CN111394781B - Method for growing uranium dioxide crystal by using borate fluxing agent - Google Patents

Method for growing uranium dioxide crystal by using borate fluxing agent Download PDF

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Publication number
CN111394781B
CN111394781B CN202010262173.6A CN202010262173A CN111394781B CN 111394781 B CN111394781 B CN 111394781B CN 202010262173 A CN202010262173 A CN 202010262173A CN 111394781 B CN111394781 B CN 111394781B
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fluxing agent
uranium dioxide
growing
temperature
crystals
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CN111394781A (en
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徐家跃
潘芸芳
李志超
冯海威
周鼎
田甜
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Shanghai Institute of Technology
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Shanghai Institute of Technology
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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
    • C30B9/00—Single-crystal growth from melt solutions using molten solvents
    • C30B9/04—Single-crystal growth from melt solutions using molten solvents by cooling of the solution
    • C30B9/08—Single-crystal growth from melt solutions using molten solvents by cooling of the solution using other solvents
    • C30B9/12—Salt solvents, e.g. flux growth
    • 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
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/16—Oxides

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)

Abstract

The invention belongs to the technical field of crystal preparation, and particularly discloses a method for growing uranium dioxide crystals by using borate fluxing agent, which comprises the following steps: (1) fluxing agent Li5U(BO3)3By stoichiometric ratio of Li2CO3、H3BO3And UO2Mixing and grinding the powder for 3 hours; (2) putting the mixed powder in the step (1) into a platinum crucible, and sintering at three-section temperature; (3) fluxing agent Li5U(BO3)3And UO2Mixing the raw materials according to a molar ratio of 83mol% to 17mol%, grinding, placing into a platinum crucible, introducing Ar/5% H2Placing in a tubular resistance furnace, heating to 1235 deg.C, and using Li5U(BO3)3Fluxing agent to react UO2Dissolving, the system reaches a molten state, and slowly cooling to reach supersaturation degree to drive crystal growth to obtain UO2And (4) crystals. The scheme is mainly used for preparing the uranium dioxide crystal, and solves the problem that the existing melt method is difficult to grow the ultrahigh-melting-point uranium dioxide crystal.

