阅读说明：本技术 超高纯铝的制备方法 (Preparation method of ultra-high purity aluminum ) 是由 李清宇 何志达 朱刘 黄杰杰 于 2021-05-31 设计创作，主要内容包括：本公开提供了一种超高纯铝的制备方法,其包括步骤：步骤一,将铝锭进行真空蒸馏,降温后取出铝；步骤二,王水处理玻璃碳舟或氮化硼舟；步骤三,将步骤一所得到铝在高纯石墨坩埚内熔化后倒入玻璃碳舟或氮化硼舟内冷却得到铝锭,步骤四,用酸溶液腐蚀铝锭；步骤五,将铝锭放入区熔炉石英管内；步骤六,将惰性气体通入石英管内一段时间,关闭阀门,开启氢气阀门,将氢气通入石英管内；步骤七,打开加热器并调节温度；步骤八,加热器行至舟尾部时,停止加热,返回至原点,进行第二次区熔作业；步骤九,区熔完成后,停止加热,将铝锭取出,去铝锭的头尾；步骤十,将得到的铝产品按步骤四至步骤九再操作一次,其能获得MBE级别的6.5N超高纯铝。(The present disclosure provides a method for preparing ultra-high purity aluminum, which comprises the steps of: step one, carrying out vacuum distillation on an aluminum ingot, and taking out aluminum after cooling; step two, treating the glass carbon boat or the boron nitride boat by aqua regia; step three, melting the aluminum obtained in the step one in a high-purity graphite crucible, pouring the molten aluminum into a glass carbon boat or a boron nitride boat, and cooling the molten aluminum to obtain an aluminum ingot, and step four, corroding the aluminum ingot with an acid solution; putting the aluminum ingot into a quartz tube of a zone melting furnace; introducing inert gas into the quartz tube for a period of time, closing the valve, opening the hydrogen valve, and introducing hydrogen into the quartz tube; step seven, turning on a heater and adjusting the temperature; step eight, stopping heating when the heater moves to the tail of the boat, returning to the original point, and performing secondary zone-melting operation; step nine, after zone melting is completed, stopping heating, taking out the aluminum ingot, and removing the head and the tail of the aluminum ingot; step ten, the obtained aluminum product is operated once again according to the step four to the step nine, and the 6.5N ultra-high purity aluminum with the MBE grade can be obtained.)

1. A preparation method of ultra-high purity aluminum is characterized by comprising the following steps:

putting 5N raw material aluminum ingots into a graphite boat raw material groove (1), wherein the graphite boat raw material groove (1) is adjacent to a graphite boat product groove (2), spaced from the graphite boat raw material groove and communicated with the graphite boat raw material groove (2) at the upper part, covering a graphite cover (3) to enable the graphite cover (3), the graphite boat raw material groove (1) and the graphite boat product groove (2) to form a cavity (S) with the other parts sealed except a communication port (P1) arranged at one side of the graphite boat product groove (2) far away from the graphite boat raw material groove (1), putting the graphite cover (3), the graphite boat raw material groove (1), the graphite boat product groove (2) and the raw material aluminum ingots into a vacuum distillation furnace, then putting a dust collecting groove (4) with a vacuumizing port (P2) to enable the inner cavity of the dust collecting groove (4) to be communicated with the communication port (P1), covering the furnace cover (5), performing vacuum distillation, and putting a first area corresponding to the graphite boat raw material groove (1) into a first area for temperature distillation, The temperature of a second area corresponding to the graphite boat product groove (2) and the temperature of the dust collecting groove (4) are controlled, when distillation is carried out, impurities at least containing titanium, vanadium and chromium with high boiling point relative to aluminum in a raw material aluminum ingot are not gasified at the temperature of the first area, the impurities with low boiling point relative to the aluminum are gasified at the temperature of the first area, the impurities with low boiling point are not condensed at the temperature of the second area, the gasified aluminum distilled out from the graphite boat product groove (2) enters the graphite boat product groove (2), liquid is condensed in the graphite boat product groove (2), and the gasified impurities with low boiling point distilled out from the graphite boat product groove (2) enter the dust collecting groove (4) through the graphite boat product groove (2) and are condensed and collected in the dust collecting groove (4); cooling and taking out the aluminum in the graphite boat product groove (2);

soaking the glass carbon boat or the boron nitride boat in aqua regia, cleaning the soaked glass carbon boat or the boron nitride boat with pure water, and drying the cleaned glass carbon boat or the boron nitride boat for later use;

step three, melting the aluminum obtained in the step one in a high-purity graphite crucible, pouring the molten aluminum into the prepared glass carbon boat or boron nitride boat in the step two, and pouring out an aluminum ingot after cooling;

step four, corroding the aluminum ingot prepared in the step three by using a solution of pure water, UP-grade nitric acid and UP-grade hydrofluoric acid in a volume ratio of (1-5) to 1, cleaning the aluminum ingot by using the pure water to be neutral, and then drying the aluminum ingot in vacuum;

