Comparative study of the effects of thermal and mechanical treatments on the structures of clay minerals

Abstract

Controlled heating (in air) of clay minerals leads to transformations into disordered structures and recrystallization into new phases at high temperatures. These phase transformations are of topotactic nature. On the other hand, prolonged dry-grinding treatments of the same silicates causes structural amorphization with no recrystallization into new phases. The mechanical energy relaxation mechanism, invoked to explain these differences, accounts for the particle size changes and the large growth of dislocations. The latters affect sensibly the reactivity of the materials submitted to such solid-state treatments.These processes are monitored mostly by XRD, DTA and IR spectroscopy. The latter method allows to study in some silicates submitted to progressive grinding the location and nature of OH groups and water molecules.

Thermally treated clay sediments as geopolymer source material

“…This meta-state is widely addressed as being reactive as pozzolana (Ambroise et al, 1985(Ambroise et al, , 1987Applied Clay Science xxx (2015) xxx-xxx He et al, 1995aHe et al, , 1995bHe et al, , 2000Baronio and Binda, 1997;Liebig and Althaus, 1997;Kakali et al, 2001;Sabir et al, 2001). Nevertheless, firing to higher temperatures results in the formation of new unreactive phases such as spinel and mullite (Mendelovici, 1997;Bondar et al, 2011a). Anyway, a careful calcination can activate the material leading to an increase of its geopolymeric reactivity (Xu and Van Deventer, 2002) and a consequent increase in terms of compression strength of the final product obtained.…”

“…Since the thermal activation can be useful for enhancing the sediment reactivity in polycondensation processes (Mendelovici, 1997;Buchwald et al, 2009), weighted amount of sediments were thermally treated at two different temperatures (400°C and 750°C for 2 h). The calcination was performed using a Nabertherm furnace with a heating rate of 10°C/min.…”

“…These materials are widely available all over the world and may show certain reactivity after a thermal activation process (He et al, 1995a). In fact the thermal activation of clay minerals in the temperature range between 500 and 800°C results generally in a dehydroxylation (Heller-Kallai, 2006), which causes the octahedral sheets lose water and decompose into a disordered metastable state (Evans and White, 1959;Mendelovici, 1997). This meta-state is widely addressed as being reactive as pozzolana (Ambroise et al, 1985(Ambroise et al, , 1987Applied Clay Science xxx (2015) xxx-xxx He et al, 1995aHe et al, , 1995bHe et al, , 2000Baronio and Binda, 1997;Liebig and Althaus, 1997;Kakali et al, 2001;Sabir et al, 2001).…”

Thermal decomposition of different types of asbestos

“…Similar to the clay minerals [29,30], thermal decomposition of asbestos minerals generally takes place according to three stages [7,31]. The first is associated with the loss of adsorbed water.…”

Geopolymerization Ability of Natural and Secondary Raw Materials by Solubility Test in Alkaline Media

“…It is well known that the thermal activation of silico-aluminate minerals in the temperature range between 400 and 800 °C results generally in a dehydroxylation [18,21], which causes the loss of the structural water and decompose into a disordered metastable state [22]. This meta-state is widely addressed as being active in pozzolanic reactions [23,24].…”