[Image above] Charles McLaren (left) and Himanshu Jain from Lehigh University have made additional insights into how applying a direct current field across glass also reduces its melting temperature. Credit: Douglas Benedict (Academic Image); Lehigh University
Earlier this year, I reported on how a team of scientists led by Lehigh University researcher Himanshu Jain was pioneering a technique called electric field-induced softening that used an electric field to lower the intense amount of heat needed to form glass.
Although the team’s results offered exciting implications for reducing the high energy requirements of glass processing—and also offered interesting possibilities for micro- and nano-structuring of glass that is not possible with other techniques—the scientists didn’t understand why it was happening.
“Gaining a better understanding of the underlying phenomenon will help us learn the limitations of glass as an electrical insulator,” Jain said in a Lehigh press release at the time. “There’s tremendous interest in using glass as a supercapacitor for energy storage, for example. But it’s critical not to use glass that deforms easily in such applications, so it would be helpful to know in advance how the glass will behave.”
Since that report, the scientists have been trying to better understand the science behind the phenomenon. And Lehigh graduate student Charles McLaren recently gained some important insight through experiments with another group in Germany.
McLaren went to the University of Marburg to work in the lab of Bernard Roling, who studies electro-thermal poling.
Electro-thermal poling is a technique with an accurate name—the method uses temperature and an electric field to induce charge migrations within glass. The technique induces the migrations while the glass is heated, and those regions are then frozen in place once the glass is cooled, creating polarized regions.
Because the two techniques have similar experimental setups, the scientists thought that studying how alkali silicate glasses react during poling might provide insight into what was happening in their previous observations with electric field-induced softening—and they were right.
According to a new Lehigh press release, “McLaren’s work in Marburg revealed a two-step process in which a thin sliver of the glass nearest the anode, called a depletion layer, becomes much more resistant to electrical current than the rest of the glass as alkali ions in the glass migrate away.”
The team showed that the depletion layer then undergoes dielectric breakdown, which McLaren says is like a high-speed avalanche—one that subsequently increases conductivity within the glass.
“The results in Germany gave us a very good model for what is going on in the electric field-induced softening that we did here. It told us about the start conditions for where dielectric breakdown can begin,” McLaren says in release.
And understanding how this process begins is important for the scientists to be able to tease out more details on the process overall.
“Charlie’s work in Marburg has helped us see the kinetics of the process,” Jain says in the release. “We could see it happening abruptly in our experiments here at Lehigh, but we now have a way to separate out what occurs specifically with the depletion layer.”
The new open-access paper, published in the Journal of The Electrochemcial Society, is “Depletion layer formation in alkali silicate glasses by electro-thermal poling” (DOI: 10.1149/2.0881609jes).