Method for preparing high-purity bulk polycrystalline diopside under hot isostatic pressing conditions

Abstract

This invention discloses a method for preparing high-purity bulk polycrystalline olivine under hot isostatic pressing, comprising: completely sealing olivine 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; using argon as the pressure transmission medium, a multi-gradient HIP forming method of first increasing pressure and then increasing temperature was used to raise the temperature inside the cylinder sample chamber to 1200 °C and the pressure to 99.7 MPa, and the temperature and pressure were maintained for 4.8 hours; a multi-gradient cylinder cooling and depressurization method was used to reduce the temperature inside the sample chamber to 174 °C and the pressure to 57.2 MPa; finally, the pressure was released and the sample chamber was cooled to room temperature to obtain a polycrystalline dipyroxene peridotite aggregate; this method fills the technical gap in the preparation of large-volume experimental samples of high-density polycrystalline dipyroxene peridotite aggregates under high temperature and high pressure conditions.

Description

Technical Field

[0001] This invention belongs to the field of experimental sample synthesis technology for bulk plutonic magmatic intrusive rocks aggregates – polycrystalline ultramafic peridotite, and particularly relates to a method for preparing high-purity bulk polycrystalline olivine rock under hot isostatic pressing conditions. Background Technology

[0002] The mineral assemblage that makes up igneous rocks refers to the phenomenon of minerals coexisting in nature according to certain rules. When it comes to a specific type of igneous rock, the mineral assemblage is mainly influenced by external factors such as temperature, pressure, and fluid composition, but also primarily constrained by the igneous rock's own chemical composition. Generally, the chemical composition of natural igneous rocks in the field not only controls the mineral assemblage but also determines the isomorphous substitution among the mineral components. In igneous rocks, silica combines with other metal oxides to form a wide variety of silicate minerals, thus determining the mineral assemblage. In igneous rocks, silica mainly exists in three different forms: supersaturated, saturated, and unsaturated, thus classifying igneous rocks into supersaturated, saturated, and unsaturated igneous rocks. When quartz is present as a single mineral in igneous rock samples collected from the field, it indicates that during the cooling and solidification process of deep magma, the main crystallization product, free silica, was in a supersaturated state, meaning there was an excess of silica. Typical igneous rocks with this characteristic include acidic rocks such as granite and quartz diorite. Therefore, quartz is the most important indicator mineral for supersaturated igneous rocks. Conversely, when forsterite or feldspar (mainly including nepheline, leucite, sodalite, zoisite, and lapis lazuli) are present in igneous rock samples collected from the field, but quartz is absent, it indicates that during the cooling and solidification process of deep magma, the main crystallization product, free silica, was in an unsaturated state, meaning there was an insufficient silica content. Typical igneous rocks with this characteristic include acidic rocks such as granite and quartz diorite. Ultrabasic rocks such as olivine, dunite, and orthopyroxene peridotite demonstrate that forsterite and feldspar are the most important marker minerals indicating unsaturated igneous rocks. When igneous rock specimens collected in the field contain only one saturated mineral such as clinopyroxene, orthopyroxene, potassium feldspar, sodium feldspar, or plagioclase, and neither forsterite nor feldspar (mainly including nepheline, leucite, sodalite, zoisite, and lapis lazuli) nor quartz, it means that during the cooling and solidification process of deep magma, the main crystallization product, free silica, was in a saturated state, i.e., the silica content was moderate. Igneous rocks with this characteristic are intermediate-basic rocks such as anorthosite, plagioclase, gabbro, and leucite. Therefore, pyroxene and feldspar are the most important marker minerals indicating saturated igneous rocks.

[0003] Field petrological data indicate that, under equilibrium thermodynamic conditions, unsaturated marker mineral olivine and supersaturated marker mineral quartz cannot coexist to form a mineral assemblage in igneous rocks. This is because olivine in silicate melts undergoes a silicification reaction with silica, producing the saturated mineral enstatite. The main reaction process can be represented as follows:

[0004] (1)

[0005] Similarly, in igneous rocks, under equilibrium thermodynamic conditions, supersaturated marker monominerals such as quartz and saturated marker monominerals such as feldspar (mainly including nepheline, leucite, sodalite, zoisite, and lapis lazuli) cannot coexist to form a mineral assemblages. This is because feldspars (such as nepheline and leucite) in silicate melts undergo silicification reactions with silica, producing saturated minerals such as albite and orthoclase. The main reaction process can be represented as follows:

[0006] (2)

[0007] (3)

[0008] Two-pyroxene peridotite, belonging to the peridotite group, is a plutonic magmatic intrusive rock composed of three minerals: olivine, orthopyroxene, and clinopyroxene. Olivine accounts for 40%–50%, with orthopyroxene and clinopyroxene contents being relatively close, and each pyroxene content exceeding 5%. Freshly collected two-pyroxene peridotite is typically dark green, predominantly granular, but inclusion structures, reaction rim structures, and sponge meteorite structures have also been observed. Two-pyroxene peridotite collected in the field can also undergo serpentinization, altering to become serpentinite. It often forms complex rock complexes with ultramafic rocks (such as dunite, orthopyroxene peridotite, and pyroxene rocks) and mafic rocks (such as gabbro, diabase, and plagioclase rocks). Typically, two-pyroxene peridotite contains small amounts of impurity minerals such as garnet, amphibole, biotite, magnetite, and chromite. Optical microstructure observation results show that the grain size of the main minerals that make up two-pyroxene peridotite transitions clearly from coarse-grained, residual porphyry, and granular phenocrysts.

