Preparation method of layer-by-layer assembled ADN-based composite microspheres

Abstract

The invention belongs to the field of preparation of propellant oxidant materials, and relates to a method for preparing ADN-based composite microspheres through layer-by-layer assembly, preparation of a binder oil phase containing solid particles, preparation of an ADN water phase, preparation of a homogeneous emulsion, preparation of the ADN-based composite microspheres through layer-by-layer assembly of the binder / solid particles and application of the ADN-based composite microspheres in a solid propellant. The hydroscopicity of the prepared microspheres is reduced by 80% or above compared with that of the raw material ADN, the obtained ADN-based composite microsphere particles are added into a solid composite propulsion formula, a combustion test is carried out under the same humidity condition, and if the raw material ADN propellant is not ignited, the ADN-based composite microsphere propellant has obvious flames and is stable in combustion. The homogeneous emulsion is simple in preparation process, mild in reaction condition and simple and safe to operate, a high polymer bonding system in the oil-phase solvent can be selected from various types, and the method for reducing the hygroscopicity of the ADN by coating a layer of hydrophobic material on the basis of introducing an active coating into the homogeneous emulsion has a remarkable anti-hygroscopicity effect.

Description

Technical Field

[0001] The invention belongs to the technical field of propellant oxidant materials, and in particular relates to a method for preparing layer-by-layer assembled ADN-based composite microspheres. Background Art

[0002] In the composite solid propellant system, the oxidizer plays a vital role. It promotes the dissociation of the oxidized components through the decomposition process, provides the necessary reaction units for the fuel, and is the core component for achieving controlled release of chemical energy. When the composite solid propellant encounters thermal excitation, the oxidizer will decompose to produce gaseous oxidation products. These products quickly come into contact with the surface of the metal fuel (such as aluminum) and, through redox reactions, efficiently convert chemical energy into kinetic energy under high temperature and high pressure conditions. This is a key step in achieving the predetermined propulsion efficiency.

[0003] High-energy, green and environmentally friendly new oxidants are of concern to people. Ammonium perchlorate (AP) has long been the first choice among oxidants due to its high oxygen balance, high formation enthalpy and high density. However, its chlorine-containing characteristics limit its environmental friendliness. In order to seek a more environmentally friendly alternative, researchers have focused on ammonium dinitramide (ADN), which has an excellent oxygen balance of 25.8% and green and harmless combustion products, and is regarded as a strong competitor to AP. However, ADN is highly hydrophilic, easy to absorb moisture, and sensitive to external mechanical stimulation. These characteristics have become challenges to its application. If you want to introduce ADN as an oxidant into the field of solid composite propellants, you must first solve the hygroscopic problem caused by its hydrophilic nature and the problem of low tolerance under mechanical stimulation. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing layer-by-layer assembled ADN-based composite microspheres, and to analyze their morphology, hygroscopicity and combustion performance. The specific process scheme is as follows:

[0005] A method for preparing layer-by-layer assembled ADN-based composite microspheres comprises the following steps:

[0006] Step 1: Preparation of Shell Oil Phase

[0007] The binder is fully dissolved in the organic solvent, and the multi-dimensional nano solid particles are evenly dispersed in the organic solvent in a homogenizer to obtain a stable oil phase as the shell layer. The concentration of the multi-dimensional material is 0.5-5.0 mg·mL -1 .

[0008] Step 2: Preparation of ADN aqueous phase in the core layer

[0009] Different masses of ADN were added to a constant volume of deionized water to obtain ADN aqueous solutions of different concentrations as the aqueous core layer. The concentration of ADN was 100-1000 mg·mL-1 .

[0010] Step 3: Preparation of homogeneous emulsion

[0011] The oil phase prepared in step 1 and the water phase prepared in step 2 are mixed by a wall-breaking emulsifier, and emulsified at 5000-10000 rpm for 5-20 minutes to obtain a stable translucent homogeneous emulsion.

[0012] Step 4: Preparation of ADN-based composite microspheres by layer-by-layer assembly

[0013] The semi-transparent homogeneous emulsion prepared in step 3 was cured by vacuum-assisted solvent evaporation to obtain layer-by-layer assembled ADN-based composite microspheres. After being placed at a temperature of 25° C. and a relative humidity of 60% for 24 hours, the hygroscopicity and combustion performance tests were conducted in a solid propellant.

[0014] The multi-dimensional nano solid particles are one of CNT, GO, 3DG, modified diatomaceous earth and modified chitosan.

