What is Quartz Glass?
Quartz is one of the most abundant and widely distributed minerals in nature. Quartz is the only stable polymorph of crystalline silica on the Earth‘s surface. It is found in all forms of rocks: igneous, metamorphic and sedimentary. It becomes concentrated in soils, bodies of water and sand when a quartz-bearing rock is weathered or eroded.
Washing and Drying
Dirt, moisture and contaminants present in the natural quartz are removed in the early stages of processing which may affect the quality and performance of the quartz glass to be produced. This is only applicable for mined quartz banger.
This process is similar to flame fusion with water-vapor free plasma flame being used as a source of heat. Plasma fused quartz glass has high purity level, low OH content, minimal bubble content and no drawing lines.
Natural quartz or a synthetic precursor may be the starting material for this method. Quartz glass produced from the combustion of a synthetic precursor in plasma flame is known as Type IV.
Electric Arc Fusion
The quartz sand is melted in an electric arc furnace. The resulting glass ingots are crushed and molded; the formed parts are dried and sintered. In this method, the quartz flask glass produced is white and opaque and does not generally belong to any types of quartz glass. However, it is comparable to transparent quartz in terms of purity level.
Shaping and Finishing Processes
A manufacturer can process quartz glass just like any other kinds of glass.
Shaping and forming of quartz glass may require diamond cutting tools due to its hardness. Also, such operating parameters must be optimized since the quartz glass is also brittle and there is a limited force that can be applied before cracking or fracture occurs. Some of the mechanical processes include:
Cutting: Band and wire saws, chop saws, CO2 lasers, and water jet cutters are used to cut the quartz glass. Using a laser cutter can leave a glazed and smooth cut, while those quartz glass which used saw cutting can leave a rough cut. Thick quartz glass sheet slabs may require multiple consecutive cuts if a single cut would not suffice. Annealing may be required to relieve the thermally-induced stress and to keep it from shattering.
Drilling: As detailed in the fused quartz glass product, holes may be produced using a diamond driller. A laser driller may be used to cut thin, small plates. Proper cooling must be ensured in order to prevent the tools from premature worn-out.
Grinding: The quartz glass surface may be smoothened and its thickness may be reduced, depending on the end-use application.
The quartz glass is quite complex to thermoform due to its high melting point and steep viscosity, allowing it to be formed on a very narrow temperature range. If the temperature is too low, the glass is solid; if the temperature is too high, the glass is less viscous and volatile resulting in evaporation of the parts. In addition to this, single or multiple annealing steps are required to relieve the thermal stress and prevent fracture induced by hot forming. The following are some hot forming methods which a manufacturer can use in order to enhance the glass product:
Welding: Two components of quartz glass are joined together through a weld. The ends of each component are heated, and a piece of quartz glass is melted to fill the gap in the seam or joint. It is critical to keep the temperature just high enough in order to avoid thermal stress.
Collapsing: In this process, quartz glass rods are reduced to a smaller diameter. A metal tube is heated to the softening temperature of the quartz glass and pressure is applied under the tube to push the glass rods.
Purity is one of the most important aspects in quartz glass manufacturing. Contaminants, even in very low levels, influence the thermal, electrical and optical properties of the resulting quartz tube glass and material in contact in their final application. Strict handling precautions must be taken at the starting material source and all stages of production to ensure high purity. The most common impurities are metal oxides (Al2O3, Fe2O3, MgO, etc.), water, and chlorine.
Quartz glass is known for its very low coefficient of thermal expansion (CTE). Thermal expansion refers to the fractional change in size of an object in response to the change of its temperature. For most materials, CTE is directly proportional to temperature change. Quartz glass also has excellent thermal shock resistance, which can withstand sudden and extreme changes in temperature. Quartz glass instrument also has low thermal conductivity.
Quartz glass has almost similar mechanical properties compared to other glass types. Quartz glass rod has high compressive strength, but also exhibits high brittleness. Surface defects can also affect the overall strength of this material. Machine-polished parts tend to be weaker than fire-polished ones. Also, the age of the glass also affects reliability due to exposure to the environment.
Quartz crucible glass has been a subject of research due to its extensive optical transmission properties, covering the ultra-violet regions, visible and infrared wavelengths. It can be further enhanced through addition of doping materials. Transmission is influenced by the quartz glass‘ purity and OH content. The increase in metallic impurities and OH-molecular vibrational and rotational excitations can lead to light absorption and hence affect the consequent transmission.