6N high-purity silver raw material for target material and preparation method of 6N high-purity silver raw material

Abstract

The invention discloses a 6N high-purity silver raw material for a target material and a preparation method thereof.The preparation method of the 6N high-purity silver raw material for the target material comprises the following steps that 4.5 N silver is placed in a vacuum intermediate frequency furnace to be smelted, and an anode plate is prepared; silver nitrate is purified through a crystallization method and a silver oxide purification method, and high-purity silver nitrate is obtained; the anode plate is loaded into a ceramic membrane, the high-purity silver nitrate is taken to be prepared into an electrolysis mother solution, then the anode plate loaded into the ceramic membrane serves as an anode, titanium-coated silver serves as a cathode, the electrolysis mother solution serves as an electrolyte, and electrolysis is conducted to prepare high-purity silver powder; and the high-purity silver powder is placed in a graphite crucible to be subjected to vacuum melting and then poured into a graphite mold, and the 6N high-purity silver raw material for the target material is prepared. According to the 6N high-purity silver raw material for the target material and the preparation method of the 6N high-purity silver raw material, the purity and stability of the 6N high-purity silver raw material are improved on the basis of guaranteeing the purity of the 6N high-purity silver raw material through combination of various modes such as raw material optimization, equipment optimization and process step improvement.

Description

Technical Field

[0001] The present invention relates to the technical field of precious metal refining, and in particular to a 6N high-purity silver raw material for a target material and a preparation method thereof. Background Art

[0002] The main component of high-purity silver targets is high-purity silver (usually with a purity of over 99.99%), in addition to some additives and matrix materials. High-purity silver has excellent electrical conductivity, thermal conductivity, and reflectivity, which can ensure the uniformity and density of the deposited film, thereby improving product performance. Additives such as metal oxides, carbides, or rare earth elements can adjust the physical properties of silver targets, such as hardness, wear resistance, and oxidation resistance. Matrix materials such as copper, aluminum, and stainless steel provide sufficient strength and stability to reduce stress concentration and deformation during use.

[0003] High-purity silver targets are widely used in various high-tech fields: (1) In the electronics field, they are used in electron beam evaporation and ion sputtering processes to produce high-quality electronic components and circuit boards; (2) In the photovoltaic field, in the manufacture of solar cells, high-purity silver paste is used as an electrode material to improve the photoelectric conversion efficiency; (3) In the semiconductor field, in semiconductor manufacturing, silver targets are used to make reflective films and wiring films to improve the performance and stability of devices; (4) In other applications, silver targets are also used in organic EL displays, lighting, touch screens, thin-film solar cells, LEDs, Low-E glass and optical recording media.

[0004] Currently, the purity of high-purity silver in China is generally 4N to 5N (4N represents 99.99% purity, 5N represents 99.999% purity). Even for 6N (6N represents 99.9999% purity) high-purity silver ingots, the national standard limits the impurity content only to metal elements such as Cu, Bi, Fe, Pb, Sb, Pd, Se, Te, As, Mg, Au, Co, Mn, Ni, Pt, Rh, Sn, Zn, Cd, Ca, and Al, and does not require content limits on the elements C, N, O, and S. High-purity silver targets, as key basic materials in the field of semiconductor integrated circuits, have increasingly higher requirements for silver purity. On top of meeting the national standard requirements for 6N pure silver, it is necessary to increase the content limits on the impurity elements C, N, O, and S, placing higher demands on the auxiliary materials and equipment used in the entire production system. Summary of the Invention

[0005] The main purpose of the present invention is to provide a 6N (6N in this article means the purity reaches 99.9999%) high-purity silver raw material for target material and its preparation method.

[0006] To achieve the above object, the method for preparing the 6N high-purity silver raw material for the target material comprises the following steps:

[0007] 4.5N (4.5N in this article means the purity reaches 99.995%) silver is placed in a vacuum medium frequency furnace for melting to make an anode plate;

[0008] Silver nitrate is purified by crystallization and silver oxide purification to obtain high-purity silver nitrate;

[0009] The anode plate is placed in a ceramic membrane, and the high-purity silver nitrate is prepared into an electrolytic mother solution. Then, electrolysis is performed using the anode plate placed in the ceramic membrane as an anode, the titanium-coated silver as a cathode, and the electrolytic mother solution as an electrolyte. During the electrolysis process, powder is automatically brushed and silver powder is collected. The collected silver powder is filtered, washed, and dried using a fully automated all-in-one machine to obtain high-purity silver powder. The high-purity silver powder is then placed in a titanium container and vacuum-packed for transfer.

[0010] The high-purity silver powder is placed in a graphite crucible and the vacuum degree is adjusted to 1*10 -1 ~1*10 -5 After the high-purity silver powder is heated to 0.15 MPa, high-purity 6N argon gas with a positive pressure of 0.15 to 0.35 MPa is input and vacuum melting is performed to make a silver melt from the high-purity silver powder, and then the silver melt is poured into a graphite mold to make a 6N high-purity silver raw material for the target material; wherein the dew point of the high-purity 6N argon gas is ≤-80°C, and a PCL air pressure monitoring device is used during the vacuum melting process. After the high-purity 6N argon gas is introduced, the melting is started, and when the air pressure in the melting chamber is greater than 0.35 MPa, vacuum extraction is started and the pressure is stabilized to 0.15 to 0.35 MPa;

[0011] The steps of purifying silver nitrate by crystallization and silver oxide purification include:

[0012] Silver nitrate is dissolved in deionized water to prepare a silver nitrate solution with a concentration of 10 to 300 g / L, GR-grade silver oxide is added to the silver nitrate solution, and 3 to 5 g of silver oxide is added to every 100 mL of the silver nitrate solution. The solution is then heated and dissolved until the pH of the solution reaches 4.8 to 5.2, cooled, and filtered using a mixed fiber membrane (hereinafter referred to as an MCE membrane) and then filtered using a polytetrafluoroethylene membrane (hereinafter referred to as a PTFE membrane) to obtain a pure silver nitrate solution.

[0013] The purified argon gas and the pure silver nitrate solution were pumped into the evaporator, stirring was started, and the temperature was raised to keep the solution in the evaporator slightly boiling for evaporation. The density was monitored during the evaporation process until the density of the solution in the evaporator reached 2.0-3.0 g / cm 3 ;

[0014] After the evaporation is completed, the solution in the evaporation kettle is transferred to a crystallization kettle for crystallization, and then filtered, washed and dried to obtain high-purity silver nitrate.

[0015] Optionally, the Na content in the 4.5N silver is not higher than 2 ppm, and the total impurity content is not higher than 50 ppm.

[0016] Optionally, the C content in the high-purity silver nitrate is less than 10 ppm, the S content is less than 10 ppm, and the trace metal ions of Te, Sn, Pd, and Bi in the high-purity silver nitrate are all less than 10 ppm; and / or,

[0017] The pore size of the mixed fiber membrane is 2-3 μm, and the pore size of the polytetrafluoroethylene membrane is 0.5-0.8 μm.

[0018] Optionally, the ceramic membrane has a purity of not less than 99.9%, a pore size of 0.1 to 1 μm, a porosity of 30 to 50%, a compressive strength ≥ 50 MPa, a roughness Ra ≤ 0.1 μm, and a resistivity ≥ 1012 Ω·cm.

[0019] Optionally, all parts in contact with silver powder in the fully automated all-in-one machine are made of Teflon or T1 titanium; and / or,

[0020] The material of the electrolytic cell used in the electrolysis includes glass fiber reinforced polypropylene, and the density of the glass fiber reinforced polypropylene is 0.90-0.91 g / cm 3 , thermal deformation coefficient ≤ 2*10 -5 K -1 .

[0021] Optionally, the water used to prepare the electrolyte mother solution is electronic grade pure water, the resistivity of the electronic grade pure water is ≥18.2 MΩ·cm (25° C.), and the number of particles with a particle size less than 0.1 μm is less than 100 / mL.

