Temperature Effects on Borosilicate Glass and Melt Structure J.F. Stebbins, Stanford University, DMR 0404972

1. Temperature Effects on Borosilicate Glass and Melt Structure J.F. Stebbins, Stanford University, DMR 0404972 Borosilicate glasses are widely used in tech-nologies from computer displays to high-strength composites to nuclear waste storage. Temperature has major effects on the structure and properties of the glass melts, but these are just beginning to be characterized. We have built a special apparatus to cool such liquids very rapidly and thus “freeze in” their struc-tures at high temperatures. Using Nuclear Magnetic Resonance (NMR) spectroscopy, we can clearly see these effects, such as the shift from boron with four oxygen neighbors ([4]B, at right) to boron with three neighbors ([3]B). Our new data on several critical elements in these glasses, including B, Al, Si, O, and F, is for the first time quantifying the interplay among their local structural environments with changing temperature, as well as composition. schematic of miniature rapid quench apparatus [3]B slow (low T) [4]B fast (high T) Boron-11 NMR spectra of commercial fiber glass with varying cooling rates

2. annealed (lowest Tf) Al-O-Al Si-O-Al Si-O-Si fast quench (highest Tf) Temperature Effects on Melt Structure: Materials Science/Geoscience/Career Links J.F. Stebbins, Stanford University, DMR 0404972 The student who built the rapid-quench apparatus, supported by our DMR grant, has completed both a Ph.D. in Geoscience and an M.S. in Materials Science at Stanford, and has gone on to a research career in the glass industry. His joint degrees are typical of the interdisciplinary nature of our program. This equip-ment, as well as currently being used for further work on borosilicate glasses, is also allowing exciting new results on geological compositions. At right are shown data obtained by a female Ph.D. student (supported by a grant from NSF-EAR) demonstrating for the first time that the disorder among “network forming” Si and Al cations increases at high temperature. This reaction is also of key importance in many technological glass-forming melts. As in the DMR project, a critical tool here is advanced, 2-dimensional NMR that resolves the atomic-scale structure around elements such as boron, aluminum and oxygen. oxygen-17 “triple quantum” NMR spectra of NaAlSiO4 glasses with different cooling rates