A method for growing zoisite single crystals under high temperature and high pressure

Abstract

The present invention provides a method for growing zoisite single crystals under high temperature and high pressure, belonging to the technical field of mineral single crystal synthesis. 2 Powder, Al 2 O 3 Powder and SiO 2 Powder is the initial raw material, Ca(OH) 2 The powder provides the essential calcium and hydrogen elements for synthesizing zoisite single crystals, Al 2 O 3 The powder provides the essential aluminum elements, SiO 2 The powder provides the silicon element essential for synthesizing zoisite single crystals, and combined with high-temperature pre-sintering, improves the mixing uniformity of the initial raw materials and promotes a certain degree of solid-phase reaction between the initial raw materials, and finally successfully synthesizes the zoisite single crystal under high temperature and high pressure conditions. In addition, in the process of growing zoisite single crystals of the present invention, the environment is pure, the sample is in a sealed environment, and is not in contact with impurities. The obtained zoisite single crystal is a pure substance with good chemical stability, which solves the technical problem of the difficulty in growing zoisite single crystals.

Description

Technical Field

[0001] The invention belongs to the technical field of mineral single crystal synthesis, and in particular relates to a method for growing zoisite single crystals under high temperature and high pressure. Background Art

[0002] Zoisite is a calcium aluminum hydroxyl isolated tetrahedral mineral, also a silicate mineral, belonging to the epidote group. Unlike other minerals in the epidote group, which belong to the monoclinic system, zoisite belongs to the orthorhombic system (space group Pnma). Zoisite has beautiful color, and transparent ones can be used as gemstones, especially tanzanite. The chemical composition of zoisite is: Ca2Al3(SiO4)3(OH).

[0003] Origin and Occurrence of Zoisite: Zoisite is a common island-shaped hydrous silicate mineral, usually produced in high-pressure and ultra-high-pressure metamorphic rocks such as schists, amphibolites and eclogites in various geological environments (such as continental collision zones and subduction zones, etc.), as well as igneous rocks such as granite. It is an important carrier of deep water circulation in the earth. As an important hydrous silicate mineral in the process of plate subduction-reentry, zoisite has a wide temperature and pressure stability range in the greenschist phase-eclogite phase.

[0004] However, there are relatively few studies on the formation mechanism of zoisite, and there is no report on the growth of artificially synthesized zoisite single crystals and their crystal structure data. Therefore, exploring the method of artificially synthesizing high-purity zoisite single crystals is an important premise and basis for further in-depth research on the crystal structure characteristics and formation mechanism of zoisite. Summary of the invention

[0005] To solve the above technical problems, the present invention proposes a method for growing zoisite single crystals under high temperature and high pressure. The method provided by the present invention solves the technical problem of the difficulty in growing zoisite single crystals. At the same time, the method has the characteristics of simple operation, easy control of conditions, and low synthesis cost.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for growing a zoisite single crystal under high temperature and high pressure, comprising the following steps:

[0008] (1) mixing Ca(OH)2 powder, Al2O3 powder and SiO2 powder uniformly to obtain a mixed material;

[0009] (2) pre-calcining the mixture obtained in step (1) at high temperature, cooling it to room temperature, forming it into a cylinder, and then placing it into a platinum tube, and sealing both ends of the platinum tube;

[0010] (3) Assembling the platinum tube in step (2) in a high-temperature and high-pressure synthesis assembly block, and then performing a high-temperature and high-pressure reaction to obtain a zoisite single crystal; the maximum temperature of the high-temperature and high-pressure reaction is 800-900°C, the maximum pressure is 2.5-4.0GPa, and the time is 80-120h.

[0011] Preferably, in step (1), the molar ratio of the Ca(OH)2 powder, Al2O3 powder and SiO2 powder is 4:3:6.

[0012] Preferably, in step (2), the high temperature pre-sintering is: heating to 500° C. at a heating rate of 100° C. / h and maintaining the temperature for 5 hours.

