Method for synthesizing fluor carbon bastnaesite single crystal under high temperature and high pressure

Abstract

The application discloses a method for synthesizing fluorocarbotantalite monocrystal under high temperature and high pressure and belongs to the technical field of mineral monocrystal sample synthesis. The synthesis method comprises the following steps: mixing TbCl3, NaF and Na2CO3 according to a chemical reaction molar ratio, and performing reaction under high-pressure and gradient temperature rising to prepare fluorocarbotantalite monocrystal. In the process of preparing fluorocarbotantalite monocrystal, the laboratory environment is pure, the sample is in a sealed environment and does not contact impurities, the obtained fluorocarbotantalite monocrystal is a pure substance, and the fluorocarbotantalite monocrystal has good chemical stability, so that the technical problem of difficulty in growing middle rare earth fluorocarbotantalite monocrystal is solved.

Description

Technical Field

[0001] This invention relates to the field of mineral single crystal sample synthesis technology, and in particular to a method for synthesizing terbium carbonate single crystals under high temperature and high pressure. Background Technology

[0002] Rare earth elements (REE) include 17 elements such as the lanthanides, yttrium, and scandium. Due to their unique and excellent physical and chemical properties such as magnetic, optical, electrical, and catalytic properties, rare earth elements are recognized as key strategic metals that future technological development must rely on. They are known as the "vitamins of modern industry" and the "treasure trove of new materials for the 21st century." They play an indispensable core role in strategic emerging industries such as new energy vehicles, wind power generation, new displays and lighting, industrial robots, electronic information, aerospace, energy conservation and environmental protection, and high-end equipment manufacturing.

[0003] Rare earth fluorocarbonate minerals are a very important class of rare earth minerals, and they are the main ore minerals in many large rare earth deposits. Among rare earth fluorocarbonate minerals, bastnaesite is one of the most widely distributed rare earth minerals and is the main mineral for extracting rare earth elements.

[0004] Rare earth elements are usually divided into three groups: light, medium, and heavy. Light rare earth elements are lanthanum (La), cerium (Ce), praseodymium (Pr), and neodymium (Nd). Medium rare earth elements are samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), and dysprosium (Dy). Heavy rare earth elements are holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and yttrium (Y).

[0005] Currently, for common light rare earth bastnaesites, such as bastnaesite (lanthanum), bastnaesite (cerium), bastnaesite (praseodymium), and bastnaesite (neodymium), relatively detailed studies have been conducted on their chemical synthesis, crystal structure, thermodynamic properties, and solubility. However, the crystal structure and thermodynamic properties of most medium rare earth bastnaesites have not been well studied, which greatly hinders our understanding of the enrichment, migration, and mineralization mechanisms of rare earth elements in nature.

[0006] Terbium (Tb) is a member of the lanthanide series and belongs to the rare earth metals. Its preciousness and many excellent properties make it irreplaceable in certain applications. It is widely used in agriculture, industry, animal husbandry, medicine and health, and high-tech industries. Terbium (Tb) is mainly found in monazite and bastnaesite, and in smaller quantities in cerium phosphate thorium sand and yttrium silicate.

[0007] Previous studies on the formation mechanism of terbium (fluorocarbonate) from the rare earth element are limited, and there are currently no reports on the growth of artificial terbium single crystals or their crystal structure. Furthermore, the synthesis methods for terbium under high temperature and high pressure conditions, as well as the particle size, morphology, and characterization of the synthesized products, are not described in detail. Therefore, exploring methods for the artificial synthesis of high-purity terbium single crystals from the rare earth element is an important prerequisite and foundation for further in-depth research on the crystal structure characteristics of terbium and the formation mechanism of rare earth fluorocarbonate minerals. Summary of the Invention

[0008] The purpose of this invention is to provide a method for synthesizing terbium carbonate single crystals under high temperature and high pressure, thereby solving the current technical problem of difficult growth of terbium carbonate single crystals. Furthermore, this method features simple experimental operation and easily controllable experimental conditions. The terbium carbonate single crystal described in this invention is a substance with a similar crystal form to cerium carbonate single crystals, also known as cerium carbonate (terbium).