[0022] Optionally, the cell circulation rate of the electrolysis process is 0.5-1 L / min, the interelectrode distance is 115-125 mm, the electrolysis adopts constant current electrolysis, and the current control area of ​​the constant current electrolysis is 500-650 A / m 3 , the cell voltage is 1.5 to 3.5 V; and / or,

[0023] The powder brushing frequency of the electrolysis process is 6 to 8 times / min.

[0024] Optionally, the washing process includes: first washing the concentrated residual liquid with electronic grade pure water at 45-55°C, then washing with electronic grade pure water at 85-95°C, and finally washing with electronic grade pure water at 45-55°C, wherein the resistivity of the electronic grade pure water is ≥18.2MΩ·cm (25°C), and the number of particles with a particle size less than 0.1μm is required to be less than 100 / mL.

[0025] Optionally, the drying air used in the drying process is first subjected to a 10,000-level primary dust removal process, and then filtered through an activated carbon filter element before entering a hot air rotary drying system to dry the material; wherein the material of the activated carbon filter element is a GHSV of 200 to 500h -1 Modified coconut shell activated carbon loaded with potassium hydroxide.

[0026] Optionally, the graphite crucible is made of high-purity graphite, and the density of the high-purity graphite is 1.85 g / cm 3 , resistance of 8 to 10 μΩm, expansion coefficient of 4.75 (6 to 10°C), porosity of 13%, ash content of 500 ppm, purified ash content of 50 ppm, particle size of 13 to 15 μm; and / or,

[0027] The graphite mold is made of high-purity graphite, and the density of the high-purity graphite is 1.85g / cm 3 , resistance is 8-10μΩm, expansion coefficient is 4.75 (6-10℃), porosity is 13%, ash content is 500ppm, purified ash content is 50ppm, and particle size is 13-15μm.

[0028] Furthermore, the present invention also provides a 6N high-purity silver raw material for a target material, and the 6N high-purity silver raw material for a target material is prepared by the preparation method of the 6N high-purity silver raw material for a target material as described above.

[0029] The technical solution provided by the present invention has at least the following beneficial effects:

[0030] (1) The silver nitrate used to prepare the electrolytic mother solution is further purified and impurities removed by crystallization and silver oxide purification. The metal impurities are hydrolyzed and precipitated by silver oxide purification, and the non-metallic particulate impurities are more fully removed by two-stage filtration using an MCE membrane and a PTFE membrane, so that the impurity content in the electrolytic mother solution reaches the target material level. Compared with the traditional method of directly dissolving silver or using commercially available silver nitrate (such as GB / T670-2007 chemical reagent grade silver nitrate) as a raw material without purification treatment and directly preparing the electrolytic mother solution, the silver nitrate after purification and impurity removal in the present application has higher purity and less impurities, and impurity contamination is eliminated from the source, thereby improving the purity and stability of the prepared product.

[0031] (2) The anode uses a ceramic membrane as the anode separator bag, so that insoluble substances such as carbon and impurity metals produced during the electrolysis process do not dissolve and penetrate into the solution. Compared with traditional polyester anode bags, the ceramic membrane used in the present invention can remove impurities more accurately, and the frame structure is not prone to causing short circuits.

[0032] (3) After the silver powder is obtained, vacuum melting is adopted. By regulating the purity of argon, the degree of vacuum during melting, the pressure during melting and the material of the vessel, the incorporation of C, N, O and S in the impurities can be effectively reduced, so that the target material prepared using 6N high-purity silver raw materials has fewer impurities and the product is higher in purity and more stable. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. Where the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased commercially. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but must be based on the ability of ordinary technicians in this field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that the combination of such technical solutions does not exist and is not within the scope of protection required by the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0034] The purity of domestic high-purity silver is generally 4N to 5N (4N represents 99.99% purity, 5N represents 99.999% purity). Even for 6N (6N represents 99.9999% purity) high-purity silver ingots, the national standard limits the impurity content only to metal elements such as Cu, Bi, Fe, Pb, Sb, Pd, Se, Te, As, Mg, Au, Co, Mn, Ni, Pt, Rh, Sn, Zn, Cd, Ca, and Al, and does not require content limits on the elements C, N, O, and S. High-purity silver targets, as key basic materials in the field of semiconductor integrated circuits, have increasingly higher requirements for silver purity. On top of meeting the national standard requirements for 6N pure silver, it is necessary to increase the content limits on the impurity elements C, N, O, and S, and place higher demands on the auxiliary materials and equipment used in the entire production system.

[0035] At present, the preparation technology of high-purity silver powder mainly involves liquid phase reduction, electrolytic smelting, pyrometallurgy, etc. The Chinese patent "A method for preparing 6N high-purity silver powder" (patent application number 202410539791.9) provides a method for preparing 6N high-purity silver powder. The method is as follows: using 1# silver ingot and silver nitrate as raw materials, then using silver nitrate solution as electrolyte, pretreated 1# silver ingot as anode, and titanium plate as cathode for electrolysis, using constant current electrolysis, and the current density is controlled at 100~900A / m 2The powder brushing cycle is controlled between 1 and 100 seconds, and the electrolysis cycle is controlled between 1 and 100 hours. The electrolytic powder obtained after exiting the tank is stirred and washed with flowing deionized water until the conductivity of the washing water is less than 10μS / cm. The washed electrolytic silver powder is evenly spread to a thickness of 1cm, placed in a forced air drying oven, and dried at 100°C for 1 to 10 hours to obtain high-purity silver powder with a purity of 99.9999% or above. The silver nitrate solution is prepared as follows: silver nitrate is dissolved in deionized water to obtain a solution with a concentration of 10 to 300g / L. The solution is filtered through an ultrafiltration membrane with a filtration accuracy of 0.01 to 1μm to obtain a filtrate. The filtrate is added with high-purity nitric acid to adjust the pH of the solution to 1. The purity of the silver nitrate is high-purity or above. The pretreated 1# silver ingot was prepared according to the following method: the 1# silver ingot was first soaked and washed in a sodium hydroxide solution with a concentration of 1 to 100 g / L for 1 hour, then soaked and washed in a dilute nitric acid solution with a concentration of 1 to 100 g / L for 1 hour, and finally soaked and washed in deionized water with a conductivity of 1.0 to 10.0 MΩ·cm for 1 hour. The washed silver ingot was dried at 100° C. for 1 hour.

[0036] However, the method used in the above patent is used to prepare silver powder. For the preparation of high-purity silver raw materials for target materials, the control of impurities is more stringent. This method has the problem of uneven control of auxiliary material impurities, equipment impurities, smelting impurities, etc., which makes the purity of high-purity silver raw materials unstable. In view of this, the present invention proposes a method for preparing 6N high-purity silver raw materials for targets, which combines various methods such as raw material optimization, equipment optimization, process steps and parameter improvements to achieve the goal of improving the purity stability of high-purity silver raw materials while ensuring their purity. Specifically, the method for preparing 6N high-purity silver raw materials for targets provided by the present invention comprises the following steps:

[0037] Step S10: smelting 4.5N silver in a vacuum medium frequency furnace to produce an anode plate;

[0038] Step S20: purifying the silver nitrate by crystallization and silver oxide purification to obtain high-purity silver nitrate;

[0039] Step S30: The anode plate is placed in a ceramic membrane, and the high-purity silver nitrate is prepared into an electrolytic mother solution. Then, electrolysis is performed using the anode plate placed in the ceramic membrane as the anode, the titanium-coated silver as the cathode, and the electrolytic mother solution as the electrolyte. During the electrolysis process, the silver powder is automatically brushed and collected. The collected silver powder is filtered, washed, and dried using a fully automated all-in-one machine to obtain high-purity silver powder. The high-purity silver powder is placed in a titanium container and vacuum-packed for transfer.

