LU503018B1

LU503018B1 - Method for preparing high-calcium, high-manganese and high-water single-crystal enstatite

Info

Publication number: LU503018B1
Application number: LU503018A
Authority: LU
Inventors: Haiying Hu; Lidong Dai
Original assignee: Inst Geochemistry Cas
Priority date: 2021-11-19
Filing date: 2022-11-08
Publication date: 2023-05-17
Also published as: ZA202205474B; CN114086256A; CN114086256B

Abstract

Disclosed is a method for preparing high-calcium, high-manganese and high-water single-crystal enstatite, including: preparing, according to enstatite chemometrics, a mixture cylinder sample using solid magnesium nitrate hexahydrate powder, solid calcium nitrate tetrahydrate powder, solid manganese(II) nitrate tetrahydrate powder, liquid tetraethoxysilane and absolute ethyl alcohol as starting materials; preparing water-sourced discs using solid natural serpentine powder, solid natural flake manganite powder and solid natural slaked lime powder as raw materials; placing the water-sourced discs at two ends of the mixture cylinder sample; and placing the mixture cylinder sample and the water-sourced discs in a gold-palladium alloy sample tube for a high-temperature and high-pressure reaction to prepare high-calcium, high-manganese and high-water single-crystal enstatite. The present invention fills in the technical blank in preparing high-calcium, high-manganese and high-water single-crystal enstatite in the prior art, so that large-grained high-calcium, high-manganese and high-water single-crystal enstatite experimental sample are obtained.

Description

DESCRIPTION

METHOD FOR PREPARING HIGH-CALCIUM, HIGH-MANGANESE AND

HIGH-WATER SINGLE-CRYSTAL ENSTATITE

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] The present invention belongs to the technical field of single-crystal mineral sample synthesis under a high-temperature and high-pressure condition, and particularly relates to a method for preparing high-calcium, high-manganese and high-water single-crystal enstatite.

[0003] 2. Description of Related Art

[0004] Enstatite (molecular formula: Mg[Si2O6]) is an important and typical mineral for the study of petrogenesis. The general chemical formula of enstatite may be expressed as X»[T20s], and a great variety of complex-composition enstatite minerals containing different impurity ions are exposed out of the earth’s surface.

[0005] Pure single-crystal enstatite prepared in the prior art is non-hydrous and has a small particle size (nano-sized generally).

BRIEF SUMMARY OF THE INVENTION

[0006] The technical issue to be settled by the present invention is to provide a method for preparing high-calcium, high-manganese and high-water single-crystal enstatite to solve the above-mentioned problems of the prior art.

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

[0008] A method for preparing high-calcium, high-manganese and high-water single-crystal enstatite, comprising: preparing, according to enstatite chemometrics, a mixture cylinder sample using solid magnesium nitrate hexahydrate powder, solid calcium 1 nitrate tetrahydrate powder, solid manganese(IT) nitrate tetrahydrate powder, liquid tetraethoxysilane and absolute ethyl alcohol as starting materials; preparing water-sourced discs using solid natural serpentine powder, solid natural flake manganite powder and solid natural slaked lime powder as raw materials; placing the water-sourced discs at two ends of the mixture cylinder sample; and placing the mixture cylinder sample and the water-sourced discs in a gold-palladium alloy sample tube for a high-temperature and high-pressure reaction to prepare high-calcium, high-manganese and high-water single-crystal enstatite.

[0009] Preferably, the mixture cylinder sample is prepared specifically by:

[0010] Step 1, placing 55 ml of absolute ethyl alcohol into a 250 ml wide-mouth glass bottle;

[0011] Step 2, weighing, according to the enstatite ((Mg, Ca, Mn)2Si2O6) chemometrics, 10 g of the solid magnesium nitrate hexahydrate powder, 50 mg of the calcium nitrate tetrahydrate powder and 40 mg of the solid manganese(Il) nitrate tetrahydrate powder, and adding the weighed starting materials into the absolute ethyl alcohol;

[0012] Step 3, adding, with a pipette, 9.1376 ml of the liquid tetraethoxysilane to the 55 ml of absolute ethyl alcohol;

