A toughened and reinforced ceramic substrate and its application on TEC cooling plate

Abstract

The application relates to the field of ceramic materials, in particular to a toughened and strengthened ceramic substrate and application of the ceramic substrate on a TEC refrigeration sheet, which is made of alumina powder, MAX phase ceramic powder, boron nitride nanowire, lanthanum borate and a sintering aid, the prepared ceramic substrate has excellent mechanical strength and better heat conduction performance, and has high volume resistivity, so that the use requirement of the TEC refrigeration sheet can be met.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials, specifically to a toughened and reinforced ceramic substrate and its application in TEC (Thermal Design Equipment) cooling chips. Background Technology

[0002] A thermoelectric cooler (TEC cooler) is a solid-state heat pump that utilizes the Peltier effect to achieve precise temperature control. It typically consists of two ceramic substrates, one above the other, and multiple pairs of P-type / N-type semiconductor thermoelectric elements sandwiched between them. The ceramic substrates not only need to provide electrical insulation and a high thermal conductivity path, but also must withstand repeated thermal cycling stresses; therefore, the mechanical and thermal properties of the substrate material are subject to extremely stringent requirements. Currently, commercially available TEC coolers mostly use alumina ceramic substrates, which are inexpensive, provide reliable insulation, and are resistant to high temperatures. However, pure alumina ceramics have low fracture toughness and flexural strength, limited thermal conductivity, and are prone to failure due to microcrack propagation under frequent temperature changes or large temperature differences, severely limiting the reliability and lifespan of the cooler during long-term service. Summary of the Invention

[0003] Purpose of the invention: To address the above-mentioned technical problems, this invention proposes a toughened and reinforced ceramic substrate and its application in TEC refrigeration chips.

[0004] The technical solution adopted is as follows: A toughened and reinforced ceramic substrate is made of alumina powder, MAX phase ceramic powder, boron nitride nanowires, lanthanum borate and sintering aids.

[0005] Furthermore, the mass ratio of the alumina powder, MAX phase ceramic powder, boron nitride nanowires, lanthanum borate, and sintering aid is 80-90:5-10:3-5:1-3:1-3.

[0006] Furthermore, the general chemical formula of the MAX phase ceramic powder is M n+1 AlN n ; Where M is a transition metal element and n is 2 or 3.

[0007] Furthermore, M represents Ti.

[0008] Furthermore, the chemical structural formula of the MAX phase ceramic powder is Ti4AlN3.

[0009] Ti4AlN3 is a typical MAX-phase layered ternary nitride, possessing both the thermal conductivity of metals and the high strength and oxidation resistance of ceramics. Its unique layered structure and nano-layered slip and twisting deformation mechanisms effectively deflect cracks and dissipate fracture energy, thus significantly reinforcing and toughening the alumina matrix. During sintering, Ti4AlN3 decomposes to form titanium nitride and alumina. Titanium nitride, as a hard phase, is dispersed at grain boundaries and pores, acting as a reinforcing agent that pins α-Al2O3 grain growth, inhibits abnormal growth, and promotes crack deflection / bridging. The alumina formed by oxidation forms a homologous interface with the matrix, effectively buffering the differences in thermal expansion coefficients between phases, optimizing interfacial bonding strength to promote the pull-out effect of residual MAX phases, and physically isolating conductive permeation channels. This significantly improves the fracture toughness and flexural strength of the composite material while ensuring its dielectric insulation properties remain intact.

[0010] Furthermore, the preparation method of the boron nitride nanowires is as follows: Boron source, nitrogen source, poloxamer 407 and catalyst are dissolved in water to form a mixed solution, which is then dried to obtain a dry gel. Under a nitrogen atmosphere, the dry gel is initiated to undergo a self-propagating combustion reaction to obtain the initial product; The initial product is obtained by heat treatment followed by washing and purification.

[0011] The boron nitride nanowires obtained by this method have a high aspect ratio and fewer structural defects. They can form a three-dimensional network in the matrix and consume fracture energy through mechanisms such as crack bridging, pull-out, and crack deflection. At the same time, their high intrinsic thermal conductivity can construct continuous thermal conduction pathways and improve thermal conductivity.

