Sapphire · heat-treated state · default condition
Sapphire Annealed Glass
Properties of the Annealed Glass condition, compared with the other Sapphire tempers.
Default choice for windows, lenses and wear parts: stress-relief annealed sapphire blank with typical polycrystal-free optical quality.
What is Sapphire Annealed Glass?
Sapphire Annealed Glass is Sapphire heat treated to Annealed Glass — default choice for windows, lenses and wear parts: stress-relief annealed sapphire blank with typical polycrystal-free optical quality. Sapphire Annealed Glass has a tensile strength of 400 MPa (58 ksi), stronger than 93% of glass grades. Elongation at break is 0% and the elastic modulus is 400 GPa (58 Msi). Sapphire Annealed Glass has a density of 3.98 g/cm³ (0.144 lb/in³), heavier than 71% of glass grades. It melts at 2,053°C (3,727 °F).
Advantages
- High service temperature — 1,800°C (3,272 °F), better than 99% of glass grades
- Stiff — 400 GPa (58 Msi), better than 95% of glass grades
- Tough — resists crack growth — 2.2 MPa·√m (2 ksi·√in), better than 95% of glass grades
- Good corrosion resistance — 95/100, better than 90% of glass grades
- Conducts heat well — 27 W/m·K (15.6 BTU/hr·ft·°F), better than 87% of glass grades
Limitations
- Difficult to machine — 5/100, worse than 90% of glass grades
- High embodied carbon — 60 kg CO₂/kg, worse than 86% of glass grades
Sapphire Annealed Glass properties
Typical room-temperature values for Sapphire Annealed Glass — 9 properties are specific to this condition; the rest are grade-level values shared by every Sapphire temper. Each bar shows where the value sits among the glass grades in FabDigit's library — further right is higher.
Physical5
Sapphire Annealed Glass has a density of 3.98 g/cm³ (0.144 lb/in³), heavier than 71% of glass grades. It melts at 2,053°C (3,727 °F).
Mechanical12
Sapphire Annealed Glass has a tensile strength of 400 MPa (58 ksi), stronger than 93% of glass grades. Elongation at break is 0% and the elastic modulus is 400 GPa (58 Msi).
Thermal5
Sapphire Annealed Glass is rated for continuous service to 1,800°C (3,272 °F). It conducts heat at 27 W/m·K (15.6 BTU/hr·ft·°F), better than 87% of glass grades. Thermal expansion is 5.8 µm/m·K (3.22 µin/in·°F).
Electrical5
Sapphire Annealed Glass is an electrical insulator with a dielectric strength of 17 kV/mm (431.8 V/mil) and a resistivity of 1×10¹⁴ Ω·m.
Chemical & Environmental2
Corrosion resistance is excellent (95/100), better than 90% of glass grades.
Sustainability4
Producing a kilogram of Sapphire Annealed Glass takes about 400 MJ of energy and emits 60 kg of CO₂ — more than 81% of glass grades. Typical recycled content is 5%.
Manufacturability2
Sapphire Annealed Glass's machinability is not recommended (5/100, worse than 90% of glass grades).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other Sapphire tempers and conditions
Sapphire is also supplied in 5 other conditions. The full side-by-side table is on the Sapphire overview.
- Annealed GlassDefaultDefault choice for windows, lenses and wear parts: stress-relief annealed sapphire blank with typical polycrystal-free optical quality.400 MPa tensile
Working with Sapphire Annealed Glass
Is Sapphire easy to machine?
No conventional cutting: use diamond wire/ID saw, diamond core drilling, creep-feed diamond grinding, laser or waterjet for rough shapes, then lap and CMP.
Can Sapphire be welded?
Not weldable; join by active-metal (Ti/Nb) brazing, diffusion bonding to Nb/Mo, or glass-frit/epoxy sealing with CTE-matched metals such as Kovar avoided in favour of Nb.
Can Sapphire be formed, bent or molded?
Shape is fixed at crystal growth (Kyropoulos, HEM, Czochralski, EFG for tubes/ribbon); no plastic forming below ~1000 °C, so near-net EFG growth is used for tubes and rods.
What surface finishes work on Sapphire?
Sub-nanometre Ra achievable by colloidal-silica CMP; AR/DLC coatings, ion-beam figuring for optics; avoid edge chipping with chamfers and keep tensile surface flaws minimal to realise full strength.
Sapphire chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance.
| Element | Spec limit (wt %) |
|---|---|
| Alstoichiometric metal fraction | ≈ 52.9 |
| Ostoichiometric oxygen fraction | ≈ 47.1 |
| Al2O3single crystal α-Al2O3; typical impurities Si, Fe, Ti, Cr, Na each < 20 ppm | ≥ 99.99 (balance) |
Sapphire Annealed Glass — frequently asked
What is Sapphire Annealed Glass used for?
Sapphire Annealed Glass is typically used for watch crystals, smartphone camera lens covers, barcode scanner and sensor windows, high-pressure and high-temperature sight glasses, IR domes and harsh-environment optics and semiconductor process chamber windows. In short: single-crystal optical sapphire.
What is the tensile strength of Sapphire Annealed Glass?
Sapphire Annealed Glass has a typical tensile strength of 400 MPa (58 ksi) — stronger than 93% of glass grades. Strength varies by condition: see the 6 listed tempers.
Is Sapphire Annealed Glass easy to machine?
Not especially — machinability is rated not recommended (5/100, worse than 90% of glass grades). No conventional cutting: use diamond wire/ID saw, diamond core drilling, creep-feed diamond grinding, laser or waterjet for rough shapes, then lap and CMP.
Can Sapphire Annealed Glass be welded?
Not weldable; join by active-metal (Ti/Nb) brazing, diffusion bonding to Nb/Mo, or glass-frit/epoxy sealing with CTE-matched metals such as Kovar avoided in favour of Nb.
What surface finishes work on Sapphire Annealed Glass?
Sub-nanometre Ra achievable by colloidal-silica CMP; AR/DLC coatings, ion-beam figuring for optics; avoid edge chipping with chamfers and keep tensile surface flaws minimal to realise full strength.
Can Sapphire Annealed Glass be formed, bent or molded?
Shape is fixed at crystal growth (Kyropoulos, HEM, Czochralski, EFG for tubes/ribbon); no plastic forming below ~1000 °C, so near-net EFG growth is used for tubes and rods.
What is the maximum service temperature of Sapphire Annealed Glass?
Sapphire Annealed Glass is rated for continuous use to about 1,800°C (3,272 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in Sapphire Annealed Glass?
Yes — Sapphire Annealed Glass is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- Sapphire (Al2O3) optical material data — Crystran Ltd (2023)
- Single Crystal Sapphire product properties — Saint-Gobain Crystals (2022)
- Sapphire single crystal technical data — Kyocera Corporation (2022)
- Engineered Materials Handbook Vol.4: Ceramics and Glasses — ASM International (1991)
- Sapphire crystal properties and orientation data — Rubicon Technology / Monocrystal (2021)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.