阅读说明：本技术 一种高钛和高含水的镁铁橄榄石单晶的制备方法 (Preparation method of high-titanium and high-water-content forsterite single crystal ) 是由 代立东 胡海英 于 2021-11-09 设计创作，主要内容包括：本发明公开了一种高钛和高含水的镁铁橄榄石单晶的制备方法,它包括：根据镁铁橄榄石化学计量学,以固体的六水合硝酸镁粉末、固体的九水合硝酸铁(III)粉末、液态的正硅酸乙酯和液态的钛酸四丁酯为初始原料制备出混合物圆柱体样品；以固体的天然滑石粉末和固体的天然水镁石粉末作为起始原料制备出重量比10:1的滑石和水镁石混合物水源圆片；将水源圆片放置在混合物圆柱体样品两端后；混合物圆柱体样品和水源圆片放入金钯合金样品管内进行高温高压反应制备出高钛的和高含水的镁铁橄榄石单晶；解决了目前的高钛的和高含水的火星地幔镁铁橄榄石制备技术空白,以获取大颗粒的高钛的高含水的镁铁橄榄石单晶实验样品。(The invention discloses a preparation method of a high-titanium and high-water content forsterite single crystal, which comprises the following steps: preparing a mixture cylinder sample by taking solid magnesium nitrate hexahydrate powder, solid iron (III) nitrate nonahydrate powder, liquid ethyl orthosilicate and liquid tetrabutyl titanate as initial raw materials according to the stoichiometric theory of the magnesium-iron olivine; preparing a water source wafer of a mixture of talc and brucite in a weight ratio of 10:1 by taking solid natural talc powder and solid natural brucite powder as starting raw materials; placing water source wafers at two ends of the mixture cylinder sample; putting the mixture cylinder sample and the water source wafer into a gold-palladium alloy sample tube for high-temperature and high-pressure reaction to prepare high-titanium and high-water content forsterite single crystals; the method solves the technical blank of the preparation of the high-titanium and high-water-content martite at present so as to obtain large-particle high-titanium and high-water-content forsterite single crystal experimental samples.)

1. A preparation method of a high-titanium and high-water content forsterite single crystal is characterized by comprising the following steps: it includes: preparing a mixture cylinder sample by taking solid magnesium nitrate hexahydrate powder, solid iron (III) nitrate nonahydrate powder, liquid ethyl orthosilicate and liquid tetrabutyl titanate as initial raw materials according to the stoichiometric theory of the magnesium-iron olivine; preparing a water source wafer of a mixture of talc and brucite in a weight ratio of 10:1 by taking solid natural talc powder and solid natural brucite powder as starting raw materials; placing water source wafers at two ends of the mixture cylinder sample; the mixture cylinder sample and the water source wafer are put into a gold-palladium alloy sample tube to carry out high-temperature high-pressure reaction to prepare the high-titanium and high-water content forsterite single crystal.

2. The method for producing a high-titanium and high-moisture fayalite single crystal according to claim 1, wherein: it specifically includes:

step 1, selecting solid magnesium nitrate hexahydrate powder with the purity of more than 99.99 percent, solid iron (III) nitrate nonahydrate powder with the purity of more than 99.99 percent, liquid ethyl orthosilicate with the purity of more than 99.99 percent, liquid tetrabutyl titanate with the purity of more than 99.99 percent, and solid natural talc powder with the purity: 99 percent, the purity of solid natural brucite powder is more than 99 percent, and the concentration of absolute ethyl alcohol is more than 99.9 percent as initial raw materials;

step 2, putting 80 ml of absolute ethyl alcohol into a 500 ml wide-mouth glass bottle; 10 g of solid magnesium nitrate hexahydrate powder and 5.254 g of solid iron (III) nitrate nonahydrate powder were weighed out into 80 ml of anhydrous ethanol solution according to the magnesium-iron olivine stoichiometry;

step 3, according to the stoichiometric theory of the fayalite, 6.092 ml of liquid tetraethoxysilane and 30 microliter of liquid tetrabutyl titanate are respectively added into 80 ml of absolute ethyl alcohol solution by a pipette;

step 4, adding a magnetic stirring rotor into the wide-mouth bottle containing the absolute ethyl alcohol mixed solution of magnesium nitrate hexahydrate, ferric nitrate (III) nonahydrate, ethyl orthosilicate and tetrabutyl titanate, and sealing the mouth of the wide-mouth bottle by using a plastic film;

step 5, placing the sealed wide-mouth bottle on a high-temperature magnetic stirring hot plate, and stirring the high-temperature magnetic stirring hot plate for 22 hours at room temperature and at the rotating speed of 850 revolutions per minute;

step 6, adding 40 ml of 69-70% concentrated nitric acid solution into the mixed solution, and sealing the opening of the wide-mouth bottle;

step 7, binding countless uniform holes on the surface of the plastic film;

step 8, placing the wide-mouth bottle on a high-temperature magnetic stirring hot plate, increasing the temperature of the hot plate to 90 ℃, and stirring the mixed solution for 25 hours at the conditions of 90 ℃ and the rotating speed of 1100 r/min;

step 9, removing the plastic film of the sealing opening, and regulating the temperature of the high-temperature magnetic stirring hot plate to 140 ℃ until the mixed solution in the whole wide-mouth bottle is completely evaporated to dryness;

