Fluorine-containing acrylate ternary random copolymer modifier, modified boron powder as well as preparation and application of fluorine-containing acrylate ternary random copolymer modifier and modified boron powder

Abstract

The invention discloses a preparation method and application of a fluorine-containing acrylate ternary random copolymer modifier and modified boron powder, and the preparation method specifically comprises the following steps: (1) stirring and mixing three fluorine-containing acrylates with different fluorocarbon chain lengths at normal temperature, and then adding a free radical initiator to obtain a fluorine-containing acrylate mixture; (2) adding the fluorine-containing acrylate mixture into a flask filled with a solvent and lauryl mercaptan in batches in an N2 atmosphere, and heating to generate a free radical polymerization reaction; (3) eluting and purifying the product obtained in the step (2) with methanol, and performing vacuum drying to obtain a ternary random copolymer containing fluorine methacrylate; the modifier is used for modifying the boron powder, and a multilayer compact fluoride coating with high fluorine density content is constructed on the surface of the boron powder by adopting three fluorine-containing acrylate random copolymers with different fluorocarbon chain lengths, so that the problems that amorphous boron powder in a boron-containing fuel-rich propellant is easy to agglomerate, low in fluidity, difficult to ignite and low in combustion efficiency when being used as a fuel component are solved.

Description

Technical Field

[0001] The invention relates to a method for preparing a modifier, in particular to a fluorine-containing acrylate ternary random copolymer modifier, modified boron powder and preparation and application thereof, belonging to the field of energy-containing technology. Background Art

[0002] Fuel-rich propellants generally contain a large amount of high calorific value reducing agent ingredients such as magnesium powder, aluminum powder, and boron powder. They can form a high negative oxygen balance combustion system with oxidants such as potassium nitrate and AP. They can release a large amount of heat energy during combustion and have a high theoretical energy density. Therefore, they have long been the focus of researchers of energetic materials. Among them, amorphous boron powder has become a hot topic in military fields such as propellants and ignition powders as a metal fuel with a wide range of applications, high safety, a theoretical mass energy density of up to 58kJ / g, and a volume energy density of up to 138kJ / cm3. However, the presence of the boron powder oxide layer and its hydrolysis product boric acid limits the further development of boron-containing fuel-rich propellants. 2 O 3 The oxide layer is a highly viscous liquid at high temperatures, which hinders the contact and further combustion of the internal boron powder with the oxidant, leading to incomplete combustion of the propellant and difficulty in ignition. In addition, the micro-nano-scale amorphous boron used in boron-rich fuel propellants is prone to hygroscopic agglomeration, resulting in low fluidity of the boron powder and blockage in the propellant preparation process. In addition, the B 2 O 3 The hydrolysis product of boric acid polymerizes with the hydroxyl group of the binder HTPB during the preparation process of the propellant, resulting in gelation, poor rheological properties of the slurry and reduced boron loading, which seriously restricts its application in boron-rich fuel propellants.

[0003] At present, in order to solve the problems of amorphous boron powder in boron-rich fuel propellant, such as easy water absorption and agglomeration, difficulty in ignition, and poor rheological properties, a common method is to use organic solvents to remove the B on its surface. 2 O 3and boric acid, and coating fluoride or energetic compounds on boron powder. Xu Huixiang ([1] Xu Huixiang, Zhao Fengqi, Li Xiaoyu. Purification of amorphous boron powder by solvent method [J]. Chinese Journal of Explosives & Propellants, 2007, 30(2): 5.) et al. proposed that using ethanol to purify boron powder can effectively remove surface impurities. In the treatment method of boron powder for boron-rich fuel propellant in CN105854124A, a composite treatment method of surface coating and agglomeration granulation is used to treat boron powder. However, after these methods of treating boron powder are exposed to air for a period of time, they inevitably return to the initial state and cannot be used as a long-term modification measure. In addition, Fei Xiao ([1] Xiao F, Chen C, Chen Z, et al. In situ precise construction of surface-activated boron powders: A new strategy to synergistically improve the interface properties and enhance combustion performance of boron [J]. Fuel, 2023, 351(000): 12.) et al. pointed out that using fluorochlorosiloxane can effectively remove B 2 O 3 , and the HF generated by the decomposition of fluoropolysiloxane can convert B 2 O 3 into gaseous products and volatilize and remove them, increasing the combustion efficiency. However, siloxane is added to the fuel surface as a flame retardant component, weakening the fluorine combustion-supporting effect in fluoropolysiloxane and further increasing the ignition difficulty.

