Metallic glass composite gradient filter material and preparation method thereof

Abstract

The invention belongs to the technical field of metal-based composite filter materials, and particularly relates to a metal glass composite gradient filter material and a preparation method thereof. The method comprises the following steps: 1) preparing glass slurry by taking a metal fiber felt as a base material, and coating the glass slurry on the surface of the metal fiber felt for surface drying to form a metal glass composite precursor; 2) connecting the metal glass composite precursor into a circuit system, electrifying to generate resistance heat, and performing Joule heat treatment to obtain a metal glass composite; and 3) coating the glass slurry on the surface of the metal glass composite body again, and then carrying out solid-phase sintering to obtain the metal glass composite gradient filter material with the gradient pore structure. Through cooperation of Joule thermal instantaneous metallurgical bonding and low-temperature solid-phase diffusion sintering, a stable gradient structure of metal-spinel-compact glass-porous glass is creatively constructed, and the interface bonding strength of heterogeneous materials is greatly improved; meanwhile, gradient pores are effectively formed, the filtering precision is greatly improved, and the filtering flux is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of metal-based composite filter material technology, and particularly relates to a metal-glass composite gradient filter material and its preparation method. Background Technology

[0002] Stainless steel sintered fiber felt possesses advantages such as high porosity, good three-dimensional connectivity, high mechanical strength, and excellent temperature resistance, maintaining good structural stability under high pressure differentials and complex operating conditions. Therefore, it has been widely used in various gas purification, liquid filtration, and solid-liquid separation applications. However, the pore size of single-metal sintered fiber felt is mostly concentrated in the range of 5–50 μm, which can only meet the needs of pre-filtration or coarse filtration, making it difficult to effectively retain submicron and micron-sized particles. Simply reducing the pore size through compaction or extending the sintering time will lead to a decrease in overall porosity, flow channel blockage, a significant increase in pressure drop, and a marked reduction in overall throughput. Simultaneously, during long-term service in highly corrosive media containing chloride ions, the surface of stainless steel fiber felt is prone to pitting corrosion, crevice corrosion, and localized failure, limiting both filtration performance and service life.

[0003] Inorganic glass or ceramic filter membranes possess excellent chemical stability, high-temperature resistance, and corrosion resistance. They can achieve fine filtration with submicron or even smaller pore sizes through pore-forming processes, making them suitable for harsh environments such as acidic, oxidizing, or chlorine-containing media. However, these materials are brittle and have poor resistance to mechanical and thermal shock, and are sensitive to bending, vibration, and temperature gradients. When used directly as self-supporting filter membranes, they often require significant thickness or complex support structures to ensure strength, increasing cost and process complexity. If loaded onto a metal substrate, the significant difference in thermal expansion coefficients between glass or ceramic and metal can easily lead to thermal stress concentration during high-temperature sintering and subsequent thermal cycling, causing coating cracking, blistering, or even peeling.

[0004] Therefore, current filter media are mainly developed and applied using single materials, such as metal, ceramic, or polymer filter media. Composite filter media are not yet available on the market. While combining different materials can overcome the limitations of single-material applications, methods for combining different materials are currently lacking. In traditional coating processes, applying coatings of different materials also presents technological challenges. For example, when applying ceramic coatings to metal surfaces, the coating and metal substrate are mainly bonded through mechanical interlocking or physical adsorption, resulting in insufficient interfacial transition. Under high-flow-rate erosion, corrosive media, and temperature fluctuations, interfacial cracking and peeling easily occur, leading to low long-term reliability. Therefore, there is an urgent need for a metal-glass composite gradient filter media with a designable structure, a clear pore size gradient, strong bonding, and simple processing, along with its preparation method, to solve the above problems. Summary of the Invention

[0005] To address the problems of current porous stainless steel filter materials, such as difficulty in reducing pore size, significant decrease in flux while improving filtration accuracy, and easy cracking and peeling due to insufficient interfacial bonding between traditional glass coatings and metal substrates, this invention proposes a metal-glass composite gradient filter material and a method for preparing the filter material.

