CN114289718A - Method for efficiently preparing nano-pore porous tungsten product with complex shape - Google Patents
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Abstract
A forming method of a porous tungsten product with a nano-pore structure belongs to the technical field of powder metallurgy. The invention relates to a forming method for preparing a porous tungsten product with a complex shape, which has the advantages of high efficiency, low cost, excellent pore characteristics, uniform tissue, complex shape, high dimensional precision and good consistency. Firstly, performing dispersion grading spheroidization on powder by combining a fluidization dispersion technology and a radio frequency plasma spheroidization technology to obtain dispersed spherical tungsten powder with narrow particle size distribution and fine particle size; then the powder and plastic-based binder are mixed evenly to prepare feed, and then the powder is subjected to micro-injection molding to prepare a tungsten product green compact with a complex shape, and finally the porous tungsten product with the complex shape is prepared by degreasing and sintering. The invention obviously optimizes the injection molding process of the raw material powder and the micro powder, and the prepared porous tungsten product with the nano-pore structure has the advantages of uniform tissue structure, grain size of less than or equal to 1 mu m, pore diameter of 100-800 nm, porosity of 15-35%, uniform pores and good connectivity.
Description
Technical Field
The invention belongs to the technical field of powder metallurgy, and particularly relates to a method for efficiently preparing a nano-pore porous tungsten product with a complex shape.
Background
The refractory metal tungsten has the characteristics of high melting point, high strength, high elastic modulus, high temperature resistance, corrosion resistance and the like, and the porous member has an irreplaceable effect in the fields of electric vacuum, atomic energy, aerospace and the like, in particular to a key part of a field emission propulsion system for a spacecraft. Therefore, for the micro-Newton level precise control, long service life and high reliability of the propulsion system, the micro-nano porous tungsten member is required to have uniform pore size, uniform distribution, good connectivity, generally complex shape (gears, grooves, needles, steps, large length-diameter ratio and the like), and high dimensional accuracy requirement for meeting the assembly requirement. However, because of high hardness, large brittleness and poor processability of metal tungsten, complex components cannot be directly prepared by mechanical processing, and the traditional process is to firstly prepare a tungsten-copper pseudo alloy which can be processed by adopting a powder metallurgy process, and then remove copper after processing the tungsten-copper pseudo alloy into components with required shapes. The method has complex process and low material utilization rate, is particularly limited by the processing process, and is difficult to prepare the porous tungsten product with the fine grain, the nano-pore structure and the micron-sized complex shape.
Powder micro-injection molding is a near-net-shape molding technology which introduces the modern plastic injection molding technology into the field of powder metallurgy, and is mainly characterized in that metal powder and a binder are mixed to form a feed material, then the feed material is subjected to injection molding by micro-injection molding equipment to form a green body, and finally the green body is degreased and sintered to obtain a required product. The method has the advantages of capability of directly preparing products with complex size, high precision and complex shape, excellent performance, high finished product rate, good product consistency and the like. The powder prepared by the powder spheroidizing treatment has uniform granularity and high sphericity and is not easy to be polluted, and the prepared porous tungsten member has uniform pore size, uniform distribution and good connectivity. Chinese patent (CN105499574A) discloses a method for preparing a special-shaped porous tungsten product with uniform pores, which is to disperse high-purity tungsten powder, collect and remove ultrafine particles (less than 2um) in the original tungsten powder and prepare a cathode substrate with uniform pore distribution. However, the pore diameter and the grain size of the prepared product are large, and a porous tungsten product with a micro-sized fine grain, nano-pore structure and complicated shape cannot be prepared. Chinese patent (CN108907214A) discloses a method for preparing tungsten-rhenium alloy powder by adopting a spray pyrolysis method and a hydrogen reduction method, and a porous tungsten-rhenium alloy part is prepared by adopting twice airflow milling treatment and selective laser melting. However, the samples which can only be prepared are generally large, the size precision is low, the grain size and the porosity are in the micron order, and the preparation of the porous tungsten product with the nano-pore structure in the complex shape is difficult. Chinese patent (CN107604188A) discloses a method for preparing porous tungsten products by sintering after press forming or hot press sintering, which cannot be used for preparing porous tungsten products with complex shapes.
Therefore, the invention adopts a novel technology for efficiently preparing the porous tungsten product with the nano-pore structure in the complex shape to prepare the porous tungsten product with the nano-pore structure, which has uniform tissue, complex shape, high size precision and good product consistency, at lower cost.
Disclosure of Invention
The invention aims to provide a method for forming a porous tungsten product with a nano-pore structure.
A method for forming a porous tungsten article having a nanoporous structure, the method comprising: taking fine-grained tungsten powder as a raw material, and performing dispersion and spheroidization on the powder by combining a fluidization dispersion technology and a radio frequency plasma spheroidization technology to obtain dispersed, narrow-granularity-distribution and fine-grained spherical tungsten powder; then preparing a porous tungsten product with a nano pore structure in a complex shape by powder micro injection molding, and finally preparing the porous tungsten product with the nano pore structure in the complex shape by degreasing sintering, wherein the method comprises the following specific steps:
1. the raw material powder is tungsten powder, the purity is more than 99.9 percent, and the granularity is less than 1 mu m;
2. adding raw material powder into a fluidized bed, filling high-purity inert gas into equipment from bottom to top to remove air before dispersion treatment, providing a gas protection environment for the powder, and performing gas-filled cleaning on the equipment; after the air in the cavity of the fluidized bed is exhausted, transferring the air into a heating device, continuously introducing high-purity inert gas with stable flow in the fluidized bed treatment process, wherein the flow speed of the air flow is 1-3L/min, the heating temperature is 100-280 ℃, and performing fluidization treatment for 100-180 min under constant flow and constant temperature. After the fluidized bed is subjected to dispersion treatment, the cavity of the fluidized bed is removed from the heating device, high-purity inert protective gas is continuously introduced, and after the fluidized bed is cooled to room temperature in the air, the introduction of the protective gas is stopped, so that powder subjected to fluidization dispersion treatment is obtained;
3. sending the treated powder into a powder feeding device, taking argon as working gas, applying pressure to form a plasma torch, carrying out spheroidization on the powder, wherein the powder feeding speed is 5-15 g/min, the treatment power is 5-25 kw, the powder feeding flow is 5-10L/min, the middle gas flow is 25-35L/min, and the side gas flow is 30-60L/min, cooling the powder after the plasma spheroidization, and collecting to obtain spheroidized powder;
4. uniformly mixing the spheroidized powder with an organic binder, and preparing into granular feed;
5. according to different application scenes of the porous tungsten product with the nano-pore structure and different requirements on the shape and the size of the product, performing micro-injection molding on a tungsten blank with a required shape and size;
6. carrying out catalytic degreasing on the injection green body by using concentrated nitric acid or concentrated oxalic acid as a catalytic medium in a catalytic degreasing furnace to remove part of the binder;
7. and (3) under the protective atmosphere of high-purity hydrogen with the purity of more than 99.9 percent, carrying out thermal de-sintering treatment on the sample dried in the step (6) in a tungsten filament sintering furnace to prepare the porous tungsten product with the complicated shape and the nano pore structure.
Further, the proportion of the binder in the step 4 is as follows: 80-88% of polyformaldehyde, 3-8% of low-density polyethylene, 3-10% of vinyl acetate copolymer, 2-5% of stearic acid, 2-10% of microcrystalline wax and 2-7% of polypropylene.
Further, the concentration of the concentrated nitric acid or concentrated oxalic acid adopted in the step 6 is 86% -95%, and the catalytic degreasing is carried out for 1-12 h at the temperature of 110-150 ℃, so that a porous network system is guaranteed to be formed, and the decomposition and volatilization of the binder in the subsequent thermal de-sintering process are facilitated.
Further, in the step 7, the thermal desorption sintering treatment process comprises the steps of heating to 200 ℃ at a speed of 0.2-0.5 ℃/min, preserving heat for 30-60 min, heating to 450 ℃ at a speed of 0.5-1 ℃/min, preserving heat for 40-90 min, heating to 550 ℃ at a speed of 0.5-0.8 ℃/min, preserving heat for 30-60 min, heating to 650 ℃ at a speed of 0.5-1 ℃/min, preserving heat for 30-60 min, heating to 750 ℃ at a speed of 2-3 ℃/min, preserving heat for 60-120 min, heating to 950 ℃ at a speed of 2-3 ℃/min, preserving heat for 60-120 min, heating to 1000-1250 ℃ at a speed of 1-3 ℃/min, preserving heat for 60-180 min, cooling to 900 ℃ at a speed of 1-3 ℃/min, cooling to 700 ℃ at a speed of 2-5 ℃/min, and cooling to room temperature at a speed of 5-10 ℃/min.
