Ceramics and glasses · Workhorse
Beryllia
BeOvalues describe: 99.5 % BeO
Why it wins
The tube industry thermal insulator: BeO moves heat like a metal while holding kilovolts, under collectors and high dissipation grids.
Why not the alternative
AlN has replaced it where it can, but BeO still wins on raw conductivity and heritage designs.
Watch out
Toxic as dust: machining is licensed, priced accordingly.
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 | wet processes only, in a controlled enclosure, effluent captured |
|---|---|
| Forbidden | ANY dry operation that can raise dust |
| Limit | occupational exposure, full stop |
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 | 1200 °C |
| Braze / H2 firing | 1500 °C |
| Metallurgical limit | service to 1800 °C |
Thermal
| CTE | 7.5 ppm/K |
|---|---|
| Thermal conductivity | 270 W/m·K |
| Specific heat | 1030 J/kg·K |
| Emissivity | 0.7 |
| Melting / softening | 2507 °C |
Mechanical
| Strength | 250 flex MPa |
|---|---|
| Elongation | nil |
| Young's modulus | 345 GPa |
| Hardness | 1200 HV |
| Density | 3.01 g/cm3 |
Electrical and magnetic
| Relative permeability | 1.0 |
|---|---|
| Resistivity | >1e14 Ω·cm |
| Dielectric strength | 12–14 kV/mm |
Engineering
| Corrosion | inert |
|---|---|
| Joining | metallised and brazed |
| Process notes | dust is a chronic inhalation hazard |
| Availability and cost | restricted, declining supply |
Brazing
Sourced pairings
| With | Filler | Atmosphere | Expansion gap at set |
|---|---|---|---|
| Oxygen-free copper C10100 / C10200
one built object
rectangular waveguide RF window for the Jefferson Lab Free Electron Laser, a warm replacement window at 1500 MHz aiming above 100 kW average power, built and power-tested at the TJNAF | Nioro | not stated by the source | expansion of side B absent: 955 °C is outside the range of copper-ofe (20 to 927 °C), never extrapolated |
| Niobium RRR 300
one built object
four-inch outside diameter by four-inch high bore seal capsule for a space electric power alternator: a 99.8 percent beryllia tube with a 0.1 inch wall thickened to 0.2 inch at the ends to widen the braze land, two beryllia back-up rings, two hemispherical Cb-1Zr end bells hydroformed from 0.015 inch sheet, and a Cb-1Zr fill tube electron-beam welded on | 60Zr-25V-15Cb | vacuum brazing furnace, then exposure in an ion-pumped thermal vacuum chamber in the 10-9 torr range | set temperature absent: no solidus recorded for zr-v-nb-60-25-15 |
| copper, grade not stated by the source
one built object
two prototypes of a symmetric pill-box RF window, 5 GHz, 500 kW for 5 s, for the ITER lower hybrid current drive heating system, built by PMB/ALCEN and power tested at NFRI in Korea: a BeO 99.5 percent disc from American Beryllia, product sheet EPS-8001, 85.89 mm across and 8.3 mm thick, brazed to a water cooled copper skirt | named only in prose: a gold copper alloy Au50/Cu50 in a layer 20 to 40 micrometres thick, chosen to avoid silver alloys. That composition is not any alloy of this catalogue: the two gold-copper entries are 37.5Au-62.5Cu and 35Au-65Cu, and neither is a half and half. | not stated by the source | no filler identified, nothing to derive |
| copper, grade not stated by the source
one built object
output window of the VGA-8000 gyroklystron, across a series of numbered tubes S/N 2, 1R, 2R2 and 2R9 built, tested and rebuilt over four years: a half-wavelength BeO ceramic disc brazed to copper cups and surrounded by a stainless steel water jacket that is not itself brazed to the ceramic | named only in prose: not named by the source. The report describes the window build and its failures without printing the filler metal. | not stated by the source | no filler identified, nothing to derive |
Preparation
- molymanganese metallization on a quarter-inch band around the surface to be brazed, screen printed and fired at 1450 C, then the metallized area nickel plated and sintered at 1000 C, then light blasting with aluminum oxide particles after the braze
- the beryllia was coated with a 1 to 3 micrometre thick layer of molybdenum by the EVAPORATION METALLIZING PROCESS before brazing, the report's own words and its own appendix A, procedure MP-1. The report gives the reason in as many words: it was believed that the wetting characteristics could be improved by metallizing the ceramic with evaporated molybdenum. The retained system is named in the report as the molybdenum-metallized low-silica Thermalox 998 brazed to Cb-1Zr with 60Zr-25V-15Cb.
- a molybdenum manganese layer on the periphery of the BeO, plus a nickel plating
- a metallizing on the ceramic, named by the source only when it fails
Chemical affinity
What documents state about a BINARY SYSTEM, one element of a filler metal faced with one element of this material. An affinity is not a verdict on a joint: a joint brings many binaries together at once, some helpful and some harmful, and what follows is the list of those the corpus can name. The count below is not written anywhere. It falls out of the crossing of this material's elements with the composition of every filler the corpus holds, so it grows on its own the day a binary enters the corpus.
Elements of this material: Be O, from the chemical name.
interfacial reaction that wets9 fillersTi against O1 source+1 statement
The two elements react at the interface and the product of that reaction is what the rest of the filler wets. This is the mechanism that makes active metal brazing work, and it is the only one of the six that a joint wants.
9 fillers: 35Au-62Cu-2Ti-1Ni, 48Ti-48Zr-4Be, 49Ti-49Cu-2Be, 56Zr-28V-16Ti, 71.5Ti-28.5Ni, Cusil-ABA, Cusin-1 ABA, Incusil-ABA, Ticusil
Conditions and verbatim
Printed page 857, section on active metal brazing. The article states that titanium is the most extensively studied and widely used active element addition to filler metals formulated to directly braze high-melting oxide ceramics, citing Ref 37 to 41, and that the critical interfacial reaction product in the case of oxide ceramics brazed with titanium-containing filler metals is either TiO or Ti2O3, with appreciably higher adhesion in systems that result in the formation of TiO, citing Ref 42. The article gives no temperature for this reaction and none is written here.
Source[A] Joining, in Engineered Materials Handbook Desk Edition, M. M. Gauthier editor, ASM International, 1995, pages 846 to 864, DOI 10.31399/asm.hb.emde.a0003056
Source conditionsHandbook article, consulted as a PDF whose printed page numbers run 846 to 864. The article is itself a digest of the Ceramics and Glasses volume 4 of the Engineered Materials Handbook, so its statements are second-hand summaries of the papers it cites by Ref number. The Ref numbers are kept in the conditions of each entry, because a reader who wants the primary measurement needs them.
Grades
| BeO 99.5 (Thermalox class) | standard high conductivity insulator grade |
|---|