LU503631B1 - Method for preparing aluminum-doped and high-water single-crystal chromite under high-temperature and high-pressure condition - Google Patents

Method for preparing aluminum-doped and high-water single-crystal chromite under high-temperature and high-pressure condition Download PDF

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LU503631B1
LU503631B1 LU503631A LU503631A LU503631B1 LU 503631 B1 LU503631 B1 LU 503631B1 LU 503631 A LU503631 A LU 503631A LU 503631 A LU503631 A LU 503631A LU 503631 B1 LU503631 B1 LU 503631B1
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temperature
chromite
sample
powder
water
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LU503631A
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French (fr)
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Lidong Dai
Haiying Hu
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Inst Geochemistry Cas
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    • CCHEMISTRY; METALLURGY
    • C30CRYSTAL GROWTH
    • C30BSINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B7/00Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions
    • C30B7/10Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions by application of pressure, e.g. hydrothermal processes
    • CCHEMISTRY; METALLURGY
    • C30CRYSTAL GROWTH
    • C30BSINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10Inorganic compounds or compositions
    • C30B29/16Oxides
    • C30B29/22Complex oxides

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  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
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Abstract

A method for preparing aluminum-doped and high-water single-crystal chromite under a high-temperature and high-pressure condition comprises: preparing a cylindrical chromite sample using solid trigonal ferrous carbonate crystals, solid basic chromium acetate crystalline powder, solid aluminum distearate powder, solid oxalic acid powder, solid α-phase goethite powder, solid aluminum hydroxide powder and liquid dilute nitric acid as starting materials; preparing two water-sourced discs from the α-phase goethite powder and the aluminum hydroxide powder according to a weight ratio of 4:1; and placing the two water-sourced discs at two ends of the cylindrical chromite sample, and then placing the cylindrical chromite sample with the water-sourced discs in a double-layer sample chamber for high-temperature and high-pressure reaction to obtain single-crystal chromite. The present invention solves the problem that there is not technique for preparing large-grained, aluminum-doped and high-water single-crystal chromite under a high-temperature and high-pressure condition, and can obtain large-grained, aluminum-doped and high-water single-crystal chromite experimental samples.

Description

METHOD FOR PREPARING ALUMINUM-DOPED AND HIGH-WATER
LU503631
SINGLE-CRYSTAL CHROMITE UNDER HIGH-TEMPERATURE AND
HIGH-PRESSURE CONDITION
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention belongs to the technical field of single-crystal mineral sample synthesis, and particularly relates to a method for preparing aluminum-doped and high-water single-crystal chromite under a high-temperature and high-pressure condition.
[0003] 2. Description of Related Art
[0004] Chromite, the chemical formula of which is FeCr204, is an important oxide mineral rich in ferrum and chromium.
[0005] Chromite with a spinel structure does not contain hy drone or hydroxyl in its molecular structure, and is manifested as an obvious nominal unhydrous mineral. There has not been yet an effective method for synthesizing chromite so far. So, it becomes particularly urgent to effectively synthesize large-grained, aluminum-doped and high-water single-crystal chromite to meet geoscientific research requirements of various high-temperature and high-pressure laboratory simulations, especially the requirement for studying the lattice preferred orientation and crystal axis anisotropy of single-crystal chromite under high pressure.
BRIEF SUMMARY OF THE INVENTION
[0006] The technical issue to be settled by the present invention is to provide a method for preparing aluminum-doped and high-water single-crystal chromite under a high-temperature and high-pressure condition, to solve the above-mentioned technical problems. 1
[0007] The technical solution of the present invention is as follows:
LU503631
[0008] A method for preparing aluminum-doped and high-water single-crystal chromite under a high-temperature and high-pressure condition, comprising: preparing a cylindrical chromite sample using solid trigonal ferrous carbonate crystals, solid basic chromium acetate crystalline powder, solid aluminum distearate powder, solid oxalic acid powder, solid a-phase goethite powder, solid aluminum hydroxide powder and liquid dilute nitric acid as starting materials; preparing two water-sourced discs from the a-phase goethite powder and the aluminum hydroxide powder according to a weight ratio of 4:1; and placing the two water-sourced discs at two ends of the cylindrical chromite sample, and then placing the cylindrical chromite sample with the water-sourced discs in a double-layer sample chamber for high-temperature and high-pressure reaction to obtain single-crystal chromite.
