Pulsed Arc Nanoparticle Synthesis
Our History with Nanoparticle Synthesis
NovaCentrix has been making nanoparticles with pulsed arc processes since 1999 (then Nanotechnologies, Inc.), when we initially used an electrothermal gun to make ceramic nanoparticles. This device was originally intended for military purposes, but we realized that if the projectile from this gun were eliminated, the intense plasma jet generated from the 100MW confined arc discharge within the bore could be used to ablate one of the electrodes as it exited. When discharged into a tank containing a reactive gas, such as oxygen or ammonia, this ablated material could combine with the gas to form the most kinetically favorable compound, such as an oxide or nitride, in nanoparticle form.
In the early 2000s, the electrothermal gun process was replaced with a more scalable version, called Pulsed Arc Nanoparticle Synthesis (PANS). This process, which is used to this day, involves the discharge of an intense (~100 kA), short-duration (~1 ms) electric arc between two metal rods in a gaseous atmosphere. The ends of the rods are ablated and heated by the arc to create a dense metal plasma that supersonically expands into the surrounding gas. This rapid mixing cools the plasma, allowing the metal vapors to condense and form a dense aerosol of nanoparticles. After formation, the gas is filtered to remove the nanoparticles and returned to the reaction chamber. The metal rods are then indexed towards each other in preparation for the subsequent arc discharge.
Unlike the electrothermal gun process, there are minimal impurities, so metal nanoparticles can also be made with the PANS process when the reaction chamber is filled with an inert gas, such as Argon or Helium.
There are few byproducts from the PANS process. Any portion of the electrodes that don’t contribute to the formation of nanoparticles is recycled. Since PANS is semi-automated, the production capacity from a single reactor is over one metric ton of nanoparticles per year.
One of the more remarkable discoveries made from the development of PANS came from varying the pulse length of the arc discharge. With that capability, the average nanoparticle size produced could be controlled by an order of magnitude, from about 10nm to 100nm. When the photonic curing process was discovered, also by NovaCentrix, in 2004 using an ordinary camera flash, the technology of the PANS process was leveraged to create the most powerful, commercially available flashlamp in the world –called PulseForge. In the spirit of the PANS process, electronic pulse length control became integral to all PulseForge tools in order to tune the power delivery to thermally process a variety of thin films.