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] One of the technical solutions of this invention is to provide a method for synthesizing terbium carbonate single crystals under high temperature and high pressure, comprising the following steps:

[0011] TbCl3, NaF and Na2CO3 were mixed in stoichiometric molar ratios according to the chemical reaction, and the reaction was carried out under high pressure and gradient temperature to obtain fluorocarbon terbium single crystals.

[0012] The pressure under the high-pressure condition is 1.2–1.8 GPa;

[0013] The gradient heating procedure is as follows: first, raise the temperature to 200-250℃ and hold for 30 minutes; then raise the temperature to 350-400℃ and hold for 30 minutes; then raise the temperature to 550-600℃ and hold for 30 minutes; finally, raise the temperature to 700-900℃ and hold for 50-100 hours.

[0014] Preferably, the raw material for TbCl3 is TbCl3 powder with a purity >99.99%; the raw material for NaF is NaF powder with a purity >99.99%; and the raw material for Na2CO3 is Na2CO3 powder with a purity >99.99%.

[0015] This invention combines knowledge from geochemistry, crystallography, and mineralogy, specifically the principle of the slow formation of terbium carbonate ore under redox conditions within the Earth. It utilizes a large-cavity laboratory press to simulate the formation process of terbium carbonate single crystals under high temperature and pressure. The main chemical reaction equations involved in this invention are as follows:

[0016] TbCl3+NaF+Na2CO3→Tb(CO3)F+3NaCl.

[0017] Preferably, the stoichiometric molar ratio of TbCl3, NaF and Na2CO3 is 1:1:1.

[0018] Preferably, the heating rate of the gradient heating is 20°C / min.

[0019] Preferably, the reaction is carried out in a high-temperature and high-pressure synthesis assembly block, the structure of which, from the inside out, includes: a sample tube for loading the sample, an insulating tube, a temperature measuring device, a heating tube, and a pressure transmitting medium.

[0020] More preferably, the sample tube is a Pt sample tube; the temperature measuring device is a K-type thermocouple; the insulating tube is an alumina insulating tube; the heating tube is a graphite heating tube; and the pressure transmitting medium is pyrophyllite.

[0021] The K-type thermocouple used in this invention is a temperature sensor, typically used in conjunction with display instruments, recording instruments, and electronic controllers. K-type thermocouples can directly measure the surface temperature of liquids, vapors, and gases, as well as solids, in various production processes ranging from 0°C to 1300°C. The nominal chemical composition of the positive electrode (KP) is Ni:Cr = 90:10, and the nominal chemical composition of the negative electrode (KN) is Ni:Si = 97:3. Its operating temperature range is -200°C to 1300°C. K-type thermocouples have advantages such as good linearity, high thermoelectric potential, high sensitivity, good stability and uniformity, strong oxidation resistance, and low cost, and are widely used. Using K-type thermocouples allows for accurate measurement of the temperature inside a sample tube.

[0022] The dimensions involved in the high-temperature, high-pressure synthesis assembly block of this invention can be specifically determined according to the dimensions of the sample mounted in the platinum sample tube. In this assembly block, pyrophyllite serves as the pressure transmission medium, graphite tube as the heating furnace, and K-type thermocouple as the temperature control device. The advantages are: ① Using K-type thermocouples for temperature control, the heating system adjusts the heating power based on the temperature feedback from the K-type thermocouples, thereby changing the temperature. This method allows for real-time temperature monitoring and is suitable for experiments requiring high temperature measurement accuracy; ② Pyrophyllite, as the pressure transmission medium, possesses excellent pressure transmission properties, machinability, heat resistance, insulation, and thermal insulation; ③ Graphite tubes, as the heating furnace, provide high temperature uniformity.

[0023] The beneficial technical effects of the present invention are as follows:

[0024] According to the synthesis method of this invention, the synthesized terbium carbonate single crystal is a single phase without impurity phases. Compared with natural terbium carbonate, which contains other impurities and whose purity is difficult to reach 70% according to existing reports, the terbium carbonate single crystal prepared by this invention is produced in a pure laboratory environment with the sample in a sealed environment, free from contact with impurities. The resulting terbium carbonate single crystal is pure and chemically stable, solving the technical problem of difficult growth of terbium carbonate single crystals in rare earth elements. In addition, the method of this invention also has the advantages of simple operation and easy control of experimental conditions. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the high-temperature and high-pressure synthesis assembly block in Embodiment 1 of the present invention.