step five, the aluminum ingot obtained in the step four is loaded into another glass carbon boat or boron nitride boat (20) prepared in the step three, then the aluminum ingot is placed into a quartz tube (21) of a zone melting furnace, two ends of the quartz tube (21) are sealed, two ends of the quartz tube (21) are provided with gas inlets and outlets (211), and a furnace cover of the zone melting furnace is closed;

opening an inert gas valve, introducing 7N high-purity inert gas into the quartz tube (21) through a gas inlet and outlet (211) of the quartz tube (21), closing the inert gas valve after a period of time, opening a hydrogen valve, and introducing 7N high-purity hydrogen into the quartz tube (21); or, the quartz tube (21) of the zone melting furnace is vacuumized to be below 0.1Pa through the gas inlet and outlet (211) of the quartz tube (21), then 7N high-purity hydrogen is filled to normal pressure, a tail gas valve is opened, the hydrogen flow is adjusted, and the hydrogen is continuously introduced;

step seven, turning on the heater (22), starting to operate after the aluminum ingot at the head of the other glass carbon boat or the boron nitride boat (20) starts to melt, and adjusting the temperature of the heater (22) in the operation process so as to maintain the length of a melting zone (M) formed after the aluminum ingot is melted within a certain range;

step eight, when the heater (22) moves to the tail part of the other glass carbon boat or the boron nitride boat (20), stopping heating, automatically returning the heater (22) to the original point at the head part of the boat according to a set program, carrying out the second zone melting operation, and repeatedly carrying out the area operation for not less than N times;

step nine, after zone melting is finished, stopping heating, after the aluminum ingot is cooled, closing a hydrogen valve, opening a furnace cover of the zone melting furnace, taking out the aluminum ingot, and removing the head and the tail of the aluminum ingot to obtain an aluminum product in the middle part;

step ten, operating the aluminum product in the middle part again according to the step four to the step nine to obtain 6.5N aluminum.

2. The method for producing ultra-high purity aluminum according to claim 1, wherein, in the first step,

the vacuum degree is below 1 Pa;

the temperature of the first zone ranges from 1100 ℃ to 1400 ℃;

the temperature of the second zone ranges from 670 ℃ to 720 ℃;

the distillation time range is 6-16 h;

the yield of the aluminum in the graphite boat product groove (2) is 60 to 80 percent.

3. The method for producing ultra-high purity aluminum according to claim 1,

in the second step, the soaking time of the glass carbon boat or the boron nitride boat in the aqua regia is more than 4 h.

4. The method for producing ultra-high purity aluminum according to claim 1,

in step three, the ash content of the high-purity graphite crucible is less than 20 ppm.

5. The method for producing ultra-high purity aluminum according to claim 1,

in the fourth step, the etching time is 0.5h-2 h.

6. The method for producing ultra-high purity aluminum according to claim 1, wherein, in step six,

the inert gas is nitrogen or argon;

the flow rate of the inert gas is 2L/min-4L/min;

the time for introducing the inert gas is 4-8 h;

the flow rate of the hydrogen is 1L/min-3L/min.

7. The method for producing ultra-high purity aluminum according to claim 1, wherein, in step seven,

the running speed of the heater (22) is 20mm/h-40 mm/h;

the length of the melting zone (M) is 8cm +/-2 cm.

8. The method for producing ultra-high purity aluminum according to claim 1,

in step eight, N is calculated according to the following formula:

N＝[L/F]+1，

wherein L is the length of the boat, F is the length of the melt zone (M), and [ L/F ] is an integer of the value of L/F.

9. The method for producing ultra-high purity aluminum according to claim 1,

in step eight, the number of times N of zone melting is 8-12.

10. The method for producing ultra-high purity aluminum according to claim 1,

in the ninth step, the length of the aluminum head and the tail of the obtained product is respectively removed in a range of 10cm-15 cm.

Technical Field

The disclosure relates to the field of high-purity metal materials, in particular to a preparation method of ultra-high-purity aluminum.

Background

The ultra-pure 6.5N aluminum is mainly prepared by using a Molecular Beam Epitaxy (MBE) technology.

The main preparation method of the high-purity aluminum at present comprises the following steps: segregation method, directional solidification method, zone melting method. The main defects of the methods are that metal impurities such as titanium, vanadium, chromium and the like cannot be effectively removed, and the product is difficult to reach the ultra-high purity aluminum standard.

Chinese patent application publication No. CN104388697A, published 3, month, and 4, 2015, discloses a method for preparing 6N high-purity aluminum, in which raw material aluminum is first volatilized in vacuum, and then zone-melting is performed, thereby preparing 6N high-purity aluminum. This method has the following drawbacks: (1) metal impurities such as titanium, vanadium, chromium and the like are difficult to effectively remove, and the product is difficult to meet the 6.5N standard; (2) after zone melting, the aluminum can adhere to the graphite boat, making it difficult to remove the aluminum and the graphite boat cannot be reused.