[0006] The main objective of this invention is: I. It simultaneously retains the toughness of metal filter media and the chemical stability and filtration accuracy of glass filter media, thus constructing a metal-glass composite filter media system. Second, ensure good bonding between the metal and glass; Third, ensure that the preparation process is simple and efficient, and suitable for large-scale production.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] A method for preparing a metal-glass composite gradient filter material. The method includes: 1) Using metal fiber felt as the substrate, a glass slurry is prepared and coated onto the surface of the metal fiber felt to form a metal-glass composite precursor. 2) After the metal-glass composite precursor is connected to the circuit system, it undergoes Joule heat treatment to generate resistance heat, thus obtaining the metal-glass composite. 3) After coating the surface of the metal-glass composite with glass slurry again, solid-phase sintering is carried out to obtain a metal-glass composite gradient filter material with a gradient pore structure.

[0009] As a preferred option Step 1) The metal fiber felt is stainless steel fiber felt; For the specific implementation of this invention, the main material is 316L stainless steel fiber felt, but in actual production and use, it should not be limited to only this one grade of stainless steel fiber felt. The stainless steel fiber felt is pretreated before use.

[0010] As a preferred option The pretreatment includes cleaning and activation; The activation solution used for activation is a 3-10 wt% hydrochloric acid aqueous solution, and the activation treatment time is 1-10 min; After activation, the product is dried at 50–70 °C for 1–3 h.

[0011] As a preferred option Step 1) The glass slurry is made of glass powder with a softening point ≤460 ℃, ground to D. 90 After the particle size is ≤5 μm, it is mixed with an organic solvent at a mass ratio of 1:(1~3) and stirred until homogeneous to obtain the final product; Specifically, for the technical solution of this invention, it is of particular importance that the selected glass powder must be zinc-containing glass powder, usually glass powder with a zinc oxide content of about 20-30%, to ensure that the Joule heat treatment of this invention can achieve the best technical effect.

[0012] As a preferred option The coating in steps 1) and 3) is performed by dip coating.

[0013] As a preferred option Step 2) The process of generating Joule heat by energizing is controlled with an energizing current of 15-25 A and an energizing duration of 5-30 s.

[0014] As a preferred option Step 2) The Joule heat treatment is performed in a protective atmosphere.

[0015] As a preferred option Step 3) The solid-state sintering temperature is controlled at 430–480 °C, and the sintering time is 30–60 min.

[0016] A metal-glass composite gradient filter material.

[0017] The core of this invention lies in the use of a two-step composite process that combines "Joule heating pre-fabricated dense transition layer" with "low-temperature solid-state diffusion sintering". Through a unique interface control mechanism, it solves the problem of poor adhesion of traditional coatings. On the one hand, the instantaneous high temperature generated by Joule heating rapidly melts the bottom glass powder and fully wets the metal surface. During this melting and wetting process, the high temperature further induces the ZnO in the glass component to react with the Cr on the metal surface to form Cr2O3. Then, ZnO and Cr2O3 react to form a thermodynamically stable zinc-chromium spinel ZnCr2O4 transition layer, thus realizing a qualitative change in the physical anchoring and chemical metallurgical bonding between the glass layer and the metal substrate. On the other hand, the subsequently coated glass powder no longer directly contacts the metal, but is attached to the dense glass layer pre-fabricated by Joule heating based on the principle of "homogeneous bonding". Utilizing the perfect thermal matching and compatibility between the same materials, a high degree of interface fusion is formed during low-temperature sintering, thereby constructing a stable gradient structure composed of "metal skeleton - spinel layer - dense glass anchoring layer - porous glass functional layer", which significantly improves the filter material's anti-stripping ability and corrosion resistance life under complex working conditions. This technology, while maintaining the high strength and three-dimensional interconnected macroporous skeleton of 316L sintered fiber felt, achieves comprehensive optimization of filtration accuracy, flux and corrosion resistance through a controllable fine-pore glass layer and a reasonable gradient pore structure design. Compared with the existing metal-glass composite filter material preparation process, it has obvious structural and process advantages.

[0018] Specifically, the first step is to pretreat the stainless steel, which includes cleaning and activation. Cleaning aims to remove contaminants such as grease and dust from the fiber surface, ensuring good wettability of the glass slurry. The hydrochloric acid activation step is particularly crucial. A 3–10 wt% dilute hydrochloric acid solution can gently erode and renew the passivation film on the stainless steel surface within 1–10 minutes, exposing a fresher and more active metal surface without significantly damaging the strength of the fiber itself. This may also create micro-roughness, increasing the specific surface area and mechanical anchoring points for subsequent glass melt wetting. This creates an optimal surface condition for the rapid interfacial reaction during the Joule heat treatment stage.

