Claire Tonon

Bio: Claire Tonon is an academic researcher from Airbus Defence and Space. The author has contributed to research in topics: Silicone & Elastomer. The author has an hindex of 7, co-authored 13 publications receiving 144 citations.

Degradation of the optical properties of ZnO-based thermal control coatings in simulated space environment

Abstract: Optical absorption and photoluminescence spectroscopy have been used to investigate the physical changes induced by proton and electron irradiation in selected thermal control coatings. This study focused on a white paint and on its two components, a polydimethylsiloxane resin and zinc oxide powder. Samples were irradiated by either 45 keV protons (fluence up to 1016 protons cm-2) or 400 keV electrons (fluence up to 6×1015 electrons cm-2). In situ reflectance measurements were made during the test and were complemented after air introduction by photoluminescence characterization. The optical properties of the paint are essentially those of the ZnO pigment. The optical degradation of the material appears to be correlated with the density of defects created by ionization in a zone close to the surface of the paint and called the optical thickness of the material. Two degradation regions of the reflectance properties in the wavelength range 250-2500 nm have been identified: one in the infrared and one in the visible blue region. The degradation in the IR region disappears on exposure to air so that no complementary technique could be used for identifying its origin. The point defects responsible for the optical degradation of the paint in the blue region are singly ionized oxygen vacancies (F+ centres) either initially present in the material or induced by irradiation. Irradiation quenches the green photoluminescence emission. The latter would be excited by the recombination of doubly ionized oxygen vacancies with photoformed electrons of the conduction band.

Electrical behaviour of a silicone elastomer under simulated space environment

Abstract: The electrical behavior of a space-used silicone elastomer was characterized using surface potential decay and dynamic dielectric spectroscopy techniques. In both cases, the dielectric manifestation of the glass transition (dipole orientation) and a charge transport phenomenon were observed. An unexpected linear increase of the surface potential with temperature was observed around Tg in thermally-stimulated potential decay experiments, due to molecular mobility limiting dipolar orientation in one hand, and 3D thermal expansion reducing the materials capacitance in the other hand. At higher temperatures, the charge transport process, believed to be thermally activated electron hopping with an activation energy of about 0.4 eV, was studied with and without the silica and iron oxide fillers present in the commercial material. These fillers were found to play a preponderant role in the low-frequency electrical conductivity of this silicone elastomer, probably through a Maxwell–Wagner–Sillars relaxation phenomenon.

Correlation between sub‐Tg relaxation processes and mechanical behavior for different hydrothermal ageing conditions in epoxy assemblies

Abstract: The aim of this study is to understand aging phenomena by monitoring physical parameters after real and simulated aging experiments. This study focuses on aluminum-epoxy assemblies, which are commonly used on spacecraft structures. Different samples are submitted to simulated aging tests. Influence of temperature and moisture is analyzed. Evolution with aging is characterized at two different scales. The macroscopic behavior of the assemblies is studied by single lap shear test. A decrease in the shear rupture stress is observed with increasing temperature and relative humidity. It is demonstrated that temperature has more important influence. The molecular behavior in the adhesive joint is studied by dynamic dielectric spectroscopy measurements. This experiment gives access to molecular mobility in the adhesive. Dipolar entities are identified as evolving with aging conditions. The temperature is more effective than moisture at this scale. An interpretation of the molecular mobility before and after aging shows that water is an important parameter of this study. A link between mechanical and molecular behavior with hydrothermal aging is found. The decrease of mechanical properties occurs while failures become interfacial. In the same time, the interactions between hydroxyether and water increase. The evolution of the macroscopic behavior of the bonded assemblies is due to this combination observed at different scales. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Basic properties of the F-type centers in halides, oxides and perovskites

Abstract: We present a short survey of the optical properties of primary radiation-induced point defects in alkali halides, simple oxides and some ABO3 perovskites. We discuss in details the optical properties of single electron F and F + centers in rock-salt (f.c.c.) alkali halides and oxides and show that the Mollwo–Ivey law well-known for the F-type centers in alkali halides may be extended for other rock-salt structure insulators. We also discuss the major differences in point defect production mechanisms in halides and oxides. We show that the Rabin–Klick diagram may be generalized for a whole family of alkali halides. The F-type center migration and aggregation into metal colloids in alkali halides and oxides is also discussed.

Design and ageing of adhesives for structural adhesive bonding - A review

Abstract: This review outlines some of the issues which have to be addressed when selecting an adhesive for a particular structural adhesive bonding application. The designer may find that a number of adhesi...

Impurity Conduction at Low Concentrations.

Abstract: The conductivity of an $n$-type semiconductor has been calculated in the region of low-temperature $T$ and low impurity concentration ${n}_{D}$. The model is that of phonon-induced electron hopping from donor site to donor site where a fraction $K$ of the sites is vacant due to compensation. To first order in the electric field, the solution to the steady-state and current equations is shown to be equivalent to the solution of a linear resistance network. The network resistance is evaluated and the result shows that the $T$ dependence of the resistivity is $\ensuremath{\rho}\ensuremath{\propto}\mathrm{exp}(\frac{{\ensuremath{\epsilon}}_{3}}{\mathrm{kT}})$. For small $K$, ${\ensuremath{\epsilon}}_{3}=(\frac{{e}^{2}}{{\ensuremath{\kappa}}_{0}}){(\frac{4\ensuremath{\pi}{n}_{D}}{3})}^{\frac{1}{3}}(1\ensuremath{-}1.35{K}^{\frac{1}{3}})$, where ${\ensuremath{\kappa}}_{0}$ is the dielectric constant. At higher $K$, ${\ensuremath{\epsilon}}_{3}$ and $\ensuremath{\rho}$ attain a minimum near $K=0.5$. The dependence on ${n}_{D}$ is extracted; the agreement of the latter and of ${\ensuremath{\epsilon}}_{3}$ with experiment is satisfactory. The magnitude of $\ensuremath{\rho}$ is in fair agreement with experiment. The influence of excited donor states on $\ensuremath{\rho}$ is discussed.

Tuning of ZnO 1D nanostructures by atomic layer deposition and electrospinning for optical gas sensor applications.

Abstract: We explored for the first time the ability of a three-dimensional polyacrylonitrile/ZnO material—prepared by a combination of electrospinning and atomic layer deposition (ALD) as a new material with a large surface area—to enhance the performance of optical sensors for volatile organic compound (VOC) detection. The photoluminescence (PL) peak intensity of these one-dimensional nanostructures has been enhanced by a factor of 2000 compared to a flat Si substrate. In addition, a phase transition of the ZnO ALD coating from amorphous to crystalline has been observed due to the properties of a polyacrylonitrile nanofiber template: surface strain, roughness, and an increased number of nucleation sites in comparison with a flat Si substrate. The greatly improved PL performance of these nanostructured surfaces could produce exciting materials for implantation in VOC optical sensor applications.