Silica-coated iron oxide fluorescent magnetic powder, and preparation method and application thereof

Abstract

This invention discloses a silica-coated iron oxide fluorescent magnetic powder, comprising an inorganic magnetic matrix and a fluorescent agent supported on the inorganic magnetic matrix by chemical covalent bonding. The inorganic magnetic matrix is ​​a micron-sized coating composed of silica-coated nano-Fe3O4, with the nano-Fe3O4 dispersed within the micron-sized coating. The preparation method disclosed in this invention involves dispersing nano-Fe3O4 in an alkaline organic solvent, adding tetraethyl orthosilicate for a coating reaction, separating and washing to obtain the Fe3O4@SiO2 magnetic matrix, and further reacting it with a silicate-esterified fluorescent agent to obtain the silica-coated iron oxide fluorescent magnetic powder. The fluorescein-coated fluorescent magnetic powder disclosed in this invention can be applied to the non-destructive testing of surface defects in magnetic material components. This invention exhibits strong dispersibility in aqueous phase, ensuring high detection sensitivity of the fluorescent magnetic powder while significantly improving its stability in a carrier liquid.

Description

Technical Field

[0001] This invention relates to a silicon oxide-coated superparamagnetic iron oxide powder, and more particularly to a fluorescent agent chemically bonded iron oxide magnetic powder, its preparation method, and its application. Background Technology

[0002] In the field of non-destructive testing of components, there are five conventional testing techniques: X-ray, penetrant testing, eddy current testing, magnetic particle testing, and ultrasonic testing. Fluorescent magnetic particle testing, in particular, is commonly used for surface and near-surface defect detection in magnetic material components, such as steel, and its non-destructive testing technology is irreplaceable. In wet fluorescent magnetic particle testing, large Fe3O4 particles with spontaneous magnetization properties exhibit high remanent magnetization M. r and correcting stubborn H c In dispersions, fluorescent magnetic powders are prone to magnetic aggregation and sedimentation. Furthermore, resin-bonded fluorescent magnetic powders are susceptible to dissolution due to the solvation effect of the carrier liquid. In long-term and high-temperature detection environments, the fluorescent agent easily peels off from the iron oxide magnetic matrix, resulting in performance deactivation. Additionally, Fe ions in the magnetic matrix have a strong quenching effect on the luminescence of the fluorescent agent, significantly impacting its fluorescence detection sensitivity. Currently, the problems of magnetic aggregation and sedimentation of fluorescent magnetic powders in carrier liquids, poor stability due to fluorescent agent peeling, and low detection sensitivity due to Fe ion fluorescence quenching not only increase detection costs but also greatly limit the range of application scenarios. Summary of the Invention

[0003] To address the shortcomings of the prior art, this invention provides a silica-coated iron oxide fluorescent magnetic powder, solving the problems in wet-process fluorescent magnetic particle detection technology where magnetic particles easily aggregate in dispersions due to magnetic attraction and the solvation effect of the carrier liquid leading to the separation of organic fluorescent agents from the inorganic magnetic matrix. This invention also provides a method for preparing the silica-coated iron oxide fluorescent magnetic powder, resulting in a chemically covalently bonded fluorescent magnetic powder that is easily and stably dispersed in an aqueous carrier liquid and where the fluorescent agent is not easily separated. Furthermore, this invention also provides an application of the silica-coated iron oxide fluorescent magnetic powder.

[0004] The technical solution of the present invention is as follows: a fluorescent magnetic powder of silicon dioxide coated iron oxide, comprising an inorganic magnetic matrix and a fluorescent agent supported on the inorganic magnetic matrix by chemical covalent bonding, wherein the inorganic magnetic matrix is ​​a micron-sized coating composed of silicon dioxide coated with nano-Fe3O4, and the nano-Fe3O4 is dispersed in the micron-sized coating.

[0005] Furthermore, the particle size of the silica-coated iron oxide fluorescent magnetic powder is less than 5 micrometers.

[0006] Furthermore, the nano-Fe3O4 is a superparamagnetic particle with a particle size of 20–100 nanometers, preferably 60–80 nanometers.

[0007] Furthermore, the fluorescent agent is silicate-esterified fluorescent yellow: R is an alkyl group.

[0008] Another technical solution of the present invention is: a method for preparing fluorescent magnetic powder of silicon dioxide coated iron oxide, comprising the steps of: dispersing nano Fe3O4 powder in an alcohol solution containing inorganic or organic base, adding ethyl silicate dropwise and then ultrasonically dispersing to obtain a mixed phase of SiO2 gel and Fe3O4, adding a silicate-esterified fluorescent agent under an inert atmosphere, and stirring under light-protected conditions to carry out a silicic acid condensation reaction, centrifuging and repeatedly washing after the reaction is completed, and obtaining the fluorescent magnetic powder of silicon dioxide coated iron oxide after filtration and air drying.

[0009] Furthermore, the ratio of the nano Fe3O4 powder to ethyl silicate is 5g:2-10mL.

[0010] Furthermore, during the silicic acid polycondensation reaction, the reaction temperature is 60–70°C and the reaction time is 10–30 hours.

[0011] Further, the nano-Fe3O4 powder is prepared by the following steps: ferric salt and organic acid surfactant are mixed and added to an ethylene glycol solution, and ultrasonically dispersed to form a sol-gel; under an inert atmosphere, the sol-gel is heated to 160-165°C and stirred until the system turns dark brown, then transferred to a high-pressure reactor and heated to 200-210°C for constant temperature reaction; after the reaction is completed, ethanol is added for flocculation, the black precipitate is separated, washed with ethanol, filtered and air-dried to obtain nano-Fe3O4 powder.

[0012] Furthermore, the organic acid surfactant is trisodium citrate.

[0013] Another technical solution of the present invention is: the application of a fluorescent magnetic powder of silicon dioxide coated iron oxide, wherein the fluorescent magnetic powder of silicon dioxide coated iron oxide is dispersed in a pure aqueous phase carrier liquid and then used for non-destructive testing of surface defects of magnetic material parts.

[0014] Compared with the prior art, the advantages of the technical solution provided by the present invention are as follows: This invention relates to fluorescent magnetic powder coated with silicon dioxide and iron oxide. The superparamagnetic nano-Fe3O4 is coated to form a micron-sized inorganic magnetic matrix, maintaining the original nanoscale superparamagnetic characteristics. The weak magnetic attraction between particles improves the dispersion stability of the magnetic powder in solution. The silicate groups grafted to the fluorescent agent undergo a condensation reaction with the Si-OH on the surface of the inorganic magnetic matrix to form chemical covalent bonds, which completely solves the problem of dissolution of the magnetic powder due to solvation effect in the carrier liquid, which leads to the peeling of the fluorescent agent and the magnetic matrix. The SiO2 coating between the Fe ions and the fluorescent agent forms a thick isolation layer, eliminating the fluorescent quenching side effect of Fe ions on the dye. The high luminescence intensity increases the fluorescence detection sensitivity.

[0015] The preparation method of this invention is simple, uses low-cost raw materials, has mild reaction conditions, and the obtained coated fluorescent magnetic powder has controllable particle size, maintaining good dispersion stability while having high fluorescence detection sensitivity. Attached Figure Description

[0016] Figure 1 The images show the X-ray diffraction characteristics of the nano Fe3O4 powder of Examples 1-3 and the silicon dioxide-coated iron oxide Fe3O4@SiO2 of Examples 4-7 of the present invention.

[0017] Figure 2 This is a particle size distribution characteristic diagram of nano Fe3O4 powder in Example 1 of the present invention.

[0018] Figure 3 This is a particle size distribution characteristic diagram of nano Fe3O4 powder in Example 2 of the present invention.

[0019] Figure 4 This is a schematic diagram of the structure of the silica-coated iron oxide fluorescent magnetic powder of the present invention.

[0020] Figure 5 This is a particle size distribution characteristic diagram of the silica-coated iron oxide fluorescent magnetic powder of Example 4 of the present invention.

[0021] Figure 6 This is a particle size distribution characteristic diagram of the silica-coated iron oxide fluorescent magnetic powder of Example 5 of the present invention.

