Deep purification method of graphite

Abstract

The invention discloses a deep purification method of graphite, which comprises the following steps: placing graphite in a double glow plasma metallurgical furnace, and vacuumizing; argon or argon and nitrogen are introduced, and the vacuum pressure is maintained to be 20-100 Pa; and starting a double glow plasma bias power supply, heating the graphite to 2800 DEG C or above, preserving heat, and removing impurities through high-temperature physical gasification to achieve the required purity. According to the double glow plasma metallurgy method, graphite is deeply purified, a double glow plasma metallurgy furnace adopts ultra-pure graphite or a C / C composite material as a source electrode, a workpiece electrode and an energy gathering ring, the graphite can be heated to 2800 DEG C or above through the discharge effect of a hollow cathode and the heat preservation and constraint effect of the energy gathering ring, heat preservation is conducted for a long enough time, and the graphite can be further purified. Hydrogen and halogen alkane gas are not adopted, impurities are removed only through a high-temperature physical gasification method, deep purification of graphite is achieved, the requirements for third-generation semiconductor preparation and the like are met, equipment is simple, tail gas does not need to be treated, and safety and environment friendliness are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of graphite purification, and particularly relates to a deep purification method of graphite. BACKGROUND

[0002] High-purity graphite is a key raw material for strategic emerging industries such as high-end equipment manufacturing, new energy, nuclear power, aerospace, military industry and the third generation of semiconductors. Therefore, the purification method of high-purity graphite has become one of the research hotspots in the field.

[0003] Acid-base method is the main method of chemical purification. CN 109336104 A invention patent discloses a hydrothermal method for low-temperature purification of graphite raw materials. Heat in dilute acid at 80-150℃ for 1-3h, heat in alkali solution at 150-180℃ for 1-4h, repeat multiple times, and finally calcine at 600-950℃ for 7-10min in N atmosphere, to obtain a purified graphite product with a maximum of 99.90%. Literature 1 (Meng Fanna, Ma Ying, Zhang Xiaochen, Kan Kan. Experimental study on purification of flake graphite by alkali-acid method. Journal of Heilongjiang University of Science and Technology, 2023, 33(2): 173-180) uses graphite: NaOH mass ratio of 10:3, calcination at 450℃, then uses cetyltrimethylammonium bromide (CTAB) assisted hydrochloric acid leaching, to purify the fixed carbon mass fraction of 95.89% of Heilongjiang Jixi natural flake graphite flotation concentrate to 99.93%. The disadvantages of acid-base method are the use of volatile and easy-to-poison explosive hydrochloric acid, which is difficult to manage safely; the low-temperature method of CN 109336104 A invention patent consumes sodium carbonate up to 1:8 of the mass ratio to purify graphite to 99.90%, and the minimum alkali consumption of high-temperature calcination method is also more than 30% of the mass of graphite, which is too high in resource and energy consumption.

[0004] High-temperature physical and chemical method is an effective method for preparing high-purity graphite at present. Literature 2 (Liang G, Zhao G, Wang Z. Research on the preparation of high-purity graphite by induction heating. Carbon technology, 2013, 32(4): 44-46) uses induction heating method to purify natural flake graphite with a purity of 96.5%, and gets high-purity graphite with a purity of 99.92%, and retains the original flake shape. This high-temperature physical method requires the induction furnace to be kept at more than 2600℃ for a long time, which puts higher requirements on the induction furnace. Literature 3 (Ling Z, Jiang W, Shao J, Liu X. Experimental study on preparation of high-purity graphite by high-temperature roasting. Non-ferrous minerals, 2020, 43(1): 37-39) uses the working condition of chlorine salt graphite ratio 1.5%, roasting temperature 2500℃, and constant temperature time 4h, which can make the fixed carbon content of graphite roasting material reach 99.9915%. This method needs to strictly regulate the treatment of a large amount of tail gas containing chlorine elements. CN117735544 A invention patent discloses a deep purification method of semiconductor grade graphite powder, which first heats at 1500-1800℃, circulates air extraction and argon filling until low-boiling-point impurities are removed, then heats at 2000-2200℃, circulates air extraction and argon filling, and mixed gas containing chlorine and fluorine elements and alkane compounds, until high-boiling-point impurities are removed. The temperature is raised to 1800℃, the air is extracted to 5mbar, then Ar is filled to 850mbar, and the cycle is repeated 5 times; continue to heat to 2200℃, and the mixed gas of Ar and CHClF2 is introduced into the cavity to 850mbar, and maintain for 1h, then extract to 5mbar, and extract and fill 10 times, the purity of graphite powder can reach 99.99999%. This method produces a large amount of tail gas containing chlorine and fluorine elements, which needs to be strictly regulated and treated. Literature 4 (Cheng Y. Purification of large flake graphite by non-transferred arc plasma torch, Dalian Maritime University, Master's thesis, 2020.6) uses non-transferred arc plasma torch to purify large flake graphite with a purity of 94.18% in Jixi City, the arc surface temperature is as high as 3350℃, but because this method makes the graphite in the arc heat for a short time, the purity can only be improved to 99.21%. SUMMARY

