CE08 - Matériaux métalliques et inorganiques et procédés associés

HYDrothermal sIntering : a Low temperature process for the densIfication of Ceramics – HYDILIC

Hydrothermal sintering : a low temperature process for the densification of ceramics

Development of a low-cost, environmentally friendly, and efficient low-temperature sintering technology to overcome the current technological .bottlenecks encountered in the densification of high-performance ceramics.

Identification of the complex mechanisms involved in hydrothermal sintering and optimization of the density (95%) at low temperature

The development of high-performance ceramics is highly dependent on the sintering processes used. The challenge is to enable densification at low temperature in order to overcome current technological barriers (low-cost and energy-saving process; sintering of metastable, low decomposition temperature and/or nanometric materials; co-sintering of multimaterials). Thus, in addition to optimizing the hydrothermal sintering process and its densification performance, we aim at identifying and understanding the complex mechanisms specific to it. We then target to evaluate the potential of hydrothermal sintering and its adaptability for the development of a wide range of materials. Our initial objective is to reach 95% relative density at sintering temperatures below 370°C (for pressures of the order of 50-350 MPa).

HYDILIC is based on the innovative hydrothermal sintering process inspired by the geological processes of densification: a uniaxial pressure P is applied to a powder in the presence of water under hydrothermal conditions over short periods of time. The main driving force lies in the intragrain stress gradients (induced by P) generating dissolution-precipitation phenomena at the liquid/solid interfaces. These mechanisms based on surface reactivity are suitable for low temperature densification of new nano- and multi-materials, which can also be metastable, with high performance.
HYDILIC relies on a consortium of chemists, ceramists and modelers whose objective is to confront experimental results and multi-scale modeling on two model materials: (nano)particles of anatase TiO2 and amorphous SiO2. The main experimental results will be used as data for the multi-scale modeling, these two approaches being thus intrinsically linked to each other.
The project is structured in three workpackages :
- WP1: Optimization of hydrated compacts (density of the green compact in the order of 55-60% and homogeneous water distribution) from commercial powders
- WP2: Hydrothermal sintering of model systems and characterization of the resulting ceramics
- WP3: Towards a better understanding via multi-scale modelling and validation of mechanisms via hydrothermal sintering of complex systems.

WP1: A study on the optimization of the preparation of concentrated TiO2 and SiO2 suspensions was carried out to obtain dense green compacts. Then, granular compacts of TiO2 and SiO2 with a density higher than 55% were elaborated with a controlled hydration rate.
WP2: Ceramics obtained by hydrothermal sintering of 300 nm silica were produced. A streamlined protocol for the advanced characterization of ceramics has been designed and validated. The device allowing in situ dilatometry measurements during hydrothermal sintering is fully operational. The work carried out on 300 nm silica has allowed to better understand the solvent/particle interactions and to show the evolution of the microstructure during the temperature dwell. Kinetic studies to determine the activation energy during the early stages of hydrothermal sintering are ongoing. Some preliminary tests have been performed on the sintering of commercial nanoscale anatase particles.
WP3: At the grain scale, fluid phase pressure and liquid water saturation of the porosity were evaluated for different initial temperatures and water mass percentages. Modelling showed that the compressive stresses at the contacts and induced by the expansion of the silica during the temperature rise are negligible compared to those calculated during the pressurization of the powder.
At the scale of the stack, high-resolution 2D images were acquired, but metallization problems make interpretation complex. However, the presence of inter- and transgranular fractures seems to indicate differential sintering. Preliminary results from two 3D image acquisition experiments have been acquired
At the macroscopic scale, a steady-state 2D axisymmetric thermal simulation of the reactor in steady state allowed to evaluate the thermal gradient between the sample and the solvent tanks.

Work program for the coming months :
- Continue hydrothermal sintering experiments (with dilatometric monitoring) on nanometric silica.
- Finalize the kinetic study of the first densification stage on 300 nm silica and nanometric silica.
- Carry out a streamlined hydrothermal sintering study on hydrated TiO2 compacts produced by IRCER
- Image acquisition (high-resolution 2D images on ion beam microscope or electron microscope with sub-nanometric resolution/pressure mode) and 3D by X-ray tomography) and analysis of the information that can be extracted from them in order to characterize the grain boundaries: fracture facies (inter and/or transgranular fractures), evolution of the necks, closed porosity.
- Continue and/or initiate modelling and simulations at different scales.

