Boron-containing fuel-rich propellant and preparation method thereof

Abstract

The invention belongs to the technical field of propellants, and provides a boron-containing fuel-rich propellant and a preparation method thereof.The propellant adopts fluorine-containing composite boron powder to replace common boron powder; a combination of hydroxyl-terminated polybutadiene and hydroxyl-terminated poly (polyethylene glycol succinate) is adopted as an adhesive; hydroxyl-terminated polyethylene glycol terephthalate containing a benzene ring rigid structure is adopted as a reinforcing agent, a polyethylene glycol chain segment, epoxy resin on the surface of boron powder and an oxidizing agent form a hydrogen bond, and hydroxyl-terminated polyether ester fixes a solid filler in a curing network and adjusts the crosslinking density at the same time; chemical bonds are generated on the surfaces of filler particles, so that the modulus of the propellant is further improved; the perfluoro diacid diester is used as a plasticizer, so that the burning efficiency is improved while the processing property of the propellant is not influenced; ferric polyacrylate, 2, 4-dinitrophenoxy ethanol and the like are used as combustion regulators to promote efficient oxidation of the boron powder. The boron-containing fuel-rich propellant provided by the invention can solve the demand problem of a solid ramjet engine on a high-modulus boron-containing fuel-rich propellant.

Description

Technical Field

[0001] This invention belongs to the technical field of fuel-rich propellants for solid ramjet engines, specifically relating to a boron-containing fuel-rich propellant and its preparation method. Background Technology

[0002] Air-breathing aircraft can cruise with power throughout their flight, possessing unique advantages such as rapid response, strong penetration capability, minimal speed loss during ballistic maneuvers, and high terminal velocity, making them one of the disruptive development directions for future aircraft. Solid scramjet engines not only offer advantages such as high specific impulse and high propulsion efficiency under hypersonic conditions, but also retain the inherent advantages of traditional solid rocket engines, including simple structure, small size, low cost, high safety and reliability, and good storage and maintainability. They can meet the engineering application requirements of aircraft, such as low cost, high reliability, strong environmental adaptability, and long-term all-weather operation.

[0003] The performance of solid ramjet engines is based on the energy performance of fuel-rich propellants; the higher the energy of the fuel-rich propellant, the greater the potential advantages of the solid ramjet engine. High-performance solid boron-rich propellants are the only metal-based solid propellants with a specific impulse exceeding 9000 N•s / kg, and their development level is a key technology restricting the application of solid ramjet engine technology.

[0004] The presence of highly viscous substances on the surface of boron powder causes it to agglomerate, severely affecting its dispersibility and consequently deteriorating the propellant's performance. To prevent these viscous substances from affecting propellant performance, washing is typically used to remove the oxide layer. However, due to the reactive nature of boron powder, washing cannot completely remove the oxide layer. Boron-containing propellants possess high mechanical strength, but excessively high boric acid content can worsen the mixing process, leading to propellant failure.

[0005] Patent 202310348864.1 describes a method for preparing composite boron powder using a two-stage condensation process. The composite uses vinylidene fluoride / acrylic acid copolymer (PVFA) as the composite agent, polyethylene glycol monobutyl ether acrylate / acrylonitrile / allylamine / hydroxyethyl acrylate copolymer (PANE) as the auxiliary composite agent, epoxy resin (TEOR) as the high-strength composite adhesive, and diethylenetriamine as the curing agent (DETA). This composite boron powder isolates the boron powder from air, solving the problem of propellant process deterioration caused by oxide formation due to environmental influences during boron powder storage. Because the composite surface contains functional groups such as amino groups, it can react with the curing agent and enter the cross-linking network, thus preserving the mechanical properties of the propellant.

[0006] In recent years, to increase strike range and enhance firepower suppression capabilities, developed Western countries have attempted to integrate ramjet engines into small tactical weapons such as rockets to extend their range. Boron-rich fuel propellants, with their high energy performance, are the preferred propellant type. Extended-range small tactical weapons require high maneuverability, necessitating propellant modulus. While boron-rich fuel propellants possess high strength, their modulus is generally around 5 MPa. Therefore, there is an urgent need to increase the propellant modulus to meet the high maneuverability requirements of extended-range small tactical weapons. Summary of the Invention

[0007] To address the problem that boron-rich fuel propellants generally have low modulus, making it difficult to meet the high mobility requirements of range-extended small tactical weapons, this invention provides a high-modulus boron-rich fuel propellant. This propellant uses secondary composite boron powder instead of ordinary boron powder. The boron powder contains fluorine compounds that can destroy the boron oxide layer, effectively promoting the combustion of the boron powder. The surface is an epoxy resin system with high mechanical strength, which gives the boron powder a regular morphology and allows it to react with the curing agent and enter the crosslinking system.

