The refractive indices of the glasses are not only dependent on wavelength, but also upon temperature. (Source: Temperature Dependence of Refractive Index The data is uncorrected for surface reflection (Fresnel) losses. Shown here is a typical transmission for a 10-mm thick IR-grade Fused Silica sample. This material grade is, however, not as good in the UV. In Contrast IR grade fused silica contains a lot fewer water traces and shows significantly less absorption in the infrared. Synthetic-grade Fused Silica is particularly likely to display water vapor absorption in the near infrared. For example, water vapor creates absorption around 1.4, 2.1, and 2.8 µ m. The Si-O bond has a very strong absorption peak near 8.9 µm and at 4.5 µm (overtone frequency).Īdditional absorption bands are present in the near infrared. On the infrared side, the source of intrinsic absorption is molecular vibration. Synthetic Fused Silica, which is manufactured from an extremely pure precursor, offers the highest transparency in the UV of any glasses. The exact location of the absorption edge is strongly affected by the presence of impurities. The absorption boundary on the ultraviolet side is deep in the UV. Shown here is a typical transmission for a 10-mm thick synthetic Fused Silica sample. Unless otherwise specified, we work with synthetic fused silica. Optical Absorptionįused Silica is transparent in the ultraviolet, visible, and near infrared. It is transparent from the deep ultraviolet (UV) to the mid-infrared. For comparison, this value is 100-fold lower than that of silicon (148W/mºK 25 C) and one eighth of that of INVAR (10.5 W/mºK 25 C).įused Silica offers a set of optical characteristics that compare favorably with other optical materials. Its thermal conductivity is only 1.38W/mºK (measured at 25✬), which is one of the lowest for any solid. Thermal Conductivityįused Silica is an excellent thermal insulator. For comparison, INVAR (a nickel-iron alloy), which has the lowest thermal expansion among all metals and alloys near room temperature, has a mean coefficient of thermal expansion that is more than twice that of Fused Silica (1.3 x 10 -6°/K over the 20☌ to 100☌ temperature range). This material characteristic imparts fused silica a high resistance to thermal shock, and makes it an excellent material for applications that require the utmost in dimensional stability over a large temperature range. 0.57 x 10 -6/K over the 0☌ to 200☌ temperature range.0.52 x 10 -6/K over the 5☌ to 35☌ temperature range.Thermal Properties Coefficient of Thermal Expansion (CTE)įused Silica has a remarkably low coefficient of thermal expansion, which varies only slightly with temperature.įused Silica Mean Coefficient of Thermal Expansion (Source: Präzisions Glas & Optik GmbH, Menden, Germany): There are only a few uncommon materials that will attack it, including HF (hydrofluoric acid) and hot KOH (Potassium hydroxide). It is compatible with the vast majority of chemicals used in the industry and in the laboratory. Chemical Compatibilityĭue to its pure composition, Fused Silica is an extremely inert glass. These contaminants affect the viscosity, optical absorption, and electrical properties of the glass. The most common impurities are metals (Al, Na and Fe among others), water (present as OH groups), and chlorine. Special precautions must be taken at all stages of the manufacturing process to maintain high purity. Purity is mostly determined by the raw material, the manufacturing method, and subsequent handling procedures. Fused Silica Chemical PurityĬontaminants, despite their presence at very low levels, have subtle yet significant effects. It has a much higher working and melting temperature than other common optical glasses, and it also has exceptional optical, thermal, and mechanical properties. Fused Silica, on the other hand, is pure SiO 2. These additional ingredients modify the optical and mechanical characteristics of the glass and lower the melt temperature of the mix. In contrast, other common glasses (Pyrex, borosilicate, soda-lime, etc.) are mixed composition glasses – in addition to SiO 2, they include such ingredients as Na 2O, CaO, and B 2O 3. This glass is composed exclusively of high-purity silica (SiO 2) in amorphous (non-crystalline) form. Translume works with Fused Silica (also called fused quartz). Chemical Properties Fused Silica Chemical Composition
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