pressure releasing to obtain the nano tungsten nitride powder material. The raw material grinding and mixing is to grind and mix the tungsten powder and the sodium azide powder in an agate mortar; the briquetting is to use a cold press to press the melamine into a cylindrical raw material with a diameter of 4 mm and a thickness of 0.75 mm, and use the 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 put the cylindrical raw material into a synthesis tool as a reaction raw material; the assembling is to put the cylindrical raw material into a heating container and put it into a synthesis cavity; the high-temperature and high-pressure synthesis is to put the sample into a six-surface hydraulic press, and keep the temperature at 1500-1800 DEG C and the pressure at 3.0-5.0 GPa for 10 minutes; and the cooling and pressure releasing is to naturally cool the assembled block to room temperature after stopping the power heating, and then reduce the pressure to normal pressure. Figure 1 The assembling schematic diagram of the present application.

[0018] The room temperature of the present application refers to 25±2 DEG C.

[0019] The embodiment of the present application is completed on a domestic SPD-6x600 type six-surface press.

[0020] In order to ensure the uniformity of the temperature of the synthesis cavity during the synthesis of the sample, the present application adopts the side heating type graphite tube power heating. In order to ensure that the sample does not react with the graphite tube generating heat, the cavity of the synthesized sample adopts hexagonal boron nitride protection.

[0021] Embodiment 1

[0022] Take the melamine with a purity of 99.99%, the sodium azide with a purity of 99.99% and the tungsten with a purity of 99.99% as raw materials. Grind and mix the tungsten powder and the sodium azide powder in an agate mortar according to a mass ratio of 5:1 to form a mixture, use a hydraulic press to press the mixture of the tungsten powder and the sodium azide and the melamine into a circular sheet with a diameter of 4 mm and a thickness of 1 mm and a circular sheet with a diameter of 4 mm and a thickness of 0.75 mm respectively by using a cold press. Put the two circular sheets pressed by the melamine to wrap the circular sheet pressed by the mixture powder to form a sandwich structure sample into the synthesis cavity. Use a graphite tube to heat the assembled cavity, use a talc to do the heat preservation material, and use hexagonal boron nitride to protect the cavity, (the assembling schematic diagram is as shown in the figure) Figure 1The synthesis pressure is 5.0 GPa, the synthesis temperature is 1600 ℃, the holding time is 10 minutes, the sample is naturally cooled to room temperature after stopping heating, and then the pressure is released. The specific X-ray diffraction (XRD) results of the tungsten nitride prepared under the above conditions are shown in Figure 2 The scanning electron microscope (SEM) images of the tungsten nitride prepared under the above conditions are shown in Figure 3 As can be seen from the two figures, the synthesized sample is a pure phase sample, and the sample is a nanosheet structure with a thickness of about 93 nm.

[0023] Example 2

[0024] The same raw materials as in Example 1 are used, the powder sample is pressed and formed, and then the same assembly as in Example 1 is used. The synthesis pressure is 5.0 GPa, the synthesis temperature is 1800 ℃, the holding time is 10 minutes, the sample is naturally cooled to room temperature after stopping heating, and then the pressure is released. As can be seen from the XRD results Figure 4 , pure phase tungsten nitride material can still be prepared under the above conditions, but as can be seen from the SEM images Figure 5 , the synthesized sample shows grain adhesion and growth. According to Example 1, it can be seen that increasing the temperature is beneficial to the growth of the grains, and is not conducive to the synthesis of nanostructured tungsten nitride.

[0025] Example 3

[0026] The same raw materials as in Example 1 are used, the powder sample is pressed and formed, and then the same assembly as in Example 1 is used. The synthesis pressure is 3.0 GPa, the synthesis temperature is 1500 ℃, the holding time is 10 minutes, the sample is naturally cooled to room temperature after stopping heating, and then the pressure is released. The sample synthesized under the above conditions is also a pure phase material, but as can be seen from the XRD pattern, there are defects. The specific XRD results are shown in Figure 6 . Figure 7 The SEM images of the synthesized sample are shown in the figure. As can be seen from the figure, the grains grow, and there is grain boundary adhesion 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 ℃.

[0027] The above-described examples only describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art should fall within the protection scope of the claims of the present application.

Claims

1. A method for producing a nano tungsten nitride material, characterized in that, The nanometer sheet-shaped tungsten nitride powder material is prepared by the process of raw material mixing, briquetting, assembling, high-temperature and high-pressure synthesis, cooling and pressure releasing and impurity removing; the raw material mixing is that the tungsten powder and sodium azide are mixed in a mass ratio of 5:1 in an agate mortar; the raw material briquetting is that the raw material is made into a cylindrical shape with a sandwich structure, i.e. two pieces of melamine wrapping one piece of the mixture cylinder made of the mixed powder of tungsten powder and sodium azide, by using a hydraulic machine according to the size of the synthesis cavity; the assembling is that the pressed cylindrical raw material is put into a heating container and placed in the synthesis cavity; the high-temperature and high-pressure synthesis is that the temperature is kept at 1500-1800 DEG C and the pressure is kept at 3.0-5.0 GPa for 10 minutes; the cooling and pressure releasing is that the assembled block is naturally cooled to room temperature after stopping the electric heating, and then the pressure is released; and the impurity removing is that the synthesized powder sample is soaked and dissolved by using dilute hydrochloric acid and cleaned by centrifugation.

2. The method of claim 1, wherein the method is characterized by: The sodium azide with good impurity removing is used as an auxiliary nitrogen source, and the melamine is used as a main nitrogen source, so that the carbon powder generated after the reaction of the melamine is naturally separated from the generated tungsten nitride, and no carbon pollution is generated.

3. A nano tungsten nitride powder material, prepared by the method of claim 1 or 2, characterized in that, The material has a nanometer sheet-shaped structure, the thickness of the nanometer sheet is about 93 nm, and there is no growth relationship between the nanometer sheets.

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