A fluorine-containing acrylic ester terpolymer modifier, modified boron powder, and preparation and application thereof

Abstract

The application discloses a fluorine-containing acrylic ester ternary random copolymer modifier, a preparation method of modified boron powder and application of the fluorine-containing acrylic ester ternary random copolymer modifier, and particularly relates to the following steps: (1) mixing three fluorine-containing acrylic esters with different fluorocarbon chain lengths at normal temperature, adding a free radical initiator to obtain a fluorine-containing acrylic ester mixture; (2) adding the fluorine-containing acrylic ester mixture into a flask containing a solvent and dodecyl mercaptan in batches under N2 atmosphere, and performing a free radical polymerization reaction by increasing temperature; (3) purifying the product obtained in the step (2) by using methanol as a washing agent, and vacuum drying to obtain a fluorine-containing methacrylic ester ternary random copolymer; and the modifier is used for modifying boron powder, a fluorine-containing coating layer with high fluorine density is constructed on the surface of the boron powder by using the random copolymer of the three fluorine-containing acrylic esters with different fluorocarbon chain lengths, and the problems of easy agglomeration, low flowability, ignition difficulty and low combustion efficiency of amorphous boron powder as a fuel component in a boron-containing fuel-rich propellant are solved.

Description

Technical Field

[0001] The invention relates to a preparation method of 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, typically formulated with high-calorific-value reducing agents such as magnesium powder, aluminum powder, and boron powder, can form a highly negative oxygen balance combustion system with oxidants such as potassium nitrate and AP. This allows for the release of substantial amounts of heat during combustion, resulting in a high theoretical energy density. Therefore, they have long attracted the attention of energetic material researchers. Amorphous boron powder, a metal fuel with a wide range of applications and high safety, boasts a theoretical mass energy density of up to 58 kJ / g and a volumetric energy density of up to 138 kJ / cm³, making it a hot topic in military applications such as propellants and ignition compounds. However, the presence of a boron oxide layer and its hydrolysis product, boric acid, has limited the further development of boron-rich propellants. The B2O3 oxide layer forms a highly viscous liquid at high temperatures, hindering contact between the boron powder and the oxidant and further combustion, leading to incomplete combustion and ignition difficulties. Furthermore, the micro- and nano-scale amorphous boron used in boron-rich propellants is prone to hygroscopic aggregation, resulting in low boron powder flowability and blockages in the propellant preparation process. Furthermore, boric acid, a hydrolysis product of B2O3, typically found in the outermost layer of boron powder particles, polymerizes with the hydroxyl groups of the HTPB binder during the propellant preparation process, resulting in gelation. This leads to poor rheological properties of the slurry and a decrease in boron loading, severely restricting its application in boron-rich fuel propellants.

[0003] At present, the common methods for solving the problems of amorphous boron powder in boron-rich fuel propellants, such as easy water absorption and aggregation, difficulty in ignition, and poor rheological properties, are to use organic solvents to remove B2O3 and boric acid on its surface, and to coat the boron powder with fluoride or energetic compounds. Xu Huixiang ([1] Xu Huixiang, Zhao Fengqi, Li Xiaoyu. Purification of amorphous boron powder by solvent method [J]. Journal of Explosives and Propellants, 2007, 30(2):5.) et al. proposed that the use of ethanol to purify boron powder can effectively remove surface impurities. CN105854124A, a method for treating boron powder for boron-rich fuel propellants, uses a composite treatment method of surface coating and agglomeration granulation to treat the boron powder. However, the boron powder treated by these methods will inevitably return to its original state after being exposed to air for a period of time, and cannot be used as a long-term modification measure. In addition, Fei Xiao ([1]Xiao F, Chen C, Chen Z, et al. In situprecise construction of surface-activated boron powders: A new strategy to synthetically improve the interface properties and enhance combustion performance of boron [J]. Fuel, 2023, 351(000): 12.) et al. pointed out that the use of fluorinated chlorosiloxane can effectively remove B2O3 from the surface of boron powder. The HF produced by the decomposition of fluorinated polysiloxane can convert B2O3 into gaseous products and volatilize and remove them, thereby increasing combustion efficiency. However, siloxane is added to the fuel surface as a flame retardant component, which weakens the combustion-supporting effect of fluorine in fluorinated polysiloxane and makes ignition more difficult.

