Steam purification equipment as well as nanoscale alloy filter element and preparation method thereof

Abstract

The invention belongs to the technical field of alloy filter elements, and particularly relates to steam purification equipment, a nanoscale alloy filter element of the steam purification equipment and a preparation method of the nanoscale alloy filter element. The composite material comprises a composite material with titanium alloy as a matrix, wherein the composite material contains a nano reinforced phase and a gradient pore structure formed by a composite pore forming agent; the nano reinforced phase comprises graphene nanosheets and silicon carbide nanoparticles; the composite pore-forming agent comprises nano-scale sodium chloride and micron-scale ammonium bicarbonate; the pore size of the gradient pore structure is gradually increased from the surface layer to the inner layer, the pore size of the surface layer is 50-100 nm, the pore size of the middle layer is 1-5 [mu] m, and the pore size of the inner layer is 10-30 [mu] m. The invention aims to provide the nanoscale alloy filter element, the preparation method of the nanoscale alloy filter element and the steam purification equipment applying the nanoscale alloy filter element, so that the problems of insufficient high-temperature and high-pressure resistance, poor corrosion resistance, low filtering precision and short service life of an existing filter element are solved, and efficient and stable operation of a steam purification system is realized.

Description

Technical Field

[0001] This invention mainly relates to the field of alloy filter technology, specifically a steam purification device and its nanoscale alloy filter element and preparation method. Background Technology

[0002] In industrial steam systems, especially in high-temperature and high-pressure boilers in thermal power, nuclear power, and chemical industries, steam quality directly affects equipment safety and operational efficiency. Currently, the core component of steam purification equipment, the filter element, is mostly made of stainless steel, ordinary titanium alloy, or ceramic materials. Stainless steel filter elements are relatively inexpensive, but they are prone to intergranular corrosion at temperatures above 300℃ and in corrosive environments containing chloride ions, leading to a decrease in filter element strength and an average replacement cycle of only 3-6 months. While ordinary titanium alloy filter elements have better corrosion resistance than stainless steel, their high-temperature strength decreases significantly above 500℃, failing to meet the operating requirements of supercritical boilers above 600℃. Ceramic filter elements, although resistant to high temperatures, are brittle and have poor impact resistance, easily cracking under high-pressure steam impact.

[0003] Existing filter cartridges have significant limitations in filtration precision. Traditional micron-sized pore structures cannot effectively trap nano-sized ionic impurities (such as sodium ions) in boiler wastewater, resulting in sodium ion content in steam often exceeding the industry standard of 0.1 ppb, leading to scaling and corrosion on boiler heating surfaces. Furthermore, existing filter cartridges have a simple pore structure design, mostly with uniform pore size, making it difficult to simultaneously meet the dual requirements of high throughput and high-precision filtration, creating a contradiction between filtration efficiency and system energy consumption.

[0004] To address the aforementioned issues, there is an urgent need in this field to develop a filter material and manufacturing process that combines high temperature and high pressure resistance, strong corrosion resistance, nanoscale filtration accuracy, and long lifespan. Through material system innovation and structural design optimization, the performance bottlenecks of traditional filter elements can be overcome to meet the stringent requirements of high temperature and high pressure steam purification. Summary of the Invention

[0005] The purpose of this invention is to provide a nano-alloy filter element, its preparation method, and a steam purification device using the filter element, so as to solve the problems of insufficient high temperature and high pressure resistance, poor corrosion resistance, low filtration accuracy, and short life of existing filter elements, and to achieve efficient and stable operation of the steam purification system.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a nanoscale alloy filter element, comprising a composite material with titanium alloy as the matrix, wherein the composite material contains a gradient pore structure formed by a nano-reinforcing phase and a composite pore-forming agent: the nano-reinforcing phase includes graphene nanosheets and silicon carbide nanoparticles; the composite pore-forming agent includes nano-sized sodium chloride and micron-sized ammonium bicarbonate; the gradient pore structure has a gradually increasing pore size from the surface layer to the inner layer, with a surface pore size of 50-100 nm, a middle layer pore size of 1-5 μm, and an inner layer pore size of 10-30 μm.

[0008] In some feasible ways, the composite material comprises the following components by mass percentage: 94.0-96.5 wt% titanium alloy, 0.8-1.2 wt% graphene nanosheets, 0.6-1.0 wt% silicon carbide nanoparticles, and 12-18 wt% composite pore-forming agent; and the mass ratio of nano-sized sodium chloride to micron-sized ammonium bicarbonate in the composite pore-forming agent is (7-8):(2-3).

[0009] In some feasible ways, the titanium alloy is TC4 titanium alloy, and the titanium alloy also contains 1.3-1.7 wt% niobium and 0.4-0.6 wt% rare earth oxides;

[0010] And / or, the oxygen content of the titanium alloy is ≤0.12wt%, and the particle size is 15-30μm.

[0011] In some feasible methods, silicon carbide nanoparticles are particles with an α-phase content of ≥90% and a particle size of 20-40 nm; rare earth oxides are La2O3 with a particle size of 5-10 nm; and niobium has a particle size of 5-10 μm and a purity of ≥99.9%.

[0012] In some feasible methods, the graphene nanosheets are monolayer graphene with a monolayer content ≥95% and a lateral dimension of 8-12 μm, and are treated with plasma etching and a silane coupling agent; the plasma etching power is 280-320 W, the argon flow rate is 1-2 L / min, and the treatment time is 4-6 minutes; the silane coupling agent is KH560 with a concentration of 1.8-2.2 wt%.

[0013] And / or, the filter element surface is sequentially provided with an anodic oxide film and a ceramic coating; the thickness of the anodic oxide film is 5-8μm, and the ceramic coating is an Al2O3-ZrO2 composite ceramic coating with a thickness of 20-30μm, wherein the ZrO2 content is 28-32%.

[0014] Secondly, the present invention provides a method for preparing a nanoscale alloy filter element, which specifically includes the following steps:

[0015] (1) Powder pretreatment: Graphene nanosheets were subjected to plasma etching and silane coupling agent treatment, and niobium powder was subjected to hydrofluoric acid solution activation treatment;

[0016] (2) Mixing: Titanium alloy powder, niobium powder and rare earth oxides are ball-milled in the first step, and then the treated graphene nanosheets, silicon carbide nanoparticles and composite pore-forming agent are added for the second step of ball milling.

[0017] (3) Sintering: The mixed powder is sintered in stages, including low-temperature debinding, high-temperature sintering and hot isostatic pressing, and then the pore-forming agent is removed;

[0018] (4) Surface treatment: The sintered blank is subjected to anodizing and ceramic coating spraying in sequence.

[0019] In some feasible ways, in step (1), the hydrofluoric acid solution has a mass fraction of 4-6% and the niobium powder is soaked for 8-12 minutes;

[0020] During silane coupling agent treatment, graphene nanosheets are dispersed in an ethanol solution, and after adding the silane coupling agent, the mixture is stirred at 60-70°C for 1.5-2.5 hours.

