Preparation method of high density, high compactness, high purity and large bulk polycrystalline lepidolite

Abstract

This invention discloses a method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite. The method involves grinding single-crystal pyrophyllite particles into pyrophyllite sample powder, compacting and sealing it under a vacuum of 10... –3 The sample was encased in a steel sheath measuring 55.91 mm (outer diameter) × 87.94 mm (height) × 3 mm (wall thickness). The steel sheath was placed inside the graphite furnace cylinder of the high-pressure vessel in a hot isostatic pressing (HIP) apparatus and sealed with a graphite cap. Using argon as the pressure transmission medium, a multi-gradient cylinder heating and pressurization method was employed to raise the temperature inside the sample chamber to 720 °C and the pressure to 101.3 MPa, and then maintain the temperature and pressure for 5.2 hours. A multi-gradient cylinder cooling and depressurization method was then employed to lower the temperature inside the sample chamber by 171 °C and the pressure to 71.4 MPa. The pressure was then released to room temperature to obtain a polycrystalline pyrophyllite polymer. This method filled the technical gap in the preparation of bulk experimental samples of high-density polycrystalline pyrophyllite polymers under high temperature and high pressure conditions.

Description

Technical Field

[0001] This invention belongs to the field of aluminosilicate mineral sample synthesis technology, and particularly relates to a method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite. Background Technology

[0002] Oxygen-containing minerals are a large class of salt compounds whose crystal lattice framework is mainly composed of oxygen-containing acid complex anions and metal cations. Based on the type of oxygen-containing acid complex anions that compose oxygen-containing minerals, such as [SiO4]... 4– [CO3] 2– [SO4] 4– [PO4] 4– Oxygen-containing salt minerals are mainly classified into silicate minerals (pyrophyllite, olivine, orthopyroxene, garnet, etc.), carbonate minerals (calcite, dolomite, siderite, aragonite, etc.), sulfate minerals (gypsum, barite, celestite, alunite, etc.), and phosphate minerals (apatite, lapis lazuli, uranium phosphate, magnesium phosphate, etc.). A comparison of the simple mineral anions (O2) that compose minerals is also important. 2– S 2– F 1– Cl 1– Oxyacid complex anions in oxygen-containing minerals (such as...) have large ionic radii and are distributed in various shapes, including triangles and tetrahedra, on a plane. The central cations constituting the interior of oxygen-containing minerals generally have high valence and small ionic radii, and are mainly bonded to the complex anions by ionic bonds, thus forming independent structural units in the mineral crystal structure. Oxyacid minerals typically exhibit excellent physicochemical properties, such as insolubility in water, high hardness, high melting point, good thermal insulation, vitreous luster (metallic and submetallic lusters are also common), and non-conductivity. Oxyacid minerals are widely distributed in the middle and lower crust and upper mantle of the Earth. Existing geological data shows that oxygen-containing minerals account for about two-thirds of all known minerals, thus they are considered by geologists to be one of the most widely distributed groups of minerals in the deep Earth. Oxyacid mineral materials have extremely wide applications in important sectors of the national economy, such as metallurgy, ceramics, chemicals, building materials, and gemstones.

[0003] Pyrophyllite (chemical formula: Al2(Si4O3)2) is a widely found, common oxygen-containing salt mineral in nature, a typical talc group mineral, rich in water and layered aluminosilicate end-member minerals. 10Pyrophyllite (Al₂O₃)(OH)₂ is a hydrous aluminum silicate mineral commonly exposed in deep subduction zones of the Earth. It is also a major mineral component of traditional seal stones and carving stones such as Shoushan stone, Qingtian stone, and Changhua stone. Based on its mineralogical composition, pyrophyllite can be further subdivided into phyllite-rich pyrophyllite, diaspore-rich pyrophyllite, kaolinite-rich pyrophyllite, and siliceous pyrophyllite. It has a dioctahedral layered structure, and low-symmetry crystal structures in monoclinic and orthorhombic systems are relatively common. The chemical composition of its mineralogical oxides by weight percentage can be expressed as: Al₂O₃ / (Al₂O₃+SiO₂+H₂O)=28.3%, SiO₂ / (Al₂O₃+SiO₂+H₂O)=66.7%, and H₂O / (Al₂O₃+SiO₂+H₂O)=5.0%. Naturally occurring pyrophyllite exhibits perfect cleavage along the {001} crystal face, displaying mineral colors such as white, light green, pale yellow, or light gray. It commonly occurs in platy, scaly, petal-like, or massive forms, exhibiting a vitreous or greasy luster, conchoidal fracture, and a soft, inelastic texture with low hardness. In the pyrophyllite crystal structure, the trivalent central cation aluminum (Al)... 3+ ), can be Fe 3+ Replacement, forming an equivalent class of isomorphic substitution; it can also be replaced by Na + K + Mg 2+ Fe 2+ Ca 2+ Si 4+ The substitution by monovalent, divalent, or tetravalent cations results in unequal isomorphic substitution, and this composition is rich in trivalent iron (Fe). 3+ The end-member component of pyrophyllite, also known as iron pyrophyllite, is found in the latest research. + K + Mg 2+ Fe 2+ Ca 2+ Fe 3+ Si 4+ (etc.) replace the central cationic aluminum (Al) 3+ Al is mainly formed in the form of charge compensation, occupying lattice sites. 3+ and Si 4+The mechanism of alteration is as follows. Geologically, under low-to-medium temperature hydrothermal geological processes, pyrophyllite is mainly a type of low-grade metamorphic mineral formed by hydrothermal alteration of aluminum-rich intermediate-acidic magmatic rocks or tuff, commonly found in metamorphic rocks such as phyllite and crystalline schist. For pyrophyllite, a product of low-temperature alteration of acidic magmatic rocks, pyrophyllization occurs, forming a co- or associated mineral assemblage of silicate, carbonate, oxide, and sulfide minerals of varying compositions, including quartz, kaolinite, dolomite, mica, kyanite, zoisite, diaspore, chlorite, alunite, pyrite, and rutile. The resulting pyrophyllite ore bodies exhibit a distinct spatial zonation, progressing from the center to the edge through diaspore alteration, pyrophyllization, silicification, and weak alteration of the surrounding rock. Large / super-large pyrophyllite deposits of significant economic value have been discovered in areas such as Mentougou (Beijing), Qingtian (Zhejiang), and Shoushan (Fujian) in my country.

[0004] To investigate the formation mechanisms and occurrence paths of common geological hazards deep within the Earth, such as volcanoes, earthquakes, and debris flows, geologists typically employ high-pressure equipment with multiple large cavities, including hydrothermal autoclaves, piston cylinder presses, and rotary shear friction testing machines, to conduct simulation experiments on the solubility, friction coefficient, shear stress, and other physical parameters of large-volume polycrystalline pyrophyllite polymers under high temperature and pressure conditions. Obtaining a large-sized polycrystalline pyrophyllite polymer sample (45.18 mm diameter × 73.59 mm height) is a crucial step in simulating these physical properties under high temperature and pressure conditions. Geologists typically use natural pyrophyllite found in the field instead of polycrystalline pyrophyllite as experimental samples. However, natural pyrophyllite has many drawbacks, including low sample density, a large number of impurity minerals (such as silicate minerals, carbonate minerals, oxide minerals, and sulfide minerals of different compositions, including quartz, kaolinite, dolomite, mica, kyanite, zoisite, diaspore, chlorite, alunite, pyrite, and rutile), large and unevenly distributed single crystal grains of the main pyrophyllite components, difficulty in eliminating optimal lattice orientation, and significant anisotropy of crystal axes. Consequently, many different high-temperature and high-pressure mineral and rock property simulation teams around the world use natural pyrophyllite as the initial sample and employ multi-faceted large-cavity high-pressure equipment such as hydrothermal autoclaves, piston cylinder presses, and rotary shear friction testers. The experimental data on the physical properties of natural pyrophyllite under high-temperature and high-pressure conditions obtained show significant differences, making it difficult to widely apply these experimental results to the interpretation of the formation mechanisms and occurrence mechanisms of geological disasters such as volcanoes, earthquakes, and debris flows.

