Carbon Black Controls Clouds - C&EN Global Enterprise (ACS

facebook · twitter · Email Alerts ... First Page Image. A NAVY chemist has proved that carbon black can make or break a cloud. ... the sun, can change...
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RESEARCH

Carbon Black Controls Clouds Carbon black cloud seeding makes weather to order A NAVY chemist has proved that carbon black can make or break a cloud. She is Florence \V. van Straten, now working with the Navy W e a t h e r Serv­ ice. W h a t van Straten's discovery means in terms of scientific w e a t h e r control is now being measured by Naval Re­ search Laboratory. But she has al­ ready demonstrated that carbon black, absorbing heat from the sun, can change atmospheric conditions enough to create clouds or to break them up quickly. F o r some time, van Straten believed she could modify clouds by influencing temperatures in parts of the atmos­ p h e r e . I n this manner, she says, cloud masses t h a t exist could b e dissipated, a n d , u n d e r sonie conditions, cloud masses could be created. She reasoned further t h a t carbon black would be the ideal material to induce the tempera­ t u r e variations because of its ability to absorb h e a t . • Testing Among t h e Clouds. In tests conducted from a Navy Constella­ tion over the Georgia coast, a pound a n d a half of carbon black sprinkled on top of a cloud dispelled the formation in 2 0 minutes. This w a s a large cloud. F r o m its base, hovering around 5000 feet, it extended into t h e air as high as 11,000 feet. Smaller clouds disap­ p e a r e d in three to four minutes after finely divided carbon was dropped, she asserts. Van Straten's theory on the cloud b r e a k u p amounts to stabilizing unstable air. Introducing the carbon black into t h e top of the cloud reduces its cooling rate. This tends to stabilize the atmos­ phere, a n d the cloud shrinks to a wisp in minutes. Creating clouds with carbon black seeding hinges on t h e amount of mois­ ture in the air, van Straten says. It would hardly work in the air over the

Chasing Clouds. In a n experiment done by a Naval Research Laboratory-Navy l e a t h e r Station team, clouds (above) get seeded with particles of carbon "black. Below, cloud is shrunk to a small size I S minutes after seeding*. Carbon black absorbs heat from the sun. This changes atmospheric conditions enough to create clouds or to break them u p in a matter of minutes

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RESEARCH j Sahara, she adds. But in the Georgia the w a n n e r ones in a distillation procj tests, carbon black strewn through a ess, would grow heavy and fall a s rain. | la\ e r of moist atmosphere did produce N R L is now conducting tests on cloud I clouds. The black was seeded on a modifications with carbon black t o ! mile run at about 4000 feet. By the measure distribution of t h e carbon o n ! time the plane turned a n d started back, release, rate of growth of w a t e r d r o p clouds had started to form between lets, and temperature effects before 3000 a n d 60ÛO feet. Here, van Straten and after seeding. sa\-s, as t h e carbon black absorbed heat, With these data, van Straten says it produced temperature differences be- tests on fog and thunderstorms will b e tween tlie seeded atmosphere and the carried out with much more knowunseeded. T h u s , instability grew how than that existing when the cloud rapidly, and t h e clouds formed. tests were made. If these are successW h a t was not recorded in the Geor- ful, equipment and techniques will b e gia tests was whether any rain fell as a worked out for using die method t o result of the seeding. However, if van control weather from aircraft, bases, Straten's hypothesis holds, a cloud and ships. She says it is too soon t o created by carbon seeding could be- speculate on t h e value of her carbuu come a thunderhead. Rain would be black technique to the military or t o produced when wanner droplets—those industry. Presumably, though, it could heated b y the carbon black—moved up- be used to start and stop rainfall, break ward into the neighborhood of cooler u p fog and thunderstorms, and to condroplets. The cooler drops, picking u p trol hurricanes and tornadoes.

Europe Looks at U - 2 3 5 new uses for \JVJ

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At the Geneva Conference, European countries talk about their studies of isotope separation

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Ο XLY the United States, Great Bri­ tain, a n d the Soviet Union have uranium-235 processing plants. Now France is thinking of building one, and other continental countries are investi­ gating processes, too. Gaseous diffusion is the method of isotope separation used in all large U-**'*"· plants. Uranium, as gaseous uranium hexafluoride. is allowed to diffuse through a barrier having very fine pores. Since the U 2 3 î i atoms are slightly lighter than the U j : t e they diffuse through the barrier pores faster. So material passing through the barrier is slightly enriched. Repeating this operation many times in a cascade system gives t h e desired degree of enrichment in U 2 3 S . • French W o r k . T h e big problems in a uranium-235 plant are developing and fabricating satisfactory porous barriers, preparing and purifying uranium hexafluoride, corrosion from UF t î . measuring isotope concentrations, and solving various chemical engineering problems o n relationships between the stages, C . FreJacques and Olegh Bilous told the Second United Nations International Conference on the Peaceful

Uses of Atomic Energy in GenevaBarrier material!» have- tt> l)c uioSt carefully chosen. The separating units containing them constitute almost a quarter of the cost of a plant. An effective porous barrier should have pores with radii between 100 and 3 0 0 A. For good permeability it should b e as thin as mechanical strength allows.

These porous barrier tubes a r e m o u n t e d in the French gaseous diffusion plants to separate the uranium isotopes