[0021] In some feasible ways, in step (2), the first ball milling speed is 380-420 r / min, the time is 3.5-4.5 hours, and the ball-to-material ratio is 8:1; the second ball milling speed is 180-220 r / min, and the time is 1.5-2.5 hours.

[0022] In some feasible ways, in step (3), the low-temperature degumming is carried out under argon protection with an argon flow rate of 7-9 L / min, the temperature is increased to 280-320℃ at 4-6℃ / min, and held for 0.8-1.2 hours; the high-temperature sintering temperature is 1080-1120℃, and held for 2-3 hours.

[0023] And / or, the hot isostatic pressing treatment is carried out at a temperature of 900-940℃, a pressure of 140-160MPa, and a holding time of 1.5-2.5 hours;

[0024] And / or, when removing the pore-forming agent, first soak it in hot water at 75-85℃ for 2.5-3.5 hours, and then use ultrasonic cleaning with 450-550W power for 0.8-1.2 hours.

[0025] In some feasible ways, in step (4), the anodizing is performed using a pulse anodizing process, the electrolyte is a mixture of 0.4-0.6M sulfuric acid and 0.08-0.12M glycerol, the voltage is 18-22V, the pulse frequency is 450-550Hz, and the processing time is 25-35 minutes;

[0026] And / or, the ceramic coating is applied using atmospheric plasma spraying technology.

[0027] Thirdly, the present invention provides a steam purification device, including the above-mentioned nano-alloy filter element; and / or, the steam purification device has a sodium ion removal rate of ≥99.95% in steam and a steam flux of 750-850 L / (m²・h).

[0028] Firstly, the nanoscale alloy filter element provided by this invention uses a titanium alloy as a matrix to form a composite material. This composite material contains a gradient pore structure formed by a nano-reinforcing phase and a composite pore-forming agent. The nano-reinforcing phase includes graphene nanosheets and silicon carbide nanoparticles; the composite pore-forming agent includes nano-sized sodium chloride and micron-sized ammonium bicarbonate. The gradient pore structure exhibits a gradually increasing pore size from the surface layer to the inner layer, with surface pores of 50-100 nm, middle layer pores of 1-5 μm, and inner layer pores of 10-30 μm. This structural design, through the synergistic effect of pores of different sizes, effectively traps nanoscale impurities while ensuring smooth steam flow. Specifically, the nanoscale pores on the surface layer can directly intercept nanoscale ionic impurities, while the larger pores in the middle and inner layers provide channels for steam flow, reducing flow resistance.

[0029] In some feasible implementations, the composite material comprises the following components by mass percentage: 94.0-96.5 wt% titanium alloy, 0.8-1.2 wt% graphene nanosheets, 0.6-1.0 wt% silicon carbide nanoparticles, and 12-18 wt% composite pore-forming agent; and the mass ratio of nano-sized sodium chloride to micron-sized ammonium bicarbonate in the composite pore-forming agent is (7-8):(2-3). In this invention, titanium alloy is used as the matrix to ensure the overall structural strength of the filter element, while the addition amounts of graphene nanosheets and silicon carbide nanoparticles must be controlled within the above range: if the addition amount is too small, its enhancing effect on material performance cannot be fully utilized; if the addition amount is too large, it may lead to particle agglomeration, which in turn affects the uniformity of the material. The content of the composite pore-forming agent and the proportion of its components are to ensure that the formed gradient pore structure can meet the filtration accuracy requirements while ensuring sufficient porosity to maintain steam flux.

[0030] In some feasible implementations, the titanium alloy is TC4 titanium alloy, containing 1.3-1.7 wt% niobium and 0.4-0.6 wt% rare earth oxides; and / or, the oxygen content of the titanium alloy is ≤0.12 wt%, and the particle size is 15-30 μm. TC4 titanium alloy itself has good comprehensive properties. The addition of niobium can further improve the high-temperature stability of the material, while rare earth oxides help to purify the grain boundaries inside the material and reduce grain boundary defects. Controlling the oxygen content and particle size of the titanium alloy is because excessive oxygen content will reduce the toughness of the titanium alloy, while a suitable particle size range is beneficial to subsequent mixing and sintering processes, ensuring the uniformity of the material.

[0031] In some feasible methods, silicon carbide nanoparticles with an α-phase content ≥90% and a particle size of 20-40 nm are selected; rare earth oxides such as La2O3 with a particle size of 5-10 nm are selected; and niobium with a particle size of 5-10 μm and a purity ≥99.9% are selected. α-phase silicon carbide has higher hardness and stability, and its smaller particle size is conducive to its uniform dispersion in the matrix, thus better exerting its strengthening effect; the small particle size of La2O3 allows it to diffuse more effectively to the grain boundaries, exerting a purification effect; the high purity and suitable particle size of niobium ensure its dissolution and dispersion effect in titanium alloys, avoiding performance fluctuations caused by impurities or excessively large particle sizes.

[0032] In some feasible methods, graphene nanosheets are selected from monolayer graphene with a monolayer ratio ≥95% and a lateral dimension of 8-12 μm, and are treated with plasma etching and a silane coupling agent. The plasma etching power is 280-320 W, the argon flow rate is 1-2 L / min, and the treatment time is 4-6 minutes; the silane coupling agent used is KH560 with a concentration of 1.8-2.2 wt%. High monolayer ratio graphene nanosheets exhibit superior mechanical and physical properties, and the lateral dimension within the above range ensures the formation of an effective network structure within the matrix. Plasma etching introduces functional groups into the graphene surface, enhancing its interaction with the matrix; while the silane coupling agent treatment further improves the interfacial bonding between graphene and titanium alloy. The selection of KH560 and the above treatment parameters are the result of multiple experimental verifications, ensuring the stability of the modification effect.

[0033] In addition, the filter element surface is sequentially coated with an anodic oxide film and a ceramic coating. The anodic oxide film has a thickness of 5-8 μm; the ceramic coating is an Al2O3-ZrO2 composite ceramic coating with a thickness of 20-30 μm, of which the ZrO2 content is 28-32%. The anodic oxide film forms a dense oxide layer on the filter element surface, improving its corrosion resistance; while the composite ceramic coating further enhances the surface's wear resistance and high-temperature resistance. The addition of ZrO2 improves the toughness of the ceramic coating, preventing excessive brittleness and cracking. The thickness of each layer and the range of ZrO2 content are determined by comprehensively considering the protective effect and the adhesion between the coating and the substrate.

[0034] Secondly, the present invention also provides a method for preparing a nanoscale alloy filter element, which specifically includes the following steps:

[0035] (1) Powder pretreatment: Graphene nanosheets were subjected to plasma etching and silane coupling agent treatment, and niobium powder was activated with hydrofluoric acid solution. Plasma etching of graphene nanosheets utilizes high-energy particles in plasma to bombard the graphene surface, creating defects and introducing oxygen-containing functional groups, thus creating conditions for subsequent silane coupling agent treatment. Silane coupling agent treatment improves the compatibility between graphene and the matrix by having one end of the coupling agent molecule bind to the functional groups on the graphene surface and the other end interact with the titanium alloy matrix. Activation of niobium powder with hydrofluoric acid solution is performed because an oxide film easily forms on the surface of niobium powder, which hydrofluoric acid can dissolve, exposing a fresh metal surface, which is beneficial for better bonding of niobium powder with other powders in subsequent processes.

