Fused Silica
Pure SiO₂ glass, for thermal shock and UV
Typical values for the temper in the title
Fused silica is amorphous SiO₂ at 99.99% purity and above. Its expansion coefficient (0.55×10⁻⁶/K) is 6 times lower than borosilicate, so it resists almost any thermal shock: it can be heated red hot and quenched in water. Continuous service is up to about 1100 °C, and the softening point about 1683 °C.
It is also transparent to deep UV (down to about 170 nm), so it is used for laser and UV optics, cuvettes, furnace tubes and wafer carriers in semiconductors, and lamps.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Modulus of elasticity E | 73 GPa | |
| Density ρ | 2.20 g/cm³ | |
| Vickers hardness HV | 600 | |
| Thermal expansion | 0.55×10⁻⁶/K | |
| Continuous service | up to about 1100 °C | |
| Machinability | Grinding and diamond only | relative rating in the site database |
Structure and production
| Feature | Value | Meaning |
|---|---|---|
| Composition | SiO₂ at 99.99% and above | amorphous |
| Expansion | 0.55×10⁻⁶/K | thermal shock resistance |
| Softening | about 1683 °C |
Typical values per producer data.
Grades and production routes
In technical glasses, the choice is by thermal expansion, service temperature and required transparency.
| Version | Properties | When to choose it |
|---|---|---|
| Fused natural quartz | tubes and furnaces | semiconductors |
| Synthetic silica | maximum purity, deep UV | optics and lasers |
| Opaque (milky) | reflects heat radiation | heat shields |
Applications
- Furnace tubes in semiconductors
- Wafer carriers
- UV and laser optics
- Cuvettes
- Lamps
Fabrication
Brittleness
Ceramics do not deform before fracture: they break suddenly from a small flaw, so strength scatters widely. Avoid sharp corners, tensile stresses and shock, and prefer compressive loading.
Machining
By grinding and diamond tools only, with coolant.
Cleanliness
At high heat, contact with salts (even fingerprints) causes surface devitrification.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| Borosilicate Glass 3.3 | — | Flame working (glass) | borosilicate: cheaper, for lower heat · material page |
| Sapphire | 400 MPa (flexural) | — | sapphire: much harder, crystalline · material page |
| Alumina (Al₂O₃ 99.5%) | 380 MPa | Not possible | alumina: opaque, strong · material page |
Common mistakes
Touching with bare hands before heating
Fingerprints cause devitrification and cracks.
Choosing borosilicate for deep UV
It blocks UV below about 320 nm.
Loading in tension
It is brittle.
Equivalents, standards and supply
| Standards | Producer specification |
|---|---|
| Forms | tube · rod · plate · optics |
| Producers | Heraeus · Momentive · Corning |
Learn more
Values are typical and for comparison only. In ceramics, strength is measured in bending and scatters widely (depending on flaws and finish), so design to producer data with suitable safety factors. Sources: ISO 513, ISO 13356, ASTM F603, producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026