This article presents an in depth look at quartz glass. Read further and learn more about the following:
Quartz is among the most common and widely distributed minerals on Earth, being the sole stable crystalline form of silica at the Earth's surface. It can be found in various rock types, such as igneous, metamorphic, and sedimentary. Quartz accumulates in soils, bodies of water, and sand as rocks that contain quartz undergo natural processes like weathering and erosion.
The chemical formula for quartz is SiO2. The bonds forming quartz are polar covalent, occurring between silicon and oxygen atoms. Silicon has four valence electrons, allowing it to bond with four oxygen atoms. Each oxygen atom bonds with two silicon atoms, creating a body-centered tetrahedral structure. This crystal structure comprises four oxygen atoms at the vertices, with a central silicon atom. Each tetrahedron has an O-Si-O bond angle of 109°. In the SiO4 network, the corner-placed oxygen atoms connect to the central silicon atoms, creating Si-O-Si bonds with a 144° angle. The open network of SiO4 tetrahedra produces spacious configurations, resulting in quartz's hexagonal crystal form.
Silica sand, integral to crafting quartz glass, is a stable and enduring mineral that naturally breaks down into sand over prolonged periods. High-quality silica sand is critical for controlling the finished product's strength, transparency, and color. Consistent chemical processes ensure each quartz glass batch meets high standards of quality and uniformity.
Quartz undergoes conversion to become quartz glass, renowned for its purity and adaptability across numerous applications. This type of glass, commonly called fused quartz or fused silica, contains no additives. The difference between them lies in production: fused quartz is crafted using pure silicon dioxide (SiO2), while fused silica comes from synthetic precursors.
The majority of quartz is extracted from silica sand, which is then refined to create high-purity quartz, enhancing strength, transparency, and color. Intense sand processing creates exceptional purity by purging impurities through detailed chemical treatment.
Quartz glass is highly coveted due to its distinctive and valuable features, such as a low coefficient of thermal expansion, superior gas permeability, and a wide range of optical transmission.
This chapter outlines the detailed process of converting raw quartz into high-purity, fused quartz glass. Understanding each step in quartz glass production is essential for industries seeking precision, durability, and superior optical performance in their components.
In the initial stages of quartz processing, dirt, moisture, and contaminants are thoroughly removed from natural quartz crystal using industrial washing systems. These cleaning protocols are critical to remove trace elements and impurities, which can significantly impact the optical clarity and chemical resistance of the finished quartz glass. This step is specifically relevant for quartz mined from natural deposits, ensuring the highest starting material purity before further fabrication. Clean, dry quartz is crucial for succeeding in the high-temperature melting of silica to create low-impurity optical glass products.
The goal of this stage in quartz glass manufacturing is to reduce the raw quartz rock into grains or powder suitable for subsequent fusion processes and advanced glassmaking machinery. Natural quartz undergoes several size-reduction procedures, including crushing, grinding, and milling (either ball milling or roll milling). Due to its brittle structure, quartz is relatively easy to comminute, but producing consistent particle size is vital for uniform melting and homogeneous glass formation. After comminution, particle size is assessed with precision sieves, and larger grains are separated for re-processing or alternative industrial silica applications. At this stage, ensuring uniform grain size enhances the transparency and structural integrity of the fused glass.
During the quartz fusion stage, thermal energy is applied to disrupt the strong silicon-oxygen (SiO2) bonds present in the quartz lattice. Elevated temperatures cause the structured crystalline arrangement to collapse, transforming the material into a less viscous, amorphous state—this is the defining step in quartz glass synthesis. Upon cooling, the melted quartz solidifies as a metastable, non-crystalline glass that exhibits excellent optical properties, low thermal expansion, and outstanding chemical purity. Control over the fusion method is crucial for tuning the quartz glass's properties such as hydroxl (OH) content, UV and IR transmission, and resistance to devitrification, all of which are critical attributes for semiconductor, laboratory, fiber optics, and photonics applications.