[0004] Patent CN116282055B, a method for purifying and modifying amorphous boron powder by acid quenching, that is, by high-temperature roasting-acid quenching treatment of amorphous crude boron powder, so that during the high-temperature roasting process, the stress changes and volume expansion coefficients of boron and impurities are different, different stress strains are generated at the interface and cracks are generated, quickly poured into the acid solution, the temperature changes sharply, large cracks are generated at the interface between boron and impurities and the boron powder bursts into tiny particles, small cracks are generated inside the boron powder and quickly deepen, impurities are exposed outward, and the acid solution enters the interior of the boron powder particles along the cracks and reacts with the impurities to remove the impurities in the reaction blind area, realizing the particle refinement and purification of amorphous crude boron powder. A large number of cracks inside the amorphous boron powder can increase its specific surface area and significantly improve the oxidation activity of the boron powder. However, its fluidity, ignition difficulty, and easy water absorption and agglomeration performance have not been improved, and this modification measure is temporary. During the long-term storage process, the boron powder will still oxidize and the active components in the boron powder will decrease.

[0005] Therefore, developing a modifier that can overcome the above defects and effectively modify boron powder has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a fluorinated acrylate terpolymer random copolymer modifier, modified boron powder, and their preparation and applications. The present invention proposes to construct a multi-layer dense fluoride coating with a high fluorine density content on the surface of boron powder using a random copolymer of three fluorinated acrylates with different fluorocarbon chain lengths, effectively solving the problems of easy agglomeration, low fluidity, difficult ignition, and low combustion efficiency of amorphous boron powder as a fuel component in boron-rich fuel propellants.

[0007] To solve the above technical problems, the present invention provides a preparation method of a fluorinated acrylate terpolymer random copolymer modifier, which specifically includes the following steps:

[0008] (1) Stir and mix three fluorinated acrylates with different fluorocarbon chain lengths at room temperature, and then add a radical initiator to obtain a fluorinated acrylate mixture;

[0009] (2) Under a nitrogen 2 atmosphere, add the fluorinated acrylate mixture to a flask containing a solvent and dodecyl mercaptan in batches, and raise the temperature to carry out a radical polymerization reaction;

[0010] (3) Elute and purify the product obtained in step (2) with methanol, and then vacuum dry it to obtain a terpolymer random copolymer of fluorinated methacrylate.

[0011] The further limited technical solution of the present invention is:

[0012] Furthermore, in the preparation method of the above-mentioned fluorinated acrylate terpolymer random copolymer modifier, the structure of the modifier is:

[0013] In the modifier, a, b, and c are all integers;

[0014] The radical initiator is azobisisobutyronitrile (AIBN);

[0015] The three fluorinated acrylates with different fluorocarbon chain lengths are perfluoroethyl methacrylate, perfluorobutyl ethyl acrylate, and perfluorodecyl ethyl acrylate in order from short to long.

[0016] In the preparation method of the above-mentioned fluorinated acrylate terpolymer random copolymer modifier, by mass ratio, in the three fluorinated acrylates with different fluorocarbon chain lengths, perfluoroethyl methacrylate: perfluorobutyl ethyl acrylate: perfluorodecyl ethyl acrylate

[0017] = 2.0 - 2.4 g : 3.0 - 3.3 g : 6.0 - 6.3 g;

[0018] The addition amount of azobisisobutyronitrile is 3 - 6% of the mass of perfluoroethyl methacrylate.

[0019] In the preparation method of the fluorinated acrylate terpolymer random copolymer modifier described above, the mass of dodecyl mercaptan is 0.1 - 0.3% of the fluorinated acrylate mixture.

[0020] In the preparation method of the fluorinated acrylate terpolymer random copolymer modifier described above, in step (1), stir at room temperature for 5 - 15 min; in step (2), the fluorinated acrylate mixture needs to be added to the reaction system in 3 - 4 batches successively. The temperature of the free radical polymerization reaction is 80°C - 90°C, and the reaction time is 2 h; the solvent is n-butyl acetate, and the mass of the solvent is 1 - 1.5 times the mass of the fluorinated acrylate mixture; the free radical polymerization reaction is a ternary random copolymerization of different fluorinated acrylates; the fluorinated acrylate terpolymer needs to be eluted and purified with methanol at least three times.

