CN112340726A - Preparation method of high-purity graphite crucible - Google Patents
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Abstract
The invention discloses a preparation method of a high-purity graphite crucible, which comprises the following steps: s1, taking a graphite crucible to be purified, and carrying out high-temperature purification reaction at the temperature of more than 2800 ℃ under the vacuum condition; s2, carrying out gas-thermal purification I reaction by adopting a purified gas A under the condition of temperature I; s3, carrying out gas-heated purification II reaction by adopting a purified gas A and a purified gas B under the condition of a temperature II; and S4, carrying out gas-heating purification III reaction on the purified gas A and the purified gas B under the temperature III condition to obtain the high-purity graphite crucible. The invention adopts the method of firstly carrying out high-temperature purification treatment and then carrying out staged gas-heat purification treatment, so that the graphite crucible achieves higher purity, the ash content and the key impurity content can be controlled within a certain range, the defects of the silicon carbide single crystal material prepared by the graphite crucible are obviously reduced, and the growth quality of the single crystal is greatly improved.
Description
Technical Field
The invention belongs to the technical field of graphite material purification, and particularly relates to a preparation method of a high-purity graphite crucible.
Background
At present, the physical vapor transport method (PVT method) is the most mature method for growing silicon carbide single crystals. In the PVT method silicon carbide single crystal growth process, silicon carbide source powder is generally adopted as a raw material, and a growth device of the silicon carbide single crystal growth process consists of a graphite crucible and a heat insulation material wrapped outside the crucible. The doping of unintended impurities not only tends to introduce defects during crystal growth, but also increases the difficulty of growing high performance silicon carbide single crystals. Therefore, the graphite crucible must adopt a reasonable purification process to meet the requirements of ash content and key impurity content.
The graphite crucible is prepared by isostatic pressing graphite and then is purified, the domestic purification technical level is limited, the ash content of the high-purity graphite crucible product is about 100ppm generally, and in the field of high-performance silicon carbide single crystals, the ash content of the high-purity crucible is required to be controlled below 20 ppm. In order to further improve the purity of the graphite crucible, a novel purification method needs to be provided to meet the growth requirement of the high-performance silicon carbide single crystal.
The high temperature method is an important method for purifying graphite in the prior art, has better purification effect compared with acid-base purification method, hydrofluoric acid method and the like, and is suitable for graphite products with special requirements on purity, for example, patent CN201811405260.1 discloses high purity graphite powder and a preparation method thereof, and high purity graphite powder with higher purity can be obtained by combining gas-heat purification and high temperature purification. However, the graphite crucible is large in volume, contains many kinds of impurity elements and has high content, and gas permeation is difficult, and a graphite crucible meeting the use requirements of the industry cannot be obtained by the method.
Disclosure of Invention
The invention aims to overcome the defects of the existing graphite crucible purification process, and provides a preparation method of a high-purity graphite crucible specially used for a SiC single crystal growth system, wherein the ash content of the graphite crucible is controlled within 20ppm, and the purification problem of the high-purity graphite crucible is effectively solved.
The purpose of the invention is realized by the following technical scheme:
a preparation method of a high-purity graphite crucible comprises the following steps:
s1, high-temperature purification: taking a graphite crucible to be purified, and carrying out high-temperature purification reaction at the temperature of more than 2800 ℃ under the vacuum condition;
s2, gas-heated purification I: carrying out gas-thermal purification I reaction on the graphite crucible purified in the step S1 by adopting a purified gas A under the condition of temperature I;
s3, gas-heated purification II: performing gas-heated purification II reaction on the graphite crucible purified in the step S2 by adopting a purified gas A and a purified gas B under the condition of temperature II;
s4, gas-heated purification III: carrying out gas-heating purification III reaction on the graphite crucible purified in the step S3 by adopting a purified gas A and a purified gas B under the condition of temperature III to obtain a high-purity graphite crucible;
the temperature I is 1820-2000 ℃, the temperature II is 2420-2600 ℃, the temperature III is 2620-2800 ℃, the purified gas A is a chlorine-containing gas, and the purified gas B is a fluorine-containing gas;
and the steps S2-S4 comprise a plurality of gas circulation steps under the condition of target temperature, wherein the gas circulation step comprises the steps of introducing fresh purified gas, maintaining pressure and extracting the purified gas.
