Method for synthesizing fluorocarbon tysonite single crystal under high temperature and high pressure

Abstract

The application discloses a method for synthesizing fluorocarbon gadolinite monocrystals under high temperature and high pressure, and relates to the technical field of rare earth minerals. The method uses GdCl3, NaF and NaHCO3 as raw materials, and performs a stage type temperature rising reaction under a predetermined pressure, so that the obtained fluorocarbon gadolinite monocrystals are pure substances and have good chemical stability, and the technical problem of difficult growth of fluorocarbon gadolinite monocrystals at present is solved. In addition, the method has the advantages of simple operation process, easy control of conditions and the like.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of rare earth ores, in particular to a method for synthesizing fluorocarbon gadolinium ore single crystals under high temperature and high pressure. BACKGROUND

[0002] Rare earths have excellent physical and chemical properties such as light, electricity and magnetism, and can be combined with other materials to synthesize various new high-performance composite materials with excellent performance and a wide variety of types, which are widely used in national defense industry, electronic industry, new energy and other fields, and are an important and key strategic resource, known as the "treasure trove" of new materials.

[0003] Global rare earth resources are abundant, with proven reserves exceeding 200 million tons. However, the global rare earth resources are mainly light rare earths, and the medium and heavy rare earths are scarce and valuable resources.

[0004] Fluorocarbon cerium ore, namely rare earth fluorocarbonate (REFCO3), is one of the most commercially valuable rare earth minerals. Fluorocarbon cerium ore contains four main light rare earth elements: lanthanum, cerium, praseodymium and neodymium, accounting for about 98% of the rare earth content of fluorocarbon cerium ore, and a small amount of medium and heavy rare earth elements samarium, europium, gadolinium and yttrium. Therefore, studying the thermodynamic properties and thermal stability of medium and heavy rare earth end-member fluorocarbon cerium ore is extremely important for clarifying the formation conditions of medium and heavy rare earth end-member fluorocarbon cerium ore, the thermodynamic properties of natural complex components of fluorocarbon cerium ore, and is also an indispensable basis for judging whether medium and heavy rare earths can crystallize into minerals.

[0005] Previous studies have mostly focused on light rare earth fluorocarbon cerium ore, but the reasons for the rare occurrence of heavy rare earth fluorocarbon cerium ore in nature have not been fully explained. At the same time, the synthesis method of high-temperature synthesized rare earth fluorocarbonates, especially medium and heavy rare earth end-member fluorocarbon cerium ore, and the particle size, morphology and characterization of the synthesis products are not detailed. At the same time, the thermodynamic data of medium and heavy rare earth end-member fluorocarbon cerium ore are not complete, and important data such as standard entropy, standard enthalpy of formation and standard Gibbs function of formation are relatively lacking, and the thermal stability research is also relatively less, which needs more experiments to verify, in order to obtain the stable temperature and pressure range of medium and heavy rare earth end-member fluorocarbon cerium ore.

[0006] Gadolinium accounts for 0.000636% of the content in the earth's crust, and mainly exists in monazite and fluorocarbon cerium ore. Gadolinium is widely used in medical, industrial, nuclear energy and other fields. Therefore, exploring the method for artificially synthesizing high-purity fluorocarbon cerium ore (gadolinium) single crystals is an important prerequisite and foundation for further studying the crystal structure characteristics of fluorocarbon cerium ore (gadolinium) and the formation mechanism of medium rare earth fluorocarbonates. SUMMARY

[0007] The application aims to provide a method for synthesizing fluorocarbon gadolinite single crystals under high temperature and high pressure, so as to solve the problems in the prior art and the technical difficulty of the growth of fluorocarbon gadolinite single crystals, and the method has the characteristics of simple operation and easy control.

[0008] To achieve the above object, the application provides the following solutions.

[0009] The application provides a method for synthesizing fluorocarbon gadolinite single crystals, comprising the following steps.

[0010] GdCl3, NaF and NaHCO3 are mixed according to the molar dosage ratio of the chemical reaction, and the obtained mixture is kept at a first temperature, a second temperature and a third temperature for 45 min under pressure conditions, and then kept at a fourth temperature for 80-100 h to obtain the fluorocarbon gadolinite single crystals.

[0011] The first temperature is 150-200 DEG C, the second temperature is 350-400 DEG C, the third temperature is 550-600 DEG C, and the fourth temperature is 700-800 DEG C.