Furthermore, the grain size of the sintered porous tungsten product with the nano-pore structure is less than or equal to 1 mu m, the pore diameter is 100-800 nm, the porosity is 15-35%, the pores are uniform, and the connectivity is good.
By adopting the technical scheme, the invention has the beneficial effects that: (1) from the viewpoint of optimizing powder raw materials, the adopted raw material powder has the particle size of less than 1 mu m, fine particle size and serious powder agglomeration, so that the requirement of micro-injection molding on the raw material powder cannot be met, and the porous tungsten product with the nano-pore structure has more closed pores and uneven pores, thereby affecting the performance of related equipment. The powder is fluidized and dispersed, so that the agglomeration of powder particles can be removed, the powder particles are dispersed and classified, and the spherical tungsten powder particles with fine granularity, high dispersion and narrow distribution can be finally obtained by utilizing plasma spheroidization. (2) Uniformly mixing the treated powder with a plastic-based binder, and preparing into granular feed; the tungsten blank prepared by micro-injection molding has higher strength and shape retention; and in the thermal desorption sintering process, a mode of sectional sintering and slow temperature rise is adopted, so that the precise control of the porosity of the porous tungsten is favorably realized. (3) The powder micro-injection molding is suitable for the precise manufacturing of micro parts with micron-sized characteristic dimensions, subsequent processing is not needed, the material utilization rate is high, and the porous tungsten product with a nano-pore structure and micron-sized characteristic in a final shape can be directly prepared. (4) The prepared porous tungsten product with the complicated shape and the nano-pore structure has low impurity content, uniform pores, grain size of less than or equal to 1 mu m, pore diameter of 100-800 nm, porosity of 15-35 percent and open pore porosity of more than 95 percent of the total porosity.
Drawings
Figure 1 is an SEM of tungsten powder before and after treatment,
figure 2 is an XRD of tungsten powder before and after treatment,
fig. 3 is a fracture SEM of the prepared porous tungsten article.
Detailed Description
Example 1
1) The raw material powder is commercially available tungsten powder, the Fisher particle size is 0.8 mu m, and the purity is more than 99.9 percent;
2) adding raw material powder into a fluidized bed, filling high-purity inert gas into equipment from bottom to top to remove air before dispersion treatment, providing a gas protection environment for the powder, and performing gas-filled cleaning on the equipment; after the air in the fluidized bed cavity is exhausted, transferring the air into a heating device, continuously introducing high-purity inert gas with stable flow in the fluidized bed treatment process, wherein the flow rate of the gas flow is 3L/min, the heating temperature is 220 ℃, and performing fluidization treatment for 100min under constant flow and constant temperature. And after the fluidized bed is subjected to dispersion treatment, the cavity of the fluidized bed is removed from the heating device, high-purity inert protective gas is continuously introduced, and after the fluidized bed is cooled to room temperature in the air, the introduction of the protective gas is stopped, so that the powder subjected to the fluidization dispersion treatment is obtained.
3) And (2) sending the treated powder into a powder feeding device, using argon as working gas, applying pressure to form a plasma torch, carrying out spheroidization on the powder, wherein the powder feeding speed is 15g/min, the treatment power is 20kw, the powder feeding gas flow is 8L/min, the middle gas flow is 35L/min, and the side gas flow is 40L/min, cooling the powder after plasma spheroidization, and collecting to obtain the spheroidized powder.
