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Serendipity; diamonds from coal
Topic Started: Jul 6 2006, 07:04 AM (75 Views)
big al
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End result of hydrogen production, storage: Diamonds
Nanocrystalline diamonds appear at the end of a process to produce and store hydrogen using anthracite coal.

"The idea we explored was based on ball milling graphite processes found in the hydrogen storage literature," said Angela D. Lueking, assistant professor of energy and geoenvironmental engineering at Penn State. "We substituted anthracite coal for graphite because it is abundant and inexpensive. Now, with 20/20 hindsight, we are struck by the fact that coal gasification is currently the most economical way to produce hydrogen."

Interest in hydrogen as a vehicular fuel has researchers investigating ways to create hydrogen inexpensively; other researchers are looking at ways to transport and store hydrogen in a safe manner.

Lueking's group was exploring a way to store hydrogen in carbon-based materials, and inadvertently stumbled upon a method that combines production and storage and produces nanocrystalline diamonds as a by-product.

Lueking and his team ball milled powdered anthracite coal with cyclohexene. Ball milling involves mixing a slurry of anthracite powder and cyclohexene with small steel balls, and mixing so the steel balls pound the coal particles and the cyclohexene, causing physical and chemical changes.

"Ball milling imparts a lot of energy to the slurry," Lueking said. "There is high pressure and temperature in every impact of the balls on the slurry, but we do not really understand the structural changes in the carbon that occur in the process."

Unlike the graphite experiments, Lueking's anthracite experiment has hydrogen gas evolving from the mixture at room temperature. The hydrogen is either within the material in a tight pore structure, or they are forming a new carbon structure. The hydrogen outgassing continued for about a year and increased with addition of moderate heat.

"At first we thought the mass spectrograph was broken because hydrogen was just coming off," Lueking said. "We tried another mass spec, and the same thing happened."

Wanting to know the structure of the ball milled product, and looking for carbon nanotubes, the researchers used transmission electron microscopy to investigate the small particles.

What the researchers had were Bucky diamonds, a nanocrystalline diamond surrounded by onion-like layers of graphite. Diamonds are a natural form of pure carbon, but with a differing molecular structure than graphite or the graphite-like coal.

"Bucky diamonds are relatively unexplored in terms of applications," Lueking said. "Nanocrystalline diamonds, however, have major industrial uses as abrasives and in electronics. These nanodiamonds are usually created by exploding TNT in a carbon source."

The ball milling process seems a simpler and gentler way of creating nanodiamonds and especially Bucky diamonds. Lueking's team said it hopes once they understand how they are forming, they can increase the yield of diamonds in the process.

"At this point, we have not isolated the step that is forming the diamond," said the Penn State researcher. "The crystallization may be hydrogen-induced, it may be a result of the high temperatures and pressures within the mill, it may be a result of the processing we have done to purify the samples for transmission electron microscopy, or it may be a combination of all of the above."

Source here: End result of hydrogen production, storage: Diamonds

Big Al
Location: Western PA

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