Particle Generation by Ultraviolet-Laser Ablation during Surface Decontamination

Abstract

A novel photonic decontamination method was developed for removal of pollutants from material surfaces. Such a method relies on the ability of a high-energy laser beam to ablate materials from a contaminated surface layer, thus producing airborne particles. In this paper, the authors presented the results obtained using a scanning mobility particle sizer (SMPS) system and an aerosol particle sizer (APS). Particles generated by laser ablation from the surfaces of cement, chromium-embedded cement, and alumina were experimentally investigated. Broad particle distributions from nanometer to micrometer in size were measured. For stainless steel, virtually no particle Ͼ500 nm in aerodynamic size was detected. The generated particle number concentrations of all three of the materials were increased as the 266-nm laser fluence (millijoules per square centimeter) increased. Among the three materials tested, cement was found to be the most favorable for particle removal, alumina next, and stainless steel the least. Chromium (dropped in cement) showed almost no effects on particle production. For all of the materials tested except for stainless steel, bimodal size distributions were observed; a smaller mode peaked at ϳ50 -70 nm was detected by SMPS and a larger mode (peaked at ϳ0.70 -0.85 m) by APS. Based on transmission electron microscopy observations, the authors concluded that particles in the range of 50 -70 nm were aggregates of primary particles, and those of size larger than a few hundred nanometers were produced by different mechanisms, for example, massive object ejection from the material surfaces. INTRODUCTIONLaser ablation is defined as the removal of material by laser irradiation from a surface of the material. Removed materials may be in the form of particulate matter, solid and/or liquid, and vapors. The interaction of high-power lasers with solid materials causes material removal through processes such as laser vaporization, desorption, sputtering, ejection, etching, spallation, and plasma generation. [1][2][3][4][5][6][7][8] Besides continuous research on laser ablation mechanisms, an enormous amount of research on applications using laser ablation has been performed. 9 -15 One recent and effective application is surface decontamination and cleaning. [11][12][13]16 Laser ablation can be applied, for example, for decontamination and decommissioning (D&D) of nuclear facilities at U.S. Department of Energy (DOE) complexes across the United States. For D&D applications, previous results 17 showed that laser ablation with an ultraviolet (UV) wavelength (266-nm) pulsed laser was most effective in particle generation compared with that with lasers of other (1064-or 532-nm) wavelengths. In this paper, the authors report, in detail, the production and transformation of particles when the UV laser was used on selected surrogate surfaces: Portland cement (cement) with or without a toxic heavy metal, chromium (Cr), prepared under laboratory conditions, stainless steel 316, and pure alumina (Al 2 O 3 ). The f...

Characterization of Aerosols Generated by Nanosecond Laser Ablation of an Acrylic Paint

“…Shape When a material is ablated by a nanosecond laser beam, the resulting aerosols are generally heterogeneous. Indeed, as in our study, aerosols are often composed both of nanoparticles (which are generally aggregated) and "larger" particles (sometimes of micrometer size) having various shapes (Heitz and Dickinson 1999;Liu et al 2004;Lee and Cheng 2006).…”

“…Hydrodynamic sputtering, spallation sputtering or phase explosion can also be considered. These latter processes are often considered for metal ablation, during which droplet ejection results from the formation of a liquid surface region (Lee and Cheng 2006).…”

“…However, it is necessary to study the "ablation products" when laser ablation is used for surface cleaning and decontamination (Savina et al 1999;Roberts et al 2000;Kusch et al 2003; Reutzel et al 2004;Géléoc and Gensdarmes 2004;Lee and Cheng 2006;Qi et al 2007;Ostrowski et al 2007;Dewalle et al 2007). Indeed, after laser beam interaction with the target, the ablated matter is present 903 in the form of an "aerosol."…”

Application of pulsed laser ablation (PLA) for the size reduction of non-steroidal anti-inflammatory drugs (NSAIDs)

“…These phenomena explain the random fluence dependency in the size distribution of the ejected particles ( Table 1). In bulk materials, the average size of the ablated particles and the FWHMs of the particles' size distribution increase with the fluence 34,35 .…”

A study of particulate matter concentration released during laser paint removal process on car coated substrate

“…By assuming the spatial distributions of energy is homogenous for each shot on the painted material, it is possible to normalize the measurements with respect to the interaction of surface area [17]. Thus, each measurement of particle mass is related to one laser shot and 1.0 cm 2 of ablated paint.…”