Preferably, the high-temperature purification reaction time in step S1 is 10 hours or more.
Preferably, step S1 is performed in a high-temperature purification apparatus, the graphite crucible to be purified is placed in the high-temperature purification apparatus, and is vacuumized until the pressure is-50 to-100 KPa, and then is heated to 2800 ℃ or higher, and then is kept warm for 10 hours or longer.
Preferably, the steps S2 to S4 are performed in a gas-heated purification device, the graphite crucible purified at a high temperature in the step S1 is placed in the gas-heated purification device, and is vacuumized, then heated, purified gas is introduced for purification when the temperature is raised to a target temperature, and in the purification process of purified gas, the purified gas is introduced for maintaining the pressure for a period of time, vacuumized, and fresh purified gas is introduced for maintaining the pressure after the purified gas is discharged, and the operation is circulated until the purification in the step S3 is finished at the temperature iii.
Preferably, the total pressure holding time of the purified gas A under the condition of the temperature I in the step S2 and the pressure of more than 5KPa is more than 2.5 h; step S3, under the condition of the temperature III, the total pressure maintaining time of the purified gas A and the purified gas B under the pressure of more than 5KPa is more than 1 h; in step S4, the total pressure holding time of the purified gas A and the purified gas B at a pressure of 5KPa or more is 5h or more under the temperature III condition.
Preferably, the reaction conditions of step S2 are: placing the graphite crucible purified in the step S1 in gas-thermal purification equipment, firstly performing vacuum-pumping treatment until the pressure is-50 to-100 KPa, then heating, stopping vacuum-pumping when the temperature is I, starting to introduce the purified gas A with the gas flow rate of 150 to 250L/h, stopping pressure-maintaining for 0.5 to 2h until the absolute pressure value of the introduced gas is more than 5KPa, then performing vacuum-pumping within 0.5h to-50 to-100 KPa, circulating the process of introducing the purified gas in the step S1, and keeping the total circulation time of the temperature I to be more than 5 h.
Preferably, the reaction conditions of step S3 are: continuously vacuumizing the graphite crucible purified in the step S2 to-50 to-100 Kpa, heating, stopping vacuumizing when the temperature is II, introducing the purified gas A and the purified gas B, wherein the gas flow of the purified gas A and the purified gas B is 150-250L/h, stopping when the absolute pressure value of the introduced purified gas is more than 5KPa, maintaining the pressure for 0.5-2 h, then vacuumizing within 0.5h to-50 to-100 KPa, and circulating the process of introducing the purified gas in the step S3, wherein the total circulation time of the temperature I is kept to be more than 3 h.
Preferably, the reaction conditions of step S4 are: continuously vacuumizing the graphite crucible purified in the step S3 to-50 to-100 Kpa, heating, stopping vacuumizing when the temperature is raised to the temperature III, introducing the purified gas A and the purified gas B, wherein the gas flow of the purified gas A and the purified gas B
150-250L/h until the absolute pressure value of the introduced purified gas is more than 5KPa, maintaining the pressure for 0.5-2 h, then vacuumizing within 0.5h to-50 to-100 KPa, circulating the process of introducing the purified gas in the step S4, and keeping the total circulation time of the temperature III to be more than 10 h.
Preferably, the method further comprises a step S5 after the step of performing the reaction of gas-thermal purification iii, wherein the step S5 is: stopping the purification operation, continuously vacuumizing, cooling to IV 1200-1600 ℃, and keeping the pressure of 101.5-110 KPa to cool to room temperature to obtain the high-purity graphite crucible.
