Preparation method of silver nanocrystalline colloid with high purity and high particle size consistency

Abstract

The invention discloses a preparation method of silver angstrom crystal colloid with high purity and high particle size consistency. The preparation method comprises the following steps: under the protection of inert gas, generating plasma through high-voltage arc, converting the plasma into atomic cluster aerosol, mixing the atomic cluster aerosol with liquid, separating, drying, returning gas, maintaining a working state until the concentration of nano-silver particles is enough, and finally concentrating the liquid to obtain the high-purity nano-crystal silver colloid. The method has the advantages that the product purity is ensured by using the high-purity silver electrode; the particle size consistency is controlled under low-voltage and small-current operation conditions; the discharge stability is improved through the design of the narrow-spacing electrodes; and the stable condensation process is ensured by an angstrom grain size homogenization technology. The system and the process are environment-friendly and harmless, the product performance is stable, the concentration of the silver nanocrystal colloid can reach 50 ppm, and the silver nanocrystal colloid does not contain dispersants and modifiers except water and silver elements and can stably exist for one year.

Description

Technical Field

[0001] The invention relates to the field of nano material preparation, and in particular to a method for preparing silver angstrom crystal colloid with high purity and high particle size consistency. Background Art

[0002] Currently, there is no public system and method for the continuous preparation of silver nanocrystal colloidal materials. It is also difficult to find high-purity, high-concentration and stably dispersed 2-4 nm silver nanocrystal (specifically referred to as silver angstrom crystals in this article) colloidal materials.

[0003] Plasma gas phase preparation of metal nanomaterials is an important and promising method for preparing nanomaterials. With its high temperature and rapid reaction characteristics, it can achieve nano-metal materials and is widely used in high-tech fields such as pharmaceuticals, catalysis, electronics, and optics. At present, the methods for preparing metal nanomaterials in plasma gas phase mainly include DC arc plasma method, radio frequency plasma method, and microwave plasma method. Among them, DC arc plasma method occupies an important position in research and application due to its relatively simple equipment and low cost.

[0004] The existing plasma gas phase preparation method of metal nanomaterials mainly uses tungsten electrode as cathode and metal as anode. However, there are the following major technical difficulties in practical application:

[0005] High-temperature jets can easily blow away molten metal, making it impossible for metal particles to be effectively deposited into nanopowders. Instead, they adhere to the container wall in the arc discharge zone, reducing the yield of collectible powder and increasing the difficulty of equipment cleaning and maintenance. Droplets in the molten metal pool are prone to splashing during the heating process, and form larger particles after cooling, affecting the uniformity and quality of the nanopowder. Due to the uneven temperature distribution in the plasma, the condensation and coagulation process of the metal vapor is unstable, and the particle size of the prepared nanopowder is uneven. At the same time, most methods for preparing silver nanocrystalline colloids are liquid reaction preparations. Due to the introduction of various reaction media and precursors, there are many impurity components in the product, and the purification cost is high. It is not easy to prepare high-purity silver nanocrystalline colloids. Summary of the invention

[0006] The purpose of the present invention is to disclose a method for preparing a silver angstrom crystal colloid with high purity and high particle size consistency, so as to provide a silver angstrom crystal colloid material with ultra-high purity and high particle size consistency for scientific research and related industrial function development.

[0007] The technical solution of the present invention is as follows:

[0008] A method for preparing a silver angstrom colloid with high purity and high particle size consistency uses a silver angstrom colloid preparation system including an inert gas supply device, an arc discharge chamber, a gas-liquid mixing device, a gas-liquid separation device, a liquid storage and liquid supply device, a gas recovery and purification device, and a liquid concentration device, and comprises the following steps:

[0009] (1) Preparation stage: high-purity deionized water is placed in the liquid storage container of the liquid storage and liquid supply device, high-purity silver electrodes are placed in pairs in the arc discharge chamber, the distance between the silver electrodes is adjusted to 0.3-1.0 mm, the airtight arc discharge chamber is evacuated by a vacuum pump, inert gas is introduced into the arc discharge chamber through an inert gas storage cylinder, the gas intake is controlled at 5-10 L / min, the power supply of the arc discharge chamber is controlled, a high-voltage arc is initiated between the silver electrodes in the arc discharge chamber, the positive and negative voltages are controlled to be 0.8-1.3 kV, the current between the positive and negative electrodes is controlled to be 7-13 mA, the pulse frequency is about 250-350 Hz, and the high-voltage arc is maintained continuously;

[0010] (2) Generating silver atom cluster aerosol: Under the protection of inert gas, a pair of high-purity silver electrode surfaces are continuously vaporized into silver atom clusters or plasma using a high-voltage arc in an arc discharge zone, and the inert gas intake rate at room temperature into the arc discharge chamber is maintained at 5 to 10 L / min. The inert gas is passed through the silver electrode gap in the arc discharge chamber to obtain an aerosol containing silver atom clusters;

[0011] (3) gas-liquid mixing: the silver atom cluster aerosol obtained in step (2) is introduced into the gas inlet channel of the gas-liquid mixing device, and the liquid is introduced into the liquid inlet channel of the gas-liquid mixing device using a liquid storage and liquid supply device, and the silver atom cluster aerosol and the liquid are fully mixed in the gas-liquid mixing device, and the silver atom clusters in the silver atom cluster aerosol are transferred to the liquid to obtain a gas-liquid mixture containing silver atom clusters, wherein the gas intake rate of the gas-liquid mixing device is maintained at 5 to 10 L / min, and the liquid intake rate of the gas-liquid mixing device is maintained at 1 to 10 ml / min;

[0012] (4) gas-liquid separation: separating the gas-liquid mixture containing the silver atomic clusters obtained in step (3) to obtain an inert gas containing a small amount of liquid water molecules and a liquid containing a large amount of silver atomic clusters;

[0013] (5) Gas residue removal and drying: The inert gas containing a small amount of liquid molecules obtained in step (4) is extracted and dried through a cold trap to remove moisture in the inert gas, and the temperature of the cold trap is controlled between minus 10 degrees and minus 50 degrees. Before the inert gas is dried, it passes through a high-density filter to remove residual silver atom cluster particles. After the inert gas is dried, it is returned to the inert gas storage cylinder in step (2);

[0014] (6) The liquid continues to mix with the silver atom cluster aerosol: maintaining step (2) while continuously introducing high-purity inert gas at room temperature into the arc discharge chamber, collecting the liquid containing a large amount of atomic clusters obtained in step (4) into a liquid temporary storage tank, mixing it with the original liquid in the liquid temporary storage tank, and continuing to introduce the mixed liquid into the liquid inlet channel of the gas-liquid mixing device described in step (3).

