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International Journal of Metalcasting | Year: 2017

Graphite degeneracy in spheroidal graphite cast iron is a common issue faced by foundries. It is generally associated with the presence of so-called poisoning elements and may in some cases be suppressed by the addition of other elements. Mastering these additions is not simple in practice since industrial alloys do generally contain many elements that can affect graphite shape even when present at low or trace levels. In this work, trace and low-level elements are considered in relation with three steps of microstructure formation: (1) nucleation of graphite; (2) growth of graphite; and (3) solid-state transformations. © 2016 American Foundry Society.

Masse J.-P.,ArcelorMittal | Poquillon D.,ENSIACET
Scripta Materialia | Year: 2013

Entangled materials can be manufactured using fibers made from various materials, such as carbon, glass or steel. The mechanical properties of these low-density materials are linked to their architecture (fiber orientation, number of contacts, etc.). Specimens can be produced with and without cross-links between fibers by sintering for steel wool or by using epoxy spraying for carbon or glass fibers. Experimental mechanical compression tests were performed on these materials. The results were analyzed taking into account the architecture thanks to the relationships existing between morphological data and macroscopic mechanical behavior. © 2012 Published by Elsevier Ltd.

Nehme N.,ENSIACET | Mathieu F.,CNRS Chemical Engineering Laboratory | Taillandier P.,ENSIACET
Food Microbiology | Year: 2010

The present study was aimed to evaluate the impact of the co-culture on the output of malolactic fermentation and to further investigate the reasons of the antagonism exerted by yeasts towards bacteria during sequential cultures. The Saccharomyces cerevisiae D strain/Oenococcus oeni X strain combination was tested by applying both sequential culture and co-culture strategies. This pair was chosen amongst others because the malolactic fermentation was particularly difficult to realize during the sequential culture. During this traditional procedure, malolactic fermentation started when alcoholic fermentation was achieved. For the co-culture, both fermentations were conducted together by inoculating yeasts and bacteria into a membrane bioreactor at the same time. Results obtained during the sequential culture and compared to a bacterial control medium, showed that the inhibition exerted by S. cerevisiae D strain in term of decrease of the malic acid consumption rate was mainly due to ethanol (75%) and to a peptidic fraction (25%) having an MW between 5 and 10 kDa. 0.4 g l-1 of l-malic acid was consumed in this case while 3.7 g l-1 was consumed when the co-culture was applied. In addition, there was no risk of increased volatile acidity during the co-culture. Therefore, the co-culture strategy was considered effective for malolactic fermentation with the yeast/bacteria pair studied. © 2009 Elsevier Ltd. All rights reserved.

Vandecandelaere N.,ENSIACET | Rey C.,ENSIACET | Drouet C.,ENSIACET
Journal of Materials Science: Materials in Medicine | Year: 2012

Nanocrystalline apatites are major constituents of hard tissues, and attempts are made worldwide to prepare synthetic analogs. However the impact of synthesis/ postsynthesis parameters is often disregarded. Based on an updated knowledge on such compounds, we inspected the effects of synthesis parameters (maturation time, temperature, pH, nature of counter-ions) and post-treatments (re-immersion in aqueous media, thermal treatment) on physicochemical characteristics. Great modifications were noticed during the 3 first days of maturation, where a progressive evolution of the apatite phase (localized in the core of the nanocrystals) toward stoichiometry was observed at the expense of the non-apatitic surface layer which progressively disappears. Similar trends were also evidenced for maturation run under increasing temperatures, studied here in the range 20-100 °C. pH impacted more specifically the chemical composition. The nature of the counter-ion in the starting phosphate salt influenced composition and nonstoichiometry, depending on its (in)ability to be incorporated in the lattice. Freeze-drying allowed to preserve a high surface reactivity, although further evolutions were noticed after re-immersion. Effects of a thermal treatment of dried samples were unveiled, suggesting a denaturation of the hydrated layer on the nanocrystals. This work underlines the necessity of a good control of synthesis/postsynthesis parameters for the production of biomimetic apatites. © Springer Science+Business Media, LLC 2012.

Carbon | Year: 2012

Carbon nanomaterial-ionic liquid hybrids represent a very interesting class of materials because of their exceptional properties and potential use in a wide range of application fields. Their unique properties, arising from the synergistic combination of both components, can be exploited as elements of electrochemical and energy storage devices, as supports for catalysis and as nanofillers for polymeric composites. Owing to the specific interactions between ionic liquids (ILs) and carbon nanomaterials, the surface properties of the nanomaterials can be modified, leading to their improved dispersion in various media, thus providing an alternative solution to the most fundamental problem in processing of these materials. Since the discovery of bucky gel, the synthesis and processing methods of carbon nanotube-ionic liquid (CNT-IL) hybrids have been extensively studied. This review is aimed at giving an overview of the main synthetic routes and potential applications of CNT-IL hybrids. Graphene has lately emerged as a promising material, and received world-wide attention due to its exceptional properties. The synthesis of graphene-IL hybrids and the role of IL in the exfoliation process of graphene sheets are also discussed along with the potential applications of these new materials. © 2012 Elsevier Ltd. All rights reserved.

