Optical Glass picture, BK7
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N-BK7 Optical Glass

Special Properties

  • High quality optical glass
  • Practically bubble and inclusion free
  • Very clear and colorless appearance
  • Made of purest raw materials

Typical Applications

N-BK7 is the arsenic and lead free successor material of BK7 which has been discontinued. It is one of the most, common technical optical glass materials for high quality optical componentsOptical BK7 windows in the visible range. N-BK7 is a relatively hard bor-crown glass and shows a good scratch resistance. N-BK7 has a very low amount of inclusions and is almost bubble-free. Another reason for choosing N-BK7 is the high linear optical transmission in the visible range down to 350nm. Because of stable chemical properties of N-BK7, no special treatment is required to grind and polish the material. N-BK7 is produced in strips and blocks up to about 350mm wide and about 70mm thick and can be fabricated to any smaller size. Larger N-BK7 strips and dimensions are available on request.

To request windows or substrates made of Schott N-BK7 Glass with your individual dimensions, please click the button below:

Request BK7

Specifications of N-BK7 Optical Glass

N-BK7 optical transmission

Optical Transmission spectrum of N-BK7

Optical Properties

  • Refractive Index nd : 1,51680 (587,6nm)
  • Abbe numbers:
    • ve = 63,96
    • vd = 64,17

Mechanical Properties

  • Density: 2,51 g/cm3
  • Young's modulus E: 82 x 103 N/mm2
  • Poisson's ratio μ: 0,206
  • Knoop hardness HK0,1/20: 610

Thermal Properties

  • Coefficient of thermal expansion:
    • 7,1 x10-6/K (-30°C to +70°C)
    • 8,3 x10-6/K (+20 to +300°C)
  • Viscosities:
    • Softening Point (107,6 dPa): 719°C
    • Annealing Point (1013 dPa): 557°C
  • Transformation temperature Tg: 557°C

Chemical Resistances

  • Climate Resistance Class 2
    Resistance against humidity is expressed
    by CR-Classes 1 (high) to 4 (low).
  • Stain Resistance Class 0
    Resistance against staining is expressed
    by FR-Classes 0 (high) to 5 (low).
  • Acid Resistance Class 1
    Resistance against acid solutions is expressed
    by SR-Classes 0 (high) to 4 (low).
  • Alkali Resistance Class 2
    Resistance against alkali solutions is expressed
    by AR-Classes 0 (high) to 4 (low).
  • Phosphate Resistance Class 2,3
    Resistance against an alkali phosphate solution
    is expressed by PR-Classes 1 (high) bis 4 (low).

Further detailed specifications on request.

All given details and specifications are mean reference values and are not guaranteed. In addition, please consider our "Notes on technical specifications"