Lucien Martinot

Use of a variable incidence angle PIXE arrangement for studying pigment multilayers

Abstract Particle induced X-ray emission (PIXE) method is used in the field of archeometry and specially to investigate pigment colored multilayers. The tilting of the sample with respect to the incident proton beam direction allows to modify the relative contribution of each layer to the fluorescence signal. The experimental results coupled to computer simulations lead to semi-quantitative information about the thickness, the position and the composition of the successive layers.

Investigation of the cathodic electropolymerization of acrylonitrile, ethylacrylate and methylmethacrylate by coupled quartz crystal microbalance analysis and cyclic voltammetry

Abstract The cathodic electropolymerization of acrylonitrile (AN), ethylacrylate (EA) and methylmethacrylate (MMA), has been monitored for the first time by coupled electrochemical quartz crystal microbalance (QCM) and cyclic voltammetry analyses. These data have been compared to the previously published analyses for methacrylonitrile (MAN). At the potential E p1 of the less cathodic of the two voltammetric peaks observed (peak I), the polymer formed is anchored firmly to the cathode even in a good solvent for it, and it remains adsorbed when the voltammetric scan is repeated up to E p1 . In parallel, a linear relationship is observed between the frequency change recorded in situ by the QCM up to E p1 and the PAN film thickness measured ex-situ by ellipsometry. However, when potentials more negative than peak I are scanned, the polymer desorption (degrafting) occurs as assessed by solubilization in a good solvent. Polymerization is also resumed but in solution and no longer as grafted chains. The major difference between the acrylic monomers (AN and EA) and the methacrylic ones (MMA and MAN) is that part of the methacrylic chains are not grafted at E p1 . This coexistence of adsorbed and desorbed chains is not observed for the polyacrylic chains in that potential range. The mass of PAN deposited onto the cathode has been approximated from the film thickness and the Sauerbrey equation, so allowing the M n of the grafted chains to be estimated.

Use of PIXE-PIGE under variable incident angle for ancient glass corrosion measurements

Abstract Although glass is usually considered as a very stable archaeological material, it can undergo severe degradation. Soda-lime glass, the most common glass throughout ancient times, is particularly sensitive to this problem. The glass surface absorbs moisture from its environment and the contact with CO 2 causes Na 2 O and NaOH to convert to Na 2 CO 3 , which is extremely hygroscopic. The subsequent unstable glass layer can be leached out and causes decomposition of the glass. The non-destructive PIGE–PIXE method of investigation allows detection of this phenomenon even if no visible effect appears. The variable incident angle method is able to discern the depth of the degradation. One aim of such studies is the possible dating or at least fake detecting of archaeological materials. Furthermore, even objects of large size can be investigated with the atmospheric PIGE–PIXE set-up. Some examples of measurements on ancient glass are given.

Electrografting of acrylic and methacrylic monomers onto metals: influence of the relative polarity and donor-acceptor properties of the monomer and the solvent

The possibility of grafting a series of alkyl polyacrylates and polymethacrylates onto a nickel cathode by electropolymerization of the parent monomers has been investigated and has emphasized the critical importance of the solvent used. Indeed, the intensity of the inhibition peak, which is the electrochemical mark of the cathode passivation as result of the polymer grafting, clearly depends on both the polarity and the donor-acceptor properties of the solvent. The Gutmann concept is used to account for these experimental results. An increase in the donicity of the solvent used for the electrochemical medium has allowed, for the very first time, several polyacrylates and polymethacrylates [such as poly(ethyl acrylate), poly(methyl methacrylate), and poly(2-trimethylsilyloxyethyl methacrylate)] to be electrografted onto Ni. This observation is consistent with a competition process between the monomer and the solvent for being adsorbed on the cathode and amassing in its very close vicinity. The outcome of this competition is controlled by the relative polarity (in case of low donicity) and the relative donor-acceptor properties (when the difference is high enough) of the monomer/solvent pair, and by the monomer concentration (in case of weak competition). A semi-quantitative relationship has also been observed between the monomer ability to be electrografted and the electron-accepting character of the vinyl β-carbon atom as measured by 13C NMR.

