Titre du document / Document title

First Observation of α-Ca₂[SiO₃(OH)] (OH)-Ca₆[Si₂O₇][SiO₄](OH)2 Phase Transformation upon Thermal Treatment in Air

Auteur(s) / Author(s)

GARBEV Krassimir ⁽¹⁾ ; GASHAROVA Biliana ⁽²⁾ ; BEUCHLE Günter ⁽¹⁾ ; KREISZ Siegfried ⁽¹⁾ ; STEMMERMANN Peter ⁽¹⁾ ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

⁽¹⁾ Institute for Technical Chemistry-Thermal Waste Treatment, Forschungszentrum Karlsruhe, 76021 Karlsruhe, ALLEMAGNE
⁽²⁾ ANKA/Institute for Synchrotron Radiation, Forschungszentrum Karlsruhe, 76021 Karlsruhe, ALLEMAGNE

Résumé / Abstract

Thermal treatment transforms α-Ca₂[SiO₃(OH)](OH) (α-C₂SH) into hydraulic Ca₂SiO₄ polymorphs, which is a process of considerable interest to the cement chemistry community. The thermal behavior of differently synthesized samples of α-C₂SH in air at ambient pressure has been investigated in detail by high-temperature powder X-ray diffraction (XRD), synchrotron-based infrared (IR) microspectroscopy of single crystals, trimethylsilylation method (TMSM), and thermal analysis. Powder XRD data on α-C₂SH samples heated to different temperatures between 300° and 500°C suggest coexistance of α-C₂SH and dellaite, Ca₆[Si₂O₇][SiO₄](OH)₂. IR absorption bands typical for the initial α-C₂SH phase diminish over the course of thermal treatment, accompanied by the appearance of bands characteristic for dellaite. The partial polymerization of the isolated SiO₃(OH) tetrahedra present in α-C₂SH to [Si₂O₇] dimers, as expected for dellaite, was proven by the presence of an IR band at 1050 cm^-1 and by TMSM. For the first time, dellaite, along with x-Ca₂SiO₄, was observed as an intermediate product of the dehydration of α-C₂SH. Until now, dellaite was believed to be only a high-pressure phase. Dellaite coexists with x-Ca₂SiΟ₄ up to 560°-620°C and decomposes to x-Ca₂SiΟ₄ at higher temperatures. Upon further heating, the latter phase transforms into α'L-Ca₂SiO₄, and finally gives β-Ca₂SiΟ₄ after cooling to room temperature. The thermal decomposition of α-C₂SH is a much more complicated process than reported previously. Different factors, such as the source of Ca and the presence of NaOH during synthesis, seem to control the mechanism of its dehydration. The presence of dellaite is shown to lower the temperature of formation of β-Ca₂SiO₄.

Revue / Journal Title

Journal of the American Ceramic Society   ISSN 0002-7820   CODEN JACTAW 

Source / Source

2008, vol. 91, n^o1, pp. 263-271 [9 page(s) (article)] (40 ref.)

Langue / Language

Anglais

Editeur / Publisher

Blackwell, Malden,MA, ETATS-UNIS  (1918) (Revue)

Mots-clés anglais / English Keywords

Quantitative analysis ; Infrared spectrometry ; Differential thermal analysis ; Thermogravimetry ; Scanning electron microscopy ; X ray diffraction ; Phase transformation ; Heat treatment ; Experimental study ; Portland cement ;

Mots-clés français / French Keywords

Analyse quantitative ; Spectrométrie IR ; Analyse thermique différentielle ; Thermogravimétrie ; Microscopie électronique balayage ; Diffraction RX ; Transformation phase ; Traitement thermique ; Etude expérimentale ; Ciment Portland ;

Mots-clés espagnols / Spanish Keywords

Análisis cuantitativo ; Espectrometría IR ; Análisis térmico diferencial ; Termogravimetría ; Microscopía electrónica barrido ; Difracción RX ; Transformación fase ; Tratamiento térmico ; Estudio experimental ; Cemento Portland ;

Localisation / Location

INIST-CNRS, Cote INIST : 101, 35400017459141.0450