A new RNX propellant and a preparation method thereof

Abstract

The application provides a novel RNX propellant and a preparation method thereof; the RNX propellant comprises the following A formula or B formula; the A formula comprises the following components in mass fraction: binder: 15-25 parts; plasticizer: 1-10 parts; oxidant: 73 parts; catalyst: 2 parts; the B formula comprises the following components in mass fraction: binder: 15-25 parts; oxidant: 73 parts; catalyst: 2 parts; process aid: 1-10 parts; the application also relates to a preparation method of the aforementioned RNX propellant; the novel RNX propellant prepared by the application adopts a tertiary butyl ferrocene catalyst, the purity of which is greater than or equal to 95%, and the catalytic effect is much higher than that of solid Fe2O3 powder; in addition, the non-volatile liquid catalyst also increases the mass fraction of the binder system, so that the propellant slurry has better fluidity, and the novel RNX propellant has a higher burning rate.

Description

Technical Field

[0001] This invention relates to the field of pyrotechnic propellants; and more particularly to a novel RNX propellant and its preparation method. Background Technology

[0002] Richard Nakka Experimental Rocket Propellant (RNX) is a well-known pyrotechnic propellant. RNX propellant is a typical example of resin-based fuels in amateur rocketry. While its oxidizer remains potassium nitrate, the binder is no longer sugar-based but epoxy resin, and the formulation contains a large amount of Fe2O3 as a combustion catalyst. Compared to traditional potassium nitrate / sugar-based pyrotechnic propellants, RNX is a mature and reliable pyrotechnic propellant with advantages such as simple manufacturing, high safety, low accident probability, good product consistency, and low cost and availability. Currently, the mature RNX propellant formulation is: 22% [epoxy resin + curing agent], 70% potassium nitrate, and 8% Fe2O3 powder.

[0003] However, this RNX propellant also has certain problems. First, the viscosity of the epoxy resin and its curing agent is very high, especially since the solid content in the RNX propellant reaches 78%. This makes it difficult to disperse KNO3 and Fe2O3 evenly after adding them to the epoxy resin and curing agent; even after kneading them evenly for a long time, the material still loses its fluidity and cannot be cast. Second, the formulation contains too much Fe2O3. In fact, thermodynamic simulations using NASA-CEA2 software revealed that this Fe2O3 is a true catalyst, undergoing almost no chemical reaction before and after combustion. Therefore, this 8% Fe2O3 is an inert substance, which not only increases the useless solid content of the propellant system and deteriorates the process performance, but also reduces the overall energy performance of the propellant. Third, RNX propellant is different from ordinary nitroglycerin propellant; it is a purely composite system. During combustion, potassium nitrate has a weak oxidizing ability on the resin matrix, and ordinary Fe2O3 has only moderate catalytic performance. This leads to a low burning rate (r) of the RNX propellant. b Very low, usually r b ≤1mm / s. Therefore, current RNX propellants all suffer from insufficient gas production, making them unsuitable for small engines with a diameter of ≤30mm, and only applicable to medium and large engines. Fourth, KNO3 is a hygroscopic substance, which will absorb a large amount of moisture in high humidity environments, leading to propellant disintegration; therefore, how to reduce the hygroscopicity of KNO3 in RNX propellants is also a problem to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a novel RNX propellant and its preparation method.

[0005] This invention is achieved through the following technical solution:

[0006] This invention relates to a novel RNX propellant, the formulation of which is either formulation A or formulation B;

[0007] in,

[0008] Formula A comprises the following components in parts by weight:

[0009] Binder: 15-25 parts; Plasticizer: 1-10 parts; Oxidizing agent: 73 parts; Catalyst: 2 parts;

[0010] Formula B comprises the following components in parts by weight:

[0011] Binder: 15-25 parts; Oxidant: 73 parts; Catalyst: 2 parts; Processing aids: 1-10 parts.

[0012] Preferably, the binder is epoxy resin E44 and curing agent 650; the oxidant is KNO3; the catalyst is liquid tert-butylferrocene; the plasticizer is dioctyl adipate; and the process aid is acetone.

[0013] Preferably, the adhesive comprises 50% epoxy resin E44 and 50% curing agent 650. Both epoxy resin E44 and curing agent 650 are inexpensive and readily available substances.

[0014] Preferably, the plasticizer is dioctyl adipate with a purity ≥95%. Dioctyl adipate (DOA), CAS No.: 123-79-5, with a purity ≥95%, is an inexpensive and readily available substance.

[0015] Preferably, the oxidant contains 25% ultrafine KNO3 and 75% ordinary KNO3.

[0016] Preferably, the particle size of the ultrafine KNO3 is d. 50 d 50 The particle size is 3–5 μm; the ordinary KNO3 has a particle size of 16 mesh. Furthermore, after the ultrafine KNO3 and ordinary KNO3 are mixed in a certain proportion, a hydrophobic coating treatment is performed.

