Method for preparing high-density high-purity and bulk polycrystalline epidote under high temperature and high pressure

Abstract

This invention discloses a method for preparing high-density, high-purity, and bulk polycrystalline epidote under high temperature and high pressure, comprising completely sealing epidote sample powder under a vacuum of 10... –3 The sample chamber was placed in a steel cladding; the steel cladding was placed inside the graphite furnace cylinder of the high-pressure vessel of a hot isostatic pressing (HIP) apparatus, and a graphite sealing cap was placed on top; argon was used as the pressure transmission medium; the temperature inside the sample chamber was raised to 780 °C and the pressure was raised to 78.2 MPa using a multi-gradient cylinder heating and pressurization method, and the temperature and pressure were maintained for 10 hours; the temperature inside the sample chamber was lowered to 170 °C and the pressure was lowered to 54.3 MPa at a cooling rate of 13.26 °C / min and a depressurization rate of 0.52 MPa / min; finally, the pressure was released and cooled to room temperature to obtain polycrystalline epidote polymer; this technique fills the technical gap in the preparation of bulk experimental samples of high-density polycrystalline epidote polymers under high temperature and high pressure conditions.

Description

Technical Field

[0001] This invention belongs to the field of experimental sample synthesis technology of bulk island-structured oxygen-containing salt mineral aggregates – polycrystalline water-rich calcium silicate minerals, and particularly relates to a method for preparing high-density, high-purity, and bulk polycrystalline epidote under high temperature and high pressure. Background Technology

[0002] As a typical alkaline silicate hydrous mineral with a double-island structure, the epidote group minerals have the general mineral chemical formula A2B3[SiO4][Si2O7]O(OH). The A position of the crystal lattice framework is mainly occupied by calcium ions with a positive valence of +2, but can also be occupied by sodium ions with a positive valence of +1, potassium ions with a positive valence of +1, magnesium ions with a positive valence of +2, manganese ions with a positive valence of +2, strontium ions with a positive valence of +2, and trivalent rare earth element cations, etc. The B position of the crystal lattice framework is mainly occupied by aluminum ions with a positive valence of +3, iron ions and manganese ions, but can also be occupied by titanium ions with a positive valence of +3, chromium ions and vanadium ions. Moreover, the cations occupying the A position of the crystal lattice and the cations occupying the B position of the crystal lattice can substitute for each other, resulting in isomorphous substitution of epidote group minerals. Typically, in epidote group minerals, cations at the A-site of the crystal lattice are mainly located in the large fissures of silicate minerals; cations at the B-site of the octahedral lattice extend along the b-axis, thereby forming folded chains with shared edges, and the chains in the structure are interconnected by [SiO4] occupying the tetrahedron and [Si2O7] occupying the ditetrahedron. Based on the chemical composition of the epidote group minerals, they are mainly divided into: epidote (chemical formula: Ca2(Fe,Al)3(SiO4)3(OH)), red epidote (chemical formula: Ca2(Al,Mn,Fe)3(SiO4)3(OH)), zoisite (chemical formula: Ca2Al3(SiO4)3(OH)), brown epidote (chemical formula: (Ca,Ce,Y)2(Al,Fe)3(SiO4)3(OH)), clinoptilolite (chemical formula: Ca2Al3(SiO4)3(OH)), and vesuvianite (chemical formula: Ca2Al3(SiO4)3(OH)). 10 Mg2Al4(SiO4)5[Si2O7]2(OH)). Generally speaking, the most common crystal structure among epidote group minerals is monoclinic, such as epidote, red epidote, and brown epidote, while zoisite and vesuvianite are two silicate minerals with typical orthorhombic and tetragonal crystal structures, respectively. In terms of geological origin and occurrence, epidote, red epidote, zoisite, clinozoisite, and vesuvianite are mainly found in calcium-rich acidic igneous rocks, hydrothermal veins, altered rocks, and medium- to high-grade metamorphic rocks, while brown epidote is mainly found in alkaline igneous rocks, intermediate igneous rocks, and granite pegmatites.

[0003] As the most important end-member mineral in the epidote group, epidote belongs to the island-like calcium silicate minerals, monoclinic crystal system, and orthorhombic prismatic hydrous crystals. It typically exhibits surface colors of grayish-black, yellow, yellowish-green, and reddish-brown. The color gradually deepens with increasing ferric iron content. A pinkish hue is achieved due to isomorphous substitution of iron by a small amount of divalent manganese. Isomorphism is highly developed in the molecular structure of epidote, with isomorphous substitutes primarily including Na. + K + Fe 2+ Mg 2+ Mn 2+ Epidote contains various monovalent and divalent cations, and can form a complete isomorphous series with zoisite. Natural epidote crystals collected in the field are often columnar, with the elongation direction parallel to the b-axis, and the crystal faces on the parallel b-axis crystal band have obvious stripes, and can also form polysynthetic twins along the (100) crystal face. The reason why epidote exhibits plate-like crystals with the elongation direction parallel to the b-axis and the (100) crystal face is related to the octahedral chains extending parallel to the b-axis in the structure and the parallel (100) chain layers they form. Radial and cluster-like aggregates can also be seen. In the crystal structure of epidote, [AlO5(OH)] exists in the form of octahedrons, which then form chains extending along the b-axis. The [AlO5(OH)] chains extending along the b-axis are connected with the octahedral [FeO6] on the same edge to form folded chains. Typically, the chains are linked together by isolated tetrahedra [SiO4] and ditetrahedra [Si2O7], while divalent calcium ions fill the large gaps between the chains, resulting in irregular octetal coordination. Epidote, a water-rich calcium silicate mineral collected in the field, is usually an important product of mesothermal and low-temperature hydrothermal processes. It is widely developed in contact metasomatic skarns and mesothermal metamorphic rocks, and single epidote crystals can also be found in various igneous and sedimentary rocks significantly altered by hydrothermal processes. In regional metamorphic rocks, epidote can be associated / symbiotic with chlorite, albite, and actinolite, forming a greenschist facies mineral assemblage; epidote can also be associated / symbiotic with common amphibole, forming an epidote-amphibolite facies mineral assemblage. Furthermore, under dynamic fracturing and retrograde metamorphic geological processes, the epidote-amphibolite facies mineral assemblage can also decompose into epidote, albite, amphibole, and lenticular epidote differentials produced in the greenschist facies. This demonstrates that epidote is a common mineral in the dynamic metamorphism of basic igneous rocks. In skarns, because epidote is often associated with calcium-rich plagioclase and other minerals from the later stages of magmatic processes, it can serve as a key indicator for prospecting and mineralization of skarn-type metallic mineral resources, possessing extremely important geoscientific significance.

[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 epidote aggregates under high temperature and pressure conditions. Obtaining a large-sized polycrystalline epidote aggregate experimental sample (47.29 mm (diameter) × 68.74 mm (height)) is a crucial step in simulating these physical properties under high temperature and pressure conditions. Geologists typically use naturally occurring epidote from the field as a substitute for polycrystalline epidote aggregates in their experiments. However, natural epidote suffers from numerous drawbacks, including low sample density, a high concentration of impurities (such as chlorite, albite, actinolite, common amphibole, and other hydrous layered aluminosilicate minerals, anhydrous alkali metal framework silicate minerals, and hydrous chain silicate minerals), large and unevenly distributed epidote single crystals, difficulty in eliminating optimal lattice orientations, and significant anisotropy of crystal axes. Consequently, many different high-temperature and high-pressure mineral and rock property simulation teams worldwide use natural epidote as the initial sample and employ various high-pressure equipment such as hydrothermal autoclaves, piston cylinder presses, and rotary shear friction testers. The experimental data obtained under high-temperature and high-pressure conditions for natural epidote show significant differences, making it difficult to widely apply these experimental results to the interpretation of the formation mechanisms and occurrence principles of geological disasters such as volcanoes, earthquakes, and debris flows.

[0005] Compared with existing technologies, artificially synthesized island-shaped silicate mineral single crystal experimental samples can be prepared under high temperature and high pressure conditions using quasi-hydrostatic presses such as YJ-3000t and Kawai-1000t, as shown 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 have a particle size ranging from 100 micrometers to 425 micrometers, and the particle size distribution is uneven. 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 blocks. 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 epidote aggregate samples (e.g., with a diameter greater than 40 mm), the top and bottom of the epidote sample 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 voids and defects during the preparation of bulk polycrystalline mineral aggregate samples. These macroscopic voids and defects cause wrinkles or pores in the central part of the cross-section of the bulk polycrystalline epidote aggregate, ultimately making it easy for the sample to undergo 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 epidote polymer samples lead to severe excessive deformation, resulting in numerous voids, folds, and cavities in the bulk polycrystalline epidote polymer samples. This significantly affects the preparation results of the bulk polycrystalline epidote polymer samples. Therefore, neither natural epidote nor small-sized (no more than 6 mm) single-crystal epidote samples obtained in the laboratory 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 epidote 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 island-like oxygen-containing salt mineral aggregates—polycrystalline water-rich calcium silicate 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-purity, and bulk polycrystalline epidote under high temperature and high pressure, thereby filling the technical gap in the preparation of bulk experimental samples of high-density polycrystalline epidote aggregates under high temperature and high pressure conditions. This method aims to obtain large-scale, high-density polycrystalline epidote aggregate experimental samples, providing important experimental sample support for the experimental simulation study of the solubility, friction coefficient, and shear stress of bulk island-like oxygen-containing salt mineral aggregates—polycrystalline water-rich calcium silicate 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 test machines.

[0007] Technical solution of the present invention:

[0008] A method for preparing high-density, high-purity, and bulk polycrystalline epidote under high temperature and high pressure includes: completely sealing epidote sample powder under a vacuum of 10... –3 The sample chamber was placed in a steel cladding; the steel cladding was placed inside the graphite furnace cylinder of the high-pressure vessel of a hot isostatic pressing equipment, and a graphite sealing cap was placed on it; argon was used as the pressure transmission medium; the temperature inside the sample chamber was raised to 780 °C and the pressure was raised to 78.2 MPa using a multi-gradient cylinder heating and pressurization method, and the temperature and pressure were maintained for 10 hours; the temperature inside the sample chamber was lowered to 170 °C and the pressure was lowered to 54.3 MPa at a cooling rate of 13.26 °C / min and a depressurization rate of 0.52 MPa / min; finally, the pressure was released and the sample was cooled to room temperature to obtain polycrystalline epidote polymer.

[0009] The method of raising the temperature to 780 °C and the pressure to 78.2 MPa within the cylinder sample chamber using a multi-gradient cylinder heating and pressurization approach includes: raising the temperature to 300 °C and the pressure to 56.3 MPa within the temperature range of room temperature–300 °C using a heating rate of 15.05 °C / min and a pressurization rate of 0.44 MPa / min; raising the temperature to 600 °C and the pressure to 68.2 MPa within the temperature range of 300 °C–600 °C using a heating rate of 15 °C / min and a pressurization rate of 0.40 MPa / min; and raising the temperature to 780 °C and the pressure to 78.2 MPa within the temperature range of 600 °C–780 °C using a heating rate of 7.2 °C / min and a pressurization rate of 0.33 MPa / min.

[0010] Beneficial effects of this invention:

[0011] 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 epidote aggregate experimental samples under high temperature and high pressure conditions.

[0012] The initial raw material selected for this invention is gem-quality single-crystal epidote 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 epidote sample powder is in a completely sealed environment protected by argon inert gas. The steel sheath containing the epidote 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 epidote aggregate. The prepared polycrystalline epidote 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.

[0013] The steel sheath used in the hot isostatic pressing (HIP) experiment of this invention has the following dimensions: 57.34 mm (outer diameter) × 84.89 mm (height) × 3 mm (wall thickness). This allows for the production of large-sized polycrystalline epidote polymer samples with diameters reaching 47.29 mm and heights reaching 68.74 mm. During the HIP experiment on the polycrystalline epidote 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 epidote 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 epidote sample powder and air within the sample chamber, effectively preventing redox reactions between the epidote 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 epidote polymer samples, potentially leading to the introduction of impurity ions.

[0014] This invention employs a multi-gradient hot isostatic pressing (HIP) process, first increasing pressure and then increasing temperature, to prepare polycrystalline epidote 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 epidote 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 epidote polymer experimental samples with near-theoretical density and extremely high sample strength.

[0015] 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 epidote aggregate experimental samples under 78.2 MPa and 780 °C conditions. 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 island-structure oxygen-containing salt mineral aggregates—polycrystalline water-rich calcium silicate 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

[0016] 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 epidote polymer are shown in the curves of temperature and pressure changes over time in the sample chamber.

[0017] Figure 2 To obtain fine-grained epidote sample powder by crushing and grinding with the help of a jaw crusher (model: BB 200) and a high-efficiency Retsch disc vibratory mill (model: RS200), the optical microscopic observation results of the epidote sample before the hot isostatic pressing experiment were obtained using a high-magnification, high-precision Olympus SZX16 research-grade stereomicroscopic imaging platform.

[0018] Figure 3 This document presents the optical microscopic observation results of the surface morphology and particle size distribution of polycrystalline epidote polymer samples obtained by hot isostatic pressing experiments at 78.2 MPa and 780 °C using the high-precision Olympus SZX16 research-grade stereomicroscopic imaging platform. Detailed Implementation

[0019] A method for preparing high-density, high-purity, and bulk polycrystalline epidote under high temperature and high pressure, comprising:

[0020] Step 1: Long columnar epidote single crystal mineral particles are used as the initial sample. A high-precision Olympus SZX16 research-grade stereomicroscope is used to accurately measure the particle size of the initial sample. The smallest particle size of the epidote single crystal is 3.9 mm and the largest is 8.7 mm. If the particle size of the epidote single crystal is too large, only a low-magnification, high-precision Olympus SZX16 research-grade stereomicroscope can be used for sample selection, making it difficult to accurately identify high-purity epidote single crystals that do not contain other symbiotic / associated minerals or impurities. If the particle size of the epidote single crystal is too small, it is difficult to effectively separate the epidote single crystal from hydrous layered aluminosilicate minerals, anhydrous alkali metal framework silicate minerals, and hydrous chain silicate minerals of different compositions, such as chlorite, albite, actinolite, and common amphibole. Furthermore, this invention requires the selection of mineral single crystals with a relatively large weight, which will consume a lot of time and manpower.