[0008] The technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a boron-containing fuel-rich propellant, comprising the following components: a binder system, an oxidant, fuel, auxiliary fuel, and a performance modifier; wherein the binder system includes a binder, a curing agent, a plasticizer, and a reinforcing agent; the reinforcing agent is hydroxyl-terminated polyethylene terephthalate (HTGA); and the fuel is composite boron powder.

[0009] Furthermore, the mass percentage of each of the above components is as follows: Adhesive system: 22-30%; Oxidizing agent: 30-40%; Composite boron powder: 30-40%; Auxiliary fuel: 6-10%; Performance modifier: 1-3%.

[0010] Furthermore, the adhesive is a combination of hydroxyl-terminated polybutadiene (HTPB) and hydroxyl-terminated polyethylene succinate (HSGA), with a mass ratio of HTPB to HSGA of 9:1; the curing agent is isophorone diisocyanate (IPDI); the plasticizer is perfluorodihexyl glutarate (FVHA), and the content of the plasticizer in the propellant component is 3wt%; the mass ratio of hydroxyl-terminated polyethylene terephthalate to hydroxyl-terminated polyethylene succinate is 1:2.

[0011] Furthermore, the aforementioned composite boron powder (MBC) is prepared by a two-stage condensation method using vinylidene fluoride / acrylic acid copolymer (PVFA) as a composite agent, a copolymer of polyethylene glycol monobutyl ether acrylate, acrylonitrile, allylamine, and hydroxyethyl acrylate (PANE) as an auxiliary composite agent, and an epoxy resin system as a coating and curing system; the particle size of the composite boron powder is 1.2~2.0μm.

[0012] Furthermore, the oxidant mentioned above is a combination of ammonium perchlorate and potassium perchlorate; the mass ratio of ammonium perchlorate to potassium perchlorate is 5:1 to 6:1.

[0013] Furthermore, the particle size of the above-mentioned oxidant includes one or more of the following four types: Type I (280~360μm), Type III (90~140μm), Type IV (5~15μm), and Type V (0.5~2μm).

[0014] Furthermore, the auxiliary fuels mentioned above are aluminum powder and / or magnesium powder with a particle size of 1~30μm.

[0015] Furthermore, the aforementioned performance modifiers include combustion performance modifiers, process aids, and antioxidants; wherein the combustion performance modifier is a mixture of ferric polyacrylate (FeAA) and 2,4-dinitrophenoxyethanol (DNE), with a mass ratio of ferric polyacrylate to 2,4-dinitrophenoxyethanol of 3:1 to 5:1; the process aid is lecithin; and the antioxidant includes one or more of N,N-diphenyl-p-phenylenediamine (DPPD), N-phenyl-2-naphthylamine (antioxidant D), and N-phenyl-N-cyclohexyl-p-phenylenediamine (antioxidant 4010).

[0016] A second aspect of the present invention provides a method for preparing the above-mentioned boron-containing rich fuel propellant, comprising the following steps: Step 1: Weighing and premixing the propellant: Weigh all components in a dry environment, add plasticizer and reinforcing agent to binder and mix well, then add performance modifier and auxiliary fuel and mix well to obtain premixed slurry. Step 2, Mixing: Add the composite boron powder and oxidant to the premixed slurry in sequence, mix evenly, then add the curing agent and continue mixing to obtain the slurry; Step 3: Propellant casting and curing: The slurry is vacuum-cast and cured in a dry environment to obtain the boron-rich fuel propellant.

[0017] Furthermore, in step one above, the order of adding the performance modifier is as follows: add the combustion performance modifier, process aid, and antioxidant in sequence. In step two, the temperature for mixing the materials is 30℃~50℃, and the mixing time is 70min~110min; In step three, the curing temperature is 50℃~70℃ and the time is 5~8 days.

[0018] The technical advantages of this invention compared to the prior art are: 1. The propellant formulation of this invention uses composite boron powder instead of conventional boron powder, improving the propellant's processability and combustion performance without affecting its mechanical properties. It employs a composite of PVFA containing a polyhydroxy fluorine structure and boron powder. The polyhydroxy structure in PVFA reacts with H3BO3 on the surface of boron powder to form borate esters, which tightly coat the boron powder surface, forming a dense coating layer. PANE contains highly active side chains, promoting the entanglement of the PANE molecular backbone with PVFA molecules, further improving the reaction efficiency of PVFA with boric acid and enhancing the structural regularity of the boron powder. The introduction of fluorine, which is in close contact with the boron powder, allows for rapid reaction with the boron powder during combustion to generate gaseous products, which helps suppress the formation of condensed phases and improves the combustion efficiency of the boron powder. Coating the boron powder surface with a high-mechanical-strength epoxy resin system significantly improves the structural regularity of the boron powder.

