Despite existing at very low levels, contaminants have subtle yet significant effects. Purity is mostly determined by the raw material, the manufacturing method and subsequent handling procedures. Special precautions must be taken at all stages of manufacture to maintain high purity. Additionally, Heraeus has different purification steps to improve the quality of the quartz sand as raw material even further.
The most common impurities are metals (such as Al, Na and Fe among others), water (present as OH groups) and chlorine. These contaminants not only affect the viscosity, optical absorption and electrical properties of the quartz glass. They can also influence the properties of material processed in contact with the quartz glass during the final use application.
The purities of fused quartz and fused silica are outstandingly high. Synthetic fused silica from Heraeus contains total metallic contamination below 1ppm. For fused quartz the amount is approximately 20 ppm and consists primarily of Al2O3 with much smaller amounts of alkalis, Fe2O3, TiO2, MgO and ZrO2.