[0005] Existing technologies utilize quasi-hydrostatic presses such as the YJ-3000t and Kawai-1000t to prepare artificially synthesized island-shaped silicate mineral single crystal experimental samples under high temperature and high pressure conditions, as seen in patent {Dai Lidong and Hu Haiying. Chinese National Invention Patent: A method for preparing low-titanium dry forsterite single crystals under high temperature and high pressure conditions. Patent No.: ZL202111317925.5}. However, this method is limited to preparing island-shaped silicate mineral single crystal experimental samples rather than polycrystalline aggregate samples. The obtained island-shaped silicate mineral single crystals range in size from 100 micrometers to 425 micrometers, with uneven particle size distribution. The size of the obtained single crystal minerals is severely limited by the sample chamber volume. The cylindrical sample size of the high-temperature and high-pressure experimental product—single crystal island-shaped silicate minerals—obtained by this method does not exceed 6 mm (bottom diameter) × 6 mm (height). Therefore, the size of the artificially synthesized island-shaped silicate mineral samples cannot meet the requirements for simulating the physical properties of minerals and rocks under high temperature and high pressure conditions in large-volume experiments. Although existing techniques, using quasi-hydrostatic presses such as the YJ-3000t and Kawai-1000t, can produce samples only a few millimeters in size, they are a relatively effective method for synthesizing single-crystal mineral samples under high temperature, high pressure, and quasi-hydrostatic conditions. However, when this method is applied to the synthesis of bulk polycrystalline pyrophyllite aggregates (e.g., with a diameter greater than 40 mm), the top and bottom of the pyrophyllite powder inevitably experience significant asymmetric shrinkage due to unidirectional compression during the high temperature, high pressure, and quasi-hydrostatic experiments. This results in numerous macroscopic void defects during the preparation of bulk polycrystalline mineral aggregate samples. These macroscopic void defects cause wrinkles or pores in the central part of the cross-section of the bulk polycrystalline pyrophyllite aggregate, ultimately making the sample prone to severe porosity or aggregation along the center of the wrinkles or pores. This is the unavoidable shrinkage and porosity effect during the synthesis of bulk polycrystalline mineral aggregate samples under high temperature, high pressure, and quasi-hydrostatic conditions. The shrinkage and porosity effects of these polycrystalline pyrophyllite polymer samples lead to severe excessive deformation, resulting in numerous voids, folds, and cavities in the bulk polycrystalline pyrophyllite polymer samples. This significantly affects the preparation results of the bulk polycrystalline pyrophyllite polymer samples. Therefore, neither natural pyrophyllite nor small-sized (no more than 6 mm) pyrophyllite single crystal samples obtained in the laboratory can meet the minimum experimental sample size requirements for mineral and rock property simulation on multi-faceted, large-cavity high-pressure equipment such as hydrothermal autoclaves, piston cylinder presses, and rotary shear friction testing machines. To date, there is still no effective synthesis method.Therefore, it is particularly urgent to effectively synthesize a high-density, high-compactness, high-purity, and large-volume polycrystalline pyrophyllite aggregate experimental sample that meets the needs of various high-temperature and high-pressure laboratory simulations in earth science research, especially for experimental simulation studies of the physical properties of large-volume layered oxygen-containing salt mineral aggregates—polycrystalline water-rich aluminosilicate minerals and rocks—under high-temperature and high-pressure conditions, such as solubility, friction coefficient, and shear stress. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite, thereby filling the technical gap in the preparation of bulk experimental samples of high-compact polycrystalline pyrophyllite polymers under high temperature and high pressure conditions. This method aims to obtain bulk high-compact polycrystalline pyrophyllite polymer experimental samples, providing important experimental sample support for the experimental simulation study of the solubility, friction coefficient, shear stress, and other properties of bulk layered oxygen-containing salt mineral polymers—polycrystalline water-rich aluminosilicate minerals and rocks—under high temperature and high pressure conditions on multi-faceted large-cavity high-pressure equipment such as hydrothermal autoclaves, piston cylinder presses, and rotary shear friction testers.

[0007] The technical solution of this invention is:

[0008] A method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite includes: grinding pyrophyllite single-crystal particles into pyrophyllite sample powder; compacting and sealing the pyrophyllite sample powder under a vacuum of 10... –3 The sample chamber was encased in a steel sheath measuring 55.91 mm (outer diameter) × 87.94 mm (height) × 3 mm (wall thickness). The steel sheath was placed inside the graphite furnace cylinder of the high-pressure vessel in a hot isostatic pressing (HIP) apparatus and sealed with a graphite cap. Using argon as the pressure transmission medium, a multi-gradient cylinder heating and pressurization method was employed to raise the temperature inside the sample chamber to 720 °C and the pressure to 101.3 MPa, and then maintain the temperature and pressure for 5.2 hours. A multi-gradient cylinder cooling and depressurization method was then employed to lower the temperature inside the sample chamber to 171 °C and the pressure to 71.4 MPa. Finally, the pressure was released and the sample was cooled to room temperature to obtain the polycrystalline pyrophyllite polymer.

[0009] Methods for preparing pyrophyllite sample powder include:

[0010] Step 1: Select square-shaped pyrophyllite single crystal mineral particles. The smallest particle size of the selected pyrophyllite single crystal is 5.8 mm, and the largest particle size is 13.6 mm.

[0011] Step 2: Place the selected pyrophyllite single crystal particles on an ultrasonic cleaner and use acetone, alcohol and deionized water as cleaning solutions in sequence for ultrasonic cleaning for 20 minutes.

[0012] Step 3: Select 235 grams of pyrophyllite single crystal particles that are complete in crystal form, uniform in color (grayish-white), fresh in surface, and free of impurities.

[0013] Step 4: Place the pyrophyllite single crystal particles in a vacuum drying oven at 200 degrees Celsius and dry for at least 36 hours;

[0014] Step 5: Crush the pyrophyllite single crystal particles into mineral single crystal particles with a particle size of less than 2 mm;

[0015] Step 6: Grind the mineral single crystal particles into fine-grained pyrophyllite sample powder with a particle size of 14.32 micrometers to 25.01 micrometers;

[0016] Step 7: Pack the pyrophyllite sample powder into a sealed paper bag and dry it in a vacuum drying oven at 85 degrees Celsius for 9 days.

[0017] The preparation method of the steel cladding includes: Step 8, selecting a continuous casting slab of No. 20 low carbon steel with a wall thickness of 3 mm as the initial raw material for the sleeve of the steel cladding, heating it to 200 °C, and then using a roughing mill and a finishing mill to cool it to a set temperature through laminar flow, and then coiling it into a steel strip coil by a coiler, and then going through 3 rolling and multiple hot rolling processes of trimming, finally obtaining a sleeve of the steel cladding with dimensions of 55.91 mm (outer diameter) × 87.94 mm (height) × 3 mm (wall thickness); selecting a continuous casting slab of No. 20 low carbon steel with a wall thickness of 3 mm as the initial raw material for the steel cladding cap, and using the same multiple hot rolling process, preparing the upper sealing cap and the lower sealing cap of the steel cladding.

[0018] The pyrophyllite sample powder was compacted and sealed under a vacuum of 10. –3 The method in the steel cladding of Pa includes: Step 9, firstly, vacuum welding the sleeve and lower sealing cap of the steel cladding, then placing the dried pyrophyllite sample powder inside the steel cladding, and then completely sealing the pyrophyllite sample powder under a vacuum of 100 kJ / m². –3 In the steel cladding of Pa; the high-temperature degassing temperature is 400 °C.

[0019] The argon gas used as the pressure transmission medium has a purity of 99.999%; the formula for calculating the amount of argon gas consumed is as follows:

[0020] ;

[0021] ;

[0022] In the formula: The target pressure for preparing polycrystalline pyrophyllite polymer samples under hot isostatic pressing is determined based on the target temperature of the hot isostatic pressing experiment. Perform calculations; t represents the internal pressure of the inert gas argon cylinder; t represents the number of 40-liter argon cylinders with a purity of 99.999% required to complete a single hot isostatic pressing experiment on a polycrystalline pyrophyllite polymer sample under high temperature and high pressure conditions.