[0019] While most glass powders with melting points meeting the requirements of this invention can be used to prepare gradient filter materials, zinc-containing (i.e., ZnO-containing) glass generally performs best. This is because ZnO effectively lowers the melting temperature and high-temperature viscosity of glass, making it easier to flow and spread under the instantaneous high temperatures generated by Joule heating. On the other hand, under the high temperatures generated by Joule heating (although the overall process is brief, the local interface temperature can be extremely high), the ZnO in the glass melt reacts with the Cr enriched on the activated 316L surface to form zinc chromium spinel (ZnCr2O4). The spinel structure (AB2O4) has high thermodynamic stability and good structural compatibility with both metals and glass, forming a thin layer between the metal and glass with a gradient transition in chemical composition, crystal structure, and coefficient of thermal expansion. This achieves a qualitative change from physical anchoring to chemical metallurgical bonding, and such interfacial reactions can significantly improve coating adhesion. Further control of glass particle size is to make it more reactive during Joule heat treatment, resulting in faster and more uniform melting. Meanwhile, fine particles are beneficial for preparing slurries with moderate solid content and good stability, ensuring that they can better penetrate into the pores of the metal fiber felt surface during impregnation and coating, forming an initial, uniform composite precursor, rather than simply accumulating on the surface.

[0020] Based on the above material combination, the most crucial processing step in this invention is Joule heat treatment. The coated and surface-dried "metal-glass composite precursor" is connected to the circuit system. Utilizing the inherent resistance of the stainless steel fiber felt, Joule heat is generated when electricity is applied. Because metal fibers have good conductivity and low heat capacity, and the heat is concentrated within the fiber network, the temperature of the fibers and the glass powder adhering to their surface can be rapidly raised to above or even higher than the glass softening point in a very short time. For the technical solution of this invention, the temperature is typically controlled to 700–900 °C. This localized ultra-high temperature field causes the zinc-containing glass powder adhering to the surface of the metal fibers to melt rapidly. Under capillary force, the high-temperature melt fully wets and spreads on the activated metal fiber surface. Simultaneously, the high temperature provides a strong kinetic driving force for the solid-phase reaction between ZnO and Cr2O3. The resulting ZnCr2O4 spinel layer acts like "chemical glue," connecting the glass and metal at the atomic scale. This bonding strength is far superior to physical adsorption. The result of this step is not the formation of a porous filter layer, but rather the formation of an extremely thin, continuous, and dense glass layer on the surface of each metal fiber, typically ranging from several micrometers to tens of micrometers in thickness. This glass layer is firmly bonded to the metal through a spinel transition layer, and its main function is "anchoring," providing a stable and highly compatible substrate for the subsequent construction of porous functional layers. It effectively isolates the corrosive medium from direct contact with the metal substrate, laying the foundation for long-term corrosion resistance.

[0021] After obtaining a composite with a stable "metal-spinel-dense glass" interface, a second coating and low-temperature sintering are performed. The second coating, a glass slurry, adheres to the existing dense glass anchoring layer of the same composition. Because the materials are identical, there is no issue of thermal expansion coefficient mismatch, resulting in perfect compatibility. This temperature is far lower than the instantaneous, localized ultra-high temperatures produced by Joule heat treatment, but sufficient to induce viscous flow and solid-phase diffusion on the surface of the glass particles. At the contact points, the particles neck, grow, and connect, forming robust sintering necks, thereby solidifying the particle network into a monolithic porous structure. Due to the lower temperature, the glass particles do not completely melt and collapse, thus preserving the pores formed by particle accumulation. By controlling the particle size distribution of the glass powder, the solid content of the slurry, and the sintering temperature / time, the pore size distribution and porosity of the final functional layer can be precisely controlled.

[0022] The beneficial effects of this invention are: This invention creatively constructs a stable gradient structure of "metal-spinel-dense glass-porous glass" through the synergy of Joule heating instantaneous metallurgical bonding and low-temperature solid-state diffusion sintering. This significantly improves the bonding strength of the heterogeneous material interface between metal and glass, while effectively forming gradient pores, greatly improving filtration accuracy and ensuring filtration flux. Attached Figure Description

