Preparation method of high-purity submicron lanthanum nitride powder

Abstract

The application provides a preparation method of high-purity submicron lanthanum nitride powder, which comprises the following steps: placing metal lanthanum powder into a molybdenum boat, placing the molybdenum boat in a sintering device, and heating to 1000 DEG C under vacuum for 2-3 hours; then, cooling to 300 DEG C-400 DEG C and keeping the temperature for 1-2 hours, and introducing a mixed gas of H2 and NH3 during the keeping process; then, heating to 850 DEG C-1100 DEG C under the condition of flowing N2 atmosphere for 2-8 hours; after the keeping process, naturally cooling the temperature to room temperature, taking out the product, and obtaining the high-purity submicron lanthanum nitride powder through crushing and sieving. The preparation process is simple, the operation cost is low, the process window is wide, the obtained powder has a particle size of 0.01-1 mu m, the purity is more than 99.99%, the method is suitable for large-scale industrial production, and the prepared lanthanum nitride powder is widely applied in the fields of magnetic materials, hydrogen energy catalysts, semiconductor devices, electronic products, dyes, steel and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to lanthanum nitride and a preparation method thereof, in particular to a preparation method of high-purity sub-micron lanthanum nitride powder. BACKGROUND

[0002] Rare earth elements are known as the treasure house of new materials in the 21st century and are widely used. Rare earth elements generally contain 4f orbits and have similar electronic structures and characteristics, while lanthanum is different from other rare earth elements in that the number of electrons in its 4f orbit is zero. Therefore, lanthanum has stronger affinity for hydrogen, oxygen and nitrogen than cerium and europium, and is more difficult to separate and purify. The main impurities in lanthanum are O, Fe, Si, Ni, Mn, Al and the like, among which O and Fe have the highest content. The earliest method for separating rare earth elements is fractional crystallization and fractional precipitation, but this method requires 15 times of recrystallization to make the purity of metallic lanthanum reach 99.98%, and the production efficiency is very low, which is difficult to realize continuous operation and is not suitable for industrial production. The commonly used separation process of metallic lanthanum in China is the sulfuric acid method and the extraction separation method, which are relatively simple to operate, but the purity of the obtained metallic lanthanum is generally low and the content of Fe impurities is high, which is difficult to meet the special requirements of high-performance rare earth functional materials.

[0003] Lanthanum nitride is an inorganic compound with a chemical formula of LaN, and most of its particle sizes are in the order of microns. It is stable at high temperatures and can be used as a high-temperature structural material. Sub-micron lanthanum nitride powder has a larger specific surface area and dispersibility, and has higher optical and electronic properties and thermal stability than micron lanthanum nitride powder. It is widely used in the fields of magnetic materials, hydrogen energy catalysts, semiconductor devices, electronic products, dyes, steel and the like.

[0004] In industry, lanthanum nitride is usually prepared by reducing hydrated lanthanum chloride with metallic calcium after dehydration, or by electrolysis of anhydrous lanthanum chloride after melting, or by mixing lanthanum with mercury to form an amalgam, obtaining a mercury alloy and then performing a nitriding reaction to obtain lanthanum nitride, or directly nitriding metallic lanthanum in an ammonia atmosphere to obtain lanthanum nitride. However, these preparation methods are relatively complex and are not suitable for large-scale industrial production. Chinese patent CN 101618865A discloses a metallic lanthanum nitride powder and a preparation method thereof. The method uses nanometer rare earth dysprosium or nanometer rare earth hydride to directly react with N2 to prepare lanthanum nitride powder, but the obtained lanthanum nitride powder has poor crystallinity and high requirements for raw materials. SUMMARY

[0005] The present application provides a high-purity sub-micron lanthanum nitride powder and a preparation method thereof, to solve the problems of low purity and complex process of the lanthanum nitride powder prepared by the prior art.

[0006] The application aims at the following technical scheme.