[0023] The beneficial effects of this invention are:

[0024] This invention organically combines general geology, magmatic petrology, crystallography, dynamics of Earth's structural evolution, ore field tectonic geology, crystal defect chemistry, meteoritics and Earth's origin, engineering geology, optical mineralogy, isotope geochemistry, genetic mineralogy, mining geology, introduction to geophysics, rock mechanics, mineralogy, petrography, geochemistry, ore deposit geology, mineral resource geology, sedimentary petrology, metamorphic petrology, regional field geology, structural geology, stratigraphy, geochronology, and experimental petrology. With a background in Earth science disciplines such as geochemistry, ore genesis, rock rheology, geodynamics, hot isostatic pressing, hot isostatic powder metallurgy, seismology, igneous magmatism, high-pressure rheology, mineral physics, deep Earth science, high-pressure materials science, materials science, and high-pressure experimental mineralogy, this team used an RD80×100‒2000–200 double 2000-type hot isostatic pressing equipment to prepare large-volume, highly dense polycrystalline pyrophyllite aggregate experimental samples under high temperature and high pressure conditions.

[0025] The initial raw material selected for this invention is gem-quality single-crystal pyrophyllite particles collected in the field, which are crushed into uniform mineral single-crystal powder. The powder is placed in a steel sheath and subjected to a series of processes including compaction, vacuuming, high-temperature degassing, high-temperature vacuum welding, argon filling, and furnace washing to ensure that the pyrophyllite sample powder is in a completely sealed environment protected by argon inert gas. The steel sheath containing the pyrophyllite sample powder is placed in the sample chamber of an RD80×100‒2000–200 double 2000 type hot isostatic pressing equipment, and sintered under high temperature and high pressure to form a large-volume, highly dense polycrystalline pyrophyllite aggregate. The prepared polycrystalline pyrophyllite aggregate sample can be widely used in the experimental simulation research of diagenesis and mineralization of mineral and rock physicochemical properties under high temperature and high pressure conditions.

[0026] The steel sheath used in the hot isostatic pressing (HIP) experiment of this invention has the following dimensions: 55.91 mm (outer diameter) × 87.94 mm (height) × 3 mm (wall thickness). This allows for the acquisition of large-sized polycrystalline pyrophyllite polymer samples with a diameter of up to 45.18 mm and a height of up to 73.59 mm. During the HIP experiment on the polycrystalline pyrophyllite polymer samples under high temperature and high pressure conditions, inert argon gas is used as the pressure transmission medium. By increasing the temperature and compressing the inert argon gas, uniform pressure and temperature are applied to the pyrophyllite sample powder in all directions, effectively avoiding the adverse effects of shrinkage cavities and porosity during the HIP experiment. The inert argon gas ensures complete isolation between the pyrophyllite sample powder and air within the sample chamber, effectively preventing redox reactions between the pyrophyllite sample powder and air during the HIP experiment. Furthermore, this invention avoids the traditional high-pressure chemical reaction method, which may introduce excessive chemical reagents during the preparation of polycrystalline pyrophyllite polymer samples, potentially leading to the introduction of impurity ions.

[0027] This invention employs a multi-gradient hot isostatic pressing (HIP) process, first increasing pressure and then increasing temperature, to prepare polycrystalline pyrophyllite polymer experimental samples with excellent physicochemical properties such as fine crystal size, high density, and high purity. This breakthrough overcomes the technical bottleneck of synthesizing large-volume experimental samples of high-density polycrystalline pyrophyllite polymers. Furthermore, this invention's multi-gradient HIP process is not limited by the shape and size of the sample, allowing for the preparation of complex polycrystalline mineral samples with irregular shapes. Compared to existing technologies that use quasi-hydrostatic presses such as the YJ-3000t and Kawai-1000t to prepare artificially synthesized island-shaped silicate mineral single crystals under high temperature and high pressure conditions, this invention's multi-gradient HIP process can obtain polycrystalline pyrophyllite polymer experimental samples with near-theoretical density and extremely high sample strength.

[0028] This invention, based on an RD80×100‒2000–200 dual 2000-type hot isostatic pressing (HIP) device, employs a multi-gradient HIP molding process involving first increasing pressure and then increasing temperature. For the first time, it yields large-volume, uniformly distributed, high-density, highly compact, and high-strength polycrystalline pyrophyllite aggregate experimental samples under conditions of 101.3 MPa and 720 °C. These samples can be widely applied to high-pressure equipment with multiple large cavities, such as hydrothermal autoclaves, piston cylinder presses, and rotary shear friction testing machines, to simulate the solubility, friction coefficient, and shear stress of large-volume layered oxygen-containing salt mineral aggregates—polycrystalline water-rich aluminosilicate mineral rocks—under high temperature and high pressure conditions. This provides crucial experimental sample support for systematically exploring the formation mechanisms and occurrence principles of common geological disasters such as deep-earth volcanoes, earthquakes, and debris flows. Attached Figure Description

[0029] Figure 1 To utilize the RD80×100‒2000–200 double 2000 type hot isostatic pressing equipment, and adopt a multi-gradient hot isostatic pressing molding process of first increasing pressure and then increasing temperature, the temperature and pressure in the sample chamber during the preparation of polycrystalline pyrophyllite polymer are shown in the curves of temperature and pressure changes over time in the sample chamber.

[0030] Figure 2 To obtain fine-grained pyrophyllite sample powder through crushing and grinding using a jaw crusher (model: BB 200) and a high-efficiency Retsch disc vibratory mill (model: RS200), optical microscopic observation results of pyrophyllite samples before hot isostatic pressing experiments were obtained using a high-precision Olympus SZX16 research-grade stereomicroscopic imaging platform.

[0031] Figure 3 This document presents the optical microscopic observation results of the surface morphology and particle size distribution of a polycrystalline pyrophyllite polymer sample obtained from a hot isostatic pressing experiment at 101.3 MPa and 720 °C, using the high-precision Olympus SZX16 research-grade stereomicroscopy platform. Detailed Implementation

[0032] A method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite polymers, comprising:

[0033] Step 1: Square block-shaped pyrophyllite single crystal mineral particles were used as the initial sample. The high-precision Olympus SZX16 research-grade stereomicroscopy imaging platform was used to accurately measure the particle size of the initial sample. The smallest particle size of the pyrophyllite single crystal was 5.8 mm and the largest particle size was 13.6 mm. If the mineral grain size of pyrophyllite single crystals is too large, only a low-magnification, high-precision Olympus SZX16 research-grade stereomicroscopy platform can be used for sample selection, making it difficult to accurately identify high-purity pyrophyllite single crystals free of other symbiotic / associated minerals and impurities. If the mineral grain size of pyrophyllite single crystals is too small, it is difficult to effectively separate pyrophyllite single crystals from silicate minerals, carbonate minerals, oxide minerals, and sulfide minerals of different compositions, such as quartz, kaolinite, dolomite, mica, kyanite, zoisite, diaspore, chlorite, alunite, pyrite, and rutile. Furthermore, this invention requires the selection of mineral single crystals with a relatively large weight, which will consume a lot of time and manpower.

[0034] Step 2: Place the selected pyrophyllite single crystal particles on an ultrasonic cleaner, and use acetone, alcohol and deionized water as cleaning solutions in sequence for ultrasonic cleaning for 20 minutes to remove impurities from the sample surface.

[0035] Step 3: Under the high-magnification, high-precision Olympus SZX16 research-grade stereomicroscopic imaging platform, 235 grams of pyrophyllite single crystal particles with complete crystal form, uniform grayish-white color, fresh surface and no other impurity minerals were carefully selected to ensure that the initial sample of pyrophyllite single crystal particles had high purity before the hot isostatic pressing experiment under high temperature and high pressure conditions.

