Do you know what quartz glass is, why it has such remarkable properties, and why it plays a critical role in modern technology? Quartz glass is an essential material supporting many advanced technologies due to its exceptional heat resistance, extremely low coefficient of thermal expansion, excellent optical transmission over a wide wavelength range, outstanding chemical stability, and superior electrical insulation.
In this article, we provide a comprehensive overview of quartz glass—from its basic definition and fundamental structure to the reasons behind its outstanding performance, the differences between natural and synthetic quartz glass, major manufacturing processes, and its wide-ranging applications in semiconductor manufacturing, optics, medicine, research and development, lighting, and other high-technology industries.
1. What Is Quartz Glass? Basic Definition
Quartz glass is one of the most important materials in modern advanced industries. Its unique properties distinguish it clearly from ordinary glass, and these properties originate from both its chemical composition and its internal structure.
Quartz glass is primarily composed of silicon dioxide (SiO₂). It is produced by melting ultra-high-purity silica and cooling it rapidly without crystallization. As a result, quartz glass is an amorphous solid, meaning it has no long-range crystal lattice. This amorphous structure is the fundamental reason for its exceptional thermal, optical, chemical, and electrical properties. Quartz glass is also commonly referred to as silica glass or fused silica.
It is important to distinguish between quartz and quartz glass, which are often confused but are fundamentally different materials.
| Item | Quartz (Crystal) | Quartz Glass (Silica Glass) |
|---|---|---|
| Principal component | Silicon dioxide (SiO₂) | Silicon dioxide (SiO₂) |
| Atomic structure | Crystalline (ordered lattice) | Amorphous (disordered structure) |
| Transparency | Transparent | Transparent |
| Formation | Naturally occurring or crystal-grown | Melted and vitrified high-purity silica |
| Typical applications | Oscillators, watches, sensors, jewelry | Semiconductors, optics, lighting, medical, research |
Thanks to its amorphous structure and ultra-high purity (typically ≥ 99.99% SiO₂), quartz glass exhibits properties not found in other glasses: extremely high heat resistance, an exceptionally low coefficient of thermal expansion, excellent optical transmission from deep ultraviolet to infrared wavelengths, outstanding chemical stability, and superior electrical insulation. These characteristics make quartz glass indispensable in modern high-technology industries.
2. Outstanding Performance of Quartz Glass
Quartz glass is widely used in advanced industrial and scientific applications because of its unique combination of physical, chemical, optical, and electrical properties.
2.1 Exceptional Heat Resistance and Extremely Low Thermal Expansion
One of the most outstanding characteristics of quartz glass is its exceptional resistance to high temperatures. It has a softening point of approximately 1680 °C, can operate continuously at temperatures of up to 1200 °C, and can withstand short-term exposure to about 1300 °C.
In addition, quartz glass has an extremely low coefficient of thermal expansion, approximately 5.5 × 10⁻⁷ /°C (20–300 °C). Because dimensional changes with temperature are minimal, quartz glass demonstrates excellent resistance to thermal shock and can withstand rapid temperature changes, such as cooling from over 1100 °C to room temperature, without cracking. This property is critical for semiconductor manufacturing equipment and precision optical systems.
| Glass Type | Softening Point (Approx.) | Thermal Expansion Coefficient | Thermal Shock Resistance |
|---|---|---|---|
| Quartz Glass | ~1680 °C | ~5.5 × 10⁻⁷ /°C | Extremely high |
| Borosilicate Glass | ~820 °C | ~3.3 × 10⁻⁶ /°C | High |
| Soda-Lime Glass | ~700 °C | ~9.0 × 10⁻⁶ /°C | Low |
2.2 Excellent Optical Transmission from UV to Infrared
Quartz glass offers outstanding optical transmission across a very wide wavelength range. It transmits light efficiently from approximately 185 nm to 2500 nm, making it especially valuable for ultraviolet applications where most other glasses absorb strongly.
For example, quartz glass exhibits more than 90% transmission at 254 nm (10 mm thickness), which is why it is widely used in UV lamps, sterilization systems, semiconductor lithography equipment, and spectroscopic instruments. It also performs well in the visible and infrared regions, enabling its use in optical fibers, laser systems, and high-precision optical components.
2.3 High Chemical Stability and Corrosion Resistance
Quartz glass exhibits excellent chemical stability and outstanding resistance to most acids, alkalis, and solvents. It is highly resistant to acidic and neutral solutions and remains stable even at elevated temperatures, making it suitable for harsh chemical environments such as semiconductor processing, laboratory equipment, and chemical reactors.
However, quartz glass is attacked by hydrofluoric acid (HF) and can also be affected by strong alkalis and high-temperature concentrated phosphoric acid. Aside from these specific cases, quartz glass offers exceptional corrosion resistance and is ideal for applications requiring high purity and chemical inertness.
