Crystallization kinetics and phase transformation characteristics in seeded monophasic cordierite gel

Abstract

Crystallization kinetics and phase transformation characteristics of μ- or α-cordierite seeded gels were compared with those of unseeded monophasic gels. The α-cordierite seeding modified the sequence of phase transformation and lowered the temperature of α-cordierite formation from amorphous gel by ∽150 °C. The μ-seeded transformation was characterized by 3-dimensional isotropic growth with essentially zero activation energy for the nucleation step. Combining the nucleation theory with the transition state theory, we have separately estimated the activation free energy of nucleation and that of growth step in the crystallization of amorphous cordierite gel. The estimated activation free energies showed that the crystallization of unseeded cordierite gel is mainly growth controlled.

Cristalización de cordierita a partir de geles y vidrios estequiométricos. Estudio comparativo

“…El gel precursor se obtuvo a partir de Al(NO 3 ) 3 á9H 2 O (Aldrich, 99% pureza), Mg(NO 3 ) 2 á6H 2 O (Fluka, >99% pureza) y Tetraetilortosilicato, TEOS (Fluka, >98% pureza) (5,12,13). Los nitratos de Mg y Al se disolvieron en etanol a 55¼C durante un d'a con agitaci-n y reflujo para evitar pŽrdidas de disolvente y garantizar una completa y homogŽnea disoluci-n. La disoluci-n resultante se dej-enfriar hasta temperatura ambiente y se a-adi-la cantidad necesaria de TEOS para la estequiometr'a deseada.…”

Rotas de síntese e a homogeneidade dos precursores de mulita e cordierita

“…Atualmente, o processo sol-gel tem sido muito estudado, por permitir a formação de precursores cerâmicos com elevado grau de homogeneidade. Nesse processo, a síntese do material cerâmico resulta da conversão de um sol em um gel e do gel, geralmente por calcinação, no produto final (óxidos, nitretos, fosfatos), mantendo-se, no entanto, ao longo desse processamento, a homogeneidade do sol e do gel [19][20][21][22][23] .…”

Effect of Ultrasonic Treatment on the Crystallization Kinetic Parameters of BaNaB9O15 Glasses

“…One could estimate E N separately by comparing the Arrhenius activation energy for the UST samples with that for the untreated samples 26 where n is the Avrami exponent for untreated samples. The activation energy for crystallization is reduced by 34±2 kJ/mol when the BNBO glasses are ultrasonicated with suspension of BNBO ceramic powder.…”