Preface: Cultivating uncertainty

This themed section explores situations of interactional uncertainty, namely contexts in which the grounds of an interaction cannot be taken for granted. How to be sure, for instance, that a barbed comment is only intended to tease and is not really meant to be offensive? In the same vein, how are we to deal with “white lies” and other strategic dissimulations in flirtatious relationships? And how can we ever be sure that a benign handshake does not in fact hide malevolent intentions? These are some of the issues the contributors address in this volume. . . . All the essays gathered here deal with opaque situations that generate uncertainty from the participants’ points of view. . . . First, several authors show that interactional uncertainty is not always reducible to accidental misunderstandings, but can also be a constitutive or “built-in” element of various social settings. Second, many contributions refuse to consider uncertainty exclusively as a problem to be faced and solved. They show not only how social agents navigate through opaque interactions, but also how they deal with opacity as a social resource enabling them to negotiate or even create relationships. In brief, they stress the productivity of uncertainty at the heart of human sociality. -Excerpt from the preface  

Manganese Dioxides Surface Properties Studied by XPS and Gas Adsorption

Structurally well defined g-MnO2 in terms of Pr and Tw were studied using X-ray photoelectron spectroscopy ~XPS! to complete surface investigations performed by high-resolution gas adsorption, water adsorption, and acid-base surface titration. The O 1s and Mn 2p spectra were deconvoluted into three components Mn-OH2 1 , Mn-OH, and Mn-O2. Analysis of the O 1s spectra in energy shift and relative intensity shows that 70 to 80% of the surface groups stay as neutral OH, 5% as Mn-OH2 and 20 to 30% as Mn-OH: their relative amount varies with Pr as well as PZC, water cross-sectional area and energetic constant C. Mn 2p spectra are far less sensitive than O 1s to the charge variation. Nevertheless a correlation is shown between the relative amount of surface species, the binding energy of Mn 5 O and O 5 Mn species and Tw

Huge Instability of Pt/C Catalysts in Alkaline Medium

International audienceThe stability of carbon-supported electrocatalysts has been largely investigated in acidic electrolytes, but the literature is much scarcer regarding similar stability studies in alkaline medium. Herein, the degradation of Vulcan XC-72-supported platinum nanoparticles (noted Pt/C), a state-of-the-art proton exchange membrane fuel cell electrocatalyst, is investigated in alkaline medium by combining electrochemical measurements and identical location transmission electron microscopy; electrochemical surface area (ECSA) losses were bridged to electrocatalyst morphological changes. The results demonstrate that the degradation in 0.1 M NaOH at 25 degrees C is severe (60% of ECSA loss after only 150 cycles between 0.1 and 1.23 V vs RHE), which is about 3 times worse than in acidic media for this soft accelerated stress test. Severe carbon corrosion has been ruled out according to Raman spectroscopy and X-ray photoelectron spectroscopy measurements, and it seems that the chemistry of the carbon support (in particular, the interface (chemical bounding)) between the Pt nanoparticles and their carbon substrate does play a significant role in the observed degradations

Natural superhydrophilicity of sol-gel derived SiO2-TiO2 composite films

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The photocatalytic activity of sol-gel derived photo-platinized TiO2 films

Sol–gel TiO2 thin films have been loaded with platinum clusters through a photo-platinization method using water/ethanol platinum solutions. The morphological and physico-chemical properties of platinized films as well as the chemical state of platinum clusters have been studied by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. These characterizations show that morphological and physico-chemical properties are strongly influenced by the water/ethanol composition of the platinum solution and temperature of the post-platinization heat-treatment, which in turn determines the photocatalytic performances of platinized films. UV-assisted photocatalytic reactions induced by platinized films follow bi-regime kinetics. The first regime is characterized by a rather high rate constant, while long term UV exposition promotes a more or less pronounced deceleration of the photocatalytic reaction. Optimization of the photocatalytic activity requires a platinization in presence of a water excess followed by a heat-treatment in the 250–400 °C thermal range. Films processed in such conditions exhibit rate constants in the first and second photocatalysis regime which are four times and three times greater, respectively, than the rate constant measured for non-platinized films

