A method for stabilization by coating an organosiloxane system through a thiolation reaction on the surface of an aluminum-lithium alloy powder

Abstract

A method for stabilization by coating an organosiloxane system through thiolation reaction on the surface of aluminum-lithium alloy powder, which relates to the technical field of preparation of metal powder materials. The purpose of the present invention is to solve the problems that the aluminum-lithium alloy powder is easily oxidized due to the high activity of lithium inside the alloy and is easily reacted with moisture in the air, resulting in a decrease in activity. Method: Under the atmosphere of protective gas, a thiol coating agent is added to an organic solvent, and after being fully dissolved, solution A is obtained; under heating conditions, the aluminum-lithium alloy powder is added to solution A, and stirred for 3 to 5 hours to obtain solution B; under the atmosphere of protective gas, tetraethyl orthosilicate and n-decanol are added to solution B, after being fully stirred, the pH is adjusted to 6 to 10, filtered under reduced pressure, and finally dried and ground to obtain aluminum-lithium alloy powder coated with an organosiloxane outer layer. The present invention can obtain a method for stabilization by coating an organosiloxane system through thiolation reaction on the surface of aluminum-lithium alloy powder.

Description

Technical Field

[0001] The present invention relates to the technical field of metal powder material preparation, and specifically relates to a method for stabilization by coating an organosiloxane system through a thiolation reaction on the surface of an aluminum-lithium alloy powder. Background Art

[0002] At present, with the rapid development of China's aerospace industry, due to its abundant reserves and low cost, metallic aluminum powder has been widely used as a reducing agent in rocket propellants to provide a large amount of reaction combustion energy. However, micron aluminum powder is limited in its effective use due to disadvantages such as a thick oxide layer, high ignition temperature, long ignition delay time, slow combustion speed, and serious two-phase flow losses. And for nano aluminum powder, due to its low active aluminum content, the overall released energy will also decrease. Therefore, scholars mainly focus their research on aluminum-lithium alloy powders with micro-explosion effects. Aluminum-lithium alloy powders have been widely used in the fields of aerospace and the like due to their advantages such as low melting point, low density, and large heat release.

[0003] Currently, the preparation of aluminum-lithium alloy powders is mainly to melt aluminum blocks and lithium blocks at high temperature and then spray them into spheres under an inert gas atmosphere, or to melt pre-alloyed aluminum-lithium alloy blocks and then supplement some metallic lithium to prepare aluminum-lithium alloys with high lithium content. However, due to the high reactivity of internal and surface metallic lithium in the prepared aluminum-lithium alloy powders, the lithium element in the metal powder is relatively sensitive to water vapor in the air and is extremely easy to absorb water and become inactivated. And after absorbing water, some hydrogen gas will be released, which may cause safety hazards during transportation and storage. Moreover, the long-term inactivation of the lithium element inside the aluminum-lithium alloy will ultimately also reduce the energy release, etc.

[0004] Therefore, the coating stabilization of aluminum-lithium alloy powders is of crucial importance. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems that the aluminum-lithium alloy powder is easily oxidized due to the high activity of lithium inside the alloy and is easily reacted with moisture in the air, resulting in a decrease in activity, and to provide a method for stabilization by coating an organosiloxane system through a thiolation reaction on the surface of the aluminum-lithium alloy powder.

[0006] A method for stabilization by coating an organosiloxane system through a thiolation reaction on the surface of an aluminum-lithium alloy powder is carried out according to the following steps:

[0007] Step 1: Under a protective gas atmosphere, add a thiol coating agent to an organic solvent, and after fully dissolving, obtain solution A;

[0008] Step 2: Under heating conditions, add the aluminum-lithium alloy powder to solution A in Step 1 and stir for 3 - 5 h to obtain solution B;

[0009] Step 3: Under a protective gas atmosphere, add tetraethyl orthosilicate and n-decanol to solution B in Step 2. After sufficient stirring, use an alkaline substance to adjust the pH of the mixed solution to 6 - 10, then perform vacuum filtration, and finally dry and grind to obtain aluminum-lithium alloy powder coated with an outer layer of organosiloxane.

[0010] Advantages of the present invention:

[0011] To solve the problem that aluminum-lithium alloy powder is extremely prone to absorbing water and deactivating in a humid environment due to the presence of relatively active lithium elements on its surface, resulting in a reduction in reaction activity, the present invention coats a layer of organic matter on the surface of the alloy powder through a mercapto (-SH) reaction. The methoxy or ethoxy groups at the end of the organic matter hydrolyze to produce hydroxyl groups under the action of n-decanol, and cross-link with the hydroxyl groups produced by the hydrolysis of tetraethyl orthosilicate under alkaline conditions to form an organic cross-linked network structure, which ultimately coats the surface of the aluminum-lithium alloy powder, effectively isolating the erosion of water vapor and maintaining non-reactivity in water, thereby improving the relative stability of the aluminum-lithium alloy in a humid environment.

