A flexible high-infrared reflectivity bismuth-yttrate nanofiber membrane and a preparation method thereof

Abstract

This invention discloses a flexible bismuth yttrium nanofiber membrane with high infrared reflectivity and its preparation method. The preparation method includes: 1) adding yttrium source, bismuth source, and methylimidazole sequentially to a mixed solvent of ethanol / water, stirring for a certain time, then adding triethylamine, and continuing to stir until homogeneous to obtain a clear and transparent mixed solution; 2) vacuum distilling the mixed solution to obtain a homogeneous and stable precursor solution; 3) spinning the precursor solution into a precursor fiber membrane using electrospinning technology; 4) calcining the precursor fiber membrane directly in a high-temperature muffle furnace under air atmosphere for a period of time, followed by cooling under vacuum to obtain a flexible bismuth yttrium nanofiber membrane. The method of this invention effectively prepares a bismuth yttrium nanofiber membrane with both high infrared reflectivity and excellent flexibility. The resulting flexible bismuth yttrium nanofiber membrane with high infrared reflectivity has advantages such as low gas-solid thermal conductivity, good infrared reflective heat insulation performance, and long service life, demonstrating good practical value and broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of textile materials technology, specifically relating to a flexible bismuth yttrium nanofiber membrane with high infrared reflectivity and its preparation method. Background Technology

[0002] Ceramic fiber materials possess advantages such as excellent high-temperature resistance, strong oxidation resistance, good resistance to mechanical vibration, and excellent thermal and chemical stability, making them key high-temperature insulation materials required for thermal protection in fields such as aerospace vehicles, nuclear power generation, and chemical metallurgy. When ceramic fibers are further refined from the micrometer to the nanometer scale, the pore size between the fibers decreases, increasing the restriction on gas molecule movement and effectively reducing gas thermal conductivity. However, current ceramic fiber insulation materials generally have low infrared reflectivity, resulting in insufficient ability to block radiative heat transfer under high-temperature conditions, limiting further improvements in their high-temperature insulation performance. Bismuth yttrium oxide (YYO ... The main methods for preparing ceramic nanofiber materials include hydrothermal method, sol-gel method, spinning method, solid-liquid-gas phase method and electrospinning method. Among them, electrospinning method has become one of the main technologies for preparing ceramic nanofiber materials due to its advantages such as simple manufacturing equipment, wide range of spinnable raw materials and good fiber structure tunability.

[0003] Currently, there are no reports, either domestically or internationally, on the preparation of bismuth yttrium nanofibers using electrospinning technology. Chinese patent CN104495922A discloses a bismuth yttrium nanorod, its preparation method, and its applications. Using bismuth nitrate and yttrium nitrate hexahydrate as metal sources, bismuth yttrium nanorods were prepared via a hydrothermal synthesis method. However, the obtained bismuth yttrium nanorods suffer from problems such as small aspect ratio, poor diameter uniformity, and poor continuity, making them unsuitable for practical applications. Summary of the Invention

[0004] The purpose of this invention is to provide a flexible bismuth yttrium nanofiber membrane with high infrared reflectivity and its preparation method, which solves the problem of insufficient radiation heat transfer insulation capacity of existing ceramic fiber materials under high temperature conditions and further improves the high temperature heat insulation and protection performance, and prepares a high-efficiency ceramic nanofiber heat insulation material with both low gas-solid thermal conductivity and high infrared shielding performance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a flexible bismuth yttrium nanofiber membrane with high infrared reflectivity includes the following steps:

[0007] Step 1: Add yttrium source, bismuth source, and methylimidazole to a mixed solvent of ethanol and water in sequence, stir for 5-100 min, then add triethylamine and continue stirring for 5-100 min to obtain a clear and transparent mixed solution.

[0008] Step 2: Vacuum distillation is performed on the mixed solution to prepare a homogeneous and stable precursor solution;

[0009] Step 3: The precursor solution is spun into a precursor fiber membrane using electrospinning technology;

[0010] Step 4: Calcine the precursor fiber membrane in air atmosphere, and then cool it under vacuum to obtain a flexible bismuth yttrium nanofiber membrane.

[0011] The yttrium source is one of yttrium nitrate hexahydrate, yttrium chloride hexahydrate, or yttrium sulfate octahydrate;

[0012] The bismuth source is one of bismuth pentahydrate, bismuth sulfate, or bismuth oxychloride.

