In-situ pressureless sintering preparation method of TiB2 / MgAl2O4 composite ceramic material

Abstract

The present invention discloses an in-situ pressureless sintering method for preparing a TiB2 / MgAl2O4 composite ceramic material, relating to the technical field of special ceramics. The method comprises the following steps: S1, ball-milling TiO2, B4C, MgO, Al2O3, and LiF, drying, and sieving to obtain a powder; S2, adding a binder to the powder for granulation; S3, press-molding the granulated powder; and S4, calcining the molded material at 1600-1700°C for 50-90 minutes, followed by holding at 500-600°C for 1-2 hours. The TiB2 / MgAl2O4 composite ceramic material is prepared using a one-step in-situ method. The composite ceramic material has a uniform microstructure, a strong reaction driving force, a simplified process, and a compact flow. It also exhibits excellent dielectric properties and can be used to manufacture absorbing materials, reducing electromagnetic wave reflection and improving stealth performance. Furthermore, the one-step in-situ reaction process produces abundant heterogeneous interfaces on a microscale, effectively improving the material's polarization loss performance.

Description

Technical Field

[0001] The present invention relates to the technical field of special ceramics, and in particular to an in-situ pressureless sintering preparation method for a TiB2 / MgAl2O4 composite ceramic material. Background Art

[0002] Titanium diboride (TiB2), an ultra-high-temperature ceramic material, is renowned for its high melting point, high hardness, excellent electrical and thermal conductivity, and superior high-temperature electrical and mechanical properties. It has a wide range of applications in hypersonic vehicles, aeroengines, high-temperature structural components, and radar absorbing systems.

[0003] Magnesium aluminum oxide (MgAl2O4), also known as magnesium aluminate or magnesium aluminum spinel, is a typical structural ceramic material, attracting widespread attention for its excellent thermal stability, low thermal expansion coefficient, high melting point, good mechanical properties, and outstanding electrical insulation. This material exhibits excellent thermal shock resistance and chemical inertness at high temperatures, and can operate stably and long-term in oxidizing and corrosive environments. It is particularly suitable for applications such as high-temperature protective coatings, plasma spray substrates, electrical insulation components, and structural supports.

[0004] TiB2 / MgAl2O4 composite ceramics have superior properties compared to titanium diboride and magnesium aluminum oxide. Currently, conventional preparation methods for TiB2 / MgAl2O4 composite ceramics typically use a two-step route: first, TiB2 powder and MgAl2O4 powder are prepared separately, followed by mixing, molding, and high-temperature sintering to produce the composite ceramic. However, this method suffers from multiple steps, complex processes, low powder reactivity, and poor interfacial bonding, hindering the large-scale, low-cost production of ceramic materials and the integrated molding of complex-shaped components. Summary of the Invention

[0005] To solve at least one of the above problems, the present invention proposes an in-situ pressureless sintering method for preparing TiB2 / MgAl2O4 composite ceramic materials.

[0006] The technical solution of the present invention is: an in-situ pressureless sintering preparation method of TiB2 / MgAl2O4 composite ceramic material, comprising the following steps:

[0007] S1. Ball-mill TiO2, B4C, MgO, Al2O3 and LiF, dry and sieve to obtain a powder;

[0008] S2, taking powder and adding binder to granulate;

[0009] S3, taking the granulated powder and pressing it into shape;

[0010] S4. Take the formed material, calcine it at 1600-1700℃ for 50-90min, and then keep it at 500-600℃ for 1-2h.

[0011] One embodiment of the present invention is that, by weight percentage, the amount of TiO2 added is 8-22%, the amount of B4C added is 5-12%, the amount of MgO added is 50-70%, the amount of Al2O3 added is 10-15%, and the amount of LiF added is 1.5-2.5%. In the present invention, the added TiO2, B4C, MgO, and Al2O3 are specific reaction raw materials, wherein TiO2 and B4C are sintered to produce TiB2, and MgO and Al2O3 are sintered to produce MgAl2O4 spinel. Lithium fluoride is used as a catalyst, which is completely volatilized during the high-temperature sintering process, and no related elements are detected in the subsequent characterization process. At the same time, in the present invention, since high-temperature sintering is required and boron element is easily volatilized under high temperature conditions, the present invention adds an excessive amount of boron element; and for the magnesium-aluminum spinel structure, the present invention adopts magnesium oxide and aluminum oxide to sinter, and at the same time, the amount of aluminum oxide added is much higher than that of magnesium oxide, so that the performance of the final composite ceramic structure is better.

