Preparation method of high-purity and high-density polycrystalline kaolinite under hot isostatic pressing condition

Abstract

The application discloses a high-density high-purity polycrystalline kaolinite preparation method under hot isostatic pressing conditions. –3 The steel ladle is placed in a graphite furnace cylinder body of a hot isostatic pressing high-pressure container, and a graphite sealing cover is covered on the steel ladle; argon is used as a pressure transmission medium, a multi-gradient cylinder body temperature and pressure increasing mode is adopted, the pressure in the cylinder sample bin is increased to 105.8 MPa, the temperature is increased to 800 DEG C, and the temperature and pressure are kept for 4.8 hours; a multi-gradient cylinder body temperature and pressure decreasing mode is adopted, the temperature in the cylinder sample bin is decreased to 177 DEG C, and the pressure is decreased to 71.8 MPa; finally, the pressure is released, the temperature is decreased to room temperature, and the polycrystalline kaolinite aggregate is obtained; and the technical blank of preparing a high-density polycrystalline kaolinite aggregate bulk body rich in aluminosilicate mineral experimental samples under high-temperature and high-pressure conditions is solved.

Description

Technical Field

[0001] This invention belongs to the field of synthesis technology of experimental samples of bulk layered oxygen-containing salt mineral aggregates – polycrystalline water-rich aluminosilicate minerals, and particularly relates to a method for preparing high-density, high-purity polycrystalline kaolinite under hot isostatic pressing. Background Technology

[0002] In the Earth's crust, oxygen and silicon have Clarke values ​​of 46.6% and 27.7%, respectively, making them the two most abundant and widely distributed elements in the Earth's internal spheres. Besides combining to form oxide minerals—quartz (molecular formula: SiO2)—silicon and oxygen primarily combine as metal cations and other complex anions to form abundant silicate minerals widely exposed on the Earth's surface. Silicate minerals are also oxygen-containing salt minerals. In nature, silicate minerals are extremely widespread, with over 600 named species, accounting for about one-quarter of all known minerals, and making up 85% of the total mass of crustal rocks. Silicate minerals are the main rock-forming minerals of the three major rock types: igneous, sedimentary, and metamorphic rocks. They provide abundant key metallic and non-metallic mineral resources essential for human survival and the habitability of the Earth. For example, most key metallic minerals, such as lithium, beryllium, niobium, tantalum, zirconium, rubidium, and strontium, which are crucial elements in defense science and technology production and manufacturing, are extracted from silicate minerals. Non-metallic mineral resources, such as kaolinite, gypsum, pyrophyllite, talc, phlogopite, and asbestos, are directly applicable to many areas of national economic and social development. In addition, many silicate minerals are also very precious gemstones on Earth, such as emerald (also known as aquamarine, whose main component is beryllium aluminum silicate mineral; common chemical formula: Be3Al2Si6O). 18 Hetian jade (main components: hydrous calcium magnesium silicate minerals; common chemical formula: Ca2(Mg,Fe)5Si8O) 22 (OH)2), Jadeite (main component: sodium aluminum silicate mineral; common chemical formula: NaAlSi2O6), Moonstone (main component: framework alkali metal ion silicate mineral; common chemical formula: (Na,K)[AlSi3O8]), Tourmaline (main component: borosilicate mineral; common chemical formula: (Na,K,Ca)(Al,Fe,Li,Mg,Mn)3 (Al,Cr,Fe,V)6(BO3)3(Si6O) 18 Based on the different ways in which the basic structural unit [SiO4] tetrahedra of silicate minerals are connected, they are mainly divided into four subclasses: layered silicate minerals, island-like silicate minerals, framework-like silicate minerals, and chain-like silicate minerals.

[0003] Kaolinite (chemical formula: Al₄Si₄O₂), a water-rich aluminosilicate mineral with a typical layered structure, is an oxygen-containing salt mineral. 10 Kaolinite (OH)8 is generally white and massive, with a typical triclinic crystal system and C1 space group. As the most important end-member component of the kaolinite group minerals and the most common mineral among the kaolinite group minerals widely distributed in nature, kaolinite has a TO-type silicate crystal structure. That is, the structural unit layer of the mineral is formed by interconnecting silicon-oxygen tetrahedral plates and aluminum hydroxide octahedral plates, forming a crystal structure layer stacked along the c-axis. The interlayer is mainly connected by hydrogen bonds. The chemical composition of its mineralogical oxides by weight percentage can be expressed as: Al2O3 / (Al2O3+SiO2+H2O)=39.51%, SiO2 / (Al2O3+SiO2+H2O)=46.54% and H2O / (Al2O3+SiO2+H2O)=13.95%. Naturally occurring kaolinite is typically an important product resulting from the weathering or alteration of feldspar and other silicate minerals under acidic conditions through hydrothermal alteration. It is soft in texture and chemically stable, often containing impurities such as framework aluminosilicate minerals, layered hydrous silicate minerals, oxide minerals, spinel group minerals, and metal sulfide minerals, along with other minerals including quartz, albite, potassium feldspar, biotite, muscovite, hematite, rutile, limonite, magnetite, anatase, pyrite, and ilmenite. As an important non-metallic mineral, kaolinite resources are abundant and widely distributed in my country, primarily found in Jingdezhen City (Jiangxi Province), Liling City (Hunan Province), Tangshan City (Hebei Province), and Suzhou City (Jiangsu Province), where large / super-large kaolinite deposits of significant economic value have been discovered. In addition, kaolinite has a wide range of industrial applications, serving as an important industrial raw material. It is mainly used in many industrial fields such as refractory material processing, high-grade paper whitening agents, chemical product production, ceramics and glaze preparation, paint production additives, plastic products, and the rubber industry.