[0012] Further, the pressure value of the pressure condition is 2.0 GPa.

[0013] Further, the pressure is increased to the preset pressure value at a pressure increasing rate of 0.5 GPa / 30 min under normal pressure.

[0014] Further, the molar ratio of GdCl3, NaF and NaHCO3 is 1:1:1.

[0015] Further, the purity grade of GdCl3, NaF and NaHCO3 is analytical pure or above.

[0016] Further, the purity of GdCl3, NaF and NaHCO3 is all greater than 99.99%.

[0017] Further, the temperature increasing rate is controlled to be 20 DEG C / min, and the temperature is sequentially increased from the first temperature to the second temperature, the third temperature and the fourth temperature.

[0018] Further, the keeping process of the mixture is carried out in a large cavity press.

[0019] Further, the mixture is placed in a high temperature and high pressure synthesis assembly block; the high temperature and high pressure synthesis assembly block comprises pyrophyllite as a pressure transmission medium, a graphite tube as a heating furnace and a thermocouple for temperature control.

[0020] Further, the thermocouple is a K-type thermocouple.

[0021] In the present application, the fluorocarbon gadolinite is heavy rare earth fluorocarbon cerinite (gadolinium).

[0022] The present application combines the knowledge of geochemistry, crystallography and mineralogy, i.e. the principle of slowly forming fluorocarbon cerinite (gadolinium) under the redox conditions in the earth interior, simulates the formation process of the middle rare earth fluorocarbon cerinite single crystal under the high temperature and high pressure conditions, adopts the large cavity press equipment, and relates to the main chemical reaction equation:

[0023] GdCl3+NaF+2NaHCO3→Gd(CO3)F+3NaCl+H2O+CO2

[0024] The present application discloses the following technical effects:

[0025] The synthesis method has the advantages of simple operation, easy control of temperature and pressure conditions, and the obtained fluorocarbon cerinite (gadolinium) single crystal sample has high purity, good crystallinity and good chemical stability, and solves the technical problems lacking in the current artificial synthesis of fluorocarbon cerinite (gadolinium) single crystal. At the same time, the mineral crystal structure data of the obtained fluorocarbon cerinite (gadolinium) single crystal sample also provides protection for the research on the chemical stability of the middle rare earth fluorocarbon cerinite and the formation mechanism of the middle rare earth fluorocarbon carbonate mineral. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0027] Figure 1 It is a schematic diagram of a case of high temperature and high pressure sample synthesis assembly of the present application;

[0028] Figure 2 It is a micrograph of the heavy rare earth fluorocarbon cerinite (gadolinium) single crystal sample synthesized in Example 1;

[0029] Figure 3 It is a Raman spectrum of the heavy rare earth fluorocarbon cerinite (gadolinium) single crystal sample synthesized in Example 1;

[0030] Figure 4 It is a synchrotron single crystal diffraction spectrum of the heavy rare earth fluorocarbon cerinite (gadolinium) single crystal sample synthesized in Example 1. DETAILED DESCRIPTION

[0031] The various exemplary embodiments of the present application will now be described in detail, which should not be considered as limiting the present application, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present application.

[0032] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Additionally, for a range of values of, an intermediate value of the upper limit and the lower limit of the range is specifically disclosed. Each smaller range between any stated value or inferred value and any other stated value or inferred value in the stated range is also specifically disclosed. The upper and lower limits of these smaller ranges can independently be included or excluded in the ranges.

[0033] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe in full the methods and / or materials which are described therein. In the case of conflict between the present specification and any document incorporated herein by reference, the present specification will control.

[0034] Many modifications and variations of the present application described in the specific embodiments of the application can be made by those skilled in the art without departing from the spirit or scope of the application. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application. The specification and examples are illustrative only.

[0035] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended terms that are intended to mean "including but not limited to".

