A method for preparing a titanium-doped and high-hydrated vanadium magnetite single crystal under high temperature and high pressure

Abstract

The application discloses a preparation method of titanium-doped and high-hydrated vanadium magnetite monocrystal under high temperature and high pressure. Solid triangular siderite crystal, solid bisacetylacetonate vanadium (IV) powder, liquid tetraisopropoxy titanium (IV), solid oxalic acid powder, solid alpha-phase goethite powder, solid titanium hydroxide powder and liquid dilute nitric acid are used as starting raw materials to prepare a cylindrical vanadium magnetite sample; alpha-phase goethite powder and titanium hydroxide powder with a weight ratio of 4:1 are used to prepare a water source sheet; the water source sheet is placed at two ends of the cylindrical vanadium magnetite sample and then is placed into an inner sleeve of a double-capsule structure sample bin, and finally high temperature and high pressure reaction is carried out to obtain the vanadium magnetite monocrystal. The application solves the blank of the preparation technology of titanium-doped and high-hydrated vanadium magnetite large-grain monocrystal under the current high temperature and high pressure condition, and obtains experimental samples of titanium-doped and high-hydrated vanadium magnetite large-grain monocrystal.

Description

Technical Field

[0001] This invention belongs to the technical field of mineral single crystal sample synthesis, and particularly relates to a method for preparing titanium-doped and high-water-content vanadium magnetite single crystals under high temperature and high pressure. Background Technology

[0002] In the naming of spinel group oxide minerals (general chemical formula AB₂O₄), there is a special subgroup of spinels called ilmenite, which encompasses both the typical "2–3 type" structure spinel – vanadium magnetite (FeV₂O₄) and the "4–2 type" structure spinel – ilmenite (TiFe₂O₄). In nature, vanadium magnetite, an important vanadium-bearing end-member component of the ilmenite subgroup, has the following oxide chemical composition percentages: FeO / (FeO+V₂O₃) = 32.40% and Cr₂O₃ / (MgO+Cr₂O₃) = 67.60%. Due to its very high vanadium content, vanadium magnetite is an important raw material for the industrial extraction and smelting of vanadium. Typically, vanadium magnetite is the most typical oxide mineral with a positive spinel structure in nature. In the corresponding unit cell, the cubic closest packing ratio of vanadium magnetite with an anti-spinel structure is 0, exhibiting extremely obvious physicochemical properties of a positive spinel structure.

[0003] Typically, naturally exposed vanadium magnetite is a spinel group mineral with a bluish-gray crystal surface color, metallic luster, medium hardness (~5), isometric crystal system, hexagonal octahedral crystal form, and exhibiting obvious subhedral granular or platy structure. Field geological data studies show that the most typical deposit rock bodies exposed in vanadium-rich magnetite mineral resource areas mainly cover the following four types: (1) with felsic rocks such as argillaceous rocks and plagioclase rocks as the main rock body indicators, often exhibiting obvious cumulate structures, and then forming argillaceous rock-plagioclase complexes after undergoing differentiation of deep-seated basic magmas; (2) with ultramafic-mafic superrocks such as dunite, pyroxene peridotite, peridotite, and pyroxene peridotite as the main rock body indicators, often exhibiting spatiotemporal distribution of rock blocks, sills, or layered rock bodies, and then forming ultramafic-mafic superrocks. (3) Rocks with pyroxene, gabbro and other rocks from orogenic belts, rift valleys and mid-ocean ridges as the main rock mass indicators, often exhibit obvious intercalation structure, inclusion structure, reaction rim structure, etc., and thus form ring-shaped ultramafic rock-gabbro type rock mass, also known as Alaska-type ring-shaped rock mass; (4) Rocks with quartz diorite, granodiorite, tonalite and other phanerocrystalline intermediate-acidic plutonic rocks as the main rock mass indicators, often exhibiting the spatial and temporal distribution of small-scale associated rock masses such as sills, dikes, stocks and sheets, and thus form intrusive diorite rock mass. There are many deposits associated with vanadium magnetite deposits, such as chromite deposits, copper-nickel sulfide deposits, platinum group element deposits, etc., while vanadium magnetite mineral resources are mainly formed in late-stage magmatic deposits, magmatic differentiation deposits and high-temperature hydrothermal deposits. In nature, vanadium magnetite ore exhibits a wide variety of structural types, including accumulated, intercalated, exsolution, cumulate, sponge meteorite, and interstitial structures; massive, banded, and disseminated structures are also widely exposed. Among these diverse natural vanadium magnetite resources, the main associated minerals include: metallic sulfide minerals (such as pyrite, chalcopyrite, galena, and sphalerite), titanomagnetite, ilmenite, and other sulfides and spinel group oxide minerals. The main gangue minerals include: olivine, pyroxene, plagioclase, and other magnesium-iron island-structured silicate minerals widely found in the Earth's deep crust and mantle spheres; calcium-aluminum chain-structured silicate minerals; and sodium-aluminum (or potassium-aluminum) framework-structured silicate minerals. Furthermore, zero-valent vanadium is a metallic element with unique physicochemical properties such as light weight, good ductility, non-magnetic properties, refractory nature, low volatility, resistance to oxidation, and hardness.Vanadium is often used as a crucial metal additive in modern production and industrial manufacturing. The addition of trace amounts of vanadium significantly enhances the superior properties of alloy castings, including shock resistance, ductility, mechanical toughness, corrosion resistance, oxidation resistance, high-temperature resistance, yield strength, and bending resistance. Therefore, vanadium is known as the "metallic vitamin," "chemical bread," and "the MSG of modern industry." Vanadium has extremely wide applications in numerous vital fields concerning national economic development and the advancement of defense science and technology, including new glass, medicine, new lightweight materials, microelectronic circuits, large-scale integrated circuits, chemical engineering, metallurgy, aerospace vehicles, aero engines, special steels, new energy vehicles, semiconductor devices, and high-performance chips.

[0004] In the crystal structure of vanadium magnetite, titanium, a transition metal located in period 4 and group IVB, readily occupies octahedral positions, leading to isomorphic substitution of trivalent cations at the B-site. Since the metallic vanadium (valence: +3) and the doped transition metal titanium (valence: +4) in vanadium magnetite have completely different valences, this isomorphic substitution is an unequal isomorphic substitution. Typically, titanium has predominant valences of -1, 0, +2, +3, and +4. It is a typical lightweight, low-density, high-mechanical-strength, highly resistant to wet chlorine corrosion, and high-melting-point refractory rare metal, finding important applications in national high-tech industries such as automobile manufacturing, aerospace, high-speed rail, electronic circuits, and defense science and technology. While titanium is relatively abundant in nature, ranking tenth in abundance, titanium ore resources are scattered and difficult to extract. Titanium-rich ores mainly include tetragonal rutile (TiO2) and trigonal ilmenite (FeTiO3), which are widely distributed in the Earth's crust and lithosphere. Furthermore, high concentrations of the rare element titanium have been found in living organisms, water bodies, soils, and rocks. Existing geological data indicate that rutile, a titanium-bearing tetragonal oxide mineral, is widely distributed in my country, particularly in the Dafushan area of ​​Zaoyang County in Hubei Province, the Nianzigou area of ​​Daixian County in Shanxi Province, the Yangchong area of ​​Xinxian County in Henan Province, and the Liujiazhuang area of ​​Laixi County in Shandong Province. Hubei Province has the richest on-slate reserves of rutile mineral resources in my country, reaching 5.3443 million tons, accounting for over 70% of the total on-slate reserves of rutile mineral resources nationwide (7.5086 million tons). Ilmenite, a titanium-bearing corundum trigonal oxide mineral, is found in several well-known large or super-large deposits worldwide, including those in the Ilmen Mountains of Russia, Kragler in Norway, Iron Mountain in Wyoming, USA, Lake Ellard in Quebec, Canada, and the Panzhihua Iron Mine in Sichuan, China. Optical microscopic observations show that natural ilmenite single crystals collected in the field exhibit a granular or platy microcrystalline structure, often associated with magnetite, and widely distributed between magnetite single crystals or within fractures.

