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Engineers working on cutting-edge projects face a persistent challenge: finding materials that withstand extreme conditions without compromising performance. Standard glasses crack under thermal stress. Conventional materials absorb critical wavelengths. Impurities contaminate sensitive processes.
Fused quartz answers this challenge. This ultra-pure form of silicon dioxide delivers properties that make it indispensable in semiconductor fabrication, precision optics, high-temperature processing, and advanced scientific research. Unlike ordinary glass, fused quartz maintains dimensional stability through dramatic temperature changes, transmits light across an extraordinary wavelength range, and provides chemical purity that prevents contamination in critical processes.
This guide explores what fused quartz is, how it’s manufactured, its key properties, and why it has become critical in high-performance applications across multiple industries.
Fused quartz is a glass consisting of nearly pure silicon dioxide (SiO₂) in an amorphous, non-crystalline form. This composition distinguishes it from all other commercial glasses. Soda-lime glass, borosilicate glass, and lead glass all contain additives that modify properties like melting temperature and optical characteristics. Fused quartz contains up to 99.98% pure silica with minimal impurities.
This exceptional purity creates the material’s remarkable properties. The absence of additives means fused quartz doesn’t have the thermal expansion issues that plague other glasses. It doesn’t introduce contaminants into sensitive processes. The pure silica composition creates an optical material with transmission characteristics unmatched by conventional glasses.
Silica is the primary constituent of most types of glass and has the chemical formula SiO₂. Mineral quartz is the main form in which silica is found in nature. Fused quartz transforms this naturally occurring material into an engineered glass with controlled properties.
You’ll encounter two terms frequently: fused quartz and fused silica. These terms are often used interchangeably, but they can refer to different manufacturing techniques that result in different trace impurities.
Fused quartz specifically refers to glass made by melting naturally occurring quartz crystals. The starting material contains trace impurities inherited from the geological origin of the quartz. These impurities, commonly including aluminum, titanium, iron, and other trace elements, can affect optical transmission, particularly at ultraviolet wavelengths.
Fused silica refers to glass produced from synthetic chemical precursors, typically derived from silicon tetrachloride (SiCl₄) through chemical vapor or flame hydrolysis process. The synthetic process creates material with even higher purity and improved UV transmission. When you need the deepest ultraviolet transparency, synthetic fused silica provides superior performance.
Despite these distinctions, both materials share the same amorphous silicon dioxide structure. Both exhibit exceptional thermal stability, low thermal expansion, and excellent chemical resistance. The choice between them depends on your specific optical requirements and budget constraints.
Understanding the difference between crystalline and amorphous structures is essential to appreciating fused quartz’s unique properties. Natural quartz crystals have atoms arranged in regular, repeating patterns called crystal lattices. This ordered structure gives crystalline quartz specific optical and physical properties.
Fused quartz, however, is amorphous. The constituent atoms have no long-range order. Their seemingly random arrangement resembles a liquid’s structure, except the atoms are fixed in place rather than moving. This glassy state profoundly influences the material’s characteristics.
The amorphous structure enables the glass transition effect—the material gradually softens when heated rather than melting at a sharp temperature. This behavior allows for thermal forming and joining techniques impossible with crystalline materials. The lack of grain boundaries eliminates weak points that cause crystalline materials to fracture along specific planes.
Fused quartz is produced by melting high-purity silica at approximately 2,200°C (4,000°F). Several manufacturing methods exist, each producing material with specific characteristics. The production method significantly impacts purity, optical transmission, and water content.
Type I (Electrically Fused) involves melting natural quartz crystals in a vacuum or inert atmosphere using electric heating. This process produces material with lower water content, making it ideal for infrared applications. The trade-off is slightly higher metallic impurity content that limits UV transmission, particularly below approximately 250 nm.
Type II (Flame Fused) melts quartz crystal powder in a high-temperature hydrogen-oxygen flame. This method always produces material with higher water content because the combustion process creates hydroxyl (OH) groups within the glass. These OH groups absorb infrared radiation around 2.7 μm, limiting IR transmission. However, flame-fused material works well for many applications where mid-IR transmission isn’t critical.
Type III (Vapor Deposition) burns silicon tetrachloride in a hydrogen-oxygen flame. This synthetic process creates the highest purity fused silica with exceptional UV transmission extending below 200 nm. Type III fused silica finds use in deep-UV lithography and precision optics where extreme UV transparency is essential.
Understanding these manufacturing differences helps you specify the right grade for your application. Don’t pay for UV-grade purity if your application only requires IR transmission.