[0013] Step 4, putting a magnetic stirring rotor in the wide-mouth bottle, and sealing a mouth of the wide-mouth bottle with a plastic film with a thickness of 0.5 mm;

[0014] Step 5, placing the wide-mouth bottle on a high-temperature magnetic stirring heater coil, and enabling the high-temperature magnetic stirring heater coil to stir a mixed solution for 20 hrs at room temperature and 940 rpm;

[0015] Step 6, opening the mouth, sealed with the plastic film, of the wide-mouth bottle to add 45 ml of a 69-70% concentrated nitric acid solution to the mixed solution, and then sealing the mouth of the wide-mouth bottle again; 2

[0016] Step 7, poking multiple 0.1 mm small holes in a surface of the plastic film;

[0017] Step 8, placing the wide-mouth bottle on the high-temperature magnetic stirring heater coil, increasing a temperature of the heater coil to 86° C, and stirring the mixed solution for 25 hrs at 86°C and 1068 rpm;

[0018] Step 9, removing the plastic film from the mouth of the wide-mouth bottle, and increasing the temperature of the high-temperature magnetic stirring heater coil to 113° C until the mixed solution in the whole wide-mouth bottle is completely desiccated;

[0019] Step 10, taking out the magnetic stirring rotor, taking, with a spoon, all mixed powder out of the wide-mouth bottle, and placing the mixed powder in a platinum crucible;

[0020] Step 11, placing the platinum crucible containing the mixed powder in a high-temperature muffle furnace, and increasing a temperature of the high-temperature muffle furnace to 1020° C at a rate of 760° C/h to calcine the mixed powder for 1.6 hrs; naturally cooling the mixed powder to room temperature, and taking out the mixed sample powder;

[0021] Step 12, uniformly grinding and mixing the mixed sample powder in an agate mortar, and pressing the mixed sample powder into a ® 14.8 mm * 7.6 mm disc on a press, and stacking three discs up in the platinum crucible;

[0022] Step 13, hanging the platinum crucible containing the disc-shaped mixture sample in a middle of a high-temperature oxygen atmosphere fumace having an open bottom, with a platinum wire connected to a wall of the platinum crucible, and injecting a gas mixture of hydrogen, argon and carbon dioxide into the platinum crucible from a top of the platinum crucible;

[0023] Step 14, placing a cup, 700 ml, of secondary deionized cold water below a furnace body of the oxygen atmosphere furnace;

[0024] Step 15, increasing a temperature of the platinum crucible containing the 3 disc-shaped mixture sample to 1690° C at a rate of 680° C/h for constant-temperature calcining for 35 min to melt the disc-shaped mixture sample into glassy-state enstatite;

[0025] Step 16, applying a 10 A current to the platinum wire connected to the wall of the platinum crucible to fuse the platinum wire, so that the platinum crucible containing the sample falls into the secondary deionized cold water from a hearth of the oxygen atmosphere furnace to realize direct quenching of the sample at a high temperature, thus obtaining enstatite glass with uniform components; and

[0026] Step 17, taking the quenched monticellite glass out of the platinum crucible, and grinding the monticellite glass into uniform sample powder in the agate mortar; and

[0027] Step 18, pressing the sample powder into a ® 3.8 mm * 3.4 mm cylinder to obtain the mixture cylinder sample.

[0028] Preferably, preparing water-sourced discs using solid natural serpentine powder, solid natural flake manganite powder and solid natural slaked lime powder as raw materials is carried out by: using natural serpentine, flake manganite and slaked lime with a weight ratio of 4:3:1 as a water source, and pressing the natural serpentine, the flake manganite and the slaked lime into two ® 3.8 mm * 0.2 mm discs on the press.