[0012] Furthermore, the catalyst is any one of a water-soluble nickel salt, a water-soluble cobalt salt, or a water-soluble iron salt.

[0013] The catalyst is uniformly dispersed at the molecular level in the precursor solution, which is beneficial for the formation of boron nitride nanowires with uniform size and high aspect ratio.

[0014] Boric acid, as a boron source, undergoes dehydration and condensation into polyboron-oxygen clusters during heating. Urea, as a nitrogen source and reducing agent, decomposes thermally to produce nitrogen-containing reactive intermediates such as ammonia and cyanuric acid. Ammonium nitrate serves as both an auxiliary nitrogen source and a solid oxidant; the oxidizing gas produced during its decomposition undergoes a vigorous redox reaction with the pyrolysis products of urea, releasing a large amount of heat energy, driving the propagation of a self-propagating combustion wave, and causing the system to heat up instantaneously, achieving rapid nitridation. The metallic nickel generated from the high-temperature decomposition of nickel hexahydrate acts as a catalyst, forming a Ni-B eutectic liquid phase with molten boron oxide. Based on the gas-liquid-solid (VLS) growth mechanism, boron nitride nuclei preferentially precipitate along specific directions, forming a one-dimensional nanowire structure. Poloxamer 407 (F127) plays a crucial role in morphology regulation: its self-assembly micelles in aqueous solution can anchor multi-boron-oxygen clusters through hydrogen bonding, achieving pre-assembly of boron, nitrogen, and catalyst at the nanoscale and effectively suppressing component segregation; the micelle network constructs mesoporous channels in the dry gel, ensuring efficient diffusion of nitrogen-containing gas to catalyst sites during combustion and reserving space for nanowire growth, preventing product agglomeration; the nanoconfining effect of poloxamer 407, synergistic with the VLS mechanism, helps to obtain high aspect ratio one-dimensional structures. In the post-processing, heat treatment removes residual carbon impurities, and hydrochloric acid washing removes nickel catalyst and metal oxides, finally yielding boron nitride nanowires.

[0015] Furthermore, the sintering aid is composed of silicon dioxide, magnesium oxide, and calcium oxide in a mass ratio of 1-3:1-3:1-3.

[0016] This ternary sintering aid generates a low-melting-point liquid phase during sintering, promoting densification. It can also react chemically with the surfaces of alumina and MAX phases, optimizing the grain boundary structure and improving grain boundary strength.

[0017] Furthermore, the preparation method of the above-mentioned toughened and reinforced ceramic substrate is as follows: Alumina powder, MAX phase ceramic powder, boron nitride nanowires, lanthanum borate and sintering aids are mixed, ball-milled, dried, granulated, pressed into green bodies, debinded, and then sintered.

[0018] Furthermore, the sintering temperature is 1550-1650℃.

[0019] This invention also provides the application of the above-mentioned toughened and reinforced ceramic substrate in TEC (Thermoelectric Cooler) chips, wherein a molybdenum-manganese metallization layer, a metal plating layer, and a metal sheet layer are formed on the toughened and reinforced ceramic substrate. Using this ceramic substrate in TEC chips allows them to withstand long-term thermal cycling shocks, significantly reducing the risk of failure due to microcrack propagation and extending the service life of the cooling chip.

[0020] The formation of the molybdenum-manganese metallization layer requires the preparation of a uniform slurry by mixing high-purity molybdenum powder, manganese powder, and glass phase materials. This slurry is then precisely coated onto the surface of the toughened and reinforced ceramic substrate using screen printing. After low-temperature drying to remove organic solvents, a dense raw material layer is formed. Subsequently, the core high-temperature sintering process begins, where the temperature is raised to 1300°C to 1550°C under the protection of a mixture of argon and ammonia. At this temperature, manganese combines with oxide to form manganese oxide, which then reacts chemically with the ceramic at high temperature to form a manganese aluminum spinel transition layer, achieving atomic-level chemical bonding.