[0017] Preferably, the purity of the catalyst is ≥95%. The catalyst is a liquid ferrocene, named tert-butylferrocene (CAS No.: 1316-98-9), with a purity ≥95%. This is an inexpensive and readily available substance, and its catalytic effect is far superior to that of solid Fe2O3 powder. Moreover, this non-volatile liquid catalyst also increases the mass fraction of the binder system, thereby giving the propellant slurry better fluidity, an effect that solid catalyst Fe2O3 cannot achieve.

[0018] This invention also relates to a method for preparing the aforementioned novel RNX propellant, comprising the following steps:

[0019] Step 1: Preparation of ultrafine KNO3: A certain amount of coarse KNO3 particles are put into a ball mill, an appropriate amount of petroleum ether is added, and an appropriate amount of alumina beads with a diameter of 3 mm are added. Then the ball mill is closed. The ball mill is turned on and the speed of the ball mill is adjusted to 350 rpm. After ball milling for 2 hours, the machine is turned off, the material is taken out, washed, filtered and dried to obtain ultrafine KNO3.

[0020] Step 2: Preparation of hydrophobic mixed KNO3 powder: A small amount of stearic acid is completely dissolved in a certain amount of dichloromethane. Then, a certain amount of ultrafine KNO3 and ordinary KNO3 powder mixed in a mass ratio of 25:75 is added to the above solution. While sonicating, the mixture is stirred with a glass rod to form a mud-like mixture. After mixing for 20 minutes, the material is basically uniform. Then, the mud-like mixture is placed in a large petri dish and placed in a water bath oven. After drying at 50°C for 24 hours, the coated hydrophobic mixed KNO3 powder is obtained.

[0021] Step 3: Preparation of RNX propellant: A certain amount of epoxy resin, curing agent, plasticizer, tert-butylferrocene, and acetone were sequentially added to a small kneader. The kneader was sealed (to prevent acetone evaporation), and kneaded for a period of time until the materials were evenly mixed. Then, a certain amount of hydrophobic mixed KNO3 powder was added in several batches. The kneader was sealed again (to prevent acetone evaporation), and after kneading for 2 hours, the materials were basically evenly mixed, resulting in a slowly flowing mud-like mixture. This mixture was then poured into a mold. After pouring, the mold was left to stand at room temperature for a period of time, and then placed in a vacuum oven. The oven was sealed, and a vacuum pump was turned on at room temperature to evacuate the air, controlling the vacuum level in the oven to ≤0.02MPa. In this way, the acetone would completely evaporate before the resin cured, leaving no pores. After a period of time, the temperature was set to 40-50℃ and vacuum drying was continued for 45 hours to obtain the novel RNX propellant column prepared in Example 1.

[0022] The present invention has the following advantages:

[0023] (1) The novel RNX propellant prepared by the present invention uses tert-butylferrocene as the catalyst, with a purity of ≥95%, which has a catalytic effect far higher than that of solid Fe2O3 powder. In addition, the non-volatile liquid catalyst also increases the mass fraction of the binding system, thereby making the propellant slurry have better fluidity and making the novel RNX propellant of the present invention have a higher burning rate.

[0024] (2) The novel RNX propellant prepared by this invention has the following characteristics: First, the hydrophobic mixed KNO3 powder is coated, which greatly reduces the water absorption of KNO3. Since only KNO3 is hygroscopic in the composition of RNX propellant, and KNO3 accounts for 73% of the RNX propellant, the hygroscopicity of the RNX propellant prepared by coating KNO3 with hydrophobic coating is correspondingly reduced. Second, the ultrafine refining of some potassium nitrate increases the burning rate of the RNX propellant. In fact, increasing the burning rate of RNX propellant is a difficult task in engineering. In this invention, the reason why the burning rate of the novel RNX propellant is higher than that of the traditional RNX propellant is the result of the combined effect of potassium nitrate refining and the highly efficient catalyst tert-butylferrocene. Third, the burning temperature of the novel RNX propellant is lower, mainly due to the application of the highly efficient catalyst tert-butylferrocene. Fourthly, because the KNO3 content in the new RNX propellant formulation is 3% higher than the potassium nitrate content in the traditional RNX, the RNX propellant has a higher gas production rate, which is the fundamental reason for its higher specific impulse and characteristic velocity.

[0025] (3) The preparation method of the present invention has the advantages of being simple, low cost, high repeatability and high safety factor. Attached Figure Description

[0026] Figure 1 These are SEM images of the ultrafine KNO3 used in the preparation method of this invention;

[0027] Figure 2 This is a comparison chart of the hygroscopicity data of hydrophobic mixed KNO3 powder and ordinary KNO3 in the preparation method of this invention;

[0028] Figure 3 This is a comparison diagram of the internal ballistic performance of the RNX propellant prepared by the method of this invention and Comparative Example 1. Detailed Implementation

[0029] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are merely further illustrations of the present invention, but the scope of protection of the present invention is not limited to the following embodiments.