[0013] Preferably, in step (3), the heating and pressurizing process of the high temperature and high pressure reaction is: first increase the pressure to a maximum pressure of 2.5-4.0 GPa at a pressure increase rate of 0.5 GPa / h, and then stepwise heating, the steps are as follows: increase the temperature to 300°C at a heating rate of 10°C / min, keep warm at 300°C for 10 minutes, then increase the temperature to 600°C at a heating rate of 20°C / min, keep warm at 600°C for 10 minutes, then increase the temperature to a maximum temperature of 800-900°C at a heating rate of 50°C / min, and react at the maximum temperature and maximum pressure conditions for 80-120 hours.

[0014] The present invention also provides a zoisite single crystal, which is synthesized according to the above method. The zoisite single crystal has an orthorhombic structure and a unit cell parameter The average size is 100-200μm, and the maximum size is 300μm.

[0015] Compared with the prior art, the present invention has the following advantages and technical effects:

[0016] (1) The present invention uses Ca(OH)2 powder, Al2O3 powder and SiO2 powder as initial raw materials. Ca(OH)2 powder provides calcium and hydrogen elements essential for synthesizing zoisite single crystals, Al2O3 powder provides aluminum elements essential for synthesizing zoisite single crystals, and SiO2 powder provides silicon elements essential for synthesizing zoisite single crystals. High-temperature pre-sintering improves the mixing uniformity of the initial raw materials and promotes a certain degree of solid-phase reaction between the initial raw materials. Finally, zoisite single crystals are synthesized under high temperature and high pressure conditions.

[0017] (2) Compared with natural zoisite samples, which may contain impurity ions such as magnesium ions, sodium ions, chromium ions, manganese ions, nickel ions, and vanadium ions, the process of growing zoisite single crystals in the present invention is pure, the sample is in a sealed environment, and is not in contact with impurities. The obtained zoisite single crystal is a pure substance with good chemical stability, which not only solves the technical problem of the difficulty in growing zoisite single crystals, but also provides important experimental sample guarantees for the measurement of physical property parameters of zoisite single crystals (such as the high-pressure crystal structure properties and anisotropic properties of zoisite). In addition, the synthesis method of the present invention has the advantages of simple operation process and easy control of conditions, and the obtained zoisite single crystal has excellent physical and chemical properties such as high purity, large size, and stable chemical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0019] Figure 1 This is a schematic diagram of assembling a platinum tube in a high-temperature and high-pressure synthesis assembly block according to the present invention;

[0020] Figure 2 This is a microscopic photograph of a zoisite single crystal synthesized in Example 1 of the present invention;

[0021] Figure 3 This is a microscopic photograph of the unsynthesized zoisite single crystal in Comparative Example 1 of the present invention;

[0022] Figure 4 This is the Raman spectrum of the zoisite single crystal synthesized in Example 1 of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] The embodiment of the present invention provides a method for growing a zoisite single crystal under high temperature and high pressure, comprising the following steps:

[0026] (1) mixing Ca(OH)2 powder, Al2O3 powder and SiO2 powder uniformly to obtain a mixed material;

[0027] (2) pre-calcining the mixture obtained in step (1) at high temperature, cooling it to room temperature, forming it into a cylinder, and then placing it into a platinum tube, and sealing both ends of the platinum tube;

[0028] (3) Assembling the platinum tube in step (2) in a high-temperature and high-pressure synthesis assembly block, and then performing a high-temperature and high-pressure reaction to obtain a zoisite single crystal; the maximum temperature of the high-temperature and high-pressure reaction is 800-900°C, the maximum pressure is 2.5-4.0GPa, and the time is 80-120h.

[0029] The present invention uniformly mixes Ca(OH)2 powder, Al2O3 powder and SiO2 powder to obtain a mixed material. The present invention uses Ca(OH)2 powder, Al2O3 powder and SiO2 powder as initial raw materials, wherein the Ca(OH)2 powder provides calcium and hydrogen elements essential for synthesizing zoisite single crystals, the Al2O3 powder provides aluminum elements essential for synthesizing zoisite single crystals, and the SiO2 powder provides silicon elements essential for synthesizing zoisite single crystals.

[0030] In a preferred embodiment, in step (1), the molar ratio of the Ca(OH)2 powder, Al2O3 powder and SiO2 powder is 4:3:6.

[0031] In a preferred embodiment, the purity of the Ca(OH)2 powder is >99.99%, the purity of the Al2O3 powder is >99.99%, and the purity of the SiO2 powder is >99.99%.

[0032] The present invention pre-sinters the mixed material obtained in step (1) at high temperature, cools it to room temperature, and forms a cylinder, which is then loaded into a platinum tube, and both ends of the platinum tube are sealed. The present invention improves the mixing uniformity of the initial raw materials through high-temperature pre-sintering and promotes a certain degree of solid-phase reaction between the initial raw materials, thereby ensuring the successful synthesis of zoisite single crystals.

[0033] In a preferred embodiment, in step (2), the high temperature pre-sintering is: heating the temperature to 500°C at a rate of 100°C / h and maintaining the temperature for 5h. The present invention has the advantage of improving the mixing uniformity of the initial raw materials by adopting the above high temperature pre-sintering process, thereby ensuring the successful synthesis of zoisite single crystals.

[0034] In a preferred embodiment, the cooling rate to room temperature is 50° C. / h.

[0035] In a preferred embodiment, the device for forming the mixed material into a cylinder is a tablet press.

[0036] In a preferred embodiment, the device for sealing both ends of the platinum tube is a welding gun.

[0037] In a preferred embodiment, the specifications of the platinum tube are: Φ4.5mm, height 4mm, wall thickness 0.1mm.

[0038] The present invention assembles the platinum tube in step (2) in a high-temperature and high-pressure synthesis assembly block, and then performs a high-temperature and high-pressure reaction to obtain a zoisite single crystal.

[0039] In a preferred embodiment, the assembling of the platinum tube in step (2) in the high-temperature and high-pressure synthetic assembly block is specifically as follows: a hole is drilled in the center of the phyllite block, and then the graphite heating tube is inserted into the hole, followed by the boron nitride insulating tube being inserted into the graphite heating tube, and then the platinum tube is inserted into the middle of the boron nitride insulating tube, and finally the upper and lower ends of the graphite heating tube are sealed with phyllite plugs.

[0040] In a preferred embodiment, the dimensions involved in the high temperature and high pressure synthesis assembly block are determined according to the dimensions of the sample contained in the platinum tube.

[0041] In a preferred embodiment, the size of the pyrophyllite block is 32.5mm×32.5mm×32.5mm, and the hole in the center of the pyrophyllite block is a 16mm circular through hole. The present invention uses the pyrophyllite block as a pressure transmission medium, which has good pressure transmission, machinability, heat resistance, heat preservation and insulation.

[0042] In a preferred embodiment, the outer diameter of the graphite heating tube is 16 mm, and the inner diameter is 14 mm. The present invention uses the graphite heating tube as a heating furnace, and the temperature uniformity is high.

[0043] In a preferred embodiment, the outer diameter of the boron nitride insulation tube is 14 mm and the inner diameter is 4.5 mm.

[0044] In a preferred embodiment, the diameter of the pyrophyllite plug is 4.5 mm.

[0045] In a preferred embodiment, a thermocouple is provided in the high temperature and high pressure synthesis assembly block, and the thermocouple is an S-type thermocouple. The present invention uses an S-type thermocouple for temperature control, and the heating system adjusts the heating power through the temperature feedback from the S-type thermocouple, thereby changing the temperature, and can achieve real-time monitoring of the temperature.

[0046] In a preferred embodiment, the assembly diagram of assembling the platinum tube in the high temperature and high pressure synthesis assembly block is as follows: Figure 1 As shown, it can be seen that the assembly block includes a pyrophyllite block, a graphite heating tube, a boron nitride insulation tube, a platinum tube and a thermocouple.

