CN111635231A - A kind of preparation method of polycrystalline diamond transparent ceramics - Google Patents

Abstract

The invention provides a method for preparing polycrystalline diamond transparent ceramics. The method uses diamond micropowder as a raw material. The process steps are as follows: (1) the carbon-containing purity of the raw material diamond micro-powder is required to be greater than 99%. The diamond micropowder is first subjected to impurity removal treatment, and then vacuum heat treatment. For the diamond micropowder with carbon purity that meets the requirements, vacuum heat treatment is directly performed to remove the oxygen, nitrogen or water vapor adsorbed on the surface of the diamond micropowder; (2) After the vacuum heat treatment The diamond fine powder is loaded into the cleaned metal foil for pre-compression molding; (3) The parison wrapped with the metal foil is sintered at a pressure of 10-30 GPa and a temperature of 1500-3000 ℃ for 10-2000s. After the sintering time is reached, the pressure is reduced and the temperature is lowered. to normal pressure and room temperature, and then use inorganic acid to remove the metal foil to obtain polycrystalline diamond transparent ceramics. The invention provides a new technical scheme for the preparation of polycrystalline diamond transparent ceramics.

Description

A kind of preparation method of polycrystalline diamond transparent ceramics

technical field

The invention belongs to the field of polycrystalline diamond transparent ceramics, and relates to a preparation method of polycrystalline diamond transparent ceramics.

Background technique

Transparent ceramics can be roughly divided into two categories according to the application characteristics: transparent ceramics with light transmission/wave transmission and transparent ceramics with special optical functional characteristics. reflect. Compared with ordinary optical materials, transparent ceramics not only have the properties of high melting point, high strength, high insulation, corrosion resistance, high temperature resistance, etc. shared by ceramic materials, but also have good light transmittance, so they can be made into a variety of optical materials. Electro-optical, electro-mechanical dual-use devices. Transparent ceramics have broad application prospects in national defense, space science, medicine, laser, infrared detection, new light sources, detection, and exploration. For example, transparent ceramics are often used in infrared detection windows, high-pressure sodium lamps, substitutes for platinum crucibles, substrates for integrated circuits, high-frequency insulating materials, high-temperature lenses, infrared components, flat panel displays, and even laser materials. It is also used in front-line combat weapons and equipment with viewing windows such as a new generation of armed helicopters and armored vehicles, as well as in military fields such as missile fairings, photoelectric radar fairings, infrared warnings, and photoelectric countermeasures.

Diamond is the hardest material known so far, and at the same time has high melting point, high thermal conductivity, high insulation, high light transmittance, high refractive index, and corrosion resistance. It is an ideal special transparent ceramic material. The sustainable development of the national economy is of great significance. Diamond is mainly divided into single crystal diamond and polycrystalline diamond transparent ceramics. In view of the anisotropy of single crystal diamond and the difficulty of preparation, researchers are mainly devoted to the preparation and application of polycrystalline diamond transparent ceramics. Polycrystalline diamond transparent ceramics have the advantages of isotropy, high hardness, good toughness, high insulation, high thermal conductivity, high visible light transmittance, and high guided wave (infrared, X-ray, neutron, etc.) rates. The existing bulk polycrystalline diamond transparent ceramic preparation method is mainly a high temperature and high pressure phase change method.

The high temperature and high pressure phase change method is a method of directly converting graphite or other non-diamond carbon (such as carbon nanotubes, glassy carbon, onion carbon, graphene, etc.) into diamond under extreme conditions of high temperature and high pressure. There are the following problems: (1) The high temperature and high pressure phase change method to prepare polycrystalline diamond transparent ceramics is extremely difficult and expensive. This is because during the sintering process, more than 20% of the sintered sample volume will collapse, which will easily lead to instability and pressure in the high temperature and high pressure cavity. The stress concentration of the anvil (the key component of high-voltage equipment) makes it extremely difficult to implement the technology; at the same time, the seal failure of the high-pressure cavity caused by the stress concentration of the anvil and the instability of the high-temperature and high-pressure cavity (commonly known as "shooting" in the field of high-pressure research) will be severely reduced The service life of the anvil will greatly increase the production cost. (2) Due to the characteristics of high melting point and high recrystallization temperature of diamond, the grain size of transparent polycrystalline diamond prepared by high temperature and high pressure phase change method is difficult to control, and most of them are nano-scale. This is because polycrystalline diamond is prepared by high pressure phase change method. The mechanism of transparent ceramics is the phase transformation of graphite or other non-diamond carbons. After the formation of diamond grains, the sintering temperature needs to be increased to above the recrystallization temperature to promote grain growth, but the existing high temperature and high pressure experimental technology cannot achieve sufficient control of grains. size temperature. (3) Due to the severe volume collapse of the sintered sample during the sintering process of the high temperature and high pressure phase change method, it is easy to cause uneven pressure field and temperature field in the high temperature and high pressure chamber, resulting in residual stress in the prepared polycrystalline diamond transparent ceramic block. Large, poor uniformity and other defects.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the prior art, and to provide a method for preparing polycrystalline diamond transparent ceramics, so as to facilitate the regulation of the crystal grain size of transparent polycrystalline diamond, and to avoid high temperature and high pressure cavity instability and anvil stress during sintering The high-pressure chamber seal fails due to concentration, or the pressure field and temperature field in the high-temperature and high-pressure chamber are uneven.

