Preparation method of double-layer high-temperature adhesive for connecting brass and aluminum oxide

Abstract

The invention relates to a preparation method of a double-layer high-temperature adhesive for connecting brass and aluminum oxide, which comprises the following steps: reacting aluminum hydroxide, zirconium hydroxide and dilute phosphoric acid to prepare an aluminum zirconium phosphate adhesive base solution, and compounding silicon powder, boron carbide, titanium powder, nickel powder and the adhesive base solution to prepare a special adhesive for coating a brass surface. And compounding silicon powder, boron carbide, titanium powder, nickel powder, aluminum oxide and the gum base solution to prepare the special adhesive for aluminum oxide surface coating. The brass surface coating special glue is brushed on the brass surface and cured, then the aluminum oxide surface coating special glue is brushed on the aluminum oxide surface, the brass coated with the adhesive and the aluminum oxide coated with the adhesive are attached together in the mode that the bonding surfaces are opposite, and the brass / aluminum oxide double-layer bonding piece is obtained after pressing and curing and can serve in the high-temperature environment. The method has the advantages that the special glue for brass surface coating and the special glue for aluminum oxide surface coating have high thermal expansion coefficient matching with brass and aluminum oxide, and thermal stress can be relieved; the double-layer adhesive can provide the bonding strength which can reach 1.3 MPa at the temperature of 500 DEG C.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of adhesive material preparation, and particularly relates to a preparation method of a double-layer high-temperature adhesive for connecting brass and aluminum oxide. BACKGROUND

[0002] Brass, with its excellent electrical and thermal conductivity, good machinability and outstanding corrosion resistance, has become a key material in the fields of electronics and aerospace. Under extreme conditions of high temperature and high load, it can maintain electrical performance and structural functionality while ensuring the reliability of the connection, and is widely used in high-temperature sensors, electronic packaging shells and various conductive structural parts. Alumina ceramic, with its high hardness and high-temperature resistance, is the preferred material for manufacturing thermal protection systems and engine components. In the field of aerospace, the use of alumina ceramic ensures the stability of the structure at high temperatures and is a key material for protecting flight safety. In recent years, brass and alumina connectors have received high attention in the thermal end sensing and electronic system packaging of hypersonic aircraft and near-space aircraft. Whether it is a high-energy physics experiment device or a military radar system and civil communication engineering, its application is widespread and has shown great potential.

[0003] Due to the significant differences in physical and chemical properties between alloys and ceramics, how to overcome the thermal performance mismatch between the two to achieve reliable connection is the primary technical problem. At the same time, under the influence of severe service environment, how to ensure the integrity of the connection interface and prevent cracking under conditions of cold and hot cycles, hot air scouring and high-temperature multi-stress impact constitutes another key technical challenge. Among existing connection methods, brazing and other technologies are the main way to achieve high-strength bonding of alloys and ceramics. However, brass components are usually light and thin, with limited temperature resistance, and the instantaneous high temperature during welding can easily cause damage to the parts, so seeking an alternative non-destructive connection is the key to preparing brass and alumina connectors. Compared with welding processes, high-temperature adhesive technology does not require complex equipment and can be directly applied to high-temperature environments after coating and curing without damaging the connected parts. It has the advantages of simple operation, high connection efficiency, excellent specific strength and strong adaptability, providing a feasible path for the new and reliable connection of brass and alumina.

[0004] However, high temperature bonding technology still faces the challenge of significant difference in thermal expansion coefficient between brass and alumina. Therefore, developing a high temperature adhesive that can adapt to the thermal mismatch of the two and has excellent heat resistance, anti-aging performance and high bonding strength has become a key technical breakthrough in the field of heterogeneous material connection. The conventional single-layer adhesive (or single-layer bonding structure) cannot effectively alleviate the interfacial thermal stress caused by the difference in thermal expansion, resulting in limited bonding strength and insufficient service life. Double-layer material structure has significant advantages in thermal stress buffering, providing a theoretical basis for the construction of double-layer high temperature adhesive and the corresponding bonding process. The double-layer high temperature adhesive and its preparation method provided by the present application is an important technical breakthrough to realize high strength and high reliability connection of brass and alumina. SUMMARY

[0005] In order to solve the above problems, the purpose of the present application is to provide a preparation method of a double-layer high temperature adhesive for connecting brass and alumina.