[0021] After sintering, nickel, iron, or copper plating is performed using chemical plating or electroplating to form a metal coating with excellent solderability. Finally, solid-phase diffusion bonding is completed with nickel foil, copper foil, or steel sheet under specific atmosphere (hydrogen + nitrogen) and high temperature and pressure conditions. This process utilizes the thermal expansion buffering characteristics of the molybdenum-manganese layer to effectively overcome the mismatch problem between ceramics and metals, achieving a seal between ceramics and metals.

[0022] Furthermore, the bonding of other metal sheets onto a toughened and reinforced ceramic substrate using the above methods is also within the scope of this patent.

[0023] Furthermore, the area ratio of metal sheets and toughened and reinforced ceramic substrates is 1%-100%, all of which are within the scope of protection of this patent.

[0024] Beneficial effects This invention provides a toughened and reinforced ceramic substrate and its application in TEC (Thermal Design Equipment) cooling chips, which has the following significant advantages compared with the prior art: This invention achieves simultaneous improvement in mechanical and thermal conductivity through multiphase synergistic composites of alumina, MAX-phase ceramics, boron nitride nanowires, and lanthanum borate. The interlayer slip and torsional deformation of the MAX-phase layered structure effectively blunt crack tips, inducing crack deflection and bridging; the high aspect ratio and flexibility of the boron nitride nanowires can form bridging and pull-out along the crack propagation path; and the La2+ released from the decomposition / partial dissociation of lanthanum borate... 3+ Segregation at α-Al₂O₃ grain boundaries inhibits abnormal matrix grain growth through solute dragging; La 3+ The large ionic radius of the material can adsorb grain boundary impurities and free oxygen, purifying the grain boundaries and reducing the low-melting glass phase. At the same time, the B2O3 component (derived from the pyrolysis / local decomposition of lanthanum borate) works synergistically with sintering aids to optimize the liquid phase composition, promoting densification and grain boundary bonding. These three strengthening and toughening mechanisms work together at different scales to endow the ceramic substrate with excellent flexural strength and fracture toughness.

[0025] Boron nitride nanowires were synthesized in situ using a specific self-propagating combustion method, resulting in products with high purity, large aspect ratio, and good dispersibility. These nanowires significantly improve the fracture toughness and thermal conductivity of the composite material compared to commercially available particulate boron nitride. Combined with optimized MAX phase content and the synergistic effect of lanthanum borate, the thermal conductivity can be improved while maintaining high density, fully meeting the requirements of TEC (Thermal Design Circuit) coolers for high thermal conductivity and high reliability.

[0026] The ceramic substrate preparation process of this invention is highly compatible with existing alumina ceramic production lines, uses readily available raw materials, is simple to operate, and is easy to industrialize. When applied to TEC (Thermal Design Circuit) coolers, it can effectively improve the thermal shock fatigue resistance of the coolers and significantly extend their service life. Attached Figure Description

[0027] Figure 1 The XRD patterns are those of boron nitride prepared in Example 1 and Comparative Example 4.

[0028] Figure 2 This is a SEM image of the boron nitride nanowires prepared in Example 1.

[0029] Figure 3 This is a SEM image of the boron nitride prepared in Comparative Example 4. Detailed Implementation

[0030] Unless otherwise specified in the examples, the conditions were performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products. Techniques not mentioned in this invention refer to existing technologies. Unless otherwise specified, the following examples and comparative examples are parallel experiments, using the same processing steps and parameters.

[0031] Alumina powder: α-Al₂O₃, average particle size 0.5 μm, purity 99.9%; Ti4AlN3: average particle size 1μm, purity 99%; Boron nitride nanowires: self-made; Lanthanum borate: self-made; Silica: average particle size 0.5μm, purity 99.9%; Magnesium oxide: average particle size 0.1 μm, purity 99.9%; Calcium oxide: average particle size 0.1 μm, purity 99.9%.

[0032] Example 1:

[0033] A toughened and reinforced ceramic substrate is made of alumina powder, Ti4AlN3, boron nitride nanowires, lanthanum borate and sintering aids in a mass ratio of 85:7.5:4:2:2.

