Method for synthesizing fluorcarbonate-hoernite single crystal under high temperature and high pressure

Abstract

The application discloses a method for synthesizing fluorocarnotite 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: HoCl3, NaF and Na2CO3 are mixed according to a stoichiometric molar ratio, and a reaction is carried out under high-pressure and gradient temperature rising, so that fluorocarnotite monocrystal is prepared. The fluorocarnotite monocrystal prepared by the method has large particle size, can fully meet the sample demand of simulation experiments such as sample monocrystal X-ray diffraction, Raman spectrum, infrared spectrum and differential thermal analysis, and breaks through the technical bottleneck of the synthesis of fluorocarnotite monocrystal of heavy rare earth.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mineral single crystal sample synthesis, and particularly relates to a method for synthesizing fluorcarbonate holmium ore single crystals under high temperature and high pressure. BACKGROUND

[0002] According to the definition of rare earth elements given by the International Union of Pure and Applied Chemistry, rare earth elements (Rare Earth Element, abbreviated as REE) are 15 lanthanide series elements (La-Lu) with atomic numbers 57-71 in the periodic table of elements of Dmitri Mendeleev, plus two chemical elements scandium (Sc) and yttrium (Y) with similar electronic structure and chemical properties with atomic numbers 21 and 39. Except for scandium (Sc) and promethium (Pm), the other 15 elements often coexist.

[0003] Rare earth is the "vitamin" of modern industry, is the strategic mineral resources that the world competes for in the 21st century, is also a key national strategic resource, is widely used in modern industry, and has irreplaceable important use in emerging industries such as new materials, new energy and information technology. At present, more than 250 kinds of rare earth minerals have been found in nature, more than 60 kinds of minerals have high content of rare earth metal elements, and more than 20 kinds of main rare earth minerals include monazite, fluorcarbonate cerium, fluorine, calcite cerium, phosphorite, silicon beryllium yttrium, brown yttrium and the like.

[0004] Rare earth fluorocarbonate minerals are a kind of very important rare earth minerals, and in many large rare earth deposits, rare earth fluorocarbonate minerals are main ore minerals. Among the rare earth fluorocarbonate minerals, fluorcarbonate cerium is one of the most widely distributed rare earth minerals, and is the main mineral for extracting rare earth elements.

[0005] At present, the rare earth elements are usually divided into light, medium and heavy three groups, the light rare earth elements are lanthanum, cerium, praseodymium and neodymium, the medium rare earth elements are samarium, europium, gadolinium, terbium and dysprosium, and the heavy rare earth elements are holmium, erbium, thulium, ytterbium, lutetium and yttrium.

[0006] At present, for the common light rare earth fluorcarbonate cerium minerals such as fluorcarbonate cerium (cerium), fluorcarbonate cerium (lanthanum), fluorcarbonate cerium (praseodymium), fluorcarbonate cerium (neodymium) and the like, people have carried out relatively detailed research work on their chemical synthesis, crystal structure, thermodynamic properties and solubility. However, the crystal structure and thermodynamic properties of most heavy rare earth fluorcarbonate cerium minerals (such as fluorcarbonate cerium (holmium), fluorcarbonate cerium (erbium), fluorcarbonate cerium (thulium), fluorcarbonate cerium (ytterbium), fluorcarbonate cerium (lutetium), fluorcarbonate cerium (yttrium) and the like) have not been well studied, which greatly hinders our understanding of the enrichment, migration and mineralization of rare earth elements in nature, and the differentiation mechanism of light and heavy rare earth elements.

[0007] The content of holmium in the earth's crust is 0.000115%, which exists in monazite and rare earth ore together with other rare earth elements. Holmium has incredible magnetism, and holmium oxide is the strongest paramagnetic substance known. The compounds of holmium can be used as additives of new ferromagnetic materials. Holmium iodide is used to manufacture metal halogen lamps-holmium lamps. Holmium lasers are also widely used in the medical field.

[0008] Holmium element: atomic number 67, relative atomic mass 164.93, appearance is silver-white, melting point 1474℃, density 8.79g / cm3, easy to be oxidized by oxygen, has certain ductility, and the use includes as additive of yttrium aluminum garnet, additive of metal halogen lamp and additive of ferromagnetic material and the like.

