Composite steel fiber and preparation method thereof

Abstract

The invention relates to a composite steel fiber and a preparation method thereof. The method comprises the following steps: carrying out plasma treatment on a steel fiber matrix to etch and activate the surface of the matrix to prepare first steel fibers; impregnating the first steel fiber with a metal salt solution, drying, and calcining to form a metal oxide on the surface of the first steel fiber to prepare a second steel fiber; reducing the metal oxide into a metal elementary substance through reducing gas under protective gas, then introducing a gas-phase carbon source, and carrying out chemical vapor deposition on the surface of the second steel fiber under the catalysis of the metal elementary substance to generate a carbon nanotube coating so as to prepare the composite steel fiber; the temperature of the chemical vapor deposition is 400 DEG C to 500 DEG C. The composite steel fiber is high in bonding strength, small in tensile strength loss and good in electrical conductivity.

Description

Technical Field

[0001] This application relates to the field of composite materials technology, and in particular to composite steel fibers and their preparation methods. Background Technology

[0002] Steel fibers, as a commonly used reinforcing material for cement concrete, can effectively overcome the inherent defects of cement matrix such as low tensile strength and high brittleness, and significantly improve the tensile, flexural strength, toughness and impact resistance of composite materials. Its reinforcement mechanism mainly relies on the energy consumed when the fiber is pulled out of the matrix.

[0003] However, the interfacial bonding between steel fibers and cement matrix on traditional smooth surfaces mainly relies on weak physical friction and mechanical anchoring forces, resulting in limited interfacial bonding strength. This can easily lead to premature pull-out of steel fibers, failing to fully realize their reinforcing potential, and may even become a weak link in the composite material due to insufficient interfacial bonding.

[0004] Therefore, traditional technologies still need improvement. Summary of the Invention

[0005] Therefore, it is necessary to provide a method for preparing composite steel fibers that have high bonding strength, low tensile strength loss, and good electrical conductivity.

[0006] The technical solution to the above-mentioned technical problems in this application is as follows:

[0007] This application provides a method for preparing composite steel fibers, comprising the following steps:

[0008] The first steel fiber was prepared by plasma treatment of the steel fiber matrix.

[0009] The first steel fiber is impregnated with a metal salt solution, dried, and then calcined to form a metal oxide on the surface of the first steel fiber, thereby preparing the second steel fiber.

[0010] Under a protective gas atmosphere, the metal oxide is reduced to a metallic element by a reducing gas. Then, a gaseous carbon source is introduced, and under the catalysis of the metallic element, a carbon nanotube coating is generated on the surface of the second steel fiber by chemical vapor deposition to prepare a composite steel fiber.

[0011] The temperature for chemical vapor deposition is 400℃~500℃.

[0012] The above-mentioned method for preparing composite steel fibers first involves plasma treatment of the steel fiber matrix to etch a rough structure on the surface of the steel fibers, increasing the specific surface area and preparing the first steel fiber. Next, the surface of the first steel fiber is impregnated with a metal salt solution, dried, and then calcined to form a metal oxide on the surface of the first steel fiber, serving as a catalyst precursor and preparing the second steel fiber. Subsequently, a reducing gas is introduced under a protective atmosphere to reduce the metal oxide to elemental metal, converting the catalyst precursor into an active catalyst. Then, a gaseous carbon source is introduced, and a continuous carbon nanotube coating is grown by vapor deposition at a specific temperature, which bonds firmly with the second steel fiber, thus preparing the composite steel fiber. Furthermore, compared with the traditional high-temperature CVD method (typically >650℃), the above-mentioned method effectively avoids thermal damage to the steel fiber matrix caused by high temperature, and avoids problems such as decreased strength and increased brittleness caused by high-temperature recrystallization and grain coarsening of the steel fiber. This ensures that the mechanical properties of the steel fiber as the reinforcing material matrix are fully preserved, thereby guaranteeing the reliability of the final composite product.