step 10, taking out the magnetic stirring rotor, taking out all mixed powder in the wide-mouth bottle by using a medicine spoon, and placing the powder in a platinum crucible;

step 11, placing the platinum crucible filled with the mixture powder in a high-temperature muffle furnace for high-temperature calcination;

step 12, grinding and uniformly mixing the calcined powder mixture sample in an agate mortar, pressing the mixture into round pieces with the diameter of phi 14.1mm multiplied by 7.5mm on a tablet press, overlapping the three pieces together, and placing the round pieces in a platinum crucible;

step 13, placing the platinum crucible filled with the wafer-shaped mixture sample in a high-temperature oxygen atmosphere furnace for high-temperature calcination;

step 14, selecting three overlapped disc-shaped samples in the middle, and grinding the samples into uniform sample powder in an agate mortar;

step 15, pressing the powder sample into a cylinder sample with phi 3.8mm multiplied by 3.5 mm;

step 16, pressing the talc and the brucite into round pieces according to the weight ratio of 10:1, placing the round pieces at two ends of a cylindrical sample, and placing the round pieces and the sample into a gold-palladium alloy sample tube;

and step 17, placing the gold-palladium alloy tube in a Kawai-1000t multi-surface top large-cavity press to perform high-temperature high-pressure reaction to obtain the high-titanium and high-water fayalite single crystal.

3. The method for producing a high-titanium and high-moisture fayalite single crystal according to claim 2, wherein: the method for placing the platinum crucible filled with the mixture powder in a high-temperature muffle furnace for high-temperature calcination comprises the following steps: placing in a high-temperature muffle furnace, raising the temperature to 1100 ℃ at the heating rate of 700 ℃/h, and roasting for 1.5 h.

4. The method for producing a high-titanium and high-moisture fayalite single crystal according to claim 2, wherein: step 13, the method for calcining the platinum crucible filled with the wafer-shaped mixture sample in the high-temperature oxygen atmosphere furnace at high temperature comprises the following steps: raising the temperature to 1600 ℃ at the temperature rise rate of 800 ℃/hour, and roasting for 25 hours; after roasting, the experimental sample in the high-temperature oxygen atmosphere furnace is cooled to room temperature at the cooling rate of 140 ℃/hour, and a sample piece is taken out.

5. The method for producing a high-titanium and high-moisture fayalite single crystal according to claim 2, wherein: step 16, the method for pressing the talc and the brucite into a circular piece according to the weight ratio of 10:1, placing the circular piece at two ends of the cylindrical sample, and placing the circular piece and the sample into the gold-palladium alloy sample tube comprises the following steps: placing talc and brucite which provide a water source and have a weight ratio of 10:1 on a tablet press to be pressed into two water source pieces with the diameter of phi 3.8mm and the diameter of 0.15mm, sequentially placing the two water source pieces at two ends of a cylindrical sample, and sealing the cylindrical sample and the two water source pieces in a gold-palladium alloy sample tube with the diameter of phi 3.8mm, the inner diameter of phi 4.0mm and the wall thickness of 0.1 mm.

6. The method for producing a high-titanium and high-moisture fayalite single crystal according to claim 2, wherein: the high-temperature high-pressure reaction method in the step 17 comprises the following steps: placing the gold-palladium alloy tube on a Kawai-1000t multi-surface top large-cavity press, setting the pressure rise rate and the temperature rise rate to be 2.0 GPa/hour and 50 ℃/minute respectively, raising the pressure and the temperature to be 7.0GPa and 1150 ℃ respectively, and carrying out hot-pressing sintering for 16 hours at constant temperature and constant pressure; after the constant temperature and the constant pressure are carried out for 16 hours, the temperature in the sample cavity is reduced from 1150 ℃ to room temperature at the cooling rate of 10 ℃/minute; after the temperature in the sample cavity is reduced to the room temperature, reducing the pressure in the sample cavity from 7.0GPa to normal pressure at the pressure reduction rate of 0.70 GPa/h; completing the high-temperature high-pressure reaction.

7. The method for producing a high-titanium and high-moisture fayalite single crystal according to claim 6, wherein: during high-temperature and high-pressure reaction, the temperature in the high-pressure sample cavity is calibrated by B-type high-temperature platinum-rhodium noble metal thermocouples, each group of high-temperature platinum-rhodium noble metal thermocouples is composed of two platinum-rhodium alloy wires with different materials, and the chemical components of the positive electrode (BP) of the thermocouple are as follows: pt_70％Rh_30％(ii) a Negative electrode (BN) chemical composition of thermocouple: pt_94％Rh_6％(ii) a The diameter of each corresponding positive and negative electrode platinum rhodium alloy wire is 0.2mm, and each group of high-temperature platinum rhodium noble metal thermocouples are symmetrically arranged on the upper side and the lower side of the outer wall of the sample cavity of the gold-palladium alloy tube, so that temperature calibration in the sample cavity is realized.

Technical Field

The invention belongs to the technical field of mineral single crystal sample synthesis under high temperature and high pressure conditions, and particularly relates to a preparation method of a high-titanium and high-water content forsterite single crystal.