The preparation method of the polycrystalline diamond transparent ceramic provided by the present invention uses diamond micropowder with a particle size of 5nm to 100μm as a raw material, and the process steps are as follows:

(1) Pretreatment of diamond powder

The carbon-containing purity of the raw diamond micropowder is required to be greater than 99%. For the diamond micropowder whose carbon-containing purity does not meet the requirements, the impurity removal treatment is performed first, and then vacuum heat treatment is performed. Remove oxygen, nitrogen or water vapor adsorbed on the surface of diamond powder;

(2) Pre-press molding

Put the diamond powder after vacuum heat treatment into the cleaned metal foil for pre-compression molding, and the density of the obtained parison should not be less than 30%;

(3) Sintering and removal of metal foil

Put the metal foil-wrapped parison into a large-cavity static high pressure device, and sinter it for 10s to 2000s under the conditions of a pressure of 10GPa-30GPa and a temperature of 1500℃-3000℃. Then, the metal foil is removed with an inorganic acid to obtain a polycrystalline diamond transparent ceramic.

It should be noted that the matching relationship between pressure and temperature during sintering is that the higher the pressure, the lower the temperature, that is, within the range of the above sintering temperature and sintering pressure, if a high sintering pressure is selected, a low sintering temperature is selected. If the sintering pressure is high, it is matched with a high sintering temperature (see example).

For the preparation method of the above-mentioned polycrystalline diamond transparent ceramics, according to the requirements of the prepared polycrystalline diamond transparent ceramics, the raw material diamond micropowder can be selected from single particle size or mixed particle size micropowder.

The preparation method of above-mentioned polycrystalline diamond transparent ceramics, the preparation method of raw material diamond micropowder includes detonation method or impact method, static high pressure method, large particle diamond pulverization method and chemical vapor deposition method, the diamond micropowder prepared by these methods has commercially available commodities , can be purchased through the market. Among them, the chemical vapor deposition method can obtain diamond micropowder with a carbon purity greater than 99%, and diamond micropowder prepared by other methods cannot meet the requirement of carbon purity greater than 99%, and needs to be treated with impurity removal.

About the impurity removal of diamond micropowder, at least one method in pickling method, electrolysis method or alkaline cleaning method can be adopted, and the pickling method adopted in the present invention operates as follows: diamond micropowder and inorganic acid are in a weight ratio of 1:(2 ~4) add it to the purification kettle, stir and heat it in a water bath to 60 ℃ ~ 70 ℃, then continue to stir at this temperature for at least 24 hours, and then wait for the powder to settle to remove the liquid and wash it with deionized water until it becomes neutral and then dry; The inorganic acid is at least one of hydrofluoric acid and hydrochloric acid, and the mass concentration of the inorganic acid is 20%-40%.

In the preparation method of the above-mentioned polycrystalline diamond transparent ceramics, the effect of vacuum heat treatment in step (1) is to remove the oxygen, nitrogen or water vapor adsorbed on the surface of the diamond micropowder, and the specific operation is as follows: the diamond micropowder whose carbon-containing purity meets the requirements is subjected to a vacuum degree of 1×10 ^-1 Pa～1×10 ^-5 Pa, and the temperature is 500℃～1200℃ for 0.1h～6h.

In the preparation method of the above-mentioned polycrystalline diamond transparent ceramics, in step (2), the metal foil material used is tantalum foil, rhenium foil or platinum foil, and needs to be cleaned before use, and the operation of cleaning treatment is: the metal foil material is sequentially Polishing, degreasing, ultrasonic cleaning, infrared drying.

In the above-mentioned preparation method of polycrystalline diamond transparent ceramics, in step (2), the pressure of pre-pressing is 400MPa-700MPa, and the pressing time is determined by the compactness of the obtained parison.

It has been found that the heating rate, cooling rate, pressure increasing rate and decompression rate have an impact on the microstructure and macroscopic properties of the final sample. By adjusting the heating rate, cooling rate, pressure increasing rate and pressure reducing rate, the stress can be effectively released. Reduce the internal micro-cracks of the sample and improve the uniformity of the sample. In the present invention, the rate of increasing the pressure from normal pressure to sintering pressure and the rate of decreasing the pressure from sintering pressure to normal pressure are 0.5GPa/h～60GPa/h, and the temperature is increased from room temperature to sintering temperature The heating rate and the cooling rate of reducing the temperature from the sintering temperature to room temperature are 1 °C/min ~ 1000 °C/min.