[0009] Preferably, the purity of the solid trigonal ferrous carbonate crystals is over 99.99%, the purity of the solid basic chromium acetate crystalline powder is over 99.99%, the purity of the solid aluminum distearate powder is over 99.99%, the purity of the solid oxalic acid powder is over 99.99%, the purity of the solid a-phase goethite powder is over 99%, the purity of the solid aluminum hydroxide powder is over 99%, and the concentration of the liquid dilute nitric acid is 10%.
[0010] Preferably, the cylindrical chromite sample is prepared by:
[0011] Step 1: measuring out 60 ml of dilute nitric acid with the concentration of 10%, and pouring it in a beaker with a notch;
[0012] Step 2: weighing out 5.0 g of trigonal ferrous carbonate crystals, adding them into the beaker with the notch, and putting a magnetic stirring rotor in the beaker with the notch;
[0013] Step 3: covering a mouth of the beaker with watch-glass, and reacting for 72 hrs at normal temperature and 700 rpm; 2
[0014] Step 4: measuring out 17.3584 g of solid basic chromium acetate crystalline
LU503631 powder and 650 mg of solid aluminum distearate powder according to chromite
Fe(Cr,Al)204 stoichiometry, and adding them into the beaker;
[0015] Step 5: covering the beaker with the watch-glass;
[0016] Step 6: placing the beaker on a high-temperature magnetic stirring heater coil in a fume hood, and stirring for 48 hrs at normal temperature and 800 rpm;
[0017] Step 7: weighing out 2 g of solid oxalic acid powder, and adding it into the beaker;
[0018] Step 8: placing the beaker on the high-temperature magnetic stirring heater coil in the fume hood, covering the beaker with the watch-glass, and setting parameters of the high-temperature magnetic stirring heater coil to 80 °C and 1000 rpm for stirring for 36 hrs;
[0019] Step 9: removing the watch-glass from the beaker, and increasing the temperature of the high-temperature magnetic stirring heater coil to 110 °C until the mixed solution in the beaker is completely desiccated;
[0020] Step 10: taking all mixed powder out of the beaker, and placing it in a graphite crucible;
[0021] Step 11: increasing the temperature of the graphite crucible containing the mixed powder to 1100 °C at arate of 300 °C/h by means of a muffle furnace which is at normal pressure and high temperature, and maintaining the graphite crucible at this temperature for 5 hrs;
[0022] Step 12: cooling the mixed powder to room temperature at a rate of 200 °C/h;
[0023] Step 13: grinding the mixed powder in a corundum mortar for 1 h;
[0024] Step 14: cold-pressing the ground mixed powder into three ® 10.0 mm * 3.0 mm sample discs, and stacking the three sample discs at a bottom of the graphite crucible from bottom to top; and 3
[0025] Step 15: hanging the graphite crucible in a middle of a high-temperature LU503631 oxygen atmosphere furnace;
[0026] Step 16: placing a stainless steel container containing secondary deionized pure cold water on one side of the high-temperature oxygen atmosphere furnace;
[0027] Step 17: connecting a top of a furnace body of the high-temperature oxygen atmosphere furnace to an argon inert gas cylinder and a proportion-adjustable carbon monoxide and carbon dioxide cylinder;
[0028] Step 18: opening an argon inert gas valve to continuously inject argon for 30 min, and under the protection of the argon, calcinating the sample at high temperature to 800 °C at a heating rate of 400 °C/h;
[0029] Step 19: when the temperature in the furnace body reaches 800 °C, switching a carbon monoxide and carbon dioxide gas control valve to enable a volume ratio of carbon monoxide and carbon dioxide in the oxygen atmosphere furnace to reach 4:1;
[0030] Step 20: when a mixed gas flow of the carbon monoxide and the carbon dioxide with the volume ratio of 4:1 in a sample chamber is stabilized, increasing the temperature of the sample chamber in the furnace body to 1430 °C at a rate of 200 °C/h to perform constant-temperature calcination for 15 min;
[0031] Step 21: after the sample is calcinated at 1430 °C for 15 min, pulling the graphite crucible containing the sample out of the furnace body, and then directly immersing it in the stainless steel container to quench the sample into chromite glass;
[0032] Step 22: taking the chromite glass out of the graphite crucible, and grinding it in the corundum mortar, and drying glassy-state chromite powder in a vacuum drying oven at 200 °C for 12 hrs; and
[0033] Step 23: cold-pressing the glassy-state chromite powder into a ® 4.0 mm (diameter) * 4.0 mm (height) cylindrical chromite sample on a cold isostatic press.
