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N-BK7

Optical borosilicate-crown glass

Special Properties

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

Typical Applications

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

Related glass types

Request for Quotation

48h-Express Service Also available in 48 h Express-Service*

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

The high optical quality is a primary technical reason why N-BK 7 glass is often used. The smooth transmission, as well as a low absorption in the entire visible wavelength range, are a crucial feature for a large number of optical applications.

Unpolished N-BK7 raw materials are produced with a maximum length of about 350 mm and a thickness of around 70 mm. SCHOTT BK7 glass blanksLarger glass dimensions are often possible on request. N-BK7 belongs to the block glasses 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 glass 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 glass material with individual dimensions, please click on the following button:

 

Request for Quotation

 

*Within our express service the following glass thicknesses are possible: 1,00 mm, 2,00 mm and 3,00 mm. Of course, at a regular delivery time, we polish to any desired thickness.

 

Note: If you are interested in glass materials with similar purity which can transmit ultraviolet light, please visit our fused-silica and quartz glass web page.

 

Material Specifications

N-BK 7 glass transmittance data

Optical transmission spectrum at 10 mm 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 N-BK7 glass against humidity is expressed by CR-Classes 1 (high) to 4 (low).
  • Stain Resistance Class 0
    The resistance of N-BK7 glass against staining is expressed by FR-Classes 0 (high) to 5 (low).
  • Acid Resistance Class 1
    The resistance of N-BK7 glass against acid solutions is expressed by SR-Classes 0 (high) to 4 (low).
  • Alkali Resistance Class 2
    The resistance of N-BK7 glass against alkali solutions is expressed by AR-Classes 0 (high) to 4 (low).
  • Phosphate Resistance Class 2,3
    The resistance of N-BK7 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. Also, please consider our "Notes on technical specifications".

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