[0047] In a preferred embodiment, the equation for the high temperature and high pressure reaction is:

[0048] 4Ca(OH)2+3Al2O3+6SiO2→2Ca2Al3(SiO4)3(OH)+3H2O.

[0049] In a preferred embodiment, the maximum temperature of the high temperature and high pressure reaction is 800-900° C., more preferably 850-900° C. The present invention controls the maximum temperature of the high temperature and high pressure reaction within the above range, thereby ensuring that the initial raw materials can fully undergo the high temperature and high pressure reaction, and at the same time provides a good crystal growth environment, thereby ensuring the successful synthesis of the zoisite single crystal. Lowering the maximum temperature of the high temperature and high pressure reaction will lead to insufficient high temperature and high pressure reaction of the initial raw materials, and increasing the maximum temperature of the high temperature and high pressure reaction will destroy the growth environment of the crystal inside the sample cavity.

[0050] In a preferred embodiment, the maximum pressure of the high temperature and high pressure reaction is 2.5-4.0 GPa, more preferably 3.0-4.0 GPa. The present invention controls the maximum pressure of the high temperature and high pressure reaction within the above range, thereby ensuring that the initial raw materials can fully undergo high temperature and high pressure reaction, while providing a good crystal growth environment, thereby ensuring the successful synthesis of zoisite single crystals. Lowering the maximum pressure of the high temperature and high pressure reaction will destroy the growth environment of the crystal inside the sample cavity, and increasing the maximum pressure of the high temperature and high pressure reaction will lead to insufficient high temperature and high pressure reaction of the initial raw materials.

[0051] In a preferred embodiment, the high temperature and high pressure reaction time is 80-120 hours, more preferably 80-100 hours. The present invention controls the high temperature and high pressure reaction time within the above range, thereby ensuring that the initial raw materials can fully undergo high temperature and high pressure reaction, while providing a good crystal growth environment, thereby ensuring the successful synthesis of zoisite single crystals. Shortening the high temperature and high pressure reaction time will lead to insufficient high temperature and high pressure reaction of the initial raw materials, and extending the high temperature and high pressure reaction time will destroy the growth environment of the crystal inside the sample cavity.

[0052] In a preferred embodiment, the heating and pressurizing process of the high temperature and high pressure reaction is: first increase the pressure to a maximum pressure of 2.5-4.0GPa at a pressure increase rate of 0.5GPa / h, and then step heating, the steps are as follows: increase the temperature to 300°C at a heating rate of 10°C / min, keep warm at 300°C for 10min, then increase the temperature to 600°C at a heating rate of 20°C / min, keep warm at 600°C for 10min, then increase the temperature to a maximum temperature of 800-900°C at a heating rate of 50°C / min, and react at the maximum temperature and maximum pressure conditions for 80-120h. The present invention has the advantages of ensuring the uniformity and stability of the pressure inside the sample chamber by adopting a pressure increase rate of 0.5GPa / h for pressure increase. Increasing the pressure increase rate will reduce the uniformity of the pressure inside the sample chamber, and reducing the pressure increase rate will reduce the stability of the pressure inside the sample chamber. The present invention adopts the above-mentioned heating program to increase the temperature, which has the advantage of prompting each initial raw material to undergo a certain degree of solid-phase reaction under corresponding temperature conditions. Changing the heating program will result in the inability to synthesize zoisite single crystals.

[0053] In a preferred embodiment, the equipment used for the high temperature and high pressure reaction is a six-sided large press.

[0054] In a preferred embodiment, after the high temperature and high pressure reaction is completed, the sample obtained by the reaction is taken out and the platinum tube is opened using a diamond cutter. After natural air drying, the zoisite single crystal is selected under a stereo microscope.

[0055] The present invention uses Ca(OH)2 powder, Al2O3 powder and SiO2 powder as initial raw materials. The Ca(OH)2 powder provides the essential calcium and hydrogen elements for synthesizing zoisite single crystals, the Al2O3 powder provides the essential aluminum element for synthesizing zoisite single crystals, and the SiO2 powder provides the essential silicon element for synthesizing zoisite single crystals. High-temperature pre-firing is used to improve the mixing uniformity of the initial raw materials and promote a certain degree of solid-phase reaction between the initial raw materials. Finally, the zoisite single crystal is synthesized under high temperature and high pressure conditions.

