Estudio por difracción de rayos X de la hidratación de mezclas de CaAl₂O₄ - Humo de silice

Abstract

Se ha estudiado la influencia del humo de sílice sobre el mecanismo de hidratación del monoaluminato de calcio (CaAl 2 O 4 ) a temperatura ambiente y con una relación agua/sólidos de 0,5. La evolución de las fases hidratadas, que se forman en los primeros instantes de la reacción, se ha estudiado por difracción de rayos X de laboratorio con una resolución temporal de 36 min. In situ X-ray difraction study of hidration of CaAl 2 O 4 -amorphous silica mixturesThe influence of the amorphous silica on the mechanism of hydration of the calcium monoaluminate (CaAl 2 O 4 ) has been studied at ambient temperature with a water/solids ratio of 0.5. The evolution of the hydrated phases, formed in the first instants of the reaction, has been studied by laboratory X ray diffraction with a time resolution of 36 min. The integration of selected diffraction peaks of the phases: Ca 2 Al 2 O 5 ·8H 2 O (Ca 2 Al 2 (OH) 10 ·3H 2 O), CaAl 2 O 4 and Ca 4 Al 2 (OH) 12 (CO 3 )·5H 2 O, has allowed to establish the kinetics of the reaction. This way, it has been shown that the amorphous silica causes a drastic decrease in the period of induction of the hydration and accelerates the formation of the metastable crystalline hydrates Ca 2 Al 2 (OH) 10 ·3H 2 O and Ca 4 Al 2 (OH) 12 (CO 3 )·5H 2 O. These results have been confirmed by Thermogravimetry, Differential Thermal Analysis and Scanning Electric Microscopy. The hydration mechanism proposed confirms previous data of Nuclear Magnetic Resonance of Solids (RMN) of 29 Si of the authors of this paper.

Dehydration of Ca3Al2(SiO4)y(OH)4(3−y) (0<y<0.176) studied by neutron thermodiffractometry

“…The formation of various short-lived crystalline phases along the dehydration process like Ca 12 Al 14−y Si y O 32 (O,OH) 1+y/2 , Ca(OH) 2 and CaO were observed. The mean (linear) thermal expansion coefficients for the hydrogarnet and katoite are calculated in the temperature range 25-250 • C.…”

“…[1][2][3] The main role of silica fume is improving the rheology of the refractory concrete mix for better pumping and stability. Silica fume is widely used in LCCs and when combined with admixtures a system with low water demand can be achieved.…”

Effect of Polycarboxylate–Ether Admixtures on Calcium Aluminate Cement Pastes. Part 2: Hydration Studies

“…An analysis of the XRD findings for the 16-h CAC pastes showed that the hexagonal hydrate content (CAH 10 and C 2 AH 8 ) was higher in the admixture-free paste than in the paste containing PC1 (see Figure and Table ) . The FTIR results for these same pastes confirmed the higher degree of paste hydration in the absence of the admixture, with more intense vibration bands (in the 3650–3400 and 1020 cm –1 regions) associated with monocalcium aluminate hydration products.…”