[0036] (2) Mixing: Titanium alloy powder, niobium powder, and rare earth oxides are ball-milled in the first step, and then treated graphene nanosheets, silicon carbide nanoparticles, and composite pore-forming agent are added for the second step of ball milling. The purpose of the first step of ball milling is to initially mix and disperse the titanium alloy powder, niobium powder, and rare earth oxides, so that the niobium powder and rare earth oxides are initially evenly distributed in the titanium alloy powder; the second step of ball milling is to add the pretreated graphene nanosheets, silicon carbide nanoparticles, and composite pore-forming agent, and achieve uniform mixing of all components by using a lower ball milling intensity, while avoiding damage to the graphene nanosheet structure.

[0037] (3) Sintering: The mixed powder is sintered in stages, including low-temperature debinding, high-temperature sintering and hot isostatic pressing, followed by removal of the pore-forming agent. Low-temperature debinding is to remove any organic impurities that may be present in the powder, and to avoid the generation of gas during high-temperature sintering, which would cause pores to appear inside the material; high-temperature sintering causes diffusion bonding between the powder particles to form an integral structure; hot isostatic pressing uses the combined effect of high temperature and high pressure to further eliminate the pores inside the material and improve the density of the material; removal of the pore-forming agent is achieved by dissolving or other methods to remove the composite pore-forming agent from the sintered green body, thereby forming the required gradient pore structure.

[0038] (4) Surface treatment: The sintered green body is subjected to anodizing treatment and ceramic coating spraying in sequence. Anodizing treatment forms an oxide film on the surface of the green body. This film layer is tightly bonded to the substrate and can directly improve the corrosion resistance of the green body. Ceramic coating spraying forms a hard ceramic layer on the surface of the oxide film, which further improves the wear resistance, high temperature resistance and corrosion resistance of the surface, and together with the oxide film, it constitutes a double protection.

[0039] In some feasible methods, in step (1), the mass fraction of the hydrofluoric acid solution is 4-6%, and the soaking time of the niobium powder is 8-12 minutes. These parameters are chosen because if the hydrofluoric acid concentration is too low or the soaking time is too short, the oxide film on the surface of the niobium powder cannot be completely removed; while if the concentration is too high or the time is too long, it may excessively corrode the niobium powder, affecting its performance. During silane coupling agent treatment, graphene nanosheets are dispersed in an ethanol solution, and after adding the silane coupling agent, the mixture is stirred at 60-70°C for 1.5-2.5 hours. The ethanol solution provides a good dispersion environment for the graphene nanosheets and the silane coupling agent, and appropriate temperature and stirring time are beneficial for the coupling agent to fully react with the graphene surface, ensuring the modification effect.

[0040] In some feasible methods, in step (2), the first ball milling speed is 380-420 r / min, the time is 3.5-4.5 hours, and the ball-to-material ratio is 8:1; the second ball milling speed is 180-220 r / min, and the time is 1.5-2.5 hours. The first ball milling uses a higher speed and a longer time to ensure that the titanium alloy powder, niobium powder, and rare earth oxides can be fully mixed and refined; the second ball milling reduces the speed and shortens the time to avoid the destruction of the sheet structure caused by excessive ball milling energy, while ensuring that the components are mixed uniformly.

[0041] In some feasible methods, in step (3), low-temperature debinding is carried out under argon protection, with an argon flow rate of 7-9 L / min, and the temperature is increased to 280-320℃ at a rate of 4-6℃ / min, and held for 0.8-1.2 hours. Argon protection can prevent the powder from being oxidized during the debinding process. Controlling the heating rate and holding temperature and time is to ensure that organic impurities can be slowly and thoroughly decomposed and removed, avoiding rapid heating that would cause impurities to volatilize rapidly and produce pores. The high-temperature sintering temperature is 1080-1120℃, and the holding time is 2-3 hours. This temperature range is the suitable temperature for titanium alloy sintering. At this temperature, sufficient diffusion and bonding can occur between the powder particles, and the holding time ensures that the diffusion process is complete. The hot isostatic pressing temperature is 900-940℃, the pressure is 140-160 MPa, and the holding time is 1.5-2.5 hours. Such parameter settings can minimize internal porosity and improve density without damaging the material structure. To remove the pore-forming agent, first soak in hot water at 75-85℃ for 2.5-3.5 hours, then ultrasonically clean with 450-550W power for 0.8-1.2 hours. Hot water dissolves the soluble components in the composite pore-forming agent, while ultrasonic cleaning further removes residual pore-forming agent, ensuring unobstructed pore structure.

[0042] In step (4), anodizing is performed using pulse anodizing technology. The electrolyte is a mixture of 0.4-0.6M sulfuric acid and 0.08-0.12M glycerol, the voltage is 18-22V, the pulse frequency is 450-550Hz, and the processing time is 25-35 minutes. Compared with traditional DC anodizing, pulse anodizing can more precisely control the growth of the oxide film and reduce film defects. The mixed electrolyte of sulfuric acid and glycerol is conducive to the formation of a dense oxide film. The selection of voltage, frequency, and processing time is to obtain an oxide film with moderate thickness and good performance. The ceramic coating is sprayed using atmospheric plasma spraying technology, which allows the ceramic material to melt at high temperature and be sprayed onto the surface of the blank at high speed to form a uniform coating that is firmly bonded to the substrate.

[0043] The steam purification equipment provided by this invention includes the aforementioned nano-alloy filter element, and the steam purification equipment achieves a sodium ion removal rate of ≥99.95% in steam, with a steam flux of 750-850 L / (m²・h). Because the nano-alloy filter element has a gradient pore structure, the surface nano-pores effectively trap nano-sized impurities such as sodium ions in the steam, while the pores in the middle and inner layers ensure the steam flow rate. Therefore, this steam purification equipment can efficiently remove impurities while maintaining a high steam flux, meeting the steam purification requirements in industrial production.

[0044] Compared with the prior art, the present invention has the following advantages:

[0045] (1) This invention significantly improves the high-temperature mechanical stability of the material by introducing niobium and rare earth oxides into the titanium alloy matrix. At room temperature, the tensile strength of the composite material is 900-950 MPa, which is the same as that of the traditional TC4 titanium alloy; at 600℃, its tensile strength remains at 550-580 MPa, which is about 20% higher than that of the traditional TC4 titanium alloy (450-480 MPa); in an environment of 700℃, the tensile strength can still be stable at 480-500 MPa, overcoming the problem of rapid strength decay of traditional titanium alloys above 500℃. From a mechanistic perspective, niobium can stabilize the β phase of titanium alloys, raising the phase transformation temperature from 995℃ to over 1050℃. At the same time, rare earth oxides form nanoscale dispersed phases at grain boundaries, which can suppress grain coarsening at high temperatures. The combined effect of these two factors ensures the structural integrity of the material under high temperature and high pressure conditions, enabling it to operate at an upper temperature limit of 690-710℃ and withstand pressure of 33-37MPa, thus meeting the operating requirements of supercritical boilers.

