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Material data · Fused silica · SiO₂ ≥ 99.99%
Quartz Glass Technical Specifications
Comprehensive material properties and performance data for FGQuartz ≥ 99.99% high-purity quartz glass, for semiconductor, optical, and high-temperature industrial environments.
The data applies to standard high-purity fused silica (SiO₂ ≥ 99.99%), produced from natural fused quartz and synthetic fused silica depending on grade and application. See the JGS1 / JGS2 / JGS3 grade guide for how the raw material source affects optical performance. Values are typical baseline figures; final tolerances for a specific component are confirmed during engineering DFM review for a standard product or custom fabrication order.
Quick answer
What are the key properties of high-purity fused silica? FGQuartz high-purity fused silica (SiO₂ ≥ 99.99%) supports continuous service to 1200°C (short-term 1300°C), has near-zero thermal expansion (5.5 × 10⁻⁷ /°C), transmits 185–3500 nm optically (grade-dependent), and resists all common acids except hydrofluoric acid and hot concentrated phosphoric acid. Full mechanical, thermal, electrical, optical, chemical, and acoustic data tables are below.
Key takeaways
- Thermal: 1200°C continuous / 1300°C short-term service, softening point ≈1680°C, near-zero thermal expansion.
- Mechanical: Mohs hardness 5.5–6.5, compressive strength 1100 MPa — strong but brittle, handle accordingly.
- Electrical: Excellent insulator (>10¹⁸ Ω·cm at 20°C), low dielectric loss — suited to high-frequency and isolation applications.
- Optical: 185–3500 nm transmission range (grade-dependent), refractive index 1.4585 at 589 nm.
- Chemical: Excellent resistance to HCl, HNO₃, H₂SO₄, aqua regia, and organic solvents — but attacked by HF and hot concentrated phosphoric acid.
- vs. Alternatives: Outperforms borosilicate glass on temperature range and UV transmission; alumina ceramic tolerates higher temperatures but is opaque and not weldable.
Written by the FGQuartz Engineering Team · Updated October 2026
On this page: Mechanical · Thermal · Electrical · Optical · Composition and purity · Additional · By product · Vs alternatives · Glossary · FAQ
Key values at a glance
Physical and mechanical properties
Material data
Relevant when specifying structural rods, tank walls, or any component under mechanical load. The low density combined with high hardness suits precision components that need minimal weight and high durability, though the material remains brittle. See the handling guidance on the individual product pages.
| Property | Value |
|---|---|
| Mohs Hardness | 5.5 – 6.5 |
| Compressive Strength | 1100 MPa |
| Flexural Strength (20°C) | 67 MPa |
| Tensile Strength | 48 MPa |
| Young’s Modulus (20°C) | 72 GPa |
| Shear Modulus | 31 GPa |
| Bulk Modulus | 37 GPa |
| Poisson’s Ratio | 0.17 |
| Density (20°C) | 2.2 g/cm³ |
In practice: the gap between compressive and tensile strength is why quartz parts are designed to carry loads in compression and to keep edges protected from impact.
Thermal properties
Material data
This is the property set behind every furnace tube, wafer boat, and crucible on this site. Near-zero thermal expansion allows a red-hot component to be quenched without cracking, which is the basis of quartz thermal shock resistance.
| Property | Value |
|---|---|
| Annealing Point | ≈ 1215 °C |
| Strain Point | ≈ 1120 °C |
| Max. Working Temp (Continuous) | 1200 °C |
| Max. Working Temp (Short Term) | 1300 °C |
| Thermal Expansion (20-300°C) | 5.5 × 10⁻⁷ /°C |
| Thermal Conductivity (20°C) | 1.4 W/(m·K) |
| Specific Heat (20°C) | 670 J/(kg·K) |
| Thermal Diffusivity (20°C) | 9.5 × 10⁻⁷ m²/s |
| Softening Point | ≈ 1680 °C |
In practice: the continuous and short-term working temperatures sit below the softening point. The annealing and strain points mark the range that matters when stress is relieved after hot work.
Electrical properties
Material data
Excellent electrical insulation with high resistivity and very low dielectric loss. Indispensable for high-frequency applications and for electrical isolation in semiconductor processing equipment, including custom threaded standoffs and isolation elements.
| Property | Value |
|---|---|
| Resistivity (at 20°C) | > 10¹⁸ Ω·cm |
| Resistivity (at 350°C) | 7 × 10⁵ Ω·cm |
| Dielectric Constant (1 MHz, 20°C) | 3.75 |
| Dielectric Strength | 25 – 40 kV/mm |
| Dielectric Loss Factor (1 MHz) | < 1 × 10⁻⁴ |
| Dielectric Loss Factor (1 GHz) | < 6 × 10⁻⁴ |
In practice: resistivity falls steeply as temperature rises, so the 20°C and 350°C values should be read together when a part must insulate at temperature.
