Structural characterization of geomaterial foams — Thermal behavior E. Prud'homme a , P. Michaud a , E. Joussein b , J.-M. Clacens c , S. Arii-Clacens c , I. Sobrados d , C. Peyratout a , A. Smith a , J. Sanz d , S. Rossignol a, ⁎ a Groupe d'Etude des Matériaux Hétérogènes (GEMH-ENSCI) Ecole Nationale Supérieure de Céramique Industrielle, 12 rue Atlantis, 87068 Limoges Cedex, France b GRESE, EA 3040, 123 avenue Albert Thomas, 87060 Limoges, France c Université de Poitiers, Laboratoire de Catalyse en Chimie Organique, UMR 6503 CNRS, 40, av. du recteur Pineau, 86022 Poitiers cedex, France d Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas (CSIC), C/Sor Juana Inés de la Cruz, 3, ES 28049 Madrid, Spain abstract article info Article history: Received 16 March 2011 Received in revised form 31 May 2011 Available online 29 July 2011 Keywords: Geopolymer foam; Aluminosilicate; Silica; NMR spectroscopy; Microstructure The structural evolution of in-situ inorganic foam based on sodium or/and potassium is investigated. The synthesis of foam based on an alkaline polysialate, is achieved at slightly elevated temperature by the alkaline activation of raw minerals and industrial waste. The structural evolution is studied through differential thermal analysis/thermogravimetric analysis (DTA-TGA) coupled with mass spectrometry, in-situ X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and 29 Si, 27 Al magic-angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR). The role of alkali cations is observed, and they are shown to have a significant effect on structure changes with temperature, leading to the onset of a crystalline phase in potassium-based foam. Shifts of MDI reflect the competition that takes place during heating between the evolution of the zeolite phase and the amorphization of the material. © 2011 Elsevier B.V. All rights reserved. 1. Introduction In recent years, industrial manufacturers have generated and released a substantial quantity of pollutants into the environment; their greatest problem is the production of by-products [1]. Currently, there is both political and societal demand for technology that can easily and cheaply uptake a substantial quantity of by-products [2]. Such products must also require little energy to manufacture and be easy to recycle. These new materials have to display analogous or even improved properties with respect to those of existing materials. Traditional materials that couple mineral binders and local raw materials can be found in all cultures and time periods [3]. An important environmental problem is Portland cement, which is widely used around the world; the market position of Portland cement is strong, with an annual consumption of 1000 Mt [4]. However, the manufacturing of cement leads to a substantial production of carbon dioxide, which is penalizing for the manufacturer through mandatory carbon taxes. The use of new cementitious materials known as geopolymers, including silicates or aluminosilicates, cannot be neglected as substitutes for conventional hydraulic binders [5]. Geopolymer materials could also be used to passivate industrial waste and as alternatives to cements, and these geopolymers have emerged as solutions to overcoming the problem of the massive production of by-products and reducing CO 2 emissions. Geopolymers have various uses; notably, they can be used to manufacture precast structure, concrete pavements, concrete products, and to immobilize toxic waste that is resistant to heat and aggressive environments [6]. Geopolymerization is a type of geosynthesis that involves naturally occurring silico-aluminates [6] and is based on the chemistry of alkali-activated inorganic binders. These amorphous, three-dimensional, alumino-silicate binder materials, the formation process of which was first explained by Glukhovsky, [4] were first introduced to the world of inorganic cementitious materials by Davidovits in 1978 [7]. Geopolymers may be synthesized at room temperature or at slightly elevated temperatures by the alkaline activation of alumino-silicates obtained from industrial wastes, calcined clays, natural minerals or mixtures of two or more of these materials. In a strong alkaline solution, alumino-silicate reactive materials rapidly dissolve to form free SiO 4 and AlO 4 tetrahedral units [8,9]. During a polycondensation reaction, the tetrahedral units are linked in an alternating manner to yield amorphous geopolymers. Geopolymer concretes are based on compounds that are generally produced from one or more solid components (binders) and one or more liquid components (activators), which react together to form strong, durable materials. Geopolymer materials could be an alternative to Ordinary Portland Cement (OPC) in the domain of building materials. Insulating materials are also important in the domain of building materials. The exclusion of certain insulating materials, such as asbestos, has led to research into new alternatives. Air is the best insulating compound, with a thermal conductivity of 0.01 W.m -1 .K -1 . The development of highly porous materials with a bare minimum of Journal of Non-Crystalline Solids 357 (2011) 3637–3647 ⁎ Corresponding author. Tel.: + 33 5 87 50 25 64. E-mail address: sylvie.rossignol@unilim.fr (S. Rossignol). 0022-3093/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2011.06.033 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol