This was the result of research involving transformations in glass that occur under intense electrical and thermal conditions. New understanding of these mechanisms could lead the way to more energy-efficient glass manufacturing, and even glass supercapacitors that leapfrog the performance of batteries now used for electric cars and solar energy.
As part of his doctoral research, Charles McLaren of Lehigh University placed a block of glass between a cathode and anode, and then exerted steady pressure on the glass while gradually heating it. McLaren and his supervisor Himanshu Jain, together with colleagues at the University of Colorado, published their discovery in Applied Physics Letters.
"This technology is relevant to companies seeking the next wave of portable, reliable energy," said Jain. "A breakthrough in the use of glass for power storage could unleash a torrent of innovation in the transportation and energy sectors, and even support efforts to curb global warming."
The implications for the finding were intriguing. In addition to making glass formulation viable at lower temperatures and reducing energy needs, designers using electrical current in glass manufacturing would have a tool to make precise manipulations not possible with heat alone.
"You could make a mask for the glass, for example, and apply an electrical field on a micron scale," said Jain. "This would allow you to deform the glass with high precision, and soften it in a far more selective way than you could with heat, which gets distributed throughout the glass."
Though McLaren and Jain had isolated the phenomenon and determined how to dial up the variables for optimal results, they did not yet fully understand the mechanisms behind it.
McLaren and Jain had been following the work of Dr. Bernard Roling at the University of Marburg, who had discovered some remarkable characteristics of glass using electro-thermal poling, a technique that employs both temperature manipulation and electrical current to create a charge in normally inert glass. The process imparts useful optical and even bioactive qualities to glass.
A High-Speed Nano-Avalanche
After going to work in Marburg, McLaren discovered 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. This is followed by a catastrophic change in the layer, known as dielectric breakdown, which dramatically increases its conductivity.
McLaren likens the process of dielectric breakdown to a high-speed avalanche, and using spectroscopic analysis with electro-thermal poling as a way to see what is happening in slow motion.
"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," explained McLaren.
"Charlie's work in Marburg has helped us see the kinetics of the process," Jain said. "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."
McLaren, Jain, Roling and his Marburg team members published their findings in the September 2016 issue of the Journal of The Electrochemical Society.
For more on developments in glass technology, read about a new self-tinting window.