Optical Glass picture, BK7
 
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N-BK7 Optical Glass

Bor-crown glass from SCHOTT

Special Properties

  • High optical quality bor-crown glass
  • Practically free of bubbles and inclusions
  • Very clear and colorless appearance
  • Made of purest raw materials

Typical Applications

  • General optical applications
  • Precision optics
  • Optical glass windows
  • Substrates for mirror coatings
  • Measurement and Sensor-Technology
  • Glass substrate for filter coatings
  • Blanks for lenses

N-BK7 glass 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, used for a large N-BK7 blanksnumber of high quality optics like optical windows, substrates and lenses in the visible range*. N-BK7 is a relatively tough bor-crown glass and shows a good scratch resistance. N-BK7 glass has a very low amount of inclusions and is almost free of bubbles. Another reason why N-BK7 material is often used for light transmitting optics, is the high linear optical transmission of the glass in the visible range down to N-BK7 polished glass window optics350nm. Because of stable chemical properties of N-BK7 glass, no special treatment is required to grind and polish the material. N-BK7 raw glass is produced in strips and blocks up to about 350mm wide and about 70mm thick. It can be fabricated to any smaller size. Larger N–BK7 strip materials and bigger dimensions are available on request. We grind, polish and shape this precision glass according to customer's specifications.


To request a quotation for a window or a substrate made of SCHOTT N-BK7 glass with custom dimensions, please click the button below:


Request for Quotation

 

 

 

*If you are interested in a glass material with similar purity that can be used in the ultraviolet range, please visit our Fused Silica & quartz glass website.

Specifications of N-BK7 Optical Glass


N-BK7 glass, optical transmission
Optical Transmission spectrum of N-BK7

 

Optical Properties

Refractive index of N-BK7 glass

Index name

Wavelength (nm)

Refractive Index

ni
365,0
1.53627
nh
404,7
1,53024
ng
435,8
1,52668
nF'
480,0
1,52283
nF
486,1
1,52238
ne
546,1
1,51872
nd
587,6
1,51680
nD
589,3
1,51673
n632,8
632,8
1,51509
nC
643,8
1,51472
nc
656,3
1,51432
nr
706,5
1,51289
ns
852,1
1,50980
nt
1014,0
1,50731
  • Abbe number:
    • 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 and information about this glass on request.


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