Authors:G. Thomas, J. J. Gruffat, and M. Soustelle
The kinetics of heterogeneous reactions are in most cases studied by means of integral curves which represent the degree of reaction as a function of the time. Recently, rate vs. time curves have also been used for this purpose. The present paper draws attention to the importance of curves giving the degree of reaction as a function of the rate of reaction; these facilitate the investigation of separate points, make possible the interpretation of various factors, and provide valuable data concerning the mechanism. Three methods are suggested for preparing these curves and the decomposition of sodium hydrogen carbonate is given as an example.
The thermal elimination of NaCl from sodium chloroacetate, a polymerization reaction that takes place between 150 and 200‡C in the solid state, leads quantitatively to the simplest polyester, polyglycolide. Byin situ IR-spectroscopy, we have shown that the reaction proceeds smoothly and directly without intermediates or by-products. The endgroups of the polymeric product — ionised carboxylate groups (-COONa) and hydrogen-bonded alcohol groups (−COH) — are clearly detectable. It is therefore concluded that the polymer forms extended chains, not rings, during the course of this solid-state reaction. That corresponds well with the idea of a polymerization reaction in the solid state. However, this experiment does not exclude the formation of polyglycolide rings as further product because they do not contain any terminating groups.
The phase diagram of solid-solid equilibria in the system Ca3(PO4)-CaNaPO4 has been studied by thermal analysis. The results are confirmed by X-ray diffraction at different temperatures. This study was limited to that of mixtures in a temperature range determined by previous results. The present work confirms the existence of two metastable diagrams which are superimposed on the stable diagram.
Authors:S. Marsaud, J. Thomas, M. Fallavier, J. Mackowski, and J. Tousset
Alpha particles backscattering has been used in order to study the thermal diffusion of gold electrodes into thin films of
chalcogenide glasses. The performances of the method allowing approximately a 2000 Å analyzing depth (below the front electrode
or near the surface when only back electrode is concerned) diffusion profiles are obtained. If the gold diffusion into As
can be considered as classical, following the Fick's law and showing a rather low activation energy (0.6 eV), the diffusion
into AsTe is quite different. A flat and deep gold profile develops through the entire thickness of the film (still below
the glass transition temperature). A tentative interpretation is proposed, based upon a “preferential path” diffusion, introducing
a new diffusion coefficient aside the bulk one. Several significant features support this interpretation and suggest further
investigations. Nevertheless we have already a good understanding of the electrical degradation of such devices trough, the
correlation with the diffusion process.
Authors:J. Giroux, M. Talvat, J. Thomas, and J. Tousset
Activation analysis by charged particles may encounter great difficulties when ‘parasitic’ reactions induce in the matrix
itself the same radionuclide as the one requested by the reaction for analytical aim. In this investigation we study reactions
inducing18F activity in silicon and we show the importance of these reactions for determining low levels of oxygen in silicon by the
. For irradiations carried out with 54 MeV α-particles, the profile of18F production in silicon presents an activity decreasing very rapidly from the surface to depths of 500 μm without any connection
activation curve. The diffusion of18F nuclides created at the surface from the oxide bed does not at all explain that result. The differences between these curves
are attributed to parasitic reactions inducing18F activity in silicon. In order to confirm the reaction
we also investigated the profile of24Na and29Al production by another parasitic reaction in silicon. It is pointed out that the choice of incident energy is quite primordial,
for analyses of oxygen in silicon with 54 MeV α-particles are not quite suitable. The best energy range appears to be around
Authors:M. Cohen, L. Porte, J-P Thomas, and J. Tousset
Une méthode d'étude de la composition stoéchiométrique de couches minces (10 à 500 μg/cm2) de verres chalcogénures est développée. L'étude des réactions nucléaire; induites par bombardement de protons de basse énergie
(<4 MeV) sur les éléments constitutifs Ge, As, Te et S, conduit à choisir la diffusion élastique et la détection de gammas
prompts pour le dosage simulatené. La précision et la sensibilité de la méthode sont discutées à partir des résultats obtenus.
L'utilisation de la résonance fine sur le soufre (p, p'γ) est appliquée à l'étude de l'homogénéité des cibles.
Authors:R. Brodzinski, J. Langford, M. Thomas, and O. Harling
Procedures are described for rapid, high yield chemical separation of niobium and vanadium from surfaces of quartz, silicon,
and carbon following thermal neutron activation. Practical detection limits for stable niobium and vanadium are 7·1010 and 6·1011 atoms respectively. Application of these procedures to controlled thermonuclear reactor materials studies is discussed.
Authors:J. Laul, M. Smith, C. Thomas, P. Jackson, and N. Hubbard
Analytical procedures for measuring various radionuclides in the238U and232Th chains in briney waters are described. Using methods such as mass spectrometry, and alpha, beta and gamma spectrometry, the desired measurement sensitivity required for each of the radionuclides is achieved.233U,228Th,208Po,212Pb, and133Ba are used as tracers for chemical yield recoveries. Typical precision of the results range from 5–20%.
Authors:R. White, P. Thomas, M. Philips, R. Wuhrer, and J. Guerbois
The deleterious interaction
of some traditional sulphide artists pigments and copper ions results in the
formation of black copper sulphides, in particular, covellite (CuS), and,
hence, the discolouration of valuable artworks. In this paper the interaction
of malachite, a source of copper(II) ions, with the pigment cadmium yellow,
a sulphide pigment comprising of a solid solution of cadmium and zinc sulphides,
is investigated by XRD and TG-MS. XRD showed the presence of the copper sulphide
and cadmium carbonate phases, produced by a simple ion exchange mechanism.
TG-MS showed the complexity of the range of metastable phases produced. The
identification of these phases, however, requires further work.
Authors:J. Thomas, M. Fallavier, J. Mackowski, C. Pijolat, J. Tousset, and M. Wehr
A review is presented summarizing the specific nuclear microanalysis methods applied in our laboratory to study amorphous
semiconductor thin films. For backscattering, ∼3 MeV Li ions are applicable when depth resolution and sensitivity are required
while up to 8 MeV α-particles allow larger depths to be probed and elemental interferences to be solved. These features are
predominant for diffusion studies between metal electrodes and chalcogenide films. On the other hand hydrogen profiling using
the1H(1 5N, αψ) resonant nuclear reactions is described and analytical problems associated with its use are discussed. Applications
to the elaboration conditions of hydrogenated (a)Si is developed.