[0021] Step 2: Place the selected epidote single crystal particles on an ultrasonic cleaner, and use acetone, alcohol and deionized water as cleaning solutions in sequence for ultrasonic cleaning for 16 minutes to remove impurities from the sample surface.

[0022] Step 3: Under the high-magnification, high-precision Olympus SZX16 research-grade stereomicroscopic imaging platform, carefully select 300 grams of epidote single crystal particles with complete crystal form, uniform color (grass green), fresh surface, and no other impurity minerals to ensure that the initial sample of epidote single crystal particles has high purity before the hot isostatic pressing experiment under high temperature and high pressure conditions.

[0023] Step 4: Place the carefully selected epidote single crystal particles in a vacuum drying oven at 200 degrees Celsius for at least 20 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 epidote crystals, making it difficult to accurately weigh the initial sample of epidote single crystal particles during further grinding. If the temperature is too high, it may cause the epidote single crystals to decompose, ultimately severely affecting the preparation effect of the hot isostatic pressing experimental sample under high temperature and high pressure conditions.

[0024] Step 5: Place the initial sample of epidote 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 6 minutes to crush the epidote 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 epidote single crystal particles with a medium particle size (less than 2 mm).

[0025] Step 6: Place the sample on a high-efficiency Retsch disc vibratory mill (model: RS200), using a high-speed mode of 1550 rpm and setting the instrument's drive power to 1.5 kW. Grind the mineral single crystal particles into fine-grained epidote mineral powder with a particle size of 11.59 μm to 20.83 μm (see...). Figure 2 The amount of single-crystal epidote sample ground in a single cycle was 100 grams, and the grinding time was 8 minutes. Epidote 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 epidote powder during the hot isostatic pressing experiment of this invention, thereby greatly improving the compactness and density of the prepared fine-grained polycrystalline epidote polymer sample.

[0026] Step 7: Considering that the epidote sample powder has a relatively fine particle size, it is easy to absorb water in the air. Therefore, put it into a paper sealed bag and dry it in a vacuum drying oven at 87 degrees Celsius for 15 days to completely remove the adsorbed water on the surface of the sample powder.

[0027] Step 8: In the process of preparing polycrystalline epidote 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 epidote 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 780 °C and pressure of 78.2 required for the preparation of polycrystalline epidote 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 green epidote 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 welding performance.

[0028] 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 a steel cladding sleeve for hot isostatic pressing of epidote sample powder with dimensions of 57.34 mm (outer diameter) × 84.89 mm (height) × 3 mm (wall thickness).

[0029] 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 hot isostatic pressing of epidote sample powder.

[0030] Step 9: First, vacuum weld the sleeve and lower sealing cap of the steel cladding. Then, place the dried epidote sample powder inside the steel cladding. After a series of processes including compaction, vacuuming, high-temperature degassing, and high-temperature vacuum welding, the epidote sample powder is completely sealed in a vacuum of 10... –3 Pa is in the steel ladle sleeve.

[0031] Achieving such a low vacuum level within the steel-clad cavity requires at least 58 hours of evacuation, while simultaneously degassing the sample at 400 °C to ensure the epidote powder is completely in a sealed vacuum environment and that all moisture is removed. The epidote 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 epidote sample powder is fully compacted, which can ensure that enough epidote sample powder is sealed in the steel sleeve, which will help increase the density of the polycrystalline epidote polymer in the hot isostatic pressing experiment, thereby greatly improving the preparation effect of the bulk polycrystalline epidote polymer sample of the final product; (2) ensuring that the epidote sample powder is fully compacted, which can ensure the filling amount of epidote sample powder sealed in the steel sleeve, which will help enhance the compactness between the epidote sample powder particles, effectively avoid the sample from deforming too much during the hot isostatic pressing experiment, thereby greatly improving the compactness of the bulk polycrystalline epidote polymer sample of the final product; (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 epidote sample powder inside it; (4) Under the condition of 400 °C, the epidote sample powder is degassed at high temperature, completely removing the water vapor that may exist 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.

[0032] Step 10: Carefully place the steel sleeve containing the epidote 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 epidote 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.

[0033] 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 epidote 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 pipelines and circuits of the high-pressure device, ensuring the absolute safety of the operators during HIP experiments.

[0034] 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.

[0035] 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 epidote 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.

[0036] Step 12: In this invention, argon is used as the pressure transmission medium. During the preparation of polycrystalline epidote 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 large-volume polycrystalline epidote polymer products.