[0009] The previous study on the formation mechanism of fluorcarbonate cerium (holmium) is less, and so far no artificial fluorcarbonate cerium (holmium) single crystal growth and its crystal structure data are reported. Therefore, exploring the method for artificially synthesizing high-purity fluorcarbonate cerium (holmium) single crystal is an important prerequisite and basis for further studying the crystal structure characteristics and formation mechanism of fluorcarbonate cerium (holmium). SUMMARY

[0010] The purpose of the present application is to provide a method for synthesizing fluorcarbonate holmium ore single crystal under high temperature and high pressure, so as to solve the technical problem of the difficulty in growing fluorcarbonate holmium ore single crystal at present, and meanwhile, the method has the characteristics of simple experimental operation and easy control of experimental conditions. The fluorcarbonate holmium ore single crystal is a substance with similar crystal form as fluorcarbonate cerium single crystal, also known as fluorcarbonate cerium (holmium).

[0011] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0012] One of the technical schemes of the present application: a method for synthesizing fluorcarbonate holmium ore single crystal under high temperature and high pressure is provided, comprising the following steps:

[0013] HoCl3, NaF and Na2CO3 are mixed according to the stoichiometric molar ratio of chemical reaction, and the reaction is carried out under high pressure condition with gradient temperature rising to obtain fluorcarbonate holmium ore single crystal;

[0014] The pressure of the high pressure condition is 1.2-1.8GPa;

[0015] The program of the gradient temperature rising is: first rising to 200-250℃, keeping for 30min, then rising to 350-400℃, keeping for 30min, then rising to 550-600℃, keeping for 30min, and finally rising to 700-800℃, keeping for 100h.

[0016] Preferably, the raw material of HoCl3 is HoCl3·6H2O powder with a purity of > 99.99%; the raw material of NaF is NaF powder with a purity of > 99.99%; and the raw material of Na2CO3 is Na2CO3 powder with a purity of > 99.99%.

[0017] The present application combines the knowledge of related disciplines such as geochemistry, crystallography and mineralogy, that is, the principle of slowly forming hydroxycarbonatofluorohohosite under the redox conditions in the earth interior, and adopts the laboratory large-cavity press experimental equipment to simulate the formation process of hydroxycarbonatofluorohohosite single crystal under high temperature and high pressure conditions. The main chemical reaction equation involved in the present application is:

[0018] HoCl3·6H2O + NaF + Na2CO3→ Ho(CO3)F + 3NaCl + 6H2O.

[0019] Under high temperature and high pressure conditions, the selected initial raw material solid HoCl3·6H2O provides the necessary holmium element for synthesizing hydroxycarbonatofluorohohosite single crystal. The initial raw material solid NaF provides the necessary fluorine element for synthesizing hydroxycarbonatofluorohohosite single crystal. The initial raw material solid Na2CO3 provides the necessary carbonate radical for synthesizing hydroxycarbonatofluorohohosite single crystal.

[0020] Preferably, the molar ratio of the chemical reaction of HoCl3, NaF and Na2CO3 is 1:1:1.

[0021] Preferably, the pressure increasing rate of the high pressure condition is 0.3 GPa / 20 min; and the temperature increasing rate of the gradient temperature increasing is 20℃ / min.

[0022] Preferably, 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 the inside to the outside, a sample tube for loading samples, an insulating tube, a temperature measuring device, a heating tube and a pressure transmitting medium.

[0023] More preferably, the sample tube is a Pt sample tube; the temperature measuring device is an S-type thermocouple; the insulating tube is a boron nitride insulating tube; the heating tube is a graphite heating tube; and the pressure transmitting medium is pyrophyllite.

[0024] The S-type thermocouple used in the application is a platinum-rhodium 10-platinum thermocouple, which is a noble metal thermocouple, the nominal chemical composition of the positive electrode (SP) of which is a platinum-rhodium alloy, wherein the rhodium content is 10%, the platinum content is 90%, and the negative electrode (SN) is pure platinum. The long-term maximum use temperature of the thermocouple is 1300 DEG C, and the short-term maximum use temperature is 1600 DEG C. The S-type thermocouple has the highest accuracy, the best stability, the widest temperature measurement interval, and the longest service life in the thermocouple series. It has good physical and chemical properties, good thermoelectric potential stability and good oxidation resistance at high temperatures, and is suitable for use in oxidizing and inert atmospheres. The use of the S-type thermocouple can accurately measure the temperature in the sample tube.

[0025] The size involved in the high-temperature and high-pressure synthesis assembly block of the application can be determined according to the size of the sample loaded in the platinum sample tube; in the assembly block, pyrophyllite is used as a pressure transmission medium, a graphite tube is used as a heating furnace, and an S-type thermocouple is used as a temperature control device. The advantages are: ① using the S-type thermocouple to control the temperature, the heating system adjusts the heating power through the temperature feedback of the S-type thermocouple to change the temperature, which can realize instant monitoring of the temperature and is suitable for experiments with high temperature measurement accuracy requirements; ② pyrophyllite has good pressure transmission, machinability, heat resistance, heat preservation and insulation; ③ the graphite tube as the heating furnace has high temperature uniformity.

