Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006. / Armistead Russell, Committee Member ; James Mulholland, Committee Member ; Rodney Weber, Committee Member ; Michael H. Bergin, Committee Chair ; Jean-Luc Jaffrezo, Committee Member.

No description available.

This thesis reports on the work performed on the manipulation of micro­-particles on substrate surfaces using short laser pulses. For particles with diameters on the order of microns, the binding forces to surfaces are significantly larger than gravitational forces. To overcome these binding forces and manipulate the particles the use of femtosecond laser pulses has been investigated. Individual micro-particles (poly-divinylbenzene, glass and silver materials) with diameters around 2 um were removed from substrate surfaces (dielectric, semiconductor and metal substrates) us­ing a Ti:Sapphire laser system. The pulses produced at 800 nm had pulse lengths around 140 fs and were tightly focussed onto the surface using 5x and 10x micro­scope objectives. The peak fluence thresholds for particle removal were determined and the surfaces examined after irradiation by a scanning electron microscope and atomic force microscope to check for damage. The experimental results indicate that ablation of the substrate below the micro-particles is most likely to be respon­sible for micro-particle removal from the substrate surface when using femtosecond pulses. Ablation pits were observed for the dielectric micro-spheres on semiconductor substrates. It is also believed that ablation is responsible for the removal of other types of micro-particles from various substrates. Unlike the dielectric micro-sphere on semiconductor substrate results, the other particle-substrate combinations show a close correspondence between the removal and substrate ablation thresholds. It is believed that these results indicate the occurrence of ablation leading to the removal of the micro-particles. Calculations of the local electromagnetic fields around the micro-particles have also been carried out and the distributions used to interpret the experimental results. / Thesis / Master of Applied Science (MASc)

No description available.

Digitized by Kansas Correctional Industries

Attrition occurs during the transport and storage of particles and leads to loss of material through dust formation and to environmental pollution. Standard tests are all specifically designed to cater for particular needs and are often indicators of relative hardness than of attrition rates. Since little progress has been made into understanding the mechanisms of attrition, the purpose here is to study one of the basic processes that determines the rate of grinding. The aim is thus to establish a fundamental framework within which past work and future developments can be assessed. An annular attrition cell was designed, constructed and commissioned to permit one of the mechanisms of attrition, namely that in failure zones of deforming solids, to be considered in isolation. Sample weights of 100 gm were more than sufficient and the results were found to be reproducible, systematic and generally independent of sample size. Several close-sized material in the size range 250-2000 µm of various shapes were studied including different grades of sodium chloride, sodium carbonate and molecular sieve beads. The mode of attrition, bodily fracture or surface grinding, was easily verified by microscopic examination of attrited product. Results followed Gwyn's empirical law W = K_p t^m where W denotes the weight fraction attrited, t time and K_p , m are characterising parameters. The reliable data permitted the development of simple kinetic models. One supposes first order loss of coarse material, another that attrition rate is dependent on radius reduction. It may be argued that the former applies to a fracturing mechanism, the latter to a surface grinding process. The first order approach has to be modified to allow for the initial high rate of attrition; the second model may be reduced to the Gwyn form. The attrition cell is useful in characterising materials; it should, in future, permit assessment of equipment performance.

No description available.

No description available.

No description available.

No description available.