A core-shell ammonium dinitramide-based composite material and its preparation method

Abstract

The present invention discloses a core-shell ammonium dinitramide-based composite material and a preparation method thereof, including the following component mass ratios: 0.02 to 0.24 parts of the intermediate layer, 4 parts of the solvent, and 0.04 parts of ADN. By adopting the above-mentioned core-shell ammonium dinitramide-based composite material and the preparation method thereof, the saturated moisture absorption rate is extremely low, the surface coating layer is complete, the preparation method is simple, and mass production can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-energy oxidants for solid propellants, and particularly relates to a core-shell ammonium dinitramide-based composite material and a preparation method thereof. Background Art

[0002] Ammonium dinitramide (ADN) is a high-energy oxidant with high energy and no pollution, which can significantly reduce the plume signal of solid propellants and reduce the environmental pollution of HCl gas in combustion products. However, as a strongly polar ionic compound, the negative charges on the crystal surface of ADN are extremely easy to combine with water molecules in the air, and its strong hygroscopicity limits the further application of ADN. Therefore, reducing the hygroscopicity of ADN is a key problem that urgently needs to be solved to promote the large-scale application of ADN in propellants.

[0003] At present, there are mainly three common methods in the academic circle to reduce the hygroscopicity of ADN: spheroidization of ADN, eutectic formation, and surface treatment. Research by Ma Yue et al. shows that the spheroidization of ADN can reduce the specific surface area, thereby reducing the hygroscopicity, but this method cannot fundamentally solve the problem of ADN hygroscopicity. Wang Haojing et al. prepared ADN / 18C6 (18-crown-6) eutectic by solvent evaporation method, and reduced the moisture absorption rate from 18% of pure ADN to 1.2% of the ADN / 18C6 composite material. Hu Yifei et al. calculated that the total saturated moisture absorption rate of the ADN / α-CD eutectic at 20 °C and 40% relative humidity is only 0.74%, which is significantly lower than 15.35% of pure ADN. Eutectic formation can greatly reduce the hygroscopicity, but the oxygen balance and energy performance are greatly reduced. Surface treatment is one of the most common methods to reduce the hygroscopicity of ADN. Xu Huixiang et al. coated polyurethane on the surface of ADN. At about 10 °C and relative humidity of 50% - 60%, the moisture absorption rate of the coated ADN was only 0.136% when exposed to air for 30 days. Lu Xianming et al. used GAP / dipropynyl succinate (BPS) cross-linked body as the coating material to cross-link and cure the spherical ADN particles through 1,3-dipolar cycloaddition reaction, and the saturated moisture absorption rate of the ADN composite material was only 0.78%.

[0004] Fluorocarbons have strong hydrophobicity. If they can be coated on the surface of ADN, the saturated moisture absorption rate of ADN will be further reduced. The present invention will provide a method for coating ADN with fluorocarbons (such as polytetrafluoroethylene, PTFE) to further reduce the saturated moisture absorption rate of ADN. Summary of the Invention

[0005] The purpose of the present invention is to provide a core-shell ammonium dinitramide-based composite material and a preparation method thereof, which have an extremely low saturated moisture absorption rate, a complete surface coating layer, a simple preparation method, and can be mass-produced.

[0006] To achieve the above object, the present invention provides a core-shell ammonium dinitramide-based composite material and a preparation method thereof, including, the mass ratio of components is as follows:

[0007] Intermediate layer: 0.02 - 0.24 parts, Solvent: 4 parts

[0008] ADN: 0.04 parts.

[0009] Preferably, the intermediate layer is 0.12 parts, chloroform is 4 parts, and ADN is 0.04 parts.

[0010] Preferably, the intermediate layer is 0.18 parts, chloroform is 4 parts, and ADN is 0.04 parts.

[0011] Preferably, the intermediate layer is 0.24 parts, chloroform is 4 parts, and ADN is 0.04 parts.

[0012] Preferably, the intermediate layer includes one of PFOA, carboxylate, sulfonate, phosphate, and sulfate fluorocarbon surfactants, sodium dodecyl sulfonate, and sodium dodecyl benzene sulfonate carbon surfactants.

[0013] Preferably, the solvent includes one of chloroform, dichloroethane, toluene, benzene, carbon tetrachloride, carbon disulfide, cyclohexane, and petroleum ether.