[0023] Figure 1 This is a cross-sectional SEM image of the metal-glass composite obtained in step 4) of Embodiment 1 of the present invention; Figure 2 This is a SEM-EDS characterization image of a cross-section of the metal-glass composite gradient filter material sample obtained in Example 1 of the present invention. Figure 3 This is a SEM image of the surface of the metal-glass composite gradient filter material sample obtained in Example 1 of the present invention. Figure 4 These are SEM images of the surface of some of the metal-glass composite gradient filter material samples obtained in Example 3 of this invention. Figure 5 This is a SEM image of a cross-section of the metal-glass composite gradient filter material sample obtained in Example 4 of the present invention. Detailed Implementation

[0024] The present invention will be further described clearly and in detail below with reference to specific embodiments and the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0025] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art. Example 1

[0026] A metal-glass composite gradient filter material is prepared by the following method: 1) 316L stainless steel sintered fiber felt was selected as the matrix. It was placed in acetone and anhydrous ethanol for 10 min of ultrasonic cleaning to remove surface oil and organic residue. Then it was immersed in 7 wt% hydrochloric acid aqueous solution for 5 min for activation treatment. After that, it was rinsed with deionized water until neutral and dried at 60 ℃ for 2 h to obtain pretreated 316L stainless steel sintered fiber felt. 2) Take glass powder (in this example, the zinc oxide content of the glass powder is approximately 25.5 wt%, and the softening point is approximately 402 ℃) and place it in a planetary ball mill for ball milling until D. 90 ≤5 μm, and then it is mixed with anhydrous ethanol at a mass ratio of 1:2 to obtain glass slurry; 3) The pretreated 316L stainless steel sintered fiber felt obtained in step 1) is immersed in the glass slurry obtained in step 2) for dip coating. Then it is taken out and left to stand at room temperature for 30 min to allow the solvent to fully evaporate. Then it is dried at 60 ℃ for 15 min to allow the slurry to be surface dry to obtain the metal-glass composite precursor. 4) Connect the metal-glass composite precursor to the power electrode and, in an argon atmosphere, use the resistance of the metal fiber matrix itself to generate Joule heating. Control the power parameters (in this example, 20 A current for 15 s) to rapidly heat the matrix, causing the attached glass powder to melt quickly and wet the surface of the metal fiber. After cooling, a uniform glass coating is formed in situ on the surface of the metal fiber to obtain the metal-glass composite. 5) The metal-glass composite obtained in step 4) is immersed again in the glass slurry obtained in step 2) for dip coating, and then solid-state sintering is carried out at 450 °C for 45 min in an air atmosphere. After cooling, the metal-glass composite gradient filter material is obtained.

[0027] The cross-sectional SEM characterization results of the metal-glass composite obtained in step 4) are as follows: Figure 1 As shown, a dense glass layer at the micrometer scale is formed after Joule heat treatment. This glass layer is tightly bonded to the substrate stainless steel fiber. The SEM and EDS characterization results of the cross-section of the metal-glass composite gradient filter material sample obtained in step 5) after solid-state sintering are shown below. Figure 2 As shown. Figure 2 It can be seen that a gradient porous layer is further formed on the basis of the dense layer grown in step 4), and the surface SEM characterization results of this gradient porous layer are as follows. Figure 3 As shown. Combined with Figure 2 and Figure 3 It can be clearly seen that the technical solution of the present invention forms a gradient-ordered porous structure, and the Joule heat treatment effectively forms a dense transition layer. This transition layer forms a mutual diffusion bond with the stainless steel substrate, which effectively ensures the bonding stability. On this basis, the solid-state sintering in step 5) is also very stable due to its homogeneous growth and bonding. The pore diameter of the formed channels is mostly between 0.5 and 2.0 μm. Example 2