[0037] 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 epidote polymers. The target pressure and temperature for the HIP experiment are 78.2 MPa and 780 °C, respectively. If the selected target pressure and temperature are too low, the steel sleeve used to seal the epidote 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—the bulk, high-density, and high-compact polycrystalline epidote polymer sample. If the selected target pressure and temperature are too high, the polycrystalline, water-rich magnesium silicate mineral—epidote—will decompose during the HIP experiment, thus having an extremely adverse effect on the prepared polycrystalline epidote polymer.

[0038] 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 the epidote 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 the epidote sample powder, precise temperature and pressure calibration of the epidote sample cavity 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 epidote polymer HIP experiment. The formula for calculating the amount of argon gas consumed is as follows:

[0039] (1)

[0040] (2)

[0041] In the formula: parameter P target The target pressure for preparing polycrystalline epidote polymer samples under hot isostatic pressing (T) is based on the target temperature of the hot isostatic pressing experiment (T). 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 epidote polymer sample under high temperature and high pressure conditions.

[0042] Step 13, vacuuming, filling with argon gas and washing the furnace, the purpose of which is to completely remove the air from the epidote 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.

[0043] Step 14: Pre-filling and pressurizing 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 78.2 MPa and the target temperature of 780 °C, at least 3 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 epidote sample chamber of the cylinder, so that the sample chamber of the cylinder is pre-filled and pressurized to 43.1 MPa.

[0044] Step 15: Multi-gradient cylinder block heating and pressurization (see...) Figure 1Taking into account the target pressure and temperature for preparing polycrystalline epidote 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 experimental procedure was precisely controlled and automatically adjusted. The specific steps are as follows: In the temperature range of room temperature–300 °C, a heating rate of 15.05 °C / min and a pressurization rate of 0.44 MPa / min were used to raise the temperature in the cylinder sample chamber to 300 °C and the pressure to 56.3 MPa; in the medium temperature range of 300 °C–600 °C, a heating rate of 15 °C / min and a pressurization rate of 0.40 MPa / min were used to raise the temperature in the cylinder sample chamber to 600 °C and the pressure to 68.2 MPa; in the high temperature range of 600 °C–780 °C, a heating rate of 7.2 °C / min and a pressurization rate of 0.33 MPa / min were used. A pressurization rate of MPa / min was used to raise the temperature inside the sample chamber to 780 °C and the pressure to 78.2 MPa. As the temperature increased, the argon gas inside the sealed chamber expanded dramatically. Since the volume of the chamber remained constant, the argon gas volume was uniformly compressed, resulting in uniform high pressure. Ultimately, the pressure inside the sample chamber was maintained at 78.2 MPa, ensuring that the layered, water-rich magnesium silicate mineral epidote was fully compacted and cemented. Epidote sample powder was kept under these conditions (78.2 MPa and 780 °C) for 10 hours. Epidote, exposed in the field, is widely distributed in metamorphic rocks (such as gneiss), amphibolites, and some igneous rocks. It is also an important indicator mineral of metamorphism, often used to characterize the temperature and pressure conditions of metamorphic processes. It is a monoclinic mineral with a P21 / m space group and low symmetry, exhibiting relatively complex crystal morphology, distinct preferred lattice orientations, and anisotropic physicochemical properties.

[0045] This invention employs a multi-gradient hot isostatic pressing (HIP) process, involving prior pressurization followed by heating, to prepare polycrystalline epidote polymer samples. The samples are held at a maximum pressure of 78.2 MPa and a maximum temperature of 780 °C for 10 hours to ensure a sufficiently long holding time. If the holding time is too short, it is difficult to form strong bonding forces between the low-symmetry and diverse crystalline morphologies of epidote mineral particles, and it is also difficult to overcome the influence of factors such as the preferred lattice orientation and anisotropy of the epidote minerals, thus affecting the density and strength of the final bulk polycrystalline epidote polymer sample. Conversely, if the holding time is too long, although a highly dense and strong polycrystalline epidote polymer can be obtained, the final bulk polycrystalline epidote polymer sample will experience particle growth, uneven particle distribution, and recrystallization under prolonged high temperature and pressure, severely affecting the preparation effect and resulting in higher experimental costs.

[0046] Step 16: Cooling and depressurizing the cylinder. After the epidote sample powder was kept at 78.2 MPa and 780 °C for 10 hours, the temperature inside the sample chamber was reduced to 170 °C and the pressure to 54.3 MPa at a relatively slow and uniform cooling rate of 13.26 °C / min and a uniform depressurization rate of 0.52 MPa / min. The relatively slow and uniform cooling and depressurization rates were adopted primarily because if the cooling and depressurization rates were too fast, the internal stress of the steel sheath would not be fully released, leading to the direct fragmentation and damage of the large-volume polycrystalline epidote polymer sample, which would severely affect the preparation results.

