Glass-ceramics for high precision reflective-optic applications.

Area of Science:

• Materials Science
• Glass-Ceramics Technology
• Optical Engineering

Background:

• Development of advanced materials for large optical components like mirror blanks is critical.
• Traditional glass materials may not meet stringent requirements for thermal stability and low expansion.
• The Li(2)Al(2)O(4)-SiO(2) system offers potential for creating novel glass-ceramics.

Purpose of the Study:

• To investigate the suitability of titania- and zirconia-nucleated glasses in the Li(2)Al(2)O(4)-SiO(2) system for casting large mirror blanks.
• To characterize the resulting glass-ceramics, focusing on their thermal expansion, transparency, and structural uniformity.
• To address processing challenges associated with large-scale fabrication.

Main Methods:

• Casting of large mirror blanks using titania- and zirconia-nucleated Li(2)Al(2)O(4)-SiO(2) glasses.
• Controlled heat treatment to induce crystallization into beta quartz solid solution.
• Characterization of thermal expansion coefficients, optical transparency, and internal strain.
• Evaluation of processing parameters for thick ware fabrication.

Main Results:

• Uniform crystallization was achieved, yielding transparent glass-ceramics.
• Achieved average expansion coefficients of 0 +/- 0.3 x 10(-7)/°C over a temperature range of 5-50°C.
• Successfully processed ware up to 15 cm thick with less than 10 micro/cm strain.
• Demonstrated consistent properties (expansion, transparency) throughout thick blanks.

Conclusions:

• Titania- and zirconia-nucleated Li(2)Al(2)O(4)-SiO(2) glass-ceramics are suitable for large mirror blank fabrication.
• The developed materials offer excellent thermal stability and transparency.
• Processing insights were gained for the fabrication of very large castings, addressing challenges of exothermic crystallization.