CN111893559B - Preparation method of ultra-high-purity cadmium crystal - Google Patents

Preparation method of ultra-high-purity cadmium crystal Download PDF

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CN111893559B
CN111893559B CN202010630158.2A CN202010630158A CN111893559B CN 111893559 B CN111893559 B CN 111893559B CN 202010630158 A CN202010630158 A CN 202010630158A CN 111893559 B CN111893559 B CN 111893559B
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cadmium
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funnel
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CN111893559A (en
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黄杰杰
朱刘
何志达
李清宇
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First Rare Materials Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B17/00—Obtaining cadmium
    • C22B17/06—Refining
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements

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Abstract

The invention discloses a preparation method of an ultra-high-purity cadmium crystal, belonging to the field of high-purity metal materials. The method melts the raw material cadmium in the funnel so that the oxidized slag in the cadmium is remained in the funnel, so that the cadmium melt dripped or flowed into the crucible along the leakage hole of the funnel can be bright without oxidation without slag removal treatment; in addition, the cadmium melt in the crucible is purified by adopting a vertical pulling method, the obtained crystal has low dislocation density, high optical uniformity, stable structure, bright and non-oxidized surface, shows the natural color of metal, does not need subsequent treatment, and can be drawn into different sizes of products according to the requirements of customers.

Description

Preparation method of ultra-high-purity cadmium crystal
Technical Field
The invention belongs to the field of high-purity metal materials, and relates to a preparation method of an ultra-high-purity cadmium crystal.
Background
The ultra-high pure cadmium crystal has the purity of 99.99999 percent (7N), and the substrate materials of the tellurium-zinc-Cadmium (CZT) nuclear radiation detector and the tellurium-cadmium-Mercury (MCT) infrared detector prepared from the ultra-high pure cadmium are widely applied to the fields of national defense, security protection, positioning, guidance infrared detection and the like. Impurities in the cadmium directly influence the service performance of CZT and MCT crystal materials, and further influence the detection range and the detection precision of the two detectors, so that the research and preparation of the ultra-high pure cadmium product with ultra-high purity and stable quality performance has great significance.
The main preparation method of the present ultra-high pure cadmium comprises the following steps: the method comprises the steps of performing a vacuum distillation method, a directional solidification method, a zone melting method and the like, wherein the methods have poor purification effect and various defects, and the development of the ultra-high pure cadmium preparation technology and a rear-end industrial chain is severely restricted, for example, products produced by the zone melting or the directional solidification need to be subjected to subsequent treatment modes such as cutting, corrosion and the like, and the procedures can cause product cross contamination, procedure extension, cost increase and the like.
Disclosure of Invention
In order to overcome the defects and shortcomings in the prior art, the invention aims to provide the preparation method of the ultra-high-purity cadmium crystal, which is simple to operate, less in subsequent treatment procedures, good in purification effect, safe, economical and environment-friendly.
The invention provides a preparation method of an ultra-high-purity cadmium crystal (with the purity of more than 7N), which comprises the following steps:
(1) placing a raw material cadmium in a funnel, completely melting the raw material cadmium under a vacuum condition or in a protective gas atmosphere to form a cadmium melt, and dripping or flowing the cadmium melt into a crucible along a leakage hole of the funnel;
(2) purifying the cadmium melt in the crucible by adopting a vertical pulling method to obtain a crystal product;
the crystal product is the ultra-high pure cadmium crystal, or the crystal product is processed for more than 1 time by repeating the steps (1) - (2), and the ultra-high pure cadmium crystal is obtained.