Disclosure of Invention

In view of the problems in the background art, it is an object of the present disclosure to provide a method for producing ultra-high purity aluminum, which is capable of obtaining 6.5N ultra-high purity aluminum of MBE grade.

In order to achieve the above object, the present disclosure provides a method for preparing ultra-high purity aluminum, comprising the steps of:

putting 5N raw material aluminum ingots into a graphite boat raw material groove, wherein the graphite boat raw material groove and a graphite boat product groove are adjacent, are spaced and are communicated with each other at the upper part, covering a graphite cover so that the graphite cover, the graphite boat raw material groove and the graphite boat product groove form a cavity with the other parts sealed except a communication port arranged at one side of the graphite boat product groove far away from the graphite boat raw material groove, putting the graphite cover, the graphite boat raw material groove, the graphite boat product groove and the raw material aluminum ingots into a vacuum distillation furnace, then putting a dust collecting tank with a vacuumizing port so that the inner cavity of the dust collecting tank is communicated with the communication port, covering the furnace cover, performing vacuum distillation, controlling the temperature of a first area corresponding to the graphite boat raw material groove, the temperature of a second area corresponding to the graphite boat product groove and the temperature of the dust collecting tank during vacuum distillation, and at least containing titanium with high boiling point relative to aluminum in the raw material aluminum ingots during distillation, The method comprises the following steps that vanadium and chromium impurities are not gasified at the first zone temperature, aluminum and impurities with low boiling points relative to the aluminum are gasified at the first zone temperature, the impurities with low boiling points are not condensed at the second zone temperature, the gasified aluminum distilled out of a graphite boat product tank enters a graphite boat product tank and is condensed into liquid in the graphite boat product tank, and the gasified impurities with low boiling points distilled out of the graphite boat product tank enter a dust collecting tank through the graphite boat product tank and are condensed and collected in the dust collecting tank; cooling and taking out the aluminum in the graphite boat product groove;

soaking the glass carbon boat or the boron nitride boat in aqua regia, cleaning the soaked glass carbon boat or the boron nitride boat with pure water, and drying the cleaned glass carbon boat or the boron nitride boat for later use;

step three, melting the aluminum obtained in the step one in a high-purity graphite crucible, pouring the molten aluminum into the prepared glass carbon boat or boron nitride boat in the step two, and pouring out an aluminum ingot after cooling;

step four, corroding the aluminum ingot prepared in the step three by using a solution of pure water, UP-grade nitric acid and UP-grade hydrofluoric acid in a volume ratio of (1-5) to 1, cleaning the aluminum ingot by using the pure water to be neutral, and then drying the aluminum ingot in vacuum;

step five, the aluminum ingot obtained in the step four is placed into another glass carbon boat or boron nitride boat prepared in the step three, then the aluminum ingot is placed into a quartz tube of a zone melting furnace, the two ends of the quartz tube are sealed, gas inlets and outlets are formed in the two ends of the quartz tube, and a furnace cover of the zone melting furnace is closed;

opening an inert gas valve, introducing 7N high-purity inert gas into the quartz tube through a gas inlet and outlet of the quartz tube, closing the inert gas valve after a period of time, opening a hydrogen valve, and introducing 7N high-purity hydrogen into the quartz tube; or, the quartz tube of the zone melting furnace is vacuumized to be below 0.1Pa through the gas inlet and outlet of the quartz tube, then 7N high-purity hydrogen is filled to normal pressure, a tail gas valve is opened, the hydrogen flow is adjusted, and the hydrogen is continuously introduced;

step seven, turning on the heater, starting to operate after the aluminum ingot at the head of the other glass carbon boat or the boron nitride boat starts to melt, and adjusting the temperature of the heater during the operation process so as to maintain the length of a melting zone formed after the aluminum ingot is melted within a certain range;

step eight, when the heater moves to the tail part of the other glass carbon boat or the boron nitride boat, stopping heating, automatically returning the heater to the original point at the head part of the boat according to a set program, performing the second zone melting operation, and repeating the zone operation for not less than N times;

step nine, after zone melting is finished, stopping heating, after the aluminum ingot is cooled, closing a hydrogen valve, opening a furnace cover of the zone melting furnace, taking out the aluminum ingot, and removing the head and the tail of the aluminum ingot to obtain an aluminum product in the middle part;

step ten, operating the aluminum product in the middle part again according to the step four to the step nine to obtain 6.5N aluminum.

In some embodiments, in step one, the vacuum is 1Pa or less; the temperature of the first zone ranges from 1100 ℃ to 1400 ℃; the temperature of the second zone ranges from 670 ℃ to 720 ℃; the distillation time range is 6-16 h; the yield of aluminum in the graphite boat product groove is 60-80%.

