resumo
The crystallisation kinetics of experimental glasses in 3 different systems: (A) Li2O-SiO2, (B) Li2O-Al2O3-SiO2 and (C) Li2O-K2O-Al2O3-SiO2 were studied under non-isothermal conditions. The DTA results revealed a stronger tendency to crystallisation of binary compositions in comparison to the ternary and quaternary compositions comprising Al2O3 and K2O which present the lower crystallisation, i.e. the crystallisation propensity follows the trend A > B > C. The devitrification process in the Li2O-SiO2 and Li2O-Al2O3-SiO2 systems began earlier and the rate was higher in comparison to that of glasses in the quaternary Li2O-K2O-Al2O3-SiO2 system. Thus, addition of Al2O3 and K2O to glasses of Li2O-SiO2 system was demonstrated to promote glass stability against crystallisation. However, the activation energy for crystallisation was shown to depend also on the SiO2/Li2O ratio with the binary system showing a decreasing trend with increasing SiO2/Li2O ratio, while the opposite tendency was being observed for compositions with added Al2O3 and K2O.
palavras-chave
DIFFERENTIAL THERMAL-ANALYSIS; TRANSITION TEMPERATURE; HEATING RATE; CHALCOGENIDE GLASS; ACTIVATION-ENERGY; PHASE-CHANGE; SYSTEM; TRANSFORMATION; DEPENDENCE; K2O
categoria
Thermodynamics; Chemistry
autores
Fernandes, HR; Tulyaganov, DU; Ferreira, JMF
nossos autores
Hugo Alexandre Gonçalves da Rocha Fernandes
Investigador Júnior
José Maria da Fonte Ferreira
Professor(a) Jubilado(a)Grupos
G3 - Materiais Eletroquímicos, Interfaces e Revestimentos
G5 - Materiais Biomiméticos, Biológicos e Vivos
agradecimentos
Hugo R. Fernandes is grateful for the financial support of CICECO and for the PhD Grant (SFRH/BD/41307/2007) from the FCT, Portugal.