[0036] Step 4: Place the carefully selected pyrophyllite single crystal particles in a vacuum drying oven at 200 degrees Celsius for at least 36 hours to completely remove adsorbed water from the sample surface. If the temperature is too low, a certain amount of adsorbed water may adhere to the surface of the pyrophyllite crystals, making it difficult to accurately weigh the initial sample pyrophyllite single crystal particles during further grinding. If the temperature is too high, it may cause a decomposition reaction in the pyrophyllite single crystals, ultimately severely affecting the preparation effect of the hot isostatic pressing experimental sample under high temperature and high pressure conditions.

[0037] Step 5: Place the initial sample of pyrophyllite single crystal particles on a jaw crusher (model: BB 200), set the instrument's drive power to 1.5 kW, and use a crushing time of 3 minutes to crush the pyrophyllite single crystal particles into mineral single crystal particles with a particle size of less than 2 mm. The purpose is to fully crush the sample to obtain medium-sized (less than 2 mm) pyrophyllite single crystal particles.

[0038] Step 6: Place the sample on a high-efficiency Retsch disc vibratory mill (model: RS200), using a high-speed mode of 1200 rpm and setting the instrument's drive power to 1.5 kW. Grind the mineral single crystal particles into fine-grained pyrophyllite mineral powder with a particle size of 14.32 μm to 25.01 μm (see...). Figure 2 The amount of single-crystal pyrophyllite sample ground in a single cycle is 100 grams, and the grinding time is 5 minutes. Pyrophyllite powder within this particle size range has a large specific surface area (surface area per unit weight of mineral powder), which significantly increases the contact area between particles due to pressure and temperature. This is more conducive to forming a strong bonding force between the particles of pyrophyllite powder during the hot isostatic pressing experiment of this invention, thereby greatly improving the compactness and density of the prepared fine-grained polycrystalline pyrophyllite polymer sample.

[0039] Step 7: Pyrophyllite sample powder with relatively fine particle size easily absorbs water in the air. Therefore, it is placed in a paper sealed bag and dried in a vacuum drying oven at 85 degrees Celsius for 9 days to completely remove the adsorbed water on the surface of the sample powder.

[0040] Step 8: In the process of preparing polycrystalline pyrophyllite polymer samples using an RD80×100‒2000–200 double 2000 type hot isostatic pressing (HIP) equipment, a sample steel sheath was prepared using low-carbon steel of No. 20 steel. No. 20 steel refers to steel with a carbon content between 0.17% and 0.23%. The low-carbon steel (No. 20 steel) sheath selected in this case has the following main superior properties: (1) The low-carbon steel (No. 20 steel) sheath does not react with the pyrophyllite sample powder, avoiding contamination of the sample during the HIP experiment and directly affecting the preparation effect; (2) The low-carbon steel (No. 20 steel) sheath can withstand the temperature of 720 °C and pressure of 101.3 required for the preparation of polycrystalline pyrophyllite polymer samples under the HIP conditions of this invention. MPa; (3) The steel sheath material of low carbon steel (20 steel) has good air tightness, which ensures that the pyrophyllite sample powder will not leak under high temperature, high pressure and argon gas pressure transmission medium conditions, and can also ensure the sealing of the steel sheath and the sealing of the weld during the vacuum exhaust process. All these properties are very reliable; (4) The steel sheath of low carbon steel (20 steel) also has excellent properties such as relatively easy edge rolling, cutting, processing, deformation and good welding performance.

[0041] This invention selects a continuously cast slab of No. 20 low-carbon steel with a wall thickness of 3 mm as the initial raw material for the steel cladding. After heating it to 200 °C, it is cooled to the set temperature by laminar flow using a roughing mill and a finishing mill. It is then rolled into a steel strip coil by a coiler, and then undergoes multiple hot rolling processes including three rolling and edge trimming to finally obtain the cladding for the hot isostatic pressing test of pyrophyllite sample powder with dimensions of 55.91 mm (outer diameter) × 87.94 mm (height) × 3 mm (wall thickness).

[0042] Similarly, a continuously cast slab of No. 20 low-carbon steel with a wall thickness of 3 mm was selected as the initial raw material for the steel cladding cover. The same hot rolling process was used to prepare the upper and lower sealing covers of the steel cladding. The sleeve, upper and lower sealing covers were welded together by high-temperature vacuum welding to prepare a complete steel cladding for the hot isostatic pressing experiment of pyrophyllite sample powder.

[0043] Step 9: First, vacuum weld the sleeve and lower sealing cap of the steel cladding. Then, place the dried pyrophyllite sample powder inside the steel cladding. After a series of processes including compaction, vacuuming, high-temperature degassing, and high-temperature vacuum welding, the pyrophyllite sample powder is completely sealed in a vacuum of 10... –3 Pa is in the steel ladle sleeve.

[0044] Achieving such a low vacuum level within the steel-clad cavity requires at least 51 hours of evacuation, while simultaneously degassing the sample at 400 °C to ensure the pyrophyllite powder is completely in a sealed vacuum environment and that all moisture is removed. The pyrophyllite powder sealed within the steel cladding must be thoroughly compacted. –3 The series of processes, including extremely low vacuum, 400 °C high-temperature degassing, and high-temperature vacuum welding, are mainly aimed at: (1) ensuring that the pyrophyllite sample powder is fully compacted, which can ensure that a sufficient amount of pyrophyllite sample powder is sealed in the steel sleeve, which will help increase the density of the polycrystalline pyrophyllite polymer of the hot isostatic pressing test product, thereby greatly improving the preparation effect of the final product bulk polycrystalline pyrophyllite polymer sample; (2) ensuring that the pyrophyllite sample powder is fully compacted, which can ensure the filling amount of pyrophyllite sample powder sealed in the steel sleeve, which will help enhance the compactness between pyrophyllite sample powder particles, effectively avoiding excessive deformation of the sample during the hot isostatic pressing test, thereby greatly improving the compactness of the final product bulk polycrystalline pyrophyllite polymer sample; (3) maintaining 10 –3 The extremely low vacuum of Pa ensures that the steel sheath is easily deformed under high temperature and high pressure, thereby uniformly transmitting the high pressure borne by the steel sheath to the pyrophyllite sample powder inside it; (4) Under the condition of 400 °C, the pyrophyllite sample powder is degassed at high temperature, completely removing any water vapor that may be present in the sample powder; (5) The steel sheath is welded by high temperature vacuum, which effectively isolates the welding head from direct contact with air, and the high temperature oxidation of the metal welding point can be completely avoided, which will greatly enhance the sealing performance of the steel sheath.

[0045] Step 10: Carefully place the steel sleeve containing the pyrophyllite sample powder into the graphite furnace cylinder of the high-pressure vessel of the hot isostatic pressing (HIP) equipment, and cover it with the graphite sealing cap. This invention uses an RD80×100‒2000–200 double 2000-type HIP equipment to densify the pyrophyllite sample powder under high temperature and high pressure conditions. The graphite furnace cylinder is the core component of this equipment and also the heating element that achieves the extremely high sample chamber temperature of 2000 degrees Celsius.

[0046] Step 11: Turn on the main power switch, dedicated computer automatic program, exhaust fan and argon concentration detection alarm of the RD80×100‒2000–200 dual 2000 type hot isostatic pressing equipment in sequence. Because the hot isostatic pressing (HIP) equipment operates at a power of 30 kW / hour, it is an ultra-high-power, high-temperature, and high-pressure instrument. Therefore, to ensure the safety of the experimental operators, the main power switch must be kept off when the equipment is not in operation. To ensure automatic control and arbitrary adjustment of temperature and pressure during HIP experiments, a dedicated computer-controlled software program has been developed for this instrument. A dual-pipeline high-power exhaust system is used to prevent leakage of the inert argon gas pressure transmission medium during the HIP experiment of polycrystalline pyrophyllite polymer samples under high temperature and pressure. Excessive argon concentration in the operating space could lead to asphyxiation for the operators. A high-sensitivity laboratory-specific argon concentration monitoring alarm is used. Its main purpose is to monitor the argon concentration in the sealed laboratory space during the operation of the HIP equipment in real time. Abnormal changes in argon concentration in the sealed space can also determine the operating status of high-pressure argon in the pipes and lines of the high-pressure device, ensuring the absolute safety of the operators during HIP experiments.

