Fields of Competences and Know-how

Elaboration

· Sol-gel synthesis

Specific sol-gel processes are adapted and applied to synthesize various nanostructured materials. Both inorganic and organic systems are investigated. The inorganic way is mainly focused on silica (SiO2) while the organic part ranges from Resorcinol-Formol (RF) and Melamine-Formol (MF) compounds to Polyurethane (PU).

Hydrolysis and polycondensation of organosilicates [US Patent n° 5795557] as well as polycondensation or addition between various organic monomers are controlled and tailored to obtain – respectively – inorganic and organic reticulated textures in good accordance with the final properties required by the dried materials.

Until now, efforts have been mainly orientated to obtain very light and porous fine materials.

First attempts of organic/inorganic hybridization have been recently initiated.

· Surface treatment

In order to promote dried materials with specific physico-chemical behavior, functionalization of the internal surface of the nanostructured wet gels can be performed (during or after the sol-gel step).

Our main activities in this area are at present concentrated on hydrophobicity and hydrophilicity characteristics.

· Insertion, impregnation and confinement

Realisation of nanocomposites (under the shape of nano-inclusions confined in the nanoporosity of the “rough” materials) is also studied. Main efforts are concentrated on insertion of noble metals (Pt, Ru…) in the nanopores by incorporating specific precursors in the sol before sol-gel reaction, or by impregnation techniques inside carbon aerogel. Electrochemical characterizations are realized by LEPMI (UMR n°5631 INPG/UJF - CNRS.

Studies on fullerenes confinement in silica nanoporosity as well as synthesis of new innovative polymeric liquid crystal have also been initiated.

· Drying

As previously mentioned, most of the final properties of the developed “aerogel-like” materials are governed by the chemical steps (sol-gel routes, functionnalization processes, …). Consequently, when dried materials are required by the applications, gentle drying procedures (i.e. permitting to preserve the tenuous nanostructure generated during gelation) must be followed [Bisson et al, 2002].

For this purpose, a direct supercritical CO2 drying route [Van Bommel – de Haan, 1994] have been adapted, implemented, operated and studied. Particular attention has been put on reproducibility of such a process. Now efforts converge on reduction of the duration.

In parallel, recent progresses in sol-gel chemistry and drying science have permitted to develop an alternative sub-critical way leading to light nanostructured xerogel materials, presenting at the end no significant differences with their aerogel homologues.

· Post-drying treatment

In order to elaborate dried materials with well-suited chemical nature and composition, specific area, shaping, etc …, post-drying treatments are also studied.

• Our main efforts in this field are focused on :
• pyrolysis of organic sol-gel matrices to obtain new families of nanostructured carbons called carbon aerogels,
• activation of carbon aerogel under air or CO2 gas flow,
• grinding “aerogel-like” materials to obtain fine homogeneous micronic powders (when the monolithic shape in not necessary for the applications).

Shaping process

Reproducible « Aerogel-like » materials are elaborated under different shapes, extending from large monolithic piece to divided systems like granules and fine powders.

Characterisations

Elaborated materials are characterized through different angles with a particular attention given to structural, thermal , electrochemical and gaseous storage points of view.

· Structure and Texture

Density is evaluated thanks to mercury pycnometry. Specific area is mesured through BET treatment of Nitrogen (N2) sorption isotherms. Pore Size Distributions are calculated from various techniques like non-intrusive mercury porosimetry [Pirard, 2000], BJH treatment of N2 sorption isotherms, water thermoporometry [Quinson, 1988]. Porous volume is obtained from BJH, t-plot, Dubinin-Radushkevitch, … tretaments.
Main aggregation parameters (like elementary particles and clusters size, mass and surface fractal exponent, total specific area, …) have been estimated from specific treatments of ultra-small angle X-ray scattering curves (USAXS) or dynamic light scattering (DLS).

Density and N2 sorption isotherms treatments are performed thanks to the Center facilities
( N2 sorption analysis performed by CEP/ SCPI) while other specific characterisations are directly performed in close collaboration with privileged partners like University of Liège (http://www.ulg.ac.be/bioreact/) and LSP (UMR CNRS n° 5588) (http://www-lsp.ujf-grenoble.fr/).

· Effective thermal conductivity

Effective thermal conductivity of monolithic samples and granular beds is directly measured at the laboratory with a method based on the hot-wire technique [Carslaw and Jaeger, 1959]. Measurements are performed at temperatures close to room temperature (i.e. from 373 to 473 K), under different gas, from atmospheric pressure to secondary vacuums.

For validation purposes, comparisons with other methods are regularly performed in collaboration with close partners CSTB Grenoble (http://www.recherche.gouv.fr/organism/cstb.htm) and EMAC (http://www.enstimac.fr) [Rigacci et al.2002].

· Gas storage density

Volumetric density of H2 (or CH4) storage is measured on different nanostructured carbons like carbon aerogel, nanotubes or carbon black nanoparticles within a large range of temperatures (from 233 K to 473 K) and pressures (up to 200 bar). The volumetric method involved permits to characterize up to 150 cm3 of material. [Langohr et al, 2002].

Correlations, Simulations and Theoretical Studies

· Correlation studies are systematically performed. They permit to link chemical and process parameters to structural/textural characteristics and final properties. Thanks to this continuous feed-back, taylorisation of the internal texture - through tuning of the sol-gel process - is then possible.

· Theoretical studies of the elaboration processes and of the final properties of the material are also performed as well as simulations of the energetic gains coming from the use of such innovative materials.

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