A method for preparing a vanadium-doped and high-hydrated mangan-chrom-iron ore single crystal under high temperature and high pressure

Abstract

The application discloses a preparation method of vanadium-doped and high-hydrated mangan-chromian spinel monocrystal under high temperature and high pressure. The cylindrical mangan-chromian spinel sample is prepared by taking solid rose triangular rhombic manganese carbonate crystal, solid chromium (III) acetate hydroxide crystalline powder, solid vanadium (IV) acetylacetonate oxide powder, solid oxalic acid powder, solid bixbyite powder, solid chromium hydroxide powder and liquid dilute nitric acid as starting raw materials; two pieces of water source sheets are made from the bixbyite powder and the chromium hydroxide powder with a weight ratio of 4:1; the two pieces of water source sheets are placed at two ends of the cylindrical mangan-chromian spinel sample and then are placed into a double-capsule structure experimental sample bin with an inner layer sleeve being a graphite tube and an outer layer sleeve being a gold-palladium alloy tube; the high temperature and high pressure reaction is carried out to obtain the mangan-chromian spinel monocrystal; and the preparation technology blank of the vanadium-doped and high-hydrated mangan-chromian spinel large-particle monocrystal under the current high temperature and high pressure conditions is solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of synthesis of mineral single crystal samples, and particularly relates to a method for preparing vanadium-doped and high-hydrated manganese-chromian spinel single crystals under high temperature and high pressure. BACKGROUND

[0002] In nature, according to the lattice site occupied by metal cations contained in spinel minerals (general chemical formula: AB2O4) and the corresponding valence state of metal elements, spinel group minerals are generally divided into two main types: 2-3 type structure spinel and 4-2 type structure spinel. For example, in the chromian spinel subfamily of spinel group minerals, manganese-chromian spinel (crystal chemical formula: MnCr2O4) is parallel to chromite (crystal chemical formula: FeCr2O4), magnesio-chromite (crystal chemical formula: MgCr2O4), cobalt-chromite (crystal chemical formula: CoCr2O4), and zinc-chromite (crystal chemical formula: ZnCr2O4) to become the five most common chromite minerals with typical spinel structure. The obvious feature of this type of chromite is that the tetrahedral A site lattice position in the spinel structure is usually occupied by cations with a positive valence of two (Mn 2+ , Fe 2+ , Mg 2+ , Co 2+ , Zn 2+ , etc.); while the octahedral B site lattice position in the spinel structure is usually occupied by cations with a positive valence of three (Cr 3+ , Fe 3+ , Al 3+ , V 3+ , etc.). Further, mineral physicists of the prior art have defined this type of spinel as “A 2+ B 3+ 2O4”, which is collectively referred to as 2-3 type structure spinel. In addition to 2-3 structure spinel, it is also found that the tetrahedral A site lattice position in the spinel structure is usually occupied by cations with a positive valence of four (Si 4+ , Ge 4+ , Ti 4+ , etc.); while the octahedral B site lattice position in the spinel structure is usually occupied by cations with a positive valence of two (Fe 2+ , Mg 2+ , Mg 3+ , etc.). Further, mineral physicists of the prior art have defined this type of spinel as “A 4+ B 2+2O4”, i.e. collectively referred to as 4-2 type structure spinel. With this 4-2 type structure spinel, we have the most common occurrence of the most important nominally anhydrous hydrous rock-forming mineral in the mantle transition zone - Linwoodite (crystal chemical formula: SiFe2O4or SiMg2O4). As an important end-member component of the chromite subfamily of spinel group minerals - manganochromite, with a crystal chemical formula of MnCr2O4, is an important oxide mineral rich in manganese and rich in chromium. The percentage of oxide chemical composition of manganochromite mineralogy can be expressed as: MnO / (MnO+Cr2O3) = 36.4% and Cr2O3 / (MnO+Cr2O3) = 63.6%. Due to the relatively high content of chromium element in manganochromite, manganochromite is an important raw material for industrial production of chromium. Generally, manganochromite is a typical positive spinel structure oxide mineral in nature, and in the corresponding unit cell, the cubic closest packing ratio of manganochromite with an inverse spinel structure is 0, showing very obvious physical and chemical properties of positive spinel structure.

[0003] Generally, the natural occurrence of the manganese-chromite ore in nature presents a kind of hexagonal granular and brownish-gray translucent mineral, the particle size can be up to 10 microns, which can be found in iron meteorites, metamorphic hydrothermal pyrite deposits, and metamorphic iron sulfide deposits under submarine felsic volcanism. The latest research data released by the International Space Research and Development Agency shows that the asteroid "Ryugu 162173" returned to Earth by the Hayabusa 2 probe found manganese-chromite minerals with a diameter of about 1.0 nanometers. From the world's 25 top-level earth and planetary science research laboratories, a series of high-precision and high-resolution in-situ analysis and precision tests such as confocal ion beam scanning electron microscopy (FIB-SEM), field emission scanning electron microscopy (FE-SEM), mineral Rachel ultrathin section analysis, transmission electron microscopy, synchrotron X-ray diffraction microstructure, nanotopology, and micro-nano surface atom probe were carried out on 350 sample particles with an average particle size of ~100 microns from the asteroid "Ryugu 162173". It was found that manganese-chromite existed in the form of a secondary mineral, associated with magnesium-chromite (crystal chemical formula: MgCr2O4), chromium green (crystal chemical formula: Cr2O3), hydroxyapatite (crystal chemical formula: Ca5(PO4)3(OH)), ilmenite (crystal chemical formula: FeTiO3), copper-containing sphalerite (crystal chemical formula: ZnS), bar phosphorus iron ore (crystal chemical formula: (Fe, Ni)2P), meteorite sulfur chromium iron ore (crystal chemical formula: FeCr2S4), iron olivine (crystal chemical formula: FeCr2S4), magnesium olivine (crystal chemical formula: MgSiO4), easy augite (crystal chemical formula: (Mg, Fe, Ca)(Mg, Fe) [Si2O6]) and unnamed sodium-rich and magnesium-rich phosphide, and a series of mineral phases, the main minerals include serpentine, talc, iron sulfide, magnetite, dolomite, iron magnesite, etc. It is particularly important that the sample brought back by the Hayabusa 2 probe also found ammonia, methane, hydrogen, water, carbon dioxide, peptides, ribose, nucleic acid bases and other substances necessary for life formation. The scientific mystery of the existence of life on extraterrestrial planets has been solved, and it is not far away.

[0004] Vanadium element is a transition group metal element in the 4th period and VB group, and its main valence is 0, +2, +3, +4 and +5. In the crystal structure of mangan-chromite, the transition group rare and dispersed metal element vanadium can easily occupy the octahedral position and form the isomorphism replacement of B-site trivalent cation. Since the metal chromium element in the crystal lattice position and the doped transition group rare and dispersed metal element vanadium in the crystal structure of mangan-chromite have the same positive trivalence, the isomorphism replacement belongs to equivalent isomorphism replacement. The existing geological data research results show that the metamorphic sulfide iron deposit under the volcanic eruption of felsic rock in the Sheffield area of southern Australia is found to have the relatively rare mangan-chromite single crystal mineral. The optical microscopic observation results show that the natural mangan-chromite mineral has a crystal grain size of about 80 microns x 800 microns, and presents a relatively complete crystal idiomorphic structure, which directly penetrates between the orpiment and the gangue mineral. Further, based on the X-ray diffraction results of the natural mangan-chromite single crystal exposed in the southern Australia, the chromium element occupying the cubic structure crystal lattice framework of mangan-chromite is often replaced by the transition group metal element vanadium, and thus forms the vanadium manganite (crystal chemical formula: (Mn, Fe) (Cr, V) 2O4). On the earth, vanadium mineral resources are widely distributed, but are very dispersed, and are one of the typical trace rare earth metal elements with wide distribution. The main ore minerals rich in vanadium include vanadium-titanium magnetite, bauxite, sulfate rock, siltstone, magnetite and uranium-containing sand ore, and 98% of the proven vanadium metal mineral resource reserves in the world come from vanadium-titanium magnetite minerals. In the earth core, vanadium element usually exists in the form of metallic vanadium. In addition, the transition group rare and dispersed metal element vanadium has unique physical and chemical properties such as light weight, good ductility, non-magnetic, difficult to melt, difficult to volatilize, not easy to be oxidized, hard texture, etc.; as an alloy additive, the addition of vanadium element will greatly improve the high temperature resistance, corrosion resistance, mechanical strength, mechanical toughness, shock resistance, yield strength, bending, ductility and other superior properties of alloy products, and thus has multiple nicknames such as "modern industrial MSG", "metal vitamin" and "chemical bread". Especially in recent years, vanadium element has been widely used in many important fields related to the lifeblood of national economic development and the progress of national defense industry and industry, such as metallurgy, new light materials, aircraft engines, spacecraft, chemical industry, special steel, medicine, renewable energy storage and other fields.

