Fused Quartz Glass
Natural fused quartz for sight glass applications
Special Properties
- Heat-resistant up to over 1000 °C (short-term)
- High thermal shock resistance
- Excellent chemical strength
- Low coefficient of expansion
- UV transparent
- Low absorption
- Crystal-clear appearance
- High uniform infrared transmission up to 2600 nm
- Non-crystalline silica glass
- More economical than fused silica
Typical Applications
- Heat-resistant sight glasses
- Front cover glass for UV lamps
- Flame monitoring
- Material for industrial quartz components
- UV LED covers
- Protective windows
- Medical UV disinfection systems
- High-temperature viewing ports
- UV drying and curing systems
- Housings for ultraviolet light sources
- Quartz parts for the chemical industry
Related Glass Types
- Quartz glass for optics (fused silica)
- BOROFLOAT® 33 (borosilicate glass)
48-hour manufacturing and delivery
Visit our Quartz Glass FAQ page to help you choose the right type of quartz material for your application.
Fused Quartz Glass: The best choice for sight glasses
Fused quartz is a non-crystalline amorphous glass made by flame melting natural silica crystals with a SiO2 content of 99.98%. Any quartz glass material contains primarily silicon and oxygen. This is also the case with fused quartz. However, it is less pure and contains more inclusions than the much more expensive optical grade fused silica materials. Since optical purity is irrelevant for the front glasses of UV lamps, high-temperature viewing ports, heat-resistant inspection windows, or other industrial use cases, fused quartz glass is the ideal and most economical material choice for such applications.
The low expansion, high thermal resistance, and excellent chemical properties of fused quartz are comparable to those of optical-grade silicon dioxide materials. Furthermore, the high transmission of ultraviolet light down to a wavelength of about 200 nm is essential for UV curing or disinfection systems. Moreover, fused quartz has a high, uniform transmission up to 2600 nm enabling many high temperature applications in the infrared. It also offers high resistivity and outstanding insulation properties.
Our fused quartz glass is made transparent by a low-cost polishing process. The thickness tolerance and parallelism achieved by this polishing process are relatively coarse, and flatness and surface quality are not on optics level. However, in most cases where these sight glass materials are used, this is completely irrelevant and helps to keep the cost low. Nevertheless, the glass is clear, and a direct straight view through the glass shows virtually no perceptible distortions or inhomogeneities.
Please click the button below to request a quote for your sight-glass-grade fused quartz window:
48-hour manufacturing and delivery
For some thicknesses, we offer 48-hour express fabrication. Please refer to the table for glass thicknesses possible for this option.
Specifications
Sight glass-quality fused quartz glass
Transmission at 3 mm in the UV-NIR range
Glass Thicknesses
Fused quartz glass is not usually available as a blank sheet, so there are no standard thicknesses. However, we continuously produce and polish several common thicknesses to offer our customers the best possible availability. Please refer to the table below for the most common fused quartz thicknesses polished for sight glass applications. Even our 48-hour delivery option is possible for these materials if needed.
Please click on glass thickness to start an inquiry:
| Thickness (mm) |
Tolerance | |
|---|---|---|
| 1.0 | ±0.2 | ✔ |
| 1.1 | ±0.2 | ✔ |
| 2.0 | ±0.3 | ✔ |
| 3.0 | ±0.3 | ✔ |
| 5.0 | ±0.5 | ✔ |
| Custom thicknesses are possible on request. | ||
| For thicknesses marked with ✔, our optional 48-hour express fabrication is possible. | ||
Optical Properties
- UV-Transmission:
Approximately 90% at 260 nm (3 mm thick) - Refractive Index: nd = 1.459
Mechanical Properties
- Density: 2.20 g/cm3
- Young's Modulus: ca. 7.2 × 1010
- Poisson's number: 0.17
Thermal Properties
- Coefficient of thermal expansion:
Approx. 0.55 × 10-6/K (25–300 °C) - Maximum operating temperature:
- Short-term use: up to approx. 1100 °C
- Long-term use: up to approx. 850 °C
- Thermal conductivity: approx. 1.4 W/K m
Electrical Properties
- Dielectric constant εr: 3.75 (1 MHz)
- Loss factor: < 2 × 10-4 (20 °C ; 1 MHz)
- Specific resistivity: 7.0 × 109 Ω x cm (350 °C)
- Insulation capacity: 5 × 10-7 V/m
If you are searching for higher-grade quartz glass suitable for optical or semiconductor applications, please refer to our Synthetic Fused Silica datasheet for detailed information.
All data and specifications given are average guide values and are not guaranteed. Moreover, please consider the “Notes on Specifications”.
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Last update: January 16, 2025.