ZERODUR K20
Grade
also Schott ZERODUR, Astronomical Mirror Glass
Companion glass-ceramic with a deliberate small positive CTE, chosen to CTE-match metals/coatings or as a lower-cost mechanically similar substrate.
Values for the K20 condition
Other ZERODUR tempers and conditions
ZERODUR is listed in 6 conditions; see the grade overview at ZERODUR.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed GlassDefault standard ceramized & fine-annealed ZERODUR, Expansion Class 2 | Default commercial delivery state: ceramized, fine-annealed blank with CTE 0 ± 0.10 ×10⁻⁶/K — use for general precision optics and mechanical metrology parts. | — | 30 | — | 620 HV | 1 W/m·K |
Expansion Class 1 | Tighter-CTE selection for telescope mirror blanks and stable structures where thermal drift budget is a few nanometres. | — | 30 | — | 620 HV | 1 W/m·K |
Expansion Class 0 | Premium selected class for EUV lithography optics, ring-laser gyros and length standards; long ceramization/selection cycle raises price and lead time. | — | 30 | — | 620 HV | 1 W/m·K |
Expansion Class 0 EXTREME | Highest-specification tolerance class, reserved for EUV mask blanks and ultra-stable metrology where CTE must be near-perfectly zero. | — | 30 | — | 620 HV | 1 W/m·K |
Thermomechanically controlled processed | Shorter ceramization route giving lower cost and shorter lead time at somewhat wider CTE tolerance — for large mirror substrates and mounts. | — | 30 | 0 | 620 HV | 1 W/m·K |
K20This page ZERODUR K20 | Companion glass-ceramic with a deliberate small positive CTE, chosen to CTE-match metals/coatings or as a lower-cost mechanically similar substrate. | — | 30 | — | 620 HV | 2 W/m·K |
What is ZERODUR K20?
ZERODUR K20 is ZERODUR in the K20 grade — companion glass-ceramic with a deliberate small positive CTE, chosen to CTE-match metals/coatings or as a lower-cost mechanically similar substrate. ZERODUR K20 has a tensile strength of 30 MPa (4.35 ksi), weaker than 80% of glass grades. The elastic modulus is 91 GPa (13.2 Msi). ZERODUR K20 has a density of 2.53 g/cm³ (0.0914 lb/in³), lighter than 66% of glass grades. Annealed Glass is the default condition FabDigit quotes; K20 is available on request or by drawing note.
Advantages
- Tough — resists crack growth — 0.9 MPa·√m (0.819 ksi·√in), better than 79% of glass grades
- Stiff — 91 GPa (13.2 Msi), better than 76% of glass grades
ZERODUR K20 properties
Typical room-temperature values for ZERODUR K20; 14 are specific to this condition. Other listed values are ZERODUR reference data and may not represent this condition. Bars are the position among glass grades.
Physical4
ZERODUR K20 has a density of 2.53 g/cm³ (0.0914 lb/in³), lighter than 66% of glass grades.
Mechanical11
ZERODUR K20 has a tensile strength of 30 MPa (4.35 ksi), weaker than 80% of glass grades. The elastic modulus is 91 GPa (13.2 Msi).
Thermal5
ZERODUR K20 is rated for continuous service to 500°C (932 °F). It conducts heat at 1.6 W/m·K (0.924 BTU/hr·ft·°F), better than 62% of glass grades. Thermal expansion is 2 µm/m·K (1.11 µin/in·°F).
Electrical5
ZERODUR K20 is an electrical insulator with a dielectric strength of 20 kV/mm (508 V/mil) and a resistivity of 1×10¹² Ω·m.
Chemical & Environmental2
Corrosion resistance is excellent (85/100), better than 65% of glass grades.
Sustainability4
Producing a kilogram of ZERODUR K20 takes about 90 MJ of energy and emits 6.5 kg of CO₂ — more than 66% of glass grades. Typical recycled content is 0%.