[0036] The high-temperature and high-pressure synthetic fluorocarbon gadoelite of the present application comprises the following steps:

[0037] Step 1, using GdCl3, NaF, NaHCO3 powder as starting material, mixing uniformly in a sufficient amount in a marver mortar according to the stoichiometric molar ratio of 1:1:1;

[0038] Step 2, using a tablet press to press the mixture powder into a shape, then filling the sample after pressing into a platinum sample tube, and sealing both ends using a welding gun;

[0039] Step 3, assembling the platinum sample tube in a high-temperature and high-pressure synthesis assembly block;

[0040] Step 4, placing the high-temperature and high-pressure synthesis assembly block in a six-surface top press to perform high-temperature and high-pressure reaction, and the high-temperature and high-pressure reaction process is as follows:

[0041] Under normal pressure, the pressure was increased to the preset maximum pressure (2.0 GPa) at a pressurization rate of 0.5 GPa / 30 min, and then the temperature was increased in stages: the temperature was increased to 200℃, 400℃, 600℃ and the maximum temperature (700-800℃) at a heating rate of 20℃ / min, and then held at 200℃, 400℃ and 600℃ for 45 min respectively, and reacted at the maximum temperature for 80-100 h.

[0042] Step 5: Remove the reacted sample and use a diamond cutter to open the platinum sample tube to obtain a gadolinium fluorocarbonate single crystal.

[0043] The bastnaesite (gadolinium) single crystal obtained in step 5 is a single phase without any impurity phases.

[0044] The gadolinium fluorocarbonate single crystals prepared by this invention have a hexagonal crystal system with space group P-62c and cell parameters [not specified]. The crystals are short columnar with an average size of 30 μm and a maximum size of 60 μm.

[0045] In step 3, the operation of assembling the platinum sample tube onto the high-temperature and high-pressure synthesis assembly block is as follows:

[0046] Drill a hole in the center of the pyrophyllite block on a lathe, then insert a graphite heating tube into the hole, then insert an alumina insulating tube into the graphite heating tube, then insert a platinum sample tube into the middle of the alumina insulating tube, and finally seal the top and bottom ends of the graphite heating tube with pyrophyllite plugs.

[0047] The high-temperature, high-pressure synthesis assembly contains thermocouples. During high-temperature, high-pressure operation, the temperature within the sample chamber is calibrated using K-type thermocouples. As a temperature sensor, K-type thermocouples are typically used in conjunction with display instruments, recording instruments, and electronic controllers. K-type thermocouples can directly measure the surface temperature of various liquid, vapor, and gaseous media, as well as solids, ranging from 0℃ to 1300℃ in production processes. 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. Their operating temperature range is -200℃ to 1300℃. K-type thermocouples are widely used due to their advantages, including good linearity, large thermoelectric potential, high sensitivity, good stability and uniformity, strong oxidation resistance, and low cost. The temperature within the sample chamber is calibrated by symmetrically placing each set of K-type thermocouples in the middle of the outer wall of the sample chamber (the outer wall of the alumina insulating tube).

[0048] In the high-temperature and high-pressure assembly block of the present invention, pyrophyllite is used as the pressure transmission medium, graphite tube is used as the heating furnace, and thermocouple is used as the temperature control device.

[0049] The dimensions of the high-temperature, high-pressure assembly block can be determined based on the dimensions of the sample housed in the platinum sample tube.Figure 1 A schematic diagram of one case of the high-temperature and high-pressure sample synthesis assembly of the present application. The high-temperature and high-pressure assembly block of the present application has the following advantages: ① using a thermocouple to control temperature, the heating system adjusts the heating power through the temperature feedback of the thermocouple, thereby changing the temperature, which can realize instant monitoring of the temperature and is suitable for experiments with high requirements for temperature measurement accuracy; ② pyrophyllite has good pressure transmission, machinability, heat resistance, heat preservation and insulation; ③ graphite tube as a heating furnace has high temperature uniformity.

[0050] The present application will be further described in detail below with reference to examples.

[0051] In the embodiments of the present application: the purity of GdCl3 powder is > 99.99%, the purity of NaF powder is > 99.99%, and the purity of NaHCO3 powder is > 99.99%.

[0052] Example 1

[0053] (1) GdCl3, NaF and NaHCO3 powders are mixed and ground uniformly according to the stoichiometric molar ratio of 1:1:1 as starting materials;

[0054] (2) The mixture powder is pressed into a cylinder (Φ5mm×5mm) using a powder tablet press, the sample is inserted into a platinum-gold tube with a diameter of Φ5mm and a wall thickness of 0.1mm, and the two ends are sealed using a welding gun;

[0055] (3) The platinum-gold sample tube is assembled in the high-temperature and high-pressure synthesis assembly block:

[0056] ① A circular through hole with a diameter of 12mm is punched in the center of a 32.5mm×32.5mm×32.5mm pyrophyllite block;