[0026] Figure 2 This is a micrograph of the fluorocarbon terbium single crystal synthesized in Example 1 of the present invention.

[0027] Figure 3 This is the Raman spectrum of the fluorocarbon terbium single crystal synthesized in Example 1 of the present invention.

[0028] Figure 4 The image shows the synchrotron radiation single-crystal diffraction pattern of the fluorocarbon terbium single crystal synthesized in Example 1 of this invention. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0030] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0032] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0033] The TbCl3 powder, NaF powder, and Na2CO3 powder used in the embodiments and comparative examples of this invention are all of analytical grade with a purity >99.99%.

[0034] Example 1

[0035] Analytical-grade TbCl3, NaF, and Na2CO3 powders were mixed in a stoichiometric molar ratio of 1:1:1 as starting materials. The mixture was thoroughly ground and mixed in an agate mortar. The powder mixture was then pressed into cylinders (Φ5mm × 5mm) using a powder press. The sample was inserted into a platinum tube with a diameter of Φ5mm, a height of 5mm, and a wall thickness of 0.2mm, and both ends were sealed with a welding torch. A hole was drilled in the center of a pyrophyllite block on a lathe. A circular graphite heating tube was then inserted into the hole. A small hole was drilled in the center of the side of the pyrophyllite block, and an alumina insulating tube was inserted into the circular graphite heating tube. The platinum sample tube was then inserted into the middle of the alumina insulating tube. A K-type thermocouple was then inserted from the small hole in the side of the pyrophyllite block to the outer wall of the boron nitride insulating tube. Finally, the circular graphite heating tube was sealed at both ends with pyrophyllite plugs, completing the high-temperature, high-pressure synthesis assembly.

[0036] Specific assembly method of high temperature and high pressure synthetic assembly block:

[0037] ① Drill a 12mm diameter circular through hole in the center of a pyrophyllite cube measuring 32.5mm×32.5mm×32.5mm;

[0038] ② A graphite heating tube with an outer diameter of 12mm and an inner diameter of 10mm is inserted into the circular through hole of the pyrophyllite block;

[0039] ③ Drill a small circular hole with a diameter of 2mm in the center of the side of a pyrophyllite cube measuring 32.5mm×32.5mm×32.5mm;

[0040] ④ Place an alumina insulating tube with an outer diameter of 10 mm and an inner diameter of 5 mm inside the graphite heating tube;

[0041] ⑤ A platinum sample tube is placed in the middle of the alumina insulating tube, and the top and bottom are sealed with alumina plugs with a diameter of 54mm;

[0042] ⑥ Insert the K-type thermocouple into the outer wall of the alumina insulating tube through a small circular hole 2mm on the side of the pyrophyllite block.

[0043] At this point, the high-temperature and high-pressure synthesis assembly is complete. A schematic diagram of the assembled high-temperature and high-pressure synthesis assembly can be found here. Figure 1The high-temperature and high-pressure (HTHP) synthesis assembly was placed in a six-sided press for HTHP reaction. The pressure was increased to 1.8 GPa at a rate of 0.2 GPa / 15 min, and the temperature was increased to 200 °C at a rate of 20 °C / min, held for 30 min, then increased to 400 °C, held for 30 min, then increased to 600 °C, held for 30 min, and finally increased to 900 °C, held for 80 h. After the HTHP reaction was completed, the sample was removed, the platinum tube was opened with a diamond cutter, and the sample was air-dried. Then, terbium carbonate single crystals were selected under a stereomicroscope.

[0044] The terbium carbonate single crystal synthesized in Example 1 of this invention has a hexagonal crystal system with space group P-62c and cell parameters [not specified]. The crystals are hexagonal plates with an average size of 30 μm and a maximum size of 600 μm.

[0045] Figure 2 This is a micrograph of the fluorocarbon terbium single crystal synthesized in Example 1.

[0046] Figure 3 The image shows the Raman spectrum of the fluorocarbon terbium single crystal synthesized in Example 1.

[0047] Figure 4 The image shows the synchrotron radiation single-crystal diffraction pattern of the fluorocarbon terbium single crystal synthesized in Example 1.

