A method for preparing industrial-grade vanadium-doped anhydrous noble spinel single crystal

Abstract

The invention discloses a method for preparing an industrial-grade vanadium-doped anhydrous noble spinel single crystal. The method comprises: using solid basic magnesium carbonate powder, solid aluminum isopropoxide powder, solid vanadium (III) triacetylacetonate powder, solid oxalic acid powder and liquid dilute nitric acid as starting raw materials, mixing the ingredients according to the stoichiometric ratio of the noble spinel to prepare a noble spinel powder sample; cold-pressing the noble spinel powder sample into sample discs, vertically stacking the discs and placing them in a graphite crucible; placing the graphite crucible in a high-temperature oxygen atmosphere furnace for high-temperature calcination to prepare a cylindrical noble spinel sample; and subjecting the cylindrical noble spinel sample to a high-temperature and high-pressure reaction to obtain a noble spinel single crystal. The method solves the current technical problems of a blank in the preparation technology of large-particle anhydrous noble spinel single crystals doped with industrial-grade vanadium under high-temperature and high-pressure conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of mineral single crystal sample synthesis, and in particular relates to a method for preparing an industrial-grade vanadium-doped anhydrous noble spinel single crystal. Background Art

[0002] Oxide minerals are a highly important mineral type that exists independently of naturally occurring elements, sulfides, hydroxides, and halides, based on their classification and nomenclature based on their distinct crystal structure, chemical composition, and physicochemical properties. To date, over 200 oxide minerals have been discovered in nature, some of which are important rock-forming minerals in the deep Earth. For example, quartz and its high-pressure phases (α-quartz, β-quartz, coesite, and staurolite) have been confirmed to be among the most important components of the deep Earth. Spinel minerals belong to the major category of oxide minerals. They are important constituent rocks of the middle and lower crust and upper mantle in the deep layers of the Earth. For example, field rock specimens are collected from the Daqingshan orogenic belt in Inner Mongolia Autonomous Region, which are aluminum-rich, silicon-poor spinel biotite plagioclase gneiss derived from metamorphic rocks in the middle and lower crust; and field rock specimens are collected from Chongli County to Shangyi County in the north of Zhangjiakou, Hebei Province, which are phlogopite spinel lherzolite derived from the upper mantle. Both of them have been found to have widespread exposure of spinel minerals.

[0003] Precious spinel, also known as magnesium spinel (chemical formula: MgAl2O4), is an isometric oxide mineral with a typical spinel structure. Its mineralogical oxide chemical composition percentages can be expressed as: MgO / (MgO + Al2O3) = 28.2% and Al2O3 / (MgO + Al2O3) = 28.2%. It is the most important end-member component of the spinel family of minerals and the most common mineral in nature. In thin-section examination of the mineral, under crossed polarization conditions, the surface color and luster of precious spinel minerals do not change with stage rotation, resulting in changes in the mineral's orientation. This demonstrates a distinct mineral homogeneity, demonstrating a typical homogeneous mineral. Thin-section examination reveals positively convex ridges and a colorless, transparent appearance. In a single magnesium-aluminum spinel unit cell, the negative divalent oxygen ions form a cubic closest packing, with the stacking layer perpendicular to the (111) direction (i.e., the tertiary axis), forming 64 tetrahedral voids and 32 octahedral voids. Typically, a single noble spinel contains 24 cations, with 16 trivalent aluminum ions occupying six times the coordination, filling half of the octahedral voids in the unit cell, forming aluminum oxide octahedra ([AlO6]); while the remaining eight divalent magnesium ions occupying four times the coordination, filling one-eighth of the tetrahedral voids in the unit cell, forming magnesium oxide tetrahedra ([MgO4]). Along the tertiary crystallographic axis, the [AlO6] octahedra and [MgO4] tetrahedra contained in the noble spinel form a single layer, arranged in an alternating layer. Within each unit cell of precious spinel crystals, the layers are interconnected by sharing corner vertices, with the corner vertices being composed of three [AlO6] octahedra and one [MgO4] tetrahedron. This connection of these corner vertices allows the spinel mineral structure to be highly flexible and accommodating, allowing A- and B-site cations of varying ionic radii to easily occupy the tetrahedral and octahedral positions, thereby forming the spinel's distorted structure. Due to the significant differences in ionic radius, anion and cation types, and other factors within spinel minerals, there are hundreds of minerals or compounds with the spinel structure. In field mineral and rock specimens, precious spinel is primarily found in the contact zone between dolomite (or dolomitic limestone) and igneous rocks, and is a typical oxide mineral of high-temperature contact metamorphic replacement minerals. Typically, in natural rock samples containing spinel collected from the field, precious spinel coexists with typical silicate minerals such as phlogopite, clinopyroxene (primarily diopside), pyrope, and chondrite. In surrounding rocks dominated by dolomitic limestone, precious spinel can be associated with the silicate mineral cordierite.

[0004] In the precious spinel crystal structure, the transition metal vanadium readily occupies tetrahedral positions, forming an isomorphic substitution of the equivalent state of the divalent cation at the A position. Typically, vanadium is a silvery-gray transition metal with an atomic number and atomic weight of 23 and 50.94, respectively, and typical valences of +2, +3, +4, and +5. With a melting point as high as 1890°C and a refractory body-centered cubic structure, vanadium possesses excellent mechanical ductility, hardness, acid and corrosion resistance, and non-magnetic properties. It is a crucial raw material for the production of new materials for modern high-tech products, defense industry manufacturing, and next-generation super semiconductors, earning it the well-deserved nickname "the MSG of modern industry." Vanadium is one of the most widely distributed trace metals in the Earth's crust. Existing geoscientists have shown that one vanadium atom is found in every 20,000 atoms of the Earth's crust, accounting for 0.02% of its composition. However, because vanadium is a typical dispersed element in geochemical research, its distribution is too dispersed, making it difficult to independently form large-scale, industrially exploitable key mineral resources. As a typical trace dispersed element, vanadium-containing mineral resources worldwide are primarily concentrated in vanadium titanomagnetite deposits. Vanadium titanomagnetite is also the most important ore mineral for vanadium production. The world's vanadium titanomagnetite reserves are relatively large, but these large and ultra-large deposits are mainly concentrated in a few countries and regions, including China, the United States, Canada, Australia, South Africa, and Russia. In addition to vanadium titanomagnetite, green sulfur vanadium ore, stone coal, potassium vanadate uranium ore, and limonite are all major minerals containing vanadium. my country is also one of the countries with relatively rich vanadium mineral resources in the world. Concentrated vanadium minerals have been found in several provinces, including Guizhou, Hunan, Sichuan, Hubei, and Shanxi. Furthermore, vanadium resources can be effectively recovered and comprehensively utilized in industrial waste and mining tailings such as bauxite, vanadium-uranium ore, carbonaceous shale, phosphate rock, spent catalysts, and petroleum combustion ash, thus transforming waste into treasure. Based on a comprehensive range of factors, including the scale of vanadium deposits identified in mineral resource exploration, mining technology, ore mineralogy, associated rare element content, beneficiation and processing technology, and market supply and demand, the cut-off and industrial grades for the development and comprehensive utilization of existing vanadium mineral resources in my country have been determined to be 0.5wt% and 0.7wt%, respectively.