It has been found through research that the selection of the time points for starting loading and unloading under the two conditions of temperature and pressure, as well as the combined action time of temperature and pressure, will also have an impact on the microstructure and macroscopic properties of the final sample. The way to lower the pressure is as follows:

First increase the pressure from normal pressure to sintering pressure and keep the sintering pressure, then increase the temperature from room temperature to sintering temperature, after the sintering time is reached, first reduce the temperature from sintering temperature to room temperature, and then reduce the pressure from sintering pressure to sintering temperature normal pressure;

Or first increase the pressure from normal pressure to sintering pressure and maintain the sintering pressure, and then increase the temperature from room temperature to sintering temperature. The pressure is reduced from sintering pressure to normal pressure;

Or first increase the pressure from normal pressure to the pressure where diamond can exist stably and maintain the pressure, then increase the temperature from room temperature to sintering temperature, and then increase the pressure to sintering pressure, after the sintering time arrives, first increase the temperature from the sintering temperature. Drop to room temperature, and then reduce the pressure from sintering pressure to normal pressure;

Or first increase the pressure from normal pressure to the pressure where diamond can exist stably and maintain the pressure, then increase the temperature from room temperature to the sintering temperature, and then increase the pressure to the sintering pressure. After the sintering time is reached, start cooling and depressurization , reduce the temperature from the sintering temperature to room temperature, and reduce the pressure from the sintering pressure to normal pressure.

The pressure at which the above diamond can exist stably is related to the sintering temperature. For the temperature and pressure range where the diamond can exist stably, please refer to the following literature:

Ghiringhelli L M, Los J H, Meijer E J, et al. Modeling the phase diagram of carbon[J]. Physical review letters, 2005, 94(14): 145701.

Khaliullin R Z,Eshet H,Kühne T D,et al.Graphite-diamond phasecoexistence study employing a neural-network mapping of the ab initiopotential energy surface[J].Physical Review B,2010,81(10):100103.

In the preparation method of the above polycrystalline diamond transparent ceramics, the inorganic acid used for removing the wrapping material in step (3) is at least one of hydrofluoric acid and nitric acid, and the mass concentration of the inorganic acid is 30%-50%.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The method of the present invention uses diamond micropowder as a raw material, and does not add any non-carbon sintering aid, which provides a new technical solution for the preparation of polycrystalline diamond transparent ceramics.

(2) Since the method of the present invention uses the diamond micropowder as the raw material, the raw material does not undergo phase change during the sintering process, and the selection of the sintering temperature and pressure will not cause the crystal grains to grow significantly, so it is convenient to control the crystal grain of the raw diamond micropowder. The grain size of the prepared polycrystalline diamond transparent ceramics can be adjusted by controlling the grain size.

(3) Since the method of the present invention uses diamond micropowder as the raw material, the raw material does not undergo phase change during the sintering process, so the sintered sample will not undergo volume collapse during sintering, which effectively eliminates the instability of the high temperature and high pressure cavity and the anvil. The source of stress concentration not only ensures the smooth progress of sintering, but also avoids the increase of preparation cost caused by equipment damage.

(4) The method of the present invention uses diamond micropowder as a raw material, which can make the pressure field and temperature field in the high temperature and high pressure chamber uniform, and at the same time, the rate and method of temperature increase and pressure increase, temperature drop and pressure drop are optimized, so the prepared polycrystalline diamond transparent ceramics The block uniformity is good, the residual stress is small, and the large-size, crack-free polycrystalline diamond transparent ceramics can be obtained (see examples)

(5) Because the method of the present invention is convenient to regulate and control the crystal grain size of the prepared polycrystalline diamond transparent ceramics, it is beneficial to the regulation of the visible light transmittance, hardness and toughness of the polycrystalline diamond transparent ceramics, and prepares a variety of light transmission properties ( Visible light transmittance 5%-95%), polycrystalline diamond transparent ceramics with different hardness and toughness.

(6) The polycrystalline diamond transparent ceramics prepared by the method of the present invention have wide application prospects in the fields of national defense and civil use. Thermal conductivity, high electrical insulation, can be used to make various window materials; ②Because of its transparent visible light, high refractive index, high wear resistance, high decorative and surface scratch and scratch resistance, it can be used to make high-grade Watch cases, glasses and other luxury goods; ③Because of its high wear resistance, it can be used to make various knives, and it is convenient to use optical means to detect internal defects such as micro-cracks; ④Because of its excellent light transmission and wave transmission The performance, high strength and high hardness can be used to prepare a diamond anvil, which can replace the existing single crystal diamond anvil, and has the advantages of low use cost and large size.

Description of drawings

Fig. 1 is the optical microscope photograph of the polycrystalline diamond transparent ceramic prepared by embodiment 1;

Fig. 2 is the optical microscope photo of the polycrystalline diamond transparent ceramics prepared by embodiment 2;

Fig. 3 is the optical microscope photo of the polycrystalline diamond transparent ceramic prepared by embodiment 3;

Fig. 4 is the optical microscope photograph of the polycrystalline diamond transparent ceramics prepared in Example 4;

Fig. 5 is the optical microscope photo of the polycrystalline diamond transparent ceramics prepared in Example 5;

Fig. 6 is the optical microscope photograph of the polycrystalline diamond transparent ceramics prepared by embodiment 6;

7 is an optical photograph of the polycrystalline diamond transparent ceramic prepared in Example 7;

Fig. 8 is the X-ray diffractogram of the polycrystalline diamond transparent ceramic prepared by embodiment 2;

Fig. 9 is the Raman spectrogram of the polycrystalline diamond transparent ceramic prepared in Example 2;

Fig. 10 is the scanning electron microscope picture (magnification 10000 times) of polycrystalline diamond transparent ceramics prepared in Example 2;

11 is a scanning electron microscope image of the polycrystalline diamond transparent ceramic prepared in Example 4 (magnified 20,000 times).