[0046] (2) This invention utilizes graphene nanosheets to form a continuously distributed physical barrier within the matrix, blocking the penetration path of corrosive media and reducing the corrosion rate of the material in 3.5% sodium chloride solution to 0.01-0.015 mm / a, significantly lower than that of traditional TC4 titanium alloy. The 5-8 μm TiO2 film formed by surface anodizing and the Al2O3-ZrO2 ceramic coating constitute a dual chemical protection, controlling the corrosion weight loss rate at 0.05-0.08 mg / cm²·d in a wide range of media with pH values ​​of 2-12, far lower than the 2.5-3.0 mg / cm²·d of stainless steel filter elements. This synergistic effect of the protective system enables the material to remain stable for a long time in high-temperature steam environments containing chloride ions.

[0047] (3) The 50-100nm nanopores in the surface layer of the filter element of this invention can effectively trap nano-sized ions in water, with a sodium ion trapping rate of 99.95%-99.96%, stabilizing the sodium ion concentration in steam at 0.04-0.06ppb, meeting the industry's requirements for steam quality (≤0.1ppb). The synergistic effect of the 1-5μm pore structure in the middle layer and the 10-30μm pore structure in the inner layer enables the steam flux to reach 750-850L / (m²・h), which is about 30% higher than that of traditional uniform pore size filter elements, while reducing the filtration resistance by 25%-30%. This result is due to the reasonable ratio of nano-sized and micro-sized pores, which reduces the residence time of fluid in the pores while ensuring filtration accuracy.

[0048] (4) Regarding service life, based on the improvements in material properties and filtration structure mentioned above, the replacement cycle of the filter element has been extended. In the actual operating environment of a 300MW coal-fired boiler unit (operating temperature 540-560℃, pressure 16-18MPa), continuous operation tests show that the filter element still maintains more than 90% of its initial filtration efficiency after 18 months; and maintains more than 85% of its filtration efficiency after 24 months. The actual replacement cycle is expected to reach 30-36 months, which is a significant improvement compared to traditional stainless steel filter elements (3-6 months) and ordinary titanium alloy filter elements (12-18 months).

[0049] In summary, this invention achieves breakthrough improvements in high temperature and high pressure resistance, corrosion resistance, filtration performance, and lifespan through niobium-rare earth composite doping, gradient pore design, and process optimization, demonstrating significant inventiveness and practical value.

[0050] The present invention will be explained in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0051] Figure 1 Line graph showing the tensile strength data of different embodiments and comparative examples of the filter elements of the present invention at room temperature, 600℃, and 700℃.

[0052] Figure 2 This is a bar chart comparing the actual service life data of filter elements in different embodiments and comparative examples of the present invention. Detailed Implementation

[0053] To facilitate understanding of the present invention, a more comprehensive description of the invention will be given below with reference to the accompanying drawings, which illustrate several embodiments of the invention. However, the invention can be implemented in different forms and is not limited to the embodiments described in the text; rather, these embodiments are provided to make the disclosure of the present invention more thorough and complete.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly associated with those skilled in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0055] The nanoscale alloy filter element of this invention uses titanium alloy as the matrix, and by introducing a nano-reinforcing phase and a composite pore-forming agent, combined with an optimized preparation process, a composite material filter element with a gradient pore structure is formed. The specific technical solution is as follows:

[0056] In terms of material composition, the composite material of the filter element of this invention uses TC4 titanium alloy as the base matrix. This titanium alloy has excellent comprehensive mechanical properties and corrosion resistance. Its oxygen content is controlled at ≤0.12wt%, and the particle size is 15-30μm. The low oxygen content can avoid oxygen embrittlement and ensure the toughness of the material. To improve high-temperature stability, 1.3-1.7wt% niobium (Nb) is also added to the matrix of this invention. Niobium forms an infinite solid solution with titanium, which can increase the β phase transformation temperature of the alloy from 995℃ to above 1050℃, so that the material still maintains a stable body-centered cubic structure at a high temperature of 700℃. At the same time, 0.4-0.6wt% rare earth oxides (preferably La2O3) are added, which can preferentially adsorb oxygen, nitrogen and other impurity atoms at the grain boundaries, purify the grain boundaries and inhibit grain coarsening, and further enhance high-temperature strength.

[0057] The nano-reinforcing phase in this invention consists of graphene nanosheets and silicon carbide nanoparticles. The graphene nanosheets are added at an amount of 0.8-1.2 wt%, using monolayer graphene with a monolayer ratio ≥95% and a lateral dimension of 8-12 μm. After plasma etching and treatment with 1.8-2.2 wt% KH560 silane coupling agent, functional groups such as hydroxyl and carboxyl groups are introduced onto the surface, enabling chemical bonding with the titanium alloy matrix. Macroscopically, this increases the interfacial bonding strength by more than 40%, and microscopically, it transfers load and suppresses dislocation movement through a bridging effect. The silicon carbide nanoparticles are added at an amount of 0.6-1.0 wt%, using particles with an α-phase content ≥90% and a particle size controlled at 20-40 nm, which is 10-20 nm finer than traditional particles. Uniformly dispersed in the matrix, they serve as a nano-reinforcing phase, improving material hardness through a dislocation pile-up strengthening mechanism while simultaneously hindering grain growth at high temperatures.

[0058] To achieve gradient filtration, 12-18 wt% of a composite pore-forming agent is added to the composite material. This pore-forming agent consists of nano-sized sodium chloride (50-100 nm particle size) and micron-sized ammonium bicarbonate (1-5 μm particle size). The size difference between the two pore-forming agents creates a gradient pore structure in the filter element that gradually increases in size from the surface to the inner layer: the 50-100 nm nanopores in the surface layer can capture nano-sized impurities such as sodium ions through the double-layer adsorption effect; the 1-5 μm mesopores in the middle layer are used to intercept micron-sized particles; and the 10-30 μm macropores in the inner layer ensure steam throughput. The synergistic effect of these three elements resolves the contradiction between "high precision and high throughput" in traditional filter elements.

[0059] In terms of preparation process, the powder is first pretreated: after the graphene nanosheets are etched by plasma, they are placed in an ethanol solution, KH560 silane coupling agent is added, and the mixture is stirred at 60-70℃ for 1.5-2.5 hours to allow one end of the coupling agent molecule to combine with the functional group of graphene and the other end to form a chemical bond with the titanium alloy, thereby enhancing compatibility; the niobium powder is then immersed in a 4-6% mass fraction hydrofluoric acid solution for 8-12 minutes to remove the Nb2O5 oxide film on the surface, expose the fresh metal surface, and reduce the diffusion resistance during sintering.

[0060] The mixing stage employs a two-step ball milling method: In the first step, TC4 titanium alloy powder, niobium powder, and La2O3 are added to a ball mill in proportion and milled at a speed of 380-420 r / min for 3.5-4.5 hours with a ball-to-material ratio of 8:1. Through high-energy collisions, niobium is uniformly diffused into the titanium alloy matrix to form a Ti-Nb solid solution precursor phase. In the second step, treated graphene, silicon carbide, and a composite pore-forming agent are added, and the speed is adjusted to 180-220 r / min for further ball milling for 1.5-2.5 hours. The lower speed avoids damage to the graphene sheet structure and ensures uniform dispersion of nanoparticles, keeping the agglomerate size ≤5 μm.

[0061] The sintering process is controlled in stages: First, under argon protection, the temperature is raised to 280-320℃ at a rate of 4-6℃ / min and held for 0.8-1.2 hours to complete low-temperature debinding and remove organic impurities from the powder, with an argon flow rate of 7-9L / min. Then, the temperature is raised to 1080-1120℃ and held for 2-3 hours for high-temperature sintering, followed by hot isostatic pressing (HIP). High pressure is used to eliminate sintering pores, increasing the material density to over 98%. Preferably, the HIP temperature is 900-940℃, the pressure is 140-160MPa, and the holding time is 1.5-2.5 hours. Finally, the green body is immersed in hot water at 75-85℃ for 2.5-3.5 hours, followed by ultrasonic cleaning with 450-550W power for 0.8-1.2 hours to thoroughly remove the pore-forming agent and form a connected gradient pore structure.

[0062] Surface treatment includes anodizing and ceramic coating spraying: Anodizing adopts pulse anodizing process, with the electrolyte being a mixture of 0.4-0.6M sulfuric acid and 0.08-0.12M glycerol. It is treated for 25-35 minutes at a voltage of 18-22V and a pulse frequency of 450-550Hz to form a 5-8μm thick TiO2 oxide film, which improves corrosion resistance through chemical passivation. Subsequently, atmospheric plasma spraying technology is used to form a 20-30μm thick Al2O3-ZrO2 composite ceramic coating on the oxide film surface. The ZrO2 content in the coating is 28-32%. ZrO2 can inhibit the crack propagation of the coating through the phase transformation toughening effect. Together with the oxide film and graphene, it forms a "triple protection system" that significantly improves the durability in high-temperature corrosion environments.

[0063] Example 1: This example provides a nanoscale alloy filter element, comprising a composite material with titanium alloy as the matrix. The composite material contains a gradient pore structure formed by a nano-reinforcing phase and a composite pore-forming agent. The nano-reinforcing phase includes graphene nanosheets and silicon carbide nanoparticles, and the composite pore-forming agent includes nano-sized sodium chloride and micron-sized ammonium bicarbonate. The pore size of the gradient pore structure gradually increases from the surface layer to the inner layer, with the surface pore size being 50-100 nm, the middle layer pore size being 1-5 μm, and the inner layer pore size being 10-30 μm.

[0064] In this embodiment, the composite material of the filter element is composed of the following components: the composite material includes the following components by mass percentage: 95.2 wt% titanium alloy, 1.0 wt% graphene nanosheets, 0.8 wt% silicon carbide nanoparticles, and 15 wt% composite pore-forming agent. The composite pore-forming agent is composed of nano-sized sodium chloride and micron-sized ammonium bicarbonate. The nano-sized sodium chloride has a particle size of 80 nm, and the micron-sized ammonium bicarbonate has a particle size of 3 μm. The mass ratio of the two is 8:2.

[0065] Preferably, in this embodiment, the TC4 titanium alloy powder has an oxygen content of 0.10 wt% and a particle size of 20 μm, containing 1.5 wt% niobium and 0.5 wt% La2O3. The niobium has a particle size of 8 μm and a purity of 99.9%; the La2O3 has a particle size of 8 nm. The graphene nanosheets have a monolayer ratio of 96% and a lateral dimension of 10 μm; the silicon carbide nanoparticles account for 0.8 wt%, with an α-phase content of 92% and a particle size of 30 nm.

[0066] On the other hand, this embodiment also provides a method for preparing the above-mentioned filter element, the specific steps of which are as follows:

[0067] (1) Powder pretreatment: The graphene nanosheets were first subjected to plasma etching with an etching power of 300W, an argon flow rate of 1.5L / min, and a treatment time of 5 minutes. Then, they were treated with 2.0wt% KH560 silane coupling agent and stirred at 65℃ for 2 hours; the niobium powder was soaked in 5% hydrofluoric acid solution for 10 minutes.

[0068] (2) Mixing: First step ball milling: Put titanium alloy powder, niobium powder and La2O3 into a ball mill and mill for 4 hours at a speed of 400 r / min. The ball-to-material ratio is 8:1. Second step ball milling: Add treated graphene nanosheets, silicon carbide nanoparticles and composite pore-forming agent and continue ball milling for 2 hours at a speed of 200 r / min.

[0069] (3) Sintering: First, low-temperature debinding is carried out under argon protection with an argon flow rate of 8L / min. The temperature is raised to 300℃ at a rate of 5℃ / min and held for 1 hour. Then, high-temperature sintering is carried out at 1100℃ for 2.5 hours. After that, hot isostatic pressing is carried out at 920℃ and 150MPa for 2 hours. Finally, the sintered green body is first soaked in hot water at 80℃ for 3 hours and then cleaned with ultrasonic power of 500W for 1 hour to remove the pore-forming agent.

[0070] (4) Surface treatment: First, pulse anodizing process is adopted, the electrolyte is a mixture of 0.5M sulfuric acid and 0.1M glycerol, the voltage is 20V, the pulse frequency is 500Hz, the treatment time is 30 minutes, and an anodized film with a thickness of 6μm is formed; then, atmospheric plasma spraying technology is adopted to spray Al2O3-ZrO2 composite ceramic coating with a thickness of 25μm, of which the ZrO2 content is 30%.

[0071] Table 1 Comparison of performance parameters between the examples and comparative examples

[0072] project Tensile strength at room temperature (MPa) Tensile strength at 600℃ (MPa) Tensile strength at 700℃ (MPa) Corrosion rate (mm / a) Example 1 930 560 490 0.012 Example 2 920 550 480 0.013 Example 3 940 570 500 0.011 Comparative Example 1 650 320 280 2.8 Comparative Example 2 880 500 430 0.05 Comparative Example 3 820 420 380 0.15 Comparative Example 4 850 480 420 0.08 Comparative Example 5 800 450 390 0.12 Comparative Example 6 860 490 440 0.06 Comparative Example 7 780 430 370 0.10

[0073] Table 2 Comparison of Performance Parameters between Examples and Comparative Examples

[0074] project Sodium ion removal rate (%) Steam flux (L / (m²・h)) Filter resistance (kPa) Service life (months) Example 1 99.96 800 15 33 Example 2 99.95 780 16 32 Example 3 99.96 820 14 34 Comparative Example 1 95.0 450 35 4 Comparative Example 2 98.5 600 25 18 Comparative Example 3 99.0 700 20 20 Comparative Example 4 99.2 720 22 22 Comparative Example 5 99.1 680 24 19 Comparative Example 6 98.8 650 23 21 Comparative Example 7 99.0 550 30 15