[0005] As a typical oxide mineral, precious spinel contains no water or hydroxyl groups in its molecular structure. It is a nominally anhydrous high-pressure mineral found in the Earth's deep lower crust and upper mantle. Existing laboratory high-temperature and high-pressure experimental simulations and theoretical mineral physics simulations indicate that anomalous elastic wave velocity and electrical conductivity behavior in the mantle transition zone (depths from 410 km to 660 km, corresponding to pressures and temperatures of 16.0-23.0 GPa and 1450-1800°C) may be caused by a phase transition between spinel and post-spinel. The main methods used to synthesize precious spinel in laboratories in materials science, both domestically and internationally, include solid-state reaction, high-temperature hydrothermal synthesis, chemical vapor deposition, and fine-grained ball milling. These existing synthesis techniques rely on simple solution chemical reactions or direct physical grinding of sample powders, making them more suitable for nanoscale precious spinel. Since high-temperature and high-pressure experimental mineralogical research typically requires micron-sized and larger mineral samples, it is obvious that the nanoscale precious spinel samples obtained by previous material synthesis have failed to meet the minimum sample size requirements, and to date, there is no effective synthesis method. In the past, earth science researchers also often used natural precious spinel samples instead of synthetic samples to meet the needs of high-temperature and high-pressure experimental mineralogical research. However, natural samples have the disadvantage of obvious uneven distribution of trace element vanadium. Therefore, it has become particularly urgent to effectively synthesize a large-particle, industrial-grade, vanadium-doped anhydrous precious spinel single crystal that can meet the scientific research needs of various high-temperature and high-pressure laboratory simulations, especially the study of the preferred lattice orientation and crystal axis anisotropy of precious spinel single crystals under high pressure. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing industrial-grade vanadium-doped anhydrous noble spinel single crystals, so as to solve the technical problems such as the current lack of preparation technology for industrial-grade vanadium-doped anhydrous noble spinel large-grain single crystals under high temperature and high pressure conditions.

[0007] The technical solution of the present invention is:

[0008] A method for preparing an industrial-grade vanadium-doped anhydrous noble spinel single crystal comprises the following steps: using solid basic magnesium carbonate powder, solid aluminum isopropoxide powder, solid vanadium (III) triacetylacetonate powder, solid oxalic acid powder, and liquid dilute nitric acid as starting raw materials, and mixing the ingredients according to the stoichiometric ratio of the noble spinel to prepare a noble spinel powder sample; cold-pressing the noble spinel powder sample into sample discs, vertically stacking the discs, and placing the discs in a graphite crucible; placing the graphite crucible in a high-temperature oxygen atmosphere furnace for high-temperature calcination to prepare a cylindrical noble spinel sample; and subjecting the cylindrical noble spinel sample to a high-temperature and high-pressure reaction to obtain a noble spinel single crystal.

[0009] The purity of the solid basic magnesium carbonate powder is greater than 99.99%, the purity of the solid aluminum isopropoxide powder is greater than 99.99%, the purity of the solid triacetylacetonate vanadium (III) powder is greater than 99.99%, the purity of the solid oxalic acid powder is greater than 99.99% and the concentration of the liquid dilute nitric acid is 10%.

[0010] A method for preparing a precious spinel powder sample using solid basic magnesium carbonate powder, solid aluminum isopropoxide powder, solid vanadium (III) triacetylacetonate powder, solid oxalic acid powder, and liquid dilute nitric acid as starting materials and mixing the ingredients according to the stoichiometric ratio of precious spinel includes:

[0011] Step 1, using solid basic magnesium carbonate powder (purity> 99.99%), solid aluminum isopropoxide powder (purity> 99.99%), solid triacetylacetonate vanadium (III) powder (purity> 99.99%), solid oxalic acid powder (purity> 99.99%) and liquid dilute nitric acid with a concentration of 10% as starting materials;

[0012] Step 2: Weigh out 60 ml of 10% dilute nitric acid and place it into a notched beaker;

[0013] Step 3: Weigh out 5.0 g of high-purity solid basic magnesium carbonate powder and add it to a beaker, and place a magnetic stirring rotor in it;

[0014] Step 4: Cover the beaker and place it on a high-temperature magnetic stirring hot plate in a fume hood, and react at room temperature and 700 rpm for 72 hours;

[0015] Step 5: According to the stoichiometric ratio of precious spinel (Mg, V)Al2O4, 22.3635 g of solid aluminum isopropoxide powder and 152.5354 mg of solid vanadium triacetylacetonate powder were weighed out and added to the dilute nitric acid solution containing basic magnesium carbonate;

[0016] Step 6: Cover the beaker with a glass watch glass to seal it;

[0017] Step 7: Place the sealed beaker on a high-temperature magnetic stirring plate in a fume hood and stir at room temperature and 800 rpm for 48 hours.

[0018] Step 8: After the reaction is completed, weigh out 2 grams of solid oxalic acid powder and add it to a beaker;

[0019] Step 9. Place the notched beaker of the mixture back on the high-temperature magnetic stirring plate in the fume hood, cover with a glass watch glass, and set the high-temperature magnetic stirring plate to 80°C and 1000 rpm for 36 hours.

[0020] Step 10: Remove the glass watch glass from the beaker and raise the temperature of the high-temperature magnetic stirring hot plate to 110° C. until the mixed solution in the notched beaker is completely evaporated.

[0021] Step 11: Take out all the mixed powders in the beaker and place them in a graphite crucible;

[0022] Step 12: Place the graphite crucible in a muffle furnace and heat it up to 1100° C. at a heating rate of 300° C. / hour, and keep the temperature constant for 5 hours; cool the mixed sample powder in the graphite crucible in the muffle furnace to room temperature at a cooling rate of 200° C. / hour;

[0023] Step 13: Place the honeycomb-shaped loose sample powder in a corundum mortar and grind it for 1 hour to obtain a powder sample.

[0024] The method of cold-pressing the precious spinel powder sample into sample discs and then vertically stacking and placing them in a graphite crucible includes:

[0025] Step 14: Cold-press the precious spinel powder sample mixture into three sample discs of Φ10.0 mm × 3.0 mm using a tungsten carbide grinding tool of a stainless steel tablet press; stack the three cold-pressed sample mixtures vertically together and place them in a graphite crucible.

[0026] The method of preparing a cylindrical precious spinel sample by placing a graphite crucible in a high-temperature oxygen atmosphere furnace and calcining it at high temperature comprises:

[0027] Step 15: Drill two holes symmetrically in the wall of the graphite crucible, pass a platinum-rhodium alloy wire through the two symmetrical circular holes in the graphite crucible wall, connect the two ends of the platinum-rhodium wire of the graphite crucible, and suspend the graphite crucible in the center of the high-temperature oxygen atmosphere furnace via the platinum-rhodium wire; place a stainless steel container containing more than 3 liters of secondary deionized pure cold water on the side of the high-temperature oxygen atmosphere furnace;

[0028] Step 16: The top of the high-temperature oxygen atmosphere furnace is connected to an argon inert gas cylinder and carbon monoxide and carbon dioxide cylinders with adjustable ratios. During the high-temperature calcination of the sample, each gas is switched and adjusted at any time through a valve;

[0029] Step 17: Open the argon inert gas valve, rotate the pointer button controlled by the gas pressure gauge, and continue to inflate for 30 minutes; under the protection of argon inert gas, calcine the sample at a high temperature of 800°C at a heating rate of 400°C / hour;

[0030] Step 18: After the temperature inside the furnace reaches 800°C, switch the carbon monoxide gas cylinder and the carbon dioxide gas control valve so that the volume ratio of carbon monoxide and carbon dioxide passing through the sample oxygen atmosphere furnace reaches 4:1;

[0031] Step 19: After the mixed gas flow of carbon monoxide and carbon dioxide in a volume ratio of 4:1 to control the oxygen fugacity in the sample chamber reaches a stable state, the temperature of the sample chamber in the furnace is increased to 1650° C. at a heating rate of 200° C. / hour and the mixture is calcined at a constant temperature for 15 minutes.

