A. Koch

A study of carbonaceous char oxidation in air by semi-quantitative FTIR spectroscopy

Abstract The aim of this study was to describe the methodology of semi-quantitative characterization of carbonaceous material oxidized under mild thermal conditions. Infrared spectroscopic analysis was applied to the determination of chemical changes induced by oxidation. A curve fitting model has thus been developed to evidence the evolution of specific chemical groups during treatment. The possibility to follow mechanisms and kinetics of carbonaceous char oxidation through data obtained by this model has been demonstrated.

Influence of the laser light absorption by the colloid on the properties of silver nanoparticles produced by laser ablation in stirred and stationary liquid

Silver nanoparticles were produced by nanosecond pulsed-laser ablation at 1064 nm of Ag in pure water. These experiments were performed using an alternative ablation cell design where a cylindrical shaped Ag target was horizontally irradiated, while the liquid was stirred by a stir rod coaxially arranged to the target. The repeatability of the generated colloids properties (extinction and size distribution) is assessed by statistical tools. The colloids properties prepared under stationary liquid are found to be unpredictable, while they are highly repeatable at high stirring speed. At the same time, electronic microscopy examinations of the irradiated Ag targets revealed that the width of the laser-machined grooves exponentially decays in stationary liquid and almost linearly under high stirring speed as the ablation proceeds. In the latter case, the decay rate was found to be constant from one experiment to the other, while it was not repeatable stationary liquid. We show that the decay of the groove width is due to an attenuation of the laser energy reaching the target surface due to the formation of a more or less dense NPs layer in front of the target as the ablation proceeds. Using the ablation time-dependence of the groove width, we can quantify the attenuation factor of the laser energy with exposure time. Finally, the relationship between the laser energy attenuation, stirring speed, and repeatability of the colloids properties is interpreted and discussed in terms of mass transfer.

Etude du Comportement Thermique de la Cellulose par Spectroscopie Infra Rouge II. Analyse in situ des évolutions spectrales entre 25 et 450°C

The part I of this work discusses the potentialities and limits of the in situ spectroscopic analysis of cellulose by Diffuse Reflectance Infrared Fourier Transform in an environment device. In this paper, we describe: the in situ evolutions of cellulose from 25 to 270°C under N2 or air; the evolution of a partially thermolyzed cellulose residue during thermal treatment from 25 to 450°C and finally the oxidation in air of a cellulose char at 300°C. We observe a limited evolution of the cellulose below 270°C. Only some carbonyle groups issued from rearrangement of cellulose chains are formed. The thermal treatment of the thermolyzed residue leads to a progressive aromatization of the solid between 270 and 450°C. The oxidation in air induces the formation of oxygenated groups (carbonyles, carboxylic acids, lactones) and proceeds by reaction on both aliphatic and aromatic sites. Some dehydration of carboxylic groups to anhydrides are observed.

Baseline Correction of Spectra in Fourier Transform Infrared: Interactive Drawing with Bezier Curves

A baseline correction tool using the method of Bézier has been developed to permit the drawing of curves in a manner that allows full control of the line curvatures by the user. The basic concepts and principle of the Bézier algorithm are explained as well as the modifications that were made to take into account the limitations imposed by the treatment of spectral data. The application of this particular curve drawing routine to an existing baseline correction module offers facilities and extended capabilities that typical polynomial methods using least-squares fitted lines cannot attain. The examples of applications that are given demonstrate how this method can be performed, as well as its efficiency.

Highly-repeatable generation of very small nanoparticles by pulsed-laser ablation in liquids of a high-speed rotating target

By irradiating a cylindrical silver target rotated at a high-speed within the range 300-2400 rpm (lateral speed 0.16-1.25 m s-1) in pure water, we prepare ligand-free Ag nanoparticles (NPs) with a size of 4 ± 2 nm which are likely to be primary particles. Usually, the generation of NPs showing such a small size requires either a laser post-treatment and/or chemical additives. As the rotation rate of the target is increased, calculated 3D flow patterns revealed different hydrodynamic regimes which clearly influence the ablation rate and repeatability of the process as well as the colloidal properties. In addition to revealing the importance of fluid dynamics in pulsed-laser ablations in liquids, this study provides a way for producing in one step pure NPs with sizes below 5 nm which are suitable for applications in catalysis.

Application de la Spectroscopie Infra Rouge à L'étude du Comportement Thermique de la Cellulose Partie I.

In this work, we describe and evaluate the use of the Fourier transform infra red (FTIR) spectroscopy in DRIFT mode (diffuse reflectance infra red Fourier transform) in an environmental device to follow the functional evolution of cellulose during thermal treatments. The potentialities (and difficulties) of the technic are given.