Chronopotentiometric determination of U(III), U(IV), UO2(VI) and Np(IV) in molten LiCl-KCl eutectic*

Summary The use of chronopotentiometry for the quantitative analysis of uranium and neptunium in a molten LiCl-KCl eutectic has been investigated: U(IV) or Np(IV) may be determined with an accuracy of ±4% and U(III) or UO 2 (VI) with an accuracy of ±6% in the temperature range 400–550°. U(III) and U(IV) may be determined in the same solution with the accuracies given above.

Determination of the stability constants of uranyl/polymer complexes by differential pulse polarography

Abstract Differential pulse polarography (DPP) allows for the determination of the stability constants ( K ) and the stoichiometry ( n ) for the complexation of the UO 2 2+ ion by various monomers and the parent polymers. The experimental observation is the shift of the totally reversible reduction wave UO 2 2+ +e − ⇌UO 2 + toward more cathodic potentials when the complexing monomer or polymer is added to an uranyl nitrate aqueous solution. This shift is, however, much greater when the polymer is used rather than the monomer, in line with a higher stability of the complexes ( K polymer ≫ K monomer ). A theoretical stability scale of the polymers/UO 2 2+ complexes was compared to an experimental one based on dynamic leaching tests.

Complexation of uranyl ion by polyvinylimidazole: Electrochemical preparation and leaching tests investigations

In this work, we intend to check the claims of an U.S. Patent (Westinghouse E.C.) which describes an original treatment for low level activity radioactive wastes. The process deals with electrochemical preparation of polyvinylimidazole (PVI) which is a polymer capable of complexing uranyl ions. We confirm the complexation of uranyl ions by PVI in various media by FT-IR and UV-Visible analysis but all these complexes were found to be soluble in water so we put forward new complexes with an additional polymer to shape out insoluble complex. Leaching tests demonstrate the efficiency of our process.

Is the external beam PIXE method suitable for determining ancient silver artifact fineness

Abstract In archeometry, the non-destructive characteristic of an analytical method is always very attractive. For most of techniques, besides the need of sampling, difficulties can originate from the shape and the size of the silver artifacts to be analyzed. The external PIXE method should be an answer to this problem but several questions are arising from the implementation of the technique to such a material. The aim of this paper is to specify the experimental procedure as to take into account several parameters, which could induce dramatic errors. Among them it can be pointed out the superficial enrichment in silver, arising from the dissolution of copper and copper oxide, the surface roughness effects, the great importance of the stability of the geometric conditions. The accuracy and the precision of the method are considered within the scope of the results obtained in ancient times by the cupellation with ashbone cupels. In addition, the process involved to obtain silver alloys has been studied in order to define its influence on the real fineness of the objects.

Potentiometric-controlled exchange of actinide and lanthanide cations by electrically conducting polymers based resin

Polypyrrole polystyrene sulfonate resins have been electrochemically synthesized, and the ability of these films to control potentiometrically the exchange of thorium, uranium and lanthanum cations has been studied using electrochenücal and nuclear methods (a counting, RBS). The actual effect of the applied Potential on the exchange process has been demonstrated. The effect of various parameters on the Th cation binding, such as the polymer thickness and the oxidation State of the resin, has also been studied. A low incorporation of uranium has been observed and rationalized by the redox instability of the polymer resin. The reversibility of the Th and La exchange has also been quantified and optimized.

Solvent effect on the electrografting of acrylonitrile on nickel

Abstract The effect of solvent on the reductive electrografting of acrylonitrile (AN) onto nickel cathodes has been studied in dimethylformamide (DMF), a solvent for polyacrylonitrile (PAN), and in non-solvents that include acetonitrile (ACN), propylene carbonate (PC) and pyridine (PY). Electrografting responsible for the cathode inhibition has been observed for the first time in PC and PY. Not only the polymer—solvent interactions but also the intrinsic polarity of the solvent have an effect on the intensity of the inhibition peak which is the signature of the electrografting reaction. Concentration of the monomer in the electrode double layer appears to decrease as the solvent polarity is increased, consistently with a more efficient displacement of the monomer by a more polar compound. That such a competition occurs is also supported by the effect of the nature and concentration of the conducting salt. The best quality films are formed in DMF, which is a solvent for PAN. Quartz microbalance experiments have emphasized the crucial importance of the potential range used for the AN electroreduction, particularly in a solvent of the polymer.