The invention adopts the method of firstly carrying out high-temperature purification treatment and then carrying out staged gas-heat purification treatment, so that the graphite crucible achieves higher purity, the ash content and the key impurity content can be controlled within a certain range, the defects of the silicon carbide single crystal material prepared by the graphite crucible are obviously reduced, and the growth quality of the single crystal is greatly improved.
Detailed Description
A preparation method of a high-purity graphite crucible comprises the following steps:
s1, high-temperature purification: taking a graphite crucible to be purified, and carrying out high-temperature purification reaction at the temperature of more than 2800 ℃ under the vacuum condition;
s2, gas-heated purification I: carrying out gas-thermal purification I reaction on the graphite crucible purified in the step S1 by adopting a purified gas A under the condition of temperature I;
s3, gas-heated purification II: carrying out gas-heating purification II reaction on the graphite crucible purified in the step S2 under the condition of temperature II by adopting purified gases A and B;
s4, gas-heated purification III: carrying out gas-heating purification III reaction on the graphite crucible purified in the step S3 by adopting purified gases A and B under the temperature III condition to obtain a high-purity graphite crucible;
steps S1-S4 are all carried out under the condition of sealing and isolating air, the temperature I is 1820-2000 ℃, the temperature II is 2420-2600 ℃, the temperature III is 2620-2800 ℃, the purified gas A is chlorine-containing gas, and the purified gas B is fluorine-containing gas;
and the steps S2-S4 comprise a plurality of gas circulation steps under the condition of target temperature, wherein the gas circulation step comprises the steps of introducing fresh purified gas, maintaining pressure and extracting the purified gas.
Firstly, carrying out coarse purification at a high temperature of more than 2800 ℃ on a graphite crucible to be purified, melting or volatilizing most impurities at the high temperature, thus removing most impurities, but still remaining part of high-melting-point impurities, then carrying out staged gas-heat purification, firstly introducing chlorine-containing gas at 1820-2000 ℃ to convert part of the high-melting-point impurities into low-melting-point chlorides so as to remove key impurities B, Al, V and the like in the graphite crucible, then introducing chlorine-containing gas and fluorine-containing gas on the basis of increasing the temperature, further converting the high-melting-point impurities which cannot be removed at 1820-2000 ℃ into low-melting-point chlorides and fluorides while carrying out fine purification on the graphite, further removing the high-melting-point impurities, finally increasing the temperature, introducing chlorine-containing gas and fluorine-containing gas to carry out purification, removing the high-melting-point impurities remaining in the graphite crucible to the maximum, and simultaneously carrying out purification stages, and (3) adopting a plurality of gas circulation steps, namely keeping the pressure for a period of time when fresh purified gas is introduced to a certain pressure value, then pumping out the purified gas acting for a period of time, and then introducing the fresh purified gas for keeping the pressure, and circulating the steps until the purification is finished. Adopt this gas circulation step, on the one hand can in time get rid of the impurity that purification produced, prevent the interior impurity saturation of system, influence the discharge of impurity in the graphite crucible, on the other hand can guarantee the purified gas purity, improve the permeability of purified gas, moreover, along with the extraction and the letting in of purified gas, the gaseous flow in the system, pressure variation, not only help impurity to discharge smoothly along with the air current motion, and help inside the purified gas infiltration graphite crucible, make the inside impurity of graphite crucible also discharge easily, improve purification efficiency, make the graphite crucible purity guarantee, the ash content is controlled below 20ppm, in order to satisfy the growth demand of high performance silicon carbide single crystal.
Preferably, the chlorine-containing gas comprises one or more combinations selected from chlorine, methyl chloride or dichloromethane, and the fluorine-containing gas is fluorine gas and/or freon. Other suitable chlorine-containing gases and fluorine-containing gases may of course be used.