[0006] In order to achieve the above-mentioned purpose, the present application provides the following technical scheme: a preparation method of a double-layer high temperature adhesive for connecting brass and alumina, specifically comprising the following steps:

[0007] (1) adjust the concentrated phosphoric acid with a concentration of 85% to about 55-65% to obtain dilute phosphoric acid;

[0008] (2) according to the mass ratio of 8-9:0.5-1.5:2-3, dilute phosphoric acid, aluminum hydroxide and zirconium hydroxide prepared in step (1) are weighed and placed separately; the dilute phosphoric acid is stirred in a constant temperature water bath at 70-75℃, and the aluminum hydroxide and zirconium hydroxide are slowly added to the dilute phosphoric acid in a stirred state, then the powder is completely dissolved, and then the mixture is uniformly mixed by mechanical stirring at a speed of 400-600r / min, and a milky white aluminum zirconium phosphate glue base solution is obtained after complete stirring;

[0009] (3) according to the mass ratio of 1-1.5:0.5-1:1.5-2:1.5-2:9.5-10.5, silicon powder, boron carbide, titanium powder, nickel powder and aluminum zirconium phosphate glue base solution prepared in step (2) are weighed and placed in a mortar and ground to a high degree of uniformity to obtain a special glue for brass surface coating;

[0010] (4) according to the mass ratio of 8-9:2-3:0.5-1.5, dilute phosphoric acid, aluminum hydroxide and zirconium hydroxide prepared in step (1) are weighed and placed separately. The dilute phosphoric acid is stirred in a constant temperature water bath at 70-75℃, and the aluminum hydroxide and zirconium hydroxide are slowly added to the dilute phosphoric acid in a stirred state, then the powder is completely dissolved, and then the mixture is uniformly mixed by mechanical stirring at a speed of 400-600r / min, and a milky white aluminum zirconium phosphate glue base solution is obtained after complete stirring;

[0011] (5) Silicon powder, boron carbide, titanium powder, nickel powder, alumina and the aluminum zirconium phosphate adhesive liquid prepared in step (4) are placed in a mortar and mixed in a mass ratio of 1-2:0.5-1.5:1-2:1-2:1-1.5:7.5-12.5. The mixture is then ground until the powder is completely gone, ensuring that the colloid reaches a highly uniform state, and a special adhesive for alumina surface coating is obtained.

[0012] (6) Apply the brass surface coating special adhesive obtained in step (3) to the brass bonding surface by brushing, and use a coater to control the thickness of the adhesive layer to be 200-500μm; dry and cure the brass coated with the brass surface coating special adhesive in the range of room temperature to 80℃ for 20-60min.

[0013] (7) Apply the special adhesive for coating the alumina surface prepared in step (5) to the alumina bonding surface with a brush, and use a coater to control the thickness of the high-temperature adhesive to 100-300μm; bond the brass and alumina coated with the high-temperature adhesive together with the bonding surfaces facing each other to form a bonded part, and then pressurize and dry the brass and alumina bonded part in the range of room temperature to 80℃ for 2-6 hours to obtain the brass / alumina heterogeneous material bonded part.

[0014] Preferably, in step (1), the concentrated phosphoric acid is analytical grade with a purity higher than 98%.

[0015] Preferably, in steps (2) and (4), the aluminum hydroxide has a purity of over 99% and a particle size of 10-25 μm; the zirconium hydroxide has a purity of over 99% and a particle size of 6-15 μm; the zirconium-aluminum ratio of the aluminum phosphate zirconium colloid prepared in steps (2) and (4) is different and cannot be interchanged or confused.

[0016] Preferably, in steps (3) and (5), the particle size of elemental silicon powder is 0.5-5 μm, the particle size of boron carbide powder is 6-10 μm, and the purity of both is higher than 99%; the particle size of titanium powder is 1-25 μm, the particle size of nickel powder is 1-5 μm, and the purity of both is higher than 98%; and the particle size of alumina is 0.5-5 μm, with a purity higher than 99%.