[0005] In addition, titanium (symbol: Ti, fourth period and group IVB, atomic number: 22) and vanadium (symbol: V, fourth period and group VB, atomic number: 23), both transition metals in the periodic table, are adjacent in element order, have similar atomic radii, and are both variable-valence metals. Therefore, they have formed numerous vanadium-titanium associated metal deposits and large rare earth metal deposits in nature. In my country, the proven reserves of vanadium-titanium rare earth metal deposits are extremely abundant and widely distributed, encompassing various types of rare earth metal mineralization characteristics and mineralization models, including granite-type, pegmatite-type, porphyry-type, quartz vein-type, skarn-type, sedimentary metamorphic type, and contact metasomatic type deposits, all of which are widely exposed. For example, the three world-renowned large or super-large vanadium-titanium magnetite deposits are: the Sichuan-Guizhou-Emeishan igneous province in the Panxi region of Sichuan Province, which exposes strata from the Middle to Late Permian; the Bayan Obo rare earth deposit in Inner Mongolia, which is a super-large vanadium-titanium magnetite magmatic deposit; and the Damiao vanadium-titanium magnetite metallogenic belt exposed in the Sinian strata of the Xuanhua-Chengde-Beipiao deep fault zone in Hebei Province. Existing regional geological data indicate that the super-large vanadium-titanium magnetite deposit discovered in the Panxi region of Sichuan Province is located in the Anninghe deep fault zone in the western part of the central section of the Kang-Dian axis. The ore-bearing rock body is mainly gabbro, about 35 km long and 2 km wide, trending northeast, with a dip angle of 50°–60°, and is a type of monoclinic rock body with good differentiation. The super-large vanadium-titanium magnetite deposit in the Panxi region of Sichuan Province is a highly typical layered late-stage magmatic crystallization differentiation deposit. Its mineral resource distribution exhibits a distinct rhythmic structure; as the stratum thickness increases, the mineral grain size increases, and the ore content and basicity of the rock also improve, showing a pattern of multiple minerals co-occurring. The ore minerals in this super-large vanadium-titanium magnetite deposit are mainly composed of oxide minerals rich in vanadium and titanium, such as magnetite, ilmenite, magnetite, ilmenite, spinel, anatase, and perovskite. It also includes metallic sulfide minerals rich in molybdenite, pyrrhotite, sulphite, pyrrhotite, and arsenic platinum ore. The ore distribution in the super-large vanadium-titanium magnetite deposit in the Panxi region of Sichuan Province exhibits a sponge-like meteorite texture, mainly characterized by mottled, massive, and layered structures. The metallic vanadium element in the ore mostly exists in the form of isomorphous formations. The ore-bearing rock mass is large in scale, the ore resources are abundant, the industrial grade of vanadium is high, and it is associated with key minerals of various transition rare earth metal elements that can be developed and utilized simultaneously, resulting in huge industrial value.

[0006] Vanadium magnetite, with its spinel structure, contains no water molecules or hydroxyl groups in its molecular structure, exhibiting the characteristics of a nominally anhydrous mineral. However, previous experiments on the water solubility of spinel under high temperature and pressure infrared spectroscopy have shown that spinel can dissolve up to hundreds of ppm of water. Water is one of the most important volatile components in the Earth's major internal spheres, especially in the mantle transition zone from 410 km to 660 km (corresponding to pressures and temperatures of 16.0-23.0 GPa and 1450-1800℃). Existing experimental studies on the physical and spectroscopic properties of minerals and rocks under high temperature and pressure, including electrical conductivity, Brillouin scattering elastic wave velocity, thermal diffusivity, thermal conductivity, and vacuum Fourier transform infrared spectroscopy, indicate that trace amounts of water in nominally anhydrous minerals can increase the physical and spectroscopic properties of minerals and rocks by several orders of magnitude, having a significant impact on their physical properties. The main methods used in the artificial synthesis of vanadium magnetite in laboratory materials science both domestically and internationally include: high-temperature solid-state reaction, polymer gelation, ammonia chemical co-precipitation, microemulsion, metal alkoxide sol-gel, freeze-drying, high-energy ball milling, and high-pressure powder hydrothermal synthesis. These existing synthesis techniques mostly involve simple solution chemical reactions or direct particle grinding of sample powders followed by high-temperature sintering, which are suitable for preparing nanoscale vanadium magnetite crystals. However, high-temperature and high-pressure experimental geoscience research typically requires mineral single-crystal samples with micron-sized or larger particles. Clearly, the nanoscale vanadium magnetite samples obtained through previous material synthesis methods fail to meet the minimum particle size requirements, and no effective synthesis method has yet been found. Previously, many geoscience researchers have also used natural vanadium magnetite samples instead of artificially synthesized samples to meet the needs of high-temperature and high-pressure experimental geoscience research. However, these natural samples suffer from the significant drawback of uneven distribution of the transition metal titanium. Therefore, it is particularly urgent to effectively synthesize a large-particle titanium-doped vanadium magnetite single crystal that meets the needs of geoscience research in various high-temperature and high-pressure laboratory simulations, especially the optimal orientation of the vanadium magnetite single crystal lattice and the study of crystal axis anisotropy under high pressure. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing titanium-doped and high-water-content vanadium magnetite single crystals under high temperature and high pressure, so as to fill the current technical gap in the preparation of large-particle titanium-doped and high-water-content vanadium magnetite single crystals under high temperature and high pressure conditions, and to obtain experimental samples of large-particle titanium-doped and high-water-content vanadium magnetite single crystals.

[0008] The technical solution of this invention is:

[0009] A method for preparing titanium-doped and high-hydration vanadium magnetite single crystals under high temperature and high pressure involves preparing cylindrical vanadium magnetite samples using solid triangular siderite crystals, solid vanadium(IV) dipentylene diacetate powder, liquid tetraisopropoxytitanium(IV) powder, solid oxalic acid powder, solid α-phase needle iron powder, solid titanium hydroxide powder, and liquid dilute nitric acid as starting materials. A water source sheet is prepared using α-phase needle iron powder and titanium hydroxide powder in a weight ratio of 4:1. The water source sheet is placed at both ends of the cylindrical vanadium magnetite sample and then placed together into the inner sleeve of a double-cell structure sample chamber. Finally, a high-temperature and high-pressure reaction is performed to obtain vanadium magnetite single crystals.

[0010] The following materials were used: solid transparent-translucent triangular siderite crystals (purity: >99.99%), solid vanadium(IV) dipentylene diacetate powder (purity: >99.99%), liquid titanium(IV) tetraisopropoxy (purity: >99.99%), solid oxalic acid powder (purity: >99.99%), solid α-phase pegmatite powder (purity: >99%), solid titanium hydroxide powder (purity: >99%), and liquid dilute nitric acid (concentration: 10%).

[0011] The method for preparing the cylindrical vanadium magnetite sample includes:

[0012] Step 1: Weigh out 60 ml of 10% dilute nitric acid and put it into a notched beaker;

[0013] Step 2: Weigh out 5.0 grams of high triangular siderite crystals and add them to a notched beaker, then place a magnetic stirring rotor inside.

[0014] Step 3: Cover the notched beaker with a glass watch glass and place it on a high-temperature magnetic stirring plate in a fume hood. React at room temperature, 700 rpm for 72 hours.

[0015] Step 4: Weigh out 22.8874 g of vanadium magnetite Fe(V,Ti)2O4 powder and 200 mL of liquid tetraisopropoxytitanium(IV) according to the stoichiometric ratio, and add them to notched beakers respectively.

[0016] Step 5: Cover the notched beaker with a glass watch glass.

[0017] Step 6: Place the notched beaker on the high-temperature magnetic stirring plate in the fume hood and stir at room temperature and 800 rpm for 48 hours.

[0018] Step 7: Weigh out 2 grams of solid oxalic acid powder and put it into a notched beaker;

[0019] Step 8: Place the notched beaker back on the high-temperature magnetic stirring plate in the fume hood, cover it with a glass watch glass, and set the conditions of the high-temperature magnetic stirring plate to 80°C, 1000 rpm, and stirring time for 36 hours.

[0020] Step 9: Remove the glass watch glass from the notched beaker, and increase the temperature of the high-temperature magnetic stirring plate to 110°C until the mixed solution in the entire notched beaker is completely evaporated.

[0021] Step 10: Remove the magnetic stirring rotor from the notched beaker and clean all the powder sample adhering to the surface into the beaker. Use a spatula to remove all the mixed powder from the notched beaker and place it in a graphite crucible.

[0022] Step 11: Place the graphite crucible containing the mixed powder into a muffle furnace under normal pressure and high temperature conditions, raise the temperature to 1150°C at a heating rate of 300°C / hour, and hold the temperature for 5 hours.

[0023] Step 12: Cool the mixed sample powder in the graphite crucible in the muffle furnace to room temperature at a cooling rate of 200℃ / hour.

[0024] Step 13: Place the sample powder in a corundum mortar and grind for 1 hour;

[0025] Step 14: Cold press the sample powder mixture into 3 sample discs with a diameter of Φ10.0mm×3.0mm. Stack the 3 cold-pressed sample discs vertically together and place them at the bottom of the graphite crucible.

[0026] Step 15: The graphite crucible containing three stacked samples is suspended in the center of the high-temperature oxygen atmosphere furnace. The two ends of the platinum-rhodium metal wire connecting the graphite crucible are fixed to the vertical four-hole alumina tube. The upper end of the four-hole alumina tube is fixed in the center of the round cover that can be put into and pulled out of the furnace body at any time.

[0027] Step 16: Place a stainless steel container filled with deionized pure cold water on the side of the high-temperature oxygen atmosphere furnace.