Background

With the rapid development of human science and the continuous innovation of technology, the heat tide of deep space exploration is raised in many countries in the world; human beings have all obtained a big margin to the internal matter formation of mars, circle layer structure and evolution history. The previous internal structure research of the spark shows that the spark has a ring layer structure: mars crust (meaning the depth of the inside of the Mars from the earth's surface to 60km, corresponding pressure and temperature: 0-0.6GPa and 210-60km to 1596km, corresponding pressure and temperature: 0.6GPa-19GPa and 366K-1880K) and mars ground core (meaning the depth inside the mars is from 1596km to 3390km, corresponding pressure and temperature: 19GPa-36GPa and 1880K-2055K). The main rock-making mineral composition of the martian mantle is fayalite, pyroxene and garnet, wherein the most important composition mineral fayalite has a molecular formula shown in the specification: (Mg)_(1-x),Fe _x)₂SiO₄) Wherein x is the molar ratio of iron and magnesium, i.e. x ═ Mg/(Mg + Fe). The existing research proves that the molar coefficient ratio of iron and magnesium in olivine on different stars such as the earth, the moon, the mars and the like has obvious difference, and the molar coefficient ratio of iron and magnesium in magnesium fayalite on the upper mantle on the earth is 0.1; in the lunar slow magnesium fayalite from the moon, the iron-magnesium molar coefficient ratio is 0.17; in the forsterite magnesium from the spark mantle on mars, the molar ratio of iron to magnesium is 0.25 or more. The geological sample of the moon returned to the earth carried by the human lunar exploration engineering probe is limited to the surface of the moon, and is rare and precious. Therefore, planet scientists artificially synthesize the mars mantle magferrite olivine with high iron content in a laboratory on the basis of the existing cognition on the internal matter composition of mars, and the mars mantle magferrite olivine has very important scientific significance for inverting the internal matter composition and the ring layer structure of the mars and disclosing the origin and evolution history of the mars.

As early as 1993, professor Harry Mcsreen, university of Tennessee, USA, in the research result published in Science, the experimental study of fused inclusion from SNC Martian meteorite (S: shergotite, pyroxene nonsphere meteorite; N: nakhlite, dittany nonsphere meteorite, C: chassignite, pure Olive nonsphere) was first reported, and the Martian mantle was first found to contain up to 1.4 wt% of water, which is the most important volatile component existing in the deep part of the Martian. In 2000, 200 of 6 ten thousand Mars photos sent back by the Mars Ring finder spacecraft of the United states space agency clearly showed the furrow caused by the water flow flowing through the meteorite crater. Because the atmosphere of the mars is very thin and the surface temperature is 63 ℃ below zero, the academic belief that "even if there is water on the mars, it can only exist in the form of ice" is completely broken. Water was present on the mars billions of years ago. The new discovery of the united states space agency proves that water is likely to exist on the fire stars, meaning that life bodies may exist on the fire stars.

In the spark mantle, traces of water (usually in the order of ppm) are present in the main diagenetic minerals at the depth of the spark mantle in the form of lattice point defects. The results of in-situ experiments and theoretical calculations of electromigration, ultrasonic wave velocity elasticity, thermophysical properties, synchrotron radiation X-ray diffraction, Raman spectrum, Brillouin scattering spectrum, infrared spectrum and the like of mineral rocks under high temperature and high pressure conditions, which are known by the predecessors, show that trace water contained in the mineral rocks can improve or reduce the physical migration properties by several orders of magnitude. In the martian mantle, water may be mainly found in important rock-forming minerals such as fayalite. It has been shown in the previous studies that natural forsterite from the upper mantle depth of the earth contains 50ppm wt% titanium and 100-200ppm wt% water, the transition metal element in natural olivine from the upper mantle depth of the moon has a titanium content of up to 2000-3000ppm wt% and is anhydrous, while natural olivine from the upper mantle depth of the moon may have a water content of 2000-3000ppm wt% and a titanium content of 3000-4000ppm wt%. High-titanium forsterite single crystals are generally obtained by a high-pressure hydrothermal synthesis method, however, until now, high-titanium forsterite single crystals are generally obtained by a high-pressure hydrothermal synthesis method, the highest titanium content in the titanium-containing olivine obtained by the prior art laboratory synthesis technology is less than 2100ppm wt%, and the synthesized experimental sample generally contains less than 1000 wt% of lattice structure water. The effective synthesis of forsterite single crystals matching the titanium content and water content existing in the spark mantle, i.e., 3000-4000ppm wt% titanium content and 2000-3000ppm wt% water content, becomes particularly urgent.

In conclusion, whether the natural olivine is adopted from the natural olivine in the earth upper mantle (containing 50ppm wt% of titanium and 100-200ppm wt% of water), or the natural olivine in the earth upper mantle (containing 3000ppm wt% of titanium and no water) on the moon, or the experimental sample containing titanium olivine (containing <2100ppm wt% of titanium and <1000ppm wt% of water) synthesized in the laboratory in the prior art cannot meet the scientific research requirements simulated in various high-temperature and high-pressure laboratories for the magueite in the aventum field (containing 3000-4000ppm wt% of titanium and 2000-3000ppm wt% of water), so that a preparation method of the magueite single crystal with high titanium and high water content needs to be invented.

