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[Sandia Lab News]

Vol. 54, No. 2        January 25, 2002
[Sandia National Laboratories]

Albuquerque, New Mexico 87185-0165    ||   Livermore, California 94550-0969
Tonopah, Nevada; Nevada Test Site; Amarillo, Texas

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Explaining water's surface behavior Architects receptive to surety concepts


On the surface: Sandia 'detective' solves strange case

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By Neal Singer

It was a small problem: a layer of water lying flat instead of slightly bumpy as it froze on a solid.

It became a larger problem when no one could explain why that might happen.

The slight difference between experimental results and established expectations might have meant nothing. But possibly it was signaling a basic scientific misunderstanding concerning the interaction of water with solids -- an area of major industrial and scientific concern.

Water-surface interactions control the rate at which water passes through microscopic pores -- a factor of increasing importance in micro- and nanotechnology. These interactions also affect the adhesion of materials in humid environments, catalytic chemical reactions, and condensation on dust particles in the upper atmosphere, to name a few.

Eventually, the problem ended up on the desk of Sandia theoretical physicist Peter Feibelman. His solution, which theorizes that water molecules dissociate near the surface rather than remain intact, was published in the Jan. 4 Science.

"This work makes the goal of understanding what happens when water contacts surfaces seem just a bit more achievable," Peter said.

The problem

Several years ago Munich experimental physicists Georg Held and Dietrich Menzel found that the initial layer of water molecules didn't lie the way they should on the precious metal ruthenium.

The researchers knew that ruthenium's surface atoms pack tightly together in a hexagonal array. They also knew that water molecules of ice crystals do the same, in hexagons only marginally bigger than the metal's. So the experimentalists expected that a frozen layer of water molecules would compress slightly and lie on the ruthenium with all the normal characteristics of a layer of ice.

But a small problem intruded from the third dimension: water molecules of ice always arrange themselves in puckered hexagons, with half the molecules higher and half lower.

Held and Menzel found no pucker.

Their layer of (heavy) water on ruthenium was almost perfectly flat.

Not only shouldn't it be flat, it shouldn't be

Peter saw an opportunity to use modern advances in theory to understand interfaces at the atomic level. "In the past, scientists could only summarize what goes on at surfaces by making assumptions that were embodied as boundary conditions," he said. "The problem is that there was often no foundation for such simplifications."

Peter hoped to use models faithful to nature at the atomic scale to interpret what was going on at the solid-water interface. He already had done significant work on the arrangements and movements of atoms on the surface of materials. At his desk, he reflected on how the chemistry of a solid surface might determine the arrangement of nearby water molecules.

Then he calculated the binding energy of the water molecules in the expected puckered structure versus their binding energy in pure ice. Peter reasoned that if ice is more favorable energetically, then water molecules will not want to spread out into a flat, essentially 2-dimensional layer on a ruthenium surface, but instead cluster together, forming a 3-D "ice cube." And that -- unfortunately -- was just what he found. "I realized I was unable to explain why there is a 2-D layer at all," he says, "to say nothing of why the layer was flat instead of puckered."

Using observed facts rather than conventional assumptions

Then Peter thought, "If you take the experimental observation seriously -- that all the oxygens are lying in same plane rather than in a puckered structure -- then each oxygen atom is at about the same distance from a ruthenium atom.

"That means all the oxygens should bond to ruthenium atoms. But the only way this can happen is if the upper molecules of the expected puckered arrangement get rid of one of their deuteriums. Oxygen atoms that lose deuteriums will need to bind to something else, and ruthenium atoms are the obvious candidate." (Note: the water in Held and Menzel's experiments was 'heavy water' -- deuterium replacing hydrogen -- used because it produced electron diffraction patterns that were easier to analyze.)

Excited by this idea, Peter tried a calculation that assumed deuterium atoms broken off from water molecules also would find someplace else to bind on the metal surface.

His results then appeared to answer both the question of why a 2-D layer exists at all, and why the oxygen atoms lie in the same plane.

"Atoms as light as deuterium barely have any effect on electron diffraction,"said Peter. "Held and Menzel's experiment by itself could only tell us where the oxygen atoms were in the heavy water layer, but not the deuteriums. Theory, however, can tell us where they lie, and this information leads to a quite new picture of how water wets to a metal. My results make it more than a little plausible that half the deuteriums separate from the water molecules where they originally were." -- Neal Singer

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Nation's top architects receptive to Labs' building surety message during conference

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By John German

No building, save perhaps some bunkers, could withstand a collision with a 100-ton airliner followed by an 800š C jet fuel inferno. The World Trade Center didn't stand a chance.

Nevertheless, the attack on one of the world's greatest architectural achievements and the idea that the structure, not the plane, killed most of the World Trade Center's victims are prompting architects and building designers to take another look at how public structures can be made safer and more secure.

A recent survey of building designers by the American Institute of Architects (AIA) found that 72 percent of respondents anticipated their clients would request additional security features in design projects currently under way.

This month Sandia's Architectural SuretyŽ program co-sponsored the AIA's annual conference Jan. 10-13. More than 250 architects, construction managers, corporate and public facility managers, and building owners gathered in Albuquerque for the event, themed "Building Security Through Design: Protecting Environments in an Open Society."

Security, function, aesthetics

The conference exposed some of the participants to the principles of surety and risk management for the first time in their careers, says Rudy Matalucci (5862), Sandia Architectural Surety program manager. Others got a unique chance to see how these principles might be applied in real settings, and how emerging technologies might enhance designers' abilities to protect building users.

It began with a windshield tour of local buildings whose designs and security considerations incorporate some of the safety, security, and reliability approaches advocated by Sandia's Architectural Surety program. One of the buildings, the United States Courthouse in downtown Albuquerque, includes features recommended by Sandia during 1997 consultations with the building's architect.

Several Sandians gave invited talks and presented displays focusing on emerging technologies useful to architects:

Dennis Miyoshi, Director of Security Systems and Technology Center 5800, gave a keynote presentation on incorporating systematic security and risk-management approaches in building designs of the future.

Rudy gave two talks focusing on the benefits of systematically considering the surety approach in preparing for the range of threats to structures -- normal (such as aging and deterioration), abnormal (such as natural disasters), and malevolent (such as terrorist attacks) -- when designing and retrofitting buildings.

Other presenters focused on striking a balance between security, function, and aesthetics; assessing the relative risks of a wide variety of threats; developing strategies to design safer buildings; and technologies and approaches available to mitigate threats.

"Even before Sept. 11 Sandia has been taking an active role in Architectural Surety," says Prof. Kuppaswamy Iyengar of the University of New Mexico School of Archictecture & Planning. "Presentations by Rudy Matalucci, Jill Glass, and others from Sandia were relevant, timely, and extremely useful. Overall, the presentations made by Sandia were unbiased and critical for the present conditions in the USA."

"I heard people talking about many of the issues we've been discussing at Sandia," says Rudy. "But I also heard people saying let's not overreact. We want to create an environment where people feel secure but not become overwhelmed with guards and concrete that ultimately make us feel 'bunkered' and actually less secure."

9/11 gives program a boost

Since the Architectural Surety program began in 1995, says Rudy, researchers from all over the Labs have contributed much to the Labs' ability to answer the nation's call following Sept. 11 with regards to the vulnerabilities of structures to attacks.

Labs security experts have traveled the country during the past four months developing and applying security assessment methodologies and other risk-management tools for the nation's dams and power systems (Lab News, Dec. 4, 2001), government buildings (Lab News, July 13, 2001), chemical plants (Lab News, Nov. 2, 2001), water supplies (Lab News, Oct. 5, 2001), and other potential targets.

Building designers now have better computer models for analysis of blast effects on structures. (Several companies approached Sandians during the conference asking how they could license Sandia's blast codes, he says.)

And Sandia has raised the awareness of risk-management and surety principles among architects and builders nationwide through conferences, speaking engagements, and university lectures.

"Sandia anticipated the growing threats to structures years ago and has developed a good foundation for a methodology to improve building surety," he says. "This conference was a great opportunity to spread the word -- Ken Frazier

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Last modified: February 6, 2002


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