[0056] The present invention also provides a zoisite single crystal, which is synthesized according to the above method. The zoisite single crystal has an orthorhombic structure and a unit cell parameter The average size is 100-200μm, and the maximum size is 300μm.

[0057] The zoisite single crystal provided by the invention has the advantages of high purity, large size and stable chemical properties.

[0058] The room temperature in the embodiments of the present invention refers to "25±2°C".

[0059] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0060] Example 1

[0061] A method for synthesizing zoisite single crystals under high temperature and high pressure conditions:

[0062] (1) Ca(OH)2 powder, Al2O3 powder and SiO2 powder are mixed in a molar ratio of 4:3:6, and then ground and mixed to obtain a mixed material; wherein the purity of the Ca(OH)2 powder is greater than 99.99%, the purity of the Al2O3 powder is greater than 99.99%, and the purity of the SiO2 powder is greater than 99.99%;

[0063] (2) placing the mixed material obtained in step (1) into a platinum crucible, and then placing the platinum crucible into a muffle furnace, and then raising the temperature to 500° C. at a heating rate of 100° C. / h, keeping the temperature constant for 5 hours, and then cooling the temperature to room temperature at a cooling rate of 50° C. / h, and then grinding and mixing the mixed material in an agate mortar to obtain a pre-fired mixed material; using a tablet press to form a Φ4.5 mm×4.5 mm cylinder, and then inserting the cylinder into a Φ4.5 mm, 4 mm high, and 0.1 mm thick platinum tube, and sealing both ends of the platinum tube with a welding gun;

[0064] (3) Drill a circular through hole with a diameter of 16 mm in the center of a 32.5 mm × 32.5 mm × 32.5 mm pyrophyllite block, then insert a graphite heating tube with an outer diameter of 16 mm and an inner diameter of 14 mm into the circular through hole, then insert a boron nitride insulating tube with an outer diameter of 14 mm and an inner diameter of 4.5 mm into the graphite heating tube, then insert the platinum tube in step (2) into the middle of the boron nitride insulating tube, and finally seal the upper and lower ends of the circular graphite heating tube with pyrophyllite plugs with a diameter of 4.5 mm, and use an S-type thermocouple to control the temperature to obtain a high-temperature and high-pressure assembly block; place the high-temperature and high-pressure assembly block into a six-sided top large press for high-temperature and high-pressure reaction, setting the maximum pressure to 2.5 GPa and the maximum temperature to 800 ℃, time is 120h, the heating and pressurization process of the high temperature and high pressure reaction is: first increase the pressure to the maximum pressure of 2.5GPa at a pressure increase rate of 0.5GPa / h, and then step heating, the steps are as follows: increase the temperature to 300℃ at a heating rate of 10℃ / min, keep warm at 300℃ for 10min, then increase the temperature to 600℃ at a heating rate of 20℃ / min, keep warm at 600℃ for 10min, then increase the temperature to the maximum temperature of 800℃ at a heating rate of 50℃ / min, and react at the highest temperature and maximum pressure conditions for 120h; after the high temperature and high pressure reaction is completed, the obtained sample is taken out, the platinum tube is opened with a diamond cutter, the sample is naturally air-dried, and the zoisite single crystal is selected under a stereo microscope.

