Ti3AlC2-MAX-phase terahertz wave absorber with inverted pyramid-like structure and preparation method of Ti3AlC2-MAX-phase terahertz wave absorber

Abstract

The invention belongs to the technical field of terahertz wave absorbing, relates to a terahertz wave absorbing material, particularly provides a Ti3AlC2-MAX-phase terahertz wave absorber with an inverted pyramid-like structure and a preparation method thereof, and provides an integrally-formed high-stress wave absorber with broadband absorption characteristics, high-temperature resistance characteristics and oxidation resistance characteristics for a terahertz frequency band. Structural shaping is performed based on the 3D printing technology, an inverted pyramid-like structure is obtained through design, then the Ti3AlC2-MAX phase inverted pyramid-like structure terahertz wave absorber is prepared in a Joule flash burning mode, the lowest reflection loss of the terahertz wave absorber in the frequency band of 1-4 THz is 25 dB, the maximum reflection loss can reach 50 dB, and the terahertz wave absorber has good absorption performance; meanwhile, the terahertz absorber has the characteristics of high temperature resistance, strong stress and the like, and shows outstanding application prospects in the field of terahertz wave absorption.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz wave absorption, and relates to terahertz wave absorbing materials. Specifically, it provides a terahertz absorber with an inverted pyramid-like structure of Ti3AlC2-MAX phase and a preparation method thereof. Background Art

[0002] Terahertz waves are an important band (0.1 THz - 10 THz) between microwaves and infrared rays, and have many very unique properties, such as good optical resolution, extremely strong penetration ability, and broadband spectrum. With the rapid development of various high-frequency electronic devices, the devices will inevitably radiate a large amount of terahertz waves into space, which has led to the emergence of problems such as terahertz wave electromagnetic interference; EMI will not only affect the normal operation of other electronic devices, but also cause serious harm to human health and the environment. Terahertz wave absorbing materials can convert incident electromagnetic waves into heat energy or other forms of energy for dissipation, thus greatly reducing the harm of electromagnetic wave radiation.

[0003] As a new type of ceramic material, MAX phase materials combine the dual characteristics of metals and ceramics, and have excellent mechanical properties, electrical conductivity, thermal stability, and oxidation resistance, etc., making them an excellent choice as functional absorbing materials. As described in the literature "Shi Y M, Luo F, Liu Y, Zhou W C, Zhang X H. Preparation and microwave absorption properties of Ti3AlC2 synthesized by pressureless sintering TiC / Ti / Al[J]. Internatioanl Journal of Applied Ceramic Technology, 2015, 12: E174–E177.", using TiC powder, Ti powder, and Al powder as raw materials, the Ti3AlC2-MAX phase material was prepared at 1350 °C by the pressureless sintering method, and the influence of different paraffin filling ratios on the wave absorption performance of the material was also studied; it was found that the reflection loss of 70 wt% MAX phase was greater than 10 dB in the X band, having the best wave absorption performance; however, its wave absorption performance is still limited by its relatively high conductivity. Therefore, when pure MAX phase is used alone as an absorber, the relatively high conductivity will cause strong reflection of electromagnetic waves, resulting in a decrease in wave absorption ability.

[0004] Using multiple scattering and reflection of periodic structures to achieve better impedance matching to reduce the impact of strong reflection is an effective strategy to improve wave absorption performance. However, traditional hot pressing molding relies on molds and can only produce simple shapes (such as flat plates and cylinders), and cannot achieve hollow, porous, cantilever or bionic structures supported by 3D printing. In addition, complex structures require multi-step processing (such as cutting and bonding), which increases the risk of defects. At the same time, mold design and processing require weeks to months, which makes it difficult to respond to rapid prototyping needs. In addition, hot pressing molding requires machining the sintered bulk material to the target shape, which will result in 30% to 70% of raw material loss (such as cutting debris). In contrast, 3D printing does not require molds, and it only takes a few hours from design to finished product. 3D printing controls the waste rate to <5% through additive manufacturing. Therefore, using additively manufactured structures to improve wave absorption performance is a feasible technical solution. As described in the literature "Liu, Pei, et al." Direct ink writing printed flexible double-layer staggered woodpile structure for multi-band compatible absorption of gigahertz and terahertz waves." Chemical Engineering Journal 478(2023):147474.", a flexible double-layer staggered woodpile structure was prepared by direct ink writing (DIW) 3D printing technology. By utilizing its unique periodic geometric design and material gradient characteristics, efficient multi-frequency compatible absorption was achieved in the GHz (1GHz~18GHz) and THz (0.1THz~2THz) frequency bands: by adjusting the size and spacing of the two-layer woodpile units and the impedance matching of the carbon-based composite ink, the reflectivity of the structure was lower than -10dB in multiple frequency bands, while being lightweight (density <0.1g / cm 3 ) and flexible bendable properties provide a new solution for cross-band stealth and electromagnetic protection; however, the integrated high-stress absorbing material with wide-band absorption characteristics, high temperature resistance and anti-oxidation properties acting in the terahertz band still needs to be developed. Summary of the invention

