Halloysite nanotubes; Lumen enlargement; Acid treatment; Catalysis; LIBS;CLAY NANOTUBES; TREATED HALLOYSITE; CONTROLLED-RELEASE; CARBON NANOTUBES; NANOCOMPOSITES; ADSORPTION; LUMEN; SEPARATION; OXIDATION; DELIVERY

Halloysite nanotubes are a type of naturally occurring inorganic nanotubes that are characterized by a different composition between their external and internal walls. The internal walls are mainly composed of alumina whilst external walls are composed of silica. This particular structure offers a dual surface chemistry that allows different selective surface treatments which can be focused on increasing the lumen, increasing porosity, etc. In this work, HNTs were chemically treated with different acids , for 72 h at a constant temperature of 50 degrees C. As per the obtained results, the treatment with sulphuric acid is highly aggressive and the particular shape of HNTs is almost lost, with a remarkable increase in porosity. The BET surface area increases from 52.9 up to 132.4 m g with sulphuric acid treatment, thus showing an interesting potential in the field of catalysis. On the other hand, the treatment with acetic acid led to milder effects with a noticeable increase in the lumen diameter that changed from 13.8 nm up to 18.4 nm which the subsequent increase in the loading capacity by 77.8%. The aluminium content was measured by X-ray fluorescence and laser induced breakdown spectroscopy . The final results using two systems, suggest a good correlation between the acid strength and the aluminium reduction. Consequently, is possible to conclude that new applications for HNTs can be derived from selective etching with acids. Sulphuric acid widens the potential of HNTs in the field of catalysis while weak acids such as acetic and acrylic acids give a controlled and homogeneous lumen increase with the corresponding increase in the loading capacity.

Double pulse laser ablation; Laser induced phase explosion; Plasma expansion; Pre plasma formation; Single pulse laser ablation; Water interaction ambient;INDUCED BREAKDOWN SPECTROSCOPY; PHASE-EXPLOSION; NANOSECOND; METALS; PLASMA; ENHANCEMENT; THRESHOLDS

In this paper, single pulse and double pulse laser ablation of an aluminum target in two interaction ambient was investigated experimentally. The interaction was performed by nanosecond Nd:YAG laser beam in air and four depths (i.e. 9, 13, 17, and 21 mm) of distilled water ambient. The irradiation was carried out in single and collinear double pulse configurations in both air and liquid ambient. Crater geometry (depth and diameter) was measured by an optical microscope. The results indicated that the crater geometry strongly depends on both single pulse and double pulse configurations and interaction ambient. In single pulse regime, the crater diameter is higher for all water depths compared to that of air. However, the crater depth, depend on water depth, is higher or lower than the crater depth in air. In double pulse laser ablation, there are greater values for both crater diameters and crater depths in the water. (C) 2016 Elsevier B.V. All rights reserved.

Double-pulse laser ablation; Molecular dynamics; Hydrodynamics; Crater depth; Plume reheating;INDUCED BREAKDOWN SPECTROSCOPY; SIGNAL ENHANCEMENT; MOLECULAR-DYNAMICS; METAL TARGETS; SPALLATION; SINGLE

We elaborated two numerical methods, two-temperature hydrodynamics and hybrid two-temperature molecular dynamics, which take into account basic mechanisms of a metal target response to ultra short laser irradiation. The model used for the description of the electronic subsystem is identical for both approaches, while the ionic part is defined by an equation of state in hydrodynamics and by an interatomic potential in molecular dynamics. Since the phase diagram of the equation of state and corresponding potential match reasonably well, the dynamics of laser ablation obtained by both methods is quite similar. This correspondence can be considered as a first step towards the development of a self consistent combined model. Two important processes are highlighted in simulations of double-pulse ablation: (1) the crater depth decrease as a result of recoil flux formation in the nascent plume when the delay between the pulses increases; (2) the plume reheating by the second pulse that gives rise to two three-fold growth of the electron temperature with the delay varying from 0 to 200 ps. (C) 2016 Published by Elsevier B.V.

LIBS stratigraphy; Galvanic coatings; Ablation rate; Plasma shielding; Light-plasma interaction; Depth profiling;INDUCED BREAKDOWN SPECTROMETRY; ION-BEAM ANALYSIS; PULSED-LASER DEPOSITION; REDUCED PRESSURE; JEWELRY INDUSTRY; PURE METALS; ABLATION; SPECTROSCOPY; FILMS; THICKNESS

Laser-induced depth profiling was applied to the investigation of galvanised steel sheets as a typical modern multi-layer coating system for environmental corrosion protection. The samples were ablated stepwise by the use of two different wavelengths of a frequency-converted Nd:YAG-laser, 266nm and 532nm, with a pulse duration of tau = 4ns at fluences ranging from F=50 to 250 J cm(-2). The emission light of the resulting plasma was analysed as a function of both penetration depth and elemental spectrum in terms of linear correlation analysis. Elemental depth profiles were calculated and compared to EDX-cross sections of the cut sample. A proven mathematical algorithm designed for the reconstruction of layer structures from distorted emission traces caused by the Gaussian ablation profile can even resolve thin intermediate layers in terms of depth and thickness. The obtained results were compared to a purely thermally controlled ablation model. Thereby light-plasma coupling is suggested to be a possible cause of deviations in the ablation behaviour of Al. The average ablation rate h as a function of fluence F for Ni ranges from 1 to 3.5 mu m/pulse for lambda = 266nm as well as for lambda =532nm. In contrast, the range of h for Al differs from 2 to 4 mu m/pulse for lambda = 532 nm and 4 to 8 mu m/pulse for lambda = 266 nm in the exact same fluence range on the exact same sample. (C) 2016 Elsevier B.V. All rights reserved.