In the preparation process of the raw material cadmium, such as 5N cadmium, a cadmium oxide film rich in impurities is formed on the surface of the raw material cadmium, if the raw material cadmium is directly placed in a crucible for melting, then when a vertical pulling method is adopted for purification subsequently, the oxidized slag materials are attached to the surface of a cadmium crystal, so that a slag skimming procedure is required to be added for removing most of slag materials, but the equipment structure is limited, and the slag materials cannot be completely removed. According to the preparation method, the raw material cadmium is melted in the funnel, the melted material is dripped or flows into the crucible along the leakage hole, and in the process, the oxidation slag material floats on the surface of the melted material to form a thin film and finally remains in the funnel, so that the melted material in the crucible can be bright and free of oxidation without slag removal treatment. In addition, the preparation method adopts a vertical pulling method to purify the cadmium melt in the crucible, the obtained crystal has stable structure, bright and non-oxidized surface and metallic natural color, does not need subsequent treatment, and can be used for drawing products with different sizes according to the requirements of customers. In addition, the vertical pulling method has the following advantages: the growth state of the crystal can be conveniently observed in the production process; the crystal grows at the surface of the melt without contact with the crucible, which significantly reduces the stress of the crystal and prevents parasitic nucleation of the pot walls; the use of directional seed and "necking" processes is facilitated and seed dislocations behind the neck are greatly reduced, thus reducing the dislocation density of the grown crystal after enlargement. In conclusion, the vertical Czochralski method has high crystal perfection, satisfactory growth rate and crystal size, low dislocation density, high optical uniformity, and no mosaic structure.
The shielding gas is generally nitrogen or inert gas, and the inert gas comprises helium, neon and argon.
Preferably, in the step (1), the raw material cadmium is firstly subjected to vacuum degree of not more than 5 × 10-3Preheating to 150-200 ℃ under Pa, preserving heat for 30-60min, then completely melting in a protective gas atmosphere of 0.1-0.15MPa, and then dripping or flowing into the crucible under 320-350 ℃.
Preferably, the vertical pulling method comprises the steps of: preheating cadmium seed crystals to prevent liquid level solidification during seeding, enabling the cadmium seed crystals to be in contact with cadmium melt in the crucible under the condition that the cadmium seed crystals rotate relative to the crucible, sequentially performing seeding, shouldering, shoulder rotating and equal-diameter growth treatment after the contact parts of the cadmium seed crystals and the cadmium melt in the crucible are melted into a whole, stopping crystal growth, and cooling to obtain the crystal product. According to the preparation method, the cadmium seed crystal rotates relative to the cadmium melt in the crucible during seeding, so that the cadmium seed crystal can better form crystals, and the subsequently obtained crystals have better structures.
Preferably, the treatment method for preheating the cadmium seed crystal comprises the following steps: and (3) placing cadmium seed crystals 5-10mm above the cadmium melt in the crucible, and preheating for 10-15min at 320-350 ℃.
Preferably, the rotating speed is 18-27 r/min; the seeding speed is 10-30 mm/min, and the seeding length is 2-5 cm; the shouldering speed is 5-10 mm/h; the speed of the shoulder rotating is 15-30 mm/h; the speed of the constant-diameter growth is 15-30 mm/h.
Preferably, when the cadmium seed crystal rotates relative to the crucible, the cadmium seed crystal and the crucible respectively perform opposite rotation motions, wherein the cadmium seed crystal rotates at a rotation speed of 10-15 r/min, and the crucible rotates at a rotation speed of 8-12 r/min.
Preferably, when the crystal growth is stopped, 10-15% of the material in the crucible is left.
Preferably, the purity of the raw material cadmium is 5N, and the number of times of repeating the treatments of the steps (1) to (2) is 1-2 times.
Preferably, the funnel and the crucible are both made of quartz, and the surfaces of the funnel and the crucible are both plated with pyrolytic carbon films. At high temperatures, quartz containers can contaminate the melt, e.g., Si causes the purity of the crystal to decrease; in addition, liquid cadmium condenses into a solid state, and the quartz fractures due to the surface tension effect. The pyrolytic carbon film is plated on the surface of the quartz device, so that impurities in the quartz device can be prevented from being brought into materials, pollution of the materials is reduced, and meanwhile, after the quartz device is plated with carbon, the materials are not adhered to the quartz device after being cooled, so that material loss can be reduced, and breakage of the quartz device can be avoided.
Preferably, the leakage hole of the funnel is 1-2 mm. When the leakage hole of the funnel is 1-2 mm, the cadmium melt is dripped into the crucible, and oxidation slag in the crucible can be well removed.
Compared with the prior art, the invention has the following advantages: the method melts the raw material cadmium in the funnel so as to leave the oxidation slag in the funnel, so that the cadmium melt dripped or flowed into the crucible along the leakage hole of the funnel can be bright and free of oxidation without slag removal treatment; in addition, the cadmium melt in the crucible is purified by adopting a vertical pulling method, the obtained crystal has low dislocation density, high optical uniformity, stable structure, bright and non-oxidized surface, shows the natural color of metal, does not need subsequent treatment, and can be drawn into products with different sizes according to the requirements of customers.
