Polyacrylamide-coated iron oxide magnetic powder as well as preparation method and application thereof

Abstract

The invention discloses polyacrylamide coated iron oxide magnetic powder, which comprises a magnetic core and a polyacrylamide coating layer coated outside the magnetic core, and the magnetic core is a mixed phase of Fe2O3 and FeOOH with Fe2O3 as a main phase. The preparation method disclosed by the invention comprises the following steps: adding a trivalent iron salt into an aqueous solution containing a surfactant, adjusting the pH value of the system to be more than 7.0 by using an alkali metal oxide, carrying out a hydrothermal reaction to obtain a precipitate, calcining the precipitate to obtain a magnetic core, dispersing the magnetic core into water, adding acrylamide and an initiator, and carrying out a polymerization reaction to obtain the product. The polyacrylamide-coated iron oxide magnetic powder disclosed by the invention can be applied to nondestructive detection of surface defects of magnetic material parts. The magnetic core is high in dispersity in a water phase, the stability of the magnetic core in a water-based carrier liquid is remarkably improved while the strong magnetism characteristic of the magnetic core is kept, in addition, the preparation method is simple, and reaction conditions are controllable.

Description

Technical Field

[0001] This invention relates to an organically coated iron oxide powder, and more particularly to a polyacrylamide-coated iron oxide magnetic powder, its preparation method, and its application. Background Technology

[0002] Magnetic particle testing, one of the five conventional non-destructive testing methods (radiological, penetrant, eddy current, magnetic particle, and ultrasonic), is a non-destructive testing technique commonly used for surface and near-surface defect detection in magnetic material components, particularly steel. Magnetic particle testing technology is divided into dry and wet methods. In wet magnetic particle testing, ordinary iron oxide magnetic powder has a high remanent magnetization at room temperature. Its strong magnetic properties allow for high aggregation of leakage magnetic fields at component defects, resulting in high defect detection sensitivity. However, the strong magnetic attraction between the powder particles causes spontaneous aggregation, making it difficult to disperse and remain stable in a carrier liquid. This limits the application of wet magnetic particle testing, especially in extreme high and low temperature environments. Summary of the Invention

[0003] To address the shortcomings of the prior art, this invention provides a polyacrylamide-coated iron oxide magnetic powder, resolving the contradiction between the high detection sensitivity of magnetic iron oxide in wet magnetic particle detection and its tendency to aggregate magnetically in aqueous carrier liquids. This invention also provides a method for preparing polyacrylamide-coated iron oxide magnetic powder, enabling the production of iron oxide magnetic powder that is easily and stably dispersed in an aqueous carrier liquid. Furthermore, this invention provides an application of the polyacrylamide-coated iron oxide magnetic powder.

[0004] The technical solution of the present invention is as follows: a polyacrylamide-coated iron oxide magnetic powder, comprising a magnetic core and a polyacrylamide coating layer covering the magnetic core, wherein the magnetic core is a mixed phase of Fe2O3 and FeOOH with Fe2O3 as the main phase.

[0005] Furthermore, the magnetic core is a mixed phase of Fe2O3 and FeOOH with γ-Fe2O3 as the main phase.

[0006] Furthermore, the degree of polymerization of the polyacrylamide in the polyacrylamide coating layer is 3000-6000.

[0007] Another technical solution of the present invention is: a method for preparing polyacrylamide-coated iron oxide magnetic powder, comprising the following steps: The ferric salt is added to an aqueous solution containing a surfactant, and the pH of the system is adjusted to above 7.0 by alkali metal oxides. A precipitate is obtained through a hydrothermal reaction. The precipitate is separated, washed, and dried to obtain a powdered product. The powdered product is then calcined to obtain a magnetic core. The magnetic core is dispersed in water, and then acrylamide and an initiator are added. Under the protection of an inert atmosphere, a polymerization reaction occurs through the action of the initiator to obtain polyacrylamide-coated iron oxide magnetic powder.

[0008] Furthermore, the pH value of the system is adjusted to 9.5–12.5 using alkali metal oxides.

[0009] Furthermore, the calcination temperature is 400–800°C, and the calcination time is 4–8 hours, preferably 550°C for 6 hours.

[0010] Furthermore, the polymerization reaction is carried out at 60-70°C for 45-60 minutes.

[0011] Furthermore, the polymerization reaction is first heated to 30-40°C at a rate of 1°C per minute and held at that temperature for 25-30 minutes, and then rapidly heated to 60-70°C at a rate of 10°C per minute.

[0012] Furthermore, the trivalent iron salt is an inorganic acid salt, and the surfactant is an alcohol surfactant.

[0013] Another technical solution of the present invention is: an application of polyacrylamide-coated iron oxide magnetic powder, wherein the polyacrylamide-coated iron oxide magnetic powder is used for non-destructive testing of surface defects in magnetic material parts.

