Nanothermite with Meringue-like Morphology: From Loose Powder to Ultra-porous Objects

This manuscript describes the synthesis of combustible aluminophosphate matrices by the reaction of orthophosphoric acid (H₃PO₄) with aluminum nanopowder. When this reaction is carried out with excess aluminum in the presence of tungsten trioxide nanopowder, it leads to a solid, porous nanothermite foam.

Transcript

The overall goal of this procedure is to describe the preparation of porous and solid aluminophosphate matrices or nanothermite foams by the reaction of aluminum nanopowder with orthophosphoric acid. This method can help answer key questions in the nanothermite field, such as how to stabilize a nanothermite loose powder into a solid, porous, monolithic, reactive object. The main advantage of this technique is that nanothermites are transformed into solid objects, which are easy to handle and do not contain free nanoparticles.

Demonstrating the procedure will be Cedric Martin, a post-doc from my laboratory. To begin this procedure, first weigh out 3.00 grams of aluminum nanopowder. Using a three milliliter polyethylene Pasteur pipette, add 4.00 grams of an 85%commercial solution of orthophosphoric acid dropwise to a 150 milliliter beaker.

Use a one milliliter polyethylene Pasteur pipette to add between zero and two milliliters of deionized water and slowly rotate the beaker by hand to homogenize the solution. Next, transfer the beaker to the explosion chamber. Add the pre-weighed aluminum nanopowder to the beaker.

Use a stainless steel spatula to quickly mix the solution. Immediately close the explosion chamber. Then wait for the foaming reaction to occur.

Once the reaction is complete, wait an additional 10 minutes for the aluminophosphate matrix to cool. After this, use a laboratory bow tong to remove the beaker from the explosion chamber. Carefully break the sample, which adheres to the beaker wall, to recover it.

To begin, add 3.00 grams of aluminum nanopowder and 3.45 grams of tungsten trioxide nanopowder to a 100 milliliter round-bottom flask. Using a vortex mixer, mix the nanopowders at 2, 500 rpm. Put on an electrostatic discharge wrist strap, and ensure that you are properly grounded.

Next, use a stainless steel spatula to gently stir the mixture. Then use the vortex mixer to further homogenize the nanothermite mixture at 2, 500 rpm. After this, use a three milliliter polyethylene Pasteur pipette to add 4.00 grams of orthophosphoric acid dropwise to a 150 milliliter beaker.

Using a one milliliter polyethylene Pasteur pipette, add between zero and two milliliters of deionized water. Slowly rotate the beaker by hand to homogenize the solution. Then transfer the beaker to the explosion chamber.

Add the prepared nanothermite mixture to the beaker. Next, use a stainless steel spatula to quickly mix the solution. After this, immediately close the explosion chamber.

Once the foaming reaction is complete, wait an additional 10 minutes for the nanothermite foam to cool. Using a laboratory bow tong, remove the beaker from the explosion chamber. Carefully break the sample, which adheres to the beaker wall, to recover it.

To begin, place either the prepared aluminophosphate matrix or the prepared nanothermite foam into the explosion chamber. Place a pyrotechnic igniter close to the chosen sample. Close the explosion chamber.

After this, connect the igniter to a secure electronic device. Next, fire the pyrotechnic chain. Using an ultrafast camera operating at a speed between 10, 000 to 30, 000 frames per second, observe the combustion through the armored window.

In this procedure, combustible aluminophosphate matrices are synthesized by the reaction between orthophosphoric acid and aluminum nanopowder. X-ray diffraction analysis confirms the presence of both crystallized aluminum and aluminum phosphate in the synthesized aluminophosphate matrix. Thermocouple data reveals that the temperature of each nanothermite paste during the foaming reaction is dependent on the concentration of orthophosphoric acid.

The higher the concentration, the faster and higher the temperature will rise. In other words, diluting the acid solution with water decelerates the rise in temperature of the reaction medium. However, drying orthophosphoric acid with a strong desiccant such as phosphorus anhydride is not advised.

Without water, the paste undergoes rapid heating, which can ignite of the energetic foam and cause a hydrogen explosion in the air. Nanothermite foams produced from these diluted solutions have greater mechanical strength but expand less. X-ray diffraction analysis reveals that these foams contain crystallized aluminum, aluminum phosphate, and tungsten trioxide, although tungsten trioxide does not chemically interact with the foaming reaction.

While attempting this procedure, it's important to remember that aluminophosphate and nanothermite forms are energetic materials which burn violently when they are ignited. After its development, this technique paved the way for research in the field of energetic materials to explore the integration of nanothermite in pyrotechnic systems. Don't forget that working with energetic nanomaterials can be extremely hazardous, and precautions such as wearing appropriate protections and operating in pyrotechnic installations should always be taken while you're performing this procedure.

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Journal (Chemistry)

Journal (Chemistry)

Nanothermite with Meringue-like Morphology: From Loose Powder to Ultra-porous Objects

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