[0029] Preferably, placing the mixture cylinder sample and the water-sourced discs in a gold-palladium alloy sample tube for a high-temperature and high-pressure reaction to prepare high-calcium, high-manganese and high-water single-crystal enstatite is carried out by: placing the gold-palladium alloy sample tube containing the mixture cylinder sample and the water-sourced discs on a Kawai-1000t multi-anvil press, setting a pressure rise rate and a temperature rise rate to 2.0 GPa/h and 50° C/min respectively, increasing the pressure and the temperature to 7.0 GPa and 1100° C respectively for hot-pressing sintering, and performing a reaction for 18 hrs under a constant-temperature and constant-pressure condition; after the reaction is performed for 18 hrs under the constant-temperature and constant-pressure condition, decreasing a temperature in a 4 sample cavity to room temperature from 1100° C at a rate of 5° C/min; after the temperature is decreased to the room temperature, decreasing a pressure in the sample cavity to normal pressure from 7.0 GPa at a rate of 0.7 GPa/h; and at the end of the high-temperature and high-pressure preparation reaction, taking an experimental sample out of the sample cavity, opening the gold-palladium alloy sample tube with a diamond slicer, and picking out the single-crystal enstatite under a high-power Olympus microscope.

[0030] Preferably, during the high-temperature and high-pressure reaction, the temperature in the high-pressure sample cavity is calibrated with two sets of B-type high-temperature platinum-rhodium noble metal thermocouples, and each of the two sets of high-temperature platinum-rhodium noble metal thermocouples is composed of two platinum-rhodium alloy wires that are made of different materials; the chemical composition of a positive pole (BP) of each said thermocouple is Pt70%Rh30%; the chemical composition of a negative pole (BN) of each said thermocouple is Pto4yRhe%; and correspondingly, a diameter of each said positive and negative platinum-rhodium alloy wire BP and BN is 0.2 mm; and each set of high-temperature platinum-rhodium noble metal thermocouples is symmetrically placed on upper and lower sides of an outer wall of the gold-palladium alloy sample tube, so that the temperature in the sample cavity is calibrated.

[00311 The present invention has the following beneficial effects:

[0032] According to the present invention, single-crystal enstatite with a high calcium content (5000-6000 ppm wt%), a high manganese content (4000-5000 ppm wt%), and a high water content (3000-4000 ppm wt%) is synthesized, and the obtained high-calcium, high-manganese and high-water single-crystal enstatite is a pure substance and has good chemical stability.

[0033] The method provided by the present invention has the obvious advantages of simple operation process, short reaction time and the like, the obtained single-crystal enstatite has good properties such as high purity, large size and stable chemical properties, and more importantly, the calcium content, manganese content and water content are high and controllable.

DETAILED DESCRIPTION OF THE INVENTION

[0034] The invention provides a method for preparing high-calcium, high-manganese and high-water single-crystal enstatite, specifically comprising:

[0035] Solid magnesium nitrate hexahydrate powder (purity: >99.99%), solid calcium nitrate tetrahydrate powder (purity: >99.99%), solid manganese(Il) nitrate tetrahydrate powder (purity: >99.99%), liquid tetraethoxysilane (purity: >99.99%), solid natural serpentine powder (purity: >99%), solid natural flake manganite powder (purity: >99%), solid natural slaked lime powder (purity: >99%) and absolute ethyl alcohol (concentration: > 99.9%) are used as starting materials.

[0036] Step 1, 55 ml of absolute ethyl alcohol is placed into a 250 ml wide-mouth glass bottle;

[0037] Step 2, 10 g of the high-purity solid magnesium nitrate hexahydrate powder, mg of the high-purity solid calcium nitrate tetrahydrate powder and 40 mg of the 6 high-purity solid manganese(II) nitrate tetrahydrate powder are weighed with a high-precision analytical balance according to enstatite ((Mg, Ca, Mn)2Si2O6) chemometrics, and are carefully added to the 55 ml of absolute ethyl alcohol.

[0038] Step 3, 9.1376 ml of the high-purity liquid tetracthoxysilane is carefully added to the 55 ml of absolute ethyl alcohol with a pipette according to the enstatite chemometrics.

[0039] Step 4, a magnetic stirring rotor is put in the wide-mouth bottle containing a mixed solution of solid magnesium nitrate hexahydrate, solid calcium nitrate tetrahydrate, solid manganese(Il) nitrate tetrahydrate, the liquid tetraethoxysilane and the absolute ethyl alcohol, and a mouth of the wide-mouth bottle is sealed with a plastic film with a thickness of 0.5 mm to prevent the initial solution in the wide-mouth bottle from splashing during the high-speed stirring process, which may otherwise compromise the synthesis accuracy of a sample.

