What is quartz glass, production of quartz glass, properties of quartz glass, processing of quartz glass

Chapter 1 What is Quartz Glass?

"Quartz is one of the most abundant and widely distributed minerals in nature. Quartz is the only stable crystal form of crystalline silica on the Earth's surface. It occurs in all forms of rock: igneous, metamorphic and sedimentary. When containing quartz When rock weathers or erodes, it collects in soil, bodies of water, and sand.

"The chemical formula of quartz is SiO2. The silicon-oxygen (Si-O) bond is polar and covalent. Elemental silicon contains four valence electrons that bond a silicon atom to four oxygen atoms. One oxygen atom bonds to two silicon The atoms are bonded to form the body-centered tetrahedral crystal system of quartz. The tetrahedral crystal system consists of four oxygen atoms at the corners and a central silicon atom. In a tetrahedron, the O-Si-O bonds form a 109° angle. In the SiO4 tetrahedral network, the corner oxygen atoms connect the central silicon atoms. Si-O-Si bonds form 144°. The structure of reticulated SiO4 has wide spaces, thus giving quartz a hexagonal crystal form.

"Quartz can be made into quartz glass, which is valued for its exceptional purity and has a wide variety of applications. Quartz glass contains no additives. It is sometimes called fused silica or fused silica; the difference between the two is the fused Quartz is made from pure silicon dioxide (SiO2), while fused silica is made from synthetic precursors. Natural quartz is rarely used in industry because it may contain several impurities; the most commonly used raw material is "cultured quartz", which is A quartz crystal grown under controlled conditions.

"Quartz glass is valued for its unique and high-value properties. Among others, it has a wide range of light transmission due to its low coefficient of thermal expansion, high gas permeability.

Chapter II Production of Quartz Glass

"This chapter describes the steps involved in the conversion of pristine quartz into shaped fused silica glass.

wash and dry

"Dirt, moisture and contaminants present in natural quartz are removed at an early stage of processing, which can affect the quality and properties of the quartz glass to be produced. This only applies to mined quartz.

crush

"The goal of this step is to reduce the raw quartz to a size suitable for the fusion method and machinery to be used. Natural quartz undergoes a series of size reduction steps such as crushing and grinding (ball or roller milling). Quartz is inherently very brittle , which makes crushing very easy. Afterwards, the particle size is analyzed and the larger particles are separated.

fusion

"At this stage, thermal energy is used to break the strong silicon-oxygen bonds. As the temperature increases, more bonds are broken, resulting in less viscous flow of the quartz. After shaping and cooling to its final form, the SiO2 molecules are effectively The ordered crystal structure is transformed into glassy, amorphous and metastable forms of quartz.

"Depending on the desired level of purity and end-use application, natural quartz can be homogenized and formed by the following fusion methods:

electrofusion

"This method produces type I quartz glass known in the industry. If high purity and low hydroxyl (OH) content (>1 ppm – 30 ppm) is to be obtained, electrofusion is used. Produced from this method has Quartz glass with low OH content has high infrared transmission, but there are aesthetic bubbles and drawing lines on the glass surface. The starting material is natural quartz grains, and the following production modes are available:

"Continuous Mode: Quartz sand is continuously fed on top of a column of refractory metal crucibles containing electrical heating. The inner cavity of the crucible is kept in a dry and vacuum-sealed atmosphere to prevent the molten quartz from reacting with the refractory material. By After heating the crucible column, the molten quartz is collected in a hole located at the bottom of the column where it is shaped and cut into plates, tubes and rods. This method is suitable for mass production.

"Batch or rolling ball mode: A mass of quartz is placed in a refractory-lined vacuum chamber that also contains electrical heating. After the quartz melts, the viscous melt is collected and formed into its final form. This method is used to create Quartz glass for more complex shapes and details.

flame fusion

"In this method, natural quartz or a synthetic precursor can be used as the starting material. The natural quartz is passed through a chamber with a high temperature hydrogen/oxygen (H2/O2) flame until the raw material is melted. If the gaseous synthetic precursor tetrachloride is to be used silicon (SiCl4), it is made to react with the H2/O2 flame. The viscous melt is deposited in a refractory lined vacuum chamber, slowly collected by a mold at the bottom of the vessel, and forms its final form. Due to its reaction with the H2/O2 flame Direct contact, the method produces quartz glass with an OH content of 150-200 ppm from natural quartz and up to 1000 ppm from synthetic silica.

"Glasses produced from crystalline quartz by flame melting are classified as Type II, and glasses produced from synthetic precursors are classified as Type III. Type III synthetic silica glass is the product of a chemical reaction. Combustion of silicon tetrachloride Synthetic quartz is produced and leaves behind environmentally toxic by-products, chlorine and hydrochloric acid.

plasma fusion

"The process is similar to flame fusion, where a water vapor-free plasma flame is used as the heat source. Plasma fused silica glass has high purity, low OH content, minimal bubble content and no wires.