[0005] The technical problem solved by the present application is to provide a deep purification method of graphite to solve the above problems of the prior art.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a deep purification method of graphite, characterized by comprising the following steps:

[0007] Step one, place the graphite in a double glow plasma metallurgy furnace and vacuumize it;

[0008] Step two, introduce argon or argon and nitrogen, and maintain the vacuum pressure at 20-100 Pa;

[0009] Step three, turn on the bias voltage power supply of the double glow plasma source electrode and workpiece electrode, heat the graphite to above 2800℃ and keep it at this temperature until all impurities are removed by high-temperature physical gasification;

[0010] Step four, turn off the power supply, cool down, continuously introduce argon and / or nitrogen, and open the furnace to take out the graphite.

[0011] The deep purification method of graphite, characterized in that the double glow plasma metallurgy furnace in step one uses ultra-high purity graphite or C / C composite material as the source electrode, workpiece electrode and energy gathering ring.

[0012] The deep purification method of graphite, characterized in that the flow ratio of nitrogen to argon in step two is not more than 0.2.

[0013] The deep purification method of graphite, characterized in that the bias voltage range of the double glow plasma source electrode and workpiece electrode bias voltage power supply in step three is -1200V to -350V.

[0014] Compared with the prior art, the present application has the following advantages:

[0015] The present application adopts double glow plasma metallurgy method to deeply purify graphite, the double glow plasma metallurgy furnace adopts ultra-high purity graphite or C / C composite material as source electrode, workpiece electrode and energy gathering ring, through the hollow cathode discharge effect and the heat preservation and restraint effect of the energy gathering ring, the graphite is heated to above 2800 DEG C and is preserved for a long time, only relying on high temperature physical gasification method to remove impurities, without using safety management difficult hydrogen, also without using halogen alkane gas which needs to strictly regulate the tail gas treatment, the graphite can reach the deep purification meeting the preparation requirements of the third generation semiconductor.

[0016] The technical solutions of the present application will be further described in detail below in combination with examples. DETAILED DESCRIPTION

[0017] Example 1

[0018] The deep purification method of graphite in this example comprises the following steps:

[0019] Step one, using ultra-high purity graphite with purity greater than 99.999999% as source electrode, workpiece electrode and energy gathering ring of double glow plasma metallurgy furnace; placing the Heilongjiang Jixi natural flake graphite flotation concentrate with fixed carbon mass fraction of 95.89% on the workpiece electrode in the double glow plasma metallurgy furnace, covering the energy gathering ring, and vacuumizing to below 5Pa;

[0020] Step two, introducing argon, maintaining the vacuum pressure of 20Pa;

[0021] Step three, opening the double glow plasma source electrode and workpiece electrode bias power supply, the source electrode bias is-1200V, the workpiece electrode bias is-400V, heating the graphite flotation concentrate to 2850 DEG C, and preserving for 48h;

[0022] Step four, closing the power supply, cooling, continuously introducing argon, and opening the furnace to take out the material.