[0032] Step 20: After the sample is calcined at a constant temperature of 1650° C. for 15 minutes, the graphite crucible containing the sample, the four-hole alumina tube, and the round cover on the furnace body are pulled out of the furnace body and directly immersed in a stainless steel container of secondary deionized pure cold water to quench into precious spinel glass;

[0033] Step 21: remove the quenched glassy noble spinel sample from the graphite crucible and grind it in a corundum mortar into a fine-grained sample powder with uniform composition; dry the glassy noble spinel sample powder in a vacuum drying oven at 200° C. for 12 hours;

[0034] Step 22: On a cold isostatic press, the dried glassy noble spinel sample powder is cold pressed using a tungsten carbide grinding tool with a diameter of Φ4.0 mm×10.0 mm to obtain a cylindrical sample with a size of Φ4.0 mm×4.0 mm.

[0035] The method for suspending a graphite crucible in the middle of a high-temperature oxygen atmosphere furnace by means of a platinum-rhodium wire is as follows: the two ends of the platinum-rhodium wire connecting the graphite crucible are fixed on a vertical four-hole alumina tube with a pore size of 0.6 mm, the outer diameter of the four-hole alumina tube being 5.0 mm and the length being 40 cm; the upper end of the four-hole alumina tube is fixed in the middle of a round cover that can be placed in and pulled out of the furnace body at any time.

[0036] The method for obtaining a single crystal of precious spinel by subjecting a cylindrical precious spinel sample to a high temperature and high pressure reaction comprises:

[0037] Step 23: seal the cylindrical precious spinel sample in a graphite tube with a diameter of 4.0 mm (inner diameter) × 4.4 mm and a wall thickness of 0.2 mm, and seal the upper and lower ends of the sample tube with graphite sheets with a diameter of 4.0 mm (diameter) × 0.2 mm (height);

[0038] Step 24: Place the graphite tube containing the sample on a typical 6-8 type multi-faceted large cavity high temperature and high pressure equipment in the laboratory (Kawai-1000t). Set the pressure and temperature increase rates to 0.5 GPa / hour and 10°C / minute, respectively. Raise the pressure and temperature to 3.0 GPa and 1050°C, respectively, and perform hot pressing sintering. The reaction time is 72 hours at constant temperature and pressure.

[0039] Step 25: After 72 hours of constant temperature and pressure, the temperature in the sample chamber is reduced from 1050° C. to 800° C. at a cooling rate of 3° C. / min and maintained at this temperature for 1 hour; then, the temperature in the sample chamber is reduced from 800° C. to room temperature at a cooling rate of 5° C. / min;

[0040] Step 26: After the temperature in the sample chamber drops to room temperature, the pressure in the sample chamber is reduced from 3.0 GPa to normal pressure at a pressure reduction rate of 0.5 GPa / hour;

[0041] Step 27: After the high-temperature and high-pressure preparation reaction is completed, the sample is taken out, and the graphite tube wrapping the sample is removed to select the precious spinel single crystal.

[0042] During high temperature and high pressure reaction, the temperature is calibrated by two sets of high temperature resistant tungsten-rhenium thermocouples. Each set of tungsten-rhenium thermocouples is symmetrically placed at the upper and lower ends of the graphite tube sample cavity. Each set of tungsten-rhenium thermocouples is composed of two different tungsten-rhenium alloys, with a chemical composition of W 95％ Re 5％ and W 74％ Re 26％ .

[0043] By changing the amount of the added initial substance, vanadium (III) triacetylacetonate powder, from 133.4685 mg to 171.6024 mg, the corresponding vanadium content in the final obtained industrial-grade vanadium-doped anhydrous precious spinel single crystal sample increased from 0.7 wt% to 0.9 wt%.

[0044] Beneficial effects of the present invention:

[0045] The present invention organically combines the backgrounds of relevant disciplines such as high-pressure experimental mineralogy, ore deposit geology, crystallography, crystal optics, structural geology, exploration geology, igneous rock petrology, sedimentary rock geology, metamorphic rock petrology, point defect chemistry, field experimental petrology, rare earth element geochemistry, dispersed element geochemistry, experimental geochemistry, mining geology, structural chemistry, and solid earth science. The present invention uses a typical laboratory Kawai-1000t 6-8 type multi-faceted large cavity high-temperature and high-pressure equipment to simulate the formation process of industrial-grade vanadium-doped anhydrous precious spinel single crystals under high-temperature and high-pressure conditions. The main chemical reaction equation involved in the present invention is:

[0046] [Mg4(OH)2(CO3)3]+8HNO3→4Mg(NO3)2+3CO2+5H2O

[0047] Mg(NO3)2+2C9H 21 AlO3→MgAl2O4+2(NH3·H2O)+6C2H2+6CO+10H2

[0048] MgAl2O4+NH4VO3→(Mg,V)Al2O4+2H2O+NO

[0049] Under high temperature and high pressure conditions, the selected starting raw material, basic magnesium carbonate [chemical formula: Mg4(OH)2(CO3)3], is a white, loose, and crisp powdered solid substance with stable chemical properties, almost insoluble in water and ethanol, and easily soluble in dilute acid solutions and foaming. The basic magnesium carbonate powder is selected because of its excellent properties of stable performance, loose texture, and easy solubility in dilute acid, making it an excellent raw material for providing magnesium in the artificial synthesis of precious spinel. The starting raw material, aluminum isopropoxide [chemical formula: C9H 21 AlO3] is a white and tetrameric powdered solid substance with strong hygroscopicity and strong chemical reactivity. It is easily decomposed when it comes into contact with water. Aluminum isopropoxide powder is selected because it is easy to decompose when it comes into contact with dilute acid solution and has strong chemical reactivity. Therefore, it is an excellent raw material for providing aluminum elements in artificially synthesized precious spinel. The starting material is vanadium triacetylacetonate [chemical formula: C 15 H 21 Vanadium acetylacetonate (V6V) is a brown powdery solid that is soluble in methanol, acetone, benzene, chloroform, and dilute acid. Vanadium acetylacetonate powder is selected because it readily dissolves in dilute nitric acid solutions and is therefore an excellent raw material for providing trace vanadium in synthetic precious spinels. Among the chemical reaction products involved in the present invention, the resulting NH3·H2O, C2H2, CO2, CO, NO, and H2 are all volatile substances at high temperatures.