[0015] The binder is a mixture of one or more of ethyl cellulose, nitrocellulose, polystyrene, acrylic rubber, cellulose acetate butyrate, and Estane5703.

[0016] The organic solvent is one of toluene, dichloromethane and liquid paraffin or a mixture of the above.

[0017] The hygroscopicity and combustion performance tests were conducted in the solid propellant. The test results showed that the hygroscopicity of the ADN composite particles was reduced by more than 80% compared with the raw material ADN. The obtained ADN-based composite microsphere particles were added to the solid composite propellant formula and a combustion test was conducted under the same humidity conditions. The raw material ADN propellant did not ignite, but the ADN-based composite microsphere propellant had an obvious flame and burned stably.

[0018] The beneficial effects of the present invention are as follows:

[0019] The present invention applies the concept of double-layer core-shell structure to the preparation of ADN. Compared with the traditional preparation method, the preparation process is simple, the operation is safe, the reaction conditions are mild, and the application range is wide. The ADN prepared by the double-layer core-shell structure has a smooth surface that is conducive to sliding and avoids frictional heat generation, and has excellent hydrophobic properties. Vacuum curing has the advantage of being able to quickly realize microscale assembly, and is expected to achieve the regulation of liquid microunits.

[0020] The present invention proposes a new preparation method - a layer-by-layer assembly preparation process, which can prepare ADN with uniform particle size distribution, fewer crystal defects, and low mechanical sensitivity, and can realize the preparation of low hygroscopic ADN, thereby meeting the needs of solid propellants and better exerting the performance of oxidants. The preparation process can also be applied to the preparation of other energetic materials, enabling it to be more widely used in solid propellants and military fields.

[0021] Compared with the traditional preparation method, the ADN prepared by the present invention has simple preparation process and low cost. The prepared ADN sample has high sphericity, low mechanical sensitivity and low hygroscopicity, and can still burn stably after being placed for a period of time. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is an optical microscope image of the emulsion of nitrocellulose / GO toluene continuous phase coated with ADN aqueous solution dispersed phase prepared by homogeneous emulsion in Example 1.

[0023] Figure 2 This is the SEM image of ADN raw material.

[0024] Figure 3 This is the SEM image of the ADN-based composite microspheres prepared in Example 1.

[0025] Figure 4 The graphs are comparison graphs of the combustion test of the raw material ADN and Example 1 after moisture absorption in the solid propellant, wherein (a) is the combustion graph of the raw material ADN, and (b) is the combustion graph of Example 1. DETAILED DESCRIPTION

[0026] The present invention relates to a method for preparing a propellant oxidizer, specifically a method for preparing a layer-by-layer assembled ADN-based composite microsphere. In order to make the technical solution of the present invention clearer, the present invention is described in detail below in conjunction with an embodiment. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention.

[0027] Embodiment 1:

[0028] This embodiment provides a method for preparing ADN-based composite microspheres by assembling them layer by layer, and the method specifically comprises the following steps:

[0029] Step 1: Preparation of Shell Oil Phase

[0030] 0.134 g of nitrocellulose was fully dissolved in 13.3 mL of oil phase toluene, and 30 mg of multidimensional nano solid particles GO were uniformly dispersed in the oil phase toluene in a homogenizer to obtain a stable oil phase as the shell layer.

[0031] Step 2: Preparation of ADN aqueous phase in the core layer

[0032] 2.68 g ADN was added to 6.7 mL of deionized water to obtain a concentration of 400 mg mL -1 ADN aqueous solution is used as the aqueous core layer.

[0033] Step 3: Preparation of homogeneous emulsion

[0034] The oil phase prepared in step 1 and the water phase prepared in step 2 were mixed by a wall-breaking emulsifier and emulsified at 8000 rpm for 10 min to obtain a stable translucent homogeneous emulsion.

[0035] Step 4: Preparation of ADN-based composite microspheres by layer-by-layer assembly

[0036] The translucent homogeneous emulsion prepared in step 3 was cured by vacuum-assisted solvent evaporation to obtain layer-by-layer assembled ADN-based composite microspheres. After being placed at a temperature of 25°C and a relative humidity of 60% for 24 hours, the moisture absorption rate of the ADN composite particles was reduced by 91.54% compared with the raw material ADN. The obtained ADN-based composite microsphere particles were added to the solid composite propulsion formula and a combustion test was carried out under the same humidity conditions. The raw material ADN propellant did not ignite, but the ADN-based composite microsphere propellant had an obvious flame and burned stably.