[0004] Patent CN116282055B discloses a method for purifying and modifying amorphous boron powder using acid quenching. The method involves high-temperature calcination and acid quenching of amorphous crude boron powder, causing different stress changes and volume expansion coefficients between boron and impurities during the high-temperature calcination process, resulting in different stress strains and cracks at the interface. The powder is then rapidly poured into an acid solution, causing a sudden temperature change. Large cracks form at the interface between boron and impurities, causing the boron powder to break into tiny particles. Small cracks form within the boron powder and rapidly deepen, exposing the impurities. The acid then enters the boron powder particles along the cracks and reacts with the impurities, removing impurities in the reaction blind zone. This allows for particle refinement and purification of the amorphous crude boron powder. The numerous cracks within the amorphous boron powder increase its specific surface area and significantly improve its oxidation activity. However, this does not improve its fluidity, difficulty in ignition, or water absorption and agglomeration properties. Furthermore, the modification is temporary, and the boron powder will continue to oxidize during long-term storage, reducing the active ingredients in the boron powder.

[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 existing technology and provide a fluorine-containing acrylate ternary random copolymer modifier, modified boron powder and their preparation and application. The present invention proposes using three random copolymers of fluorine-containing acrylates with different fluorocarbon chain lengths to construct a multi-layer dense fluoride coating with high fluorine density on the surface of the boron powder, effectively solving the problems of amorphous boron powder in boron-containing fuel-rich propellants being easy to agglomerate as a fuel component, having low fluidity, difficult ignition and low combustion efficiency.

[0007] In order to solve the above technical problems, the present invention provides a method for preparing a fluorinated acrylate ternary random copolymer modifier, which specifically comprises the following steps:

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

[0009] (2) adding the fluorinated acrylate mixture in batches to a flask containing a solvent and dodecyl mercaptan under a nitrogen atmosphere, and heating the flask to cause a free radical polymerization reaction;

[0010] (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.

[0011] The technical solution further defined in the present invention is:

[0012] Furthermore, in the preparation method of the aforementioned fluorinated acrylate ternary random copolymer modifier, the structure of the modifier is:

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

[0014] The free radical initiator was azobisisobutyronitrile (AI BN);

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

[0016] In the preparation method of the fluorinated acrylate ternary random copolymer modifier, the three fluorinated acrylates with different fluorocarbon chain lengths are: perfluoroethyl methacrylate, perfluorobutyl ethyl acrylate, and perfluorodecyl ethyl acrylate.

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

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

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

[0020] In the preparation method of the aforementioned fluorinated acrylate ternary random copolymer modifier, step (1) is stirring at room temperature for 5-15 minutes; step (2) the fluorinated acrylate mixture needs to be divided into 3-4 batches and added to the reaction system successively, the temperature of the free radical polymerization reaction is 80°C-90°C, and the reaction time is 2 hours; 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; and the fluorinated acrylate ternary copolymer needs to be eluted with methanol and purified at least three times.

[0021] The present invention also designs a fluorinated acrylate ternary random copolymer modifier, the preparation principle of which is as follows:

[0022]

[0023] The present invention also provides an application of a fluorine-containing acrylate ternary random copolymer modifier, which is applied to the modification of amorphous boron powder used for fuel in boron-containing fuel-rich propellants.

[0024] The present invention also provides a method for modifying amorphous boron powder for fuel in boron-containing fuel-rich propellant, which specifically comprises the following steps:

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

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

[0027] (3) Modification and refinement: in an N2 atmosphere, the pretreated boron powder and the fluorinated acrylate ternary random copolymer solution are added to a three-necked flask motor, mixed, heated and refluxed at a constant temperature for a period of time, cooled and rotary evaporated, vacuum dried, ground and sieved to obtain the modified boron powder. In the above modification method, the boron powder in the pretreatment of step (1) is selected from amorphous boron powder with a particle size of less than 5μm, the heating temperature of the boron powder is 80-90℃, the heating time is 2-4h, the stirring speed is 300-400rpm, the filtration process requires the use of diatomaceous earth filtration, and the amount of ethanol added needs to be above the surface of the boron powder and not more than 2 / 3 of the container volume;

[0028] In step (2), when 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 fluorinated acrylate ternary random copolymer accounts for 3-6% of the mass of the pretreated boron powder, and the amount of the modifier solvent added is sufficient to ensure 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 screen is used for sieving.

[0030] A modified boron powder has a water contact angle of 145-152 degrees, refines boron powder agglomeration, and significantly improves the ignition delay time of the modified boron powder to 16ms, which is 126ms shorter than the 142ms of unmodified boron powder, thereby improving combustion efficiency.

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

[0032] The present invention designs and selects three fluorine-containing acrylates with different fluorocarbon chain lengths as monomers for ternary random copolymerization. The three monomers are fluorine-containing compounds with 2, 4, and 8 perfluorocarbon chain lengths respectively. The short, medium, and long multi-level spatial structure can overcome the steric hindrance of a single fluorine-containing acrylate CF long chain. The short and medium-length fluorocarbon chains can be inserted into the gaps in the fluorine-containing compounds with large molecular weight and long chain matching, thereby increasing the degree of polymerization of the fluorine-containing acrylate on the surface of the boron powder and increasing the fluorine density at the same time, achieving a dense coating effect on the boron powder. Due to the introduction of the fluorocarbon chain, the hydrophobicity of the boron powder can be significantly improved, and the hygroscopicity of the modified boron powder will decrease compared to the hygroscopicity of the original boron powder, solving the problem that the boron powder is easy to absorb moisture and agglomerate and has poor fluidity. In addition, the dense high-fluorine density film on the surface of the boron powder can avoid direct contact between the boron powder and oxygen and water, and can show higher boron activity when used as a fuel component of a fuel-rich propellant. On the other hand, during the combustion process of the propellant, HF or short-chain fluorocarbons produced by the high-temperature decomposition of fluorocarbons can react with viscous B2O3 to generate gaseous boron fluoride. The reaction promotes further combustion of boron powder and reduces the difficulty of ignition of boron powder.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] (1) The boron powder modifier used is a ternary copolymer of fluorinated acrylates. CF, CH, and CO bonds are widely distributed in the copolymer and can be adsorbed on the surface of the boron powder through multilayer hydrogen bonds. The boron powder has an excellent coating effect and strong surface adhesion.

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

[0036] (3) The modified boron powder of the present invention has a high degree of polymerization of the fluorine-carbon chain on its surface and a high fluorine density content. Compared with the boron powder modified by a single polymerized fluorine-containing polymer, it has an excellent combustion-supporting effect under the same space 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 The SEM images of the boron powders of Comparative Example 1 and Example 1 are shown;

[0039] Figure 3 The XPS graphs of the boron powders of Comparative Example 1 and Example 1 are shown;

[0040] Figure 4 TG / DSC graphs of the boron powders of Comparative Example 1 and Example 1;

[0041] Figure 5 The laser ignition combustion diagrams of boron powder in Comparative Example 1 and Example 1 are shown;