In some embodiments, in the second step, the soaking time of the glass carbon boat or the boron nitride boat in the aqua regia is more than 4 h.

In some embodiments, the ash content of the high purity graphite crucible is < 20ppm in step three.

In some embodiments, in step four, the etch time is from 0.5h to 2 h.

In some embodiments, the inert gas is nitrogen or argon; the flow rate of the inert gas is 2L/min-4L/min; the time for introducing the inert gas is 4-8 h; the flow rate of the hydrogen is 1L/min-3L/min.

In some embodiments, in step seven, the heater operating speed is 20mm/h to 40 mm/h; the length of the melting zone is 8cm +/-2 cm.

In some embodiments, in step eight, N is calculated according to the following formula: n ═ L/F ] +1, where L is the length of the boat, F is the length of the melt zone (M), and [ L/F ] is an integer to the value of L/F.

In some embodiments, in step eight, the number of zone smelts, N, is 8-12.

In some embodiments, in step nine, the aluminum heads and tails of the obtained products are respectively removed in a length range of 10cm to 15 cm.

The beneficial effects of this disclosure are as follows: firstly, before the zone melting of aluminum, a vacuum distillation process is added, and impurities such as titanium, vanadium, chromium and the like and part of other impurities which are difficult to remove in the zone melting process are removed. The purification time is shortened, and the production efficiency is improved; secondly, the hydrogen is used as protective gas, so that materials can be prevented from being oxidized, and meanwhile, the hydrogen can react with part of impurities to generate gas to be discharged (for example, selenium can react with the hydrogen to generate hydrogen selenide gas), so that the purification effect is improved; thirdly, the glass carbon boat or the PBN (boron nitride) boat is used as a material containing tool, so that the problems that materials are tightly adhered to the graphite boat and are difficult to take out when the graphite boat is used as a zone melting boat are solved, the materials can be repeatedly utilized, and the production cost is reduced; and finally, the purification effect is remarkable, the total impurities of the product obtained by vacuum distillation and zone melting are less than 500ppb, and single impurities are in a standard range, so that the requirement of the impurity content of the ultra-high purity aluminum is met, and the use requirement of the ultra-high purity aluminum in the MBE field in the current market is completely met.

Drawings

Fig. 1 is a schematic view of a distillation apparatus used in a distillation process in the production method of ultra-high purity aluminum of the present disclosure.

Fig. 2 is a schematic view of a zone melting apparatus used in a zone melting process in the ultra-high purity aluminum production method of the present disclosure.

The reference numerals are explained below:

100 distillation apparatus

1 graphite boat raw material groove

2 graphite boat product groove

3 graphite lid

P1 communication port

S cavity

P2 vacuum-pumping port

4 dust collecting tank

5 furnace cover

6A first temperature zone induction heating coil

6B second temperature zone induction heating coil

7 end heat-insulating layer

8 circumferential heat-insulating layer

9A first temperature zone thermocouple

9B second temperature zone thermocouple

10 vacuum interface

11A first inlet of cooling water

11B cooling water second inlet

First outlet of 12A cooling water

12B cooling water second outlet

13 baffle

200 zone melting device

20 glass carbon or boron nitride boat

21 quartz tube

211 gas inlet and outlet

22 heater

M melting zone

Detailed Description

Fig. 1 and 2 below illustrate in detail a method for preparing ultra-high purity aluminum according to the present disclosure.

The preparation method of the ultra-high purity aluminum according to the present disclosure comprises the steps of:

putting 5N raw material aluminum ingots into a graphite boat raw material groove 1, wherein the graphite boat raw material groove 1 and a graphite boat product groove 2 are adjacent, spaced and communicated with each other, covering a graphite cover 3 to enable the graphite cover 3, the graphite boat raw material groove 1 and the graphite boat product groove 2 to form a cavity S with the other parts sealed except a communication port P1 arranged at one side of the graphite boat product groove 2 far away from the graphite boat raw material groove 1, putting the graphite cover 3, the graphite boat raw material groove 1, the graphite boat product groove 2 and the raw material aluminum ingots into a vacuum distillation furnace, putting a dust collecting tank 4 with a vacuumizing port (P2) to enable the inner cavity of the dust collecting tank 4 to be communicated with the communication port P1, covering the furnace cover 5 for vacuum distillation, controlling the temperature of a first area corresponding to the graphite boat raw material groove 1, the temperature of a second area corresponding to the graphite boat product groove 2 and the temperature of the dust collecting tank 4 during the vacuum distillation, when distillation is carried out, impurities at least containing titanium, vanadium and chromium with high boiling point relative to aluminum in a raw material aluminum ingot are not gasified at the temperature of a first zone, the aluminum and the impurities with low boiling point relative to the aluminum are gasified at the temperature of the first zone, the impurities with low boiling point are not condensed at the temperature of a second zone, the gasified aluminum distilled from the graphite boat product tank 2 enters the graphite boat product tank 2 and is condensed into liquid in the graphite boat product tank 2, and the impurities with low boiling point and gasified from the graphite boat product tank 2 enter the dust collecting tank 4 through the graphite boat product tank 2 and are condensed and collected in the dust collecting tank 4; cooling and taking out the aluminum in the graphite boat product groove 2;

