Thermal Properties

Thermal properties are very important for the annealing, heat treatment, thermal shock, molding and coating of optical glasses. The thermal properties are characterized by transformation temperature (T_g), sag temperature (T_s), annealing point (T₁₀¹³), softening point (T₁₀^7.6), mean coefficient of linear thermal expansion ( α_-30/+70ºC, α_100/300ºC), Thermal Conductivity (λ) and specific heat capacity (C_p).

Transformation temperature is determined by the temperature at an intersecting point of two tangents in lower and higher temperature bounds of a thermal expansion curved as shown in figure 1. Around this temperature, the glass gradually transforms from a low temperature solid glassy state to a higher temperature super-cooled liquid state.

Sag temperature indicates a temperature at which expansion stops and contraction starts.

The annealing point (T₁₀¹³) is important for the annealing of glass. At this temperature, the internal stresses in a glass are relieved within 30 minutes and the glass has a viscosity of 10¹³dPa·s.

The so-called softening point ( T₁₀^7.6) indicates a temperature at which a glass deforms under its own weight and the glass has a viscosity of 10^7.6dPa·s.

The mean coefficient of linear thermal expansion is given in two temperature ranges. One is from -30°C to 70°C for room temperature, while the other is from 100°C to 300°C for high temperature.

Properties:  

• Refractive Index, Abbe Value and Dispersion Formula
• Transmittance
• Temperature Coefficient of Refractive Index (dn/dT) (Source: SCHOTT North America, Inc.)
• Glass Designations
• Thermal Properties
• Chemical properties (Source: SCHOTT North America, Inc.)
• Mechanical Properties (Source: SCHOTT North America, Inc.)
• Abbe Diagram (n_d-v_d) Graphic (Source: SCHOTT North America, Inc.)
• N-BK7 Datasheet (Source: SCHOTT North America, Inc.)