4) Uniformly mixing the spheroidized powder with an organic binder (polyformaldehyde 86%, low-density polyethylene 4%, vinyl acetate copolymer 3%, stearic acid 2%, microcrystalline wax 3% and polypropylene 2%) to prepare a granular feed, wherein the volume fraction of the powder in the feed is 52%;
5) feeding the granular material on a micro-injection molding machine, and performing micro-injection molding to obtain a tungsten blank with a required shape and size;
6) the organic binder in the tungsten green body is completely removed by adopting a proper process, and the degreasing process is to degrease for 12 hours in a catalytic degreasing furnace at 110 ℃ by adopting 90% concentrated nitric acid, so that a porous network system is ensured to be formed, and the decomposition and volatilization of the binder in the thermal degreasing process are facilitated; then, carrying out thermal release sintering in a tubular furnace under the protective atmosphere of high-purity hydrogen with the purity of more than 99.9 percent, heating to 200 ℃ at the speed of 0.5 ℃/min, preserving heat for 60min, heating to 450 ℃ at the speed of 1 ℃/min, preserving heat for 90min, heating to 550 ℃ at the speed of 0.8 ℃/min, preserving heat for 60min, heating to 650 ℃ at the speed of 1 ℃/min, preserving heat for 60min, heating to 750 ℃ at the speed of 3 ℃/min, preserving heat for 120min, heating to 950 ℃ at the speed of 3 ℃/min, heating to 1050 ℃ at the speed of 3 ℃/min, preserving heat for 180min, cooling to 900 ℃ at the speed of 3 ℃/min, cooling to 700 ℃ at the speed of 5 ℃/min, and finally cooling to room temperature at the speed of 10 ℃/min. The finally prepared porous tungsten product with the complicated shape nano-pore structure has low impurity content, uniform pores, 1.0 mu m of grain size, 500nm of average pore diameter and 22 percent of open porosity, and the open porosity accounts for more than 98 percent of the total porosity.
Example 2
1) The raw material powder is commercially available tungsten powder, the Fisher particle size is 0.6 mu m, and the purity is more than 99.9 percent;
2) adding raw material powder into a fluidized bed, filling high-purity inert gas into equipment from bottom to top to remove air before dispersion treatment, providing a gas protection environment for the powder, and performing gas-filled cleaning on the equipment; after the air in the fluidized bed cavity is exhausted, transferring the air into a heating device, continuously introducing high-purity inert gas with stable flow in the fluidized bed treatment process, wherein the flow rate of the gas flow is 2L/min, the heating temperature is 180 ℃, and the fluidization treatment is carried out for 120min at constant current and constant temperature. And after the fluidized bed is subjected to dispersion treatment, the cavity of the fluidized bed is removed from the heating device, high-purity inert protective gas is continuously introduced, and after the fluidized bed is cooled to room temperature in the air, the introduction of the protective gas is stopped, so that the powder subjected to the fluidization dispersion treatment is obtained.
3) And (2) sending the treated powder into a powder feeding device, using argon as working gas, applying pressure to form a plasma torch, carrying out spheroidizing treatment on the powder, wherein the powder feeding speed is 10g/min, the treatment power is 15kw, the powder feeding gas flow is 6L/min, the middle gas flow is 30L/min, the side gas flow is 35L/min, and collecting the powder after plasma spheroidizing after cooling to obtain the treated powder.
4) Uniformly mixing the spheroidized powder with an organic binder (polyformaldehyde 84%, low-density polyethylene 5%, vinyl acetate copolymer 3%, stearic acid 2%, microcrystalline wax 4% and polypropylene 2%) to prepare a granular feed, wherein the volume fraction of the powder in the feed is 48%;
5) feeding the granular material on a micro-injection molding machine, and performing micro-injection molding to obtain a tungsten blank with a required shape and size;
6) the organic binder in the tungsten green body is completely removed by adopting a proper process, and the degreasing process is to degrease for 8 hours in a catalytic degreasing furnace at 120 ℃ by adopting 95% concentrated nitric acid, so that a porous network system is ensured to be formed, and the decomposition and volatilization of the binder in the thermal degreasing process are facilitated; then the heat removing sintering is carried out in a tube furnace under the protective atmosphere of high-purity hydrogen with the purity of more than 99.9 percent, heating to 200 deg.C at a rate of 0.3 deg.C/min, maintaining for 60min, heating to 450 deg.C at a rate of 0.5 deg.C/min, maintaining for 60min, heating to 550 deg.C at a rate of 0.8 deg.C/min, maintaining for 60min, heating to 650 deg.C at a rate of 1 deg.C/min, maintaining for 60min, then heating to 750 ℃ at the speed of 2 ℃/min, preserving heat for 120min, heating to 950 ℃ at the speed of 3 ℃/min, preserving heat for 120min, heating to 1150 ℃ at the rate of 3 ℃/min, preserving heat for 180min, cooling to 900 ℃ at the rate of 3 ℃/min, cooling to 700 ℃ at the rate of 4 ℃/min, and finally cooling to room temperature at the rate of 10 ℃/min, wherein the finally prepared porous tungsten product with the complex-shaped nano-pore structure has the advantages of low impurity content, uniform pores, 0.7 mu m of grain size, 450nm of average pore diameter, 21% of open porosity and more than 97% of total porosity.