[0017] The double-layer high-temperature adhesive for joining brass and alumina and its preparation method provided by this invention have the following beneficial effects:

[0018] 1. The preparation process is simple, green, and pollution-free, using renewable materials as raw materials, which meets the requirements of environmental protection and sustainable development;

[0019] 2. High-temperature adhesives can provide a bond strength of over 0.5 MPa for brass and alumina bonding within a temperature range of 100-500℃, with a maximum of 1.3 MPa;

[0020] 3. The coefficient of thermal expansion of the special adhesive used for coating alumina surfaces is 12.64 × 10⁻⁶. -6 K -1 The highest coefficient of thermal expansion for the special adhesive used to coat brass surfaces is 17.12 × 10⁻⁶. -6 K -1 The two form a gradient transition structure of thermal expansion coefficient, which effectively alleviates thermal stress and improves the reliability of the connection part;

[0021] 4. The adhesive layer achieves close contact with the interface, maintains a high compatibility interface with the substrate, and ensures that the bonding strength remains stable under wide temperature changes without significant performance degradation. Attached Figure Description

[0022] Figure 1 These are the shear strength curves of the brass and alumina double-layer bonded parts prepared in Example 1, measured at room temperature after different temperature treatments;

[0023] Figure 2 The test force-displacement curves of the brass and alumina double-layer bonded part prepared in Example 1 after treatment at 500℃ and shear test at room temperature are shown.

[0024] Figure 3 The XRD pattern of the brass surface coated with the special adhesive prepared in Example 1 after treatment at 200°C;

[0025] Figure 4 The XRD pattern of the brass surface coated with the special adhesive prepared in Example 1 after treatment at 500°C;

[0026] Figure 5 The XRD pattern of the alumina surface coating adhesive prepared in Example 1 after treatment at 200°C;

[0027] Figure 6 The XRD pattern of the alumina surface coating adhesive prepared in Example 1 after treatment at 500°C;

[0028] Figure 7 The curve shows the thermal expansion of the brass surface coating adhesive prepared in Example 1 after heat treatment at 500°C.

[0029] Figure 8 The curve of thermal expansion of the special adhesive for alumina surface coating prepared in Example 1 after heat treatment at 500°C is shown. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments.

[0031] Example 1

[0032] This embodiment provides a method for preparing a double-layer high-temperature adhesive for joining brass and alumina, comprising the following steps performed in sequence:

[0033] (1) Add water to 85% concentrated phosphoric acid to adjust the concentration to about 60% to obtain dilute phosphoric acid;

[0034] (2) Weigh out the dilute phosphoric acid, aluminum hydroxide and zirconium hydroxide prepared in step (1) in a mass ratio of 8.5:1:2.5 and place them separately; stir the dilute phosphoric acid in a constant temperature water bath at 72℃, and slowly add aluminum hydroxide and zirconium hydroxide into the dilute phosphoric acid in sequence while stirring. After the powder is completely dissolved, stir it evenly at a speed of 500r / min. After stirring is complete, a milky white aluminum zirconium phosphate gel-based liquid is obtained.

[0035] (3) Weigh silicon powder, boron carbide, titanium powder, nickel powder and the aluminum zirconium phosphate colloid prepared in step (2) in the following mass ratios of 1.2:0.8:1.8:1.8:10, mix and grind them in a mortar until the colloid is highly uniform, and obtain a special adhesive for coating brass surfaces.

[0036] (4) Weigh out the dilute phosphoric acid, aluminum hydroxide, and zirconium hydroxide prepared in step (1) in a mass ratio of 8.5:2.5:1 and place them separately. Stir the dilute phosphoric acid in a constant temperature water bath at 72°C. While stirring, slowly add aluminum hydroxide and zirconium hydroxide into the dilute phosphoric acid in sequence. After the powder is completely dissolved, mechanically stir at a speed of 500 r / min to mix evenly. After stirring is complete, a milky white aluminum zirconium phosphate colloid solution is obtained.

[0037] (5) Silicon powder, boron carbide, titanium powder, nickel powder, alumina and the aluminum zirconium phosphate adhesive liquid prepared in step (4) are placed in a mortar and mixed in a mass ratio of 1.5:0.8:1.5:1.5:1.3:10. The mixture is then ground until the powder is completely gone, ensuring that the colloid reaches a highly uniform state, and a special adhesive for alumina surface coating is obtained.

[0038] (6) Apply the special adhesive for brass surface coating obtained in step (3) to the brass bonding surface by brushing, and use a coater to control the thickness of the adhesive layer to 300μm; dry and cure the brass coated with the special adhesive at 40℃ for 40min.

[0039] (7) Apply the special adhesive for coating the alumina surface prepared in step (5) to the alumina bonding surface with a brush, and use a coater to control the thickness of the high-temperature adhesive to 200μm; bond the brass and alumina coated with the high-temperature adhesive together with the bonding surfaces facing each other to form a bonded part, and then dry and cure the brass and alumina bonded part under pressure at 40℃ for 4h to obtain the brass / alumina heterogeneous material bonded part.