[0021] The present invention also designs a fluorinated acrylate terpolymer random copolymer modifier, and its preparation principle is as follows:

[0022]

[0023] The present invention also designs an application of the fluorinated acrylate terpolymer random copolymer modifier, and applies it to the modification of amorphous boron powder used as fuel in boron-rich fuel propellants.

[0024] The present invention also designs a modification method for amorphous boron powder used as fuel in boron-rich fuel propellants, which specifically includes the following steps:

[0025] (1) Pretreatment: Add boron powder to ethanol, stir with a motor and heat under reflux for a period of time, then filter by suction and vacuum dry to remove impurities on the surface of the boron powder;

[0026] (2) Preparation of the modifier: Prepare a solution of fluorinated acrylate terpolymer random copolymer, and heat and ultrasonicate until completely dissolved;

[0027] (3) Modification and refinement: Under N 2 atmosphere, add the pretreated boron powder and the solution of fluorinated acrylate terpolymer random copolymer to a three-necked flask, mix with a motor and heat under reflux at a constant temperature for a period of time, then cool, rotary evaporate, vacuum dry, and grind and sieve to obtain the modified boron powder. In the above modification method, in step (1) pretreatment, the boron powder is selected from amorphous boron powder with a particle size < 5 μm, the heating temperature of the boron powder is 80 - 90°C, the heating time is 2 - 4 h, the stirring speed is 300 - 400 rpm, the suction filtration process needs to use diatomaceous earth for filtration, and the addition amount of ethanol needs to submerge the surface of the boron powder, not exceeding 2 / 3 of the container volume;

[0028] In step (2) of preparing the modifier, the solvent in the terpolymer solution of fluorinated acrylate is one of toluene, tetrahydrofuran, and acetone. The mass of the fluorinated acrylate terpolymer in the modifier accounts for 3-6% of the mass of the pretreated boron powder. The addition amount of the modifier solvent satisfies that the liquid level covers the surface of the boron powder and does not exceed 2 / 3 of the volume of the container. The ultrasonic temperature is 25-40 °C, and the ultrasonic time is 15-20 min.

[0029] In step (3), the heating temperature is 80-100 °C, the heating time is 2-4 h, the stirring speed is 300-400 rpm, the rotary evaporation temperature is 40-50 °C, and a 200-250 mesh sieve is selected during sieving.

[0030] For a modified boron powder, the water contact angle of the prepared modified boron powder is 145-152°. The agglomeration phenomenon of the refined boron powder is greatly improved. The ignition delay time of the modified boron powder is 16 ms, compared with 142 ms of the unmodified boron powder, which is reduced by 126 ms, and the combustion efficiency is improved.

[0031] The beneficial effects of the present invention are as follows:

[0032] In the present invention, three fluorinated acrylates with different fluorocarbon chain lengths are selected as the monomers for terpolymerization. The three monomers are fluorinated compounds with 2, 4, and 8 full fluorocarbon chain lengths respectively. The multi-level size space structure of short, medium, and long can overcome the steric hindrance of the single C-F long chain of fluorinated acrylate. The short and medium chain length fluorocarbon chains can be inserted into the gaps of fluorinated compounds with large molecular weight and long chain matching, thereby increasing the degree of polymerization of fluorinated acrylate on the surface of boron powder and simultaneously increasing the fluorine density, achieving a dense coating effect on boron powder. Due to the introduction of fluorocarbon chains, the hydrophobicity of boron powder can be significantly improved, and the hygroscopicity of the modified boron powder will decrease compared with that of the original boron powder, solving the problems of easy moisture absorption and agglomeration and poor fluidity of boron powder. In addition, the dense high-fluorine-density film on the surface of boron powder can avoid the direct contact of boron powder with oxygen and water. When used as a fuel component of a fuel-rich propellant, it can exhibit higher boron activity. On the other hand, during the combustion of the propellant, HF decomposed from fluorocarbon compounds at high temperature or short-chain fluorocarbon compounds can react with viscous B 2 O 3 to generate gaseous boron fluoride, and the reaction promotes the further combustion of boron powder and reduces the ignition difficulty of boron powder.