The invention content is as follows:

the technical problem to be solved by the invention is as follows: provides a preparation method of a high-titanium and high-water content forsterite single crystal, which thoroughly solves the blank of the current high-titanium and high-water content martian mantle forsterite preparation technology so as to obtain large-particle high-titanium and high-water content forsterite single crystal experimental samples.

The technical scheme of the invention is as follows:

a method for preparing a high-titanium and high-water content forsterite single crystal, which comprises the following steps: preparing a mixture cylinder sample by taking solid magnesium nitrate hexahydrate powder, solid iron (III) nitrate nonahydrate powder, liquid ethyl orthosilicate and liquid tetrabutyl titanate as initial raw materials according to the stoichiometric theory of the magnesium-iron olivine; preparing a water source wafer of a mixture of talc and brucite in a weight ratio of 10:1 by taking solid natural talc powder and solid natural brucite powder as starting raw materials; placing water source wafers at two ends of the mixture cylinder sample; the mixture cylinder sample and the water source wafer are put into a gold-palladium alloy sample tube to carry out high-temperature high-pressure reaction to prepare the high-titanium and high-water content forsterite single crystal.

The preparation method of the high-titanium and high-water content forsterite single crystal specifically comprises the following steps:

step 1, selecting solid magnesium nitrate hexahydrate powder with the purity of more than 99.99 percent, solid iron (III) nitrate nonahydrate powder with the purity of more than 99.99 percent, liquid ethyl orthosilicate with the purity of more than 99.99 percent, liquid tetrabutyl titanate with the purity of more than 99.99 percent, and solid natural talc powder with the purity: 99 percent, the purity of solid natural brucite powder is more than 99 percent, and the concentration of absolute ethyl alcohol is more than 99.9 percent as initial raw materials;

step 2, putting 80 ml of absolute ethyl alcohol into a 500 ml wide-mouth glass bottle; 10 g of solid magnesium nitrate hexahydrate powder and 5.254 g of solid iron (III) nitrate nonahydrate powder were weighed out into 80 ml of anhydrous ethanol solution according to the magnesium-iron olivine stoichiometry;

step 3, according to the stoichiometric theory of the fayalite, 6.092 ml of liquid tetraethoxysilane and 30 microliter of liquid tetrabutyl titanate are respectively added into 80 ml of absolute ethyl alcohol solution by a pipette;

step 4, adding a magnetic stirring rotor into the wide-mouth bottle containing the absolute ethyl alcohol mixed solution of magnesium nitrate hexahydrate, ferric nitrate (III) nonahydrate, ethyl orthosilicate and tetrabutyl titanate, and sealing the mouth of the wide-mouth bottle by using a plastic film;

step 5, placing the sealed wide-mouth bottle on a high-temperature magnetic stirring hot plate, and stirring the high-temperature magnetic stirring hot plate for 22 hours at room temperature and at the rotating speed of 850 revolutions per minute;

step 6, adding 40 ml of 69-70% concentrated nitric acid solution into the mixed solution, and sealing the opening of the wide-mouth bottle;

step 7, binding countless uniform holes on the surface of the plastic film;

step 8, placing the wide-mouth bottle on a high-temperature magnetic stirring hot plate, increasing the temperature of the hot plate to 90 ℃, and stirring the mixed solution for 25 hours at the conditions of 90 ℃ and the rotating speed of 1100 r/min;

step 9, removing the plastic film of the sealing opening, and regulating the temperature of the high-temperature magnetic stirring hot plate to 140 ℃ until the mixed solution in the whole wide-mouth bottle is completely evaporated to dryness;

step 10, taking out the magnetic stirring rotor, taking out all mixed powder in the wide-mouth bottle by using a medicine spoon, and placing the powder in a platinum crucible;

step 11, placing the platinum crucible filled with the mixture powder in a high-temperature muffle furnace for high-temperature calcination;

step 12, grinding and uniformly mixing the calcined powder mixture sample in an agate mortar, pressing the mixture into round pieces with the diameter of phi 14.1mm multiplied by 7.5mm on a tablet press, overlapping the three pieces together, and placing the round pieces in a platinum crucible;

step 13, placing the platinum crucible filled with the wafer-shaped mixture sample in a high-temperature oxygen atmosphere furnace for high-temperature calcination;

step 14, selecting three overlapped disc-shaped samples in the middle, and grinding the samples into uniform sample powder in an agate mortar;

step 15, pressing the powder sample into a cylinder sample with phi 3.8mm multiplied by 3.5 mm;

step 16, pressing the talc and the brucite into round pieces according to the weight ratio of 10:1, placing the round pieces at two ends of a cylindrical sample, and placing the round pieces and the sample into a gold-palladium alloy sample tube;

and step 17, placing the gold-palladium alloy tube in a Kawai-1000t multi-surface top large-cavity press to perform high-temperature high-pressure reaction to obtain the high-titanium and high-water fayalite single crystal.

The method for placing the platinum crucible filled with the mixture powder in a high-temperature muffle furnace for high-temperature calcination comprises the following steps: placing in a high-temperature muffle furnace, raising the temperature to 1100 ℃ at the heating rate of 700 ℃/h, and roasting for 1.5 h.

Step 13, the method for calcining the platinum crucible filled with the wafer-shaped mixture sample in the high-temperature oxygen atmosphere furnace at high temperature comprises the following steps: raising the temperature to 1600 ℃ at the temperature rise rate of 800 ℃/hour, and roasting for 25 hours; after roasting, the experimental sample in the high-temperature oxygen atmosphere furnace is cooled to room temperature at the cooling rate of 140 ℃/hour, and a sample piece is taken out.

Step 16, the method for pressing the talc and the brucite into a circular piece according to the weight ratio of 10:1, placing the circular piece at two ends of the cylindrical sample, and placing the circular piece and the sample into the gold-palladium alloy sample tube comprises the following steps: placing talc and brucite which provide a water source and have a weight ratio of 10:1 on a tablet press to be pressed into two water source pieces with the diameter of phi 3.8mm and the diameter of 0.15mm, sequentially placing the two water source pieces at two ends of a cylindrical sample, and sealing the cylindrical sample and the two water source pieces in a gold-palladium alloy sample tube with the diameter of phi 3.8mm, the inner diameter of phi 4.0mm and the wall thickness of 0.1 mm.

The high-temperature high-pressure reaction method in the step 17 comprises the following steps: placing the gold-palladium alloy tube on a Kawai-1000t multi-surface top large-cavity press, setting the pressure rise rate and the temperature rise rate to be 2.0 GPa/hour and 50 ℃/minute respectively, raising the pressure and the temperature to be 7.0GPa and 1150 ℃ respectively, and carrying out hot-pressing sintering for 16 hours at constant temperature and constant pressure; after the constant temperature and the constant pressure are carried out for 16 hours, the temperature in the sample cavity is reduced from 1150 ℃ to room temperature at the cooling rate of 10 ℃/minute; after the temperature in the sample cavity is reduced to the room temperature, reducing the pressure in the sample cavity from 7.0GPa to normal pressure at the pressure reduction rate of 0.70 GPa/h; completing the high-temperature high-pressure reaction.

During high-temperature and high-pressure reaction, the temperature in the high-pressure sample cavity is calibrated by B-type high-temperature platinum-rhodium noble metal thermocouples, each group of high-temperature platinum-rhodium noble metal thermocouples is composed of two platinum-rhodium alloy wires with different materials, and the chemical components of the positive electrode (BP) of the thermocouple are as follows: pt_70％Rh_30％(ii) a Negative electrode (BN) chemical composition of thermocouple: pt_94％Rh_6％(ii) a The diameter of each corresponding positive and negative electrode platinum rhodium alloy wire is 0.2mm, and each group of high-temperature platinum rhodium noble metal thermocouples are symmetrically arranged on the upper side and the lower side of the outer wall of the sample cavity of the gold-palladium alloy tube, so that temperature calibration in the sample cavity is realized.

The invention has the beneficial effects that:

the invention organically combines the related subject backgrounds of deep substance science of mars, celestial chemistry, meteority, science of earth and planet, high-pressure mineral physics, isotope geochemistry and the like, namely the principle of slowly forming the high-titanium and high-water content fayalite under the redox condition of the mars mantle. The former high-pressure mineral physics and isotope geochemistry research data show that the titanium content in the depth range of the spark mantle can reach 3000-4000ppm wt% and the water content can reach 2000-3000ppm wt%. A laboratory Kawai-1000t multi-surface top large-cavity high-temperature high-pressure experimental device is adopted to simulate the formation process of high-titanium (3000-:

12[Mg(NO₃)₂·6H₂O]+4[Fe(NO₃)₃·9H₂O]+8C₈H₂₀O₄Si→8[(Mg_0.75,Fe_0.25)₂SiO₄]+36NH₃·H₂O+18H₂O+64CO+49O₂

(Mg_0.75,Fe_0.25)₂SiO₄+Ti(OCH₂CH₂CH₂CH₃)₄→[(Mg_0.75,Fe_0.25)₂(Si,Ti)O₄]+4CO+6CH₄+3C₂H₄

2[Mg₃(Si₄O₁₀)(OH)₂]→3Mg₂Si₂O₆+2SiO₂+2H₂OMg(OH)₂→MgO+H₂O

the invention selects magnesium nitrate hexahydrate of initial raw material solid under the conditions of high temperature and high pressure [ molecular formula: mg (NO)₃)₂·6H₂O]The essential magnesium element for synthesizing the forsterite single crystal is provided; iron (III) nitrate nonahydrate of the starting solid material [ formula: fe (NO)₃)₃·9H₂O]Provides the iron element essential for synthesizing the forsterite single crystal. Initial raw material of tetraethoxysilane (molecular formula: C)₈H₂₀O₄Si) which provides a silicon element essential for synthesizing the forsterite single crystal; tetrabutyl titanate (molecular formula: Ti (OCH))₂CH₂CH₂CH₃)₄) Provides the essential titanium element for synthesizing the forsterite single crystal. Selected starting material talc [ formula: mg (magnesium)₃(Si₄O₁₀)(OH)₂]Is a typical hydrous mineral, and can be dehydrated under the conditions of normal pressure and 430 ℃, and the dehydration product-enstatite (molecular formula: MgSiO: magnesium niobate oxide)₃) And quartz (molecular formula: SiO 2₂) The silicon activity in the high-pressure sample cavity can be well controlled, and a large amount of water is released at the same time. According to the existing temperature-pressure phase diagram of talc dehydration reaction under high temperature and high pressure conditions, the dehydration temperature of talc is 802.4 ℃ under the pressure of 7.0GPa set by the invention. The initial starting material chosen, brucite [ formula: mg (OH)₂]Also typical of the hydrous minerals, brucite undergoes a dehydration reaction at temperatures above 700 ℃ to produce periclase (formula: MgO) with the release of large amounts of water. Placing talcum and water-containing mineral in a certain proportion in a high-pressure sample cavityThe brucite can generate dehydration reaction under the conditions of high temperature and high pressure to generate a large amount of water, thereby providing a good water source for synthesizing the high-titanium and high-water content forsterite single crystal. Adding concentrated nitric acid into the reaction product to generate NH₃·H₂O、CO、CH₄、C₂H₄And O₂Are all volatile substances.

