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.
The chemical formula of quartz is SiO2. The silicon-oxygen (Si-O) bond is polar and covalent. Elemental silicon contains four valence electrons making the silicon atom bonded to four oxygen atoms. One oxygen atom is bonded to two silicon atoms, making the body-centered tetrahedral crystal system of quartz. The tetrahedral crystal system is composed of four oxygen atoms at the corners and a central silicon atom. In one tetrahedron, the O-Si-O bond makes a 109° angle. In a network of SiO4 tetrahedra, the corner oxygen atoms link the central silicon atom. The Si-O-Si bond makes a 144°. The structure of the networked SiO4 is open with wide spaces, hence giving quartz a hexagonal crystalline form.
Quartz can be manufactured into quartz glass, which is valued for its exceptional purity and serves a wide range of applications. Quartz glass does not contain additives. It is sometimes referred to as fused quartz or fused silica; the difference between the two is that fused quartz is made from pure silicon dioxide (SiO2) while fused silica is made from synthetic precursor. Natural quartz is rarely used in the industry since it may contain several impurities; the most commonly used raw material is "cultured quartz", which is quartz crystals that are grown in controlled conditions.
Quartz glass is valued due to its distinct and high value characteristics. Among these are because of its low coefficient of thermal expansion, high gas permeability, and extensive optical transmission.
Production of Quartz Glass
This chapter presents the steps in transforming the raw quartz into a formed, fused quartz glass.
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.
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.