[0040] Step S40: Place the high-purity silver powder in a graphite crucible and adjust the vacuum degree to 1*10 -1 ~1*10 -5After Pa, high-purity 6N argon gas with a positive pressure of 0.2MPa is input and vacuum melting is carried out to make the high-purity silver powder into a silver melt, and then the silver melt is poured into a graphite mold to make a 6N high-purity silver raw material for the target material; wherein, the dew point of the high-purity 6N argon gas is ≤-80°C, and a PCL air pressure monitoring device is used during the vacuum melting process. After the high-purity 6N argon gas is introduced, the melting is started. When the air pressure in the melting chamber is greater than 0.2MPa, vacuum extraction is started and the pressure is stabilized to 0.2MPa, so that a small amount of impurity gas produced by the melting can be diluted and extracted.

[0041] It should be noted that the above embodiment only takes the preparation method of the target material using 6N high-purity silver raw material as an example, which is implemented in the order of step S10, step S20, step S30, and step S40, to explain and illustrate the preparation method provided by the present invention in detail. The present invention does not limit the order between step S10 and step S20. Step S10 may be in front and step S20 may be in the back, or step S20 may be in front and step S10 may be in the back, or step S10 and step S20 may be performed simultaneously, as long as the anode plate and the high-purity silver nitrate are prepared separately before step S30.

[0042] Furthermore, in this solution, the step of purifying silver nitrate by using a crystallization method and a silver oxide purification method in step S20 includes:

[0043] Step S21, dissolving silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 10 to 300 g / L, adding GR grade (super pure grade) silver oxide to the silver nitrate solution, adding 3 to 5 g of silver oxide per 100 mL of the silver nitrate solution, then heating and dissolving the solution until the pH value of the solution is 4.8 to 5.2, cooling, performing primary filtration using an MCE membrane, and performing secondary filtration using a PTFE membrane to obtain a pure silver nitrate solution;

[0044] Step S22: Pump the purified argon gas and the pure silver nitrate solution into the evaporator, start stirring, and heat to 60-70°C to keep the solution in the evaporator slightly boiling for evaporation. Monitor the density during the evaporation process until the density of the solution in the evaporator reaches 2.0-3.0 g / cm 3 ;

[0045] Step S23: After the evaporation is completed, the solution in the evaporation kettle is transferred to a crystallization kettle for crystallization, and then filtered, washed, and dried to obtain high-purity silver nitrate.

[0046] Among them, the filtration, washing and drying in step S23 are preferably performed in a three-in-one process using automated equipment to improve efficiency and reduce impurity incorporation.

[0047] The technical solution provided by the present invention has at least the following beneficial effects:

[0048] (1) The silver nitrate used to prepare the electrolytic mother solution is further purified and impurities removed by crystallization and silver oxide purification. The metal impurities are hydrolyzed and precipitated by silver oxide purification, and the non-metallic particulate impurities are more fully removed by two-stage filtration using an MCE membrane and a PTFE membrane, so that the impurity content in the electrolytic mother solution reaches the target material level. Compared with the traditional method of directly dissolving silver or using commercially available silver nitrate (such as GB / T 670-2007 chemical reagent grade silver nitrate) as a raw material without purification treatment and directly preparing the electrolytic mother solution, the silver nitrate after purification and impurity removal in the present application has higher purity and less impurities, and impurity contamination is eliminated from the source, thereby improving the purity and stability of the prepared product.

[0049] (2) The anode uses a ceramic membrane as the anode separator bag, so that insoluble substances such as carbon and impure metals produced during the electrolysis process do not dissolve and penetrate into the solution. Compared with traditional polyester anode bags, the ceramic membrane used in the present invention can remove impurities more accurately, and the ceramic membrane frame structure has a hollow interlayer. Compared with traditional anode bags, it is not easy to cause adhesion and cause the anode and cathode to short-circuit through the accumulation of silver powder.

[0050] (3) After the silver powder is obtained, vacuum melting is adopted. By regulating the purity of argon, the degree of vacuum during melting, the pressure during melting and the material of the vessel, the incorporation of C, N, O and S in the impurities can be effectively reduced, so that the target material prepared using 6N high-purity silver raw materials has fewer impurities and the product is higher in purity and more stable.

[0051] In some embodiments of the present invention, the Na content of the 4.5N silver is no more than 2 ppm, and the total impurity content is no more than 50 ppm. Thus, through strict selection of anode silver raw materials, compared to the current enterprise standard of using national standard No. 1 silver plate as anode, 4.5N silver can more stably produce 6N high-purity silver raw materials for target materials, reducing the instability of finished product impurities caused by fluctuations in mother liquor impurities, and further helping to improve the purity and stability of the product. Furthermore, the cathode of the present invention uses titanium-clad silver, which has the advantages of corrosion resistance and excellent electrical conductivity.

[0052] Further, in some embodiments of the present invention, the smelting temperature of the smelting in step S10 is 1000-1100°C, for example, it can be 1000°C, 1010°C, 1020°C, 1030°C, 1040°C, 1050°C, 1060°C, 1070°C, 1080°C, 1090°C or 1100°C, etc., preferably 1000°C; the smelting time of the smelting is 25-35 min, for example, it can be 25 min, 26 min, 27 min, 28 min, 29 min, 30 min, 31 min, 32 min, 33 min, 34 min or 35 min, etc., preferably 30 min.

[0053] The method for purifying and refining silver nitrate using a crystallization method and a silver oxide purification method provided by the present invention has a higher purity and fewer impurities in the high-purity silver nitrate obtained after purification and impurity removal. Preferably, in some embodiments of the present invention, the C in the high-purity silver nitrate described in step S23 is less than 10ppm, and the S is less than 10ppm, and the trace metal ions of Te, Sn, Pd, and Bi in the high-purity silver nitrate are all less than 10ppm. By purifying and removing impurities from silver nitrate, high-purity silver nitrate with higher purity and impurity content less than 10ppm can be obtained, and impurity contamination can be eliminated from the source, so that the cathode plate is not easily contaminated with impurities during subsequent electrolysis, thereby improving the purity and stability of the silver powder obtained by electrolysis, and thereby improving the purity of the 6N high-purity silver raw material product for the target material and its low impurity stability.

[0054] In the present invention, a dual-stage filtration method using an MCE membrane and a PTFE membrane can reduce the amount of trace particulate impurities in the silver nitrate solution, especially non-metallic particulate matter. Furthermore, in some embodiments of the present invention, the pore size of the MCE membrane in step S21 is 2-3 μm, preferably 2.6 μm, and the pore size of the PTFE membrane is 0.5-0.8 μm. In this way, after the dual-stage filtration using the MCE membrane and PTFE membrane, a filtrate with a maximum allowable number of 100-1000 particles / mL for particles ≥0.1 μm can be obtained, thereby obtaining a purer silver nitrate solution.

[0055] In the present invention, ceramic membranes are used as anode bags to isolate anode mud from seepage, such as trace carbon particles and silicon, enabling more precise impurity removal. Specifically, in some embodiments of the present invention, the ceramic membranes used in step S30 have a purity of no less than 99.9%, a pore size of 0.1 to 1 μm, a porosity of 30 to 50%, a compressive strength of 50 MPa or greater, a roughness Ra of 0.1 μm or less, and a resistivity of 1012 Ω·cm or greater. These parameters provide for better impurity removal and stability.

[0056] In some embodiments of the present invention, the material of the electrolytic cell used for electrolysis in step S30 includes glass fiber reinforced polypropylene, and the density of the glass fiber reinforced polypropylene is 0.90-0.91 g / cm 3 , thermal deformation coefficient ≤ 2*10 - 5 K -1 The electrolytic cell is made of glass fiber reinforced polypropylene, which has the advantage of not easily shedding impurities, helping to ensure the purity and stability of the silver powder obtained by electrolysis, and can withstand electrolysis at a certain heating temperature.

[0057] Furthermore, in some embodiments of the present invention, all components in the fully automated all-in-one machine that come into contact with the silver powder in step S30 are made of Teflon or T1 titanium. This effectively prevents fluid carryover and ensures the purity and stability of the silver powder obtained by electrolysis. It is understood that the "all components in the fully automated all-in-one machine that come into contact with the silver powder" include at least, but are not limited to, the linings of all containers used for filtering, washing, and drying the silver powder, as well as the linings of pipes used to transport the silver powder. Components that can be made of non-metallic materials can be made of Teflon, while components that require metal materials (including but not limited to screws, nuts, and other connectors) can be made of T1 titanium.