[0013] In some embodiments, the metal in the metal salt solution includes one or more of copper, iron, and nickel;

[0014] And / or, the concentration of the metal salt solution is 0.05M~0.1M;

[0015] And / or, the impregnation method includes using an equal-volume impregnation method.

[0016] In some embodiments, the calcination temperature is 350°C to 450°C, and the calcination time is 30 min to 60 min.

[0017] In some embodiments, the reduction temperature is 300°C to 400°C, and the time is 5 min to 30 min.

[0018] In some embodiments, the protective gas includes one or more of nitrogen, argon, and helium.

[0019] In some embodiments, the flow rate of the protective gas is 150 mL / min to 250 mL / min; and / or,

[0020] The flow rate of the reducing gas is 150 mL / min to 250 mL / min.

[0021] In some embodiments, the gaseous carbon source is selected from one or more of propylene, ethylene, acetylene, and methane.

[0022] In some embodiments, the flow rate of the gaseous carbon source is 150 mL / min to 300 mL / min.

[0023] In some embodiments, the plasma treatment has a power of 50W to 150W, a temperature of 80°C to 120°C, a time of 20min to 40min, and the gas type includes one or more of oxygen, nitrogen, and argon.

[0024] Another aspect of this application provides a composite steel fiber, which is obtained by the above-described method for preparing composite steel fibers. Detailed Implementation

[0025] The following detailed description, in conjunction with specific embodiments, illustrates a composite steel fiber and its preparation method according to this application. This application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0027] As used herein, the terms “and / or,” “or / and,” and “and / or” may include any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all the related listed items.

[0028] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the weights mentioned in the embodiments of this application can be well-known units of mass in the chemical industry, such as μg, mg, g, and kg.

[0029] In this application, numerical intervals (i.e., numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the aforementioned numerical intervals are considered continuous and include the two endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints. In this document, this is equivalent to directly listing every integer. For example, if t is an integer selected from 1 to 10, it means that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Furthermore, when multiple ranges are provided to describe features or characteristics, these ranges can be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0030] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0031] The standard unit of flow rate (SLM) is the "standard unit of flow rate" for gas, which refers to the volumetric flow rate of a gas under standard conditions (0°C, 1 standard atmosphere).

[0032] In this invention, mmol / L and mM both represent millimoles per liter and can be used interchangeably. mol / L and M both represent moles per liter and can be used interchangeably.

[0033] The applicant's long-term research has revealed that carbon nanotubes (CNTs) possess extremely high theoretical strength (approximately 100 GPa) and excellent electrical and thermal conductivity. Introducing CNTs into the cement matrix is ​​considered a key approach to preparing high-performance, multifunctional intelligent cement-based composite materials. Currently, there are several methods for introducing CNTs into the cement matrix: one is the direct dispersion method, where CNTs are directly dispersed as nanofillers in cement paste. This method suffers from problems such as easy agglomeration of CNTs, difficulty in dispersion in alkaline cement paste, and poor dispersion stability, leading to uneven CNT dispersion, difficulty in forming an effective reinforcing network, and high cost. Another method is the fiber loading method, where CNTs are pre-loaded onto the surface of macroscopic fibers (such as steel fibers, polypropylene fibers, etc.) before being incorporated into concrete. This method avoids the problems of direct CNT dispersion and can achieve local enrichment and directional distribution of CNTs in the matrix, resulting in higher efficiency. Among these methods, chemical vapor deposition (CVD) is one of the most effective methods for achieving in-situ growth of CNTs on fiber surfaces due to its relatively mature process and large-scale production capability.

[0034] However, traditional CVD processes face several key technical challenges when applied to steel fibers. One is high-temperature damage: conventional CVD growth of CNTs requires high temperatures (typically above 600℃, even 700℃). At these high temperatures, steel fibers undergo recrystallization, grain coarsening, and phase transformation, leading to severe degradation of their core mechanical properties such as tensile strength and hardness, thus losing their fundamental value as reinforcing materials. Another problem is catalyst deactivation and weak interfacial bonding: Catalyst particles such as Fe, Ni, and Co are typically introduced onto the surface of the steel fibers. During high-temperature processes, catalyst elements easily interdiffusion with elements in the steel matrix, leading to catalyst "poisoning" or sintering and agglomeration, resulting in loss of catalytic activity. Simultaneously, the CNTs grown at high temperatures are mostly physically attached to the matrix, with weak interfacial bonding, making them prone to detachment during the vigorous mixing and pouring of concrete.