[0042] In the picture: Figure 1 a is a 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 deionized water contact angle diagram of the modified boron powder of Example 1; Figure 1 c is a 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 a scanning electron microscope image of the unmodified boron powder of Comparative Example 1 of the present invention at different magnifications; Figure 2 b is a scanning electron microscope image of the modified boron powder of Example 1 of the present invention at different magnifications; Figure 3 a is the XPS graph of the modified boron powder of Example 1 of the present invention; Figure 3 b is the XPS graph of the unmodified boron powder of Comparative Example 1 of the present invention; Figure 4 a is the TG graph of the boron powder of Comparative Example 1 and Example 1 of the present invention; Figure 4 b is the DSC graph of the boron powder of Comparative Example 1 and Example 1 of the present invention; Figure 5 a is a laser ignition combustion diagram of boron powder in Comparative Example 1 of the present invention; Figure 5 b is a laser ignition combustion diagram of the modified boron powder in Example 1 of the present invention. DETAILED DESCRIPTION

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

[0045] Example 1

[0046] This embodiment provides a method for preparing a fluorinated acrylate ternary random copolymer modifier, specifically comprising:

[0047] 2.40 g of perfluoroethyl methacrylate, 3.16 g of perfluorobutyl ethyl acrylate, and 6.16 g of perfluorodecyl ethyl acrylate were added to the flask in sequence and stirred at room temperature for 10 min. Then, 0.10 g of AI BN was added thereto. After evacuation three times, the mixture was divided into four batches under a N2 atmosphere and added successively to a flask containing 15.0 g of n-butyl acetate and 0.024 g of dodecyl mercaptan. The mixture was heated to 90 ° C in an oil bath and reacted for 2 h. The reactant was poured into 40 ml of methanol, filtered, and impurities were washed off with methanol. The mixture was dried in vacuo at 50 ° C to obtain 6.42 g of a white powdery solid modifier.

[0048] The above modifier is applied to the modification of amorphous boron powder for fuel in boron-rich fuel propellant, specifically:

[0049] To a three-necked flask containing 108 g of boron powder, 370 ml of anhydrous ethanol was added, and the mixture was heated to 90°C and refluxed for 2 h at a stirring speed of 300 rpm. The mixture was filtered while hot and vacuum-dried to obtain 104 g of pretreated boron powder. 3 g of modifier was added to 370 ml of toluene at 30°C, and the modifier was completely dissolved by ultrasonication for 15 min. The modifier solution was added to a three-necked flask containing 100 g of pretreated boron powder under a N2 atmosphere, and the mixture was heated to 90°C and refluxed for 3 h at a stirring speed of 300 rpm. The mixture was rotary evaporated, ground, and passed through a 200-mesh sieve to obtain modified boron powder.

[0050] Example 2

[0051] This embodiment provides a method for preparing a fluorinated acrylate ternary random copolymer modifier, specifically comprising:

[0052] 2.28 g of perfluoroethyl methacrylate, 3.08 g of perfluorobutyl ethyl acrylate, and 6.20 g of perfluorodecyl ethyl acrylate were added to the flask in sequence and stirred at room temperature for 10 min. Then, 0.10 g of AI BN was added thereto. After evacuation 3 times, the mixture was divided into three batches under a N2 atmosphere and added successively to a flask containing 15.0 g of n-butyl acetate and 0.020 g of dodecyl mercaptan. The mixture was heated to 90 ° C and reacted for 2 h. The reactant was poured into 40 ml of methanol, filtered, and impurities were washed away with methanol. The mixture was dried in vacuo at 50 ° C to obtain 6.30 g of a white powdery solid modifier.

[0053] The above modifier is applied to the modification of amorphous boron powder for fuel in boron-rich fuel propellant, specifically:

[0054] To a three-necked flask containing 110 g of boron powder, 370 ml of anhydrous ethanol was added, and the mixture was heated to 90°C and refluxed for 2 h at a stirring speed of 300 rpm. The mixture was filtered while hot and vacuum-dried to obtain 106 g of pretreated boron powder. 6 g of modifier was added to 370 ml of toluene at 30°C, and the modifier was completely dissolved by ultrasonication for 15 min. The modifier solution was added to a three-necked flask containing 100 g of pretreated boron powder under a N2 atmosphere, and the mixture was heated to 90°C and refluxed for 2 h at a stirring speed of 350 rpm. The mixture was rotary evaporated, ground, and passed through a 250-mesh sieve to obtain modified boron powder.