[0005] The molecular structure of the manganese-chromite with spinel structure does not contain water molecules or hydroxyl groups, and shows obvious nominal anhydrous mineral properties. However, previous water solubility experiments of spinel infrared spectrum under high temperature and high pressure conditions show that the amount of water dissolved by spinel can be as high as hundreds of ppm. Water is one of the most important volatile components in the main layers of the earth's interior, especially in the mantle transition zone from 410 km to 660 km (corresponding to pressure and temperature: 16.0-23.0 GPa and 1450-1800 ℃). The existing experimental research results of physical properties and spectroscopy of minerals and rocks under high temperature and high pressure conditions, such as conductivity, Brillouin scattering elastic wave velocity, thermal diffusivity, thermoelectric conductivity, and vacuum Fourier transform infrared spectroscopy, show that the trace water in the nominal anhydrous mineral can improve the physical and spectral properties of the mineral and rock by several orders of magnitude, and has a very important influence on the mineral physics properties. Looking at the artificial synthesis of manganese-chromite in the field of laboratory materials science at home and abroad, the main methods include: high-pressure powder hydrothermal method, microwave solid-phase activation method, polyvinyl acetate alcoholysis method, carbonate chemical coprecipitation method, metal alkoxide sol-gel method, high-temperature solid-phase sintering method, and freeze-drying method. Due to the existing synthesis technology, most of which adopts simple solution chemical reaction or direct physical grinding of sample powder, and then high-temperature sintering, it is more suitable for preparing nanoscale manganese-chromite crystals. Since the high temperature and high pressure experimental geoscience field usually needs micron-sized or larger particle mineral single crystal experimental samples, it is obvious that the nanoscale manganese-chromite samples obtained by the previous material synthesis cannot meet the minimum particle size requirement. So far, there is no effective synthesis method. More geoscience researchers usually use natural manganese-chromite samples to replace artificial samples to meet the needs of high temperature and high pressure experimental geoscience research, but these natural samples have the disadvantage of uneven distribution of transition group rare earth dispersed metal element vanadium. Therefore, it is particularly urgent to effectively synthesize a large particle vanadium-doped and high-water manganese-chromite single crystal to meet the needs of various high temperature and high pressure laboratory simulation of geoscience research, especially the research on the preferred orientation and anisotropy of the manganese-chromite single crystal mineral lattice under high pressure. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a preparation method of vanadium-doped and high-water manganese-chromite single crystal under high temperature and high pressure, to completely solve the current technical blank of preparation of large particle vanadium-doped and high-water manganese-chromite single crystal under high temperature and high pressure, and to obtain experimental samples of large particle vanadium-doped and high-water manganese-chromite single crystal.

[0007] The technical scheme of the present application is:

[0008] A method for preparing vanadium-doped and high-hydrated manganese-chromite single crystals under high temperature and high pressure, the method comprising: preparing a cylindrical manganese-chromite sample by using rose rhombohedral manganese carbonate crystals in solid state, chromium(III) acetate hydroxide crystalline powder in solid state, bisacetylacetone vanadium(IV) oxide powder in solid state, oxalic acid powder in solid state, bixbyite powder in solid state, chromium hydroxide powder in solid state, and dilute nitric acid in liquid state as starting materials; preparing two water source pieces by using bixbyite powder and chromium hydroxide powder in a weight ratio of 4:1; placing the two water source pieces at two ends of the cylindrical manganese-chromite sample and then putting them into a double-capsule experimental sample bin with an inner layer of graphite tube and an outer layer of gold-palladium alloy tube; and performing high temperature and high pressure reaction to obtain manganese-chromite single crystals.

[0009] The purity of the rose rhombohedral manganese carbonate crystals is greater than 99.99%, the purity of the chromium(III) acetate hydroxide crystalline powder is greater than 99.99%, the purity of the bisacetylacetone vanadium(IV) oxide powder is greater than 99.99%, the purity of the oxalic acid powder is greater than 99.99%, the purity of the bixbyite powder is greater than 99%, the purity of the chromium hydroxide powder is greater than 99%, and the concentration of the dilute nitric acid is 10%.

[0010] The method for preparing the cylindrical manganese-chromite sample comprises:

[0011] Step 1, weighing 60 milliliters of dilute nitric acid with a concentration of 10% into a notch beaker;

[0012] Step 2, weighing 5.0 grams of rhombohedral manganese carbonate crystals in solid state into the notch beaker, and placing a magnetic stirring rotor into the notch beaker;

[0013] Step 3, covering the notch beaker with a glass surface dish, and placing it on a high-temperature magnetic stirring hot plate in a fume hood, and stirring at a speed of 700 revolutions per minute for 72 hours at room temperature;

[0014] Step 4, weighing 17.4949 grams of high-purity chromium(III) acetate hydroxide crystalline powder and 135 milligrams of high-purity bisacetylacetone vanadium(IV) oxide powder according to the stoichiometric ratio of manganese-chromite Mn(Cr,V)2O4, and adding them into the dilute nitric acid solution in the notch beaker;

[0015] Step 5, covering the notch beaker with a glass surface dish;

[0016] Step 6, placing the notch beaker on a high-temperature magnetic stirring hot plate in a fume hood, and stirring at a speed of 800 revolutions per minute for 48 hours at room temperature;

[0017] Step 7, weighing 2 grams of high-purity oxalic acid powder into the notch beaker;

[0018] Step 8, the notch beaker is placed again on the high-temperature magnetic stirring hot plate in the fume hood, covered with a glass surface dish, and the high-temperature magnetic stirring hot plate is set to 80°C, 1000 rpm, and stirred for 36 hours;

[0019] Step 9, remove the glass surface dish of the beaker, increase the temperature of the high-temperature magnetic stirring hot plate to 110°C, and stir until the entire mixture in the notch beaker is completely evaporated;

[0020] Step 10, remove the magnetic stirring rotor from the notch beaker, and clean all the surface-bonded powder samples into the beaker. Remove all the mixed powder from the notch beaker and place it in a graphite crucible;

[0021] Step 11, place the graphite crucible containing the mixed powder in a muffle furnace under normal pressure conditions, and increase the temperature to 1100°C at a rate of 300°C / hour, and maintain the temperature for 5 hours;

[0022] Step 12, again at a cooling rate of 200°C / hour, the mixed sample powder in the graphite crucible in the muffle furnace is cooled to room temperature;

[0023] Step 13, place the sample powder in a corundum mortar and grind for 1 hour to obtain the powder experimental sample;

[0024] Step 14, cold-press the powder experimental sample into 3 pieces of Φ10.0mm×3.0mm sample round pieces using a tungsten carbide die of a stainless steel tablet press; vertically stack the 3 cold-pressed sample mixtures together and place them at the bottom of a graphite crucible;

[0025] Step 15, hang the graphite crucible in the center of a high-temperature oxygen atmosphere furnace, connect the platinum-rhodium wire at both ends of the graphite crucible to the vertical four-hole alumina tube, and fix the four-hole alumina tube to the center of the round cover that can be put into and pulled out of the furnace body;

[0026] Step 16, place a stainless steel container containing secondary deionized pure cold water on the side of the high-temperature oxygen atmosphere furnace;

[0027] Step 17, at the top of the high-temperature oxygen atmosphere furnace, connect the argon inert gas cylinder, the proportionally adjustable carbon monoxide and carbon dioxide cylinders;

[0028] Step 18, open the argon inert gas valve for 30 minutes, and under the protection of argon inert gas, heat the sample to 800°C at a rate of 400°C / hour;

[0029] Step 19, after the temperature in the furnace body reaches 800°C, switch the carbon monoxide and carbon dioxide cylinder control valves to make the volume ratio of carbon monoxide and carbon dioxide in the sample oxygen atmosphere furnace reach 4:1;

[0030] Step 20, increase the temperature of the sample chamber in the furnace body to 1480℃ at a temperature increasing rate of 200℃ / hour, and keep constant temperature roasting for 15 minutes to melt into glassy manganese chromium iron ore;

[0031] Step 21, after constant temperature roasting for 15 minutes, pull out the graphite crucible containing the sample, the four-hole alumina tube and the upper round cover of the furnace body together from the furnace body, and directly immerse in the water in the stainless steel container to quench into manganese chromium iron ore glass;

[0032] Step 22, take out the quenched manganese chromium iron ore glass from the graphite crucible, grind in the corundum mortar to obtain fine particle and composition uniform sample powder; and place the sample powder in a vacuum drying box at 200℃ for drying for 12 hours;

[0033] Step 23, cold press the dried sample powder into a cylindrical manganese chromium iron ore sample with a diameter of 4.0mm and a height of 4.0mm on a cold isostatic pressing machine using a tungsten carbide die.