[0007] The application provides submicron lanthanum nitride powder, the particle size of which is 0.01-1 microns, and the purity is greater than or equal to 99.99%.

[0008] The preparation method of the high-purity submicron lanthanum nitride powder comprises the following steps.

[0009] The metal lanthanum powder particles are put into a molybdenum boat, the molybdenum boat is placed in a sintering device, vacuum is extracted to-0.1 Mpa, the temperature is raised to 1000 DEG C, and the temperature is kept for 2-3 hours; then, the temperature is lowered to 300 DEG C-400 DEG C, and the temperature is kept for 1-2 hours, and a mixed gas of H2 and NH3 is introduced during the temperature keeping process; then, the temperature is raised to 850 DEG C-1100 DEG C under the condition of flowing N2 atmosphere, and the temperature is kept for 2-8 hours; after the temperature keeping is completed, the temperature is naturally cooled to room temperature, the product is taken out, and the high-purity submicron lanthanum nitride powder is obtained through crushing and sieving.

[0010] The molybdenum boat is a three-layer molybdenum boat, the uppermost layer and the lowermost layer of which are molybdenum plates, the molybdenum plate of the uppermost layer is provided with uniform holes, and the middle layer is a screen mesh; the metal lanthanum powder particles are located on the uppermost layer of the molybdenum boat.

[0011] Further, the particle size of the metal lanthanum powder particles is 3-10 mm.

[0012] Further, the diameter of the holes on the molybdenum plate of the uppermost layer of the molybdenum boat is 0.1-2 mm; the screen mesh of the middle layer is composed of molybdenum wires, and the aperture is 200-500 mesh.

[0013] Further, the heating rate for raising the temperature to 1000 DEG C is 30-50 DEG C / min; the cooling rate for lowering the temperature to 300 DEG C-400 DEG C is 10-30 DEG C / min; and the heating rate for raising the temperature to 850 DEG C-1100 DEG C is 5 DEG C / min.

[0014] Further, the volume ratio of H2 to NH3 in the mixed gas of H2 and NH3 is (1-5):(5-9), and the flow rate is controlled to be 0.5-1.5 L / min.

[0015] Further, the flow rate of N2 is controlled to be 5-10 L / h.

[0016] Further, the crushing is carried out in a vacuum vibration mill.

[0017] The application has the following beneficial effects.

[0018] The application provides a preparation method of high-purity submicron lanthanum nitride powder.

[0019] The method has no strict requirement on the particle size of raw materials, and the particle size of the lanthanum metal powder is 3-10 mm. In the preparation process, high-temperature sintering at 1000 DEG C is firstly performed after vacuumizing, so as to effectively remove impurities such as oxygen and oil stains on the surface of the raw materials. The process of high-temperature sintering at 1000 DEG C is creatively selected to be performed in a three-layer molybdenum crucible. Since the upper layer and the middle layer of the three-layer molybdenum crucible have holes or screens, the molten lanthanum ingot (since the melting point of the lanthanum metal is 920 DEG C, the sintering temperature 1000 DEG C exceeds the melting point of the lanthanum ingot, so that the lanthanum ingot is melted to form a molten state) is filtered from the upper layer to the lower layer in a fluid form, and the impurities of Fe (melting point 1535 DEG C), Si (melting point 1410 DEG C) and Mn (1246 DEG C) with high melting points are retained in the upper layer of the crucible, so that the impurities of Fe, Si and Mn with high melting points are effectively removed, and the purity of the final product lanthanum nitride powder is improved to a certain extent. In addition, after high-temperature sintering, the method further performs cooling and introduces a mixed gas of hydrogen and ammonia during the sintering process. The cooling process makes the molten lanthanum metal gather. With the introduction of the mixed gas of hydrogen and ammonia, the gathered lanthanum metal reacts with the mixed gas of hydrogen and ammonia to generate hydrogen fragmentation, so that the raw material is more conducive to the later nitriding, the nitriding rate and the purity of the lanthanum nitride powder are improved, the ductility of the metal block after hydrogen fragmentation is reduced, the brittleness is increased, the later crushing treatment is more conducive, the particle size of the powder is reduced, and the powder particles reach the submicron level. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The XRD pattern of the lanthanum nitride prepared in Example 1.