[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 kaolinite aggregates under high temperature and pressure conditions. Obtaining a large-sized polycrystalline kaolinite aggregate sample (45.69 mm in diameter × 69.89 mm in height) is a crucial step in simulating these physical properties under high temperature and pressure conditions. Geologists typically use naturally occurring kaolinite from the field as a substitute for polycrystalline kaolinite in their experimental samples. However, naturally occurring kaolinite samples have several drawbacks: low density, numerous impurity minerals (such as framework aluminosilicate minerals, layered hydrous silicate minerals, oxide minerals, spinel group minerals, and metal sulfide minerals of varying compositions, including quartz, albite, potassium feldspar, biotite, muscovite, hematite, rutile, limonite, magnetite, anatase, pyrite, and ilmenite), and relatively large and unevenly distributed single crystals of the kaolinite, the main constituent mineral. The kaolinite exhibits numerous insurmountable drawbacks, such as the 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 worldwide use natural kaolinite as the initial sample and employ various high-pressure equipment with multiple large cavities, such as hydrothermal autoclaves, piston cylinder presses, and rotary shear friction testers. However, the experimental data on the physical properties of natural kaolinite under high-temperature and high-pressure conditions 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 mineral 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 kaolinite aggregate samples (e.g., with a diameter greater than 40 mm), the top and bottom of the kaolinite 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 kaolinite 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 kaolinite polymer samples lead to severe excessive deformation, resulting in numerous voids, folds, and cavities in the bulk polycrystalline kaolinite polymer samples. This significantly affects the preparation results of the bulk polycrystalline kaolinite polymer samples. Therefore, neither natural kaolinite nor small-sized (no more than 6 mm) kaolinite 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 kaolinite 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-purity polycrystalline kaolinite under hot isostatic pressing conditions, thereby filling the technical gap in the preparation of large-volume experimental samples of high-density polycrystalline kaolinite aggregates under high temperature and high pressure conditions. This method provides important experimental sample support for the experimental simulation study of the solubility, friction coefficient, shear stress, and other properties of large-cavity oxygen-containing salt mineral aggregates—polycrystalline water-rich aluminosilicate minerals and rocks—under high temperature and high pressure conditions on multi-faceted top 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-purity polycrystalline kaolinite under hot isostatic pressing, comprising: compacting and sealing kaolinite sample powder to a vacuum degree of 10. –3 The sample was placed in a steel cladding with dimensions of 55.05 mm outer diameter × 87.02 mm height × 3 mm wall thickness. The steel cladding was then placed inside the graphite furnace cylinder of a hot isostatic pressure vessel and covered with a graphite sealing cap. Using argon as the pressure transmission medium, a multi-gradient cylinder heating and pressurization method was employed to raise the pressure inside the cylinder sample chamber to 105.8 MPa and the temperature to 800 °C, and then maintain the temperature and pressure for 4.8 hours. A multi-gradient cylinder cooling and depressurization method was then employed to lower the temperature inside the cylinder sample chamber to 177 °C and the pressure to 71.8 MPa. Finally, the pressure was released and the sample was cooled to room temperature to obtain a polycrystalline kaolinite polymer.

[0009] The method of raising the pressure inside the cylinder sample chamber to 105.8 MPa and the temperature to 800 °C using a multi-gradient cylinder heating and pressurization method, and holding the temperature and pressure for 4.8 hours includes:

[0010] Step 15: Within the temperature range of room temperature to 600 °C, using a heating rate of 18.18 °C / min and a pressurization rate of 0.98 MPa / min, raise the temperature inside the sample chamber of the cylinder to 600 °C and the pressure to 89.2 MPa; within the medium temperature range of 600 °C to 700 °C, using a heating rate of 6.93 °C / min and a pressurization rate of 0.75 MPa / min, raise the temperature inside the sample chamber of the cylinder to 700 °C and the pressure to 100.4 MPa, and maintain this temperature and pressure for 1.0 hour; within the high temperature range of 700 °C to 800 °C, using a heating rate of 6.67 °C / min and a pressurization rate of 0.36 MPa / min, raise the temperature inside the sample chamber of the cylinder to 800 °C and 105.8 MPa, and maintain this pressure and temperature at 105.8 MPa and 800 MPa respectively. Kaolinite sample powder was kept under temperature and pressure for 4.8 hours at °C.