[0014] Preferably, it includes the following steps:

[0015] First step, prepare ADN@PFOA. Weigh PFOA and dissolve it in chloroform, shake it at a shaking speed of 600 rpm for 1 h to completely dissolve PFOA. Weigh ADN and add it to the above chloroform solution of PFOA, shake it at a shaking speed of 600 rpm for 6 h, then filter and wash it twice, and dry it at 45 °C for 12 h;

[0016] Second step, prepare ADN@PFOA@PTFE. Use a magnetron sputtering coater, set the parameters, and add a self-made vibration device to ensure uniform coating on the surface of the particle sample, so that the surface of the particle sample is uniformly coated with a PTFE layer to obtain a core-shell ADN@PFOA@PTFE composite energetic material.

[0017] Preferably, the set parameters include a power of 100 W, an Ar flow rate of 5 sccm, a circulating water cooling set at 18 °C, and controlling the sample stage temperature below 30 °C.

[0018] Therefore, the present invention adopts the above-mentioned core-shell ammonium dinitramide-based composite material and its preparation method, and its technical effects are as follows:

[0019] A PTFE film was deposited on the surface of ADN by a magnetron sputtering coater to achieve superhydrophobic treatment of the ADN surface and reduce the hygroscopicity of ADN. If the film was directly deposited on the ADN surface, PTFE showed non-wetting and it was difficult to form a uniform film on the ADN surface. Therefore, the perfluorocarbon surfactant PFOA was selected as the intermediate layer. PFOA was enriched on the ADN surface, and the polar head carboxyl group was adsorbed on the ADN surface through hydrogen bonds. PTFE was adhered to the tail end of PFOA through dispersion forces, realizing the preparation of the ADN@PFOA@PTFE composite energetic material. ADN@PFOA could significantly reduce the hygroscopicity of ADN. Further, after depositing PTFE on the outer layer of ADN@PFOA, ADN@PFOA@PTFE had stronger hydrophobicity and lower hygroscopicity.

[0020] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Description of the Drawings

[0021] Figure 1 It is a process flow chart of a preparation method of a core-shell ammonium dinitramide-based composite material of the present invention;

[0022] Figure 2 It is the scanning electron microscope result of ADN@PFOA;

[0023] Figure 3 It is the mapping image of the F element in ADN@PFOA;

[0024] Figure 4 It is the mapping image of the C element in ADN@PFOA;

[0025] Figure 5 It is the mapping image of the N element in ADN@PFOA;

[0026] Figure 6 It is the scanning electron microscope image of ADN@PFOA@PTFE in Example 1;

[0027] Figure 7 It is the mapping image of the F element in ADN@PFOA@PTFE in Example 1;

[0028] Figure 8 It is the mapping image of the C element in ADN@PFOA@PTFE in Example 1;

[0029] Figure 9 It is the mapping image of the N element in ADN@PFOA@PTFE in Example 1;

[0030] Figure 10 It is the scanning electron microscope image of ADN@PFOA@PTFE in Example 2;

[0031] Figure 11 It is the mapping image of F element in ADN@PFOA@PTFE of Example 2;

[0032] Figure 12 It is the mapping image of C element in ADN@PFOA@PTFE of Example 2;

[0033] Figure 13 It is the mapping image of N element in ADN@PFOA@PTFE of Example 2;

[0034] Figure 14 It is the scanning electron microscope image of ADN@PFOA@PTFE of Example 3;

[0035] Figure 15 It is the mapping image of F element in ADN@PFOA@PTFE of Example 3;

[0036] Figure 16 It is the mapping image of C element in ADN@PFOA@PTFE of Example 3;

[0037] Figure 17 It is the mapping image of N element in ADN@PFOA@PTFE of Example 3;

[0038] Figure 18 It is the hygroscopicity test of ADN and the ADN composite material after coating of Example 1. Detailed implementation manners

[0039] The technical solutions of the present invention will be further described below with reference to the drawings and examples.

[0040] Unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0041] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the gist or basic features of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention, and any reference signs in the claims should not be regarded as limiting the claimed rights.

[0042] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment contains only an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. These other embodiments are also covered by the protection scope of the present invention.

[0043] It should also be understood that the specific embodiments described above are only used to explain the present invention, and the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention / invention.