[0005] The purpose of the present invention is to provide a Ti3AlC2-MAX phase inverted pyramid-like structure terahertz absorber and its preparation method, so as to provide an integrally formed high-stress absorber with broadband absorption characteristics, high-temperature resistance characteristics, and antioxidant characteristics in the terahertz frequency band; the present invention is based on 3D printing technology for structural shaping, designs an inverted pyramid-like structure, and then prepares a Ti3AlC2-MAX phase inverted pyramid-like structure terahertz absorber by means of Joule flash sintering. Its minimum reflection loss is 25 dB and the maximum reflection loss can reach 50 dB in the frequency band of 1-4 THz, having good absorption performance; at the same time, this terahertz absorber has characteristics such as high-temperature resistance and high stress, and shows outstanding application prospects in the field of terahertz wave absorption.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A Ti3AlC2-MAX phase inverted pyramid-like structure terahertz absorber, characterized in that the terahertz absorber has a grid structure, and each grid unit adopts an inverted pyramid-like structure; the inverted pyramid-like structure is a cavity structure, which is composed of N layers of square wires stacked in sequence, the centers of the square wires in each layer coincide, and the side lengths of the square wires increase equally in sequence from bottom to top; the square wires are made of Ti3AlC2-MAX phase material.

[0008] Further, in the inverted pyramid-like structure, the value range of the number of layers of the square wires is: N≥4.

[0009] Further, in the inverted pyramid-like structure, the unit period of the grid unit is 2-5 mm.

[0010] Further, in the inverted pyramid-like structure, the wire diameters of the square wires in each layer are the same, specifically: 0.8 mm-1.2 mm.

[0011] Further, the preparation method of the Ti3AlC2-MAX phase inverted pyramid-like structure terahertz absorber is characterized by including the following steps:

[0012] Step 1: Use sodium carboxymethyl cellulose (CNF) as a binder, ball-mill and mix the binder with Ti source raw materials, C source raw materials, and Al source raw materials to obtain a mixed material; mix the mixed material with deionized water to form a CNF@Ti3AlC2-MAX precursor 3D printing ink.

[0013] Step 2: Print a CNF@Ti3AlC2 MAX precursor embryo through inkjet direct writing (DIW) 3D printing technology.

[0014] Step 3: Sinter the CNF@Ti3AlC2-MAX precursor green body at 1375 - 1425 °C for 1 - 3 min using the Joule flash sintering process to obtain a terahertz absorber with a Ti3AlC2-MAX phase and a quasi-inverted pyramid structure.

[0015] Further, in Step 1, the ratio of the Ti source raw material, C source raw material, and Al source raw material is Ti:C:Al = 3:2:1.2.

[0016] Further, in Step 1, the mass ratio of sodium carboxymethyl cellulose (CNF) is 2 wt% - 6 wt%.

[0017] Further, in Step 1, the specific process of mixing the mixed material with deionized water is as follows: Add deionized water to the mixed material at a ratio of 10.33:3 and mix to form a gel state; add deionized water again at a ratio of 10.33:3.5 and mix to form the CNF@Ti3AlC2-MAX precursor 3D printing ink.

[0018] Further, in Step 2, the printing process is specifically as follows: Use a desktop dispensing machine driven by three axes as the printing device, and set the printing parameters as follows: nozzle diameter 0.8 - 1.2 mm, X / Y axis movement speed: 30 - 40 mm / s, Z axis movement speed: 20 - 30 mm / s, printing speed: 1 - 2 mm / s, printing pressure: 0.25 - 0.40 Mpa.