[0022] Figure 7 This is a particle size distribution characteristic diagram of the silica-coated iron oxide fluorescent magnetic powder of Example 6 of the present invention.

[0023] Figure 8 This is a particle size distribution characteristic diagram of the silica-coated iron oxide fluorescent magnetic powder of Example 7 of the present invention.

[0024] Figure 9 This is a hysteresis loop characteristic diagram of the fluorescent magnetic powder of silicon dioxide coated iron oxide in Example 5 of the present invention.

[0025] Figure 10 This is a characteristic diagram of the phosphor stripping time of the silica-coated iron oxide fluorescent magnetic powder of Example 5 of the present invention. Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments. It should be understood that these embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention. After reading this description, any modifications of this description in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0027] Preparation of nano Fe3O4 powder.

[0028] In Example 1, 1.35 g of FeCl3·6H2O and 3.6 g of anhydrous sodium acetate were mixed and added to 40 mL of ethylene glycol. The mixture was ultrasonically dispersed at 1.5 kW for 30 minutes to form a sol-gel. Under a nitrogen atmosphere, the sol-gel was vigorously stirred and heated to 160 °C for 1.0 hour. After the system completely changed from yellow to dark brown, it was quickly transferred to a high-pressure reactor lined with polytetrafluoroethylene and heated to 200 °C at a rate of 10 °C / min, and held at that temperature for 36 hours. After the reaction was completed and the mixture was allowed to cool naturally, ethanol was added to flocculate and form a black precipitate. The ethanol was separated, the precipitate was washed three times, filtered, and air-dried to obtain dark black superparamagnetic Fe3O4 powder.

[0029] In Example 2, 1.35 g of FeCl3·6H2O and 20.0 g of trisodium citrate were mixed and added to 40 mL of ethylene glycol. The mixture was ultrasonically dispersed at 1.5 kW for 30 minutes to form a sol-gel. Under a nitrogen atmosphere, the sol-gel was vigorously stirred and heated to 160 °C for 1.0 hour. After the system completely changed from yellow to dark brown, it was quickly transferred to a high-pressure reactor with a polytetrafluoroethylene liner, and the temperature was increased to 200 °C at a rate of 10 °C / min and held at that temperature for 36 hours. After the reaction was completed, the mixture was allowed to cool naturally. Ethanol was added to flocculate and form a black precipitate. The ethanol was separated, the precipitate was washed three times, filtered, and air-dried to obtain dark black superparamagnetic Fe3O4 powder.

[0030] In Example 3, 1.35 g of FeCl3·6H2O and 20.0 g of trisodium citrate were mixed and added to 40 mL of ethylene glycol. The mixture was ultrasonically dispersed at 1.5 kW for 30 minutes to form a sol-gel. Under a nitrogen atmosphere, the sol-gel was vigorously stirred and heated to 165 °C for 1.0 hour. After the system completely changed from yellow to dark brown, it was quickly transferred to a high-pressure reactor with a polytetrafluoroethylene liner, and the temperature was increased to 210 °C at a rate of 10 °C / min and held at that temperature for 30 hours. After the reaction was completed, the mixture was allowed to cool naturally. Ethanol was added to flocculate and form a black precipitate. The ethanol was separated, the precipitate was washed three times, filtered, and air-dried to obtain dark black superparamagnetic Fe3O4 powder.

[0031] According to X-ray powder diffraction analysis, such as Figure 1 As shown, Examples 1 to 3 all yielded Fe3O4 spinel phases. Laser particle size analysis was performed on samples prepared using different organic acid surfactants (anhydrous sodium acetate and trisodium citrate), and the results are as follows. Figure 2 and Figure 3 As shown, the sample of Example 2, obtained using trisodium citrate, exhibits excellent particle size uniformity, with the particle size concentrated at 95 nanometers. The sample of Example 3 also shows similar characteristics. In contrast, the sample of Example 1, obtained using sodium acetate, shows particle size distribution in three regions: 0.1, 0.6, and 11.0 micrometers. Therefore, the Fe3O4 powder prepared using trisodium citrate as the organic acid surfactant exhibits better particle size uniformity.

