Acid geopolymer materials based on different aluminosilicate sources

Geopolymers synthetized from the reaction of metakaolin (or alumino-silicate) in an alkali medium are studied since decades [1]. However, in order to develop composites, alkali medium is undesirable due to the detrimental effect of alkali ions on fibers. As an alternative, the use of an acid medium seems promising as some authors demonstrated an increase of mechanical properties with acid-based geopolymers [2, 3]. The aim of this work is to investigate the various formulations and to understand the reactional mechanisms. The work is based on the activation of an alumino-silicate source with phosphoric acid to obtain geopolymer The various formulations consist to determine the Al/P ratio leading to consolidation at various temperatures (from 20 to 70°C). The samples were characterized by Fourier Transform Infrared and Nuclear Magnetic Resonance spectroscopies and X-Ray Diffraction measurements in order to study their structure. The thermal and mechanical properties were correlated with the microstructure [4]. Consolidated geopolymers were synthetized with different Al/P ratios. The consolidation time decreases with increasing Al/P ratio. For instance, the material realized with Si/Al=1,17 consolidates at 20°C in 15 and 8 days with Al/P=4 and 1, respectively. Tow behaviors can be distinguished samples presenting good fire resistance (Si/Al=1,17 and Al/P=1) or presenting poorly water resistant (Si/Al=1,17 and Al/P=4). Consequently, the impact of the reactivity of the alumino-silicate source on the geopolymerisation kinetics leads to different types of structures (secondary and metastable phases) in relation with the phosphor content. References: [1] J.Davidovits, J. Therm. Anal. 37 (1991) 1633-1656. [2] D. S. Perrera, J Mater Sci, vol. 3, pp. 6562-6566, 2008. [3] H. K. Tchakouté and C. Rüscher, Applied Clay Science, vol. 140, pp. 81-87,2017. [4] H.Celerier and al., under submission

Influence de différents mélanges de métakaolins sur les propriétés des géopolymères

International audienc

Development of ceramic coating for hollow-core photonic crystal fibers

International audienceIn this invited communication, the history and recent progress made on the hollow-core photonic crystal fibers are first reviewed. In particular, we discuss hollow-core fibers guiding by the inhibited coupling mechanism making it possible to achieve new performances including the association of ultralow losses with effective singlemode guidance and record attenuations in the visible and ultraviolet domains. Then, a new way to post-process these fibers is introduced to further enhance their potentiality into applications. For this, a specific process from the sol-gel approach has been adapted for those fibers to permit deposition of ceramic materials in nanolayer scale at the core/clad interface

Méthode originale de dépôt multi-matériaux appliquée aux fibres optiques à coeur creux

National audienc

Al/P ratio variation of acid-based geopolymers: structural investigation by NMR and XRD analysis

International audienc

Influence of metakaolins reactivity on the properties of geopolymers

The search for new, more economical, energy-efficient and less polluting binders, such as geopolymer materials, has been favored by the imperatives of preserving the environment and in the context of sustainable development. These binders result from the activation of aluminosilicate sources of different origin (metakaolin, fly ash…) by either an alkaline or acidic solution. Due to their wide field of applications, the properties of these materials and reagents are largely studied. However, to date, these studies are still very dependent on the initial reagents, and the fundamental link between the global characteristics of the aluminosilicate source, their reactivity and the final properties of the geopolymers, has not yet been defined. To answer this problem, the proposed work consists in studying a selection of several metakaolins, pure or mixed, to characterize their reactivity and to understand how they will influence the properties of the samples. First, mixtures of French metakaolins of different chemical composition and purities were carried out in order to assess their reactivity towards the activating solution, using physicochemical (wettability, zeta potential) and structural (X-ray diffraction, Fourier transform infrared spectroscopy…) techniques. The results show that whatever the techniques used, the behavior of metakaolins mixtures strongly depend on the molar ratio of aluminum in the composition. Also, geopolymers have been formulated from these mixtures and submitted to mechanical tests including compressive strength in order to compare the variations in composition, reactivity and mechanical properties

Composites synthesized with acid-based geopolymers

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Characterization of the Alkoxide-based Sol-gel Derived La9.33Si6O26 Powder and Ceramic

In this study, we report on the acid-catalysed synthesis of La9.33Si6O26 from lanthanum nitrate or acetate and silicon ethoxide (TEOS) in the ethanol solvent, upon the transition from liquid to amorphous and crystalline phases. The similarity of the Fourier transform infrared spectra of the lanthanum-salt solutions and lanthanum-silicon sols indicates that the lanthanum environment is not changed in the reaction of the La-salt with TEOS. In the nitric-acid catalysed synthesis, the hydrolysis reaction was almost instantaneous, as a consequence of a higher amount of water in this system, which contributed to a high level of chemical heterogeneity in the product. The acetic acid-based synthesis ensured a good mixing of the reagents at the nanometre level, which gave rise to the formation of the pure La9.33Si6O26 powder upon heating at 900 degrees C, and single phase ceramics with 94 % relative density after sintering at 1400 degrees C for 3 h in air, which is 200 degrees C lower temperature then usually reported for the apatite material