Elimination of Secondary Nucleation and Grain Coarsening May be Key to Controlled Thin-Film Morphologies
- PDF / 322,026 Bytes
- 2 Pages / 612 x 792 pts (letter) Page_size
- 60 Downloads / 156 Views
about the perpendicular bisecting plane. When an extra CO molecule is added to CuCO and FeCO, the topographical images displayed symmetry. However, the plane containing the Fe(CO)2 molecule is orthogonal to the plane containing the Cu(CO)2 molecule. Detailed information of chemical bonding was provided by single-molecule vibrational spectroscopy using the STM. Different stretched and hindered rotation energies of CO molecules were obtained by using different C and O isotopes. This way, a basis of Cu/Fe comparison was established. The Cu/Fe carbonyl molecules may be deconstructed the same way they are made. Deconstruction, however, is a less controlled procedure. In the case of Cu(CO)2, the tip picked up one CO molecule (at 100 nA and 250 mV) and dropped it off. When the tip returned for the second CO molecule, however (at 100 nA and 500 mV), the molecule’s whereabouts were less precise. For the case of Fe(CO)2 and FeCO, the tip had difficulty picking up the CO molecule, even at 1 V and 100 nA. According to the researchers, this study demonstrates the utility and versatility of the STM. In addition, atomic-scale manipulation of molecules using the STM can provide a new means of nanofabrication. JUNE LAU
Accelerated Aging of Concrete and Triaxial Test Provide Insight for Long-Term Safety of Nuclear-Storage Containers At a meeting of the American Society of Civil Engineers held in May in Austin, Texas, Franz-Josef Ulm of the Massachusetts Institute of Technology (MIT) presented the work of his team on determining the long-term safety of concrete for holding nuclear waste. The current laboratory test can predict aging to about 300 years. While this accelerates concrete aging by a factor of 3 over what other researchers have achieved, Ulm, the Gilbert T. Winslow Career Development Associate Professor of civil and environmental engineering, is confident that the work can be further extrapolated to over 1,000 years. Concrete weakens over time when water leaches calcium from the material, and calcium is what gives concrete its strength. To accelerate the leaching process, the researchers from MIT and the Commissariat à l’Energie Atomique in France replaced the water with a highly concentrated solution of ammonium nitrate, which caused the calcium to leach at a much higher rate. They coupled this with an oscillating table that ensured an even concentration of solution around each sample. 8
To expose the weathered materials to stress, the team placed samples into a triaxial high-pressure steel chamber that applied pressures up to 10 MPa from all sides. When they applied a shear, or slightly larger stress from one side, slivers of the material slipped apart. The researchers found a significant loss of frictional performance in the artificially aged cement paste. The leached calcium left large pores that collapsed under the pressure, allowing the material to slip apart. Ulm said that the microstructure of the leached cement paste, as visualized with an environmental scanning electron microscope, “showed a strong similarity t
Data Loading...