[0050] The present invention requires the synthesis of large-grained anhydrous noble spinel single crystals with a high vanadium content reaching industrial grade (0.7wt%-0.9wt%). The synthesized sample contains vanadium-doped noble spinel single crystals that match the development and comprehensive utilization of vanadium mineral resources, and is widely used in experimental simulation studies of rock formation and mineralization of mineral rocks under high temperature and high pressure conditions. Compared with natural spinel samples exposed in nature, which may be substituted by impurity ions such as vanadium ions, iron ions, and chromium ions, during the preparation process of the industrial-grade vanadium-doped anhydrous noble spinel single crystals of the present invention, the laboratory environment is pure, the sample is in a sealed environment, and is not in contact with impurities. The obtained industrial-grade vanadium-doped anhydrous noble spinel single crystals are pure and have good chemical stability, providing important experimental sample guarantees for measuring the physical property parameters of industrial-grade vanadium-doped anhydrous noble spinel single crystals, especially for exploring the crystal axis anisotropy and lattice preferred orientation of the physical and chemical properties of spinel single crystal minerals under high pressure.

[0051] Compared with the artificially synthesized precious spinel single crystals previously seen, which use solid-state reaction method, high-temperature hydrothermal synthesis method, chemical vapor deposition method, fine-grained ball milling method and other synthesis methods, the preparation method of the present invention has obvious advantages such as simple operation process and short reaction time. The obtained precious spinel single crystals have excellent physical and chemical properties such as high purity, large size, and stable chemical properties. More importantly, the vanadium content is high, reaching the existing boundary grade (0.5wt%) and industrial grade (0.7wt%) for the development and comprehensive utilization of vanadium mineral resources, and the vanadium content in the spinel can be fully controlled. The large particle size of precious spinel single crystals can fully meet the sample requirements of single crystal mineral properties and spectroscopic experimental simulations under high temperature and high pressure conditions, such as electrical conductivity, synchrotron radiation X-ray diffraction, confocal Raman spectroscopy, and vacuum Fourier transform infrared spectroscopy on diamond pressure cell high-pressure equipment. This method provides important experimental sample guarantees for the measurement of physical property parameters of industrial-grade vanadium-doped anhydrous precious spinel single crystals, especially for the study of the preferred lattice orientation and crystal axis anisotropy of single crystal minerals under high pressure, breaking through the technical bottleneck of existing spinel single crystal synthesis.

[0052] The invention solves the technical problems such as the lack of technology for preparing large-grained single crystals of anhydrous noble spinel doped with industrial grade vanadium under the conditions of high temperature and high pressure. DETAILED DESCRIPTION

[0053] A method for preparing an industrial-grade vanadium-doped anhydrous noble spinel single crystal, comprising:

[0054] Step 1: Use solid basic magnesium carbonate powder (purity: >99.99%), solid aluminum isopropoxide powder (purity: >99.99%), solid triacetylacetonate vanadium (III) powder (purity: >99.99%), solid oxalic acid powder (purity: >99.99%) and liquid dilute nitric acid (concentration: 10%) as starting materials.

[0055] The high-purity solid basic magnesium carbonate powder used as the starting material in the present invention is a white, loose, and crisp substance with stable chemical properties. It is virtually insoluble in water and ethanol, yet readily soluble in dilute acid solutions and foams. Basic magnesium carbonate powder is an optimal raw material for providing magnesium in synthetic precious spinel due to its stable performance, loose texture, and easy solubility in dilute acid.

[0056] The high-purity solid aluminum isopropoxide powder used as the starting material in the present invention is a white, tetrameric substance with strong hygroscopicity and chemical reactivity, easily decomposing upon contact with water. Aluminum isopropoxide powder is selected because of its superior properties of readily decomposing upon contact with dilute acid solutions and its strong chemical reactivity, making it an optimal raw material for providing the aluminum element in the synthetic precious spinel.

[0057] The starting material selected in the present invention is a high-purity solid vanadium triacetylacetonate powder, also known as vanadium acetylacetonate. It is a brown solid and soluble in methanol, acetone, benzene, chloroform, dilute acid, etc. The vanadium acetylacetonate powder is selected because it easily dissolves in dilute nitric acid solution and is therefore the best raw material for providing the trace element vanadium in the synthetic precious spinel.

[0058] The high-purity solid oxalic acid selected as the starting material of the present invention is a chelating agent for metal substances. Its purpose is that oxalic acid powder has a great influence on the bioavailability of minerals and has a strong coordination effect. When oxalic acid combines with divalent alkaline earth metal magnesium ions, its solubility can be greatly reduced. For example, calcium oxalate is almost insoluble in water, and then forms an alkali metal magnesium ion complex sol in dilute nitric acid solution. At the same time, when oxalic acid combines with the transition metal cation vanadium, due to its coordination effect, a soluble transition metal cation complex is formed, and the solubility of the divalent vanadium cation is significantly enhanced, so that it is fully dissolved in dilute nitric acid solution.

[0059] The dilute nitric acid (concentration: 10%) used as the starting material in the present invention, if the nitric acid concentration is too low, due to its limited solubility, may result in residues of basic magnesium carbonate, aluminum isopropoxide and oxalic acid powder; if the nitric acid concentration is too high, due to its enhanced oxidizing property, the sample may undergo rapid oxidation reaction and direct decomposition, and generate thick smoke, which may bring certain risks to the preparation.

[0060] Step 2. Open the chemical fume hood, select a standard volume 100 ml volumetric flask, accurately weigh out 60 ml of 10% dilute nitric acid, place the glass pipette rod in a 500 ml notched beaker, and carefully transfer all the liquid dilute nitric acid into the beaker along the pipette rod. The notched beaker is chosen as the reaction container mainly because the beaker is not completely sealed after the glass watch glass is covered, and the gas generated can easily evaporate in the fume hood.

[0061] Step 3: Accurately weigh 5.0 g of high-purity solid basic magnesium carbonate powder on a 10 μg high-precision analytical balance, carefully add it to a notched beaker containing 10% dilute nitric acid solution, and place a magnetic stirring rotor.

[0062] Step 4: Use a glass watch glass to cover the notched beaker containing the dilute nitric acid solution of solid basic magnesium carbonate powder and place it on a high-temperature magnetic stirring hot plate in a fume hood. In order to fully dissolve the solid basic magnesium carbonate powder as the initial material in the dilute nitric acid solution and simultaneously cause it to undergo hydrolysis and acidification reactions, the reaction conditions are room temperature, a speed of 700 rpm, and a reaction time of 72 hours.

[0063] Step 5: According to the stoichiometric ratio of precious spinel (Mg, V)Al2O4, 22.3635 g of high-purity solid aluminum isopropoxide powder and 152.5354 mg of high-purity solid vanadium triacetylacetonate powder were accurately weighed on a high-precision analytical balance, and carefully added to the dilute nitric acid solution containing basic magnesium carbonate.

[0064] Step 6: Place the dilute nitric acid solution containing solid basic magnesium carbonate powder, solid aluminum isopropoxide powder, and solid vanadium (III) triacetylacetonate powder in a beaker and cover it with a glass watch glass to ensure that the gas generated by the reaction evaporates from the gap in the beaker and to prevent the dilute nitric acid solution of the initial material in the beaker from splashing out during the high-speed stirring process, which would cause danger and affect the accuracy of the precious spinel synthesis.

[0065] Step 7: Place the sealed beaker containing the initial dilute nitric acid mixture and the magnetic stirring rotor on a high-temperature magnetic stirring hot plate in a fume hood. At room temperature, a rotation speed of 800 rpm, and a stirring time of 48 hours, completely dissolve the initial solid triacetylacetonate vanadium (III) powder in the dilute nitric acid solution mixture without any residue. At the same time, volatile substances such as NH3·H2O, C2H2, CO2, CO, NO, and H2 are more easily volatilized in the fume hood.