LIBS; Femtosecond; Organic solar cell; Selective ablation; Depth profiling;DEPTH-RESOLVED ANALYSIS; SELECTIVE ABLATION; SOLAR-CELLS; SPECTROMETRY; LIBS; ABSORPTION; COATINGS; SPECTRA; SAMPLES; PULSES

The potential of laser induced breakdown spectroscopy (LIBS) as a non-contact probe, for characterizing organic photovoltaic devices during selective laserscribing, was investigated. Samples from organic solar cells were studied, which consisted of several layers of materials including a top electrode (Al, Mg or Mo), organic layer, bottom electrode (indium tin oxide), silicon nitride barrier layer and substrate layer situated from the top consecutively. The thickness of individual layers varies from 115 to 250 nm. LIBS measurements were performed by use of a 40 femtosecond Ti:Sapphire laser operated at very low pulse energy (<10 micro-joule) to ensure a fine depth-profiling of the very thin layers. Probing a fixed spot on the sample with successive laser pulses, produced plasma emission spectra corresponding to individual laser ablation events. This enabled discrimination of the different layers on the basis of characteristic spectral lines reflecting key elemental constituents of each layer in the organic solar cell structure, demonstrating the potential of LIBS for fast, non-contact characterization of organic photovoltaic coatings. (C) 2016 The Author(s). Published by Elsevier B.V.

Laser induced plasma; Laser-ablation; Laser induced breakdown spectroscopy;INDUCED BREAKDOWN SPECTROSCOPY; ABLATION; DIAGNOSTICS; PICOSECOND; DEPOSITION; EMISSION; DYNAMICS; SURFACE; PULSES; SINGLE

A detailed theoretical and experimental analysis is performed for a wide range of laser operating conditions, typical for laser induced breakdown spectroscopy(LIBS) and laser ablation (LA) experiments on copper metallic target. The plasma parameters were experimentally estimated from the line intensities ratio which reflects the relative population of neutral excited species in the plasma. In the case of LA experiments the highest temperature observed was 8210 +/- 370 K. In case of LIBS measurements, a maximum temperature of 8123 K has been determined. The experimental results are in good agreement with a stationary, hydrodynamic model. We have theoretically investigated the plasma emission based on the generalized collisional-radiative model as implemented in the ADAS interconnected set of computer codes and data collections. The ionic population density distribution over the ground and excited states into the cooper plasma is graphically displayed as output from the code. The theoretical line intensity ratios are in good agreement with experimental values for the electron density and temperature range measured in our experiments. (C) 2017 Elsevier B.V. All rights reserved.

Wear resistant coatings; Tungsten carbide; Elemental profiling; Laser induced breakdown spectroscopy; Energy dispersive X-ray spectroscopy; Laser cladded coating;TUNGSTEN CARBIDE; MICROSTRUCTURAL CHARACTERIZATION; COMPOSITE COATINGS; ABLATION; STEEL; LIBS; WEAR; EXCITATION; PLASMA; PULSES

Multilayer tungsten carbide wear resistant coatings were analyzed by laser induced breakdown spectroscopy (LIBS) and energy dispersive X-ray (EDX) spectroscopy. Coaxial laser cladding technique was utilized to produce tungsten carbide coating deposited on low alloy steel substrate with additional inconel 625 interlayer. EDX and LIBS techniques were used for elemental profiling of major components (Ni, W, C, Fe, etc.) in the coating. A good correlation between EDX and LIBS data was observed while LIBS provided additional information on light element distribution (carbon). A non-uniform distribution of tungsten carbide grains along coating depth was detected by both LIBS and EDX. In contrast, horizontal elemental profiling showed a uniform tungsten carbide particles distribution. Depth elemental profiling by layer by-layer LIBS analysis was demonstrated to be an effective method for studying tungsten carbide grains distribution in wear resistant coating without any sample preparation. (C) 2017 Published by Elsevier B.V.

Laser ablation; Dust deposition; COMSOL Multiphysics 4.4; Thermal conduction; Urban-industrial aerosols; Limestone;ROMANIA; MODEL; LIDAR; IASI

This paper reports preliminary results concerning thermal effects induced by urban/industrial air pollutants deposited on a limestone rock when heated by pulsed laser in the cleaning process. The process of laser cleaning treatment of the crust is simulated using COMSOL Multiphysics 4.4, finite element analysis software. Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy and Laser Induced Breakdown Spectroscopy techniques have been used to analyze the chemical composition of the samples. Two elements found as being present into the dust and in the crust, such as iron and magnesium particles are used for simulation in COMSOL. Therefore, the profiles heat evolutions on the crust surface and inside limestone are obtained as thermal interactions between the three components (iron, magnesium and limestone), simulating the non-homogeneous materials. It has been observed that iron impurities caused by the dust deposition may damage the limestone through a process of overheating, as a consequence of a high thermal conduction phenomenon, recorded for the region with iron impurities and sizes of micrometric order are localized. The thermal contact between the three components results in plots that reflect their thermal interactions. (c) 2017 Elsevier B.V. All rights reserved.