[0055] Example 3

[0056] This embodiment provides a method for preparing a fluorinated acrylate ternary random copolymer modifier, specifically comprising:

[0057] 2.34g of perfluoroethyl methacrylate, 3.52g of perfluorobutyl ethyl acrylate, and 6.20g of perfluorodecyl ethyl acrylate were added to a flask in sequence and stirred at room temperature for 5 minutes. 0.10g of AI BN was then added. After evacuation three times, the mixture was added in three batches to a flask containing 15.0g of n-butyl acetate and 0.034g of dodecyl mercaptan under a nitrogen atmosphere. The mixture was heated to 90°C and reacted for 2 hours. The reactants were poured into 20ml of methanol, filtered, and washed with methanol to remove impurities. The mixture was then dried in vacuo at 50°C to obtain 7.12g of a white powdery solid modifier.

[0058] The above modifier is applied to the modification of amorphous boron powder for fuel in boron-rich fuel propellant, specifically:

[0059] To a three-necked flask containing 110 g of boron powder, 370 ml of anhydrous ethanol was added, and the mixture was heated to 90 ° C and refluxed for 2 h at a stirring speed of 300 rpm. It was filtered while hot and vacuum dried to obtain 106 g of pretreated boron powder. 3 g of modifier was added to 370 ml of toluene at 30 ° C, and the modifier was completely dissolved by ultrasonication for 15 min. The modifier solution was added to a three-necked flask containing 100 g of pretreated boron powder under a N2 atmosphere, and the mixture was heated to 90 ° C and refluxed for 4 h at a stirring speed of 350 rpm. It was rotary evaporated, ground, and passed through a 250-mesh sieve to obtain modified boron powder.

[0060] Example 4

[0061] This embodiment provides a method for preparing a fluorinated acrylate ternary random copolymer modifier, specifically comprising:

[0062] 2.09 g of perfluoroethyl methacrylate, 3.20 g of perfluorobutyl ethyl acrylate, and 6.11 g of perfluorodecyl ethyl acrylate were added to the flask in sequence and stirred at room temperature for 10 min. Then, 0.07 g of AI BN was added thereto. After evacuation three times, the mixture was divided into three batches under a N2 atmosphere and added successively 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 reactant was poured into 40 ml of methanol, filtered, and impurities were washed away with methanol. The mixture was dried in vacuo at 50 ° C to obtain 7.82 g of a white powdery solid modifier.

[0063] The above modifier is applied to the modification of amorphous boron powder for fuel in boron-rich fuel propellant, specifically:

[0064] To a three-necked flask containing 110 g of boron powder, 370 ml of anhydrous ethanol was added, and the mixture was heated to 90 ° C and refluxed for 2 h at a stirring speed of 300 rpm. It was filtered while hot and vacuum dried to obtain 103 g of pretreated boron powder. 3 g of modifier was added to 380 ml of tetrahydrofuran at 30 ° C, and the modifier was completely dissolved by ultrasonication for 15 min. The modifier solution was added to a three-necked flask containing 100 g of pretreated boron powder under a N2 atmosphere, and the mixture was heated to 80 ° C and refluxed for 2 h at a stirring speed of 350 rpm. It was rotary evaporated, ground, and passed through a 250-mesh sieve to obtain modified boron powder.

[0065] In Examples 1-4, the boron powder is selected from amorphous boron powder with a particle size of less than 5 μm.

[0066] Comparative Example 1

[0067] This comparative example provides unmodified boron powder: the amorphous boron powder is not coated with a modifier and is not pretreated with ethanol. The unmodified boron powder is directly ground and passed through a 200-mesh sieve.