"Natural quartz or synthetic precursors may be the starting material for this method. The quartz glass produced by the combustion of synthetic precursors in a plasma flame is known as Type IV.

arc fusion

"Quartz sand is melted in an electric arc furnace. The resulting glass ingot is crushed into shape; the shaped part is dried and sintered. In this method, the quartz glass produced is white and opaque and is generally not of any type of quartz glass. However , which is comparable to clear quartz in terms of purity levels.

Forming and finishing processes

"Manufacturers can process quartz glass like any other kind of glass.

mechanical forming

"Shaping and shaping of quartz glass may require diamond cutting tools due to its hardness. Furthermore, such operating parameters must be optimized, as quartz glass is also brittle and there is a limit to the force that can be applied before cracking or fracture occurs. Some mechanical processes include :

"Cutting: Quartz glass is cut using band and wire saws, dicing saws, CO2 lasers, and water jet cutters. Using laser cutters can leave glazed and smooth cuts, while those using sawn quartz glass can leave rough If one cut is not enough, thick quartz glass plates may require several consecutive cuts. Annealing may be required to relieve thermally induced stress and prevent it from shattering.

"Drilling: As described in Fused Silica Glass Products, diamond drilling machines can be used to produce holes. Laser drilling machines can be used to cut thin and small sheets. Proper cooling must be ensured to prevent premature tool wear.

"Grinding: The surface of quartz glass can be smoothed and the thickness can be reduced, depending on the end-use application.

Thermoforming

"Quartz glass is very complex for thermoforming due to its high melting point and steep viscosity, enabling it to be formed within a very narrow temperature range. If the temperature is too low, the glass is solid; if the temperature is too high, the glass' viscosity and volatilization Less rigid, leading to part evaporation. In addition to this, one or more annealing steps are required to relieve thermal stress and prevent thermoforming-induced fractures. Here are some thermoforming methods that manufacturers can use to strengthen glass products:

"Welding: Two parts of quartz glass joined together by a weld. The end of each component is heated and a piece of quartz glass is melted to fill the gap in the seam or joint. To avoid thermal stress, keep the temperature high enough to close important.

"Collapse: In this process, the quartz glass rod is 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 rod.

"Elongation and Compression: The application of a positive or negative radial force elongates or compresses a silica glass rod to its final diameter. This is done at the softening temperature of the silica glass and optimum force must be applied to prevent fracture and cracking .

"Glassblowing: With the help of a blowpipe, a piece of fused quartz glass is inflated to obtain a hollow shape.

Chapter 3 Properties of Quartz Glass

"This chapter presents the salient properties and properties of Quartz Glass.

chemical purity

"Purity is one of the most important aspects in the manufacture of quartz glass. Contaminants, even at very low levels, can affect the thermal, electrical and optical properties of the resulting quartz glass and contact materials in the final application. Strict handling precautions must be taken at all stages to ensure high purity.The most common impurities are metal oxides (Al2O3, Fe2O3, MgO, etc.), water and chlorine.

"Water exists in quartz glass in the form of hydroxyl (OH) groups. The OH content will vary depending on heat treatment and the amount of moisture the quartz glass is exposed to at high temperatures. OH affects infrared transmission, viscosity, and attenuation. High levels of OH will Reduces infrared transmittance. OH also reduces thermal stability; higher OH content means that quartz glass is not suitable for high temperature end applications. The annealing step can reduce the OH content of quartz glass in fused silica glass.

chemical behavior

"Quartz glass is chemically inert to most compounds (water, salts and acids), making it an advantageous material in chemical laboratories and industry. It is essentially impermeable to gases. Hydrofluoric and phosphoric acids are the only Reagents that etch and decompose quartz glass. However, alkaline earth and alkaline earth agents can attack the surface, causing acceleration distortion. 0.1 mg of alkali compound per square centimeter can be amplified to transform all semi-stable molecules. Even fingerprints containing trace amounts of alkali can cause loss live.

thermal performance

"Quartz glass is known for its very low coefficient of thermal expansion (CTE). Thermal expansion is the fractional change in the size of an object in response to a change in its temperature. For most materials, the CTE is directly proportional to the change in temperature. Quartz glass also has excellent Excellent thermal shock resistance, can withstand sudden and extreme changes in temperature.Quartz glass also has low thermal conductivity.

"Quartz glass softens from 1630°C and behaves like most glass types at high temperatures as a viscous liquid. This state occurs over a wide temperature range and the viscosity decreases with increasing temperature. The viscosity also will increase due to the presence of impurities.