[0034] The sintering aid consists of silicon dioxide, magnesium oxide, and calcium oxide in a mass ratio of 1:1:1.

[0035] The preparation method of the above-mentioned toughened and reinforced ceramic substrate is as follows: 15g boric acid, 10g urea, 25g ammonium nitrate, 2g poloxamer 407, and 1.5g nickel nitrate hexahydrate (catalyst) were dissolved sequentially in 200mL of deionized water at 80℃. The solution was stirred vigorously until a transparent solution was formed. The transparent solution was then heated and stirred until a dry gel was formed. The dry gel was transferred to a self-propagating high-temperature synthesis apparatus. High-purity nitrogen was introduced into the reaction chamber to replace the air. The dry gel was then ignited using electrodes to initiate a self-propagating reaction. After the reaction was completed, the initial product was cooled and removed. The initial product was then placed in a muffle furnace and heat-treated at 600℃ for 2 hours in air. It was then washed sequentially with 1mol / L hydrochloric acid and deionized water until neutral. Finally, it was dried in a vacuum drying oven at 80℃ for 12 hours to obtain boron nitride nanowires. The XRD pattern of the nanowires is shown in [Figure number missing]. Figure 1 SEM image (see) Figure 2 .

[0036] Take 60 mL of a 0.1 mol / L lanthanum nitrate solution in a beaker, then add 1.27 g of citric acid to the solution while stirring. After the citric acid dissolves, continue stirring at room temperature for 15 minutes. Then add 0.37 g of boric acid to the solution and continue stirring for 30 minutes. Heat and stir the mixture until a dry gel forms. Transfer the dry gel to a self-propagating high-temperature synthesis apparatus. Purge the reaction chamber with high-purity nitrogen to replace the air, then ignite the dry gel using electrodes to initiate a self-propagating reaction. After the reaction is complete, cool and remove the product. Place the product in a muffle furnace and heat-treat at 700 °C for 2 hours in air atmosphere to obtain lanthanum borate. The above-mentioned alumina powder, Ti4AlN3, boron nitride nanowires, lanthanum borate, and sintering aids were added to a ball mill jar, and anhydrous ethanol was used as the ball milling aid. The mixture was ball milled for 10 hours in a planetary ball mill, dried in a vacuum drying oven at 80°C for 12 hours, and granulated using a 5wt% polyvinyl alcohol solution as a binder. The resulting granules were passed through an 80-mesh sieve and pressed into blanks under a pressure of 100 MPa. The blanks were heated to 600°C at a rate of 1°C / min and held for 2 hours to remove the binder, and then heated to 1600°C at a rate of 10°C / min and held for 2 hours to sinter.

[0037] Example 2:

[0038] The embodiment is basically the same as Example 1, except that the toughened and reinforced ceramic substrate provided in this embodiment is made of alumina powder, Ti4AlN3, boron nitride nanowires, lanthanum borate and sintering aids in a mass ratio of 90:5:5:1:3.

[0039] Example 3:

[0040] Similar to Example 1, except that the toughened and reinforced ceramic substrate provided in this example is made of alumina powder, Ti4AlN3, boron nitride nanowires, lanthanum borate and sintering aids in a mass ratio of 80:10:3:3:1.

[0041] Example 4:

[0042] This example is basically the same as Example 1, except that the sintering aid in this example is composed of silicon dioxide, magnesium oxide and calcium oxide in a mass ratio of 3:1:3.

[0043] Example 5:

[0044] This example is basically the same as Example 1, except that the sintering aid in this example is composed of silicon dioxide, magnesium oxide and calcium oxide in a mass ratio of 1:3:3.

[0045] Example 6:

[0046] This example is basically the same as Example 1, except that the sintering aid in this example is composed of silicon dioxide, magnesium oxide and calcium oxide in a mass ratio of 3:3:1.

[0047] Comparative Example 1: It is basically the same as Example 1, except that Ti4AlN3 is not added.

[0048] Comparative Example 2: It is basically the same as Example 1, except that boron nitride nanowires are not added.