[0015] (7) Maintaining the above working state until the liquid in the gas-liquid separator contains silver atom cluster particles at a sufficient concentration.

[0016] (8) Liquid concentration: The liquid containing the atomic clusters obtained in step (7) is concentrated to obtain atomic cluster liquid dispersions of different concentrations, namely, silver angstrom crystal colloids.

[0017] Furthermore, the arc discharge positive and negative voltage is 1 kV, the positive and negative current is 10 mA, and the pulse frequency is 300 Hz.

[0018] Furthermore, the distance between arc discharge electrodes is 0.5 mm, and the electrode diameter is 3 to 6 mm.

[0019] Furthermore, the purity of the high-purity silver electrode in step (1) is 99.999%, and the sum of other impurity elements in the electrode does not exceed 1 ppm; the inert gas is argon, the purity of argon is greater than 99.999%, and the moisture content is below 0.05 ppm.

[0020] Furthermore, in step (3), the gas-liquid ratio (volume flow rate) in the gas-liquid mixture is maintained at gas:liquid=500:1.

[0021] Furthermore, the system pressure in step (4) is lower than that in steps (1) to (3), the temperature is 20°C to 40°C, and the system pressure is 900 mbar to 1013 mbar.

[0022] Furthermore, in the liquid concentration process described in step (8), reduced pressure distillation is adopted.

[0023] Furthermore, the present invention also provides a method for preparing elemental silver angstrom crystal powder, wherein the silver angstrom crystal colloidal liquid prepared by the above method is dried, and the drying process is carried out in a freeze-drying manner, and the freezing temperature is -4°C to 0°C. The liquid is fully dried to obtain nano elemental silver powder.

[0024] Furthermore, the present invention also provides another method for preparing silver angstrom crystal powder, wherein the silver angstrom crystal colloid prepared by the above method is dried, and the drying process is carried out in a drying manner, and the drying temperature is 50° C. to 70° C. When the temperature is higher than 70° C., it is carried out in a nitrogen and argon atmosphere with a purity of 99.95% or more. The liquid is fully dried to obtain the silver angstrom crystal powder.

[0025] In order to improve the existing plasma gas phase preparation method of silver angstrom crystal material and solve the problems existing in the prior art, the technical solution proposed in the present invention mainly includes the following improvements:

[0026] Use of high-purity silver electrodes: In the present invention, both the anode and cathode of the arc discharge zone are made of high-purity silver electrodes. This configuration ensures that there will be no doping of other electrode materials during the preparation process, thereby ensuring that the output has extremely high purity. The use of high-purity silver electrodes helps to improve the quality of nanomaterials, making them show better performance in high-tech applications.

[0027] Low voltage and low current operating conditions: The present invention uses a relatively low voltage and a relatively small current for operation. This low power operating condition helps to control the energy input of the arc discharge, so that the particle size of the produced metal nanocrystalline particles is sufficiently small and has a high consistency. Under low voltage and low current conditions, the condensation process of the metal vapor is more stable, which is conducive to the formation of uniform nanopowder.

[0028] Narrow-pitch electrode design: In order to solve the problem of unstable arc discharge at low voltage and low current, the present invention adopts a design in which the metal anode and the metal cathode are placed at a very narrow distance. This design makes the ionization process easier to occur, and the arc can exist stably and continuously during the preparation process. The narrow-pitch electrode design not only improves the stability of the discharge, but also reduces the disturbance of the arc, ensuring that the metal vapor is evenly condensed into nanocrystalline powder.

[0029] Angstrom grain size homogenization technology: Inert gas is blown through the silver electrode discharge gap to introduce air flow disturbance, promote the uniform condensation of silver atom clusters, and reduce the width of the generated silver nanoparticle size distribution. The disturbed cooling airflow forms a multi-stage cooling process, gradually reducing the temperature during the condensation of metal vapor, ensuring the stability and uniformity of the condensation process.

[0030] The advantages of the present invention are: through the above improvements, the technical solution of the present invention not only solves the main problems encountered in the existing process, but also significantly improves the purity of the silver angstrom colloid and ensures the consistency of the silver angstrom particle size distribution. This will provide more reliable and efficient technical support for the practical application of nanocrystalline materials.

[0031] The present invention provides a continuous preparation process for a high-purity, high-particle-size-consistency 2-4 nm angstrom colloid, wherein the raw materials are readily available, the preparation process is simple, the carrier gas is recycled, the environment is harmless, and the product performance is stable. The concentration of the obtained silver angstrom colloid can reach 50 ppm, and the colloid does not contain a dispersant or a modifier other than water and silver elements, and can stably exist for 1 year. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 is a process flow chart of the present invention;

[0034] Figure 2 is a schematic diagram of the placement of electrodes in the arc discharge zone;

[0035] Figure 3 It is a structural schematic diagram of a gas-liquid mixing device.

[0036] Figure 4 a is a TEM image of the silver angstrom colloid prepared in Example 6 of the present invention;

[0037] Figure 4 b is a particle size distribution diagram of the silver angstrom colloid prepared in Example 6 of the present invention;

[0038] Figure 5 This is the XRD pattern of the silver angstrom powder prepared in Example 7 of the present invention;

[0039] Figure 6 This is the XRD-standard PDF card of silver single crystal powder;

[0040] Figure 7 is the relationship between the concentration of silver angstrom colloid and different cycle times;

[0041] Figure 8 is a graph showing the relationship between the concentration of silver angstrom colloid and different gas-liquid ratios in Example 9;

[0042] Fig. 9 The particle size distribution diagram of the silver angstrom colloid in Example 9 with a gas-liquid ratio between 100:1 and 500:1;

[0043] Fig.10 The particle size distribution diagram of the silver angstrom colloid in Example 9 with a gas-liquid ratio between 600:1 and 900:1;

[0044] Fig.11 The particle size distribution diagram of silver angstrom colloid in Example 9 with a gas-liquid ratio between 1000:1 and 1500:1;

[0045] Fig.12 a is deionized water without Tyndall effect;

[0046] Fig.12b is the Tyndall effect of the low-stage gas-liquid ratio (100:1-500:1) of Example 5;

[0047] Fig.12 c is the Tyndall effect of the gas-liquid ratio (600:1 to 900:1) in the stage of Example 5;

[0048] Fig.12 d is the Tyndall effect of high-stage gas-liquid ratio (1000:1-1500:1) in Example 5. DETAILED DESCRIPTION

[0049] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than 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.