[0066] Step 8. Accurately weigh 2 grams of high-purity solid oxalic acid powder on a high-precision analytical balance and add the high-purity oxalic acid powder, which serves as an important metal chelating agent, to a dilute nitric acid solution containing solid basic magnesium carbonate powder, solid aluminum isopropoxide powder, and solid triacetylacetonate vanadium (III) powder. The purpose is that oxalic acid powder has a significant impact on the bioavailability of minerals and has a strong coordination effect. When oxalic acid combines with alkaline earth metal divalent magnesium ions, its solubility can be greatly reduced. For example, calcium oxalate is almost insoluble in water, and thus forms an alkali metal magnesium ion complex sol in dilute nitric acid solution. At the same time, when oxalic acid combines with transition metal cation vanadium, due to its coordination effect, a soluble transition metal cation complex is formed, which significantly enhances the solubility of the divalent vanadium cation, allowing it to be fully dissolved in the dilute nitric acid solution.

[0067] Step 9. Place the notched beaker of the mixed solution back on the high-temperature magnetic stirring hot plate in the fume hood, cover it with a glass watch glass, and set the conditions of the high-temperature magnetic stirring hot plate to 80°C, 1000 rpm, and stirring time for 36 hours, so that all the initial reagents form a uniform sol under the action of the mixed solution of dilute nitric acid and oxalic acid.

[0068] Step 10: Remove the glass watch glass from the beaker and raise the temperature of the high-temperature magnetic stirring hot plate to 110° C. until the mixed solution in the notched beaker is completely evaporated.

[0069] Step 11: Remove the magnetic stirring rotor from the notched beaker on the high-temperature magnetic stirring hot plate and remove any powder sample adhered to its surface into the beaker. Carefully remove the mixed powder from the notched beaker using a spatula and place it in a graphite crucible. The purpose of using a graphite crucible is to control the oxygen fugacity within the precious spinel graphite crucible, as the carbon in the crucible inevitably produces a certain concentration of carbon monoxide and carbon dioxide during the high-temperature calcination process. This ultimately constrains the valence state of the variable-valence element vanadium in the precious spinel sample.

[0070] Step 12: The graphite crucible containing the powder mixture was heated in a muffle furnace at atmospheric pressure and high temperature at a relatively slow heating rate of 300°C / hour to 1100°C and held at this temperature for 5 hours. The relatively slow high-temperature calcination rate and longer hold time facilitated the control of the oxygen atmosphere within the graphite sample chamber and facilitated the complete removal of residual nitric acid, oxalic acid, and other organic matter from the powder mixture.

[0071] The mixed sample powder in the graphite crucible in the muffle furnace was cooled to room temperature at a cooling rate of 200°C / hour. Compared with the heating rate, a slower cooling rate was selected to more easily form a honeycomb-shaped loose sample powder. The mixed sample powder was carefully taken out.

[0072] Step 13: Place the honeycomb-shaped loose sample powder in an ultra-hard thickened corundum mortar and grind it thoroughly for 1 hour to obtain a fine-grained and homogenized experimental powder sample.

[0073] Step 14: Cold-press the uniform and fine-grained noble spinel powder sample mixture into three 10.0 mm x 3.0 mm sample discs using a stainless steel tablet press with a high-precision tungsten carbide grinding tool measuring 10.0 mm x 10.0 mm. The three cold-pressed sample mixtures are stacked vertically and placed in a graphite crucible.

[0074] Step 15. Use a high-speed electric drill to symmetrically drill two 1.0 mm diameter circular holes in the graphite crucible containing the three stacked samples. Carefully thread a 0.5 mm platinum-rhodium alloy wire through the two 0.8 mm symmetrical circular holes in the graphite crucible wall and suspend it in the center of the high-temperature oxygen atmosphere furnace. The ends of the platinum-rhodium wire connecting the graphite crucible are fixed to a vertical 0.6 mm diameter four-hole alumina tube with an outer diameter of 5.0 mm and a length of 40 cm. The upper end of the four-hole alumina tube is fixed in the center of the round lid, which can be inserted and removed from the furnace at any time.

[0075] A stainless steel container containing 3 liters of secondary deionized pure cold water is placed in advance on the side of the high-temperature oxygen atmosphere furnace. Its purpose is to immerse the graphite crucible containing the sample directly in the 3 liters of secondary deionized water in the cold stainless steel container at extremely high temperatures to quickly cool it down. Its main purpose is to avoid the valence element vanadium from being oxidized / reduced again during the slow cooling of the furnace body, to achieve rapid quenching of the sample, and to completely preserve the glassy state of the precious spinel sample.

[0076] Step 16: At the top of the high-temperature oxygen atmosphere furnace, a cylinder of argon inert gas and cylinders of carbon monoxide and carbon dioxide with adjustable ratios are connected. A barometer controls the amount of gas introduced into the sample chamber. During the high-temperature calcination of the sample, each gas can be switched and adjusted at any time via valves. The present invention uses argon inert gas to provide an absolutely reducing oxygen atmosphere when the furnace temperature is below 800°C.

[0077] The present invention utilizes carbon monoxide and carbon dioxide in an adjustable ratio to effectively control the oxygen fugacity of samples during high-temperature calcination when the furnace temperature exceeds 800°C. Continuing to introduce argon inert gas above 800°C would lead to over-reduction within the sample chamber, potentially reducing the variable-valence element vanadium to metallic vanadium. Therefore, at temperatures above 800°C, a carbon monoxide and carbon dioxide mixture with an adjustable ratio is used to control the oxygen fugacity of samples within the high-temperature oxygen atmosphere furnace chamber. The reaction principle is 2CO + O₂ = 2CO₂, effectively adjusting the oxygen partial pressure within the sample chamber to any desired value, thereby achieving a variable-valence vanadium state in industrial-grade vanadium-doped anhydrous precious spinel single crystals.

[0078] The maximum rated temperature of a high-temperature oxygen atmosphere furnace is 1800°C. Turn on the circulating cooling water in the high-temperature oxygen atmosphere furnace to lower the upper and lower temperatures of the furnace body to prevent the entire furnace body from overheating, which may cause carbon monoxide and carbon dioxide to leak, thus causing danger.

[0079] Turn on the highly sensitive argon, carbon monoxide and carbon dioxide concentration monitoring alarms to avoid gas leakage during high-temperature calcination in the oxygen atmosphere furnace and ensure the safety of operators.

[0080] Step 17: Open the argon inert gas valve and rotate the pointer button controlled by the gas pressure gauge to continue inflating for 30 minutes to properly expel excess air from the sample chamber. Under the protection of argon inert gas, calcine the sample at a high temperature of 800°C at a heating rate of 400°C / hour.

[0081] Step 18. After the temperature inside the furnace reaches 800°C, quickly switch the carbon monoxide cylinder and the carbon dioxide gas control valve, and rotate the pointer button of the gas pressure gauge control to make the volume ratio of carbon monoxide and carbon dioxide passing through the sample oxygen atmosphere furnace reach 4:1. The purpose is that during the high-temperature calcination process, the carbon monoxide and carbon dioxide mixed gas with this volume ratio can well regulate the oxygen fugacity in the sample chamber.