[0014] Compared with the prior art, the advantages of the technical solution provided by the present invention are as follows: The polyacrylamide-coated iron oxide magnetic powder of this invention, through the coating of polyacrylamide surface, forms hydrogen bonds with water molecules by grafted amide groups, exhibits strong dispersibility in aqueous phase, and has a coercive field and remanent magnetization of 5.6 kOe and 0.23 emu / g at room temperature, respectively. While maintaining the strong magnetic characteristics of the magnetic core, it significantly improves its stability in water-based carrier liquid.

[0015] The preparation method of this invention is simple, the particle size of the coated magnetic powder is controllable, the reaction conditions are mild, and the raw material cost is low. Attached Figure Description

[0016] Figure 1 X-ray diffraction characteristic images of red powders obtained by hydrothermal reaction of precursor solutions with different pH values ​​according to embodiments of the present invention.

[0017] Figure 2 This is a schematic diagram of the structure of polyacrylamide-coated iron oxide magnetic powder of the present invention.

[0018] Figure 3 The X-ray diffraction characteristics of polyacrylamide-coated iron oxide magnetic powder obtained at different polymerization reaction times according to embodiments of the present invention are shown.

[0019] Figure 4 The infrared spectral characteristics of polyacrylamide-coated iron oxide magnetic powder and uncoated pure iron oxide powder of the present invention are shown.

[0020] Figure 5 This is a characteristic diagram of the hysteresis loop of the polyacrylamide-coated iron oxide magnetic powder of the present invention. Detailed Implementation

[0021] 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.

[0022] Example:

[0023] Six equal 20 mL portions of 0.1 mol / L FeCl3 aqueous solution were each mixed with 2.0 mL of ethylene glycol and stirred thoroughly. Then, 1.0 mol / L NaOH aqueous solution was added to adjust the pH to 7.40, 9.85, 11.09, 12.06, 12.94, and 13.73, respectively. The resulting precursor solutions were transferred to six 50 mL high-pressure hydrothermal reactors and hydrothermally reacted at 150 °C for 12 hours. After the reaction, the reactors were allowed to cool naturally to room temperature. The resulting samples were centrifuged and washed twice with deionized water. The product was then dried in a 60 °C oven for 5 hours to obtain a red powder. X-ray powder diffraction analysis showed that... Figure 1 As shown, all six samples were FeOOH phase. Laser particle size analyzer tests showed that the samples with pH values ​​of 9.85, 11.09, and 12.06 had better particle size uniformity, with the sample with pH value of 9.85 having the most uniform particle size, approximately 2.3 micrometers in diameter.

[0024] Samples with a pH of 9.85 were calcined at controlled temperatures: 400°C was heated at a rate of 10°C per minute and held at that temperature for 8 hours; 550°C was heated at a rate of 10°C per minute and held at that temperature for 6 hours; and 800°C was heated at a rate of 10°C per minute and held at that temperature for 4 hours. After natural cooling, the samples were analyzed by X-ray powder diffraction. The products were all dominated by γ-Fe₂O₃ with trace amounts of FeOOH phase.

[0025] 0.15 g of the calcined sample, which had been calcined at 550℃ for 6 hours, was dispersed in 5 mL of water and sonicated for 30 minutes before being placed in a three-necked flask. 5 mL of water containing 0.075 g of acrylamide and 0.0011 g of potassium persulfate was added to the flask. Nitrogen gas was introduced, and the mixture was stirred at 1100 rpm for 10 minutes. Afterward, the nitrogen flow was stopped, the entire reaction apparatus was sealed, and the temperature was slowly increased to 30℃ at a rate of 1℃ per minute and held for 30 minutes. Then, the temperature was rapidly increased to 60℃ at a rate of 10℃ per minute and the reaction was carried out for 45 minutes. After the reaction was completed, the mixture was stirred continuously and allowed to cool naturally. It was then filtered, washed, and dried at 60℃ to obtain polyacrylamide-coated iron oxide magnetic powder. The structure of this polyacrylamide-coated iron oxide magnetic powder is as follows: Figure 2 As shown, it includes a magnetic core and a polyacrylamide coating layer surrounding the magnetic core. The magnetic core is a mixed phase of Fe2O3 and FeOOH with γ-Fe2O3 as the main phase. Based on the final polymerization reaction time at 60℃, it is named Fe2O3@PAM (45 min), and the polymer molecular weight of the polyacrylamide coating layer is 3800.

[0026] The polymerization reaction time at the final 60℃ was extended to 60 minutes (1 h) and 120 minutes (2 h). After the reaction, the product was cleaned and dried. The resulting polyacrylamide-coated iron oxide magnetic powder was named Fe2O3@PAM(1 h), with a polymer molecular weight of 4500, and Fe2O3@PAM(2 h), with a polymer molecular weight of 5200. Elemental analysis, infrared spectroscopy, and thermal decomposition tests revealed that the polyacrylamide content in the product decreased after 1 hour of polymerization. Therefore, the optimal polymerization reaction time is 45–60 minutes. The X-ray diffraction characteristics of the polyacrylamide-coated iron oxide magnetic powder obtained at different polymerization reaction times are shown below. Figure 3 As shown in the figure. The infrared spectral characteristics of polyacrylamide-coated iron oxide magnetic powder and commercially available high-purity γ-Fe2O3 are as follows. Figure 4 As shown.