[0013] Further, in step 1, the molar ratio of yttrium source to bismuth source is 1:3, the ratio of the total mass of yttrium source and bismuth source to the amount of mixed solvent is 10g:10-90mL, the volume ratio of ethanol to water in the mixed solvent is 1:0.5-5, the molar ratio of yttrium source to methylimidazole is 1:0.5-2.5, and the molar ratio of yttrium source to triethylamine is 1:1-5.

[0014] Furthermore, in step 2, the parameters for vacuum distillation are: working pressure 10... 4 The working temperature is 30-85℃, and the working time is 5-30 min; the dynamic viscosity of the precursor solution is 0.5-10 Pa·s, and the conductivity is 5-60 mS / m.

[0015] Furthermore, in step 3, the electrospinning process parameters are as follows: under the conditions of a spinning environment temperature of 10-50℃ and a relative humidity of 10-80%, the precursor solution is injected at a flow rate of 0.5-15mL / h, and the spinneret is connected to a high-voltage power supply of 10-60kV for spinning. The distance between the receiving device and the spinneret is 5-35cm.

[0016] Further, in step 4, the calcination involves directly placing the precursor fiber membrane into a muffle furnace at a temperature of 600–1100°C, holding it at that temperature for 10–600 min, and then cooling the furnace chamber under vacuum at a pressure of 0–0.15 MPa.

[0017] The bismuth yttrium nanofiber membranes prepared by the above method have an average fiber diameter of 30–600 nm and a relative standard deviation of 0.2–10%, with an internal grain size of 3–65 nm. The flexible bismuth yttrium nanofiber membranes exhibit a softness of 0–100 mN, an average infrared reflectance ≥92% in the near-infrared band, and a thermal conductivity of 0.03–0.15 W / (m·K) in the 200–1200℃ range. The fiber diameter range represents the fiber thickness; smaller fiber diameters result in better single-fiber softness and improved membrane flexibility. The relative standard deviation can be used to characterize the uniformity of fiber diameter distribution; a smaller relative deviation value indicates better fiber uniformity. The grain size is closely related to the mechanical properties of single fibers; smaller grain sizes result in higher single-fiber mechanical properties and better membrane flexibility.

[0018] The first step of this invention involves sequentially adding a yttrium source, a bismuth source, and methylimidazole to a mixed solvent of ethanol / water. Yttrium and bismuth ions bridge and self-assemble with methylimidazole, forming long-chain molecules with a specific topological structure. Subsequently, the end-group ligand triethylamine is added. Triethylamine forms hydrogen bonds with yttrium and bismuth hydroxyl groups, reducing excessive condensation and coordination between molecular chains. The long chains of the topological molecules intertwine, forming a clear and transparent mixed solution with a certain degree of viscoelasticity. The mixed solution is then subjected to rapid vacuum distillation to obtain a homogeneous and stable spinnable precursor solution, increasing its viscosity and enhancing its spinnability. Electrospinning can be performed directly from this precursor solution without the addition of polymers, resulting in a higher inorganic component content in the precursor fiber and preventing the destruction of the intact skeletal structure of the single fiber due to the decomposition of a large amount of organic components. Because the system has a high content of inorganic components, the precursor fiber membrane is directly placed into a muffle furnace at a certain temperature without going through the traditional step heating method, which reduces the excessive growth of grains. After holding at the temperature for a certain time, the furnace is cooled under vacuum, avoiding the phase transformation and secondary growth of grains during the cooling process, thereby obtaining a flexible bismuth yttrium nanofiber membrane.

[0019] Beneficial effects:

[0020] (1) There are currently no reports on the preparation of bismuth yttrium nanofibers at home and abroad. The bismuth yttrium nanofibers prepared by the method provided in this invention have good continuity, few single fiber defects, and the preparation process is simple, highly operable and easy to industrialize.

[0021] (2) Unlike traditional ceramic nanofiber processing methods, no polymer is added to the precursor solution of the present invention, which avoids the ceramic fibers from breaking due to the instability and decomposition of a large number of organic components during calcination.

[0022] (3) The bismuth yttrium nanofiber membrane of the present invention has excellent properties such as good flexibility, high infrared reflectivity and good high temperature insulation, and is expected to obtain a high-efficiency ceramic fiber thermal insulation material with both low gas-solid thermal conductivity and high infrared shielding performance. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0024] Example 1

[0025] A method for preparing a flexible bismuth yttrium nanofiber membrane with high infrared reflectivity, comprising the following steps:

[0026] (1) Yttrium hexahydrate, bismuth pentahydrate and methylimidazole were dissolved in a mixed solvent of ethanol / water in sequence. After stirring for 30 min, triethylamine was added and stirring was continued for 60 min. The molar ratio of yttrium source, bismuth source, methylimidazole and triethylamine in the solution was 1:3:2:2. The ratio of yttrium source, bismuth source and solvent was 10 g:55 mL. The volume ratio of ethanol and water was 1:1. The mixed solution contained long chains of topological molecules that were intertwined.

[0027] (2) A homogeneous and stable precursor solution was prepared by vacuum distillation of the mixed solution. The parameters of vacuum distillation were: working pressure 5 Pa, working temperature 40 °C, and working time 15 min. The dynamic viscosity of the precursor solution was 8 Pa·s and the conductivity was 20 mS / m.

[0028] (3) The above precursor solution was spun into a precursor fiber membrane using electrospinning technology. The process parameters for electrospinning were: ambient temperature 26℃, relative humidity 52%, injection speed 2mL / h, voltage 44kV, and distance between the receiving device and the spinneret 27cm.

[0029] (4) The precursor fiber membrane was placed directly into a high-temperature muffle furnace at 800°C for 240 min in air atmosphere, and then cooled under vacuum at a pressure of 0.01 MPa to finally obtain a flexible bismuth yttrium nanofiber membrane.

[0030] The performance of the prepared flexible bismuth yttrium nanofiber membrane was tested. Referring to the national standard GB / T34520.2-2017 "Test Methods for Continuous Silicon Carbide Fibers Part 2: Single Fiber Diameter", the average diameter of the bismuth yttrium nanofibers was measured to be 350 nm, with a relative standard deviation of 2.4%. According to GB / T 23413-2009 "Determination of Grain Size and Microstrain of Nanomaterials - X-ray Diffraction Line Broadening Method", the bismuth yttrium nanofiber grain size inside the fiber was measured to be 33 nm. Referring to the national standard GB / T8942-2016 "Determination of Paper Softness", the softness of the flexible bismuth yttrium nanofiber membrane was measured to be 59 mN. According to the national standard GB / T 18319-2019 "Test Methods for Photothermal Storage Performance of Textiles", the average infrared reflectance of the flexible bismuth yttrium nanofiber membrane in the near-infrared band was measured to be 93%. According to 5990-2006 "Test Method for Thermal Conductivity of Refractory Materials (Hot Wire Method)," the thermal conductivity in the range of 200-1200℃ is measured to be 0.035-0.14 W / (m·K).

[0031] Example 2

[0032] A method for preparing a flexible bismuth yttrium nanofiber membrane with high infrared reflectivity, comprising the following steps:

[0033] (1) Yttrium chloride hexahydrate, bismuth nitrate pentahydrate and methylimidazole were dissolved in a mixed solvent of ethanol / water in sequence. After stirring for 30 min, triethylamine was added and stirring was continued for 90 min. The molar ratio of yttrium source, bismuth source, methylimidazole and triethylamine in the solution was 1:3:2.5:3. The ratio of yttrium source and bismuth source to solvent was 10 g:50 mL. The volume ratio of ethanol to water was 1:1. The mixed solution contained long chains of topological molecules that were intertwined.

[0034] (2) A homogeneous and stable precursor solution was prepared by vacuum distillation of the mixed solution. The parameters of vacuum distillation were: working pressure 1 Pa, working temperature 50 °C, and working time 10 min. The dynamic viscosity of the precursor solution was 7 Pa·s and the conductivity was 20 mS / m.

[0035] (3) The above precursor solution was spun into a precursor fiber membrane using electrospinning technology. The process parameters for electrospinning were: ambient temperature 32℃, relative humidity 55%, injection speed 3mL / h, voltage 36kV, and distance between the receiving device and the spinneret 21cm.

[0036] (4) The precursor fiber membrane was placed directly into a high-temperature muffle furnace at 900℃ for 120 min in air atmosphere, and then cooled under vacuum at a pressure of 0.1 MPa to finally obtain a flexible bismuth yttrium nanofiber membrane.