[0050] Embodiment 1:

[0051] Angstrom: The approximate particle size range of nanocrystalline materials in academia is 1 to 10 nm. In the present invention, because the silver nanocrystalline particles determined by the process can be stably distributed in a colloidal state in water, "Angstrom" is used to represent high-purity, highly consistent particle size distribution, and highly dispersed nanocrystalline colloids with a particle size of 2 to 4 nm.

[0052] Plasma gas phase preparation of metal nanocrystalline materials is an important and promising method for preparing nanomaterials. With its high temperature and rapid reaction characteristics, it can achieve nano-crystalization of metal materials, and the prepared products are widely used in high-tech fields such as catalysis, electronics, and optics. At present, the methods for preparing metal nanomaterials in plasma gas phase mainly include DC arc plasma method, radio frequency plasma method and microwave plasma method. Among them, DC arc plasma method occupies an important position in research and application due to its relatively simple equipment and low cost.

[0053] Most of the existing plasma gas phase preparation methods for metal nanocrystalline materials use a tungsten electrode as the cathode and the metal to be prepared as the anode. Although this method is theoretically feasible, there are still many technical problems that need to be solved in practical applications. The following are the main problems encountered in the current DC arc plasma method for preparing metal nanocrystalline powders:

[0054] Jet problems of plasma injection: The high-temperature jet of plasma injection can easily blow away the molten metal itself, causing these blown-away metal particles to be unable to effectively deposit into metal nanocrystalline powders, but to adhere to the container wall in the arc discharge area. This not only reduces the yield of collectible metal nanocrystalline powders, but also increases the difficulty of cleaning and maintenance of the equipment. In addition, the metal nanoparticles attached to the container wall will affect the purity and consistency of subsequent experiments, reducing the overall quality of the product.

[0055] Droplet splashing during heating: During the heating process, droplets in the molten metal pool tend to splash out. These splashed droplets form larger particles after cooling, resulting in large particles always existing in the nanopowder. The presence of large particles not only affects the uniformity and quality of the product, but also has an adverse effect on subsequent application performance. For example, in catalyst applications, nanocrystalline powders with a wide particle size distribution can lead to uneven catalytic reactions, thereby reducing catalytic efficiency.

[0056] The problem of uneven particle size of nanocrystalline powder: The particle size of nanocrystalline powder prepared by the current process is uneven and the particle size distribution is wide. This is mainly due to the uneven temperature distribution in the plasma, which leads to unstable condensation and coagulation of metal vapor. The uneven particle size will directly affect the physical and chemical properties of nanomaterials and reduce their performance in practical applications. For example, in electronic materials, nanocrystalline powder with uneven particle size will affect the conductivity and stability of the material.

[0057] At the same time, most methods for preparing silver nanocrystal colloids are liquid reaction preparations. Due to the introduction of various reaction media and precursors, there are many impurity components in the product, the purification cost is high, and it is not easy to prepare high-purity silver nanocrystal colloids.

[0058] To this end, the present invention proposes a method for preparing high-purity silver angstrom colloid by physical vapor phase method plus gas phase transport, which can stably prepare high-purity and high-particle consistency silver angstrom colloid in one time without complicated post-purification treatment, and has the advantages of simple process and good consistency of nano silver particles.

[0059] Figure 1 The invention is a simplified process flow chart, which uses a silver angstrom crystal colloid preparation system including an inert gas supply device, an arc discharge chamber, a gas-liquid mixing device, a gas-liquid separation device, a liquid storage and supply device, a gas recovery and purification device, and a liquid concentration device.

[0060] Argon gas at room temperature is passed through the gas passage 13 into the arc discharge chamber of the arc discharge zone 11, and the concentration of the silver atom cluster aerosol formed is ensured to be 0.1ppm per minute, and then quickly enters the gas-liquid mixing device of the gas-liquid mixing zone 30 at a volume flow rate of 5L / min. The flow rate of the aerosol entering the gas-liquid mixing zone 30 is controlled at 6L / min, and the flow rate of the liquid (high-purity deionized water is initially collected and mixed with the silver angstrom crystal colloidal solution during the preparation process) entering the gas-liquid mixing zone 30 through the liquid passage 33 is controlled at 10mL / min. The gas-liquid mixing volume ratio in the gas-liquid mixing zone 30 is 600:1, the mixing volume of a single gas-liquid mixing zone is 2mL, and the mixing time is 0.02 seconds. The mixed liquid is then passed into the gas-liquid separation device 20 to form independent argon gas and independent silver angstrom crystal colloids. The argon gas is returned to the gas collection and purification device of the inert gas storage area 10, and is sent to the inert gas supply device after purification, and the silver angstrom crystal colloid is collected in the liquid storage and liquid supply device in the silver angstrom crystal colloid storage area 21. The argon gas is continuously circulated into the arc discharge chamber of the arc discharge area 11, and continuously mixed with the liquid at a predetermined flow rate in the gas-liquid mixing device of the subsequent gas-liquid mixing area 30, and finally forms a high concentration of silver angstrom crystal colloid through continuous mixing through circulation.

[0061] Before the formal preparation begins, various preparations are usually carried out. High-purity deionized water is placed in the liquid storage container of the liquid storage and liquid supply device. The deionized water is used to elute the silver atomic clusters from the transport gas. High-purity silver electrodes are placed in pairs in the arc discharge chamber. Unlike the usual gas phase physical preparation method of nanometal materials, the prior art uses tungsten metal with a very high melting point as the cathode, and the target metal to be prepared, such as silver, as the anode. Inert gases such as argon are used as protective atmosphere and transport gas. Usually, in order to prevent oxidation reactions at high temperatures, a small amount of highly reducing hydrogen is mixed into the inert gas to prevent the target metal (such as metallic silver) from being oxidized at high temperatures. Most of the prior art is industrialized production, and the voltage used is relatively high, so the distance between the anode and the cathode is also relatively large. In order to achieve the effect of stable preparation, the spacing of the silver electrodes is adjusted to 0.3-1.0 mm in this method. In order to ensure that the silver electrode or nanosilver particles will not be oxidized due to oxidation during the working process, the airtight arc discharge chamber will be evacuated with a vacuum pump in the preparation stage, and then the inert gas will be introduced into the arc discharge chamber through the inert gas storage device. In order to achieve a better inert gas protection atmosphere, after the inert gas is introduced into the arc discharge chamber, the air pump on the gas circulation path can be turned on to circulate the gas on the gas circulation path. The collected inert gas will pass through the filter chamber and the cold trap in turn, and then the gas in the gas circulation path will be discharged. The inert gas storage is maintained and the gas circulation path is ventilated for more than 2 minutes to ensure that the non-inert gas impurities in the circulation path are well isolated before starting the formal preparation. At the same time, in order to further improve the purity of the inert protective gas in the gas circulation path, the arc discharge chamber and the gas circulation path can be evacuated twice, the extracted gas can be discharged, and high-purity inert gas can be introduced into the arc discharge chamber again to ensure that there is no impurity interfering gas in the gas circulation path.

