Ceramics and glasses · Workhorse
Boron carbide
B4Cvalues describe: hot-pressed B₄C
Why it wins
Third hardest material, low Z, neutron hungry: FEL apertures and beam-facing absorbers that must not ablate high-Z debris onto optics, neutron shielding inserts.
Why not the alternative
Metals ablate and coat mirrors; graphite dusts.
Watch out
Brittle; joining is clamping, not brazing, in most designs.
Properties
The values below are candidate: compiled from the sources named, not yet individually validated. Provisional provenance: CERN Accelerator School, vacuum and materials proceedings; Semiconductor chamber materials and plasma-resistant coating literature.
Wet cleaning
| Recipe | solvent and DI rinse, dry; hot-pressed grades have residual porosity so bake after |
|---|---|
| Forbidden | oxidising cleaners hot |
| Limit | porosity of the grade |
Vacuum and outgassing
| Outgassing, unbaked (10 h) | 5e-9 mbar·L/s/cm² |
|---|---|
| Outgassing, baked | 5e-12 mbar·L/s/cm² |
| Vapour pressure | none |
Temperature
| Bake, assembled | 450 °C |
|---|---|
| Vacuum degas | 1200 °C |
| Braze / H2 firing | 1500 °C |
| Metallurgical limit | oxidises above 600 °C in air |
Thermal
| CTE | 5 ppm/K |
|---|---|
| Thermal conductivity | 30–40 W/m·K |
| Specific heat | 950 J/kg·K |
| Emissivity | 0.9 |
| Melting / softening | 2450 °C |
Mechanical
| Strength | 350–400 flex MPa |
|---|---|
| Elongation | nil |
| Young's modulus | 450 GPa |
| Hardness | 2800–3200 HV |
| Density | 2.52 g/cm3 |
Electrical and magnetic
| Relative permeability | 1.0 |
|---|---|
| Resistivity | 0.1–10 Ω·cm |
Engineering
| Corrosion | good |
|---|---|
| Joining | clamped; brazing is difficult |
| Process notes | neutron absorption plus extreme hardness plus low Z |
| Availability and cost | to drawing, long lead |
Outgassing
2 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: no unbaked reading unbaked to 1e-13 baked.
| Material as published | Species | State | Pumping time | Rate |
|---|---|---|---|---|
| Boron carbide ceramic | total | baked | the abscissa of the curve below | 1.00e-11 at 5 h to 2.49e-12 at 16801.5 h |
| Boron carbide ceramic | total | baked | the abscissa of the curve below | 3.07e-12 at 29 h to 7.41e-14 at 8766 h |
Sources: S-SEMENOV-IPAC2021. Full citations and conditions at the base and in /data/outgassing.json.
Grades
| Hot pressed B4C | apertures and absorber tiles |
|---|---|
| Enriched B-10 grades | neutron duty |
Sources · 2
- European XFEL photon transport design reports
- CERN Accelerator School, beam intercepting devices