[0019] Boron powder prepared by reacting fluoride with the surface oxide of boron powder and then using a high-mechanical-strength epoxy resin for secondary composite preparation solves the problem that boron oxide on the surface of boron powder affects the propellant process in boron-rich fuel propellants. During combustion, the rapid reaction of boron powder with the fluoride to generate gaseous products helps to suppress the formation of condensed phase and improve the combustion efficiency of boron powder.

[0020] 2. The adhesive system of this invention includes an adhesive, a curing agent, a plasticizer, and a reinforcing agent: the propellant is essentially a composite material with an adhesive as the matrix and solid powders such as oxidants and fuels as fillers. For composite materials, solid particles with rigid structures, acting as non-crosslinking points of the polymer chains, contribute to the tensile strength of the polymer material and reinforce the matrix material. The number of groups in the solid particles that can form hydrogen bonds with the matrix material determines the strength of the reinforcing effect; a higher number of hydrogen-bonding groups is beneficial for improving the strength and modulus of the composite material.

[0021] HTPB adhesive matrix possesses high matrix strength, maintaining the propellant's high strength. Both HSGA and HTGA are hydroxyl-terminated polyether ester compounds. The polyethylene glycol segments in the hydroxyl-terminated polyether ester form hydrogen bonds with the oxidant and the epoxy resin on the boron powder surface, while the hydroxyl groups react with the curing agent and enter the adhesive network. After the propellant cures, the crosslinked network has a large molecular weight. The hydroxyl-terminated polyether ester tightly fixes the solid filler within the cured network while simultaneously regulating the crosslinking density and increasing the modulus.

[0022] HSGA is a flexible material in which ethylene glycol segments form a coiled crown ether structure, which can effectively chelate NH4. + and K +This improves the adhesion between the oxidant and the binder, and increases the modulus.

[0023] HTGA is a hydroxyl-terminated polyether ester compound containing a rigid benzene ring structure. While increasing the propellant modulus, its crown ether structure also creates additional crosslinking points on the filler particle surface through chemical bonding, further enhancing the propellant modulus. However, due to the benzene ring structure, HTGA has high cohesive energy; excessive addition can affect processing performance. Therefore, its addition amount is half that of HSGA. The use of hydroxyl-terminated polyether ester compounds improves the propellant modulus. The polyethylene glycol segments in the hydroxyl-terminated polyether ester form hydrogen bonds with the epoxy resin and oxidant on the boron powder surface, while the hydroxyl groups react with the curing agent to enter the binder network. After the propellant cures, the crosslinked network has a large molecular weight. The hydroxyl-terminated polyether ester tightly fixes the solid filler within the cured network while adjusting the crosslinking density, thus increasing the modulus.

[0024] Boron-rich fuel propellants use composite boron powder as fuel, which has reactive groups on its surface. These groups have a high binding energy with the binder system, and the propellant itself has high mechanical strength, so no additional bonding agent is needed.

[0025] The composite boron powder contains fluorine, which can promote the ignition and combustion of the boron powder during primary combustion. However, the PVFA content on the surface coating is limited and cannot further reduce the formation of condensed phase. To improve combustion performance, additional fluorine-containing compounds must be added.

[0026] Fluorinated plasticizers can act as oxidants, reacting with boron during propellant combustion to form boron oxyfluoride (BOF) gas and disrupting the boron oxide condensate phase, thus improving propellant combustion efficiency. However, because most fluorinated compounds are highly electronegative, they exert strong interactions with the propellant system, causing the binder and filler to agglomerate, leading to deterioration of propellant processing performance.

[0027] Perfluorodiacetate compounds are alkyl-terminated with fluorine-containing structures in the middle of the chain segment. The chain length of the fluorine-containing group is relatively short, and the activity is greatly reduced. The electronegativity of the fluorine-containing chain segment has a significant reduced impact on the propellant system, and the propellant will not agglomerate due to the electronegativity of the fluorine-containing chain segment.

[0028] Selecting appropriate perfluorodiacetic acid diesters (PFDAs) for different propellants can improve combustion efficiency without affecting propellant processing performance. Studies have found that adding FVHA to boron-containing propellants results in optimal processing and combustion performance; therefore, FVHA was chosen as the plasticizer. Replacing conventional plasticizers with perfluorodiacetic acid diesters, which have very low fluorine segment reactivity and electronegativity, prevents propellant agglomeration due to the electronegativity of the fluorinated segments, thus maintaining propellant processing performance. During combustion, FVHAs can react with boron to form boron oxyfluoride gas, improving combustion efficiency without compromising processing performance, disrupting the boron oxide condensation phase, and further enhancing propellant combustion efficiency.

[0029] In summary, using a combination of hydroxyl-terminated polybutadiene and hydroxyl-terminated polyethylene succinate as a binder results in a propellant matrix with high mechanical strength. Simultaneously, the polyethylene glycol segments in the hydroxyl-terminated polyether ester form hydrogen bonds with the epoxy resin and oxidant on the boron powder surface, while the hydroxyl groups react with the curing agent and enter the binder network, where the hydrocarbon segments entangle with the binder molecular segments. After propellant curing, the cross-linked network has a large molecular weight. The hydroxyl-terminated polyether ester tightly fixes the solid filler within the cured network while adjusting the cross-linking density and increasing the modulus. Furthermore, using hydroxyl-terminated polyethylene terephthalate with a rigid benzene ring structure as a reinforcing agent increases the propellant modulus. Its crown ether structure also generates additional cross-linking points on the filler particle surface through chemical bonds, further enhancing the propellant modulus. This ensures the propellant maintains high mechanical strength while simultaneously increasing the cross-linking density and modulus.

[0030] 3. The auxiliary fuel of the present invention is one or a combination of aluminum powder (Al) and magnesium powder (Mg): The combustion process of the propellant firstly decomposes the binder into small hydrocarbon fragments, and then burns and releases heat. The decomposition process of the binder is an endothermic process. Therefore, it is necessary to add substances that can increase the primary combustion temperature of the propellant, improve the primary combustion temperature of the propellant, ensure the temperature environment for the oxidation of boron powder, and promote the primary combustion of boron powder.

[0031] Al and Mg have high primary combustion temperatures and excellent ignition performance. Adding a small amount of Al and Mg can compensate for the heat loss of the propellant caused by the decomposition of the binder, making the combustion more stable.

[0032] 4. The performance modifier of this invention uses a mixture of iron polyacrylate and 2,4-dinitrophenoxyethanol as a combustion modifier to promote efficient oxidation of boron powder. Iron polyacrylate (FeAA) is an ion-polymer type combustion rate modifier that improves the combustion performance of boron powder through the redox reaction of iron ions. The combustion chamber of a solid-fuel engine is relatively small. According to the Clapeyron equation PV=nRT, pressure and temperature are directly proportional when the volume remains constant; lower combustion chamber pressure means lower combustion temperature. At lower temperatures, iron ions ionize and act as oxygen transfer agents, catalyzing the decomposition of the oxidizer and improving the low-pressure combustion performance of the propellant. At higher temperatures, polyacrylate decomposes endothermically, lowering the combustion temperature and delaying the decomposition of the oxidizer. At this time, DNE decomposes into small nitrogen-containing fragments, which react exothermically with the polyacrylate decomposition fragments, making the high-pressure combustion rate of the propellant less affected by the acrylic acid fragments, thus maintaining a high combustion rate and pressure index. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments.

[0034] Example 1 (1) Propellant composition (2) Propellant performance Example 2 (1) Propellant composition (2) Propellant performance Example 3 (1) Propellant composition (2) Propellant performance Example 4 (1) Propellant composition (2) Propellant performance Example 5 (1) Propellant composition (2) Propellant performance Example 6 (1) Propellant composition (2) Propellant performance Comparative Example 1 This comparative example uses the same boron-rich propellant formulation as Example 6, except that it does not contain HSGA+HTGA, and iron oxide is used instead of FeAA and DNE as a performance modifier for comparison. Since the mixing process of ordinary boron powder propellant is poor and it cannot be processed into a drug, the comparative examples all use composite boron powder as fuel.

[0035] (1) Propellant composition (2) Propellant performance As can be seen from Comparative Example 1, using iron oxide instead of FeAA and DNE as the combustion catalyst reduces the propellant burning rate at low pressure, while maintaining a similar burning rate at high pressure. This increases the propellant pressure index and reduces injection and combustion efficiency. Furthermore, the propellant modulus decreases significantly due to the absence of HSGA and HTGA in the propellant.

[0036] Comparative Example 2 To verify the effects of different plasticizers on propellants, loading tests were conducted using different fluorinated plasticizers: Dipentyl perfluorosuccinate, diisooctyl perfluoroadipate, and dibutyl perfluoroadipate were selected to replace dihexyl perfluoroglutarate. The propellant process performance was severely deteriorated, and it could not be processed into a drug.