[0034] The preparation method of the water source sheet is:

[0035] Step 24, cold press the hydroxymanganite powder and the chromium hydroxide powder into two pieces of water source sheet with a diameter of 4.0mm and a height of 0.1mm on a cold isostatic pressing machine using a tungsten carbide die at a weight ratio of 4:1.

[0036] Place the two pieces of water source sheet on the two ends of the cylindrical manganese chromium iron ore sample, and then place them in a double capsule structure experimental sample chamber with the inner layer sleeve being a graphite tube and the outer layer sleeve being a gold-palladium alloy tube; the method for obtaining manganese chromium iron ore single crystal through high temperature and high pressure reaction comprises the following steps:

[0037] Step 25, seal the cylindrical manganese chromium iron ore sample and the two pieces of water source sheet in the double capsule structure experimental sample chamber with the inner layer sleeve being a graphite tube and the outer layer sleeve being a gold-palladium alloy tube; place the cylindrical manganese chromium iron ore sample in the middle of the graphite inner layer sleeve; and place the two pieces of water source sheet on the two ends of the graphite inner layer sleeve close to the sample;

[0038] Step 26, place the double capsule structure 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 increasing rate and the temperature increasing rate to be 0.5GPa / hour and 10℃ / minute respectively, increase the pressure and the temperature to 3.0GPa and 1080℃ respectively, and perform hot-pressing sintering under the conditions of constant temperature and constant pressure for 72 hours;

[0039] Step 27, after 72 hours of constant temperature and constant pressure, reduce the temperature in the sample chamber from 1080℃ to 800℃ at a temperature decreasing rate of 3℃ / minute, and keep constant temperature for 1 hour; then reduce the temperature in the sample chamber from 800℃ to room temperature at a temperature decreasing rate of 5℃ / minute.

[0040] Step 28, after the temperature in the sample cavity is reduced to room temperature, the pressure in the sample cavity is reduced from 3.0 GPa to normal pressure at a pressure reduction rate of 0.5 GPa / hour;

[0041] Step 29, the sample is taken out of the Kawai-1000t typical 6-8 type multi-face top large cavity high temperature and high pressure equipment; the graphite tube and gold-palladium alloy tube wrapped around the sample are removed, and the cylindrical sample is cut in half in the middle using a diamond wire cutter; the single crystal of mangan-chromite is selected under an Olympus microscope with 20 times magnification.

[0042] During the high temperature and high pressure reaction, two groups of high temperature resistant tungsten-rhenium thermocouples are used to calibrate the temperature; each group of tungsten-rhenium thermocouples is composed of two tungsten-rhenium alloys with different materials, and the chemical composition is W 95％ Re 5％ and W 74％ Re 26％ ; each group of tungsten-rhenium thermocouples is symmetrically placed at the upper and lower ends of the double capsule structure sample chamber composed of graphite tube and gold-palladium alloy tube.

[0043] The beneficial effects of the present application are:

[0044] The present application combines organic crystallography, mineralogy, petrology, ore deposit geology, geophysics, advanced geochemistry, dispersed element geochemistry, rare earth element geochemistry, trace element geochemistry, meteoritics, magmatic petrology, sedimentary petrology, metamorphic petrology, celestial chemistry, planetary science, structural geology, planetary geology, crystal optics, optical mineralogy, field experimental geology, global regional geology, stratigraphy, high pressure mineral physics, mineral crystal structure chemistry and other related disciplines of earth science. The present application simulates the formation process of vanadium-doped and high water-containing mangan-chromite single crystal under high temperature and high pressure conditions by using a Kawai-1000t typical 6-8 type multi-face top large cavity high temperature and high pressure equipment. The main chemical reaction equation of the present application is:

[0045] MnCO3+2HNO3→Mn(NO3)2+CO2+H2O

[0046] 3Mn(NO3)2+2[Cr3(OH)2(OOCCH3)7]→3MnCr2O4+6(NH3·H2O)+4CH4+8CO2+16CO

[0047] 2MnCr2O4+4C 10 H 14 O5V→2Mn(Cr,V)2O4+15C2H2+10CO2+13H2

[0048] Mn(OH)2→MnO+H2O

[0049] 2Mn(OH)2→ Mn2O3 + H2O + H2

[0050] 2Cr(OH)3→ Cr2O3 + 3H2O

[0051] The selected initial raw material manganese carbonate [chemical formula: MnCO3, also known as manganous carbonate (II), manganese white or rhodochrosite] is a rose-colored trigonal rhombic crystal solid material, which has stable chemical properties, is soluble in dilute acid, and is insoluble in water and ethanol and other solvents. In the research and development field of soft magnetic ferrite of telecommunication equipment, manganese carbonate is an essential raw material for synthesizing manganese dioxide and producing other manganese salts; as a desulfurization catalyst, manganese carbonate is widely used in the pigment industry of enamel, paint and varnish, as well as additives for fertilizers and feeds; as an important raw material for producing electrolytic manganese, it is widely used in the fields of medicine, welding rod auxiliary materials and the like. The rose-colored trigonal rhombic manganese carbonate crystal is selected because of its stable performance and the superior characteristics of being easily soluble in dilute acid, so it is an excellent raw material for providing manganese elements in artificial synthesized manganese spinel. The initial raw material chromium (III) acetate hydroxide [also known as: chromium (III) acetate hydroxide or basic chromium acetate, chemical formula: Cr3(OH)2(OOCCH3)7] is a light gray green to blue solid crystalline powder, which is stable in chemical properties at room temperature, does not decompose, is non-toxic and soluble in water. Chromium (III) acetate hydroxide can be used in the production of high-purity metal chromium, certain glaze, colored glass and other industries. The chromium (III) acetate hydroxide crystalline powder is selected because of its superior characteristics of being easily decomposed and chemically reactive in dilute acid solution, so it is an excellent raw material for providing chromium elements in artificial synthesized manganese chromium ore. The initial raw material bisacetylacetone vanadium (IV) oxide [also known as: acetylacetone vanadyl, diacetylacetone vanadium oxide or bisacetylacetone acid vanadium (IV) oxide, chemical formula: C 10 H 14O5V], blue solid crystal powder, soluble in ethanol, acetone, ether, chloroform, benzene and other solvents, commonly used in the field of inorganic synthesis intermediates, paint drier, pigment, industrial catalyst, etc. Because of the high water chemical activity of vanadium (IV) acetylacetone oxide and the solubility in dilute nitric acid solution, vanadium (IV) acetylacetone oxide is an excellent raw material for providing transition group rare earth dispersed metal element vanadium in artificial synthesis of manganese chromium iron ore. The initial raw material of solid hydroxymanganite [also known as: sheet water manganite, molecular formula: Mn (OH) 2] belongs to a typical manganese-containing water mineral. Hydroxymanganite undergoes a first dehydration reaction at a temperature of 300 DEG C to generate pyrolusite (MnO); when the temperature continues to rise to 560 DEG C, a second dehydration reaction occurs to generate Mn2O3, while releasing a large amount of water. The initial raw material of solid chromium hydroxide [molecular formula: Cr (OH) 3] belongs to a typical gray-green chromium-containing water powder, which can react with acid and strong base to produce corresponding chromium salt and water, showing the physical and chemical properties of a typical amphoteric hydroxide, which can be used for industrial production and raw material processing of trivalent chromium salt, chromium trioxide, chromium pigment, etc. Generally, chromium hydroxide undergoes a dehydration reaction at a temperature of 500 DEG C to generate green chromium oxide (chrome green), while releasing a large amount of water. In the high-pressure sample chamber, the hydroxymanganite and chromium hydroxide containing water in a certain ratio are placed, and a dehydration reaction occurs under high temperature and high pressure conditions to generate a large amount of water, which provides a good water source for synthesizing vanadium-doped and high-water manganese chromium iron ore single crystals. In the chemical reaction products involved in the present application, NH3·H2O, CH4, C2H2, CO2, CO and H2 are all high-temperature volatile substances.