Drawings
FIG. 1 is a schematic view of a single crystal furnace used in various embodiments;
the method comprises the following steps of 1-cadmium raw material melt, 2-cadmium single crystal product, 3-seed crystal, 4-seed crystal clamp, 5-seed crystal rod, 6-quartz crucible, 7-graphite crucible, 8-heating temperature field, 9-furnace body shell, 10-slag removing rod, 11-hanging rod, 12-quartz funnel, 13-pressure gauge, 14-heating electrode and 15-graphite crucible base.
Detailed Description
To better illustrate the objects, aspects and advantages of the present invention, the present invention is further illustrated by the following examples. It is apparent that the following examples are only a part of the embodiments of the present invention, and not all of them. It should be understood that the embodiments of the present invention are only for illustrating the technical effects of the present invention, and are not intended to limit the scope of the present invention.
Example 1
This example is an embodiment of the method for preparing ultra-high purity cadmium crystal of the present invention. The device adopted by the preparation method of the ultra-high pure cadmium crystal is shown in figure 1 and comprises the following steps:
(1) putting 5N raw material cadmium into a quartz funnel, aligning the quartz funnel and a quartz crucible up and down, closing a furnace door of the single crystal furnace, starting a vacuum pump to pump vacuum to 5 multiplied by 10-3Pa below;
(2) preheating to 150 ℃, then continuously vacuumizing, preheating and preserving heat for 30 min;
(3) closing the vacuum pump, filling purified high-purity nitrogen (more than 6N) into the furnace body until the pressure is 0.1MPa, and closing the gas charging valve;
(4) adjusting heating power, melting 5N of cadmium as raw material, dropping the cadmium into a quartz crucible from a quartz funnel, stabilizing the temperature at 320 ℃ after the cadmium as raw material is completely melted, and keeping the temperature for 30 min;
(5) adjusting a seed crystal rod, lowering the seed crystal to a position 10mm away from the melt, and preheating the seed crystal for 10 min;
(6) the seed rod rotates anticlockwise at the rotating speed of 10r/min, and the graphite crucible rotates clockwise at the rotating speed of 8 r/min;
(7) slowly lowering the seed crystal to be in contact with the cadmium melt in the quartz crucible, starting manual inching for seeding after the seed crystal and the melt are melted into a whole, setting the seeding speed to be 10mm/min and the seeding length to be 2 cm;
(8) after seeding is finished, automatically controlling the system, and starting shouldering operation, wherein the shouldering speed is set to be 5 mm/h;
(9) shouldering to the required shoulder surface size, and starting to perform shoulder rotating operation, wherein the shoulder rotating speed is set to be 15 mm/h;
(10) after the shoulder is turned, performing equal-diameter growth operation, wherein the equal-diameter growth speed is 15 mm/h;
(11) stopping crystal growth when 15% of the material in the quartz crucible is remained, lifting the crystal to be separated from the melt, closing heating, cooling and discharging to obtain a product of 6N cadmium;
(12) repeating the operation of the step 1-11 to re-pull the 6N cadmium once, wherein the parameters are unchanged, and obtaining the 7N ultra-high purity cadmium crystal. And (4) sampling the obtained ultra-high-purity cadmium crystal product and sending the ultra-high-purity cadmium crystal product to GDMS for detection.