[0058] In some embodiments of the present invention, the water used to prepare the electrolyte mother solution in step S30 is electronic-grade pure water, wherein the electronic-grade pure water has a resistivity of ≥18.2 MΩ·cm at 25°C and a particle size of less than 100 particles / mL with a particle size less than 0.1 μm. Using electronic-grade pure water with these parameters can reduce impurities at the source, ensuring the purity and stability of the silver powder obtained by electrolysis.

[0059] Furthermore, in some embodiments of the present invention, the silver content of the electrolytic mother solution in step S30 is 100-120 g / L, and the free nitric acid content is 20-25 g / L.

[0060] In some embodiments of the present invention, the electrolysis process in step S30 has a tank circulation rate of 0.5 to 1 L / min, an interelectrode distance of 115 to 125 mm, and constant current electrolysis is employed. The current control area of ​​the constant current electrolysis is 500 to 650 A / m 3 , the cell voltage is 1.5~3.5V.

[0061] In some embodiments of the present invention, the powder brushing frequency of the electrolysis process in step S30 is 6 to 8 times / min.

[0062] In the scheme of the present invention, a fully automated all-in-one machine is used to perform a three-in-one process of filtering, washing, and drying the silver powder obtained by electrolysis. A fully enclosed automated titanium mesh is used to filter the silver powder, a fully enclosed washing system is used and electronic-grade pure water is added to wash the silver powder, and then the silver powder is dried in a fully automatic and sealed manner in the washing chamber to reduce the entry of air impurities and prevent manual contact. Compared with traditional separate operations, the doping of atmospheric dust, sulfides, carbon, Fe and other impurities during the process can be reduced, and the impurity stability of the product can be increased by more than 60%. More preferably, in some embodiments of the present invention, the fully automated all-in-one machine also includes automatic powder brushing and unloading components, such as using an automatic funnel trough to receive the silver powder for the next process. That is, in a preferred embodiment of the present invention, the fully automated all-in-one machine as a whole can realize the integrated operation of powder brushing, unloading, filtering, washing, and drying for the silver powder obtained by electrolysis, greatly improving work efficiency, reducing the possibility of silver powder carrying impurities, and ensuring the purity and stability of the silver powder to a greater extent.

[0063] Specifically, in some embodiments of the present invention, the washing process in step S30 is carried out in a fully enclosed washing system, and the specific washing process includes: first washing the concentrated residual liquid with electronic-grade pure water at 45-55°C, then washing with electronic-grade pure water at 85-95°C, and finally washing with electronic-grade pure water at 45-55°C, wherein the resistivity of the electronic-grade pure water at 25°C is ≥18.2MΩ·cm, and the number of particles with a particle size less than 0.1μm is required to be less than 100 / mL.

[0064] In some embodiments of the present invention, the drying air used in the drying process in step S30 is first subjected to a 10,000-level primary dust removal before heating to reduce the entry of particulate matter in the air, and then filtered through an activated carbon filter element before entering a hot air rotary drying system to dry the material. In this way, the sulfur dioxide in the air can be reduced during the air intake rotary drying; wherein, preferably, the activated carbon filter element is loaded in a 1000-mesh filter bag, the micropore diameter of the activated carbon filter element is less than 2 nm, and the material of the activated carbon filter element is a GHSV (Gas Hourly Space Velocity) reaching 200 to 500 h -1 Modified coconut shell activated carbon loaded with potassium hydroxide.

[0065] In addition, in some embodiments of the present invention, the material of the graphite crucible in step S30 is high-purity graphite, and the density of the high-purity graphite is 1.85 g / cm 3, resistance 8-10μΩm, expansion coefficient 4.75 (6-10°C), porosity 13%, ash content 500ppm, purified ash content 50ppm, and particle size 13-15μm. Strict control of the graphite crucible material density can minimize carbon dusting and incorporation from the crucible surface. Strict control of the graphite crucible material ash content can also minimize incorporation of base metals from the crucible components through contact, thereby ensuring the purity and stability of the 6N high-purity silver raw material used in the target.

[0066] Furthermore, in some embodiments of the present invention, the material of the graphite mold in step S30 is high-purity graphite, and the density of the high-purity graphite is 1.85 g / cm 3 , resistance 8-10μΩm, expansion coefficient 4.75 (6-10°C), porosity 13%, ash content 500ppm, purified ash content 50ppm, and particle size 13-15μm. Similarly, strict control of the density of the graphite mold material can minimize carbon dusting and incorporation from the crucible surface. Strict control of the ash content of the graphite mold material can also minimize the incorporation of base metals from the mold components through contact, thereby ensuring the purity and stability of the 6N high-purity silver raw material used in the target.

[0067] The embodiment of the present invention comprises the following steps in the preparation of 6N high-purity silver raw materials for targets, including the selection of anode plate silver raw materials, the selection of anode bag materials, the optimization of the purity of silver nitrate used for preparing electrolytic mother liquor, the optimization of the grade of water used for preparing electrolytic mother liquor, the selection of materials for electrolytic cells and all parts that need to come into contact with silver powder, the integrated treatment of powder brushing, feeding, filtering, washing and drying of silver powder obtained by electrolysis, the dust removal and filtering treatment of hot air required for drying, the control of various process conditions and vessel materials in the vacuum melting process, etc. By purifying and removing impurities from the source in each step of the entire process where impurities may be introduced, the purity and stability of the 6N high-purity silver raw materials for targets can be ultimately improved.

[0068] The present invention also proposes a 6N high-purity silver raw material for a target material. The 6N high-purity silver raw material for a target material is prepared by the preparation method of the 6N high-purity silver raw material for a target material provided in the above embodiment of this document. The 6N high-purity silver raw material for a target material not only has the content of metal impurity elements that meets the national standard requirements for 6N high-purity silver, but also the content of non-metallic impurity elements C, N, O, and S can also meet the purity requirements for high-purity silver raw materials.

[0069] The technical solutions of the present invention are further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0070] Example 1

[0071] (1) Place 4.5N silver (the Na content in 4.5N silver is not higher than 2ppm and the total impurities are not higher than 50ppm) in a vacuum medium frequency furnace and smelt it at 1000℃ for 30min to make an anode plate.

[0072] (2) dissolving silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 150 g / L, adding GR grade silver oxide to the silver nitrate solution, adding 4 g of silver oxide to every 100 mL of silver nitrate solution, then heating and dissolving the solution until the pH of the solution is 5.0, cooling, and performing primary filtration using an MCE membrane (the pore size of the MCE membrane is 2.6 μm) and secondary filtration using a PTFE membrane (the pore size of the PTFE membrane is 0.65 μm) to obtain a filtrate with a maximum allowable number of 100 to 1000 particles / mL under a particle size of ≥0.1 μm, thereby obtaining a pure silver nitrate solution; pumping the impurity-removed argon gas and the pure silver nitrate solution into an evaporator, starting stirring, heating to 60 to 70°C to keep the solution in the evaporator slightly boiling for evaporation, and monitoring the density during the evaporation process until the density of the solution in the evaporator reaches 2.0 to 3.0 g / cm 3 After the evaporation is completed, the solution in the evaporation kettle is transferred to a crystallization kettle for crystallization, and then the solution is filtered, washed, and dried automatically using automated equipment to obtain high-purity silver nitrate. After testing, the C content of the obtained high-purity silver nitrate is less than 10ppm, the S content is less than 10ppm, and the trace metal ions single standard Pd is 2ppm, Fe is 2ppm, and Cu is 2ppm.