[0047] This invention uses argon as an inert gas as the pressure transfer medium. Argon is chosen because it is a colorless, tasteless, odorless, non-toxic, chemically stable, and thermally conductive inert gas. Compared with nitrogen, argon has more stable chemical properties and can completely maintain the chemical composition and process performance of the prepared material, thereby greatly improving the repeatability of the preparation molding process and the reliability of the product performance. However, in the hot isostatic pressing experiment, the main drawbacks of choosing nitrogen as the pressure transfer medium are as follows: (1) Under high temperature and high pressure conditions, nitrogen inevitably reacts with various metals or alloys, especially for samples containing multiple active metals such as titanium, aluminum, and zirconium. The samples will be nitrided, and a nitride layer will be formed on the surface of the sample, which will seriously change the mechanical properties and chemical composition of the prepared product; (2) When preparing oxide ceramics (such as alumina, zirconium oxide, etc.) or many other functional ceramics through hot isostatic pressing, if nitrogen is chosen as the pressure transfer medium, nitrogen can easily enter the crystal in the form of defects or vacancies during the high temperature and high pressure experiment. (3) Nitrogen used in industrial applications often contains trace amounts of water, carbon dioxide and oxygen. If the purification is incomplete or incomplete, the oxidation, denitrification and decarbonization reactions of the sample will be accelerated during the high temperature and high pressure experiment, which will seriously affect the physicochemical properties of the sample product. (4) Although nitrogen has a lower cost advantage compared to argon, for high-value-added hot isostatic pressing workpieces such as aerospace parts and medical implants, the aviation safety cost, health cost and scrap loss cost caused by the nitriding reaction are far greater than the gas pressure transmission medium cost of the hot isostatic pressing experiment itself. Compared with hydrogen, argon can be mixed with oxygen in the air in any proportion, and hydrogen may also cause an explosion hazard under high temperature and high pressure. Compared with other common inert gases such as helium and neon, argon has unique advantages such as good thermal conductivity and lower price.

[0048] This invention uses high-purity argon gas with a purity of 99.999% as the pressure transmission medium. Its main purpose is to: (1) inject argon gas into the cylinder through a high-pressure pipeline and with the help of a booster pump, and then heat it in the cylinder by a high-temperature resistant graphite furnace. The isotropic temperature and pressure will be uniformly transmitted to the pyrophyllite sample powder compaction to complete the hot isostatic pressing experiment; (2) Argon gas has excellent thermal conductivity, so the temperature distribution in the furnace is relatively uniform; (3) Selecting high-purity inert gas argon gas isolates other gases in the environment and can completely avoid the steel cladding from being oxidized during the hot isostatic pressing experiment; (4) Selecting high-purity inert gas argon gas plays an important protective role for the core component of the RD80×100‒2000–200 double two thousand type hot isostatic pressing equipment - the graphite heating element, and extends its service life.

[0049] Step 12: In this invention, argon is selected as the pressure transmission medium. During the preparation of polycrystalline pyrophyllite polymers on an RD80×100‒2000–200 dual 2000-type hot isostatic pressing (HIP) device, a multi-gradient HIP molding process of first increasing pressure and then increasing temperature is employed. Given that the initial material of this invention is a mineral powder that is difficult to mold, using argon as the inert gas pressure transmission medium and selecting a multi-gradient HIP molding process of first increasing pressure and then increasing temperature can greatly improve the density and compactness of bulk polycrystalline pyrophyllite polymer products.

[0050] This invention employs a multi-gradient hot isostatic pressing (HIP) process, first increasing pressure and then increasing temperature, to synthesize bulk experimental samples of high-density, high-compactness, and high-purity polycrystalline pyrophyllite polymers. The target pressure and temperature for the HIP experiment are 101.3 MPa and 720 °C, respectively. If the selected target pressure and temperature are too low, the steel sleeve used to seal the pyrophyllite sample powder during the HIP experiment will not be sufficiently compressed and effectively deformed, making it difficult for the sample to be fully compacted and sintered. This severely affects the preparation effect of the experimental product—bulk, high-density, and high-compact polycrystalline pyrophyllite polymer samples. Conversely, if the selected target pressure and temperature are too high, the polycrystalline, water-rich aluminosilicate mineral—pyrophyllite—will undergo a decomposition reaction during the HIP experiment, thus having an extremely adverse effect on the prepared polycrystalline pyrophyllite polymer product.

[0051] This invention uses argon gas as the pressure transmission medium. The target pressure and temperature values ​​are obtained by inputting argon gas into a gas cylinder. Therefore, before the hot isostatic pressing (HIP) experiment of pyrophyllite sample powder, it is necessary to accurately calculate the amount of argon gas required for the target pressure and temperature values. Through multiple repeatable low-temperature high-pressure empty furnace HIP experiments, high-temperature low-pressure empty furnace HIP experiments, and high-temperature high-pressure empty furnace HIP experiments of pyrophyllite sample powder, precise temperature and pressure calibration of the pyrophyllite sample chamber is performed. Finally, based on the RD80×100‒2000–200 dual 2000-type HIP equipment, high-purity inert argon gas is selected as the pressure transmission medium to complete the sample preparation for a single large-volume polycrystalline pyrophyllite polymer HIP experiment. The formula for calculating the amount of argon gas consumed is as follows:

[0052] (1)

[0053] (2)

[0054] In the formula: parameter P target The target pressure for preparing polycrystalline pyrophyllite polymer samples under hot isostatic pressing is based on the target temperature (T) of the hot isostatic pressing experiment. target ) Perform the calculation; parameter P bottleThe pressure inside the cylinder represents the inert gas argon; parameter t represents the number of 40-liter large-volume and high-purity inert gas argon (purity: 99.999%) cylinders required to complete a single hot isostatic pressing experiment on a polycrystalline pyrophyllite polymer sample under high temperature and high pressure conditions.

[0055] Step 13, vacuuming, filling with argon gas and cleaning the furnace, the purpose of which is to completely remove the air from the sample chamber. The specific operation steps are as follows: (1) Vacuuming: turn on the gas vacuum pump control switch to evacuate the air in the high-pressure sample chamber that is directly connected to the gas vacuum pump. When the detection value of the vacuum degree instrument digital display reaches 10 –4 (1) When the pressure reaches 15 MPa, turn off the gas vacuum pump; (2) Fill the cylinder directly connected to the high-purity inert gas argon with argon gas, and stop filling the pressure medium when the pressure in the sample chamber reaches 15 MPa; (3) Clean the furnace: turn on the gas vacuum pump and pump the vacuum in the sample chamber to 10 MPa. –4 MPa, repeated evacuation and filling three times, thus completely removing all the air from the sample chamber.

[0056] Step 14: Pre-pressurization of the sample chamber. Specific operation steps: (1) Calculate the amount of inert argon gas according to Formula 1 and Formula 2. In order to achieve the target pressure of 101.3 MPa and the target temperature of 720 °C, at least 4 argon cylinders with an internal pressure of 15 MPa are required; (2) Fill the argon cylinders with an internal pressure of 15 MPa evenly into the high-pressure pressurization tank of the hot isostatic pressing equipment. Then, through the high-pressure delivery pipeline, fill the cylinder with argon gas from the high-pressure pressurization tank, so that the pressure of the high-pressure pressurization tank and the pressure in the cylinder are balanced; (3) Turn on the diaphragm compressor and pump all the remaining argon gas in the high-pressure tank into the pyrophyllite sample chamber of the cylinder, so that the pre-pressurization of the sample chamber in the cylinder is pressurized to 59.8 MPa.