soaking the glass carbon boat or the boron nitride boat in aqua regia, cleaning the soaked glass carbon boat or the boron nitride boat with pure water, and drying the cleaned glass carbon boat or the boron nitride boat for later use;

step three, melting the aluminum obtained in the step one in a high-purity graphite crucible, pouring the molten aluminum into the prepared glass carbon boat or boron nitride boat in the step two, and pouring out an aluminum ingot after cooling;

step four, corroding the aluminum ingot prepared in the step three by using a solution of pure water, UP-grade nitric acid and UP-grade hydrofluoric acid in a volume ratio of (1-5) to 1, cleaning the aluminum ingot by using the pure water to be neutral, and then drying the aluminum ingot in vacuum;

step five, the aluminum ingot obtained in the step four is loaded into another glass carbon boat or boron nitride boat 20 prepared in the step three, then the aluminum ingot is placed into a quartz tube 21 of a zone melting furnace, two ends of the quartz tube 21 are sealed, two ends of the quartz tube 21 are provided with a gas inlet and outlet 211, and a furnace cover of the zone melting furnace is closed;

opening an inert gas valve, introducing 7N high-purity inert gas into the quartz tube 21 through a gas inlet and outlet 211 of the quartz tube 21, closing the inert gas valve after a period of time, opening a hydrogen valve, and introducing 7N high-purity hydrogen into the quartz tube 21; or, the quartz tube 21 of the zone melting furnace is firstly vacuumized to be below 0.1Pa through the gas inlet and outlet 211 of the quartz tube 21, then 7N high-purity hydrogen is filled to normal pressure, a tail gas valve is opened, the hydrogen flow is adjusted, and the hydrogen is continuously introduced;

step seven, turning on the heater 22, turning on the heater for operation after the aluminum ingot at the head of the other glass carbon boat or the boron nitride boat 20 starts to melt, and adjusting the temperature of the heater 22 during the operation process so as to maintain the length of a melting zone M formed after the aluminum ingot is melted within a certain range;

step eight, when the heater 22 moves to the tail part of the other glass carbon boat or the boron nitride boat 20, stopping heating, automatically returning the heater 22 to the original point at the head part of the boat according to a set program, performing the second zone melting operation, and repeating the zone operation for not less than N times;

step nine, after zone melting is finished, stopping heating, after the aluminum ingot is cooled, closing a hydrogen valve, opening a furnace cover of the zone melting furnace, taking out the aluminum ingot, and removing the head and the tail of the aluminum ingot to obtain an aluminum product in the middle part;

step ten, operating the aluminum product in the middle part again according to the step four to the step nine to obtain 6.5N aluminum.

In the first step, the graphite boat raw material tank 1, the graphite boat product tank 2 and the dust collecting tank 4 are arranged and vacuum distillation is carried out under the control of the temperature of the graphite boat raw material tank, the graphite boat product tank and the dust collecting tank, impurities at least containing titanium, vanadium and chromium with high boiling point relative to aluminum, aluminum and impurities with low boiling point relative to aluminum are separated as three parts, so that the purity of aluminum obtained by vacuum melting is improved, and further basic guarantee is provided for obtaining 6.5N (namely the total amount of impurities is less than 500ppb) of aluminum through subsequent steps. In addition, the three parts are separated simultaneously through vacuum distillation, so that the purification time is shortened, and the production efficiency is improved.

In the first step, the graphite boat raw material tank 1 and the graphite boat product tank 2 are spaced from each other, so that the molten raw material aluminum ingot in the graphite boat raw material tank 1 and the aluminum condensed into liquid in the graphite boat product tank 2 are prevented from flowing toward each other again during vacuum distillation, and the purity of the aluminum condensed into liquid in the graphite boat product tank 2 is ensured. In some embodiments, as shown in fig. 1, graphite boat feedstock slots 1 and graphite boat product slots 2 are spaced from one another by spacers 13. In some embodiments, the graphite boat stock tank 1, the graphite boat product tank 2, and the spacer 13 are integrally formed.

In some embodiments, referring to fig. 1, in step one, the control of the first zone temperature is performed by controlling the first temperature zone induction heating coil 6A, and the control of the second zone temperature is performed by controlling the second temperature zone induction heating coil 6B. Real-time detection of the first zone temperature is achieved by the first zone temperature thermocouple 9A. Real-time detection of the second zone temperature thermocouple 9B.

