Applicazioni dei geopolimeri come materiali compositi coibentanti e refrattari

Geopolymers are inorganic polymeric materials based on aluminosilicates. Geopolymers belong to the class of the chemically bonded ceramics (CBCs): geopolymeric resin acts as a glue for different fillers that funzionalize the material. They are synthesised at low temperature (T<350?C), they do not include water in the structure in contrast with hydraulic cements and they can withstand up to 1200?C. For this reason geopolymers could be used for high temperature and fire proof applications in the automotive and aerospace industries, non-ferrous foundries and metallurgy, civil engineering, plastics industries, waste management.I geopolimeri sono materiali polimerici inorganici a base allumino-silicatica. Appartengono alla classe delle ceramiche consolidate per via chimica (chemically bonded ceramics, CBCs) e sono dei materiali compositi: la resina geopolimerica ? il collante per le cariche che funzionalizzano il materiale. Diversamente dai cementi idraulici, i geopolimeri non contengono acqua di idratazione e sebbene siano lavorati a basse temperature (T<350?C), con tecniche usate comunemente per la presa delle resine organiche, possono resistere fino a 1200?C, anche per lunghe esposizioni. Materiali a base geopolimerica sono pertanto utilizzati in applicazioni ad alta temperatura, come stampi per fonderia, pannelli e pareti isolanti-coibentanti, materiali a prova di fuoco per automobili e aerei, refrattari, adesivi, leganti e rivestimenti per alte temperature

Geopolimeri: "ceramiche" per uno sviluppo sostenibile

Geopolymers are inorganic polymeric materials developed in 70\u27s by Joseph Davidovits. Geopolymers mimic natural minerals and they are the products of a geo-synthesis, i.e. a reaction that chemically integrates minerals. Geopolymers belong to the class of the chemically bonded ceramics (CBCs): they are synthesised at low temperature from a variety of materials including recycled resources and mineral wastes, reducing the energy demands and environmental impact during their production. For this reason geopolymers could be considered environmentally friendly. Geopolymers enable product designers to envisage the use of ceramic type materials with the same facility as some plastics and organic removing heavy equipment and high temperatures from the ceramic industrial plants. Geopolymer technology allows the production of a wide range of versatile materials already finding applications in many fields of industry. These applications are to be found in the automotive and aerospace industries, non-ferrous foundries and metallurgy, civil engineering, plastics industries, waste management, restoring, art and decoration, biomaterials, etc.. Geopolymers are the natural product of green chemistry, that works for a sustainable development.I geopolimeri sono materiali polimerici inorganici sviluppati negli anni \u2770 da Joseph Davidovits. I geopolimeri mimano le rocce naturali e sono il prodotto di una geosintesi, cio? una reazione che ricostituisce chimicamente le rocce. I geopolimeri appartengono alla cosiddetta classe delle ceramiche consolidate per via chimica (chemically bonded ceramics, CBCs): sono sintetizzati a bassa temperatura da una variet? di materiali includendo scarti della produzione industriale quali ceneri volanti o scorie d\u27altoforno, riducendo cos? la richiesta energetica e l\u27impatto ambientale durante la loro produzione. Per questa ragione i geopolimeri possono essere considerati ecocompatibili, "environmentally friendly". I geopolimeri consentono l\u27utilizzo di materiali con propriet? ceramiche con le stesse modalit? di alcune materie plastiche, rimuovendo gli equipaggiamenti pesanti e le alte temperature dagli impianti ceramici industriali. La tecnologia dei geopolimeri permette la produzione di una vasta gamma di materiali versatili che trovano gi? un impiego in diversi settori industriali, quali: ingegneria civile, trattamento dei rifiuti industriali, industria dell\u27automobile ed aerospaziale, fonderie di metalli non ferrosi e metallurgia, industrie plastiche, restauro, arte e decorazione, biomateriali, ecc.. I geopolimeri sono il prodotto naturale della cosiddetta "chimica verde", che lavora per uno sviluppo sostenibile

Alkali-bonded composites for thermal and acoustic insulation

Geopolymers are alkali bonded ceramics that thank to their fully inolrganic nature have high temperature resistance depending on their compositions. An overview of the research of ISTEC on Alkali-bonded composites for thermal and acoustic insulation have been presente

Properties of slip-cast and pressureless sintered ZrB2-SiC composites

In view of the perspective to produce near-net shapes of ultra-refractory ceramics, ZrB2-SiC composite were produced by slip casting on plaster mould and pressureless sintered at 2150?C with holding time of 120 minutes, using silicon nitride as sintering aids. After sintering, slip cast samples reached a very high relative density over 98%, while, for comparison, the density of cold isostatic pressed samples was about 94%. Traces of the formation of secondary phases such as B4C, graphite, BN were found in all samples, while no grain boundary phases were revealed. RT flexural strength of as-sintered slip cast bars was affected by the presence of an external porous layer of coarse ZrB2 particles, while at 1500?C flexural strength increased, as a glassy layer sealed the superficial defects. Due to the absence of softening grain boundary phases, sub-critical crack growth did not occur during high temperature strength test