[0033] Compared with the existing technology, the present invention:

[0034] (1) The boron powder modifier used is a terpolymer of fluorinated acrylate. A large number of C-F, C-H, and C-O bonds are distributed in the copolymer, which can be adsorbed in multiple layers on the surface of boron powder through hydrogen bonds. The coating effect of boron powder is excellent, and the surface adhesion is strong.

[0035] (2) In common fluorinated polysiloxane modifiers, the polysiloxane structure shows a negative effect on combustion, and the residue rate in the combustion products is high. The fluorinated acrylate used in the present invention can decompose during the combustion process and has an effect of assisting the combustion of boron powder.

[0036] (3) The modified boron powder of the present invention has a high degree of polymerization of fluorocarbon chains on its surface and a high fluorine density content. Compared with the boron powder modified by a single polymerized fluorinated polymer, it has an excellent combustion assisting effect under the same spatial coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is the contact angle of the boron powder of Comparative Examples 1, 2 and Example 1;

[0038] Figure 2 is the SEM diagram of the boron powder of Comparative Example 1 and Example 1;

[0039] Figure 3 is the XPS diagram of the boron powder of Comparative Example 1 and Example 1;

[0040] Figure 4 is the TG / DSC diagram of the boron powder of Comparative Example 1 and Example 1;

[0041] Figure 5 is the laser ignition combustion diagram of the boron powder of Comparative Example 1 and Example 1;

[0042] In the figure: Figure 1 a is the static contact angle diagram of deionized water of the unmodified boron powder of Comparative Example 1 of the present invention; Figure 1 b is the contact angle diagram of deionized water of the modified boron powder of Example 1; Figure 1 c is the static contact angle diagram of deionized water of the modified boron powder of Comparative Example 2 of the present invention;

[0043] Figure 2 a is the scanning electron microscope diagram of different magnifications of the unmodified boron powder of Comparative Example 1 in the present invention; Figure 2 b is the scanning electron microscope diagram of different magnifications of the modified boron powder of Example 1 in the present invention; Figure 3 a is the XPS diagram of the modified boron powder of Example 1 of the present invention; Figure 3 b is the XPS diagram of the unmodified boron powder of Comparative Example 1 of the present invention; Figure 4 a is the TG diagram of the boron powder of Comparative Example 1 and Example 1 of the present invention; Figure 4 b is the DSC diagram of the boron powder of Comparative Example 1 and Example 1 of the present invention; Figure 5 a is the laser ignition combustion diagram of the boron powder in Comparative Example 1 of the present invention; Figure 5 b is the laser ignition combustion diagram of the modified boron powder in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] All raw materials in this embodiment are commercially available.

[0045] Example 1

[0046] This example provides a preparation method of a fluorinated acrylate terpolymer modifier, specifically as follows:

[0047] Add 2.40 g of perfluoroethyl methacrylate, 3.16 g of perfluorobutyl ethyl acrylate, and 6.16 g of perfluorodecyl ethyl acrylate into a flask in sequence. After stirring at room temperature for 10 min, add 0.10 g of AIBN. After evacuating and replacing the gas 3 times, divide the above mixed solution into four batches under N 2 atmosphere, and gradually add it to a flask containing 15.0 g of n-butyl acetate and 0.024 g of dodecyl mercaptan. Heat it to 90 °C in an oil bath and react for 2 h. Pour the reactant into 40 ml of methanol, filter it by suction, wash away the impurities with methanol, and dry it under vacuum at 50 °C to obtain 6.42 g of a white powdery solid modifier.

[0048] Apply the above modifier to the modification of amorphous boron powder used as fuel in boron-rich fuel propellants, specifically as follows:

[0049] Add 370 ml of absolute ethanol to a three-necked flask containing 108 g of boron powder, heat it to 90 °C and reflux for 2 h at a stirring speed of 300 rpm. Filter it by suction while it is hot, and after vacuum drying, obtain 104 g of pretreated boron powder. Add 3 g of the modifier to 370 ml of toluene at 30 °C, and ultrasonically dissolve the modifier completely for 15 min. Under N 2 atmosphere, add the modifier solution to a three-necked flask containing 100 g of pretreated boron powder, heat it to 90 °C and reflux for 3 h at a stirring speed of 300 rpm, rotary evaporate, grind, and pass through a 200-mesh sieve to obtain modified boron powder.