[0019] Further, in Step 3, the specific process of Joule flash sintering is as follows: sintering gas pressure: 0.1 - 0.12 Mpa, heating-up time 5 - 10 s, heat preservation time: 1 - 3 min, cooling time: 8 - 10 min, sintering temperature: 1375 - 1425 °C.

[0020] Based on the above technical solutions, the beneficial effects of the present invention are as follows:

[0021] The present invention provides a terahertz absorber with a Ti3AlC2-MAX phase and a quasi-inverted pyramid structure and a preparation method thereof. First, the CNF@Ti3AlC2 MAX precursor ink is prepared; on this basis, a quasi-inverted pyramid structure is designed through the direct ink writing (DIW) 3D printing technology, which has good self-supporting performance; finally, a terahertz absorber with a Ti3AlC2-MAX phase and a quasi-inverted pyramid structure is prepared by means of Joule flash sintering. The minimum reflection loss of this material in the frequency band of 1 - 4 THz is 25 dB, and the maximum reflection loss can reach 50 dB, showing good absorption performance. At the same time, it has the advantages of high temperature resistance and strong stress, and demonstrates outstanding application prospects in the field of terahertz wave absorption. Description of the Drawings

[0022] Figure 1This is the rheological property diagram of the 3D printing ink of the CNF@Ti3AlC2 MAX precursor in the present invention.

[0023] Figure 2 This is the structural schematic diagram of the inverted pyramid-like structure in the present invention.

[0024] Figure 3 This is the schematic diagram of the principle of direct ink writing (DIW) 3D printing.

[0025] Figure 4 This is the physical picture of the inverted pyramid-like structure embryo of the CNF@Ti3AlC2 MAX precursor in the present invention.

[0026] Figure 5 This is the SEM diagram of the sintered sample of the CNF@Ti3AlC2 MAX phase inverted pyramid-like structure in the present invention.

[0027] Figure 6 This is the XRD diagram of the sintered sample of the CNF@Ti3AlC2 MAX phase inverted pyramid-like structure in the present invention.

[0028] Figure 7 This is the reflection loss frequency domain diagram of the sintered sample of the CNF@Ti3AlC2 MAX phase inverted pyramid-like structure in the present invention. Detailed implementation manners

[0029] To make the objectives, technical solutions and beneficial effects of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0030] This embodiment provides a terahertz absorber with an inverted pyramid-like structure of the Ti3AlC2-MAX phase and a preparation method thereof. The terahertz absorber with the inverted pyramid-like structure is prepared by 3D printing, and mainly includes: preparation of the 3D printing ink of the CNF@Ti3AlC2-MAX precursor, 3D printing of the inverted pyramid-like structure based on direct ink writing (DIW), and sintering of the CNF@Ti3AlC2 MAX phase material based on Joule flash sintering. The technical solutions of this embodiment will be described in detail below with reference to the tests.

[0031] 1. Preparation of the 3D printing ink of the CNF@Ti3AlC2 MAX precursor;

[0032] Weigh the raw materials according to the molar ratio of Ti:C:Al = 3:2:1.2, 7.2 g of Ti powder, 1.2 g of graphite powder, and 1.62 g of Al powder, and add sodium carboxymethyl cellulose according to 3 wt% mass percentage (relative to the total mass of Ti powder, graphite powder and Al powder); then pour the powder into the ball milling tank, seal a circle of sealing glue at the edge of the tank body to reduce the oxidation effect of oxygen in the air, and then put the ball milling tank into the planetary ball mill, adjust the planetary ball mill to a working frequency of 20 Hz, and carry out ball milling for 8 h in the positive and negative modes to obtain the CNF@Ti3AlC2-MAX precursor powder;

[0033] Subsequently, put the ball-milled precursor powder into an agate mortar, first inject 3 g of deionized water with a pipette, stir and grind it in the agate mortar for 5 min until there is no powdery sample in the mortar, that is, the powder and deionized water are fully mixed to form a gel; then add 3.5 g of deionized water, a total of 6.5 g of deionized water, and adjust the viscosity of the powder to a suitable range to prepare the CNF@Ti3AlC2 MAX precursor ink for 3D printing.