[0075] Analysis of the relevant data in Tables 1 and 2 above shows that the filter elements of Examples 1-3 of this invention exhibit significant advantages due to their core innovations: First, through the synergistic effect of niobium-rare earth composite doped titanium alloy matrix and graphene-silicon carbide nano-reinforcement, a tensile strength of 480-500 MPa is maintained at 700℃, solving the problem of high-temperature strength decay in traditional materials; Second, the gradient pore structure (surface layer 50-100 nm, middle layer 1-5 μm, inner layer 10-30 μm) achieves a sodium ion removal rate of over 99.95% and a high steam flux of 780-820 L / (m²・h), overcoming the contradiction between "high precision and high flux"; Third, the optimization of processes such as plasma etching and segmented sintering reduces the corrosion rate to as low as 0.011-0.013 mm / a, extending the service life to 32-34 months, which is 5-8 times higher than that of traditional filter elements. All performance parameters remain stable within the scope of the claims, verifying the rationality of the material composition and process design.

[0076] Comparative Examples 1-7 exhibited significant performance degradation due to the absence of the core innovation of this invention: Comparative Example 1 (ordinary stainless steel filter element) lacked a titanium alloy matrix and nano-reinforcing phase, resulting in insufficient high-temperature strength and a corrosion rate as high as 2.8 mm / a, with a lifespan of only 4 months; Comparative Example 2 (without gradient pores) had a 25% reduction in steam flux due to its simple pore structure; Comparative Example 3 (without nano-reinforcing phase) lacked the reinforcing effect of graphene and silicon carbide, leading to a 25% decrease in strength at 600℃; Comparative Example 4 (without powder pretreatment) had a 6-fold increase in corrosion rate due to poor interfacial bonding; Comparative Example 5 (non-segmented sintering) had a 60% increase in filtration resistance due to insufficient density; Comparative Example 6 (components below the range) had a sodium ion removal rate reduced to 98.8% due to insufficient pore-forming agent and reinforcing phase; and Comparative Example 7 (components exceeding the range) had a 33% decrease in steam flux due to particle agglomeration.

[0077] The testing methods and standards for the above performance parameters are explained below:

[0078] 1. Tensile strength at room temperature and high temperature: According to GB / T228.1-2010 and GB / T4338-2015, the standard tensile specimens were tested using a universal testing machine. The room temperature test environment was 25℃, and the high temperature test was carried out in a constant temperature environment of 600℃ and 700℃ respectively. Each parameter was tested 3 times and the average value was taken.

[0079] 2. Corrosion rate: According to GB / T10124-2021, the sample was immersed in a 3.5% sodium chloride solution (simulating the corrosion environment of a boiler). After 60 days, the mass loss was measured and the uniform corrosion rate was calculated.

[0080] 3. Sodium ion removal rate: Referring to GB / T11904-1989, the sodium ion concentration in the steam before and after filtration was detected by flame atomic absorption spectrophotometer, and the removal rate was calculated.

[0081] 4. Steam flux and filtration resistance: Using a self-made testing device, saturated steam was introduced at a pressure of 16 MPa and a temperature of 550 °C. The flux per unit area and pressure loss were measured by a flow meter and a differential pressure gauge, respectively.

[0082] 5. Service life: Continuous operation in a 300MW coal-fired boiler system, with periodic testing of filtration efficiency (indicated by sodium ion removal rate), and recording the operating time when the efficiency drops to 80% of the initial value.

[0083] Example 2: This example provides a nanoscale alloy filter element, comprising a composite material with titanium alloy as the matrix. The composite material contains a gradient pore structure formed by a nano-reinforcing phase and a composite pore-forming agent. The nano-reinforcing phase includes graphene nanosheets and silicon carbide nanoparticles, and the composite pore-forming agent includes nano-sized sodium chloride and micron-sized ammonium bicarbonate. The pore size of the gradient pore structure gradually increases from the surface layer to the inner layer, with the surface pore size being 50-100 nm, the middle layer pore size being 1-5 μm, and the inner layer pore size being 10-30 μm.

[0084] In this embodiment, the composite material of the filter element is composed of the following components: the composite material includes the following components by mass percentage: 96.5 wt% titanium alloy, 0.8 wt% graphene nanosheets, 0.6 wt% silicon carbide nanoparticles, and 12 wt% composite pore-forming agent. The composite pore-forming agent is composed of nano-sized sodium chloride and micron-sized ammonium bicarbonate. The nano-sized sodium chloride has a particle size of 50 nm, and the micron-sized ammonium bicarbonate has a particle size of 1 μm. The mass ratio of the two is 7:3.

[0085] Preferably, in this embodiment, the TC4 titanium alloy powder has an oxygen content of 0.12 wt% and a particle size of 15 μm, containing 1.3 wt% niobium and 0.4 wt% La2O3. The niobium has a particle size of 5 μm and a purity of 99.9%; the La2O3 has a particle size of 5 nm. The graphene nanosheets have a monolayer ratio of 95% and a lateral dimension of 8 μm; the silicon carbide nanoparticles have an α-phase content of 90% and a particle size of 20 nm.

[0086] On the other hand, this embodiment also provides a method for preparing the above-mentioned filter element, the specific steps of which are as follows:

[0087] (1) Powder pretreatment: Graphene nanosheets were first plasma etched with a power of 280W, an argon flow rate of 1L / min, and a treatment time of 4 minutes. Then, they were treated with 1.8wt% KH560 silane coupling agent and stirred at 60℃ for 1.5 hours. Niobium powder was soaked in 4% hydrofluoric acid solution for 8 minutes.

[0088] (2) Mixing: First step ball milling: Titanium alloy powder, niobium powder and La2O3 are ball milled at 380 r / min for 3.5 hours with a ball-to-material ratio of 8:1; Second step ball milling: The treated graphene, silicon carbide and composite pore-forming agent are added and ball milled at 180 r / min for 1.5 hours.

[0089] (3) Sintering: Low-temperature debinding is carried out under the protection of argon flow rate of 7L / min, and the temperature is increased to 280℃ at 4℃ / min and held for 0.8 hours; high-temperature sintering is carried out at 1080℃ for 2 hours; hot isostatic pressing is carried out at 900℃ and 140MPa for 1.5 hours; then soaking in 75℃ hot water for 2.5 hours, and then ultrasonic cleaning with 450W power for 0.8 hours to remove the pore-forming agent.

[0090] (4) Surface treatment: Pulse anodizing uses a mixed electrolyte of 0.4M sulfuric acid and 0.1M glycerol, voltage 18V, pulse frequency 450Hz, and treatment for 30 minutes to form an oxide film with a thickness of 5μm; then an Al2O3-ZrO2 composite ceramic coating with a thickness of 20μm is sprayed by atmospheric plasma, in which the ZrO2 content is 28%.

