Reasons to use fused Quartz

High chemical purity and resistance

High softening temperature and thermal resistance 

High thermal shock resistance and low thermal expansion

High transparency from the ultraviolet to the infrared spectral range

Properties of Fused Quartz

Fused quartz is an extraordinary material for numerous industrial applications. The single-component glass consists solely of silica (SiO2). Through its unique combination of thermal, mechanical and optical properties, fused quartz is one of the most important materials for industry and research. 

For the Semiconductor an Solar industries, fused quartz is used in high temperature processes because of its high softening point, low thermal expansion and excellent thermal shock resistance. It can withstand temperatures up to 1300°C and can be rapidly heated and cooled with virtually no risk of breakage. Because of its high purity, parts and systems made of fused quartz are ideal suited for industry equipment. 

For the Lighting industry, fused quartz is an indispensable material due to the high optical transmission from ultraviolet through the infrared light.    

For the Chemical industry and for laboratory equipmentation, fused quartz is used because of its resistance to acids, bases and water. With the exception of hydrofluoric acid, phosphoric acid, and alkaline compounds its properties are unaffected.

For the Electronics industry, fused quartz is characterized by high dielectric strength, low electrical conductivity and superior microwave transmission even at high temperatures.

The Properties in Detail

Critical to the efficient transmission of light, clear fused quartz contains very low levels of impurities (as measured in parts per million). This single component glass is further distinguished from other glass material by a very high transmission of ultra violet light. The higher the purity of the material, the higher the transmittance in UV-range. For this reason, synthetically manufactured fused quartz materials show the highest transmission for ultraviolet light.


The UV transmission properties of fused quartz can be modified by the incorporation of a dopant in the material.  The doping causes the material to absorb a certain range of wavelengths. 


Hydroxyl (OH- ) groups in the material may cause absorption bands in infrared range.  The strongest of these bands, at 2,73 μm is used to determinate the OH-content in fused quartz materials. The higher the OH-content, the higher the absorption at this wavelength.


The light transmission of fused quartz may be reduced or even extinguished when the material is exposed to high-energy UV-radiation, X-rays, gamma rays and particle bombardment.

Mechanical Properties (at 20°C)

Mechanical property measurements are dependent upon geometry, thermal gradient and surface quality. For proper strength calculations, the lower pressure variable should be used.

Density2,20 g/cm3 Bending Strength68 N/mm2
Compressive Strength1150 N/mm2 Elasticity modulus7,5x104 N/mm2
Tensile Strength50 N/mm2 Mohs Hardness5,5-6,5


Electrical Properties

Dielectric loss factor
(at a frequency of 7,5 GHz)
tg δ ≈ 5 x 10-4
Dielectric constant ε ≈ 3,7 
(at 20 °C / 7,5 GHz)
Dielectric strength
at 20°C
at 500°C


250 - 400 kV / cm
  40 -  50 kV / cm

Specific electrical resistance 
at different temperatures:
at 20°C       1018 Ωm
at 100°C       1016 Ωm
at 200°C    4x1013 Ωm
at 400°C        1010 Ωm
at 800°C   6,3x106 Ωm
at 1000°C          106 Ωm
at 1200°C   1,3x106 Ωm

Chemical Properties

Hydrolytic resistance per DIN 12111 ( 1.class)
Acid resistance per DIN 12116 ( 1.class)
Alkaline resistance per DIN 52322 ( 1.class)

Thermal Properties


ilmasil® PN

ilmasil® PI


ilmasil® PO 1 /
PO 2

ilmasil® PQ

ilmasil® PN 235

ilmasil® PN 350

ilmasil® PS

ilmasil® PE

Softening Point
lg h (in dPas)=7.6










Annealing Point
lg h (in dPas)=13




1159°C /






Strain Point 
lg h (in Pas)=14.5




1043°C /








Transformation Range1075 - 1210°C
Processing Range
at lg h (in dPas) = 5 - 8  

Max. Usable Temperature

long term
short term



Coefficient of Thermal Expansion
  ca. 5,5 x 10-7 / °C



Devitrification is dependent upon surface cleanliness, atmospheric conditions and temperature cycling. Below 1025°C devitrification takes place very slowly, but above 1425°C devitrification is rapid. If heating cycles take the product above 1025°C , devitrification will be minimized if a minimum temperature of 250°C is maintained.



< 2,5 µl gas/g under vacuum at 1000°C.


OH-content determination of fused quartz glass

Basis for the determination is the OH- absorption band at 2,73 µm. A sample is tested by Infrared -spectrometer in the range of 2,5 - 3 µm.


COH = 0,1 x log (I0 / I) x 1/d x 104COH OH-content in ppm
 I0 Basic Intensity at 2,73 µm
 IIntensity of maximum absorption
 dsample thickness in mm
  Coefficient of extinction: 77,5 l / Mol cm

Handling - Cleaning - Storage of Fused Quartz

Fused quartz requires care in handling and use to achieve good performance. Cleanliness will help reduce devitrification and maximize the life of this material. Handle fused quartz with care and only with clean cotton gloves to avoid contamination . Wrap and store quartz in a clean, dry environment

Cleaning recommendation:

1. Cleaning with non-alkali cleaning agent and/or isopropyl alcohol.

2. Rinse with deionized (distilled) water

3. Air dry in clean environment and clean wrapping