[0028] Step 17: Connect the top of the high-temperature oxygen atmosphere furnace to an argon inert gas cylinder and a carbon monoxide and carbon dioxide cylinder with adjustable ratios.

[0029] Step 18: Open the argon inert gas valve and continue to purge for 30 minutes; under the protection of argon inert gas, calcine the sample to 800°C at a heating rate of 400°C / hour.

[0030] Step 19: After the furnace body temperature reaches 800℃, switch the control valves of the carbon monoxide cylinder and the carbon dioxide cylinder to make the volume ratio of carbon monoxide and carbon dioxide passing through the sample oxygen atmosphere furnace reach 4:1.

[0031] Step 20: Increase the temperature of the sample chamber inside the furnace to 1600℃ at a heating rate of 200℃ / hour, and calcine at a constant temperature for 15 minutes to melt it into a glassy state of vanadium magnetite.

[0032] Step 21: After constant temperature roasting for 15 minutes, pull out the graphite crucible containing the sample, the four-hole alumina tube, and the round cover on the furnace body together from the furnace body and immerse them directly in a stainless steel container to quench into vanadium magnetite glass.

[0033] Step 22: Take the quenched glassy vanadium magnetite sample out of the graphite crucible and grind it into fine and uniform sample powder in a corundum mortar; place the glassy vanadium magnetite powder in a vacuum drying oven at 200°C and dry for 12 hours.

[0034] Step 23: The glassy vanadium magnetite powder is cold-pressed into cylindrical vanadium magnetite samples with a diameter of Φ4.0mm × 4.0mm (height) using a tungsten carbide mold on a cold isostatic press.

[0035] The preparation method of the water source tablet is as follows:

[0036] Step 24: On a cold isostatic press, α-phase needle iron ore powder and titanium hydroxide powder are cold-pressed into two water source sheets with a weight ratio of 4:1 using a tungsten carbide mold. The sheets are Φ4.0mm (diameter) × 0.1mm (height).

[0037] The method of obtaining vanadium magnetite single crystals by placing water source slices at both ends of a cylindrical vanadium magnetite sample and then placing them together into the inner sleeve of a double-celled sample chamber, followed by a high-temperature and high-pressure reaction, includes:

[0038] Step 25: Seal the cylindrical vanadium magnetite sample and two water source plates in a double-cell experimental sample chamber with an inner graphite tube and an outer gold-palladium alloy tube; when sealing, place the two water source plates at both ends of the cylindrical vanadium magnetite sample.

[0039] Step 26: Place the double-capsule sample chamber on a typical 6–8 type multi-faceted top large-cavity high-temperature and high-pressure equipment Kawai-1000t in the laboratory. Set the pressure increase rate and temperature increase rate to 0.5 GPa / hour and 10 °C / minute, respectively. Under the conditions of raising the pressure and temperature to 4.0 GPa and 1250 °C, respectively, hot pressing sintering is carried out. The reaction time is 72 hours under constant temperature and pressure.

[0040] Step 27: Then, reduce the temperature inside the sample chamber from 1250℃ to 800℃ at a cooling rate of 3℃ / min and hold the temperature for 1 hour; then, reduce the temperature inside the sample chamber from 800℃ to room temperature at a cooling rate of 5℃ / min.

[0041] Step 28: After the temperature inside the sample chamber drops to room temperature, reduce the pressure inside the sample chamber from 4.0 GPa to atmospheric pressure at a depressurization rate of 0.5 GPa / hour.

[0042] Step 29: After the high-temperature and high-pressure preparation reaction is completed, the sample is taken out from the typical 6–8 type multi-faceted top large cavity high-temperature and high-pressure equipment of Kawai-1000t, the graphite tube and gold-palladium alloy tube of the double-capsule sample chamber that encloses the sample are removed, the cylindrical sample is cut from the middle with a diamond wire cutter, and the vanadium magnetite single crystal is selected under a 20x Olympus microscope.

[0043] During the high-temperature and high-pressure reaction, two sets of tungsten-rhenium thermocouples were used for temperature calibration; each set of tungsten-rhenium thermocouples was composed of two different tungsten-rhenium alloys with the chemical composition W... 95％ Re 5％ and W 74％ Re 26％ Each set of tungsten-rhenium thermocouples is symmetrically placed at the upper and lower ends of the double-capsule sample chamber composed of graphite tubes and gold-palladium alloy tubes.

[0044] The beneficial effects of this invention are:

[0045] This invention organically combines backgrounds from general geology, mineral deposit geology, crystallography, mineralogy, genetic mineralogy, mineral deposit mineralogy, petrology, isotope geochemistry, rare earth element geochemistry, trace element geochemistry, advanced geochemistry, field experimental petrology, regional tectonic geology, igneous petrology, sedimentary petrology, metamorphic petrology, mineral crystal structure chemistry, mining geology, economic geology, crystal chemistry, stratigraphy, ore field structural geology, mineral facies, exploration geophysics, deep earth materials science, and high-pressure mineral physics. It utilizes a typical 6–8 type multi-faceted large-cavity high-temperature and high-pressure laboratory Kawai-1000t equipment to simulate the formation process of titanium-doped and high-water-content vanadium magnetite single crystals under high-temperature and high-pressure conditions. The main chemical reaction equations involved in this invention are:

[0046] FeCO3+2HNO3→Fe(NO3)2+CO2+H2O

[0047] Fe(NO3)2+2C 10 H 14 O5V→FeV2O4+2(NH3·H2O)+CH4+5CO2+7C2H2

[0048] FeV₂O₄ + 2C 12 H 28 O4Ti→Fe(V,Ti)2O4+10C2H2+4CO2+18H2

[0049] 2α(FeOOH)→α(Fe2O3)+H2O

[0050] 2α(FeOOH)→6 / (6-x)αFe (2-x / 3) (OH) x O (3-x) +(6-4x) / (6-x)H2O

[0051] →α(Fe₂O₃)+3x / (6-x)H₂O

[0052] Ti(OH)4 → TiO2 + 2H2O

[0053] In this invention, the initial raw material selected is siderite [chemical formula: FeCO3, also known as ferrous carbonate], a light grayish-white, vitreous, transparent-to-translucent triangular crystalline solid. It is chemically stable, almost insoluble or slightly soluble in water, readily soluble in dilute acid solutions, and foams. The triangular crystalline siderite crystals are chosen because of their stability and superior solubility in dilute acids, making them an excellent raw material for providing iron in the artificial synthesis of vanadium magnetite. The initial raw material is vanadium(IV) dipentylene diacetylacetonate oxide [also known as vanadium(IV) acetylacetonate, vanadium(IV) diacetylacetonate oxide, or vanadium(IV) diacetylacetonate oxide, chemical formula: C]. 10 H 14 Vanadium dipentylene oxide (IV) is a blue solid crystalline powder soluble in solvents such as ethanol, acetone, diethyl ether, chloroform, and benzene. It is commonly used as an intermediate in inorganic synthesis, as a paint drying agent, pigment, and industrial catalyst. Due to its high hydrochemical reactivity and solubility in dilute nitric acid solution, vanadium dipentylene oxide (IV) is an excellent raw material for providing the transition metal vanadium in artificially synthesized vanadium magnetite. The initial raw material is tetraisopropoxytitanium (IV) [also known as tetrapropyl titanate, tetra-n-propyl titanate, or tetraisopropyl titanate, chemical formula: C]. 12 H 28[O4Ti] is a colorless, liquid organic compound that readily absorbs moisture from the air and undergoes hydrolysis. It exhibits high hydrochemical activity and is readily soluble in mineral oil, isopropanol, hexane, cyclohexane, and organic solvents such as benzene and toluene. Tetraisopropoxytitanium (IV) is primarily used as a catalyst in transesterification and condensation reactions during mechanical synthesis, as well as in the preparation and production of adhesives, adhesion promoters, and Ziegler catalysts for metal or rubber products, demonstrating its wide range of applications. Due to its high hydrochemical activity and solubility in dilute nitric acid solution, tetraisopropoxytitanium (IV) is an excellent raw material for providing rare trace amounts of titanium, a transition metal element, in synthetic vanadium magnetite. The initial raw material, solid α-phase serrata iron ore [molecular formula: FeOOH], is a typical iron-bearing hydrous mineral. One previous academic viewpoint suggests that α-phase serrata iron ore undergoes a dehydration reaction at 270℃, directly forming hematite while releasing a large amount of water. Another viewpoint suggests that α-phase serrata iron ore undergoes a first dehydration reaction at 238℃, producing superstructured hematite [molecular formula: FeOOH]. (2-x / 3) (OH) x O (3-x) The superstructured hematite undergoes a second dehydration reaction at 800℃, producing hematite and releasing a large amount of water. The initial raw material, solid titanium hydroxide [molecular formula: Ti(OH)4], is a typical titanium-containing, hydrated white powder, belonging to an amphoteric oxide soluble in both acids and alkalis, and can be used as a mordant, acetylene polymerization catalyst, etc. At temperatures above 650℃, titanium hydroxide undergoes a dehydration reaction, producing rutile (TiO2) and releasing a large amount of water. In a high-pressure sample chamber, α-phase needle iron ore and titanium hydroxide, in a specific ratio, undergo a dehydration reaction under high temperature and pressure, producing a large amount of water, providing an excellent water source for the synthesis of titanium-doped and highly hydrated vanadium magnetite single crystals. The chemical reaction products involved in this invention, including NH3·H2O, CH4, C2H2, CO2, and H2, are all highly volatile substances at high temperatures.

[0054] This invention aims to synthesize titanium-doped and high-water-content vanadium magnetite single crystals. The synthesized samples contain titanium-doped vanadium magnetite single crystals suitable for the development and comprehensive utilization of titanium mineral resources. These crystals will be widely applied in diagenetic and mineralization simulation studies of the physicochemical properties of minerals and rocks under high temperature and high pressure conditions. Compared to naturally exposed vanadium magnetite samples, which may contain impurities such as iron, cobalt, and titanium ions, the preparation process of titanium-doped and high-water-content vanadium magnetite single crystals in this invention utilizes a pure laboratory environment. The samples are kept in a sealed environment, preventing contact with impurities. The resulting titanium-doped and high-water-content vanadium magnetite single crystals are pure substances with good chemical stability. This provides crucial experimental sample support for measuring the physical properties of titanium-doped and high-water-content vanadium magnetite single crystals, especially for investigating the anisotropy of crystal axes and optimal lattice orientation of vanadium magnetite single crystals under high pressure.

[0055] Compared to previous methods for artificially synthesizing vanadium magnetite single crystals, including high-temperature solid-state reaction, polymer gelation, ammonia chemical co-precipitation, microemulsion, metal alkoxide sol-gel, freeze-drying, high-energy ball milling, and high-pressure powder hydrothermal synthesis, the preparation method of this invention offers significant advantages such as simple operation and short reaction time. The resulting vanadium magnetite single crystals exhibit superior physicochemical properties, including high purity, large size, and stable chemical performance. Crucially, the synthesized vanadium magnetite product has a high vanadium content (7500-8500 ppm wt%) and a high water content (300-400 ppm), while the titanium and water contents can be completely controlled. The large particle size of vanadium magnetite single crystals fully meets the sample requirements for high-temperature and high-pressure experiments on diamond pressure chambers, including simulations of the physical properties and spectroscopic parameters of single crystal minerals under high temperature and high pressure conditions, such as conductivity, synchrotron radiation X-ray diffraction, confocal Raman spectroscopy, and vacuum Fourier transform infrared spectroscopy. This method provides important experimental sample support for measuring the physical property parameters of titanium-doped and high-water-content vanadium magnetite single crystals, especially for exploring the optimal orientation of the single crystal lattice and the anisotropy of the crystal axis under high pressure, thus breaking through the technical bottleneck of existing vanadium magnetite single crystal synthesis. Detailed Implementation

[0056] The preparation method of the present invention includes:

[0057] Solid transparent-translucent triangular siderite crystals (purity: >99.99%), solid vanadium(IV) dipentylene diacetate powder (purity: >99.99%), liquid tetraisopropoxytitanium(IV) (purity: >99.99%), solid oxalic acid powder (purity: >99.99%), solid α-phase styrene powder (purity: >99%), solid titanium hydroxide powder (purity: >99%), and liquid dilute nitric acid (concentration: 10%) were used as starting materials.

[0058] The high-purity siderite crystals selected as the starting material in this invention are a light grayish-white solid with a vitreous luster. They are chemically stable, almost insoluble or slightly soluble in water, readily soluble in dilute acid solutions, and foam. Triangular crystalline siderite crystals are chosen because their stability and easy solubility in dilute acids make them an excellent raw material for providing iron in the artificial synthesis of vanadium magnetite.

[0059] The high-purity vanadium dipentylene oxide (IV) selected as the starting material in this invention is a blue solid crystalline powder that is soluble in solvents such as ethanol, acetone, diethyl ether, chloroform, and benzene. It is commonly used as an intermediate in inorganic synthesis, as a paint drying agent, pigment, and industrial catalyst. Due to its high hydrochemical reactivity and solubility in dilute nitric acid solution, vanadium dipentylene oxide (IV) is an excellent raw material for providing the transition metal vanadium in artificially synthesized vanadium magnetite.

[0060] The high-purity tetraisopropoxytitanium(IV) selected as the starting material in this invention is a colorless, liquid organic compound that readily absorbs moisture from the air and undergoes hydrolysis. It exhibits high hydrochemical activity and is readily soluble in mineral oil, isopropanol, hexane, cyclohexane, and organic solutions such as benzene and toluene. Tetraisopropoxytitanium(IV) is primarily used as a catalyst in transesterification and condensation reactions during organogenesis, as well as in the preparation and production of adhesives, adhesion promoters, and Ziegler catalysts for metal or rubber products, demonstrating its wide range of applications. Due to its high hydrochemical activity and solubility in dilute nitric acid solution, tetraisopropoxytitanium(IV) is an excellent raw material for providing the rare trace element titanium in artificially synthesized vanadium magnetite.

[0061] The high-purity solid oxalic acid selected as the initial material in this invention is a chelating agent for metal substances. Its purpose is to leverage the significant impact of oxalic acid powder on the bioavailability of minerals, exhibiting a strong chelating effect. When oxalic acid combines with trivalent vanadium ions (a transition metal), it greatly reduces their solubility, thus forming a complex sol of trivalent vanadium ions in dilute nitric acid solution. Simultaneously, when oxalic acid combines with the transition metal cation titanium, due to its chelating effect, a soluble transition metal cation titanium complex is formed. The solubility of the tetravalent titanium cation in acid solution is significantly enhanced, allowing it to fully dissolve in dilute nitric acid solution. The high-purity solid α-spindle iron ore selected as the initial material in this invention is a typical iron-bearing hydrous mineral. One previous academic viewpoint suggests that α-spindle iron ore undergoes a dehydration reaction at 270℃, directly forming hematite while releasing a large amount of water. Another academic viewpoint suggests that α-spindle iron ore undergoes a first dehydration reaction at 238℃, producing superstructured hematite [molecular formula: Fe]. (2-x / 3) (OH) x O (3-x)The superstructured hematite undergoes a second dehydration reaction at 800℃, forming hematite and releasing a large amount of water. The high-purity solid titanium hydroxide selected for this invention is a typical titanium-containing, hydrous white powder, belonging to an amphoteric oxide that is soluble in both acids and alkalis, and can be used as a mordant, acetylene polymerization catalyst, etc. At temperatures above 650℃, titanium hydroxide undergoes a dehydration reaction, forming rutile (TiO2) and releasing a large amount of water.

[0062] The initial material selected in this invention is dilute nitric acid (concentration: 10%). If the concentration of nitric acid is too low, its limited solubility may result in residues of solid siderite crystals, solid vanadium dipentyl oxydioxy (IV) powder, liquid tetraisopropoxytitanium (IV) and solid oxalic acid powder. If the concentration of nitric acid is too high, its enhanced oxidizing properties may cause the siderite crystals in the sample to undergo rapid oxidation or decomposition directly, producing dense fumes, which may pose certain dangers to the preparation process.

[0063] Step 1: Open the chemical fume hood, select a standard 100 ml volumetric flask, accurately weigh out 60 ml of 10% dilute nitric acid, place a glass pipette in a 500 ml notched beaker, and carefully transfer all the liquid dilute nitric acid into the beaker along the pipette. The notched beaker is chosen as the reaction vessel mainly because it is not completely sealed after the glass watch glass is covered, and the generated gas can easily evaporate in the fume hood.

[0064] Step 2: Accurately weigh 5.0 grams of high-purity transparent to translucent triangular siderite crystals on a 10 microgram high-precision analytical balance, carefully add them to a notched beaker containing a 10% concentration of dilute nitric acid solution, and place a magnetic stirring rotor inside.

[0065] Step 3: Using a glass petri dish, cover the notched mouth of the beaker containing the dilute nitric acid solution of solid siderite crystals and place it on a high-temperature magnetic stirring plate in a fume hood. In order to fully dissolve the initial solid siderite crystals in the dilute nitric acid solution and at the same time allow them to undergo hydrolysis and acidification reactions, the reaction conditions are room temperature, 700 rpm, and 72 hours.

[0066] Step 4: According to the stoichiometric ratio of vanadium magnetite Fe(V,Ti)2O4, accurately weigh 22.8874 g of high-purity solid vanadium dipentyl oxydioxy (IV) powder and 200 ml of high-purity liquid tetraisopropoxytitanium (Ⅳ) on a high-precision analytical balance, and carefully add them separately to a dilute nitric acid solution containing siderite crystals.