2.4 Electrical Properties and Mechanical Strength
Quartz glass is also valued for its excellent electrical properties. It has an extremely high electrical resistivity of > 10¹⁸ Ω·cm at 20 °C, low dielectric loss, and high dielectric strength (typically 25–40 kV/mm). These properties make it an excellent electrical insulator, especially in high-frequency and high-temperature environments.
Mechanically, quartz glass is a brittle material, but it exhibits relatively high strength and surface hardness. Typical values include a compressive strength of about 1100 MPa, tensile strength around 48 MPa, and Mohs hardness of 5.5–6.5. These characteristics provide good wear resistance and dimensional stability for precision-machined components.
3. Types of Quartz Glass and Manufacturing Methods
The properties of quartz glass vary depending on raw materials and manufacturing processes. Quartz glass is generally classified into natural quartz glass and synthetic quartz glass.
3.1 Natural vs. Synthetic Quartz Glass
| Item | Natural Quartz Glass | Synthetic Quartz Glass |
|---|---|---|
| Raw materials | Natural quartz crystal | Chemically synthesized silica (e.g. SiCl₄) |
| Purity | High, limited by natural mineral impurities | Ultra-high purity |
| OH content | Process-dependent | Process-dependent (low-OH or high-OH grades available) |
| Bubbles | Relatively more | Very few |
| UV transmission | Limited in deep UV | Excellent, including deep UV |
| Manufacturing cost | Lower | Higher |
| Typical applications | Lamps, crucibles, protective tubes | Semiconductor equipment, precision optics, optical fiber substrates |
Synthetic quartz glass is essential for semiconductor manufacturing and advanced optical systems where extremely high purity and superior deep-UV transmission are required. Natural quartz glass is commonly used in applications that require the core properties of quartz glass at a lower cost.
3.2 Major Manufacturing Processes
Melting Methods (Natural Quartz Glass)
- Electric melting: Simple process but may retain impurities and bubbles.
- Flame melting: Higher temperatures, improved purity, but higher OH incorporation.
Synthetic Methods
- Flame hydrolysis (VAD, OVD): Produces high-purity silica soot, widely used for optical fibers.
- MCVD: Used mainly for optical fiber preforms with complex refractive index profiles.
- Plasma methods: Enable ultra-low OH content and excellent deep-UV performance, ideal for semiconductor lithography optics.
4. Major Applications of Quartz Glass
4.1 Semiconductor Manufacturing
Quartz glass is indispensable in semiconductor fabrication due to its high purity, thermal stability, and chemical inertness. Typical applications include:
- Process tubes for diffusion, oxidation, and CVD
- Wafer boats and carriers
- Jigs, liners, and reaction vessels
- Gas distribution plates (shower plates)
4.2 Advanced Optics and Photonics
Quartz glass is widely used in optical systems thanks to its broad transmission range and dimensional stability:
| Application | Examples | Key Advantages |
|---|---|---|
| Optical components | Lenses, prisms, windows | Wide spectral transmission, low thermal expansion |
| Optical fibers | Communication, medical imaging | Low loss, high purity |
| Laser optics | High-power laser systems | High laser damage threshold |
| Analytical instruments | Spectroscopy cells, UV windows | Excellent UV transmission |
4.3 Medical, Research, and Scientific Applications
Quartz glass is used in medical devices, analytical instruments, and research equipment due to its purity, chemical stability, and UV transparency. Applications include UV sterilization systems, analytical cells, laboratory vessels, biotechnology equipment, and plasma research systems.
4.4 Lighting and Other Industrial Applications
Quartz glass is essential for high-performance lighting such as halogen lamps, mercury lamps, metal-halide lamps, and UV germicidal lamps. It is also widely used in aerospace, solar cell manufacturing, vacuum technology, industrial furnaces, and precision measurement equipment.
5. Comparison with Other Glass Types
Compared with soda-lime and borosilicate glass, quartz glass offers far superior heat resistance, lower thermal expansion, better UV transmission, higher chemical stability, and superior electrical insulation, making it the preferred material for extreme and high-precision environments.
6. Conclusion
Quartz glass is a specialized, ultra-high-purity silica material whose exceptional properties make it indispensable to modern technology. From semiconductor manufacturing and advanced optics to medical devices, lighting, and aerospace applications, quartz glass plays a foundational role in enabling innovation. As technologies such as 5G/6G communication, quantum computing, renewable energy, and next-generation medical systems continue to evolve, demand for high-performance quartz glass will only increase. Quartz glass remains a critical material supporting both today’s technologies and the innovations of the future.