Manufacturability3
ZERODUR K20's machinability is poor (20/100, better than 56% of glass grades).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with ZERODUR K20
Is ZERODUR easy to machine?
Diamond grinding, core drilling, lapping and ultrasonic machining only — no conventional cutting; keep coolant flooded and avoid edge chipping, then acid-etch or fine-grind to remove subsurface damage.
Can ZERODUR be welded?
Not weldable; parts are joined by optical contacting, low-stress epoxy/silicate bonding, frit bonding or Invar/steel flexure mounts.
Can ZERODUR be formed, bent or molded?
Supplied as cast, ceramized blanks; near-net shapes (lightweighted honeycomb mirrors) are produced by machining the blank, not by hot forming, since re-heating above ~600 °C alters the crystal phase and CTE.
What surface finishes work on ZERODUR?
Polishes to sub-nanometre rms and accepts ion-beam figuring plus Al/Ag/dielectric and multilayer coatings; a light etch after grinding recovers much of the bending strength.
ZERODUR 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. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| SiO2network former | 54 – 58 | 55.5 |
| Al2O3 | 24 – 26 | 25.3 |
| P2O5 | 6.5 – 8.5 | 7.5 |
| Li2Oforms high-quartz solid solution crystals | 3 – 4.5 | 3.7 |
| TiO2nucleating agent | 2 – 2.6 | 2.3 |
| ZrO2nucleating agent | 1.5 – 2.2 | 1.9 |
| ZnO | 1 – 1.8 | 1.4 |
| MgO | 0.5 – 1.5 | 1 |
| Na2O | 0.2 – 0.8 | 0.5 |
| K2O | 0 – 0.8 | 0.5 |
| As2O3fining agent in classic composition; arsenic-free melts also offered | 0 – 0.6 | 0.4 |
ZERODUR K20 — frequently asked
What is ZERODUR K20 used for?
ZERODUR K20 is typically used for telescope mirror blanks, astronomical optics, lightweighted honeycomb mirror substrates, metrology reference plates and straightedges, ring laser gyroscope bodies and lithography stages and mask blanks. In short: zero-expansion glass-ceramic.
What is the tensile strength of ZERODUR K20?
ZERODUR K20 has a typical tensile strength of 30 MPa (4.35 ksi) — weaker than 80% of glass grades. Strength varies by condition: see the 6 listed tempers.
Is ZERODUR K20 easy to machine?
Not especially — machinability is rated poor (20/100, better than 56% of glass grades). Diamond grinding, core drilling, lapping and ultrasonic machining only — no conventional cutting; keep coolant flooded and avoid edge chipping, then acid-etch or fine-grind to remove subsurface damage.
Can ZERODUR K20 be welded?
Not weldable; parts are joined by optical contacting, low-stress epoxy/silicate bonding, frit bonding or Invar/steel flexure mounts.
What surface finishes work on ZERODUR K20?
Polishes to sub-nanometre rms and accepts ion-beam figuring plus Al/Ag/dielectric and multilayer coatings; a light etch after grinding recovers much of the bending strength.
Can ZERODUR K20 be formed, bent or molded?
Supplied as cast, ceramized blanks; near-net shapes (lightweighted honeycomb mirrors) are produced by machining the blank, not by hot forming, since re-heating above ~600 °C alters the crystal phase and CTE.
What is the maximum service temperature of ZERODUR K20?
ZERODUR K20 is rated for continuous use to about 500°C (932 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- ZERODUR — Zero Expansion Glass Ceramic, technical data — SCHOTT AG (2023)
- Strength of ZERODUR (TIE-33 / strength brochure) — SCHOTT AG (2021)
- ASM Engineered Materials Handbook Vol. 4: Ceramics and Glasses — ASM International (1991)
- Glass-ceramic property compilations (LAS system) — MatWeb / Ceramic Industry data (2022)
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.