[0067] Step 5: Place the solid siderite crystals, solid vanadium(IV) dipentylene oxide powder, and liquid tetraisopropoxytitanium(IV) in a beaker containing a dilute nitric acid solution. Cover the beaker with a glass watch glass to ensure that the gas generated by the reaction evaporates through the beaker's notch. This also prevents the dilute nitric acid solution of the initial materials from splashing out during high-speed stirring, which could cause danger and affect the accuracy of the vanadium magnetite single crystal synthesis.

[0068] Step 6: Place the sealed beaker containing the initial materials, the dilute nitric acid mixture, and the magnetically stirred rotor on a high-temperature magnetic stirring plate inside a fume hood. Under conditions of room temperature, a stirring speed of 800 rpm, and a stirring time of 48 hours, the solid siderite crystals, solid vanadium(IV) dipentylene diacetate powder, and liquid tetraisopropoxytitanium(IV) of the initial materials will be completely dissolved in the dilute nitric acid mixture without any residue. Simultaneously, this process facilitates the evaporation of volatile substances such as NH3·H2O, CH4, C2H2, CO2, and H2 within the fume hood.

[0069] Step 7: Accurately weigh 2 grams of high-purity solid oxalic acid powder using a high-precision analytical balance. Add the high-purity oxalic acid powder, which acts as an important metal chelating agent, to a dilute nitric acid solution containing solid siderite crystals, solid vanadium dipentyl oxyacetate (IV) powder, and liquid tetraisopropoxy titanium (IV). The purpose is that oxalic acid powder has a significant impact on the bioavailability of minerals and has a very strong chelating effect. When oxalic acid combines with trivalent vanadium ions, it can greatly reduce their solubility, thereby forming a complex sol of trivalent vanadium ions in the dilute nitric acid solution. At the same time, when oxalic acid combines with the transition metal cation titanium, due to its chelating effect, a soluble transition metal cation titanium complex is formed. The solubility of the tetravalent titanium cation in the acid solution will be significantly enhanced, allowing it to fully dissolve in the dilute nitric acid solution.

[0070] Step 8: Place the notched beaker of the mixture back on the high-temperature magnetic stirring plate in the fume hood, cover it with a glass watch glass, and set the conditions of the high-temperature magnetic stirring plate to 80°C, 1000 rpm and stirring time for 36 hours, so that all the initial reagents form a uniform sol under the combined action of the mixed solution of dilute nitric acid and oxalic acid.

[0071] Step 9: Remove the glass watch glass from the beaker, and increase the temperature of the high-temperature magnetic stirring plate to 110°C until the mixed solution in the entire notched beaker is completely evaporated.

[0072] Step 10: Remove the magnetic stirring rotor from the notched beaker on the high-temperature magnetic stirring plate and clean all the powder sample adhering to its surface into the beaker. Carefully remove all the mixed powder from the notched beaker with a spatula and place it in a graphite crucible. The purpose of using a graphite crucible is that the carbon that makes up the graphite crucible inevitably produces a certain concentration of carbon monoxide and carbon dioxide during the high-temperature calcination process, thereby controlling the oxygen fugacity of the vanadium magnetite sample inside the graphite crucible, and ultimately constraining the valence states of the variable-valence metal cations iron, vanadium, and titanium in the vanadium magnetite sample.

[0073] Step 11: Place the graphite crucible containing the mixed powder into a muffle furnace under normal pressure and high temperature conditions, raise the temperature to 1150°C at a relatively slow heating rate of 300°C / hour, and hold at that temperature for 5 hours. The relatively slow high-temperature calcination rate and the longer holding time are intended to better control the oxygen atmosphere within the graphite sample chamber, and to better remove residual nitric acid, oxalic acid, and other organic matter from the mixed powder.

[0074] Step 12: Cool the mixed sample powder in the graphite crucible in the muffle furnace to room temperature at a cooling rate of 200℃ / hour. Compared with the heating rate, choosing a slower cooling rate makes it easier to form a honeycomb-like loose sample powder. Carefully remove the mixed sample powder.

[0075] Step 13: Place the honeycomb-shaped loose vanadium magnetite sample powder in an ultra-hard thickened corundum mortar and grind it thoroughly for 1 hour to obtain a fine-grained and homogenized powder experimental sample.

[0076] Step 14: Mix the uniform and fine-grained vanadium magnetite powder sample and, using a high-precision tungsten carbide die with dimensions Φ10.0mm×10.0mm on a stainless steel tablet press, cold-press it into three sample discs with dimensions Φ10.0mm×3.0mm. Carefully stack the three cold-pressed sample discs vertically together at the bottom of a graphite crucible.

[0077] Step 15: On the wall of the graphite crucible containing three stacked samples, drill two symmetrical circular holes with a diameter of 1.0 mm using a high-speed electric drill. Carefully thread a 0.5 mm platinum-rhodium alloy wire through the two symmetrical circular holes in the graphite crucible wall, suspending it in the center of the high-temperature oxygen atmosphere furnace. Fix the two ends of the platinum-rhodium wire connecting the graphite crucible to a vertical four-hole alumina tube with a diameter of 0.6 mm. The four-hole alumina tube has 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 a circular lid that allows for easy insertion and removal of the furnace body.

[0078] Step 16: Place a 3-liter stainless steel container filled with deionized purified cold water on the side of the high-temperature oxygen atmosphere furnace. The purpose is to allow the graphite crucible containing the sample to be pulled directly out of the high-temperature oxygen atmosphere furnace at extremely high temperatures and quickly immersed in the 3-liter stainless steel container of deionized water for rapid cooling. The main purpose is to prevent the variable valence elements iron, vanadium, and titanium contained in the vanadium magnetite sample from being oxidized / reduced again during the slow cooling process of the furnace, thus achieving rapid quenching of the sample and completely preserving the glassy state of the vanadium magnetite sample.

[0079] Step 17: At the very top of the high-temperature oxygen atmosphere furnace, it is interconnected with argon inert gas cylinders and adjustable proportions of carbon monoxide and carbon dioxide cylinders. The amount of gas introduced into the sample chamber is controlled by a pressure gauge. During the high-temperature calcination of the sample, each gas can be switched and adjusted at any time via valves. This invention uses argon inert gas to provide an absolutely reducing oxygen atmosphere environment when the furnace temperature is below 800°C.

[0080] This invention employs a precisely proportioned mixture of carbon monoxide and carbon dioxide to effectively control the oxygen fugacity of samples during high-temperature calcination when the furnace temperature exceeds 800°C. If argon inert gas is continuously introduced when the furnace temperature exceeds 800°C, it will lead to over-reduction within the sample chamber, potentially causing variable-valence elements such as iron, vanadium, and titanium to be sequentially reduced to metallic iron, metallic vanadium, and metallic titanium. Therefore, at temperatures above 800°C, we use a precisely proportioned mixture of carbon monoxide and carbon dioxide to control the oxygen fugacity of samples within the high-temperature oxygen atmosphere furnace chamber. The reaction principle is as follows: It can effectively adjust the partial pressure of oxygen in the sample chamber, thereby controlling the valence states of variable-valence metals iron, vanadium, and titanium in titanium-doped and high-water-content vanadium magnetite single crystals.

[0081] The maximum rated temperature of the high-temperature oxygen atmosphere furnace body of this invention is 1800℃. The circulating cooling water of the high-temperature oxygen atmosphere furnace is turned on to reduce the temperature of the furnace body, preventing the overall furnace body temperature from becoming too high, which could cause carbon monoxide and carbon dioxide leaks and thus pose a danger.

[0082] Activate the highly sensitive monitoring alarms for argon, carbon monoxide, and carbon dioxide concentrations to prevent gas leaks during the high-temperature calcination process in the oxygen atmosphere furnace and ensure operator safety.

[0083] Step 18: Open the argon inert gas valve and rotate the pointer button controlled by the gas pressure gauge to continuously purge the sample chamber for 30 minutes. This is to properly expel excess air from the sample chamber. Under the protection of argon inert gas, calcine the sample to 800℃ at a heating rate of 400℃ / hour.

[0084] Step 19: After the furnace body temperature reaches 800℃, quickly switch the carbon monoxide cylinder and carbon dioxide gas control valve, and rotate the pointer button controlled by the gas pressure gauge to make the volume ratio of carbon monoxide and carbon dioxide in the sample oxygen atmosphere furnace reach 4:1. The purpose is that during the high-temperature calcination process, the mixed gas of carbon monoxide and carbon dioxide with this volume ratio can effectively regulate the oxygen fugacity in the sample chamber.