[0035] Based on this, one embodiment of this application provides a method for preparing composite steel fibers, including steps S100 to S300.

[0036] Step S100: The steel fiber matrix is ​​subjected to plasma treatment to etch and activate the matrix surface, thereby preparing the first steel fiber.

[0037] Step S200: The first steel fiber is impregnated with a metal salt solution, dried, and then calcined to form a metal oxide on the surface of the first steel fiber, thereby preparing the second steel fiber.

[0038] Step S300: Under a protective gas atmosphere, the metal oxide is reduced to a metallic element by a reducing gas. Then, a gaseous carbon source is introduced, and under the catalysis of the metallic element, a carbon nanotube coating is formed on the surface of the second steel fiber by chemical vapor deposition to prepare a composite steel fiber. The temperature of the chemical vapor deposition is 400℃~500℃.

[0039] The above-mentioned method for preparing composite steel fibers first involves plasma treatment of the steel fiber matrix to etch a rough structure on the surface of the steel fibers, increasing the specific surface area and preparing the first steel fiber. Then, the surface of the first steel fiber is impregnated with a metal salt solution, dried, and calcined to form a metal oxide on the surface of the first steel fiber, serving as a catalyst precursor and preparing the second steel fiber. Subsequently, a reducing gas is introduced under a protective atmosphere to reduce the metal oxide to elemental metal, converting the catalyst precursor into an active catalyst. Then, a gaseous carbon source is introduced, and a continuous carbon nanotube coating is grown by vapor deposition at a specific temperature, which bonds firmly to the second steel fiber, thus preparing the composite steel fiber. Furthermore, compared with traditional high-temperature CVD methods (typically >650℃), the method of this application effectively avoids thermal damage to the steel fiber matrix caused by high temperatures, and avoids problems such as decreased strength and increased brittleness caused by high-temperature recrystallization and grain coarsening of the steel fibers. This ensures that the electrical properties of the steel fiber as the reinforcing material matrix are fully preserved, thereby guaranteeing the reliability of the final composite product.

[0040] It should be noted that the temperature range for vapor phase chemical deposition is "400℃~500℃", which includes the minimum and maximum values ​​within this range, as well as every value between these values. Specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, or 500℃; or any range consisting of any two of these values; for example, 430℃~480℃.

[0041] In some embodiments, the plasma treatment power is 50W~150W, the temperature is 80℃~120℃, and the time is 20min~40min. For example, the power can be 50W, 60W, 70W, 80W, 90W, 100W, 110W, 120W, 130W, 140W, or 150W; the temperature can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, or 120℃; and the time can be 20min, 21min, 22min, 23min, 24min, 25min, 26min, 27min, 28min, 29min, 30min, 31min, 32min, 33min, 34min, 35min, 36min, 37min, 38min, 39min, or 40min. In some examples, it can be any two of these values ​​as endpoints within a range, and the same applies below.

[0042] In some embodiments, the gas type in the plasma processing described above includes one or more of oxygen, nitrogen, and argon.

[0043] Understandably, the introduction of oxygen-containing functional groups to activate the surface creates a strong chemical interaction with the subsequent catalyst precursor, which is used to prepare composite steel fibers and further avoids the problem of easy peeling of CNT coatings in traditional physical coating methods.