Detailed ways

The preparation method of the polycrystalline diamond transparent ceramics of the present invention will be further described below through examples and in conjunction with the accompanying drawings. Obviously, the described embodiments are only some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

In the following examples, the large-cavity static high-pressure device is a domestic hinged six-sided top press, model DS 6×8MN, manufacturer: Zhangjiakou Prospecting Machinery Factory; all raw materials used are purchased from the market.

Example 1

The steps of preparing polycrystalline diamond transparent ceramics in the present embodiment are as follows:

(1) Pretreatment of diamond powder

The single crystal diamond micropowder with a particle size range of 10nm to 50nm prepared by a commercially available detonation method is used as a raw material, and firstly, it is subjected to impurity removal treatment: the raw material diamond micropowder and hydrofluoric acid (mass concentration of 20%) are in a weight ratio of 1:3 Add it to the purification kettle, stir and heat it to 60 ℃ in a water bath, and then continue to stir at this temperature for 48 hours, then wait for the powder to settle and pour out the liquid, and wash it with deionized water until it becomes neutral, and then mix the washed diamond micropowder with Hydrochloric acid (mass concentration of 25%) was added to the purification kettle at a weight ratio of 1:3, stirred and heated to 60°C in a water bath, and then continued to stir at this temperature for 48h, and then the powder was settled and the liquid was poured out, and deionized Wash with water until neutral, repeat the above acid-dissolving and impurity-removing steps for 2 times, and dry the treated diamond micropowder;

The dried diamond powder was treated for 3 hours under the conditions of vacuum degree of 5×10 ^-4 Pa and temperature of 700°C to remove impurities such as oxygen, nitrogen and water vapor adsorbed on the surface of the diamond powder;

(2) Pre-press molding

Using tantalum foil as the wrapping material, conventional polishing, degreasing, ultrasonic cleaning, and infrared drying were performed on the surface of the wrapping material tantalum foil; The pressure is maintained for 1 min, and pre-compression molding is performed to obtain a parison with a compactness of 45%;

(3) Sintering and removal of metal foil

The metal foil-wrapped parison was placed in a large-cavity static high-pressure device, and sintered for 600s at a pressure of 15GPa and a temperature of 2200°C. The temperature and pressure loading method, unloading method and process conditions are as follows: increase the pressure by 10GPa at a pressure increase rate of 3GPa/h and keep the pressure unchanged, then increase the temperature to 2200℃ at a heating rate of 100℃/min and keep the temperature unchanged, and then use After the pressure increase rate of 20GPa/h was increased to 15GPa, the pressure remained unchanged, and sintered at 15GPa and 2200 °C for 600s. After the sintering time was reached, cooling and depressurization were started at the same time, and the temperature was lowered at a cooling rate of 3 °C/min. To room temperature, the pressure was reduced to normal pressure at a depressurization rate of 1 GPa/h.

Put the obtained sample into a mixed acid composed of hydrofluoric acid with a mass concentration of 30% and nitric acid with a mass concentration of 40% (the volume ratio of hydrofluoric acid and nitric acid is 1:1) to remove the wrapping material tantalum, and then grind the sample with a grinding disc. When it is bright, polycrystalline diamond transparent ceramics are obtained.

Example 2

The steps of preparing polycrystalline diamond transparent ceramics in the present embodiment are as follows:

(1) Pretreatment of diamond powder

The single crystal diamond micropowder with an average particle size of about 500nm prepared by a commercially available detonation method is used as a raw material, firstly, it is subjected to impurity removal treatment: the raw material diamond micropowder and hydrofluoric acid (mass concentration of 40%) are added in a weight ratio of 1:2 In the purification kettle, stir and heat in a water bath to 70 ° C, and then continue to stir at this temperature for 72 hours, then wait for the powder to settle and pour out the liquid, and wash with deionized water until neutral, and then wash the diamond powder and hydrochloric acid. (mass concentration is 35%) is added to the purification kettle according to the weight ratio of 1:2, stirred and heated to 70 ° C in a water bath, and then continued to stir at this temperature for 72 h, and then the liquid is poured out after the powder settles, and deionized water is used. Wash to neutrality, repeat the above acid dissolving and impurity removal steps for 3 times, and then dry the treated diamond micropowder;

The dried diamond powder was treated for 5 hours under the conditions of vacuum degree of 4×10 ^-3 Pa and temperature of 800°C to remove impurities such as oxygen, nitrogen and water vapor adsorbed by the diamond surface powder;