[0028] A metal-glass composite gradient filter material is prepared by the following method: 1) 316L stainless steel sintered fiber felt was selected as the matrix. It was placed in acetone and anhydrous ethanol for 10 min of ultrasonic cleaning to remove surface oil and organic residue. Then it was immersed in 7 wt% hydrochloric acid aqueous solution for 5 min for activation treatment. After that, it was rinsed with deionized water until neutral and dried at 60 ℃ for 2 h to obtain pretreated 316L stainless steel sintered fiber felt. 2) Take glass powder (in this example, the zinc oxide content of the glass powder is approximately 25.5 wt%, and the softening point is approximately 402 ℃) and place it in a planetary ball mill for ball milling until D. 90 ≤5 μm, and then it is mixed with anhydrous ethanol at a mass ratio of 1:2 to obtain glass slurry; 3) The pretreated 316L stainless steel sintered fiber felt obtained in step 1) is immersed in the glass slurry obtained in step 2) for dip coating. Then it is taken out and left to stand at room temperature for 30 min to allow the solvent to fully evaporate. Then it is dried at 60 ℃ for 15 min to allow the slurry to be surface dry to obtain the metal-glass composite precursor. 4) Connect the metal-glass composite precursor to the power electrode and, in an argon atmosphere, use the resistance of the metal fiber matrix itself to generate Joule heating. Control the power parameters (in this example, a current of 10-30 A and a processing time of 5-30 s) to rapidly heat the matrix, causing the attached glass powder to melt quickly and wet the surface of the metal fiber. After cooling, a uniform glass coating is formed on the surface of the metal fiber to obtain the metal-glass composite. 5) The metal-glass composite obtained in step 4) is immersed again in the glass slurry obtained in step 2) for dip coating, and then solid-state sintering is carried out at 450 °C for 45 min in an air atmosphere. After cooling, the metal-glass composite gradient filter material is obtained.

[0029] Samples with different current-joule heat treatment times were subjected to ultrasonic vibration tests and thermal shock stability tests (15 min in an ice water bath ↔ 15 min in an 80 ℃ hot water bath, 5 cycles) in an aqueous medium at 1500 W / 30 min.

[0030] The results are shown in the table below.

[0031]

[0032] In the table: the ultrasonic column data represents the mass loss rate after the ultrasonic vibration test, and the thermal shock column data represents the mass loss rate after the thermal shock stability test.

[0033] The data in the table above clearly shows that the appropriate current for the Joule heat treatment of this invention is approximately 15–25 A. Within this range, the optimal processing parameters can be effectively adjusted. However, when the current is too low (10 A, 15 s experimental group), the glass powder does not completely melt, and a large number of independent granular protrusions are still visible on the surface. The glass phase fails to fully spread and wet the metal fibers, resulting in a large accumulation of glass components on the surface during subsequent solid-state sintering, leading to the closure of the pores.

[0034] Excessive current can cause the instantaneous temperature to rise too high, resulting in enormous thermal stress between the glass and the metal substrate during the cooling process. The presence of this thermal stress will significantly deteriorate its performance in thermal shock tests, and even reducing the treatment time cannot effectively improve the situation.

[0035] It is evident that, as the core process of this invention, the magnitude of the processing current and the processing time of the Joule heat treatment will directly and significantly affect the overall structural stability. Example 3

[0036] A metal-glass composite gradient filter material is prepared by the following method: 1) 316L stainless steel sintered fiber felt was selected as the matrix. It was placed in acetone and anhydrous ethanol for 10 min of ultrasonic cleaning to remove surface oil and organic residue. Then it was immersed in 7 wt% hydrochloric acid aqueous solution for 5 min for activation treatment. After that, it was rinsed with deionized water until neutral and dried at 60 ℃ for 2 h to obtain pretreated 316L stainless steel sintered fiber felt. 2) Take glass powder (in this example, the zinc oxide content of the glass powder is approximately 25.5 wt%, and the softening point is approximately 402 ℃) and place it in a planetary ball mill for ball milling until D. 90 ≤5 μm, and then it is mixed with anhydrous ethanol at a mass ratio of 1:2 to obtain glass slurry; 3) The pretreated 316L stainless steel sintered fiber felt obtained in step 1) is immersed in the glass slurry obtained in step 2) for dip coating. Then it is taken out and left to stand at room temperature for 30 min to allow the solvent to fully evaporate. Then it is dried at 60 ℃ for 15 min to allow the slurry to be surface dry to obtain the metal-glass composite precursor. 4) Connect the metal-glass composite precursor to the power electrode and, in an argon atmosphere, use the resistance of the metal fiber matrix itself to generate Joule heat. Control the power parameters (in this example, 20 A current for 15 s) to rapidly heat the matrix, causing the attached glass powder to melt quickly and wet the surface of the metal fiber. After cooling, a uniform glass coating is formed on the surface of the metal fiber to obtain the metal-glass composite. 5) The metal-glass composite obtained in step 4) is immersed again in the glass slurry obtained in step 2) for dip coating, and then solid-state sintering is carried out in air atmosphere at 450 °C for 15 to 75 min. After cooling, the metal-glass composite gradient filter material is obtained.