[0012] One embodiment of the present invention is that, in S1, the sieve mesh number is 200 mesh, and the powder with low particle size has higher activity in the subsequent molding and sintering processes, and makes the mixing of various materials more uniform.

[0013] One embodiment of the present invention is that in S2, the binder is polyvinyl alcohol, and the amount thereof added is 6-10% of the mass of the powder.

[0014] Furthermore, S2 also includes the following steps: passing the granulated product through a 100-mesh sieve, and using the sieve residue as the powder after granulation. In this process, the powder not bound by the adhesive is mainly removed, so that the product obtained by subsequent molding is more uniform and stable.

[0015] According to one embodiment of the present invention, in S3 , the pressure of the press molding is 25-35 MPa.

[0016] One embodiment of the present invention is that in S4, the calcination operation is performed under a protective atmosphere, and the heat preservation operation is performed under an air atmosphere. Beneficial effects

[0017] 1. The method for preparing TiB2 / MgAl2O4 of the present invention is a one-step in-situ method with uniform microstructure, strong reaction driving force, simplified process and compact flow, avoiding the "powder presynthesis + mixing + secondary sintering" process in the traditional method.

[0018] 2. The present invention produces a TiB2 / MgAl2O4 composite ceramic material through a one-step in-situ process. This material exhibits excellent dielectric properties and can be used to manufacture absorbing materials, reducing electromagnetic wave reflection and improving stealth performance. The one-step in-situ reaction process produces abundant heterogeneous interfaces at the microscopic scale, effectively improving the material's polarization loss performance. The resulting TiB2 and MgAl2O4 both exhibit excellent high-temperature resistance, giving the TiB2 / MgAl2O4 composite ceramic material prepared by the present invention great potential for application in the field of high-temperature stealth. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the XRD test spectrum, where Figure 1 (a) is TMA15, standard TiB2, standard MgAl2O4 spinel and standard Al 18 B4O 33 XRD pattern of Figure 1 (b) in the figure shows the XRD patterns of TMA9, TMA12, TMA15, TMA18 and TMA21;

[0020] Figure 2 This is the SEM test result diagram, where: Figure 2 (a) is the microstructure of TMA15. Figure 2 (b) is the microstructure diagram of TMA-MS;

[0021] Figure 3 The dielectric constant test results of the composite ceramic materials prepared in Examples 1 to 5 of the present invention are shown in FIG. Figure 3 (a) is the graph showing the change of the real part of the dielectric constant (ε′) with frequency. Figure 3 (b) is the imaginary part of the dielectric constant ( ε″ ) changes with frequency, Figure 3 (c) is the curve of loss tangent changing with frequency;

[0022] Figure 4 Graph showing dielectric constant test results of composite ceramic materials of Example 1 and Comparative Example 1, wherein: Figure 4 (a) is a comparison diagram of the change of the real part of the dielectric constant (ε′) of Example 1 and Comparative Example 1 with frequency. Figure 4 (b) is the imaginary part of the dielectric constant of Example 1 and Comparative Example 1 ( ε″ ) with frequency changes, Figure 4 (c) is a comparison diagram of the change of loss tangent with frequency in Example 1 and Comparative Example 1;

[0023] Figure 5 This is the reflection loss test result diagram, where: Figure 5(a) in the figure is the test result of TMA15. Figure 5 (b) in the figure is the test result of TMA-MS. DETAILED DESCRIPTION

[0024] The specific implementation methods of the present invention will be clearly and completely described below with reference to examples. Obviously, the examples described are only part of the embodiments of the present invention, rather than all the embodiments.

[0025] Example 1: A method for preparing a TiB2 / MgAl2O4 composite ceramic material by in-situ pressureless sintering, comprising the following steps:

[0026] S1. Take 222g of TiO2, 126g of B4C, 885g of Al2O3, 190g of MgO and 29g of LiF, place them in a ball mill and add a small amount of ethanol for ball milling. Place the product in a drying oven, dry it at 120°C, and then pass it through a 200-mesh sieve to obtain a powder.