The thermal properties of fused quartz set it apart from virtually all other materials. The coefficient of thermal expansion measures only 0.55 × 10⁻⁶ per °C—approximately ten times lower than borosilicate glass. This extraordinarily low expansion means fused quartz maintains dimensional stability through temperature changes that would shatter conventional materials.
This extremely low coefficient accounts for fused quartz’s remarkable ability to undergo large, rapid temperature changes without cracking. Under appropriate conditions, you can heat fused quartz with a torch and plunge it into cold water without fracturing—a demonstration impossible with standard glass.
The softening point reaches approximately 1,665°C, allowing continuous operation at temperatures exceeding 1,200°C. This high-temperature capability makes fused quartz invaluable for furnace components, crucibles, and processing equipment operating in extreme thermal environments. The material doesn’t oxidize and retains useful mechanical strength at temperatures where metallic materials rapidly lose strength.
A thermal conductivity of 1.3 W/(m·K) provides moderate heat transfer while maintaining electrical insulation. This combination proves useful in applications requiring thermal management without electrical conduction. The thermal shock resistance exceeds that of most glasses and engineering materials, enabling rapid thermal cycling in processing applications.
Optical transparency represents one of fused quartz’s most valuable properties. The material transmits light from deep ultraviolet wavelengths around 180 nm through the visible spectrum and into the infrared beyond 3,500 nm. This extraordinary transmission range surpasses all conventional optical glasses.
UV-grade synthetic fused silica transmits approximately 50% at 170 nm through a 1 cm thickness. This deep UV transmission makes the material essential for spectroscopy, UV photolithography, and excimer laser optics. The material doesn’t solarize (develop color) under UV exposure as readily as other glasses.
IR-grade fused quartz, produced by electric fusion with minimal water content, transmits effectively to 3.6 μm. This extended infrared transmission suits thermal imaging systems, IR spectroscopy, and laser optics operating at longer wavelengths. The lower water content eliminates the strong absorption bands that limit flame-fused material.
The refractive index of 1.4585 at 587.6 nm provides excellent optical properties for lens design. The high Abbe number of 67.8 indicates very low dispersion, making fused quartz ideal for achromatic optical systems. The material maintains optical quality through thermal cycling that would permanently damage conventional optics.
Chemical inertness makes fused quartz valuable in corrosive environments. The material resists most mineral acids across a wide range of concentrations, with the notable exception of hydrofluoric acid. This broad chemical resistance allows fused quartz components to operate reliably in aggressive chemical processing environments where metals corrode rapidly.The high purity means fused quartz doesn’t leach mobile ions into solutions—a critical requirement for analytical chemistry and semiconductor processing. Even trace contamination from container materials can compromise experiments or contaminate wafers. Fused quartz maintains chemical purity that prevents these problems.
Strong bases attack fused quartz slowly, particularly at elevated temperatures, though less aggressively than HF. Hot phosphoric acid also etches the material. Despite these limitations, fused quartz withstands most industrial chemicals. The chemical resistance extends to high temperatures where many polymer alternatives decompose or lose structural integrity.
Electrical resistivity exceeding 10¹⁸ Ω·m at room temperature makes fused quartz an outstanding electrical insulator. This extremely high resistance results in very low leakage currents,even at elevated temperatures. The material maintains effective insulating properties above 1,000°C where many ceramics become conductive.
The dielectric constant of 3.75 at 1 MHz provides low capacitance for high-frequency applications. This low value minimizes signal loss and coupling in RF and microwave systems. The dielectric loss factor below 0.0004 indicates minimal energy dissipation.
Dielectric strength between 250-400 kV/cm allows fused quartz to withstand high voltages without breakdown. This property proves valuable in high-voltage insulation, vacuum tube envelopes, and electrical feedthroughs. The material’s optical transparency allows visual inspection while maintaining reliable electrical isolation.
The semiconductor industry depends heavily on fused quartz for critical manufacturing equipment. Wafer processing tools incorporate fused quartz components such as chamber liners, windows, and fixtures due to their ultra-high purity and chemical stability. Any contamination from processing equipment ruins wafers and destroys integrated circuits. The predictable behavior and resistance to metallic contamination make fused quartz essential for maintaining wafer yield and device performance.
Photolithography processes depend on synthetic fused silica substrates for photomasks (reticles) and projection optics. The low thermal expansion of fused quartz maintains dimensional stability and flatness through thermal cycles, ensuring accurate pattern transfer. Its high transparency at deep-UV wavelengths supports advanced lithography at 248 nm and 193 nm for fine feature fabrication.fused quartz’s combination of strength, thermal stability, and UV transparency makes it well suited for photolithography optics and mask substrates. In silicon crystal growth, the Czochralski method uses fused quartz crucibles that withstand molten silicon at 1,410°C without contamination.