[0062] After the gas circulation path is established and maintained in normal operation, the inert gas intake is controlled at 5-10L / min, the power supply of the arc discharge chamber is controlled, a high-voltage arc is triggered between the silver electrodes of the arc discharge chamber, the positive and negative electrode voltages are controlled at 0.8-1.3kV, the current between the positive and negative electrodes is controlled at 7-13mA, and the pulse frequency is about 250-350Hz, so as to maintain the continuous existence of the high-voltage arc;

[0063] It should be noted here that the voltage for initiating a high-voltage arc is often higher than the normal working voltage for preparation. After the arc is initiated, the working voltage needs to be controlled to a lower working voltage. At the same time, the initial current intensity when the arc is initiated is often greater than the normal working current for preparation, but the large current will affect the consistency and particle size of the prepared silver angstrom crystal particles. Therefore, it is particularly important in the present invention that after the normal preparation begins, the positive and negative electrode voltages are controlled to be 0.8-1.3 kV, the current between the positive and negative electrodes is 7-13 mA, and the pulse power supply is pulsed with a pulse frequency of about 250-350 Hz to maintain the continuous existence of the high-voltage arc. The lower voltage and smaller current relative to the prior art, the pulse power supply is the core feature of the present invention. Only in this state can the prepared silver angstrom crystal particles maintain better size consistency.

[0064] In the normal continuous preparation process, the preparation of silver angstrom colloids first requires the generation of silver atom cluster aerosol. Under the protection of inert gas, a pair of high-purity silver electrode surfaces are continuously vaporized into silver atom clusters or plasma using a high-voltage arc in the arc discharge zone, and the inert gas intake rate of room temperature entering the arc discharge chamber is maintained at 5 to 10 L / min. The inert gas is passed through the silver electrode gap of the arc discharge chamber to obtain an aerosol containing silver atom clusters; room temperature argon gas is passed through the gas passage 13 into the arc discharge chamber of the arc discharge zone 11, and the high-voltage arc in the arc discharge zone continuously vaporizes the surface of a pair of high-purity silver electrodes into silver atom clusters or plasma. The vaporized silver atom clusters quickly diffuse around the silver electrode gap. Under the premise that the inert gas intake rate is 5 to 10 L / min, the inert gas quickly mixes with the silver atom clusters around the silver electrode gap, cools the silver atom clusters and fully mixes with the inert gas to form a silver atom cluster aerosol, and the concentration of the silver atom cluster aerosol formed per minute is controlled to be 0.1 ppm. Due to the closed airtight space of the arc discharge chamber, the aerosol generated when the argon gas is continuously introduced will enter the gas circulation passage through the gas exhaust channel of the arc discharge chamber and be introduced into the gas-liquid mixing area 30 .

[0065] It is understandable that the concentration of silver atom cluster aerosol formed per minute here is very critical. The concentration of the aerosol is adjusted by various working parameters of the arc discharge device, including arc discharge voltage, maintained current intensity, pulse frequency of pulse power supply, etc., and is also closely related to the spacing between the electrodes. The above parameters determine the rate at which metallic silver is stripped from the electrode, as well as the size of the stripped silver atom clusters. Furthermore, since the silver atom clusters will still collide and combine in the arc discharge chamber after being stripped from the silver electrode by the arc discharge plasma, it is very important to introduce sufficient flow of argon gas in time to cool the silver atom clusters and allow the silver atom clusters to diffuse into the argon gas to form aerosols. The volume flow rate of argon gas entering the arc discharge chamber here needs to be accurately set, and the gas passage path needs to effectively pass through the electrode gap in the arc discharge zone to effectively cool the silver atom clusters and transport them in time. Insufficient ventilation will lead to various conditions that are not conducive to the transport of silver atom clusters. One typical feature is that the silver atom clusters cannot be effectively cooled under insufficient ventilation, and will diffuse and adhere in the arc discharge chamber. Insufficient ventilation is often found in the arc discharge chamber. A large amount of silver metal powder is often found adhering to the inner wall of the arc discharge chamber, which is a strong proof. However, it should be noted that too much ventilation will affect the stability of the arc discharge arc.

[0066] The next step is gas-liquid mixing. The silver atom cluster aerosol discharged from the gas exhaust channel of the arc discharge chamber is introduced into the gas inlet channel of the gas-liquid mixing device. The liquid is introduced into the liquid inlet channel of the gas-liquid mixing device using a liquid storage and liquid supply device. In the gas-liquid mixing device, the silver atom cluster aerosol and the liquid are fully mixed. The silver atom clusters in the silver atom cluster aerosol are transferred to the liquid to obtain a gas-liquid mixture containing silver atom clusters, wherein the gas intake volume of the gas-liquid mixing device is maintained at 5 to 10 L / min, and the liquid intake volume of the gas-liquid mixing device is maintained at 1 to 10 ml / min.

[0067] A gas-liquid mixing device is provided in the gas-liquid mixing area. The gas-liquid mixing device generally has a gas inlet channel, a liquid inlet channel and a gas-liquid mixture outlet channel. The flow rate of aerosol entering the gas-liquid mixing area 30 is controlled at 5-10L / min, and the flow rate of liquid entering the gas-liquid mixing area 30 through the liquid passage 33 is controlled at 1-10ml / min. When the gas-liquid mixing volume ratio is 100:1-1500:1, the overall mixing volume of the gas-liquid mixing area is 2mL. There are many mixing chambers arranged in sequence inside the gas-liquid mixing device. The gas and liquid are fully shaken and mixed during the process of passing through multiple mixing chambers. The silver atomic clusters transported in the gas are transferred to the liquid during the mixing process. The overall mixing time through the gas-liquid mixing area is 0.02 seconds. It should be pointed out that at the beginning of the preparation, the liquid storage container of the liquid storage and liquid supply device contains high-purity deionized water to ensure the high purity of the prepared silver angstrom colloid. During the preparation process, the silver atom clusters are transferred to the product of high-purity deionized water, and the low-concentration silver angstrom colloidal solution after gas-liquid separation will be collected in a liquid storage container. That is, at the beginning of the preparation, the liquid mixed with the silver atom cluster aerosol is high-purity deionized water, but during the preparation process, the liquid mixed with the silver atom cluster aerosol is an intermediate concentration silver angstrom colloidal solution, that is, a silver angstrom colloidal solution with a gradually increasing concentration during the continuous preparation cycle.

