An Innovative and Novel Aluminum Metal Microsphere Production and Deposition Method Using a Pulsed DC Cold Plasma Process

Abstract

Abstract Metal microspheres have numerous applications including sintering, heat transfer fluids, electromagnetic fluids, catalysis and electrical components. We have now successfully produced aluminum metal microspheres using a novel method by means of a pulsed DC cold plasma process. There are two types of plasmas: hot plasma, 10,000–100,000 K, and cold plasmas with temperatures slightly above ambient room temperature. Cold plasma temperature is as high as hot plasmas, but the temperature of the neutral species is approximately ambient temperature. Cold plasma can operate in a vacuum, partial vacuum, or atmospheric conditions and can be used for surface modifications and material depositions applications. Its application to metal microsphere production, however, prior to our efforts presented here, has been undocumented. In this primarily experimental work, we review a new, innovative, and novel metal microsphere production method leveraging cold (atmospheric pressure) plasma. Nitrogen was the ionized gas and a high-purity aluminum wire source was used to produce the aluminum metal microspheres, which were simultaneously deposited onto a copper foil substrate. Repeatable depositions of discreet microspheres on to the substrate are possible. Particle adhesion occurs from the molten metal cooling on the substrate surface. Optimal process parameters were found at a pulse cycle time value of 40% using deposition durations of two minutes. Although the particle deposition was not uniform, partial size distributions using this process are repeatable with over 50% of the deposited particles between 0–0.8 μm in diameter. The primary advantage of this deposition process is that it can be performed in open-air at atmospheric pressures, lending itself to a continuous deposition process.