Laser powder bed fusion spatters of Zr-Cu-Al-Nb metallic glass

International audienceUnderstanding the morphology, composition and structural changes experienced by metallic glass powder particles upon laser powder bed fusion (LPBF) is the first step towards evaluating the impact of spatter generation on part quality and on feedstock degradation. This study presents the characterization of Zr-Cu-Al-Nb spatter particles by means of scanning and transmission electron microscopy with automated crystallographic orientation mapping and energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. The powder exposed to the LPBF environment exhibits an average surface composition similar to the original feedstock, but with a rougher morphology. The typical spatter encountered in the remaining lack-of-fusion is a vapour-entrained particle, which probably underwent partial melting leading to the formation of α-Zr(O) dendrites, and "bigcube" Cu 2 Zr 4 O nanocrystals in its heat affected zone. In the present work, spatter characteristics are discussed considering glass properties and their connection to lack-of-fusion defects is addressed

Ar-implantation on AISI 304 stainless steel against pit initiation processes

Ion implantation has been widely used as a surface modification technique to improve surface properties. However, a few works have been performed using argon as implanted element in order to modify the corrosion behaviour of stainless steels (SS). In the present study, the implanted ion was Ar+ at an energy of 80 keV and the implanted dose was in the range of 1 × 1015 to 1 × 1017 Ar+/cm2 in an AISI 304 stainless steel. The surface bombardment with inert gases mainly produces structural changes, modifying topography and morphology. Nevertheless, the surface analysis carried out by X-ray Photoelectron Spectroscopy (XPS) shows that Ar-implantation modifies the surface composition of the passive layer and, therefore, the protective properties of the SS. In order to measure these modifications on the corrosion behaviour, electrochemical noise tests at open circuit potential were performed. The results obtained show that Ar-implantation decrease the corrosion resistance of AISI 304 SS and this effect is more important with the increasing implantation dose

Photocatalytic activity and photo-induced superhydrophilicity of sol-gel derived TiO2 films

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Photo-induced hydrophilicity of TiO2 films deposited on stainless steel via sol-gel technique

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Benefits and limitations of Pt nanoparticles supported on highly porous antimony-doped tin dioxide aerogel as alternative cathode material for proton-exchange membrane fuel cells

International audienceAn electron-conducting metal-oxide substrate must fulfill three criteria to represent a viable alternative to conventional carbon blacks used as supports for Pt-based nanoparticles in proton-exchange membrane fuel cell (PEMFC): (i) be electron-conducting, (ii) be corrosion resistant and (iii) possess an opened porous structure compatible with facile ionomer insertion and efficient mass-transport properties. Using a sol-gel route, antimony-doped tin dioxide (Sb-doped SnO2, ATO) aerogels with such characteristics were synthesized: an optimal Sb content of 10 at.% was found in terms of specific surface area and electrical conductivity. Pt nanoparticles were loaded onto 10 at.% Sb-doped SnO2 (Pt/ATO), undoped SnO2 (Pt/SnO2) and Vulcan XC72 (Pt/C) via a modified polyol route, and their electrocatalytic activity for the oxygen reduction reaction (ORR) was evaluated. A 2-fold enhancement in ORR specific activity was measured on Pt/ATO over Pt/C. An accelerated stress test (AST) protocol, mimicking start-up/shutdown events in a PEMFC, was used to determine the long-term ORR performance of the Pt/ATO and the reference Pt/C electrocatalysts. The carbon support was not robust enough in these harsh conditions, as observed from the massive detachment of Pt nanoparticles from Vulcan XC72. On the contrary, the Pt nanoparticles did not detach from the ATO support. However, a core@shell structure with a Sb-poor surface covering a core featuring a Sb content close to the nominal formed during the AST. This core@shell structure restricted the capacity of the Pt nanoparticles to exchange electrons, as evidenced by the attenuated Pt surface oxide formation/reduction features, and led to decreased catalytic activity for the ORR