Science des Procédés Céramiques et de Traitements de Surface (SPCTS)

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Centre National de la Recherche Scientifique (CNRS)
Université de Limoges
Ecole Nationale Supérieure de Céramique Industrielle (ENSCI)


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Accueil du site > Axes de recherche > Axe 1 "Procédés céramiques" > Suspensions et Procédés > Suspensions and Processes

Suspensions and Processes

Contact

Arnaud VIDECOQ : arnaud.videcoq unilim.fr


Context/objectives

Our group works in the field of shaping processes of ceramics in two ways :
  • A fundamental approach which aims to better understand and control the structure of colloidal suspensions. The latter influence the flow properties (i.e. the rheology) and ultimately the properties of parts. Our approach actually consists in linking the surface chemistry of particles to the structuring of associated suspensions on the basis of numerical simulations and experiments.
  • The optimizing of conventional shaping methods (tape casting, extrusion, electrophoresis ...) and the development of original shaping processes that rely in part on the fundamental approach. In this context, we focus on rapid prototyping technologies (stereolithography, ink jet printing...).


Activities

Suspensions

Numerical simulations / rheology

Simulations of the behavior of ceramic particles suspended in a liquid are implemented in collaboration with Riccardo FERRANDO (University of Genoa, Italy) and Tapio ALA-NISSILA (Aalto University, Helsinki, Finland). These simulations are based on Brownian Dynamics (BD) and Stochastic Rotation Dynamics (SRD). SRD takes into account hydrodynamic effects.

When only one type of particle is present in the suspension, the DLVO theory gives an idea of ​​the tendency of particles to agglomerate or remain dispersed. However, when the suspension contains particles of different types, it is difficult to predict the stability only by the DLVO theory. Numerical simulations help to understand what are the parameters that govern the stability of suspensions, agglomeration phenomena and to some extent the rheology.

The results of numerical simulations are compared to the structuring of colloidal suspensions of model particles, labeled with fluorescent dyes. The surface chemistry of model particles is specifically adapted during their synthesis (e.g. modified Stöber synthesis processes). Experimentally, the structuring of suspensions is characterized using techniques such as cryo-SEM, confocal microscopy and light scattering coupled with rheology.

Hetero-agglomeration of silica-like (red) and alumina-like (green) particles at pH 5.5 under the effect of opposite surface charges in suspensions loaded at 3vol.%
("R" mass of silica / total mass of oxide, "Phi" volume fraction of solid in sediments)
Granulation by colloidal routes

Colloidal processes allow shaping parts with complex architectures by precisely controlling the initial structure of suspensions and their evolution during manufacturing. These processes require most of the time the preparation of suspensions containing high solid contents. Thus, the control of the dispersion of the powder in the liquid phase is a key point. But, with nanopowders or powders of high specific surface areas typically greater than 50 m2.g-1, high concentrations of solids are difficult to obtain and the use of dilute suspensions together with innovative shaping methods are good alternatives to handle nanopowders. In this context, our research is focused on the formulation of aqueous suspensions of oxide powders. The selection of relevant additives allows modifying the surface chemistry of powders to agglomerate them in a controlled manner.

Hetero-agglomeration of TiO2 nanopowders and Latex microspheres :
a) Distribution of spheres (porosity : 80vol.%), b) Porosity due to Latex pyrolysis (32vol.%, d=4µm),
c) Intergranular porosity 37vol.%, 20nm<d<800nm, d) Intragranular porosity (10vol.%,d=8nm)

Innovative shaping processes - rapid prototyping

Stereolithography

In line with the development of ceramic parts directly to the final dimensions and shapes with high dimensional accuracy (net-shape forming) and implementation of specific architectures leading to new and/or improved properties, we develop an innovative rapid prototyping technology based on stereolithography. This process, known in the field of polymers, has major advantages as for the complexity and precision of the objects obtained without any mold. Stereolithography consists in building a 3D part layer by layer. A doctor blade made ​​layering of ceramic pastes possibly down to 25 microns. A paste contains a ceramic powder load, a photopolymerisable monomer and a photo-initiator. A UV laser beam, whose positioning is controlled from a CAD file, then locally consolidates the surface of each layer by polymerization. When the stack of layers is completed, the green part is removed from the uncured volume by washing. It is finally debinded and sintered.

 
Cranial implant made ​​of hydroxyapatite (HAP), manufactured by stereolithography
Collaboration with the University Hospital of Limoges (CHU)
  Al2O3 photonic band gap antenna
Collaboration with XLIM
Ink jet printing
The inkjet printing (IJP) rapid prototyping technology, developed at SPCTS since 2001, aims manufacturing three-dimensional structures. A previous work has shown the feasibility of ceramic structures made of high aspect ratio micropillars (about 40μm in diameter after sintering) fromPZT colloidal suspensions. This work has led to the creation of a spin-off company (Ceradrop, todays 13 employees) in March 2006 utilizing the expertise of the laboratory from an exclusive license of a CNRS patent. Since 2006, IJP has been used to show the feasibility of multi-material structures or multifunctional structures, along with two main axes :
  • The feasibility of ceramic/metal components for microelectronics and power electronics from colloidal suspensions.
  • The fabrication of microdots arrays of functionalized mesoporous silica (e.g. biosensors). This activity, initiated under the REX FAME, is conducted in close collaboration with colleagues from the LCMCP (Team of Clément SANCHEZ, Collège de France, Paris) and ICG (Team of Michel WONG CHI MAN, Montpellier, France) laboratories. It aims coupling click chemistry approaches, evaporation-induced self-assembly (EISA) and inkjet printing.
 
Mesostructured silica microdots array fabricated and one-pot functionalized by IJP   TEM image of lamellar mesoporosity arrangement inside a silica microdot


Key facts

  • Implementation of numerical simulations (BD, SRD) that allow predicting the structuring of colloidal suspensions - Application to shaping by hetero-agglomeration
  • Development of the activities linked to rapid prototyping
    • Stereolithography in collaboration with 3DCeram Company
    • Ink jet printing in collaboration with Ceradrop Company
    • Development of the Aerosol Deposition Method in collaboration with CTTC (Center for Technology Transfers in Ceramics)

Updated June 26, 2012

© SPCTS - Centre Européen de la Céramique - 12 Rue Atlantis - 87068 LIMOGES Cedex - Tél : 05 87 50 23 03 - Fax : 05 87 50 23 09 - Courriel : spcts unilim.fr