[0037] The performance was measured using the same testing method as in Example 1. The average diameter of the bismuth yttrium nanofibers was 420 nm, the relative standard deviation of the diameter was 3.2%, the bismuth yttrium grain size inside the fibers was 19 nm, the flexibility of the flexible bismuth yttrium nanofiber membrane was 25 mN, the average infrared reflectance of the flexible bismuth yttrium nanofiber membrane in the near-infrared band was 94%, and the thermal conductivity in the range of 200–1200 °C was 0.036–0.108 W / (m·K).

[0038] Example 3

[0039] A method for preparing a flexible bismuth yttrium nanofiber membrane with high infrared reflectivity, comprising the following steps:

[0040] (1) Yttrium sulfate octahydrate, bismuth nitrate pentahydrate and methylimidazole were dissolved in a mixed solvent of ethanol / water in sequence. After stirring for 20 min, triethylamine was added and stirring was continued for 75 min. The molar ratio of yttrium source, bismuth source, methylimidazole and triethylamine in the solution was 1:3:1:1.5, the ratio of yttrium source and bismuth source to solvent was 10 g:70 mL, the volume ratio of ethanol to water was 1:0.5, and the mixed solution had long topological molecular chains that were intertwined.

[0041] (2) A homogeneous and stable precursor solution was prepared by vacuum distillation of the mixed solution. The parameters of vacuum distillation were: working pressure 100 Pa, working temperature 55 °C, and working time 8 min. The dynamic viscosity of the precursor solution was 8.5 Pa·s and the conductivity was 25 mS / m.

[0042] (3) The above precursor solution was spun into a precursor fiber membrane using electrospinning technology. The process parameters for electrospinning were: ambient temperature 26℃, relative humidity 43%, injection speed 2mL / h, voltage 49kV, and distance between the receiving device and the spinneret 20cm.

[0043] (4) The precursor fiber membrane was placed directly into a high-temperature muffle furnace at 1100℃ for 30 minutes in air atmosphere, and then cooled under vacuum at a pressure of 0.05MPa to finally obtain a flexible bismuth yttrium nanofiber membrane.

[0044] The performance was measured using the same testing method as in Example 1. The average diameter of the bismuth yttrium nanofibers was 390 nm, the relative standard deviation of the diameter was 2.5%, the bismuth yttrium grain size inside the fibers was 46 nm, the flexibility of the flexible bismuth yttrium nanofiber membrane was 86 mN, the average infrared reflectance of the flexible bismuth yttrium nanofiber membrane in the near-infrared band was 92%, and the thermal conductivity in the range of 200–1200 °C was 0.034–0.135 W / (m·K).

[0045] Example 4

[0046] A method for preparing a flexible bismuth yttrium nanofiber membrane with high infrared reflectivity, comprising the following steps:

[0047] (1) Yttrium source hexahydrate, bismuth source bismuth sulfate and methylimidazole were dissolved in a mixed solvent of ethanol / water in sequence. After stirring for 35 min, triethylamine was added and stirring was continued for 50 min. The molar ratio of yttrium source, bismuth source, methylimidazole and triethylamine in the solution was 1:3:1.8:3.6, the ratio of yttrium source and bismuth source to solvent was 10 g:45 mL, the volume ratio of ethanol to water was 1:1.5, and the mixed solution had long topological molecular chains that were intertwined.

[0048] (2) A uniform and stable precursor solution is prepared by vacuum distillation of the mixed solution. The parameters of vacuum distillation are: working pressure 50 Pa, working temperature 60 °C, working time 15 min; the dynamic viscosity of the precursor solution is 9 Pa·s and the conductivity is 35 mS / m.

[0049] (3) The above precursor solution was spun into a precursor fiber membrane using electrospinning technology. The process parameters for electrospinning were: ambient temperature 23℃, relative humidity 54%, injection speed 1.5mL / h, voltage 52kV, and distance between the receiving device and the spinneret 18cm.

[0050] (4) The precursor fiber membrane was placed directly into a high-temperature muffle furnace at 1000℃ for 90 minutes in air atmosphere, and then cooled under vacuum at a pressure of 0.12MPa to finally obtain a flexible bismuth yttrium nanofiber membrane.