[0085] Step 20: After the mixed gas flow of carbon monoxide and carbon dioxide (volume ratio 4:1) controlling the oxygen fugacity in the sample chamber reaches stability (this step requires approximately 3-5 minutes), the temperature of the sample chamber inside the furnace is then increased to 1600°C at a heating rate of 200°C / hour, and calcined at this constant temperature for 15 minutes to melt it into a glassy state of vanadium magnetite. During the heating process in the high-temperature oxygen atmosphere furnace, two completely different heating rates of 400°C / hour and 200°C / hour are applied to the sample chamber within different temperature ranges: from room temperature to 800°C and from 800°C to 1600°C. This invention, by applying a relatively slow heating rate as the temperature of the sample chamber inside the high-temperature oxygen atmosphere furnace increases, is more conducive to the formation of strong ionic bonds such as Fe–O, V–O, and Ti–O in titanium-doped vanadium magnetite; it achieves more precise temperature control of the sample chamber inside the high-temperature oxygen atmosphere furnace; and it completely avoids excessively high temperatures in localized areas of the furnace due to unbalanced heat transfer within the sample chamber, which could easily damage the heating element of the oxygen atmosphere furnace, among other objectives.

[0086] The purpose of the high-temperature calcination process using a mixed gas of carbon monoxide and carbon dioxide under controlled oxygen atmosphere in this invention is to provide a purer glassy vanadium magnetite material for the synthesis of large-particle titanium-doped and highly hydrated vanadium magnetite single crystals. High-temperature calcination under oxygen atmosphere conditions can better control the valence states of variable-valence metal elements iron, vanadium, and titanium in the product. The relatively high calcination temperature of 1600℃ ensures that any small amounts of volatiles, nitric acid, oxalic acid, organic matter, and other substances that may remain after high-temperature calcination in a muffle furnace and affect sample preparation have been completely volatilized.

[0087] A relatively short calcination time of 15 minutes at a constant temperature is used because vanadium magnetite powder melts rapidly at temperatures above 1550℃. If the calcination time is too short, some initial powder residue may remain in the molten vanadium magnetite, severely affecting the chemical composition of the prepared vanadium magnetite sample. A short calcination time also hinders the sufficient chemical diffusion of metal cations such as iron, vanadium, and titanium ions, and is detrimental to the formation of stable chemical bonds in the strong ionic bonds such as Fe–O, V–O, and Ti–O in vanadium magnetite. Furthermore, a short calcination time can lead to uneven distribution of the doped transition metal titanium element in the vanadium magnetite, such as stratification and differentiation, severely affecting the preparation effect. A short calcination time also reduces the density of the product, making it difficult to form high-density vanadium magnetite glass. However, a calcination time exceeding 15 minutes may result in excessive melting, causing the vanadium magnetite sample to adhere firmly to the graphite crucible wall, making it difficult to clean and increasing sample preparation costs.

[0088] Step 21: After the sample has been calcined at a constant temperature of 1600℃ 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 double-deionized pure cold water to rapidly quench it into vanadium magnetite glass. The purpose of rapid quenching is to preserve the glassy vanadium magnetite sample with uniform composition at high temperature.

[0089] Step 22: Carefully remove the quenched glassy vanadium magnetite sample from the graphite crucible and grind it thoroughly in a corundum mortar to form a fine and homogeneous powder. Place the glassy vanadium magnetite powder in a vacuum drying oven at 200°C and dry for 12 hours.

[0090] Step 23: On a cold isostatic press, vanadium magnetite glass powder is cold-pressed into cylindrical vanadium magnetite samples with a diameter of 4.0 mm × 10.0 mm using a high-precision tungsten carbide mold of Φ4.0 mm × 4.0 mm.

[0091] To obtain vanadium magnetite with high water content, this invention uses α-phase spruce iron ore powder (molecular formula: FeOOH) and titanium hydroxide powder (molecular formula: Ti(OH)4) in a weight ratio of 4:1 as the water source. The choice of a mixture of α-phase spruce iron ore and titanium hydroxide as the water source is mainly based on the following considerations: First, both α-phase spruce iron ore and titanium hydroxide are typical hydrous substances with low dehydration temperatures. High-purity solid α-phase spruce iron ore is a typical iron-bearing hydrous mineral. One previous academic viewpoint suggests that α-phase spruce iron ore undergoes a dehydration reaction at 270℃, directly generating hematite while releasing a large amount of water. Another academic viewpoint suggests that α-phase spruce iron ore undergoes a first dehydration reaction at 238℃, producing superstructured hematite [molecular formula: FeOOH]. (2-x / 3) (OH) x O (3-x) Superstructured hematite undergoes a second dehydration reaction at 800℃, forming hematite and releasing a large amount of water. High-purity solid titanium hydroxide is a typical titanium-containing, hydrated white powder, belonging to the amphoteric oxide class, soluble in both acids and alkalis, and can be used as a mordant and acetylene polymerization catalyst. At temperatures above 650℃, titanium hydroxide undergoes a dehydration reaction, forming rutile (TiO2) and releasing a large amount of water. Therefore, this dehydration temperature condition can be achieved within the lower temperature range of the high-temperature, high-pressure preparation process of titanium-doped vanadium magnetite single crystals, ensuring that the titanium-doped vanadium magnetite single crystals are in a sufficiently water-rich environment for a long enough time to ensure sufficient diffusion of lattice water and formation of lattice sites. Furthermore, both α-phase needle iron and titanium hydroxide are iron-rich and titanium-rich substances, respectively, which can effectively control the iron and titanium activities of the main lattice sites during the preparation of titanium-doped and highly hydrated vanadium magnetite single crystals within the sample chamber under high-temperature, high-pressure conditions. Finally, the α-phase pegmatite and titanium hydroxide, placed at both ends of the sample in a 4:1 weight ratio, dehydrate the water source material combination, ultimately producing oxide minerals such as hematite and rutile. None of these products react chemically with the sample, ensuring the purity of the titanium-doped and high-water-content vanadium magnetite single crystal samples. Furthermore, by adjusting the weight ratio of the α-phase pegmatite and titanium hydroxide providing the water source material, as well as the corresponding height of the water source sheet, the water content in the titanium-doped and high-water-content vanadium magnetite single crystal samples can be adjusted.

[0092] Step 24: On a cold isostatic press, α-phase needle iron ore powder and titanium hydroxide powder are cold-pressed using a high-precision tungsten carbide mold with a diameter of 4.0 mm × 10.0 mm at a weight ratio of 4:1, and the resulting water source sheets are shaped into two pieces with a diameter of 4.0 mm × 0.1 mm.

[0093] Step 25: Seal the cylindrical vanadium magnetite sample (dimensions: Φ4.0mm (diameter) × 4.0mm (height)) and two water source plates (dimensions: Φ4.0mm (diameter) × 0.1mm (height)) sequentially within a double-capsule experimental sample chamber consisting of an inner sleeve – a graphite tube (dimensions: Φ4.4mm (outer diameter) × 4.4mm (height), wall thickness 0.2mm) and an outer sleeve – a gold-palladium alloy tube (dimensions: Φ4.6mm (outer diameter) × 4.6mm (height), wall thickness 0.1mm). In this invention, the titanium-doped vanadium magnetite sample is placed in the exact center of the inner graphite sleeve; while the two water source plates, containing α-phase pyrrhotite and titanium hydroxide in a 4:1 weight ratio, are placed at the symmetrical ends of the inner graphite sleeve close to the sample.

[0094] The inner sleeve of the double-cell sample chamber of this invention uses graphite as the sealing material. Its main purpose is to control the oxygen fugacity values ​​of carbon monoxide and carbon dioxide within the sample chamber, thereby confining the valence states of variable-valence metal elements iron, vanadium, and titanium in the vanadium magnetite sample.

[0095] The outer sleeve of the double-capsule sample chamber of this invention uses a gold-palladium alloy as the sealing material. The main purposes are: firstly, the gold-palladium alloy seal isolates the sample from other pressure-transmitting materials, effectively preventing sample contamination during the preparation of vanadium magnetite samples under high temperature and pressure; secondly, the gold-palladium alloy seal effectively prevents water from escaping from the sample tube during the preparation of vanadium magnetite samples under high temperature and pressure; finally, the double-capsule sample chamber, composed of a graphite tube and a gold-palladium alloy tube, creates a more sealed oxygen atmosphere, better controlling the oxygen fugacity within the sample chamber, thereby more effectively constraining the valence states of the variable-valence metals iron, vanadium, and titanium in the vanadium magnetite sample.

[0096] Step 26: Vanadium magnetite is one of the important iron-rich and vanadium-rich oxide minerals in the lower crust and upper mantle regions of Earth and other terrestrial planets. To realistically simulate the growth environment of vanadium magnetite in the lower crust of Earth and other terrestrial planets, and to invert the temperature and pressure conditions for the stable existence of vanadium magnetite mineral phases, a double-capsule sample chamber composed of graphite tubes and gold-palladium alloy tubes was placed on a typical 6–8 type multi-faceted top large cavity high-temperature and high-pressure equipment of Kawai-1000t in the laboratory. The pressure and temperature were set to 0.5 GPa / hour and 10℃ / minute, respectively. Hot pressing sintering was carried out under the conditions of 4.0 GPa and 1250℃, respectively, and the reaction time was constant temperature and pressure for 72 hours.