[0065] Example 2

[0066] A method for synthesizing zoisite single crystals under high temperature and high pressure conditions:

[0067] (1) Ca(OH)2 powder, Al2O3 powder and SiO2 powder are mixed in a molar ratio of 4:3:6, and then ground and mixed to obtain a mixed material; wherein the purity of the Ca(OH)2 powder is greater than 99.99%, the purity of the Al2O3 powder is greater than 99.99%, and the purity of the SiO2 powder is greater than 99.99%;

[0068] (2) placing the mixed material obtained in step (1) into a platinum crucible, and then placing the platinum crucible into a muffle furnace, and then raising the temperature to 500° C. at a heating rate of 100° C. / h, keeping the temperature constant for 5 hours, and then cooling the temperature to room temperature at a cooling rate of 50° C. / h, and then grinding and mixing the mixed material in an agate mortar to obtain a pre-fired mixed material; using a tablet press to form a Φ4.5 mm×4.5 mm cylinder, and then inserting the cylinder into a Φ4.5 mm, 4 mm high, and 0.1 mm thick platinum tube, and sealing both ends of the platinum tube with a welding gun;

[0069] (3) Drill a circular through hole with a diameter of 16 mm in the center of a 32.5 mm × 32.5 mm × 32.5 mm pyrophyllite block, then insert a graphite heating tube with an outer diameter of 16 mm and an inner diameter of 14 mm into the circular through hole, then insert a boron nitride insulating tube with an outer diameter of 14 mm and an inner diameter of 4.5 mm into the graphite heating tube, then insert the platinum tube in step (2) into the middle of the boron nitride insulating tube, and finally seal the upper and lower ends of the circular graphite heating tube with pyrophyllite plugs with a diameter of 4.5 mm, and use an S-type thermocouple to control the temperature to obtain a high-temperature and high-pressure assembly block; place the high-temperature and high-pressure assembly block into a six-sided top large press for high-temperature and high-pressure reaction, setting the maximum pressure to 3.0 GPa and the maximum temperature to 850 ℃, time is 100h, the heating and pressurization process of the high temperature and high pressure reaction is: first increase the pressure to the maximum pressure of 3.0GPa at a pressure increase rate of 0.5GPa / h, and then step heating, the steps are as follows: increase the temperature to 300℃ at a heating rate of 10℃ / min, keep warm at 300℃ for 10min, then increase the temperature to 600℃ at a heating rate of 20℃ / min, keep warm at 600℃ for 10min, then increase the temperature to the maximum temperature of 850℃ at a heating rate of 50℃ / min, and react at the highest temperature and maximum pressure conditions for 100h; after the high temperature and high pressure reaction is completed, the obtained sample is taken out, the platinum tube is opened with a diamond cutter, the sample is naturally air-dried, and the zoisite single crystal is selected under a stereo microscope.

[0070] Example 3

[0071] A method for synthesizing zoisite single crystals under high temperature and high pressure conditions:

[0072] (1) Ca(OH)2 powder, Al2O3 powder and SiO2 powder are mixed in a molar ratio of 4:3:6, and then ground and mixed to obtain a mixed material; wherein the purity of the Ca(OH)2 powder is greater than 99.99%, the purity of the Al2O3 powder is greater than 99.99%, and the purity of the SiO2 powder is greater than 99.99%;

[0073] (2) placing the mixed material obtained in step (1) into a platinum crucible, and then placing the platinum crucible into a muffle furnace, and then raising the temperature to 500° C. at a heating rate of 100° C. / h, keeping the temperature constant for 5 hours, and then cooling the temperature to room temperature at a cooling rate of 50° C. / h, and then grinding and mixing the mixed material in an agate mortar to obtain a pre-fired mixed material; using a tablet press to form a Φ4.5 mm×4.5 mm cylinder, and then inserting the cylinder into a Φ4.5 mm, 4 mm high, and 0.1 mm thick platinum tube, and sealing both ends of the platinum tube with a welding gun;