[0011] The method of reducing the temperature inside the cylinder sample chamber to 177 °C and the pressure to 71.8 MPa using a multi-gradient cylinder cooling and depressurization approach includes:

[0012] Step 16: Using a cooling rate of 6.67 °C / min and a depressurization rate of 0.31 MPa / min, the temperature inside the sample chamber of the cylinder is reduced to 700 °C and the pressure is reduced to 101.2 MPa, and the temperature and pressure are maintained at the same level for 1.0 hour; using a relatively large cooling rate of 12.76 °C / min and a depressurization rate of 0.72 MPa / min, the temperature inside the sample chamber of the cylinder is reduced to 177 °C and the pressure is reduced to 71.8 MPa.

[0013] The beneficial effects of this invention are:

[0014] 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 kaolinite aggregate experimental samples under high temperature and high pressure conditions.

[0015] The initial raw material selected for this invention is dense, massive single-crystal kaolinite particles collected in the field, which are crushed into uniform mineral single-crystal powder. The powder is then 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 kaolinite sample powder is in a completely sealed environment protected by argon inert gas. The steel sheath containing the kaolinite sample powder is then placed in the sample chamber of an RD80×100‒2000–200 double 2000 type hot isostatic pressing (HIP) device, where it is sintered under high temperature and high pressure to form a large, dense polycrystalline kaolinite aggregate. The prepared polycrystalline kaolinite 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.

[0016] The steel sheath used in the hot isostatic pressing (HIP) experiment of this invention has the following dimensions: 55.05 mm (outer diameter) × 87.02 mm (height) × 3 mm (wall thickness). This allows for the acquisition of large-sized polycrystalline kaolinite polymer samples with a diameter of up to 45.69 mm and a height of up to 69.89 mm. During the HIP experiment on the polycrystalline kaolinite 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 kaolinite 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 kaolinite sample powder and air within the sample chamber, effectively preventing redox reactions between the kaolinite 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 kaolinite polymer samples, potentially leading to the introduction of impurity ions.

[0017] This invention employs a multi-gradient hot isostatic pressing (HIP) process, first increasing pressure and then increasing temperature, to prepare polycrystalline kaolinite 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 kaolinite 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 kaolinite polymer experimental samples with near-theoretical density and extremely high sample strength.

[0018] 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 kaolinite aggregate experimental samples under conditions of 105.8 MPa and 800 °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

[0019] 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 kaolinite polymer are shown in the curves of temperature and pressure changes over time in the sample chamber.

[0020] Figure 2 To obtain fine-grained kaolinite 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 kaolinite sample before the hot isostatic pressing experiment were obtained using a high-precision Olympus SZX16 research-grade stereomicroscopic imaging platform.

[0021] Figure 3 This document presents the optical microscopic observation results of the surface morphology and particle size distribution of polycrystalline kaolinite polymer samples obtained from hot isostatic pressing experiments at 105.8 MPa and 800 °C using the high-precision Olympus SZX16 research-grade stereomicroscopy platform. Detailed Implementation

[0022] A method for preparing high-density, high-purity polycrystalline kaolinite under hot isostatic pressing, comprising:

[0023] Step 1: Use dense, massive kaolinite single crystal mineral particles as the initial sample; use a high-precision Olympus SZX16 research-grade stereomicroscopy imaging platform to accurately measure the particle size of the initial sample. The smallest particle size of the kaolinite single crystal is 6.9 mm and the largest particle size is 14.6 mm. If the mineral grain size of a kaolinite single crystal 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 kaolinite single crystals that do not contain other symbiotic / associated minerals or impurities. If the mineral grain size of a kaolinite single crystal is too small, it is difficult to effectively separate the kaolinite single crystal from framework aluminosilicate minerals, layered hydrous silicate minerals, oxide minerals, spinel group minerals, and metal sulfide minerals of different compositions, such as quartz, albite, potassium feldspar, biotite, muscovite, hematite, rutile, limonite, magnetite, anatase, pyrite, and ilmenite. Furthermore, this invention requires the selection of mineral single crystals with a relatively large weight, which will consume a lot of time and manpower.

[0024] Step 2: Place the selected kaolinite single crystal particles on an ultrasonic cleaner, and use acetone, alcohol and deionized water as cleaning solutions in sequence for ultrasonic cleaning for 15 minutes to remove impurities from the sample surface.

[0025] Step 3: Using a high-magnification, high-precision Olympus SZX16 research-grade stereomicroscopic imaging platform, carefully select 290 grams of kaolinite single crystal particles with complete crystal form, uniform white color, fresh surface, and no other impurity minerals to ensure that the initial sample of kaolinite single crystals has high purity before the hot isostatic pressing experiment under high temperature and high pressure conditions.