[0034] Preferably, preparing two water-sourced discs from the a-phase goethite 4 powder and the aluminum hydroxide powder according to a weight ratio of 4:1 comprises: LU503631 cold-pressing the a-phase goethite powder and the aluminum hydroxide powder by a D 4.0 mm (diameter) * 10.0 mm tungsten carbide grinding tool according to the weight ratio of 4:1 to obtain two ® 4.0 mm (diameter) * 0.1 mm (height) water-sourced discs.
[0035] Preferably, placing the two water-sourced discs at two ends of the cylindrical chromite sample and then placing the cylindrical chromite sample with the water-sourced discs in a double-layer sample chamber for high-temperature and high-pressure reaction to obtain single-crystal chromite comprise:
[0036] Step 24: sequentially sealing the cylindrical chromite sample and the two water-sourced discs in a double-layer experimental sample chamber with an inner tube being a graphite tube and an outer tube being a gold-palladium alloy tube, wherein the cylindrical chromite sample is placed in a middle of the inner graphite tube, and the water-sourced discs are placed at two symmetrical ends of the inner graphite tube close to the sample;
[0037] Step 25: placing the double-layer sample chamber in a typical Kawai-1000t 6-8 multi-anvil, large-volume, high-temperature and high-pressure apparatus, and increasing the pressure and temperature to 3.0 GPa and 1100 °C at a rate of 0.5 GPa/h and a rate of 10 °C/min respectively for hot-pressing sintering, and reacting at constant temperature and constant pressure for 72 hrs;
[0038] Step 26: after reacting at 3.0 GPa and 1100 °C for 72 hrs, decreasing the temperature in a sample cavity from 1100 °C to 800 °C at a rate of 3 °C/min, and maintaining the temperature for 1h; then, decreasing the temperature in the sample cavity from 800 °C to room temperature at a rate of 5 °C/min;
[0039] Step 27: when the temperature in the sample cavity is decreased to room temperature, decreasing the pressure in the sample cavity from 3.0 GPa to normal pressure at arate of 0.5 GPa; and
[0040] Step 28: after the high-temperature and high-pressure reaction is completed,
LU503631 taking the sample out of the typical Kawai-1000t 6-8 multi-anvil, large-volume, high-temperature and high-pressure apparatus, removing the graphite tube and the gold-palladium alloy tube of the double-layer sample chamber outside the sample, cutting the cylindrical sample in the middle with a diamond wire cutter, and picking out single-crystal chromite under an Olympus microscope.
[0041] Preferably, during the high-temperature and high-pressure reaction, two sets of tungsten-rhenium thermocouples are used for temperature calibration; each of the two sets of tungsten-rhenium thermocouples is composed of two tungsten-rhenium alloy wires made of different materials, the chemical composition of which is W95%Re5% and
W74%Re26%; and the two sets of tungsten-rhenium thermocouples are symmetrically disposed at an upper end and a lower end of the double-layer sample chamber composed of a graphite tube and a gold-palladium alloy tube.
[0042] The present invention has the following beneficial effects:
[0043] The aluminum-doped and high-water single-crystal chromite obtained through the method of the present invention is a pure substance and has good chemical stability. The method of the present invention has the remarkable advantages of a simple operation process and a short reaction time, and the obtained single-crystal chromite has good physical and chemical properties such as high purity, large size and stable chemical properties. Most importantly, the synthesized chromite has a high aluminum content (8000-9000 ppm wt%) and a high water content (250-450 ppm), and the aluminum content and the water content can be controlled. Particularly, the single-crystal chromite provides an important experimental sample guarantee for exploring the lattice preferred orientation and crystal axis anisotropy of single-crystal minerals under high pressure and breaks through the technical bottleneck of single-crystal chromite synthesis. 6
DETAILED DESCRIPTION OF THE INVENTION
LU503631
[0044] The present invention provides a method for preparing aluminum-doped and high-water single-crystal chromite under a high-temperature and high-pressure condition, which specifically comprises:
[0045] Solid transparent-semitransparent trigonal ferrous carbonate crystals (purity > 99.99%), solid lightgray-green-blue basic chromium acetate crystalline powder (purity > 99.99%), solid aluminum distearate powder (purity > 99.99%), solid oxalic acid powder (purity > 99.99%), solid a-phase goethite powder (purity > 99%), solid aluminum hydroxide powder (purity > 99%) and liquid dilute nitric acid (concentration: 10%) are used as starting materials.