(2) Pre-press molding

Using rhenium foil as the wrapping material, conventional polishing, degreasing, ultrasonic cleaning, and infrared drying were performed on the surface of the wrapping material rhenium foil; then, the pretreated diamond powder in step (1) was loaded into the wrapping material rhenium foil at 700MPa. The pressure is maintained for 5 minutes, and pre-compression molding is performed to obtain a parison with a compactness of 55%;

(3) Sintering and removal of metal foil

The metal foil-wrapped parison was placed in a large-cavity static high-pressure device, and sintered for 1800s at a pressure of 16GPa and a temperature of 2200°C. The temperature and pressure loading method, unloading method and process conditions are as follows: increase the pressure by 16GPa at a pressure increase rate of 10GPa/h and keep the pressure unchanged, then increase the temperature to 2200℃ at a heating rate of 200℃/min and keep sintering for 1800s, and the sintering time reaches After that, the temperature reduction and depressurization were started simultaneously, the temperature was lowered to room temperature at a cooling rate of 1.5°C/min, and the pressure was lowered to normal pressure at a depressurization rate of 0.5GPa/h.

The obtained sample is put into nitric acid with a mass concentration of 50% to remove the wrapping material rhenium, and then the sample is polished to a bright spot with a grinding disc to obtain a polycrystalline diamond transparent ceramic.

Example 3

The steps of preparing polycrystalline diamond transparent ceramics in the present embodiment are as follows:

(1) Pretreatment of diamond powder

The single crystal diamond micropowder with an average particle size of about 500nm prepared by the commercially available detonation method and the single crystal diamond micropowder with an average particle size of about 5μm prepared by the commercially available pulverized large-particle diamond method were used as raw materials, and the weight ratio of the two was 1:1. , carry out impurity removal treatment after mixing them uniformly: raw material diamond micropowder and hydrofluoric acid (mass concentration is 30%) are added in purification kettle according to weight ratio 1: 2, stir and heat in water bath to 60 ℃, then at this temperature Continue to stir for 48h, then wait for the powder to settle and pour out the liquid, and wash with deionized water until neutral, and then add the washed diamond micropowder and hydrochloric acid (mass concentration of 25%) into the purification kettle according to a weight ratio of 1:2, Stir and heat in a water bath to 60°C, and then continue to stir at this temperature for 48 hours. Then, after the powder settles, the liquid is poured out, and the liquid is washed with deionized water until neutral. After the diamond powder is dried.

The dried diamond powder was treated for 6 hours under the conditions of vacuum degree of 1×10 ^-5 Pa and temperature of 500°C to remove oxygen, nitrogen, water vapor and other impurities adsorbed on the surface of the diamond powder;

(2) Pre-press molding

Using tantalum foil as the wrapping material, conventional polishing, degreasing, ultrasonic cleaning, and infrared drying were performed on the surface of the wrapping material tantalum foil; The pressure is maintained for 1 min, and the pre-compression molding process is performed to obtain a parison with a compactness of 35%;

(3) Sintering and removal of metal foil

The metal foil-wrapped parison was placed in a large-cavity static high-pressure device, and sintered for 900s at a pressure of 16GPa and a temperature of 2300°C. The temperature and pressure loading method, unloading method and process conditions are as follows: increase the pressure by 16GPa at a pressure increase rate of 20GPa/h and keep the pressure unchanged, then increase the temperature to 2300℃ at a heating rate of 10℃/min and keep sintering for 900s, and the sintering time ends. Then, the temperature was lowered to room temperature at a cooling rate of 1000°C/min, and then the pressure was lowered to normal pressure at a rate of 0.5GPa/h after the cooling.

Put the obtained sample into a mixed acid composed of 40% hydrofluoric acid by mass and 40% nitric acid by mass (the volume ratio of hydrofluoric acid and nitric acid is 1:1) to remove the wrapping material tantalum, and then use a grinding disc to polish the sample to bright , that is, to obtain polycrystalline diamond transparent ceramics.

Example 4

The steps of preparing polycrystalline diamond transparent ceramics in the present embodiment are as follows:

(1) Pretreatment of diamond powder

The single crystal diamond micropowder with an average particle size of about 1 μm prepared by the commercially available pulverized large-particle diamond method is used as the raw material, firstly, it is subjected to impurity removal treatment: the raw material diamond micropowder and hydrofluoric acid (mass concentration of 20%) are in a weight ratio of 1: 3 Add it to the purification kettle, stir and heat it to 60°C in a water bath, and then continue to stir at this temperature for 24 hours, then wait for the powder to settle and pour out the liquid, and wash it with deionized water until it becomes neutral, and then wash the diamond micropowder with water. Add hydrochloric acid (mass concentration of 25%) into the purification kettle in a weight ratio of 1:3, stir and heat in a water bath to 60 ° C, then continue to stir at this temperature for 24 hours, and then wait for the powder to settle and pour out the liquid, and use Washing with ionized water until neutral, repeating the above acid-dissolving and impurity-removing steps for 3 times, drying the treated diamond micropowder;

