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Mohamud S.,College of William and Mary | Ta Phuoc V.,University of Tours | Del Campo L.,CEMHTI Conditions Extremes et Materiaux Haute Temperature et Irradiation | Massa N.E.,National University of La Plata | Pagola S.,College of William and Mary
Synthetic Metals | Year: 2016

TTF-DDQ (DDQ = 2,3-dichloro-5,6-dicyano-p-benzoquinone) is an ionic and diamagnetic charge transfer salt. Polycrystalline powders of TTF-DDQ were obtained by three synthetic methods: solvent evaporation from MeCN solution (1), MeCN vapor digestion (2), and mechanochemistry (liquid assisted grinding with DMSO) (3). The analysis of the synchrotron X-ray powder diffraction data of 1 afforded the crystal structure, which is isomorphous to that of the black polymorph of TTF-CA (CA = chloranil). TTF-DDQ is composed of (TTF+•)2 and (DDQ-•)2 dimeric radical ions arranged in segregated columnar stacks, linked by weak hydrogen bonds. The -Cl and -CN substituents in DDQ are disordered, and this was modeled by Rietveld analysis. The FT-IR absorption spectra as a function of the temperature in the 300-10 K interval showed an absorption edge, indicating that TTF-DDQ is a semiconductor with a small band gap of (0.21 ± 0.01) eV. The monotonous evolution of the FT-IR spectra denotes the absence of crystallographic phase transitions in the temperature interval studied, likely due to the thermodynamic stability of this packing motif compared to the less stable donor-acceptor alternating stacks; or the segregated, potentially conducting stacks. © 2016 Elsevier B.V. All rights reserved.


Poirier J.,CEMHTI Conditions Extremes et Materiaux Haute Temperature et Irradiation | Poirier J.,Ecole Polytechnique - Palaiseau | Prigent P.,TRB | Bouchetou M.-L.,CEMHTI Conditions Extremes et Materiaux Haute Temperature et Irradiation | Bouchetou M.-L.,Ecole Polytechnique - Palaiseau
Revue de Metallurgie. Cahiers D'Informations Techniques | Year: 2013

Refractory castables containing alumina-magnesia/self-forming spinel (MgAl2O4) are used in impact pads of steel ladles in steelmaking processes. In order to understand the wear mechanisms of refractory materials, several recipes were tested from a corrosion, slag resistance and thermal shock point of view. The results show that the corrosion is extremely limited at the slag/refractory interface for all cases. Nevertheless, for higher cement alumina content castables, the formation of cracks is observed in refractory castables into which slag can penetrate. The slag reacts with the alumina to form a new phase such as hibonite (CA6) and calcium dialuminate (CA2). The volumetric change of these reactions involving CA2 and CA6 lead to the apparition of macro-cracks. Thus, the penetration of slag and steel are increased, causing hot mechanical properties to degrade. For lower cement alumina castables, the formation of micro-cracks is avoided by controlling volume expansion. Thus, the slag deposit reacts with alumina grains and the matrix at the slag/refractory interface to produce a monomineral layer of hibonite. In this way, the monomineral layer acts as a barrier and limits the penetration of slag and steel into the refractory lining. Thus, to increase the lifetime of refractory castables containing alumina-magnesia/self-forming spinel, it is advised to control volume expansion in order to avoid the formation of cracks and limit the penetration of secondary metallurgy steel ladle slag. © EDP Sciences 2014.


Bourgel C.,CEMHTI Conditions Extremes et Materiaux Haute Temperature et Irradiation | Poirier J.,CEMHTI Conditions Extremes et Materiaux Haute Temperature et Irradiation | Defoort F.,CEA Grenoble | Seiler,CEA Grenoble | Peregrina C.,CIRSEE
Ceramic Transactions | Year: 2011

The context of the present study relates to the gasification of dried sludge under high temperature. The aim of this work is to shed new light on the impacts of sludge ashes in gasification process. The purification sludge can contain up to 50% of inorganic matter. The objective of this study is to understand the role of these inorganics during the heating. Several techniques are used to solve this problem. First, using thermodynamic calculations (Factsage®) the evolution of the volatility of the inorganics is observed and the condensed phases formed during the heat treatment are determined. The simulations are done under atmospheric pressure condition, from 500 to 1500°C. Second, to compare with the calculus, an XRD and XRF in situ measurement experiment is developed in the CEMHTI Laboratory in order to determine which species volatilize. The major inorganic elements of the sludge are Si, Al, Fe, P and Ca. The calculations allow us to determine the formed gases, and the condensed phases during heat treatment. The major formed gases are CO, H2, H2O, CO2, CH4 and N 2. The minor formed gases are H2S, COS, HF, HCl and NH3. On the contrary, Na, K, Fe and P elements don't volatilize entirely during the heating. Indeed, they are found in the condensed phases formed of sodium and potassium alumino-silicate, iron silicate and calcium phosphate. Finally, these results will be confronted to the experimental measurements.


Prigent P.,CEMHTI Conditions Extremes et Materiaux Haute Temperature et Irradiation | Prigent P.,Ecole Polytechnique - Palaiseau | Berjonneau J.,CEMHTI Conditions Extremes et Materiaux Haute Temperature et Irradiation | Bouchetou M.-L.,CEMHTI Conditions Extremes et Materiaux Haute Temperature et Irradiation | And 3 more authors.
Industrial Ceramics | Year: 2010

Refractory castables containing alumina-magnesia/self-forming spinel (MgAl2O4) are used in impact pads of steel ladles in steeimaking processes. In order to understand the wear mechanisms of refractory materials, several recipes were tested from a corrosion, slag resistance and thermal shock point of view. The results show that the corrosion is extremely limited at the interface slag/refractory for all cases. Nevertheless, for higher cement alumina content castables, the formation of micro cracks is observed in refractory castables into which slag deposit can penetrate. The slag reacts with alumina to form anew phase such as hibonite (CA6) and calcium dialuminate (CA2). The expansive reactions involving CA2 and G46 lead to macro-cracks. Thus, the penetration of slag and steel are increased causing hot mechanical properties to degrade. For lower cement alumina castables, the formation of micro cracks is avoided by controlling volume expansion. Thus, the slag deposit reacts with alumina grains and the matrix at the slag/refractory interface to produce a monomineral layer of hibonite. In this way, the monomineral layer acts as a barrier and limits the penetration of slag and steel into the refractory lining. Thus, to increase the life time of refractory castables containingalumina-magnesia/self-formingspinel, it is advisable to control volume expansion in order to avoid the formation of cracks and to limit the penetration of secondary metallurgy steel ladle slag.

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