[0068] Comparative Example 2

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

[0070] 6.20 g of perfluorodecyl ethyl acrylate was added to the flask in sequence and stirred at room temperature for 5 min. Then, 0.10 g of AI BN was added thereto. After evacuation 3 times, the mixture was divided into three batches under a N2 atmosphere and added successively 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 reactant was poured into 20 ml of methanol, filtered, and impurities were washed off with methanol. The mixture was dried in vacuo at 50°C to obtain 4.12 g of a white powdery solid modifier.

[0071] To a three-necked flask containing 110 g of boron powder, 370 ml of anhydrous ethanol was added, and the mixture was heated to 90 ° C and refluxed for 2 h at a stirring speed of 300 rpm. It was filtered while hot and vacuum dried to obtain 103 g of pretreated boron powder. 3 g of modifier was added to 380 ml of toluene at 30 ° C, and the modifier was completely dissolved by ultrasonication for 15 min. The modifier solution was added to a three-necked flask containing 100 g of pretreated boron powder under a N2 atmosphere, and the mixture was heated to 80 ° C and refluxed for 2 h at a stirring speed of 350 rpm. It was rotary evaporated, ground, and passed through a 250-mesh sieve to obtain modified boron powder.

[0072] The performance of the modified boron powder prepared above was characterized, and the results were as follows:

[0073] The deionized water contact angles of the boron powder before and after modification were measured using an XG-CAME powder contact angle meter. The powdered boron powder was tableted before testing. Figure 1 The water contact angle of the modified boron powder in Example 1 is shown as 0°, indicating that the unmodified micron-sized amorphous boron powder will be quickly wetted by water when in contact with water, resulting in a decrease in the activity of the boron powder and significant agglomeration between the powders. Figure 1 b shows an angle of 150°, which indicates a super-hydrophobic interface. The dense fluorocarbon chains wrapped in the outermost layer of the boron powder isolate the boron powder from water. The super-hydrophobic nature means that the agglomeration problem of the refined boron powder can be greatly improved. Figure 1 c shows a 128° angle, significantly lower than that of Example 1. This is due to the high steric hindrance during the polymerization of a single long-chain perfluorodecylethyl acrylate, resulting in a lower degree of polymerization of the resulting fluorinated acrylate polymer than the ternary polymerized fluorinated acrylate polymer, making it impossible to form a dense fluoride coating on the boron powder surface. The contact angle values ​​of Examples 2-4 are similar, all around 150°, indicating that the ternary random fluorinated acrylate polymer was successfully coated and had an excellent hydrophobic effect. The specific water contact angles of the boron powders in each comparative example and example are shown in Table 1.

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

[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 surface morphology of the amorphous boron powder before and after modification was observed and analyzed using a Hitach i8010 scanning electron microscope. Figure 2 As shown, Example 1 Figure 2 Modified boron powder in b and comparative example 1 Figure 2The boron powder in Example a showed no significant change in morphology and structure, exhibiting a rough, porous, amorphous structure. However, the modified boron powder in Example 1 was more evenly dispersed, had a smaller particle size, and contained almost no large boron powder agglomerates, demonstrating that imparting hydrophobicity to boron powder can resolve the problem of fine 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 are attributed to O1s and B1s in B2O3 and boric acid respectively. Figure 3 In spectrum a, the peaks at 688.8ev, 532.3ev, 291.6ev, and 187.9ev are attributed to F1s, O1s, C1s in the fluorinated acrylate terpolymer and B1s in B2O3, respectively, indicating that the fluorinated acrylate terpolymer is successfully coated on the surface of the boron powder.