[0030] Example 1

[0031] This embodiment relates to a method for preparing a novel RNX propellant, comprising the following steps:

[0032] Step 1: Preparation of ultrafine KNO3: 200g of coarse KNO3 particles were placed in a ball mill, 150mL of petroleum ether was added, and then 250g of alumina beads with a diameter of 3mm were added. The ball mill was then closed. The ball mill was turned on and the speed was adjusted to 350rpm. After ball milling for 2 hours, the mill was turned off, the material was collected, washed, filtered, and dried to obtain ultrafine KNO3.

[0033] Step 2: Preparation of hydrophobic mixed KNO3 powder: 3 grams of stearic acid were completely dissolved in a certain amount of dichloromethane. Then, 300 grams of ultrafine KNO3 and ordinary KNO3 powder mixed in a mass ratio of 25:75 were added to the above solution. While sonicating, the mixture was stirred with a glass rod to form a mud-like mixture. After mixing for 20 minutes, the material was basically uniform. Then, the mud-like mixture was placed in a large petri dish and placed in a water bath oven. After drying at 50°C for 24 hours, the coated hydrophobic mixed KNO3 powder was obtained.

[0034] Step 3: Preparation of RNX propellant: 25g epoxy resin, 25g curing agent, 4g tert-butylferrocene, and 10mL acetone were sequentially added to a small kneader. The kneader was sealed (to prevent acetone evaporation), and kneaded for 20 minutes until the materials were completely mixed. Then, 146g of hydrophobic mixed KNO3 powder was added in 5 batches. The kneader was sealed again (to prevent acetone evaporation), and kneaded for 2 hours until the materials were basically mixed evenly, resulting in a slow-flowing, muddy mixture. This mixture was then poured into a mold. After pouring, the mold was left to stand at room temperature for 30 minutes, then placed in a vacuum oven. The oven was sealed, and a vacuum pump was turned on at room temperature to evacuate the mold, controlling the vacuum level in the oven to ≤0.02MPa. This allows the acetone to completely evaporate before the resin cures, leaving no pores. After 3 hours, the temperature was set to 50℃, and vacuum drying was continued for 45 hours to obtain the novel RNX propellant grain.

[0035] Example 2

[0036] This embodiment relates to a method for preparing a novel RNX propellant, comprising the following steps:

[0037] Step 1: Preparation of ultrafine KNO3: 200g of coarse KNO3 particles were placed in a ball mill, 150mL of petroleum ether was added, and then 250g of alumina beads with a diameter of 3mm were added. The ball mill was then sealed. The ball mill was turned on and the speed was adjusted to 350rpm. After ball milling for 2 hours, the mill was turned off, the material was collected, washed, filtered, and dried to obtain ultrafine KNO3.

[0038] Step 2: Preparation of hydrophobic mixed KNO3 powder: 3 grams of stearic acid were completely dissolved in a certain amount of dichloromethane. Then, 300 grams of ultrafine KNO3 and ordinary KNO3 powder mixed in a mass ratio of 25:75 were added to the above solution. While sonicating, the mixture was stirred with a glass rod to form a mud-like mixture. After mixing for 20 minutes, the material was basically uniform. Then, the mud-like mixture was placed in a large petri dish and placed in a water bath oven. After drying at 50°C for 24 hours, the coated hydrophobic mixed KNO3 powder was obtained.

[0039] Step 3: Preparation of RNX propellant: 15g of epoxy resin, 15g of curing agent, 4g of tert-butylferrocene, and 20g of DOA were sequentially added to a small kneader. The kneader was sealed and kneaded for 20 minutes until the materials were completely mixed. Then, 146g of hydrophobic mixed KNO3 powder was added in 5 batches. The kneader was sealed again and kneaded for 2 hours until the materials were basically mixed evenly, resulting in a slow-flowing, muddy mixture. This mixture was then poured into a mold. After pouring, the mold was left to stand at room temperature for 3 hours, and then placed in a vacuum oven at 40℃ for 45 hours to dry, yielding the novel RNX propellant grains.

[0040] Comparative Example 1

[0041] Comparative Example 1 relates to a method for preparing a propellant, comprising the following steps:

[0042] 22 grams of epoxy resin and 22 grams of curing agent were added to a small kneader. After the materials were mixed evenly, 140 grams of ordinary KNO3 powder (passed through a 16-mesh metal sieve) and 16 grams of Fe2O3 powder were added in 5 batches. After kneading for 2 hours, the materials were basically mixed evenly, resulting in a non-flowing, mud-like mixture. Then, the mud-like mixture was scooped out with a small spoon and pressed little by little into a mold. After compacting it completely, the mold was left to stand at room temperature for 2 hours, then placed in a vacuum oven, sealed, and the temperature set to 50°C. After drying for 48 hours, the mixture was cured, yielding the RNX propellant grains.