[0044] In some embodiments, the oxygen flow rate of the plasma treatment is 20 SLM to 50 SLM, the distance between the spray gun and the fiber is 5 mm to 15 mm, and the scanning speed is 5 mm / s to 10 mm / s. For example, the air flow rate can be 20 SLM, 22 SLM, 24 SLM, 26 SLM, 28 SLM, 30 SLM, 32 SLM, 34 SLM, 36 SLM, 38 SLM, 40 SLM, 42 SLM, 44 SLM, 46 SLM, 48 SLM, or 50 SLM; the distance between the spray gun and the fiber can be 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, or 15 mm; and the scanning speed can be 5 mm / s, 6 mm / s, 7 mm / s, 8 mm / s, 9 mm / s, or 10 mm / s.

[0045] In some embodiments, the metal in the metal salt solution includes one or more of copper, iron, and nickel.

[0046] In some embodiments, the concentration of the metal salt solution is 0.05 M to 0.1 M. For example, the concentration can be 0.05 M, 0.06 M, 0.07 M, 0.08 M, 0.09 M or 0.1 M.

[0047] In some embodiments, the metal salts mentioned above include one or more of copper acetate, iron acetate, and copper nitrate.

[0048] In some embodiments, the solvent in the metal salt solution includes one or more of water and ethanol.

[0049] In some embodiments, the above-described impregnation method includes using an equal-volume impregnation method.

[0050] As can be understood, the equal-volume impregnation method refers to a method where the pore volume of the substrate and the volume of the impregnation solution are the same, and the impregnation solution just completely covers the pores on the substrate surface. By using the above-mentioned equal-volume impregnation method and controlling the concentration range of the metal salt solution, the catalyst loading can be controlled, ensuring that the catalyst precursor is uniformly distributed on the surface of the steel fiber. This avoids the agglomeration and growth of CNTs caused by excessive local catalyst concentration, thereby obtaining a uniformly covered and structurally consistent CNT reinforcement layer.

[0051] In some embodiments, the volume used in the above-described equal-volume impregnation method is 5 mL to 10 mL.

[0052] In some embodiments, the calcination temperature is 350°C to 450°C, and the calcination time is 30 min to 60 min. For example, the temperature can be 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, or 450°C; the time can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min.

[0053] It is understandable that while decomposing metal salts to form metal oxides, it is necessary to avoid aggravated oxidation of the steel fiber surface or initial lattice distortion.

[0054] In some embodiments, the reduction temperature is 300°C to 400°C, and the time is 5 min to 30 min. As examples, the temperature can be 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, or 400°C; and the time can be 5 min, 10 min, 15 min, 20 min, 25 min, or 30 min.

[0055] It is understandable that the metal oxide is reduced to active metal nanoparticles, and the reduction temperature is controlled within the above range to avoid recrystallization of steel fibers, while also avoiding excessive growth of metal particles and thermal interaction with the steel fiber matrix.

[0056] In some embodiments, the protective gas includes one or more of nitrogen, argon, and helium.

[0057] In some embodiments, the flow rate of the protective gas is 150 mL / min to 250 mL / min, and the flow rate of the reducing gas is 150 mL / min to 250 mL / min; as an example, the flow rate of the protective gas can be 150 mL / min, 160 mL / min, 170 mL / min, 180 mL / min, 190 mL / min, 200 mL / min, 210 mL / min, 220 mL / min, 230 mL / min, 240 mL / min, or 250 mL / min; the flow rate of the reducing gas can be 150 mL / min, 160 mL / min, 170 mL / min, 180 mL / min, 190 mL / min, 200 mL / min, 210 mL / min, 220 mL / min, 230 mL / min, 240 mL / min, or 250 mL / min.

[0058] In some embodiments, the gaseous carbon source is selected from one or more of propylene, ethylene, acetylene, and methane;

[0059] In some embodiments, the flow rate of the gaseous carbon source is 150 mL / min to 300 mL / min; as an example, the flow rate of the gaseous carbon source can be 150 mL / min, 160 mL / min, 170 mL / min, 180 mL / min, 190 mL / min, 200 mL / min, 210 mL / min, 220 mL / min, 230 mL / min, 240 mL / min, 250 mL / min, 260 mL / min, 270 mL / min, 280 mL / min, 290 mL / min, or 300 mL / min.