Preferably, the high-temperature purification time of step S1 is more than 10 hours, which can sufficiently ensure the purification effect, but the too long purification time will result in increased production cost and decreased efficiency, and therefore, is preferably not more than 30 hours. Specifically, step S1 is: putting the graphite crucible to be purified in high-temperature purification equipment, firstly carrying out vacuum-pumping treatment until the pressure is between-50 and-100 KPa, then heating to more than 2800 ℃, and then preserving heat for more than 10 hours. Vacuumizing and heating are carried out firstly, so that the materials in the furnace can be protected, and the influence of oxygen is reduced.
Preferably, the steps S2 to S4 are performed in a gas-heated purification device, the vacuum-pumping process is performed first, the temperature is raised again, when the temperature is raised to the target temperature, the purified gas is introduced for purification, in the purification process of the purified gas, the purified gas is introduced for maintaining the pressure for a period of time, after the purified gas is discharged by vacuum-pumping, the fresh purified gas is introduced for maintaining the pressure, and the operation is cycled until the purification of the step S3 at the temperature iii is finished.
In order to ensure the purification effect, the total pressure maintaining time of the purified gas A under the condition of the temperature I in the step S2 and the pressure of more than 5KPa is preferably more than 2.5 h; step S3, under the condition of the temperature III, the total pressure maintaining time of the purified gas A and the purified gas B under the pressure of more than 5KPa is more than 1 h; step S4 the total dwell time of purified gases A and B at a pressure of 5KPa or more is 5h or more under the condition of temperature III.
Specifically, the reaction conditions in step S2 are as follows: placing the graphite crucible purified in the step S1 in gas-thermal purification equipment, firstly carrying out vacuum-pumping treatment until the pressure is-50 to-100 KPa, fully discharging the gas in the equipment, heating, stopping vacuum-pumping when the temperature is I, starting to introduce the purified gas A with the gas flow rate of 150 to 250L/h until the absolute pressure value of the introduced purified gas is more than 5KPa, maintaining the pressure for 0.5 to 2h, then carrying out vacuum-pumping within 0.5h to-50 to-100 KPa, and circulating the process of introducing the purified gas in the step S1, wherein the total circulation time of the temperature I is kept to be more than 5 h.
The reaction conditions of the step S3 are as follows: and (3) continuously vacuumizing the graphite crucible purified in the step S2 to-50 to-100 Kpa, heating, stopping vacuumizing when the temperature is II, introducing a purified gas A and a purified gas B, wherein the gas flow rates of the purified gas A and the purified gas B are both 150-250L/h until the absolute pressure value of the introduced purified gas is more than 5KPa, maintaining the pressure for 0.5-2 h, then vacuumizing within 0.5h to-50 to-100 KPa, circulating the process of introducing the purified gas in the step S3, and keeping the total circulation time of the temperature I to be more than 3 h.
The reaction conditions of the step S4 are as follows: and (3) continuously vacuumizing the graphite crucible purified in the step S3 to-50 to-100 Kpa, heating, stopping vacuumizing when the temperature is raised to III, introducing a purified gas A and a purified gas B, keeping the pressure for 0.5 to 2 hours until the absolute pressure value of the introduced purified gas is more than 5KPa, vacuumizing within 0.5 hour to-50 to-100 KPa, circulating the process of introducing the purified gas in the step S4, and keeping the total circulation time of the temperature III to be more than 10 hours.
Preferably, after the reaction of gas-heated purification III, the method further comprises step S5, wherein step S5 is: and continuously vacuumizing, cooling to IV 1200-1600 ℃, and keeping the micro-positive pressure to cool to room temperature to obtain the high-purity graphite crucible. The micro positive pressure is maintained, so that external gas and impurities can be prevented from entering the furnace, and the purity of the graphite crucible is prevented from being influenced. The micro-positive pressure is about 101.5 to 110 KPa.
