Borosilicate glass is produced mainly using silica and boron oxide. Borosilicate glasses are known for having very low coefficients of thermal expansion (~3 x 10−6 /°C at 20°C), and this makes it resistant to thermal shock, much more than any other common glass. Common glass is used in applications less subject to thermal stress, for reagent bottles and some microscope slides.
Borosilicate glass is highly resistant to water, neutral and acid solutions, concentrated acids and acid mixtures, and to chlorine, bromine, iodine and organic substances. Its chemical resistance is superior to that of most metals and other materials, even during prolonged periods of exposure and at temperatures above 100°C.
Only hydrofluoric acid, concentrated phosphoric acid and strong alkali cause appreciable surface removal of the glass (glass corrosion) at elevated temperatures (>100°C).
Borosilicate glass has the following approximate composition (%)
|Hydrolytic resistance class (DIN ISO 719)||class 1|
|Acid class (DIN 12 116)||class 1|
|Alkali class (DIN ISO 695)||class 2|
|Coefficient of mean linear thermal expansion α (20°C; 300°C)|
acc. to DIN ISO 7991
|3.3 x 10?6 K?1|
|Transformation temperature T g||525°C|
|Temperature of the Glass at viscosity η in dPa x s:|
1013 (annealing point)
|107.6 (softening point)||825°C|
|104 (working point)||1260°C|
|Maximum short?time working temperature||500°C|
|Density ρ at 25°C||2,23 g x cm?3|
|Modulus of elasticity E (Young's modulus)||64 x 103N x mm?2|
|Poisson's ratio µ||0,20|
|Thermal conductivity λw at 90 °C||1,2 W x m?1 x K?1|
|Temperature for the specific electrical resistance of 108 Ω x cm|
(DIN 52 326) t k 100
|Logarithm of the electrical volume resistance (Ω x cm)||at 250°C 8/at 350°C 6,5|
|Dielectrical properties (I MHz, 25°C) Dielectric constant ε||4,6|
|Dielectric loss factor tan δ||37 x 10 ?4|
|Refractive index(λ = 587.6 nm) nd||1,473|
|Stress?optical coefficient (DIN 52 314) K||4,0 x 10?6 mm² x N?1|
In the spectral range from about 310 to 2200 nm the absorption is negligible. It is clear and colourless. Viewed through a great thicknesses, such as an axial view through pipes, then brosilicate glass appear slightly yellow/greenish.