Method for improving CT image contrast based on gadolinium-modified carbon fiber

Abstract

The invention discloses a method for improving computed tomography (CT) image contrast based on gadolinium-modified carbon fibers, and belongs to the technical field of nondestructive testing of composite materials. According to the method, the gadolinium element is stably modified on the surface of the carbon fiber through chemical bonding and an in-situ reduction process: firstly, the carbon fiber is activated by adopting mixed acid, then the carbon fiber is immersed into a gadolinium nitrate solution, and a-O-Gd < 3 + > bonding structure is formed through a coordination reaction; then stabilizing the gadolinium complex by using an ethylenediamine tetraacetic acid (EDTA) or diethylene triamine pentaacetic acid (DTPA) chelating agent; and finally, reducing by using sodium borohydride (NaBH4) to generate elemental gadolinium nanoparticles. According to the gadolinium-modified carbon fiber and the preparation method thereof, covalent linkage is formed between gadolinium and the carbon fiber through chemical bonding, the X-ray absorption efficiency is remarkably improved through the high atomic number of elementary substance gadolinium, and the CT value of the modified carbon fiber is remarkably improved. The method is suitable for nondestructive testing and structure-function integrated evaluation of carbon fiber composite materials in the fields of aerospace, rail transit and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of nondestructive testing of composite materials, and specifically relates to a method for stably modifying gadolinium on the surface of carbon fiber through chemical bonding and in-situ reduction processes, which is used to enhance the contrast of computed tomography (CT) imaging of the internal structure of carbon fiber composite materials. Background Art

[0002] Carbon fiber composites, due to their lightweight, high-strength, and corrosion-resistant properties, have become a core material in fields such as aerospace and rail transportation. However, process fluctuations during the material's manufacturing process, as well as impact loads and environmental erosion during service, can easily induce internal defects such as cracks, delamination, and fiber breakage. These defects not only weaken the material's mechanical properties but can also lead to catastrophic failure under certain operating conditions. Therefore, the use of non-destructive testing (NDT) technologies to monitor the health of carbon fiber composites throughout their lifecycle has become essential to ensure their safe application. Commonly used NDT methods for carbon fiber composites include ultrasonic testing (UT), eddy current testing (ECT), infrared thermography (IRT), and computed tomography (CT). While ultrasonic testing can effectively identify delamination and cracks, the acoustic wave propagation path is susceptible to interference when inspecting complex components, resulting in insufficient defect location accuracy. Eddy current testing is only suitable for surface and near-surface defects in conductive materials and is ineffective for detecting deep-seated defects within carbon fiber composites. While NDT can quickly screen large areas, it is significantly affected by ambient temperature and has low sensitivity for detecting minor defects. In comparison, computed tomography (CT) can penetrate the multi-layer structure of complex components, is not restricted by the shape of the components and the direction of the fiber layup, and can perform three-dimensional reconstruction of X-ray scanning data at different angles, and intuitively present the location, size, and shape of internal defects in the material with high-precision digital grayscale images, providing comprehensive and accurate information for the structural integrity assessment of composite materials. [1-3] The principle is that when X-rays pass through an object, they interact with the atoms in the object, causing the X-ray intensity to attenuate. The detector array and X-ray source rotate around the sample to obtain a series of attenuation profiles or projections, which are mathematically processed to construct a three-dimensional image of the object. Despite the above advantages, traditional CT imaging still has a significant defect when applied to carbon fiber composites, namely, the low contrast between carbon fiber and resin matrix limits the detection accuracy, making the attenuation contrast of tiny defects in carbon fiber composites unclear. [1,4,5]Studies have shown that by adding appropriate contrast agents to the matrix material, the CT imaging contrast between carbon fiber and resin matrix can be effectively improved. Contrast agents aggregate in the target tissue or interact specifically with the target tissue, changing the target tissue's absorption characteristics for X-rays, thereby increasing the contrast between the target tissue and surrounding tissues [6-9]. Contrast agents have been widely used in the medical field and are key auxiliary agents for improving the accuracy of medical imaging diagnosis [10,11].