[0032] The silicate esterified fluorescent agent used in the preparation of silica-coated iron oxide fluorescent magnetic powder is methyl silicate fluorescent yellow, and its structural formula is as follows: .

[0033] The methyl silicate fluorescent yellow can be purchased from Jiangsu Puyang New Material Technology Co., Ltd. The preparation method is as follows: commercially available fluorescent yellow and silicate are mixed and added to acetate solution. Under the condition of a small amount of BF3, the mixture is heated to 80°C and stirred for 2 hours under N2 atmosphere protection. After the reaction is completed, the fraction below 120°C is removed by rotary evaporation. The resulting yellow solid is washed with ethanol, filtered and air-dried to obtain methyl silicate fluorescent yellow powder.

[0034] In Example 4, 0.05 g of 95 nm Fe3O4 powder prepared in Example 2 was added to 50 mL of ethanol containing 3 mL of ammonia. After ultrasonic dispersion for 10 minutes, 0.02 mL of tetraethyl orthosilicate was slowly added dropwise, and ultrasonic dispersion was continued for another 10 minutes to obtain a mixed phase of SiO2 gel and Fe3O4. Under a N2 atmosphere, 0.1 g of silicate esterified fluorescent yellow was added, and the mixture was heated to 65 °C and stirred vigorously under light-protected conditions to carry out a silicic acid condensation reaction between the magnetic matrix and the fluorescent agent for 20 hours. After the reaction was completed, the mixture was centrifuged and washed three times each with ethanol and deionized water to remove unreacted chemicals. The mixture was then filtered and air-dried to obtain dark gray fluorescent magnetic powder of silica-coated iron oxide supported by fluorescent agent.

[0035] In Example 5, 0.05 g of 95 nm Fe3O4 powder prepared in Example 2 was added to 50 mL of ethanol containing 3 mL of ammonia. After ultrasonic dispersion for 10 minutes, 0.05 mL of tetraethyl orthosilicate was slowly added dropwise, and ultrasonic dispersion was continued for another 10 minutes to obtain a mixed phase of SiO2 gel and Fe3O4. Under a N2 atmosphere, 0.1 g of silicate-esterified fluorescent yellow was added, and the mixture was heated to 65 °C and stirred vigorously under light-protected conditions to carry out a silicic acid condensation reaction between the magnetic matrix and the fluorescent agent for 20 hours. After the reaction was completed, the powder was centrifuged and washed three times each with ethanol and deionized water to remove unreacted chemicals. The powder was then filtered and air-dried to obtain dark gray fluorescent magnetic powder of silica-coated iron oxide supported by fluorescent agent.

[0036] In Example 6, 0.05 g of 95 nm Fe3O4 powder prepared in Example 2 was added to 50 mL of ethanol containing 3 mL of ammonia. After ultrasonic dispersion for 10 minutes, 0.1 mL of tetraethyl orthosilicate was slowly added dropwise, and ultrasonic dispersion was continued for another 10 minutes to obtain a mixed phase of SiO2 gel and Fe3O4. Under a N2 atmosphere, 0.1 g of silicate esterified fluorescent yellow was added, and the mixture was heated to 65 °C and stirred vigorously under light-protected conditions to carry out a silicic acid condensation reaction between the magnetic matrix and the fluorescent agent for 20 hours. After the reaction was completed, the mixture was centrifuged and washed three times each with ethanol and deionized water to remove unreacted chemicals. The mixture was then filtered and air-dried to obtain dark gray fluorescent magnetic powder of silica-coated iron oxide supported by fluorescent agent.

[0037] In Example 7, 0.05 g of 95 nm Fe3O4 powder prepared in Example 2 was added to 50 mL of ethanol containing 3 mL of ammonia. After ultrasonic dispersion for 10 minutes, 0.2 mL of tetraethyl orthosilicate was slowly added dropwise, and ultrasonic dispersion was continued for another 10 minutes to obtain a mixed phase of SiO2 gel and Fe3O4. Under a N2 atmosphere, 0.1 g of silicate esterified fluorescent yellow was added, and the mixture was heated to 65 °C and stirred vigorously under light-protected conditions to carry out a silicic acid condensation reaction between the magnetic matrix and the fluorescent agent for 20 hours. After the reaction was completed, the unreacted chemical substances were removed by centrifugation and repeated washing with ethanol and deionized water three times each. The mixture was then filtered and air-dried to obtain dark gray fluorescent magnetic powder of silica-coated iron oxide supported by fluorescent agent.

[0038] In addition, by adjusting the temperature and time of the silica polycondensation reaction to 60°C for 30 hours and 70°C for 10 hours, respectively, fluorescent magnetic powder with dark gray fluorescent agent-supported silica and iron oxide coated was successfully prepared.

[0039] The schematic diagrams of the results of the dark gray fluorescent agent-supported silica-coated iron oxide fluorescent magnetic powder obtained in Examples 4-7 above are shown below. Figure 4As shown, the middle part is a non-polar magnetic matrix formed by a micron-sized coating of silicon dioxide and nano-Fe3O4, which has a dragon fruit core structure. Its exterior is chemically covalently bonded to organic fluorescent yellow FL.

[0040] Laser particle size analysis revealed that the particle size distribution of silica-coated iron oxide fluorescent magnetic powder varied depending on the amount of tetraethyl orthosilicate added. For example... Figures 5 to 8 As shown, increasing the amount of tetraethyl orthosilicate added from 0.02 mL to 0.20 mL resulted in an increase in the particle size of the fluorescent magnetic powder from ~4.5 μm to 11 μm. Particle size analysis data also revealed that all samples exhibited a wide range of particle size distributions. Figure 5 The particle size distribution range of the sample in Example 4 is 1.0 to 11.7 micrometers, with the main particle size concentrated at 4.5 micrometers, and a small peak appearing at 10.2 micrometers; Figure 6 The particle size distribution of the sample in Example 5 showed two peak values ​​of 4.5 μm and 10.2 μm, but the number of particles at 10.2 μm increased significantly. Figure 7 and Figure 8 The changes shown are more pronounced. In Example 6, the number of small particles with a diameter of 4.5 micrometers decreased while the number of particles with a diameter of 10.2 micrometers increased significantly. In Example 7, the number of large particles accounted for the absolute value.

[0041] The silica-coated iron oxide fluorescent magnetic powders obtained in Examples 4-7 of this invention were compared in water solubility experiments. The silica-coated iron oxide fluorescent magnetic powder of Example 4, with a main particle size of 4.5 micrometers, showed good water solubility, reaching a maximum of 3.6 g / L. However, its water solubility decreased significantly with the increase in the number of 10.2-micrometer particles. The water solubility of the sample in Example 7 did not exceed 0.7 g / L. It should be emphasized that no dispersant or defoamer was added to the aqueous dispersions of the samples from Examples 4 to 7. Furthermore, the dispersion in the oil phase carrier liquid showed the same pattern, but the sample of Example 3, which had the largest dispersion in the aqueous phase carrier liquid, did not exceed 0.3 g / L in the oil phase carrier liquid.

[0042] The water-dispersible and oil-dispersible fluorescent magnetic powders obtained in Examples 4-7 of this invention were subjected to black light experiments. It was found that the oil-based carrier liquid exhibited very weak fluorescence brightness under black light, while the water-dispersible samples all emitted a bright yellow color. Based on the dispersibility and fluorescence brightness experiments under black light, it is clear that the fluorescent magnetic powders obtained in this invention are more suitable for water-based detection.

[0043] The hysteresis loop characteristic diagram of the sample obtained in Example 5 is shown below. Figure 9 As shown, the coercive field H under room temperature conditions C The remanent magnetization Mr is 51 Oe and 2.7 emu / g, respectively, exhibiting superparamagnetism.