In some embodiments, referring to fig. 1, in step one, in order to improve the temperature accuracy of the first zone temperature and the second zone temperature, an end insulation layer 7 and a circumferential insulation layer 8 may be further provided. Tip heat preservation 7 sets up the axial one end that deviates from dust collecting tank 4 at product raw material groove 1, and the combination that graphite boat raw material groove 1, graphite boat product groove 2 and graphite lid 3 formed is surrounded along circumference to circumference heat preservation 8, circumference heat preservation 8 and tip heat preservation 7 sealing connection. In the case where the end insulating layer 7 and the circumferential insulating layer 8 are provided, the first temperature zone induction heating coil 6A and the second temperature zone induction heating coil 6B are provided between the circumferential insulating layer 8 and the combined body formed by the graphite boat raw material tank 1, the graphite boat product tank 2, and the graphite cover 3.

In some embodiments, referring to fig. 1, in step one, the furnace lid 5 is provided with a vacuum interface 10. Vacuum interface 10 connects outside evacuation equipment, through vacuum interface 10 and dust collecting tank 4 vacuum pumping mouth P2 that has, carries out the evacuation to the graphite boat raw material groove 1, graphite boat product groove 2, graphite lid 3 and the dust collecting tank 4 that connect.

The temperature of the dust collection tank 4 can be set to normal temperature, thereby ensuring that the gasified low-boiling-point impurities distilled out of the graphite boat product tank 2 enter the dust collection tank 4 through the communication port P1 and are condensed in the dust collection tank 4. In an alternative embodiment, the furnace lid 5 is provided with a first inlet 11A for cooling water, a second inlet 11B for cooling water, a first outlet 12A for cooling water, and a second outlet 12B for cooling water, with respective flow passages provided inside the furnace lid 5 itself, as shown in fig. 1, in particular, the first inlet 11A for cooling water communicates with the first outlet 12A for cooling water via a corresponding flow passage inside the furnace lid 5 itself, and the second inlet 11B for cooling water communicates with the second outlet 12B for cooling water via a corresponding flow passage inside the furnace lid 5 itself. As shown in the figure, the furnace cover 5 covers the entire circumferential surface of the dust collection chute 4 and one axial end of the dust collection chute 4, whereby it is also ensured by convection heat transfer that vaporized low-boiling impurities distilled off from the graphite boat product chute 2 enter the dust collection chute 4 via the communication opening P1 and condense in the dust collection chute 4.

In some embodiments, in step one, the vacuum degree is below 1Pa, the temperature of the first zone ranges from 1100 ℃ to 1400 ℃, the temperature of the second zone ranges from 670 ℃ to 720 ℃, the distillation time ranges from 6h to 16h, and the yield of aluminum in the graphite boat product tank 2 is 60% -80%.

In some embodiments, in step one, the vacuum is 1Pa or less, the temperature in the first zone ranges from 1200 ℃ to 1300 ℃, the temperature in the second zone ranges from 680 ℃ to 700 ℃, and the distillation time ranges from 12h to 16 h.

In the second step, a glass carbon boat or a PBN (boron nitride) boat is used as a material containing tool, so that the problems that materials are tightly adhered to the graphite boat and are difficult to take out when the graphite boat is used as a zone melting boat are solved.

In the second step, the glass carbon boat or the boron nitride boat is soaked in aqua regia to remove impurities on the surface of the glass carbon boat or the boron nitride boat, so that the impurities are prevented from being brought into the final product to influence the purity of the product.

In some embodiments, in the second step, the soaking time of the glass carbon boat or the boron nitride boat in the aqua regia is more than 4 h.

In some embodiments, the ash content of the high purity graphite crucible is < 20ppm in step three, avoiding the introduction of impurities such as calcium, silicon, sulfur, phosphorus, etc. from the graphite crucible.

In the fourth step, the aluminum ingot prepared in the third step is corroded by using a solution of pure water, UP-grade nitric acid and UP-grade hydrofluoric acid in a certain volume ratio, so that oxides on the surface of the aluminum ingot can be removed, and the impurities are prevented from being brought into a final product to further influence the purity of the product. In some embodiments, in step four, the etch time is from 0.5h to 2 h.

In the sixth step, inert gas or hydrogen is used to perform air cleaning (or scavenging) on the quartz tube 21 before zone melting, so as to avoid the influence of various possible impurities contained in the original air on the purity of the product. Further, the use of an inert gas or hydrogen gas as a protective gas prevents the aluminum ingot of the other boat 20 from being oxidized, and further, hydrogen gas can be discharged by reacting with a part of impurities in the aluminum ingot to form a gas (e.g., selenium can react with hydrogen gas to form hydrogen selenide gas), thereby improving the purification effect.

In some embodiments, in step six, the inert gas is nitrogen or argon; the flow rate of the inert gas is 2L/min-4L/min; the time for introducing the inert gas is 4-8 h; the flow rate of the hydrogen is 1L/min-3L/min.