The invention needs to synthesize the fayalite single crystal with higher titanium content (3000-. In general, in natural olivines existing on the earth, magnesium at lattice positions can be homomorphically substituted with divalent metal elements such as iron, nickel, manganese, and calcium, thereby forming olivines such as fayalite, nickel olivine, manganese olivine, and calcium olivine, and also containing metal ion impurities of rare transition elements such as titanium, scandium, vanadium, and cadmium. Compared with natural samples, in the preparation process of the high-titanium and high-water content forsterite single crystal, the laboratory environment is pure, the sample is in a sealed environment and does not contact with impurities, the obtained high-titanium and high-water content forsterite single crystal is a pure substance and has good chemical stability, and important experimental sample guarantee is provided for measuring physical property parameters of the high-titanium and high-water content forsterite single crystal and particularly researching the preferred orientation of crystal lattices under high pressure.

Compared with the reported artificial synthesis method of the high-titanium and high-water content forsterite single crystal, the preparation method has the obvious advantages of simple operation process, short reaction time and the like, the obtained high-titanium and high-water content forsterite single crystal has the characteristics of high and controllable titanium content, high purity, large size, stable chemical performance and the like, the size of the single crystal can meet the requirements of high-temperature and high-pressure experimental samples such as diamond pressure chamber high-temperature and high-pressure experimental tests, single crystal Brillouin scattering, synchrotron radiation single crystal X-ray diffraction and the like, and the method provides important experimental sample guarantee for measuring the physical property parameters of the high-titanium and high-water content forsterite single crystal, particularly exploring crystal lattice optimization orientation research under high pressure, and breaks through the technical bottleneck of the synthesis of the existing high-titanium and high-water content forsterite single crystal.

The specific implementation mode is as follows:

a method for preparing a high-titanium and high-water content forsterite single crystal, which comprises the following steps: preparing a mixture cylinder sample by taking solid magnesium nitrate hexahydrate powder, solid iron (III) nitrate nonahydrate powder, liquid ethyl orthosilicate and liquid tetrabutyl titanate as initial raw materials according to the stoichiometric theory of the magnesium-iron olivine; preparing a water source wafer of a mixture of talc and brucite in a weight ratio of 10:1 by taking solid natural talc powder and solid natural brucite powder as starting raw materials; placing water source wafers at two ends of the mixture cylinder sample; the mixture cylinder sample and the water source wafer are put into a gold-palladium alloy sample tube to carry out high-temperature high-pressure reaction to prepare the high-titanium and high-water content forsterite single crystal.

The method comprises the following steps:

step 1, solid magnesium nitrate hexahydrate powder (purity: > 99.99%), solid iron (III) nitrate nonahydrate powder (purity: > 99.99%), liquid ethyl orthosilicate (purity: > 99.99%), liquid tetrabutyl titanate (purity: > 99.99%), solid natural talc powder (purity: > 99%), solid natural brucite powder (purity: > 99%) and anhydrous ethanol concentration (concentration: > 99.9%) were used as starting materials.

And 2, putting 80 ml of absolute ethyl alcohol into a 500 ml wide-mouth glass bottle.

Step 3, according to the magnesium iron olivine ((Mg)_0.75,Fe _0.25)₂(Si,Ti)O₄) Stoichiometry, accurately weigh 10 grams of high purity solid magnesium nitrate hexahydrate powder and 5.254 grams of high purity solid iron (III) nitrate nonahydrate powder on a high precision analytical balance and carefully add them to 80 milliliters of absolute ethanol solution.

And 4, according to the stoichiometric theory of the fayalite, carefully adding 6.092 ml of high-purity liquid tetraethoxysilane and 30 microliter of high-purity liquid tetrabutyl titanate into 80 ml of absolute ethanol solution by using a pipette gun.

And 5, adding a magnetic stirring rotor into the wide-mouth bottle containing the absolute ethyl alcohol mixed solution of magnesium nitrate hexahydrate, ferric nitrate (III) nonahydrate, ethyl orthosilicate and tetrabutyl titanate, and sealing the mouth of the wide-mouth bottle by using a thick plastic film with the thickness of 0.5 mm to prevent the initial solution in the wide-mouth bottle from being sprayed out in the high-speed stirring process, so that the accuracy of sample synthesis is influenced.

And 6, placing the wide-mouth bottle filled with the sealed initial mixed solution and the magnetic stirring rotor on a high-temperature magnetic stirring hot plate, and stirring the high-temperature magnetic stirring hot plate for 22 hours at room temperature and 850 revolutions per minute in order to dissolve the magnesium nitrate hexahydrate powder, the ethyl orthosilicate and the tetrabutyl titanate of the initial materials in the absolute ethanol solution so as to realize full dissolution and no residue between the materials.