[0043] The ultrafine-treated potassium nitrate in Examples 1 and 2 is shown in [reference needed]. Figure 1 As shown in the figure, the particle size of the ultrafine-treated potassium nitrate is d. 50 ≈3~5μm. This meets the particle size standard for ultrafine powders.

[0044] from Figure 2 As can be seen, after hydrophobic treatment, the moisture absorption rate of mixed potassium nitrate in an environment with 90% humidity is significantly lower than that of ordinary potassium nitrate without coating treatment.

[0045] The energy performance of the RNX propellants prepared in Examples 1 and 2 of this invention is compared with that of the conventional RNX propellant prepared in Comparative Example 1, as shown in Table 1.

[0046] Table 1

[0047]

[0048] Table 1 shows that the RNX propellants prepared in Examples 1 and 2 exhibit lower hygroscopicity, higher specific impulse, higher characteristic velocity, lower combustion temperature, and significantly lower average molecular weight of combustion products. The lower combustion temperature implies reduced ablation of the propellant during combustion. The lower average molecular weight of combustion products indicates significantly higher gas production during combustion of the RNX propellants prepared in Examples 1 and 2, which is the fundamental reason for their higher specific impulse and characteristic velocity.

[0049] The internal ballistic performance and engine parameters of the RNX propellants prepared in Examples 1 and 2 of this invention and the conventional RNX propellant prepared in Comparative Example 1 are shown in Table 2.

[0050] Table 2

[0051]

[0052] As can be seen from the data in Table 2, under a pressure of 1 atm, the burning rates of Examples 1 and 2 are significantly higher than that of Comparative Example 1, while the combustion pressure indices of Examples 1 and 2 are significantly lower than those of Comparative Example 1. The engine parameters of the three examples are basically the same. The significantly higher burning rates of Examples 1 and 2 are mainly due to the use of tert-butylferrocene as a combustion catalyst, which has better catalytic performance. In addition, the formulation also contains a large amount of ultrafine potassium nitrate, which is also an important reason for the increased burning rate.

[0053] from Figure 3 As can be seen, under the condition that the inner hole and end face are flammable, the internal ballistic curves of the RNX propellant prepared in Example 1 are basically consistent with those of the RNX propellant prepared in Comparative Example 1, while the RNX propellant prepared in Example 2 has a shorter combustion time and the highest combustion pressure. The highest pressure achieved in Example 1 is also higher than that achieved in Comparative Example 1. This indicates that the RNX propellants prepared in Examples 1 and 2 have significantly higher gas production, resulting in higher combustion chamber pressures under the same propellant loading conditions.

[0054] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a novel RNX propellant, comprising the following steps: Step 1: Preparation of ultrafine KNO3: A certain amount of coarse KNO3 particles are put into a ball mill, an appropriate amount of petroleum ether is added, and an appropriate amount of alumina beads with a diameter of 3 mm are added. Then the ball mill is closed. The ball mill is turned on and the speed of the ball mill is adjusted to 350 rpm. After ball milling for 2 hours, the machine is turned off, the material is taken out, washed, filtered and dried to obtain ultrafine KNO3. Step 2: Preparation of hydrophobic mixed KNO3 powder: A small amount of stearic acid is completely dissolved in a certain amount of dichloromethane. Ultrafine KNO3 and ordinary KNO3 powder mixed in a mass ratio of 25:75 are added to the dichloromethane solution, sonicated and stirred to obtain a mud-like mixture. After 20 minutes, the mud-like mixture is placed in a petri dish and then placed in a water bath oven. After drying at 50°C for 24 hours, the coated hydrophobic mixed KNO3 powder is obtained. Step 3: Preparation of RNX propellant: A certain amount of epoxy resin, curing agent, plasticizer, tert-butylferrocene and acetone are added to a small kneader in sequence. The kneader is sealed and after it is mixed evenly, hydrophobic mixed KNO3 powder is added in batches. The kneader is sealed and kneaded for 2 hours. After it is mixed evenly, a muddy mixture is obtained. After pouring the mud-like mixture into the mold, the mold was left to stand at room temperature and then placed in a vacuum oven. The vacuum pump was turned on at room temperature to draw a vacuum, and the vacuum degree in the oven was controlled to be ≤0.02MPa. The temperature was then set to 40-50℃ and vacuum drying was continued for 45 hours to obtain the new RNX propellant. The oxidant contains 25% ultrafine KNO3 and 75% ordinary KNO3. The ultrafine KNO3 has a particle size of 3–5 μm; the ordinary KNO3 has a particle size of 16 mesh.

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