[0009] 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 olivine aggregates under high temperature and pressure conditions. Obtaining a large-sized polycrystalline olivine aggregate sample (46.96 mm (diameter) × 69.23 mm (height) is a crucial step in simulating these physical properties under high temperature and pressure conditions. Geologists typically use naturally occurring two-pyroxene peridotite from the field as a substitute for polycrystalline two-pyroxene peridotite as experimental samples. However, natural two-pyroxene peridotite suffers from numerous drawbacks, including low sample density, a high concentration of impurities (such as garnet, amphibole, biotite, magnetite, chromite, and other island silicate, chain silicate, layered silicate, and spinel group minerals), large and unevenly distributed olivine, orthopyroxene, and clinopyroxene crystals (the main constituent minerals), difficulty in eliminating preferred 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 two-pyroxene peridotite 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 two-pyroxene peridotite 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.

[0010] 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 rock 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, 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 large-volume polycrystalline olivine aggregate samples (e.g., with a diameter greater than 40 mm), significant asymmetric shrinkage inevitably occurs at the top and bottom of the olivine powder sample during high temperature, high pressure, and quasi-hydrostatic experiments due to unidirectional compression. This results in numerous macroscopic voids and defects during the preparation of large-volume polycrystalline rock aggregate samples. These macroscopic voids and defects cause wrinkles or pores in the central part of the cross-section of the large-volume polycrystalline olivine aggregate, ultimately making the sample prone to severe porosity or aggregation along the center of the wrinkles or pores. This is the unavoidable shrinkage and porosity effect during the synthesis of large-volume polycrystalline rock aggregate samples under high temperature, high pressure, and quasi-hydrostatic conditions. The shrinkage and porosity effects of these polycrystalline olivine aggregate samples lead to severe excessive deformation, resulting in numerous voids, fracture wrinkles, and cavities in the prepared bulk polycrystalline olivine aggregate samples. This significantly affects the preparation results of bulk polycrystalline olivine aggregate samples. Therefore, neither natural olivine nor small-sized (no more than 6 mm) olivine samples obtained in the laboratory meet the minimum 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 testers. 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 olivine 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 petrological properties of large-volume plutonic magmatic intrusive rock aggregates—polycrystalline ultramafic olivine minerals—under high-temperature and high-pressure conditions, such as solubility, friction coefficient, and shear stress. Summary of the Invention

[0011] The technical problem this invention aims to solve is to provide a method for preparing high-purity bulk polycrystalline olivine rock under hot isostatic pressing conditions. This method fills the technical gap in the preparation of large-scale experimental samples of high-density polycrystalline olivine rock aggregates under high temperature and high pressure conditions. It provides important experimental sample support for the experimental simulation study of the solubility, friction coefficient, and shear stress of large-scale plutonic magmatic intrusive rock aggregates—polycrystalline ultramafic peridotite-like minerals—under high temperature and high pressure conditions on multi-faceted large-cavity high-pressure equipment such as hydrothermal autoclaves, piston cylinder presses, and rotary shear friction testers.

[0012] Technical solution of the present invention:

[0013] A method for preparing high-purity bulk polycrystalline olivine under hot isostatic pressing, the method comprising: completely sealing olivine sample powder under a vacuum of 10... –3 The steel cladding was placed in the high-pressure vessel of a hot isostatic pressing (HIP) apparatus, and a graphite sealing cap was placed on top. Using argon as the pressure transmission medium, a multi-gradient HIP method was employed to raise the temperature inside the sample chamber to 1200 °C and the pressure to 99.7 MPa, and then maintain the temperature and pressure for 4.8 hours. A multi-gradient cooling and depressurization method was then used to lower the temperature inside the sample chamber to 174 °C and the pressure to 57.2 MPa. Finally, the pressure was released and the sample was cooled to room temperature to obtain a polycrystalline olivine aggregate.

[0014] The method of raising the temperature inside the cylinder sample chamber to 1200 °C and the pressure to 99.7 MPa using a multi-gradient hot isostatic pressing (HIP) method (prioritizing pressure increase followed by temperature increase) includes: raising the temperature inside the cylinder sample chamber to 600 °C and the pressure to 72.1 MPa within the temperature range of room temperature–600 °C using a heating rate of 18.13 °C / min and a pressure increase rate of 0.64 MPa / min; raising the temperature inside the cylinder sample chamber to 1100 °C and the pressure to 95.3 MPa within the temperature range of 600 °C–1100 °C using a heating rate of 12.5 °C / min and a pressure increase rate of 0.58 MPa / min, and maintaining this temperature and pressure for 1.0 hour; and raising the temperature inside the cylinder sample chamber to 1170 °C within the temperature range of 1100 °C–1170 °C using a heating rate of 7 °C / min and a pressure increase rate of 0.23 MPa / min. °C and pressure were increased to 97.6 MPa; in the high-temperature zone of 1170 °C–1200 °C, the temperature inside the cylinder sample chamber was increased to 1200 °C and the pressure to 99.7 MPa at a heating rate of 3 °C / min and a pressurization rate of 0.21 MPa / min, and the temperature and pressure were maintained for 4.8 hours.

[0015] The method of reducing the temperature in the sample chamber to 174 °C and the pressure to 57.2 MPa using a multi-gradient cylinder cooling and depressurization approach includes: reducing the temperature in the sample chamber to 1170 °C and the pressure to 97.8 MPa using a cooling rate of 3 °C / min and a depressurization rate of 0.19 MPa / min; reducing the temperature in the sample chamber to 1100 °C and the pressure to 94.3 MPa using a cooling rate of 7 °C / min and a depressurization rate of 0.35 MPa / min, and maintaining this temperature and pressure at the same level for 1.0 hour; and after maintaining this temperature and pressure at the same level for 1.0 hour, reducing the temperature in the sample chamber to 174 °C and the pressure to 57.2 MPa using a cooling rate of 15.69 °C / min and a depressurization rate of 0.63 MPa / min.