[0037] The average pore size and filtration flux under the same conditions were characterized for samples with different solid-state sintering times. The filtration flux was compared with the sample of Example 1 (450 °C solid-state sintering for 45 min experimental group) as a benchmark.

[0038] The results are shown in the table below.

[0039]

[0040] In the table: the flux change rate is the ratio of the flux change of the corresponding experimental group to the experimental group sintered at 450 ℃ for 45 min. "-" indicates a decrease and "+" indicates an increase.

[0041] Characterization results show that with the extension of sintering time, the average pore size exhibits a trend of first increasing and then decreasing. This is due to the sintering necking that occurs during sintering, a process that stabilizes the microstructure. For example, the experimental group sintered at 450 °C for 15 min showed a mass loss of over 10% after ultrasonic vibration and thermal shock tests, while the experimental group sintered at 450 °C for 30 min showed a significant decrease in mass loss to less than 1%. When the sintering time was extended to 45 min, the mass loss reached a stable state of <0.1%. When the sintering time continued to be extended, such as... Figure 4 As shown, excessively long sintering time can also lead to a sharp decrease in pore size and flux, which is detrimental to filtration.

[0042] Similarly, too low a sintering temperature will lead to densification and a decrease in the sintering necking rate. When the sintering temperature reaches 410℃, the average pore size cannot be effectively expanded to more than 1 μm, the throughput is extremely low, and the stability is poor. When the sintering temperature is too high, reaching 490℃, the pores will be severely blocked, and the average pore size will shrink to close to 0.2 μm. Therefore, the optimal sintering temperature is between 430 and 470℃. Example 4

[0043] A metal-glass composite gradient filter material is prepared by the following method: 1) 316L stainless steel sintered fiber felt was selected as the matrix. It was placed in acetone and anhydrous ethanol for 10 min of ultrasonic cleaning to remove surface oil and organic residue. Then it was immersed in 7 wt% hydrochloric acid aqueous solution for 5 min for activation treatment. After that, it was rinsed with deionized water until neutral and dried at 60 ℃ for 2 h to obtain pretreated 316L stainless steel sintered fiber felt. 2) Take glass powder (in this example, the zinc oxide content of the glass powder is approximately 25.5 wt%, and the softening point is approximately 402 ℃) and place it in a planetary ball mill for ball milling until D. 90 ≤5 μm, and then it is mixed with anhydrous ethanol at a mass ratio of 1:2 to obtain glass slurry; 3) The pretreated 316L stainless steel sintered fiber felt obtained in step 1) is immersed in the glass slurry obtained in step 2) for dip coating. Then it is taken out and left to stand at room temperature for 30 min to allow the solvent to fully evaporate. Then it is dried at 60 ℃ for 15 min to allow the slurry to be surface dry to obtain the metal-glass composite precursor. 4) The metal-glass composite precursor obtained in step 3) is immersed in the glass slurry obtained in step 2) for dip coating, and then solid-state sintering is carried out at 450 °C for 45 min in an air atmosphere. After cooling, the metal-glass composite gradient filter material is obtained.

[0044] Cross-sectional SEM characterization of the sintered product as follows Figure 5 As shown, it is difficult to form effective interdiffusion, the resulting glass layer has low adhesion to the substrate, and the mass loss rate after ultrasonic vibration and thermal shock both reach more than 15%. Example 5

[0045] A metal-glass composite gradient filter material is prepared by the following method: 1) 316L stainless steel sintered fiber felt was selected as the matrix. It was placed in acetone and anhydrous ethanol for 10 min of ultrasonic cleaning to remove surface oil and organic residue. Then it was immersed in 7 wt% hydrochloric acid aqueous solution for 5 min for activation treatment. After that, it was rinsed with deionized water until neutral and dried at 60 ℃ for 2 h to obtain pretreated 316L stainless steel sintered fiber felt. 2) Take glass powder (in this example, the zinc oxide content of the glass powder is approximately 12.6 wt%, and the softening point is approximately 416 ℃) and place it in a planetary ball mill for ball milling until D. 90 ≤5 μm, and then it is mixed with anhydrous ethanol at a mass ratio of 1:2 to obtain glass slurry; 3) The pretreated 316L stainless steel sintered fiber felt obtained in step 1) is immersed in the glass slurry obtained in step 2) for dip coating. Then it is taken out and left to stand at room temperature for 30 min to allow the solvent to fully evaporate. Then it is dried at 60 ℃ for 15 min to allow the slurry to be surface dry to obtain the metal-glass composite precursor. 4) Connect the metal-glass composite precursor to the power electrode and, in an argon atmosphere, use the resistance of the metal fiber matrix itself to generate Joule heating. Control the power parameters (in this example, 20 A current for 15 s) to rapidly heat the matrix, causing the attached glass powder to melt quickly and wet the surface of the metal fiber. After cooling, a uniform glass coating is formed in situ on the surface of the metal fiber to obtain the metal-glass composite. 5) The metal-glass composite obtained in step 4) is immersed again in the glass slurry obtained in step 2) for dip coating, and then solid-state sintering is carried out at 450 °C for 45 min in an air atmosphere. After cooling, the metal-glass composite gradient filter material is obtained.