[0068] The mixed gas and liquid are discharged from the gas-liquid mixture discharge channel of the gas-liquid mixing device and sent to the gas-liquid separation device by the liquid passage. The gas-liquid mixture containing silver atomic clusters is subjected to gas-liquid separation in the gas-liquid separation device to obtain an inert gas containing a small amount of liquid molecules and a liquid containing a large amount of atomic clusters, respectively. The gas-liquid separation device used in the present invention is actually a horizontally placed gas-liquid mixture channel, which is generally columnar with a circular or elliptical cross-section. Multiple layers of mutually staggered baffles are respectively arranged on the upper and lower layers of the channel. The gas-liquid separation device is usually placed nearly horizontally, with the outlet end slightly lower and tilted downward. Under the action of gravity and inertial force, after passing through the multiple layers of baffles, the liquid in the gas is effectively separated to the lower layer of the channel, and the gas containing a small amount of liquid molecules is discharged from the upper gas discharge channel at the outlet end of the gas-liquid separation device, and the liquid containing silver atomic clusters is discharged from the liquid discharge channel at the lower part of the outlet end of the gas-liquid separation device. Since the volume ratio of gas and liquid in the gas-liquid mixture is between 1500:1 and 100:1, the flow rate of the liquid is usually relatively small. A small hole is opened at the bottom of the baffle plate arranged at the lower layer of the gas-liquid separation device so that the separated liquid can flow out through the small hole. The separated liquid containing silver atomic clusters is collected into the liquid storage container of the liquid storage and liquid supply device through the liquid path. In fact, this liquid storage container is often directly arranged at the outlet end of the gas-liquid separation device. The liquid containing silver atomic clusters is discharged from the liquid discharge channel at the lower part of the outlet end of the gas-liquid separation device and directly enters the liquid storage container. After mixing with the existing liquid in the container, it is continuously sent to the gas-liquid mixing device by the liquid supply device to participate in the preparation cycle.

[0069] The gas separated by the gas-liquid separation device will be recycled and processed to continue to participate in the preparation cycle. The recycled gas is first de-residualized and dried. The inert gas containing a small amount of liquid molecules is extracted and dried through a cold trap to remove moisture from the inert gas. The temperature of the cold trap is controlled between minus 10 degrees Celsius and minus 50 degrees Celsius. Before drying, the inert gas passes through a high-density filter to remove residual silver atomic cluster particles. After drying, the inert gas is returned to the inert gas storage cylinder. The above-mentioned inert gas extraction generates a negative pressure in the gas-liquid separation zone, which can effectively promote the gas-liquid mixture to effectively pass through the gas-liquid separation channel. Since the recovered inert gas may still contain some residual silver angstrom crystal particles, in order to prevent the silver angstrom crystal particles from adhering to the subsequent gas passage and gas storage cylinder, a gas filter device is usually set to remove the residual silver angstrom crystal particles. The inert gas after gas-liquid separation contains some water vapor. If the water vapor enters the arc discharge area, it may affect the normal operation of the arc discharge area and may cause the doping effect of the silver angstrom particle product. Therefore, the present invention sets a cold trap on the gas passage to dry the inert gas to remove the moisture in the inert gas. The temperature of the cold trap is controlled between minus 10 degrees Celsius and minus 50 degrees Celsius. The filtered and dried argon gas is sent to the argon gas storage cylinder for subsequent circulation preparation.

[0070] The argon gas in the argon storage cylinder is continuously introduced into the arc discharge chamber of the arc discharge zone 11 after the flow rate is adjusted. The silver atomic clusters generated in the arc discharge chamber are transported out and continuously mixed with the circulating deionized water or silver nanocrystal colloid solution in the subsequent gas-liquid mixing zone at a predetermined flow rate. The silver nanocrystal colloid is finally formed with a higher concentration through continuous mixing in the circulation.

[0071] Features and advantages of the present invention:

[0072] High-purity products: High-purity silver electrodes and inert gases are used to ensure that the generated silver angstrom colloid is of high purity.

[0073] High efficiency: The yield and stripping efficiency of silver atom clusters are improved by using multiple pairs of silver electrodes and adjusting the corresponding gas flow.

[0074] Stable and continuous arc discharge: The current increases proportionally with the silver electrode pair to ensure a stable supply of arc discharge energy.

[0075] Optimized gas processing: The system uses a low-temperature cold trap to effectively remove moisture from the gas and reduce the interference of water vapor on system operation.

[0076] Embodiment 2:

[0077] The present invention aims to obtain a non-surface-modified silver angstrom colloidal aqueous solution (2-4nm, ≥20ppm)

[0078] The raw materials are obtained as follows:

[0079] Argon: purity 99.999%, available on the market.

[0080] Deionized water: Available in the market.

[0081] The purity of the silver electrode is 99.999%, and the sum of other impurity elements in the electrode does not exceed 1ppm.

[0082] Silver plasma: Plasma is generated between uniform, mirror-symmetrical silver electrodes, and metal plasma volatilization occurs in the arc discharge zone to form silver atom clusters or silver plasma.

[0083] Arc plasma preparation of silver nanocrystals technology principle description:

[0084] Figure 2: Schematic diagram of the placement of electrodes in the arc discharge zone. In DC arc plasma, free electrons in the gas are accelerated by the electric field under the action of the electric field. When their speed (kinetic energy) reaches a certain value, neutral atoms or molecules are ionized to obtain more free electrons. These electrons further accelerate and excite other neutral particles to produce an ionization process similar to the avalanche phenomenon, resulting in gas discharge to form plasma. The high temperature of plasma (up to 3000K-30000K) is used to melt and evaporate metals to form gaseous metal atoms.

[0085] Silver atom cluster aerosol generation: First, use arc evaporation target to generate metal plasma. The arc temperature generated by the high-voltage pulse between metal electrodes in an inert atmosphere at normal pressure is about 3000K-6000K, which can instantly heat and evaporate the atoms on the surface of the metal electrode, and then quickly diffuse into the inert gas molecule atmosphere. Most of them will cool and condense into atomic clusters due to Brownian motion and collision with gas molecules. At this time, the surface energy of the atomic clusters is relatively high. In order to better avoid impurities affecting surface activity and purity, they need to be mixed with relevant media as soon as possible. The parameters in this process are controlled as follows:

[0086] Positive and negative voltage: 0.8-1.2 kV, preferably 1 kV;

[0087] Current between positive and negative electrodes: 8-15mA, preferably controlled at 10mA;

[0088] Pulse frequency: between 220Hz and 360Hz, preferably about 300Hz

[0089] Distance between electrodes: 0.3-0.5 mm, preferably 0.5 mm

[0090] The electrode diameter is 3mm to 6mm, preferably 6mm

[0091] Electrode cross section: circular, elliptical, teardrop-shaped

[0092] Embodiment 3:

[0093] Figure 3 It is a structural schematic diagram of a gas-liquid mixing device.