[0040] Example 2

[0041] This embodiment provides a method for preparing a double-layer high-temperature adhesive for joining brass and alumina, comprising the following steps performed in sequence:

[0042] (1) Add water to 85% concentrated phosphoric acid to adjust it to about 55% to obtain dilute phosphoric acid;

[0043] (2) Weigh out the dilute phosphoric acid, aluminum hydroxide and zirconium hydroxide prepared in step (1) in a mass ratio of 8:0.5:2 and place them separately; stir the dilute phosphoric acid in a constant temperature water bath at 70°C, and slowly add aluminum hydroxide and zirconium hydroxide into the dilute phosphoric acid in sequence while stirring. After the powder is completely dissolved, stir it mechanically at a speed of 400 r / min until it is uniform. After stirring, a milky white aluminum zirconium phosphate gel-based liquid is obtained.

[0044] (3) Weigh silicon powder, boron carbide, titanium powder, nickel powder and the aluminum zirconium phosphate adhesive liquid prepared in step (2) in the mass ratio of 1:0.5:1.5:1.5:9.5, mix and grind them in a mortar until the colloid is highly uniform, and obtain a special adhesive for coating brass surface.

[0045] (4) Weigh out the dilute phosphoric acid, aluminum hydroxide, and zirconium hydroxide prepared in step (1) in a mass ratio of 8:2:0.5 and place them separately. Stir the dilute phosphoric acid in a constant temperature water bath at 70°C. While stirring, slowly add aluminum hydroxide and zirconium hydroxide into the dilute phosphoric acid in sequence. After the powder is completely dissolved, stir mechanically at a speed of 400 r / min until it is evenly mixed. After stirring is complete, a milky white aluminum zirconium phosphate colloid solution is obtained.

[0046] (5) Silicon powder, boron carbide, titanium powder, nickel powder, alumina and the aluminum zirconium phosphate adhesive liquid prepared in step (4) are placed in a mortar and mixed in a mass ratio of 1:0.5:1:1:1:7.5. The mixture is ground until the powder is completely gone, ensuring that the colloid reaches a highly uniform state, and a special adhesive for alumina surface coating is obtained.

[0047] (6) Apply the brass surface coating special adhesive obtained in step (3) to the brass bonding surface by brushing, and use a coater to control the thickness of the adhesive layer to 200μm; dry and cure the brass coated with the brass surface coating special adhesive at room temperature for 20min.

[0048] (7) Apply the special adhesive for coating the alumina surface prepared in step (5) to the alumina bonding surface with a brush, and use a coater to control the thickness of the high-temperature adhesive to 100μm; bond the brass and alumina coated with the high-temperature adhesive together with the bonding surfaces facing each other to form a bonded part, and then dry and cure the brass and alumina bonded part under pressure at room temperature for 2 hours to obtain the brass / alumina heterogeneous material bonded part.

[0049] Example 3

[0050] This embodiment provides a method for preparing a double-layer high-temperature adhesive for joining brass and alumina, comprising the following steps performed in sequence:

[0051] (1) Add water to 85% concentrated phosphoric acid to adjust it to about 65% to obtain dilute phosphoric acid;

[0052] (2) Weigh out the dilute phosphoric acid, aluminum hydroxide and zirconium hydroxide prepared in step (1) in a mass ratio of 9:1.5:3 and place them separately; stir the dilute phosphoric acid in a constant temperature water bath at 75°C, and slowly add aluminum hydroxide and zirconium hydroxide into the dilute phosphoric acid in sequence while stirring. After the powder is completely dissolved, stir it mechanically at a speed of 600 r / min until it is uniform. After stirring, a milky white aluminum zirconium phosphate gel-based liquid is obtained.

[0053] (3) Weigh silicon powder, boron carbide, titanium powder, nickel powder and the aluminum zirconium phosphate colloid prepared in step (2) in the mass ratio of 1.5:1:2:2:10.5, mix and grind them in a mortar until the colloid is highly uniform, and obtain a special adhesive for coating brass surface.