[0052] The present application needs to synthesize vanadium-doped and high-water manganese chromium iron ore single crystals. The synthesized sample contains vanadium-doped manganese chromium iron ore single crystals matching the development and comprehensive utilization of vanadium mineral resources, and is widely used in the experimental simulation research of mineral and rock physical and chemical properties under high temperature and high pressure conditions. Compared with the natural manganese chromium iron ore samples exposed in nature, which may contain impurity ions such as iron ions, manganese ions and aluminum ions, the vanadium-doped and high-water manganese chromium iron ore single crystals prepared in the present application are pure and have good chemical stability, which provides important experimental sample guarantee for the measurement of physical property parameters of vanadium-doped and high-water manganese chromium iron ore single crystals, especially the research of crystal axis anisotropy and lattice optimization orientation of manganese chromium iron ore single crystal minerals under high pressure.

[0053] Compared with the synthetic pyrochlore single crystals available in the prior art, the synthetic methods adopted by the prior art include high-pressure powder hydrothermal method, microwave solid-phase activation method, polyvinyl acetate alcoholysis method, carbonate chemical coprecipitation method, metal alkoxide sol-gel method, high-temperature solid-phase sintering method, and freeze-drying method, etc. The preparation method of the present application has obvious advantages such as simple operation process and short reaction time, and the obtained pyrochlore single crystal has superior physical and chemical properties such as high purity, large size, and stable chemical properties. More importantly, the vanadium content of the synthetic pyrochlore product is high (5000-6000 ppm wt%) and the water content is high (200-300 ppm), and the vanadium content and water content can be completely controlled. The pyrochlore single crystal has a large particle size, which can completely meet the sample requirements of conductivity, synchrotron X-ray diffraction, confocal Raman spectroscopy, vacuum Fourier transform infrared spectroscopy, and other high-temperature and high-pressure single crystal mineral physical and spectral experimental simulation under high-temperature and high-pressure conditions on the diamond pressure cell high-pressure equipment. The method provides important experimental sample guarantee for the measurement of the physical property parameters of vanadium-doped and high-water-content pyrochlore single crystals, especially the research of the single crystal mineral lattice preferred orientation and crystal axis anisotropy under high pressure, and breaks through the technical bottleneck of the existing synthesis of pyrochlore single crystals. DETAILED DESCRIPTION

[0054] The specific preparation method of the present application includes:

[0055] Solid rose trianguar rhombic manganese carbonate crystal (purity: >99.99%), solid chromium (III) acetate hydroxide crystalline powder (purity: >99.99%), solid vanadium (IV) bisacetylacetone oxide powder (purity: >99.99%), solid oxalic acid powder (purity: >99.99%), solid bixbyite powder (purity: >99%), solid chromium hydroxide powder (purity: >99%), and liquid dilute nitric acid (concentration: 10%) are used as starting materials.

[0056] The high-purity solid manganese carbonate selected as the initial material in the present application is a rose trianguar rhombic crystal material, which has stable chemical properties, is soluble in dilute acid, and is insoluble in water and ethanol and other solvents. In the research and development field of telecommunication equipment soft magnetic ferrite, manganese carbonate is an essential raw material for synthesizing manganese dioxide and producing other manganese salts; as a desulfurization catalyst, manganese carbonate is widely used in the pigment industry of enamel, paint, and varnish, as well as in the field of fertilizer and feed additives; as an important raw material for producing electrolytic manganese, it is widely used in the fields of medicine, welding rod auxiliary materials, etc. The selection of rose trianguar rhombic manganese carbonate crystal is an excellent raw material for providing manganese elements in synthetic manganese spinel due to its stable performance and excellent characteristics of being easily soluble in dilute acid.

[0057] The high-purity chromium acetate hydroxide selected as the initial material in the present application is a light gray-green to blue-green solid crystalline powder, which is stable in chemical properties at room temperature, does not decompose, is non-toxic and soluble in water. The chromium acetate hydroxide can be used as a raw material for the industrial production of high-purity metallic chromium, certain glazes, colored glass and the like. The selection of the chromium acetate hydroxide crystalline powder is because it can easily decompose and chemically react with dilute acid solution and has strong chemical reactivity, and thus is an excellent raw material for providing chromium element in the artificial synthesis of manganese-chromium-iron ore.

[0058] The high-purity vanadium (IV) oxide bisacetylacetone selected as the initial material in the present application is a blue solid crystalline powder, which is soluble in solvents such as ethanol, acetone, diethyl ether, chloroform and benzene, and is commonly used in the fields of intermediate for inorganic synthesis, paint drier, pigment, industrial catalyst and the like. Since the vanadium (IV) oxide bisacetylacetone has high water chemical activity and is soluble in dilute nitric acid solution, the vanadium (IV) oxide bisacetylacetone is an excellent raw material for providing transition group rare earth dispersed metal element vanadium in the artificial synthesis of manganese-chromium-iron ore.

[0059] The high-purity solid oxalic acid selected as the initial material in the present application is a chelating agent for metal substances, and the purpose is that the oxalic acid powder has a great influence on the bioavailability of minerals and has a strong coordination function. When the oxalic acid is combined with divalent manganese ions, the solubility of the divalent manganese ions can be greatly reduced, and a complex sol of the divalent manganese ions is formed in the dilute nitric acid solution. At the same time, when the oxalic acid is combined with trace amounts of rare earth metal element vanadium cations, a soluble complex of the trace amounts of rare earth metal element cations is formed due to the coordination function of the oxalic acid. The solubility of the trivalent vanadium metal cations in the acid solution is significantly enhanced, so that the trivalent vanadium metal cations are fully dissolved in the dilute nitric acid solution.

[0060] The high-purity solid bixbyite selected as the initial material in the present application is a typical manganese-containing hydrous mineral. When the temperature of the bixbyite is 300℃, a first dehydration reaction occurs to generate pyrolusite (MnO). When the temperature continues to rise to 560℃, a second dehydration reaction occurs to generate Mn2O3, and a large amount of water is released. The high-purity solid chromium hydroxide selected as the initial material in the present application is a typical gray-green chromium-containing hydrous powder substance, which can chemically react with both acid and strong base to produce corresponding chromium salt and water, and exhibits a clear physical and chemical characteristic of amphoteric hydroxide. The chromium hydroxide can be used in the industrial production and raw material processing preparation of trivalent chromium salt, chromium sesquioxide and chromium pigment. Generally, the chromium hydroxide undergoes a dehydration reaction at a temperature of 500℃ to generate green chromium oxide (chromium green), and a large amount of water is released.

[0061] The initial substance selected by the present application is dilute nitric acid (concentration: 10%), if the concentration of nitric acid is too low, it has limited solubility, which may cause the residual of solid manganese carbonate crystals, solid chromium (III) acetate hydroxide crystalline powder, solid bisacetylacetone vanadium (IV) oxide powder and oxalic acid powder; if the concentration of nitric acid is too high, it has enhanced oxidizing property, which may cause the direct rapid oxidation reaction or direct decomposition of manganese carbonate crystals in the sample, and produce dense smoke, which may bring certain danger to the preparation.

[0062] Step 1, open the chemical fume hood, select a standard volume of 100 ml volumetric flask, accurately weigh 60 ml of dilute nitric acid with a concentration of 10%, place the glass transfer pipette in a 500 ml notch beaker, and carefully transfer the liquid dilute nitric acid along the transfer pipette to the beaker, and select the notch beaker as the reaction container. The main consideration is that after the beaker is covered on the glass surface dish cover, it is not completely sealed, and the generated gas can be easily volatilized in the fume hood.

[0063] Step 2, accurately weigh 5.0 grams of solid rose triangular rhombic manganese carbonate crystals on a 10 microgram high-precision analytical balance, and carefully add them to the dilute nitric acid solution in the notch beaker, and place the magnetic stirring rotor.

[0064] Step 3, cover the dilute nitric acid solution containing solid manganese carbonate crystals in the notch beaker with a glass surface dish, and place it on a high-temperature magnetic stirring hot plate in the fume hood. In order to fully dissolve the initial material solid manganese carbonate crystals in the dilute nitric acid solution, and at the same time make it undergo hydrolysis reaction and acidification reaction, the reaction conditions are room temperature, 700 rpm rotation speed and reaction time 72 hours.

[0065] Step 4, according to the stoichiometric ratio of manganese chromium iron ore Mn(Cr, V)2O4, accurately weigh 17.4949 grams of high-purity solid chromium (III) acetate hydroxide crystalline powder and 135 milligrams of high-purity solid bisacetylacetone vanadium (IV) oxide powder on a high-precision analytical balance, and carefully add them to the dilute nitric acid solution containing manganese carbonate crystals, respectively.

[0066] Step 5, cover the dilute nitric acid solution containing solid manganese carbonate crystals, solid chromium (III) acetate hydroxide crystalline powder and solid bisacetylacetone vanadium (IV) oxide powder with a glass surface dish to ensure that the gas generated by the reaction is volatilized from the notch of the beaker, and at the same time avoid the dilute nitric acid solution of the initial material in the beaker from being splashed out during high-speed stirring, thereby causing danger and affecting the accuracy of the synthesis of manganese chromium iron ore single crystal.