[0016] The beneficial effects of this invention are:

[0017] 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 advanced geochemistry, ore genesis, rock rheology, geodynamics, hot isostatic pressing materials science, hot isostatic powder metallurgy, seismology, igneous magmatism, high-pressure rheology, mineral physics, deep Earth materials science, high-pressure materials science, materials science, and high-pressure experimental mineralogy, large-volume, highly dense polycrystalline olivine aggregate experimental samples were prepared under high temperature and high pressure conditions using an RD80×100‒2000–200 double 2000 type hot isostatic pressing equipment.

[0018] The initial raw material selected for this invention is field-collected, unaltered, fresh-surfaced, and mineral-free olivine rock without impurities. This rock is crushed into uniformly sized polycrystalline 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 cleaning to ensure the olivine rock sample powder is in a completely sealed environment protected by argon inert gas. The steel sheath containing the olivine rock sample powder is 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 pressure into a large, highly dense polycrystalline olivine rock aggregate. The prepared polycrystalline olivine rock aggregate sample can be widely used in diagenetic and mineralization simulation studies of the physicochemical properties of minerals and rocks under high temperature and high pressure conditions.

[0019] The steel sheath used in the hot isostatic pressing (HIP) experiment of this invention has the following dimensions: 56.61 mm (outer diameter) × 84.43 mm (height) × 3 mm (wall thickness). This allows for the acquisition of large-sized polycrystalline olivine aggregate samples with diameters reaching 46.96 mm and heights reaching 69.23 mm. During the HIP experiment on the polycrystalline olivine aggregate 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 olivine 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 olivine sample powder and air within the sample chamber, effectively preventing redox reactions between the olivine 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 olivine aggregate samples, potentially leading to the introduction of impurity ions.

[0020] This invention employs a multi-gradient hot isostatic pressing (HIP) process, first increasing pressure and then increasing temperature, to prepare polycrystalline olivine aggregate samples with excellent physicochemical properties such as fine crystal size, high density, and high purity. This overcomes the technical bottleneck of synthesizing large-volume experimental samples of high-density polycrystalline olivine aggregates. Furthermore, this invention, using a multi-gradient HIP process, is not limited by the shape or size of the sample and can produce complex polycrystalline rock 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, this invention, using a multi-gradient HIP process, can obtain polycrystalline olivine aggregate experimental samples with near-theoretical density and extremely high sample strength.

[0021] This invention, based on an RD80×100‒2000–200 double 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 olivine aggregate experimental samples under conditions of 99.7 MPa and 1200 °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 plutonic magmatic intrusive rock aggregates—polycrystalline ultramafic olivine-like minerals—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

[0022] 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 dipyroxene peridotite polymer are shown in the curves of temperature and pressure changes over time in the sample chamber.

[0023] Figure 2 To obtain fine-grained olivine sample powder by crushing and grinding with the aid of a jaw crusher (model: BB 200) and a high-efficiency Retsch disc vibratory mill (model: RS200), optical microscopic observation results of the olivine sample before hot isostatic pressing experiment were obtained using a high-magnification, high-precision Olympus SZX16 research-grade stereomicroscopic imaging platform.

[0024] Figure 3 This document presents the optical microscopic observation results of the surface morphology and grain size distribution of a polycrystalline olivine aggregate sample, a product of hot isostatic pressing experiments at 99.7 MPa and 1200 °C, using the high-precision Olympus SZX16 research-grade stereomicroscopic imaging platform. Detailed Implementation

[0025] A method for preparing high-purity bulk polycrystalline olivine under hot isostatic pressing conditions, comprising:

[0026] Step 1: A dense, massive olivine dipyroxene was used as the initial sample. A high-precision Olympus SZX16 research-grade stereomicroscope was used to accurately measure the grain size of the initial sample. The smallest olivine dipyroxene sample size was 5.5 mm, and the largest was 14.1 mm. If the olivine dipyroxene sample size 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 olivine dipyroxene samples free of other associated / symbiotic minerals and impurities. If the olivine dipyroxene sample size is too small, it is difficult to effectively separate the olivine dipyroxene from island silicate minerals, chain silicate minerals, layered silicate minerals, and spinel group minerals of different compositions, such as garnet, amphibole, biotite, magnetite, and chromite. Furthermore, this invention requires selecting a relatively large amount of olivine dipyroxene sample, which will consume significant time and manpower.

[0027] Step 2: Place the selected olivine block sample on an ultrasonic cleaner and use acetone, alcohol and deionized water as cleaning solutions in sequence for ultrasonic cleaning for 18 minutes to remove impurities from the sample surface.

[0028] Step 3: Using a high-magnification, high-precision Olympus SZX16 research-grade stereomicroscopic imaging platform, carefully select 285 grams of blocky olivine sample with uniform color, dark green hue, fresh surface, and no other impurity minerals to ensure that the initial olivine sample has high purity before the hot isostatic pressing experiment under high temperature and high pressure conditions.

[0029] Step 4: Place the carefully selected olivine block samples in a vacuum drying oven at 200 degrees Celsius for at least 26 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 olivine sample, making it difficult to accurately weigh the initial olivine sample during further grinding. If the temperature is too high, it may cause a decomposition reaction in the olivine sample, ultimately severely affecting the preparation effect of the hot isostatic pressing (HIP) experiment sample under high temperature and high pressure conditions.

[0030] Step 5: Place the initial sample of pyroxene peridotite 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 pyroxene peridotite into rock particles with a diameter of less than 2 mm. The purpose is to fully crush the sample to obtain a medium-sized (less than 2 mm) pyroxene peridotite sample.

