resumo
The crystallization kinetics of a glass with a molar composition 40BaO-20ZnO-30B(2)O(3)-10SiO(2) was investigated. The kinetic parameters, activation energy for crystallization (E-c) and Avrami exponent (n), were evaluated under non-isothermal conditions using the results obtained by differential thermal analysis (DTA) performed at different heating rates. DTA curves exhibited two overlapping exothermic peaks associated with the crystallization of the glass. Barium borate (BaB4O7) was the first crystalline phase to be formed and it was followed by the formation of barium zinc silicate (BaZnSiO4), as identified by XRD. For the first exothermic peak, when the fraction of crystallization (v) increased from 0.1 to 0.9, the local activation energy (Ec(v)) decreased from 700 to 500 kJ/mol, while for the second exothermic peak, E-c(chi) slightly increased from 490 to 570 kJ/mol. For the range of 0.1 < chi < 0.9, the local Avrami exponent (n(chi)) increased from similar to 1 to 1.4 for the first exothermic peak and it decreased from similar to 1.7 to 1.4 for the second exothermic peak. Observation by SEM of the microstructure of sintered glass samples revealed that crystallization started at the surface of glass particles, with growth of lamellar crystallites, that together with some quasi-spherical nano-sized crystallites progressed towards the inside of the glass at the highest sintering temperatures. The change of the local activation energy with the fraction of crystallization suggested that a multi-step kinetic reaction took place during sintering and crystallization of the glass. (C) 2013 Elsevier B.V. All rights reserved.
palavras-chave
DIFFERENTIAL THERMAL-ANALYSIS; PHASE-TRANSFORMATION; LOW-TEMPERATURE; MECHANISM; CERAMICS; BEHAVIOR; OXIDE; PLOT
categoria
Chemistry; Materials Science; Metallurgy & Metallurgical Engineering
autores
Lopes, AAS; Monteiro, RCC; Soares, RS; Lima, MMRA; Fernandes, MHV
nossos autores
Maria Helena Figueira Vaz Fernandes
Professor(a) Jubilado(a)agradecimentos
This work was supported by the Fundacao para a Ciencia e a Tecnologia (Portugal), through Project PTDC/CTM/102141/2008 and through funding to I3N/CENIMAT (Strategic Project PEst-C/CTM/LA0025/2013).