The dried diamond powder is treated for 0.5h under the conditions of vacuum degree of 5×10 ^-4 Pa and temperature of 1000℃ to remove impurities such as oxygen, nitrogen and water vapor adsorbed on the surface of the diamond powder;

(2) Pre-press molding

Using rhenium foil as the wrapping material, conventional polishing, degreasing, ultrasonic cleaning, and infrared drying were performed on the surface of the wrapping material rhenium foil; then, the pretreated diamond powder in step (1) was loaded into the wrapping material rhenium foil at 600MPa The pressure is maintained for 2 minutes, and pre-compression molding is performed to obtain a parison with a compactness of 50%;

(3) Sintering and removal of metal foil

The metal foil-wrapped parison was placed in a large-cavity static high-pressure device, and sintered for 10s at a pressure of 12GPa and a temperature of 2800°C. The temperature and pressure loading method, unloading method and process conditions are as follows: increase the pressure by 12GPa at a pressure increase rate of 60GPa/h and keep the pressure unchanged, then increase the temperature to 2800℃ at a heating rate of 500℃/min and keep sintering for 10s, and the sintering time ends. After that, the temperature was lowered to room temperature at a cooling rate of 1000 °C/min, and the pressure was reduced to normal pressure at a pressure reduction rate of 30 GPa/h after 10 min of cooling.

The obtained sample is put into hydrofluoric acid with a mass concentration of 50% to remove the wrapping material rhenium, and then the sample is polished with a grinding disc to become bright, thus obtaining a polycrystalline diamond transparent ceramic.

Example 5

The steps of preparing polycrystalline diamond transparent ceramics in the present embodiment are as follows:

(1) Pretreatment of diamond powder

The single crystal diamond micropowder with an average particle size of about ^500nm prepared by a commercially available chemical vapor deposition method was used as the raw material, and its carbon purity was greater than 99%. Under treatment for 0.5h to remove oxygen, nitrogen, water vapor and other impurities adsorbed on the surface of diamond micro-powder;

(2) Pre-press molding

Using tantalum foil as the wrapping material, conventional polishing, degreasing, ultrasonic cleaning, and infrared drying were performed on the surface of the wrapping material tantalum foil; The pressure is maintained for 1 min, and pre-compression molding is performed to obtain a parison with a compactness of 45%;

(3) Sintering and removal of metal foil

The metal foil-wrapped parison was placed in a large-cavity static high-pressure device, and sintered for 300s at a pressure of 15GPa and a temperature of 2300°C. The temperature and pressure loading method, unloading method and process conditions are as follows: increase the pressure by 15GPa at a pressure increase rate of 25GPa/h and keep the pressure unchanged, then increase the temperature to 2300℃ at a heating rate of 500℃/min and keep sintering for 300s, and the sintering time ends. Then, the temperature was lowered to room temperature at a cooling rate of 20°C/min, and then reduced to normal pressure at a rate of 3GPa/h after cooling for 10 minutes.

Put the obtained sample into a mixed acid composed of 30% hydrofluoric acid and 30% nitric acid by mass (the volume ratio of hydrofluoric acid and nitric acid is 1:1) to remove the wrapping material tantalum, and then use a grinding disc to polish the sample to bright , that is, to obtain polycrystalline diamond transparent ceramics.

Example 6

The steps of preparing polycrystalline diamond transparent ceramics in the present embodiment are as follows:

(1) Pretreatment of diamond powder

The single crystal diamond micropowder with an average particle size of about 10 μm prepared by a commercially available static high pressure method is used as the raw material, and firstly, it is subjected to impurity removal treatment: the raw material diamond micropowder and hydrofluoric acid (mass concentration of 30%) are added in a weight ratio of 1:4 In the purification kettle, stir and heat in a water bath to 60°C, and then continue to stir at this temperature for 48 hours. Then, after the powder settles, the liquid is poured out, and washed with deionized water until neutral, and then washed with diamond powder and hydrochloric acid. (mass concentration of 35%) was added to the purification kettle according to the weight ratio of 1:3, stirred and heated to 60°C in a water bath, and then continued to stir at this temperature for 48h, then the powder was settled and the liquid was poured out, and deionized water was used. Wash to neutrality, repeat the above acid dissolving and impurity removal steps for 2 times, and then dry the treated diamond micropowder.

Treat the dried diamond micropowder for 1 hour under the conditions of vacuum degree of 5×10 ^-2 Pa and temperature of 900°C to remove impurities such as oxygen, nitrogen and water vapor adsorbed on the surface of the diamond micropowder;

(2) Pre-press molding

Using tantalum foil as the wrapping material, routine polishing, degreasing, ultrasonic cleaning, and infrared drying were performed on the surface of the wrapping material tantalum foil; Hold the pressure for 3 minutes, carry out pre-compression molding, and obtain a parison with a compactness of 52%;

(3) Sintering and removal of metal foil

The metal foil-wrapped parison was placed in a large-cavity static high-pressure device, and sintered for 1800s at a pressure of 28GPa and a temperature of 1800°C. The temperature and pressure loading method, unloading method and process conditions are as follows: increase the pressure to 22GPa at a pressure increase rate of 6GPa/h and keep the pressure unchanged, then increase the temperature to 1800℃ at a heating rate of 50℃/min and keep the temperature unchanged, and then use After the pressure increase rate of 20GPa/h is increased to 28GPa, the pressure remains unchanged, and the pressure and temperature conditions of 28GPa and 1800℃ are maintained for sintering for 1800s. Depressurize to normal pressure at a depressurization rate of 1GPa/h.