[0040] Step 5, the wide-mouth bottle containing the sealed initial mixed solution and magnetic stirring rotor is placed on a high-temperature magnetic stirring heater coil, and in order to dissolve the starting materials, namely the magnesium nitrate hexahydrate, the calcium nitrate tetrahydrate, the manganese(IT) nitrate tetrahydrate and the liquid tetraethoxysilane in the absolute ethyl alcohol, the high-temperature magnetic stirring heater coil is made to stir the materials at room temperature and 940 rpm for 20 hrs, so that the materials are sufficiently dissolved without residues.

[0041] Step 6, the mouth, sealed with the plastic film, of the wide-mouth bottle is opened, 45 ml of a 69-70% concentrated nitric acid solution is added to the mixed solution to accelerate the preparation reaction of enstatite, and then the mouth of the wide-mouth bottle is sealed again with the plastic film to prevent the initial solution in the wide-mouth bottle from splashing during the high-temperature stirring process, which may otherwise compromise the synthesis accuracy of the sample. 7

[0042] Step 7, multiple 0.1 mm small holes are poked in the surface of the plastic film with sharp tweezers to allow volatile substances such as NH3*H>O, CO and O2 produced during the reaction to be volatilized more easily and to prevent the concentrated nitric acid in the wide-mouth bottle from splashing during the high-temperature stirring process, which may otherwise compromise the synthesis accuracy of the sample.

[0043] Step 8, the wide-mouth bottle is placed on the high-temperature magnetic stirring heater coil, and the temperature of the heater coil is increased to 86° C, and the mixed solution is stirred at a high temperature of 86° C and a high speed of 1068 rpm for hrs, so that all initial reagents are thoroughly dissolved in a mixed solution of the absolute ethanol and the concentrated nitric acid.

[0044] Step 9, the plastic film sealing the mouth of the wide-mouth bottle is removed, and the temperature of the high-temperature magnetic stirring heater coil is increased to 113° C until the mixed solution in the whole wide-mouth bottle is completely desiccated.

[0045] Step 10, the magnetic stirring rotor is taken out, and all mixed powder in the wide-mouth bottle is taken out carefully with a spoon and is placed in a platinum crucible.

[0046] Step 11, the platinum crucible containing the mixed powder is placed in a high-temperature muffle furnace, and the temperature of the high-temperature muffle furnace is increased to 1020° C at a rate of 760° C/h to calcine the mixed powder for 1.6 hrs to remove residual nitric acid and organic matter in the mixed powder.

[0047] The mixed powder is slowly and naturally cooled to room temperature, and then the mixed sample powder is taken out.

[0048] Step 12, a calcined powdery mixture sample is uniformly ground and mixed in an agate mortar, and the mixture sample is pressed into a ® 14.8 mm (diameter) * 7.6 mm (height) disc on the press, and three discs are stacked up in the platinum 8 crucible.

[0049] Step 13, the platinum crucible containing the disc-shaped mixture sample is hung in the middle of a high-temperature oxygen atmosphere fumace having an open bottom, with a platinum wire connected to a wall of the platinum crucible, and a gas mixture of hydrogen, argon and carbon dioxide is injected into the platinum crucible from a top of the platinum crucible to control the oxygen atmosphere in a fumace body in the high-temperature calcining process.

[0050] A cup, 700 ml, of secondary deionized cold water is placed below the furnace body of the oxygen atmosphere furnace, so that the sample can be directly quenched at a high temperature.

[0051] Step 14, the temperature of the platinum crucible containing the disc-shaped mixture sample is increased to 1690° C at a rate of 680° C/h for constant-temperature calcining for 35 min to melt the disc-shaped mixture sample into glassy-state enstatite. Generally, the melting point of the enstatite is 1610° C, so when the temperature is over 1600° C, the enstatite will be in a glassy state. The high-temperature calcining process under the controlled oxygen atmosphere is carried out to provide a purer mixture initial material, namely the enstatite glass, to realize the synthesis of the high-calcium, high-manganese and high-water single-crystal enstatite; the high-temperature calcination under the oxygen atmosphere can better control the valence state of the variable-valence element, namely metallic manganese, in the product; and the relatively short calcination time ensures that the enstatite can be quickly melted into a glass phase when the temperature is over 1610° C and possible residual substances that may affect the sample preparation, such as water, organic matter and nitric acid can be volatilized completely.