Example 3
1) The raw material powder is commercially available tungsten powder, the Fisher particle size is 0.4 mu m, and the purity is more than 99.9 percent;
2) adding raw material powder into a fluidized bed, filling high-purity inert gas into equipment from bottom to top to remove air before dispersion treatment, providing a gas protection environment for the powder, and performing gas-filled cleaning on the equipment; after the air in the fluidized bed cavity is exhausted, transferring the air into a heating device, continuously introducing high-purity inert gas with stable flow in the fluidized bed treatment process, wherein the flow rate of the gas flow is 1L/min, the heating temperature is 150 ℃, and the fluidized treatment is carried out for 180min under constant flow and constant temperature. And after the fluidized bed is subjected to dispersion treatment, the cavity of the fluidized bed is removed from the heating device, high-purity inert protective gas is continuously introduced, and after the fluidized bed is cooled to room temperature in the air, the introduction of the protective gas is stopped, so that the powder subjected to the fluidization dispersion treatment is obtained.
3) And (2) sending the treated powder into a powder feeding device, using argon as working gas, applying pressure to form a plasma torch, carrying out spheroidizing treatment on the powder, wherein the powder feeding speed is 5g/min, the treatment power is 10kw, the powder feeding gas flow is 5L/min, the middle gas flow is 25L/min, the side gas flow is 30L/min, and collecting the powder after plasma spheroidizing after cooling to obtain the treated powder.
4) Uniformly mixing the spheroidized powder with an organic binder (polyformaldehyde 80%, low-density polyethylene 3%, vinyl acetate copolymer 5%, stearic acid 2%, microcrystalline wax 6% and polypropylene 4%) to prepare a granular feed, wherein the volume fraction of the powder in the feed is 45%;
5) feeding the granular material on a micro-injection molding machine, and performing micro-injection molding to obtain a tungsten blank with a required shape and size;
6) the organic binder in the tungsten green body is completely removed by adopting a proper process, and the degreasing process is to degrease for 4 hours in a catalytic degreasing furnace at 130 ℃ by adopting 90% concentrated oxalic acid, so that a porous network system is ensured to be formed, and the decomposition and volatilization of the binder in the thermal degreasing process are facilitated; then the heat removing sintering is carried out in a tube furnace under the protective atmosphere of high-purity hydrogen with the purity of more than 99.9 percent, heating to 200 deg.C at a rate of 0.2 deg.C/min, maintaining for 60min, heating to 450 deg.C at a rate of 0.5 deg.C/min, maintaining for 60min, heating to 550 deg.C at a rate of 0.5 deg.C/min, maintaining for 60min, heating to 650 deg.C at a rate of 1 deg.C/min, maintaining for 60min, then heating to 750 ℃ at the speed of 2 ℃/min, preserving heat for 120min, heating to 950 ℃ at the speed of 2 ℃/min, preserving heat for 120min, raising the temperature to 1250 ℃ at the rate of 3 ℃/min, preserving the heat for 180min, reducing the temperature to 900 ℃ at the rate of 3 ℃/min, reducing the temperature to 700 ℃ at the rate of 3 ℃/min, and finally reducing the temperature to room temperature at the rate of 10 ℃/min, wherein the finally prepared porous tungsten product with the complex-shaped nano-pore structure has the advantages of low impurity content, uniform pores, 0.8 mu m of crystal grain size, 350nm of average pore diameter, 20 percent of open porosity and more than 96 percent of open porosity.
Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (5)
1. A method for efficiently preparing a micro-nano porous tungsten product with a complex shape is characterized in that fine-grained tungsten powder is used as a raw material, and a method combining a fluidization dispersion technology and a radio frequency plasma spheroidization technology to carry out dispersion grading spheroidization on the powder and microinjection molding is adopted to prepare the micro-nano porous tungsten product with the complex shape, and the method comprises the following specific steps:
1) the raw material powder is tungsten powder, the purity is more than 99.9 percent, and the granularity is less than 1 mu m;
2) adding raw material powder into a fluidized bed, filling high-purity inert gas into equipment from bottom to top to remove air before dispersion treatment, providing a gas protection environment for the powder, and performing gas-filled cleaning on the equipment; after the air in the cavity of the fluidized bed is exhausted, transferring the air into a heating device, continuously introducing high-purity inert gas with stable flow in the fluidized bed treatment process, wherein the flow rate of the gas flow is 1-3L/min, the heating temperature is 100-280 ℃, and performing fluidization treatment for 100-180 min under constant flow and constant temperature; after the fluidized bed is subjected to dispersion treatment, the cavity of the fluidized bed is removed from the heating device, high-purity inert protective gas is continuously introduced, and after the fluidized bed is cooled to room temperature in the air, the introduction of the protective gas is stopped, so that powder subjected to fluidization dispersion treatment is obtained;
3) sending the treated powder into a powder feeding device, taking argon as working gas, applying pressure to form a plasma torch, carrying out spheroidization on the powder, wherein the powder feeding speed is 5-15 g/min, the treatment power is 5-25 kw, the powder feeding flow is 5-10L/min, the middle gas flow is 25-35L/min, and the side gas flow is 30-60L/min, cooling the powder after the plasma spheroidization, and collecting to obtain spheroidized powder;
4) uniformly mixing the spheroidized powder with an organic binder, and preparing into granular feed;
5) according to different application scenes of the porous tungsten product with the nano-pore structure and different requirements on the shape and the size of the product, performing micro-injection molding on a tungsten blank with a required shape and size;
6) carrying out catalytic degreasing on the injection green body by using concentrated nitric acid or concentrated oxalic acid as a catalytic medium in a catalytic degreasing furnace to remove part of the binder;
7) and (3) under the protective atmosphere of high-purity hydrogen with the purity of more than 99.9 percent, carrying out thermal de-sintering treatment on the dried sample in the step 6) in a tungsten filament sintering furnace to prepare the porous tungsten product with the complicated shape and the nano pore structure.
2. The method for efficiently preparing the micro-nano porous tungsten product with the complex shape according to claim 1, wherein the proportion of the binder in the step 4) is as follows: 80-88% of polyformaldehyde, 3-8% of low-density polyethylene, 3-10% of vinyl acetate copolymer, 2-5% of stearic acid, 2-10% of microcrystalline wax and 2-7% of polypropylene.
3. The method for efficiently preparing the micro-nano porous tungsten product with the complex shape according to claim 1, wherein the concentration of concentrated nitric acid or concentrated oxalic acid adopted in the step 6) is 86% -95%, and the catalytic degreasing is carried out for 1-12 h at the temperature of 110-150 ℃, so that a porous network system is ensured to be formed, and the decomposition and volatilization of a binder in the subsequent thermal de-sintering process are facilitated.
4. The method for efficiently preparing the micro-nano porous tungsten product with the complex shape according to claim 1, which is characterized in that the thermal desorption sintering treatment process in the step 7) is to heat up to 200 ℃ at a rate of 0.2-0.5 ℃/min, preserve heat for 30-60 min, heat up to 450 ℃ at a rate of 0.5-1 ℃/min, preserve heat for 40-90 min, heat up to 550 ℃ at a rate of 0.5-0.8 ℃/min, preserve heat for 30-60 min, heat up to 650 ℃ at a rate of 0.5-1 ℃/min, preserve heat for 30-60 min, heat up to 750 ℃ at a rate of 2-3 ℃/min, preserve heat for 60-120 min, heat up to 950 ℃ at a rate of 2-3 ℃/min, preserve heat for 60-120 min, heat up to 1000-1250 ℃ at a rate of 1-3 ℃/min, preserve heat for 60-180 min, cool down to 900 ℃ at a rate of 1-3 ℃/min, cool down to 700 ℃ at a rate of 2-5 ℃/min, and cool down to room temperature at a rate of 5-10 ℃/min.
5. The method for efficiently preparing the micro-nano porous tungsten product with the complex shape according to claim 1, wherein the grain size of the sintered porous tungsten product with the nano-scale pore structure is less than or equal to 1 micron, the pore diameter is 100-800 nm, the porosity is 15-35%, the pores are uniform, and the connectivity is good.
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