[0023] The graphite powder in example 1 is detected by GDMS (glow discharge mass spectrometry), and the detection result is shown in table 1, the purity of the graphite reaches above 99.99997%.

[0024] Table 1 GDMS detection result of the purified sample in example 1

[0025]

[0026]

[0027] Example 2

[0028] The deep purification method of graphite in this example comprises the following steps:

[0029] Step one, using the purity of more than 99.999999% of ultra-high purity C / C composite material as the source of double glow plasma metallurgy furnace, workpiece and energy ring; the fixed carbon mass fraction of 98.5% of the petroleum coke produced by Panjin Liaohe oilfield is placed on the workpiece of double glow plasma metallurgy furnace, covered with energy ring, and vacuumed to below 5Pa;

[0030] Step two, argon and nitrogen are introduced, the flow ratio of nitrogen and argon is 0.1, and the vacuum pressure is maintained at 50Pa;

[0031] Step three, the bias power supply of double glow plasma source and workpiece is turned on, the source bias is-1100V, the workpiece bias is-350V, and the petroleum coke is heated to 3050℃, and the temperature is maintained for 24h;

[0032] Step four, turn off the power, cool down, continue to introduce argon, open the furnace and take out the material.

[0033] The graphite powder in example 2 is detected by GDMS (glow discharge mass spectrometry), and the detection results are shown in table 2, and the purity of the graphite reaches more than 99.999995%.

[0034] Table 2 GDMS detection results of purified sample in example 2

[0035]

[0036]

[0037] Example 3

[0038] The deep purification method of one kind of graphite in this embodiment comprises the following steps:

[0039] Step one, using the purity of more than 99.999999% of ultra-high purity graphite as the source of double glow plasma metallurgy furnace, workpiece, using the purity of more than 99.999999% of ultra-high purity C / C composite material as the energy ring of double glow plasma metallurgy furnace; the fixed carbon mass fraction of more than 99.9995% of Sigley R6510 material is placed on the workpiece of double glow plasma metallurgy furnace, covered with energy ring, and vacuumed to below 5Pa;

[0040] Step two, argon and nitrogen are introduced, the flow ratio of nitrogen and argon is 0.2, and the vacuum pressure is maintained at 100Pa;

[0041] Step three, the bias power supply of double glow plasma source and workpiece is turned on, the source bias is-1200V, the workpiece bias is-450V, and the R6510 is heated to 3250℃, and the temperature is maintained for 12h;

[0042] Step four, turn off the power, cool down, continue to introduce argon, open the furnace and take out the material.

[0043] The graphite powder in Example 3 was subjected to GDMS (glow discharge mass spectroscopy) detection, and the detection results are shown in Table 3. The purity of the graphite reached 99.999998% or more.

[0044] Table 3 GDMS detection results of the sample after purification in Example 3

[0045]

[0046]

[0047] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical range disclosed by the present application, and these modifications or replacements should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for deep purification of graphite, characterized in that, Includes the following steps: Step 1: Place the graphite in a double glow plasma metallurgical furnace and evacuate it; Step 2: Introduce argon or a mixture of argon and nitrogen to maintain a vacuum pressure of 20–100 Pa; Step 3: Turn on the dual-glowing plasma source and workpiece bias power supply, heat the graphite to above 2800℃ and keep it at that temperature until all impurities are removed by high-temperature physical vaporization. Step 4: Turn off the power, cool down, continuously introduce argon and / or nitrogen gas, and then open the furnace to remove the material.

2. The method for deep purification of graphite according to claim 1, characterized in that, The dual-glow plasma metallurgical furnace described in step one uses ultra-high purity graphite or C / C composite material as the source electrode, workpiece electrode, and focusing ring.

3. The method for deep purification of graphite according to claim 1, characterized in that, In step two, when argon and nitrogen are introduced, the flow rate ratio of nitrogen to argon should not exceed 0.

2.

4. The method for deep purification of graphite according to claim 1, characterized in that, The bias voltage range of the dual-glowing plasma source electrode and the workpiece electrode bias power supply mentioned in step three is -1200V to -350V.

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