X-ray imaging of powder particles driven from a surface by a nearby electrostatic discharge

S Mukhopadhyay, K Hom, A deJong, T Long, TC Hufnagel, A Das, KS Shanks, M Schoenitz, EL Dreizin

In a new publication from a team of CHEXS users from the New Jersey Institute of Technology and the Johns Hopkins University, the interaction between ESD-generated mild shockwaves and a set of particles in the micrometer size range was studied using high speed X-ray imaging at the FAST beamline.

graph of particle trajectories

What is the discovery?

Electrostatic discharges (ESD) can generate laboratory-scale shockwaves measured in millimeters and microseconds, which makes studies of interactions between shocks and powder particles readily accessible. ESD-induced powder particle motion has recently been investigated in the context of removal of powder contaminants from surfaces, formation of radioactive aerosols following a nuclear explosion, and ignition of certain reactive powders. Now, in a new publication from a team of CHEXS users from the New Jersey Institute of Technology and the Johns Hopkins University, the interaction between ESD-generated mild shockwaves and a set of particles in the micrometer size range was studied using high speed X-ray imaging at the FAST beamline. The use of x-ray imaging enabled observations of early motion patterns of the moving particles, which would have been obscured using optical techniques due to the bright emission of the spark plasma. The team observed several new features that were not previously predicted for these shockwave-lifted powder motions across multiple test materials, including the formation of vertical column structures and the presence of fast-moving molten particles.

ESD schematic
Figure 1 | The ESD device (schematic) generates a small shockwave by discharging a spark across a 2mm gap between pin electrodes. The shockwave interacts with a bed of powder materials which sit just below the ESD gap, within the 2.5mm wide x 1mm tall x-ray field of view.

Why is this important?

Electrostatic spark discharge is studied widely for its use in automobile engines, ordnance triggering, material synthesis and process safety. However, the motion of powder particles adjacent to a spark discharge and interacting with the generated shock and heat has not been characterized comprehensively. Without direct empirical data, models are currently relied on to describe many relevant scenarios, including removal of powder contaminants from surfaces and powder entrainment by a nuclear fireball. In addition, powders lifted by ESD, similar to powders lifted by and entrained in a nuclear fireball may experience physical changes such as agglomeration, fragmentation and melting in ways which are difficult to model. This x-ray imaging work provides the direct empirical characterization which has been lacking, particularly at short times after the ESD when optical techniques are still “blinded” by the flash.

x-ray snapshots of the powder particles
Figure 2 | Four x-ray image snapshots, after image processing and labelling, showing powder particles lifted from the surface as a result of interaction with the ESD shockwave. The formation of column structures at early times is unexpected and was observed to be ubiquitous across different materials with different particle sizes.​​​

 

Why did this research need CHEXS?

The FAST beamline at CHEXS is dedicated to answering complex materials engineering questions in dynamic systems, with a focus on processing and performance. This is the first user publication from FAST to make use of the new high-bandwidth multilayer monochromator, which was commissioned in 2022 with a mission to enable radiography and diffraction at shorter timescales. (This new monochromator is interchangeable with the standard cryogenic Si monochromator at FAST, which offers a higher-resolution but lower-flux beam for other types of experiments.) FAST combines world-leading flux at high energy with state-of-the-art fast-framing x-ray detectors and is built to integrate a wide variety of custom, user-designed sample environments such as the ESD device used here. With the Dynamic Compression Sector at the APS currently shut down for the APS-U upgrade, at this time FAST is uniquely able to perform these types of destructive, time resolved measurements with high-energy x-rays.

How was the work funded?

The Center for High Energy X-ray Sciences (CHEXS), NSF MPS/BIO/ENG (DMR-1829070)

US Defense Threat Reduction Agency, Award HDTRA12020001 / 2004756624

Reference

X-ray imaging of powder particles driven from a surface by a nearby electrostatic discharge

S Mukhopadhyay, K Hom, A deJong, T Long, TC Hufnagel, A Das, KS Shanks, M Schoenitz, EL Dreizin

Advanced Powder Technology 35, 104472 (2024); https://doi.org/10.1016/j.apt.2024.104472