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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.

Comminution

The objective of this step is to reduce the raw quartz into a size suitable for the fusion method and machinery to be utilized. Natural quartz undergoes a series of size reduction steps such as crushing and milling (ball milling or roll milling). Quartz is very brittle in nature, which makes comminution quite easy. Afterwards, the particle size is analyzed and larger grains are separated.

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.

Mechanical forming

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.

Chemical Purity

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.

Thermal Properties

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 is softened starting at 16300C and acts like a viscous liquid at high temperatures like most glass types. This state occurs at a wide range of temperature, and viscosity decreases with increasing temperature. Viscosity is also increased by the presence of impurities.

Mechanical Properties

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.

Optical Properties

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.

Electrical Properties

Quartz glass is an excellent electrical insulator, retaining high resistivity at elevated temperatures. It has a high dielectric strength. This is due to the absence of charged mobile ions in the molecular lattice and the strong silicon-oxygen bond which imparts very low polarizability to the structure.