[0021] Figure 2 The SEM pattern of the lanthanum nitride prepared in Example 1. DETAILED DESCRIPTION

[0022] The following examples are used to further illustrate the application, but do not limit the application in any form.

[0023] Example 1

[0024] A preparation method of high-purity submicron lanthanum nitride powder is as follows:

[0025] Put 3-10mm metal lanthanum powder into three layers of molybdenum boat (the uppermost layer and the lowermost layer of the molybdenum boat are molybdenum plates, the uppermost layer of the molybdenum plate has a hole with a diameter of 2mm; the mesh of the middle layer is composed of molybdenum wires, and the aperture is 200 meshes), and place the molybdenum boat in a sintering device. Vacuumize to -0.1Mpa, and heat to 1000℃ at a rate of 50℃ / min. Keep the temperature for 3h. Then, cool to 400℃ at a rate of 10℃ / min, and keep the temperature for 2h. During the process of keeping the temperature, flow the mixed gas of H2 and NH3 with a volume ratio of 3:7 at a gas flow rate of 1L / min. Then, heat to 900℃ at a rate of 5℃ / min under the condition of N2 flow rate of 8L / h, and sinter for 4h. After sintering, take out the product after natural cooling to room temperature, and crush the product in a vacuum vibration mill. Screen to obtain high-purity submicron lanthanum nitride powder.

[0026] The nitriding rate = actual weight gain / theoretical weight gain.

[0027] The nitriding rate of the lanthanum nitride powder prepared by the method of the present application is 100% according to the above formula. Test the XRD, and compare the XRD test results with the lanthanum nitride standard card. The results are shown in Figure 1 It can be seen that it is pure LaN. As shown in Table 1, the ICP detection results show that the purity of the lanthanum nitride powder is 99.99%. As shown in Figure 2 The SEM image of the lanthanum nitride powder is shown in

[0028] Example 2

[0029] A method for preparing high-purity submicron lanthanum nitride powder is as follows:

[0030] Put 3-10mm metal lanthanum powder into three layers of molybdenum boat (the uppermost layer and the lowermost layer of the molybdenum boat are molybdenum plates, the uppermost layer of the molybdenum plate has a hole with a diameter of 2mm; the mesh of the middle layer is composed of molybdenum wires, and the aperture is 200 meshes), and place the molybdenum boat in a sintering device. Vacuumize to -0.1Mpa, and heat to 1000℃ at a rate of 50℃ / min. Keep the temperature for 3h. Then, cool to 400℃ at a rate of 10℃ / min, and keep the temperature for 2h. During the process of keeping the temperature, flow the mixed gas of H2 and NH3 with a volume ratio of 3:7 at a gas flow rate of 1L / min. Then, heat to 900℃ at a rate of 5℃ / min under the condition of N2 flow rate of 8L / h, and sinter for 4h. After sintering, take out the product after natural cooling to room temperature, and crush the product in a vacuum vibration mill. Screen to obtain high-purity submicron lanthanum nitride powder. The lanthanum nitride powder has a particle size of 0.01-1μm, a nitriding rate of 99%, and a purity of 99.5% after detection.