[0044] The fluorescent agent stripping experiment was performed on the sample prepared in Example 5, and the results are as follows: Figure 10 As shown, silica-coated iron oxide fluorescent magnetic powder was dispersed in water and stirred and exfoliated at 60°C. Fluorescence intensity was measured in the aqueous phase after magnetic separation at different times. The experiment showed that a sudden exfoliation of the fluorescent agent occurred after 20 hours of dispersion, while almost no fluorescent agent was exfoliated from the magnetic powder matrix within 15 hours. Samples prepared in Examples 4, 6, and 7 also showed almost no fluorescent agent exfoliation from the magnetic powder matrix within 15 hours. Since the exfoliation experiment temperature was 60°C, the corresponding stable dispersion time of the fluorescent magnetic powder at room temperature can reach 60 hours (approximately 3 days).

[0045] Based on comprehensive performance considerations, the silica-coated iron oxide fluorescent magnetic powder prepared in Example 5 of this invention has the best performance as a raw material for non-destructive testing of surface defects in magnetic material components.

[0046] Finally, the silica-coated iron oxide fluorescent magnetic powder prepared by this invention can be added to a pure aqueous phase carrier liquid for non-destructive testing of surface defects in magnetic material components without the need for other dispersing and defoaming agents, making it a safe and environmentally friendly product.

Claims

1. A fluorescent magnetic powder of silica-coated iron oxide, characterized by, It includes an inorganic magnetic matrix and a fluorescent agent supported on the inorganic magnetic matrix by chemical covalent bonding. The inorganic magnetic matrix is ​​a micron-sized coating composed of silicon dioxide coated with nano-Fe3O4, and the nano-Fe3O4 is dispersed in the micron-sized coating.

2. The silica-coated iron oxide fluorescent magnetic powder according to claim 1, characterized by, The particle size of the silica-coated iron oxide fluorescent magnetic powder is less than 5 micrometers.

3. The silica-coated iron oxide fluorescent magnetic powder according to claim 1, characterized by, The nano-Fe3O4 is a superparamagnetic particle with a particle size of 20–100 nanometers.

4. The silica-coated iron oxide fluorescent magnetic powder according to claim 1, wherein, The fluorescent agent is silicate-esterified fluorescent yellow: R is an alkyl group.

5. A method for preparing fluorescent magnetic powder of silicon dioxide coated iron oxide according to any one of claims 1 to 4, characterized in that, The process includes the following steps: dispersing nano-Fe3O4 powder in an alcohol solution containing inorganic or organic bases, adding ethyl silicate dropwise and then ultrasonically dispersing to obtain a mixed phase of SiO2 gel and Fe3O4, adding a silicate-esterified fluorescent agent under an inert atmosphere, and stirring under light-protected conditions to carry out a silicic acid polycondensation reaction. After the reaction is completed, centrifuging and repeated washing are performed, followed by filtration and air drying to obtain the silica-coated iron oxide fluorescent magnetic powder.

6. The method for preparing silica-coated iron oxide fluorescent magnetic powder according to claim 5, characterized in that, The ratio of nano Fe3O4 powder to ethyl silicate is 5g: 2-10ml / L.

7. The method for preparing silica-coated iron oxide fluorescent magnetic powder according to claim 5, characterized in that, When carrying out the silicic acid polycondensation reaction, the reaction temperature is 60-70℃ and the reaction time is 10-30 hours.

8. The method for preparing silica-coated iron oxide fluorescent magnetic powder according to claim 5, characterized in that, The nano-Fe3O4 powder is prepared by the following steps: a mixture of ferric salt and organic acid surfactant is added to an ethylene glycol solution and ultrasonically dispersed to form a sol-gel. Under an inert atmosphere, the sol-gel was heated to 160–165°C and stirred until the system turned dark brown. Then it was transferred to a high-pressure reactor and heated to 200–210°C for constant temperature reaction. After the reaction was completed, ethanol was added for flocculation, the black precipitate was separated, washed with ethanol, filtered and air-dried to obtain nano Fe3O4 powder.

9. The method for preparing silica-coated iron oxide fluorescent magnetic powder according to claim 5, characterized in that, The organic acid surfactant is trisodium citrate.

10. The application of a fluorescent magnetic powder of silicon dioxide coated with iron oxide, characterized in that, The silica-coated iron oxide fluorescent magnetic powder described in any one of claims 1 to 4 is dispersed in a pure aqueous carrier liquid and then used for non-destructive testing of surface defects in magnetic material components.

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