[0050] Example 2

[0051] This example provides a preparation method of a fluorinated acrylate terpolymer modifier, specifically as follows:

[0052] Add 2.28 g of perfluoroethyl methacrylate, 3.08 g of perfluorobutyl ethyl acrylate, and 6.20 g of perfluorodecyl ethyl acrylate into a flask in sequence. After stirring at room temperature for 10 min, add 0.10 g of AIBN. After evacuating and replacing the gas 3 times, divide the above mixed solution into three batches under N 2 atmosphere, and gradually add it to a flask containing 15.0 g of n-butyl acetate and 0.020 g of dodecyl mercaptan. Heat it to 90 °C and react for 2 h. Pour the reactant into 40 ml of methanol, filter it by suction, wash away the impurities with methanol, and dry it under vacuum at 50 °C to obtain 6.30 g of a white powdery solid modifier.

[0053] Apply the above modifier to modify the amorphous boron powder used as fuel in boron-rich fuel propellants, specifically as follows:

[0054] Add 370 ml of absolute ethanol to a three-necked flask containing 110 g of boron powder, heat and raise the temperature to 90 °C under reflux for 2 h at a stirring speed of 300 rpm, filter while it is hot, and obtain 106 g of pretreated boron powder after vacuum drying. Add 6 g of the modifier to 370 ml of toluene at 30 °C, and completely dissolve the modifier by ultrasonic treatment for 15 min. Under N 2 atmosphere, add the modifier solution to a three-necked flask containing 100 g of pretreated boron powder, heat and raise the temperature to 90 °C under reflux for 2 h at a stirring speed of 350 rpm, perform rotary evaporation, grinding, and pass through a 250-mesh sieve to obtain modified boron powder.

[0055] Example 3

[0056] This example provides a preparation method for a fluorinated acrylate terpolymer modifier, specifically as follows:

[0057] Add 2.34 g of perfluoroethyl methacrylate, 3.52 g of perfluorobutyl ethyl acrylate, and 6.20 g of perfluorodecyl ethyl acrylate to a flask in sequence, stir at room temperature for 5 min, then add 0.10 g of AIBN. After evacuating and replacing the gas 3 times, divide the above mixed solution into three batches under N 2 atmosphere, and gradually add it to a flask containing 15.0 g of n-butyl acetate and 0.034 g of dodecyl mercaptan, and react at 90 °C for 2 h. Pour the reactant into 20 ml of methanol, filter, wash away impurities with methanol, and vacuum dry at 50 °C to obtain 7.12 g of a white powdery solid modifier.

[0058] Apply the above modifier to modify the amorphous boron powder used as fuel in boron-rich fuel propellants, specifically as follows:

[0059] Add 370 ml of absolute ethanol to a three-necked flask containing 110 g of boron powder, heat and raise the temperature to 90 °C under reflux for 2 h at a stirring speed of 300 rpm, filter while it is hot, and obtain 106 g of pretreated boron powder after vacuum drying. Add 3 g of the modifier to 370 ml of toluene at 30 °C, and completely dissolve the modifier by ultrasonic treatment for 15 min. Under N 2 atmosphere, add the modifier solution to a three-necked flask containing 100 g of pretreated boron powder, heat and raise the temperature to 90 °C under reflux for 4 h at a stirring speed of 350 rpm, perform rotary evaporation, grinding, and pass through a 250-mesh sieve to obtain modified boron powder.

[0060] Example 4

[0061] This example provides a preparation method for a fluorinated acrylate terpolymer modifier, specifically as follows:

[0062] In a flask, 2.09 g of perfluoroethyl methacrylate, 3.20 g of perfluorobutylethyl acrylate, and 6.11 g of perfluorodecylethyl acrylate were successively added. After stirring at room temperature for 10 min, 0.07 g of AI BN was added thereto. After evacuating and replacing the gas three times, the above mixed solution was divided into three batches under a nitrogen 2 atmosphere and successively added to a flask containing 12.00 g of n-butyl acetate and 0.020 g of dodecyl mercaptan. The mixture was heated to 80 °C and reacted for 2 h. The reaction product was poured into 40 ml of methanol, filtered by suction, washed with methanol to remove impurities, and dried in vacuo at 50 °C to obtain 7.82 g of a white powdery solid modifier.

