![]() T is occupied by tetrahedrally coordinated Si, P, S, V, As, etc. M1 and M2 are two independent polyhedral cationic positions occupied by Ca. According to the nomenclature, the roman superscript denotes the coordination of the polyhedra. Ellestadites belong to the apatite supergroup with the general formula IXM1 4 VIIM2 6( IVTO 4) 6 × 2. Exact compositions and their changes as a function of temperature are not well understood. The ellestadite group is notorious for its versatility in terms of chemical composition and structure. Another source for the formation of SCE (and synthetic chlorapatite) along with KCl, is the use of industrial waste materials such as PVC or other chlorine-containing polymers as alternative fuels in cement kilns. Wastes from AAC contain sulfate from several sources, e.g., CaSO 4 added for achieving an initial strength of the green body during its production or due to the inevitable contamination with masonry during demolition. The use of autoclaved aerated concrete (AAC) wastes as a raw material for the synthesis of a C 2S cement clinker provides the sulfate needed within the Ca-silicate matrix for the formation of ternesite or SCE. Due to their high electronegativity, such agents change the properties of the melt and facilitate the dissolution and diffusion of CaO, thus accelerating the C 2S synthesis at significantly lower temperatures. SCE is a common phase formed by calcination processes in course of the production of alternative cement clinker rich in belite (Ca 2SiO 4 or C 2S according to the cement nomenclature, with C, S denoting CaO and SiO 2, respectively), when CaCl 2 is used as a mineralizing (or flux) agent. ![]() Synthetically obtained chlorellestadite (SCE) was already reported by Pliego-Cuervo and only recently, its natural analogue was confirmed by Środek et al. At temperatures above 900 ☌ in air, ellestadite is carbonate-free and above 1000 ☌ chlorine loss starts in all samples.Ĭhlorellestadite, Ca 10(SiO 4) 3(SO 4) 3Cl 2, is a chlorine endmember of the ellestadite group of minerals. ![]() At low temperatures, SCE coexists with spurrite intermixed on a very fine nm scale. Incorporation of CO 3 results in a shorter unit cell parameters and smaller cell volume similar to CO 3−apatite. Raman spectroscopy proved the partial substitution of sulfate by CO 3 2− groups in ellestadites formed at 800 ☌ and 900 ☌ in air. Rietveld refinements revealed the presence of chlorine and calcium vacancies. At lower temperatures of formation, a non-stoichiometric SCE seems to crystallize in a monoclinic symmetry similar to hydroxylellestadite. In general, the amount of SCE depends mainly on the sulfate content and to a lesser extent on the synthesis temperature. Samples were investigated by X-ray diffraction and Raman spectroscopy. Synthetic chlorellestadite (SCE Ca 10(SiO 4) 3(SO 4) 3Cl 2) forms in experiments at temperatures between 7 ☌. The synthesis of low-temperature belite (C 2S) clinker from wastes of autoclaved aerated concrete and limestone was studied in the presence of CaCl 2 as a mineralizing agent.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |