A microscale continuous flow preparation method for ultrafine boron / potassium nitrate ignition powder

Abstract

The present invention is a micro-scale continuous flow preparation method for ultra-fine boron / potassium nitrate ignition powder. It includes the following steps: (1) potassium nitrate and a binder are respectively prepared into solutions, and boron powder is dissolved in one phase of the solution to form a boron suspension system B-X1, (2) equipment assembly, the boron suspension system B-X1 and another solution phase X2 are placed in a fluid drive unit, the molding chamber is vacuumed, and the inlet of the atomizer is passed through an inert gas of 0.1-6.0kpa, and the temperature in the molding chamber is set to 80°C-200°C; (3) the boron suspension system B-X1 and another phase solution X2 are driven to flow into a micro-mixing unit, and the boron potassium nitrate suspension system generated by mixing in the micro-mixing unit flows into the atomizer and forms atomized droplets under the action of the inert gas, and the atomized droplets enter the molding chamber and are dried and then molded to obtain ultra-fine boron / potassium nitrate ignition powder. The present invention overcomes the problem that the output is not easy to amplify faced by the current micro-chemical process, the whole process is continuous, there is no three wastes, and it is easy to realize the green and controllable macro-preparation of boron / potassium nitrate ignition powder.

Description

Technical Field

[0001] The invention belongs to the field of energetic materials, and in particular relates to a micro-scale continuous flow preparation method of ultrafine boron / potassium nitrate ignition powder. Background Art

[0002] Ignition powder, also known as ignition powder, is one of the most important pyrotechnic agents. Its function is to locally heat the agent to be ignited to the ignition point and promote its stable and reliable combustion. Under the action of external initial impulse energy, the ignition powder can undergo a rapid combustion reaction, releasing a large amount of heat, gas and hot solid residue. Boron / potassium nitrate (BPN) is one of the commonly used high-energy ignition powders. It has the characteristics of high flame sensitivity, easy ignition, high calorific value, large explosion heat, large amount of combustion residue, strong ignition ability and safety insensitivity. It is a high-energy ignition powder with good performance. It can replace black powder and has been widely used in conventional weapons and aerospace. It is the only in-line ignition powder allowed in the US military standard MIL-STD-1901A.

[0003] The structural morphology, particle size and particle size distribution of boron / potassium nitrate ignition powder are important factors affecting its energy release characteristics and sensitivity. At present, mechanical mixing is usually used to prepare ignition powder. This traditional macroscopic preparation method is difficult to ensure the uniformity of mixing, and it is impossible to accurately regulate the microscale structure of boron / potassium nitrate; and the consistency between different batches of products is poor, which greatly affects the stable energy release of boron / potassium nitrate in practical applications. A precise and controllable preparation environment is the key to obtaining high-quality energetic materials. In recent years, some researchers have tried to prepare core-shell boron / potassium nitrate ignition powder (CN 110526790 A, CN 107304150A) by electrostatic spraying, trying to improve the performance of ignition powder and improve the consistency of boron / potassium nitrate ignition powder. However, the disadvantages of the electrostatic spraying method are also obvious: it cannot be continuous; it is difficult to scale up production; the process controllability is limited; the preparation method based on the action of the electrostatic field has a certain impact on the process safety of energetic materials. Summary of the invention

[0004] The purpose of the present invention is to provide a micro-scale continuous flow preparation method for ultrafine boron / potassium nitrate ignition powder, so as to realize on-demand regulation of the particle size and micro-scale structure of BPN composite particles.

[0005] The technical solution to achieve the purpose of the present invention is: a micro-scale continuous flow preparation method of ultrafine boron / potassium nitrate ignition powder, comprising the following steps:

[0006] Step (1): According to the ignition powder formula, potassium nitrate and a binder are prepared into solutions in corresponding amounts, and boron powder is dissolved in one of the solutions to form a boron suspension system B-X1.