[0094] The key point of silver aerosol transport is gas-liquid mixing to elute the silver atom clusters into the solution.

[0095] The newly formed atomic cluster aerosol quickly enters the gas path of the gas-liquid mixing chamber through the gas inlet channel of the gas-liquid mixing device, and is divided into two paths according to probability, which intersect each other in a serpentine shape; at the same time, high-purity water (or the low-concentration silver angstrom colloid solution that has been generated) enters the liquid path of the gas-liquid mixing chamber through the liquid inlet channel of the gas-liquid mixing chamber, and moves forward in a straight line. The intersection of the two gas paths serpentinely forward is connected to the cross passage of the liquid path, and the faster airflow brings the water in the liquid path or the low-concentration silver angstrom colloid solution that has been generated into the airflow for oscillation and mixing. The gas-liquid mixture that reaches the gas-liquid mixing chamber is discharged from the channel to complete the mixing. The parameters in this process are controlled as follows:

[0096] The gas is argon, the purity of argon is greater than 99.999%, the moisture content is below 0.05ppm, and the air intake volume is 5-10L / min.

[0097] The liquid is deionized water, and the liquid inlet rate is 1-10 ml / min.

[0098] The gas-liquid ratio (volume flow rate) in the gas-liquid mixture is maintained at gas:liquid = 1000:1 to 500:1.

[0099] The temperature is 20°C to 40°C, and the system pressure is 900mbar to 1013mbar.

[0100] In the actual preparation process of silver angstrom crystal colloid, if the final required silver angstrom crystal colloid has a higher concentration than the silver angstrom crystal colloid directly prepared by the system, the solution obtained in the gas-liquid separator can usually be heated and concentrated to obtain silver angstrom crystal colloid solutions of different concentrations. In order to prevent the silver element from reacting with the environment during the heating process and introducing unnecessary impurities, silver angstrom crystal colloid solutions of different concentrations can be further prepared by reduced pressure distillation to improve production efficiency and ensure the high purity of the silver angstrom crystal colloid solution.

[0101] Embodiment 4:

[0102] The method provided by the present invention can also be used to prepare a single substance silver angstrom crystal powder with high purity and high particle size consistency. The single substance silver angstrom crystal powder is obtained by heating and concentrating the solution obtained in the gas-liquid separator and fully drying the liquid. Since the single substance silver angstrom crystal powder has a high surface energy and is easily adsorbed by impurity gas molecules when directly exposed to the air, it should be noted that the preparation of the silver angstrom crystal powder usually needs to be carried out at a lower temperature. The present invention provides two methods for preparing silver angstrom crystal powder:

[0103] Method 1: Dry the silver angstrom crystal colloidal liquid prepared by the above method, and the drying process is carried out in a freeze-drying manner, and the freezing temperature is -4°C to 0°C.

[0104] The liquid is fully dried to obtain silver angstrom crystal powder.

[0105] Method 2: Dry the silver angstrom crystal colloidal liquid prepared by the above method, and the drying process is carried out in a drying manner at a drying temperature of 50°C to 70°C.

[0106] The liquid is fully dried to obtain silver angstrom crystal powder.

[0107] Example 5

[0108] According to the above-mentioned embodiment, especially the operation of the arc discharge chamber:

[0109] A cylindrical high-purity silver electrode with a cross-sectional diameter of 6 mm was used for arc discharge to generate silver atom clusters.

[0110] Before the reaction starts, ensure that the gas in the arc discharge zone reaches a vacuum degree below 0.01Mpa, and then introduce protective gas (such as argon) to ensure the purity and stability of the reaction.

[0111] It is also possible to increase the yield and efficiency of silver atom clusters by using multiple pairs of electrodes. However, it should be noted that the current should be increased in proportion to the number of silver electrode pairs while keeping the arc discharge voltage constant.

[0112] It should be noted that the use of multiple pairs of silver electrodes increases the generation efficiency and stripping efficiency of silver atom clusters. However, if the arc discharge current is not increased synchronously, the energy allocated to each electrode pair may not be enough to maintain the stable operation of the arc discharge current, causing work interruption, requiring manual intervention, and reducing the system output efficiency.

[0113] At the same time, for each additional silver electrode pair, the volume flow rate of the introduced inert gas (such as argon) needs to be increased synchronously to ensure that the silver atomic clusters can be transported to the next processing unit in a timely manner.

[0114] Working parameters details:

[0115] Arc discharge zone parameters:

[0116] Cylindrical silver electrode diameter: 6mm

[0117] Arc discharge current: Increases in proportion to the number of silver electrode pairs, 10mA per pair of electrodes Initial vacuum: Below 0.01Mpa

[0118] Protective gas: high purity inert gas (such as argon).

[0119] Example 6

[0120] Argon gas at room temperature is introduced into the arc discharge zone, and the concentration of the silver atom cluster aerosol formed per minute is controlled to be 0.1ppm. Then it quickly enters the gas-liquid mixing zone at a volume flow rate of 6L / min. The flow rate of the aerosol entering the gas-liquid mixing zone is controlled at 6L / min, and the flow rate of the liquid entering the gas-liquid mixing zone is controlled at 10mL / min. The gas-liquid mixing volume ratio is 600:1, the mixing volume of a single gas-liquid mixing zone is 2mL, the mixing time is 0.02 seconds, and the total liquid amount is 200mL. The mixed liquid is then passed into a gas-liquid separator to form independent argon gas and independent silver nanocrystal colloid. The separated argon gas is then circulated into the arc discharge zone, and continuously mixed with the silver nanocrystal colloid in the subsequent gas-liquid mixing zone at a predetermined flow rate. After continuous mixing through circulation, after 1 hour of circulation, a specific concentration of silver angstrom crystal colloid is finally formed, with a concentration of 23ppm. The silver angstrom crystal colloid was taken and tested for its morphology and particle size using TEM, which was in the range of 2 to 4nm, see Figure 4 . Figure 4 a is a TEM image of the silver angstrom colloid prepared in Example 2 of the present invention; Figure 4 b is a particle size distribution diagram of the silver angstrom colloid prepared in Example 6 of the present invention;

[0121] The test results show that the silver angstrom colloid prepared under the conditions of this embodiment has a silver particle size of 2 to 4 nm.