Put the obtained sample into a mixed acid composed of 30% hydrofluoric acid by mass and 40% nitric acid by mass (the volume ratio of hydrofluoric acid and nitric acid is 1:1) to remove the wrapping material tantalum, and then use a grinding disc to polish the sample to bright , that is, to obtain polycrystalline diamond transparent ceramics.

Example 7

The steps of preparing polycrystalline diamond transparent ceramics in the present embodiment are as follows:

(1) Pretreatment of diamond powder

The single crystal diamond micropowder with an average particle size of about 50 μm prepared by a commercially available static high pressure method was used as the raw material, and firstly, it was subjected to impurity removal treatment: the raw material diamond micropowder and hydrofluoric acid (mass concentration of 20%) were added in a weight ratio of 1:3 In the purification kettle, stir and heat in a water bath to 60°C, and then continue to stir at this temperature for 48 hours. Then, after the powder settles, the liquid is poured out, and washed with deionized water until neutral, and then washed with diamond powder and hydrochloric acid. (mass concentration of 25%) was added to the purification kettle according to the weight ratio of 1:3, heated to 60°C with stirring in a water bath, and then continued to stir for 48h at this temperature, and then the powder was settled and the liquid was poured out, and deionized water was used. Wash to neutrality, repeat the above acid dissolving and impurity removal steps 3 times, and then dry the treated diamond micropowder.

The dried diamond powder was treated for 3 hours under the conditions of vacuum degree of 5×10 ^-2 Pa and temperature of 800°C to remove oxygen, nitrogen, water vapor and other impurities adsorbed on the surface of the diamond powder;

(2) Pre-press molding

Using tantalum foil as the wrapping material, conventional polishing, degreasing, ultrasonic cleaning, and infrared drying were performed on the surface of the wrapping material tantalum foil; The pressure is maintained for 1 min, and pre-compression molding is performed to obtain a parison with a compactness of 45%;

(3) Sintering and removal of metal foil

The metal foil-wrapped parison was placed in a large-cavity static high-pressure device, and sintered for 1800s at a pressure of 15GPa and a temperature of 2000°C. The temperature and pressure loading method, unloading method and process conditions are as follows: increase the pressure by 15GPa at a pressure increase rate of 3GPa/h and keep the pressure unchanged, then increase the temperature to 2000℃ at a heating rate of 100℃/min and keep sintering for 1800s, and the sintering time ends. Then, the temperature was lowered to room temperature at a cooling rate of 4 °C/min, and then the pressure was lowered to normal pressure at a depressurization rate of 1 GPa/h after the cooling.

Put the obtained sample into a mixed acid composed of 30% hydrofluoric acid and 30% nitric acid by mass (the volume ratio of hydrofluoric acid and nitric acid is 1:1) to remove the wrapping material tantalum, and then use a grinding disc to polish the sample to bright , that is, to obtain polycrystalline diamond transparent ceramics.

The structure of the polycrystalline diamond transparent ceramics prepared in the examples is analyzed below.

▲The optical micrographs of the polycrystalline diamond transparent ceramic samples prepared in Example 1-6 were collected by an optical microscope (see Figure 1-6) and the light transmission performance was evaluated, and the polycrystalline diamond transparent ceramic samples prepared in Example 7 were collected. Optical photos (see Figure 7) and evaluation of light transmission performance, see Table 1 for evaluation of light transmission performance. The diameter and height of the polycrystalline diamond transparent ceramic samples prepared in Examples 1-7 were counted, and the results are shown in Table 1.

Table 1 Size and visible light transmittance test results of polycrystalline diamond transparent ceramic samples

Diameter(mm) Height(mm) Visible light transmittance Example 1 3 2 better Example 2 3.5 2.5 excellent Example 3 3.5 2 better Example 4 4 3 better Example 5 3 2.5 better Example 6 5 3 poor Example 7 10 6 Difference

As can be seen from Table 1, the method of the present invention can prepare large-sized bulk polycrystalline diamond transparent ceramics with different light transmittances.

▲X-ray diffraction test and Raman spectrum test were performed on the polycrystalline diamond transparent ceramic samples prepared in Examples 1-7, wherein the X-ray diffraction spectrum corresponding to Example 2 is shown in Figure 8, and the Raman spectrum is shown in Figure 8 9, the test results show that the polycrystalline diamond transparent ceramic sample obtained by the preparation method provided by the present invention only has a diamond phase.

