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N-BK7

Optical borosilicate-crown glass

Special Properties

  • Particularly high optical quality
  • Uniform transmission in the visible
  • Virtually free of bubbles and inclusions
  • Very clear, practically colorless appearance
  • High purity of raw materials

Typical Applications

  • Demanding optical applications
  • Precision optics
  • Optical windows and lenses
  • Substrates for mirror and filter coatings
  • Measurement and sensor-technology use
  • Lenses and prims

 

N-BK7 is a very pure, universal optical glass. It is one of the most common glasses used to produce high-quality optical components, especially for the visible spectrum. Polished window optics made of BK 7 optical glass The relatively hard borosilicate crown glass is made of purest materials. It contains very few inclusions and is almost free of bubbles.

The high optical quality is a common technical reason for the use of N-BK 7. The uniform transmission as well as a low absorption in the entire visible wavelength range are a key feature for a large number optical applications.

Unpolished N-BK7 raw material is produced with a maximum length of about 350 mm and a thickness of around 70 mm. SCHOTT BK7 glass blanksLarger dimensions are often possible on request. N-BK7 is a block glass and does not come in the form of smooth glass sheets. The material is therefore generally sawn, ground, polished and shaped according to customer's specification. Due to stable chemical properties and high stain resistance, a special treatment of N-BK7 is not necessary before it is ground and polished.

 

If you would like to request windows, substrates, wafers or other optical components from N-BK 7 with individual dimensions, please click on the following button:

 

Request for Quotation

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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 we polish to any desired thickness.

 

Note: If you are interested in glasses 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 material 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"