[0012] The present invention uses a mercapto coating agent to coat and stabilize the aluminum-lithium alloy powder. Since there are many high-activity sites on the surface of the aluminum-lithium alloy, it is easy to react with water vapor in the air and cause the active components to fail. Therefore, the present invention is carried out under the presence of a protective gas throughout the process. The present invention first passivates the surface of the aluminum-lithium alloy with a mercapto coating agent. Under argon, tetraethyl orthosilicate and n-decanol are added to promote the hydrolysis of the siloxane end of the coating agent into silanol groups, which cross-link with the hydroxyl groups produced by the hydrolysis of tetraethyl orthosilicate under alkaline adjustment to form a three-dimensional network structure, effectively preventing the erosion of water vapor and maintaining the stability of the aluminum-lithium alloy in a humid environment. Compared with simply using a common silane coupling agent, the present invention innovatively proposes the application of the lithium-sulfur reaction in powder coating, and more specifically, draws on related fields such as lithium-sulfur batteries. A single silane coupling agent can only act on a single site of the powder, and the long-chain carbon groups that are branched out cannot be cross-linked again, but only form a single branched structure attached to the surface of the powder. Moreover, the branched structure part that is branched out has groups such as amino groups, which are also relatively easy to absorb water, making it difficult to achieve long-term storage of aluminum-lithium alloy powder, etc. However, when using a mercapto coupling agent for coating, due to the high reactivity and strong binding energy of metallic lithium and mercapto, methoxy or ethoxy branched chains are branched out on the surface of the aluminum-lithium alloy powder, and adjacent groups will undergo dehydration condensation reactions under alkaline conditions to form a large number of cross-linked network structures, achieving stabilization while enhancing the densification of the coating layer.

[0013] The present invention can obtain a method for stabilizing aluminum-lithium alloy powder by coating an organosiloxane system through a mercapto reaction on the surface of the aluminum-lithium alloy powder. Description of the Drawings

[0014] Figure 1 It is a scanning electron microscope image of Al-5Li before coating;

[0015] Figure 2 Scanning electron microscope image of Al-5Li coated with 3-mercaptopropyltrimethoxysilane;

[0016] Figure 3 Mapping image of Al-5Li coated with 3-mercaptopropyltrimethoxysilane;

[0017] Figure 4 It is Figure 3 Distribution map of O element in

[0018] Figure 5 It is Figure 3 Distribution map of Al element in

[0019] Figure 6 It is Figure 3 Distribution map of C element in

[0020] Figure 7 It is Figure 3 Distribution map of S element in

[0021] Figure 8 It is Figure 3 Distribution map of Si element in

[0022] Figure 9 Li 1s photoelectron spectroscopy of Al-5Li coated with 3-mercaptopropyltrimethoxysilane, A represents Al-5Li, B represents Al-5Li + 3-mercaptopropyltrimethoxysilane, 1 represents Li2CO3, 2 represents Li, 3 represents Li2CO3, 4 represents Li-S-C;

[0023] Figure 10 Contact angle test image of Al-5Li coated with 3-mercaptopropyltrimethoxysilane. Specific implementation mode

[0024] Specific implementation mode one: A method for stabilizing by coating an organosiloxane system through a thiolation reaction on the surface of an aluminum-lithium alloy powder is carried out according to the following steps:

[0025] Step one: Under a protective gas atmosphere, add a mercapto coating agent to an organic solvent, and after fully dissolving, obtain solution A;

[0026] Step two: Under heating conditions, add the aluminum-lithium alloy powder to solution A in step one, stir for 3 - 5 h, and obtain solution B;

[0027] Step three: Under a protective gas atmosphere, add tetraethyl orthosilicate and n-decanol to solution B in step two, fully stir, adjust the pH of the mixed solution to 6 - 10 using an alkaline substance, then carry out vacuum filtration, and finally dry and grind to obtain an aluminum-lithium alloy powder coated with an organosiloxane outer layer.

[0028] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the protective gas described in Step 1 and Step 3 is nitrogen or argon.

[0029] Other steps are the same as those in Specific Embodiment 1.

[0030] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that the mercapto coating agent described in Step 1 is 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 3-mercaptopropylmethyldimethoxysilane, or 3-mercaptopropyltrimethoxysilane.

[0031] Other steps are the same as those in Specific Embodiment 1 or 2.

[0032] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that the organic solvent in Step 1 is toluene, N,N-dimethylformamide, N-methylpyrrolidone, tetrahydrofuran, or 1,4-dioxane.

