Silicate glass is something that we interact with on a regular basis, most notably in display screens and in the glass fibres that power our very internet. But now, researchers from Lehigh University in the US have discovered a way to bend the laws of physics to give it new structural and functional possibilities.
Publishing their findings in Scientific Reports, the scientists and engineers showed that under certain conditions, electrically heated silicate glass defies a long-accepted law of physics known as Joule’s first law.
In the 19th century, James Prescott Joule demonstrated that heat is generated when electrical current is passed through a resistor. The resulting Joule’s law has affirmed that heat is produced in proportion to the square of an electrical current that passes through a material.
However, the researchers demonstrated that alkali silicate glass can melt specifically near the anode, or even evaporate, while remaining solid elsewhere. Infrared imaging showed that the localised temperature was in a direct current or alternating current state.
‘The calculations did not add up’
“In our experiments, the glass became more than 1,000 degrees Celsius hotter near the positive side than in the rest of the glass, which was very surprising considering that the glass was totally homogeneous to begin with,” said Himanshu Jain of the research team. “The cause of this result is shown to be in the change in the structure and chemistry of glass on nanoscale by the electric field itself, which then heats up this nano-region much more strongly.”
These observations unravel the origin of a recently discovered electric field-induced softening of glass, whereby the softening temperature of glass heated in a furnace can be reduced by a couple of hundred degrees Celsius just by applying 100 volts across a sheet just one inch thick.
“The calculations did not add up to explain what we were seeing as simply standard Joule heating,” Jain said. “Even under very moderate conditions, we observed fumes of glass that would require thousands-of-degrees-higher temperature than Joule’s law could predict!”
The researchers believe that this work shows it is possible to produce heat in a glass on a much finer scale than by methods used so far, possibly down to the nanoscale. This would allow for manufacturers to create new optical or other complex structures on glass surfaces with incredible precision.
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