[0037] The boron-containing fuel-rich propellant formulation and performance are as follows, obtained by replacing the plasticizer in Example 6 with the conventional inert plasticizer diisooctyl sebacate (DOS).

[0038] (1) Propellant composition (2) Propellant performance As can be seen from Comparative Example 2, replacing FVHA with DOS reduces the low-pressure burning rate of the propellant, resulting in decreased injection and combustion efficiency. While the fluorine in FVHA can form bonds with the binder system, DOS does not contain fluorine capable of forming hydrogen bonds with the binder, thus leading to a decrease in modulus.

[0039] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A boron-containing fuel-rich propellant, characterized in that: It contains the following components: binder system, oxidant, fuel, auxiliary fuel and performance modifier; The adhesive system includes an adhesive, a curing agent, a plasticizer, and a reinforcing agent; The reinforcing agent is hydroxyl-terminated polyethylene terephthalate (PET). The fuel is composite boron powder.

2. The boron-containing rich fuel propellant according to claim 1, characterized in that: The mass percentage of the component is: Adhesive system: 22-30%; Oxidizing agent: 30-40%; Composite boron powder: 30-40%; Auxiliary fuel: 6-10%; Performance modifier: 1-3%.

3. The boron-containing rich fuel propellant according to claim 1, characterized in that: The adhesive is a combination of hydroxyl-terminated polybutadiene and hydroxyl-terminated polysuccinic acid polyethylene glycol ester, with a mass ratio of hydroxyl-terminated polybutadiene to hydroxyl-terminated polysuccinic acid polyethylene glycol ester of 9:

1. The curing agent is isophorone diisocyanate; The plasticizer is dihexyl perfluoroglutarate, and the content of the plasticizer in the propellant component is 3 wt%. The mass ratio of hydroxyl-terminated polyethylene terephthalate to hydroxyl-terminated polyethylene succinate is 1:

2.

4. The boron-containing rich fuel propellant according to claim 1, characterized in that: The composite boron powder is prepared by a two-stage condensation method using a copolymer of vinylidene fluoride / acrylic alcohol as the composite agent, a copolymer of polyethylene glycol monobutyl ether acrylate, acrylonitrile, allylamine, and hydroxyethyl acrylate as the auxiliary composite agent, and an epoxy resin system as the coating and curing system. The particle size of the composite boron powder is 1.2~2.0μm.

5. The boron-containing rich fuel propellant according to claim 1, characterized in that: The oxidant is a combination of ammonium perchlorate and potassium perchlorate; The mass ratio of ammonium perchlorate to potassium perchlorate is 5:1 to 6:

1.

6. The boron-containing rich fuel propellant according to claim 1, characterized in that: The particle size of the oxidant includes one or more of the following four types: Type I: 280~360μm, Type III: 90~140μm, Type IV: 5~15μm, and Type V: 0.5~2μm.

7. The boron-containing rich fuel propellant according to claim 1, characterized in that: The auxiliary fuel is aluminum powder and / or magnesium powder with a particle size of 1~30μm.

8. The boron-containing rich fuel propellant according to claim 1, characterized in that: The performance modifier includes a combustion performance modifier, a process aid, and an antioxidant; wherein the combustion performance modifier is a mixture of ferric polyacrylate and 2,4-dinitrophenoxyethanol, and the mass ratio of ferric polyacrylate to 2,4-dinitrophenoxyethanol is 3:1 to 5:1; the process aid is lecithin; and the antioxidant includes one or more of N,N-diphenyl-p-phenylenediamine, N-phenyl-2-naphthylamine, and N-phenyl-N-cyclohexyl-p-phenylenediamine.

9. A method for preparing a boron-containing rich fuel propellant according to claim 1, characterized in that: Includes the following steps: Step 1: Weighing and premixing the propellant: Weigh all components in a dry environment, add plasticizer and reinforcing agent to the binder and mix well, then add performance modifier and auxiliary fuel and mix well to obtain premixed slurry. Step 2, Mixing: Add the composite boron powder and oxidant to the premixed slurry in sequence, mix evenly, then add the curing agent and continue mixing to obtain the slurry; Step 3: Propellant casting and curing: The slurry is vacuum-cast and cured in a dry environment to obtain the boron-rich fuel propellant.

10. The method for preparing boron-containing rich fuel propellant according to claim 9, characterized in that: In step one, the order of adding the performance modifier is as follows: add the combustion performance modifier, process aid and antioxidant in sequence; In step two, the temperature for mixing the materials is 30℃~50℃, and the mixing time is 70min~110min; In step three, the curing temperature is 50℃~70℃ and the time is 5~8 days.

Images