[0067] Step 6, the beaker containing the mixed solution of the initial materials and the magnetic stirring rotor is placed on the high-temperature magnetic stirring hot plate in the fume hood, and the initial materials of solid manganese carbonate crystals, solid chromium (III) acetate hydroxide crystal powder and solid vanadium (IV) bisacetylacetone oxide powder are all dissolved in the mixed solution of dilute nitric acid solution without any residue under the conditions of room temperature, 800 rpm and stirring time of 48 hours. At the same time, NH3·H2O, CH4, C2H2, CO2, CO and H2 volatile substances are more easily volatilized in the fume hood.

[0068] Step 7, accurately weigh 2 grams of high-purity solid oxalic acid powder on a high-precision analytical balance, and add high-purity oxalic acid powder as an important metal chelating agent to the dilute nitric acid solution containing solid manganese carbonate crystals, solid chromium (III) acetate hydroxide crystal powder and solid vanadium (IV) bisacetylacetone oxide powder. The 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 manganese ions, it can greatly reduce its solubility, and then form a complex sol of divalent manganese ions in dilute nitric acid solution. At the same time, when oxalic acid combines with trace amounts of rare earth metal element vanadium cations, due to its coordination effect, it forms a soluble complex of trace amounts of rare earth metal element vanadium cations. The solubility of trivalent vanadium metal cations in acid solution will be significantly enhanced, so that it is fully dissolved in dilute nitric acid solution.

[0069] Step 8, the notch beaker of the mixed solution is placed on the high-temperature magnetic stirring hot plate in the fume hood again, covered with a glass surface dish, and the condition parameters of the high-temperature magnetic stirring hot plate are set to 80°C, 1000 rpm and stirring time of 36 hours. All the initial reagents are uniformly solubilized in the mixed solution of dilute nitric acid and oxalic acid.

[0070] Step 9, remove the glass surface dish of the beaker, and adjust the temperature of the high-temperature magnetic stirring hot plate to 110°C until the mixed solution in the entire notch beaker is completely evaporated.

[0071] Step 10, remove the magnetic stirring rotor in the notch beaker on the high-temperature magnetic stirring hot plate, and clean all the powder samples adhered to its surface into the beaker. Carefully take out all the mixed powder in the notch beaker with a medicine spoon and place it in a graphite crucible. The purpose of using a graphite crucible is that the carbon that constitutes the graphite crucible inevitably produces a certain concentration of carbon monoxide and carbon dioxide during high-temperature calcination, thereby controlling the oxygen fugacity of the manganese-chromium-iron ore sample in the graphite crucible, and finally realizing the valence of the valence metal cations of manganese, chromium and vanadium in the manganese-chromium-iron ore sample.

[0072] Step 11, the graphite crucible containing the mixture powder is raised to a temperature of 1100°C at a lower rate of 300°C / hour in a muffle furnace under normal pressure and high temperature conditions. The slower high temperature calcination rate and longer constant temperature time are intended to more favorably control the oxygen atmosphere in the graphite sample chamber and more favorably remove residual nitric acid, oxalic acid and other organic substances in the mixture powder.

[0073] Step 12, the mixed sample powder in the graphite crucible in the muffle furnace is lowered to room temperature at a rate of 200°C / hour. A slower cooling rate is selected compared to the heating rate to more easily form a honeycomb loose sample powder. The mixture sample powder is carefully removed.

[0074] Step 13, the honeycomb loose sample powder of the manganese-chromite is placed in an ultra-hard thick corundum mortar and ground for 1 hour to obtain a fine-grained and homogenized powder experimental sample.

[0075] Step 14, the homogenized and fine-grained manganese-chromite powder sample mixture is cold-pressed into 3 sample discs of Φ10.0mm x 3.0mm using a high-precision tungsten carbide die of the stainless steel tablet press with a size of Φ10.0mm x 10.0mm. The 3 cold-pressed sample mixtures are stacked vertically and carefully placed at the bottom of the graphite crucible.

[0076] Step 15, two 1.0mm diameter symmetrical round holes are drilled symmetrically on the wall of the graphite crucible containing the 3 stacked samples using a high-speed electric drill. A 0.5mm platinum-rhodium alloy wire is carefully threaded through the two 1.0mm symmetrical round holes in the wall of the graphite crucible, suspended in the center of the high-temperature oxygen atmosphere furnace. The two ends of the platinum-rhodium wire connecting the graphite crucible are fixed to the vertical 0.6mm diameter four-hole alumina tube with an outer diameter of 5.0mm and a length of 40cm. The upper end of the four-hole alumina tube is fixed to the center of the round cover that can be put into and pulled out of the furnace at any time.

[0077] Step 16, a 3-liter stainless steel container containing secondary deionized pure cold water is placed on the side of the high-temperature oxygen atmosphere furnace in advance, which is intended to allow the graphite crucible containing the sample to be directly pulled out of the high-temperature oxygen atmosphere furnace at a very high temperature and quickly immersed in the 3-liter secondary deionized water cold stainless steel container for rapid cooling. The main purpose is to avoid the oxidation / reduction of the variable elements manganese, chromium and vanadium during the slow cooling process of the furnace, to achieve rapid quenching of the sample and to completely retain the glassy manganese-chromite sample.

[0078] Step 17, the top of the furnace body of the high-temperature oxygen atmosphere furnace is connected with an argon inert gas cylinder, a proportionally adjustable carbon monoxide cylinder and a carbon dioxide cylinder, the amount of gas entering the sample chamber is controlled by a gas pressure gauge, and each gas can be switched and adjusted at any time during the high-temperature calcination of the sample. The argon inert gas is used in the present application, which provides an absolutely reduced oxygen atmosphere environment when the temperature of the furnace body is lower than 800°C.

[0079] The present application uses proportionally adjustable carbon monoxide and carbon dioxide, which can well control the oxygen fugacity of the sample during high-temperature calcination when the temperature of the furnace body is higher than 800°C. When the temperature of the furnace body is higher than 800°C, continuing to introduce argon inert gas will cause over-reduction in the sample chamber, which may cause the variable valence elements manganese, chromium and vanadium to be reduced to metallic manganese, chromium and vanadium in turn. Therefore, when the temperature is higher than 800°C, the present application uses proportionally adjustable carbon monoxide and carbon dioxide mixed gas to control the oxygen fugacity of the sample in the high-temperature oxygen atmosphere furnace chamber, and the reaction principle is The oxygen partial pressure in the sample chamber can be well adjusted, and the valence of the variable valence metal elements manganese, chromium and vanadium in the vanadium-doped and high-hydrated manganochromite single crystal can be well controlled.

[0080] The maximum rated temperature of the high-temperature oxygen atmosphere furnace is 1800°C. The circulating cooling water of the high-temperature oxygen atmosphere furnace is opened to reduce the temperature of the furnace body, so as to avoid the temperature of the whole furnace body being too high, which may cause leakage of carbon monoxide and carbon dioxide, thereby causing danger.

[0081] A high-sensitivity argon, carbon monoxide and carbon dioxide concentration monitoring alarm is opened to avoid gas leakage during the high-temperature calcination process of the oxygen atmosphere furnace and to ensure the safety of the operator.

[0082] Step 18, the argon inert gas valve is opened, the pointer button controlled by the gas pressure gauge is rotated, and the gas is continuously filled for 30 minutes, which is to properly expel the excess air in the sample chamber. The sample is subjected to high-temperature calcination at a temperature increasing rate of 400°C / hour under the protection of argon inert gas to 800°C.

[0083] Step 19, after the temperature in the furnace body reaches 800°C, the carbon monoxide gas cylinder and the carbon dioxide gas control valve are quickly switched, the pointer button controlled by the gas pressure gauge is rotated, and the volume ratio of carbon monoxide and carbon dioxide in the sample oxygen atmosphere furnace reaches 4:1, which is to well adjust the oxygen fugacity in the sample chamber during the high-temperature calcination process.

[0084] Step 20, after the volume ratio of 4:1 carbon monoxide and carbon dioxide control sample bin oxygen fugacity gas flow to reach stable, the time required for this step is about 3-5 minutes, then the temperature of the sample bin in the furnace is increased to 1480℃ at a heating rate of 200℃ / h, and the temperature is kept constant for 15 minutes to melt into glassy manganese chromite. During the heating process of the high-temperature oxygen atmosphere furnace, the sample bin is heated at two different rates of 400℃ / h and 200℃ / h in different temperature ranges of room temperature-800℃ and 800℃-1480℃, respectively. The present application, with the temperature of the sample bin in the high-temperature oxygen atmosphere furnace, is more beneficial to the formation of strong ionic bonds such as Mn-O, Cr-O and V-O in vanadium-doped manganese chromite; it can more accurately control the temperature of the sample bin in the high-temperature oxygen atmosphere furnace; it can completely avoid the imbalance of heat transfer of the sample bin, which leads to the overheating of the local area of the furnace body, and thus easily damages the heating body of the oxygen atmosphere furnace.