[0060] In some embodiments, the time for introducing the gaseous carbon source is 5 min to 60 min; as an example, the time can be 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min.

[0061] Another embodiment of this application provides a composite steel fiber, which is obtained by the above-described method for preparing composite steel fibers.

[0062] Understandably, when the composite steel fibers produced by the above preparation method are used in concrete systems, carbon nanotubes can fully exert their nanoscale reinforcement and bridging effects, forming a multi-scale synergistic effect mechanism with steel fibers. On the one hand, this significantly improves the macroscopic mechanical properties of composite materials (such as tensile strength, flexural toughness, and crack resistance), and on the other hand, it endows traditional cement-based materials with new intelligent sensing functions (such as stress / strain monitoring), achieving a dual breakthrough in mechanical enhancement and functional expansion.

[0063] To make the objectives, technical solutions, and advantages of this application clearer and more concise, the following specific embodiments are used for illustration, but this application is by no means limited to these embodiments. The embodiments described below are merely preferred embodiments of this application and can be used to describe this application, but should not be construed as limiting the scope of this application. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

[0064] To better illustrate this application, the following description, in conjunction with embodiments, further explains the content of this application.

[0065] The following is a specific embodiment. In the embodiment, the steel fiber matrix is ​​an end-hooked steel fiber, which is prepared by steel wire cutting method, with a length of 60mm, a diameter of 0.75mm, and a tensile strength of 1100MPa.

[0066] Example 1

[0067] (1) Place the steel fiber matrix in an analytical grade acetone (≥99.5%) solution, ultrasonically clean for 10 min, then take it out and clean it with anhydrous ethanol for 5 min, and dry it in an 80℃ drying oven for 30 min.

[0068] (2) The steel fiber matrix obtained in step (1) above is placed in a plasma device, and the oxygen flow rate is set to 40 SLM, the power to 100W, the distance between the spray gun and the fiber to 15mm, the scanning speed to 10mm / s, the sample temperature to 100℃, and the treatment is carried out for 30min to etch and activate the surface of the matrix to obtain the first steel fiber.

[0069] (3) Using a 0.05M aqueous solution of copper acetate as the impregnation liquid, the first steel fiber is impregnated by the equal volume impregnation method. Specifically, the pore volume of the surface of the first steel fiber is tested, and then an equal volume of impregnation liquid is prepared. Under stirring, 6 mL of impregnation liquid is slowly and evenly added to the first steel fiber so that it is completely absorbed and forms a wet material with a uniform appearance. Then, it is dried at 80℃ for 12 hours, placed in a muffle furnace, and the furnace temperature is raised from room temperature to 350℃ at a heating rate of 10℃ / min. The temperature is kept constant at 350℃ for 30 minutes to obtain the second steel fiber.

[0070] (4) The second steel fiber is placed in a tube furnace. The argon flow rate is set to 200 mL / min. The temperature is increased to 500℃ at a heating rate of 10℃ / min. Then, hydrogen is introduced. The hydrogen flow rate is set to 150 mL / min. The temperature is maintained for 5 min. The hydrogen flow rate is kept constant. The argon flow rate is set to 250 mL / min. The temperature is decreased to 450℃ at a cooling rate of 10℃ / min. Then, the acetylene flow rate is set to 150 mL / min. The temperature is maintained for 60 min. Carbon nanotubes are grown on the surface of the second steel fiber to obtain composite steel fiber.

[0071] Example 2

[0072] The preparation method of composite steel fiber in Example 2 is basically the same as that in Example 1. The difference is that in the process of preparing the second steel fiber in step (3), 0.05M copper acetate ethanol solution is used as impregnation liquid, and the first steel fiber is impregnated by the equal volume impregnation method, and then dried at 80℃ for 12h to obtain the second steel fiber.

[0073] Other conditions and parameters are the same as in Example 1. Please see Table 1 for specific test results.

