Evelyne Darque-Ceretti

Structure and physicochemistry of anodic oxide films on titanium and TA6V alloy

Anodization of titanium and its alloys is an important surface treatment, especially for adhesion applications, but is not as well studied as for aluminium alloys. This paper deals with the morphological, structural and physicochemical characterization of anodic oxide films grown on titanium and Ti–6Al–4V (TA6V) in chromic acid solution without (CA) or with (CA/HF) hydrofluoric acid addition. Several investigations methods are used: high-resolution scanning electron microscopy (HR-SEM), reflection high-energy electron diffraction (RHEED), x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), nuclear reaction analysis (NRA) and wetting angle measurements. The occurrence and morphology of the nanoporous structure for CA/HF anodization are described. The compact films grown in CA solution are amorphous and the porous films grown in the CA/HF solution are partially crystalline. The thickness and morphology of the films are described and discussed as a function of the anodizing conditions and of the composition of the underlying substrate. The composition of the film appears to be TiO2+Al2O3 (with Ti/Al atomic ratio ∽5), with incorporation of fluorine from the solution in the porous films and of small quantities of vanadium in the films that are grown. The specific role played by the Cr(VI) and F species on the film growth-and-dissolution formation process is discussed and a growth mechanism is proposed. Copyright

Anodic oxidation of titanium and TA6V alloy in chromic media. An electrochemical approach

In order to optimise anodisation surface treatment of titanium alloys, the electrochemical conditions of anodic oxidation of pure titanium and of a TA6V (Ti-6% Al-4% V) alloy were investigated. Both voltametric (potentio-dynamic) and chrono-amperometric (constant voltage, either applied directly or progressively increased during the first steps of the treatment) experiments are conducted. The electrolyte is a chromic acid (CA) (0.5 mol l−1 Cr2O3) solution with and without hydrofluoric acid (HF) addition (9.5×10−2 mol l−1). A thin oxide compact film is formed in CA electrolyte and a duplex film composed of a compact layer surmounted by a columnar porous layer grows from the fluorinated electrolyte. The voltametric results indicate a breakdown of the compact film (in non-fluorinated medium) for potential around 3 V/SCE, and a strong influence of the alloying elements of TA6V on the formation of porous films in fluorinated medium. The chrono-amperometric measurements reveal a complex growth process of the porous film, in which the residual current participates in the thickening of both compact and porous layers of the film. The overall electrochemical efficiency is small and decreases with the treatment time. A growth mechanism involving a poisoning (by CrVI-containing ions) and antidote (by F-containing species) competition is proposed.

Influence of additives segregation on surface composition of automotive coatings: effects of an ethanol cleaning

Abstract The automotive topcoat is constituted of a pigmented basecoat, covered by a transparent and shiny clearcoat. This layer protects the basecoat from the environment damage and determines the paint appearance. For white plain colour, the basecoat/clearcoat system is replaced by a layer of lacquer. The surface analyses are used to determine the influence of the topcoat composition on the adhesion of pressure-sensitive adhesives. X-ray photoelectron spectroscopy (XPS) and secondary ions mass spectrometry (ToF-SIMS) study the automotive topcoats chemistries. These analyses point out that polysiloxane additives are detected on the clearcoats but not on the lacquers. The impact of the different additives families (anti-UV agents and surface levelling additives) on the topcoat surface chemistry is identified. Moreover, the aluminium pigments do not appear on the metallic basecoat surface because of a siloxane additives layer, which also covers the polyester–polyurethane network. XPS studies on the basecoats covered by a clearcoat formulated without additive bring to the fore that the basecoat siloxane additives segregate towards the clearcoat/air interface during the curing process. The clearcoats additives can be removed with an ethanol cleaning according to the XPS analyses but this solvent cleaning is not able to remove all the additives from the basecoat surface, which seem to be partly cross-linked with the basecoat polyurethane network.

An Investigation of Gold/Ceramic and Gold/Glass Interfaces

This paper describes how various characterisation methods can be used to investigate the physicochemical and spectral properties of gold films in contact with glass or ceramic. The interface between the metal and substrate has been given special attention. The examples chosen to illustrate this include: liquid gold films (decorated and fired) or inlayed gold layers on ceramic wares and “sandwich” gold foils between two glass sheets for mosaic application. Characterisation methods include: microanalytical scanning electron microscopy, X-ray diffraction, ion beam analyses (PIXE: particle induced X-ray emission; RBS: Rutherford back-scattering spectrometry), photo-spectrometry and colorimetry. The adhesion mechanism and colour behaviour of the coated objects is discussed.

Gold like lustre: nanometric surface treatment for decoration of glazed ceramics in ancient Islam, Moresque Spain and Renaissance Italy

Abstract Lustre is one of the most fascinating surface decorative effects produced on glazed ceramics. This technique seems to have been born in the ninth century in factories created by the Arabs during their conquests in the Orient (Mesopotamia, Egypt and Persia). Arab potters spread their knowhow all over the Mediterranean basin, especially Spain. Italian Renaissance potters succeeded in applying it to their production. The technique is based on a specific firing of the glazed pottery in a reducing atmosphere in the presence of metallic salts. The result is a surface layer with a metallic appearance, exhibiting various colours, from gold to brown or red. This paper provides the chemical nature and the physical structure of ancient gold like lustre layers and compares them with contemporary lustres produced by a Spanish craftsman reproducing the traditional Islamic techniques. Various analytical investigations (atomic force microscopy, high resolution SEM, particle induced X-ray emission, Rutherford backscattering, TEM, X-ray induced photoelectron spectroscopy, time of flight SIMS and grazing X-ray diffraction) were carried out as well as investigations into the coloured appearance by spectrophotometry. The results show that the lustre layer consists of silver and copper particles of nanometric dimensions dispersed in a glassy matrix. A model of the lustre formation is proposed wherein the development of a new superficial glaze is described. Comparison between ancient and modern production shows how the techniques have varied through the ages.