[0085] The purpose of the high-temperature roasting process of the carbon monoxide and carbon dioxide mixed gas controlled oxygen atmosphere is to provide a more pure manganese chromite glassy material for the synthesis of large particle vanadium-doped and high water content manganese chromite single crystal; the high-temperature calcination under oxygen atmosphere can better control the valence of manganese, chromium and vanadium in the product; the higher calcination temperature of 1480℃ can ensure that the volatile matter, nitric acid, oxalic acid and organic matter that may be present in a small amount after the muffle furnace high-temperature calcination are all completely volatilized.

[0086] The constant temperature roasting time is 15 minutes, and the relatively short roasting time is adopted because the manganese chromite powder will melt rapidly at a temperature higher than 1430℃. If the roasting time is too short, there may be some residual initial powder in the manganese chromite melted product, which seriously affects the chemical composition of the prepared manganese chromite sample; if the roasting time is too short, it is not conducive to the chemical diffusion of manganese ions, chromium ions and vanadium ions; it is also not conducive to the formation of stable chemical bonds of strong ionic bonds Mn-O, Cr-O and V-O in manganese chromite; if the roasting time is too short, the dispersed transition rare earth metal vanadium element will be stratified and differentiated in manganese chromite, which will seriously affect the preparation effect; if the roasting time is too short, the density of the product will be reduced, and it may be difficult to form high-density manganese chromite glass. However, if the roasting time is higher than 15 minutes, it may lead to excessive melting, which will make the manganese chromite sample firmly adhere to the graphite crucible wall, making it difficult to clean, and also increasing the cost of sample preparation.

[0087] Step 21, after the sample is baked at a temperature of 1480°C for 15 minutes, the graphite crucible containing the sample, the four-hole alumina tube, and the upper round cover of the furnace body are pulled out of the furnace body and directly immersed in a 3-liter stainless steel container containing secondary deionized pure cold water to rapidly quench the manganochromite glass. The purpose of rapid quenching is to well preserve the glassy manganochromite sample with uniform composition at high temperature.

[0088] Step 22, the quenched glassy manganochromite sample is carefully taken out of the graphite crucible and thoroughly ground in a corundum mortar to obtain fine and uniform composition sample powder. The glassy manganochromite powder is placed in a vacuum drying box at 200°C and dried for 12 hours.

[0089] Step 23, the manganochromite glass powder is cold-pressed on a cold isostatic press using a high-precision Φ4.0mm (diameter) x 10.0mm tungsten carbide die to form a cylindrical manganochromite sample with a diameter of Φ4.0mm and a height of 4.0mm.

[0090] In order to obtain the high water content of manganese chromium iron ore, we use the weight ratio of 4:1 of the hydroxyl manganese ore powder (molecular formula: Mn(OH)2) and the chromium hydroxide powder (molecular formula: Cr(OH)3) as the water source. The mixture of the hydroxyl manganese ore and the chromium hydroxide is selected as the water source, mainly based on the following considerations: first, the hydroxyl manganese ore and the chromium hydroxide are both typical water-containing substances, and the dehydration temperature is low. The high-purity solid hydroxyl manganese ore is a typical manganese-containing water-containing mineral. The hydroxyl manganese ore generates the first dehydration reaction at a temperature of 300 DEG C to generate pyrolusite (MnO). When the temperature continues to rise to 560 DEG C, the second dehydration reaction occurs to generate Mn2O3, and a large amount of water is released. And the high-purity solid chromium hydroxide is a typical gray-green chromium-containing water-containing powder substance. The dehydration reaction of the chromium hydroxide usually occurs at a temperature of 500 DEG C, and the product is green chromium green (Cr2O3), and a large amount of water is released. Therefore, the dehydration temperature condition is in the lower temperature interval of the process of preparing the vanadium-doped manganese chromium iron ore single crystal under high temperature and high pressure conditions, that is, it can be realized. It fully guarantees that the vanadium-doped manganese chromium iron ore single crystal is in a long enough water environment to ensure the full diffusion of the sample lattice water and the formation of the lattice site. Secondly, the hydroxyl manganese ore and the chromium hydroxide are both manganese-rich and chromium-rich substances, which can well control the manganese activity and chromium activity of the main lattice site in the process of preparing the vanadium-doped and high water content manganese chromium iron ore single crystal in the sample cavity under high temperature and high pressure conditions. Finally, the dehydration final product of the water source substance combination of the weight ratio of 4:1 of the hydroxyl manganese ore and the chromium hydroxide placed at both ends of the sample is pyrolusite, chromium green, manganese sesquioxide and other oxides. All these products will not chemically react with the sample, ensuring the purity of the sample of the vanadium-doped and high water content manganese chromium iron ore single crystal. In addition, by adjusting the weight ratio of the hydroxyl manganese ore and the chromium hydroxide of the water source water-containing substance and the corresponding water source sheet height, the water content in the vanadium-doped and high water content manganese chromium iron ore single crystal sample can be adjusted.

[0091] Step 24, in the cold isostatic press, the hydroxyl manganese ore powder and the chromium hydroxide powder are cold pressed into two pieces of water source sheets with a weight ratio of 4:1 by using a high-precision Φ4.0mm(diameter)×10.0mm tungsten carbide grinding tool to cold press into Φ4.0mm(diameter)×0.1mm(height).

[0092] Step 25, cylindrical sample of mangan-chromite (size: Φ4.0mm (diameter) x 4.0mm (height)) and two pieces of water source sheet (size: Φ4.0mm (diameter) x 0.1mm (height)) are sealed in the experimental sample chamber of the double capsule structure of the inner sleeve-graphite tube (size: Φ4.4mm (outer diameter) x 4.4mm (height), wall thickness of 0.2mm) and outer sleeve-gold-palladium alloy tube (size: Φ4.6mm (outer diameter) x 4.6mm (height), wall thickness of 0.1mm) in turn. The vanadium-doped mangan-chromite sample is placed in the middle of the graphite inner sleeve; and the two pieces of water source sheet of 4:1 weight ratio of hydroxyl manganite and chromium hydroxide are placed at the symmetrical ends of the graphite inner sleeve close to the sample.

[0093] The inner sleeve of the double capsule structure sample chamber of the present application uses graphite as the sealing material, the main purpose of which is to control the oxygen fugacity value of carbon monoxide and carbon dioxide in the sample chamber, and ultimately to constrain the valence of manganese, chromium and vanadium, which are variable valence metal elements in the mangan-chromite sample.

[0094] The outer sleeve of the double capsule structure sample chamber of the present application uses gold-palladium alloy as the sealing material, the main purpose of which is: first, to use gold-palladium alloy sealing to isolate the exchange of substances or elements between the sample and other surrounding pressure-transmitting materials, effectively avoiding contamination of the mangan-chromite sample during its preparation under high temperature and high pressure; second, to use gold-palladium alloy sealing to effectively prevent water from escaping from the sample tube during the preparation of the mangan-chromite sample under high temperature and high pressure; and finally, the present application uses a double capsule structure sample chamber composed of a graphite tube and a gold-palladium alloy tube to form a more airtight oxygen atmosphere environment, better control the oxygen fugacity in the sample chamber, and thus more effectively constrain the valence of manganese, chromium and vanadium, which are variable valence metal elements in the mangan-chromite sample.

[0095] Step 26, mangan-chromite is one of the important manganese-rich and chromium-rich oxide minerals in the lower crust and upper mantle of the Earth and other terrestrial planets, in order to truly simulate the growth environment of mangan-chromite at the depth of the lower crust of the Earth and other terrestrial planets, and to reverse the temperature and pressure conditions for the stable existence of the mangan-chromite mineral phase, the double capsule structure sample chamber composed of a graphite tube and a gold-palladium alloy tube is 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 are set to 3.0GPa and 1080℃ respectively, the pressure and temperature are raised at a rate of 0.5GPa / hour and 10℃ / minute respectively, and the reaction time is 72 hours under constant temperature and pressure.