[0063] The above modifier was applied to modify amorphous boron powder used as fuel in boron-rich fuel propellants, specifically:

[0064] 370 ml of absolute ethanol was added to a three-necked flask containing 110 g of boron powder. The mixture was heated to 90 °C and refluxed for 2 h at a stirring speed of 300 rpm. It was filtered by suction while it was hot and dried in vacuo to obtain 103 g of pretreated boron powder. At 30 °C, 3 g of the modifier was added to 380 ml of tetrahydrofuran. After ultrasonic treatment for 15 min, the modifier was completely dissolved. Under a nitrogen 2 atmosphere, the modifier solution was added to a three-necked flask containing 100 g of pretreated boron powder. The mixture was heated to 80 °C and refluxed for 2 h at a stirring speed of 350 rpm, then rotary evaporated, ground, and passed through a 250-mesh sieve to obtain modified boron powder.

[0065] In Examples 1-4, the boron powder was selected from amorphous boron powder with a particle size < 5 μm.

[0066] Comparative Example 1

[0067] This comparative example provided a boron powder that was not modified: the amorphous boron powder was not coated with a modifier and was not pretreated with ethanol. It was directly ground and passed through a 200-mesh sieve to obtain the unmodified boron powder.

[0068] Comparative Example 2

[0069] This comparative example provided a modified boron powder:

[0070] 6.20 g of perfluorodecylethyl acrylate was successively added to a flask. After stirring at room temperature for 5 min, 0.10 g of AI BN was added thereto. After evacuating and replacing the gas three times, the above mixed solution was divided into three batches under a nitrogen 2 atmosphere and successively added to a flask containing 6.70 g of n-butyl acetate and 0.010 g of dodecyl mercaptan. The mixture was heated to 80 °C and reacted for 2 h. The reaction product was poured into 20 ml of methanol, filtered by suction, washed with methanol to remove impurities, and dried in vacuo at 50 °C to obtain 4.12 g of a white powdery solid modifier;

[0071] Add 370 ml of absolute ethanol to a three-necked flask containing 110 g of boron powder, heat it up to 90 °C under stirring at 300 rpm and reflux for 2 h, filter it while it is hot, and obtain 103 g of pretreated boron powder after vacuum drying. Add 3 g of modifier to 380 ml of toluene at 30 °C, and ultrasonicate for 15 min until the modifier is completely dissolved. Under N 2 atmosphere, add the modifier solution to a three-necked flask containing 100 g of pretreated boron powder, heat it up to 80 °C under stirring at 350 rpm and reflux for 2 h, rotary evaporate, grind, and pass through a 250-mesh sieve to obtain modified boron powder.

[0072] Perform performance characterization on the above-prepared modified boron powder, and the results are as follows:

[0073] The deionized water contact angles of the boron powder before and after modification are measured using an XG-CAME powder contact angle measuring instrument. The powdery boron powder is tableted before testing. The water contact angle of the boron powder in Comparative Example 1 is Figure 1 shown in a as 0°, indicating that the micron-sized amorphous boron powder without modification will be quickly wetted by water when contacting water, resulting in a decrease in the activity of the boron powder and significant agglomeration between the powders. The water contact angle of the modified boron powder in Example 1 is Figure 1 shown in b as 150°, showing superhydrophobic interfacial properties. The dense fluorocarbon chains wrap around the outermost layer of the boron powder, isolating the contact between the boron powder and water. The superhydrophobic property means that the agglomeration problem of the refined boron powder can be greatly improved. The water contact angle of the boron powder in Comparative Example 2 is Figure 1 shown in c as 128°, and the hydrophobicity is significantly lower than that in Example 1. This is because the steric hindrance during the polymerization of the single long-chain perfluorodecylethyl acrylate is relatively high, and the degree of polymerization of the obtained fluorinated acrylate polymer is lower than that of the ternary polymerized fluorinated acrylate polymer, and a dense fluoride coating cannot be formed on the surface of the boron powder. The contact angle values of Examples 2-4 are similar, all around 150°, indicating that the ternary random copolymer of fluorinated acrylate is successfully coated and has excellent hydrophobic effects. The water contact angles of the boron powder in each comparative example and example are shown in Table 1.