[0031] Step 6: Place the sample on a high-efficiency Retsch disc vibratory grinder (model: RS200), using a high-speed mode of 1280 rpm and setting the instrument's drive power to 1.5 kW. Grind the rock particles into fine-grained dipyroxene peridotite sample powder with a particle size of 10.51 μm to 23.46 μm (see...). Figure 2 The amount of olivine rock sample ground in a single cycle was 100 grams, and the grinding time was 5 minutes. Olivine rock powder within this particle size range has a large specific surface area (surface area per unit weight of rock powder), which significantly increases the contact area between particles due to pressure and temperature. This is more conducive to forming strong cementing forces between the particles of the olivine rock powder during the hot isostatic pressing experiment of this invention, thereby greatly improving the compactness and density of the prepared fine-grained polycrystalline olivine rock aggregate sample.

[0032] Step 7: Considering that the fine-grained olivine sample powder is very easy to absorb water in the air, it is placed in a paper sealed bag and dried in a vacuum drying oven at 85 degrees Celsius for 11 days to completely remove the adsorbed water on the surface of the sample powder.

[0033] Step 8: In the process of preparing polycrystalline olivine aggregate samples using an RD80×100‒2000–200 double 2000 type hot isostatic pressing (HIP) equipment, a sample steel cladding 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) cladding selected in this case has the following main superior properties: (1) The low-carbon steel (No. 20 steel) cladding does not react with the olivine 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) cladding can withstand the temperature of 1200 °C and the pressure of 99.7 ppm required for the preparation of polycrystalline olivine aggregate samples under the HIP conditions of this invention. MPa; (3) The steel sheath material of low carbon steel (No. 20 steel) has good air tightness, which ensures that the powder of the olivine sample 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 (No. 20 steel) also has excellent properties such as relatively easy edge rolling, cutting, processing, deformation and welding performance.

[0034] This invention selects a continuously cast slab of No. 20 low-carbon steel with a wall thickness of 3 mm as the initial raw material for the steel cladding. After heating it to 200 °C, it is cooled to the set temperature by laminar flow using a roughing mill and a finishing mill. It is then rolled into a steel strip coil by a coiler, and then undergoes multiple hot rolling processes including three rolling and edge trimming to finally obtain the cladding for the hot isostatic pressing test of the olivine sample powder with dimensions of 56.61 mm (outer diameter) × 84.43 mm (height) × 3 mm (wall thickness).

[0035] 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 multi-hot rolling process was used to prepare the upper and lower sealing covers of the steel cladding. The sleeve, upper and lower sealing covers were welded together by high-temperature vacuum welding to prepare a complete steel cladding for the hot isostatic pressing experiment of the olivine sample powder.

[0036] Step 9: First, vacuum weld the sleeve and lower sealing cap of the steel cladding. Then, place the dried olivine sample powder into the steel cladding. After a series of processes including compaction, vacuuming, high-temperature degassing, and high-temperature vacuum welding, the olivine sample powder is completely sealed in a vacuum of 100 kJ / L. –3 Pa is in the steel ladle sleeve.

[0037] Achieving such a low vacuum level within the steel-clad cavity requires at least 62 hours of evacuation, while simultaneously degassing the sample at 400 °C to ensure the olivine powder sample is completely in a sealed vacuum environment and that all moisture is removed. The olivine powder sample 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 olivine sample powder is fully compacted, which can ensure that a sufficient amount of olivine sample powder is sealed in the steel sleeve, which will help increase the density of the polycrystalline olivine aggregate produced by the hot isostatic pressing experiment, thereby greatly improving the preparation effect of the final product bulk polycrystalline olivine aggregate sample; (2) ensuring that the olivine sample powder is fully compacted, which can ensure the filling amount of olivine sample powder sealed in the steel sleeve, which will help enhance the compactness between the olivine 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 olivine aggregate sample; (3) maintaining 10 –3 The extremely low vacuum of Pa ensures that the steel sheath is easily deformed under high temperature and high pressure, thereby uniformly transmitting the high pressure borne by the steel sheath to the olivine sample powder sealed inside it; (4) Under the condition of 400 °C, the olivine 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 weld head from direct contact with air, and the high temperature oxidation of the metal weld point can be completely avoided, which will greatly enhance the sealing performance of the steel sheath.

[0038] Step 10: Carefully place the steel sleeve containing the olivine 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 olivine 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.

[0039] 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 olivine aggregate 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.

[0040] 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.

[0041] 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 olivine sample powder compaction piece 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.

[0042] Step 12: In this invention, argon is used as the pressure transmission medium. During the preparation of polycrystalline dipyroxene peridotite aggregates on an RD80×100‒2000–200 double 2000-type hot isostatic pressing (HIP) equipment, 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 rock powder, which is difficult to mold, the use of argon as the inert gas pressure transmission medium and the selection of 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 dipyroxene peridotite aggregate products.

[0043] This invention employs a multi-gradient hot isostatic pressing (HIP) process, first increasing pressure and then increasing temperature, to synthesize large-scale experimental samples of high-density, high-compactness, and high-purity polycrystalline olivine aggregates. The target pressure and temperature for the HIP experiment are 99.7 MPa and 1200 °C, respectively. If the selected target pressure and temperature are too low, the steel cladding used to seal the olivine sample powder during the HIP experiment will not be sufficiently compressed and effectively deformed, making it difficult to fully compact and sinter the sample. This severely affects the preparation effect of the experimental product—large-scale, high-density, and high-compact polycrystalline olivine aggregate samples. Conversely, if the selected target pressure and temperature are too high, the polycrystalline ultramafic plutonic magmatic intrusive rock aggregate—olivine aggregate—will undergo a decomposition reaction during the HIP experiment, thus having an extremely adverse effect on the prepared polycrystalline olivine aggregate.