▲Scanning electron microscope test was carried out on the polycrystalline diamond transparent ceramic samples prepared in Examples 1-7, wherein the scanning electron microscope images corresponding to Example 2 and Example 4 are shown in Figure 10 and Figure 11. The test results show that through the present invention The polycrystalline diamond transparent ceramic sample obtained by the preparation method has high compactness, the grain size is basically the same as that of the raw material powder, and a large-area and tightly bonded high-strength diamond-diamond bonding interface is formed between the diamond grains.

Claims (10)

1. a preparation method of polycrystalline diamond transparent ceramics is characterized in that taking granularity 5nm～100 μm diamond micropowder as raw material, and processing steps are as follows: (1) Pretreatment of diamond powder The carbon-containing purity of the raw diamond micropowder is required to be greater than 99%. For the diamond micropowder whose carbon-containing purity does not meet the requirements, the impurity removal treatment is performed first, and then vacuum heat treatment is performed. Remove oxygen, nitrogen or water vapor adsorbed on the surface of diamond powder; (2) Pre-press molding Put the diamond powder after vacuum heat treatment into the cleaned metal foil for pre-compression molding, and the density of the obtained parison should not be less than 30%; (3) Sintering and removal of metal foil Put the metal foil-wrapped parison into a large-cavity static high pressure device, and sinter it for 10s to 2000s under the conditions of a pressure of 10GPa-30GPa and a temperature of 1500℃-3000℃. Then, the metal foil is removed with an inorganic acid to obtain a polycrystalline diamond transparent ceramic. 2 . The method for preparing polycrystalline diamond transparent ceramics according to claim 1 , wherein in step (3), the matching relationship between pressure and temperature during sintering is that the temperature is low when the pressure is high. 3 . 3. according to the preparation method of the described polycrystalline diamond transparent ceramics of claim 1 and 2, it is characterised in that in step (3), the pressure is increased from normal pressure to the rate of increase of sintering pressure and the pressure is reduced from sintering pressure to normal The pressure reduction rate is 0.5GPa/h～60GPa/h, the temperature rise rate from room temperature to sintering temperature and the temperature drop rate from sintering temperature to room temperature are 1℃/min～1000℃/min. 4. according to the preparation method of the described polycrystalline diamond transparent ceramics of claim 3, it is characterized in that the mode of temperature increase and pressure rise and temperature drop and pressure drop are as follows: First increase the pressure from normal pressure to sintering pressure and keep the sintering pressure, then increase the temperature from room temperature to sintering temperature, after the sintering time is reached, first reduce the temperature from sintering temperature to room temperature, and then reduce the pressure from sintering pressure to sintering temperature normal pressure; Or first increase the pressure from normal pressure to sintering pressure and maintain the sintering pressure, and then increase the temperature from room temperature to sintering temperature. The pressure is reduced from sintering pressure to normal pressure; Or first increase the pressure from normal pressure to the pressure where diamond can exist stably and maintain the pressure, then increase the temperature from room temperature to sintering temperature, and then increase the pressure to sintering pressure, after the sintering time arrives, first increase the temperature from the sintering temperature. Drop to room temperature, and then reduce the pressure from sintering pressure to normal pressure; Or first increase the pressure from normal pressure to the pressure where diamond can exist stably and maintain the pressure, then increase the temperature from room temperature to the sintering temperature, and then increase the pressure to the sintering pressure. After the sintering time is reached, start cooling and depressurization , reduce the temperature from the sintering temperature to room temperature, and reduce the pressure from the sintering pressure to normal pressure. 5. according to the preparation method of the described polycrystalline diamond transparent ceramics of claim 1 and 2, it is characterized in that in step (1), the vacuum degree of vacuum heat treatment is 1 × 10 ^-1 Pa～1 × 10 ^-5 Pa, and temperature is 500℃～1200℃, the holding time is 0.1h～6h. 6. The method for preparing polycrystalline diamond transparent ceramics according to claim 3, wherein in step (1), the vacuum degree of vacuum heat treatment is 1×10 ^-1 Pa～1×10 ^-5 Pa, and the temperature is 500° C. ～1200℃, the holding time is 0.1h～6h. 7. The method for preparing polycrystalline diamond transparent ceramics according to claim 4, wherein in step (1), the vacuum degree of vacuum heat treatment is 1×10 ^-1 Pa～1×10 ^-5 Pa, and the temperature is 500° C. ～1200℃, the holding time is 0.1h～6h. 8. The method for preparing polycrystalline diamond transparent ceramics according to claim 1 or 2, characterized in that in step (2), the pressure of the pre-compression molding is 400 MPa to 700 MPa, and the pressing time is determined by the compactness of the obtained parison. 9 . The method for preparing polycrystalline diamond transparent ceramics according to claim 3 , wherein in the step (2), the pressure of the pre-compression molding is 400 MPa to 700 MPa, and the pressing time is determined by the compactness of the obtained parison. 10 . 10 . The method for preparing polycrystalline diamond transparent ceramics according to claim 1 or 2 , wherein the metal foil material is tantalum foil, rhenium foil or platinum foil. 11 .

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