[0003] Gadolinium (Gd, Z=64), a high atomic number lanthanide element, has demonstrated unique advantages as a contrast agent in the field of medical imaging. Compared with traditional iodine contrast agents, gadolinium has a mass absorption coefficient of 4.2 cm at 120 kV. 2 / g, about iodine (2.3cm 2 / g), and its K-edge energy (50keV) is highly matched with the commonly used CT energy spectrum range (80-140kVp), which significantly improves the photon absorption efficiency. In addition, the paramagnetic properties of gadolinium ions enable it to be used in MRI imaging, providing a new approach to achieving structural-functional integrated testing of composite materials. [10，12] Through chelating agents such as ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA), Gd 3+ It can form stable complexes, effectively reducing toxicity risks. However, the current research and application of gadolinium-based contrast agents are mainly focused on the biomedical field, and their potential in non-destructive testing of composite materials has not been fully explored. In practical applications, how to efficiently and stably anchor gadolinium to the carbon fiber surface while ensuring its long-term stability under complex loads are key issues that need to be addressed. Summary of the Invention

[0004] The present invention proposes a novel method for preparing gadolinium-modified carbon fibers, in which a gadolinium compound is fixed to the carbon fiber surface by chemical bonding and then reduced to elemental gadolinium, thereby significantly improving CT imaging contrast.

[0005] The specific steps include:

[0006] Step 1: Mix a certain concentration of nitric acid and sulfuric acid in a certain proportion in a beaker, immerse the carbon fiber in the mixed acid, set the reaction temperature and time, continue stirring for a while after cooling to room temperature, take out, wash with deionized water and dry.

[0007] Step 2: Prepare gadolinium nitrate (Gd(NO3)3) solution and add ammonia water to adjust the pH.

[0008] Step 3: Take a certain amount of the solution in step 3, immerse the activated carbon fiber in the solution, set the temperature and reaction time, and form -O-Gd 3+ Coordination structure.

[0009] Step 4: Add ethylenediaminetetraacetic acid (EDTA) solution and soak for a period of time to form a Gd-EDTA complex.

[0010] Step 5: Add NaBH4 solution dropwise, adjust the pH, and reduce at room temperature for a period of time;

[0011] Step 6: Remove the carbon fiber, wash it with deionized water, and vacuum dry it for a period of time to successfully obtain gadolinium-modified carbon fiber.

[0012] Preferably, the concentrations of nitric acid and sulfuric acid in step 1 are 0.1-0.3 M, the ratio is HNO3:H2SO4=2-3:1, the amount of carbon fiber is 0.1-0.5 g, the mixed acid is 5-25 mL, the reaction temperature is 80°C, the time is 2 h, and after cooling to room temperature, the stirring time is continued for 1-2 h.

[0013] Preferably, the concentration of the gadolinium nitrate (Gd(NO 3 ) 3 ) solution in step 2 is 0.1-0.2 M, and the pH is controlled to be 5-6.

[0014] Preferably, the amount of the solution in step 3 is 5-25 mL, the reaction temperature is 60-80° C., and the reaction time is 2-4 h.

[0015] Preferably, the concentration of the EDTA solution in step 4 is 0.05-0.1 M, and the immersion time is 30 min.

[0016] Preferably, the concentration of the NaBH4 solution in step 5 is 0.3-0.5 M, the amount added is 5-25 mL, the pH is adjusted to 5-6, and the reduction time is 1-2 h.

[0017] Preferably, in step 6, the vacuum drying temperature is set to 60° C. and the time is 12 h.

[0018] Compared with the prior art, the present invention has the following significant advantages:

[0019] (1) According to the present invention, the atomic number of the elemental gadolinium (Z=64) is significantly higher than that of the carbon fiber and the resin matrix. Under 120kV conditions, the CT value contrast of the modified carbon fiber is significantly improved, and tiny defects can be clearly identified.

[0020] (2) With the present invention, chemical bonding allows gadolinium to form a covalent connection with carbon fibers, thus preventing particle shedding caused by physical mixing;

[0021] (3) The present invention can be expanded to MRI / CT combined detection in the future to achieve simultaneous evaluation of the mechanical properties and internal structure of composite materials; DETAILED DESCRIPTION

[0022] Example 1:

[0023] Step 1: Take 0.3g of T800 carbon fiber and immerse it in 15mL of mixed acid solution (HNO3:H2SO4=3:1, concentration 0.1M). React at 80℃ for 2h. After cooling, continue stirring for 1.5h. Remove and wash with deionized water three times, and vacuum dry at 60℃ for later use.

[0024] Step 2: Prepare 0.15M Gd(NO3)3 solution and add ammonia water to adjust the pH to 5.8.

[0025] Step 3: Immerse the activated carbon fiber in 20 mL of gadolinium nitrate solution and stir at 70° C. for 3 h.