[0033] Other steps are the same as those in Specific Embodiments 1 to 3.

[0034] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that the volume ratio of the mercapto coating agent to the organic solvent in Step 1 is 1:(30 - 70).

[0035] Other steps are the same as those in Specific Embodiments 1 to 4.

[0036] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that the heating condition in Step 2 is 60 - 120°C (not exceeding the boiling point of the solvent), and the heating method is oil bath or water bath.

[0037] Other steps are the same as those in Specific Embodiments 1 to 5.

[0038] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that the mass fraction of lithium element in the aluminum-lithium alloy powder in Step 2 is 1 - 10%, and the particle size is 1 - 100 μm.

[0039] Other steps are the same as those in Specific Embodiments 1 to 6.

[0040] Specific Embodiment 8: The difference between this embodiment and any one of Specific Embodiments 1 to 7 is that the ratio of the mass of the aluminum-lithium alloy powder to the volume of the mercapto coating agent in Solution A in Step 2 is 100 g:(20 - 100) mL.

[0041] Other steps are the same as those in Specific Embodiments 1 to 7.

[0042] Specific embodiment nine: The difference between this embodiment and specific embodiments one to eight is that the amount of tetraethyl silicate added in step three is 1 to 3 times the mass of the aluminum-lithium alloy powder, and the mass ratio of n-decanol to the mercapto capping agent is (20 to 100):100.

[0043] The other steps are the same as those in Specific Embodiments 1 to 8.

[0044] Specific embodiment ten: The difference between this embodiment and specific embodiments one to nine is that the alkaline substance described in step three is ethylenediamine, triethylamine, sodium acetate or ammonia water; in step three, vacuum drying is performed at 30-60°C, and the drying time is 3-6h.

[0045] The other steps are the same as those in Specific Embodiments 1 to 9.

[0046] The following examples are used to verify the beneficial effects of the present invention:

[0047] Example 1: A method for stabilizing the surface of aluminum-lithium alloy powder by coating an organic silicon-oxygen system with a thiol reaction, which is carried out according to the following steps:

[0048] Step 1: Set up a condensation reflux device in a glove box (nitrogen atmosphere), add 1 mL of 3-mercaptopropyltrimethoxysilane to 50 mL of toluene, and stir until fully dissolved to obtain solution A;

[0049] Step 2: Add 1 g of aluminum-lithium alloy powder to solution A in step 1 under oil bath or water bath conditions at 100° C. and stir for 3 hours to obtain solution B; the mass fraction of lithium element in the aluminum-lithium alloy powder is 5%, and the average particle size is 17 μm;

[0050] Step 3: Under a nitrogen atmosphere, add 2 mL of tetraethyl silicate and 1 mL of n-decanol to solution B in step 2. After sufficient stirring, use ethylenediamine to adjust the pH of the mixed solution to 8, then filter under reduced pressure, and finally vacuum dry at 40°C for 3 h. Grind to obtain aluminum-lithium alloy powder coated with an organic silicon oxide outer layer.

[0051] Figure 1 This is the scanning electron microscope image before Al-5Li coating. Figure 2 This is a scanning electron microscope image of Al-5Li coated with 3-mercaptopropyltrimethoxysilane. Figure 1-2 These are scanning electron microscope images of the aluminum-lithium alloy powder before and after coating. The overall particle size of the aluminum-lithium alloy powder after coating has not changed, proving that the coating layer is relatively thin; and the morphology before and after coating is similar, and the surface of the aluminum-lithium alloy powder after coating is smooth, so the coating has not changed the overall morphology of the aluminum-lithium alloy particles.

[0052] Figure 3Mapping diagram of Al-5Li coated with 3-mercaptopropyltrimethoxysilane Figure 4 is Figure 3 the distribution diagram of O element in Figure 5 is Figure 3 the distribution diagram of Al element in Figure 6 is Figure 3 the distribution diagram of C element in Figure 7 is Figure 3 the distribution diagram of S element in Figure 8 is Figure 3 the distribution diagram of Si element in. As Figure 3-8 shown, the O, C, S, and Si elements of the coated aluminum-lithium alloy powder are significantly distributed on the surface of the aluminum-lithium alloy powder and appear spherical in the mapping diagram. Therefore, it is proved that the coating layer is evenly distributed and the coating effect is good.