Article : Surface modification of titania nanoparticles by catechol derivative molecules: preparation of concentrated suspensions. Fadoua Sallem, Lucas Villatte, Pierre-Marie Geffroy, Graziella Goglio and Cécile Pagnoux, Colloid and Surface A, 602 (2020) 125167

Talks :
FORMULA X (Manchester) 06/19, Study of the dispersant effect on the dispersion behavior of aqueous titania suspension, Fadoua Sallem, Lucas Villatte, Pierre-Marie Geffroy, Graziella Goglio, Cécile Pagnoux

XVI ECErs Conference 06/2019, Turin , Unconventional low temperature sintering process of ceramics and multimaterials : the hydrothermal sintering. G. Goglio, A. Ndayishimiye, A. Largeteau, M. Prakasam, L. Villatte, J.M. Thibaud, C. Elissalde

CERAMICS 2020, 03/2020, reprogrammée avril 2021 (distance) Unconventional low temperature sintering process of ceramics and multimaterials : the hydro/solvothermal sintering, G. Goglio, A. Ndayishimiye , L. Villatte , C. Elissalde , M. Prakasam , A. Largeteau (keynote)

GFC (Caen) 03/20 reprogrammée 03/2021, Frittage hydrothermal et Cold Sintering Process : lorsque la chimie s’invite aux interfaces, G Goglio (conférence plénière)

GFC (Caen) 03/20 reprogrammée 03/2021, Mise en forme colloïdale de compacts hydratés à base de TiO2 adaptés au frittage hydrothermal, F. Sallem, L. Villatte, P.M. Geffroy, C. Elissalde, G. Goglio, C. Pagnoux

Posters :
XVI ECErs Conference ( Turin) 06/19, the hydrothermal sintering for low temperature densification of silica and anatase, L.Villatte, J.M. Thibault, A. Largeteau, M. Prakasam, J.M. Heintz, C. Pagnoux, F. Sallem, P.M. Geffroy, M.H. Delville, C. Elissalde et G. Goglio

ICACC 2020 01/20, Hydrothermal sintering: a low temperature densification process of ceramics, L.Villatte, S. Bordère, D. Bernard, M.A. Dourges, A. Largeteau, C. Elissalde et G. Goglio

The development of high performance ceramics is strongly related to sintering processes. The challenge is to perform densification at low temperature in order to overcome current technological barriers (energy- and cost-efficiency of the process; sintering of metastable, low temperature decomposition and/or nanometric materials; cosintering of multimaterials). In this context, HYDILIC deals with the innovative hydrothermal sintering process inspired from geological densification process: a powder mixed with water is externally and mechanically compressed under hydrothermal conditions over short time periods. The main driving force is the stress gradient within grains induced by external uniaxial compression which allows the activation of the dissolution/precipitation phenomena at the solid/liquid interfaces. These mechanisms based on surface reactivity are suitable for the densification at low temperature of high performance nano- or multimaterials, which can also be metastable. HYDILIC relies upon a consortium of chemists, ceramists and modelling theoreticians who aim at coupling experimentation and multiscale modelling focused on two model materials: anatase TiO2 and amorphous SiO2 (nano)particles. Main experimental outputs will be used as inputs for the multiscale modelling, which makes both approaches intrinsically interrelated.
The HYDILIC project is then structured into four workpackages:
- W0 : coordination (the communication between partners needs to be efficient as workpackages are strongly dependent one from another) and strategy for dissemination
- WP1 : optimization of hydrated green pellets (at least 55-60% green density and homogeneous water distribution) starting from commercial powders
- WP2 : hydrothermal sintering of model systems and characterization of as-obtained ceramics
- WP3 : towards a better understanding via multiscale modelling and validation of the mechanisms via hydrothermal sintering of complex systems
Besides an optimization of the process and of its densification performances, we then aim at evidencing and understanding all the involved complex mechanisms. This strategy will allow us to reach deep insight into this process in order to evaluate both its potential and adaptability towards the elaboration of a wide range of materials. We then take up the challenge to reach 95% of relative density for temperatures lower than 370°C (pressure being in the range 50-350 MPa). In this way, HYDILIC aims at developing a forceful affordable and environmentally friendly technology that surmounts the current technological barriers.Moreover, hydrothermal sintering is a springboard for the design and fabrication of complex multimaterials, integrating nanotechnology.
In the long term, HYDILIC aims to favor the competitiveness of French small and medium size companies and to totally integrate all environmental and social constraints (energy economy, green solvents, safe process).

Project coordination

Graziella GOGLIO (INSTITUT DE CHIMIE DE LA MATIERE CONDENSEE DE BORDEAUX)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

ICMCB INSTITUT DE CHIMIE DE LA MATIERE CONDENSEE DE BORDEAUX
IRCER institut de recherche sur les céramiques

Help of the ANR 338,472 euros
Beginning and duration of the scientific project: December 2018 - 42 Months

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