[0091] Example 3: This example provides a nanoscale alloy filter element, comprising a composite material with titanium alloy as the matrix. The composite material contains a gradient pore structure formed by a nano-reinforcing phase and a composite pore-forming agent. The nano-reinforcing phase includes graphene nanosheets and silicon carbide nanoparticles, and the composite pore-forming agent includes nano-sized sodium chloride and micron-sized ammonium bicarbonate. The pore size of the gradient pore structure gradually increases from the surface layer to the inner layer, with the surface layer pore size being 50-100 nm, the middle layer pore size being 1-5 μm, and the inner layer pore size being 10-30 μm.

[0092] In this embodiment, the composite material of the filter element is composed of the following components: the composite material includes the following components by mass percentage: 94.0 wt% titanium alloy, 1.2 wt% graphene nanosheets, 1.0 wt% silicon carbide nanoparticles, and 18 wt% composite pore-forming agent. The composite pore-forming agent is composed of nano-sized sodium chloride and micron-sized ammonium bicarbonate. The nano-sized sodium chloride has a particle size of 100 nm, and the micron-sized ammonium bicarbonate has a particle size of 5 μm. The mass ratio of the two is 3:1.

[0093] Preferably, in this embodiment, the TC4 titanium alloy powder has an oxygen content of 0.11 wt% and a particle size of 30 μm, containing 1.7 wt% niobium and 0.6 wt% La2O3. The niobium has a particle size of 10 μm and a purity of 99.9%; the La2O3 has a particle size of 10 nm; the graphene nanosheets contain 1.2 wt% with a monolayer ratio of 97% and a lateral dimension of 12 μm. The silicon carbide nanoparticles have an α-phase content of 93% and a particle size of 40 nm.

[0094] On the other hand, this embodiment also provides a method for preparing the above-mentioned filter element, the specific steps of which are as follows:

[0095] (1) Powder pretreatment: Graphene nanosheets were plasma etched at a power of 320W and an argon flow rate of 2L / min for 6 minutes, and then treated with 2.2wt% KH560 silane coupling agent at 70℃ for 2.5 hours; Niobium powder was soaked in 6% hydrofluoric acid solution for 12 minutes.

[0096] (2) Mixing: First step ball milling: titanium alloy powder, niobium powder and La2O3 are ball milled at 420 r / min for 4.5 hours with a ball-to-material ratio of 8:1; Second step ball milling: the treated graphene, silicon carbide and composite pore-forming agent are added and ball milled at 220 r / min for 2.5 hours.

[0097] (3) Sintering: Low-temperature debinding is carried out under the protection of argon flow rate of 9L / min, and the temperature is increased to 320℃ at 6℃ / min and held for 1.2 hours; high-temperature sintering is carried out at 1120℃ for 3 hours; hot isostatic pressing is carried out at 940℃ and 160MPa for 2.5 hours; then soaking in 85℃ hot water for 3.5 hours, and then ultrasonic cleaning with 550W power for 1.2 hours to remove the pore-forming agent.

[0098] (4) Surface treatment: Pulse anodizing uses a mixed electrolyte of 0.6M sulfuric acid and 0.12M glycerol, voltage 22V, pulse frequency 550Hz, and treatment for 35 minutes to form an 8μm thick oxide film; then an Al2O3-ZrO2 composite ceramic coating with a thickness of 30μm is sprayed by atmospheric plasma, in which the ZrO2 content is 32%.

[0099] Comparative Example 1: This comparative example uses a 316L stainless steel filter element (ordinary alloy filter element). The difference from Example 1 is that it does not contain a titanium alloy matrix, nano-reinforcing phase, or gradient pore structure. Its material consists only of 316L stainless steel powder with a particle size of 50 μm, and no pore-forming agents or nano-additives are added. During preparation, it is directly sintered at 1200°C for 4 hours without surface treatment.

[0100] Comparative Example 2: The difference between this comparative example and Example 1 is that the composite pore-forming agent is a single micron-sized ammonium bicarbonate with a particle size of 3μm, which makes the pore structure uniform with a size between 5-10μm and no gradient pore structure.

[0101] In this comparative example, the material composition is the same as in Example 1, except that the composite pore-forming agent (15 wt%) is entirely micron-sized ammonium bicarbonate. In the preparation method, except that the pores formed after the removal of the pore-forming agent have no gradient difference, the remaining steps are the same as in Example 1.

[0102] Comparative Example 3: The difference between this comparative example and Example 1 is that it does not contain graphene nanosheets and silicon carbide nanoparticles (no nano-reinforcing phase).

[0103] In this comparative example, the material composition consists of 97.0 wt% TC4 titanium alloy powder, which includes 1.5 wt% niobium and 0.5 wt% La2O3, and 15 wt% composite pore-forming agent. The remainder is the same as in Example 1. In the preparation method, no nano-reinforcing phase is added during the mixing step; the rest is the same as in Example 1.

[0104] Comparative Example 4: The difference between this comparative example and Example 1 is that the graphene nanosheets were not subjected to plasma etching and silane coupling agent treatment, and the niobium powder was not subjected to hydrofluoric acid activation treatment (no powder pretreatment).

[0105] The material composition of this comparative example is the same as that of Example 1. In the preparation method, the powder pretreatment step is omitted, and untreated graphene nanosheets and niobium powder are directly mixed. The remaining steps are the same as in Example 1.

[0106] Comparative Example 5: The difference between this comparative example and Example 1 is that the sintering process does not use segmented sintering, but sintering at a single temperature, holding at 1100°C for 4 hours, and does not perform low-temperature debinding and hot isostatic pressing (non-segmented sintering).

[0107] The material composition of this comparative example is the same as that of Example 1. In the preparation method, the mixed powder is directly heated to 1100°C and sintered for 4 hours, and the remaining steps are the same as in Example 1.

[0108] Comparative Example 6: The difference between the comparative example and Example 1 is that the amount of composite pore-forming agent, graphene nanosheets and silicon carbide nanoparticles added in the raw material components is lower than the relevant parameter range in the claims. The composite pore-forming agent is 8 wt% (nano-sized sodium chloride and micron-sized ammonium bicarbonate mass ratio 8:2), the graphene nanosheets are 0.5 wt%, and the silicon carbide nanoparticles are 0.3 wt%.

[0109] In this comparative example, TC4 titanium alloy powder accounts for 91.2 wt%, which includes 1.5 wt% niobium and 0.5 wt% La2O3, with the remainder being the same as in Example 1. The preparation method is the same as in Example 1.

[0110] Comparative Example 7: The difference between this comparative example and Example 1 is that the amount of composite pore-forming agent, graphene nanosheets and silicon carbide nanoparticles added in the raw material components exceeds the relevant parameter range in the claims. The composite pore-forming agent is 25 wt% (nano-sized sodium chloride and micron-sized ammonium bicarbonate mass ratio 8:2), the graphene nanosheets are 2.0 wt%, and the silicon carbide nanoparticles are 1.5 wt%.

