Pascale Guigue

Bio: Pascale Guigue is an academic researcher from Centre National D'Etudes Spatiales. The author has contributed to research in topics: Temperature cycling & Aluminium alloy. The author has an hindex of 8, co-authored 19 publications receiving 201 citations.

Mechanical behavior of black anodic films on 7175 aluminium alloy for space applications

Abstract: Because of their low outgassing and their thermo-optical properties, black anodized aluminium parts are often used near optical instruments to manage thermal control in space applications. However, critical cases of flaking of the film were observed after simulated thermal ageing. To understand the mechanisms leading to flaking, the influence of the initial porosity of the film on its mechanical behavior during and after the black anodizing process has been investigated. The decrease of limit tensile stress with the porosity, the coloring and the sealing combined to thermal stresses due to the difference of thermal expansion coefficients between film and substrate have been shown to cause crazing in particular conditions. For high initial porosity films, thermal cycling ageing has a detrimental influence on the adhesion measured by scratch-testing. Numerical simulation has been used to simulate the combined effects of thermal stresses and film cracking on the stress field at the interface.

Investigations into the coefficient of thermal expansion of porous films prepared on AA7175 T7351 by anodizing in sulphuric acid electrolyte

Abstract: The aim of this study was to investigate the Coefficient of Thermal Expansion (CTE) of anodic films on 7175 T7351 aluminium alloy and to evaluate the influence of the film characteristics on this value. In particular, effects of porosity and post-treatments, such as coloring and sealing, were studied. Beam bending analysis was used as the experimental method and a numerical finite element model was developed to verify theoretical relationships hypotheses. The values determined and the choice of experimental method were then validated by comparing the experimental cracking temperature of anodic films with a theoretical value directly depending on the previously determined CTE.

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...

On conversion coating treatments to replace chromating for Al alloys: Recent developments and possible future directions

Abstract: Anticorrosive protection of Al alloys still depends heavily on the use of chromates, which are widely and universally employed as chromate conversion coating and chromic acid anodising pretreatments. The replacement of chromate based treatments with more environmentally compliant processes and materials has been identified as a high priority. The aim of this paper is to review the most recent developments in the application of common inorganic protection layers based on conversion coatings for Al alloys. The review lists and discusses the majority of conversion coatings, including those formed through anodisation, on Al alloys as potential replacements to the most widely used treatments based on chromate chemistry.

PEO Coatings with Active Protection Based on In-Situ Formed LDH-Nanocontainers

Abstract: In the present work, for the first time Zn-Al layered double hydroxide (LDH) nanocontainers were grown in-situ on the surface and in the pores of plasma electrolytic oxidation (PEO) layer and then loaded with a corrosion inhibitor to provide an active protection. The developed LDHbased conversion process ensures partial sealing of the pores and provides an effective corrosion inhibition on demand leading to increased fault-tolerance and self-healing properties. The structure, morphology and composition of the LDH-sealed PEO coatings on 2024 aluminum alloy were investigated using SEM, TEM/FIB, XRD and GDOES. Electrochemical impedance spectroscopy and scanning vibrating electrode techniques show a remarkable increase in the corrosion resistance and fault tolerance when PEO coating is sealed with a LDH-inhibitor

Preparation of black high absorbance and high emissivity thermal control coating on Ti alloy by plasma electrolytic oxidation

Abstract: It is of great significance for the research of thermal control coatings on Ti alloys due to their wide applications in aerospace and satellites and many other fields. In this work, black thermal control coatings were prepared on Ti–6Al–4V alloy by plasma electrolytic oxidation (PEO) technique. The coatings were characterized by SEM, EDS and XRD, respectively. The thermal control properties (solar absorbance, αS and emissivity, e) were investigated by ultraviolet–visible-near infrared spectrophotometer instrument and solar absorption reflectometer. Meantime, the thermal shock properties of the coated samples were investigated as well. The results show that the ceramic coatings are black and porous and the elements such as Fe, Co and Ni and W from the electrolyte incorporate into the coating and exist in the form of an amorphous state. The coatings are of high emissivity and high absorbance character, which are influenced by the doping of Na2WO4 and the PEO time. Increasing the concentration of Na2WO4, αS increases firstly and then remains constant while e increases gradually. Extending PEO time, both αS and e increase. The annealing treatment reduces the solar absorbance greatly, but does not influence the emissivity apparently, which may be due to the improvement of the crystallization of the coating. When the dosage of Na2WO4 is 7.5 g/L and the reaction time is 25 min, the best coating is obtained with αS and e of 0.93 and 0.88, respectively. This work not only provides an effective method to prepare thermal control coating for Ti alloys as the engineering materials, but also expands the application range of PEO technique in the fields of functional coatings.

Influence of hydrogen bonds on glass transition and dielectric relaxations of cellulose

Abstract: The molecular dynamics in hydrated cellulose has been investigated by a combination of thermal analyses and dielectric spectroscopy. Differential scanning calorimetry shows the dependence upon hydration of the glass transition temperature Tg. A physical ageing phenomenon has been observed. At the molecular scale, bound water is hydrogen bonded to polar sites of cellulose macromolecules. At the macroscopic scale, water molecules play the role of a plasticizer for cellulose lowering its Tg. Dynamic dielectric spectroscopy combined with thermostimulated currents have allowed us to follow more localized molecular mobility. The β relaxation mode is characterized by activation entropies that vanish for higher water contents indicating molecular mobility localization. It is plasticized by water like the glass transition. This analogy is explained by a common origin of both mechanisms: the mobility of the cellulose backbone. The evolution of the γ mode upon hydration follows an anti-compensation law. Water acts as an anti-plasticizer in a hydrogen bonded network.