[0046] In this example, glass powder with a low zinc oxide content was used to prepare the filter material. Although the prepared product could also form a dense layer similar to the sample in Example 1, its bonding degree was significantly lower than that of the sample in Example 1. The mass loss rates after ultrasonic vibration and thermal shock reached approximately 3.2% and 1.9%, respectively, indicating a significant decrease in its bonding degree.

[0047] Through comparative experiments, the following experimental groups (zinc content 20.2%, softening point approximately 422 ℃, zinc content 21.9%, softening point approximately 431 ℃, zinc content 29.7%, softening point approximately 411 ℃) of glass powder all produced good preparation results, with ultrasonic and thermal shock mass loss rates both <0.1%. However, the following experimental groups (zinc content 17.6%, softening point approximately 430 ℃, zinc content 15.2%, softening point approximately 414 ℃, zinc content 28.6%, softening point approximately 453 ℃) of glass powder produced samples with ultrasonic and thermal shock mass loss rates both >1%, showing significant differences. However, the solid-state sintering temperature of the glass powder experimental group with a zinc content of 28.6% and a softening point of approximately 453 ℃ in step 5) increased to 470℃. The mass loss rate decreased after ℃, which indicates that the softening point of the glass powder should also be adapted to the solid-state sintering temperature, usually needing to be lower than the solid-state sintering temperature. Therefore, it is necessary to ensure that the softening point is ≤460 ℃.

Claims

1. A method for preparing a metal-glass composite gradient filter material, characterized in that, The method includes: 1) Using metal fiber felt as the substrate, a glass slurry is prepared and coated onto the surface of the metal fiber felt to form a metal-glass composite precursor. 2) After the metal-glass composite precursor is connected to the circuit system, it undergoes Joule heat treatment to generate resistance heat, thus obtaining the metal-glass composite. 3) After coating the surface of the metal-glass composite with glass slurry again, solid-phase sintering is carried out to obtain a metal-glass composite gradient filter material with a gradient pore structure.

2. The method for preparing a metal-glass composite gradient filter material according to claim 1, characterized in that, Step 1) The metal fiber felt is stainless steel fiber felt; The stainless steel fiber felt is pretreated before use.

3. The method for preparing a metal-glass composite gradient filter material according to claim 2, characterized in that, The pretreatment includes cleaning and activation; The activation solution used for activation is a 3-10 wt% hydrochloric acid aqueous solution, and the activation treatment time is 1-10 min; After activation, the product is dried at 50–70 °C for 1–3 h.

4. The method for preparing a metal-glass composite gradient filter material according to claim 1, characterized in that, Step 1) The glass slurry is made of glass powder with a softening point ≤460 ℃, ground to D. 90 After the particle size is ≤5 μm, it is mixed with an organic solvent at a mass ratio of 1:(1~3) and stirred until homogeneous.

5. The method for preparing a metal-glass composite gradient filter material according to claim 1 or 4, characterized in that, The coating in steps 1) and 3) is performed by dip coating.

6. The method for preparing a metal-glass composite gradient filter material according to claim 1, characterized in that, Step 2) describes the process of generating Joule heat by energizing the device. The energizing current is controlled to be 15–25 A, and the energizing time is 5–30 s.

7. A method for preparing a metal-glass composite gradient filter material according to claim 1 or 6, characterized in that, Step 2) The Joule heat treatment is performed in a protective atmosphere.

8. The method for preparing a metal-glass composite gradient filter material according to claim 1, characterized in that, Step 3) The solid-state sintering temperature is controlled at 430–480 °C, and the sintering time is 30–60 min.

9. A metal-glass composite gradient filter material prepared by any one of claims 1 to 8.

Images