[0046] Step 1: a chemical fume hood is opened, a volumetric flask with a standard volume of 100 ml is selected to accurately measure out 60 ml of dilute nitric acid with the concentration of 10%, a glass pipette is placed in a 500 ml beaker with a notch, and the liquid diluted nitric acid is completely transferred into the beaker carefully through the pipette, wherein due to the fact that the beaker with the notch will not be completely sealed after the beaker is covered with watch-glass, the beaker with the notch is used as a reaction container to ensure that generated gas can be easily volatilized in the fume hood.
[0047] Step 2: 5.0 g of high-purity transparent-semitransparent trigonal ferrous carbonate crystals are accurately weighed out with a 10 ug high-precision analytical balance, and are carefully added into the beaker containing the dilute nitric acid solution with the concentration of 10%, and a magnetic stirring rotor is put in the beaker.
[0048] Step 3: a mouth of the beaker containing the dilute nitric acid solution with the solid ferrous carbonate crystals is covered with watch-glass, and then the beaker is placed on a high-temperature magnetic stirring heater coil in the fume hood; in order to fully dissolve the starting material, namely the solid ferrous carbonate crystals, in the dilute nitric acid solution and make the solid ferrous carbonate crystals undergo hydrolysis 7 reaction and acidification reaction, the reaction temperature is normal temperature, the
LU503631 rotational speed is 700 rpm, and the reaction time is 72 hrs.
[0049] Step 4: 17.3584 g of high-purity basic chromium acetate crystalline powder and 650 mg of high-purity solid aluminum distearate powder are accurately weighed out with the high-precision analytical balance according to chromite Fe(Cr, Al)204 stoichiometry, and are carefully added to the dilute nitric acid solution containing ferrous carbonate.
[0050] Step 5: the beaker containing the dilute nitric acid solution with the solid ferrous carbonate crystals, the solid basic chromium acetate crystalline powder and the solid aluminum distearate powder is covered with watch-glass to ensure that gas generated during reaction is volatilized via the notch of the beaker, and the starting material, namely the dilute nitric acid solution, in the beaker is prevented from splashing during the high-speed stirring process, which may otherwise raise a risk and compromise the synthesis accuracy of single-crystal chromite.
[0051] Step 6: the beaker containing the sealed dilute nitric acid solution and magnetic stirring rotor is placed on the high-temperature magnetic stirring heater coil in the fume hood; stirring is performed at normal temperature and 800 rpm for 48 hrs to enable the starting materials, namely the solid ferrous carbonate crystals, the solid basic chromium acetate crystalline powder and the solid aluminum distearate powder, to be completely dissolved in the dilute nitric acid solution without any residues, and volatile substances such as NH3-H2O, CH4, C2H2, CO2, CO and H2 can be volatilized more easily in the fume hood.
[0052] Step 7: 2 g of high-purity solid oxalic acid powder is accurately weighed out with the high-precision analytical balance, and is added to the diluted nitric acid solution containing the solid ferrous carbonate crystals, the solid basic chromium acetate crystalline powder and the solid aluminum distearate powder, as an important 8 metal -chelator.
LU503631
[0053] Step 8: the beaker containing the mixed solution is placed on the high-temperature magnetic stirring heater coil in the fume hood again, and then the beaker is covered with the watch-glass; the parameters of the high-temperature magnetic stirring heater coil are set to 80 °C and 1000 rpm for stirring for 36 hrs to enable all the starting materials to form uniform colloidal sol under the combined action of dilute nitric acid and oxalic acid.
[0054] Step 9: the watch-glass is removed from the beaker, and the temperature of the high-temperature magnetic stirring heater coil is increased to 110 °C until the mixed solution in the beaker is completely desiccated.
[0055] Step 10: the magnetic stirring rotor in the beaker on the high-temperature magnetic stirring heater coil is taken out, all sample powder adhering to the surface of the magnetic stirring rotor is stripped into the beaker, and all mixed powder in the beaker is carefully taken out with a spoon and is placed in a graphite crucible.
[0056] Step 11: the temperature of the graphite crucible containing the mixed powder is increased to 1100 °C at a low heating rate of 300 °C/h by means of a muffle furnace which is at normal pressure and high temperature, and the graphite crucible is maintained at this temperature for 5 hrs. The high-temperature calcination rate is low, and the temperature maintaining time is long.
[0057] Step 12: the mixed powder in the graphite crucible in the muffle furnace is cooled to room temperature at a rate of 200 °C/h. Compared with the heating rate, a relatively low cooling rate is more beneficial to the formation of cellular loose sample powder. The mixed powder is taken out carefully.
