Please use this identifier to cite or link to this item: doi:10.22028/D291-24576
Title: Crystallization kinetics of mullite from single-phase gel determined by isothermal differential scanning calorimetry
Author(s): Tkalcec, Emilija
Nass, Rüdiger
Schmauch, J.
Schmidt, Helmut K.
Kurajica, S.
Bezjak, A.
Ivankovic, Hrvoje
Language: English
Year of Publication: 1998
OPUS Source: Journal of Non-Crystalline Solids. - 223. 1998, S. 57-72
SWD key words: Kristallisation
Differential scanning calorimetry
Isotherme Reaktion
DDC notations: 620 Engineering and machine engineering
Publikation type: Journal Article
Abstract: Transformation kinetics of single-phase gel with mullite composition was studied by isothermal differential calorimetry (DSC) in temperature range from 937 to 959°C. Single exotherm was observed for annealing temperatures below 947°C, and two overlapped exothermic peaks were seen above this temperature. According to XRD analysis, mullite was the only phase crystallized either under non-isothermal or isothermal heat treatment. Johnson-Mehl-Avrami (JMA) equation for nucleation and growth could not describe mullite crystallization adequately, even below 947°C. Using bimodal JMA-type model, that proposes mullite crystallization in two steps, the fitting was remarkably good in the whole temperature range. Obtained kinetics data do not allow one to characterize the gel, either as typical single phase one (nucleation-controlled process with two rate constants and small apparent activation energies), or as hybrid gel (mullite formation via spinel and high apparent activation energies). The rate constants were an order of magnitude smaller than is proposed for single phase gel. The apparent activation energies, however (Eal = 1053 ± 51 kJ/mol, and Ea2 = 1028 ± 22 kJ/mol), were in great discrepancy to those already cited for single phase gels, but they were in very good agreement with data evaluated for diphasic and hybrid gels. Mullite a-axis length and effective fraction of mullite that is formed in the first and second step of the process provided an insight in the mechanism of mullite crystallization. It is assumed that not the nucleation and crystallization limitations, rather the phase separation is the controlling process in mullite formation from single phase gel under applied experimental conditions.
Link to this record: urn:nbn:de:bsz:291-scidok-28823
Date of registration: 10-Jun-2010
Faculty: SE - Sonstige Einrichtungen
Department: SE - INM Leibniz-Institut für Neue Materialien
SciDok - Der Wissenschaftsserver der Universität des Saarlandes

Files for this record:
File Description SizeFormat 
sm199801.pdf1,05 MBAdobe PDFView/Open

Items in SciDok are protected by copyright, with all rights reserved, unless otherwise indicated.