[0096] The high pressure of 3.0 GPa and the sintering temperature of 1080 DEG C in the preparation process of the application are completely designed based on the physical and chemical properties of manganese-chromite itself. The specific purposes are as follows: firstly, the preparation process of high temperature and high pressure, relatively slow pressure and temperature rising rate and long constant temperature and constant pressure reaction time can completely ensure the complete mineral phase transformation from the initial manganese-chromite glass phase powder to the manganese-chromite crystal phase, and the final product manganese-chromite mineral phase can exist stably under the temperature and pressure conditions; secondly, the preparation process of high temperature and high pressure, relatively slow pressure and temperature rising rate and long constant temperature and constant pressure reaction time can significantly increase the self-diffusion coefficient and chemical diffusion coefficient of metal cations such as manganese ions, chromium ions and vanadium ions, so that the equivalent isomorphism substitution of vanadium ions on metal chromium ions in manganese-chromite crystal is realized, and the reaction is complete and there is no free vanadium element residue, thereby forming a perfect transition group rare earth dispersed metal element vanadium doped manganese-chromite single crystal sample; thirdly, the preparation process of high temperature and high pressure, relatively slow pressure and temperature rising rate and long constant temperature and constant pressure reaction time can completely ensure the formation of stable chemical bonds such as Mn-O, Cr-O and V-O, thereby avoiding the uneven distribution of the doped transition group rare earth dispersed metal vanadium element in manganese-chromite, and realizing the uniform vanadium doped manganese-chromite single crystal of isometric system; fourthly, the preparation process of high temperature and high pressure, relatively slow pressure and temperature rising rate and long constant temperature and constant pressure reaction time can make the dehydrated reaction of the water-containing substance combination of hydro-manganese ore and chromium hydroxide with a weight ratio of 4:1, and a large amount of water is generated, and the final dehydrated product is mixed oxides such as soft manganite, chromium green and manganese sesquioxide, and the water in the sample bin is fully diffused in the vanadium doped manganese-chromite single crystal, thereby ensuring that the manganese-chromite sample has a high enough water content; finally, the preparation process of high temperature and high pressure, relatively slow pressure and temperature rising rate and long constant temperature and constant pressure reaction time can make the vanadium element in the final preparation product manganese-chromite more uniformly distributed, and at the same time, the density, strength and particle size of the product are increased, so that the vanadium doped manganese-chromite single crystal sample with uniform element distribution, high mechanical strength, large density and other superior physical and chemical properties is prepared.

[0097] In the high temperature and high pressure reaction of the application, two groups of tungsten-rhenium thermocouples are used to accurately calibrate the temperature. The tungsten-rhenium thermocouple has the advantages of good temperature-potential linear relationship, reliable thermal stability and low price, can realize the temperature calibration range of 0-2300 DEG C, and is widely used in the fields of high pressure mineral physics experiment, high new metallurgical industry, high temperature electronic thermoelectric system structure engineering, space carrier, nuclear reactor and other fields of ultra-high temperature temperature calibration. Each group of tungsten-rhenium thermocouples is composed of two kinds of tungsten-rhenium alloys with different materials, and the chemical composition is W 95％ Re 5％ and W 74％ Re26％ Different material tungsten-rhenium thermocouple metal wires with a diameter of 0.1 mm are connected at one end and suspended into a ball shape by using a bench clamp; the other end of the different material tungsten-rhenium thermocouple metal wires with a diameter of 0.1 mm is connected to the positive and negative poles of a high-power welding stabilized direct-current power source respectively. The output current control knob of the high-power welding stabilized direct-current power source is adjusted so that a larger current is passed through the metal wires, the ball-shaped tungsten-rhenium high-temperature thermocouple wire is completely immersed in the saturated sodium chloride solution, and the ball-shaped thermocouple wire is melted and welded into a spherical shape, and the oxide layer on the surface of the spherical thermocouple wire is removed. The same technical scheme is used to prepare two groups of hot tungsten-rhenium thermocouples respectively, and each group of tungsten-rhenium thermocouples is symmetrically arranged at the upper and lower ends of the double-capsule structure sample chamber composed of a graphite tube and a gold-palladium alloy tube. In the present application, the tungsten-rhenium double thermocouples are arranged at the upper and lower ends of the sample chamber, which can not only realize accurate temperature calibration in the sample cavity, but also accurately indicate the temperature gradient at the upper and lower ends of the sample chamber, so as to ensure that the manganese-chromite sample is in a stable constant temperature zone during the synthesis process.

[0098] Step 27, after constant temperature and pressure for 72 hours under the conditions of 3.0 GPa and 1080℃, the temperature in the sample cavity is reduced from 1080℃ to 800℃ at a cooling rate of 3℃ / min, and then the temperature is kept constant for 1 hour; then the temperature in the sample cavity is reduced from 800℃ to room temperature at a cooling rate of 5℃ / min. The stepwise cooling and the heating rate (10℃ / min) relative to the sample preparation, and the relatively slow constant pressure cooling rate will further improve the superior physical and chemical properties of the vanadium-doped manganese-chromite single crystal sample, such as uniform vanadium element distribution, high mechanical strength and large density, completely avoiding the non-uniform stress of the sample caused by the too fast cooling rate, and further causing cracks and damage of the manganese-chromite crystal, and the preparation process will be more beneficial to the crystal growth of the large particle manganese-chromite single crystal, so as to realize the preparation of the micron-level manganese-chromite large particle single crystal sample.

[0099] Step 28, after the temperature in the sample cavity is reduced to room temperature, the pressure in the sample cavity is reduced from 3.0 GPa to normal pressure at a depressurization rate of 0.5 GPa / hour. In addition, the present application adopts the preparation process of hot-pressing sintering to obtain the vanadium-doped and high-hydrated manganese-chromite single crystal sample, and the preparation process is pure and free of any impurities introduced from the sample itself, high-pressure sample assembly, etc.

[0100] Step 29, after the high-temperature and high-pressure preparation reaction is completed, the sample is taken out from the Kawai-1000t typical 6-8 type multi-surface top large cavity high-temperature and high-pressure equipment. The graphite tube and the gold-palladium alloy tube of the double-capsule structure sample chamber wrapped around the sample are carefully removed, and a high-precision diamond wire cutting instrument is used to cut the cylindrical sample in half from the center. Under a 20-fold high-precision Olympus microscope, the manganese-chromite single crystal is selected.

[0101] The obtained single crystal of mangan-chromite is a single phase without any other impurity phase; the electron probe (EPMA) detection result shows that the molecular formula of the obtained single crystal of mangan-chromite is MnCr2O4; the multi-functional ion mass spectrometer (ICP-MS) detection result shows that the vanadium content in the obtained single crystal of mangan-chromite is 5852 ppm wt%; and the vacuum Fourier transform infrared spectroscopy (FT-IR) detection result shows that the water content of the obtained single crystal of mangan-chromite sample is 273 ppm wt, which has a relatively high water content.

[0102] The obtained single crystal of vanadium-doped and high-water-content mangan-chromite is of a cubic crystal system, a space group of Fd3m (no. 227), and a crystal lattice parameter of α = β = γ = 90°, and a unit cell volume of The average particle size is 160 microns, and the maximum particle size is 525 microns.