Description

Method for growing uranium dioxide crystal by using borate fluxing agent
Technical Field
The invention belongs to the technical field of crystal preparation, and particularly discloses a method for growing uranium dioxide crystals by using borate fluxing agent.
Background
Uranium dioxide has semiconductor properties and the resistivity decreases with increasing temperature. Uranium dioxide has been widely used in the manufacture of reactor fuel elements because of its properties of being non-anisotropically deformed when subjected to intense radiation, being non-lattice-changing at high temperatures, non-volatile and non-chemically reactive with water.
Uranium dioxide is one of the thermodynamically stable states in the uranium-oxygen system, and belongs to the cubic system, the face-centered cubic structure (fluorite type, space group Fm3m), and a 547 pm. The thermal conductivity was 0.09W/cm ℃ at 100 ℃. Can slowly react with hydrochloric acid, sulfuric acid and nitric acid at room temperature, is easily dissolved in nitric acid to generate brilliant yellow UO2(NO3)2And (3) solution. Insoluble in water and alkali, but soluble in hydrogen peroxide-containing alkali or carbonAcid salt solution to produce a perborate salt. Is stable in air at room temperature, and is oxidized into UO when heated to 200-500 deg.C3Oxidized to U above 500 ℃3O8. The uranium dioxide is in the form of uranium fuel for light water reactor, heavy water reactor and fast breeder reactor in atomic power station, and is a stable ceramic fuel. In the uranium process, uranium dioxide is an important intermediate product and is a raw material for producing uranium tetrafluoride by a dry method. Can be prepared by reducing uranium trioxide or triuranium octoxide with hydrogen, or by uranyl ammonium tricarbonate (NH)4)4[UO2(CO3)3]Directly calcining and reducing to obtain the catalyst. The uranium tetrafluoride is a nuclear fuel widely used in a power reactor and an important raw material for preparing the uranium tetrafluoride by a dry method.
The uranium dioxide is in a stable polycrystalline state at normal temperature. The uranium dioxide single crystal is not only an excellent material form for researching the high-temperature nuclear reaction characteristics of the nuclear fuel, but also an excellent functional material, and has great application potential in the fields of solar energy, thermoelectricity, semiconductor devices and the like. Because the melting point of the uranium dioxide crystal is as high as 2878 ℃, the uranium dioxide crystal is difficult to obtain by the existing melt method growth technology. The cosolvent can greatly reduce the crystal growth temperature and is beneficial to solving the problem of uranium dioxide crystal preparation.
Disclosure of Invention
The invention aims to provide a method for growing uranium dioxide crystals by using a borate fluxing agent, which aims to solve the problem that the uranium dioxide crystals are difficult to obtain by the existing melt growth technology.
In order to achieve the purpose, the technical scheme of the invention is as follows: method for growing uranium dioxide crystal by using borate fluxing agent, (1) Li5U(BO3)3Flux passing Li in stoichiometric ratio2CO3、H3BO3And UO2Mixing and grinding the powder for 3 hours;
(2) putting the mixed powder in the step (1) into a platinum crucible, sealing the platinum crucible, and carrying out Ar/5% H treatment2Sintering at three temperatures in the atmosphere; the first stage sintering temperature is 500 ℃ for 12h, and the second stage sintering temperature is 800 DEG CSintering for 12h at 1250 ℃ for 2h in the third-stage sintering temperature, cooling, taking out the mixture, and grinding to obtain Li5U(BO3)3Fluxing agent;
(3) fluxing agent Li5U(BO3)3And UO2Mixing the raw materials according to a molar ratio of 83mol% to 17mol%, grinding, placing into a platinum crucible, introducing Ar/5% H2Placing in a tubular resistance furnace, heating to 1235 deg.C, and using Li5U(BO3)3Fluxing agent to react UO2Dissolving, the system reaches a molten state, and slowly cooling to reach supersaturation degree to drive crystal growth to obtain UO2And (4) crystals.
Further, Li in step (1)2CO3Purity of 99.99%, H3BO3Purity of 99.99%, UO2The purity was 99.99%.
Further, the platinum crucible in the step (3) has a thickness of 1mm and a size of Φ 40 × H40 mm.
Further, the vertical temperature gradient of the hearth of the tubular resistance furnace in the step (3) is less than 1 ℃/cm so as to keep the temperature distribution of the melt as uniform and consistent as possible.
Further, the temperature of the melt material in the step (3) is 1235 ℃, and the temperature is kept for 24h to ensure that the raw material is fully melted, namely UO2Fully dissolved in the fluxing agent to fully homogenize the melt.
Further, after the temperature is raised to 1235 ℃ in the step (3) and the temperature is kept for 24h, the temperature is slowly reduced at the rate of 0.2 ℃/h to 1160 ℃, the melt is supersaturated during the period of time, crystals are separated out, the temperature is reduced to 800 ℃ at the rate of 7 ℃/h, and finally the temperature is slowly cooled to the room temperature.
The working principle of the technical scheme and the beneficial effects of the technical scheme are as follows:
(1) in this scheme, UO2Melting point 2878 deg.C, crystal growth at 2900 deg.C, borate as fluxing agent, UO at 1200 deg.C2Crystal, significantly reduces UO2The crystal growth temperature.
(2) The crucible which does not meet the requirement in the existing melt growth method adopts borate as a fluxing agent, the growth temperature is reduced, the crucible such as platinum and the like can be used, the growth difficulty is obviously reduced, and the method is favorable for the industrialization of crystals.
Detailed Description
The following is further detailed by way of specific embodiments:
the invention discloses a method for growing uranium dioxide crystals by using borate fluxing agent, which comprises the following steps:
(1) fluxing agent Li5U(BO3)3By stoichiometric ratio of Li2CO3、H3BO3And UO2Mixing and grinding the powder for 3 hours; in this example Li2CO3Purity of 99.99%, H3BO3Purity of 99.99%, UO2The purity was 99.99%.
(2) And (2) loading the mixed powder in the step (1) into a platinum crucible, wherein the thickness of the platinum crucible is 1mm, and the size of the platinum crucible is phi 40 multiplied by H40 mm. Sealing the platinum crucible in Ar/5% H2Sintering at three temperatures in the atmosphere; sintering at 500 deg.C for 12h, sintering at 800 deg.C for 12h, sintering at 1250 deg.C for 2h, cooling, taking out the mixture, and grinding to obtain Li5U(BO3)3Fluxing agent;
(3) mixing and grinding fluxing agent Li5U (BO3)3 and UO2 according to a molar ratio of 83mol% to 17mol%, putting into a platinum crucible, introducing Ar/5% H2, placing into a tubular resistance furnace, heating to 1235 ℃, wherein the vertical temperature gradient of the hearth of the tubular resistance furnace is less than 1 ℃/cm, so as to keep the temperature distribution of the melt as uniform as possible. And (3) dissolving UO2 in a Li5U (BO3)3 fluxing agent to ensure that the system reaches a molten state, the temperature of the melting material is 1235 ℃, and keeping the temperature for 24h to ensure that the raw materials are fully molten, and fully dissolving UO2 in the fluxing agent to ensure that the melt is fully homogenized. Heating to 1235 ℃, keeping the temperature for 24h, slowly cooling at the cooling rate of 0.2 ℃/h, cooling to 1160 ℃, wherein the melt is supersaturated, separating out crystals, cooling to 800 ℃ at the cooling rate of 7 ℃/h, and finally slowly cooling to room temperature. Crystal growth was driven by slow cooling to supersaturation, resulting in UO2 crystals. The obtained UO2 crystal and Li5U (BO3)3 flux were peeled off from a platinum crucible, and Li5U (BO3)3 flux was dissolved in dilute hydrochloric acid to obtain UO2 single crystal.
The foregoing is merely an example of the present invention, and common general knowledge in the field of known specific structures and characteristics is not described herein in any greater extent than that known in the art at the filing date or prior to the priority date of the application, so that those skilled in the art can now appreciate that all of the above-described techniques in this field and have the ability to apply routine experimentation before this date can be combined with one or more of the present teachings to complete and implement the present invention, and that certain typical known structures or known methods do not pose any impediments to the implementation of the present invention by those skilled in the art. It should be noted that, for those skilled in the art, without departing from the structure of the present invention, several changes and modifications can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicability of the patent. The scope of the claims of the present application shall be determined by the contents of the claims, and the description of the embodiments and the like in the specification shall be used to explain the contents of the claims.

