Short communication Synthesis of nano-layered vermiculite of low density by thermal treatment Y. El Mouzdahir a , A. Elmchaouri a, ⁎, R. Mahboub a , A. Gil b , S.A. Korili b a Université Hassan II Mohammedia, Faculté des Sciences et Techniques, Laboratoire d'Electrochimie et Chimie Physique, BP 146, 20650 Mohammedia, Morocco b Department of Applied Chemistry, Los Acebos Building, Public University of Navarre, Campus of Arrosadia, E-31006 Pamplona, Spain ABSTRACT ARTICLE INFO Article history: Received 5 December 2007 Received in revised form 4 June 2008 Accepted 21 June 2008 Available online 27 June 2008 Keywords: Exfoliation Thermal treatment Vermiculite The present work consists in the study of the modification of a nano-layered vermiculite by thermal treatment up to 900 °C. Changes in the structure and texture after thermal treatment were used for evaluation of dehydration properties of the studied material. The dehydration properties of the clay are strongly affected by the crystal structure. The Differential Thermal Analysis (DTA) allows the determination of the specific temperatures at which phase modifications take place, principally the ones attributed to the removal of the interlayer water molecules and the formation of a series of less hydrated phases. Structural and textural studies were carried out using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) analysis. The SEM micrographs reveal structural changes of the sample, such as exfoliation phenomena and contraction of the vermiculite, related to the heating temperature. These observations are confirmed by the XRD patterns, which demonstrate that the d-spacing of the first basal diffraction varies depending on the applied heating temperature, this showing several states of dehydration. As a complementary characterization, porosity analysis by Hg-porosimetry has also been carried out. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Vermiculite is a mica-type mineral used for insulation, in composite cements, in horticulture and as a substitute for asbestos. It has been exploited widely over the past 50 years or more and because of the low particle size it is used as coating, lightweight additive, etc [1]. This natural silicate mineral is usually formed by the hydrothermal alteration of mica minerals such as biotite and phlogopite [2,3]. Although its dimensions vary from microscopic particles of clay mineral to lustrous brown sheets up to half a meter in size, the particle diameter is usually in the range of 1 mm to 1 cm. Most vermiculites when heated quickly to above 230 °C lose their interlayer water and this results in the flakes exfoliating to form concertina-shaped granules. Being lightweight and resistant to thermal decomposition, this exfoliated vermiculite is valuable as an insulation material and filler, among its many other uses [4–7]. Various methods have been proposed for delaminating and reducing the particle size of vermiculites, such as sonication [8], mechanical treatment and chemical process using hydrogen peroxide [9]. These methods have been used to prepare nanometric vermiculite particles [10,11]. Sonication produces delamination in the [00l] direction and breaking of layers in the other crystallographic directions, while the crystalline character is retained [11]. Muromtsev et al. [12] found that in the reaction between the vermiculite and a 30 % hydrogen peroxide solution, the exfoliation is related to the separation of silicate layers with oxygen formed by the decomposition of peroxide and also to the disruption of the equilibrium between the layers and the interlayer cations, due to vigorous release of hydroxide groups from the structure. Upon heating quickly at elevated temperatures, the vermiculite exfoliates and the bulk volume increases 8–12 times [13]. The expansion is related to the separation of the layers due to the sudden release of water; the highest expansion was shown by samples containing mica or mica-vermiculite, which at lower temperatures produced thermal effects compared to pure vermiculites [14,15]. The thickness of a single layer of this silicate material is actually of nanometer size: it is known that the platelets of a vermiculite type layered clay mineral can be exfoliated to single layers that are 1 nm thick [16]. The objective of this work is to study the effect of thermal treatment up to 900 °C on the structure and texture of Palabora vermiculite. Data obtained by DTA, XRD, SEM and mercury porosimetry were used with the aim of revealing the exfoliation mechanism. 1.1. Experimental The vermiculite samples used in this work were supplied by Palabora Mining Co., South Africa, in particles having an average size of 0.7 × 0.5 cm and a thickness between 0.1 and 0.3 cm. The chemical composition was determined by X-ray fluorescence analysis on a Philips PW 1480 spectrometer and the results are given in Table 1 . The cation exchange Powder Technology 189 (2009) 2–5 ⁎ Corresponding author. E-mail address: elmchaouri@hotmail.com (A. Elmchaouri). 0032-5910/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2008.06.013 Contents lists available at ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec