Product Focus: Fused Silica Vs Fused Quartz

22, Jul. 2024

 

Product Focus: Fused Silica Vs Fused Quartz

Fused silica and fused quartz are amongst some of the most popular optical materials. However, there can be some confusion between the two due to their similar properties, to the components, they are used for. In this article, we'll look at the differences and similarities between fused quartz and fused silica.

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Key Takeaways

  • Fused Silica is a synthetic material and the purest form of glass, offering high transmission in the UV spectrum.
  • Fused quartz is made from naturally occurring material in the form of crystalline quartz or silica grains. Fused quartz glass is manufactured by melting the natural quartz crystals, with the results containing more impurities than fused silica.
  • Due it's purity, fused silica can be the ideal material for applications such as items of optical equipment which rely on UV transmission.
  • Despite it's lower optical quality, fused quartz has excellent optical, electrical and thermal properties, as well as being highly resistant to corrosion.
  • Both Fused silica and quartz offer low thermal expansion, high working, and melting temperatures, and are highly corrosion resistant.

What is Fused Silica?

Fused silica is a synthetic material. It is a non-crystalline silica glass and is made from either pure silicon gas or non-crystalline silica sand. Fused silica is the purest form of glass, offering high transmission in the UV spectrum.

It can be manufactured in translucent or opaque form and the purity it offers makes it the ideal material for applications such as items of optical equipment which rely on UV transmission. An example of this would be equipment which uses UV rays in order to sterilise surfaces and or/equipment for medical purposes. The purity it offers also makes fused silica the material of choice for the manufacture of semi-conductor and laboratory equipment. 

What is Fused Quartz?

Unlike fused silica, fused quartz is made from naturally occurring material in the form of crystalline quartz or silica grains. Fused quartz glass is manufactured by melting the natural quartz crystals, with the results containing more impurities than fused silica.

This means that fused quartz has a lower OH content than the synthetic alternative, as well as lower optical quality and more flaws and bubbles. In most cases, fused quartz glass is transparent and, despite being inferior in quality to fused silica, can still offer excellent optical, electrical and thermal properties, as well as being highly resistant to corrosion.

The degree to which fused quartz glass contains impurities and/or naturally occurring flaws will be governed by the quality of the quartz sourced for its manufacture. Although fused quartz glass contains more flaws than fused silica, it should be noted that these flaws will not be visible to the naked eye, and only impact upon the viability of fused quartz as a material for applications with extremely high optical requirements.

Properties shared by Fused Quartz and Fused Silica

Despite their differences, fused quartz and fused silica do share some properties, such as the following:

  • They both offer low thermal expansion
  • They both offer excellent optical properties
  • They both offer high working and melting temperatures ' the maximum temperature at which both can be used is °C, while both can be used for a sustained period at temperatures of 1,100°C. In both cases the softening point of the glass will be hit at roughly 1,730°C.
  • They are both highly corrosion resistant ' each offers acid resistance which is 150 times more than stainless-steel and 30 times more than ceramics. The only acid likely to cause any reaction in fused quartz or fused silica glass is hydrofluoric acid.

Both types of glass ' fused quartz and fused silica ' are widely used in sectors such as:

  • Metallurgy
  • Chemical and Pharmaceutical
  • Construction
  • Communications
  • Semiconductors
  • Defence/Military
  • Environmental protection

Choosing between Fused Silica and Fused Quartz

When a client comes to UQG Optics with a requirement they sometimes know whether they need fused quartz or fused silica, but in other cases they may not be entirely clear. We will draw on our expertise and experience to advise as to which of the materials will be best suited to the optical component in question.

Fused silica, for example, is manufactured using a process known as flame hydrolysis. Although this offers the highest possible level of purity it is also expensive, complex and time consuming, and is only needed in those components which demand the very highest levels of optical purity.

For many applications, fused quartz glass provides sufficient levels of optical purity as well as the other shared properties detailed above, whilst being less expensive and time consuming to manufacture. For those reasons we will often recommend it to clients, particularly if they are seeking large-scale production of optical components or working to tighter budgets and deadlines.

Custom and Stock Fused Quartz and Silica

If you'd like to learn more about fused silica, fused quartz and the differences between the two types of glass, or have a specific project which you need to discuss, please call us on or our sales team at

What Is the Difference Between Silica and Fused ...

Oct. 13,

Silica and fused silica lenses, while sharing a similar chemical composition, exhibit distinctive characteristics that make them suitable for different applications in the field of optics. To comprehend the differences between these two types of lenses, it's essential to delve into their composition, manufacturing processes, properties, and applications.

 

Silica Lenses

 

Silica lenses, also known as quartz lenses, are crafted from naturally occurring silica, which is a compound of silicon and oxygen (SiO2). Silica is one of the most abundant minerals on Earth and can be found in various forms, including quartz crystals and sand.

