Optical Glass picture, BK7
 
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N-BK7 Optical Glass

Borosilicate-crown glass from SCHOTT

Special Properties

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

Typical Applications

  • General optics
  • Precision optics
  • Optical glass windows
  • Substrate glass for mirror coatings
  • Measurement and sensor-technology use
  • Glass substrate for filter coatings
  • Wafers for micro-optics
  • Glass blanks for lenses

N-BK7 glass is the arsenic- and lead-free successor material of BK7 glass. It is one of the most common optical glass materials, used for a large number of high quality optics like optical windows, substrates and lenses in the visible range*. Also glass wafers for micro-optics applications are often made of this high purity glass material. Polished windows optics made of BK7 optical glass The relatively tough bor-crown glass shows a good scratch resistance. N-BK7 only has a very low amount of inclusions and is almost free of bubbles, which is of great importance for high quality optics. Another common reason to use this borosilicate-crown glass material for light transmitting optics, is the very linear optical transmission of the glass in the visible range down to 350 nm. Because of stable chemical properties of N-BK7 glass, no special treatment is required to grind and polish the material. The raw-glass is produced in strips and blocks up to about 350 mm wide and about 70 mm thick. It can be fabricated to any smaller size. However, larger N-BK7 strip materials and bigger glass dimensions for larger optical windows are available on request. We grind, polish and shape the glass according to customer's specifications.

 

To request a quotation for windows, substrates, wafers or any other optics made of SCHOTT N-BK7 high quality borosilicate-crown glass with custom dimensions, please click the button below:

 

Request for Quotation

 

 

*If you are interested in glass materials with similar purity, that can be used for the ultraviolet range, please visit our fused-silica and quartz glass pages.

Specifications of N-BK7 glass


N-BK7 glass transmitance data
Optical Transmission spectrum of N-BK7 glass

 

Optical Properties

Refractive index data of N-BK7 glass

Refractive 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 °C to +300 °C)
  • Viscosities:
    • Softening Point (107,6 dPa): 719 °C
    • Annealing Point (1013 dPa): 557 °C
  • Transformation temperature Tg: 557 °C
  • Thermal conductivity: 1,114 W/(m x K)
  • Specific heat capacity: 0,858 J/(g x K)
    (20 °C ; 100°C)

Chemical Resistance

  • 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 about NBK7 glass are available on request.

 

 

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