[0103] The obtained single crystal of vanadium-doped and high-water-content mangan-chromite sample has high purity, large particle size, stable chemical properties, high mechanical strength and other superior performances, and more importantly, the vanadium content is high (5852 ppm wt%) and the vanadium content in the single crystal of mangan-chromite can be completely controlled. By changing the amount of the added initial solid-state high-purity vanadium (IV) oxide powder of bis-acetylacetone from 115.3371 mg to 138.4045 mg, the corresponding vanadium content in the obtained single crystal of vanadium-doped and high-water-content mangan-chromite sample can be finally realized from 5000 ppm wt% to 6000 ppm wt%; by changing the weight ratio of the water-containing substance of manganite powder and the chromium hydroxide powder providing the water source and adjusting the different heights of the corresponding two water source sheets, the total water amount generated by the dehydration reaction of the water-containing substance enclosed in the double-capsule structure sample bin composed of a graphite tube and a gold-palladium alloy tube is controlled, and the water content in the single crystal of mangan-chromite is finally realized. The obtained single crystal of vanadium-doped and high-water-content mangan-chromite sample can completely meet the needs of physical experiment 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, and breaks through the technical bottleneck of the existing synthesis of single crystal of mangan-chromite, and provides important experimental sample support for the study of lattice preferred 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 producing vanadium-doped and high-hydrated manganchromite single crystals at high temperature and high pressure, characterized by: The method is: taking solid rose rhombic carbonic acid manganese crystal, solid acetic acid chromium (III) hydroxide crystalline powder, solid bisacetyl propionone vanadium (IV) oxide powder, solid oxalic acid powder, solid hydroxyl manganese ore powder, solid chromium hydroxide powder and liquid dilute nitric acid as starting materials to prepare a cylindrical manganese-chromium-iron ore sample; taking hydroxyl manganese ore powder and chromium hydroxide powder with a weight ratio of 4:1 to make two pieces of water source sheet; placing the two pieces of water source sheet at the two ends of the cylindrical manganese-chromium-iron ore sample and then putting them into a double-capsule structure experimental sample bin with an inner layer sleeve of graphite pipe and an outer layer sleeve of gold-palladium alloy pipe; carrying out high-temperature and high-pressure reaction to obtain a manganese-chromium-iron ore single crystal; and the preparation method of the cylindrical manganese-chromium-iron ore sample is: Step 1, weigh 60 milliliters of dilute nitric acid with a concentration of 10% into a notch beaker; Step 2, weigh 5.0 grams of solid rhombic carbonic acid manganese crystal of triangular crystal system into the notch beaker, and put a magnetic stirring rotor into the beaker; Step 3, cover the notch beaker with a glass surface dish, and place it on a high-temperature magnetic stirring hot plate in a fume hood, and stir at a speed of 700 rpm for 72 hours at room temperature; Step 4, according to the stoichiometric ratio of manganese-chromium-iron ore Mn(Cr, V)2O4, weigh 17.4949 grams of high-purity solid acetic acid chromium (III) hydroxide crystalline powder and 135 milligrams of high-purity solid bisacetyl propionone vanadium (IV) oxide powder into the dilute nitric acid solution in the notch beaker respectively; Step 5, cover the notch beaker with a glass surface dish; Step 6, place the notch beaker on a high-temperature magnetic stirring hot plate in a fume hood, and stir at a speed of 800 rpm for 48 hours at room temperature; Step 7, weigh 2 grams of high-purity solid oxalic acid powder into the notch beaker; Step 8, place the notch beaker again on the high-temperature magnetic stirring hot plate in the fume hood, cover it with a glass surface dish, and set the condition parameters of the high-temperature magnetic stirring hot plate to 80 °C and 1000 rpm for 36 hours; Step 9, remove the glass surface dish of the beaker, increase the temperature of the high-temperature magnetic stirring hot plate to 110 °C, and evaporate the mixed solution in the whole notch beaker until it is completely evaporated; Step 10, take out the magnetic stirring rotor in the notch beaker, clean all the powdery samples adhered to the surface into the beaker, and take out all the mixed powders in the notch beaker and put them into a graphite crucible; Step 11, put the graphite crucible containing the mixed powders into a muffle furnace under normal pressure conditions, increase the temperature to 1100 °C at a rate of 300 °C / hour, and keep the temperature constant for 5 hours; Step 12, further reduce the temperature of the mixed sample powders in the graphite crucible in the muffle furnace to room temperature at a rate of 200 °C / hour; Step 13, grind the sample powders in a corundum mortar for 1 hour to obtain a powdery experimental sample; Step 14, cold-press the powdery experimental sample into 3 pieces of sample round sheet with a diameter of Φ 10.0 mm × 3.0 mm by using a tungsten carbide mold of a stainless steel tablet press; vertically stack the 3 pieces of cold-pressed sample mixture together and place them at the bottom of the graphite crucible. Step 15, the graphite crucible is hung in the middle of the high-temperature oxygen atmosphere furnace, the platinum-rhodium metal wires connected to the graphite crucible are fixed on the vertical four-hole alumina tube, and the upper end of the four-hole alumina tube is fixed in the middle of the round cover that can be put into and pulled out of the furnace body; Step 16, a stainless steel container containing secondary deionized pure cold water is placed on the side of the high-temperature oxygen atmosphere furnace; Step 17, the top end of the high-temperature oxygen atmosphere furnace is connected to the argon inert gas cylinder, the proportionally adjustable carbon monoxide and carbon dioxide cylinders; Step 18, open the argon inert gas valve for 30 minutes of continuous gas filling, and perform high-temperature calcination on the sample at a temperature rising rate of 400 °C / hour to 800 °C under the protection of argon inert gas; Step 19, after the temperature in the furnace body reaches 800 °C, switch the carbon monoxide and carbon dioxide cylinder control valves to make the volume ratio of carbon monoxide and carbon dioxide in the sample oxygen atmosphere furnace reach 4:1; Step 20, increase the temperature of the sample chamber in the furnace body to 1480 °C at a temperature rising rate of 200 °C / hour, and maintain the temperature for 15 minutes for constant temperature roasting, so that the sample is melted into glassy manganese-chromite; 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 directly immerse them in the water in the stainless steel container to quench the manganese-chromite glass; Step 22, take out the quenched manganese-chromite glass from the graphite crucible, grind it in a corundum mortar to obtain a fine and uniform sample powder, and place the sample powder in a vacuum drying box at 200 °C for drying for 12 hours; Step 23, use a tungsten carbide mold to cold-press the dried sample powder into a cylindrical manganese-chromite sample with a diameter of 4.0 mm and a height of 4.0 mm on a cold isostatic pressing machine.

2. A method for preparing a vanadium-doped and high-hydrated manganochromite spinel single crystal at high temperature and high pressure according to claim 1, characterized in that: The purity of the rose-colored trigonal rhombic manganese carbonate crystal is greater than 99.99%, the purity of the solid chromium (III) acetate hydroxide crystal powder is greater than 99.99%, the purity of the solid vanadium (IV) acetylacetonate oxide powder is greater than 99.99%, the purity of the solid oxalic acid powder is greater than 99.99%, the purity of the solid bixbyite powder is greater than 99%, the purity of the solid chromium hydroxide powder is greater than 99%, and the concentration of the liquid dilute nitric acid is 10%.

3. A method of producing a vanadium-doped and high-hydrated schreyerite single crystal at high temperature and high pressure according to claim 1, characterized by: The preparation method of the water source sheet is as follows: Step 24, cold-press the bixbyite powder and the chromium hydroxide powder in a weight ratio of 4:1 into two water source sheets with a diameter of 4.0 mm and a height of 0.1 mm on a cold isostatic pressing machine using a tungsten carbide mold.

4. A method of producing a vanadium-doped and high-hydrated manganochromite iron ore single crystal at high temperature and high pressure according to claim 1, characterized by: Place the two water source sheets at the two ends of the cylindrical manganese-chromite sample in a double-capsule experimental sample chamber with an inner graphite tube and an outer gold-palladium alloy tube; The method for obtaining a manganese-chromite single crystal through high-temperature and high-pressure reaction comprises the following steps: Step 25, seal the cylindrical manganese-chromite sample and the two water source sheets in a double-capsule experimental sample chamber with an inner graphite tube and an outer gold-palladium alloy tube; place the cylindrical manganese-chromite sample in the middle of the graphite inner tube; and place the two water source sheets symmetrically at the two ends of the graphite inner tube close to the sample. Step 26, place the double capsule structure sample bin on the laboratory Kawai-1000t typical 6-8 type multi-face top large cavity high temperature and high pressure equipment, set the pressure increasing rate and temperature increasing rate to be 0.5 GPa / hour and 10 °C / minute respectively, increase the pressure and temperature to 3.0 GPa and 1080 °C respectively, and carry out hot-pressing sintering, the reaction time is 72 hours of constant temperature and constant pressure; Step 27, after 72 hours of constant temperature and constant pressure, reduce the temperature in the sample cavity from 1080 °C to 800 °C at a rate of 3 °C / minute, and keep the temperature constant for 1 hour; then reduce the temperature in the sample cavity from 800 °C to room temperature at a rate of 5 °C / minute; Step 28, after the temperature in the sample cavity is reduced to room temperature, reduce the pressure in the sample cavity from 3.0 GPa to normal pressure at a rate of 0.5 GPa / hour; Step 29, take the sample out of the Kawai-1000t typical 6-8 type multi-face top large cavity high temperature and high pressure equipment; remove the graphite tube and gold-palladium alloy tube wrapped around the sample, and cut the cylindrical sample in half from the middle using a diamond wire cutter; Select the single crystal of manganese-chromium-iron ore under 20 times of Olympus microscope.

5. The method of claim 1, wherein the vanadium-doped and high-hydrated schreyerite single crystal is prepared at high temperature and high pressure. The temperature of the high-temperature and high-pressure reaction is calibrated by two groups of high-temperature-resistant tungsten-rhenium thermocouples; each group of tungsten-rhenium thermocouples is composed of two tungsten-rhenium alloys with different materials, and the chemical composition is W 95% Re 5% and W 74% Re 26% ; each group of tungsten-rhenium thermocouples is symmetrically placed at the upper and lower ends of the double-caps structure sample bin composed of a graphite tube and a gold-palladium alloy tube.