[0026] Step 4: Place the carefully selected kaolinite single crystal particles in a vacuum drying oven at 200 degrees Celsius for at least 55 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 kaolinite crystals, making it difficult to accurately weigh the initial kaolinite single crystal particles during further grinding. If the temperature is too high, it may cause a dehydration phase transition reaction in the kaolinite single crystals, ultimately severely affecting the preparation effect of the hot isostatic pressing experimental sample under high temperature and high pressure conditions.

[0027] Step 5: Place the initial sample of kaolinite 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 natural kaolinite single crystals 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) kaolinite single crystal particles.

[0028] Step 6: Place the sample on a high-efficiency Retsch disc vibratory mill (model: RS200), using a high-speed mode of 1170 rpm and setting the instrument's drive power to 1.5 kW. Grind the mineral single crystal particles into fine-grained kaolinite mineral powder with a particle size of 7.58 μm to 18.04 μm (see...). Figure 2 The amount of single-crystal kaolinite sample ground in a single cycle was 100 grams, and the grinding time was 4 minutes. Kaolinite 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 effects. This is more conducive to forming a stronger bonding force between the kaolinite powder particles during the hot isostatic pressing experiment of this invention, thereby greatly improving the compactness and density of the prepared fine-grained polycrystalline kaolinite polymer sample.

[0029] Step 7: Considering that the kaolinite sample powder with a relatively fine particle size is easy to absorb water in the air, it is placed in a paper sealed bag and dried in a vacuum drying oven at 87 degrees Celsius for 18 days to completely remove the adsorbed water on the surface of the sample powder.

[0030] Step 8: In the process of preparing polycrystalline kaolinite 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 kaolinite 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 800 °C and the pressure of 105.8 °C required for the preparation of polycrystalline kaolinite 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 kaolinite 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.

[0031] 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 sleeve. 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 processes and edge trimming. Finally, a hot isostatic pressing test steel cladding sleeve with the dimensions of 55.05 mm (outer diameter) × 87.02 mm (height) × 3 mm (wall thickness) of kaolinite sample powder is obtained.

[0032] 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 kaolinite sample powder.

[0033] Step 9: First, vacuum weld the sleeve and lower sealing cap of the steel cladding. Then, place the dried kaolinite sample powder inside the steel cladding. After a series of key steps, including compaction, vacuuming, high-temperature degassing, and high-temperature vacuum welding, the kaolinite sample powder is completely sealed in a vacuum of 10... –3 Pa is in the steel ladle sleeve.

[0034] Achieving such a low vacuum level within the steel-clad cavity requires at least 82 hours of evacuation, while simultaneously degassing the sample at 400 °C to ensure the kaolinite powder is completely in a sealed vacuum environment and that all moisture is removed. The kaolinite 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 kaolinite sample powder is fully compacted, which can ensure that enough kaolinite sample powder is sealed in the steel sleeve, which will help increase the density of the hot isostatic pressing product polycrystalline kaolinite polymer, thereby greatly improving the preparation effect of the final product bulk polycrystalline kaolinite polymer sample; (2) ensuring that the kaolinite sample powder is fully compacted, which can ensure the filling amount of kaolinite sample powder sealed in the steel sleeve, which will help enhance the compactness between kaolinite sample powder particles, effectively avoiding excessive deformation of the sample during the hot isostatic pressing experiment, thereby greatly improving the compactness of the final product bulk polycrystalline kaolinite polymer sample; (3) maintaining 10 –3The 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 kaolinite sample powder inside it; (4) Under the condition of 400 °C, the kaolinite 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.

[0035] Step 10: Carefully place the steel sleeve containing the kaolinite 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 kaolinite 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.

[0036] 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 kaolinite 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.

[0037] 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.

[0038] 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 kaolinite sample powder pressing parts to complete the hot isostatic pressing molding 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.

[0039] Step 12: In this invention, argon is used as the pressure transmission medium. During the preparation of polycrystalline kaolinite 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 kaolinite polymer products.

[0040] 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 kaolinite polymers. The target pressure and temperature for the HIP experiment are 105.8 MPa and 800 °C, respectively. If the selected target pressure and temperature are too low, the steel sleeve used to seal the kaolinite 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 kaolinite polymer sample. If the selected target pressure and temperature are too high, the layered, water-rich aluminosilicate mineral—kaolinite—will undergo a dehydration phase transition reaction during the HIP experiment, which will have an extremely adverse effect on the prepared polycrystalline kaolinite polymer.

[0041] 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 kaolinite 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 kaolinite sample powder, precise temperature and pressure calibration of the kaolinite sample cavity is performed. Finally, based on the RD80×100‒2000–200 double 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 kaolinite polymer HIP experiment. The formula for calculating the amount of argon gas consumed is as follows:

[0042] (1)

[0043] (2)

[0044] In the formula: parameter P target The target pressure for preparing polycrystalline kaolinite 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 kaolinite polymer sample under high temperature and high pressure conditions.