[0053] Figure 9 is the Li 1s photoelectron spectroscopy diagram of Al-5Li coated with 3-mercaptopropyltrimethoxysilane; as Figure 9 shown, peaks of Li2CO3 (55.2 eV) and Li (54.8 eV) exist on the surface of 5% aluminum-lithium alloy, which also proves that the current commercial aluminum-lithium alloy is mainly stabilized by carbon dioxide, and there is still a small amount of elemental lithium on the surface. After treatment with 3-mercaptopropyltrimethoxysilane, the peak of elemental lithium disappears, and a characteristic peak of Li-S-C (56.2 eV) appears. Therefore, it is proved that lithium reacts with the mercapto group to form Li-S-C bonds, proving that 3-mercaptopropyltrimethoxysilane is successfully used to coat the aluminum-lithium alloy powder in this invention.

[0054] Table 1 shows the hygroscopicity test of the aluminum-lithium alloy before and after coating in a 60°C saturated brine environment. It is placed in a saturated brine environment and kept at a constant temperature of 60°C for 7 days, and the weight change is measured to calculate the weight gain. The weight of the Al-5Li alloy powder raw material increased by 80.59% after seven days. The weight gain of the sample treated with 3-mercaptopropyltrimethoxysilane and tetraethyl orthosilicate was less than 2% after seven days in a humid environment, and the weight gain was extremely small. It can be seen that the aluminum-lithium alloy powder treated with the mercapto coupling agent and tetraethyl orthosilicate will effectively increase its stability in a humid environment, and it further proves the relative stability of the coated sample in water.

[0055] Table 1 shows the hygroscopicity test of the aluminum-lithium alloy before and after coating in a 60°C saturated brine environment;

[0056] Table 1

[0057]

[0058] Figure 10 is the contact angle test diagram of Al-5Li coated with 3-mercaptopropyltrimethoxysilane; asFigure 10 As shown, since the uncoated aluminum-lithium alloy powder reacts immediately when it comes into contact with water, the contact angle of the pure sample cannot be measured. The contact angle of the coated aluminum-lithium alloy powder is 47.01°, indicating that the coated sample has a certain hindering effect on the erosion of water.

Claims

1. A method for stabilization by coating an organosiloxane system through a thiolation reaction on the surface of an aluminum-lithium alloy powder, characterized in that The method proceeds as follows: Step 1: Under a protective gas atmosphere, a thiol capping agent is added to an organic solvent and fully dissolved to obtain a solution A; The mercapto capping agent described in step 1 is 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 3-mercaptopropylmethyldimethoxysilane or 3-mercaptopropyltrimethoxysilane; Step 2: Under heating conditions, add aluminum-lithium alloy powder to solution A in step 1, and stir for 3 to 5 hours to obtain solution B; The mass fraction of lithium element in the aluminum-lithium alloy powder of step 2 is 1-10%, and the particle size is 1-100 μm; The ratio of the mass of the aluminum-lithium alloy powder in step 2 to the volume of the mercapto coating agent in solution A is 100 g: (20-100) mL; Step 3: under a protective gas atmosphere, tetraethyl silicate and n-decanol are added to the solution B of step 2, and after sufficient stirring, the pH of the mixed solution is adjusted to 6-10 using an alkaline substance, and then the mixture is filtered under reduced pressure, and finally dried and ground to obtain an aluminum-lithium alloy powder coated with an organic silicon oxygen outer layer; In step 3, the amount of tetraethyl silicate added is 1 to 3 times the mass of the aluminum-lithium alloy powder, and the mass ratio of n-decyl alcohol to the mercapto capping agent is (20 to 100):

100.

2. A method for stabilization by coating an organosiloxane system through a thiolation reaction on the surface of aluminum-lithium alloy powder according to claim 1, characterized in that The protective gases described in step 1 and step 3 are nitrogen or argon.

3. A method for stabilization by coating an organosiloxane system through a thiolation reaction on the surface of aluminum-lithium alloy powder according to claim 1, characterized in that The organic solvent in step 1 is toluene, N,N-dimethylformamide, N-methylpyrrolidone, tetrahydrofuran or 1,4-dioxane.

4. A method for achieving stabilization by coating an organosiloxane system through a thiolation reaction on the surface of aluminum-lithium alloy powder according to claim 1 or 3, characterized in that In step 1, the volume ratio of the thiol capping agent to the organic solvent is 1:(30-70).

5. A method for stabilization by coating an organosiloxane system through a thiolation reaction on the surface of an aluminum-lithium alloy powder according to claim 1, characterized in that In step 2, the heating condition is 60-120° C., and the heating method is an oil bath or a water bath.

6. A method for stabilization by coating an organosiloxane system through a thiolation reaction on the surface of aluminum-lithium alloy powder according to claim 1, characterized in that The alkaline substance described in step 3 is ethylenediamine, triethylamine, sodium acetate or ammonia water; in step 3, vacuum drying is performed at 30-60° C., and the drying time is 3-6 hours.

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