[0058] Step 13: the cellular loose chromite sample powder is fully ground in a super-hard thickened corundum mortar for 1 h to obtain a fine-grained and uniform experimental powder sample. 9
[0059] Step 14: the fine-grained and uniform chromite powder sample is
LU503631 cold-pressed into three ® 10.0 mm * 3.0 mm sample discs by a high-precision tungsten carbide grinding tool (size: ® 10.0 mm * 10.0 mm) of a stainless steel press; the three sample discs are stacked from bottom to top and are then carefully placed at the bottom of the graphite crucible.
[0060] Step 15: two circular holes with a diameter of 1.0 mm are symmetrically drilled in the wall of the graphite crucible, in which the three sample discs are stacked, by means of a high-speed electric drill. A 0.5 mm platinum-rhodium alloy wire is made to penetrate through the two symmetrical 1.0 mm circular holes in the wall of the graphite crucible carefully to hang the graphite crucible in the middle of a high-temperature oxygen atmosphere furnace. Two ends of the platinum-rhodium alloy wire penetrating through the graphite crucible are connected and fixed to a vertical four-hole aluminum tube with a bore diameter of 0.6 mm, an outer diameter of 5.0 mm and a length of 40 mm. An upper end of the four-hole aluminum tube is fixed to the middle of a circular cover capable of being pushed into and pulled out of a furnace body at any time.
[0061] Step 16: a stainless steel container containing 3 L of secondary deionized pure cold water is placed on one side of the high-temperature oxygen atmosphere furnace in advance.
[0062] Step 17: the top of the furnace body of the high-temperature oxygen atmosphere furnace is connected to an argon inert gas cylinder and a proportion-adjustable carbon monoxide and carbon dioxide cylinder, the quantity of gas injected into a sample chamber is controlled through a barometer, and during the high-temperature calcination process, each gas can be switched and regulated in time through a valve.
[0063] Step 18: an argon inert gas valve is opened, and a pointer button controlled by the gas barometer is rotated to continuously inject argon for 30 min; under the protection of the argon, the sample is calcinated at high temperature to 800 °C at a heating rate of 400 °C/h.
LU503631
[0064] Step 19: when the temperature in the furnace body reaches 800 °C, a carbon monoxide and carbon dioxide gas control valve is switched quickly and the pointer button controlled by the gas barometer is rotated to enable the volume ratio of carbon monoxide and carbon dioxide in the oxygen atmosphere fumace to reach 4:1.
[0065] Step 20: when a mixed gas flow of the carbon monoxide and the carbon dioxide with the volume ratio of 4:1 in the sample chamber is stabilized, which takes about 3-5 min, the temperature of the sample chamber in the furnace body is increased to 1430 °C at arate of 200 °C/h to perform constant-temperature calcination for 15 min to melt the sample into glassy-state chromite.
[0066] Step 21: after the sample is calcinated at 1430 °C for 15 min, the graphite crucible containing the sample, the four-hole aluminum oxide tube and the circular cover on the furnace body are pulled out of the furnace body and then directly immersed in the stainless steel container containing 3L of secondary deionized pure cold water to quickly quench the sample into chromite glass.
[0067] Step 22: the chromite glass is taken out of the graphite crucible carefully, and is fully ground into fine-grained and uniform-composition sample powder in the corundum mortar. The chromite glass powder is dried in a vacuum drying oven at 200 °C for 12 hrs.
[0068] Step 23: the chromite glass powder is cold-pressed on a cold isostatic press by a high-precision ® 4.0 mm (diameter) * 10.0 mm tungsten carbide grinding tool to obtain a ® 4.0 mm (diameter) * 4.0 mm (height) cylindrical chromite sample.
