Engineering topics

Aleksandrov, A

Publications and source records attributed to Aleksandrov, A.

3 records

DOE OSTI2019

Electron- and Thermal-Stimulated Synthesis of Water on Boehmite (y-AlOOH) Nanoplates

Utilizing a combination of electron stimulated desorption, infrared spectroscopy and temperature program desorption measurements, we show that molecular water is synthesized during electron irradiation on boehmite nanoplates and postulate that the reaction proceeds first through decomposition of the hydroxyl to produce trapped hydrogen atoms. Once released, these hydrogen atoms can react with a neighboring hydroxyl resulting in adsorbed water. In addition, molecular water is readily formed on the surface of the boehmite nanosheets through thermal induced recombinative desorption. Peak water production via recombinative desorption occurs at 750 K in agreement with previous studies. We have also identified a weak desorption feature near 400 K which is likely strongly adsorbed water. The derived experimental desorption activation energy of water assuming full coverage is 98.6 kJ mol-1.

Jones, Brant M.↗

DOE OSTI2018

Molecular water adsorption and reactions on (alpha)-Al2O3(0001) and (alpha)-Alumina Particles

The adsorption and reaction of water on single crystal, -Al2O3(0001) in ultrahigh vacuum, and -alumina particles in ambient conditions, was investigated using temperature programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS), diffuse reflectance infrared Fourier transform spectra (DRIFTS) and other surface science techniques. For a water coverage of 1 H2O/(surface Al3+) on -Al¬2O3(0001), no evidence for the surface hydroxyls expected from dissociative adsorption was observed in the infrared spectra, while the 2 vibration of molecular water was observed. Electron-stimulated desorption of molecular water at low coverages also indicated molecular or mixed (molecular plus dissociative) adsorption. Analysis of Kr TPD spectra showed that the water films wet the alumina substrate and suggested that the films were initially growing layer-by-layer. In contrast with the single crystal results, DRIFTS of water adsorption on alumina particles indicated the presence of surface hydroxyls that persist even after annealing to high temperatures in oxygen. For water on -Al2O3(0001) at coverages less than 0.3 H2O/(surface Al3+), water desorbed over a broad temperature range extending from ~250 K to 700 K. For larger coverages, water desorption occurred at temperatures between ~160 K and 250 K, consistent with desorption of molecular water. The results, which are consistent with at most a small amount of water dissociation on the Al-terminated (0001) surface, are difficult to reconcile with calculations suggesting that the barrier to dissociation is small. However, the results are consistent with recent vibrational sum frequency experiments showing that the hydroxylation of the Al-terminated (0001) surface takes many days even at ambient pressures and temperatures.

Petrik, Nikolay G.↗

DOE OSTI2011

Simple Low-Frequency Beam Pickup

Detection of the field induced by a beam outside of the beam pipe can be used as a beam diagnostic. Wires placed in longitudinal slots in the outside wall of the beam pipe can be used as a beam pickup. This has a very small beam-coupling impedance and avoids complications of having a feedthrough. The signal can be reasonably high at low frequencies. We present a field waveform at the outer side of a beam pipe, obtained as a result of calculations and measurements. We calculate the beam-coupling impedance due to a long longitudinal slot in the resistive wall and the signal induced in a wire placed in such a slot and shielded by a thin screen from the beam. These results should be relevant for impedance calculations of the slot in an antechamber and for slots in the PEP-II distributed ion pump screens. The design of the low-frequency beam position monitor is very simple. It can be used in storage rings, synchrotron light sources, and free electron lasers, like LINAC coherent light source.

43 PARTICLE ACCELERATORS↗