Example 1
The high-purity graphite crucible is prepared according to the following steps:
(1) putting a graphite crucible to be purified into high-temperature purification equipment, vacuumizing until the pressure is-99 KPa, starting heating, heating to 2800 ℃, preserving heat for 15h, cooling to room temperature, and taking out the crucible;
(2) putting the graphite crucible treated in the step 1 into gas-thermal purification equipment, firstly carrying out vacuum-pumping treatment, heating and keeping vacuum-pumping after the pressure is-99 KPa, stopping vacuum-pumping when the temperature is increased to 1820 ℃, starting to introduce chlorine gas with the flow of 200L/h until the absolute pressure value of the gas is more than 5KPa, keeping the pressure for 0.5h, then vacuumizing until the pressure is-99 KPa (about 0.5h), stopping vacuum-pumping again, introducing chlorine gas with the same absolute pressure value, and circulating for multiple times in such a way that the total pressure-maintaining time is 4.5h and the total circulation time is more than 9 h;
(3) continuously vacuumizing to-99 Kpa, discharging chlorine, heating and keeping vacuumizing, stopping vacuumizing when the temperature is raised to 2420 ℃, simultaneously introducing chlorine and fluorine gas, wherein the flow rates of the chlorine and the fluorine gas are both 200L/h, stopping when the absolute pressure value is more than 5KPa, maintaining the pressure for 1h, vacuumizing to-99 Kpa (about 0.5h), stopping vacuumizing again, introducing chlorine and fluorine gas with the same absolute pressure value, and circulating for multiple times in such a way that the total pressure maintaining time is 2h and the total circulation time is more than 3 h;
(4) continuously vacuumizing to-99 Kpa, discharging chlorine and fluorine gas, heating and keeping vacuumizing, stopping vacuumizing when the temperature is raised to 2620 ℃, introducing the chlorine and fluorine gas with the flow rate of 200L/h until the absolute pressure value of the gas is more than 5KPa, maintaining the pressure for 0.5h, vacuumizing to-99 Kpa (about 0.5h), stopping vacuumizing again, introducing the chlorine and fluorine gas with the same absolute pressure value, and circulating for multiple times to ensure that the total pressure maintaining time is 5h and the total circulation time is more than 10 h;
(5) stopping the purification operation, continuously vacuumizing, cooling to 1400 ℃, keeping the micro-positive pressure (102KPa) to cool to room temperature, and discharging.
The working dimensions of the purification apparatus in this example are 600X 800 mm.
The graphite crucible to be purified in this example (phi 230 x 200mm, thickness 10mm) was prepared using isostatic graphite and had an ash content of about 200ppm, and the high purity graphite crucible prepared by this example was tested to have an ash content of 0.0017% and 20ppm or less, wherein the critical impurities B0.01 ppm, Al 0.06ppm, V0.01 ppm, and Fe 0.06ppm, completely satisfied the silicon carbide single crystal growth requirements.
Example 2
The high-purity graphite crucible is prepared according to the following steps:
(1) putting a graphite crucible to be purified into high-temperature purification equipment, vacuumizing until the pressure is-99 KPa, starting heating, heating to 3000 ℃, preserving heat for 20h, cooling to room temperature, and taking out the crucible;
(2) putting the graphite crucible treated in the step 1 into gas-thermal purification equipment, firstly carrying out vacuum-pumping treatment, heating and keeping vacuum-pumping after the pressure is-99 KPa, stopping vacuum-pumping when the temperature is raised to 2000 ℃, starting to introduce chlorine gas with the flow of 200L/h until the absolute pressure value is more than 5KPa, maintaining the pressure for 0.5h, then vacuumizing until the pressure is-99 KPa (about 0.5h), stopping vacuum-pumping again, introducing chlorine gas with the same absolute pressure value, and circulating for multiple times in such a way that the total pressure-maintaining time is 5h and the total circulation time is more than 10 h;