[0052] Step 15, after the sample is calcined at 1690° C for 35 min, a 10 A current is applied to the platinum wire connected to the wall of the platinum crucible to fuse the 9 platinum wire, so that the platinum crucible containing the sample instantly falls into the secondary deionized cold water from a hearth of the oxygen atmosphere furnace to realize direct quenching of the sample at a high temperature, thus obtaining enstatite glass with uniform components, wherein fast quenching ensures that the enstatite sample in the glassy state is preserved in good condition at a high temperature.

[0053] Step 16, the enstatite glass, quenched with the secondary deionized cold water, is taken out of the platinum crucible and is sufficiently ground into uniform sample powder in the agate mortar.

[0054] Step 17, the sample powder is placed on the press and is pressed into a ® 3.8 mm (diameter) * 3.4 mm (height) cylinder, and in order to obtain high-water enstatite, natural serpentine (molecular formula: MgsSi4O10(OH)s), flake manganite (molecular formula: Mn(OH);, also called pyrochroite) and slaked lime (molecular formula: Ca(OH)z) with a weight ratio of 4:3:1 are used as a water source. The serpentine, flake manganite and slaked lime, as typical hydrous minerals, will undergo a dehydration reaction under a set pressure of 7.0 GPa when the temperature is over 802° C, thus being widely applied to mineral combinations for providing a water source during high-temperature and high-pressure experimental simulation. By using the natural serpentine, sufficient water can be released by dehydrated products of the hydrous minerals under a high-temperature and high-pressure condition to provide a water source for synthesizing the high-water enstatite, and a large quantity of forsterite, enstatite, and quartz can be generated to control the silicon activity during the preparation process of the high-calcium, high-manganese and high-water single-crystal enstatite in the sample cavity under the high-temperature and high-pressure condition. In addition, by using the natural serpentine, the flake manganite and the slaked lime with the weight ratio of 4:3:1 as a water source, all products of the dehydration reaction are magnesium-containing silicate minerals (forsterite and enstatite) and oxides (quartz, pyrolusite, manganic oxide and unslaked lime) that will not react with the enstatite sample, so that the sample is effectively prevented from being contaminated during the preparation process.

[0055] Step 18, the serpentine, the flake manganite and the slaked lime with the weight ratio of 4:3:1 for providing the water source are placed on the press and pressed into two ® 3.8 mm (diameter) * 0.2 mm (thickness) discs, which are sequentially placed at two ends of the sample, and the sample and the water-sourced discs (the serpentine, the flake manganite and the slaked lime with the weight ratio of 4:3:1 for providing the water source) are sealed in a ® 3.8 mm (inner diameter) * 4.0 mm (height) gold-palladium alloy sample tube with a wall thickness of 0.1 mm, wherein the gold-palladium alloy sample tube is made of an optimal sealing material that can effectively prevent water from escaping from the sample tube during the sample preparation process under the high-temperature and high-pressure condition.

[0056] Enstatite is one of the important magnesium-containing silicate minerals in the mantle region of the earth and other terrestrial planets; in order to truly simulate the growth environment of enstatite deep in the mantle region of the earth and other terrestrial planets and invert the temperature and pressure conditions for the stable existence of the enstatite mineral phase, the gold-palladium alloy sample tube containing the sample and the two water-sourced discs (the serpentine, the flake manganite and the slaked lime with the weight ratio of 4:3:1 for providing the water source) is placed on a Kawai-1000t multi-anvil press, a pressure rise rate and a temperature rise rate are set to 2.0 GPa/h and 50° C/min respectively, the pressure and the temperature are increased to 7.0 GPa and 1100° C respectively for hot-pressing sintering, and a reaction is performed for 18 hrs under a constant-temperature and constant-pressure condition.