Example 2
This example is an embodiment of the method for preparing ultra-high purity cadmium crystal of the present invention. The device adopted by the preparation method of the ultra-high pure cadmium crystal is shown in figure 1 and comprises the following steps:
(1) putting 5N raw material cadmium into a quartz funnel, aligning the quartz funnel and a quartz crucible up and down, closing a furnace door of the single crystal furnace, starting a vacuum pump to pump vacuum to 5 multiplied by 10-3Pa below;
(2) preheating to 180 ℃, then continuously vacuumizing, preheating and preserving heat for 30 min;
(3) closing the vacuum pump, filling purified high-purity nitrogen (more than 6N) into the furnace body until the pressure is 0.1MPa, and closing the gas charging valve;
(4) adjusting heating power, melting 5N of cadmium as raw material, dropping the cadmium into a quartz crucible from a quartz funnel, stabilizing the temperature at 340 ℃ after the cadmium as raw material is completely melted, and keeping the temperature for 30 min;
(5) adjusting a seed crystal rod, lowering the seed crystal to a position 10mm away from the melt, and preheating the seed crystal for 10 min;
(6) the seed rod rotates anticlockwise at the rotating speed of 12r/min, and the graphite crucible rotates clockwise at the rotating speed of 10 r/min;
(7) slowly lowering the seed crystal to be in contact with the melt, starting manual inching for seeding after the seed crystal and the melt are melted into a whole, and setting the seeding speed to be 20mm/min and the seeding length to be 2 cm;
(8) after seeding is finished, automatically controlling the system, and starting shouldering operation, wherein the shouldering speed is set to be 10 mm/h;
(9) shouldering to the required shoulder surface size, and starting to perform shoulder rotating operation, wherein the shoulder rotating speed is set to be 30 mm/h;
(10) after the shoulder is turned, performing equal-diameter growth operation, wherein the equal-diameter growth speed is 30 mm/h;
(11) stopping crystal growth when 15% of the material in the quartz crucible is remained, lifting the crystal to be separated from the melt, closing heating, cooling and discharging to obtain a product of 6N cadmium;
(12) repeating the operation of the step 1-11 to re-pull the 6N cadmium once, wherein the parameters are unchanged, and obtaining the 7N ultra-high purity cadmium crystal. And (4) sampling the obtained ultra-high-purity cadmium crystal product and sending the ultra-high-purity cadmium crystal product to GDMS for detection.
Example 3
This example is an embodiment of the method for preparing ultra-high purity cadmium crystal of the present invention. The device adopted by the preparation method of the ultra-high pure cadmium crystal is shown in figure 1 and comprises the following steps:
(1) putting 5N raw material cadmium into a quartz funnel, aligning the quartz funnel and a quartz crucible up and down, closing a furnace door of the single crystal furnace, starting a vacuum pump to pump vacuum to 5 multiplied by 10-3Pa below;
(2) preheating to 200 ℃, then continuously vacuumizing, preheating and preserving heat for 30 min;
(3) closing the vacuum pump, filling purified high-purity nitrogen (more than 6N) into the furnace body until the pressure is 0.1MPa, and closing the gas charging valve;
(4) adjusting heating power, melting 5N of cadmium as raw material, dropping the cadmium into a quartz crucible from a quartz funnel, stabilizing the temperature at 350 ℃ after the cadmium as raw material is completely melted, and keeping the temperature for 30 min;
(5) adjusting a seed crystal rod, lowering the seed crystal to a position 10mm away from the melt, and preheating the seed crystal for 10 min;
(6) the seed rod rotates anticlockwise at the rotating speed of 15r/min, and the graphite crucible rotates clockwise at the rotating speed of 12 r/min;
(7) slowly lowering the seed crystal to be in contact with the melt, starting manual inching for seeding after the seed crystal and the melt are melted into a whole, and setting the seeding speed to be 30mm/min and the seeding length to be 2 cm;
(8) after seeding is finished, automatically controlling the system, and starting shouldering operation, wherein the shouldering speed is set to be 10 mm/h;
(9) shouldering to the required shoulder surface size, and starting to perform shoulder rotating operation, wherein the shoulder rotating speed is set to be 15 mm/h;
(10) after the shoulder is turned, performing equal-diameter growth operation, wherein the equal-diameter growth speed is 30 mm/h;
(11) stopping crystal growth when 10% of the material in the quartz crucible is remained, lifting the crystal to be separated from the melt, closing heating, cooling and discharging to obtain a product of 6N cadmium;
(12) repeating the operation of the step 1-11 to re-pull the 6N cadmium once, wherein the parameters are unchanged, and obtaining the 7N ultra-high purity cadmium crystal. And (4) sampling the obtained ultra-high-purity cadmium crystal product and sending the ultra-high-purity cadmium crystal product to GDMS for detection.