[0045] 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.

[0046] 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 105.8 MPa and the target temperature of 800 °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 kaolinite sample chamber of the cylinder, so that the sample chamber of the cylinder is pre-filled and pressurized to 59.9 MPa.

[0047] Step 15: Multi-gradient cylinder block heating and pressurization (see...) Figure 1). Taking into account the target pressure and temperature for preparing polycrystalline kaolinite polymer samples in hot isostatic pressing (HIP), as well as the safety, reliability, and durability of the graphite heating element itself, a precise and automatic multi-gradient cylinder heating and pressurization HIP procedure was implemented. The specific steps are as follows: Within the temperature range of room temperature–600 °C, a heating rate of 18.18 °C / min and a pressurization rate of 0.98 MPa / min were used to raise the temperature in the cylinder sample chamber to 600 °C and the pressure to 89.2 MPa; within the medium temperature range of 600 °C–700 °C, a heating rate of 6.93 °C / min and a pressurization rate of 0.75 MPa / min were used to raise the temperature in the cylinder sample chamber to 700 °C and the pressure to 100.4 MPa, maintaining this temperature and pressure for 1.0 hour to ensure that the layered, water-rich aluminosilicate mineral—kaolinite—was fully compacted and cemented; after 1.0 hour of constant temperature and pressure, the temperature and pressure were further increased in the high temperature range of 700 °C… Within a temperature range of °C–800 °C, the temperature inside the sample chamber was raised to 800 °C and 105.8 MPa using a heating rate of 6.67 °C / min and a pressurization rate of 0.36 MPa / min. 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, resulting in uniform high pressure. Ultimately, the pressure inside the sample chamber was maintained at 105.8 MPa. The kaolinite sample powder was then held at this temperature and pressure for 4.8 hours at 105.8 MPa and 800 °C. As a layered, water-rich aluminosilicate mineral, kaolinite is an important volatile-rich oxide mineral found in the deep crust and subduction zones of the Earth. It exhibits a typical C1 space group and a low-symmetry triclinic crystal system, along with relatively complex crystal morphology, distinct lattice orientations, and anisotropic physicochemical properties.

[0048] This invention employs a multi-gradient hot isostatic pressing (HIP) process, involving prior pressurization followed by heating, to prepare polycrystalline kaolinite polymer samples. During the pressurization and heating process, the samples are held at 700 °C and 800 °C for 1.0 hour and 4.8 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 crystal morphologies of kaolinite mineral particles, and it is also difficult to overcome the influence of many unfavorable factors such as the preferred lattice orientation and anisotropy of kaolinite minerals, thus affecting the density and strength of the final bulk polycrystalline kaolinite polymer sample. Conversely, if the holding time is too long, although a highly dense and strong polycrystalline kaolinite polymer can be obtained, the final bulk polycrystalline kaolinite 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.

[0049] Step 16: Multi-gradient cylinder cooling and depressurization. After the kaolinite sample powder was kept at 800 °C and 105.8 MPa for 4.8 hours, the temperature inside the cylinder sample chamber was reduced to 700 °C and the pressure to 101.2 MPa at a cooling rate of 6.67 °C / min and a depressurization rate of 0.31 MPa / min, and kept at the same temperature and pressure for 1.0 hour. After 1.0 hour of constant temperature and pressure, the temperature inside the cylinder sample chamber was reduced to 177 °C and the pressure was reduced to 71.8 MPa at a slower cooling rate of 12.76 °C / min and a slower depressurization rate of 0.72 MPa / min. Compared to the pressurization process, a slower cooling and depressurization rate is adopted. This is mainly because if the cooling and depressurization rates are too fast, the internal stress of the steel cladding will not be fully released, which will lead to the fragmentation and damage of the bulk polycrystalline kaolinite polymer product, thus seriously affecting the preparation effect.

[0050] This invention selects a sample chamber temperature of 177 °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 high 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 temperature is below 160 °C, the resulting 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 removed during the pressure relief process in the HIP experiment.

[0051] 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.

[0052] 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 177 °C to room temperature (~25 °C).

[0053] Step 19: Set the control program for the hot isostatic pressing (HIP) equipment, open the furnace chamber, carefully remove the polycrystalline kaolinite polymer steel-clad workpiece sealed after the HIP experiment, and accurately measure the dimensions of the steel cladding after the HIP forming experiment: 51.69 mm (outer diameter) × 79.89 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 19.06%. This invention exhibits such a large volumetric shrinkage rate (η) of the steel sheath. 钢包套 =19.06%), confirming that the steel sleeve used to seal and encapsulate the kaolinite sample powder underwent sufficient compression and effective deformation during the hot isostatic pressing experiment.