Depending on the required purity, transmittance, and intended application—ranging from high-precision optical lenses to semiconductor fabrication—natural quartz may be homogenized and processed using specialized fusion methods:
This method yields Type I quartz glass, offering typically 100 to 130 ppm OH content in its initial state. For applications requiring exceptionally high purity and lower hydroxyl (OH) levels (ranging from >1 ppm to 30 ppm), electric fusion is the preferred technique in advanced glassmaking. The vacuum annealing process further reduces OH content to targeted thresholds essential for ultraviolet (UV) and infrared (IR) optical applications. Lower OH concentrations enhance UV transmission and improve laser resistance—crucial for fiber optic preforms, UV light guides, and semiconductor components. The starting material for electric fusion is carefully screened natural quartz grains, which proceed through one of two core production methods:
This quartz glass manufacturing method can utilize either naturally derived quartz sand or a synthetic silica precursor as the feedstock. In natural quartz processing, quartz crystals are exposed to a high-temperature hydrogen/oxygen (H2/O2) flame that melts the raw material, while synthetic fusion starts with volatile precursors like silicon tetrachloride (SiCl4). The resulting chemical vapor reacts directly in the flame, producing high-purity silica glass through direct oxidation.
The molten quartz is deposited into a refractory-lined vacuum chamber, gradually drawn through a precision die into specific forms, such as ingots, tubes, or optical fibers. Quartz glass from this flame fusion process exhibits a high and stable OH content (150-200 ppm for natural quartz, up to 1000 ppm for synthetic precursors), which cannot be further reduced by vacuum annealing. The material demonstrates a lower softening point and operating temperature, properties that can be leveraged for specific optical and scientific glassware applications requiring thermal shock resistance or unique transmission windows.
Quartz glass produced from crystal quartz by flame fusion is classified as Type II, while glass produced from synthetic silica via chemical vapor deposition (CVD) is classified as Type III. Type III synthetic silica glass is created through the combustion of silicon tetrachloride, yielding synthetic quartz but also generating hazardous byproducts such as chlorine and hydrochloric acid. Responsible environmental management is essential for manufacturers utilizing this method to ensure compliance with industry regulations on emissions control and waste handling.
In plasma fusion, cutting-edge manufacturing utilizes a water-vapor-free plasma flame to achieve the ultra-high temperatures necessary for fusing quartz or synthetic precursors. Plasma-fused quartz glass stands out for its extremely high purity, very low OH content, minimal bubble formation, and an absence of drawing lines or striations, making it ideal for demanding optical, laser, and semiconductor fabrication. This process supports both natural and synthetic silica sources, with resultant glass classified as Type IV when generated from combustion of a synthetic precursor in a plasma flame. Manufacturers of analytical equipment, UV optics, and precision semiconductor substrates value plasma-fused quartz for its exceptional homogeneity, chemical resistance, and superior performance metrics.
This specialized quartz glassmaking process involves melting quartz sand in an electric arc furnace. The resulting vitreous fused glass contains micro-bubbles that diffract light, resulting in an opaque, white glass. Electric arc fusion products are commonly used for thermal insulation, UV blocking shields, and specialty industrial applications, rather than high-end optics. The glass ingots produced are crushed, shaped, and dried, then sintered to achieve their final structural form. This category is not included among standard industry quartz glass types and typically exhibits an OH content from 100 to 130 ppm.
The forming and precision finishing of quartz glass components differ greatly from general glass manufacturing. Due to quartz glass’s unique thermophysical properties—non-flowing, high softening point, and significant viscosity at elevated temperatures—specialized equipment and manufacturing controls are necessary. These unique challenges are why quartz glass is preferred in industries such as microelectronics, spectroscopic instrumentation, and fiber optics, where purity and dimensional accuracy are critical.