[0037] Embodiment 2:

[0038] This embodiment provides a method for preparing ADN-based composite microspheres by layer-by-layer assembly. Steps 2 and 3 of the method are the same as those in Embodiment 1, and the difference lies in steps 1 and 4.

[0039] Step 1: Preparation of Shell Oil Phase

[0040] 0.134 g of ethyl cellulose was fully dissolved in 13.3 mL of oil phase toluene, and 30 mg of multidimensional nano solid particles GO were uniformly dispersed in the oil phase toluene in a homogenizer to obtain a stable oil phase as the shell layer.

[0041] Step 4: Preparation of layer-by-layer ADN-based composite microspheres and their application in solid propellants

[0042] The semi-transparent homogeneous emulsion prepared in step 3 was cured by vacuum-assisted solvent evaporation to obtain layer-by-layer assembled ADN-based composite microspheres. After being placed at 25°C and 60% relative humidity for 24 hours, the moisture absorption rate of the ADN composite particles was reduced by 89.52% compared with the raw material ADN.

[0043] Embodiment 3:

[0044] This embodiment provides a method for preparing ADN-based composite microspheres by layer-by-layer assembly. Steps 2 and 3 of the method are the same as those in Embodiment 1, and the difference lies in steps 1 and 4.

[0045] Step 1: Preparation of Shell Oil Phase

[0046] 0.134 g of nitrocellulose was fully dissolved in 13.3 mL of oil phase toluene, and 30 mg of multi-dimensional nano solid particles CNT were uniformly dispersed in the oil phase toluene in a homogenizer to obtain a stable oil phase as the shell layer.

[0047] Step 4: Preparation of layer-by-layer ADN-based composite microspheres and their application in solid propellants

[0048] The semi-transparent homogeneous emulsion prepared in step 3 was cured by vacuum-assisted solvent evaporation to obtain layer-by-layer assembled ADN-based composite microspheres. After being placed at 25°C and 60% relative humidity for 24 hours, the moisture absorption rate of the ADN composite particles was reduced by 87.49% compared with the raw material ADN.

Claims

1. A method for preparing ADN-based composite microspheres by assembling them layer by layer, characterized in that: The following steps are involved: Step 1: Preparation of Shell Oil Phase The binder is fully dissolved in an organic solvent, and the multi-dimensional nano solid particles are uniformly dispersed in the organic solvent in a homogenizer to obtain a stable oil phase as a shell layer; wherein the mass percentage concentration of the multi-dimensional nano solid particles is 0.5-5.0 mg·mL -1 ; Step 2: Preparation of ADN aqueous phase in the core layer Different masses of ADN were added to a constant volume of deionized water to obtain ADN aqueous solutions of different concentrations as the aqueous core layer; the mass percentage concentration of ADN was 100-1000 mg·mL -1 ; Step 3: Preparation of homogeneous emulsion The oil phase prepared in step 1 and the water phase prepared in step 2 are mixed by a wall-breaking emulsifier, and emulsified at 5000-10000 rpm for 5-20 min to obtain a stable translucent homogeneous emulsion; Step 4: Preparation of ADN-based composite microspheres by layer-by-layer assembly The translucent homogeneous emulsion prepared in step 3 was solidified by vacuum-assisted solvent evaporation to obtain layer-by-layer assembled ADN-based composite microspheres, which were placed in a solid propellant at a temperature of 25° C. and a relative humidity of 60% for 24 hours for hygroscopicity and combustion performance tests.

2. The preparation method according to claim 1, characterized in that: The multidimensional nano solid particles described in step 1 are one of CNT, GO, 3DG, modified diatomaceous earth and modified chitosan.

3. The preparation method according to claim 1, characterized in that: The binder described in step 1 is a mixture of one or more of ethyl cellulose, nitrocellulose, polystyrene, acrylic rubber, cellulose acetate butyrate, and Estane5703.

4. The preparation method according to claim 1, characterized in that: The organic solvent described in step 1 is one or a mixture of toluene, dichloromethane and liquid paraffin.

5. The preparation method according to claim 1, characterized in that: The hygroscopicity and combustion performance tests were carried out in the solid propellant as described in step 4. The test results showed that the hygroscopicity of the ADN composite particles was reduced by more than 80% compared with the raw material ADN. The obtained ADN-based composite microsphere particles were added to the solid composite propellant formula, and a combustion test was carried out under the same humidity conditions. The raw material ADN propellant did not ignite, but the ADN-based composite microsphere propellant had an obvious flame and burned stably.

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