[0054] Step 20: Using a high-speed diamond saw blade cutter with a 1.0 mm thick diamond saw blade, the polycrystalline kaolinite polymer sample was carefully peeled from the steel ladle. The weight of the sample after the experiment was accurately measured to be 289 grams, and the tare weight of the steel ladle was 500 grams. This shows that the weight of the kaolinite 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 kaolinite polymer sample obtained after the HIP experiment: 45.69 mm (diameter) × 69.89 mm (height). Comparing this to the initial volume of kaolinite 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. 高岭石 Its calculation formula can be expressed as: η 高岭石 =(V 实验前高岭石 –V 实验后高岭石 ) / V 实验前高岭石 The volume shrinkage rate (η × 100%) is 21.26%. This invention exhibits such a large volume shrinkage rate (η × 100%) in the kaolinite sample powder. 高岭石 =21.26%), confirming that during the hot isostatic pressing experiment, the kaolinite sample powder placed in the steel cladding was fully compacted and sintered under high temperature and high pressure conditions.

[0055] This invention utilizes an RD80×100‒2000–200 dual 2000-type hot isostatic pressing (HIP) apparatus to synthesize a polycrystalline kaolinite polymer from the initial material—a single-phase kaolinite single crystal—through crushing into medium-sized kaolinite single crystal particles, grinding into fine-grained kaolinite powder, and finally the polycrystalline kaolinite polymer. Employing a multi-gradient HIP process of first increasing pressure and then increasing temperature, high-density, high-compactness, high-purity, and bulk polycrystalline kaolinite polymers are prepared. No other impurity phases are introduced during the entire preparation process, and the purity of the resulting polycrystalline kaolinite polymer sample can reach 100%.

[0056] Under epoxy resin embedding protection, a representative sample (20 mm × 20 mm cross-section) was cut from the polycrystalline kaolinite 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 kaolinite polymer sample were tested. The test results are shown in (see...). Figure 3 The polycrystalline kaolinite 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 cladding 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 kaolinite 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 kaolinite polymer products, including particle growth, uneven particle distribution, and recrystallization.

[0057] High-resolution scanning electron microscopy was used to observe the microstructure of the polycrystalline kaolinite polymer sample obtained from the hot isostatic pressing experiment, and precise density tests were performed. The obtained polycrystalline kaolinite 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 kaolinite polymer samples: (1) a higher pre-pressurization pressure (59.9 MPa); (2) a multi-gradient gradually decreasing cylinder heating mode, i.e., in the low-temperature zone (room temperature–600 °C), the heating rate is 18.18 °C / min; in the medium-temperature zone (600 °C–700 °C), the heating rate is 6.93 °C / min; in the high-temperature zone (700 °C–800 °C), the heating rate is 6.67 °C / min; (3) a multi-gradient gradually decreasing cylinder pressurization mode, i.e., in the low-pressure zone (59.9 MPa–89.2 MPa), the pressurization rate is 0.98 MPa / min; in the medium-pressure zone (89.2 MPa–100.4 MPa), the pressurization rate is 0.75 MPa / min. MPa / min; High pressure zone: 100.4MPa–105.8 MPa pressure conditions, the pressurization rate is 0.36 MPa / min; (4) Multi-gradient gradually steepening cylinder cooling mode, that is, in the high temperature zone: 800 °C–700 °C temperature conditions, the cooling rate is 6.67 °C / min; in the medium and low temperature zone: 700 °C–177 °C temperature conditions, the cooling rate is 12.76 °C / min; (5) Multi-gradient gradually steepening cylinder depressurization mode, that is, in the high pressure zone: 105.8 MPa–101.2 MPa pressure conditions, the depressurization rate is 0.31 MPa / min; in the medium and low pressure zone: 101.2 MPa–71.8 MPa pressure conditions, the depressurization rate is 0.72 MPa / min; (6) Multi-gradient cylinder isothermal and isostatic mode, that is, in the hot isostatic pressure experiment, the 700 At °C and 100.4 MPa, the thermostatic pressing (HIP) was maintained for 1.0 hour; at the highest temperature (800 °C) and highest pressure (105.8 MPa), a sufficiently long thermostatic pressing period of 4.8 hours was ensured; and at a temperature of 700 °C and a pressure of 101.2 MPa, the HIP was maintained for 1.0 hour. All these optimized and improved HIP experimental schemes promote sufficient diffusion and particle aggregation between kaolinite sample powders during the HIP experiment, eliminating the adverse effects of dendritic formation between sample powders, thus forming a uniform equiaxed grain structure; they also promote uniform isotropic temperature and pressure transfer during the HIP experiment, preventing local weaknesses or cracks, thereby greatly improving the compactness of the polycrystalline kaolinite polymer sample produced by the HIP experiment.In addition, this invention applies a high temperature (800 °C), a high pressure (105.8 MPa), and a sufficiently long heat and pressure holding time (4.8 hours) to promote the formation of good bonding force between the particles of kaolinite sample powder, thereby greatly improving the density and strength of the polycrystalline kaolinite 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 experimental products produced by the existing technology that uses quasi-hydrostatic presses such as YJ-3000t and Kawai-1000t to synthesize island silicate mineral single crystals.