Claims (4)

1. A method for growing uranium dioxide crystals by using a borate fluxing agent is characterized by comprising the following steps:
(1) fluxing agent Li5U(BO3)3The preparation of (1): by mixing Li in stoichiometric ratio2CO3、H3BO3And UO2Mixing and grinding the powder for 3 hours;
(2) putting the mixed powder in the step (1) into a platinum crucible, sealing the platinum crucible, and carrying out Ar/5% H treatment2Sintering at three temperatures in the atmosphere; sintering at 500 deg.C for 12h, sintering at 800 deg.C for 12h, sintering at 1250 deg.C for 2h, cooling, and taking out the mixture to obtain Li5U(BO3)3Polycrystallization, grinding to obtain Li5U(BO3)3Fluxing agent for later use;
(3) fluxing agent Li5U(BO3)3And UO2Mixing the raw materials according to a molar ratio of 83mol% to 17mol%, grinding, placing into a platinum crucible, introducing Ar/5% H2Placing in a tubular resistance furnace, heating to 1235 deg.C, and using Li5U(BO3)3Fluxing agent to react UO2Dissolving, melting the system, keeping the temperature of the melt material at 1235 ℃, and keeping the temperature for 24h to ensure that the raw materials are fully melted, namely UO2Fully dissolving in a fluxing agent to fully homogenize a melt; heating to 1235 ℃, keeping the temperature for 24h, slowly cooling at the cooling rate of 0.2 ℃/h, cooling to 1160 ℃, wherein the melt is supersaturated, separating out crystals, cooling to 800 ℃ at the cooling rate of 7 ℃/h, finally slowly cooling to room temperature, slowly cooling to reach the supersaturation degree to drive the crystal to grow, and obtaining UO2And (4) crystals.
2. The method for growing uranium dioxide crystals using borate flux as claimed in claim 1, wherein in step (1), Li2CO3Purity of 99.99%, H3BO3Purity of 99.99%, UO2The purity was 99.99%.
3. A method for growing uranium dioxide crystals with borate flux according to claim 1, wherein in step (3) the platinum crucible has a thickness of 1mm and dimensions Φ 40 × H40 mm.
4. The method for growing uranium dioxide crystals by using borate flux as claimed in claim 1, wherein the vertical temperature gradient of the hearth of the tubular resistance furnace in the step (3) is less than 1 ℃/cm so as to keep the temperature distribution of the melt as uniform as possible.
CN202010262173.6A 2020-04-06 2020-04-06 Method for growing uranium dioxide crystal by using borate fluxing agent Expired - Fee Related CN111394781B (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB968785A (en) * 1961-12-29 1964-09-02 Ct D Etude De L En Nucleaire C Method and apparatus for producing single crystals of refractory material
CN108364703A (en) * 2018-01-23 2018-08-03 中国科学院高能物理研究所 Application of the ammonium chloride in uranium dioxide is detached with lanthanide oxide
CN110528087A (en) * 2019-08-29 2019-12-03 国家电投集团科学技术研究院有限公司 The Preparation equipment of refractory oxides monocrystalline

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB968785A (en) * 1961-12-29 1964-09-02 Ct D Etude De L En Nucleaire C Method and apparatus for producing single crystals of refractory material
CN108364703A (en) * 2018-01-23 2018-08-03 中国科学院高能物理研究所 Application of the ammonium chloride in uranium dioxide is detached with lanthanide oxide
CN110528087A (en) * 2019-08-29 2019-12-03 国家电投集团科学技术研究院有限公司 The Preparation equipment of refractory oxides monocrystalline

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
超高温氧化物晶体及其生长技术;徐家跃等;《应用技术学报》;20171231;第17卷(第4期);283-288 *

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