[0026] Step 4: Add 0.08 M EDTA solution and soak for 30 minutes to form a Gd-EDTA complex.

[0027] Step 5: Add 15 mL of 0.4 M NaBH4 solution (pH = 6) dropwise and reduce at room temperature for 1.5 h.

[0028] Step 6: Wash with deionized water until neutral, and dry under vacuum at 60°C for 12 h.

[0029] Example 2:

[0030] Step 1: Immerse 0.3g of T800 carbon fiber in 15mL of a mixed acid solution (HNO3:H2SO4=3:1, 0.1M concentration) at 80°C for 2h. After cooling, continue stirring for 1.5h. Remove and wash with deionized water three times, then vacuum dry at 60°C for later use.

[0031] Step 2: prepare 0.3M Gd(NO3)3 solution and add ammonia water to adjust the pH to 5.8.

[0032] Step 3: Immerse the activated carbon fiber in 20 mL of gadolinium nitrate solution and stir at 70° C. for 3 h.

[0033] Step 4: Add 0.08 M EDTA solution and soak for 30 minutes to form a Gd-EDTA complex.

[0034] Step 5: Add 15 mL of 0.4 M NaBH4 solution (pH = 6) dropwise and reduce at room temperature for 1.5 h.

[0035] Step 6: Wash with deionized water until neutral, and dry under vacuum at 60°C for 12 h.

[0036] Example 3:

[0037] Step 1: Take 0.3g of T800 carbon fiber and immerse it in 15mL of mixed acid solution (HNO3:H2SO4=3:1, concentration 0.1M). React at 80℃ for 2h. After cooling, continue stirring for 1.5h. Remove and wash with deionized water three times, and vacuum dry at 60℃ for later use.

[0038] Step 2: prepare 0.15M Gd(NO3)3 solution and add ammonia water to adjust the pH to 5.8.

[0039] Step 3: Immerse the activated carbon fiber in 20 mL of gadolinium nitrate solution and stir at a constant temperature of 60° C. for 4 h.

[0040] Step 4: Add 0.08 M EDTA solution and soak for 30 minutes to form a Gd-EDTA complex.

[0041] Step 5: Add 15 mL of 0.4 M NaBH4 solution (pH = 6) dropwise and reduce at room temperature for 1.5 h.

[0042] Step 6: Wash with deionized water until neutral, and dry in vacuum at 60°C for 12 h.

[0043] Example 4:

[0044] Step 1: Take 0.3g of T800 carbon fiber and immerse it in 15mL of mixed acid solution (HNO3:H2SO4=3:1, concentration 0.1M). React at 80℃ for 2h. After cooling, continue stirring for 1.5h. Remove and wash with deionized water three times, and vacuum dry at 60℃ for later use.

[0045] Step 2: prepare 0.15M Gd(NO3)3 solution and add ammonia water to adjust the pH to 5.8.

[0046] Step 3: Immerse the activated carbon fiber in 20 mL of gadolinium nitrate solution and stir at 70° C. for 3 h.

[0047] Step 4: Add 0.05M DTPA solution and soak for 30 minutes to form a Gd-DTPA complex.

[0048] Step 5: Add 15 mL of 0.4 M NaBH4 solution (pH = 6) dropwise and reduce at room temperature for 1 h.

[0049] Step 6: Wash with deionized water until neutral, and dry under vacuum at 60°C for 12 h.

[0050] Example 5:

[0051] Step 1: Take 0.3g T800 carbon fiber and immerse it in 15mL mixed acid solution (HNO3:H2SO4=3:1, concentration 0.1M), react at 80℃ for 2h, continue stirring for 1.5h after cooling. After taking out, wash it with deionized water three times, and vacuum dry it at 60℃ for use.

[0052] Step 2: prepare 0.15M Gd(NO3)3 solution and add ammonia water to adjust the pH to 5.8.

[0053] Step 3: Immerse the activated carbon fiber in 20 mL of gadolinium nitrate solution and stir at 70° C. for 3 h.

[0054] Step 4: Add 0.08 M EDTA solution and soak for 30 minutes to form a Gd-EDTA complex.

[0055] Step 5: Add 15 mL of 0.4 M NaBH4 solution (pH = 6) dropwise and reduce at room temperature for 1 h.

[0056] Step 6: Wash with deionized water until neutral, and dry under vacuum at 60°C for 12 h.

[0057] Comparative Example 1:

[0058] This comparative example is basically the same as Example 1, except that in step 1, no acid activation was performed, and the gadolinium powder and carbon fiber were directly physically mixed.