And 7, opening the plastic film seal of the wide-mouth bottle, adding 40 ml of 69-70% concentrated nitric acid solution into the mixed solution for accelerating the magnesium-iron-olivine preparation reaction, and sealing the seal of the plastic film to avoid the initial solution in the wide-mouth bottle from splashing in the high-temperature stirring process, thereby influencing the synthesis precision of the sample.

Step 8, pricking small holes of 0.1mm on the surface of the film by using a sharp-pointed forceps so as to generate NH generated by the reaction₃·H₂O、CO、CH₄、C₂H₄And O₂When volatile matter volatilizees more easily, can also avoid simultaneously the concentrated nitric acid in the wide-necked bottle at the high-speed stirring process splash to influence the synthetic precision of sample.

And 9, placing the wide-mouth bottle on a high-temperature magnetic stirring hot plate, increasing the temperature of the hot plate to 90 ℃, and stirring the mixed solution at high temperature and high speed for 25 hours at the conditions of 80 ℃ and 1100 r/min to fully dissolve all the initial reagents in the mixed solution of the anhydrous ethanol and the concentrated nitric acid.

And 10, removing the sealing film of the sealing opening, increasing the temperature of the high-temperature magnetic stirring hot plate to 140 ℃ until the mixed solution in the whole wide-mouth bottle is completely evaporated to dryness.

And 11, taking out the magnetic stirring rotor, mixing all the powder in the wide-mouth bottle by using a medicine spoon, carefully taking out all the powder, and putting the powder in a platinum crucible.

And 12, placing the platinum crucible filled with the mixture powder in a high-temperature muffle furnace, raising the temperature to 1100 ℃ at the temperature rise rate of 700 ℃/hour, roasting for 1.5 hours, and mainly removing residual nitric acid and organic matters in the mixture powder through high-temperature calcination.

And step 13, slowly and naturally cooling to room temperature, and taking out mixture sample powder.

And step 14, grinding and uniformly mixing the calcined powder mixture sample in an agate mortar, pressing the mixture into a wafer with the diameter of 14.1mm multiplied by 7.5mm (height) on a tablet press, overlapping the three wafers together, and placing the wafer in a platinum crucible.

And step 15, placing the platinum crucible filled with the wafer-shaped mixture sample in a high-temperature oxygen atmosphere furnace, raising the temperature to 1600 ℃ at the temperature rise rate of 800 ℃/hour, and roasting for 25 hours. The high-temperature calcination process for controlling the oxygen atmosphere aims to: the invention realizes the synthesis of large-particle high-titanium dry forsterite single crystals and provides a purer initial mixture sample; the high-temperature calcination under the oxygen atmosphere condition can better control the valence states of the valence elements iron and titanium in the product; the relatively long roasting time ensures that all substances such as water, organic matters, nitric acid and the like possibly remained and influencing the preparation of the sample are volatilized.

And step 16, in order to ensure that the high-temperature experimental product is well stored and the electric furnace wire of the oxygen atmosphere furnace is protected, slowly cooling the experimental sample in the high-temperature oxygen atmosphere furnace to room temperature at the cooling rate of 140 ℃/hour, and taking out the sample piece.

And step 17, in order to avoid possible pollution to the surface of the sample in the high-temperature oxygen atmosphere sintering process of the sample, selecting three wafer-shaped samples overlapped together and arranged in the middle, and grinding the three wafer-shaped samples in an agate mortar to obtain uniform sample powder.

Step 18, placing it on a tablet press and pressing the powder sample into a cylinder of phi 3.8mm (diameter) x 3.5mm (height) to obtain a high water contentThe content of fayalite is 10:1 (molecular formula: Mg) by weight₃(Si₄O₁₀)(OH)₂) And brucite (molecular formula: mg (OH)₂) As a water source. Talc and brucite are the most typical hydrous minerals and are widely used in the most common water source-providing mineral combinations in high temperature and high pressure experimental simulations because they undergo dehydration reactions at temperatures below 900 ℃. The weight ratio of talc to brucite of 10:1 was chosen because talc, in the dehydrated product, in addition to releasing large amounts of water, also produced a large amount of enstatite, periclase and quartz mineral combination that could well control the silicon activity during the synthesis of high water content forsterite in the sample cavity under high temperature and pressure conditions.

And step 19, placing the talc and the brucite which provide the water source in a weight ratio of 10:1 on a tablet press, pressing the talc and the brucite into two round pieces with phi 3.8mm (diameter) multiplied by 0.15mm (thickness), sequentially placing the two round pieces at two ends of a sample, and sealing the sample and the two water source pieces (the talc and the brucite which provide the water source in a weight ratio of 10: 1) in a gold-palladium alloy sample tube with phi 3.8mm (inner diameter) multiplied by 4.0mm (height) and 0.1mm of wall thickness, wherein the gold-palladium alloy tube is an optimal sealing material which can effectively prevent water from escaping from the sample tube in the sample preparation process under the conditions of high temperature and high pressure.