[0057] According to the present invention, the temperature in the high-pressure sample cavity is accurately calibrated with two sets of B-type high-temperature platinum-rhodium noble metal thermocouples. Because of its advantages of high accuracy, 11 good stability, wide temperature measurement range, long service life and high temperature-measurement upper limit, the B-type high-temperature platinum-rhodium noble metal thermocouples are widely used for temperature measurement of glass, ceramic, and industrial salt-bath furnaces. The high-temperature platinum-rhodium thermocouples are common noble metal thermocouples in many high-temperature and high-pressure mineral physics research laboratories at home and abroad and can measure a maximum temperature of 2315° C. Each set of high-temperature platinum-rhodium noble metal thermocouples is composed of two platinum-rhodium alloy wires that are made of different materials; (the chemical composition of a positive pole (BP) of each thermocouple is Pt70%Rh30%; the chemical composition of a negative pole (BN) of each thermocouple is PtosyRhee; and correspondingly, the diameter of each positive and negative platinum-rhodium alloy wire (BP and BN) is 0.2 mm), and each set of high-temperature platinum-rhodium noble metal thermocouples is symmetrically placed on upper and lower sides of an outer wall of the gold-palladium alloy sample tube, so that the temperature in the sample cavity is accurately calibrated.

[0058] Step 19, when the temperature is increased to 802° C under a pressure of 7.0 GPa, the serpentine, the flake manganite and the slaked lime with the weight ratio of 4:3:1 sealed at the two ends of the gold-palladium alloy sample tube and used for providing the water source will undergo a dehydration reaction to release sufficient water, so that a good water source is provided. Moreover, when the serpentine and the slaked lime undergo the dehydration reaction under the high-temperature and high-pressure condition, a large quantity of mineral combinations of forsterite, enstatite, unslaked lime and quartz will be generated to control the silicon activity during the preparation process of the high-calcium, high-manganese and high-water single-crystal enstatite in the sample cavity under the high-temperature and high-pressure condition.

[0059] Step 20, after the reaction is performed for 18 hrs under the 12 constant-temperature and constant-pressure condition, the temperature in the sample cavity is decreased to room temperature from 1100° C at a rate of 5° C/min. Compared with the temperature rise rate (50° C/min) for sample preparation, a low temperature fall rate under a constant pressure is more beneficial for crystal growth of large-sized single-crystal enstatite.

[0060] After the temperature in the sample cavity is decreased to the room temperature, the pressure in the sample cavity is decreased to normal pressure from 7.0

GPa at a rate of 0.7 GPa/h.

[0061] At the end of the high-temperature and high-pressure preparation reaction, an experimental sample is taken out of the sample cavity, the gold-palladium alloy sample tube is opened with a diamond slicer, and single-crystal enstatite is picked out under a high-power Olympus microscope.

[0062] The obtained single-crystal enstatite is a single phase without any other impurity phases. A test result obtained with an electron-probe microanalyzer (EPMA) shows that the single-crystal enstatite has a molecular formula of Mgs[Si20s]. A test result obtained with multifunctional inductively coupled plasma-mass spectrometry (ICP-MS) shows that the calcium content and manganese content of the single-crystal enstatite are 5427 ppm wt% and 4085 ppm wt% respectively. A test result obtained with vacuum

Fourier transform-infrared spectroscopy (FT-IR) shows that the single-crystal enstatite has a high water content of 3819 ppm wt%.

[0063] The obtained high-calcium, high-manganese and high-water single-crystal enstatite is an orthorhombic system with a space group of Pbcn (no.60), lattice parameters: a = 18.234 À, b = 8.812 A and c = 5.186 A, a unit cell volume of 832.87 A3, an average particle size of 201 um, and a maximum particle size of 472 um.

[0064] The high-calcium, high-manganese and high-water single-crystal enstatite obtained through the method provided by the present invention has superior properties 13 such as high purity, large size, and stable chemical properties, and more importantly, the calcium content, the manganese content and the water content are high and controllable.