[0044] 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 olivine rock 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, high-temperature low-pressure, and high-temperature high-pressure HIP experiments of the olivine rock sample powder, precise temperature and pressure calibration of the olivine rock sample cavity were performed. Finally, based on the RD80×100‒2000–200 dual 2000-type HIP equipment, high-purity inert argon gas was selected as the pressure transmission medium to complete the sample preparation for a single large-volume polycrystalline olivine rock aggregate HIP experiment. The formula for calculating the amount of argon gas consumed is as follows:

[0045] (1)

[0046] (2)

[0047] In the formula: parameter P target The target pressure for preparing polycrystalline olivine aggregate samples under hot isostatic pressing (T0) is based on the target temperature of the hot isostatic pressing experiment (T0). 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 large-volume and high-purity inert gas argon (purity: 99.999%) cylinders required to complete a single hot isostatic pressing experiment on a polycrystalline olivine aggregate sample under high temperature and high pressure conditions.

[0048] 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.

[0049] Step 14: Pre-pressurization of the sample chamber. Specific operation steps: (1) Calculate the amount of inert argon gas according to Formula 1 and Formula 2. In order to achieve the target pressure of 99.7 MPa and the target temperature of 1200 °C, at least 4 argon cylinders with an internal pressure of 15 MPa are required; (2) Fill the argon cylinders with an internal pressure of 15 MPa evenly into the high-pressure pressurization tank of the hot isostatic pressing equipment. Then, through the high-pressure delivery pipeline, fill the cylinder with argon gas from the high-pressure pressurization tank, so that the pressure of the high-pressure pressurization tank and the pressure in the cylinder are balanced; (3) Turn on the diaphragm compressor and pump all the remaining argon gas in the high-pressure tank into the cylinder of the olivine sample chamber, so that the pre-pressurization of the sample chamber in the cylinder is pressurized to 52.9 MPa.

[0050] Step 15: Multi-gradient cylinder block heating and pressurization (see...) Figure 1Taking into account the target pressure and temperature for preparing polycrystalline olivine aggregate 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: Within the temperature range of room temperature to 600 °C, a heating rate of 18.13 °C / min and a pressurization rate of 0.64 MPa / min were used to raise the temperature in the cylinder sample chamber to 600 °C and the pressure to 72.1 MPa; within the medium temperature range of 600 °C to 1100 °C, a heating rate of 12.5 °C / min and a pressurization rate of 0.58 MPa / min were used to raise the temperature in the cylinder sample chamber to 1100 °C and the pressure to 95.3 MPa. The sample was subjected to constant temperature and pressure (COP) for 1.0 hour to ensure thorough compaction and cementation of the polycrystalline ultramafic plutonic magmatic intrusive aggregate – olivine rock sample. After 1.0 hour of COP, the temperature inside the sample chamber was increased to 1170 °C and the pressure to 97.6 MPa within the medium temperature range of 1100 °C–1170 °C using a heating rate of 7 °C / min and a pressurization rate of 0.23 MPa / min. Within the high temperature range of 1170 °C–1200 °C using a heating rate of 3 °C / min and a pressurization rate of 0.21 MPa / min, the temperature inside the sample chamber was increased to 1200 °C and the pressure to 99.7 MPa. As the temperature increased, the argon gas inside the sealed cylinder expanded dramatically, while the cylinder volume remained constant, meaning the argon gas volume was uniformly compressed, resulting in uniform high pressure. Ultimately, the pressure inside the sample chamber was maintained at 99.7 MPa. Two-pyroxene peridotite sample powder was kept under pressure and temperature of 99.7 MPa and 1200 °C for 4.8 hours. Two-pyroxene peridotite is the most important silicate rock in the deep mantle region, and its main constituent minerals (olivine, orthopyroxene, and clinopyroxene) have relatively complex crystal morphology, obvious preferred lattice orientation, and anisotropic physicochemical properties.

[0051] This invention employs a multi-gradient hot isostatic pressing (HIP) process, involving prior pressurization followed by heating, to prepare polycrystalline olivine dipyroxene aggregates. During the pressurization and heating process, temperatures of 1100 °C and 1200 °C are maintained 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 particles of the olivine dipyroxene sample powder with its diverse crystal morphologies, and it is also difficult to overcome the influence of factors such as the preferred lattice orientation and anisotropy of olivine dipyroxene, thus affecting the density and strength of the final bulk polycrystalline olivine dipyroxene aggregate sample. Conversely, if the holding time is too long, although a highly dense and strong polycrystalline olivine dipyroxene aggregate can be obtained, the final bulk polycrystalline olivine dipyroxene aggregate 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.

[0052] Step 16: Multi-gradient cooling and depressurization of the cylinder. After the olivine sample powder was kept at a constant temperature and pressure of 99.7 MPa and 1200 °C for 4.8 hours, the temperature inside the cylinder sample chamber was reduced to 1170 °C and the pressure to 97.8 MPa using a cooling rate of 3 °C / min and a depressurization rate of 0.19 MPa / min. Then, the temperature inside the cylinder sample chamber was reduced to 1100 °C and the pressure was reduced to 94.3 MPa using a cooling rate of 7 °C / min and a depressurization rate of 0.35 MPa / min, and kept at a constant temperature and pressure for 1.0 hour. After being kept at a constant temperature and pressure for 1.0 hour, the temperature inside the cylinder sample chamber was reduced to 174 °C and the pressure was reduced to 57.2 MPa using a relatively slow cooling rate of 15.69 °C / min and a relatively slow depressurization rate of 0.63 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 olivine aggregate product, thus seriously affecting the preparation effect.

[0053] This invention selects a sample chamber temperature of 174 °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 expelled during the pressure relief process in the HIP experiment.

[0054] 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.

[0055] Step 18, Cooling. After all the inert argon gas in the pipeline has been completely removed, the cooling system connected to the furnace body of the hot isostatic pressing equipment continues to be turned on, and the natural cooling program is started to reduce the temperature inside the furnace from 174 °C to room temperature (~25 °C).

