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Materials 2010, 3(12), 5246-5262; doi:10.3390/ma3125246
Review

Bond Strength—Coordination Number Fluctuation Model of Viscosity: An Alternative Model for the Vogel-Fulcher-Tammann Equation and an Application to Bulk Metallic Glass Forming Liquids

1,*  and 2
1 Course of General Education, Natural Science, Fukui National College of Technology, Geshi-chou, Sabae, Fukui 916-8507, Japan 2 Department of Physics, Graduate School of Science and Technology, Kumamoto University, Kumamoto 860-8555, Japan
* Author to whom correspondence should be addressed.
Received: 3 November 2010 / Revised: 1 December 2010 / Accepted: 7 December 2010 / Published: 10 December 2010
Download PDF [920 KB, 16 December 2010; original version 10 December 2010]

Abstract

The Vogel-Fulcher-Tammann (VFT) equation has been used extensively in the analysis of the experimental data of temperature dependence of the viscosity or of the relaxation time in various types of supercooled liquids including metallic glass forming materials. In this article, it is shown that our model of viscosity, the Bond Strength—Coordination Number Fluctuation (BSCNF) model, can be used as an alternative model for the VFT equation. Using the BSCNF model, it was found that when the normalized bond strength and coordination number fluctuations of the structural units are equal, the viscosity behaviors described by both become identical. From this finding, an analytical expression that connects the parameters of the BSCNF model to the ideal glass transition temperature T0 of the VFT equation is obtained. The physical picture of the Kohlrausch-Williams-Watts relaxation function in the glass forming liquids is also discussed in terms of the cooperativity of the structural units that form the melt. An example of the application of the model is shown for metallic glass forming liquids.
Keywords: viscosity; VFT equation; BSCNF model; fragility; cooperativity viscosity; VFT equation; BSCNF model; fragility; cooperativity
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Ikeda, M.; Aniya, M. Bond Strength—Coordination Number Fluctuation Model of Viscosity: An Alternative Model for the Vogel-Fulcher-Tammann Equation and an Application to Bulk Metallic Glass Forming Liquids. Materials 2010, 3, 5246-5262.

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