[0111] In this comparative example, TC4 titanium alloy powder accounted for 71.5 wt%, including 1.5 wt% niobium and 0.5 wt% La2O3, with the remainder consistent with Example 1. The preparation method was the same as in Example 1, but severe agglomeration of nanoparticles occurred during mixing.

[0112] Any numerical values ​​cited herein include all values ​​ranging from a lower limit to an upper limit, increasing by one unit, with at least two units between any lower and any higher value. For example, if the quantity of a component or the value of a process variable (e.g., temperature, pressure, time, etc.) is described as being from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, the purpose is to illustrate that values ​​such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 are also explicitly listed in this specification. For values ​​less than 1, a unit is appropriately considered to be 0.0001, 0.001, 0.01, 0.1, etc. These are merely examples intended for explicit expression, and it can be assumed that all possible combinations of values ​​listed between the minimum and maximum values ​​are similarly explicitly stated in this specification.

[0113] Unless otherwise stated, all ranges include the endpoints and all numbers between them. The terms "approximately" or "about" used with ranges apply to both endpoints of the range. Thus, "approximately 20 to 30" is intended to cover "approximately 20 to approximately 30," including at least the specified endpoints.

[0114] It should be understood that the above description is for illustrative purposes and not for limitation. Many embodiments and applications beyond the provided examples will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the invention should not be determined by reference to the above description, but rather by reference to the appended claims and the full scope of their equivalents. For purposes of completeness, all articles and references, including patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the preceding claims is not intended as a waiver of that subject matter, nor should it be construed as an indication that the inventors have not considered that subject matter as part of the disclosed inventive subject matter.

[0115] The present invention has been described by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvement made by adopting the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, shall be within the protection scope of the present invention.

Claims

1. A nanoscale alloy filter element, characterized in that, The invention includes a composite material based on a titanium alloy, wherein the composite material contains a gradient pore structure formed by a nano-reinforcing phase and a composite pore-forming agent; the nano-reinforcing phase includes graphene nanosheets and silicon carbide nanoparticles; the composite pore-forming agent includes nano-sized sodium chloride and micron-sized ammonium bicarbonate; the gradient pore structure has a gradually increasing pore size from the surface layer to the inner layer, with a surface pore size of 50-100 nm, a middle layer pore size of 1-5 μm, and an inner layer pore size of 10-30 μm. According to claim 1, the nanoscale alloy filter element is characterized in that the composite material comprises the following components by mass percentage: 94.0-96.5 wt% titanium alloy, 0.8-1.2 wt% graphene nanosheets, 0.6-1.0 wt% silicon carbide nanoparticles, and 12-18 wt% composite pore-forming agent; and the mass ratio of nanoscale sodium chloride to micron-scale ammonium bicarbonate in the composite pore-forming agent is (7-8):(2-3).

2. The nanoscale alloy filter element according to claim 2, characterized in that, The titanium alloy is TC4 titanium alloy, and the titanium alloy also contains 1.3-1.7 wt% niobium and 0.4-0.6 wt% rare earth oxides; And / or, the oxygen content of the titanium alloy is ≤0.12wt%, and the particle size is 15-30μm.

3. The nanoscale alloy filter element according to claim 3, characterized in that, The silicon carbide nanoparticles are particles with an α-phase content of ≥90% and a particle size of 20-40 nm; the rare earth oxide is La2O3 with a particle size of 5-10 nm; the niobium has a particle size of 5-10 μm and a purity of ≥99.9%.

4. The nanoscale alloy filter element according to any one of claims 1-4, characterized in that, The graphene nanosheets are monolayer graphene with a monolayer content ≥95%, a lateral dimension of 8-12 μm, and are treated with plasma etching and a silane coupling agent; the plasma etching power is 280-320 W, the argon flow rate is 1-2 L / min, and the treatment time is 4-6 minutes; the silane coupling agent is KH560 with a concentration of 1.8-2.2 wt%. And / or, the surface of the filter element is sequentially provided with an anodic oxide film and a ceramic coating; the thickness of the anodic oxide film is 5-8 μm, and the ceramic coating is an Al2O3-ZrO2 composite ceramic coating with a thickness of 20-30 μm, wherein the ZrO2 content is 28-32%.

5. A method for preparing a nanoscale alloy filter element, used to prepare the nanoscale alloy filter element as described in any one of claims 1-5, characterized in that, Includes the following steps: (1) Powder pretreatment: Graphene nanosheets were subjected to plasma etching and silane coupling agent treatment, and niobium powder was subjected to hydrofluoric acid solution activation treatment; (2) Mixing: Titanium alloy powder, niobium powder and rare earth oxides are ball-milled in the first step, and then the treated graphene nanosheets, silicon carbide nanoparticles and composite pore-forming agent are added for the second step of ball milling. (3) Sintering: The mixed powder is sintered in stages, including low-temperature debinding, high-temperature sintering and hot isostatic pressing, and then the pore-forming agent is removed; (4) Surface treatment: The sintered blank is subjected to anodizing and ceramic coating spraying in sequence.

6. The preparation method according to claim 6, characterized in that, In step (1), the mass fraction of the hydrofluoric acid solution is 4-6%, and the soaking time of the niobium powder is 8-12 minutes; During the silane coupling agent treatment, graphene nanosheets are dispersed in an ethanol solution, and after adding the silane coupling agent, the mixture is stirred at 60-70°C for 1.5-2.5 hours.

7. The preparation method according to claim 6, characterized in that, In step (1), the mass fraction of the hydrofluoric acid solution is 4-6%, and the soaking time of the niobium powder is 8-12 minutes; During the silane coupling agent treatment, graphene nanosheets are dispersed in an ethanol solution, and after adding the silane coupling agent, the mixture is stirred at 60-70°C for 1.5-2.5 hours.

8. The preparation method according to claim 7, characterized in that, In step (2), the first ball milling speed is 380-420 r / min, the time is 3.5-4.5 hours, and the ball-to-material ratio is 8:1; the second ball milling speed is 180-220 r / min, and the time is 1.5-2.5 hours.

9. The preparation method according to claim 8, characterized in that, In step (3), the low-temperature degumming is carried out under argon protection, with an argon flow rate of 7-9 L / min, and the temperature is increased to 280-320℃ at 4-6℃ / min and held for 0.8-1.2 hours; The high-temperature sintering temperature is 1080-1120℃, and the holding time is 2-3 hours; And / or, the hot isostatic pressing treatment is performed at a temperature of 900-940℃, a pressure of 140-160MPa, and a holding time of 1.5-2.5 hours; And / or, when removing the pore-forming agent, first soak it in hot water at 75-85℃ for 2.5-3.5 hours, and then use ultrasonic cleaning with 450-550W power for 0.8-1.2 hours.

10. A steam purification device, characterized in that, Includes the nanoscale alloy filter element as described in any one of claims 1-5; And / or, the steam purification equipment has a sodium ion removal rate of ≥99.95% in the steam and a steam flux of 750-850 L / (m²・h).

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