[0058] The Archimedes method using organically combined secondary deionized water and the water intrusion method for porous and complex structures were employed to accurately measure the density of polycrystalline kaolinite polymer samples obtained from hot isostatic pressing experiments. The measured density of the polycrystalline kaolinite polymer was 2.67 g / cm³. 3 This density value falls exactly within the theoretical density of 2.54 g / cm³ for naturally collected kaolinite, as measured by geologists. 3 -2.68 g / cm 3Within the specified range, the obtained bulk polycrystalline kaolinite polymer samples exhibited extremely high density. The high density of these polycrystalline kaolinite polymer products is highly correlated with the optimized molding process employed during this hot isostatic pressing experiment, including kaolinite 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. Kaolinite sample powder pretreatment, specifically fine-grained kaolinite mineral powder with a particle size ranging from 7.58 μm to 18.04 μm, is used. Kaolinite within this particle size range has a large specific surface area, significantly increasing the contact area between sample particles. This promotes stronger bonding and greatly enhances the density of the prepared polycrystalline kaolinite polymer sample. A 3 mm thick 20# low-carbon steel continuous casting slab serves 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 evenly transferred to the kaolinite sample powder enclosed within, further increasing the density of the prepared polycrystalline kaolinite polymer sample. An optimized and improved cooling and depressurization hot isostatic pressing process is employed, particularly using a slower, multi-gradient cylinder depressurization mode (pressurization rate: 0.36 MPa / min – 0.98 MPa / min; depressurization rate: 0.31 MPa / min – 0.72 MPa / min). (MPa / min) ensures that the internal stress of large-volume polycrystalline kaolinite 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 kaolinite polymer sample. A high-temperature degassing optimization molding process is performed at 400 °C. The kaolinite sample powder is sealed in a steel sleeve and subjected to high-temperature vacuum degassing at 400 °C to minimize gas residue, thereby obtaining a polycrystalline kaolinite polymer experimental sample 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 polycrystalline kaolinite under hot isostatic pressing, characterized in that: The method includes: compacting and sealing the kaolinite sample powder to a vacuum degree of 10. –3 The sample was placed in a steel cladding with dimensions of 55.05 mm outer diameter × 87.02 mm height × 3 mm wall thickness. The steel cladding was then placed inside the graphite furnace cylinder of a hot isostatic pressure vessel and covered with a graphite sealing cap. Using argon as the pressure transmission medium, a multi-gradient cylinder heating and pressurization method was used to raise the pressure inside the cylinder sample chamber to 105.8 MPa and the temperature to 800 °C, and then maintain the temperature and pressure for 4.8 hours. A multi-gradient cylinder cooling and depressurization method was then used to lower the temperature inside the cylinder sample chamber to 177 °C and the pressure to 71.8 MPa. Finally, the pressure was released and the sample was cooled to room temperature to obtain a polycrystalline kaolinite polymer.

2. The method for preparing high-density, high-purity polycrystalline kaolinite under hot isostatic pressing according to claim 1, characterized in that: The method for preparing the kaolinite sample powder includes: Step 1: Select kaolinite single crystal mineral particles with a minimum particle size of 6.9 mm and a maximum particle size of 14.6 mm as the initial sample; Step 2: Place the selected kaolinite single crystal mineral particles on an ultrasonic cleaner, and use acetone, alcohol and deionized water as cleaning solutions in sequence for ultrasonic cleaning for 15 minutes. Step 3: Select 290 grams of kaolinite single crystal particles that are complete in crystal form, uniform in color and white, fresh in surface and free of impurities. Step 4: Place 290 grams of the selected kaolinite single crystal particles in a vacuum drying oven at 200 degrees Celsius and dry for at least 55 hours. Step 5: Crush the dried kaolinite 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 kaolinite mineral powder with a particle size of 7.58 micrometers to 18.04 micrometers; Step 7: Pack the kaolinite mineral powder into a paper sealed bag and dry it in a vacuum drying oven at 87 degrees Celsius for 18 days to obtain kaolinite sample powder.

3. The method for preparing high-density, high-purity polycrystalline kaolinite under hot isostatic pressing according to claim 1, characterized in that: The preparation method of the steel cladding includes: selecting a 3 mm thick 20# low carbon steel continuous casting slab as the initial raw material for the steel cladding sleeve, 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. The slab is then coiled into a steel strip coil by a coiler, and then undergoes three rolling processes and multiple hot rolling processes including edge trimming to finally obtain a steel cladding sleeve with dimensions of 55.05 mm (outer diameter) × 87.02 mm (height) × 3 mm (wall thickness). Selecting a 3 mm thick 20# low carbon steel continuous casting slab as the initial raw material for the steel cladding cap, the same multiple hot rolling process is used to prepare the upper sealing cap and the lower sealing cap of the steel cladding. The sleeve, the upper sealing cap, and the lower sealing cap are welded together by high temperature vacuum welding to prepare the steel cladding.