[0047] This invention selects a sample chamber temperature of 170 °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 temperature exceeds 180 °C, the resulting internal pressure is too high, which could easily damage the graphite heating furnace and potentially cause a safety accident with the HIP equipment. Conversely, if the sample chamber temperature is below 160 °C, the resulting internal pressure is too low, making it difficult to ensure that the argon inert pressure-transmitting medium sealed within the sample chamber is completely removed during the pressure relief process in the HIP experiment.

[0048] 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.

[0049] 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 170 °C to room temperature (~25 °C).

[0050] Step 19: Set the control program for the hot isostatic pressing (HIP) equipment, open the furnace chamber, carefully remove the polycrystalline epidote polymer steel-clad workpiece sealed after the HIP experiment, and accurately measure the dimensions of the steel cladding after the HIP forming experiment: 53.29 mm (outer diameter) × 78.74 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 19.88%. This invention exhibits such a large volumetric shrinkage rate (η) of the steel sheath. 钢包套=19.88%), confirming that the steel sleeve used to seal and encapsulate the epidote sample powder underwent sufficient compression and effective deformation during the hot isostatic pressing experiment.

[0051] Step 20: Using a high-speed diamond saw blade cutter with a 1.0 mm thick diamond saw blade, the polycrystalline epidote polymer sample was carefully peeled from the steel ladle. The weight of the sample after the experiment was accurately measured to be 299 grams, and the tare weight of the steel ladle was 500 grams. This shows that the weight of the epidote 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 epidote polymer sample obtained after the HIP experiment: 47.29 mm (diameter) × 68.74 mm (height). Comparing the volume of the initial epidote powder sample 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. 绿帘石 Its calculation formula can be expressed as: η 绿帘石 =(V 实验前绿帘石 –V 实验后绿帘石 ) / V 实验前绿帘石 The volume shrinkage rate (η × 100%) is 22.13%. This invention exhibits such a large volume shrinkage rate (η) in epidote sample powder. 绿帘石 =22.13%), confirming that during the hot isostatic pressing experiment, the epidote sample powder placed in the steel cladding was fully compacted and sintered under high temperature and high pressure conditions.

[0052] This invention utilizes an RD80×100‒2000–200 dual 2000-type hot isostatic pressing (HIP) apparatus to synthesize a polycrystalline epidote polymer from the initial material—a single-phase epidote single crystal—which is then crushed into medium-sized epidote single crystal particles, ground into fine-grained epidote powder, and finally synthesized into the final product. Employing a multi-gradient HIP process involving first increasing pressure and then increasing temperature, high-density, high-compactness, high-purity, and bulk polycrystalline epidote polymers are prepared. No other impurity phases are introduced during the entire preparation process, and the purity of the resulting polycrystalline epidote polymer samples can reach 100%.

[0053] Under epoxy resin inlay protection, a representative sample (17 mm × 17 mm cross-section) was cut from the polycrystalline epidote polymer workpiece, a product of the hot isostatic pressing experiment. The sample underwent epoxy resin inlay 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 epidote polymer sample were tested. The test results are shown in (see...). Figure 3The polycrystalline epidote 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 sample from gases such as nitrogen, oxygen, and water vapor, thus achieving a uniform particle distribution, preventing particle growth and recrystallization in the polycrystalline epidote polymer. 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 molding process that first increases pressure and then increases temperature, effectively overcoming numerous drawbacks of polycrystalline epidote polymer products, including particle growth, uneven particle distribution, and recrystallization.

[0054] High-resolution scanning electron microscopy was used to observe the microstructure of the polycrystalline epidote polymer sample obtained from the hot isostatic pressing experiment, and precise density tests were performed. The obtained polycrystalline epidote 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 epidote polymer samples: (1) a higher pre-charge pressure (43.1 MPa); (2) a multi-gradient gradually decreasing cylinder heating mode, i.e., in the low-temperature zone of the HIP experiment (room temperature–300 °C), the heating rate is 15.05 °C / min; in the medium-temperature zone (300 °C–600 °C), the heating rate is 15 °C / min; and in the high-temperature zone (600 °C–780 °C), the heating rate is 7.2 °C / min; (3) a multi-gradient gradually decreasing cylinder pressure mode, i.e., in the low-pressure zone of the HIP experiment (43.1 MPa–56.3 MPa), the pressure rate is 0.44 MPa / min; and in the medium-pressure zone (56.3 MPa–68.2 MPa), the pressure rate is 0.44 MPa / min. Under MPa pressure conditions, the pressurization rate is 0.40 MPa / min and under high pressure conditions: 68.2 MPa–78.2 MPa pressure conditions, the pressurization rate is 0.33 MPa / min; (4) The relatively slow cylinder uniform cooling and depressurization mode, under 78.2 MPa–54.3 MPa pressure conditions, the uniform cooling rate and depressurization rate are 13.26 °C / min and 0.52 MPa / min, respectively; (5) The long-term constant temperature and constant pressure mode, at the highest temperature (780 °C) and the highest pressure (78.2 MPa), ensures a sufficiently long constant temperature and constant pressure of 10 hours. All these optimized and improved hot isostatic pressing (HIP) experimental schemes can promote sufficient diffusion and particle aggregation between epidote 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 transmission during HIP, prevent the occurrence of local weaknesses or cracks, and thus greatly improve the compactness of the polycrystalline epidote polymer sample produced by HIP. In addition, this invention applies a higher temperature (780 °C), a higher pressure (78.2 MPa), and a sufficiently long heat and pressure holding time (10 hours) to promote the formation of good bonding force between the particles of epidote sample powder, thereby greatly improving the density and strength of the polycrystalline epidote 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 product that exist in the existing technology for synthesizing island silicate mineral single crystals by means of quasi-hydrostatic presses such as YJ-3000t and Kawai-1000t.

