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| Chemistry Creates Self-Stirring Liquids Posted: 29 Jan 2010 02:09 PM PST In a tail wagging the dog reversal, researchers have found that simple chemical reactions can mix a solution. Usually, chemicals are stirred to enhance a reaction, but a new study finds that the reverse is also true: Simple chemical reactions can trigger fluid flows, reports a paper in the January 29 Physical Review Letters.
De Wit and her colleagues wondered what would happen to fluid flows if the reacting liquids were left alone and not stirred. The researchers watched a very simple reaction — the neutralization that occurs between hydrochloric acid and sodium hydroxide, a common chemical base — in the absence of stirring. The researchers carefully injected the denser sodium hydroxide into a container and then added the hydrochloric acid. The sodium hydroxide stayed on the bottom and the hydrochloric acid sat on top. Where the two reactive chemicals met, the reaction's products — table salt and water — began to form. As the salty solution formed, it crept upward and hit the lower-density acid, creating tendrils that started to mix the solution. But the same didn't happen below the reaction line. This difference in how the reaction product interacted with each of its chemical parents drove the mixing the team observed.
These asymmetrical patterns, the researchers say, distinguish mixing during a chemical reaction from what happens when two nonreactive liquids meet, which may look more like diffusion or other kinds of mixing. "These kinds of beautiful patterns can be observed with very well-known reactions," says study coauthor Christophe Almarcha, also of the Université Libre de Bruxelles. "This is quite fascinating for someone who's done this reaction hundreds of times." The researchers also describe reaction-driven mixing mathematically by creating a model that predicted a pattern that looked like the real thing. The model can be tweaked to predict patterns for other chemical reactions, which would vary widely, Almarcha says. "Our little model system says 'pay attention,'" De Wit says. "If there are reactions, then new things will happen." For instance, if stored carbon leaches into an aquifer and starts reacting with water, "those reactions will trigger flows, which will enhance the mixture," she says. Image and Video: C. Almarcha/Université Libre de Bruxelles See Also: |
| NASA Releases First Free E-Book, on History of X-15 Rocket Plane Posted: 29 Jan 2010 11:34 AM PST NASA continues tostay ahead of the government pack when it comes to public outreach. In addition to its many popular Twitter streams, iPhone apps and opportunities for citizens to participate in scientific programs, the agency is jumping into thee-book space. For space geeks looking for a little e-reading this weekend, NASA recently added an e-book section to its publications list and rolled out the first free title for the Kindle and Sony Reader, a history of the x-15 hypersonic test aircraft. More titles are on the way. The agency already has plentyof technical papers, presentations, case studiesand other publications on its website that could eventually land in your e-reader. NASA says it will eventually make titles available for the Nook as well. And Luddites can still order hard copies of the X-15 book, along with a CD or a PDF. No word on whether NASA will put together a version for devices like the iPad that could integrate text, photos and video into the kind ofpublication many are hoping will be the next generation of books. Image: X-15 aircraft./NASA See Also: |
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