[0027] S2. Take the powder prepared in S1, add 8 wt% of polyvinyl alcohol by weight of the powder, stir evenly, and pass through a 100-mesh sieve to obtain the residue.

[0028] S3. Take the sieve residue, place it in a mold, and use a hydraulic press to press the sieve residue at a pressure of 30 MPa to die-cast the sieve residue.

[0029] S4. Take the formed material, place it in a tube furnace, and calcine it at 1650°C in a nitrogen atmosphere for 1 hour. After calcination, cool it to 550°C and keep it at this temperature for 2 hours in an air atmosphere. Cool it to room temperature to obtain the composite ceramic material TMA15.

[0030] The final product was analyzed and found that the mass percentage of TiB2 in the composite ceramic material was about 15wt%, and the rest was MgAl2O4 spinel structure, and also contained a small amount of Al 18 B4O 33 impurities.

[0031] Example 2: The difference from Example 1 is that the added amounts of TiO2, B4C, Al2O3, MgO and LiF are 133g, 76g, 949g, 204g and 28g respectively, and the rest are the same, and finally the composite ceramic material TMA9 is obtained.

[0032] Analysis of the final product shows that the mass percentage of TiB2 in the composite ceramic material is about 9wt%, and the rest is MgAl2O4 spinel structure.

[0033] Example 3: The difference from Example 1 is that the added amounts of TiO2, B4C, Al2O3, MgO and LiF are 178g, 101g, 917g, 198g and 28g respectively, and the rest are the same, and finally the composite ceramic material TMA12 is obtained.

[0034] Analysis of the final product shows that the mass percentage of TiB2 in the composite ceramic material is about 12wt%, and the rest is MgAl2O4 spinel structure.

[0035] Example 4: The difference from Example 1 is that the added amounts of TiO2, B4C, Al2O3, MgO and LiF are 267g, 152g, 853g, 184g and 30g respectively, and the rest are the same, and finally the composite ceramic material TMA18 is obtained.

[0036] The final product was analyzed and found that the mass percentage of TiB2 in the composite ceramic material was about 18wt%, and the rest was MgAl2O4 spinel structure, and also contained a small amount of Al 18 B4O 33 impurities.

[0037] Example 5: The difference from Example 1 is that the added amounts of TiO2, B4C, Al2O3, MgO and LiF are 312g, 177g, 821g, 176g and 30g respectively, and the rest are the same, and finally the composite ceramic material TMA21 is obtained.

[0038] The final product was analyzed and found that the mass percentage of TiB2 in the composite ceramic material was about 21wt%, and the rest was MgAl2O4 spinel structure, and also contained a small amount of Al 18 B4O 33 impurities.

[0039] Comparative Example 1: The difference from Example 1 is that in S1, 150 g of titanium diboride and 850 g of magnesium aluminum spinel are taken as raw materials for ball milling, and the rest are the same, and finally a composite ceramic material TMA-MS is obtained.

[0040] In order to illustrate the advantages of the composite ceramic material prepared by the embodiment of the present invention, it is tested below.

[0041] 1. Microstructure and phase analysis

[0042] XRD analysis: XRD analysis was performed on the composite ceramic material obtained in the above embodiment, and the results are as follows: Figure 1 As shown. Among them, Figure 1 (a) is TMA15, standard TiB2, standard MgAl2O4 spinel and standard Al 18 B4O 33The XRD pattern of TiB2 shows that the characteristic diffraction peaks of TiB2 are clearly visible, appearing at approximately 27.60°, 34.13°, 44.44°, 56.99°, 61.10°, 68.13°, 68.33°, 71.89° and 78.64°, respectively, corresponding to its (001), (100), (101), (002), (110), (102), (111), (200) and (201) crystal planes, indicating that TMA15 contains a typical hexagonal lattice structure of TiB2. In addition to the TiB2 peak, the diffraction peaks at 37.6°, 45.6° and 62.7° also belong to the (311), (222) and (400) planes of MgAl2O4 (PDF#89-1627), indicating that MgAl2O4 has been successfully incorporated into the composite structure. In addition, the broad peaks near 22° and 30° correspond to Al 18 B4O 33 The (001) and (111) planes of the composite material confirm its presence in the composite material. TMA15 contains two main structures of TiB2 and MgAl2O4 spinel, and also contains a small amount of Al 18 B4O 33 impurities.