[0056] Step 19: Set the control program for the hot isostatic pressing (HIP) equipment, open the furnace chamber, carefully remove the polycrystalline olivine polymer steel-clad workpiece sealed after the HIP experiment, and accurately measure the dimensions of the steel clad after the HIP forming experiment: 52.96 mm (outer diameter) × 79.23 mm (height). Compare the volume of the steel clad before the HIP experiment and calculate the volume shrinkage rate (η) of the steel clad 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 17.86%. This invention exhibits such a large volumetric shrinkage rate (η × 100%) for the steel sheath. 钢包套 =17.86%), confirming that the steel cladding used to seal and encapsulate the powdered olivine sample during the hot isostatic pressing experiment was fully compressed and effectively deformed.

[0057] Step 20: Using a high-speed diamond saw blade cutter with a 1.0 mm thick diamond saw blade, the polycrystalline olivine aggregate sample was carefully peeled from the steel ladle. The weight of the sample after the experiment was accurately measured to be 284 grams, and the tare weight of the steel ladle was 500 grams. This indicates that the weight of the olivine 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 olivine aggregate sample obtained after the HIP experiment: 46.96 mm (diameter) × 69.23 mm (height). Comparing the initial volume of the olivine 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. 二辉橄榄岩 Its calculation formula can be expressed as: η 二辉橄榄岩 =(V 实验前二辉橄榄岩 –V 实验后二辉橄榄岩 ) / V 实验前二辉橄榄岩 The volume shrinkage rate (η × 100%) is 19.92%. This invention exhibits such a large volume shrinkage rate (η × 100%) in the olivine sample powder. 二辉橄榄岩 =19.92%), confirming that during the hot isostatic pressing experiment, the olivine sample powder placed in the steel cladding was fully compacted and sintered under high temperature and high pressure conditions.

[0058] This invention utilizes an RD80×100‒2000–200 dual 2000-type hot isostatic pressing (HIP) apparatus to synthesize a polycrystalline olivine aggregate from the initial material—a single-phase dipyroxene peridotite—through crushing into medium-sized dipyroxene peridotite particles, grinding into fine-grained dipyroxene peridotite powder, and finally producing the final product. Employing a multi-gradient HIP process of first increasing pressure and then increasing temperature, high-density, high-compactness, high-purity, and large-volume polycrystalline olivine aggregate is prepared. No other impurity phases are introduced during the entire preparation process, and the purity of the resulting polycrystalline olivine aggregate sample can reach 100%.

[0059] Under epoxy resin inlay protection, representative samples (20 mm × 20 mm cross-section) were cut from the polycrystalline dipyroxene peridotite polymer workpiece, a product of hot isostatic pressing experiments. These samples underwent epoxy resin inlay protection, cutting, grinding, and surface polishing. The surface morphology and grain size distribution characteristics of the experimental product—polycrystalline dipyroxene peridotite polymer—were then tested using a high-precision Olympus SZX16 research-grade stereomicroscopic imaging platform. The test results (see...) Figure 3The polycrystalline olivine aggregate exhibits clear grain boundary continuity, with minimal differences in the proportion of samples with different particle sizes, demonstrating a distinctly uniform particle size distribution. This invention utilizes a fully sealed steel cladding, inert argon gas pressure transmission medium, and a consistently closed vacuum environment for the sample powder during the hot isostatic pressing (HIP) experiment. This effectively isolates the sample from gases such as nitrogen, oxygen, and water vapor, thus achieving uniform particle distribution, no particle growth, and no recrystallization in the polycrystalline olivine aggregate. Compared to existing technologies that use quasi-hydrostatic presses such as the YJ-3000t and Kawai-1000t to synthesize island-shaped silicate mineral single crystals under high temperature and high pressure, this invention employs a multi-gradient HIP process that first increases pressure and then increases temperature, effectively overcoming numerous drawbacks in polycrystalline olivine aggregate products, such as particle growth, uneven particle distribution, and recrystallization.