[0073] (3) The anode plate obtained in step (1) is placed in a ceramic membrane, wherein the purity of the ceramic membrane is not less than 99.9%, the pore size is 0.1 to 1 μm, the porosity is 30 to 50%, the compressive strength is ≥50 MPa, the roughness Ra is ≤0.1 μm, and the resistivity is ≥1012 Ω·cm; the high-purity silver nitrate obtained in step (2) is taken and added with electronic grade pure water to prepare an electrolytic mother solution having a silver content of 110 g / L and a free nitric acid content of 22.5 g / L, wherein the resistivity of the electronic grade pure water is ≥18.2 MΩ·cm (25° C.) and the number of particles with a particle size of less than 0.1 μm is less than 100 particles / mL; and then the mixture is stirred in 150 L of glass fiber reinforced polypropylene (the density of glass fiber reinforced polypropylene is 0.90 to 0.91 g / cm 3 , thermal deformation coefficient ≤ 2*10 -5 K -1 ) is used in an electrolytic cell with an anode plate encased in a ceramic membrane as the anode, titanium-coated silver as the cathode, and the prepared electrolyte mother solution as the electrolyte. The electrolysis process is carried out at a cell circulation rate of 0.75 L / min, an interelectrode distance of 120 mm, constant current electrolysis, and a current control area of ​​575 A / m 3 , the cell voltage is 2.5V.

[0074] (4) During the electrolysis process of step (3), powder is automatically brushed at a frequency of 7 times / min. The silver powder is collected by an automatic funnel trough and enters the processing chamber of the fully automated all-in-one machine. The lining and parts that all silver powder passes through or contacts in the fully automated all-in-one machine are made of Teflon or T1 titanium. The collected silver powder is filtered, washed, and dried by the fully automated all-in-one machine. The silver powder is first filtered through a fully enclosed automated titanium mesh; then enters the fully enclosed washing system and is added with electronic grade pure water. The resistivity of electronic grade pure water is ≥18.2M Ω·cm (25℃), the particle size requirement is less than 0.1μm and the number of particles is less than 100 / mL. First, use 50℃ electronic grade pure water to wash the concentrated residual liquid, then use 90℃ electronic grade pure water to wash, and finally use 50℃ electronic grade pure water to wash; then carry out fully closed drying in the washing chamber. The hot air used for drying is first subjected to 10,000-level primary dust removal before heating, and then passes through the activated carbon filter element loaded in the 1000-mesh filter bag (the micropore diameter of the activated carbon filter element is less than 2nm, and the material is GHSV reaching 200-500h -1 The modified coconut shell activated carbon (with potassium hydroxide attached) is filtered and then enters the hot air rotary drying system to perform hot air rotary drying on the material; after the automatic three-in-one filtering, washing and drying process, high-purity silver powder is obtained, and the high-purity silver powder is placed in a titanium container and vacuum-packed for transfer.

[0075] After testing, the purity of the prepared high-purity silver powder reached 99.9998%, and the main impurities included: Pd, 0.2ppm; C, reaching 0.2ppm; S, reaching 0.4ppm; O, reaching 270ppm; N, reaching 145ppm.

[0076] (5) The high-purity silver powder obtained in step (4) is placed in a graphite crucible, the material of the graphite crucible is a density of 1.85g / cm 3 , resistance 8 ~ 10μΩm, expansion coefficient 4.75 (6 ~ 10 ℃), porosity 13%, ash 500ppm, purified ash 50ppm, particle size 13 ~ 15μm high purity graphite, adjust the vacuum degree to 1*10 -1 ~1*10 -5 After the positive pressure of 0.2MPa is input, high-purity 6N argon gas (dew point of high-purity 6N argon gas ≤-80℃) is vacuum melted and melted to 1000℃. Then, it is poured into the graphite mold to make high-purity silver raw materials. The material of the graphite mold is a density of 1.85g / cm 3, high-purity graphite with a resistance of 8 to 10 μΩm, an expansion coefficient of 4.75 (6 to 10°C), a porosity of 13%, an ash content of 500 ppm, a purified ash content of 50 ppm, and a particle size of 13 to 15 μm; wherein, a PCL air pressure monitoring device is used in the vacuum melting process, and the melting is started after the high-purity 6N argon gas is introduced. When the air pressure in the melting chamber is greater than 0.2 MPa, vacuum extraction is started and the pressure is stabilized to 0.2 MPa, so that a small amount of impurity gas produced by the melting can be diluted and extracted.

[0077] After testing, the purity of the produced high-purity silver raw material reached 6N, and the main impurities included: Pd, 0.2ppm; C, reaching 1ppm; S, reaching 0.2ppm; O, reaching 1ppm; N, reaching 1ppm; the non-metallic element content of the high-purity silver raw material reached the target material standard.

[0078] Example 2

[0079] (1) 4.5N silver (the Na content in 4.5N silver is not higher than 2 ppm and the total impurities are not higher than 50 ppm) is placed in a vacuum medium frequency furnace and smelted at 1050°C for 35 minutes to make an anode plate.

[0080] (2) dissolving silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 10 g / L, adding GR grade silver oxide to the silver nitrate solution, adding 3 g of silver oxide to every 100 mL of silver nitrate solution, and then heating and dissolving the solution until the pH of the solution is 4.8, cooling, and performing primary filtration using an MCE membrane (the pore size of the MCE membrane is 2 μm) and secondary filtration using a PTFE membrane (the pore size of the PTFE membrane is 0.5 μm) to obtain a filtrate with a maximum allowable number of 100 to 1000 particles / mL under a particle size of ≥0.1 μm, thereby obtaining a pure silver nitrate solution; pumping the impurity-removed argon gas and the pure silver nitrate solution into an evaporator, starting stirring, and heating to 60 to 70°C to keep the solution in the evaporator slightly boiling for evaporation, monitoring the density during the evaporation process until the density of the solution in the evaporator reaches 2.0 to 3.0 g / cm 3 After the evaporation is completed, the solution in the evaporation kettle is transferred to a crystallization kettle for crystallization, and then the solution is filtered, washed, and dried automatically using automated equipment to obtain high-purity silver nitrate. After testing, the C content of the obtained high-purity silver nitrate is less than 10ppm, the S content is less than 10ppm, and the trace metal ions single standard Pd is 2ppm, Fe is 2ppm, and Cu is 2ppm.

[0081] (3) The anode plate obtained in step (1) is placed in a ceramic membrane, wherein the purity of the ceramic membrane is not less than 99.9%, the pore size is 0.1 to 1 μm, the porosity is 30 to 50%, the compressive strength is ≥50 MPa, the roughness Ra is ≤0.1 μm, and the resistivity is ≥1012 Ω·cm; the high-purity silver nitrate obtained in step (2) is taken and added with electronic grade pure water to prepare an electrolytic mother solution with a silver content of 100 g / L and a free nitric acid content of 20 g / L, wherein the resistivity of the electronic grade pure water is ≥18.2 MΩ·cm (25° C.) and the number of particles with a particle size of less than 0.1 μm is less than 100 particles / mL; and then the mixture is stirred in 150 L of glass fiber reinforced polypropylene (the density of glass fiber reinforced polypropylene is 0.90 to 0.91 g / cm 3 , thermal deformation coefficient ≤ 2*10 -5 K -1 ) is used in an electrolytic cell with an anode plate encased in a ceramic membrane as the anode, titanium-coated silver as the cathode, and the prepared electrolyte mother solution as the electrolyte. The electrolysis process is carried out at a cell circulation rate of 0.5 L / min, an interelectrode distance of 115 mm, constant current electrolysis, and a current control area of ​​500 A / m 3 , the cell voltage is 1.5V.

