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Category Archive: Fused Silica

Material of the Month: Fused Silica

Fused silica is a glass form of silicon dioxide, a chemical compound that occurs naturally in quartz and many types of sand. Unlike quartz glass, fused silica is entirely synthetic when produced at an industrial level. Typically manufactured using silicon gas, fused silica is the most technically pure glass available.

Fused silica has a non-crystalline structure that lacks long range order at an atomic level — standard for glass materials. Its three-dimensional structure is highly cross-linked, which accounts for its low coefficient of thermal expansion and high use temperature. Its superior ultraviolet (UV) properties, such as UV transmission, are a result of the specialized methods used for its production.

Transparency plate abstractThermal Properties

Due to its chemical composition and production method, fused silica exhibits excellent thermal properties, most notably a low coefficient of thermal expansion that varies little over different temperature ranges.

Coefficient of Thermal Expansion

From -100 °C (-148 °F) to +200 °C (392 °F), fused silica’s thermal expansion coefficient averages at 0.48 x 10-6/K. Focusing that temperature range slightly, its coefficient in the 5 °C (41 °F) to 35 °C (95 °F) temperature range is an average of 0.52 x 10-6/K. At a higher temperature range, from 0 °C (32 °F) to 200 °C (392 °F), the coefficient is an average of 0.57 x 10-6/K.

Such a low coefficient of thermal expansion across all temperature ranges also allows for a very high resistance to thermal shock, making fused silica glass ideal for applications that experience temperature fluctuations. By comparison, the lowest known coefficient of thermal expansion among metals, found in a nickel-iron alloy, is twice that of fused silica’s.

Thermal Conductivity

When measured at ambient temperatures of 25 °C (77 °F), fused silica has a thermal conductivity of only 1.38 W/(mK). Among the lowest thermal conductivities of known solid materials, this makes fused silica glass an excellent choice for thermal insulation applications.

By comparison, the above-mentioned nickel-iron alloy has a thermal conductivity about 10 times lower, at 10.5 W/(mK). Standard silicon’s is 100 times lower, at 148 W/(mK).

Optical Properties

Fused silica also exhibits strong optical properties, particularly in the infrared and ultraviolet regions of the light spectrum. These properties can be affected by both the purity of the material and the manufacturing process, so some variation does occur; these variations can even be intentionally introduced, depending on the desired end use of the glass.

Key Traits and Benefits

Fused silica is a strong, highly pure material with the strongest temperature-related characteristics of any glass available; it also features excellent optical transmission properties, especially in the ultraviolet spectrum. Aside from the coefficient of thermal expansion, thermal shock resistance, and transparency properties discussed above, fused silica glass also features:

  • Strong chemical inertness
  • Ability to be lapped or polished to very fine finishes
  • Low dielectric constant and loss

To learn more about fused silica and other popular types of glass, download our Glass Material Properties Chart.

glass-specs-chart

Quartz vs. Fused Silica: What’s the Difference?

If your project demands high performance material, you may have more options than you think. Quartz, Fused Quartz and Fused Silica are all part of an extremely pure family of materials with high working and melting temperatures and superior optical properties as well as low coefficient of expansion.

While they’re often used interchangeably, the fundamental structures and creation of quartz and fused silica are different. Both are highly specialized, but their particular performances vary.Quartz/Fused Silica

Quartz

Quartz is a very versatile, naturally occurring substance with good electrical, optical and thermal performance and corrosion resistance. In production, quartz glass or fused quartz is created from grains of natural material that are melted and purified.

Key Traits

  • Crafted from naturally occurring crystalline quartz or silica grains
  • Amorphous
  • Non-crystalline product
  • Retains some residual impurities from raw material (affects ultraviolet transparency)
  • Low OH content

Fused Silica

Fused Silica is an entirely synthetic material, and is technically the purest glass. It has the highest temperature characteristics of any glass, and it often begins as pure silicon gas. Because of the way fused silica is made, it has superior ultraviolet performance to natural quartz and is ideal for applications such as UV transmitting optics.

Key Traits

  • Crafted from silicon gas or silica sand (non-crystalline)
  • Amorphous
  • Cross-linked, 3D structure
  • Significant transparency into deep ultraviolet
  • Retains some residual impurities from water vapor in processing (affects infrared transparency)

High Performance Materials at Swift Glass

Both of these materials are ideal for semiconductor fabrication, technical and laboratory equipment. Distinctive features they share include:

  • Extremely low coefficient of expansion (very shock resistant)
  • Extremely high temperature resistance
  • Exceptional optical transmission

The Swift Glass Team specializes in custom work, and we’re proud to maintain a vast material inventory. Having a wide range of choices makes it easy to find the perfect glass for your next project, but it also requires careful consideration and attention to subtle qualities.

Remember to evaluate the key traits you need, even once you’ve narrowed your search to a high-performance material:

  • Thickness
  • Normal Service Temperatures
  • Extreme Service Temperatures
  • Maximum Temperature, Thermal Shock
  • Maximum Temperature, Thermal Gradient
  • In/In/F Coefficient of Thermal Expansion

We stock a range of quartz and fused silica glasses from different manufacturers, each with its own particular strengths. Check our online resources and eBooks to learn more, or call the team for more insight — we’ll find just the right glass for your next project.

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