[0057] Step 15: Multi-gradient cylinder block heating and pressurization (see...) Figure 1Taking into account the target pressure and temperature for preparing polycrystalline pyrophyllite polymer samples in the hot isostatic pressing (HIP) experiment, as well as the safety, reliability, and durability of the graphite heating element itself, a multi-gradient cylinder heating and pressurization HIP procedure was precisely controlled and automatically adjusted. The specific steps are as follows: Within the temperature range of room temperature–600 °C, a heating rate of 18.17 °C / min and a pressurization rate of 0.99 MPa / min were used to raise the temperature in the cylinder sample chamber to 600 °C and the pressure to 89.4 MPa; Within the medium temperature range of 600 °C–620 °C, a heating rate of 2 °C / min and a pressurization rate of 0.65 MPa / min were used to raise the temperature in the cylinder sample chamber to 620 °C and the pressure to 95.9 MPa, and the temperature and pressure were maintained at constant temperature and pressure for 1.0 hour to ensure that the hydrous layered silicate mineral pyrophyllite was fully compacted and cemented; After maintaining constant temperature and pressure for 1.0 hour, the temperature and pressure were further increased in the high temperature range of 620 °C–720 °C. Within a temperature range of °C, using a heating rate of 5 °C / min and a pressurization rate of 0.27 MPa / min, the temperature inside the sample chamber was increased to 720 °C and the pressure to 101.3 MPa. As the temperature increased, the argon gas inside the sealed cylinder expanded dramatically, while the cylinder volume remained constant, meaning the argon gas volume was uniformly compressed, thus generating uniform high pressure. Ultimately, the pressure inside the sample chamber was maintained at 101.3 MPa. The pyrophyllite sample powder was then held at this temperature and pressure for 5.2 hours under the conditions of 101.3 MPa and 720 °C. Pyrophyllite is one of the important hydrous minerals in subduction zones, exhibiting typical C1 or C2 / m space group and low-symmetry monoclinic / orthorhombic crystal systems, as well as relatively complex crystal morphology, distinct lattice preferred orientations, and anisotropic physicochemical properties.

[0058] This invention employs a multi-gradient hot isostatic pressing (HIP) process, involving prior pressurization followed by heating, to prepare polycrystalline pyrophyllite polymer samples. During the pressurization and heating process, the samples are held at 620 °C and 720 °C for 1.0 hour and 5.2 hours respectively, ensuring sufficiently long stepped holding times. If the holding time is too short, it is difficult to form strong bonding forces between the low-symmetry and diverse crystalline pyrophyllite mineral particles, and it is also difficult to overcome the adverse effects of the preferred lattice orientation and anisotropy of the pyrophyllite minerals, thus affecting the density and strength of the final bulk polycrystalline pyrophyllite polymer sample. Conversely, if the holding time is too long, although a highly dense and strong polycrystalline pyrophyllite polymer can be obtained, the final bulk polycrystalline pyrophyllite polymer sample will experience particle growth, uneven particle distribution, and recrystallization under prolonged high temperature and high pressure, severely affecting the preparation effect and resulting in higher experimental costs.

[0059] Step 16: Multi-gradient cylinder cooling and depressurization. After the pyrophyllite sample powder was kept at 101.3 MPa and 720 °C for 5.2 hours, the temperature inside the cylinder sample chamber was reduced to 620 °C and the pressure to 96.1 MPa at a cooling rate of 5 °C / min and a depressurization rate of 0.26 MPa / min, and kept at the same temperature and pressure for 1.0 hour. After 1.0 hour of constant temperature and pressure, the cylinder temperature inside the sample chamber was reduced to 171 °C and the pressure to 71.4 MPa at a relatively slow cooling rate of 12.14 °C / min and a relatively slow depressurization rate of 0.67 MPa / min. Compared with the pressurization process, a slower cooling and depressurization rate was used mainly because if the cooling and depressurization rates were too fast, the internal stress of the steel casing would not be fully released, which would lead to the fragmentation and damage of the bulk polycrystalline pyrophyllite polymer product, thus seriously affecting the preparation effect.

[0060] This invention selects a sample chamber cylinder temperature of 171 °C because this temperature falls within the safe temperature range (160 °C–180 °C) that the RD80×100‒2000–200 dual 2000-type hot isostatic pressing (HIP) equipment can withstand direct pressure relief. If the sample chamber cylinder temperature exceeds 180 °C, the resulting excessive internal pressure in the sample chamber could easily damage the graphite heating furnace and may also cause a safety accident with the HIP equipment. Conversely, if the sample chamber cylinder temperature is below 160 °C, the resulting excessively low internal pressure in the sample chamber makes it difficult to ensure that the argon inert pressure-transmitting medium sealed within the sample chamber is completely expelled during the pressure relief process in the HIP experiment.

[0061] Step 17, Depressurization. First, allow the argon gas in the hot isostatic pressing (HIP) cylinder to flow freely back to the high-pressure pressurization tank through the pipeline. Then, when the cylinder pressure and the high-pressure pressurization tank pressure reach equilibrium, turn on the diaphragm compressor to vent the gas in the cylinder and discharge all residual gas through the pipeline.

[0062] Step 18, Cooling. After all the inert argon gas in the pipeline has been completely removed, the cooling system connected to the hot isostatic pressing furnace body continues to be turned on, and the natural cooling program is started to reduce the temperature inside the furnace from 171 °C to room temperature (~25 °C).

[0063] Step 19: Set the control program for the hot isostatic pressing (HIP) equipment, open the furnace chamber, carefully remove the polycrystalline pyrophyllite polymer steel-clad workpiece sealed after the HIP experiment, and accurately measure the dimensions of the steel cladding after the HIP forming experiment: 51.18 mm (outer diameter) × 83.59 mm (height). Compare the volume of the steel cladding before the HIP experiment and calculate the volume shrinkage rate (η) of the steel cladding before and after the HIP experiment. 钢包套 Its calculation formula can be expressed as: η 钢包套 =(V实验前钢包套 –V 实验后钢包套 ) / V 实验前钢包套 The shrinkage rate (η × 100%) is 20.35%. This invention exhibits such a large volumetric shrinkage rate (η) of the steel sheath. 钢包套 =20.35%), confirming that the steel sleeve used to seal and encapsulate the pyrophyllite sample powder underwent sufficient compression and effective deformation during the hot isostatic pressing experiment.

[0064] Step 20: Using a high-speed diamond saw blade cutter with a 1.0 mm thick diamond blade, the polycrystalline pyrophyllite polymer sample was carefully peeled from the steel ladle. The weight of the sample after the experiment was accurately measured to be 234 grams, and the tare weight of the steel ladle was 500 grams. This indicates that the weight of the pyrophyllite sample remained essentially unchanged before and after the multi-gradient hot isostatic pressing (HIP) experiment, which involved increasing pressure followed by increasing temperature. Further precise measurements were taken of the dimensions of the polycrystalline pyrophyllite polymer sample obtained after the HIP experiment: 45.18 mm (diameter) × 73.59 mm (height). Comparing the initial volume of pyrophyllite powder encapsulated in the steel ladle before the HIP experiment, the volume shrinkage rate (η) of the sample before and after the HIP experiment was calculated. 叶蜡石 Its calculation formula can be expressed as: η 叶蜡石 =(V 实验前叶蜡石 –V 实验后叶蜡石 ) / V 实验前叶蜡石 The volume shrinkage rate (η × 100%) is 22.63%. This invention achieves such a large volume shrinkage rate (η × 100%) for pyrophyllite sample powder. 叶蜡石 =22.63%), confirming that during the hot isostatic pressing experiment, the pyrophyllite sample powder placed in the steel cladding was fully compacted and sintered under high temperature and high pressure conditions.

[0065] This invention utilizes an RD80×100‒2000–200 dual 2000-type hot isostatic pressing (HIP) apparatus to synthesize a polycrystalline pyrophyllite polymer from the initial material—a single-phase pyrophyllite single crystal—which is then crushed into medium-sized pyrophyllite single crystal particles, ground into fine-grained pyrophyllite powder, and finally synthesized into the final product. A multi-gradient HIP process, involving prior pressurization followed by heating, is employed to prepare high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite polymers. No other impurity phases are introduced during the entire preparation process, and the purity of the resulting polycrystalline pyrophyllite polymer samples can reach 100%.