[0074] Example 3

[0075] The preparation method of composite steel fiber in Example 3 is basically the same as that in Example 1. The difference is that in the process of preparing composite steel fiber in step (4), the temperature of vapor deposition is 400℃. Specifically, the hydrogen flow rate is kept constant, the argon flow rate is 250mL / min, and the temperature is lowered to 400℃ at a cooling rate of 10℃ / min. Then, the acetylene flow rate is set to 150mL / min, and the temperature is maintained for 60min. Carbon nanotubes are grown on the surface of the second steel fiber to obtain composite steel fiber.

[0076] Other conditions and parameters are the same as in Example 1. Please see Table 1 for specific test results.

[0077] Example 4

[0078] The preparation method of composite steel fiber in Example 4 is basically the same as that in Example 1. The difference is that in the process of preparing composite steel fiber in step (4), the temperature of vapor deposition is 500℃, specifically, the hydrogen flow rate is kept constant, the argon flow rate is 250mL / min, the temperature is 500℃, the acetylene flow rate is set to 150mL / min, and the temperature is kept for 60min. Carbon nanotubes are grown on the surface of the second steel fiber to obtain composite steel fiber.

[0079] Other conditions and parameters are the same as in Example 1. Please see Table 1 for specific test results.

[0080] Example 5

[0081] The preparation method of the composite steel fiber in Example 5 is basically the same as that in Example 1. The difference is that in the process of preparing the second steel fiber in step (3), the first steel fiber is impregnated by an aqueous solution of 0.05M ferric acetate as the impregnation liquid and by an equal volume impregnation method. Then, it is dried at 80°C for 12 hours to obtain the second steel fiber.

[0082] Other conditions and parameters are the same as in Example 1. Please see Table 1 for specific test results.

[0083] Example 6

[0084] The preparation method of the composite steel fiber in Example 6 is basically the same as that in Example 1. The difference is that in the process of preparing the second steel fiber in step (3), the first steel fiber is impregnated by an aqueous solution of 0.075M copper acetate and then dried at 80°C for 12 hours to obtain the second steel fiber.

[0085] Other conditions and parameters are the same as in Example 1. Please see Table 1 for specific test results.

[0086] Example 7

[0087] The preparation method of the composite steel fiber in Example 7 is basically the same as that in Example 1. The difference is that in the process of preparing the second steel fiber in step (3), the first steel fiber is impregnated by an aqueous solution of 0.1M copper acetate as the impregnation liquid and by an equal volume impregnation method. Then, it is dried at 80°C for 12 hours to obtain the second steel fiber.

[0088] Other conditions and parameters are the same as in Example 1. Please see Table 1 for specific test results.

[0089] Example 8

[0090] The preparation method of the composite steel fiber in Example 8 is basically the same as that in Example 1. The difference is that in the process of preparing the second steel fiber in step (3), the first steel fiber is impregnated by an aqueous solution of 0.05M copper nitrate as the impregnation liquid and by an equal volume impregnation method. Then, it is dried at 80°C for 12 hours to obtain the second steel fiber.

[0091] Other conditions and parameters are the same as in Example 1. Please see Table 1 for specific test results.

[0092] Example 9

[0093] The preparation method of composite steel fiber in Example 9 is basically the same as that in Example 1. The difference is that in the process of preparing the first steel fiber in step (1), the steel fiber matrix is ​​placed in a concentrated nitric acid solution (68wt%), activated at 60°C for 30 min, washed with water until the pH value is 7, and then dried at 150°C for 2 h to obtain the first steel fiber.

[0094] Other conditions and parameters are the same as in Example 1. Please see Table 1 for specific test results.

[0095] Example 10

[0096] The preparation method of composite steel fiber in Example 10 is basically the same as that in Example 1. The difference is that in the process of preparing the second steel fiber in step (3), 0.05M copper acetate aqueous solution is used as impregnation liquid. The first steel fiber is immersed in an excess of impregnation liquid (specifically 15mL) for impregnation, and then dried at 80℃ for 12h to obtain the second steel fiber.