Furnace tubes for diffusion and oxidation processes operate at temperatures exceeding 1,000°C for extended periods. Fused quartz tubes provide the necessary thermal stability and purity while their transparency allows visual monitoring of wafers during processing.
Optical applications leverage fused quartz’s exceptional transmission characteristics. Lenses, windows, prisms, and mirrors for UV and IR systems require materials transparent at these wavelengths. Standard optical glasses absorb UV radiation and don’t transmit beyond 2.5 μm in the infrared.
Precision optical substrates demand materials with very low thermal expansion to maintain surface figure under temperature variations. Fused quartz provides excellent dimensional stability and is widely used for precision mirrors, optical benches, and spaceborne and airborne optical components where thermal distortion must be minimized.
Fiber optic communications depend on ultra-pure synthetic fused silica for optical fiber production. The material’s transparency at telecommunications wavelengths (1.3-1.55 μm) combined with controlled refractive index profiles enables long-distance signal transmission. The low optical loss allows signals to travel dozens of kilometers between optical amplifiers.
UV laser optics require materials that withstand intense UV radiation without degrading. Excimer lasers operating at 193 nm and 248 nm would rapidly damage conventional optics. UV-grade fused silica transmits these wavelengths while exhibiting strong resistance to solarization under high-energy UV exposure.Laboratory and Scientific Equipment
Laboratory glassware manufactured from fused quartz serves applications where borosilicate glass proves inadequate. High-temperature crucibles for materials synthesis often operate up to 1,200°C. Standard glassware softens and deforms at these temperatures. Fused quartz crucibles maintain mechanical integrity and dimensional stability through repeated heating cycles.
Spectroscopy cuvettes require optical windows transparent across a broad spectral range. Fused quartz cuvettes enable measurements from approximately 200 nm in the UV through the visible and into the near-infrared (≈2.5–2.7 µm) using a single cell design. This broad transmission eliminates the need for different cells at different wavelengths.
Quartz sample introduction components used in atomic absorption spectroscopy and inductively coupled plasma instruments operate in close proximity to high-temperature plasmas while maintaining dimensional stability. The chemical inertness prevents sample contamination and analytical interference in analytical measurements.
Spacecraft window systems incorporate fused quartz as part of multi-layer assemblies where thermal shock resistance, optical clarity, and radiation stability are critical. In vehicles such as the Space Shuttle and the International Space Station, fused silica layers contribute to window designs that withstand the severe thermal and mechanical stresses of launch, orbital operation, and reentry while maintaining excellent optical performance.Halogen and high-intensity discharge (HID) lamp envelopes operate at high temperatures that would soften or melt conventional glass. Fused quartz envelopes maintain integrity at operating temperatures exceeding 900°C while transmitting visible and near-UV radiation efficiently.
High-temperature processing equipment – including furnace tubes, trays, and crucibles – leverage fused quartz’s thermal capabilities and purity. These components are widely used in glass manufacturing, semiconductor processing, and ceramic sintering applications, where high temperatures and thermal cycling demand materials with low thermal expansion and resistance to deformation.Comparing Fused Quartz Grades: UV vs. IR SpecificationsSelecting the appropriate fused quartz grade requires understanding the trade-offs between UV and IR transmission:
| Property | UV Grade (Synthetic Fused Silica) | IR Grade (Electrically Fused Quartz) |
| Manufacturing | Flame hydrolysis / flame fusion from SiCl₄ | Electric fusion of high-purity natural quartz |
| Chemical Purity | Ultra-high purity, extremely low metallic impurities | High purity, slightly higher trace metal content |
| UV Transmission Cutoff | ~180 nm | ~220–250 nm (limited deep-UV performance) |
| IR Transmission | Limited by OH absorption | Excellent transmission to ~3.6 µm |
| OH Content | High (typically 800–1300 ppm) | Very low (typically <10 ppm) |
| Typical Applications | UV optics, photolithography, excimer lasers | IR spectroscopy, thermal imaging, IR optics |
UV-grade synthetic fused silica provides the deepest UV transmission needed for spectroscopy, photolithography, and UV laser applications. Choose this grade when transmission below 250 nm is essential.
IR-grade fused quartz excels in infrared applications. The low water content eliminates absorption bands around 2.7 μm. This grade suits thermal imaging, IR spectroscopy, and applications requiring extended IR transmission.
What is the difference between fused quartz and regular glass?