[0066] Under epoxy resin embedding protection, a representative sample (20 mm × 20 mm cross-section) was cut from the polycrystalline pyrophyllite polymer workpiece, a product of the hot isostatic pressing experiment. The sample underwent epoxy resin embedding protection, cutting, grinding, and surface polishing. Using a high-precision Olympus SZX16 research-grade stereomicroscopic imaging platform, the surface morphology and particle size distribution characteristics of the polycrystalline pyrophyllite polymer sample were tested. The test results are shown in (see...). Figure 3The polycrystalline pyrophyllite polymer exhibits clear grain boundary continuity, with minimal differences in the proportion of sample particles of different sizes, demonstrating a distinctly uniform particle size distribution. This invention utilizes a fully sealed steel sheath and inert argon gas pressure transmission medium throughout the hot isostatic pressing (HIP) experiment, ensuring the sample powder remains in a closed vacuum environment. This effectively isolates the polymer from gases such as nitrogen, oxygen, and water vapor, thus achieving uniform particle distribution, no particle growth, and no recrystallization. Compared to existing technologies that use quasi-hydrostatic presses such as the YJ-3000t and Kawai-1000t to synthesize island-shaped silicate mineral single crystals under high temperature and high pressure, this invention employs a multi-gradient HIP process that first increases pressure and then increases temperature, effectively overcoming numerous drawbacks of polycrystalline pyrophyllite polymer products, including particle growth, uneven particle distribution, and recrystallization.

[0067] High-resolution scanning electron microscopy was used to observe the microstructure of the polycrystalline pyrophyllite polymer sample obtained from the hot isostatic pressing experiment, and precise density tests were performed. The obtained polycrystalline pyrophyllite polymer had a density as high as 99.8%, exhibiting extremely high compactness. In the hot isostatic pressing (HIP) experiment, this invention improves the following specific experimental scheme to ensure the acquisition of highly dense polycrystalline pyrophyllite polymer samples: (1) a higher pre-pressurization pressure (59.8 MPa); (2) a multi-gradient gradually decreasing cylinder heating mode, namely, in the low-temperature zone of the HIP experiment (room temperature–600 °C), the heating rate is 18.17 °C / min; in the medium-temperature zone (600 °C–620 °C), the heating rate is 2 °C / min; and in the high-temperature zone (620 °C–720 °C), the heating rate is 5 °C / min; (3) a multi-gradient gradually decreasing cylinder pressure mode, namely, in the low-pressure zone of the HIP experiment (59.8 MPa–89.4 MPa), the pressure rate is 0.99 MPa / min; and in the medium-pressure zone (89.4 MPa–95.9 MPa), the pressure rate is 0.99 MPa / min. Under pressure of MPa, the pressurization rate is 0.65 MPa / min and under pressure of 95.9 MPa–101.3 MPa, the pressurization rate is 0.27 MPa / min; (4) a multi-gradient, slower cylinder cooling mode, that is, under temperature of 720 °C–620 °C in the high-temperature zone of the thermo-isostatic pressure test, the cooling rate is 5 °C / min and under temperature of 620 °C–171 °C in the medium-low temperature zone, the cooling rate is 12.14 °C / min; (5) a multi-gradient, slower cylinder depressurization mode, that is, under pressure of 101.3 MPa–96.1 MPa in the high-pressure zone of the thermo-isostatic pressure test, the depressurization rate is 0.26 MPa / min; under pressure of 96.1 MPa–71.4 MPa in the medium-low pressure zone, the depressurization rate is 0.67 MPa / min. MPa / min; (6) Multi-gradient cylinder constant temperature and pressure mode, that is, when the temperature and pressure during the heating and pressurization process of the hot isostatic pressure test are 620 °C and 95.9 MPa, the constant temperature and pressure is maintained for 1.0 hours; at the highest temperature (720 °C) and the highest pressure (101.3 MPa), the constant temperature and pressure is maintained for a sufficiently long time of 5.2 hours; when the temperature is reduced to 620 °C and the pressure is 96.1 MPa, the constant temperature and pressure is maintained for 1.0 hours.All these optimized and improved hot isostatic pressing (HIP) experimental schemes can promote sufficient diffusion and particle aggregation between pyrophyllite sample powders during HIP, eliminate the adverse effects of dendritic formation between sample powders, and thus form a uniform equiaxed grain structure; they can also promote the uniform isotropic temperature and pressure transfer during HIP, prevent the occurrence of local weaknesses or cracks, and thus greatly improve the compactness of the polycrystalline pyrophyllite polymer samples produced by HIP. In addition, this invention applies a higher temperature (720 °C), a higher pressure (101.3 MPa), and a sufficiently long heat and pressure holding time (5.2 hours) to promote the formation of good bonding force between the particles of pyrophyllite sample powder, thereby greatly improving the density and strength of the polycrystalline pyrophyllite polymer sample produced by hot isostatic pressing. It also effectively overcomes the unavoidable temperature gradient, pressure gradient, and many adverse factors such as pores, voids, cracks, and healing defects in the prepared experimental product that exist in the existing technology for synthesizing island silicate mineral single crystals by using quasi-hydrostatic presses such as YJ-3000t and Kawai-1000t.

[0068] The Archimedes method using organically combined secondary deionized water and the water intrusion method for porous complex structures were employed to accurately measure the density of polycrystalline pyrophyllite polymer samples obtained from hot isostatic pressing experiments. The measured density of the polycrystalline pyrophyllite polymer was 2.87 g / cm³. 3 This density value falls exactly within the theoretical density of 2.65 g / cm³ of naturally collected pyrophyllite, as measured by geologists. 3 –2.90 g / cm 3Within the specified range, the obtained bulk polycrystalline pyrophyllite polymer samples exhibited extremely high density. The achievement of such high-density polycrystalline pyrophyllite polymer products is highly related to the optimized molding process employed during this hot isostatic pressing experiment, including pretreatment of the pyrophyllite sample powder raw material, selection of No. 20 steel sample cladding, a reasonable cooling and depressurization hot isostatic pressing molding process, and high-temperature degassing at 400 °C. The pyrophyllite sample powder raw material pretreatment, namely fine-grained pyrophyllite mineral powder with a particle size of 14.32 μm to 25.01 μm, is used. Pyrophyllite in this particle size range has a large specific surface area, which significantly increases the contact area between sample particles, making it more conducive to the formation of strong and good cementing force, thereby greatly improving the density of the prepared polycrystalline pyrophyllite polymer sample. A 3 mm thick 20# low-carbon steel continuous casting slab is used as the steel cladding, possessing excellent physical properties such as low strength, low hardness, high plasticity, and good toughness. This allows the high pressure borne by the steel cladding to be uniformly transferred to the pyrophyllite sample powder enclosed within it, thus greatly improving the density of the prepared polycrystalline pyrophyllite polymer sample. An optimized and improved hot isostatic pressing process is adopted, especially using a multi-gradient, relatively slow cylinder pressure increase and decrease mode (pressurization rate: 0.27 MPa / min – 0.99 MPa / min; depressurization rate: 0.26 MPa / min – 0.67 MPa / min). (MPa / min) ensures that the internal stress of large-volume polycrystalline pyrophyllite polymer workpieces is fully released, effectively overcoming the adverse effects of delamination, cracks, and fissures in the sample product, and greatly improving the density of the polycrystalline pyrophyllite polymer sample. A high-temperature degassing optimization molding process at 400 °C is used, sealing the pyrophyllite sample powder in a steel sleeve and performing high-temperature vacuum degassing at 400 °C to minimize gas residue, thereby obtaining polycrystalline pyrophyllite polymer experimental samples with a very uniform density distribution under hot isostatic pressing. In contrast, existing technologies, such as the synthesis of island silicate mineral single crystals using quasi-hydrostatic presses like the YJ-3000t and Kawai-1000t, inevitably generate internal friction due to the unidirectional pressing, leading to uneven density distribution and delamination problems in the experimental product.