 

Composition

 

Silica lenses are made from naturally mined quartz or synthetic fused silica. The chemical composition of silica lenses is SiO2, the same as that of silica, and this gives them a crystalline structure. The clarity and transparency of silica lenses make them ideal for various optical applications.

 

Natural or Synthetic

 

Silica lenses can be manufactured from either naturally mined quartz or synthetic fused silica. Natural quartz is sourced from geological formations, while synthetic fused silica is created through high-temperature melting and cooling processes. Both offer excellent optical properties, but synthetic fused silica lenses are often preferred for specific applications due to their higher purity and controlled manufacturing.

 

Optical Properties

 

Silica lenses are known for several key optical properties:

 

- Transparency: Silica lenses are optically clear, allowing them to transmit light with minimal distortion.

- High Refractive Index: Silica has a high refractive index, which makes it suitable for applications where focusing and bending of light are necessary.

- Thermal Resistance: Silica lenses can withstand high temperatures without significant optical degradation, making them valuable in high-temperature applications.

 

Applications

 

Silica lenses are commonly used in a range of optical systems and devices, including:

 

- Camera Lenses: Silica lenses are used in cameras to focus and capture images.

- Microscopes: They are employed in microscopes for magnifying and observing small objects.

- Spectrometers: Silica lenses help disperse and analyze light in spectrometry.

- Laser Systems: These lenses are utilized in laser systems to focus and shape laser beams.

- Telescopes: Silica lenses are part of optical systems in telescopes, aiding in viewing distant celestial objects.

 

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Fused Silica Lenses

 

Fused silica lenses are synthetic lenses crafted from fused silica, a pure form of amorphous silicon dioxide (SiO2). The amorphous structure of fused silica sets it apart from crystalline silica, and it is this structure that contributes to its distinct optical properties.

 

Manufacturing Process

 

The manufacturing process of fused silica lenses involves producing pure silicon tetrachloride (SiCl4) and then burning it in a high-temperature flame to create amorphous silica particles. These particles are subsequently fused together as they cool, resulting in a solid material with exceptional optical properties.

 

Optical Properties

 

Fused silica lenses exhibit unique optical characteristics:

 

- High Purity: Fused silica is highly pure, with minimal impurities and inclusions, making it valuable in applications requiring optical precision.

- Low Thermal Expansion: Fused silica has a low coefficient of thermal expansion, making it resistant to thermal shock. This property is beneficial in high-temperature applications.

- UV Transparency: Fused silica is highly transparent in the ultraviolet (UV) region of the electromagnetic spectrum, making it essential in UV optics.

 

Applications

 

Fused silica lenses find application in various optical systems and industries, including:

 

- Semiconductor Manufacturing: Fused silica lenses are used in photolithography for semiconductor manufacturing, where precision and UV transparency are critical.

- Analytical Instruments: These lenses are employed in analytical instruments like spectrophotometers and fluorescence microscopes.

- Astronomy: Fused silica lenses are used in telescopes and astronomical observatories to observe celestial objects in the UV range.

- Medical Instruments: They find application in medical devices such as UV spectrometers and analytical equipment.

 

Differences Between Silica and Fused Silica Lenses

 

Now that we've explored the characteristics of silica and fused silica lenses, let's summarize the key differences between the two types of lenses:

 

1. Origin: Silica lenses can be crafted from natural quartz or synthetic fused silica, whereas fused silica lenses are exclusively manufactured from synthetic fused silica.

 

2. Structure: Silica lenses have a crystalline structure, while fused silica lenses have an amorphous (non-crystalline) structure.

 

3. Purity: Fused silica lenses are known for their high purity, with minimal impurities and inclusions, while silica lenses may have impurities depending on their source.

 

4. Thermal Properties: Fused silica lenses have a lower coefficient of thermal expansion, making them highly resistant to thermal shock, whereas silica lenses may not be as resilient in high-temperature applications.

 

5. UV Transparency: Fused silica lenses exhibit superior transparency in the UV range, making them indispensable in applications requiring UV optics.

 

Conclusion

 

In conclusion, while both silica and fused silica lenses share a SiO2 chemical composition, they differ significantly in their origins, structures, properties, and applications. Silica lenses, whether derived from natural quartz or synthetic fused silica, are renowned for their optical clarity and transparency, making them ideal for various optical systems. In contrast, fused silica lenses, created through a controlled manufacturing process, offer superior purity, low thermal expansion, and exceptional UV transparency. These properties make them essential in high-precision applications, particularly in the fields of semiconductor manufacturing, analytical instrumentation, astronomy, and UV optics. Understanding these distinctions is essential for selecting the appropriate lenses for specific optical requirements and industries.

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