Fused quartz consists of nearly pure silicon dioxide (> 99.98% SiO₂) with minimal additives, while regular glass contains sodium, calcium, and other modifiers. This purity gives fused quartz an exceptionally low thermal expansion coefficient – an order of magnitude lower than soda-lime glass – along with superior chemical resistance, and optical transmission extending into deep UV and mid-infrared wavelengths.
Can fused quartz be machined or fabricated?
Yes, fused quartz can be machined using diamond-impregnated tools, as well as ground, lapped, and polished to high-precision finishes. Mechanical processing requires diamond wheels, drill bits, and saws, as conventional cutting tools are ineffective due to the material’s hardness and brittleness.
Fused quartz can also be thermally formed by flame working at temperatures approaching and exceeding its softening point (~1,660–1,700°C) using high-temperature oxy-hydrogen flames. This enables the fabrication of complex shapes, though careful annealing is required to relieve thermal stresses.
Why is fused quartz so expensive compared to other glasses?
The high production temperatures (often approaching 1,700-2,000°C), specialized manufacturing equipment, and high-purity starting materials increase costs significantly. The energy required to melt pure silica far exceeds that for conventional glasses. Despite higher initial costs, the exceptional durability often provides better value through extended service life.
Does fused quartz conduct electricity?
No, fused quartz is an excellent electrical insulator with resistivity exceeding 10¹⁸ Ω·m at room temperature. It maintains insulating properties even at temperatures above 1,000°C where many materials become conductive.
What chemicals can damage fused quartz?
Hydrofluoric acid (HF) rapidly etches fused quartz and is the primary chemical to avoid. Hot concentrated phosphoric acid also attacks the material. Strong alkaline solutions (caustic soda) etch fused quartz slowly, particularly at elevated temperatures. Aside from these exceptions, fused quartz exhibits excellent resistance to most other acids, solvents, and chemicals.
Can fused quartz withstand thermal shock?
Yes, fused quartz exhibits exceptional thermal shock resistance due to its extremely low thermal expansion coefficient (0.55 × 10⁻⁶/°C). This allows fused quartz components to tolerate rapid temperature changes that would fracture conventional glasses. In many cases, thin or well-designed fused quartz parts can be heated to red heat and rapidly quenched in cold water without cracking—a demonstration impossible with conventional glasses.
What is the maximum operating temperature for fused quartz?
Fused quartz can operate continuously at temperatures up to 1,200°C, with short-term exposure possible to 1,650°C (near the softening point). At higher temperatures, the material softens and may deform under its own weight.
Why does fused quartz transmit UV light better than regular glass?
Regular glass contains iron and other transition metal impurities that absorb UV wavelengths. The additives used to lower melting temperature also limit UV transmission. Fused quartz’s high purity eliminates these absorbing species, allowing transmission deep into the UV spectrum.
Is fused quartz the same as crystalline quartz?
No, despite having the same chemical composition (SiO₂), fused quartz and crystalline quartz have fundamentally different structures. Crystalline quartz has atoms arranged in an ordered crystal lattice. Fused quartz is amorphous (glassy) with randomly arranged atoms and different optical properties.
Can fused quartz be joined or sealed to other materials?
Yes, fused quartz can be fusion-bonded to itself by heating above 1,600°C, creating monolithic seals. Graded seals allow joining to materials with different thermal expansion, including borosilicate glass and certain metals, typically through the use of intermediate glass compositions or matched-expansion transition layers. Proper seal design considers thermal expansion differences, geometry, and cooling rates to prevent stress fractures.
Material quality determines project success in demanding applications. Working with a supplier who understands fused quartz properties and can provide the right grade for your specific requirements is essential. AdValue Technology specializes in high-performance materials for engineers developing advanced systems.
Whether you need UV-grade fused silica for optical applications, IR-grade fused quartz for high-temperature processes, or standard optical grade for laboratory equipment, AdValue Technology supplies materials meeting your specifications. The company stocks multiple grades and can source specialized materials for unique requirements.
Technical support helps you navigate the complexities of material selection. Not sure whether UV or IR grade best suits your application? The team at AdValue Technology brings expertise to help you specify the right material. This guidance prevents costly mistakes and ensures optimal performance.
Custom fabrication capabilities transform raw material into finished components. From simple discs and windows to complex geometries, AdValue Technology can provide fabricated parts ready for integration into your systems.Don’t compromise performance with inappropriate materials. Discover how fused quartz’s exceptional properties can enable your next breakthrough application. Contact AdValue Technology today to discuss your specific requirements. Visit AdValue Technology to explore the complete range of fused quartz and other advanced materials. Your success starts with the right material partner.