[0049] Comparative Example 3: The method is essentially the same as in Example 1, except that commercially available boron nitride particles (average particle size 1 μm) are used instead of boron nitride nanowires.

[0050] Comparative Example 4: The preparation was essentially the same as in Example 1, except that poloxamer 407 was not added. The XRD pattern of the resulting boron nitride is shown in [Figure 1]. Figure 1 SEM image (see) Figure 3 .

[0051] Comparative Example 5: It is basically the same as Example 1, except that lanthanum borate is not added.

[0052] Performance testing: The samples prepared in each embodiment and comparative example were subjected to performance tests.

[0053] The sample dimensions were 25mm × 5mm × 2.5mm, with a chamfer of 0.3mm, and it was ground and polished. The bending strength was tested using the three-point bending method on a CMT5105 benchtop electronic tensile testing machine, with the indenter moving at a speed of 0.5mm / min and a span of 20mm.

[0054] The fracture toughness of the sample was tested using the single-edge cutting method. The sample size was 25mm×5mm×2.5mm, the kerf width was 0.2mm, the depth was 1.8-2.0mm, the span was 20mm, and the indenter descending speed was 0.05mm / min.

[0055] Thermal conductivity was tested using a TC-3000 thermal conductivity meter, based on the transient hot wire method.

[0056] A three-electrode resistivity testing platform was constructed in accordance with IEC 62631-3 standard. The platform consists of five parts: a high-temperature, high-pressure sealed measurement chamber, a temperature control unit, a high-voltage DC power supply, a weak current measurement system, and a PC acquisition program. The volume resistivity calculation formula used in the volume resistivity test is: ρ = R × A / h, where R is the sample resistance in Ω; A is the effective area of ​​the protected electrode in m². 2 h represents the sample thickness in meters (m).

[0057] The test results are shown in Table 1 below.

[0058]

[0059] As shown in Table 1 above, the ceramic substrate prepared by the present invention has excellent mechanical strength and good thermal conductivity, and high volume resistivity, which can meet the application requirements of TEC cooling chips.

[0060] Example 1 achieved a synergistic breakthrough in mechanical and thermal conductivity by simultaneously introducing the MAX phase Ti4AlN3, boron nitride nanowires, and lanthanum borate. Comparative Example 1, without the addition of the MAX phase, lacks the micro / nano-scale toughening mechanism provided by the layered structure. Under load, Ti4AlN3 can undergo interlaminar slip and twisting, forcing crack deflection and consuming a large amount of fracture energy; it also lacks the reinforcing effect of its decomposition products on the matrix. The absence of the MAX phase results in low crack propagation resistance and increased phonon scattering, thus significantly reducing strength, toughness, and thermal conductivity.

[0061] Comparative Example 2 did not introduce boron nitride nanowires; the matrix was toughened solely by the MAX phase. Lacking the bridging, pull-out, and crack pinning effects of the one-dimensional nanophase, the energy dissipation in the fracture process was insufficient, resulting in a simultaneous decrease in both strength and toughness. The high aspect ratio of boron nitride nanowires could construct a continuous thermally conductive network in the matrix; their absence led to the breakage of thermal conductive pathways, hindered phonon transport, and a significant decrease in thermal conductivity, lower than some other comparative examples.

[0062] Comparative Example 3 uses commercially available boron nitride particles instead of nanowires. The particles lack a high aspect ratio and flexibility, making it difficult to form effective bridging and pull-out, resulting in a weak toughening effect. At the same time, the contact area between particles is small and the interfacial thermal resistance is high, making it impossible to build an efficient thermally conductive network. Therefore, the strength, toughness and thermal conductivity are far inferior to those of Example 1.