[0054] (4) Weigh out the dilute phosphoric acid, aluminum hydroxide, and zirconium hydroxide prepared in step (1) in a mass ratio of 9:3:1.5 and place them separately. Stir the dilute phosphoric acid in a constant temperature water bath at 75°C. While stirring, slowly add aluminum hydroxide and zirconium hydroxide into the dilute phosphoric acid in sequence. After the powder is completely dissolved, stir mechanically at a speed of 600 r / min until it is evenly mixed. After stirring is complete, a milky white aluminum zirconium phosphate gel-based liquid is obtained.

[0055] (5) Silicon powder, boron carbide, titanium powder, nickel powder, alumina and the aluminum zirconium phosphate adhesive liquid prepared in step (4) are placed in a mortar and mixed in a mass ratio of 2:1.5:2:2:1.5:12.5. The mixture is ground until the powder is completely gone, ensuring that the colloid reaches a highly uniform state, and a special adhesive for alumina surface coating is obtained.

[0056] (6) Apply the brass surface coating special adhesive obtained in step (3) to the brass bonding surface by brushing, and use a coater to control the thickness of the adhesive layer to 500μm; dry and cure the brass coated with the brass surface coating special adhesive at 80℃ for 60min.

[0057] (7) Apply the special adhesive for coating the alumina surface prepared in step (5) to the alumina bonding surface with a brush, and use a coater to control the thickness of the high-temperature adhesive to 300μm; bond the brass and alumina coated with the high-temperature adhesive together with the bonding surfaces facing each other to form a bonded part, and then dry and cure the brass and alumina bonded part under pressure at 80℃ for 6h to obtain the brass / alumina heterogeneous material bonded part.

[0058] This invention provides a high-temperature adhesive system specifically designed for joining dissimilar materials such as brass and alumina. It uses a zirconium aluminum phosphate adhesive as the bonding matrix, which is prepared by chemically reacting phosphoric acid with aluminum hydroxide and zirconium hydroxide. The prepared brass / alumina connector exhibits excellent bonding strength and mechanical property stability within a temperature range of room temperature to 500°C, meeting the requirements for direct use under high-temperature conditions. In this double-layer structure, the coefficient of thermal expansion of the adhesive coating the alumina surface is higher than that of the adhesive coating the brass surface. The two adhesives, through a reasonable combination, form a continuous gradient transition in the coefficient of thermal expansion, effectively alleviating interfacial stress caused by thermal mismatch between the dissimilar materials. The difference in the aluminum-zirconium ratio in the two adhesives regulates the amount of zirconium oxide generated, thereby achieving precise control over the thermal expansion behavior of the adhesive layer. Both adhesives contain silicon powder and boron carbide, whose volume expansion during high-temperature oxidation compensates for the sintering shrinkage of the adhesive layer, helping to maintain the integrity of the adhesive structure. Simultaneously, both can further react with other components in the adhesive to generate high-temperature resistant components, improving the heat resistance of the adhesive.

[0059] Compared to adhesives specifically designed for brass surfaces, adhesives for alumina surfaces incorporate an appropriate amount of alumina filler. This significantly improves the adhesive's temperature resistance and mechanical strength, and allows for precise control of the coefficient of thermal expansion by adjusting the filler content. This two-layer adhesive system, through the synergistic effect of component formulation and structural design, maintains structural stability at high temperatures, significantly extending the service life of the joints under thermal cycling conditions. In summary, this bonding method ensures the stability of the adhesive at high temperatures, effectively preventing structural damage caused by thermal expansion and contraction, and improving its service life under extreme conditions.

[0060] To verify the effectiveness of the high-temperature adhesive provided in the above embodiments, the inventors conducted the following experiments:

[0061] 1) Preparation of brass and alumina double-layer bonded parts: Brass and alumina double-layer connectors are prepared according to the method described in the embodiments of the present invention.

[0062] 2) High-temperature calcination treatment: The prepared brass and alumina double-layer bonded parts were calcined for 1 hour at different temperatures (100℃, 200℃, 300℃, 400℃, 500℃).

[0063] 3) Room Temperature Shear Test: The shear strength of the brass and alumina double-layer bonded parts after treatment at different temperatures was tested using a CSS-44001 universal testing machine. Comparative experiments were conducted to evaluate the bond strength of the double-layer high-temperature adhesive. The shear strength of the bonded parts after different temperature treatments is shown below. Figure 1 As shown; simultaneously, the test force-displacement curves of the shear test conducted at room temperature after treatment at 500℃ were recorded, as shown. Figure 2 As shown.