[0074] (3) Drill a circular through hole with a diameter of 16 mm in the center of a 32.5 mm × 32.5 mm × 32.5 mm pyrophyllite block, then insert a graphite heating tube with an outer diameter of 16 mm and an inner diameter of 14 mm into the circular through hole, then insert a boron nitride insulating tube with an outer diameter of 14 mm and an inner diameter of 4.5 mm into the graphite heating tube, then insert the platinum tube in step (2) into the middle of the boron nitride insulating tube, and finally seal the upper and lower ends of the circular graphite heating tube with pyrophyllite plugs with a diameter of 4.5 mm, and use an S-type thermocouple to control the temperature to obtain a high-temperature and high-pressure assembly block; place the high-temperature and high-pressure assembly block into a six-sided top large press for high-temperature and high-pressure reaction, setting the maximum pressure to 3.5 GPa and the maximum temperature to 90 0℃, time is 80h, the heating and pressurization process of the high temperature and high pressure reaction is: first increase the pressure to the maximum pressure of 3.5GPa at a pressure increase rate of 0.5GPa / h, and then step heating, the steps are as follows: increase the temperature to 300℃ at a heating rate of 10℃ / min, keep warm at 300℃ for 10min, then increase the temperature to 600℃ at a heating rate of 20℃ / min, keep warm at 600℃ for 10min, then increase the temperature to the maximum temperature of 900℃ at a heating rate of 50℃ / min, and react at the highest temperature and maximum pressure conditions for 80h; after the high temperature and high pressure reaction is completed, the obtained sample is taken out, the platinum tube is opened with a diamond cutter, the sample is naturally air-dried, and the zoisite single crystal is selected under a stereo microscope.

[0075] Example 4

[0076] A method for synthesizing zoisite single crystals under high temperature and high pressure conditions:

[0077] (1) Ca(OH)2 powder, Al2O3 powder and SiO2 powder are mixed in a molar ratio of 4:3:6, and then ground and mixed to obtain a mixed material; wherein the purity of the Ca(OH)2 powder is greater than 99.99%, the purity of the Al2O3 powder is greater than 99.99%, and the purity of the SiO2 powder is greater than 99.99%;

[0078] (2) placing the mixed material obtained in step (1) into a platinum crucible, and then placing the platinum crucible into a muffle furnace, and then raising the temperature to 500° C. at a heating rate of 100° C. / h, keeping the temperature constant for 5 hours, and then cooling the temperature to room temperature at a cooling rate of 50° C. / h, and then grinding and mixing the mixed material in an agate mortar to obtain a pre-fired mixed material; using a tablet press to form a Φ4.5 mm×4.5 mm cylinder, and then inserting the cylinder into a Φ4.5 mm, 4 mm high, and 0.1 mm thick platinum tube, and sealing both ends of the platinum tube with a welding gun;

[0079] (3) Drill a circular through hole with a diameter of 16 mm in the center of a 32.5 mm × 32.5 mm × 32.5 mm pyrophyllite block, then insert a graphite heating tube with an outer diameter of 16 mm and an inner diameter of 14 mm into the circular through hole, then insert a boron nitride insulating tube with an outer diameter of 14 mm and an inner diameter of 4.5 mm into the graphite heating tube, then insert the platinum tube in step (2) into the middle of the boron nitride insulating tube, and finally seal the upper and lower ends of the circular graphite heating tube with pyrophyllite plugs with a diameter of 4.5 mm, and use an S-type thermocouple to control the temperature to obtain a high-temperature and high-pressure assembly block; place the high-temperature and high-pressure assembly block into a six-sided top large press for high-temperature and high-pressure reaction, set the maximum pressure to 4.0 GPa, and the maximum temperature to 90 0℃, time is 80h, the heating and pressurization process of the high temperature and high pressure reaction is: first increase the pressure to the maximum pressure of 4.0GPa at a pressure increase rate of 0.5GPa / h, and then step heating, the steps are as follows: increase the temperature to 300℃ at a heating rate of 10℃ / min, keep warm at 300℃ for 10min, then increase the temperature to 600℃ at a heating rate of 20℃ / min, keep warm at 600℃ for 10min, then increase the temperature to the maximum temperature of 900℃ at a heating rate of 50℃ / min, and react at the highest temperature and maximum pressure conditions for 80h; after the high temperature and high pressure reaction is completed, the obtained sample is taken out, the platinum tube is opened with a diamond cutter, the sample is naturally air-dried, and the zoisite single crystal is selected under a stereo microscope.

