Rice University researchers from the lab of James Tour have shown that Thomas Edison’s original 1879 carbon-filament light bulbs possibly included a graphene-forming regime, suggesting that one of history’s most iconic inventions may have inadvertently produced turbostratic graphene long before it was formally isolated.
Image from: ACS Nano
Turbostratic graphene can be produced by applying a voltage across a resistant carbon-based material and rapidly heating it to 2,000-3,000 degrees Celsius. In modern terms, that method is called flash Joule heating. But the method available to Edison in 1879 was simply turning on one of his newly patented, stable light bulbs. Unlike modern incandescent light bulbs that rely on tungsten filaments, early versions often used resistant carbon-based filaments like Japanese bamboo. Flipping a switch applied a voltage that rapidly heated the filaments, producing light. Or, perhaps, graphene....
“I was developing ways to mass produce graphene with readily available and affordable materials,” explains Lucas Eddy, first author on the paper and a former Rice graduate student in Tour’s lab. “I was looking at everything from arc welders, which were more efficient than anything I’d ever built, to lightning struck trees, which were complete dead ends.” But then, as his lab partner put it, he had a light bulb moment. “I was trying to figure out the smallest, easiest piece of equipment you could use for flash Joule heating, and I remembered that early light bulbs often used carbon-based filaments.”
Unlike many other early light bulbs, Edison’s patented design reached the critical 2,000-degree Celsius temperature. As a bonus, Edison’s 1879 patent gave Eddy a precise blueprint to work from when replicating the experiment. Eddy’s first few attempts to procure an Edison-style light bulb proved unsuccessful with “carbon” filaments turning out to be tungsten in disguise. But Eddy finally managed to acquire artisan Edison-style light bulbs that were exactly like Edison’s, down to the Japanese bamboo filaments. Even the diameters of the filaments were close with Eddy’s filaments measuring only 5 micrometers larger than Edison’s.
Just like Edison, Eddy attached the light bulb to a 110-volt DC electricity source. He flipped the switch on for only 20 seconds. Longer periods of heating, he explains, can result in graphite forming rather than graphene. The modern lenses of an optical microscope, a tool centuries older than Edison, showed the carbon filament had gone from a dark gray to a “lustrous silver”, signaling a transformation.
To characterize the change, Eddy used a technique developed in the 1930s: Raman spectroscopy. This technique uses lasers to identify the substances through their atomic signatures, like reading a barcode. Advances over the last century allow it to do so with great precision. The spectroscopy confirmed what Eddy had hoped - parts of the filament had turned into turbostratic graphene. Edison, in his quest to develop a practical light bulb that could be used in everyday life, may have produced graphene.
Of course, there is no way to know what really happened with Edison’s long-ago experiment. Even if the original light bulb Edison used was available to analyze, any graphene produced likely would have turned to graphite during its first 13-hour test. “To reproduce what Thomas Edison did, with the tools and knowledge we have now, is very exciting,” said Tour, the T.T. and W.F. Chao Professor of Chemistry and corresponding author on the paper. “Finding that he could have produced graphene inspires curiosity about what other information lies buried in historical experiments. What questions would our scientific forefathers ask if they could join us in the lab today? What questions can we answer when we revisit their work through a modern lens?”