Claims

1. A method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite, characterized in that: The method includes: grinding pyrophyllite single crystal particles into pyrophyllite sample powder; compacting and sealing the pyrophyllite sample powder under a vacuum of 10... –3 The sample chamber was encased in a steel sheath measuring 55.91 mm (outer diameter) × 87.94 mm (height) × 3 mm (wall thickness). The steel sheath was placed inside the graphite furnace cylinder of the high-pressure vessel in a hot isostatic pressing (HIP) apparatus, and a graphite sealing cap was placed on top. Using argon as the pressure transmission medium, a multi-gradient cylinder heating and pressurization method was employed to raise the temperature inside the sample chamber to 720 °C and the pressure to 101.3 MPa, and the temperature and pressure were maintained for 5.2 hours. A multi-gradient cylinder cooling and depressurization method was then employed to lower the temperature inside the sample chamber to 171 °C and the pressure to 71.4 MPa. Finally, the pressure was released and the sample was cooled to room temperature to obtain the polycrystalline pyrophyllite polymer.

2. The method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite according to claim 1, characterized in that: Methods for preparing pyrophyllite sample powder include: Step 1: Select square-shaped pyrophyllite single crystal mineral particles. The smallest particle size of the selected pyrophyllite single crystal is 5.8 mm, and the largest particle size is 13.6 mm. Step 2: Place the selected pyrophyllite single crystal particles on an ultrasonic cleaner and use acetone, alcohol and deionized water as cleaning solutions in sequence for ultrasonic cleaning for 20 minutes. Step 3: Select 235 grams of pyrophyllite single crystal particles that are complete in crystal form, uniform in color (grayish-white), fresh in surface, and free of impurities. Step 4: Place the pyrophyllite single crystal particles in a vacuum drying oven at 200 degrees Celsius and dry for at least 36 hours; Step 5: Crush the pyrophyllite single crystal particles into mineral single crystal particles with a particle size of less than 2 mm; Step 6: Grind the mineral single crystal particles into fine-grained pyrophyllite sample powder with a particle size of 14.32 micrometers to 25.01 micrometers; Step 7: Pack the pyrophyllite sample powder into a sealed paper bag and dry it in a vacuum drying oven at 85 degrees Celsius for 9 days.

3. The method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite according to claim 1, characterized in that: The preparation method of the steel cladding includes: Step 8, selecting a continuous casting slab of No. 20 low carbon steel with a wall thickness of 3 mm as the initial raw material for the sleeve of the steel cladding, heating it to 200 °C, and then using a roughing mill and a finishing mill to cool it to a set temperature through laminar flow, and then coiling it into a steel strip coil by a coiler, and then going through 3 rolling and multiple hot rolling processes of trimming, finally obtaining a sleeve of the steel cladding with dimensions of 55.91 mm (outer diameter) × 87.94 mm (height) × 3 mm (wall thickness); selecting a continuous casting slab of No. 20 low carbon steel with a wall thickness of 3 mm as the initial raw material for the steel cladding cap, and using the same multiple hot rolling process, preparing the upper sealing cap and the lower sealing cap of the steel cladding.

4. The method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite according to claim 1, characterized in that: The pyrophyllite sample powder was compacted and sealed under a vacuum of 10. –3 The method in the steel cladding of Pa includes: Step 9, firstly, vacuum welding the sleeve and lower sealing cap of the steel cladding, then placing the dried pyrophyllite sample powder inside the steel cladding, and then completely sealing the pyrophyllite sample powder under a vacuum of 100 kJ / m². –3 In the steel cladding of Pa; the high-temperature degassing temperature is 400 °C.

5. The method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite according to claim 1, characterized in that: The argon gas used as the pressure transmission medium has a purity of 99.999%; the formula for calculating the amount of argon gas consumed is as follows: ； ； In the formula: The target pressure for preparing polycrystalline pyrophyllite polymer samples under hot isostatic pressing is determined based on the target temperature of the hot isostatic pressing experiment. Perform calculations; t represents the internal pressure of the inert gas argon cylinder; t represents the number of 40-liter argon cylinders with a purity of 99.999% required to complete a single hot isostatic pressing experiment on a polycrystalline pyrophyllite polymer sample under high temperature and high pressure conditions.

6. The method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite according to claim 4, characterized in that: Methods for purging pressure-transmitting media include: Step 13, Vacuuming, Argon Filling and Furnace Cleaning: (1) Vacuuming: Turn on the gas vacuum pump control switch to evacuate the air in the high-pressure sample chamber directly connected to the gas vacuum pump. When the detection value of the vacuum degree instrument digital display reaches 10 –4 (1) When the pressure reaches 15 MPa, turn off the gas vacuum pump; (2) Fill with gas: Fill with argon gas, the pressure transmission medium, until the pressure in the sample chamber reaches 15 MPa, then stop filling with the pressure transmission medium; (3) Clean the furnace: Turn on the gas vacuum pump and evacuate the vacuum in the sample chamber to 10 MPa. –4 MPa, repeat the evacuation and filling process three times; Step 14, Pre-pressurization of the sample chamber: (1) Calculate the amount of argon gas. To achieve the target pressure of 101.3 MPa and the target temperature of 720 °C, at least 4 argon cylinders with an internal pressure of 15 MPa are required. (2) Fill the argon cylinders with an internal pressure of 15 MPa into the high-pressure pressurization tank of the hot isostatic pressing equipment. Fill the cylinder with argon gas from the high-pressure pressurization tank through the high-pressure delivery pipeline so that the pressure in the high-pressure pressurization tank and the pressure in the cylinder are balanced. (3) Turn on the diaphragm compressor and pump all the remaining argon gas in the high-pressure tank into the pyrophyllite sample chamber of the cylinder so that the sample chamber of the cylinder is pre-pressurized to 59.8 MPa.

7. The method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite according to claim 1, characterized in that: The multi-gradient cylinder heating and pressurization method includes: Step 15, within the temperature range of room temperature to 600 °C, using a heating rate of 18.17 °C / min and a pressurization rate of 0.99 MPa / min, raising the temperature inside the cylinder sample chamber to 600 °C and the pressure to 89.4 MPa; within the medium temperature range of 600 °C to 620 °C, using a heating rate of 2 °C / min and a pressurization rate of 0.65 MPa / min, raising the temperature inside the cylinder sample chamber to 620 °C and the pressure to 95.9 MPa, and maintaining the temperature and pressure for 1.0 hour; within the high temperature range of 620 °C to 720 °C, using a heating rate of 5 °C / min and a pressurization rate of 0.27 MPa / min, raising the temperature inside the cylinder sample chamber to 720 °C and the pressure to 101.3 MPa, and maintaining the temperature and pressure for 5.2 hours.

8. The method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite according to claim 1, characterized in that: The multi-gradient cylinder cooling and depressurization method includes: Step 16, after being kept at a constant temperature and pressure of 101.3 MPa and 720 °C for 5.2 hours, the temperature inside the cylinder sample chamber is reduced to 620 °C and the pressure is reduced to 96.1 MPa by a cooling rate of 5 °C / min and a depressurization rate of 0.26 MPa / min, and kept at a constant temperature and pressure for 1.0 hour; the cylinder temperature inside the sample chamber is reduced to 171 °C and the pressure is reduced to 71.4 MPa by a cooling rate of 12.14 °C / min and a depressurization rate of 0.67 MPa / min.

9. The method for preparing high-density, high-compactness, high-purity, and bulk polycrystalline pyrophyllite according to claim 1, characterized in that: Methods for obtaining polycrystalline pyrophyllite polymers by depressurization and cooling to room temperature include: Step 17: Allow the argon gas in the cylinder of the hot isostatic pressing equipment to flow freely back to the high-pressure pressurization tank through the pipeline; when the cylinder pressure and the high-pressure pressurization tank pressure reach equilibrium, turn on the diaphragm compressor to release the gas in the cylinder and discharge all the residual gas through the pipeline. Step 18: After all the inert argon gas in the pipeline has been completely removed, the cooling system connected to the furnace body of the hot isostatic pressing equipment continues to be turned on, and the natural cooling program is started to reduce the temperature inside the furnace from 171 °C to room temperature. Step 19: Open the furnace chamber of the equipment, remove the steel bladder containing the polycrystalline pyrophyllite polymer sealed after the hot isostatic pressing test, and use a diamond saw blade cutter to peel the polycrystalline pyrophyllite polymer sample from the steel bladder.

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