[0097] The preparation process using a high pressure of 4.0 GPa and a sintering temperature of 1250 °C selected in this invention is designed entirely based on the physicochemical properties of vanadium magnetite itself. The specific objectives are as follows: First, the preparation process under these high-temperature, high-pressure conditions, with a relatively slow rate of pressure and temperature increase and a relatively long isothermal reaction time, can completely guarantee the mineral phase transformation from the glassy state of the initial vanadium magnetite to the crystalline phase of vanadium magnetite, and the final product, the vanadium magnetite crystalline mineral phase, can exist stably under these temperature and pressure conditions. Second, this preparation process under these high-temperature, high-pressure conditions, with a relatively slow rate of pressure and temperature increase and a relatively long isothermal reaction time, significantly increases the self-diffusion coefficient and chemical diffusion coefficient of metal cations such as iron ions, vanadium ions, and titanium ions. This achieves the non-equivalent isomorphic substitution of trivalent vanadium ions by tetravalent titanium ions in the vanadium magnetite crystal, ensuring complete reaction and no residual free titanium element, thereby forming a perfect transition metal. The first sample is a titanium-doped vanadium magnetite single crystal. Secondly, the high-temperature, high-pressure conditions, relatively slow pressure and temperature increase rates, and long isothermal and isobaric reaction time ensure the formation of stable chemical bonds such as Fe–O, V–O, and Ti–O, thus avoiding uneven elemental distribution such as stratification and differentiation of the doped transition metal titanium in the vanadium magnetite. This results in a uniform isometric crystal system of titanium-doped vanadium magnetite single crystal. Furthermore, the high-temperature, high-pressure conditions, relatively slow pressure and temperature increase rates, and long isothermal and isobaric reaction time cause a dehydration reaction in the 4:1 weight ratio of α-phase styrene and titanium hydroxide, producing a large amount of water. The final dehydration products are mixed oxide minerals such as hematite and rutile. This dehydration temperature condition can be achieved within the lower temperature range of the process for preparing titanium-doped vanadium magnetite single crystals under high temperature and high pressure. This ensures that the titanium-doped vanadium magnetite single crystals are in a water-rich environment for a sufficiently long time, guaranteeing sufficient diffusion of water in the sample lattice and the formation of lattice sites. Because the titanium-doped vanadium magnetite single crystals are in a water-rich environment for a sufficiently long time, water diffusion within the sample chamber is significantly enhanced, thus ensuring a high water content in the final vanadium magnetite single crystal sample. Finally, the high temperature and high pressure conditions, the relatively slow rate of pressure and temperature increase, and the long isothermal and isobaric reaction time of the preparation process result in a more uniform distribution of titanium in the final vanadium magnetite single crystal, while also increasing the density, strength, and particle size of the product. This leads to the preparation of titanium-doped, high-water-content, large-particle, isometric vanadium magnetite single crystal samples with superior physicochemical properties such as uniform elemental distribution, high mechanical strength, and high density.

[0098] Temperature was precisely calibrated using two sets of high-temperature resistant tungsten-rhenium thermocouples. Tungsten-rhenium thermocouples offer advantages such as good temperature-potential linearity, reliable thermal stability, and low cost, enabling temperature calibration within a range of 0-2300℃. They are widely used in ultra-high temperature calibration in fields such as high-pressure mineral physics experiments, advanced metallurgical industries, high-temperature electronic thermoelectric system structural engineering, space vehicles, and nuclear reactors. Each set of tungsten-rhenium thermocouples is composed of two different tungsten-rhenium alloys with the following chemical composition: W... 95％ Re 5％ and W 74％ Re 26％ Tungsten-rhenium thermocouple wires of different materials, each with a diameter of 0.1 mm, were joined together at one end and twisted into a spiral shape using a vise. The other ends of the wires were connected to the positive and negative terminals of a high-power welding regulated DC power supply. The output current control knob of the power supply was adjusted to apply a large current to the wires, completely immersing the twisted tungsten-rhenium thermocouple wires in a saturated sodium chloride solution. The wires were melted and welded into spheres, and the oxide layer on the surface of the spherical thermocouple wires was removed. Using the same technique, two sets of tungsten-rhenium thermocouples were prepared, and each set was symmetrically placed at the upper and lower ends of a double-capsule sample chamber composed of a graphite tube and a gold-palladium alloy tube. This invention employs a dual thermocouple consisting of tungsten and rhenium placed at the top and bottom of the sample chamber. This technology enables precise temperature calibration within the sample chamber and accurately indicates the temperature gradient at both ends of the sample chamber, ensuring that the vanadium magnetite sample remains in a stable isothermal zone during the synthesis process.

[0099] Step 27: After maintaining a constant temperature and pressure for 72 hours at 4.0 GPa and 1250℃, the temperature inside the sample chamber is reduced from 1250℃ to 800℃ at a cooling rate of 3℃ / min, and held at that temperature for 1 hour. Then, the temperature inside the sample chamber is reduced from 800℃ to room temperature at a cooling rate of 5℃ / min. This stepped cooling and relatively slow constant-pressure cooling rate, compared to the sample preparation heating rate (10℃ / min), further enhances the superior physicochemical properties of the titanium-doped vanadium magnetite single crystal sample, which exhibits uniform vanadium distribution, high mechanical strength, and high density. It completely avoids the uneven stress caused by excessively rapid cooling, which could lead to cracks and breakage in the vanadium magnetite crystal. Furthermore, this preparation process is more conducive to the crystal growth of large-particle vanadium magnetite single crystals, thus enabling the preparation of vanadium magnetite large-particle single crystal samples at the hundred-micron scale.

[0100] Step 28: After the temperature inside the sample chamber drops to room temperature, the pressure inside the sample chamber is reduced from 4.0 GPa to atmospheric pressure at a depressurization rate of 0.5 GPa / hour. Furthermore, this invention provides a process for preparing titanium-doped and high-water-content vanadium magnetite single crystal samples via hot-pressing sintering. The preparation process is pure, without the introduction of any possible impurities from the sample itself, high-pressure sample assembly, or other sources.

[0101] Step 29: After the high-temperature and high-pressure preparation reaction is completed, the sample is removed from the typical 6–8 type multi-faceted top large-cavity high-temperature and high-pressure equipment of the Kawai-1000t. Carefully remove the graphite tube and gold-palladium alloy tube from the double-capsule sample chamber containing the sample. Using a high-precision diamond wire cutter, cut the cylindrical sample in half lengthwise. Under a high-precision Olympus microscope at 20x magnification, select the vanadium magnetite single crystals.

[0102] The vanadium magnetite single crystal obtained by this invention is a single phase without any other impurity phases; electron probe microanalysis (EPMA) results show that the molecular formula of the obtained vanadium magnetite single crystal is FeV2O4; multifunctional ion mass spectrometry (ICP-MS) results show that the titanium content in the obtained vanadium magnetite single crystal is 7826 ppm wt%; vacuum Fourier transform infrared spectroscopy (FT-IR) results show that the water content of the obtained vanadium magnetite single crystal sample is 326 ppm wt, which is relatively high.

[0103] The titanium-doped and highly hydrated vanadium magnetite single crystals obtained in this invention are cubic with space group Fd3m (no. 227) and lattice parameters of [missing information]. α=β=γ=90°, unit cell volume is The average particle size is 189 micrometers, and the maximum particle size is 591 micrometers.

[0104] The titanium-doped and highly hydrated vanadium magnetite single crystal samples obtained by this invention exhibit superior properties such as high purity, large particle size, stable chemical properties, and high mechanical strength. Most importantly, they possess a high titanium content (7826 ppm wt%), and the titanium content within the vanadium magnetite single crystals can be completely controlled. By varying the amount of the initial liquid high-purity tetraisopropoxytitanium(IV) chemical reagent added from 191.6611 mL to 217.2159 mL, the corresponding titanium content in the obtained titanium-doped and highly hydrated vanadium magnetite single crystal samples can be adjusted from 7500 ppm wt% to 8500 ppm wt%. Furthermore, by changing the weight ratio of the solid α-phase needle iron powder and solid titanium hydroxide powder used as the water source, and adjusting the different heights of the two water source plates, the total water content generated by the dehydration reaction of the water-containing material within the double-capsule sample chamber composed of a graphite tube and a gold-palladium alloy tube can be controlled, ultimately achieving the adjustment of the water content in the vanadium magnetite single crystals. The obtained titanium-doped and high-water-content vanadium magnetite single crystal samples can fully meet the needs of physical experiments simulating minerals in the lower crust and upper mantle of Earth and other terrestrial planets under high temperature and high pressure conditions. This breakthrough overcomes the existing technical bottleneck in the synthesis of vanadium magnetite single crystals and provides important experimental sample support for the study of the optimal orientation of the crystal lattice and the anisotropy of the crystal axis of single crystal minerals in the lower crust and upper mantle of Earth and other terrestrial planets under high temperature and high pressure conditions.