Mechanical behavior

"Quartz glass has almost similar mechanical properties compared to other glass types. Quartz glass has high compressive strength but also exhibits high brittleness. Surface defects also affect the overall strength of this material. Machine polished parts Tends to be weaker than fire polished parts. Also, the age of the glass can affect reliability due to exposure to the environment.

optical properties

"Quartz glass has been the subject of research due to its wide range of optical transmission properties, covering the ultraviolet region, visible light and infrared wavelengths. It can be further enhanced by adding doping materials. The transmittance is affected by the purity and OH content of the quartz glass. The concentration of metal impurities The increase and the vibrational and rotational excitation of OH molecules lead to light absorption, which affects the subsequent transmission.

electrical characteristics

"Quartz glass is an excellent electrical insulator, maintaining high resistivity at high temperatures. It has high dielectric strength. This is due to the absence of charged mobile ions and strong silicon-oxygen bonds in the molecular lattice, which give Very low polarizability of the structure...

Chapter Four Application of Quartz Glass

"The following are common applications of quartz glass:

optical instrument

"Most applications of quartz glass take advantage of its optical properties due to its wide range of transparency and excellent light transmission from the ultraviolet to the infrared region. Quartz glass is not easily damaged by ultraviolet and high-energy radiation. Light can be routed in functionalized light paths Minimal distortion through quartz glass. Examples of products with optical applications include: prisms, lenses, beam splitters, polarizers, mirrors and windows.

lighting device

"High-purity quartz glass is used in various lamps and lighting systems such as mercury lamps, halogen lamps, xenon lamps, ultraviolet lamps, arc lamps and filament lamps that provide high-temperature light sources. These lamps are used in many industries, including food and medical Sterilization and cleaning equipment in the industry and exposure equipment in the semiconductor industry.

Chemical equipment and equipment

"Quartz glass material is a good but expensive alternative because it is chemically inert to other glass types that cannot withstand purpose-specific high temperature applications. Common applications include glassware, sheet and tubing.

refractory material

"Fused silica is used as a material in the manufacture of refractory materials such as crucibles, trays, shrouds and rollers for high temperature processes including steelmaking and glass production.

Chapter 5 Processing of Quartz Glass

"This section gives recommended practices when handling or using quartz glass products in order to preserve their valuable properties and maximize their useful life:

Instructions

deal with:

"Quartz glass can last for a long time if it is kept clean before and after use. Even small amounts of impurities can promote gradual deactivation. It is recommended to use clean lint-free, powder-free or cotton gloves when handling quartz glass to prevent further contamination .

cleaning:

"Quartz glass can be cleaned by immersing it in >7% ammonium bifluoride solution for no longer than ten minutes or in >10% by volume hydrofluoric acid solution for no longer than five minutes. After cleaning, it must be rinsed thoroughly with deionized or distilled water and dried.

storage:

"Quartz glass must be stored in closed containers when not in use to protect it from surface defects and moisture that may affect the quality and performance of the quartz glass. Ideally, the glass must be wrapped. If is a tube and must cover the end opening.

Operation precautions

Rapid temperature changes:

"Quartz glass is more resistant to extreme heat and thermal shock than other glass types. However, when the quartz glass is thicker, the heat resistance and thermal shock resistance are lower. In addition, thick and opaque glass products degrade rapidly with temperature. changes to create cracks.

Operations above the distortion point:

"Before annealing, the quartz reaches the deformation point, or strain point. When the quartz glass is cooled very rapidly after the deformation temperature (approximately 1100°C), deformation can occur again.

Use a different material:

"Quartz glass has a relatively low coefficient of thermal expansion. Fused silica can crack if another material with a significantly higher coefficient is attached, fixed or clamped.

Precautions when putting in the furnace:

"Because of its low thermal conductivity, cracks may appear on the glass surface at temperatures above the deformation point when the glass is locally heated or in contact with a flame. In addition, the viscosity of quartz glass decreases with increasing temperature. It is recommended Consider the phenomena listed when using quartz glass as a finished product or as a component of other plants or installations.

Inactivate

"Deactivation shortens the useful life of quartz glass and completely removes all of quartz's desirable properties. Deactivation is the transformation of metastable quartz glass into stable crystalline paraffinite. When quartz is heated at high temperatures for long periods of time, Or when it is heated, it can happen even if impurities are attached to its surface, even in small amounts. Since no impurities are present, aberration usually starts at 1200°C and accelerates as the temperature increases. Impurities lower the deactivation threshold.

in conclusion

"Quartz glass is valued for its excellent optical properties (i.e., light transmission), low coefficient of thermal expansion, and good chemical resistance.

"The starting materials for the production of quartz glass are natural quartz, cultured quartz or synthetic precursors such as silicon tetrachloride.

"The crystal structure of quartz includes strong covalent silicon-oxygen bonds; individual molecules form a tetrahedral geometry. SiO4 molecular networks form body-centered crystals in the form of hexagonal prisms. When processed, the crystal structure transforms into a metastable, amorphous