By changing the chemical dosage of the initial material, solid calcium nitrate tetrahydrate powder, from 46.0691 mg to 55.2829 mg, the calcium content of the finally obtained high-calcium, high-manganese and high-water single-crystal enstatite is increased from 5000 ppm wt% to 6000 ppm wt%. By changing the chemical dosage of the initial material, solid manganese(II) nitrate tetrahydrate powder, from 39.1742 mg to 48.9678 mg, the manganese content of the finally obtained high-calcium, high-manganese and high-water single-crystal enstatite is increased from 4000 ppm wt% to 5000 ppm wt%. By changing the weight ratio of the hydrous minerals, natural serpentine powder, natural flake manganite powder and natural slaked lime powder, for providing the water source and the different heights of the two corresponding water-sourced discs, the total amount of water generated by the dehydration reaction of the hydrous minerals sealed in the gold-palladium alloy sample tube can be controlled, and thus, the water content of the high-calcium, high-manganese and high-water single-crystal enstatite can be adjusted. The obtained high-calcium, high-manganese and high-water single-crystal enstatite can fully meet the requirements for experimental physics simulation of minerals in the mantle region of the earth and other terrestrial planets, breaks through the existing technical bottlenecks in the synthesis of single-crystal enstatite, and provides an important experimental sample support for exploring the optimal orientation and crystal axis anisotropy of single-crystal minerals in the mantle region of the earth and other terrestrial planets under a high-temperature and high-pressure condition. 14

Claims

CLAIMS What is claimed is:

1. A method for preparing high-calcium, high-manganese and high-water single-crystal enstatite, comprising: preparing, according to enstatite chemometrics, a mixture cylinder sample using solid magnesium nitrate hexahydrate powder, solid calcium nitrate tetrahydrate powder, solid manganese(II) nitrate tetrahydrate powder, liquid tetracthoxysilane and absolute ethyl alcohol as starting materials; preparing water-sourced discs using solid natural serpentine powder, solid natural flake manganite powder and solid natural slaked lime powder as raw materials; placing the water-sourced discs at two ends of the mixture cylinder sample; and placing the mixture cylinder sample and the water-sourced discs in a gold-palladium alloy sample tube for a high-temperature and high-pressure reaction to prepare high-calcium, high-manganese and high-water single-crystal enstatite.

2. The method for preparing high-calcium, high-manganese and high-water single-crystal enstatite according to Claim 1, wherein the mixture cylinder sample is prepared specifically by: Step 1, placing 55 ml of absolute ethyl alcohol into a 250 ml wide-mouth glass bottle; Step 2, weighing, according to the enstatite (Mg, Ca, Mn)2Si206) chemometrics, 10 g of the solid magnesium nitrate hexahydrate powder, 50 mg of the calcium nitrate tetrahydrate powder and 40 mg of the solid manganese(II) nitrate tetrahydrate powder, and adding the weighed starting materials into the absolute ethyl alcohol; Step 3, adding, with a pipette, 9.1376 ml of the liquid tetraethoxysilane to the 55 ml of absolute ethyl alcohol; Step 4, putting a magnetic stirring rotor in the wide-mouth bottle, and sealing a mouth of the wide-mouth bottle with a plastic film with a thickness of 0.5 mm; Step 5, placing the wide-mouth bottle on a high-temperature magnetic stirring heater coil, and enabling the high-temperature magnetic stirring heater coil to stir a mixed solution for 20 hrs at room temperature and 940 rpm;

Step 6, opening the mouth, sealed with the plastic film, of the wide-mouth bottle to add 45 ml of a 69-70% concentrated nitric acid solution to the mixed solution, and then sealing the mouth of the wide-mouth bottle again;

Step 7, poking multiple 0.1 mm small holes in a surface of the plastic film;

Step 8, placing the wide-mouth bottle on the high-temperature magnetic stirring heater coil, increasing a temperature of the heater coil to 86° C, and stirring the mixed solution for 25 hrs at 86°C and 1068 rpm;

Step 9, removing the plastic film from the mouth of the wide-mouth bottle, and increasing the temperature of the high-temperature magnetic stirring heater coil to 113° C until the mixed solution in the whole wide-mouth bottle is completely desiccated;

Step 10, taking out the magnetic stirring rotor, taking, with a spoon, all mixed powder out ofthe wide-mouth bottle, and placing the mixed powder in a platinum crucible;

Step 11, placing the platinum crucible containing the mixed powder in a high-temperature muffle furnace, and increasing a temperature of the high-temperature muffle furnace to 1020° C at a rate of 760° C/h to calcine the mixed powder for 1.6 hrs; naturally cooling the mixed powder to room temperature, and taking out the mixed sample powder;

