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Microporous and Mesoporous Solids
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Elaine A. Moore, Lesley E. Smart
The zeolites fall into three main categories. The channels may be parallel to (a) a single direction, so that the crystals are fibrous; (b) two directions arranged in planes, so that the crystals are lamellar; or (c) three directions, such as cubic axes, in which there is strong bonding in three directions. The most symmetrical structures have cubic symmetry. By no means do all zeolites fall neatly into this classification; some, ZSM-11, for instance, have a dominant two-dimensional structure interlinked by smaller channels. A typical fibrous zeolite is edingtonite (EDI, Ba[(AlO2)2(SiO2)3]4H2O), which has a characteristic chain formed by the regular repetition of five tetrahedra. The lamellar zeolites occur frequently in sedimentary rocks, for example, phillipsite (PHI,(K/Na)5[(SiO2)11(AlO2)5]⋅10H2O), which is a well-known example. In terms of their useful properties, zeolites are conveniently discussed based on their pore size.
Synthesis of nano-alumina and their effect on structure, mechanical and thermal properties of geopolymer
Published in Journal of Asian Ceramic Societies, 2019
Z. Zidi, M. Ltifi, Z. Ben Ayadi, L. El Mir
New developments in technology today aim to produce more efficient, cheaper and less toxic materials. In the construction field, cement is the most interesting material. Thus, extensive research is aimed at improving its properties. In 1970, Davidovits discovered a new type of inorganic polymer called a geopolymer with excellent mechanical properties which enabled it to become a competitor with Portland cement [1]. Geopolymers are becoming more and more interesting materials due to their properties, such as high early compressive strength, acid resistance, high fire resistance, and a small quantity of embedded CO2 [1,2]. Geopolymers are synthesized from alumino-silicate sources and activated by high alkaline solutions in three successive steps: dissolution, polycondensation, and stabilization [3]. Many efforts have been directed to improving the performance of geopolymers [4]. Recent studies have shown that the introduction of nano-materials (SiO2, Fe2O3, Al2O3, ZnO, carbon nano-tubes WCNT …) to the geopolymers matrix improves its mechanical, structural and thermal properties. Several of these have studied the influence of nanoparticles on fresh and hardened geopolymers [5,6]. They concluded that the inclusion of extremely fine particles in cement is more advantageous than inclusion of traditional additives. Nanoparticles with perfect structures can be used as nano-filler because of the low porosity and high density obtained by decreasing the interfacial transition zone [7,8]. They are also used as catalysts to accelerate geo-polymerization reactions. Other researchers asserted that raising nano-materials, quantity increases the amount of N-A-S-H gel, which improves the mechanical properties of the material [9]. Phoo-ngernkham et al. (2014) showed, more over that the incorporation of nano-alumina has a more effective influence on the structural and mechanical properties of hardened geopolymers than nano-silica [10]. They reported that the microstructure of concrete containing nano-Al2O3 is highly compact and has a short setting time. In addition, Stefanidou et al. (2017) found that nano-alumina can improve the strength and the density of the geopolymer matrix [11]. Similar results have been observed by Gowda et al. (2017) for Portland cement [12]. Using ATR-FTIR spectroscopy, Rees et al. (2008) reported that the incorporation of nano-alumina stimulates the formation of nuclei in the geopolymer system and leads to the formation of zeolite Na–F with a edingtonite structure that had not previously been observed in pure geopolymers [13].