Bk-7 Glass, an Optical Borosilicate Crown Glass, has a high transmission and is free of bubbles and inclusions. With superior physical properties, it can be polished like leaded glass, making it suitable for lenses and prisms for lasers and optics. It weighs about 15% less than full (24%) leaded glass (crystal).
Since BK7 performs well in all chemical tests, no special handling is required, resulting in lower manufacturing costs.
SiO2=69.13% B2O3=10.75% BaO=3.07% Na2O=10.40% K2O=6.29% As2O3=0.36%
|Thermal Coefficient of Expansion||(0/300℃): 70 X 10 -7/℃|
|Annealing Point||550℃ / 1022 °F|
|Softening Point||719℃ / 1326 °F|
|Strain Point||624℃ / 1155 °F|
|Young's Modulus||8.20 X 109 dynes/mm2|
|Hydrolytic Resistance||class 2|
|Acid Resistance||class 1|
|Alkali Resistance||class 1|
BK-7 Glass provides excellent transmittance through-out the visible and near infrared spectra and down to 350 nm in the ultraviolet: