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Journal of Materials Science

, Volume 30, Issue 24, pp 6281–6287 | Cite as

Silica fracture

Part III Five- and six-fold ring contraction models
  • J. K. West
  • L. L. Hench
Article

Abstract

In part I of this series, a ring contraction model was proposed as the basic mechanism of slow crack growth in silica glass. AM1 molecular orbital theory running on a CAChe workstation was used to find the transition state for the contraction of a 4-fold ring into a 3-fold ring. Using the same AM1 method, the predicted transition state has been found for the contraction of a 5-fold ring into a 4-fold ring. The activation barrier to fracture for this contraction is Ef = +7.9 Kcal mol−1 using Unrestricted Hartree Fock (UHF) theory. As would be expected, the barrier calculated for Restricted Hartree Fock (RHF) was a little higher at Ef = +14.8 Kcal mol−1. This confirms our initial hypothesis that ring contraction can lead to much lower fracture energies than expected from simple Si-O bond breaking. Several different schemes of ring contractions are possible for both 5-fold and 6-fold ring structures. All contraction paths have different intermediate structures that lead to the same end point of slow crack growth. The various barriers to fracture range from +8 to +52 Kcal mol−1 for the 5-fold ring contractions and from +9 to +41 Kcal mol−1 for 6-fold ring contractions.

Keywords

Fracture Energy Activation Barrier Silica Glass Bond Breaking Orbital Theory 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Chapman & Hall 1995

Authors and Affiliations

  • J. K. West
    • 1
  • L. L. Hench
    • 1
  1. 1.Advanced Materials Research CenterUniversity of FloridaAlachuaUSA

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