(3) continuously vacuumizing to-99 Kpa, discharging chlorine and fluorine gas, heating and keeping vacuumizing, stopping vacuumizing when the temperature is raised to 2500 ℃, simultaneously introducing chlorine and fluorine gas, wherein the flow rates of the chlorine and fluorine gas are both 200L/h, stopping when the absolute pressure value is more than 5KPa, maintaining the pressure for 1h, vacuumizing to-99 Kpa (about 0.5h), stopping vacuumizing again, introducing chlorine and fluorine gas with the same absolute pressure value, and circulating for multiple times in such a way that the total pressure maintaining time is 3h and the total circulation time is more than 4.5 h;
(4) continuously vacuumizing to-99 Kpa, discharging chlorine and fluorine gas, heating and keeping vacuumizing, stopping vacuumizing when the temperature is raised to 2800 ℃, introducing chlorine and fluorine gas, wherein the flow rates of the chlorine and fluorine gas are both 200L/h, stopping when the absolute pressure value of the gas is more than 5KPa, maintaining the pressure for 0.5h, then vacuumizing to-99 Kpa (about 0.5h), stopping vacuumizing again, introducing chlorine and fluorine gas with the same absolute pressure value, and circulating for multiple times to ensure that the total pressure maintaining time is 5h and the total circulation time is more than 10 h;
(5) stopping the purification operation, continuously vacuumizing, cooling to 1400 ℃, keeping the micro-positive pressure (102KPa) to cool to room temperature, and discharging.
The ash content of the high-purity graphite crucible prepared by the embodiment is 18ppm, wherein key impurities B is 0.04ppm, Al is 0.07ppm, V is less than 0.01ppm, and Fe is 0.03ppm, and the high-purity graphite crucible completely meets the growth requirement of the silicon carbide single crystal.
Example 3
The high-purity graphite crucible is prepared according to the following steps:
(1) putting a graphite crucible to be purified into high-temperature purification equipment, vacuumizing until the pressure is-99 KPa, starting heating, heating to 2900 ℃, preserving heat for 10 hours, cooling to room temperature, and taking out the crucible;
(2) putting the graphite crucible treated in the step 1 into gas-thermal purification equipment, firstly carrying out vacuum-pumping treatment, heating and keeping vacuum-pumping after the pressure is-80 KPa, stopping vacuum-pumping when the temperature is raised to 1900 ℃, starting to introduce chlorine gas with the flow of 200L/h until the absolute pressure value is more than 5KPa, maintaining the pressure for 1h, then vacuumizing until the pressure is-80 KPa (the time is about 25min), stopping vacuum-pumping again, introducing chlorine gas with the same absolute pressure value, and circulating for multiple times in such a way that the total pressure-maintaining time is 4h and the total circulation time is more than 9 h;
(3) continuously vacuumizing to-80 Kpa, discharging chlorine and fluorine gas, heating and keeping vacuumizing, stopping vacuumizing when the temperature is raised to 2600 ℃, simultaneously introducing chlorine and fluorine gas, wherein the flow rates of the chlorine and fluorine gas are 250L/h, stopping when the absolute pressure value is more than 5KPa, maintaining the pressure for 0.5h, vacuumizing to-80 Kpa (about 25min), stopping vacuumizing again, introducing chlorine and fluorine gas with the same absolute pressure value, and circulating for multiple times in such a way that the total pressure maintaining time is 2h and the total circulation time is more than 4 h;
(4) continuously vacuumizing to-80 Kpa, discharging chlorine and fluorine gas, heating and keeping vacuumizing, stopping vacuumizing when the temperature is increased to 2700 ℃, introducing chlorine and fluorine gas, keeping the flow rate of the chlorine and fluorine gas at 200L/h until the absolute pressure value of the gas is more than 5Kpa, maintaining the pressure for 2h, vacuumizing until the pressure is-99 Kpa (about 25min), stopping vacuumizing again, introducing chlorine and fluorine gas with the same absolute pressure value, and circulating for multiple times in such a way that the total pressure maintaining time is 8h and the total circulation time is more than 10 h;
(5) stopping the purification operation, continuously vacuumizing, cooling to 1600 ℃, keeping the micro-positive pressure (105KPa) and cooling to room temperature, and discharging.