[0051] The performance was measured using the same testing method as in Example 1. The average diameter of the bismuth yttrium nanofibers was 290 nm, the relative standard deviation of the diameter was 2.3%, the bismuth yttrium grain size inside the fibers was 32 nm, the flexibility of the flexible bismuth yttrium nanofiber membrane was 55 mN, the average infrared reflectance of the flexible bismuth yttrium nanofiber membrane in the near-infrared band was 93%, and the thermal conductivity in the range of 200–1200 °C was 0.045–0.146 W / (m·K).

[0052] Examples 5-9

[0053] The preparation steps of Examples 5-9 are the same as those of Example 1. The parameters of the precursor solution, electrospinning and calcination parameters, and performance parameters of the flexible bismuth yttrium fiber membrane are shown in the table below (Note: Stirring time 1 is the stirring time after adding yttrium source, bismuth source, and methylimidazole to the ethanol / water mixed solvent, and stirring time 2 is the stirring time after adding triethylamine).

[0054]

Claims

1. A method for preparing a flexible bismuth yttrium nanofiber membrane with high infrared reflectivity, comprising the following steps: Step 1: Add yttrium source, bismuth source, and methylimidazole to a mixed solvent of ethanol and water in sequence, stir for 5-100 min, then add triethylamine and continue stirring for 5-100 min to obtain a clear and transparent mixed solution. Wherein, the yttrium source is one of yttrium nitrate hexahydrate, yttrium chloride hexahydrate, or yttrium sulfate octahydrate; the bismuth source is one of bismuth nitrate pentahydrate, bismuth sulfate, or bismuth oxychloride; the molar ratio of yttrium source to bismuth source is 1:3; the ratio of the total mass of yttrium source and bismuth source to the amount of mixed solvent is 10g:10-90mL; the volume ratio of ethanol to water in the mixed solvent is 1:0.5-5; the molar ratio of yttrium source to methylimidazole is 1:0.5-2.5; and the molar ratio of yttrium source to triethylamine is 1:1-5. Step 2: Vacuum distillation is performed on the mixed solution to prepare a homogeneous and stable precursor solution; The parameters for vacuum distillation are: working pressure 104–1 Pa, working temperature 30–85 °C, and working time 5–30 min; the dynamic viscosity of the precursor solution is 0.5–10 Pa·s, and the conductivity is 5–60 mS / m. Step 3: The precursor solution is spun into a precursor fiber membrane using electrospinning technology; The process parameters for electrospinning are as follows: under the conditions of spinning environment temperature of 10-50℃ and relative humidity of 10-80%, the precursor solution is injected at a flow rate of 0.5-15mL / h, and the spinneret is connected to a high voltage power supply of 10-60kV for spinning. The distance between the receiving device and the spinneret is 5-35cm. Step 4: Calcine the precursor fiber membrane in air atmosphere, and then cool it under vacuum to obtain a flexible bismuth yttrium nanofiber membrane. The calcination process involves placing the precursor fiber membrane directly into a muffle furnace at a temperature of 600–1100°C, holding it at that temperature for 10–600 minutes, and then cooling the furnace chamber under vacuum at a pressure of 0–0.15 MPa. The bismuth yttrium nanofiber membranes prepared by the above method have an average fiber diameter of 30–600 nm and a relative standard deviation of 0.2–10%, an internal grain size of 3–65 nm, a flexibility of 0–100 mN, an average infrared reflectance of ≥92% in the near-infrared band, and a thermal conductivity of 0.03–0.15 W / (m·K) in the range of 200–1200 °C. The first step of the above method involves adding yttrium source, bismuth source, and methylimidazole sequentially to a mixed solvent of ethanol / water. Yttrium ions, bismuth ions, and methylimidazole self-assemble through bridging, forming long-chain molecules with a topological structure. Subsequently, the terminal ligand triethylamine is added. Triethylamine can form hydrogen bonds with yttrium hydroxyl and bismuth hydroxyl groups, reducing excessive condensation and coordination between molecular chains. The long chains of the topological molecules intertwine and form a clear and transparent mixed solution with a certain degree of viscoelasticity. Then, the mixed solution is subjected to rapid vacuum distillation to obtain a homogeneous and stable spinnable precursor solution, which increases the viscosity and enhances the spinnability of the precursor solution.

2. The flexible bismuth yttrium nanofiber membrane with high infrared reflectivity prepared by the method described in claim 1.

Images