[0069] To obtain high-water chromite, the a-phase goethite powder (molecular formula: FeOOH) and the aluminum hydroxide powder (molecular formula: AI(OH)3), the weight ratio of which is 4:1, are used as a water source. The mixture of a-phase goethite and aluminum hydroxide is used as the water source mainly for the following reasons: 11 first, the a-phase goethite and the aluminum hydroxide are both typical hydrous
LU503631 substances and have low dehydration temperature, some researchers believe that the a-phase goethite undergoes dehydration reaction at 270 °C to directly produce hematite and release a large amount of water at the same time, the other researchers hold that the a-phase goethite undergoes dehydration reaction at 238 °C to produce super-structural hematite [molecular formula: Fe(2-x/3)(OH)xO(3-x)] and the super-structural hematite undergoes dehydration reaction at 800 °C to produce hematite and release a large amount of water at the same time, the aluminum hydroxide 1s a typical aluminum-rich white, amorphous, powdery and hydrous solid substances and undergoes dehydration reaction at 230 °C, 300 °C and 500 °C respectively to produce mono-hydrous aluminum oxide, crystalline aluminum oxide and corundum and release a large amount of water at the same time, and all these dehydration temperatures are within a relatively low temperature interval during the process of preparing aluminum-doped single-crystal chromite under a high-temperature and high-pressure condition, which fully guarantees that the aluminum-doped single-crystal chromite is in a water environment long enough, thus ensuring sufficient diffusion of lattice water of the sample and the formation of lattice sites; second, the a-phase goethite and the aluminum hydroxide are both ferrum-rich and aluminum-rich substances, so the ferrum activity and the aluminum activity can be controlled in the process of preparing aluminum-doped and high-water single-crystal chromite under a high-temperature and high-pressure condition in a sample cavity; and finally, final products of the a-phase goethite and the aluminum hydroxide with the weight ratio of 4:1, which are used for providing the water source and disposed at two ends of the sample, are hematite (Fe203) and corundum (AI203) which will not chemically react with the sample, thus ensuring the purity of a prepared aluminum-doped and high-water single-crystal chromite sample. In addition, by adjusting the weight ratio of the a-phase goethite and the aluminum hydroxide for providing the water source and the height of the 12 corresponding water-source discs, the water content of the aluminum-doped and
LU503631 high-water single-crystal chromite sample can be adjusted.
[0070] Step 24: the a-phase goethite powder and the aluminum hydroxide powder are cold-pressed on a cold isostatic press by a high-precision ® 4.0 mm (diameter) * 10.0 mm tungsten carbide grinding tool according to the weight ratio of 4:1 to obtain two D 4.0 mm (diameter) * 0.1 mm (height) water-sourced discs.
[0071] Step 25: the cylindrical chromite sample (size: ® 4.0 mm (diameter) * 4.0 mm (height)) and the two water-sourced discs (size: ® 4.0 mm (diameter) * 0.1 (height)) are sequentially sealed in a double-layer experimental sample chamber with an inner tube being a graphite tube (size: ® 4.4 mm (outer diameter) * 4.4 mm (height), 0.2 mm (wall thickness)) and an outer tube being a gold-palladium alloy tube (size: ® 4.6 mm (outer diameter) * 4.6 mm (height), 0.1 mm (wall thickness)). In the present invention, the aluminum-doped chromite sample is placed in the middle of the inner graphite tube, the two water-sourced discs prepared from the a-phase goethite and the aluminum hydroxide with the weight ratio of 4:1 are placed at two symmetrical ends of the graphite inner tube close to the sample.
[0072] In the present invention, the inner tube of the double-layer sample chamber uses graphite as a sealing material.
[0073] Step 26: chromite is one of the important ferrum-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 chromite deep in the lower crust of the earth and other terrestrial planets and invert the temperature and pressure conditions for stable existence of the chromite phase, the double-layer sample chamber composed of the graphite tube and the gold-palladium alloy tube is placed in a typical Kawai-1000t 6-8 multi-anvil, large-volume, high-temperature and high-pressure apparatus, the pressure and temperature are increased to 3.0 GPa and 1100 °C at a rate of 0.5 GPa/h and a rate of 10 13
°C/min respectively for hot-pressing sintering, and the reaction time is 72 hrs.
LU503631
[0074] Step 27: after the reaction is performed at 3.0 GPa and 1100 °C for 72 hrs, the temperature in a sample cavity is decreased from 1100 °C to 800 °C at a rate of 3 °C/min, and the temperature 1s maintained at 800 °C for 1 h; then, the temperature in the sample cavity is decreased from 800 °C to room temperature at a rate of 5 °C/min.
[0075] Step 28: when the temperature in the sample cavity is decreased to room temperature, the pressure in the sample cavity 1s decreased from 3.0 GPa to normal pressure at a rate of 0.5 GPa.
[0076] Step 29: after the high-temperature and high-pressure reaction is completed, the sample is taken out of the typical Kawai-1000t 6-8 multi-anvil, large-volume, high-temperature and high-pressure apparatus. The graphite tube and the gold-palladium alloy tube of the double-layer sample chamber outside the sample are removed carefully, and the cylindrical sample is cut in the middle with a high-precision diamond wire cutter.