[0055] 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 epidote polymer samples obtained from hot isostatic pressing experiments. The measured density of the polycrystalline epidote polymer was 3.48 g / cm³. 3 This density value falls exactly within the theoretical density of 3.25 g / cm³ for naturally collected epidote, as measured by geologists. 3 -3.50 g / cm 3 Within the specified range, the obtained bulk polycrystalline epidote polymer samples exhibited extremely high density. The high density of these polycrystalline epidote polymer products is highly correlated with the optimized molding process employed during this hot isostatic pressing experiment, including epidote sample powder pretreatment, selection of No. 20 steel sample cladding, a reasonable cooling and depressurization hot isostatic pressing process, and high-temperature degassing at 400 °C. Epidote sample powder pretreatment, specifically fine-grained epidote mineral powder with a particle size ranging from 11.59 micrometers to 20.83 micrometers, is used. Epidote within this particle size range has a large specific surface area, significantly increasing the contact area between sample particles. This is more conducive to the formation of strong and effective bonding forces, thereby greatly improving the density of the prepared polycrystalline epidote polymer sample. A 3 mm thick 20# low-carbon steel continuous casting slab is used as the steel cladding. This cladding possesses excellent physical properties such as low strength, low hardness, high plasticity, and good toughness, allowing the high pressure borne by the cladding to be uniformly transferred to the epidote sample powder enclosed within, further enhancing the density of the prepared polycrystalline epidote polymer sample. An optimized and improved cooling and depressurization hot isostatic pressing process is employed, particularly using a slow, uniform, and multi-gradient cylinder depressurization mode (pressurization rate: 0.33 MPa / min – 0.44 MPa / min; depressurization rate: 0.52 MPa / min). (MPa / min) ensures that the internal stress of large-volume polycrystalline epidote 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 epidote polymer sample. A high-temperature degassing optimization molding process is performed at 400 °C. The epidote sample powder is sealed in a steel sleeve and subjected to high-temperature vacuum degassing at 400 °C to minimize gas residue, thereby obtaining polycrystalline epidote 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-purity, and bulk polycrystalline epidote under high temperature and high pressure, characterized in that: The method includes: completely sealing the epidote sample powder in a vacuum of 10... –3 The sample chamber was placed in a steel cladding; the steel cladding was placed inside the graphite furnace cylinder of the high-pressure vessel of a hot isostatic pressing equipment, and a graphite sealing cap was placed on it; argon was used as the pressure transmission medium; the temperature inside the sample chamber was raised to 780 °C and the pressure was raised to 78.2 MPa using a multi-gradient cylinder heating and pressurization method, and the temperature and pressure were maintained for 10 hours; the temperature inside the sample chamber was lowered to 170 °C and the pressure was lowered to 54.3 MPa at a cooling rate of 13.26 °C / min and a depressurization rate of 0.52 MPa / min; finally, the pressure was released and the sample was cooled to room temperature to obtain polycrystalline epidote polymer.

2. The method for preparing high-density, high-purity, and bulk polycrystalline epidote under high temperature and high pressure according to claim 1, characterized in that: The methods for preparing epidote sample powder include: Step 1: Select epidote single crystal mineral particles with a minimum particle size of 3.9 mm and a maximum particle size of 8.7 mm as initial samples; Step 2: Place the selected epidote single crystal mineral particles on an ultrasonic cleaner, and use acetone, alcohol and deionized water as cleaning solutions in sequence for ultrasonic cleaning for 16 minutes. Step 3: Select 300 grams of epidote single crystal mineral particles that are complete in crystal form, uniform in color (grass green), fresh in surface, and free of impurities. Step 4: Place the selected epidote single crystal mineral particles in a vacuum drying oven at 200 degrees Celsius and dry for at least 20 hours. Step 5: Crush the dried epidote single crystal mineral particles into mineral single crystal particles with a particle size of less than 2 mm. Step 6: Grind the single crystal particles of the mineral into epidote mineral powder with a particle size of 11.59 micrometers to 20.83 micrometers; Step 7: Pack the epidote mineral powder into a paper sealed bag and dry it in a vacuum drying oven at 87 degrees Celsius for 15 days to obtain epidote sample powder.