[0044] Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the said technologies, methods, and devices should be regarded as part of the specification.

[0045] The content disclosed in the prior art documents cited in the specification of the present invention is incorporated into the present invention by reference in its entirety, and thus is part of the disclosure content of the present invention.

[0046] Example 1

[0047] As Figure 1 shown, a preparation method of a core-shell type ammonium dinitramide-based composite material provided by the present invention further reduces the saturated moisture absorption rate of ADN. The key lies in solving the problems that fluorocarbons are not easily adhered to the surface of ADN and the coating is uneven. Since ADN is strongly polar and PTFE is non-polar, PTFE is not wetted on the surface of ADN and it is difficult to further uniformly coat. It is considered to first coat the surface of ADN with weakly polar molecules to weaken the surface polarity of ADN. The method is to select a molecule with a strong interaction (van der Waals force or hydrogen bond) with ADN at one end and a fluorinated hydrophobic chain or a fluorinated polymer (such as perfluorooctanoic acid, PFOA) at the other end. The PFOA molecule has a hydrophilic carboxyl (-COOH) end group and a hydrophobic fluorocarbon short chain, and is theoretically an ideal raw material for the fluoride intermediate layer. Its hydrophilic carboxyl can form a good interaction (van der Waals force or hydrogen bond) with ADN, and the hydrophobic short chain faces outward, enabling ADN to obtain good moisture-proof performance. At the same time, the fluorocarbon short chain can theoretically enable PTFE to form good adhesion on the surface of ADN@PFOA.

[0048] Using 0.12 g of PFOA, 4 g of chloroform, and 0.04 g of ADN, a core-shell type ADN@PFOA@PTFE composite energetic material is prepared according to the following preparation method, which specifically includes the following steps:

[0049] The first step is to prepare ADN@PFOA. Perfluorooctanoic acid (PFOA) (which can be replaced by fluorocarbon surfactants such as carboxylates (RfCOO-M), sulfonates (RfSO3-M), phosphates (RfOPO3M) and sulfates (RfOSO3-M), or carbon surfactants such as sodium dodecyl sulfonate and sodium dodecylbenzene sulfonate) is used as the middle layer. PFOA is weighed and dissolved in chloroform (or low polarity or non-polar solvents such as dichloroethane, toluene, benzene, carbon tetrachloride, carbon disulfide, cyclohexane, petroleum ether, etc.), and oscillated at a speed of 600 rpm for 1 hour to completely dissolve PFOA. Weigh ADN (granular, flake, block, spherical, etc.) and add it to the above PFOA chloroform solution. Oscillate at a speed of 600 rpm for 6 hours, then filter and wash twice, and dry at 45°C for 12 hours.

[0050] The second step is to prepare ADN@PFOA@PTFE. Use a magnetron sputtering coater with the following parameters: power 100W, Ar flow rate 5sccm, circulating water cooling set to 18°C, sample stage temperature controlled below 30°C, and a self-made vibration device to ensure uniform coating on the surface of the particle sample. The surface of the particle sample is evenly coated with a PTFE (or fluorocarbon polymers such as PVDF and FPE) layer to obtain a core-shell ADN@PFOA@PTFE composite energetic material.

[0051] Embodiment 2

[0052] The preparation method of Example 1 was adopted, and the formula was modified to 0.18 g PFOA, 4 g chloroform, and 0.04 g ADN.

[0053] Embodiment 3

[0054] The preparation method of Example 1 was adopted, and the formula was modified to 0.24 g PFOA, 4 g chloroform, and 0.04 g ADN.

[0055] Embodiment 4

[0056] Performance Testing

[0057] 1. Adhesion and distribution of fluorocarbons on the ADN surface

[0058] The PFOA molecule contains 8 C atoms and 15 F atoms. The theoretical fluorine-carbon ratio F / C is 1.875. According to the table below, the actual fluorine-carbon ratio is 2.89 / 1.56≈1.85. The total weight of C atoms in the PFOA molecule is 96, and the total weight of F atoms is 285. The theoretical mass ratio is about 2.97. According to the table below, the actual mass ratio is 3.89 / 1.33≈2.92. Figure 2 , Figure 3 , Figure 4 , Figure 5It can be determined from Table 1 that in ADN@PFOA, PFOA can effectively coat the surface of ADN and is evenly dispersed.

