Optical Glass banner picture
 
Home / Products / Technical Glass / N-BK7 Optical Glass

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 or prisms

N-BK7 glass is the arsenic- and lead-free successor material of BK7 glass. It represents an industry standard for optics and is one of the most common optical glass materials, used for a large number of high quality optics like optical windows, substrates, prisms and lenses in the visible transmission spectrum*. Also glass wafers for micro-optics applications are often made this high purity glass material. Polished window optics made of BK 7 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 a glass of which high quality optics should be made of. Another common reason to use N-BK 7 borosilicate-crown glass material, which has an Abbe number of around 64, for light transmitting optics, is the very uniform optical transmission in the visible range down to 350 nm. Because of the stable chemical properties of this optical glass, no special treatment is required to grind and polish the material. N–BK 7 raw-glass is produced in strips and blocks up to about 350 mm wide and about 70 mm thick by SCHOTT. It can be fabricated to any smaller size. However, larger strip materials and bigger glass dimensions for larger optical windows are available on request. We grind, polish and shape N-BK7 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

48h- Express Service icon


48-h Express Optics Service available

Within our express service the following glass thicknesses are possible: 1,00 mm ; 2,00 mm and 3,00 mm

Of course, at normal delivery time any desired thickness can be manufactured.

 

*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 information pages.

Specifications

 

N-BK 7 glass transmittance data

Optical transmission spectrum at 10mm glass thickness

 

Optical Properties

Refractive index data

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

Further detailed specifications about SCHOTT N-BK 7 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"