In some embodiments, in step seven, the operating speed of heater 22 is 20mm/h to 40 mm/h. In some embodiments, in step seven, the length of the melt zone M is 8cm + -2 cm, in other words the length of the melt zone M is 6cm-10 cm. In some embodiments, in step seven, the operating speed of heater 22 is between 25mm/h and 35 mm/h.

In step eight, since impurities such as titanium, vanadium, chromium, etc. may be concentrated in the head of the zone-melting ingot (i.e., the end of the zone-melting ingot in the unidirectional traveling direction of the heater 22) during the zone-melting process, in some embodiments, in step eight, N is calculated according to the following formula: n ═ L/F ] +1, where L is the length of the boat, F is the length of the melt zone M, and [ L/F ] is the integer for the L/F result.

In some embodiments, in step eight, the number of zone smelts, N, is 8-12.

In some embodiments, in step nine, the aluminum heads and tails of the obtained products are respectively removed in a length range of 10cm to 15 cm. In some embodiments, in step nine, the aluminum heads and tails of the obtained products are respectively removed in a length range of 12cm-15 cm. The reason for removing the tail is because during the zone-melting process, other impurities can be concentrated at the tail, such as: silicon, iron, copper, magnesium, and the like.

In summary, in the method for preparing ultra-high purity aluminum of the present disclosure, impurities at least containing titanium, vanadium, and chromium, which have a high boiling point relative to aluminum, and impurities having a low boiling point relative to aluminum are separated as three parts by vacuum distillation in the first step, impurities on the surface of a glassy carbon boat or a boron nitride boat are removed in the second step, oxides on the surface of an aluminum ingot are removed in the fourth step, the influence of air originally existing in a quartz tube is removed in the sixth step, and an inert gas or hydrogen gas is protected, and finally, 6.5N ultra-high purity aluminum is obtained by repeating the zone-melting process in the seventh to ninth steps and the tenth step.

The test procedure of the disclosed embodiment is explained next.

Example 1

Ultra-high purity aluminum was prepared as follows.

The method comprises the following steps: putting 5N raw material aluminum ingots into a graphite boat raw material groove 1, wherein the graphite boat raw material groove 1 is adjacent to a graphite boat product groove 2, the graphite boat raw material groove 1 and the graphite boat product groove 2 are separated from each other and communicated with each other, covering a graphite cover 3 to enable the graphite cover 3, the graphite boat raw material groove 1 and the graphite boat product groove 2 to form a cavity S with a communication port P1 except for one side of the graphite boat product groove 2 far away from the graphite boat raw material groove 1, putting the graphite cover 3, the graphite boat raw material groove 1, the graphite boat product groove 2 and the raw material aluminum ingots into a vacuum distillation furnace, putting a dust collecting tank 4 with a vacuumizing port P2 to enable the inner cavity of the dust collecting tank 4 to be communicated with the communication port P1, covering a furnace cover 5, and vacuumizing equipment outside the connected graphite boat raw material groove 1, the graphite boat product groove 2, the graphite cover 3 and the dust collecting tank 4 through a vacuumizing port P2 arranged on the vacuum interface 10 and the dust collecting tank 4 to vacuumize the connected graphite boat raw material groove 1, the graphite boat raw material groove 2 and the graphite boat raw material groove 2, and the dust collecting tank 4 to be communicated with the vacuum collecting tank, The vacuum degree in the graphite boat product groove 2, the graphite cover 3 and the dust collecting groove 4 reaches below 1Pa, then a vacuum interface 10 is sealed, cooling water is started to cool, the cooling water flows through a flow passage formed by a cooling water first inlet 11A, a corresponding flow passage in the furnace cover 5 and a cooling water first outlet 12A, a cooling water second inlet 11B, a corresponding flow passage in the furnace cover 5 and a flow passage formed by a cooling water second outlet 12B, a first temperature area induction heating coil 6A and a second temperature area induction heating coil 6B are started simultaneously for vacuum distillation, the temperature of a first area corresponding to the graphite boat raw material groove 1 is controlled to be 1200 ℃ by detecting a first area temperature thermocouple 9A and a second area temperature thermocouple 9B during vacuum distillation, the temperature of a second area corresponding to the graphite boat product groove 2 is controlled to be 680 ℃, and the distillation time is 16h, taking out the aluminum in the graphite boat product groove 2 after cooling, weighing, wherein the yield of the aluminum in the graphite boat product groove 2 is 75% (namely, the weight of the aluminum in the graphite boat product groove 2 is divided by the weight of the raw material aluminum ingot);

step two: soaking the glass carbon boat or the boron nitride boat in aqua regia for 4h, cleaning with pure water, and drying for later use;

step three: melting the aluminum obtained in the step one in a high-purity graphite crucible, pouring the molten aluminum into the prepared glass carbon boat or boron nitride boat in the step two, and pouring out an aluminum ingot after cooling;

