Glass-ceramic with ultra-low expansion：

Glass-ceramic with ultra-low expansion is a kind of inorganic glass with the lowest expansion coefficient. It ensures the high accuracy of component’ shape and size in spite of the change in environment temperature, and is suitable to make all optical and mechanical parts for astronomical instruments, optical instruments, scientific research, and national high-tech industry, such as reflectors, models, precision planes, and Straightedges.

Technical performance：

1. Average coefficient of linear expansion（α 0～50℃）

Class 1：     0±1.0×10-7/℃ ；

Class 2：     0±1.5×10-7/℃

2．Stress birefringence（nm/cm）

Type I：   ≤φ1m：  ≤5；     ＞φ1m：≤10。

TypeⅡ：   ≤φ1m： ≤10；    ＞φ1m：≤15。

Note: The distance between the measuring point of the outer circle and the edge of the mirror base is 5% of the mirror base’ diameter.

3.Bubbles

Note: A prolate bubble’ diameter is the arithmetic mean value of the longest axis and the shortest axis. Calculi, crystal and other inclusions would be counted as bubbles.

4.Main performance parameter