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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Is the structural relaxation of glasses controlled by equilibrium shear viscosity?

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Lancelotti, Ricardo Felipe [1, 2] ; Cassar, Daniel Roberto [2] ; Nalin, Marcelo [3] ; Peitl, Oscar [2] ; Zanotto, Edgar Dutra [2]
Total Authors: 5
[1] Univ Fed Sao Carlos, Grad Program Mat Sci & Engn, Sao Carlos, SP - Brazil
[2] Univ Fed Sao Carlos, Dept Mat Engn Ctr Res Technol & Educ Vitreous Mat, Sao Carlos, SP - Brazil
[3] Sao Paulo State Univ, UNESP, Inst Chem, Araraquara, SP - Brazil
Total Affiliations: 3
Document type: Journal article
Source: Journal of the American Ceramic Society; v. 104, n. 5 JAN 2021.
Web of Science Citations: 1

Knowledge of relaxation processes is fundamental in glass science and technology because relaxation is intrinsically related to vitrification, tempering as well as to annealing and several applications of glasses. However, there are conflicting reports-summarized here for different glasses-on whether the structural relaxation time of glass can be calculated using the Maxwell equation, which relates relaxation time with shear viscosity and shear modulus. Hence, this study aimed to verify whether these two relaxation times are comparable. The structural relaxation kinetics of a lead metasilicate glass were studied by measuring the refractive index variation over time at temperatures between 5 and 25 K below the fictive temperature, which was initially set 5 K below the glass-transition temperature. Equilibrium shear viscosity was measured above and below the glass-transition range, expanding the current knowledge by one order of magnitude. The Kohlrausch equation described very well the experimental structural relaxation kinetics throughout the investigated temperature range and the Kohlrausch exponent increased with temperature, in agreement with studies on other glasses. The experimental average structural relaxation times were much longer than the values computed from isostructural viscosity, as expected. Still, they were less than one order of magnitude higher than the average relaxation time computed through the Maxwell equation, which relies on equilibrium shear viscosity. Thus, these results demonstrate that the structural relaxation process is not controlled by isostructural viscosity and that equilibrium shear viscosity only provides a lower boundary for structural relaxation kinetics. (AU)

FAPESP's process: 17/12491-0 - Kinetic processes in glass and formulation of new glasses using machine learning
Grantee:Daniel Roberto Cassar
Support Opportunities: Scholarships in Brazil - Post-Doctoral
FAPESP's process: 19/15108-8 - Structural relaxation of lead metasilicate and lithium disilicate glasses
Grantee:Ricardo Felipe Lancelotti
Support Opportunities: Scholarships in Brazil - Master
FAPESP's process: 13/07793-6 - CEPIV - Center for Teaching, Research and Innovation in Glass
Grantee:Edgar Dutra Zanotto
Support Opportunities: Research Grants - Research, Innovation and Dissemination Centers - RIDC