[0060] High-resolution scanning electron microscopy was used to observe the microstructure of the polycrystalline olivine aggregate sample obtained from the hot isostatic pressing experiment, and precise density tests were performed. The obtained polycrystalline olivine aggregate had a density as high as 99.8%, exhibiting extremely high compactness.In the hot isostatic pressing (HIP) experiment, the present invention improves the following specific experimental scheme to ensure the acquisition of highly dense polycrystalline olivine aggregate samples: (1) a higher pre-pressurization pressure (52.9 MPa); (2) a multi-gradient gradually decreasing cylinder heating mode, namely, in the low-temperature zone of the HIP experiment: room temperature–600 °C, the heating rate is 18.13 °C / min; in the medium-temperature zone: 600 °C–1100 °C, the heating rate is 12.5 °C / min; in the medium-temperature zone: 1100 °C–1170 °C, the heating rate is 7 °C / min; and in the high-temperature zone: 1170 °C–1200 °C, the heating rate is 3 °C / min; (3) a multi-gradient gradually decreasing cylinder pressure mode, namely, in the low-pressure zone of the HIP experiment: 52.9 MPa–72.1 MPa. Under pressure of MPa, the pressurization rate is 0.64 MPa / min; under pressure of 72.1 MPa–95.3 MPa in the medium pressure zone, the pressurization rate is 0.58 MPa / min; under pressure of 95.3 MPa–97.6 MPa in the medium pressure zone, the pressurization rate is 0.23 MPa / min; and under pressure of 97.6 MPa–99.7 MPa in the high pressure zone, the pressurization rate is 0.21 MPa / min; (4) The cylinder cooling mode with gradually steepening gradients, that is, under temperature conditions of 1200 °C–1170 °C in the high temperature zone, the cooling rate is 3 °C / min; under temperature conditions of 1170 °C–1100 °C in the medium temperature zone, the cooling rate is 7 °C / min; and under temperature conditions of 1100 °C–174 °C in the low temperature zone, the cooling rate is 15.69 MPa / min. °C / min; (5) Multi-gradient gradually steepening cylinder depressurization mode, that is, in the high pressure zone: 99.7 MPa–97.8 MPa pressure conditions, the depressurization rate is 0.19 MPa / min; in the medium pressure zone: 97.8 MPa–94.3 MPa pressure conditions, the depressurization rate is 0.35 MPa / min; in the low pressure zone: 94.3 MPa–57.2 MPa pressure conditions, the depressurization rate is 0.63 MPa / min; (6) Multi-gradient cylinder isothermal and isothermal mode, that is, in the hot isostatic pressing experiment, when the temperature is 1100 °C and the pressure is 95.3 MPa during the heating and pressurization process, the isothermal and isothermal is maintained for 1.0 hour; at the highest temperature (1200 °C) and the highest pressure (99.7 MPa), a sufficiently long isothermal and isothermal is maintained for 4.8 hours; in the hot isostatic pressing experiment, when the temperature is 1100 °C and the pressure is 94.3 MPa during the cooling and depressurization process, the isothermal and isothermal is maintained for 1.0 hour; at the highest temperature (1200 °C) and the highest pressure (99.7 MPa), the isothermal and isothermal is maintained for 4.8 hours ... in the hot isostatic pressing experiment, when the temperature is 1100 °C and the pressure is 94.3 MPa during the cooling and pressurization process, the isothermal and isothermal is maintained for 4.8 hours. At MPa, constant temperature and pressure for 1.0 hour.All these optimized and improved hot isostatic pressing (HIP) experimental schemes can promote sufficient diffusion and particle aggregation between the powder particles of the olivine sample during the HIP experiment, eliminate the adverse effects of dendritic structures formed between the powder particles, and thus form a uniform equiaxed grain structure; they can also promote the uniform isotropic temperature and pressure transmission during the HIP experiment, prevent the occurrence of local weaknesses or cracks, and thus greatly improve the compactness of the polycrystalline olivine aggregate sample of the HIP experimental product. In addition, this invention applies a higher temperature (1200 °C), a higher pressure (99.7 MPa), and a sufficiently long heat and pressure holding time (4.8 hours) to promote the formation of good cementation between the particles of the olivine sample powder, thereby greatly improving the density and strength of the polycrystalline olivine aggregate 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 using quasi-hydrostatic presses such as YJ-3000t and Kawai-1000t.

[0061] 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 olivine aggregate samples obtained from hot isostatic pressing experiments. The measured density of the polycrystalline olivine aggregate was 3.41 g / cm³. 3 This density value falls exactly within the theoretical density of 3.20 g / cm³ for naturally collected olivine diopside, as measured by geologists. 3 -3.50 g / cm 3Within the specified range, the obtained bulk polycrystalline olivine aggregate samples exhibited extremely high density. The high density of these polycrystalline olivine aggregate products is highly correlated with the optimized molding process employed during this hot isostatic pressing experiment, including pretreatment of the olivine sample powder raw material, selection of No. 20 steel sample cladding, a reasonable cooling and depressurization hot isostatic pressing process, and high-temperature degassing at 400 °C. Pretreatment of the raw material for dipyroxene peridotite sample powder, specifically fine-grained dipyroxene peridotite sample powder with a particle size ranging from 10.51 micrometers to 23.46 micrometers, is performed. This particle size range of dipyroxene peridotite 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 cementation, thereby greatly increasing the density of the prepared polycrystalline dipyroxene peridotite aggregate sample. A 3 mm thick continuously cast slab of No. 20 low-carbon steel is used as the steel cladding. This cladding possesses excellent physical properties such as low strength, low hardness, high plasticity, and good toughness, thus uniformly transferring the high pressure borne by the steel cladding to the dipyroxene peridotite sample powder enclosed within it, further increasing the density of the prepared polycrystalline dipyroxene peridotite aggregate sample. An optimized and improved cooling and depressurization hot isostatic pressing process is employed, particularly using a more symmetrical multi-gradient cylinder depressurization mode (pressurization rate: 0.21 MPa / min – 0.64 MPa / min; depressurization rate: 0.19 MPa / min – 0.63 MPa / min). (MPa / min) ensures that the internal stress of large-volume polycrystalline olivine aggregate 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 olivine aggregate sample. A high-temperature degassing optimization molding process at 400 °C is used, sealing the olivine sample powder in a steel sleeve and performing high-temperature vacuum degassing at 400 °C to minimize gas residue, thereby obtaining polycrystalline olivine aggregate experimental samples with 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 unidirectional pressing, leading to uneven density distribution and delamination problems in the experimental product.

Claims

1. A method for preparing high-purity bulk polycrystalline olivine under hot isostatic pressing, characterized in that: The method includes: completely sealing the olivine sample powder in a vacuum of 10... –3 The steel cladding was placed in the high-pressure vessel of a hot isostatic pressing (HIP) apparatus, and a graphite sealing cap was placed on top. Using argon as the pressure transmission medium, a multi-gradient HIP method was employed to raise the temperature inside the sample chamber to 1200 °C and the pressure to 99.7 MPa, and then maintain the temperature and pressure for 4.8 hours. A multi-gradient cooling and depressurization method was then used to lower the temperature inside the sample chamber to 174 °C and the pressure to 57.2 MPa. Finally, the pressure was released and the sample was cooled to room temperature to obtain a polycrystalline olivine aggregate.