step four: corroding the aluminum ingot obtained in the step three with a solution of pure water, UP-grade nitric acid and UP-grade hydrofluoric acid in a volume ratio of 2:2:1 for 1h, cleaning the aluminum ingot with pure water to be neutral, and then drying the aluminum ingot in vacuum;

step five: putting the aluminum ingot obtained in the fourth step into another glass carbon boat or boron nitride boat 20 prepared in the third step, then putting the aluminum ingot into a quartz tube 21 of a zone melting furnace, sealing two ends of the quartz tube 21, arranging gas inlets and outlets 211 at two ends of the quartz tube 21, and closing a furnace cover of the zone melting furnace, wherein the length of the other glass carbon boat or boron nitride boat 20 is 66 cm;

step six: opening an inert gas valve, introducing 7N high-purity inert gas into the quartz tube 21 through a gas inlet and outlet 211 of the quartz tube 21, wherein the flow rate of nitrogen is 2L/min, closing the inert gas valve after 8h, opening a hydrogen valve, and introducing 7N high-purity hydrogen into the quartz tube 21, wherein the hydrogen flow rate is 2L/min;

step seven: and (3) turning on the heater 22, and starting to operate after the aluminum ingot at the head of the other glass carbon boat or the boron nitride boat 20 starts to melt, wherein the operating speed of the heater is 30 mm/h. Adjusting the temperature of the heater 22 during the operation process, so that the length of a melting zone M formed after the aluminum ingot is melted is maintained at 6 cm;

step eight: when the heater 22 moves to the tail of the other glassy carbon boat or boron nitride boat 20, stopping heating, automatically returning the heater 22 to the original point at the head of the boat according to a set program, performing the second zone melting operation, and repeating the zone operation for 12 times, wherein the length of the other glassy carbon boat or boron nitride boat 20 is L, F is the length of the melting zone M, and [ L/F ] +1 is 12;

step nine: stopping heating after zone melting is finished, closing a hydrogen valve after the aluminum ingot is cooled, opening a furnace cover of the zone melting furnace, taking out the aluminum ingot, and removing the head and the tail of the aluminum ingot by 12cm respectively to obtain an aluminum product in the middle part;

step ten: and (4) operating the aluminum product in the middle part once again according to the fourth step to the ninth step to obtain 6.5N aluminum, and sending the aluminum to GDMS for detection and analysis.

Example 2

The procedure was the same as in example 1, except that,

in the first step, the temperature of a first area corresponding to the graphite boat raw material tank 1 is 1300 ℃, the temperature of a second area corresponding to the graphite boat product tank 2 is controlled to be 700 ℃, the distillation time is 12h, and the yield of aluminum in the graphite boat product tank 2 is 71%;

in step five, the length of the other glass carbon boat or the boron nitride boat 20 is 72 cm;

in the seventh step, the operation speed of the heater 22 is 25mm/h, and the length of a melting zone M formed after the aluminum ingot is melted is maintained at 8 cm;

in step eight, repeating the zone operation for 10 times;

in the ninth step, the head and the tail of the aluminum ingot are respectively 15 cm.

Example 3

The procedure was the same as in example 1, except that,

in the first step, the temperature of a first area corresponding to the graphite boat raw material tank 1 is 1250 ℃, the temperature of a second area corresponding to the graphite boat product tank 2 is controlled to be 680 ℃, the distillation time is 14h, and the yield of aluminum in the graphite boat product tank 2 is 78%;

in the fourth step, the volume ratio of the pure water to the nitric acid in the UP stage to the hydrofluoric acid in the UP stage is 3:2: 1;

in step five, the length of the other glass carbon boat or the boron nitride boat 20 is 80 cm;

in the sixth step, the flow of the nitrogen is 4L/min, the nitrogen gas valve is closed after 8 hours, and the flow of the hydrogen is 2L/min;

in the seventh step, the operation speed of the heater 22 is 35mm/h, and the length of the melting zone M is maintained at 10 cm;

in step eight: repeating the operation of the region for 9 times;

in the ninth step: the head and the tail of the aluminum ingot are 15cm respectively.

Table 1 shows the results of GDMS measurements on the final aluminum products of examples 1-3.

TABLE 1 GDMS test results (unit: ppbw) of final aluminum products of examples 1-3

As can be seen from Table 1, after one-time vacuum distillation and a plurality of times of zone melting, the total content of impurities in the aluminum is controlled below 500ppb, namely 6.5N ultra-high purity aluminum is obtained, and the single impurities are in the standard range (likewise, titanium, vanadium and chromium which are difficult to remove in the prior art are also removed and reach the standard), so that the requirements of the ultra-high purity aluminum on the impurity content are met, and the use requirements of the ultra-high purity aluminum in the MBE field in the current market are completely met.