Claims

1. A method for preparing titanium-doped and high-hydration vanadium magnetite single crystals under high temperature and high pressure, characterized in that: Cylindrical vanadium magnetite samples were prepared using solid triangular siderite crystals, solid vanadium(IV) dipentadione oxide powder, liquid tetraisopropoxytitanium(IV) powder, solid oxalic acid powder, solid α-phase needle iron powder, solid titanium hydroxide powder, and liquid dilute nitric acid as starting materials. A water source sheet was prepared using α-phase needle iron powder and titanium hydroxide powder in a weight ratio of 4:

1. The water source sheets were placed at both ends of the cylindrical vanadium magnetite sample and then placed together into the inner sleeve of a double-cell structure sample chamber. Finally, a high-temperature and high-pressure reaction was carried out to obtain vanadium magnetite single crystals. The preparation method of the cylindrical vanadium magnetite sample includes: Step 15: The graphite crucible containing three stacked samples is suspended in the center of the high-temperature oxygen atmosphere furnace. The two ends of the platinum-rhodium metal wire connecting the graphite crucible are fixed to the vertical four-hole alumina tube. The upper end of the four-hole alumina tube is fixed in the center of the round cover that can be put into and pulled out of the furnace body at any time. Step 16: Place a stainless steel container filled with deionized pure cold water on the side of the high-temperature oxygen atmosphere furnace. Step 17: Connect the top of the high-temperature oxygen atmosphere furnace to an argon inert gas cylinder and a carbon monoxide and carbon dioxide cylinder with adjustable ratios. Step 18: Open the argon inert gas valve and continue to purge for 30 minutes; under the protection of argon inert gas, calcine the sample to 800 °C at a heating rate of 400 °C / hour. Step 19: After the furnace body temperature reaches 800 °C, switch the control valves of the carbon monoxide cylinder and the carbon dioxide cylinder to make the volume ratio of carbon monoxide and carbon dioxide passing through the sample oxygen atmosphere furnace reach 4:

1. Step 20: Increase the temperature of the sample chamber inside the furnace to 1600 °C at a heating rate of 200 °C / hour, and calcine at a constant temperature for 15 minutes to melt it into a glassy state of vanadium magnetite. Step 21: After constant temperature roasting for 15 minutes, pull out the graphite crucible containing the sample, the four-hole alumina tube, and the round cover on the furnace body together from the furnace body and immerse them directly in a stainless steel container to quench into vanadium magnetite glass. Step 22: Take the quenched glassy vanadium magnetite sample out of the graphite crucible and grind it into fine and uniform sample powder in a corundum mortar; place the glassy vanadium magnetite powder in a vacuum drying oven at 200 °C and dry for 12 hours. Step 23: The glassy vanadium magnetite powder is cold-pressed into cylindrical vanadium magnetite samples with a diameter of Φ4.0 mm and a height of 4.0 mm using a tungsten carbide mold on a cold isostatic press.

2. The method for preparing titanium-doped and high-hydration vanadium magnetite single crystals under high temperature and high pressure according to claim 1, characterized in that: The following materials were used: solid transparent-translucent triangular siderite crystals with a purity >99.99%; solid vanadium dipentadione oxide (IV) powder with a purity >99.99%; liquid tetraisopropoxytitanium (IV) with a purity >99.99%; solid oxalic acid powder with a purity >99.99%; solid α-phase pegmatite powder with a purity >99%; solid titanium hydroxide powder with a purity >99%; and liquid dilute nitric acid with a concentration of 10%.

3. The method for preparing titanium-doped and high-hydration vanadium magnetite single crystals under high temperature and high pressure according to claim 1, characterized in that: The preparation methods for three stacked samples include: Step 1: Weigh out 60 ml of 10% dilute nitric acid and put it into a notched beaker; Step 2: Weigh out 5.0 grams of high triangular siderite crystals and add them to a notched beaker, then place a magnetic stirring rotor inside. Step 3: Cover the notched beaker with a glass watch glass and place it on a high-temperature magnetic stirring plate in a fume hood. React at room temperature, 700 rpm for 72 hours. Step 4: Weigh out 22.8874 g of vanadium magnetite Fe(V,Ti)2O4 powder and 200 mL of liquid tetraisopropoxytitanium(IV) according to the stoichiometric ratio, and add them to notched beakers respectively. Step 5: Cover the notched beaker with a glass watch glass. Step 6: Place the notched beaker on the high-temperature magnetic stirring plate in the fume hood and stir at room temperature and 800 rpm for 48 hours. Step 7: Weigh out 2 grams of solid oxalic acid powder and put it into a notched beaker; Step 8: Place the notched beaker back on the high-temperature magnetic stirring plate in the fume hood, cover it with a glass watch glass, and set the conditions of the high-temperature magnetic stirring plate to 80 °C, 1000 rpm, and stirring time for 36 hours. Step 9: Remove the glass watch glass from the notched beaker, and increase the temperature of the high-temperature magnetic stirring plate to 110 °C until the entire mixture in the notched beaker is evaporated. Step 10: Remove the magnetic stirring rotor from the notched beaker and clean all the powder sample adhering to the surface into the beaker. Use a spatula to remove all the mixed powder from the notched beaker and place it in a graphite crucible. Step 11: Place the graphite crucible containing the mixed powder into a muffle furnace under normal pressure and high temperature conditions, raise the temperature to 1150 °C at a heating rate of 300 °C / hour, and hold the temperature for 5 hours. Step 12: 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 sample powder in a corundum mortar and grind for 1 hour; Step 14: Cold press the sample powder mixture into 3 sample discs with a diameter of Φ 10.0 mm × 3.0 mm. Stack the 3 cold-pressed sample discs vertically together and place them at the bottom of the graphite crucible.

4. The method for preparing titanium-doped and high-hydration vanadium magnetite single crystals under high temperature and high pressure according to claim 1, characterized in that: The preparation method of the water source tablet is as follows: Step 24: On a cold isostatic press, α-phase needle iron ore powder and titanium hydroxide powder are cold-pressed into two water source sheets with a diameter of Φ 4.0 mm × height of 0.1 mm using a tungsten carbide mold at a weight ratio of 4:

1.

5. The method for preparing titanium-doped and high-hydration vanadium magnetite single crystals under high temperature and high pressure according to claim 1, characterized in that: The method of obtaining vanadium magnetite single crystals by placing water source slices at both ends of a cylindrical vanadium magnetite sample and then placing them together into the inner sleeve of a double-celled sample chamber, followed by a high-temperature and high-pressure reaction, includes: Step 25: Seal the cylindrical vanadium magnetite sample and two water source plates in a double-cell experimental sample chamber with an inner graphite tube and an outer gold-palladium alloy tube; when sealing, place the two water source plates at both ends of the cylindrical vanadium magnetite sample. Step 26: Place the double-capsule sample chamber on a typical 6–8 type multi-faceted top large-cavity high-temperature and high-pressure equipment of Kawai 1000t in the laboratory. Set the pressure increase rate and the temperature increase rate to 0.5 GPa / hour and 10 °C / minute, respectively. Under the conditions of raising the pressure and temperature to 4.0 GPa and 1250 °C, respectively, hot pressing sintering is carried out, and the reaction time is constant temperature and pressure for 72 hours. Step 27: Then, reduce the temperature inside the sample chamber from 1250 °C to 800 °C at a cooling rate of 3 °C / min and hold the temperature for 1 hour; then, reduce the temperature inside the sample chamber from 800 °C to room temperature at a cooling rate of 5 °C / min. Step 28: After the temperature inside the sample chamber drops to room temperature, reduce the pressure inside the sample chamber from 4.0 GPa to atmospheric pressure at a depressurization rate of 0.5 GPa / hour. Step 29: After the high-temperature and high-pressure preparation reaction is completed, the sample is taken out from the typical 6–8 type multi-faceted top large cavity high-temperature and high-pressure equipment of Kawai 1000t, the graphite tube and gold-palladium alloy tube of the double-capsule sample chamber that encloses the sample are removed, the cylindrical sample is cut from the middle with a diamond wire cutter, and the vanadium magnetite single crystal is selected under a 20x Olympus microscope.

6. The method for preparing titanium-doped and high-hydration vanadium magnetite single crystals under high temperature and high pressure according to claim 1, characterized in that: During the high-temperature and high-pressure reaction, two sets of tungsten-rhenium thermocouples were used for temperature calibration; each set of tungsten-rhenium thermocouples was composed of two different tungsten-rhenium alloys with the chemical composition W... 95% Re 5% and W 74% Re 26% Each set of tungsten-rhenium thermocouples is symmetrically placed at the upper and lower ends of the double-capsule sample chamber composed of graphite tubes and gold-palladium alloy tubes.