2. The method for preparing high-purity bulk polycrystalline olivine under hot isostatic pressing according to claim 1, characterized in that: The method for preparing the olivine sample powder includes: Step 1: Select two-pyroxene peridotite samples with a minimum sample size of 5.5 mm and a maximum sample size of 14.1 mm as initial samples; Step 2: Place the selected olivine rock on an ultrasonic cleaner and use acetone, alcohol and deionized water as cleaning solutions in sequence for ultrasonic cleaning for 18 minutes. Step 3: Select 285 grams of blocky olivine rock with uniform dark green color, fresh surface and no impurities. Step 4: Place the selected olivine samples in a vacuum drying oven at 200 degrees Celsius and dry for at least 26 hours; Step 5: Crush the dried olivine rock into rock particles with a diameter of less than 2 mm; Step 6: Grind the rock particles into a powder of olivine sample with a particle size of 10.51 micrometers to 23.46 micrometers; Step 7: Pack the olivine sample powder into a paper sealed bag and dry it in a vacuum drying oven at 85 degrees Celsius for 11 days.

3. The method for preparing high-purity bulk polycrystalline olivine rock under hot isostatic pressing according to claim 1, characterized in that: The methods for preparing steel sheaths include: 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 the roughing mill and finishing mill to cool it to the set temperature through laminar flow. The slab is then rolled 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 56.61 mm (outer diameter) × 84.43 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 same hot rolling process was used to prepare the upper and lower sealing caps of the steel cladding. 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-purity bulk polycrystalline olivine under hot isostatic pressing conditions according to claim 1, characterized in that: The olivine sample powder was completely sealed in a vacuum of 10. –3 The methods in the steel ladle sleeve of Pa include: Step 9: First, vacuum weld the sleeve and lower sealing cap of the steel cladding. Then, place the dried olivine sample powder into the steel cladding. After compaction, vacuuming, high-temperature degassing, and high-temperature vacuum welding, the olivine sample powder is completely sealed in a vacuum of 100 kJ / L. –3 The sample is encased in a steel bladder containing Pa; vacuuming is required for at least 62 hours; the sample is degassed at 400 °C.

5. The method for preparing high-purity bulk polycrystalline olivine under hot isostatic pressing 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: ； ； In the formula: parameter P target The target pressure for preparing polycrystalline olivine aggregate samples under hot isostatic pressing (T0) is based on the target temperature of the hot isostatic pressing experiment (T0). 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 olivine aggregate sample under high temperature and high pressure conditions.

6. The method for preparing high-purity bulk polycrystalline olivine 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: 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; Filling: Fill the cylinder directly connected to the high-purity inert gas argon with argon gas, the pressure-transmitting medium, until the pressure inside the sample chamber reaches 15 MPa, then stop filling with the pressure-transmitting medium; Furnace cleaning: Turn on the gas vacuum pump and evacuate the vacuum level inside the sample chamber to 10 MPa. –4 MPa, repeat the evacuation and filling process three times; Step 14, Pre-pressurization of the sample chamber: Calculate the required amount of argon gas; uniformly fill the high-pressure pressurization tank of the hot isostatic pressing equipment with an internal pressure of 15 MPa using an argon gas cylinder, and then freely fill the cylinder with the argon gas from the high-pressure pressurization tank through a 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 olivine sample chamber of the cylinder, so that the sample chamber in the cylinder is pre-pressurized to 52.9 MPa.

7. The method for preparing high-purity bulk polycrystalline olivine under hot isostatic pressing according to claim 1, characterized in that: The method of raising the temperature inside the cylinder sample chamber to 1200 °C and the pressure to 99.7 MPa using a multi-gradient hot isostatic pressing (HIP) method (prioritizing pressure increase followed by temperature increase) includes: raising the temperature inside the cylinder sample chamber to 600 °C and the pressure to 72.1 MPa within the temperature range of room temperature–600 °C using a heating rate of 18.13 °C / min and a pressure increase rate of 0.64 MPa / min; raising the temperature inside the cylinder sample chamber to 1100 °C and the pressure to 95.3 MPa within the temperature range of 600 °C–1100 °C using a heating rate of 12.5 °C / min and a pressure increase rate of 0.58 MPa / min, and maintaining this temperature and pressure for 1.0 hour; and raising the temperature inside the cylinder sample chamber to 1170 °C within the temperature range of 1100 °C–1170 °C using a heating rate of 7 °C / min and a pressure increase rate of 0.23 MPa / min. °C and pressure were increased to 97.6 MPa; in the high-temperature zone of 1170 °C–1200 °C, the temperature inside the cylinder sample chamber was increased to 1200 °C and the pressure to 99.7 MPa at a heating rate of 3 °C / min and a pressurization rate of 0.21 MPa / min, and the temperature and pressure were maintained for 4.8 hours.

8. The method for preparing high-purity bulk polycrystalline olivine under hot isostatic pressing according to claim 1, characterized in that: The method of reducing the temperature in the sample chamber to 174 °C and the pressure to 57.2 MPa using a multi-gradient cylinder cooling and depressurization approach includes: reducing the temperature in the sample chamber to 1170 °C and the pressure to 97.8 MPa using a cooling rate of 3 °C / min and a depressurization rate of 0.19 MPa / min; reducing the temperature in the sample chamber to 1100 °C and the pressure to 94.3 MPa using a cooling rate of 7 °C / min and a depressurization rate of 0.35 MPa / min, and maintaining this temperature and pressure at the same level for 1.0 hour; and after maintaining this temperature and pressure at the same level for 1.0 hour, reducing the temperature in the sample chamber to 174 °C and the pressure to 57.2 MPa using a cooling rate of 15.69 °C / min and a depressurization rate of 0.63 MPa / min.

9. The method for preparing high-purity bulk polycrystalline olivine under hot isostatic pressing according to claim 1, characterized in that: Methods for obtaining polycrystalline olivine aggregates by depressurization and cooling to room temperature include: Step 17, Depressurization: First, let the argon gas in the cylinder of the hot isostatic press 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 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 174 °C to room temperature. Step 19: Open the furnace chamber and remove the small workpiece from the steel ladle. Step 20: Use a diamond saw blade cutter to peel the polycrystalline dipyroxene peridotite aggregate sample from the steel sheath.

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