[0043] Figure 1 (b) is the XRD pattern of TMA9, TMA12, TMA15, TMA18 and TMA21. It can be seen from the figure that with the increase of TiB2 content, the diffraction peak intensity of TiB2 phase in the sample gradually increases, and is always accompanied by the presence of MgAl2O4 phase, indicating that during the entire in-situ reaction process, MgAl2O4 spinel structure can be stably generated and coexist with TiB2. In addition, in samples with higher TiB2 content (such as 15wt.%, 18wt.%, 21wt.%), a small amount of Al 18 B4O 33 The presence of a phase may be related to the secondary reaction of the residual aluminum source during the reaction. Overall, no other impurity phases were detected in the samples, indicating that this one-step in-situ method has a clear reaction path, well-controlled phase composition, and good phase purity and reproducibility.

[0044] SEM (Scanning Electron Microscope) Analysis: Take the composite ceramic material TMA15 and TMA-MS, use SEM to characterize its microstructure, and finally Figure 2 shown.

[0045] in, Figure 2(a) shows the microstructure of TMA15. The cross-sectional morphology reveals a uniformly distributed, plate-like structure of the TiB2 phase, forming numerous densely bonded heterojunction interfaces with the matrix. The interfaces are devoid of significant pores, demonstrating excellent interfacial bonding. This demonstrates that the in-situ pressureless sintering method of this embodiment promotes a close intergrowth between TiB2 and MgAl2O4, resulting in a rich heterojunction interface and enhancing the composite's stability and functionality at high temperatures.

[0046] Figure 2 (b) is the microstructure diagram of TMA-MS. It can be seen from the figure that the distribution of TiB2 is not as good as that of Figure 2 (a) is uniform, with significant agglomeration. Part of the interface between TiB2 and the matrix is ​​relatively loose, indicating poor interfacial fusion. This suggests that the composite ceramic material produced using the two-step sintering method has fewer heterojunction surfaces formed within the material, hindering subsequent performance improvements.

[0047] 2. Characterization of dielectric constant

[0048] Take the composite ceramic materials TMA9, TMA12, TMA15, TMA18 and TMA21, and test their dielectric properties. The final results are as follows: Figure 3 and Figure 4 shown.

[0049] Figure 3 (a) shows the change of the real part of the dielectric constant (ε′) with frequency. As can be seen from the figure, it increases significantly with the increase of TiB2 content. Among them, the ε′ value of the TMA21 sample is the highest, indicating that it has the strongest polarization ability. This significant improvement is attributed to the introduction of the high conductivity of TiB2 and the uniform conductive path formed in the matrix, which effectively enhances the interfacial polarization effect. In addition, each group of samples has a good performance in the 13-18 GHz frequency band. ε′ The changes are smooth, reflecting good dielectric stability.

[0050] Figure 3 (b) is the imaginary part of the dielectric constant ( ε″ ) changes with frequency, which further reveals that the dielectric loss capacity increases with the increase of TiB2 content. The TMA21 sample maintains the highest ε″ value, indicating that it can more efficiently convert electromagnetic energy into thermal energy and has excellent wave absorption potential.

[0051] Figure 3 (c) in the figure is the curve of loss tangent changing with frequency. It can be seen from the figure that the loss tangent increases as the TiB2 content increases. The TMA21 sample shows an obvious peak at the high-frequency end, further verifying that it has stronger energy dissipation ability under the action of high-frequency electromagnetic waves.