[0082] (4) During the electrolysis process of step (3), powder is automatically brushed at a frequency of 6 times / min. The silver powder is collected by an automatic funnel trough and enters the processing chamber of the fully automated all-in-one machine. The lining and parts that all silver powder passes through or contacts in the fully automated all-in-one machine are made of Teflon or T1 titanium. The collected silver powder is filtered, washed, and dried by the fully automated all-in-one machine. The silver powder is first filtered through a fully enclosed automated titanium mesh; then enters the fully enclosed washing system and is added with electronic grade pure water. The resistivity of electronic grade pure water is ≥18.2M Ω·cm (25℃), the particle size requirement is less than 0.1μm and the number of particles is less than 100 / mL. First, use 45℃ electronic grade pure water to wash the concentrated residual liquid, then use 85℃ electronic grade pure water to wash, and finally use 45℃ electronic grade pure water to wash; then carry out fully enclosed drying in the washing chamber. The hot air used for drying is first subjected to 10,000-level primary dust removal before heating, and then passes through the activated carbon filter element loaded in the 1000-mesh filter bag (the micropore diameter of the activated carbon filter element is less than 2nm, and the material is GHSV reaching 200-500h -1 The modified coconut shell activated carbon (containing potassium hydroxide) is filtered and then enters the hot air rotary drying system to perform hot air rotary drying on the material; after the three-in-one process of filtration, washing, and drying, high-purity silver powder is obtained, and the high-purity silver powder is placed in a titanium container and vacuum-packed for transfer.

[0083] After testing, the purity of the prepared high-purity silver powder reached 99.9998%, and the main impurities included: Pd, 0.2ppm; C, reaching 0.2ppm; S, reaching 0.4ppm; O, reaching 290ppm; N, reaching 160ppm.

[0084] (5) The high-purity silver powder obtained in step (4) is placed in a graphite crucible, the material of the graphite crucible is a density of 1.85g / cm 3 , resistance 8 ~ 10μΩm, expansion coefficient 4.75 (6 ~ 10 ℃), porosity 13%, ash 500ppm, purified ash 50ppm, particle size 13 ~ 15μm high purity graphite, adjust the vacuum degree to 1*10 -1 ~1*10 -5 After the positive pressure of 0.2MPa is input, high-purity 6N argon gas (dew point of high-purity 6N argon gas ≤-80℃) is vacuum melted and melted to 1000℃. Then, it is poured into the graphite mold to make high-purity silver raw materials. The material of the graphite mold is a density of 1.85g / cm 3 , high-purity graphite with a resistance of 8 to 10 μΩm, an expansion coefficient of 4.75 (6 to 10°C), a porosity of 13%, an ash content of 500 ppm, a purified ash content of 50 ppm, and a particle size of 13 to 15 μm; wherein, a PCL air pressure monitoring device is used in the vacuum melting process, and the melting is started after the high-purity 6N argon gas is introduced. When the air pressure in the melting chamber is greater than 0.2 MPa, vacuum extraction is started and the pressure is stabilized to 0.2 MPa, so that a small amount of impurity gas produced by the melting can be diluted and extracted.

[0085] After testing, the purity of the high-purity silver raw material reached 6N, and the main impurities included: Pd, 0.2ppm; C, reaching 1ppm; S, reaching 0.2ppm; O, reaching 1ppm; N, reaching 1ppm. The non-metallic element content of the high-purity silver raw material met the target material standard.

[0086] Example 3

[0087] (1) Place 4.5N silver (the Na content in 4.5N silver is not higher than 2ppm and the total impurities are not higher than 50ppm) in a vacuum medium frequency furnace and smelt it at 1100℃ for 25min to make an anode plate.

[0088] (2) dissolving silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 300 g / L, adding GR grade silver oxide to the silver nitrate solution, adding 5 g of silver oxide to every 100 mL of silver nitrate solution, then heating and dissolving the solution until the pH of the solution is 5.2, cooling, and performing primary filtration using an MCE membrane (the pore size of the MCE membrane is 3 μm) and secondary filtration using a PTFE membrane (the pore size of the PTFE membrane is 0.8 μm) to obtain a filtrate with a maximum allowable number of 100 to 1000 particles / mL under a particle size of ≥0.1 μm, thereby obtaining a pure silver nitrate solution; pumping the impurity-removed argon gas and the pure silver nitrate solution into an evaporator, starting stirring, heating to 60 to 70°C to keep the solution in the evaporator slightly boiling for evaporation, and monitoring the density during the evaporation process until the density of the solution in the evaporator reaches 2.0 to 3.0 g / cm 3 After the evaporation is completed, the solution in the evaporation kettle is transferred to a crystallization kettle for crystallization, and then the solution is filtered, washed, and dried automatically using automated equipment to obtain high-purity silver nitrate. After testing, the C content of the obtained high-purity silver nitrate is less than 10ppm, the S content is less than 10ppm, and the trace metal ions single standard Pd is 2ppm, Fe is 2ppm, and Cu is 2ppm.

[0089] (3) The anode plate obtained in step (1) is placed in a ceramic membrane, wherein the purity of the ceramic membrane is not less than 99.9%, the pore size is 0.1 to 1 μm, the porosity is 30 to 50%, the compressive strength is ≥50 MPa, the roughness Ra is ≤0.1 μm, and the resistivity is ≥1012 Ω·cm; the high-purity silver nitrate obtained in step (2) is taken and added with electronic grade pure water to prepare an electrolytic mother solution having a silver content of 120 g / L and a free nitric acid content of 25 g / L, wherein the resistivity of the electronic grade pure water is ≥18.2 MΩ·cm (25° C.) and the number of particles with a particle size of less than 0.1 μm is less than 100 particles / mL; and then the mixture is stirred in 150 L of glass fiber reinforced polypropylene (the density of glass fiber reinforced polypropylene is 0.90 to 0.91 g / cm 3 , thermal deformation coefficient ≤ 2*10 -5 K -1 ) is used in an electrolytic cell with an anode plate encased in a ceramic membrane as the anode, titanium-coated silver as the cathode, and the prepared electrolyte mother solution as the electrolyte. The electrolysis process is carried out at a cell circulation rate of 1 L / min, an interelectrode distance of 125 mm, constant current electrolysis, and a current control area of ​​650 A / m 3 , the cell voltage is 3.5V.

[0090] (4) During the electrolysis process of step (3), powder is automatically brushed at a frequency of 8 times / min. The silver powder is collected by an automatic funnel trough and enters the processing chamber of the fully automated all-in-one machine. The lining and parts that all silver powder passes through or contacts in the fully automated all-in-one machine are made of Teflon or T1 titanium. The collected silver powder is filtered, washed, and dried by the fully automated all-in-one machine. The silver powder is first filtered through a fully enclosed automated titanium mesh; then enters the fully enclosed washing system and is added with electronic grade pure water. The resistivity of electronic grade pure water is ≥18.2M Ω·cm (25℃), the particle size requirement is less than 0.1μm and the number of particles is less than 100 / mL. First, use 55℃ electronic grade pure water to wash the concentrated residual liquid, then use 95℃ electronic grade pure water to wash, and finally use 55℃ electronic grade pure water to wash; then carry out fully enclosed drying in the washing chamber. The hot air used for drying is first subjected to 10,000-level primary dust removal before heating, and then passes through the activated carbon filter element loaded in the 1000-mesh filter bag (the micropore diameter of the activated carbon filter element is less than 2nm, and the material is GHSV reaching 200-500h -1 The modified coconut shell activated carbon (containing potassium hydroxide) is filtered and then enters the hot air rotary drying system to perform hot air rotary drying on the material; after the three-in-one process of filtration, washing, and drying, high-purity silver powder is obtained, and the high-purity silver powder is placed in a titanium container and vacuum-packed for transfer.

[0091] After testing, the purity of the prepared high-purity silver powder reached 99.9998%, and the main impurities included: Pd, 0.2ppm; C, reaching 0.2ppm; S, reaching 0.4ppm; O, reaching 240ppm; N, reaching 140ppm.