[0063] Comparative Example 4, without the addition of poloxamer 407, exhibited significantly lower flexural strength, fracture toughness, and thermal conductivity compared to Example 1. This is because the absence of poloxamer 407 leads to uncontrolled growth of boron nitride nanowires: the boron source, nitrogen source, and nickel catalyst cannot achieve uniform pre-assembly at the nanoscale, easily inducing local component segregation. Consequently, the boron nitride products generated during self-propagating combustion are mostly curved rod-shaped, lacking a high aspect ratio one-dimensional nanostructure, severely weakening the bridging, pull-out, and crack pinning toughening effects of the nanowires. Furthermore, the introduction of poloxamer 407 increases internal defects in the composite material, reduces load transfer efficiency, and makes it difficult to construct continuous and efficient phonon thermal conduction pathways. Therefore, both mechanical strength and thermal conductivity deteriorate simultaneously, confirming the crucial role of poloxamer 407 in inducing controllable growth of boron nitride nanowires and ensuring the comprehensive performance of the composite material.

[0064] Comparative Example 5, without the addition of lanthanum borate, lacked a eutectic phase at the grain boundaries to promote densification, resulting in increased residual porosity and microcracks, leading to reduced load transfer efficiency and fracture resistance. Lanthanum borate can also optimize grain boundary bonding, alleviate thermal mismatch stress between alumina and the reinforcing phase, and suppress excessive phonon scattering at grain boundaries. Its absence not only degrades mechanical properties but also affects thermal conductivity.

[0065] In summary, Example 1 exhibits superior overall performance. The absence or substitution of a single component weakens the corresponding mechanism, leading to a comprehensive decline in performance. Regarding volume resistivity, all examples and comparative examples achieve 10-1. 11 With a strength above the Ω·m level, it meets the general standards for insulating ceramics and satisfies the stringent requirements of TEC cooling chips for electrical insulation performance.

[0066] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. The description of the relevant mechanisms is only a theoretical speculation based on current experimental data and does not constitute a limitation on the technical solutions of the present invention and its inventiveness.

Claims

1. A toughened and reinforced ceramic substrate, characterized in that, It is made of alumina powder, MAX phase ceramic powder, boron nitride nanowires, lanthanum borate and sintering aids.

2. The toughened and reinforced ceramic substrate as described in claim 1, characterized in that, The mass ratio of alumina powder, MAX phase ceramic powder, boron nitride nanowires, lanthanum borate, and sintering aid is 80-90:5-10:3-5:1-3:1-3.

3. The toughened and reinforced ceramic substrate as described in claim 1, characterized in that, The chemical formula of the MAX phase ceramic powder is M n+1 AlN n ; Where M is a transition metal element and n is 2 or 3.

4. The toughened and reinforced ceramic substrate as described in claim 3, characterized in that, M represents Ti.

5. The toughened and reinforced ceramic substrate as described in claim 4, characterized in that, The chemical structural formula of the MAX phase ceramic powder is Ti4AlN3.

6. The toughened and reinforced ceramic substrate as described in claim 1, characterized in that, The boron nitride nanowires are prepared as follows: Boron source, nitrogen source, poloxamer 407 and catalyst are dissolved in water to form a mixed solution, which is then dried to obtain a dry gel. Under a nitrogen atmosphere, the dry gel is initiated to undergo a self-propagating combustion reaction to obtain the initial product; The initial product is obtained by heat treatment followed by washing and purification.

7. The toughened and reinforced ceramic substrate as described in claim 6, characterized in that, The catalyst is any one of water-soluble nickel salt, water-soluble cobalt salt, or water-soluble iron salt.

8. The toughened and reinforced ceramic substrate as described in claim 1, characterized in that, The sintering aid is composed of silicon dioxide, magnesium oxide and calcium oxide in a mass ratio of 1-3:1-3:1-3.

9. The toughened and reinforced ceramic substrate as described in claim 1, characterized in that, Its preparation method is as follows: Alumina powder, MAX phase ceramic powder, boron nitride nanowires, lanthanum borate and sintering aids are mixed, ball-milled, dried, granulated, pressed into green bodies, debinded, and then sintered.

10. An application of a toughened and reinforced ceramic substrate as described in any one of claims 1-9 on a TEC refrigeration chip, wherein the TEC refrigeration chip includes the toughened and reinforced ceramic substrate, and a molybdenum-manganese metallization layer, a metal plating layer, and a metal sheet layer are formed on the toughened and reinforced ceramic substrate.

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