[0052] Figure 4 The comparison chart of TMA15 and TMA-MS test results is shown in Figure 2. Figure 4 As shown in (a), the one-step in-situ synthesis sample ε′ The overall value is significantly higher than that of the multi-step synthesis sample, showing a stronger dielectric polarization ability, and the fluctuation is small during the frequency change, reflecting good dielectric stability; Figure 4 From (b) in the figure, we can see that ε″ The comparison of the values ​​further shows that the in-situ synthesized material has a higher dielectric loss capacity in the entire frequency band, indicating that it can effectively convert electrical energy into thermal energy under the action of electromagnetic waves; Figure 4 As can be seen in (c), the change in loss tangent further verifies this point. The loss tangent value of the one-step in-situ sample is significantly higher than that of the multi-step synthesis sample, and a peak appears at the high-frequency end, indicating that it has stronger wave absorption performance in the high-frequency band. This result is mainly attributed to the formation of a rich and uniformly distributed heterojunction interface between the TiB2 phase and the MgAl2O4 matrix in the one-step in-situ reaction, which effectively enhances the interface polarization and thus improves the overall dielectric properties. The uneven distribution of TiB2 and poor interface bonding in the multi-step synthesis sample limit the charge accumulation and polarization behavior, resulting in a significant decrease in its dielectric properties. The above results fully illustrate the significant advantages of the one-step in-situ synthesis strategy adopted in the present invention in optimizing the microstructure of composite materials and improving electromagnetic parameters.

[0053] The above results show that as the TiB2 content increases, more and more evenly distributed conductive phases and heterojunction interfaces are formed in the composite material, significantly enhancing the interface polarization and conductivity loss effects, thereby effectively improving the overall dielectric properties and microwave absorption capabilities. In contrast, the traditional multi-step synthesis method limits polarization behavior and energy dissipation due to uneven TiB2 distribution and poor interface bonding. This shows that the one-step in situ synthesis strategy adopted by the present invention shows significant advantages in optimizing microstructure and improving electromagnetic response performance.

[0054] 3. Reflection loss test

[0055] Take TMA15 and TMA-MS to test the reflection loss of electromagnetic waves of composite ceramic materials with different thicknesses. The final results are as follows: Figure 5 shown.

[0056] Figure 5 (a) is the test result of TMA15. It can be seen from the figure that it exhibits excellent wave absorption performance in the thickness range of 1.0~1.4 mm, and when the sample thickness is 1.0 mm, it achieves the minimum reflection loss (RL) at 17.94 GHz. min) reaches –18.73 dB; when the sample thickness is 1.2 mm and it presents a wide-band effective absorption bandwidth in the range of 12.4–18 GHz (EAB=3.03 GHz, RL < –10 dB), the absorption performance is significant. Figure 5 (b) is the test result of TMA-MS. It can be seen from the figure that its overall performance is relatively poor. Even at its optimal thickness (1.4mm), its RL min It's also only -9.91 dB, and there's no EAB.

[0057] The above test results demonstrate that the one-step in-situ reaction process of the present invention forms a uniform and dense heterojunction interface between TiB2 and MgAl2O4, effectively enhancing the impedance matching capability of the composite material while also strengthening the interface polarization and multiple loss mechanisms of electromagnetic wave energy, thereby significantly improving electromagnetic wave absorption performance. In contrast, in the multi-step synthesis sample, the uneven distribution of TiB2 particles and the discontinuous interface result in insufficient electromagnetic wave reflection loss in the material, leading to a significant decline in performance.

[0058] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a TiB2 / MgAl2O4 composite ceramic material by in-situ pressureless sintering, characterized in that: The following steps are involved: S1. Ball-mill TiO2, B4C, MgO, Al2O3 and LiF, dry and sieve to obtain a powder; S2, taking powder and adding binder to granulate; S3, taking the granulated powder and pressing it into shape; S4. Take the formed material, calcine it at 1600-1700°C for 50-90 minutes, and then keep it at 500-600°C for 1-2 hours; In terms of mass percentage, the amount of TiO2 added is 8-22%, the amount of B4C added is 5-12%, the amount of MgO added is 50-70%, the amount of Al2O3 added is 10-15%, and the amount of LiF added is 1.5-2.5%.

2. The method according to claim 1, characterized in that In S1, the sieve mesh number is 200 mesh.

3. The method according to claim 1, characterized in that In S2, the binder is polyvinyl alcohol, and the amount added is 6-10% of the powder mass.

4. The method according to claim 3, characterized in that S2 further includes the following steps: passing the granulated product through a 100-mesh sieve, and using the sieve residue as the granulated powder.

5. The method according to claim 1, wherein In S3, the pressure of the press molding is 25 to 35 MPa.

6. The method according to claim 1, characterized in that In S4, the calcination operation is carried out under a protective atmosphere, and the heat preservation operation is carried out under an air atmosphere.

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