Silicon Dioxide – Glass – Quartz – Fused Silica
Silicon Dioxide (SiO2) is the simplest chemical composition of glass. Quartz is the most stable crystal modification at normal temperature and pressure conditions. Quartz is one of the most common minerals in the earth's crust. Glass (from “glasa”, Germanic for amber, the shiny or shimmery) also consists of silicon and oxide, but is a uniform amorphous solid material. Many glass varieties are clear and transparent respectively. This means transmissibility for the visible spectrum of light. In general, such material is associated with the term glass. Transparent materials allow light to pass through them without diffusing (scattering) the light.
Most common types of glass
At least 2000 years ago humans learned how to lower the glass softening temperatures by adding lime and soda before heating, which resulted in a glass containing sodium and calcium oxide.
Glass – Additives and the industrial use of glass
The use of glass as one of the oldest, but also very important materials for the industry is linked with the application of additives. Chemicals like soda (sodium carbonate, Na2CO3) and in the past also potash (potassium carbonate, K2CO3), manganese oxide and metal oxides influence the properties of glass. Manufactured glass is a material formed by heating a mixture of sand, soda and lime to a high temperature and stays in a molten, liquid state. Glass can be made from pure silica, but quartz glass (also referred as quartz) has a high glass transition point at around 1200°C, which makes it difficult to form into panes or bottles.
Quartz glass is the purest form of SiO2 and therefore the most valuable and sophisticated variety. Extremely clear glass can be used for optical fibers. Therefore synthetic quartz glass is used to transmit light across many kilometers. Many glasses block ultraviolet radiation, but only pure fused silica (only SiO2) is transparent for wavelengths < 350 nm (UV). Quartz glass also exists as an opaque variety and with different coloration to change the physical and chemical properties like transmission or absorption for specific wavelengths (filter glass). The opaque material at Heraeus, OM® 100, is also used as a heat barrier or for diffuse scattering of IR radiation.