Example 4
The high-purity graphite crucible is prepared according to the following steps:
(1) putting a graphite crucible to be purified into high-temperature purification equipment, vacuumizing until the pressure is-99 KPa, starting heating, heating to 2900 ℃, preserving heat for 12 hours, cooling to room temperature, and taking out the crucible;
(2) putting the graphite crucible treated in the step 1 into gas-thermal purification equipment, firstly carrying out vacuum-pumping treatment, heating and keeping vacuum-pumping after the pressure is-99 KPa, stopping vacuum-pumping when the temperature is raised to 1950 ℃, starting to introduce chlorine gas with the flow of 150L/h, stopping when the absolute pressure value is more than 5KPa, maintaining the pressure for 1.5h, then vacuumizing until the pressure is-99 KPa (about 0.5h), stopping vacuum-pumping again, introducing chlorine gas with the same absolute pressure value, and circulating for multiple times in such a way that the total pressure-maintaining time is 4.5h and the total circulation time is more than 6 h;
(3) continuously vacuumizing to-99 Kpa, discharging chlorine and fluorine gas, heating and keeping vacuumizing, stopping vacuumizing when the temperature is increased to 2550 ℃, simultaneously introducing chlorine and fluorine gas, wherein the flow rates of the chlorine and fluorine gas are both 200L/h, stopping when the absolute pressure value is more than 5KPa, maintaining the pressure for 1.5h, then vacuumizing to-99 Kpa (about 0.5h), stopping vacuumizing again, introducing chlorine and fluorine gas with the same absolute pressure value, and circulating for multiple times in such a way that the total pressure maintaining time is 3h and the total circulation time is more than 4 h;
(4) continuously vacuumizing to-99 Kpa, discharging chlorine and fluorine gas, heating and keeping vacuumizing, stopping vacuumizing when the temperature is increased to 2650 ℃, introducing chlorine and fluorine gas, wherein the flow rates of the chlorine and fluorine gas are both 200L/h, stopping when the absolute pressure value of the gas is more than 5KPa, maintaining the pressure for 1.5h, vacuumizing until the pressure is-99 Kpa (about 0.5h), stopping vacuumizing again, introducing chlorine and fluorine gas with the same absolute pressure value, and circulating for multiple times to ensure that the total pressure maintaining time is 9h and the total circulation time is more than 12 h;
(5) stopping the purification operation, continuously vacuumizing, cooling to 1200 ℃, keeping the micro-positive pressure (110KPa) and cooling to room temperature, and discharging.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention. It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (9)
1. The preparation method of the high-purity graphite crucible is characterized by comprising the following steps of:
s1, high-temperature purification: taking a graphite crucible to be purified, and carrying out high-temperature purification reaction at the temperature of more than 2800 ℃ under the vacuum condition;
s2, gas-heated purification I: carrying out gas-thermal purification I reaction on the graphite crucible purified in the step S1 by adopting a purified gas A under the condition of temperature I;
s3, gas-heated purification II: performing gas-heated purification II reaction on the graphite crucible purified in the step S2 by adopting a purified gas A and a purified gas B under the condition of temperature II;
s4, gas-heated purification III: carrying out gas-heating purification III reaction on the graphite crucible purified in the step S3 by adopting a purified gas A and a purified gas B under the condition of temperature III to obtain a high-purity graphite crucible;
the temperature I is 1820-2000 ℃, the temperature II is 2420-2600 ℃, the temperature III is 2620-2800 ℃, the purified gas A is a chlorine-containing gas, and the purified gas B is a fluorine-containing gas;
and the steps S2-S4 comprise a plurality of gas circulation steps under the condition of target temperature, wherein the gas circulation step comprises the steps of introducing fresh purified gas, maintaining pressure and extracting the purified gas.
2. The method of manufacturing a high purity graphite crucible according to claim 1,
the high-temperature purification reaction time of the step S1 is more than 10 h.