Mechanical shaping of quartz glass frequently requires diamond cutting tools, ultrasonic machining, and other precision methods due to its Mohs hardness rating of 7 and brittle nature. Operators must finely optimize cutting speeds and forces since improper handling can induce micro-fractures or stress that degrade performance for critical optical, semiconductor, or laboratory applications. Mechanical processes used in custom quartz fabrication include:
Hot forming fused quartz glass is challenging due to its exceptionally high melting temperature and narrow viscosity range. Quartz glass can only be shaped within a carefully controlled temperature window: if too cool, the material cannot be formed; if overheated, evaporation and volatilization may occur, risking defects or loss of purity. Thermoforming processes require precise temperature monitoring and the use of high-purity refractory tools. Sequential annealing steps are performed to relieve residual stress, preventing fractures and ensuring dimensional accuracy in the final part. Core hot-forming methods in industrial quartz glass fabrication include:
In summary, the production of quartz glass—whether for optical, industrial, electronic, or scientific use—involves a highly controlled series of processes. Success relies on stringent raw material selection, advanced purification, precise fusion and annealing, and exacting finishing techniques. As global industries evolve, demand for custom, high-purity quartz glass continues to grow for use in lasers, semiconductors, solar energy, telecommunications, and high-performance laboratory environments.
Quartz glass processing machines play a vital role in the fabrication of high-purity quartz components, widely used in industries such as optics, lighting, semiconductors, photovoltaic solar panel production, and chemical laboratory equipment. High-precision manufacturing equipment is essential to ensure superior surface quality, accurate dimensions, and consistent performance of quartz glass for demanding applications. This comprehensive overview will highlight some of the industry’s most reputable manufacturers and suppliers of state-of-the-art equipment for quartz glass processing, cutting, and finishing.
Haas CNC machining centers are renowned for their precision in quartz glass machining, offering advanced capabilities for cutting, drilling, milling, and edge grinding. These computer numerical control (CNC) systems enable the fabrication of complex quartz glass parts with tight tolerances, making them ideal for custom optics, scientific glassware, and microelectronics manufacturing. Thanks to automated processes and robust design, Haas machines deliver efficiency and repeatability in high-volume quartz processing environments.
Meyer Burger's diamond wire saws are industry leaders for precision cutting of quartz glass and other brittle, high-hardness materials. Utilizing a fine wire coated with synthetic diamonds, these saws minimize kerf loss and edge chipping, preserving material integrity during processing. The diamond wire saw technology is especially valuable for slicing quartz glass wafers, rods, and tubes used in solar cell manufacturing, electronics, and specialty optical applications. Meyer Burger machines are engineered for minimal contamination and high throughput, supporting both R&D and industrial-scale production.
Schiatti Angelo's glass lathes are precision-engineered tools for rotational shaping, turning, and threading of quartz glass components. Leveraging diamond or carbide-tipped tooling, these lathes support the accurate production of cylindrical, conical, and threaded quartz shapes—essential for laboratory glassware, vacuum parts, and photonics devices. With programmable controls and rigid mechanical design, Schiatti Angelo ensures repeatability and high-quality surface finishes for intricate quartz applications.
BENTELER’s glass grinding machines offer highly specialized solutions for the precision finishing of quartz glass panels, disks, and tubes. Designed with advanced abrasive technology, these machines can achieve superior surface roughness and flatness essential for optical clarity, semiconductor substrates, and laboratory apparatus. BENTELER’s customizable grinding platforms accommodate different thicknesses, geometries, and batch sizes, while integrated automation supports consistent quality in continuous production settings.
The DMG Mori DMU 50 is a cutting-edge 5-axis CNC machining center engineered for the high-precision processing of quartz glass. This model excels at intricate milling, contouring, drilling, and slotting of quartz components, thanks to its rigid structure and advanced motion control. The DMU 50 is particularly suitable for prototyping, custom manufacturing, and the production of specialized optical, electronic, or analytical quartz glass parts. Its user-friendly interface, together with next-generation cooling systems, ensures accuracy and minimal thermal stress during processing.
When evaluating quartz glass processing equipment, key factors often include required dimensional tolerances, surface finish, production volume, machine automation, support for advanced materials, and cost-effectiveness. Ensuring compatibility with specific quartz substrate requirements and secondary processes (such as polishing, annealing, or ultrasonic cleaning) can also optimize overall product quality and operational efficiency. For detailed specifications, price quotes, and application guidance on quartz glass manufacturing solutions available in the United States and Canada, it is advisable to contact equipment manufacturers directly or consult with specialized industry distributors and technical consultants.