[0031] Example 3

[0032] A method for preparing high-purity sub-micron lanthanum nitride powder is as follows:

[0033] Put 3-10 mm metal lanthanum powder particles into a three-layer molybdenum boat (the uppermost and lowermost layers of the molybdenum boat are molybdenum plates, and the uppermost molybdenum plate has a hole with a diameter of 2 mm; the middle layer is a screen composed of molybdenum wires with a pore size of 200 mesh), and place the molybdenum boat in a sintering device. Vacuumize to -0.1 Mpa, and then heat to 1000℃ at a rate of 30℃ / min, and keep the temperature for 2 hours. Then, cool to 300℃ at a rate of 30℃ / min, and keep the temperature for 1 hour. During the keeping process, pass a mixed gas of H2 and NH3 with a volume ratio of 5:9 at a flow rate of 1.5 L / min. Then, heat to 1100℃ at a rate of 5℃ / min in an atmosphere of N2 with a flow rate of 5 L / h, and keep the temperature for 2 hours. After the keeping process is completed, naturally cool to room temperature, take out the product, and place the product in a vacuum vibration mill for crushing. Screen the product to obtain high-purity sub-micron lanthanum nitride powder. The particle size of the lanthanum nitride powder is 0.01-1 μm, the nitriding rate is 100%, and the purity is 99.96%.

[0034] Example 4

[0035] Put 3-10 mm metal lanthanum powder particles into a three-layer molybdenum boat (the uppermost and lowermost layers of the molybdenum boat are molybdenum plates, and the uppermost molybdenum plate has a hole with a diameter of 0.1 mm; the middle layer is a screen composed of molybdenum wires with a pore size of 500 mesh), and place the molybdenum boat in a sintering device. Vacuumize to -0.1 Mpa, and then heat to 1000℃ at a rate of 50℃ / min, and keep the temperature for 3 hours. Then, cool to 400℃ at a rate of 10℃ / min, and keep the temperature for 2 hours. During the keeping process, pass a mixed gas of H2 and NH3 with a volume ratio of 3:7 at a flow rate of 1 L / min. Then, heat to 900℃ at a rate of 5℃ / min in an atmosphere of N2 with a flow rate of 8 L / h, and sinter for 4 hours. After the sintering process is completed, naturally cool to room temperature, take out the product, and place the product in a vacuum vibration mill for crushing. Screen the product to obtain high-purity sub-micron lanthanum nitride powder. The particle size of the lanthanum nitride powder is 0.01-0.05 μm, the nitriding rate is 100%, and the purity is 99.995%.

[0036] Comparative Example 1

[0037] A method for preparing high-purity sub-micron lanthanum nitride powder is the same as that in Example 1, except that the three-layer molybdenum boat in Example 1 is replaced by a common crucible.

[0038] The nitriding rate of the lanthanum nitride prepared by the method in this example is 97% when calculated in the same way.

[0039] Comparative Example 2

[0040] The 3-10 mm metal lanthanum powder particles were placed in a common crucible, the crucible was placed in a sintering device, and the temperature was raised to 400°C at a rate of 10°C / min, and the temperature was maintained for 2 h. During the temperature maintaining process, a mixed gas of H2 and NH3 with a volume ratio of 3:7 was introduced at a gas flow rate of 1 L / min. Then, the temperature was raised to 900°C at a rate of 5°C / min under the condition of a N2 flow rate of 5 L / h, and the temperature was maintained for 4 h. After the temperature maintaining process was completed, the product was taken out after natural cooling to room temperature, and crushing and sieving were completed in an inert gas environment to obtain high-purity sub-micron lanthanum nitride powder.

[0041] The nitriding rate of the lanthanum nitride prepared by the method of the present example was 95% according to the method of Example 1.

[0042] Comparative Example 3

[0043] The 3-10 mm metal lanthanum powder particles were placed in a three-layer molybdenum boat, the molybdenum boat was placed in a sintering device, and the temperature was raised to 1000°C at a rate of 50°C / min under a vacuum of 0.1 Mpa, and the temperature was maintained for 3 h. Then, the temperature was reduced to 400°C at a rate of 10°C / min, and the temperature was maintained for 2 h. After that, the temperature was raised to 900°C at a rate of 5°C / min under the condition of a N2 flow rate of 8 L / h, and the temperature was maintained for 4 h. After the temperature maintaining process was completed, the product was taken out after natural cooling to room temperature, and crushing was performed in a vacuum vibration mill, and high-purity sub-micron lanthanum nitride powder was obtained by sieving.

[0044] The nitriding rate of the lanthanum nitride prepared by the method of the present example was 85% according to the method of Example 1.

[0045] ICP tests were performed on Example 1, Comparative Example 1 and Comparative Example 2, respectively, and the test results are shown in Table 1.

[0046] Table 1. ICP test results

[0047]

[0048] As can be seen from the ICP test results shown in Table 1, the O content and Fe content in the lanthanum nitride powder prepared in Example 1 are obviously lower than those in the lanthanum nitride powder prepared in Comparative Examples 1 and 2. This is because, in the preparation method of Example 1, high-temperature sintering at 1000°C is performed after vacuumizing, and the process is performed in a three-layer molybdenum crucible. On the one hand, high-temperature sintering can effectively remove the oxygen impurities contained in the lanthanum ingot. On the other hand, because the melting point of metallic lanthanum is 920°C, the sintering temperature of 1000°C exceeds the melting point of the lanthanum ingot, which causes the lanthanum ingot to melt into a molten state. The upper and middle layers of the three-layer molybdenum crucible have holes or screens, and the molten lanthanum ingot will be filtered from the upper layer to the lower layer in the form of a fluid, so that the Fe impurities (melting point 1535°C), Si impurities (melting point 1410°C), and Mn impurities (1246°C) with a high melting point are retained in the upper layer of the crucible, thereby achieving the effect of effectively removing the Fe / Si / Mn impurities with a high melting point, and obtaining high-purity lanthanum nitride powder.

Claims

1. A method for preparing high-purity lanthanum nitride powder, characterized in that: The high-purity submicron lanthanum nitride powder has a particle size of 0.01-1 μm and a purity of ≥99.99%. The preparation method thereof comprises the following steps: The lanthanum metal powder is placed in a molybdenum boat, and the molybdenum boat is placed in a sintering device. The vacuum is evacuated to -0.1Mpa, and the temperature is raised to 1000°C and kept warm for 2-3 hours. Then, the temperature is lowered to 300°C-400°C and kept warm for 1-2 hours. A mixed gas of H2 and NH3 is introduced during the holding process. Thereafter, the temperature is raised to 850-1100°C under a circulating N2 atmosphere and kept warm for 2-8 hours. After the holding is completed, the temperature is naturally cooled to room temperature, the product is taken out, and high-purity submicron lanthanum nitride powder is obtained by crushing and sieving. The molybdenum boat is a three-layer molybdenum boat, the top and bottom layers of which are both molybdenum plates, the top molybdenum plate has uniform holes, and the middle layer is a screen; the metal lanthanum powder particles are located on the top layer of the molybdenum boat.

2. The method for preparing high-purity lanthanum nitride powder according to claim 1, wherein The particle size of the metal lanthanum powder is 3-10 mm.

3. The method for preparing high-purity lanthanum nitride powder according to claim 1, wherein The diameter of the holes on the molybdenum plate on the top layer of the molybdenum boat is 0.1-2 mm; The screen of the middle layer is made of molybdenum wire with a pore size of 200-500 mesh.

4. The method for preparing high-purity lanthanum nitride powder according to claim 1, wherein The heating rate for heating to 1000°C is 30-50°C / min; the cooling rate for cooling to 300-400°C is 10-30°C / min; and the heating rate for heating to 850-1100°C is 5°C / min.

5. The method for preparing high-purity lanthanum nitride powder according to claim 1, wherein In the mixed gas of H2 and NH3, the volume ratio of H2 to NH3 is (1-5): (5-9), and the flow rate is controlled at 0.5-1.5 L / min.

6. The method for preparing high-purity lanthanum nitride powder according to claim 1, wherein The flow rate of N2 is controlled at 5-10 L / h.

7. The method for preparing high-purity lanthanum nitride powder according to claim 1, wherein The crushing is carried out in a vacuum vibration mill.

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