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Corning Low Expansion Glass Pyrex

The most widely used low expansion glass is corning Pyrex®. It is mostly made from code 7740 Pyrex borosilicate glass that has been specially treated to achieve low thermal expansion. It is highly resistant to chemical attack and is able to tolerate almost all temperatures used in laboratories. It is designed for use in the tough environment requiring high resistance to strong acids, alkalis and huge thermal shock, and it is suited to applications such as mirror substrates or windows in high or low temperature environments. On the other hand, it is less homogeneous and contains more bubbles than optical glass.

The visible light transmittance of code 7740 glass is 92% at 2mm thickness. Here is a figure of internal transmittance.


Figure 1: External transmittance curve of Pyrex at sample thickness of 2 mm

  Wavelength (nm)
Refractive Index
Wavelength (nm) Refractive Index  
1.479 587.6 1.474  
  514.5 1.477 643.8 1.472  
  Abbe Constant
  Density (g/cm3)
  Young's Modulus (Kg/m2)
  Poisson's Ratio
  Coefficient of Thermal Expansion (m/m·°C) 3.25X10-6 (0°C~300°C)  
  Softening Point (°C) 820
  Annealing Point (°C) 565
  Melting Point (°C) 1250
  Table 1:Pyrex Properties

Low Expansion Materials :  

Pyrex® is a registered trademark of Corning Inc.

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