[0034] The rheological properties of the ink are as Figure 1 shown, Figure 1 in which a is the curve of the complex viscosity (η*) varying with the oscillation angular frequency (ω), Figure 1 in which b is the curve of G’ and G” varying with the oscillating shear stress, Figure 1 in which c is the curve of η* under two cyclic loads of low shear rate (10 -1 rad / s) and high shear rate (10 2 rad / s), Figure 1 in which d is the corresponding yield stress at the intersection of G' and G”; as can be seen from the figure, the printing ink shows good shear thinning performance, and as the shear frequency increases, the viscosity of the ink also decreases, and this characteristic is beneficial to the smooth extrusion of the ink. The printing ink shows a relatively high complex viscosity at low shear frequencies, and the order of magnitude is all above 10 5 ; at high shear frequencies, the complex viscosity decreases significantly, changing to above 10 3 ; when two cycles are experienced and then restored to high shear frequencies, the viscosity retention rate is all above 99%, showing good thixotropic properties. The yield stress of the ink is 137.69 Pa, which meets the requirements of 3D printing of ceramic materials quite well, and at the same time has good G’, which also makes the ink have good self-supporting properties.

[0035] 2. 3D printing of an inverted pyramid-like structure based on direct ink writing (DIW);

[0036] For electromagnetic wave absorption, the absorbing structure composed of absorbing materials is required to have strong electromagnetic loss ability; on the other hand, a gradient structure also needs to be designed to form a gradient distribution in the incident direction of electromagnetic waves; therefore, in order to achieve a high-performance absorbing unit structure with broadband absorption, such as Figure 2 As shown, a hierarchical gradient structure is proposed, the number of hierarchical orders is at least 4, and each unit adopts a quasi-inverted pyramid structure. The quasi-inverted pyramid structure is a cavity structure, which is specifically composed of N layers of square wires stacked in sequence with the centers of the square wires in each layer coinciding. According to the order from bottom to top, the side lengths of the square wires increase equally in sequence. The hierarchical gradient design strategy can enable the electromagnetic wave absorption structure to achieve better impedance matching. At the same time, the grid structure helps the absorbing material to dissipate electromagnetic waves because the electromagnetic waves are reflected multiple times in the periodic structure, accompanied by loss absorption in the medium.

[0037] The quasi-inverted pyramid structure is prepared by direct ink writing (DIW) 3D printing. For direct ink writing (DIW) 3D printing, its principle is as Figure 3 As shown. Using the above ink, a desktop dispenser driven by three axes is used as the printing device, and a pneumatic extrusion device is used to perform DIW 3D printing according to the designed 3D printing path. After printing, the sample is transferred to a well-ventilated and dry place and dried at room temperature for 24 h to obtain a quasi-inverted pyramid structure embryo of CNF@Ti3AlC2 MAX precursor, as Figure 4 As shown. The specific printing parameters are shown in Table 1:

[0038] Table 1

[0039]

[0040] 3. Sintering of CNF@Ti3AlC2 MAX phase material based on Joule flash sintering;

[0041] The quasi-inverted pyramid structure embryo of CNF@Ti3AlC2 MAX precursor formed by 3D printing is subjected to Joule rapid sintering in an inert atmosphere with argon protection to obtain the CNF@Ti3AlC2 MAX phase material. The specific sintering parameters are shown in Table 2:

[0042] Table 2

[0043]

[0044] To further characterize the crystal structure and phase composition of the material, SEM and XRD are used to determine the crystal phases present in the material. As Figure 5 Shown is the SEM image of the sintered sample of the CNF@Ti3AlC2 MAX phase quasi-inverted pyramid structure, and the typical layered structure of the Ti3AlC2 MAX phase material can be seen. As Figure 6The XRD pattern of the sintered sample with a CNF@Ti3AlC2 MAX-phase inverted pyramid-like structure is shown. The main diffraction peak is the main diffraction peak of Ti3AlC2 corresponding to the (104) crystal plane at 38.985°. This indicates that at this temperature, the Ti3AlC2 MAX-phase material accounts for the majority in the overall material, which also demonstrates the effectiveness of sintering.

[0045] To further illustrate the beneficial effects of the present invention, the microwave absorption performance will be described in detail below.

[0046] The test system used for microwave absorption characterization is a terahertz time-domain spectroscopy system (THz-TDS), and the available test frequency range is 0.5 - 4 THz;

[0047] As Figure 7 shown by the reflection loss curve, it can be seen that the inverted pyramid-like structure has good absorption of more than 22 dB in the frequency band of 0.5 - 4 THz, and the maximum reflection loss can reach 50 dB, showing good absorption performance.