Emerging trends in the industry include automation integration, CNC upgrades, and multi-axis control for complex forms, which help facilities meet rising demands for high-purity quartz components used in photonics, advanced optics, and semiconductor fabrication.
This chapter highlights the key properties and characteristics of quartz glass.
Purity is crucial in the manufacturing of quartz glass. Even trace amounts of contaminants can affect the thermal, electrical, and optical properties of the final product and its performance in applications. To maintain high purity, strict handling precautions are necessary throughout all stages of production, starting from the raw material. Common impurities include metal oxides (such as Al2O3, Fe2O3, MgO), water, and chlorine.
Water appears in quartz glass as hydroxyl (OH) groups. The OH content can vary based on thermal treatment and moisture exposure at elevated temperatures. OH affects infrared transmission, viscosity, and attenuation. High OH levels can decrease infrared transmission and lower thermal stability, making the quartz glass unsuitable for high-temperature applications. An annealing step can help reduce OH content, particularly in electric fused quartz glass.
Quartz glass is chemically inert to most substances, including water, salt, and acids, making it a valuable material in chemical laboratories and industries. It is virtually impermeable to gases. The only agents that can etch or disintegrate quartz glass at ambient temperatures are hydrofluoric acid and phosphoric acid. However, alkali and alkali earth compounds can attack the surface, leading to accelerated devitrification. Even small amounts, such as 0.1 mg of alkali per square centimeter, can significantly transform semi-stable molecules. Additionally, even fingerprints, which contain traces of alkali, can trigger devitrification.
Quartz glass is renowned for its exceptionally low coefficient of thermal expansion (CTE), which measures the fractional change in size of a material in response to temperature variations. Unlike many materials, where CTE increases with temperature changes, quartz glass maintains stability. Additionally, it boasts excellent thermal shock resistance, allowing it to endure sudden and extreme temperature fluctuations. Quartz glass also exhibits low thermal conductivity.
Quartz glass begins to soften at temperatures around 1630°C and behaves like a viscous liquid at elevated temperatures, similar to other types of glass. Its viscosity decreases with increasing temperature, and the presence of impurities can further increase viscosity.
Quartz glass shares many mechanical properties with other types of glass, including high compressive strength. However, it also exhibits significant brittleness, and surface defects can impact its overall strength. Machine-polished surfaces are generally weaker compared to fire-polished ones. Additionally, the glass's reliability can be influenced by its age and environmental exposure.
Quartz glass is extensively studied for its exceptional optical transmission properties across ultraviolet, visible, and infrared wavelengths. These properties can be further enhanced by adding doping materials. The transmission characteristics of quartz glass are influenced by its purity and OH content. Increased metallic impurities and OH molecular vibrational and rotational excitations can lead to light absorption, thereby affecting the overall transmission.
Quartz glass is an excellent electrical insulator, maintaining high resistivity even at elevated temperatures. It features high dielectric strength, attributable to the absence of charged mobile ions within its molecular lattice and the strong silicon-oxygen bonds, which impart very low polarizability to the material.