Single-crystal chromite is picked out under a 20-power high-precision Olympus microscope. 14

Claims (6)

What is claimed is: LU503631
1. À method for preparing aluminum-doped and high-water single-crystal chromite under a high-temperature and high-pressure condition, comprising: preparing a cylindrical chromite sample using solid trigonal ferrous carbonate crystals, solid basic chromium acetate crystalline powder, solid aluminum distearate powder, solid oxalic acid powder, solid a-phase goethite powder, solid aluminum hydroxide powder and liquid dilute nitric acid as starting materials; preparing two water-sourced discs from the a-phase goethite powder and the aluminum hydroxide powder according to a weight ratio of 4:1; and placing the two water-sourced discs at two ends of the cylindrical chromite sample, and then placing the cylindrical chromite sample with the water-sourced discs in a double-layer sample chamber for high-temperature and high-pressure reaction to obtain single-crystal chromite.
2. The method for preparing aluminum-doped and high-water single-crystal chromite under a high-temperature and high-pressure condition according to Claim 1, wherein the purity of the solid trigonal ferrous carbonate crystals is over 99.99%, the purity of the solid basic chromium acetate crystalline powder is over 99.99%, the purity of the solid aluminum distearate powder is over 99.99%, the purity of the solid oxalic acid powder is over 99.99%, the purity of the solid a-phase goethite powder is over 99%, the purity of the solid aluminum hydroxide powder is over 99%, and the concentration of the liquid dilute nitric acid is 10%.
3. The method for preparing aluminum-doped and high-water single-crystal chromite under a high-temperature and high-pressure condition according to Claim 1, wherein the cylindrical chromite sample is prepared by: Step 1: measuring out 60 ml of dilute nitric acid with the concentration of 10%, and pouring it in a beaker with a notch; Step 2: weighing out 5.0 g of trigonal ferrous carbonate crystals, adding them into the beaker with the notch, and putting a magnetic stirring rotor in the beaker with the notch; LU503631
Step 3: covering a mouth of the beaker with watch-glass, and reacting for 72 hrs at normal temperature and 700 rpm:
Step 4: measuring out 17.3584 g of solid basic chromium acetate crystalline powder and 650 mg of solid aluminum distearate powder according to chromite Fe(Cr,Al)204 stoichiometry, and adding them into the beaker;
Step 5: covering the beaker with the watch-glass;
Step 6: placing the beaker on a high-temperature magnetic stirring heater coil in a fume hood, and stirring for 48 hrs at normal temperature and 800 rpm;
Step 7: weighing out 2 g of solid oxalic acid powder, and adding it into the beaker;
Step 8: placing the beaker on the high-temperature magnetic stirring heater coil in the fume hood, covering the beaker with the watch-glass, and setting parameters of the high-temperature magnetic stirring heater coil to 80 °C and 1000 rpm for stirring for 36 hrs;
Step 9: removing the watch-glass from the beaker, and increasing the temperature of the high-temperature magnetic stirring heater coil to 110 °C until the mixed solution in the beaker is completely desiccated;
Step 10: taking all mixed powder out of the beaker, and placing it in a graphite crucible;
Step 11: increasing the temperature of the graphite crucible containing the mixed powder to 1100 °C at a rate of 300 °C/h by means of a muffle furnace which is at normal pressure and high temperature, and maintaining the graphite crucible at this temperature for 5 hrs;
Step 12: cooling the mixed powder to room temperature at a rate of 200 °C/h;
Step 13: grinding the mixed powder in a corundum mortar for 1 h;
Step 14: cold-pressing the ground mixed powder into three ® 10.0 mm * 3.0 mm sample discs, and stacking the three sample discs at a bottom of the graphite crucible from
16 bottom to top; and LU503631 Step 15: hanging the graphite crucible in a middle of a high-temperature oxygen atmosphere furnace; Step 16: placing a stainless steel container containing secondary deionized pure cold water on one side of the high-temperature oxygen atmosphere furnace; Step 17: connecting a top of a furnace body of the high-temperature oxygen atmosphere furnace to an argon inert gas cylinder and a proportion-adjustable carbon monoxide and carbon dioxide cylinder; Step 18: opening an argon inert gas valve to continuously inject argon for 30 min, and under the protection of the argon, calcinating the sample at high temperature to 800 °C at a heating rate of 400 °C/h; Step 19: when the temperature in the furnace body reaches 800 °C, switching a carbon monoxide and carbon dioxide gas