[0027] Comparative Example: Commercially available high-purity γ-Fe₂O₃ was used as the magnetic core. 0.15 g was dispersed in 5 mL of water and sonicated for 30 minutes before being placed in a three-necked flask. 5 mL of water containing 0.075 g acrylamide and 0.0011 g potassium persulfate was added to the flask. Nitrogen gas was introduced, and the mixture was stirred at 1100 rpm for 10 minutes. Nitrogen gas was then stopped, the entire reaction apparatus was sealed, and the mixture was slowly heated to 30°C at a rate of 1°C per minute and held at that temperature for 30 minutes. The temperature was then rapidly increased to 60°C at a rate of 10°C per minute and the reaction was continued for 45 minutes. After the reaction was complete, the mixture was stirred continuously and allowed to cool naturally. It was then filtered, washed, and dried at 60°C to obtain polyacrylamide-coated iron oxide magnetic powder.

[0028] The polyacrylamide-coated iron oxide magnetic powder obtained in the embodiments of the present invention and the polyacrylamide-coated iron oxide magnetic powder obtained in the comparative example were subjected to water solubility tests. The polyacrylamide-coated iron oxide magnetic powder of the embodiments had good water solubility, reaching up to 7.6 g / L, while the polyacrylamide-coated iron oxide magnetic powder of the comparative example had much lower water solubility, not exceeding 0.3 g / L. This may be related to the different surface polymerization coating effects of the magnetic cores.

[0029] The hysteresis loop characteristic diagram of Fe2O3@PAM (45min) prepared in the example is shown below. Figure 5 As shown, the coercive field and remanent magnetization at room temperature are 5.6 kOe and 0.23 emu / g, respectively.

[0030] Finally, the polyacrylamide-coated iron oxide magnetic powder prepared by this invention can be added to an aqueous carrier liquid for non-destructive testing of surface defects in magnetic material components.

Claims

1. A polyacrylamide-coated iron oxide magnetic powder, characterized in that, It includes a magnetic core and a polyacrylamide coating layer covering the magnetic core, wherein the magnetic core is a mixed phase of Fe2O3 and FeOOH with Fe2O3 as the main phase.

2. The polyacrylamide-coated iron oxide magnetic powder according to claim 1, characterized in that, The magnetic core is a mixed phase of Fe2O3 and FeOOH with γ-Fe2O3 as the main phase.

3. The polyacrylamide-coated iron oxide magnetic powder according to claim 1, characterized in that, The degree of polymerization of the polyacrylamide in the polyacrylamide coating layer is 3000-6000.

4. A method for preparing polyacrylamide-coated iron oxide magnetic powder according to any one of claims 1 to 3, characterized in that, Including the following steps: The ferric salt is added to an aqueous solution containing a surfactant, and the pH of the system is adjusted to above 7.0 by alkali metal oxides. A precipitate is obtained through a hydrothermal reaction. The precipitate is separated, washed, and dried to obtain a powdered product. The powdered product is then calcined to obtain a magnetic core. The magnetic core is dispersed in water, and then acrylamide and an initiator are added. Under the protection of an inert atmosphere, a polymerization reaction occurs through the action of the initiator to obtain polyacrylamide-coated iron oxide magnetic powder.

5. The method for preparing polyacrylamide-coated iron oxide magnetic powder according to claim 4, characterized in that, The pH value was adjusted to 9.5–12.5 using alkali metal oxides.

6. The method for preparing polyacrylamide-coated iron oxide magnetic powder according to claim 4, characterized in that, The calcination temperature is 400–800℃, and the calcination time is 4–8 hours.

7. The method for preparing polyacrylamide-coated iron oxide magnetic powder according to claim 4, characterized in that, The polymerization reaction is carried out at 60-70°C for 45-60 minutes.

8. The method for preparing polyacrylamide-coated iron oxide magnetic powder according to claim 7, characterized in that, The polymerization reaction is first heated to 30-40°C at a rate of 1°C per minute and held at that temperature for 25-30 minutes, and then rapidly heated to 60-70°C at a rate of 10°C per minute.

9. The method for preparing polyacrylamide-coated iron oxide magnetic powder according to claim 4, characterized in that, The ferric salt is an inorganic acid salt, and the surfactant is an alcohol surfactant.

10. An application of polyacrylamide-coated iron oxide magnetic powder, characterized in that, The polyacrylamide-coated iron oxide magnetic powder according to any one of claims 1 to 3 is used for non-destructive testing of surface defects in magnetic material components.

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