[0078] The thermal properties of boron powder before and after modification were measured by TG / DSC in air atmosphere at a temperature range of 50℃-1000℃ and a heating rate of 10℃ / 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, where TG focuses on oxidation weight gain; Figure 4 b is the DSC graph of the boron powder of Comparative Example 1 and Example 1 of the present invention, focusing on the initial oxidation temperature. The boron in Example 1 has a slightly greater weight gain in air oxidation than that in Comparative Example 1, and the initial oxidation temperature of 769.65°C is 13.60°C earlier than that of 783.25°C in Comparative Example 1. This is because the fluorine-containing compound coating decomposes into HF or short-chain fluoride at around 380°C, which reacts with the sticky B2O3 on the surface of the boron powder 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 of 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 difficulty of the boron powder before and after modification was measured by weighing 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 using an analytical balance. The laser ignition power was set to 80 W and the results were recorded and observed using a high-speed camera. Figure 5The laser ignition combustion images of Comparative Example 1 and Example 1 are shown. The time from the appearance of a bright spot to the appearance of an obvious flame is defined as the ignition delay time. Figure 5 a The ignition delay time is 142ms, Example 1 Figure 5 The ignition delay time of boron powder b is 16ms. This is because the fluorine-containing modifier decomposes into gaseous HF when heated. HF reacts with the sticky B2O3 on the surface of the boron powder to produce gaseous products, which inhibit the accumulation of oxide film on the boron surface. The generated gas can also increase the spatial dispersion of boron particles and the contact area between boron and oxygen, which is conducive to the smooth progress of the oxidation reaction. The combustion intensity of boron increases, and the energy release rate of boron powder is increased, thus shortening the ignition delay time.

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

[0081] In addition to the above embodiments, the present invention may also have other implementations. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for preparing a fluorinated acrylate ternary random copolymer modifier, characterized in that: The specific steps include: (1) Three fluorinated acrylates with different fluorocarbon chain lengths were stirred and mixed, and a free radical initiator was added; The three fluorocarbon chain lengths of the fluorinated acrylates are calculated by mass ratio. : : =2.0-2.4g:3.0-3.3g:6.0-6.3g; The free radical initiator is azobisisobutyronitrile, and the amount of azobisisobutyronitrile added is 3-6% of mass; (2) Adding the fluorinated acrylate mixture in batches to a flask containing a solvent and dodecyl mercaptan under a nitrogen 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 modifier containing 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.

3. The method for preparing the modifier according to claim 1, wherein: The mass of the dodecyl mercaptan is 0.1-0.3% of the fluorinated acrylate mixture.

4. The method for preparing the modifier according to claim 1, wherein: The temperature of the free radical polymerization reaction is 80° C.-90° C., and the solvent is n-butyl acetate.

5. A fluorinated acrylate ternary random copolymer modifier prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the fluorinated acrylate ternary random copolymer modifier as claimed in claim 5 for modifying amorphous boron powder for fuel in boron-containing fuel-rich propellants.

7. A method for modifying amorphous boron powder for fuel in boron-rich fuel propellant, characterized in that: The specific steps include: (1) Pretreatment: Add boron powder to ethanol, stir, heat and reflux for a period of time, then filter and vacuum dry to remove impurities on the surface of the boron powder; (2) Preparation of the modifier: prepare a solution of the fluorinated acrylate ternary random copolymer modifier as described in claim 5, and heat and ultrasonicate the solution until it is completely dissolved; (3) Modification and refinement: In a N2 atmosphere, the pretreated boron powder and fluorinated acrylate ternary random copolymer solution were added to a three-necked flask, mixed, heated and refluxed for a period of time, then cooled and rotary evaporated, vacuum dried, ground and sieved to obtain the modified boron powder.

8. The modification method according to claim 7, characterized in that: The boron powder in the pretreatment of step (1) 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 h, 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 pretreated boron powder, the ultrasonic temperature is 25-40°C, and the ultrasonic time is 15-20 min; The heating temperature in step (3) is 80-100° C., the heating time is 2-4 h, and the stirring speed is 300-400 rpm.

9. A modified boron powder obtained by the modification method according to claim 7, 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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