[0080] Comparative Example 1

[0081] The only difference from Example 1 is that in step (3), the heating and pressurizing process of the high temperature and high pressure reaction is: increasing the pressure to 2.5 GPa at a pressure increasing rate of 0.5 GPa / h, then increasing the temperature to 800°C at a rate of 20°C / min, and keeping the temperature for 120 hours.

[0082] It can be observed that under these conditions, no single crystal of zoisite can be synthesized.

[0083] Comparative Example 2

[0084] The only difference from Example 2 is that in step (3), the high temperature and high pressure reaction time is 48 hours.

[0085] It can be observed that under these conditions, no single crystal of zoisite can be synthesized.

[0086] Comparative Example 3

[0087] The only difference from Example 3 is that step (2) is: the mixed material obtained in step (1) is made into a Φ4.5 mm×4.5 mm cylinder using a tablet press, and then the cylindrical sample is stuffed into a platinum tube with a diameter of 4.5 mm, a height of 4 mm, and a wall thickness of 0.1 mm, and both ends of the platinum tube are sealed using a welding gun.

[0088] It can be observed that under these conditions, no single crystal of zoisite can be synthesized.

[0089] Comparative Example 4

[0090] The only difference from Example 1 is that in step (2), the temperature is increased to 300° C. at a heating rate of 100° C. / h and maintained at this temperature for 5 h.

[0091] It can be observed that under these conditions, no single crystal of zoisite can be synthesized.

[0092] Comparative Example 5

[0093] The only difference from Example 1 is that in step (2), the temperature is increased to 500° C. at a heating rate of 100° C. / h and maintained at this temperature for 30 min.

[0094] It can be observed that under these conditions, no single crystal of zoisite can be synthesized.

[0095] Figure 2 This is a microscopic photograph of a zoisite single crystal synthesized in Example 1 of the present invention. Figure 2 It can be seen that the zoisite single crystal is successfully synthesized by the method provided by the present invention, and the obtained zoisite single crystal is a single phase without impurity phase.

[0096] Figure 3 This is a microscopic photograph of the unsynthesized zoisite single crystal in Comparative Example 1 of the present invention. Figure 3 It can be seen that the method in Comparative Example 1 cannot be used to synthesize a zoisite single crystal.

[0097] Figure 4 This is the Raman spectrum of the zoisite single crystal synthesized in Example 1 of the present invention. Figure 4It can be seen that the zoisite single crystal is successfully synthesized by the method provided by the present invention.

[0098] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for growing zoisite single crystals under high temperature and high pressure, characterized in that: The following steps are involved: (1) mixing Ca(OH)2 powder, Al2O3 powder and SiO2 powder uniformly to obtain a mixed material; wherein the molar ratio of the Ca(OH)2 powder, Al2O3 powder and SiO2 powder is 4:3:6; (2) pre-calcining the mixture obtained in step (1) at high temperature, cooling it to room temperature and forming it into a cylinder, which is then placed in a platinum tube and sealed at both ends of the platinum tube; the high temperature pre-calcination is: heating the temperature to 500° C. at a heating rate of 100° C. / h and maintaining the temperature for 5 hours; (3) Assembling the platinum tube in step (2) in a high-temperature and high-pressure synthesis assembly block, and then conducting a high-temperature and high-pressure reaction to obtain a zoisite single crystal; the maximum temperature of the high-temperature and high-pressure reaction is 800-900°C, the maximum pressure is 2.5-4.0GPa, and the time is 80-120h; the heating and pressurizing process of the high-temperature and high-pressure reaction is: first increasing the pressure to a maximum pressure of 2.5-4.0GPa at a pressure increase rate of 0.5GPa / h, and then step-by-step heating, the steps are as follows: heating to 300°C at a heating rate of 10°C / min, keeping at 300°C for 10min, then heating to 600°C at a heating rate of 20°C / min, keeping at 600°C for 10min, then heating to a maximum temperature of 800-900°C at a heating rate of 50°C / min, and reacting at the maximum temperature and maximum pressure conditions for 80-120h.

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