[0122] Example 7

[0123] Argon gas at room temperature is introduced into the arc discharge zone, and the concentration of the silver atom cluster aerosol formed per minute is controlled to be 0.1ppm, and then it quickly enters the gas-liquid mixing zone at a volume flow rate of 6L / min. The flow rate of the aerosol entering the gas-liquid mixing zone is controlled at 6L / min, and the flow rate of the liquid entering the gas-liquid mixing zone is controlled at 10mL / min. The gas-liquid mixing volume ratio is 600:1, the mixing volume of a single gas-liquid mixing zone is 2mL, the mixing time is 0.02 seconds, and the total liquid volume is 200mL. The mixed liquid is then passed into the gas-liquid separator to form independent argon gas and independent silver angstrom crystal colloid. The separated argon gas is then circulated into the arc discharge zone, and continuously mixed with the silver nanocrystal colloid in the subsequent gas-liquid mixing zone at a predetermined flow rate. After continuous mixing through circulation, a specific concentration of silver angstrom crystal colloid is finally formed after 8 hours of circulation. The prepared silver angstrom colloid was freeze-dried to obtain silver angstrom powder. XRD testing showed that the powder had obvious diffraction peaks and was consistent with the standard PDF diffraction powder card of single crystal silver, confirming that it was a crystalline structure. Figure 5 This is the XRD pattern of the silver angstrom powder prepared in Example 7 of the present invention; Figure 6 This is the XRD-standard PDF card of silver single crystal powder;

[0124] The test results show that the silver angstrom powder prepared under the conditions of this embodiment is a silver single crystal.

[0125] Example 8

[0126] Argon gas at room temperature is introduced into the arc discharge zone, and the concentration of the silver atom cluster aerosol formed per minute is controlled to be 0.1ppm, and then it quickly enters the gas-liquid mixing zone at a volume flow rate of 6L / min. The flow rate of the aerosol entering the gas-liquid mixing zone is controlled at 6L / min, and the flow rate of the liquid entering the gas-liquid mixing zone is controlled at 10mL / min. The gas-liquid mixing volume ratio is 600:1, the mixing volume of the gas-liquid mixing zone is 2mL, the mixing time is 0.02 seconds, and the total liquid volume is 200mL. The mixed liquid is then introduced into a gas-liquid separator to form independent argon gas and independent silver angstrom crystal colloids. The separated argon gas is then circulated into the arc discharge zone and continuously mixed with the silver angstrom crystal colloid in the subsequent gas-liquid mixing zone at a predetermined flow rate. The concentration values ​​of 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, and 12h are recorded, and the correlation between the concentration value and the total cycle time is analyzed, see Figure 7 The relationship between the concentration of silver angstrom colloid and different circulation times;

[0127] The test results show that the concentration increases very slowly under the conditions of this embodiment from 8h to 12h, which is not cost-effective. The previous concentration increase is linearly positively correlated with time.

[0128] Example 9

[0129] Argon gas at room temperature was introduced into the arc discharge zone to ensure that the concentration of the formed silver aerosol was 0.1 ppm per minute, and then it quickly entered the gas-liquid mixing zone at a volume flow rate of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 L / min. The flow rate of aerosol entering the gas-liquid mixing zone is controlled at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 L / min, the flow rate of liquid entering the gas-liquid mixing zone is controlled at 10 mL / min, the gas-liquid mixing volume ratio is 100:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, 1000:1, 1100:1, 1200:1, 1300:1, 1400:1, 1500:1, the mixing volume of the gas-liquid mixing zone is 2 mL, the mixing time is 0.02 seconds, and the total amount of liquid is 200 mL. The mixed liquid is then passed into a gas-liquid separator to form independent argon gas and independent silver angstrom crystal colloid. The separated argon gas is then circulated into the arc discharge zone and continuously mixed with the silver angstrom colloid in the subsequent gas-liquid mixing zone at a predetermined flow rate, and continuously mixed through circulation for 8 hours. The concentration values ​​of the gas-liquid ratio of 100:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, 1000:1, 1100:1, 1200:1, 1300:1, 1400:1, 1500:1 are recorded, and the correlation between the concentration value and the gas-liquid ratio is analyzed, see Figure 8 The relationship between the concentration of silver angstrom colloid and different gas-liquid ratios;

[0130] The correlation analysis between the concentration value and the gas-liquid ratio shows that, among different gas-liquid mixing ratios, the concentration of silver angstrom colloid is higher when the gas-liquid ratio is between 500:1 and 1000:1, and then gradually decreases; the gas-liquid ratio is lower between 100:1 and 500:1, and the concentration of silver angstrom increases slowly with the increase of the gas-liquid ratio. The specific reasons are analyzed as follows: in this embodiment, the flow rate of liquid entering the gas-liquid mixing zone is controlled at 10 mL / min. When the gas-liquid ratio is between 100:1 and 500:1, the flow rate of inert gas entering the arc discharge chamber is too low. The low gas flow rate is insufficient for cooling the silver atom clusters generated by the arc discharge, so that the silver atom clusters cannot be sufficiently cooled to form agglomerations, and the silver atom clusters with large kinetic energy are sputtered for a long distance and attached to the stainless steel wall of the arc discharge chamber, reducing the number of silver atom clusters that can be transported out. The arc discharge chamber has been verified by inspection.

[0131] Then, silver angstrom colloids with a gas-liquid ratio between 100:1 and 500:1 were mixed and tested by TEM, such as Fig. 9 ; Mix the silver angstrom colloid in the 600:1 to 1000:1 stage and test TEM, such as Fig.10; Mix the silver angstrom colloid in the 1000:1 to 1500:1 stage and test TEM, such as Fig.11 ;

[0132] The correlation analysis between particle size distribution and gas-liquid ratio was carried out according to normal distribution statistics. The experimental results showed that in the low-stage gas-liquid ratio stage (100:1-500:1), the particle size distribution of silver angstrom colloids was 2.99nm±1.05nm, accounting for 67.2%, and the particle size distribution was 2.99±2.10nm, accounting for 95.4%. In the medium-stage gas-liquid ratio (600:1-900:1), the particle size distribution of silver angstrom colloids was 2.30nm±1.05nm, accounting for 67.2%, and the particle size distribution was 2.30nm±2.10nm, accounting for 95.4%. In the high-stage gas-liquid ratio (1000:1-1500:1), the particle size distribution of silver angstrom colloids was 1.74nm±0.40nm, accounting for 67.2%, and the particle size distribution was 1.74nm±0.80nm, accounting for 95.4%.

