Fabrice Ferauche

Durability of mortars modified with metakaolin

Abstract Results of an investigation to determine the effects of metakaolin additions on transport properties of mortars are reported. Comparisons are made to ordinary Portland cement (OPC) to determine the influence of addition and replacement percentage. Cement is replaced on a mass basis of 5–20% for metakaolin. A mixture with natural kaolin is also studied. The transport properties and chemical behaviors are analyzed by means of chloride diffusion tests and sulfate immersion. Observations after more than 100 days are used to prescribe mixtures that reduce the rate of chloride diffusion and sulfate degradation. For metakaolin, the optimum seems to be between 10% and 15% with regard to inhibition effect on chloride diffusion and sulfate attack.

Preparation of low-density xerogels by incorporation of additives during synthesis

Abstract Low-density xerogels were prepared by incorporation of an additive to alcogels prior to gelation. The additives studied are 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS), 3-aminopropyltrimethoxysilane (AMS), propyltrimethoxysilane (PMS), tetramethylorthosilicate (TMOS) and 3-aminopropyltriethoxysilane (AES) using tetraethylorthosilicate (TEOS) as main silica precursor. Samples were also prepared with EDAS as additive and TMOS as main silica reagent. When the additive contains methoxy groups, it reacts first, forms nuclei on which the main reagent TEOS reacts to form the silica particles. The nucleation mechanism by the additive occurs only in case of a difference of reactivity between additive and main silica precursor. The other group of the additive (amine, alkyl group, …) influences only the gelation time. In case of ethoxy groups (series AES/TEOS) or methoxy groups (series EDAS/TMOS) for both additive and main reagent, there is no nucleation by the additive.

Ag/SiO2 and Cu/SiO2 cogelled xerogel catalysts for benzene combustion and 2-butanol dehydrogenation

Ag/SiO2 and Cu/SiO2 xerogel catalysts were synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of Ag and Cu with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS). The resulting catalysts are composed of completely accessible metallic crystallites with a diameter of about 3 nm located inside silica particles exhibiting a monodisperse microporous distribution centered on a pore size of about 0.8 nm and larger metallic particles with a diameter of 20 to 40 nm located outside the silica network. The activity of Ag/SiO2 and Cu/SiO2 catalysts has been shown for benzene combustion and 2-butanol dehydrogenation.