Step 12, uniformly grinding and mixing the mixed sample powder in an agate mortar, and pressing the mixed sample powder into a ® 14.8 mm * 7.6 mm disc on a press, and stacking three discs up in the platinum crucible;

Step 13, hanging the platinum crucible containing the disc-shaped mixture sample in a middle of a high-temperature oxygen atmosphere furnace having an open bottom, with a platinum wire connected to a wall of the platinum crucible, and injecting a gas mixture of hydrogen, argon and carbon dioxide into the platinum crucible from a top of the platinum

16 crucible; Step 14, placing a cup, 700 ml, of secondary deionized cold water below a furnace body of the oxygen atmosphere furnace; Step 15, increasing a temperature of the platinum crucible containing the disc-shaped mixture sample to 1690° C at a rate of 680° C/h for constant-temperature calcining for 35 min to melt the disc-shaped mixture sample into glassy-state enstatite; Step 16, applying a 10 A current to the platinum wire connected to the wall of the platinum crucible to fuse the platinum wire, so that the platinum crucible containing the sample falls into the secondary deionized cold water from a hearth of the oxygen atmosphere furnace to realize direct quenching of the sample at a high temperature, thus obtaining enstatite glass with uniform components; and Step 17, taking the quenched monticellite glass out of the platinum crucible, and grinding the monticellite glass into uniform sample powder in the agate mortar; and Step 18, pressing the sample powder into a ® 3.8 mm * 3.4 mm cylinder to obtain the mixture cylinder sample.

3. The method for preparing high-calcium, high-manganese and high-water single-crystal enstatite according to Claim 1, wherein preparing water-sourced discs using solid natural serpentine powder, solid natural flake manganite powder and solid natural slaked lime powder as raw materials is carried out by: using natural serpentine, flake manganite and slaked lime with a weight ratio of 4:3:1 as a water source, and pressing the natural serpentine, the flake manganite and the slaked lime into two ® 3.8 mm * 0.2 mm discs on the press.

4. The method for preparing high-calcium, high-manganese and high-water single-crystal enstatite according to Claim 1, wherein placing the mixture cylinder sample and the water-sourced discs in a gold-palladium alloy sample tube for a high-temperature and high-pressure reaction to prepare high-calcium, high-manganese and high-water 17 single-crystal enstatite is carried out by: placing the gold-palladium alloy sample tube containing the mixture cylinder sample and the water-sourced discs on a Kawai-1000t multi-anvil press, setting a pressure rise rate and a temperature rise rate to 2.0 GPa/h and 50° C/min respectively, increasing the pressure and the temperature to 7.0 GPa and 1100° C respectively for hot-pressing sintering, and performing a reaction for 18 hrs under a constant-temperature and constant-pressure condition; after the reaction is performed for 18 hrs under the constant-temperature and constant-pressure condition, decreasing a temperature in a sample cavity to room temperature from 1100° C at a rate of 5° C/min; after the temperature is decreased to the room temperature, decreasing a pressure in the sample cavity to normal pressure from 7.0 GPa at a rate of 0.7 GPa/h; and at the end of the high-temperature and high-pressure preparation reaction, taking an experimental sample out of the sample cavity, opening the gold-palladium alloy sample tube with a diamond slicer, and picking out the single-crystal enstatite under a high-power Olympus microscope.

5. The method for preparing high-calcium, high-manganese and high-water single-crystal enstatite according to Claim 4, wherein during the high-temperature and high-pressure reaction, the temperature in the high-pressure sample cavity is calibrated with two sets of B-type high-temperature platinum-rhodium noble metal thermocouples, and each of the two sets of high-temperature platinum-rhodium noble metal thermocouples is composed of two platinum-rhodium alloy wires that are made of different materials; the chemical composition of a positive pole (BP) of each said thermocouple is Pt7o0%Rh30%; the chemical composition of a negative pole (BN) of each said thermocouple is Pto4xRh6%; and correspondingly, a diameter of each said positive and negative platinum-rhodium alloy wire BP and BN is 0.2 mm; and each set of high-temperature platinum-rhodium noble metal thermocouples is symmetrically placed on upper and lower sides of an outer wall of the gold-palladium alloy sample tube, so that 18 the temperature in the sample cavity is calibrated. 19