[0026] The beneficial technical effects of the application are as follows:

[0027] According to the synthesis method of the application, the fluorocarbon holmium ore single crystal synthesized is a single phase without impurity phase. Compared with natural fluorocarbon holmium ore samples, some other rare earth element impurities may exist in the form of isomorphism. In the preparation process of the fluorocarbon holmium ore single crystal of the application, the laboratory environment is pure, and the sample is in a sealed environment and does not contact impurities. The obtained fluorocarbon holmium ore single crystal is a pure substance with good chemical stability, which not only solves the technical problem of difficult growth of fluorocarbon holmium ore single crystal, but also provides important experimental sample guarantee for the measurement of physical and chemical property parameters such as crystal structure of fluorocarbon holmium ore single crystal.

[0028] The fluorocarbon holmium ore single crystal prepared by the application has large particle size, which can completely meet the sample demand of sample single crystal X-ray diffraction, Raman spectrum, infrared spectrum, differential thermal analysis and other simulation experiments, and breaks through the technical bottleneck of existing heavy rare earth fluorocarbon holmium ore single crystal synthesis. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a schematic diagram of the high-temperature and high-pressure synthesis assembly block in Example 1 of the application.

[0030] Figure 2 It is a micrograph of the fluorocarbon holmium ore single crystal synthesized in Example 1 of the application.

[0031] Figure 3Raman spectrum of fluor-carbon monazite single crystal synthesized for Example 1 of the present application.

[0032] Figure 4 Synchrotron single crystal diffraction spectrum of fluor-carbon monazite single crystal synthesized for Example 1 of the present application. DETAILED DESCRIPTION

[0033] Various exemplary embodiments of the present application are now described in detail by way of examples. The description is not to be considered to be limiting the application, but rather to be exemplary, illustrative, and complete enough to convey the scope of the application to others skilled in the art. It is understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present application.

[0034] Further, for numerical ranges expressed in the disclosure, it is understood that every numerical value between the upper and lower limits of this range is specifically contemplated. The disclosure contemplates any smaller ranges falling within the specified ranges, as well as the upper and lower limits of the ranges. The upper and lower limits of these smaller ranges can independently be included or excluded in the ranges.

[0035] 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.

[0036] 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".

[0037] The HoCl3·6H2O powder, NaF powder and Na2CO3 powder used in the examples and comparative examples of the present application are all of analytical purity, with a purity of >99.99%.

[0038] Example 1

[0039] The starting material is prepared by mixing analytical pure HoCl3·6H2O, NaF and Na2CO3 powders in a stoichiometric molar ratio of 1:1:1, grinding and mixing uniformly in a corundum mortar, and pressing the mixture powder (about 180 mg) into a cylinder (Φ4 mm×4 mm) using a powder tablet press. The sample is inserted into a platinum tube with a diameter of Φ4 mm and a height of 4 mm, and the two ends are sealed using a welding gun. A hole is drilled in the center of a pyrophyllite block on a lathe, and then a circular graphite heating tube is inserted into the hole. A small hole is drilled in the center of the side of the pyrophyllite block, and then a boron nitride insulation tube is inserted into the circular graphite heating tube. The platinum sample tube is inserted into the middle of the boron nitride insulation tube, and then an S-type thermocouple is inserted into the outer wall of the boron nitride insulation tube from the small hole in the side of the pyrophyllite block. Finally, the pyrophyllite block is used to seal the upper and lower ends of the circular graphite heating tube, and the high-temperature and high-pressure synthesis assembly block is completed.

[0040] Specific assembly method of high-temperature and high-pressure synthesis assembly block:

[0041] ① A 32.5 mm×32.5 mm×32.5 mm pyrophyllite cube is drilled with a circular through-hole with a diameter of 14 mm in the center;

[0042] ② A graphite heating tube with an outer diameter of 14 mm and an inner diameter of 12 mm is inserted into the circular through-hole of the pyrophyllite block;

[0043] ③ A 32.5 mm×32.5 mm×32.5 mm pyrophyllite cube is drilled with a circular small hole with a diameter of 2 mm in the center of the side;

[0044] ④ A boron nitride insulation tube with an outer diameter of 12 mm and an inner diameter of 4 mm is placed in the graphite heating tube;

[0045] ⑤ A platinum sample tube is placed in the middle of the boron nitride insulation tube, and the upper and lower ends are sealed with boron nitride plugs with a diameter of 4 mm;

[0046] ⑥ An S-type thermocouple is inserted into the outer wall of the boron nitride insulation tube from the 2 mm circular small hole in the side of the pyrophyllite block.