[0092] (5) The high-purity silver powder obtained in step (4) is placed in a graphite crucible, the material of the graphite crucible is a density of 1.85g / cm 3 , resistance 8 ~ 10μΩm, expansion coefficient 4.75 (6 ~ 10 ℃), porosity 13%, ash 500ppm, purified ash 50ppm, particle size 13 ~ 15μm high purity graphite, adjust the vacuum degree to 1*10 -1 ~1*10 -5 After the positive pressure of 0.2MPa is input, high-purity 6N argon gas (dew point of high-purity 6N argon gas ≤-80℃) is vacuum melted and melted to 1000℃. Then, it is poured into the graphite mold to make high-purity silver raw materials. The material of the graphite mold is a density of 1.85g / cm 3, high-purity graphite with a resistance of 8 to 10 μΩm, an expansion coefficient of 4.75 (6 to 10°C), a porosity of 13%, an ash content of 500 ppm, a purified ash content of 50 ppm, and a particle size of 13 to 15 μm; wherein, a PCL air pressure monitoring device is used in the vacuum melting process, and the melting is started after the high-purity 6N argon gas is introduced. When the air pressure in the melting chamber is greater than 0.2 MPa, vacuum extraction is started and the pressure is stabilized to 0.2 MPa, so that a small amount of impurity gas produced by the melting can be diluted and extracted.

[0093] After testing, the purity of the produced high-purity silver raw material reached 6N, and the main impurities included: Pd, 0.2ppm; C, reaching 1ppm; S, reaching 0.2ppm; O, reaching 1ppm; N, reaching 1ppm; the non-metallic element content of the high-purity silver raw material reached the target material standard.

[0094] Comparative Example 1

[0095] (1) In an ordinary 150L electrolytic cell (made of ordinary yellow PP), add a pure silver anode plate with a purity of 99.99%, use a 1000 mesh polyester anode bag to cover the anode, add ordinary commercially available silver nitrate according to GB / T 670-2007 to prepare an electrolyte with a silver content of 110g / L and a free nitric acid content of 22.5g / L. After testing, the C content in the electrolyte is 50ppm, the S content is 28ppm, and the trace metal ions are Pd 2ppm, Fe 15ppm, and Cu 15ppm. Set the cell circulation rate to 0.75L / min, the electrode distance to 120mm, constant current electrolysis, and the control current area to 575A / m 3 The cell voltage was 2.5V. After electrolysis, the powder was manually washed three times with pure water and dried to obtain silver powder. Testing showed that the purity of the obtained silver powder reached 99.9991%. The main impurities were: Fe, 1ppm; Pd, 0.2ppm; C, 20ppm; S, 30ppm; O, 500ppm; N, 380ppm.

[0096] (2) The silver powder obtained in step (1) is subjected to ordinary first-level vacuum melting (no continuous vacuum during the melting process) using an ordinary conventional graphite crucible and a graphite mold to obtain a high-purity silver raw material.

[0097] After testing, the main impurities of the obtained high-purity silver raw materials are: Fe, 1ppm; Pd, 0.2ppm; C, reaching 50ppm; S, reaching 30ppm; O, reaching 100ppm; N, reaching 50ppm. The purity of the high-purity silver raw materials did not reach 6N, and the content of non-metallic elements exceeded the standard.

[0098] Comparative Example 2

[0099] (1) In a 150L glass fiber reinforced polypropylene electrolytic cell (the density of glass fiber reinforced polypropylene is 0.90-0.91 g / cm 3 , thermal deformation coefficient ≤ 2*10 -5 K -1 ), a pure silver anode plate with a purity of 99.99% (the impurity Na content in 4N pure silver is less than 2ppm, and the total impurity content is less than 50ppm), a ceramic membrane is used as an anode bag to cover the anode, the ceramic membrane has a purity of not less than 99.9%, a pore size of 0.1-1μm, a porosity of 30-50%, a compressive strength ≥50MPa, a roughness Ra≤0.1μm, and a resistivity ≥1012Ω·cm, and high-purity silver nitrate (prepared by the same purification and purification steps as in step (2) in Example 1) is added to prepare an electrolyte with a silver content of 110g / L and a free nitric acid content of 22.5g / L; after testing, the C content in the electrolyte is less than 10ppm, the S content is less than 10ppm, and the trace metal ions are Pd 2ppm, Fe 2ppm, and Cu 2ppm. Set the tank circulation rate to 0.75L / min, the interelectrode distance to 120mm, constant current electrolysis, and control the current area to 575A / m 3 The cell voltage is 2.5V. After electrolysis, the powder is automatically brushed and then filtered, washed, and dried using a fully automated all-in-one machine to produce silver powder. Testing shows the silver powder has a purity of 99.9998%. The main impurities are: Pd, 0.2ppm; C, 0.5ppm; S, 0.5ppm; O, 520ppm; and N, 400ppm.

[0100] (2) The silver powder obtained in step (1) is subjected to ordinary first-level vacuum melting (no continuous vacuum during the melting process) using an ordinary conventional graphite crucible and a graphite mold to obtain a high-purity silver raw material.

[0101] After testing, the main impurities of the obtained high-purity silver raw material are: Pd, 0.2ppm; C, reaching 50ppm; S, reaching 30ppm; O, reaching 100ppm; N, reaching 50ppm. The purity of the high-purity silver raw material reaches 6N, but the content of non-metallic elements exceeds the standard.

[0102] Comparative Example 3

[0103] The steps are the same as those in Example 1, except that the purification and preparation of high-purity silver nitrate in step (2) is not performed, and the electrolyte is prepared with ordinary commercially available silver nitrate in accordance with GB / T 670-2007 in step (3).

[0104] After testing, the C content in the electrolyte prepared using commercially available silver nitrate was 50 ppm, the S content was 28 ppm, and the trace metal ion single standard Pd was 2 ppm, Fe was 15 ppm, and Te was 15 ppm.

[0105] After testing, the purity of the silver powder obtained in step (4) reached 4.5N, and the main impurities were: Fe, 2 ppm; Te, 2 ppm; Bi, 1 ppm.

[0106] After testing, the purity of the high-purity silver raw material obtained in step (5) reaches 4.5N, and the main impurities are: Fe, 2ppm; Te, 2ppm; Bi, 1ppm; C, 100ppm; N, 155ppm; O, 270ppm; S, 80ppm; the purity of the high-purity silver raw material does not reach 6N, and the content of metal impurity elements exceeds the standard, and the content of non-metallic impurity elements exceeds the standard.

[0107] Comparative Example 4

[0108] The steps are the same as those in Example 1, except that in step (3), a 1000-mesh polyester anode bag is used to cover the anode plate.

[0109] After testing, the purity of the silver powder obtained in step (4) reaches 5N, and the main impurities are: Pd, 0.2ppm; C, reaching 290ppm; S, reaching 20ppm; O, reaching 420ppm; N, reaching 400ppm.

[0110] After testing, the purity of the high-purity silver raw material obtained in step (5) reaches 5N, and the main impurities are: Fe, 1ppm; Pd, 0.2ppm; C, reaching 250ppm; S, reaching 30ppm; O, reaching 100ppm; N, reaching 50ppm; the purity of the high-purity silver raw material does not reach 6N, and the content of non-metallic element Fe exceeds the standard, and the content of non-metallic element C exceeds the standard.

[0111] Comparative Example 5

[0112] The steps are the same as those in Example 1, except that the silver powder obtained by electrolysis in step (3) is not processed by a fully automatic integrated machine, but is manually washed three times with pure water and then dried.

[0113] After testing, the purity of the silver powder obtained in step (4) reaches 4N, and the main impurities are: Pd, which is 0.4ppm; Fe, which is 2ppm; and it contains particulate matter Si and C.

[0114] After testing, the purity of the high-purity silver raw material obtained in step (5) reaches 4N, and the main impurities are: Pd, 0.4ppm; Fe, 2ppm; C, 240ppm; N, 80ppm; O, 120ppm; S, 6ppm; and contains particulate matter Si; the purity of the high-purity silver raw material does not reach 6N, and the content of the metal element Fe exceeds the standard, and the content of non-metallic elements exceeds the standard.

[0115] The comparison and analysis of the above embodiments and comparative examples are as follows:

[0116] (1) The methods provided in Examples 1 to 3 can all stably prepare 6N high-purity silver raw materials for targets that meet the expected standard requirements.