control valve to enable a volume ratio of carbon monoxide and carbon dioxide in the oxygen atmosphere furnace to reach 4:1; Step 20: when a mixed gas flow of the carbon monoxide and the carbon dioxide with the volume ratio of 4:1 in a sample chamber is stabilized, increasing the temperature of the sample chamber in the furnace body to 1430 °C at a rate of 200 °C/h to perform constant-temperature calcination for 15 min; Step 21: after the sample is calcinated at 1430 °C for 15 min, pulling the graphite crucible containing the sample out of the furnace body, and then directly immersing it in the stainless steel container to quench the sample into chromite glass; Step 22: taking the chromite glass out of the graphite crucible, and grinding it in the corundum mortar, and drying glassy-state chromite powder in a vacuum drying oven at 200 °C for 12 hrs; and Step 23: cold-pressing the glassy-state chromite powder into a ® 4.0 mm (diameter) *
4.0 mm (height) cylindrical chromite sample on a cold isostatic press. 17
4. The method for preparing aluminum-doped and high-water single-crystal chromite LU503631 under a high-temperature and high-pressure condition according to Claim 1, wherein preparing two water-sourced discs from the a-phase goethite powder and the aluminum hydroxide powder according to a weight ratio of 4:1 comprises: cold-pressing the a-phase goethite powder and the aluminum hydroxide powder by a ® 4.0 mm (diameter) * 10.0 mm tungsten carbide grinding tool according to the weight ratio of 4:1 to obtain two D 4.0 mm (diameter) * 0.1 mm (height) water-sourced discs.
5. The method for preparing aluminum-doped and high-water single-crystal chromite under a high-temperature and high-pressure condition according to Claim 1, wherein placing the two water-sourced discs at two ends of the cylindrical chromite sample and then placing the cylindrical chromite sample with the water-sourced discs in a double-layer sample chamber for high-temperature and high-pressure reaction to obtain single-crystal chromite comprise: Step 24: sequentially sealing the cylindrical chromite sample and the two water-sourced discs in a double-layer experimental sample chamber with an inner tube being a graphite tube and an outer tube being a gold-palladium alloy tube, wherein the cylindrical chromite sample is placed in a middle of the inner graphite tube, and the water-sourced discs are placed at two symmetrical ends of the inner graphite tube close to the sample; Step 25: placing the double-layer sample chamber in a typical Kawai-1000t 6-8 multi-anvil, large-volume, high-temperature and high-pressure apparatus, and increasing the pressure and temperature to 3.0 GPa and 1100 °C at a rate of 0.5 GPa/h and a rate of °C/min respectively for hot-pressing sintering, and reacting at constant temperature and constant pressure for 72 hrs; Step 26: after reacting at 3.0 GPa and 1100 °C for 72 hrs, decreasing the temperature in a sample cavity from 1100 °C to 800 °C at a rate of 3 °C/min, and maintaining the temperature for 1h; then, decreasing the temperature in the sample cavity from 800 °C to 18 room temperature at a rate of 5 °C/min; LU503631 Step 27: when the temperature in the sample cavity 1s decreased to room temperature, decreasing the pressure in the sample cavity from 3.0 GPa to normal pressure at a rate of
0.5 GPa; and Step 28: after the high-temperature and high-pressure reaction is completed, taking the sample out of the typical Kawai-1000t 6-8 multi-anvil, large-volume, high-temperature and high-pressure apparatus, removing the graphite tube and the gold-palladium alloy tube of the double-layer sample chamber outside the sample, cutting the cylindrical sample in the middle with a diamond wire cutter, and picking out single-crystal chromite under an Olympus microscope.
6. The method for preparing aluminum-doped and high-water single-crystal chromite under a high-temperature and high-pressure condition according to Claim 1, wherein during the high-temperature and high-pressure reaction, two sets of tungsten-rhenium thermocouples are used for temperature calibration; each of the two sets of tungsten-rhenium thermocouples is composed of two tungsten-rhenium alloy wires made of different materials, the chemical composition of which is W95%Re5% and W74%Re26%; and the two sets of tungsten-rhenium thermocouples are symmetrically disposed at an upper end and a lower end of the double-layer sample chamber composed of a graphite tube and a gold-palladium alloy tube. 19
LU503631A 2022-12-13 2023-03-14 Method for preparing aluminum-doped and high-water single-crystal chromite under high-temperature and high-pressure condition LU503631B1 (en)

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