[0133] In summary, it can be seen that, considering the cost, this process can be used to prepare 2-4 nm silver angstrom colloids at a medium gas-liquid ratio.

[0134] Silver angstrom colloid itself has Tyndall effect. Fig.12 For its Tyndall effect photo.

[0135] Example 10

[0136] Quality control during the preparation of the silver angstrom crystal colloidal solution, i.e., nano silver single substance powder, provided by the present invention:

[0137] Particle size test: obtain silver angstrom colloidal solution, take samples for TEM test and particle size statistics to ensure that the particle size distribution is 2-4nm and has obvious single crystals, and further dry the powder to obtain XRD test to ensure that it is a single crystal.

[0138] Concentration test: obtain a silver angstrom colloidal solution, take a sample for ICP-MS testing, and ensure that the final silver angstrom colloidal concentration is not less than 20ppm.

[0139] Stability test: The formed colloidal solution is placed at 37°C away from light for 3 months without precipitation and still has the Tyndall effect. The tested particle size and concentration remain at 2-4nm and ≥20ppm.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-purity and high-diameter silver angstrom colloid, using a nano silver colloid preparation system comprising an inert gas supply device, an arc discharge chamber, a gas-liquid mixing device, a gas-liquid separation device, a liquid storage and liquid supply device, a gas recovery and purification device, and a liquid concentration device, characterized in that The following steps are involved: (1) Preparation stage: high-purity deionized water is placed in the liquid storage container of the liquid storage and liquid supply device, high-purity silver electrodes are placed in pairs in the arc discharge chamber, the distance between the silver electrodes is adjusted to 0.3-1.0 mm, the airtight arc discharge chamber is evacuated by a vacuum pump, inert gas is introduced into the arc discharge chamber through an inert gas storage cylinder, the gas intake is controlled at 5-10 L / min, the power supply of the arc discharge chamber is controlled, a high-voltage arc is initiated between the silver electrodes in the arc discharge chamber, the positive and negative voltages are controlled to be 0.8-1.3 kV, the current between the positive and negative electrodes is controlled to be 7-13 mA, the pulse frequency is about 250-350 Hz, and the high-voltage arc is maintained continuously; (2) Generating silver atom cluster aerosol: Under the protection of inert gas, a pair of high-purity silver electrode surfaces are continuously vaporized into silver atom clusters or plasma using a high-voltage arc in an arc discharge zone, and the inert gas intake rate at room temperature into the arc discharge chamber is maintained at 5 to 10 L / min. The inert gas is passed through the silver electrode gap in the arc discharge chamber to obtain an aerosol containing silver atom clusters; (3) gas-liquid mixing: the silver atom cluster aerosol obtained in step (2) is introduced into the gas inlet channel of the gas-liquid mixing device, and the liquid is introduced into the liquid inlet channel of the gas-liquid mixing device using a liquid storage and liquid supply device, and the silver atom cluster aerosol and the liquid are fully mixed in the gas-liquid mixing device, and the silver atom clusters in the silver atom cluster aerosol are transferred to the liquid to obtain a gas-liquid mixture containing silver atom clusters, wherein the gas intake of the gas-liquid mixing device is maintained at 5 to 10 L / min, and the liquid intake of the gas-liquid mixing device is maintained at 1 to 10 ml / min; (4) gas-liquid separation: separating the gas-liquid mixture containing silver atomic clusters obtained in step (3) to obtain an inert gas containing a small amount of liquid molecules and a liquid containing a large amount of atomic clusters; (5) Gas residue removal and drying: The inert gas containing a small amount of liquid molecules obtained in step (4) is extracted and dried through a cold trap to remove moisture in the inert gas, and the temperature of the cold trap is controlled between minus 10 degrees and minus 50 degrees. Before the inert gas is dried, it passes through a high-density filter to remove residual silver atomic clusters. After the inert gas is dried, it is returned to the inert gas storage cylinder described in step (2); (6) The liquid continues to mix with the silver atom cluster aerosol: the high-purity inert gas at room temperature is continuously introduced into the arc discharge chamber as described in step (2), the liquid containing a large number of atomic clusters obtained in step (4) is collected into a liquid temporary storage tank, mixed with the original liquid in the liquid temporary storage tank, and the mixed liquid continues to be introduced into the liquid inlet channel of the gas-liquid mixing device described in step (3); (7) maintaining the above working state until the liquid in the gas-liquid separator contains a sufficient concentration of atomic clusters; (8) Liquid concentration: The liquid containing the atomic clusters obtained in step (7) is concentrated to obtain atomic cluster liquid dispersions of different concentrations, namely, silver angstrom crystal colloids.

2. The preparation method according to claim 1, characterized in that: Arc discharge positive and negative voltage: 1kV, positive and negative current: 10mA, pulse frequency is 300Hz.

3. The preparation method according to claim 1, characterized in that: Distance between arc discharge electrodes: 0.5mm, electrode diameter 3~6mm.

4. The preparation method according to claim 1, characterized in that: The purity of the high-purity silver electrode in step (1) is greater than 99.999%, and the sum of other impurity elements in the electrode does not exceed 1 ppm; The inert gas described in step (1) is argon, the purity of argon is greater than 99.999%, and the moisture content is below 0.05ppm.

5. The preparation method according to claim 1, characterized in that: In step (3), the gas-liquid ratio (volume flow rate) in the gas-liquid mixture is maintained at gas:liquid=500:

1.

6. The preparation method according to claim 1, characterized in that: The system pressure in step (4) is lower than that in steps (1) to (3), the temperature is 20°C to 40°C, and the system pressure is 900mbar to 1013mbar.

7. The preparation method according to claim 1, characterized in that: In the liquid concentration process described in step (8), reduced pressure distillation is adopted.

8. A method for preparing nano silver powder according to claim 1, characterized in that: The nano silver colloidal liquid prepared by the above method is dried, and the drying process is carried out in a freeze drying manner, and the freezing temperature is -4°C to 0°C; The liquid is fully dried to obtain elemental silver angstrom powder.

9. A method for preparing silver angstrom powder according to claim 1, characterized in that: The silver angstrom colloidal liquid prepared by the above method is dried, and the drying process is carried out in a drying method, and the drying temperature is 50° C. to 70° C. When the temperature is higher than 70° C., it is carried out in a nitrogen or argon atmosphere with a purity of 99.95% or more; The liquid is fully dried to obtain silver angstrom crystal powder.

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