Reticulated porous silicon nitride-based ceramics

The interest towards the production of porous silicon nitride originates from the unique combination of light weight, of mechanical and physical properties typical of this class of ceramics that make them attractive for many engineering applications. Although pores are generally believed to deteriorate the mechanical properties of ceramics (the strength of porous ceramics decreases exponentially with an increase of porosity), the recent literature reports that porous silicon nitride can exhibit outstanding mechanical properties even at certain porosity levels, such as heat resistance and chemical resistance, damage tolerance, the thermal shock resistance and the strain tolerance. A study on silicon nitride characterized by high porosity content (more than 70%) has been carried out, focusing on the comparison of different processing procedures to produce silicon nitride with tailored novel porous structures and a high porosity content. Three technologies were compared to produce reticulated porous silicon nitride: 1) impregnation of templating structures (sponges) with ceramic powder slurries. Production of highly porous ceramic bodies using pyrolizable porous templates is quite a common process for almost any kind of ceramic material. Open porosities over 50% vol. can be easily achieved by using solid foamed sponges, both in polymeric materials and cellulose. 2) using a consolidator/binder and a pore former, 3) from foamed suspensions stabilized through organic additives. Some mechanical properties are reported and discussed in terms of microstructure and fabrication technique

Preparation of thermally stable geopolymers as new catalysts or supports

Geopolymers are alkali bonded ceramics (ABC\u27s) and are produced using an energy saving process involving chemical reactions in aqueous medium at T < 120?C. Thermally stable geopolymers may have many industrial applications, considering that their preparation allows to produce near-net-shape pieces, also simultaneously to the foaming. ABC\u27s have a three-dimensional aluminosilicate network, in which polymeric Si-O-Al-O bonds form under alkaline conditions in presence of aluminosilicates. The final structure of a fully reacted ABC consists of nanoparticulates ranging from 5 to 15 nm, pores of 3 to 10 nm with specific surface area in the range 20-140 m2/g. Finally, the functional and structural properties of the ABC\u27s can be tailored by introducing specific ceramic fillers. The geopolymer network and the zeolite framework have close similarity in the exchange with charge balancing cations; ABC\u27s network also enables incorporation of transition metal ions or protonic extra-network sites as active centres for catalytic reactions. However, it must be noted that geopolymers posses some advantages in comparison to zeolites, such as formation at room or low temperature, mesoporosity and low preparation cost, opening potential interests for the synthesis of new robust catalysts for heterogeneous reactions. Aim of this study was to set up the preparation method for new geopolymers (pellets and/or foams) to be applied as catalysts or support

Achievement and exploitation of porous geopolymer-based spheres

Several spherification processes were applied to obtain porous geopolymer spheres, different in term of porosity, specific surface area and adsorption properties. The processes are based on the formulation of metakaolin-based geopolymer slurries, produced using a potassium- or sodium-based alkaline activating solution, and exploiting an injection-solidification method in different mediums, i.e. polyethylene glycol (PEG), liquid nitrogen or calcium chloride, to produce the spheres. When liquid nitrogen was used, the geopolymer slurries underwent a maturation step (several hours at room temperature) to trigger the geopolymerization without reaching a complete chemical consolidation. Spheres were obtained injecting in liquid N2 the mixture as it is or mixed with water, to modulate the final porosity (ice-templating process). The spheres were then freeze dried to remove the solidified water and complete the chemical consolidation of the geopolymer. Please click Additional Files below to see the full abstract

Materie prime di origine naturale nel processo di geopolimerizzazione

Geopolymers are inorganic materials prepared via a room temperature treatment (25-120?C) with alkali activation. The main applications of these materials is in the field of building materials, recycle and inertization of waste, restoration. The production and final product is optimised by a careful selection of starting materials, i.e. aluminosilicate powders. In this paper are presented aluminosilicates from natural source, as an example kaolin, clays or volcanic ash. Metakaolin is the most reactive due to its amorphous structure and aluminium coordination; its reactivity is also influenced by its mineralogical origin, morphology of grains, and calcinations method. Volcanic ash present lower reactivity and the better consolidation temperature to obtain mechanically strong materials appears to be around 400?CI materiali geopolimerici sono materiali inorganici ottenuti con consolidamento a bassa temperatura (25-120?C) mediante una reazione chimica in ambiente alcalino. Sono utilizzati per applicazioni ad alta temperatura e strutturali in edilizia, per il riciclo e /o l?inertizzazione di scorie industriali, per il restauro. L?opportuna selezione di materie prime alluminosilicatiche ? alla base dell?ottimizzazione del ciclo produttivo e del prodotto finale. Vengono presentate materie prime di origine naturale, quali il metacaolino, derivato dalla calcinazione del caolino, e le ceneri vulcaniche. Il metacaolino ? la materia prima pi? reattiva grazie alla struttura amorfa e alla coordinazione dell?alluminio: sulla reattivit? influiscono sia la morfologia e le caratteristiche del caolino di origine, sia la metodologia di calcinazione. Le ceneri vulcaniche hanno una minore reattivit? che pu? esser ovviata tramite un consolidamento a circa 400?C portando a prodotti geopolimerici con buone prestazioni meccanich

Lightweight insulating geopolymer material based on expanded perlite

Expanded perlite, owing to its lightweight and excellent thermal insulating properties, has been extensively used in different industrial sectors to produce self-standing insulating boards bonded with various organic polymers or calcium-silicates. In order to improve the high temperature behavior and mechanical performances of such materials inorganic binders, such as geopolymers, can be regarded as a promising alternative. Please click Additional Files below to see the full abstract

Porcelain stoneware scraps recycle in alkali bonded insulating panels

Ground porcelain stoneware scraps were recycled as main component (up to 80 wt%) in alkali bonded insulating panels. Sandwich panels were prepared by varying the scraps dimension and amount in the core and skins.The binder for the alkali bonding was prepared by using highly reactive metakaolin as raw powder, while the alkali aqueous solution was KOH/K2SiO3 mixture. The setting was performed at 80?C for 24 h. The thermal conductivity at room temperature was 0.7 W.m-1.K-1. Dilatometric analyses were performed up to1200?C to study the structural modification. A thermal treatment of conditioning at 600?C prevented any structural degradation upon long term immersion in wate