[0082] Step 19: After the mixed gas flow of carbon monoxide and carbon dioxide (CO2) in a 4:1 volume ratio, controlling the oxygen fugacity within the sample chamber, reaches a stable state (this step takes approximately 3–5 minutes), the sample chamber temperature within the furnace is then raised to 1650°C at a heating rate of 200°C / hour and calcined at this constant temperature for 15 minutes to melt the precious spinel into a glassy state. During the heating process in the high-temperature oxygen atmosphere furnace, the heating rate of the sample chamber is reduced from 400°C / hour to 200°C / hour at different temperature ranges, from room temperature to 800°C and from 800°C to 1650°C. This slower heating rate is intended to facilitate the formation of stronger ionic bonds, such as those of Mg–O, Al–O, and V–O, in the vanadium-doped precious spinel.

[0083] The purpose of this high-temperature calcination process in an oxygen atmosphere controlled by a mixture of carbon monoxide and carbon dioxide is to provide a purer noble spinel glassy material for the present invention to synthesize large-particle industrial-grade vanadium-doped anhydrous noble spinel single crystals; high-temperature calcination in an oxygen atmosphere can better control the metallic valence state of the variable valence element vanadium in the product; and the higher calcination temperature of 1650°C ensures that any small amount of volatile matter, nitric acid, oxalic acid, organic matter, and other substances that may remain after high-temperature calcination in a muffle furnace and affect sample preparation are completely volatilized.

[0084] The 15-minute constant temperature calcination is a relatively short calcination time because the precious spinel powder will melt rapidly at temperatures above 1600°C. If the calcination time is too short, some residual starting powder may remain in the precious spinel melt product, seriously affecting the chemical composition of the prepared precious spinel sample. If the calcination time is too short, it is not conducive to the sufficient chemical diffusion of metal cations such as magnesium ions, aluminum ions, and vanadium ions, nor is it conducive to the formation of strong chemical bonds such as Mg–O, Al–O, and V–O in the spinel. If the calcination time is too short, the doped vanadium element will undergo stratification and differentiation in the precious spinel, resulting in uneven distribution, which will seriously affect the preparation effect. If the calcination time is too short, the density of the product will be reduced, and it may be difficult to form high-density precious spinel glass. However, calcination for more than 15 minutes may lead to excessive melting, causing the sample to adhere firmly to the wall of the graphite crucible, making it difficult to clean, and also increase the sample preparation cost.

[0085] Step 20. After the sample is calcined at a constant temperature of 1650°C for 15 minutes, the graphite crucible containing the sample, the four-hole alumina tube and the round cover on the furnace body are pulled out of the furnace body and directly immersed in a stainless steel container containing 3 liters of secondary deionized pure cold water to be rapidly quenched into precious spinel glass. The purpose of rapid quenching is to well preserve the glassy precious spinel sample with uniform composition at high temperature.

[0086] Step 21: Carefully remove the quenched glassy noble spinel sample from the graphite crucible and thoroughly grind it in a corundum mortar to form a fine-grained and uniform sample powder. Place the glassy noble spinel powder in a vacuum drying oven at 200°C for 12 hours.

[0087] Step 22: On a cold isostatic press, the precious spinel glass powder is cold pressed using a high-precision Φ4.0 mm (diameter) × 10.0 mm tungsten carbide grinding tool to form a Φ4.0 mm × 4.0 mm cylindrical sample.

[0088] Step 23: Seal the cylindrical precious spinel sample in a graphite tube with a diameter of Φ4.0 mm (inner diameter) × 4.4 mm and a wall thickness of 0.2 mm. Graphite sheets with a diameter of Φ4.0 mm (diameter) × 0.2 mm (height) are used at the upper and lower ends of the sample tube. Graphite is used as a sealing material. The main purpose is to control the oxygen fugacity values ​​of carbon monoxide and carbon dioxide in the sample chamber to be within the controlled range, and ultimately to achieve the valence state of the variable valence element vanadium in the precious spinel sample.

[0089] Precious spinel is one of the important magnesium-rich and aluminum-rich oxide minerals in the lower crust and upper mantle of the Earth and other terrestrial planets. In order to realistically simulate the growth environment of precious spinel in the lower crust of the Earth and other terrestrial planets, and to invert the temperature and pressure conditions for the stable existence of precious spinel mineral phase,

[0090] Step 24. Place the sample-containing graphite tube on a typical 6-8 type multi-faceted large cavity high-temperature and high-pressure equipment of the laboratory Kawai-1000t, set the pressure increase rate and temperature increase rate to 0.5 GPa / 1 hour and 10°C / minute respectively, increase the pressure and temperature to 3.0 GPa and 1050°C respectively, and perform hot pressing sintering. The reaction time is 72 hours of constant temperature and pressure.

[0091] The present invention, the selected preparation process of 3.0GPa high pressure and 1050℃ sintering temperature is designed entirely based on the physical and chemical properties of spinel itself. The specific purposes are as follows: First, the preparation process of high temperature and high pressure conditions, relatively slow pressure and temperature increase rate and long constant temperature and pressure reaction time can fully guarantee the complete mineral phase transformation from the initial spinel glass phase powder to the precious spinel crystal phase, and the final product precious spinel phase mineral phase can stably exist under the temperature and pressure conditions; secondly, the preparation process of high temperature and high pressure conditions, relatively slow pressure and temperature increase rate and long constant temperature and pressure reaction time can significantly increase the self-diffusion and chemical diffusion coefficients of metal cations such as magnesium ions, aluminum ions and vanadium ions, thereby realizing the isomorphic replacement of vanadium ions for metal magnesium ions in precious spinel crystals, and the reaction is complete and no free vanadium element remains, thereby forming a perfect rare earth element vanadium-doped precious spinel single crystal sample; secondly, the high temperature The preparation process of high-pressure conditions, relatively slow pressure and heating rates, and long constant temperature and pressure reaction times can fully ensure the formation of stable chemical bonds such as Mg–O, Al–O, and V–O, thereby avoiding the uneven distribution of the doped vanadium element in the precious spinel, such as stratification and differentiation, and thus achieving a uniform equiaxed vanadium-doped precious spinel single crystal sample; finally, the preparation process of high-temperature and high-pressure conditions, relatively slow pressure and heating rates, and long constant temperature and pressure reaction times makes the vanadium element distribution of the final prepared product precious spinel more uniform, while increasing the density, strength, and particle size of the product, thereby preparing a large-grained equiaxed vanadium-doped precious spinel single crystal sample with excellent physical and chemical properties such as uniform element distribution, high mechanical strength, and high density.

[0092] In the present invention, the temperature is accurately calibrated using two sets of high-temperature resistant tungsten-rhenium thermocouples. Tungsten-rhenium thermocouples have the advantages of good temperature-potential linear relationship, reliable thermal stability, low price, etc., and can achieve a temperature calibration range of 0-2300℃. They are widely used in high-pressure mineral physics experiments, high-tech metallurgical industry, high-temperature electronic thermoelectric system structure engineering, space vehicles, nuclear reactors and other fields for ultra-high temperature calibration. Each set of tungsten-rhenium thermocouples is composed of two different tungsten-rhenium alloys, whose chemical composition is W 95％ Re 5％ and W 74％ Re 26％. Put together one end of tungsten-rhenium thermocouple wires of different materials with a diameter of 0.1 mm, and hang them together with a vise to form a twist; connect the other end of the tungsten-rhenium thermocouple wires of different materials with a diameter of 0.1 mm to the positive and negative poles of the 36 Ford voltage regulator. Rotate the voltage regulator button to pass a large current through the wire, so that the twisted tungsten-rhenium high-temperature thermocouple wire is completely immersed in the saturated sodium chloride solution, melt it, and weld it into a ball. Remove the oxide layer of the spherical thermocouple wire to prepare two groups of hot tungsten-rhenium thermocouples, and symmetrically place each group of tungsten-rhenium thermocouples at the upper and lower ends of the graphite tube sample cavity. Each group of tungsten-rhenium thermocouples of the present invention uses double thermocouples placed at the upper and lower ends. This technology can realize the precise calibration of the temperature in the sample cavity, and can also accurately indicate the temperature gradient at the upper and lower ends of the sample chamber, ensuring that the sample is in a stable constant temperature zone during the synthesis process of the precious spinel sample.