[0048] Example 2

[0049] Compared with Example 1, the only difference is that the parameters of the high temperature and high pressure reaction are adjusted as follows: the pressure is set to increase to 1.6 GPa at a rate of 0.2 GPa / 15 min, and the temperature is set to increase to 200°C at a rate of 20°C / min, hold for 30 min, then increase to 400°C, hold for 30 min, then increase to 600°C, hold for 30 min, and finally increase to 750°C and hold for 100 h.

[0050] Example 3

[0051] Compared with Example 1, the only difference is that the parameters of the high temperature and high pressure reaction are adjusted as follows: the pressure is set to increase to 1.6 GPa at a rate of 0.2 GPa / 15 min, and the temperature is set to increase to 200°C at a rate of 20°C / min, hold for 30 min, then increase to 400°C, hold for 30 min, then increase to 600°C, hold for 30 min, and finally increase to 900°C and hold for 90 h.

[0052] Example 4

[0053] Compared with Example 1, the only difference is that the parameters of the high temperature and high pressure reaction are adjusted as follows: the pressure is set to increase to 1.6 GPa at a rate of 0.2 GPa / 15 min, and the temperature is set to increase to 200°C at a rate of 20°C / min, hold for 30 min, then increase to 400°C, hold for 30 min, then increase to 600°C, hold for 30 min, and finally increase to 800°C and hold for 90 h.

[0054] Example 5

[0055] Compared with Example 1, the only difference is that the parameters of the high temperature and high pressure reaction are adjusted as follows: the pressure is set to increase to 1.2 GPa at a rate of 0.2 GPa / 15 min, and the temperature is set to increase to 200°C at a rate of 20°C / min, hold for 30 min, then increase to 400°C, hold for 30 min, then increase to 600°C, hold for 30 min, and finally increase to 700°C and hold for 100 h.

[0056] The fluorocarbon terbium single crystals synthesized in Examples 2-5 are the same as those in Example 1.

[0057] Comparative Example 1

[0058] Compared with Example 1, the only difference is that the parameters of the high temperature and high pressure reaction are adjusted as follows: the pressure is set to increase to 1.8 GPa at a rate of 0.2 GPa / 15 min, the temperature is set to increase to 900 °C at a rate of 20 °C / min, and the temperature is held for 80 h.

[0059] It can be observed that under these conditions, fluorocarbon terbium single crystals cannot be synthesized.

[0060] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for synthesizing a fluorocarnotite single crystal at high temperature and high pressure, characterized by, The method comprises the following steps: TbCl3, NaF and Na2CO3 are mixed in a stoichiometric molar ratio, and a fluorocarbon terbium ore single crystal is prepared by gradient temperature rising under high pressure conditions; The pressure of the high pressure condition is 1.2-1.8 GPa; The gradient temperature rising procedure is: first rising to 200-250 DEG C, keeping for 30 min, then rising to 350-400 DEG C, keeping for 30 min, then rising to 550-600 DEG C, keeping for 30 min, finally rising to 700-900 DEG C, keeping for 50-100 h; The stoichiometric molar ratio of the TbCl3, NaF and Na2CO3 is 1:1:

1.

2. The method of synthesizing a fluorocarbon chernovite single crystal at high temperature and high pressure according to claim 1, characterized by, The raw material of the TbCl3 is TbCl3 powder with a purity of >99.99%; the raw material of the NaF is NaF powder with a purity of >99.99%; and the raw material of the Na2CO3 is Na2CO3 powder with a purity of >99.99%.

3. The method of synthesizing a fluorocarbon chernovite single crystal at high temperature and high pressure according to claim 1, characterized by, The pressure rising rate of the high pressure condition is 0.2 GPa / 15 min; and the temperature rising rate of the gradient temperature rising is 20 DEG C / min.

4. The method of synthesizing a fluorocarbon chernovite single crystal at high temperature and high pressure according to claim 1, characterized by, The reaction is carried out in a high temperature and high pressure synthesis assembly block, and the structure of the high temperature and high pressure synthesis assembly block comprises, from inside to outside, a sample tube for loading samples, an insulating tube, a temperature measuring device, a heating tube and a pressure transmitting medium.

5. The method of synthesizing a fluorocarbon chernovite single crystal at high temperature and high pressure according to claim 4, characterized in that, The sample tube is a Pt sample tube; the temperature measuring device is a K-type thermocouple; the insulating tube is an alumina insulating tube; the heating tube is a graphite heating tube; and the pressure transmitting medium is pyrophyllite.

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