[0057] ② A graphite heating tube with an outer diameter of 12mm and an inner diameter of 10mm is sleeved in the circular through hole of the pyrophyllite block;

[0058] ③ An alumina insulation tube with an outer diameter of 10mm and an inner diameter of 5mm is placed in the graphite heating tube;

[0059] ④ The platinum-gold sample tube is placed in the middle of the alumina insulation tube, and the upper and lower ends are sealed with pyrophyllite plugs with a diameter of 5mm;

[0060] (4) Put the high temperature and high pressure synthesis assembly block into the six-surface top big press machine to carry out high temperature and high pressure reaction (the reaction process is controlled by thermocouple temperature): under normal pressure, the pressure is increased to the preset maximum pressure (2.0 GPa) at the pressure increasing rate of 0.5 GPa / 30 min, and then the temperature is increased in steps: the temperature is increased to 200℃, 400℃, 600℃ and the maximum temperature (700℃) respectively at the temperature increasing rate of 20℃ / min, and the temperature is kept at 200℃, 400℃, 600℃ for 45 min respectively, and the reaction is carried out at the maximum temperature for 100 h.

[0061] (5) After the high temperature and high pressure reaction is completed, the obtained sample is taken out, a diamond cutter is used to open the platinum sample tube, the sample is naturally air-dried, and then the fluorcarbonatohohite (gadolinium) single crystal is taken out under the stereomicroscope.

[0062] The fluorcarbonatohohite (gadolinium) single crystal obtained in Example 1 is hexagonal crystal structure, the space group is P-62c, and the cell parameters are a=0.41 nm, c=2.36 nm. The crystal presents a short column shape, the average size is 30 μm, and the maximum size is 60 μm.

[0063] Figure 2 It is a micrograph of the heavy rare earth fluorcarbonatohohite (gadolinium) single crystal sample synthesized in Example 1;

[0064] Figure 3 It is a Raman spectrum of the heavy rare earth fluorcarbonatohohite (gadolinium) synthesized in Example 1;

[0065] Figure 4 It is a synchrotron single crystal diffraction spectrum of the heavy rare earth fluorcarbonatohohite (gadolinium) synthesized in Example 1.

[0066] Example 2

[0067] (1) GdCl3, NaF and NaHCO3 powders are mixed according to the stoichiometric molar ratio of 1:1:1 to prepare starting materials;

[0068] (2) The mixture powder is pressed into a cylinder (Φ5 mm×5 mm) using a powder tablet press, the sample is inserted into a platinum tube with a diameter of Φ5 mm and a wall thickness of 0.1 mm, and the two ends are sealed using a welding gun;

[0069] (3) The platinum sample tube is assembled in the high temperature and high pressure synthesis assembly block:

[0070] ① A circular through hole with a diameter of 12 mm is punched in the center of a 32.5 mm×32.5 mm×32.5 mm pyrophyllite block;

[0071] ② A graphite heating tube with an outer diameter of 12 mm and an inner diameter of 10 mm is sleeved in the circular through hole of the pyrophyllite block;

[0072] ③ Place an alumina insulating tube with an outer diameter of 10 mm and an inner diameter of 5 mm inside the graphite heating tube;

[0073] ④ A platinum sample tube is placed in the middle of the alumina insulating tube, and the top and bottom are sealed with pyrophyllite plugs with a diameter of 5mm;

[0074] (4) The high-temperature and high-pressure synthesis assembly block is placed in a six-sided top press for high-temperature and high-pressure reaction (the temperature is controlled by thermocouples during the reaction): Under normal pressure, the pressure is increased to the preset maximum pressure (2.0GPa) at a pressurization rate of 0.5GPa / 30min, and then the temperature is increased in stages: the temperature is increased to 200℃, 400℃, 600℃ and the maximum temperature (750℃) at a heating rate of 20℃ / min, and the temperature is held at 200℃, 400℃ and 600℃ for 45min respectively, and the reaction is carried out at the maximum temperature for 90h.

[0075] (5) After the high temperature and high pressure reaction is completed, the obtained sample is taken out, the platinum sample tube is opened with a diamond cutter, the sample is air-dried naturally, and the bastnaesite (gadolinium) single crystal is taken out under a stereomicroscope.