[0093] Step 25: After maintaining constant temperature and pressure at 3.0 GPa and 1050°C for 72 hours, reduce the temperature in the sample chamber from 1050°C to 800°C at a cooling rate of 3°C / min and maintain the temperature for 1 hour; then reduce the temperature in the sample chamber from 800°C to room temperature at a cooling rate of 5°C / min.

[0094] By adopting a step-by-step cooling method and a relatively slow constant pressure cooling rate relative to the sample preparation heating rate (10°C / minute), the superior physical and chemical properties of the vanadium-doped precious spinel single crystal sample with uniform element distribution, high mechanical strength and high density will be further improved, and the occurrence of precious spinel crystal cracks caused by uneven stress in the sample due to an excessively fast cooling rate will be completely avoided. In addition, this preparation process will be more conducive to the crystal growth of large-grained precious spinel single crystals, thereby realizing the preparation of large-grained precious spinel single crystal samples of hundreds of microns.

[0095] Step 26: After the temperature in the sample chamber drops to room temperature, the pressure in the sample chamber is reduced from 3.0 GPa to normal pressure at a pressure reduction rate of 0.5 GPa / hour.

[0096] In addition, the present invention uses a sample preparation process for obtaining vanadium-doped anhydrous spinel by hot pressing and sintering. The preparation process is pure and does not involve any possible water-source substances such as the sample itself or high-pressure sample assembly.

[0097] Step 27: After the high-temperature, high-pressure preparation reaction is complete, the sample is removed from the Kawai-1000t, a typical 6-8-meter multi-faceted, large-cavity, high-temperature, high-pressure apparatus. The graphite tube encasing the sample is carefully removed, and the cylindrical sample is cut down the middle using a high-precision diamond wire cutter. The precious spinel single crystal is selected under a high-precision Olympus microscope at 20x magnification.

[0098] The precious spinel single crystal obtained by the present invention is a single physical phase without any other impurity phases; the electron probe microanalyzer (EPMA) detection result shows that the molecular formula of the precious spinel single crystal obtained is MgAl2O4; the multifunctional ion mass spectrometer (ICP-MS) detection result shows that the vanadium content in the precious spinel single crystal obtained is 0.7996wt%, far exceeding the industrial grade of vanadium mineral resources of 0.7wt%; the vacuum Fourier transform infrared spectroscopy (FT-IR) detection result shows that the water content of the precious spinel sample obtained is less than 6ppmwt%, which has a low water content and is an anhydrous oxide mineral.

[0099] The industrial grade vanadium-doped anhydrous precious spinel single crystal obtained by the present invention is a cubic crystal system with a space group of Fd3m (no.227) and a lattice parameter of α=β=γ=90°, the unit cell volume is The average particle size was 142 microns and the maximum particle size was 368 microns.

[0100] The industrial-grade vanadium-doped anhydrous noble spinel single crystals obtained by the present invention have superior properties such as high purity, large particle size, stable chemical properties, and high mechanical strength. More importantly, the vanadium content is high, reaching the existing boundary grade (0.5wt%) and industrial grade (0.7wt%) for the development and comprehensive utilization of vanadium mineral resources. Moreover, the vanadium content in the spinel can be fully controlled. By varying the amount of the chemical reagent, triacetylacetonate vanadium (III) powder, added as the initial substance, from 133.4685 mg to 171.6024 mg, the corresponding vanadium content in the obtained industrial-grade vanadium-doped anhydrous noble spinel single crystal samples can be increased from 0.7wt% to 0.9wt%. The obtained industrial-grade vanadium-doped anhydrous precious spinel single crystals can fully meet the needs of physical experimental simulation of minerals in the lower crust and upper mantle regions of the Earth and other terrestrial planets under high temperature and high pressure conditions, breaking through the existing technical bottleneck of precious spinel single crystal synthesis, and providing important experimental sample support for the study of the preferred lattice orientation and crystal axis anisotropy of single crystal minerals in the lower crust and upper mantle regions of the Earth and other terrestrial planets under high temperature and high pressure conditions.

Claims

1. A method for preparing an industrial-grade vanadium-doped anhydrous noble spinel single crystal, characterized by: The method comprises: using solid basic magnesium carbonate powder, solid aluminum isopropoxide powder, solid vanadium (III) triacetylacetonate powder, solid oxalic acid powder and liquid dilute nitric acid as starting raw materials, and mixing the ingredients according to the stoichiometric ratio of precious spinel to prepare a precious spinel powder sample; cold-pressing the precious spinel powder sample into sample discs, vertically stacking the discs and placing them in a graphite crucible; placing the graphite crucible in a high-temperature oxygen atmosphere furnace for high-temperature calcination to prepare a cylindrical precious spinel sample; and subjecting the cylindrical precious spinel sample to a high-temperature and high-pressure reaction to obtain a precious spinel single crystal. The method for preparing a cylindrical precious spinel sample comprises: Step 15: Drill two holes symmetrically in the wall of the graphite crucible, pass a platinum-rhodium alloy wire through the two symmetrical circular holes in the graphite crucible wall, connect the two ends of the platinum-rhodium wire of the graphite crucible, and suspend the graphite crucible in the center of the high-temperature oxygen atmosphere furnace via the platinum-rhodium wire; place a stainless steel container containing more than 3 liters of secondary deionized pure cold water on the side of the high-temperature oxygen atmosphere furnace; Step 16: The top of the high-temperature oxygen atmosphere furnace is connected to an argon inert gas cylinder and carbon monoxide and carbon dioxide cylinders with adjustable ratios. During the high-temperature calcination of the sample, each gas is switched and adjusted at any time through a valve; Step 17: Open the argon inert gas valve, rotate the pointer button controlled by the gas pressure gauge, and continue to inflate for 30 minutes; under the protection of argon inert gas, calcinate the sample at a high temperature of 800 °C at a heating rate of 400 °C / hour; Step 18: After the furnace temperature reaches 800°C, switch the carbon monoxide cylinder and carbon dioxide gas control valves so that the volume ratio of carbon monoxide to carbon dioxide in the sample oxygen atmosphere furnace reaches 4:1; Step 19: After the mixed gas flow of carbon monoxide and carbon dioxide in a volume ratio of 4:1 to control the oxygen fugacity in the sample chamber reaches a stable state, the temperature of the sample chamber in the furnace is increased to 1650°C at a heating rate of 200°C / hour and calcined at a constant temperature for 15 minutes; Step 20: After the sample is calcined at a constant temperature of 1650°C for 15 minutes, the graphite crucible containing the sample, the four-hole alumina tube, and the round cover on the furnace body are pulled out of the furnace body and directly immersed in a stainless steel container with secondary deionized pure cold water to quench into precious spinel glass; Step 21: remove the quenched glassy noble spinel sample from the graphite crucible and grind it in a corundum mortar into a fine-grained sample powder with uniform composition; place the glassy noble spinel sample powder in a vacuum drying oven at 200° C. for 12 hours; Step 22: On a cold isostatic press, the dried glassy noble spinel sample powder is cold pressed using a tungsten carbide mold with a diameter of Φ 4.0 mm × 10.0 mm to obtain a cylindrical sample with a size of Φ 4.0 mm × 4.0 mm.

