Date of Award

8-2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Materials Science and Engineering

Advisor

Richardson, Kathleen

Committee Member

Fotheringham , Ulrich

Committee Member

Joseph , Paul

Committee Member

Luzinov , Igor

Committee Member

Petit , Laeticia

Abstract

This thesis contains results of our efforts to develop a method for defining key glass material properties that must be known and modeled for the design and experimental validation of a precision glass molding (PGM) process for optical glasses. Viscosity, calorimetric, and thermal expansion properties of two commercial glass types N-BK7 and P-SK57 of SCHOTT were characterized to establish a proof-of-concept protocol for the experimental determination of meaningful material properties. Experimental results were determined in order to be incorporated into a computational model predicting final glass size and shape following a molding cycle. Experimental methods were confirmed on the two 'known' glass types and extended to a moldable, OHARA (L-BAL35), which had never-before been characterized using this protocol, for molding applications.
Beam-bending and parallel-plate techniques were employed to measure the glass viscosity, and the well-known VFT equation was used to interpolate viscosity data through the molding region. Expansion behavior below and above the glass transition temperature, Tg and transition region was quantified using rate-heating and isothermal expansion measurements, respectively. Differential Scanning Calorimetry measurements were performed and curve-fitted using the Tool-Narayanaswamy-Moynihan (TNM) model for structural relaxation, and from these calculations kinetic glass property response in the transition region was determined. Finally, a model for predicting the thermal expansion behavior of the glass optical lens upon cooling from the molding temperature was compiled using experimentally determined variables derived within this effort. The results show that a simple, linear thermal expansion model cannot be used and that structural relaxation must be implemented in order to precisely define the glass expansion properties upon rapid cooling through the glass transition region.

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