[0007] Step (2): connecting the outlets of the two fluid driving units to the inlet of the micro-mixing unit, and connecting the inlet of the micro-mixing unit to the inlet of the atomizer (8) on the molding chamber (6); placing the boron suspension system B-X1 and another solution phase X2 into the fluid driving unit, evacuating the molding chamber (8), introducing 0.1 to 6.0 kPa of inert gas into the inlet of the atomizer (8), and setting the temperature in the molding chamber (8) to 80°C-200°C;

[0008] Step (3): start two fluid driving units to drive the boron suspension system B-X1 and another phase solution X2 to flow into the micro-mixing unit, and the boron potassium nitrate suspension system mixed by the micro-mixing unit flows into the atomizer (8) to form atomized droplets under the action of the inert gas, and the atomized droplets enter the molding chamber (6) to be dried and then molded to obtain ultrafine boron / potassium nitrate ignition powder, and the ultrafine boron / potassium nitrate ignition powder is collected by the collection unit below the molding chamber.

[0009] Furthermore, the contents of potassium nitrate, binder and boron powder in step (1) are as follows in mass percentage: 20%-80%, 0.1%-20% and 5%-70%.

[0010] Furthermore, the solvent of potassium nitrate is water, and the solvent of the binder is alcohol.

[0011] Furthermore, the average particle size of the boron powder used in step (1) is not greater than 300 μm.

[0012] Furthermore, the concentrations of the boron suspension system B-X1 prepared in step (1) and the other solution phase X2 are 0.1 g / L-40 g / L.

[0013] Furthermore, in step (3), the flow rate of the boron suspension system B-X1 and the other solution phase X2 is 1 ml / min-20 ml / min.

[0014] Furthermore, the two fluid driving units adopt a pumping mechanism.

[0015] Furthermore, the micro-mixing structure of the micro-mixing unit is a two-dimensional "Y" type, vortex type or spiral type, or a three-dimensional chaotic convection type.

[0016] Furthermore, the three-dimensional chaotic convection micromixer is composed of two chips engraved with channels, and the shape of the channels is set to be square, circular or triangular; the channels of the two chips are set to remain continuous in the horizontal direction to ensure that the fluid can pass smoothly, and in the vertical direction to ensure that the fluid produces a chaotic convection mixing effect in the mixer.

[0017] An ultrafine boron / potassium nitrate ignition powder is prepared by the above method.

[0018] Compared with the prior art, the present invention has the following significant advantages:

[0019] 1. The present application adopts a microscale continuous flow preparation method for ultrafine boron / potassium nitrate ignition powder, by atomizing the suspension through an inert gas passing through an atomizer, to achieve continuous preparation of spherical particles, and by adjusting the flow rate ratio of the fluid drive unit, ignition powders with different morphologies can be prepared. The method of the present invention has certain potential in the microscale structure regulation of boron / potassium nitrate ignition powder.

[0020] 2. This application adopts a micro-scale continuous flow preparation method for ultrafine boron / potassium nitrate ignition powder. The continuous and uniform atomization process ensures the consistency of the sample and avoids the problem of poor product consistency under macroscopic mechanical mixing to a certain extent. Compared with electrostatic spraying and other methods that have emerged in recent years, the atomization unit is easier to achieve a certain scale of batch preparation of boron / potassium nitrate ignition powder.

[0021] 3. The present application adopts a microscale continuous flow preparation method for ultrafine boron / potassium nitrate ignition powder. The microscale composite structure formed by boron / potassium nitrate microparticles is beneficial to inhibiting the oxidation of boron powder and ensuring the energy output characteristics of boron / potassium nitrate ignition powder. Compared with other macroscopic preparation methods, the atomization unit can accurately control the particle size of spherical ultrafine potassium nitrate, the size of the boron powder aggregation structure, and the composite structure of potassium nitrate and boron powder at the microscale by changing parameters such as atomization temperature, atomization time, atomization nozzle structure, and material ratio, thereby realizing on-demand regulation of the microscale structure of micro-nano boron / potassium nitrate ignition powder.

[0022] 4. This application adopts a micro-scale continuous flow preparation method for ultrafine boron / potassium nitrate ignition powder, which is simple in experimental operation, low in cost, short in cycle, has a high yield, and the reagents used are green and harmless; the continuous flow preparation strategy coupled with the atomization unit overcomes the problem of difficult scale-up of production currently faced by the micro-chemical industry. The whole process is continuous and free of three wastes, and it is easy to achieve green and controllable macro-scale preparation of boron / potassium nitrate ignition powder. Atomization drying, as an effective means of reducing sensitivity, makes the preparation environment safe and mild, which is conducive to further engineering application in the later stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the preparation system used in the present invention.

[0024] Figure 2 The BPN is prepared according to the experimental scheme of specific example 1.

[0025] Figure 3 The BPN is prepared according to the experimental scheme of specific example 2.

[0026] Figure 4 This is the BPN prepared according to the experimental scheme of Example 3.

[0027] Figure 5 This is the BPN prepared according to the experimental scheme of Example 4.

[0028] Figure 6 This is the BPN prepared according to the experimental scheme of Example 5.

[0029] Figure 7 The effect of the composite component ratio (B / KNO3) on the microscale core-shell structure of the composite energetic microspheres; (a) is a B / KNO3 ratio of 8 / 2, (b) is a B / KNO3 ratio of 6.5 / 3.5, (c) is a B / KNO3 ratio of 5 / 5, (d) is a B / KNO3 ratio of 3.5 / 6.5, (e), (f), (g), and (h) are partial enlarged images of (a), (b), (c), and (d), respectively.

[0030] Description of reference numerals:

[0031] 1- fluid driving unit, 2- solution phase, 3- suspension phase, 4- micro-mixing unit, 5- collecting unit, 6- forming chamber, 7- compressed air, 8- atomizer. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0033] Combination Figure 1 The present invention is a micro-scale continuous flow preparation method for ultrafine boron / potassium nitrate ignition powder. The preparation system adopted includes a fluid driving unit 1, a solution phase 2, a suspension phase 3, a mixing unit 4, a collecting unit 5, a molding chamber 6, compressed air 7, an atomizer 8 and a connecting component.

[0034] For the atomization unit, the air in the molding chamber 6 is extracted until the interior reaches a near vacuum state, and the compressed gas is passed into the atomizer 8, and the gas pressure range is controlled to be 0.1-6.0 kPa. When the airflow is stable, the temperature in the molding chamber is set, and the temperature in the molding chamber is waited for to reach the preset value (80°C-200°C). According to the ignition powder formula ratio, appropriate amounts of boron powder, potassium nitrate and binder are weighed to prepare corresponding solutions and suspensions, and the suspensions are stably dispersed in a certain way, and the configured solutions and suspensions are transported to the micro-mixing unit through the fluid drive unit in the system. After being fully mixed in the micro-mixing unit, the mixed system is input into the atomizer. Under the action of the high-temperature airflow, the mixed system is broken into micro-droplets and gradually volatilized to produce solid powder. The obtained ignition powder is gently scraped and collected in the collection unit to complete the preparation of boron / potassium nitrate ignition powder.

[0035] The present application of the present invention adopts a micro-scale continuous flow preparation method of ultrafine boron / potassium nitrate ignition powder, and the specific preparation steps are as follows:

[0036] 1. According to the selected ignition powder formula, weigh appropriate amounts of boron powder, potassium nitrate and binder to prepare corresponding solutions and suspensions, and make the suspensions stably dispersed by a certain method;

[0037] 2. Connect system pipelines to ensure stable fluid transportation;

[0038] 3. Turn on the fluid delivery device, set the parameters, and place the prepared solution and suspension into the fluid delivery device for later use;

[0039] 4. For the atomization unit, extract the air in the molding chamber until the interior reaches a near vacuum state;

[0040] 5. Open the valve of the nitrogen bottle and adjust the air pressure to 0.1-6.0 kPa, thus completing the airflow control of the molding chamber;

[0041] 6. Start the temperature control unit of the atomizing unit, set the molding chamber temperature (80°C-200°C) and wait for the molding chamber temperature to reach the preset value;

[0042] 7. Start the fluid driving unit so that the two-phase fluid stably flows into the micro-mixing unit under the set flow parameters, and the mixed system flowing out of the micro-mixing unit flows into the atomization unit for atomization.

[0043] 8. When all the mixed liquid flows into the atomizer and no solid powder is produced in the collecting unit, the atomization process ends, and the collecting unit is removed to collect the sample, thereby completing the preparation of the boron / potassium nitrate ignition powder.

[0044] The following examples are only intended to further illustrate the present invention and should not be construed as limiting the present invention.

[0045] Example 1

[0046] Boron / potassium nitrate ignition powder is prepared by a microscale continuous flow preparation method for ultrafine boron / potassium nitrate ignition powder. Potassium nitrate aqueous solution and binder solution, weigh an appropriate amount of boron powder and add it to the prepared potassium nitrate solution, start the ultrasonic vibrator, set the ultrasonic level to 20 and act on the suspension to make the B / KNO3 suspension stably dispersed. The mixing unit uses a dual-chamber passive vortex chip, connects each part of the pipeline, and completes the transition connection between the hard pipe and the soft pipe through an adapter. Adjust the peristaltic pump used to drive the two-phase fluid and set the parameter to 6.4. Start the atomization unit to evacuate the vacuum. When the oxygen content drops to the default value that allows the atomization unit to work safely, the indicator light goes out and subsequent operations can be performed. Open the nitrogen bottle valve and adjust the air pressure to 2kpa. Set the molding room temperature to 95°C and wait for the indoor temperature to reach the set value. Start the peristaltic pump, and the two-phase fluid flows into the chip and the atomization unit respectively under certain parameters. After atomization and drying, the final product boron / potassium nitrate ignition powder is obtained, such as Figure 2Under this condition, the BPN composite system obtained by atomization has initially achieved sphericalization, but a part of the boron powder is still not well coated and forms agglomerates. The reason is that the boron powder cannot be well dispersed in the potassium nitrate solution with water as the solvent. During the peristaltic pump driving process, the boron powder is deposited in the pipeline, causing the boron powder particles to agglomerate after physical and chemical drying.

[0047] Example 2

[0048] The operation steps are the same as those in Example 1, except that 100 mg of nano boron powder is weighed and added to the phenolic resin / ethanol solution, and the solution is stably dispersed by an ultrasonic rod. The parameter settings are the same as those in Example 1. The sample is obtained as Figure 3 As shown. For this sample, the agglomeration phenomenon is significantly improved compared with Example 1, and the BPN composite system is further spheroidized under the action of atomization, with a better morphology. Experimental observations show that the boron powder can be well dispersed by adding the basic liquid in this way, and the binder may play a certain role in dispersion.

[0049] Example 3

[0050] The operation steps are the same as those in Example 2, except that the mixing unit uses a Y-shaped chip. The parameter settings are the same as those in Example 2. The sample is obtained as Figure 4 shown.

[0051] Example 4

[0052] The operation steps are the same as those in Example 2, except that the mixing unit uses a continuous focusing flow. The parameter settings are the same as those in Example 2. The sample is obtained as Figure 5 shown.

[0053] Example 5

[0054] The operation steps are the same as those in Example 2, except that the mixing unit adopts a three-dimensional chaotic convection type. The parameter settings are the same as those in Example 2. The sample is obtained as Figure 6 shown.

[0055] In Examples 1-2, we optimized the method of adding the basic liquid, and finally chose to use the method described in Example 2 to configure the basic liquid. For Examples 3-5, we replaced different micromixers for experiments, and the samples obtained were relatively good. In addition, this patent would like to emphasize that the personalized design of different micromixers is essentially to achieve BPN microscale mixing enhancement, and the difference is that different micromixers have different mixing effects due to their different structures. Therefore, the scope of protection of this patent should cover micromixing units of different structures, which is also reflected in the claims.

[0056] Example 6

[0057] The experiment analyzed the evolution of BPN core-shell microsphere structure from multiple dimensions. The component ratio ultimately regulates the construction of the multi-level core-shell structure by affecting the shell thickness of the multi-level core-shell structure and the self-assembly process of the agglomerated structure. The mass fraction of the binder was fixed at 5%, and the component mass ratio (B / KNO3) was set to 8 / 2, 6.5 / 3.5, 5 / 5, and 3.5 / 6.5 respectively. The effect of the composite component ratio (B / KNO3) on the microscale core-shell structure of the composite energetic microsphere was analyzed, such as Figure 7 As shown. It can be seen that when B / KNO3=3.5 / 6.5, BPN microspheres with better sphericity can be obtained ( Figure 7 b) As the mass fraction of boron powder increases, the quality of BPN microspheres gradually deteriorates, and the composite system cannot achieve sphericalization when B / KNO3=6.5 / 3.5.

Claims

1. A micro-scale continuous flow preparation method for ultrafine boron / potassium nitrate ignition powder, characterized in that: The steps include: Step (1): according to the ignition powder formula, corresponding amounts of potassium nitrate and a binder are respectively prepared into solutions, and nano boron powder is dissolved in the binder phase solution to form a boron suspension system B-X1, wherein the contents of potassium nitrate, binder and boron powder are as follows in mass percentage: 20% - 80%, 0.1% - 20% and 5% - 70%; the solvent of potassium nitrate is water, and the solvent of the binder is alcohol; Step (2): connecting the outlets of the two fluid driving units to the inlet of the micro-mixing unit, and connecting the inlet of the micro-mixing unit to the inlet of the atomizer (8) on the molding chamber (6); placing the boron suspension system B-X1 and another solution phase X2 into the fluid driving unit, evacuating the molding chamber (8), introducing an inert gas of 0.1-6.0 kPa into the inlet of the atomizer (8), and setting the temperature in the molding chamber (8) to 80°C-200°C; Step (3): start the two fluid driving units to drive the boron suspension system B-X1 and another phase solution X2 to flow into the micro-mixing unit, and the boron potassium nitrate suspension system generated by mixing in the micro-mixing unit flows into the atomizer (8) to form atomized droplets under the action of the inert gas, and the atomized droplets enter the molding chamber (6) to be dried and then molded to obtain ultrafine boron / potassium nitrate ignition powder, and the ultrafine boron / potassium nitrate ignition powder is collected by the collection unit below the molding chamber.

2. The method according to claim 1, characterized in that The average particle size of the boron powder used in step (1) is not greater than 300 μm.

3. The method according to claim 2, characterized in that The concentrations of the boron suspension system B-X1 prepared in step (1) and the other solution phase X2 are 0.1 g / L - 40 g / L.

4. The method according to claim 3, characterized in that In step (3), the flow rate of the boron suspension system B-X1 and the other solution phase X2 is 1 ml / min - 20 ml / min.

5. The method according to claim 4, characterized in that The two fluid drive units adopt a pumping mechanism.

6. The method according to claim 5, characterized in that The micro-mixing structure of the micro-mixing unit is a two-dimensional structure of "Y" type, vortex type or spiral type, or a three-dimensional chaotic convection type.

7. The method according to claim 6, characterized in that The three-dimensional chaotic convection micromixer is composed of two chips with channels engraved thereon, and the shape of the channels is set to be square, circular or triangular; the channels of the two chips are set to be continuous in the horizontal direction to ensure that the fluid can pass smoothly, and in the vertical direction to ensure that the fluid produces a chaotic convection mixing effect in the mixer.

8. An ultrafine boron / potassium nitrate ignition powder, characterized in that: The method is prepared by any one of claims 1 to 7.

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