A new breakthrough in 3D printing technology developed by researchers at Purdue University can make 3D printing of explosives materials possible. Using a novel method, tiny droplets of energetic materials such as explosives, propellants, and pyrotechnics can be deposited onto a substrate to form a nanothermite. These nanothermites generate a lot of heat, thrust and a loud shockwave when ignited at over 2,500 Kelvin (K) or 4,000° Fahrenheit (F).
3D Printing Industry
Additive manufacturing (AM) or 3D printing is a process of creating three dimensional (3D) solid objects by depositing several successive layers of thin horizontal slices to form the 3D structure of the object1. Structures made of different materials such as metal, fabrics, biological materials, etc. This 12 Billion $ industry is predicted to generate revenue that exceeds $ 21 Billion by the year 20201. Therefore, additive manufacturing is a powerful tool that is going to revolutionize how objects are created in the future.
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Purdue’s Effort to 3D Print Explosives
Micro-level energetics are used in a variety of micromechanical systems. For example, airbags in vehicles are deployed by using a small amount of solid propellant. Dr. Jeff Rhoads’ team at Purdue University developed a new method to safely 3D print energetic materials or explosives. To 3D print explosives, this research team used two separate inert suspensions, of which include: aluminum, which acts as a fuel and copper oxide, which acts as an oxidizer. The suspensions of both these materials were prepared by dissolving the nanoparticles of aluminum or copper oxide in dimethyl-formamide (DMF)2,3.
Based on the software program, droplets of picoliter (pL) volumes of these two materials were deposited onto a substrate using a piezoelectric inkjet printer2,3. To allow for the in situ mixing of aluminum and copper oxide, the droplets of these two materials were deposited adjacently in an overlapping fashion2,3. Multiple layers of the aluminum and copper oxide were deposited onto a substrate to form the final energetic material2,3.
There are two major challenges in 3D printing explosives using this technique. 1. Obtaining optimum droplet volume and pattern, and 2. Accurate deposition of droplets. To solve this first problem, Dr. Jeff Rhoads’ team used a tube that flexes when a voltage is applied. The size of the droplets deposited could be controlled by varying the voltage which allows for 0.1-micrometer increments in droplet size. Unlike the traditional 3D printing machinery, where the stage is fixed and has a moving nozzle, the 3D printer used by Purdue used a stationary nozzle and a moving stage2. The precise movement of the stage in micrometer scale ensures the accurate deposition of the suspension droplets2.
Samples composed of 3, 5 and 7 layers of the material were ignited using a spark igniter to test the energetic performance of the materials. High-speed cameras were used to record the explosion to compare the energetic performance to a premixed nanothermite3. With the help of high-speed thermal imaging, the team concluded that the samples printed by Purdue’s single nozzle would require a maximum reaction temperature of 200 K greater than the comparable samples printed with dual nozzle technique3. Therefore, the new technique developed by Dr. Jeff Rhoads’ team at Purdue University is safer than the previously existing 3D printing techniques to prepare 3D printed explosives.
Taken together, this 3D printing technique developed at Purdue appears to have a great potential to utilize reactive inkjet printing as a powerful tool for depositing inert suspensions of energetic materials3. This work published in the Journal of Applied Physics sheds light on new possibilities of safer printing of energetic materials using AM techniques.
- “What is 3D Printing?” – 3DPrinting.com
- “3D Printing with Explosives” – Machine DesignMurray, A. L., Isik, T., Ortalan, V., Gundux, E., Son, S. F., Chiu, G. T. C., & Rhoads, J. F.
- Two component additive manufacturing of nanothermite structures via reactive inkjet printing. (2017). Journal of Applied Physics. 122:184901.