Calcium phosphate apatites are inorganic compounds encountered in many different mineralized tissues. Bone mineral, for example, is constituted of nanocrystalline nonstoichiometric apatite, and the production of "analogs" through a variety of methods is frequently reported. In another context, the ability of solid surfaces to favor the nucleation and growth of "bone-like" apatite upon immersion in supersaturated fluids such as SFB is commonly used as one evaluation index of the " bioactivity" of such surfaces. Yet, the compounds or deposits obtained are not always thoroughly characterized, and their apatitic nature is sometimes not firmly assessed by appropriate physicochemical analyses. Of particular importance are the "actual" conditions in which the precipitation takes place. The precipitation of a white solid does not automatically indicate the formation of a "bone-like carbonate apatite layer" as is sometimes too hastily concluded: "all that glitters is not gold." The identification of an apatite phase should be carefully demonstrated by appropriate characterization, preferably using complementary techniques. This review considers the fundamentals of calcium phosphate apatite characterization discussing several techniques: electron microscopy/EDX, XRD, FTIR/Raman spectroscopies, chemical analyses, and solid state NMR. It also underlines frequent problems that should be kept in mind when making "bone-like apatites." © 2013 Christophe Drouet.

Marcelin S.,ENSIACET | Pebere N.,ENSIACET | Regnier S.,Catholic Institute of Toulouse
Electrochimica Acta | Year: 2013

This paper focuses on the characterisation of the electrochemical behaviour of a martensitic stainless steel in 0.1 M NaCl + 0.04 M Na2SO 4 solution and is a part of a study devoted to crevice corrosion resistance of stainless steels. Polarisation curves and electrochemical impedance measurements were obtained for different experimental conditions in bulk electrolyte. X-ray photoelectron spectroscopy (XPS) was used to analyse the passive films. At the corrosion potential, the stainless steel was in the passive state and the corrosion process was controlled by the properties of the passive film formed during air exposure. During immersion in the deaerated solution, the passive film was only slightly modified, whereas it was altered both in composition and thickness during immersion in the aerated solution. After cathodic polarisation of the stainless steel electrode surface, the oxide film was almost totally removed and the surface appeared to be uniformly active for oxygen reduction. The new passive film, formed at the corrosion potential, was enriched with iron species and less protective. Impedance diagrams allowed the characterisation of both the oxide film (high-frequency range) and the charge transfer process (low-frequency range). © 2012 Elsevier Ltd.

ChemCatChem | Year: 2013

The effect of several parameters that include carbon nanotube (CNT) pretreatment and diameter, and the nature of the metal (Co, Ru, Pd), the metal precursor (nitrate, chloride, organometallic complexes), and the solvent on the filling yield of metallic nanoparticles in CNT channels is reported. The obtained results show that it is possible to modulate the filling yield between 10 and 80 % by controlling the CNT opening and playing on the molecular recognition of the inner/outer surfaces by the metal molecular precursor. Interestingly, the best filling yields have been obtained on nitric acid oxidized nanotubes; a treatment often used for the preparation of most CNT-supported metal catalysts. The confined nanoparticles systematically show a smaller particle size than those supported on the external surface. All the prepared samples were tested for the selective hydrogenation of cinnamaldehyde, and clear correlations were established between the catalytic performances and the filling yields. Are you in? Most of the studies that deal with carbon nanotubes (CNTs) for catalysis neglect the possibility of confinement of the active phase in the CNT inner cavity. This study should prompt researchers who study CNT-supported metal catalysts to integrate the possibility of confinement effects to rationalize catalytic results. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Acta Biomaterialia | Year: 2010

This review paper on amorphous calcium phosphates (ACPs) provides an update on several aspects of these compounds which have led to many studies and some controversy since the 1970s, particularly because of the lack of irrefutable proof of the occurrence of an ACP phase in mineralised tissues of vertebrates. The various synthesis routes of ACPs with different compositions are reported and the techniques used to characterise this phase are reviewed. We focus on the various physico-chemical properties of ACPs, especially the reactivity in aqueous media, which have been exploited to prepare bioactive bone substitutes, particularly in the form of coatings and cements for orthopaedic applications and composites for dental applications. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Maury F.,ENSIACET | Duminica F.-D.,ENSIACET
Surface and Coatings Technology | Year: 2010

Titanium oxynitride coatings were deposited on various substrates by an original atmospheric pressure metal organic chemical vapor deposition (MOCVD) process using titanium tetra-iso-propoxide as titanium and oxygen precursors and hydrazine as a nitrogen source. The films composition was monitored by controlling the N2H4 mole fraction in the initial reactive gas phase. The variation of the N content in the films results in significant changes in morphological, structural and mechanical properties. When a large excess of the nitrogen source is used the resulting film contains ca 17 at % of nitrogen and forms dense and amorphous TiOxNy films. Growth rates of these amorphous TiO1.5N0.5 coatings as high as 14μm/h were obtained under atmospheric pressure. The influence of the deposition conditions on the morphology, the structure, the composition and the growth rate of the films is presented. For the particular conditions leading to the growth of amorphous TiO1.5N0.5 coatings, first studies on the mechanical properties of samples grown on stainless steel have revealed a high hardness, a low friction coefficient, and a good wear resistance in unlubricated sliding experiments against alumina which make them very attractive as protective metallurgical coatings. © 2010 Elsevier B.V.

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