[0064] Depend onFigure 1 It is known that this double-layer high-temperature adhesive can provide a bonding strength of not less than 0.5 MPa for the connection of brass and alumina within a processing temperature range of 200-400℃; and at 500℃, it can provide a bonding strength of not less than 1 MPa and even as high as close to 1.3 MPa. Therefore, it can be seen that the double-layer high-temperature adhesive for connecting brass and alumina prepared in this invention has excellent bonding performance.

[0065] Depend on Figure 2 It can be seen that the test force-displacement curve of the bonded part drops sharply after reaching the highest point, indicating that the adhesive is brittle and has high stiffness, which is consistent with the characteristics of ceramics.

[0066] 4) Adhesive composition analysis: The composition of the brass-coated adhesive and the alumina-coated adhesive prepared in the examples after treatment at different temperatures was analyzed using an XRD instrument (D / Max 2500v / PC, Rigaku). The XRD patterns of the brass-coated adhesive after treatment at 200℃ and 500℃ are shown below. Figure 4 and Figure 5 As shown; XRD patterns of alumina surface coated with special adhesive after treatment at 200℃ and 500℃ are as follows. Figure 5 and Figure 6 As shown.

[0067] according to Figure 3 and Figure 4 XRD analysis revealed that during the high-temperature sintering process (200℃-500℃), the composition of the adhesive did not change significantly, with only the formation of a new phase, SiO2. Si, Ti, and Ni existed in elemental form. Literature review indicates that due to the low sintering temperature and high inorganic filler content, the reaction conditions were not yet met. Alternatively, a small portion reacted, but the content was low, resulting in weak diffraction peaks. Therefore, this temperature range (200℃-500℃) did not significantly affect the phase composition of the adhesive. A new phase formed near 2θ = 20°-25° and 30°-35°, but the peak intensity was low, possibly indicating a partial reaction. SiO2, as an inorganic filler, can fill the pores of the colloidal material, improving mechanical strength and high-temperature resistance. Si can act as a reducing agent and can also sinter into SiO2, inhibiting excessive metal oxidation and protecting the colloidal structure. Ni, as a metallic filler, can improve thermal conductivity in the colloidal material and enhance impact resistance and toughness through the metal-inorganic interface. Ti can oxidize at high temperatures to form dense TiO2, protecting the internal structure of the colloid from oxidation. However, this effect is not observed in this colloid due to the low sintering temperature.

[0068] according to Figure 5 and Figure 6XRD analysis revealed that at 200℃, due to exposure to a humid environment, some intermediate products adsorbed moisture and reformed into Al(OH)3, with its characteristic diffraction peaks clearly visible. As the treatment temperature increased to 300-500℃, Al(OH)3 underwent dehydration, its characteristic diffraction peaks disappeared, and a stable Al2O3 phase was formed. Al2O3, a common high-temperature filler, has a high melting point and can significantly improve the upper limit of the colloid's high-temperature resistance, increase its hardness, wear resistance, and tensile strength, and reduce shrinkage deformation at high temperatures. During the heating process, Si oxidizes to SiO2. SiO2, as an inorganic filler, can fill the pores of the colloid, improving mechanical strength and high-temperature resistance. XRD analysis also confirmed that at 500℃, the adhesive still retains elemental components such as Si, Ti, and Ni. These residual elements provide potential reactivity for the performance evolution of the adhesive at higher temperatures.

[0069] 5) Thermal Expansion Performance Analysis: The thermal expansion coefficients of the brass and alumina surface coating adhesives prepared in the examples were tested using a German Netzsch DIL 402C thermomechanical analysis instrument after heat treatment at 500℃, as shown in the temperature curves. Figure 7 , Figure 8 As shown.

[0070] from Figure 7 The coefficient of thermal expansion of the special adhesive used to coat brass surfaces increases rapidly in the low-temperature range, reaching a stable value of 17.12 × 10⁻⁶ at around 150°C. -6 K -1 Near the surface, its coefficient of thermal expansion remains essentially constant as the temperature rises further, indicating good thermal stability over a high temperature range. This suggests that the adhesive exhibits a significant expansion response during the transition from low to medium temperatures, but displays stable properties at high temperatures.