3. The method of manufacturing a high purity graphite crucible according to claim 2,
step S1 is carried out in a high-temperature purification device, the graphite crucible to be purified is placed in the high-temperature purification device, the vacuum pumping treatment is firstly carried out until the pressure is-50 to-100 KPa, then the temperature is raised to more than 2800 ℃, and the temperature is preserved for more than 10 h.
4. The method of manufacturing a high purity graphite crucible according to claim 1,
and (3) performing steps S2-S4 in a gas-heated purification device, placing the graphite crucible purified at the high temperature in the step S1 in the gas-heated purification device, vacuumizing, heating, introducing purified gas for purification when the temperature is raised to a target temperature, introducing the purified gas for maintaining the pressure for a period of time in the purification process of the purified gas, vacuumizing, discharging the purified gas, introducing fresh purified gas for maintaining the pressure, and circulating the operation until the purification in the step S3 is finished at the temperature III.
5. The method of manufacturing a high purity graphite crucible according to claim 4,
step S2, under the condition of the temperature I, the total pressure maintaining time of the purified gas A under the pressure of more than 5KPa is more than 2.5 h; step S3, under the condition of the temperature III, the total pressure maintaining time of the purified gas A and the purified gas B under the pressure of more than 5KPa is more than 1 h; in step S4, the total pressure holding time of the purified gas A and the purified gas B at a pressure of 5KPa or more is 5h or more under the temperature III condition.
6. The method of manufacturing a high purity graphite crucible according to claim 5,
the reaction conditions of the step S2 are as follows: placing the graphite crucible purified in the step S1 in gas-thermal purification equipment, firstly performing vacuum-pumping treatment until the pressure is-50 to-100 KPa, then heating, stopping vacuum-pumping when the temperature is I, starting to introduce the purified gas A with the gas flow rate of 150 to 250L/h, stopping pressure-maintaining for 0.5 to 2h until the absolute pressure value of the introduced gas is more than 5KPa, then performing vacuum-pumping within 0.5h to-50 to-100 KPa, circulating the process of introducing the purified gas in the step S1, and keeping the total circulation time of the temperature I to be more than 5 h.
7. The method of manufacturing a high purity graphite crucible according to claim 4,
the reaction conditions of the step S3 are as follows: continuously vacuumizing the graphite crucible purified in the step S2 to-50 to-100 Kpa, heating, stopping vacuumizing when the temperature is II, introducing the purified gas A and the purified gas B, wherein the gas flow of the purified gas A and the purified gas B is 150-250L/h, stopping when the absolute pressure value of the introduced purified gas is more than 5KPa, maintaining the pressure for 0.5-2 h, then vacuumizing within 0.5h to-50 to-100 KPa, and circulating the process of introducing the purified gas in the step S3, wherein the total circulation time of the temperature I is kept to be more than 3 h.
8. The method of manufacturing a high purity graphite crucible according to claim 5,
the reaction conditions of the step S4 are as follows: and (3) continuously vacuumizing the graphite crucible purified in the step S3 to-50 to-100 Kpa, heating, stopping vacuumizing when the temperature is raised to III, introducing the purified gas A and the purified gas B, wherein the gas flow of the purified gas A and the purified gas B is 150-250L/h until the absolute pressure value of the introduced purified gas is more than 5KPa, maintaining the pressure for 0.5-2 h, then vacuumizing within 0.5h to-50 to-100 KPa, and circulating the process of introducing the purified gas in the step S4, wherein the total circulation time of the temperature III is kept to be more than 10 h.
9. The method of manufacturing a high purity graphite crucible according to claim 1,
after the reaction of gas-heated purification III, the method also comprises a step S5, wherein the reaction conditions of the step S5 are as follows: stopping the purification operation, continuously vacuumizing, cooling to IV 1200-1600 ℃, and keeping the pressure of 101.5-110 KPa to cool to room temperature to obtain the high-purity graphite crucible.
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