[0074] Table 1 Water contact angles of unmodified / modified boron powder in each comparative example and example

[0075] Unmodified / Modified Boron Powder Water Contact Angle / ° Comparative Example 1 0 Comparative Example 2 128 Example 1 150 Example 2 152 Example 3 148 Example 4 150

[0076] The particle surface morphology distribution of the amorphous boron powder before and after modification is observed microscopically and analyzed by image using a Hitachi i8010 scanning electron microscope. The results are as Figure 2 shown, and in Example 1 Figure 2 b, the modified boron powder and Comparative Example 1 Figure 2The boron powder in a has no significant change in morphology and structure, and all presents a rough and porous amorphous structure. However, the modified boron powder in Example 1 is more evenly dispersed, has a smaller particle size, and has almost no agglomerates of large particles of boron powder, which also verifies that giving boron powder hydrophobicity can solve the problem of its refinement and agglomeration.

[0077] The elemental analysis of boron powder before and after modification was determined using a PHIQUANTERA II X-ray photoelectron spectrometer. The results are as follows: Figure 3 Comparative Example 1 Figure 3 In the spectrum b, the peaks at 531.8ev and 186.9ev belong to B respectively. 2 O 3 and O1 s, B1 s in boric acid. Figure 3 In the spectrum a, the peaks at 688.8ev, 532.3ev, 291.6ev, and 187.9ev are respectively attributed to F1s, O1s, C1s, and B in the fluorinated acrylate terpolymer. 2 O 3 B1 s in the graphite indicates that the fluorinated acrylate terpolymer was successfully coated on the surface of the boron powder.

[0078] The thermal properties of the boron powder before and after modification were measured by TG / DSC in an air atmosphere at a temperature range of 50°C-1000°C and a heating rate of 10°C / min. The results are as follows: Figure 4 shown. Figure 4 a is the TG graph of the boron powder of Comparative Example 1 and Example 1 of the present invention, and TG focuses on oxidation weight gain; Figure 4 b is the DSC graph of the boron powder of comparative example 1 and embodiment 1 of the present invention, focusing on the initial oxidation temperature. The weight gain of boron in Example 1 in air is slightly greater than that of comparative example 1, and the initial oxidation temperature of 769.65°C is 13.60°C earlier than that of 783.25°C of comparative example 1. This is because the fluorine-containing compound coating layer decomposes into HF or short-chain fluoride at around 380°C, thereby bonding with the surface viscosity of the boron powder. 2 O 3 The reaction takes place to obtain gaseous boron fluoride, which promotes the contact between the boron powder and the air, thereby achieving the combustion-supporting effect of increasing the oxidation efficiency of the boron powder and reducing the initial oxidation temperature. In addition, as the mass of the modifier increases, the initial oxidation temperature of the modified boron powder measured in Example 2 is 752.45°C, which is 30.8°C earlier than that in Comparative Example 1. However, considering that the increase in the mass of the modifier improves the thermal efficiency on the one hand, but reduces the content of the active ingredient in the boron powder on the other hand, its mass cannot exceed 7% of the mass of the boron powder, and the mass of the modifier needs to be strictly controlled.

[0079] The ignition ease of boron powder before and after modification was measured by using an analytical balance to weigh 20 mg of boron powder before and after modification into a quartz tube with an inner diameter of 3 mm and a height of 5 mm, and then performing laser ignition measurement with a power setting of 80 W, and observing and recording with a high-speed camera. Figure 5 The laser ignition combustion diagrams of Comparative Example 1 and Example 1 are shown. The time between the appearance of a bright spot and the appearance of an obvious flame in the image was defined as the ignition delay time. Comparative Example 1 Figure 5 a The ignition delay time was 142 ms, and for Example 1 Figure 5 b The ignition delay time of boron powder was 16 ms. This is because the fluorinated modifier decomposes into gaseous HF when heated, and HF reacts with the viscous B 2 O 3 to form gaseous products, inhibiting the accumulation of the oxide film on the surface of B, and the generated gas can increase the discreteness of B particles in space, increase the contact area of B / O, facilitate the smooth progress of the oxidation reaction, increase the combustion intensity of B, and improve the energy release rate of B powder. Therefore, the ignition delay time is shortened.