Example 4
This example is an embodiment of the method for preparing ultra-high purity cadmium crystal of the present invention. The device adopted by the preparation method of the ultra-high pure cadmium crystal is shown in figure 1 and comprises the following steps:
(1) putting 5N raw material cadmium into a quartz funnel, aligning the quartz funnel and a quartz crucible up and down, closing a furnace door of the single crystal furnace, starting a vacuum pump to pump vacuum to 5 multiplied by 10-3Pa below;
(2) preheating to 150 ℃, then continuously vacuumizing, preheating and preserving heat for 30 min;
(3) closing the vacuum pump, filling purified high-purity nitrogen (more than 6N) into the furnace body until the pressure is 0.1MPa, and closing the gas charging valve;
(4) adjusting heating power, melting 5N of cadmium as raw material, dropping the cadmium into a quartz crucible from a quartz funnel, stabilizing the temperature at 320 ℃ after the cadmium as raw material is completely melted, and keeping the temperature for 30 min;
(5) adjusting a seed crystal rod, lowering the seed crystal to a position 10mm away from the melt, and preheating the seed crystal for 10 min;
(6) the seed rod rotates anticlockwise at the rotating speed of 12r/min, and the graphite crucible rotates clockwise at the rotating speed of 12 r/min;
(7) slowly lowering the seed crystal to be in contact with the melt, starting manual inching for seeding after the seed crystal and the melt are melted into a whole, and setting the seeding speed to be 30mm/min and the seeding length to be 2 cm;
(8) after seeding is finished, automatically controlling the system, and starting shouldering operation, wherein the shouldering speed is set to be 10 mm/h;
(9) shouldering to the required shoulder surface size, and starting to perform shoulder rotating operation, wherein the shoulder rotating speed is set to be 30 mm/h;
(10) after the shoulder is turned, performing equal-diameter growth operation, wherein the equal-diameter growth speed is 30 mm/h;
(11) stopping crystal growth when 10% of the material in the quartz crucible is remained, lifting the crystal to be separated from the melt, closing heating, cooling and discharging to obtain a product of 6N cadmium;
(12) repeating the operation of the step 1-11 to re-pull the 6N cadmium once, wherein the parameters are unchanged, and obtaining the 7N ultra-high purity cadmium crystal. And (4) sampling the obtained ultra-high-purity cadmium crystal product and sending the ultra-high-purity cadmium crystal product to GDMS for detection.
Example 5
This example is an embodiment of the method for preparing ultra-high purity cadmium crystal of the present invention. The device adopted by the preparation method of the ultra-high pure cadmium crystal is shown in figure 1 and comprises the following steps:
(1) putting 5N raw material cadmium into a quartz funnel, aligning the quartz funnel and a quartz crucible up and down, closing a furnace door of the single crystal furnace, starting a vacuum pump to pump vacuum to 5 multiplied by 10-3Pa below;
(2) preheating to 200 ℃, then continuously vacuumizing, preheating and preserving heat for 30 min;
(3) closing the vacuum pump, filling purified high-purity nitrogen (more than 6N) into the furnace body until the pressure is 0.1MPa, and closing the gas charging valve;
(4) adjusting heating power, melting 5N of cadmium as raw material, dropping the cadmium into a quartz crucible from a quartz funnel, stabilizing the temperature at 330 ℃ after the cadmium as raw material is completely melted, and keeping the temperature for 30 min;
(5) adjusting a seed crystal rod, lowering the seed crystal to a position 10mm away from the melt, and preheating the seed crystal for 10 min;
(6) the seed rod rotates anticlockwise at the rotating speed of 15r/min, and the graphite crucible rotates clockwise at the rotating speed of 10 r/min;
(7) slowly lowering the seed crystal to be in contact with the melt, starting manual inching for seeding after the seed crystal and the melt are melted into a whole, and setting the seeding speed to be 10mm/min and the seeding length to be 2 cm;
(8) after seeding is finished, automatically controlling the system, and starting shouldering operation, wherein the shouldering speed is set to be 5 mm/h;
(9) shouldering to the required shoulder surface size, and starting to perform shoulder rotating operation, wherein the shoulder rotating speed is set to be 15 mm/h;
(10) after the shoulder is turned, performing equal-diameter growth operation, wherein the equal-diameter growth speed is 15 mm/h;
(11) stopping crystal growth when 15% of the material in the quartz crucible is remained, lifting the crystal to be separated from the melt, closing heating, cooling and discharging to obtain a product of 6N cadmium;
(12) repeating the operation of the step 1-11 to re-pull the 6N cadmium once, wherein the parameters are unchanged, and obtaining the 7N ultra-high purity cadmium crystal. And (4) sampling the obtained ultra-high-purity cadmium crystal product and sending the ultra-high-purity cadmium crystal product to GDMS for detection.