3. The method for preparing high-density, high-purity, and bulk polycrystalline epidote under high temperature and high pressure according to claim 1, characterized in that: The preparation method of the steel sheath includes: Step 8: Select a continuous casting slab of No. 20 low carbon steel with a wall thickness of 3 mm, heat it to 200 °C, and then use a roughing mill and a finishing mill to cool it to a set temperature through laminar flow. The slab 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 a green steel sheath tube with dimensions of 57.34 mm (outer diameter) × 84.89 mm (height) × 3 mm (wall thickness). A continuous casting slab of No. 20 low carbon steel with a wall thickness of 3 mm was selected. The upper and lower sealing caps of the steel cladding were prepared by using the same multi-hot rolling process. The cladding, upper and lower sealing caps were welded together by high temperature vacuum welding to prepare a complete steel cladding.

4. The method for preparing high-density, high-purity, and bulk polycrystalline epidote under high temperature and high pressure according to claim 1, characterized in that: The epidote sample powder was completely sealed in a vacuum of 10. –3 The method in the steel cladding of Pa includes: vacuum welding the sleeve and lower sealing cap of the steel cladding; then placing the dried epidote sample powder inside the steel cladding; and finally, compacting, vacuuming, high-temperature degassing, and high-temperature vacuum welding to completely seal the epidote sample powder under a vacuum of 10... –3 The sample is encased in a steel bladder containing Pa; vacuuming is required for at least 58 hours, while simultaneously degassing the sample at 400 °C.

5. The method for preparing high-density, high-purity, and bulk polycrystalline epidote under high temperature and high pressure according to claim 1, characterized in that: The argon gas purity is 99.999%; the formula for calculating the amount of argon gas consumed is: (1)； (2)； In the formula: parameter P target The target pressure for preparing polycrystalline epidote polymer samples under hot isostatic pressing (T) is based on the target temperature of the hot isostatic pressing experiment (T). target ) Perform the calculation; parameter P bottle The pressure inside the cylinder represents the inert gas argon; parameter t represents the number of 40-liter cylinders with 99.999% argon purity required to complete a single hot isostatic pressing experiment on a polycrystalline epidote polymer sample under high temperature and high pressure conditions.

6. The method for preparing high-density, high-purity, and bulk polycrystalline epidote under high temperature and high pressure according to claim 1, characterized in that: Argon gas filling methods include: Step 13, Vacuuming: Turn on the gas vacuum pump control switch to evacuate the air sealed in the high-pressure sample chamber, which is directly connected to the gas vacuum pump. Evacuate until the vacuum level instrument's digital display reaches 10... –4 At MPa, turn off the gas vacuum pump; Fill the cylinder directly connected to argon gas with argon gas, and stop filling when the pressure in the sample chamber reaches 15 MPa; 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: Calculate the amount of inert argon gas and prepare at least 3 argon cylinders with an internal pressure of 15 MPa. Evenly fill the 15 MPa argon cylinders into the high-pressure tank of the hot isostatic pressing equipment. Then, through a high-pressure delivery pipeline, freely fill the cylinder with the argon gas from the high-pressure tank, thus balancing the pressure in the high-pressure tank and the cylinder. Turn on the diaphragm compressor to pump all the remaining argon gas from the high-pressure tank into the epidote sample chamber of the cylinder, pre-pressurizing the sample chamber to 43.1 MPa.

7. The method for preparing high-density, high-purity, and bulk polycrystalline epidote under high temperature and high pressure according to claim 1, characterized in that: The method of raising the temperature to 780 °C and the pressure to 78.2 MPa within the cylinder sample chamber using a multi-gradient cylinder heating and pressurization approach includes: raising the temperature to 300 °C and the pressure to 56.3 MPa within the temperature range of room temperature–300 °C using a heating rate of 15.05 °C / min and a pressurization rate of 0.44 MPa / min; raising the temperature to 600 °C and the pressure to 68.2 MPa within the temperature range of 300 °C–600 °C using a heating rate of 15 °C / min and a pressurization rate of 0.40 MPa / min; and raising the temperature to 780 °C and the pressure to 78.2 MPa within the temperature range of 600 °C–780 °C using a heating rate of 7.2 °C / min and a pressurization rate of 0.33 MPa / min.

8. The method for preparing high-density, high-purity, and bulk polycrystalline epidote under high temperature and high pressure according to claim 1, characterized in that: Methods for obtaining polycrystalline epidote 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 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 170 °C to room temperature. Step 19: Open the furnace chamber and remove the steel ladle sleeve after the hot isostatic pressing test; Step 20: Use a diamond saw blade cutter to separate the polycrystalline epidote polymer sample from the steel ladle.

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