[0080] In the present invention, a random copolymer of fluorinated acrylates with three different fluorocarbon chain lengths was used to construct a multi-layer dense fluoride coating with a high fluorine density content on the surface of boron powder to solve the problems of easy agglomeration, low fluidity, difficult ignition, and low combustion efficiency of amorphous boron powder as a fuel component in boron-containing fuel-rich propellants.

[0081] In addition to the above embodiments, the present invention may have other embodiments. All technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A method for preparing a fluorinated acrylate ternary random copolymer modifier, characterized in that: The specific steps include: (1) stirring and mixing three fluorinated acrylates with different fluorocarbon chain lengths and adding a free radical initiator; (2) adding the fluorinated acrylate mixture in batches into a flask containing a solvent and dodecyl mercaptan under a N2 atmosphere, and heating the flask to cause a free radical polymerization reaction; (3) The product obtained in step (2) is purified by eluting with methanol, and then vacuum dried to obtain a ternary random copolymer of fluorinated methacrylate.

2. The preparation method according to claim 1, characterized in that: The structure of the modifier is: In the modifier, a, b, and c are all integers; The free radical initiator is azobisisobutyronitrile; The three fluorine-containing acrylates with different fluorocarbon chain lengths are, from shortest to longest, perfluoroethyl methacrylate, perfluorobutyl ethyl acrylate, and perfluorodecyl ethyl acrylate.

3. The method for preparing the modifying agent according to claim 2, characterized in that: The mass ratio of the three fluorine-containing acrylates with different fluorocarbon chain lengths is 2.0-2.4 g perfluoroethyl methacrylate: 3.0-3.3 g perfluorodecyl ethyl acrylate: 6.0-6.3 g. The added amount of azobisisobutyronitrile is 3-6% of the mass of perfluoroethyl methacrylate.

4. The method for preparing the modifying agent according to claim 1, characterized in that: The mass of the dodecyl mercaptan is 0.1-0.3% of the fluorinated acrylate mixture.

5. The method for preparing the modifying agent according to claim 1, characterized in that: The temperature of the free radical polymerization reaction is 80° C.-90° C., the solvent is n-butyl acetate; and the free radical polymerization reaction is a ternary random copolymerization of different fluorine-containing acrylates.

6. A fluorinated acrylate ternary random copolymer modifier prepared by the preparation method described in any one of claims 1 to 5.

7. Application of a fluorinated acrylate ternary random copolymer modifier, which is used to modify amorphous boron powder used as fuel in boron-rich fuel propellants.

8. A method for modifying amorphous boron powder for fuel in boron-rich fuel propellant, characterized in that: The specific steps include: (1) Pretreatment: adding boron powder to ethanol, stirring, heating and refluxing for a period of time, and then filtering and vacuum drying to remove impurities on the surface of the boron powder; (2) preparing a modifier, preparing a fluorinated acrylate ternary random copolymer solution, heating and ultrasonicating until it is completely dissolved; (3) Modification and refinement: In a N2 atmosphere, the pretreated boron powder and the fluorinated acrylate ternary random copolymer solution are added into a three-necked flask, mixed, heated and refluxed for a period of time, and then cooled and rotary evaporated, vacuum dried, ground and sieved to obtain the modified boron powder.

9. The modification method according to claim 8, characterized in that: In the step (1) of pretreatment, the boron powder is selected from amorphous boron powder with a particle size of less than 5 μm, the heating temperature of the boron powder is 80-90° C., the heating time is 2-4 hours, and the stirring speed is 300-400 rpm; in the step (2) of preparing the modifier, the solvent in the fluorinated acrylate ternary random copolymer solution is one of toluene, tetrahydrofuran, and acetone, the mass of the modifier accounts for 3-6% of the mass of the boron powder after pretreatment, the ultrasonic temperature is 25-40° C., and the ultrasonic time is 15-20 minutes. The heating temperature in step (3) is 80-100° C., the heating time is 2-4 hours, and the stirring speed is 300-400 rpm.

10. A modified boron powder obtained by the modification method of claim 8, characterized in that: The water contact angle of the modified boron powder is 145-152°; the ignition delay time of the modified boron powder is 16ms.

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