[0117] (2) Compared with the embodiment, in Comparative Example 1, an electrolytic cell made of ordinary materials, a polyester anode bag, ordinary commercially available silver nitrate, manual washing and drying of the silver powder obtained by electrolysis, and ordinary first-level vacuum melting of the silver powder were used. The purity of the high-purity silver raw material finally obtained could not reach 6N, and impurity Fe was introduced during the process. The content of C, N, O, and S was also higher, resulting in the non-metallic element content of the high-purity silver raw material exceeding the standard, which did not meet the standard requirements for high-purity silver raw materials for targets.

[0118] (3) Compared with the embodiment, in comparative example 2, the silver powder was subjected to ordinary first-level vacuum melting to prepare the target material. The purity of the high-purity silver raw material finally prepared can reach 6N, but the content of non-metallic elements C, N, O, and S exceeds the standard, which does not meet the standard requirements for high-purity silver raw materials for targets.

[0119] (4) Compared with the embodiment, in comparative example 3, ordinary commercially available silver nitrate was used. The current was unstable during the electrolysis process, which easily caused safety problems. In addition, the purity of the high-purity silver raw material finally produced did not reach 6N, and the content of metal impurities and non-metallic impurities exceeded the standard, which did not meet the standard requirements for high-purity silver raw materials for target materials.

[0120] (5) Compared with the embodiment, comparative example 4 uses a polyester anode bag, and the purity of the high-purity silver raw material finally produced does not reach 6N, the content of the metal element Fe exceeds the standard, and the content of the non-metallic element C exceeds the standard, which does not meet the standard requirements for high-purity silver raw materials for target materials.

[0121] (6) Compared with the embodiment, in comparative example 5, the silver powder obtained by electrolysis was manually washed and dried. The purity of the high-purity silver raw material finally obtained did not reach 6N, the content of the metal element Fe exceeded the standard, the content of the non-metallic element C exceeded the standard, and impurity particles Si were introduced, which did not meet the standard requirements for high-purity silver raw materials for targets.

[0122] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of the present invention.

Claims

1. A method for preparing 6N high-purity silver raw material for target material, characterized in that: The method for preparing the 6N high-purity silver raw material for the target material comprises the following steps: 4.5N silver is placed in a vacuum medium frequency furnace for melting to make anode plates; Silver nitrate is purified by crystallization and silver oxide purification to obtain high-purity silver nitrate; The anode plate is placed in a ceramic membrane, and the high-purity silver nitrate is prepared into an electrolytic mother solution. Then, electrolysis is performed using the anode plate placed in the ceramic membrane as an anode, the titanium-coated silver as a cathode, and the electrolytic mother solution as an electrolyte. During the electrolysis process, powder is automatically brushed and silver powder is collected. The collected silver powder is filtered, washed, and dried using a fully automated all-in-one machine to obtain high-purity silver powder. The high-purity silver powder is then placed in a titanium container and vacuum-packed for transfer. The high-purity silver powder is placed in a graphite crucible and the vacuum degree is adjusted to 1*10 -1 ~1*10 -5 After the high-purity silver powder is heated to 0.15 MPa, high-purity 6N argon gas with a positive pressure of 0.15 to 0.35 MPa is input and vacuum melting is performed to make a silver melt from the high-purity silver powder, and then the silver melt is poured into a graphite mold to make a 6N high-purity silver raw material for the target material; wherein the dew point of the high-purity 6N argon gas is ≤-80°C, and a PCL air pressure monitoring device is used during the vacuum melting process. After the high-purity 6N argon gas is introduced, the melting is started, and when the air pressure in the melting chamber is greater than 0.35 MPa, vacuum extraction is started and the pressure is stabilized to 0.15 to 0.35 MPa; The steps of purifying silver nitrate by crystallization and silver oxide purification include: Dissolving silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 10 to 300 g / L, adding GR-grade silver oxide to the silver nitrate solution at a rate of 3 to 5 g per 100 mL of the silver nitrate solution, heating and dissolving the solution until the pH value reaches 4.8 to 5.2, cooling, and performing primary filtration using a mixed fiber membrane and secondary filtration using a polytetrafluoroethylene membrane to obtain a pure silver nitrate solution; The purified argon gas and the pure silver nitrate solution were pumped into the evaporator, stirring was started, and the temperature was raised to keep the solution in the evaporator slightly boiling for evaporation. The density was monitored during the evaporation process until the density of the solution in the evaporator reached 2.0-3.0 g / cm 3 ; After the evaporation is completed, the solution in the evaporation kettle is transferred to a crystallization kettle for crystallization, and then filtered, washed and dried to obtain high-purity silver nitrate.

2. The method for preparing a 6N high-purity silver raw material for a target according to claim 1, wherein: The Na content in the 4.5N silver is not higher than 2 ppm, and the total amount of impurities is not higher than 50 ppm.

3. The method for preparing a 6N high-purity silver raw material for a target according to claim 1, wherein: The C content in the high-purity silver nitrate is less than 10 ppm, the S content is less than 10 ppm, and the trace metal ions of Te, Sn, Pd, and Bi in the high-purity silver nitrate are all less than 10 ppm; and / or The pore size of the mixed fiber membrane is 2-3 μm, and the pore size of the polytetrafluoroethylene membrane is 0.5-0.8 μm.

4. The method for preparing a 6N high-purity silver raw material for a target according to claim 1, wherein: The ceramic membrane has a purity of not less than 99.9%, a pore size of 0.1 to 1 μm, a porosity of 30 to 50%, a compressive strength of ≥50 MPa, a roughness Ra ≤0.1 μm, and a resistivity of ≥1012 Ω·cm.

5. The method for preparing a 6N high-purity silver raw material for a target according to claim 1, wherein: All parts of the fully automated all-in-one machine that come into contact with the silver powder are made of Teflon or T1 titanium; and / or, The material of the electrolytic cell used in the electrolysis includes glass fiber reinforced polypropylene, and the density of the glass fiber reinforced polypropylene is 0.90-0.91 g / cm 3 , thermal deformation coefficient ≤ 2*10 -5 K -1 .

6. The method for preparing a 6N high-purity silver raw material for a target according to claim 1, wherein: The water used to prepare the electrolyte mother solution is electronic grade pure water, wherein the resistivity of the electronic grade pure water is ≥18.2MΩ·cm (25°C), and the number of particles with a particle size less than 0.1μm is less than 100 / mL.

7. The method for preparing a 6N high-purity silver raw material for a target according to claim 1, wherein: The electrolysis process has a tank circulation rate of 0.5 to 1 L / min, an interelectrode distance of 115 to 125 mm, and constant current electrolysis is adopted. The current control area of ​​the constant current electrolysis is 500 to 650 A / m 3 , the cell voltage is 1.5 to 3.5 V; and / or, The powder brushing frequency of the electrolysis process is 6 to 8 times / min.

8. The method for preparing a 6N high-purity silver raw material for a target according to claim 1, wherein: The drying air used in the drying process is first subjected to a 10,000-level primary dust removal process, and then filtered through an activated carbon filter element before entering a hot air rotary drying system to dry the material; wherein, the material of the activated carbon filter element is a GHSV of 200-500h -1 Modified coconut shell activated carbon loaded with potassium hydroxide.

9. The method for preparing a 6N high-purity silver raw material for a target according to claim 1, wherein: The graphite crucible is made of high-purity graphite, and the density of the high-purity graphite is 1.85 g / cm 3 , resistance of 8 to 10 μΩm, expansion coefficient of 4.75 (6 to 10°C), porosity of 13%, ash content of 500 ppm, purified ash content of 50 ppm, particle size of 13 to 15 μm; and / or, The graphite mold is made of high-purity graphite, and the density of the high-purity graphite is 1.85g / cm 3 , resistance is 8-10μΩm, expansion coefficient is 4.75 (6-10℃), porosity is 13%, ash content is 500ppm, purified ash content is 50ppm, and particle size is 13-15μm.

10. A 6N high-purity silver raw material for a target, characterized in that: The 6N high-purity silver raw material for the target material is prepared by the preparation method of the 6N high-purity silver raw material for the target material according to any one of claims 1 to 9.