[0048] In summary, the present invention combines 3D printing technology to provide a terahertz absorber with a Ti3AlC2-MAX-phase inverted pyramid-like structure and its preparation method, which can achieve beneficial microwave absorption performance in the terahertz frequency band.

[0049] The above is only the specific implementation manner of the present invention. Any feature disclosed in this specification, unless specifically described, can be replaced by other equivalent or similar-purpose alternative features; all the features disclosed, or all the steps in any method or process, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A terahertz absorber with an inverted pyramid-like structure of Ti3AlC2-MAX phase, characterized in that, The terahertz absorber has a grid structure, and each grid unit adopts a quasi-inverted pyramid structure; the quasi-inverted pyramid structure is a cavity structure, which is composed of N layers of square wires stacked in sequence, the centers of the square wires in each layer coincide, and the side lengths of the square wires increase equally in sequence from bottom to top; the square wires are made of Ti3AlC2-MAX phase material.

2. The Ti3AlC2-MAX phase inverted pyramid structure terahertz absorber according to claim 1, characterized in that, In the quasi-inverted pyramid structure, the value range of the number of layers of the square wires is: N≥4.

3. The Ti3AlC2-MAX phase-based inverted pyramid structure terahertz absorber according to claim 1, characterized in that, In the quasi-inverted pyramid structure, the unit period of the grid unit is 2-5 mm.

4. The Ti3AlC2-MAX phase-based inverted pyramid structure terahertz absorber according to claim 1, characterized in that, In the quasi-inverted pyramid structure, the wire diameters of the square wires in each layer are the same, specifically: 0.8 mm-1.2 mm.

5. The preparation method of the Ti3AlC2-MAX phase inverted pyramid structure terahertz absorber according to claim 1, characterized in that It includes the following steps: Step 1: Use sodium carboxymethyl cellulose (CNF) as a binder, ball-mill and mix the binder with Ti source raw material, C source raw material, and Al source raw material to obtain a mixed material; mix the mixed material with deionized water to form CNF@Ti3AlC2-MAX precursor 3D printing ink. Step 2: Print a CNF@Ti3AlC2 MAX precursor embryo through inkjet direct writing (DIW) 3D printing technology. Step 3: Use the Joule flash sintering process to sinter the CNF@Ti3AlC2-MAX precursor embryo at 1375-1425 °C for 1-3 min to obtain a terahertz absorber with a quasi-inverted pyramid structure of Ti3AlC2-MAX phase.

6. The preparation method of the Ti3AlC2-MAX phase inverted pyramid-like structure terahertz absorber according to claim 5, characterized in that, In Step 1, the ratio of the Ti source raw material, C source raw material, and Al source raw material is: Ti:C:Al = 3:2:1.

2.

7. The preparation method of the Ti3AlC2-MAX phase inverted pyramid-like structure terahertz absorber according to claim 5, characterized in that, In Step 1, the mass ratio of sodium carboxymethyl cellulose (CNF) is 2 wt%-6 wt%.

8. The preparation method of the Ti3AlC2-MAX phase inverted pyramid-like structure terahertz absorber according to claim 5, characterized in that, In Step 1, the specific process of mixing the mixed material with deionized water is: add deionized water to the mixed material according to a ratio of 10.33:3, and mix it into a gel state; add deionized water again according to a ratio of 10.33:3.5, and mix to form CNF@Ti3AlC2-MAX precursor 3D printing ink.

9. The preparation method of the Ti3AlC2-MAX phase inverted pyramid-like structure terahertz absorber according to claim 5, characterized in that, In Step 2, the printing process is specifically: use a desktop dispensing machine driven by three axes as the printing device, and set the printing parameters as: nozzle diameter 0.8-1.2 mm, X / Y axis movement speed: 30-40 mm / s, Z axis movement speed: 20-30 mm / s, printing speed: 1-2 mm / s, printing pressure: 0.25-0.40 Mpa.

10. The preparation method of the Ti3AlC2-MAX phase inverted pyramid-like structure terahertz absorber according to claim 5, characterized in that, In Step 3, the specific process of Joule flash sintering is: sintering gas pressure: 0.1-0.12 Mpa, heating time 5-10 s, holding time: 1-3 min, cooling time: 8-10 min, sintering temperature: 1375-1425 °C.

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