4. The method for preparing high-density, high-purity polycrystalline kaolinite under hot isostatic pressing according to claim 1, characterized in that: The kaolinite sample powder was compacted and sealed to a vacuum degree of 10. –3 The method for using a steel cladding with dimensions of 55.05 mm outer diameter × 87.02 mm height × 3 mm wall thickness includes: Step 9, firstly, vacuum-sealing the sleeve and lower sealing cap of the steel cladding, then placing the kaolinite sample powder inside the steel cladding, and then completely sealing the kaolinite sample powder under a vacuum of 10... –3 The steel cladding of Pa was evacuated for at least 82 hours and then degassed at 400°C.

5. The method for preparing high-density, high-purity polycrystalline kaolinite under hot isostatic pressing 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: parameter P target The target pressure for preparing polycrystalline kaolinite 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 cylinders.

6. The method for preparing high-density, high-purity polycrystalline kaolinite under hot isostatic pressing according to claim 1, characterized in that: The methods for purging argon gas, the pressure-transmitting medium, include: Step 13: Vacuuming, Argon Filling, and Furnace Cleaning; 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. The vacuum level is maintained until the digital display of the vacuum instrument 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 three times to completely remove all the air from the sample chamber; Step 14: Pre-pressurization of the sample chamber; calculate the amount of inert argon gas, and prepare at least 3 argon cylinders with an internal pressure of 15 MPa; uniformly fill the 15 MPa argon cylinders into the high-pressure pressurization tank of the hot isostatic pressing equipment, and then freely fill the cylinder with the 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 reach equilibrium; turn on the diaphragm compressor to pump all the remaining argon gas in the high-pressure tank into the kaolinite sample chamber of the cylinder, so that the sample chamber in the cylinder is pre-pressurized to 59.9 MPa.

7. The method for preparing high-density, high-purity polycrystalline kaolinite under hot isostatic pressing according to claim 1, characterized in that: The method of raising the pressure inside the cylinder sample chamber to 105.8 MPa and the temperature to 800 °C using a multi-gradient cylinder heating and pressurization method, and holding the temperature and pressure for 4.8 hours includes: Step 15: Within the temperature range of room temperature to 600 °C, using a heating rate of 18.18 °C / min and a pressurization rate of 0.98 MPa / min, raise the temperature inside the sample chamber of the cylinder to 600 °C and the pressure to 89.2 MPa; within the medium temperature range of 600 °C to 700 °C, using a heating rate of 6.93 °C / min and a pressurization rate of 0.75 MPa / min, raise the temperature inside the sample chamber of the cylinder to 700 °C and the pressure to 100.4 MPa, and maintain this temperature and pressure for 1.0 hour; within the high temperature range of 700 °C to 800 °C, using a heating rate of 6.67 °C / min and a pressurization rate of 0.36 MPa / min, raise the temperature inside the sample chamber of the cylinder to 800 °C and 105.8 MPa, and maintain this pressure and temperature at 105.8 MPa and 800 MPa respectively. Kaolinite sample powder was kept under temperature and pressure for 4.8 hours at °C.

8. The method for preparing high-density, high-purity polycrystalline kaolinite under hot isostatic pressing according to claim 1, characterized in that: The method of reducing the temperature inside the cylinder sample chamber to 177 °C and the pressure to 71.8 MPa using a multi-gradient cylinder cooling and depressurization approach includes: Step 16: Using a cooling rate of 6.67 °C / min and a depressurization rate of 0.31 MPa / min, the temperature inside the sample chamber of the cylinder is reduced to 700 °C and the pressure is reduced to 101.2 MPa, and the temperature and pressure are maintained at the same level for 1.0 hour; using a relatively large cooling rate of 12.76 °C / min and a depressurization rate of 0.72 MPa / min, the temperature inside the sample chamber of the cylinder is reduced to 177 °C and the pressure is reduced to 71.8 MPa.

9. The method for preparing high-density, high-purity polycrystalline kaolinite under hot isostatic pressing according to claim 1, characterized in that: Methods for obtaining polycrystalline kaolinite polymers by depressurization and cooling to room temperature include: Step 17, Depressurization: First, allow the argon gas in the cylinder of the hot isostatic pressing equipment to flow freely back to the high-pressure pressurizing tank through the pipeline; when the cylinder pressure and the high-pressure pressurizing 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, Cooling: 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 177 °C to room temperature. Step 19: Set the control program for the hot isostatic pressing equipment, open the furnace chamber, and remove the polycrystalline kaolinite polymer steel-clad workpiece sealed after the hot isostatic pressing experiment. Step 20: Use a diamond saw blade cutter to separate the polycrystalline kaolinite polymer sample from the ladle.

Images