The simplest element: Turning hydrogen into 'graphene'

This image is a comparison of the carbon compound graphene with a similar hydrogen-based structure synthesized by Carnegie scientists. Credit: Carneige's Ivan Naumov and Russell Hemley

New work from Carnegie's Ivan Naumov and Russell Hemley delves into the chemistry underlying some surprising recent observations about hydrogen, and reveals remarkable parallels between hydrogen and graphene under extreme pressures. Their work is the cover story in the December issue of Accounts of Chemical Research.

Hydrogen is the most-abundant element in the cosmos. With only a single electron per atom, it is deceptively simple. As a result, hydrogen has been a testing ground for theories of the chemical bond since the birth of quantum mechanics a century ago. Understanding the nature of chemical bonding in extreme environments is crucial for expanding our understanding of matter over the broad range of conditions found in the universe.

Observing hydrogen's behavior under very high pressures has been a great challenge for researchers. But recently teams have been able to observe that at pressures of 2-to-3.5 million times normal atmospheric pressure it transforms into an unexpected structure consisting of layered sheets, rather than a close-packed metal as had been predicted many years ago.

These hydrogen sheets resemble the carbon compound graphene. Graphene's layers are each constructed of a honeycomb structure made of six-atom carbon rings. This conventional carbon graphene, first synthesized about a decade ago, is very light, but incredibly strong, and conducts heat and electricity very efficiently. These properties promise revolutionary technology, including advanced optical electronics for screens, high-functioning photovoltaic cells, and enhanced batteries and other energy storage devices.

The new work from Naumov and Hemley shows that the stability of the unusual hydrogen structure arises from the intrinsic stability of its hydrogen rings. These rings form because of so-called aromaticity, which is well understood in carbon-containing molecules such as benzene, as well as in graphene. Aromatic structures take on a ring-like shape that can be thought of as alternating single and double bonded carbons. But what actually happens is that the electrons that make up these theoretically alternating bonds become delocalized and float in a shared circle around the inside of the ring, increasing stability.

Naumov and Hemley's study also indicates that hydrogen initially becomes a dark poorly conducting metal like graphite instead of a conventional shiny metal and a good conductor, as was originally suggested in theoretical calculations going back to the 1930's using early quantum mechanical models for solids.

Though the discovery of this layered sheet character of dense hydrogen has come as a surprise to many, chemists 30 years ago--before the discovery of graphene--predicted the structure based on simple chemical considerations. Their work is validated and extended by the new findings.

"Overall, our results indicate that chemical bonding occurs over a much broader range of conditions than people had previously considered. However, the structural effects of that chemical bonding under extreme conditions can be very different than that observed under the ordinary conditions that are familiar to us," Hemley said.

Source: Carnegie Institution

3-D printed Shelby Cobra

This Shelby Cobra sports car, 3D-printed at Department of Energy's Manufacturing Demonstration Facility at Oak Ridge National Laboratory, will be on display this week at the Detroit Auto Show Technology Showcase. Credit: Image courtesy of Oak Ridge National Laboratory

With a 3-D printed twist on an automotive icon, the Department of Energy's Oak Ridge National Laboratory is showcasing additive manufacturing research at the 2015 North American International Auto Show in Detroit.

ORNL's newest 3-D printed vehicle pays homage to the classic Shelby Cobra in celebration of the racing car's 50th anniversary. The 3-D printed Shelby will be on display January 12-15 as part of the show's inaugural Technology Showcase.

Researchers printed the Shelby car at DOE's Manufacturing Demonstration Facility at ORNL using the Big Area Additive Manufacturing (BAAM) machine, which can manufacture strong, lightweight composite parts in sizes greater than one cubic meter. The approximately 1400-pound vehicle contains 500 pounds of printed parts made of 20 percent carbon fiber.
Recent improvements to ORNL's BAAM machine include a smaller print bead size, resulting in a smoother surface finish on the printed pieces. Subsequent work by Knoxville-based TruDesign produced a Class A automotive finish on the completed Shelby.

"Our goal is to demonstrate the potential of large-scale additive manufacturing as an innovative and viable manufacturing technology," said Lonnie Love, leader of ORNL's Manufacturing Systems Research group. "We want to improve digital manufacturing solutions for the automotive industry."

The team took six weeks to design, manufacture and assemble the Shelby, including 24 hours of print time. The new BAAM system, jointly developed by ORNL and Cincinnati Incorporated, can print components 500 to 1000 times faster than today's industrial additive machines. ORNL researchers say the speed of next-generation additive manufacturing offers new opportunities for the automotive industry, especially in prototyping vehicles.

"You can print out a working vehicle in a matter of days or weeks," Love said. "You can test it for form, fit and function. Your ability to innovate quickly has radically changed. There's a whole industry that could be built up around rapid innovation in transportation."

The Shelby project builds on the successful completion of the Strati, a fully 3-D printed vehicle created through a collaboration between Local Motors and ORNL.

The lab's manufacturing and transportation researchers plan to use the 3-D printed Shelby as a laboratory on wheels. The car is designed to "plug and play" components such as battery and fuel cell technologies, hybrid system designs, power electronics, and wireless charging systems, allowing researchers to easily and quickly test out new ideas.

Source: Oak Ridge National Laboratory

From video camera to driverless shuttle vehicle

The EZ 10 shuttle vehicle. Credit: © EasyMile

A new type of driverless shuttle vehicle has been developed thanks to innovative computer vision guidance technology that enables the vehicle to locate itself on a roadway reliably and inexpensively. The technology, which is based on the use of simple video cameras, was developed by researchers at Institut Pascal (CNRS/Université Blaise Pascal de Clermont Ferrand/IFMA)[1]. It lies at the heart of the EZ-10 autonomous shuttle vehicle developed by Ligier Group[2], which will be unveiled at the Michelin Challenge Bibendum in Chengdu (China) from 11 to 14 November 2014.

Since the 2000s, a number of companies have sought to make cars autonomous using expensive and sometimes unreliable technologies[3]. In 2003, researchers at Institut Pascal decided to work on automated driving of urban electric vehicles using simple video cameras. 
The technology they developed is based on two stages. The aim of the first stage is to identify all the significant points in the immediate environment of the path followed, in a video recorded during an initial journey in which the vehicle is driven manually. The second stage corresponds to the automatic mode during which the vehicle continuously monitors its path, ensuring that the images provided by the on-board cameras correspond as far as possible to the sequence initially filmed. The initial video thus plays the role of a virtual track that the vehicle must follow when it travels in autonomous mode.

Since 2006, the researchers at Institut Pascal, in collaboration with Ligier Group, have been developing automatic driverless shuttle vehicles that can transport up to 10 people along short routes (in the region of one kilometer), rather like a horizontal elevator. The vehicles, which are designed to be used at specific sites such as industrial sites, airports and amusement parks, are able to deal with obstacles thanks to laser rangefinders fitted on all four sides of the vehicle. The shuttle vehicle can detect the presence of an obstacle at a distance of 50 meters and in this way modify its speed or even stop, depending on the potential danger. The researchers now intend to turn their attention to running a fleet of five vehicles at the Michelin Europe Technology Center at Ladoux. The aim is to deal with multiple and potentially simultaneous requests from call points or smartphones, in real time and on a large industrial site, rather like an automatic taxi service.

The localization technology, which is reliable and inexpensive, will be unveiled at the Michelin Challenge Bibendum in Chengdu (China) from 11 to 14 November 2014. Equipped with an access ramp for people with reduced mobility, the new EZ-10 shuttle vehicle will provide visitors with a completely automated transport service.

[1] Within the framework of the IMobS3 Laboratory of Excellence.

[2] It is marketed by the EasyMile company, a joint venture between Ligier and Robosoft Technology.

[3] For example: differential GPS (which is different from the GPS commonly used in cars) is not always reliable, especially in city centers, where the satellite signals can be reflected off the façades of buildings. This phenomenon can lead to erroneous location calculations.

Source: CNRS

Is natural gas a 'bridge' to a hotter future?

This image shows a natural gas plant in Moss Landing, California. Credit: Carnegie President Matthew Scott

Natural gas power plants produce substantial amounts of gases that lead to global warming. Replacing old coal-fired power plants with new natural gas plants could cause climate damage to increase over the next decades, unless their methane leakage rates are very low and the new power plants are very efficient.

These are the principal findings of new research from Carnegie's Ken Caldeira and Xiaochun Zhang, and Nathan Myhrvold of Intellectual Ventures that compares the temperature increases caused by different kinds of coal and natural gas power plants. Their work is published in Environmental Research Letters.

There is an ongoing debate among people concerned with power plants and the future of energy policy and greenhouse gas emissions. Does it makes sense to replace old coal-fired power plants with new natural gas power plants today, as a bridge to a longer-term transition toward near zero-emission energy generation technologies such as solar, wind, or nuclear power? A key issue in considering the decision has been the potential climate effects of natural gas versus coal. Studies have yielded different results by focusing on power plants with different characteristics and using different definitions of what it means to be "better" for climate.

Carnegie's Caldeira and Zhang, along with Myhrvold, aimed to identify the key factors that are responsible for most of the difference in greenhouse gas emissions between individual gas and coal plants. The key factors, they found, are power plant efficiency and, in the case of natural gas plants, methane leakage during the supply process. They used these factors to derive a simple model for resulting temperature change caused by the carbon dioxide and methane released by a particular plant.

The team chose a simple and understandable way to compare climate effects of different types of power plants. They predicted how much global warming would be produced by different kinds of power plants during and after their period of operation.

They found that because natural gas plants are overall more efficient than coal plants, producing more energy per unit of carbon, they could cause less warming in the long term. However, it all depends on the amount of methane leakage that occurs. Natural gas plants that leak a substantial amount of methane during their supply process can produce more warming than comparable coal plants.

"If there is substantial natural gas leakage, then building new natural gas plants would lead to more near term climate damage than using the old dirty coal plants," explained Caldeira. "But natural gas plants would help reduce other types of air pollution that damage our health, and would be somewhat better for climate in the long term."

If faced with the choice of shutting down either a typical coal plant or a typical gas plant and methane leakage from the natural gas plant is below about 2 percent of total fuel, there would be a short-term climate benefit to shutting down the coal plant instead of the natural gas plant, the team found. But if methane leakage would be greater than 2 percent, there would be less warming in the near term if the natural gas plant were shut down instead of the coal plant.

Regardless, the team emphasized that meeting upcoming greenhouse gas emission targets will require deeper emissions cuts than just building natural gas plants with low methane leakage. If natural gas is to be a part of a future near-zero emission energy economy, methods for capturing and storing carbon from gas-fired power plants will likely be necessary.

Source: Carnegie Institution