Step 20, the fayalite is the most important constituent mineral of the martial mantle, in order to truly simulate the growth environment of the martial mantle fayalite and invert the temperature and pressure conditions of stable existence of the fayalite mineral phase, a gold-palladium alloy pipe filled with a sample and two water source pieces (talc and brucite which provide a weight ratio of water sources of 10: 1) is placed on a Kawai-1000t multi-surface top large cavity press, the pressure increasing rate and the temperature increasing rate are set to be 2.0 GPa/hour and 50 ℃/minute respectively, the pressure and the temperature are increased to be 7.0GPa and 1150 ℃ (the temperature and pressure range in the middle of the martial mantle) respectively, hot-pressing sintering is carried out, and the reaction time is constant temperature and constant pressure for 16 hours.

Step 21, the invention adopts B-type high-temperature platinum-rhodium noble metal thermocouple to accurately calibrate the temperature in the high-pressure sample cavity, and has the advantages of high accuracy, strong stability, wide temperature measurement range and long service lifeLong length, high upper limit of temperature measurement, and the like, and is widely applied to temperature measurement of glass, ceramics, industrial salt bath furnaces and the like. The high-temperature platinum-rhodium thermocouple is a noble metal thermocouple which is common in numerous high-temperature high-pressure mineral physics research laboratories at home and abroad, the highest temperature can be realized to be 2315 ℃, and each group of high-temperature platinum-rhodium noble metal thermocouples is composed of platinum-rhodium alloy wires with two different materials (chemical components of positive electrodes (BP) of the thermocouples: Pt)_70％Rh_30％(ii) a Negative electrode (BN) chemical composition of thermocouple: pt_94％Rh_6％(ii) a The diameter of each corresponding positive and negative electrode platinum rhodium alloy wire (BP and BN): 0.2mm), and each group of high-temperature platinum-rhodium noble metal thermocouples are symmetrically arranged on the upper side and the lower side of the outer wall of the sample cavity of the gold-palladium alloy tube, so that the temperature in the sample cavity can be accurately calibrated.

And step 22, under the condition of pressure of 7.0GPa, raising the temperature to 803 ℃, and sealing the talc and the brucite which are arranged at the two ends of the gold-palladium alloy sample tube and provide a water source and have the weight ratio of 10:1, so that dehydration reaction can be carried out, a large amount of water is released, and a good water source is provided. Meanwhile, the talc and the brucite are subjected to dehydration reaction to generate a large amount of combinations of enstatite, periclase and quartz minerals, and the mineral combinations can well control the silicon activity in the preparation process of the high-titanium and high-water content forsterite in the sample cavity under the conditions of high temperature and high pressure.

And 23, after the temperature and the pressure are constant for 16 hours, reducing the temperature in the sample cavity from 1150 ℃ to room temperature at a cooling rate of 10 ℃/minute, and compared with the heating rate (50 ℃/minute) of sample preparation, the crystal growth of the large-particle olivine single crystal is facilitated at a slower constant-pressure cooling rate.

And 24, reducing the pressure in the sample cavity from 7.0GPa to normal pressure at a pressure reduction rate of 0.70 GPa/h after the temperature in the sample cavity is reduced to room temperature.

And 25, after the high-temperature and high-pressure preparation reaction is finished, taking out the obtained experimental sample from the sample cavity, opening the gold-palladium alloy sample tube by adopting a diamond slicer, and selecting the forsterite single crystal under a high-power Olive microscope.

The obtained forsterite single crystalIs a single phase without any other impurity phase; the molecular formula of the obtained forsterite single crystal is (Mg) according to the detection result of an Electron Probe (EPMA)_0.75,Fe_0.25)₂SiO₄(ii) a The content of the obtained forsterite single crystal titanium is 3389ppm wt% according to the detection result of a multifunctional ion mass spectrometer (ICP-MS); as a result of vacuum Fourier transform infrared spectroscopy (FT-IR) detection, the obtained forsterite single crystal has an extremely high water content of 2530ppm wt%.

The obtained high-titanium and high-water content forsterite single crystal is an orthorhombic system, the space group is Pnma (No.62), and the lattice parameter isUnit cell volume ofThe average particle size was 185 microns and the maximum particle size was 432 microns.

The high-titanium and high-water content forsterite single crystal obtained by the invention has the advantages of high purity, large size, stable chemical property and the like, and particularly, the titanium content is high and controllable. By changing the amount of the chemical reagent added as the starting material of liquid tetrabutyl titanate from 26.5564 microliters to 35.4085 microliters, the titanium content in the corresponding obtained forsterite single crystal sample from 3000ppm wt% to 4000ppm wt% was finally achieved. The total water amount generated by the dehydration reaction of the hydrous mineral enclosed in the gold-palladium alloy sample tube is controlled by changing the weight ratio of the hydrous mineral natural talc powder and the natural brucite powder which provide water sources and the different heights of the two corresponding water source pieces, and finally the water content in the high titanium-containing and high water-containing forsterite single crystal samples is adjusted. The obtained high-titanium and high-water content forsterite single crystal can completely meet the simulation requirement of the physical property experiment of the high-titanium minerals of the martian mantle, breaks through the technical bottleneck of the synthesis of the existing high-titanium and high-water content forsterite single crystal, and provides important experimental sample support for researching the preferred orientation of the mineral crystal lattice of the martian mantle area under the conditions of high temperature and high pressure.