The table below summarizes some of the key property coefficients relevant to quartz glass, as discussed in this article:
| Property | Value |
|---|---|
| Density | 2.2 x 10-3 kg/m3 |
| Hardness | 5.5 – 6.5 in Mohs‘ scale |
| Design tensile strength | 7,000 psi |
| Design compressive strength | 160,000 psi |
| Rigidity Modulus | 4.5x106 psi |
| Coefficient of Thermal Expansion | 0.55 x 10-6/°C |
| Thermal Conductivity (20°C) | 1.4 W/m-°C |
| Specific Heat (20°C) | 670 J/kg-°C |
| Softening Point | 1683°C |
| Annealing Point | 1215°C |
| Strain Point | 1120°C |
| Electrical Resistivity (350°C) | 7x10-7/° ohm-cm |
| Dielectric Properties (20°C, 1 MHz) · Constant · Strength |
3.75 5x10-7 V/m |
| Index of refraction | 1.4585 |
| Constringence (Nu value) | 67.56 |
| Velocity of Sound-Shear Wave | 3.75 x 10-3/° m/s |
| Velocity of Sound/Compressional Wave | 5.90 x 10-3° m/s |
| Sonic Attentuation | < 11dB/m MHz |
| Permeability Constants (700°C) | |
| Helium | 2.1 x 10-8 mm/cm°2 sec. cm Hg |
| Hydrogen | 2.1 x 10-9 mm/cm°2 sec. cm Hg |
| Deutrium | 1.7 x 10-9 mm/cm°2 sec. cm Hg |
| Neon | 9.5 x 10-10 mm/cm°2 sec. cm Hg |
Here are some common applications of quartz glass:
Quartz glass is widely used for its optical properties, thanks to its broad transparency range and excellent light transmittance across ultraviolet to infrared wavelengths. It is resistant to damage from ultraviolet and high-energy radiation, allowing light to pass through with minimal distortion. Common optical applications of quartz glass include prisms, lenses, beam splitters, polarizers, mirrors, and windows.
High-purity quartz glass is employed in various lamps and lighting systems, including mercury lamps, halogen lamps, xenon lamps, ultraviolet lamps, and arc and filament lamps, all of which operate at high temperatures. These lamps are used across several industries, such as sterilization and cleaning equipment in the food and medical fields, as well as exposure devices in the semiconductor industry.
Quartz glass is a valuable, though costly, alternative to other types of glass for high-temperature applications due to its chemical inertness. It is commonly used in applications such as glassware, plates, and tubes, where its ability to withstand elevated temperatures is essential.
Fused silica offers exceptional wave transmission in the ultraviolet spectrum, making it ideal for manufacturing ultraviolet windows, lenses, and optics.
This section outlines recommended practices for handling and using quartz glass products to maintain their valuable properties and extend their service life:
Quartz glass can have a long service life if kept clean before and after use. Even minor impurities can lead to gradual devitrification. It is advisable to use clean, lint-free, powder-free, or cotton gloves when handling quartz glass to prevent contamination and maintain its integrity.
To clean quartz glass, immerse it in a solution of >7% ammonium bifluoride for no more than ten minutes, or a >10% hydrofluoric acid solution for no more than five minutes. After cleaning, thoroughly rinse the glass with deionized or distilled water and allow it to dry completely.
When not in use, quartz glass should be stored in an enclosed container to protect it from surface damage and moisture, which could impact its quality and performance. Ideally, the glass should be wrapped, and if it is in tube form, the end openings should be covered.
Quartz glass offers superior resistance to extreme heat and thermal shock compared to other types of glass. However, its resistance decreases with thickness. Additionally, thick and opaque quartz glass products may develop cracks if exposed to rapid temperature changes.
Before annealing, quartz glass reaches a distortion point, also known as the strain point. If quartz glass is cooled too quickly after reaching this distortion temperature (approximately 1100°C), it may develop distortions.
Quartz glass has a relatively low thermal expansion coefficient. Fused quartz may crack if it is attached to, fastened, or clamped with another material that has a significantly higher coefficient of thermal expansion.
Due to its low thermal conductivity, quartz glass can develop surface cracks if it is locally heated or exposed to a flame at temperatures above its distortion point. Additionally, quartz glass becomes less viscous as the temperature increases. It is important to consider these factors when using quartz glass as a finished product or as a component in other equipment or devices.
Devitrification can shorten the service life of quartz glass, and drastically remove all the desirable characteristics of quartz. Devitrification is the conversion of the metastable quartz glass into a stable, crystalline cristobalite. This occurs when quartz is heated at high temperatures into an extended period of time, or when it is heated with impurities attached to its surface, even in small amounts. With no impurities present, devitrification normally starts at 1200°C, and hastens with increased temperature. Impurities lower the devitrification threshold.
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