Optical properties
Material data
Unrivaled UV transmission and optical clarity make fused silica a staple for spectroscopy, laser optics, and deep-UV applications. Values below are for standard clear material; grade-specific transmission bands (JGS1 / JGS2 / JGS3) are detailed on the optical quartz glass page and in the grade guide.
| Property | Value |
|---|---|
| Refractive Index (589 nm, 20°C) | 1.4585 |
| Refractive Index (1060 nm) | 1.4496 |
| Transmission Range | 185 – 3500 nm (JGS1 185–2500 · JGS2 220–2500 · JGS3 260–3500) |
| UV Transmission (254 nm, 10mm) | > 90% |
| Abbe Number | 67.8 |
| Stress Optical Coefficient | 3.5 × 10⁻⁶ MPa⁻¹ |
In practice: the 185–3500 nm range spans all three optical grades; any single grade covers only part of it, so choose the grade by working wavelength.
Chemical composition and purity
Material data
Ultra-high purity with controlled metallic impurities keeps contamination risk low during sensitive wafer fabrication and wet processing. Material composition is verified for every production batch.
| Property | Value |
|---|---|
| SiO₂ Content | ≥ 99.99% |
| OH Content | < 10 ppm |
| Al Impurity | < 10 ppm |
| Fe Impurity | < 5 ppm |
| Na + K Impurities | < 5 ppm |
| Total Metal Impurities | < 20 ppm |
| Acid Resistance | Excellent vs. HCl, HNO₃, H₂SO₄, aqua regia, organic solvents |
| Known Limitations | Attacked by HF and hot concentrated phosphoric acid; caution with strong hot alkalis |
In practice: trace-impurity levels vary more by grade than most physical properties do. Material certificates of conformance are available with production orders.
Additional properties
Material data
Material characteristics covering acoustic transmission, radiation resistance, and vacuum surface integrity, relevant to specialized applications such as sensor components and vacuum chamber viewports.
| Property | Value |
|---|---|
| Acoustic Velocity (Longitudinal) | 5968 m/s |
| Acoustic Velocity (Transverse) | 3764 m/s |
| Radiation Resistance | Good |
| Permeability (He at 700°C) | Low |
| Surface Energy | ≈ 300 mJ/m² |
| Outgassing Rate (Vacuum) | Very Low |
These values are typical baseline figures like the rest of this page.
Which properties matter for which product
By product
Use this to find the data tables most relevant to the product you are specifying.
| Product | Properties that matter most |
|---|---|
| Quartz glass tubes | Thermal, chemical resistance, purity |
| Quartz glass plates and windows | Optical, thermal, surface condition |
| Quartz glass rods | Mechanical, thermal, optical (for optical rods) |
| Quartz wafer boats | Thermal, purity, thermal shock resistance |
| Quartz crucibles | Thermal, purity, chemical limits |
| Quartz tanks | Chemical resistance, purity, mechanical |
| Quartz inline heaters | Chemical resistance, electrical insulation, thermal shock |
Quartz glass vs borosilicate glass vs alumina
Material comparison
A qualitative comparison. For numeric values on quartz, use the tables above.
| Aspect | Fused quartz | Borosilicate glass | Alumina ceramic |
|---|---|---|---|
| Maximum temperature | High; 1200°C continuous | Lower than quartz | Higher than quartz |
| UV transmission | Excellent; grade dependent | Lower than quartz | Opaque |
| Thermal shock resistance | Excellent | Lower than quartz | Lower than quartz |
| Weldable | Yes, by flame welding | Yes | No |
| Main limits | HF, hot concentrated phosphoric acid, hot strong alkalis | Lower temperature range | No visual access; not weldable |
More detail: quartz glass vs borosilicate glass.
Glossary of the terms on this page
Glossary
| Term | Meaning |
|---|---|
| Softening point | The temperature at which the glass begins to deform under its own weight. |
| Annealing point | The temperature at which internal stress relaxes quickly enough to be removed by annealing. |
| Strain point | The temperature below which stress relaxes too slowly to matter in practice. Annealed parts are cooled slowly through it. |
| Thermal expansion (CTE) | The fractional change in length per degree of temperature change. Low values mean good thermal shock resistance. |
| Dielectric loss factor | A measure of the energy a material dissipates as heat in an alternating electric field. Lower is better for high-frequency use. |
| Abbe number | A measure of how much the refractive index varies with wavelength. A higher value means less dispersion. |
| Mohs hardness | A scratch-resistance scale from 1 to 10. |
Procurement questions
FAQ
Hydrofluoric acid (HF) and hot concentrated phosphoric acid both attack and etch the SiO2 network. Strong hot alkaline solutions should also be used with caution.
Yes, material certificates of conformance are available with production orders.
Most physical, thermal, and electrical properties are consistent across natural and synthetic material. Optical transmission and trace-impurity levels vary more significantly by grade.
These are typical baseline values for standard high-purity fused silica. Final tolerances for a specific geometry are confirmed during engineering DFM review.