[0071] Figure 8 The special adhesive for coating alumina surfaces also exhibits a rapid increase in its coefficient of thermal expansion when the temperature rises to around 100℃, reaching approximately 12.64 × 10⁻⁶. -6 K -1 The coefficient of thermal expansion then stabilizes and remains consistently lower than that of the special adhesive for brass surfaces. This means that the thermal expansion reaction of the special adhesive for alumina surfaces is relatively mild, making it more suitable for applications where thermal expansion requirements are lower.

Claims

1. A method for preparing a double-layer high-temperature adhesive for bonding brass and alumina, characterized in that, This includes the following steps performed in sequence: (1) Add water to 85% concentrated phosphoric acid to adjust it to about 55-65% to obtain dilute phosphoric acid; (2) According to a mass ratio of 8-9: 0.5-1.5:2-3 Weigh out the dilute phosphoric acid, aluminum hydroxide and zirconium hydroxide prepared in step (1) in sequence and place them separately; stir the dilute phosphoric acid in a constant temperature water bath at 70-75℃, and slowly add aluminum hydroxide and zirconium hydroxide into the dilute phosphoric acid in sequence while stirring. After the powder is completely dissolved, stir mechanically at a speed of 400-600r / min to mix evenly. After stirring is complete, a milky white aluminum zirconium phosphate gel-based liquid is obtained. (3) Weigh silicon powder, boron carbide, titanium powder, nickel powder and the aluminum zirconium phosphate colloid prepared in step (2) in the following mass ratios: 1-1.5: 0.5-1: 1.5-2: 1.5-2: 9.5-10.5, place them in a mortar and mix and grind until the colloid is highly uniform to obtain a special adhesive for coating brass surfaces. (4) Weigh out the dilute phosphoric acid, aluminum hydroxide, and zirconium hydroxide prepared in step (1) in a mass ratio of 8-9:2-3:0.5-1.5 and place them separately. Stir the dilute phosphoric acid in a constant temperature water bath at 70-75℃. While stirring, slowly add aluminum hydroxide and zirconium hydroxide into the dilute phosphoric acid in sequence. After the powder is completely dissolved, mechanically stir at a speed of 400-600 r / min to mix evenly. After stirring is complete, a milky white aluminum zirconium phosphate colloid solution is obtained. (5) Silicon powder, boron carbide, titanium powder, nickel powder, alumina and the aluminum zirconium phosphate adhesive liquid prepared in step (4) are placed in a mortar and mixed in a mass ratio of 1-2:0.5-1.5:1-2:1-2:1-1.5:7.5-12.

5. The mixture is then ground until the powder is completely gone, ensuring that the colloid reaches a highly uniform state, and a special adhesive for alumina surface coating is obtained. (6) Apply the brass surface coating special adhesive obtained in step (3) to the brass bonding surface by brushing, and use a coater to control the thickness of the adhesive layer to be 200-500μm; dry and cure the brass coated with the brass surface coating special adhesive in the range of room temperature to 80℃ for 20-60min. (7) Apply the special adhesive for coating the alumina surface prepared in step (5) to the alumina bonding surface with a brush, and use a coater to control the thickness of the high-temperature adhesive to 100-300μm; bond the brass and alumina coated with the high-temperature adhesive together with the bonding surfaces facing each other to form a bonded part, and then pressurize and dry the brass and alumina bonded part in the range of room temperature to 80℃ for 2-6 hours to obtain the brass / alumina heterogeneous material bonded part.

2. The method for preparing a double-layer high-temperature adhesive for joining brass and alumina according to claim 1, characterized in that: In step (1), the concentrated phosphoric acid is analytical grade with a purity higher than 98%.

3. The method for preparing a double-layer high-temperature adhesive for joining brass and alumina according to claim 1, characterized in that: In steps (2) and (4), the purity of aluminum hydroxide is higher than 99% and the particle size is 10-25 μm; the purity of zirconium hydroxide is higher than 99% and the particle size is 6-15 μm; the zirconium-aluminum ratio of the aluminum phosphate zirconium colloid prepared in steps (2) and (4) is different and cannot be interchanged or confused.

4. The method for preparing a double-layer high-temperature adhesive for joining brass and alumina according to claim 1, characterized in that: In steps (3) and (5), the particle size of elemental silicon powder is 0.5-5 μm, the particle size of boron carbide powder is 6-10 μm, and the purity of both is higher than 99%; the particle size of titanium powder is 1-25 μm, the particle size of nickel powder is 1-5 μm, and the purity of both is higher than 98%; the particle size of alumina is 0.5-5 μm, and the purity is higher than 99%.

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