[0059] Table 1 Element content on the surface of ADN@PFOA

[0060]

[0061]

[0062] From Example 1 Figure 6 , Figure 7 , Figure 8 and Figure 9 , from Example 2 Figure 10 , Figure 11 , Figure 12 and Figure 13 , from Example 3 Figure 14 , Figure 15 , Figure 16 and Figure 17 It can be seen that the fluorocarbon compound can effectively coat the surface of ADN and is evenly dispersed. Combining Table 2, Table 3 and Table 4, it can be seen that the content of F element in ADN@PFOA@PTFE has a significant increase compared with ADN@PFOA, which proves that PTFE can adhere to the surface of ADN@PFOA by the magnetron sputtering method.

[0063] Table 2 Element content on the surface of ADN@PFOA@PTFE in Example 1

[0064] Element Intensity Mass fraction % Mass error % Atomic ratio % Corrn. Sigma CK 1.1692 4.23 0.28 5.01 NK 0.6319 87.02 0.50 88.43 FK 0.1552 8.75 0.44 6.56 Total 100.00

[0065] Table 3 Element content on the surface of ADN@PFOA@PTFE in Example 2

[0066] Element Intensity Mass fraction % Mass error % Atomic ratio % Corrn. Sigma CK 1.1330 5.42 0.57 6.45 NK 0.5650 82.94 1.00 84.77 FK 0.1620 11.64 0.91 8.77 Total 100.00

[0067] Table 4 Element content on the surface of ADN@PFOA@PTFE in Example 3

[0068] Element Intensity Mass fraction % Mass error % Atomic ratio % Corrn. Sigma CK 0.7141 22.51 0.76 30.00 NK 0.1893 15.65 1.08 17.89 FK 0.4513 61.85 1.01 52.12 Total 100.00

[0069] 2. Hygroscopicity test

[0070] Weigh a certain mass of ADN, ADN@PTFE, ADN@PFOA and ADN@PFOA@PTFE, and record the mass as mdry. After drying the sample in a freeze dryer for 3 h, place it in a constant temperature and humidity chamber at 25 °C - 75% RH for 24 h, take out the sample and weigh its mass, and record it as mwet. The calculation method of the moisture absorption rate is as follows:

[0071]

[0072] Figure 18 The results of the hygroscopicity test of ADN and the ADN composite material after coating are shown. It can be seen from the figure that the hygroscopicity rate of the ADN raw material is 5.13% at 25°C - 75% RH. The hygroscopicity rate of ADN@PFOA has decreased significantly, being 2.78%, which proves that PFOA is adsorbed sufficiently on the surface of ADN and has a certain hydrophobic effect. ADN@PFOA@PTFE hardly absorbs water, only being 0 - 0.45%, far lower than the ADN raw material. The results prove that the presence of PFOA is beneficial to the binding of PTFE on the surface of ADN, making the ADN composite material have excellent moisture-proof absorption performance.

[0073] Therefore, the present invention adopts the above-mentioned core-shell ammonium dinitramide-based composite material and its preparation method, which has an extremely low saturated hygroscopicity rate, a complete surface coating layer, a simple preparation method, and can be mass-produced.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation method of a core-shell ammonium dinitramide-based composite material, characterized in that, It includes the following steps: The first step is to prepare ADN@PFOA. Weigh PFOA and dissolve it in chloroform. Oscillate at a speed of 600 rpm for 1 h to completely dissolve PFOA. Then weigh ADN and add it to the above chloroform solution of PFOA. Oscillate at a speed of 600 rpm for 6 h, and then filter and wash twice, and dry at 45 °C for 12 h; The second step is to prepare ADN@PFOA@PTFE. Use a magnetron sputtering coater, set the parameters, and add a self-made vibration device to ensure uniform coating on the surface of the particle sample, so that the surface of the particle sample is uniformly coated with a PTFE layer to obtain a core-shell type ADN@PFOA@PTFE composite energetic material.

2. The preparation method of a core-shell ammonium dinitramide-based composite material according to claim 1, characterized in that, The set parameters include a power of 100 W, an Ar flow rate of 5 sccm, a circulating water cooling set at 18 °C, and the sample stage temperature is controlled below 30 °C.

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