[0076] Example 3

[0077] (1) GdCl3, NaF and NaHCO3 powders were mixed evenly by grinding in a stoichiometric molar ratio of 1:1:1 as the starting material;

[0078] (2) Use a powder press to press the mixture powder into a cylinder (Φ5mm×5mm), insert the sample into a Φ5mm, 0.1mm thick platinum tube, and seal both ends with a welding gun;

[0079] (3) Assemble the platinum sample tubes into the high-temperature and high-pressure synthesis assembly block:

[0080] ① Drill a 12mm diameter circular through hole in the center of a pyrophyllite block measuring 32.5mm×32.5mm×32.5mm;

[0081] 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;

[0082] ③ Place an alumina insulating tube with an outer diameter of 10 mm and an inner diameter of 5 mm inside the graphite heating tube;

[0083] ④ A platinum sample tube is placed in the middle of the alumina insulating tube, and the top and bottom are sealed with pyrophyllite plugs with a diameter of 5mm;

[0084] (4) Put the high temperature and high pressure synthesis assembly block into a six-surface top large press for high temperature and high pressure reaction (the reaction process is controlled by a thermocouple) : under normal pressure, the pressure is increased to the preset maximum pressure (2.0 GPa) at a pressure increasing rate of 0.5 GPa / 30 min, and then the temperature is increased in stages: the temperature is increased to 200℃, 400℃, 600℃ and the maximum temperature (800℃) respectively at a temperature increasing rate of 20℃ / min, and the temperature is kept at 200℃, 400℃, 600℃ for 45 min respectively, and the reaction is carried out at the maximum temperature for 100 h.

[0085] (5) After the high temperature and high pressure reaction is completed, the obtained sample is taken out, the platinum gold sample tube is opened by using a diamond cutter, the sample is naturally air-dried, and then the fluor carbon cerite (gadolinium) single crystal is taken out under a stereomicroscope.

[0086] Comparative Example 1

[0087] The difference from Example 1 is only that the stage temperature increasing mode is not used, and the high temperature and high pressure reaction process of step (4) is as follows:

[0088] The reaction is carried out at 700℃ and a pressure of 2.0 GPa for 100 h.

[0089] The results show that the powder sample in the platinum gold sample tube is solidified into a block, and a single crystal sample is not formed, and the block sample is not fluor carbon cerite (gadolinium) either, and the fluor carbon cerite (gadolinium) single crystal sample cannot be synthesized without using the stage temperature increasing mode.

[0090] The above described examples only describe the preferred modes of the present application, and do not limit the scope of the present application, and various modifications and improvements to the technical solutions of the present application made by those skilled in the art without departing from the design spirit of the present application shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method of synthesizing a fluorocarbon chernovite single crystal, characterized by, The method comprises the following steps: GdCl3, NaF and NaHCO3 are mixed in a molar ratio of 1:1:1, and the obtained mixture is kept at a first temperature, a second temperature and a third temperature respectively for 45 min under a pressure of 2.0 GPa, and then kept at a fourth temperature for 80-100 h to obtain the fluorocarbon gadolinium ore single crystal; The first temperature is 150-200 DEG C, the second temperature is 350-400 DEG C, the third temperature is 550-600 DEG C, and the fourth temperature is 700-800 DEG C.

2. The method of synthesizing a fluorocarbon chernovite single crystal according to claim 1, characterized in that, The pressure is increased to a preset pressure value at a pressure increasing rate of 0.5 GPa / 30 min under normal pressure.

3. The method of synthesizing a fluorocarbon chernovite single crystal according to claim 1, wherein, The purity of the GdCl3, NaF and NaHCO3 is all greater than 99.99%.

4. The method of synthesizing a fluorocarbon chernovite single crystal according to claim 1, wherein The temperature increasing rate is controlled to be 20 DEG C / min, and the temperature is sequentially increased from the first temperature to the second temperature, the third temperature and the fourth temperature.

5. The method of synthesizing a fluorocarbon chernovite single crystal of claim 1, wherein, The keeping process of the mixture is carried out in a large cavity press.

6. The method of synthesizing a fluorocarbon chernovite single crystal according to claim 5, wherein The mixture is placed in a high temperature and high pressure synthesis assembly block; the high temperature and high pressure synthesis assembly block comprises pyrophyllite as a pressure transmission medium, a graphite tube as a heating furnace and a thermocouple for temperature control.

7. The method of synthesizing a fluorocarbon chernosynite single crystal according to claim 6, wherein The thermocouple is a K-type thermocouple.

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