[0047] At this point, the high-temperature and high-pressure synthesis assembly block is completed, and the schematic diagram of the completed high-temperature and high-pressure synthesis assembly block is shown in Figure 1The high-temperature and high-pressure synthesis assembly block is placed into a six-surface top big press for high-temperature and high-pressure reaction, the pressure is set to be increased to 1.2 GPa at a pressure increasing rate of 0.3 GPa / 20 min, the temperature is set to be increased to 200 ℃ at a rate of 20 ℃ / min, and then increased to 400 ℃, and then increased to 600 ℃, and then increased to 700 ℃, and then kept for 100 h. After the high-temperature and high-pressure reaction is completed, the obtained sample is taken out, the platinum gold tube is opened by using a diamond cutter, and the sample is naturally air-dried, and then fluorcarbonohosite single crystals are selected under a stereomicroscope.

[0048] The fluorcarbonohosite single crystal synthesized in Example 1 has a hexagonal crystal structure, a space group of P-62c, and cell parameters of a = 7. 1 A, c = 23. 1 A. The crystal has a hexagonal plate shape, an average size of 100 μm, and a maximum size of 200 μm.

[0049] Figure 2 It is a micrograph of the fluorcarbonohosite single crystal synthesized in Example 1.

[0050] Figure 3 It is a Raman spectrum of the fluorcarbonohosite single crystal synthesized in Example 1.

[0051] Figure 4 It is a synchrotron radiation single crystal diffraction spectrum of the fluorcarbonohosite single crystal synthesized in Example 1.

[0052] Example 2

[0053] Compared with Example 1, the difference is only that the parameter setting of the high-temperature and high-pressure reaction is adjusted as follows: the pressure is set to be increased to 1.6 GPa at a pressure increasing rate of 0.3 GPa / 20 min, and the temperature is set to be increased to 200 ℃ at a rate of 20 ℃ / min, and then increased to 400 ℃, and then increased to 600 ℃, and then increased to 750 ℃, and then kept for 100 h.

[0054] Example 3

[0055] Compared with Example 1, the difference is only that the parameter setting of the high-temperature and high-pressure reaction is adjusted as follows: the pressure is set to be increased to 1.8 GPa at a pressure increasing rate of 0.3 GPa / 20 min, and the temperature is set to be increased to 200 ℃ at a rate of 20 ℃ / min, and then increased to 400 ℃, and then increased to 600 ℃, and then increased to 800 ℃, and then kept for 100 h.

[0056] The fluorcarbonohosite single crystals synthesized in Examples 2-3 are the same as those in Example 1.

[0057] Comparative Example 1

[0058] Compared with Example 1, the difference is that the parameters of the high-temperature and high-pressure reaction are adjusted as follows: the pressure is set to be increased to 1.2 GPa at a pressure increasing rate of 0.3 GPa / 20 min, and the temperature is set to be increased to 750 ℃ at a rate of 20 ℃ / min first, and then kept for 100 h.

[0059] It can be observed that fluorcarbonatoholmite single crystals cannot be synthesized under this condition.

[0060] The above-described examples are only used to describe the preferred modes of the present application, and are not used to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope of the present application defined by the claims.

Claims

1. A method for synthesizing a fluorcarbonate-hoernite single crystal at high temperature and high pressure, characterized by, The method comprises the following steps: HoCl3, NaF and Na2CO3 are mixed in a stoichiometric molar ratio, and a fluorocarbotricite 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, and finally rising to 700-800 DEG C, keeping for 100 h; The stoichiometric molar ratio of HoCl3, NaF and Na2CO3 is 1:1:

1.

2. The method of claim 1, wherein the method is characterized by: The raw material of HoCl3 is HoCl3.6H2O powder with a purity of >99.99%; the raw material of NaF is NaF powder with a purity of >99.99%; and the raw material of Na2CO3 is Na2CO3 powder with a purity of >99.99%.

3. The method of claim 1, wherein the method is characterized by: The pressure rising rate of the high pressure condition is 0.3 GPa / 20 min; and the temperature rising rate of the gradient temperature rising is 20 DEG C / min.

4. The method of claim 1, wherein the method is 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 claim 4, wherein the method is characterized by: The sample tube is a Pt sample tube; the temperature measuring device is an S-type thermocouple; the insulating tube is a boron nitride insulating tube; the heating tube is a graphite heating tube; and the pressure transmitting medium is pyrophyllite.

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