The ultra-high purity cadmium crystal products obtained in examples 1 to 5 were single crystals, and their GDMS analysis results are shown in Table 1.
TABLE 1 ultra-high purity cadmium impurity statistics table (unit: ppb)
Impurities Ag Al Ca Cr Cu Fe Zn Mg Ni Pb Sn
National standard <5 <5 <5 <5 <5 <10 <20 <5 <5 <5 <5
Example 1 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5
Example 2 <5 <5 <5 5 <5 6 5 <5 <5 6 <5
Example 3 <5 <5 <5 <5 <5 7 10 <5 <5 <5 <5
Example 4 <5 <5 <5 <5 <5 5 8 <5 <5 <5 <5
Example 5 <5 <5 <5 <5 <5 6 7 <5 <5 <5 <5
As can be seen from Table 1, after 2 times of purification by the vertical pulling method, the impurity content of cadmium can be controlled below 100ppba, and single impurity is in a standard range, which meets the requirement of ultra-high purity cadmium impurity content.
Meanwhile, the obtained parameter design with reasonable process is as follows: vacuum degree of 5X 10-3Below Pa, preheating at the temperature of 150-200 ℃, maintaining the temperature of 320-350 ℃ after the materials are melted, controlling the rotating speeds of the seed rod and the graphite crucible to be 10-15 r/min and 8-12 r/min respectively, controlling the seeding speed to be 10-30 mm/min, controlling the shouldering speed to be 5-15 mm/h, controlling the shouldering speed to be 15-30 mm/h, controlling the constant-diameter growth speed to be 15-30 mm/h, and remaining 10-15% of the materials in the quartz crucible;
the optimal parameter control is as follows: vacuum degree of 5X 10-3The preheating temperature is below Pa, the preheating temperature is 150 ℃, the temperature is maintained at 320 ℃ after the materials are melted, the rotating speeds of the seed rod and the graphite crucible are respectively 10r/min and 8r/min, the seeding speed is 10mm/min, the shouldering speed is 5mm/h, the shouldering speed is 15mm/h, the isodiametric growth speed is 15mm/h, and the materials in the quartz crucible are left for 10-15%.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims (4)

1. A preparation method of ultra-high-purity cadmium crystal is characterized by comprising the following steps:
(1) placing the raw material cadmium in a funnel, and then keeping the vacuum degree not higher than 5 multiplied by 10-3Preheating to 150 ℃ under the condition of Pa, preserving heat for 30min, then melting in protective gas atmosphere, dripping the formed cadmium melt into a crucible along a leakage hole of the funnel, stabilizing the temperature at 320 ℃ after the raw material cadmium is completely melted, and preserving heat for 30 min;
(2) purifying the cadmium melt in the crucible by adopting a vertical pulling method to obtain a crystal product;
the crystal product is the ultra-high pure cadmium crystal, or the crystal product is processed for more than 1 time by repeating the steps (1) - (2), and the ultra-high pure cadmium crystal is obtained;
the vertical Czochralski method comprises the following steps: placing cadmium seed crystals at a position 10mm above a cadmium melt in a crucible, preheating for 10min, contacting the cadmium seed crystals with the cadmium melt in the crucible under the condition that the cadmium seed crystals and the crucible rotate reversely, performing seeding, shouldering, shoulder rotating and equal-diameter growth treatment in sequence after the contact parts of the cadmium seed crystals and the cadmium melt in the crucible are melted into a whole, stopping crystal growth when 10% of materials in the crucible remain, and cooling to obtain a crystal product, wherein the rotating speed of the cadmium seed crystals is 10r/min, and the rotating speed of the crucible is 8 r/min; the seeding speed is 10mm/min, and the seeding length is 2 cm; the shouldering speed is 5 mm/h; the speed of the shoulder rotating is 15 mm/h; the speed of the equal-diameter growth is 15 mm/h;
the ultra-high purity cadmium crystal is a single crystal.
2. The method according to claim 1, wherein the purity of the cadmium raw material is 5N, and the number of times of repeating the treatments of the steps (1) to (2) is 1 to 2.
3. The method according to claim 1, wherein the funnel and the crucible are made of quartz, and surfaces of the funnel and the crucible are coated with pyrolytic carbon film.
4. The preparation method according to claim 1, wherein the leakage hole of the funnel is 1-2 mm.
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