Heraeus Clear Fused Quartz
a century of material experience

Clear Fused Quartz

Heraeus Clear Fused Quartz solutions offer the best in class, lowest levels of inclusions and bubbles, meeting even the requirements of the most challenging applications. Convince yourself and have a clear view on your world with Heraeus Clear Fused Quartz.

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In-house material purification

With the increasing demands of today’s applications, material quality and stability are critical factors to maintaining control of your manufacturing process. In order to have full control and visibility on material quality we utilize our fully in-house raw material purification. This is further supported by our accredited chemical laboratory to ensure stability and reliability of Heraeus quartz materials.

Lowest inclusions and bubbles

If your application requires extremely low level of inclusions and bubbles Heraeus CFQ products can support your needs. Our materials offer the best in class, lowest levels of inclusions and bubbles, meeting even the requirements of the most challenging applications.

Full service company

Only Heraeus Conamic can offer a full spectrum portfolio of fused quartz and fused silica grades to support the right material for all applications. We provide all fusion methods and products, ranging from standard fused quartz grades to high-end fused silica synthetics. This allows Heraeus to offer all grades with the same quality and material excellence, supported by our outstanding material competence. We can recommend the perfect matching materials for your requirements, and supply it.

Full portfolio in shape and size

Heraeus CFQ products can be provided in multiple configurations to optimally support your component design, and reduce wasted material. Typical formats for our materials are rods, tubes, ingots, cylinders, plates and discs. Additionally many of our products are also available in square and rectangular format. We have the matching material solution to support the grade, shape and size your design needs.

100 years of experience

For over a century Heraeus has been a leader in the field of fused quartz materials. The experience collected over 100 years makes Heraeus the best choice to help you master your quartz and silica material challenges. From customized doping of quartz materials, to the efficient mass production of high quality synthetic fused silicas, Heraeus has the knowledge, experience and products to solve your design challenges.


The electric fusion is the most commonly used melting process for manufacturing quartz glass. The name is derived from the method of heating up the material, in this case: an electric current is heating a resistive heater, hence the name "Electrical Fusion".

The benefits of Electrical Fusion is the lower OH-content, compared to other fusion methods. Typical values are in the range of <30ppm. As the OH-content is directly influencing the maximum possible working temperature for the fused quartz, Electrical Fused quartz is especially suitable for high temperature applications.

Electrical Fusion can be used in both – continuous fusion or batch/boule fusion and therefore offer a large variety of geometries, shapes and dimensions.


In opposite to the Electrical Fusion, the Flame Fusion is not using an electric current, but is using am H2/O2-Flame to heat up and melt the material. Heraeus chemist Richard Küch was the first person to ever melt quartz over 100 years ago, he used a flame fusion process for his pioneer endeavor.

Heraeus Conamic is the only material manufacturer who can produce fused quartz in a continuous flame fusion process, combining the benefits of a continuous process with the properties of flame fused quartz.

The extreme low bubble content makes Heraeus flame fused quartz the best choice for plasma etch applications.

Heraeus Conamic also offers flame fused material in very large size ingots in the range of 1.5m x 1.2m and larger.


The main difference between so-called natural quartz material and synthetic quartz material, is the used raw material. While natural quartz is produced from quartz sand minded in a quartz mine, synthetic quartz is using chemical gases as raw material. Such chemical gas containing a silicon source will be put into reaction with oxygen forming pure silicon dioxide. The purity achievable by this manufacturing procedure is magnitudes higher compared to natural quartz.

Synthetic fused quartz (sometimes also called fused silica) is the ideal choice for most demanding applications in which purity of the process environment is of the essence.

Our synthetic fused silica materials are available in the same portfolio of shape, geometry and dimensions as our electrical fused material.

Electrical properties

Parameter Electrically Fused Quartz Flame Fused Quartz Fused Silica
Electrical resistivity (Ω × m) 20 °C
1200 °C
1.3 × 105
1.3 × 105
1.3 × 105
Dielectric strength (KV/mm) 20 °C 25 ... 40 25 ... 40 25 ... 40
Dielectric loss angle (tg δ) 1 MHz 1.0 × 10-4 1.0 × 10-4 1.0 × 10-4
Dielectric constant (ε) 20 °C 1 MHz 3.70 3.70 3.70

Mechanical properties

Electrically Fused Quartz Flame Fused Quartz Fused Silica
Density (g/cm3) 2.203 2.203 2.201
Mohs hardness 5.5 ... 6.5 5.5 ... 6.5 5.5 ... 6.5
Micro hardness (N/mm2) 8600 ... 9800 8600 ... 9800 8600 ... 9800
Knoop hardness (N/mm2) 5800 ... 6100 5800 ... 6100 5800 ... 6200
Modulus of elasticity 20 °C (N/mm2) 7.25 × 104 7.25 × 104 7.25 × 104
Modulus of torsion (N/mm2) 3.0 × 104 3.1 × 104 3.0 × 104
Poisson’s ratio 0.17 0.17 0.17
Compressive strength (MPa) 1150 1150 1150
Tensile strength (MPa) 50 50 50
Bending strength (MPa) 67 67 67
Torsional strength (MPa) 30 30 30
Sound velocity (m/s) 5720 5720 5720

Thermal properties

Technical properties Electrically Fused Quartz Flame Fused Quartz Fused Silica
Max. working temperature continuous (°C)
short-term (°C)
Mean specific heat (J·g-1·K-1) 772 772 772
Heat conductivity (W·m-1·K-1) 20 °C 1.38 1.38 1.38
Mean expansion coefficient (K–1) 0.47 × 10–6 0.47 × 10–6 0.47 × 10–6