2. The method for preparing an industrial-grade vanadium-doped anhydrous noble spinel single crystal according to claim 1, characterized in that: The purity of the solid basic magnesium carbonate powder is greater than 99.99%, the purity of the solid aluminum isopropoxide powder is greater than 99.99%, the purity of the solid vanadium (III) triacetylacetonate powder is greater than 99.99%, the purity of the solid oxalic acid powder is greater than 99.99%, and the concentration of the liquid dilute nitric acid is 10%.

3. The method for preparing an industrial-grade vanadium-doped anhydrous noble spinel single crystal according to claim 1, characterized in that: A method for preparing a precious spinel powder sample using solid basic magnesium carbonate powder, solid aluminum isopropoxide powder, solid vanadium (III) triacetylacetonate powder, solid oxalic acid powder, and liquid dilute nitric acid as starting materials and mixing the ingredients according to the stoichiometric ratio of precious spinel includes: Step 1, using solid basic magnesium carbonate powder with a purity greater than 99.99%, solid aluminum isopropoxide powder with a purity greater than 99.99%, solid vanadium (III) triacetylacetonate powder with a purity greater than 99.99%, solid oxalic acid powder with a purity greater than 99.99%, and liquid dilute nitric acid with a concentration of 10% as starting materials; Step 2: Weigh out 60 ml of 10% dilute nitric acid and place it into a notched beaker; Step 3: Weigh out 5.0 g of high-purity solid basic magnesium carbonate powder and add it to a beaker, and place a magnetic stirring rotor in it; Step 4: Cover the beaker and place it on a high-temperature magnetic stirring hot plate in a fume hood, and react at room temperature and 700 rpm for 72 hours; Step 5: According to the stoichiometric ratio of precious spinel (Mg, V)Al2O4, 22.3635 g of solid aluminum isopropoxide powder and 152.5354 mg of solid vanadium triacetylacetonate powder were weighed out and added to the dilute nitric acid solution containing basic magnesium carbonate; Step 6: Cover the beaker with a glass watch glass to seal it; Step 7: Place the sealed beaker on a high-temperature magnetic stirring plate in a fume hood and stir at room temperature and 800 rpm for 48 hours. Step 8: After the reaction is completed, weigh out 2 grams of solid oxalic acid powder and add it to a beaker; Step 9. Place the notched beaker of the mixture back on the high-temperature magnetic stirring plate in the fume hood, cover with a glass watch glass, and set the high-temperature magnetic stirring plate to 80 °C and 1000 rpm for 36 hours. Step 10: Remove the glass watch glass from the beaker and increase the temperature of the high-temperature magnetic stirring hot plate to 110°C until the mixed solution in the notched beaker is completely evaporated. Step 11: Take out all the mixed powders in the beaker and place them in a graphite crucible; Step 12: Place the graphite crucible in a muffle furnace and raise the temperature to 1100 °C at a heating rate of 300 °C / hour, and keep the temperature constant for 5 hours; cool the mixed sample powder in the graphite crucible in the muffle furnace to room temperature at a cooling rate of 200 °C / hour; Step 13: Place the honeycomb-shaped loose sample powder in a corundum mortar and grind it for 1 hour to obtain a powder sample.

4. The method for preparing an industrial-grade vanadium-doped anhydrous noble spinel single crystal according to claim 1, wherein: The method of cold-pressing the precious spinel powder sample into sample discs and then vertically stacking and placing them in a graphite crucible comprises: Step 14: Cold-press the precious spinel powder sample mixture into three sample discs of Φ 10.0 mm × 3.0 mm using a tungsten carbide die of a stainless steel tablet press; stack the three cold-pressed sample mixtures vertically together and place them in a graphite crucible.

5. The method for preparing an industrial-grade vanadium-doped anhydrous noble spinel single crystal according to claim 1, characterized in that: The method for suspending a graphite crucible in the middle of a high-temperature oxygen atmosphere furnace by means of a platinum-rhodium wire is as follows: the two ends of the platinum-rhodium wire connecting the graphite crucible are fixed on a vertical four-hole alumina tube with a pore size of 0.6 mm, the outer diameter of the four-hole alumina tube being 5.0 mm and the length being 40 cm; the upper end of the four-hole alumina tube is fixed in the middle of a round cover that can be placed in and pulled out of the furnace body at any time.

6. The method for preparing an industrial-grade vanadium-doped anhydrous noble spinel single crystal according to claim 1, characterized in that: The method for obtaining a single crystal of precious spinel by subjecting a cylindrical precious spinel sample to a high temperature and high pressure reaction comprises: Step 23: The cylindrical precious spinel sample is sealed in a graphite tube with an inner diameter of Φ 4.0 mm and a wall thickness of 4.4 mm and a wall thickness of 0.2 mm. The upper and lower ends of the sample tube are sealed with graphite sheets with a diameter of Φ 4.0 mm and a height of 0.2 mm. Step 24. Place the graphite tube containing the sample on a typical Kawai‒1000t laboratory 6-8 type multi-faceted large cavity high temperature and high pressure equipment. Set the pressure and temperature increase rates to 0.5 GPa / 1 hour and 10 °C / minute, respectively. Raise the pressure and temperature to 3.0 GPa and 1050 °C, respectively, and perform hot pressing sintering. The reaction time is 72 hours at constant temperature and pressure. Step 25: After 72 hours of constant temperature and pressure, the temperature in the sample chamber was reduced from 1050°C to 800°C at a cooling rate of 3°C / min and maintained at that temperature for 1 hour; then, the temperature in the sample chamber was reduced from 800°C to room temperature at a cooling rate of 5°C / min; Step 26: After the temperature in the sample chamber drops to room temperature, the pressure in the sample chamber is reduced from 3.0 GPa to normal pressure at a pressure reduction rate of 0.5 GPa / hour; Step 27: After the high-temperature and high-pressure preparation reaction is completed, the sample is taken out, and the graphite tube wrapping the sample is removed to select the precious spinel single crystal.

7. The method for preparing an industrial-grade vanadium-doped anhydrous noble spinel single crystal according to claim 6, characterized in that: During high temperature and high pressure reaction, the temperature is calibrated by two sets of high temperature resistant tungsten-rhenium thermocouples. Each set of tungsten-rhenium thermocouples is symmetrically placed at the upper and lower ends of the graphite tube sample cavity. Each set of tungsten-rhenium thermocouples is composed of two different tungsten-rhenium alloys, with a chemical composition of W 95% Re 5% and W 74% Re 26% .

8. The method for preparing an industrial-grade vanadium-doped anhydrous noble spinel single crystal according to claim 3, characterized in that: By changing the amount of chemical reagent added as the starting material triacetylacetonate vanadium (III) powder from 133.4685 mg to 171.6024 mg, the corresponding vanadium content in the final industrial grade vanadium-doped anhydrous precious spinel single crystal sample was increased from 0.7 wt% to 0.9 wt%.