[0059] The results showed that the gadolinium loading on the physically hybrid carbon fibers was only 3.5 wt %, the shear strength was 4.7 MPa (15.2 MPa in Example 1), the CT value was 105 HU, and the gadolinium loss rate was 42% after a 500-hour salt spray test.

[0060] Comparative Example 2:

[0061] This comparative example is basically the same as Example 1, except that EDTA chelation was not used.

[0062] The results showed that gadolinium particles were severely agglomerated (SEM showed particle size > 500 nm), CT values ​​fluctuated by ± 50 HU, and MRI relaxation rate r1 decreased to 8.3 mM. -1 s -1 (Example 1 is 12.5).

[0063] Comparative Example 3:

[0064] This comparative example is basically the same as Example 1, the only difference being that no reduction treatment (Gd 3+ state)

[0065] The results showed that the CT value of carbon fiber was 285HU (the absorption efficiency of single substance gadolinium was reduced), and X-ray photoelectron spectroscopy (XPS) showed that Gd 3+ Accounting for 98%.

[0066] Comparative Example 4:

[0067] This comparative example is basically the same as Example 1, except that step 2 is to adjust the pH to 8.0.

[0068] The results showed that Gd(OH)3 was precipitated (XRD detected gadolinium hydroxide phase), with an effective gadolinium loading of only 2.1wt% and a CT value of 75HU.

[0069] References

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Claims

1. A method for improving CT image contrast based on gadolinium-modified carbon fiber, characterized in that: The following steps are involved: Step 1: Immerse the carbon fiber in a mixed acid solution of nitric acid and sulfuric acid for surface activation treatment, followed by washing and drying; Step 2: Prepare gadolinium nitrate (Gd(NO3)3) solution and adjust the pH to 5-6; Step 3: Immerse the activated carbon fiber in a gadolinium nitrate solution to undergo coordination reaction to form -O-Gd 3+ bonding structure; Step 4: adding a chelating agent solution for impregnation to form a gadolinium-chelate complex; Step 5: Add sodium borohydride (NaBH4) solution dropwise and adjust the pH to 5-6 to perform a reduction reaction to generate elemental gadolinium (Gd 0 ); Step 6: Wash and vacuum dry to obtain gadolinium-modified carbon fibers.

2. The method according to claim 1, characterized in that In step 1, the volume ratio of nitric acid to sulfuric acid in the mixed acid solution is 3:1, and the total concentration is 0.1M; the activation treatment temperature is 80°C, and the time is 1-2 hours; and the amount ratio of carbon fiber to mixed acid solution is 0.1-0.5g:5-25mL.

3. The method according to claim 1, characterized in that In step 2, the concentration of the gadolinium nitrate solution is 0.1-0.2 M; and the pH is adjusted by dropwise addition of ammonia water.

4. The method according to claim 1, wherein In step 3, the reaction temperature is 60-80° C., the reaction time is 2-4 hours, and the ratio of gadolinium nitrate solution to carbon fiber is 5-25 mL: 0.1-0.5 g.

5. The method according to claim 1, wherein In step 4, the chelating agent is ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA); the concentration of the chelating agent solution is 0.05-0.1M; and the immersion time is 30 minutes.

6. The method according to claim 1, wherein In step 5, the concentration of the sodium borohydride solution is 0.3-0.5 M; the amount of sodium borohydride solution added is 5-25 mL; and the reduction reaction time is 1-2 h.

7. The method according to claim 1, characterized in that In step 6: the vacuum drying temperature is 60° C. and the time is 12 h. Gadolinium-modified carbon fiber prepared by the method according to any one of claims 1 to 7, characterized in that: the gadolinium loading is 4.5-5.2 wt% (EDS analysis); the particle size of the elemental gadolinium nanoparticles is 50-100 nm (SEM observation); and the CT value reaches 420-450 HU (120 kV tube voltage).

8. The gadolinium-modified carbon fiber according to claim 1, wherein: After 500h in 85℃ / 85%RH damp heat environment, the CT value decay rate is less than 5%; fatigue load (10 6 After 3 cycles, 200 MPa stress amplitude), the CT value retention rate is greater than 95%.

9. A method for nondestructive testing of composite materials, characterized in that: The method comprises the following steps: compounding the gadolinium-modified carbon fiber according to claims 8-9 with a resin matrix, detecting internal defects by computer tomography (CT) or MRI / CT dual-mode imaging technology, and identifying cracks or delaminations ≥10 μm.