Ceramics and glasses · Workhorse
Fused silica and borosilicate (Kodial)
SiO2values describe: fused silica
Why it wins
Cheap optical access: standard viewports, cold-atom glass cells (anodic bonding), Kodial CTE-matches Kovar.
Why not the alternative
Sapphire is better and pricier; polymers are not in the conversation.
Watch out
Helium permeation through glass is real for sealed devices; thermal shock limits.
Properties
The values below are candidate: compiled from the sources named, not yet individually validated. Provisional provenance: CoorsTek, CeramTec, Kyocera technical ceramic data; Electron tube and ceramic-to-metal sealing practice.
Wet cleaning
| Recipe | detergent, DI rinse, then RCA or piranha for optics, ultrapure rinse |
|---|---|
| Forbidden | HF unless you mean to etch; alkaline attack above pH 10 |
| Limit | helium permeation is a physical property no cleaning fixes |
Vacuum and outgassing
| Outgassing, unbaked (10 h) | 1e-9 mbar·L/s/cm² |
|---|---|
| Outgassing, baked | 1e-12 mbar·L/s/cm² |
| Vapour pressure | none |
Temperature
| Bake, assembled | 450 °C |
|---|---|
| Vacuum degas | 900 °C |
| Braze / H2 firing | 1100 °C |
| Metallurgical limit | annealing point 1140 °C, softening 1665 °C |
Thermal
| CTE | 0.55 silica; 4.9 Kodial ppm/K |
|---|---|
| Thermal conductivity | 1.4 W/m·K |
| Specific heat | 740 J/kg·K |
| Emissivity | 0.9 |
| Melting / softening | 1665 soft. °C |
Mechanical
| Strength | 50 flex MPa |
|---|---|
| Elongation | nil |
| Young's modulus | 73 GPa |
| Hardness | 600–700 HV |
| Density | 2.2 g/cm3 |
Electrical and magnetic
| Relative permeability | 1.0 |
|---|---|
| Resistivity | >1e18 Ω·cm |
| Dielectric strength | 25–40 kV/mm |
Engineering
| Corrosion | inert except HF |
|---|---|
| Joining | Kodial is matched to Kovar; silica needs graded seals |
| Process notes | helium walks through it: a real leak path at 1e-11 |
| Availability and cost | Heraeus, Corning, in stock |
Outgassing
3 sourced measurements for this card. A rate means nothing without the pumping time it was read at, so each one states it or declares it missing. The whole base, filters included, is at /tools/outgassing/.
Signature: 1e-8 unbaked to no baked reading baked.
| Material as published | Species | State | Pumping time | Rate |
|---|---|---|---|---|
| Pyrex glass | total | unbaked | NOT STATED by the source | 2.13e-10mbar·L/s/cm² |
| Pyrex (fresh) | total | unbaked | the abscissa of the curve below | 9.80e-9 at 1 h to 7.33e-10 at 10 h |
| Pyrex (1 month in air) | total | unbaked | the abscissa of the curve below | 1.55e-9 at 1 h to 2.13e-10 at 10 h |
Sources: S-LIGO-E960050-V13, S-ELSEY-1975-II. Full citations and conditions at the base and in /data/outgassing.json.
Grades
| Corning 7980 / Suprasil | UV fused silica, high OH: viewports and precision optics |
|---|---|
| Infrasil 301 | low OH for IR transmission |
| Schott 8330 (Duran) | borosilicate cells and glassware |
| 7056 (Kodial) | the Kovar-sealing glass of standard viewports |