HOW TO BURN ALUMINUM

FROM:  LOS ALAMOS NATIONAL LABORATORY 

Photo Caption: nanoparticles-When dry, aluminum nanoparticles look like simple dark gray dust.  LANL photo.

Scientists Ignite Aluminum Water Mix

Combustion mechanism of aluminum nanoparticles and water published in prestigious German chemistry journal

LOS ALAMOS, N.M., June 30, 2014—Don't worry, that beer can you’re holding is not going to spontaneously burst into flames, but under the right circumstances aluminum does catch fire, and the exact mechanism that governs how, has long been a mystery.

Now, new research by Los Alamos National Laboratory explosives scientist Bryce Tappan, published as the cover story in the prestigious German journal of chemistry Angewandte Chemie, for the first time confirms that chemical kinetics — the speed of a chemical reaction — is a primary function in determining nanoaluminum combustion burn rates.

"It's been long understood that nanoscale aluminum particles, 110 nanometers and smaller, are highly reactive. Aluminum particles at this scale have been used in novel explosives, propellants, and pyrotechnic formulations," said Tappan. "The understanding of the combustion mechanism impacts how we look at the design of ever smaller aluminum particles like molecular aluminum clusters as well as possible nanoaluminum applications like hydrogen fuel storage devices — and this might be a little 'out there' — but also energetic formulations that could use extraterrestrial water as the oxidizer in rocket fuel."

Tappan and his co-authors, Matthew Dirmyer of Los Alamos, and Grant Risha of Penn State University, made this discovery by looking for the "kinetic isotope effect" in nanoaluminum particles 110, 80, and 38 nanometers in size. The particles consisted of a "core-shell" structure with an elemental aluminum core and a two to five nanometer oxide shell. The particles are mixed with deionized water, H2O, or deuterium, D2O, to the gooey consistency of cake batter.

The kinetic isotope effect is observed in a chemical reaction when an atom of one of the reactants (water) is substituted with its isotope (deuterium, or "heavy water") and the two reactions are compared for differences. This effect is considered one of the most important tools in determining chemical reaction mechanisms.

Tappan and his team obtained burn rates by putting water/deuterium nanoaluminum mixtures in small glass tubes, placing the tubes in pressure vessels, igniting the nanoaluminum with a laser and taking measurements as the mixture burned.

For many years it’s been proposed that other mechanisms like oxygen diffusion through the particles, or tiny aluminum “explosions” in the mixture might govern the rates of the burning process. “Now we know that reaction kinetics are a major player,” said Tappan.

"Knowing much more about the mechanisms at work in metal combustion gives you a chance to refine the models that govern these reactions," Tappan added. "This fundamental knowledge gives us a window on how to better control these processes."

The research was funded by the Laboratory Directed Research and Development program at Los Alamos National Laboratory, with additional funding from the Defense Threat Reduction Agency.

SCIENTISTS FIND THE DESTINATION OF CHARCOAL

At NSF's Florida Coastal Everglades LTER site, charcoal is part of the dissolved organic carbon. Credit: Wikimedia Commons

 

FROM: NATIONAL SCIENCE FOUNDATION
Where Does Charcoal, or Black Carbon, in Soils Go?
Scientists have uncovered one of nature's long-kept secrets--the true fate of charcoal in the world's soils.

The ability to determine the fate of charcoal is critical to knowledge of the global carbon budget, which in turn can help understand and mitigate climate change.

However, until now, researchers only had scientific guesses about what happens to charcoal once it's incorporated into soil. They believed it stayed there.

Surprisingly, most of these researchers were wrong.

The findings of a new study that examines the result of charcoal once it is deposited into the soil are outlined in a paper published this week in the journal Science.

The international team of researchers was led by scientists Rudolf Jaffe of Florida International University and Thorsten Dittmar of the German Max Planck Society.

"Most scientists thought charcoal was resistant," says Jaffe. "They believed that once it was incorporated into soils, it stayed there. But if that were the case, soils would be black."

Charcoal, or black carbon, is a residue generated by combustion including wildfires and the burning of fossil fuels.

When charcoal forms, it is usually deposited into the soil.

"From a chemical perspective, no one really thought it dissolved, but it does," Jaffe says.

"It doesn't accumulate for a long time. It's exported into wetlands and rivers, eventually making its way to the oceans."

It all started with a strange finding in the Everglades.

At the National Science Foundation (NSF) Florida Coastal Everglades Long-Term Ecological Research (LTER) site--one of 26 such NSF LTER sites in ecosystems around the world--Jaffe studied the glades' environmental chemistry.

Dissolved organic carbon is known to be abundant in wetlands such as the Everglades and plays a critical role in the ecology of these systems.

Jaffe wanted to learn more about what comprised the organic carbon in the Everglades.

He and colleagues discovered that as much as 20 percent of the total dissolved organic carbon in the Everglades is charcoal.

Surprised by the finding, the researchers shifted their focus to the origin of the dissolved charcoal.

In an almost serendipitous scientific journey, Dittmar, head of the Max Planck Research Group for Marine Geochemistry at the University Oldenburg in Germany, was also tracing the paths of charcoal, but from an oceanographic perspective.

To map out a more comprehensive picture, the researchers joined forces. Their conclusion is that charcoal in soils is making its way into the world's waters.

"This study affirms the power of large-scale analyses made possible through international collaborations," says Saran Twombly, program director in NSF's Division of Environmental Biology, which funded the research along with NSF's Directorate for Geosciences.

"What started out as a puzzling result from the Florida Everglades engaged scientists at other LTER sites in the U.S., and eventually expanded worldwide," says Twombly. "The result is a major contribution to our understanding of the carbon cycle."

Fire is probably an integral part of the global carbon cycle, says Dittmar, its effects seen from land to sea.

The discovery carries significant implications for bioengineering, the scientists believe.

The global carbon budget is a balancing act between sources that produce carbon and sources that remove it.

The new findings show that the amount of dissolved charcoal transported to the oceans is keeping pace with the total charcoal generated by fires annually on a global scale.

While the environmental consequences of the accumulation of black carbon in surface and ocean waters are currently unknown, Jaffe said the findings mean that greater consideration should be given to carbon sequestration techniques.

Biochar addition to soils is one such technique.

Biochar technology is based on vegetation-derived charcoal that is added to agricultural soils as a means of sequestering carbon.

As more people implement biochar technology, says Jaffe, they should take into consideration the potential dissolution of the charcoal to ensure that these techniques are environmentally friendly.

Jaffe and Dittmar agree that there are still many unknowns when it comes to the environmental fate of charcoal, and both plan to move on to the next phase of the research.

They've proved where charcoal goes.

Now they'd like to answer how that happens, and what the environmental consequences are.

The more scientists can understand the process and the environmental factors controlling it, says Jaffe, the better the chances of developing strategies for carbon sequestration and mitigating climate change.

The research was also conducted at NSF's Bonanza Creek; Konza Prairie; Hubbard Brook; Coweeta; and Georgia Coastal Ecosystems LTER sites, and at other locations around the world.

Other authors of the paper are: Yan Ding of Florida International University; Jutta Niggemann of the Max Planck Research Group for Marine Geochemistry; Anssi Vahatalo of the University of Helsinki; Aron Stubbins of the Skidaway Institute of Oceanography in Savannah, Georgia; Robert Spencer of the Woods Hole Research Center in Massachusetts; and John Campbell of the USDA Forest Service.

-NSF-