Physico-chemical characterisation of native air-formed oxide films on Al-Mg alloys at low temperature. Influence of water

Natural oxide films on two cold-rolled Al-Mg alloys were studied using several techniques (XPS, SIMS, ToF-SIMS, GDOS, SEM, TEM, Wetting measurements). The aim was to characterise and compare the oxide layers formed on the two materials in order to better understand the influence of the thermomechanical history. The experimental tools used allowed the determination of the influence of the annealing process on the nature and structure of the oxides. The hydration and Brönsted behaviour were also investigated. The thickness of the layer, the amount of magnesium oxide and its dissolving resistance in water are strongly modified by the annealing. The oxide film formed on the annealed material is twice as thick as the one on the non-reheated material. The layer on the annealed material contains more magnesium oxide and contains the crystalline forms:β-Al2O3 and bayerite (Al(OH)3). On the contrary, the oxide film formed on the as-rolled material seems to be amorphous. The magnesium oxide is less soluble in water in the annealed film than in the non-reheated one. Furthermore, aluminium and magnesium oxides were found to be hydroxylated on both alloys, and the layer surfaces to behave like a Brönsted meaning base.

Correlation between Lewis donor/acceptor properties determined by XPS and Brnsted acid/base properties determined by rest-potential measurements, for aluminium and silicon oxides

In order to qualify the reactivity of various aluminium and silicon oxide substrates for elastomer adhesion applications, X-ray photoelectron spectroscopy (XPS) and rest-electrochemical potential measurements have been performed on those surfaces. The interpretation of XPS binding energy shift measurements in terms of Fermi level variation from one surface to another, as proposed by Mullins and Averbach in 1988, is discussed in view of results on an aluminosilicate compound surface. The correlation with electrochemical restpotential measurements on an anodized aluminium surface and a silane coupling agent is described and discussed. The possibility of surface reactivity assessment through correlated XPS and electrochemical measurements for metal oxides is demonstrated.

Adhesion of pressure-sensitive adhesives to automotive coatings: influence of topcoat composition

This study characterizes the influence of automotive coating composition on the adhesion of pressure-sensitive adhesives (PSA). Automotive topcoats are generally constituted of a basecoat/clearcoat system, but a layer of lacquer is used for white colour coating. X-ray Photoelectron Spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS) are used to study the topcoat surface composition. Siloxane additives are detected on the clearcoat surface but not on the lacquer surface. Peel tests show that the adhesion of PSA to the lacquer is higher than to the clearcoat. Moreover, study of clearcoat formulated without additives confirms that the siloxane additives are unfavourable to the adhesion of PSA. When the PSA is peeled from a clearcoat, analyses of failure surfaces indicate that the failure seems to propagate within the PSA near the interface. On the contrary, the failure seems to propagate within the bulk of the lacquer during peeling. This difference is explained by XPS analysis of lacquer: the outermost surface is constituted of a layer of oxygenated unidentified compounds, which are detected on the failure surface of PSA. Chemical bonds between these compounds and the lacquer network seem to be weaker than the bonds between these compounds and the PSA. Analyses point out that the ethanol cleaning can remove the additives from the topcoat surface and improve considerably the adhesion to the clearcoat. If the topcoat is cleaned before applying the PSA, the failure propagates deeper within the PSA than if the topcoat is not cleaned.

Gilding of cultural heritage artefacts: an elaborated technology

Abstract Gilding has been used to decorate, one may say sublimate, the surface appearance of artworks since the beginning of gold use in art. Gold foils and leaves were used first, thanks to the high ductility of that metal, and the progress of gilding art through centuries has been linked to: (1) the evolution of the thickness of the gold film used for the process; (2) the continuous research for efficient adhesive materials adapted to the various substrates; and (3) the development of techniques of direct adhesion of the gold coating, especially on metals. This paper, based on recent laboratory results obtained through laboratory studies of various museum artworks, discusses these three aspects. First, it shall develop a mechanical modelling of gold leaf beating. Second, it shall detail the properties of the main classes of adhesive materials used for leaf gilding on various materials. Finally, the importance of the diffusion phenomena at the interface between a metal substrate and a gold coating shall be discussed, especially in the case of gilding involving a high temperature treatment.

Numerical and experimental analyses of a fracture mechanics test for adhesively bonded joints

The use of a fracture mechanics test to evaluate the joint strength through the determination of the strain energy release rate G is nowadays well established. The joint strength for fluorinated polymer (PVDF) sheets bonded with an epoxy adhesive was studied using a double cantilever beam (DCB). In order to obtain small-scale yielding, the adhesive joint of the polymer specimens was strengthened by steel sheets. Pre-cracks were initiated at the center of the bond thickness separating the two PVDF surfaces, with nominal lengths ranging from 5 to 27.5 mm. We did not measure the evolution of the crack length, which is generally very difficult to obtain with good precision. The measurement of the load-point displacement was used instead. The opening load versus this load-point displacement was recorded. The slope of the first part of this curve gives the value of the initial stiffness of the joint specimen. The stiffness of the various specimens enables us to access the real experimental initial crack length,...