[0097] Other conditions and parameters are the same as in Example 1. Please see Table 1 for specific test results.

[0098] Comparative Example 1

[0099] The preparation method of composite steel fiber in Comparative Example 1 is basically the same as that in Example 1. The difference is that in the process of preparing composite steel fiber in step (4), the temperature of vapor deposition is 600℃. Specifically, the hydrogen flow rate is kept constant, the argon flow rate is 250mL / min, and the temperature is raised to 600℃ at a heating rate of 10℃ / min. Then, the acetylene flow rate is set to 150mL / min, and the temperature is maintained for 60min. Carbon nanotubes are grown on the surface of the second steel fiber to obtain composite steel fiber.

[0100] Other conditions and parameters are the same as in Example 1. Please see Table 1 for specific test results.

[0101] test:

[0102] (1) The tensile strength retention rate of the composite steel fibers prepared in the examples and comparative examples was tested, and the specific reference standard was GB / T 228.1-2021.

[0103] (2) The fiber-cement matrix bond strength of the composite steel fibers prepared in the examples and comparative examples was tested, and the specific reference standard was JG / T 472-2015.

[0104] (3) The resistivity of the composite steel fibers prepared in the examples and comparative examples was tested, and the specific reference standard was GB / T 3048.2-2007.

[0105] Please see Table 1 for specific test results.

[0106] Table 1

[0107]

[0108] The data above show that, compared with the comparative example, the bond strength between the steel fiber and cement provided in this application is significantly enhanced, and the tensile strength loss of the steel fiber is relatively small. The steel fiber in this application exhibits good electrical conductivity in cement, which is beneficial for monitoring concrete structures.

[0109] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application specification.

[0110] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be defined by the appended claims.

Claims

1. A method for preparing composite steel fibers, characterized in that, The method comprises the following steps: plasma treating a steel fiber substrate to prepare a first steel fiber; immersing the first steel fiber in a metal salt solution, drying and then calcining to form a metal oxide on the surface of the first steel fiber, thereby preparing a second steel fiber; under a protective gas, reducing the metal oxide to a metal element by a reducing gas, and then introducing a gaseous carbon source to perform chemical vapor deposition on the surface of the second steel fiber to form a carbon nanotube coating under the catalysis of the metal element, thereby preparing a composite steel fiber; the temperature of the chemical vapor deposition is 400-500℃.

2. The method of claim 1, wherein the steel fiber is a complex steel fiber. the metal in the metal salt solution comprises one or more of copper, iron and nickel; and / or, the concentration of the metal salt solution is 0.05-0.1M; and / or, the immersing method comprises using an equal-volume immersing method.

3. The method of claim 1, wherein the steel fiber is a complex steel fiber. the temperature of the calcining is 350-450℃, and the time of the calcining is 30-60min.

4. The method of claim 1, wherein the steel fiber is a complex steel fiber. the temperature of the reducing is 300-400℃, and the time of the reducing is 5-30min.

5. The method of producing a multi-steel fiber according to any one of claims 1 to 4, characterized by the protective gas comprises one or more of nitrogen, argon and helium.

6. The method of making a steel fiber composite according to any one of claims 1 to 4, wherein the flow rate of the protective gas is 150-250mL / min; and / or, the flow rate of the reducing gas is 150-250mL / min.

7. The method of making a steel fiber composite according to any one of claims 1 to 4, wherein the gaseous carbon source is selected from one or more of propylene, ethylene, acetylene and methane.

8. The method of making a steel fiber composite according to any one of claims 1 to 4, wherein the flow rate of the gaseous carbon source is 150-300mL / min.

9. The method of making a steel fiber composite according to any one of claims 1 to 4, wherein the power of the plasma treatment is 50-150W, the temperature is 80-120℃, the time is 20-40min, and the gas type comprises one or more of oxygen, nitrogen and argon.

10. A composite steel fiber characterized by, obtained by using the method for preparing a composite steel fiber according to any one of claims 1-9.

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