Ceramics and glasses · Future bench (deployed)

CVD diamond windows

C*values describe: CVD diamond

Big science (accelerators, light sources, public fusion)Fusion, privateVacuum electronics & X-ray sources

What it enables

X-ray and RF windows at power densities beryllium cannot survive, with extreme thermal conductivity: synchrotron and XFEL optics, gyrotron windows for fusion heating.

Status and pusher

Commercial at small apertures, growing. Pushed by synchrotron optics and fusion heating suppliers.

Properties

The values below are candidate: compiled from the sources named, not yet individually validated. Provisional provenance: CERN Accelerator School, vacuum and materials proceedings; CoorsTek, CeramTec, Kyocera technical ceramic data.

Wet cleaning

Recipesolvent, then acid clean for optical grades, ultrapure rinse
Forbiddenoxidising conditions above 600 °C
Limitsurface graphitisation, not contamination

Vacuum and outgassing

Outgassing, unbaked (10 h)5e-10 mbar·L/s/cm²
Outgassing, baked5e-13 mbar·L/s/cm²
Vapour pressurenone

Temperature

Bake, assembled450 °C
Vacuum degas1000 °C
Braze / H2 firingnot-applicable2018
Metallurgical limitgraphitises above 700 °C in vacuum

Thermal

CTE1 ppm/K
Thermal conductivity1800–2200 W/m·K
Specific heat520 J/kg·K
Emissivity0.03

Mechanical

Strength800–1000 flex MPa
Elongationnil
Young's modulus1100 GPa
Hardness10 000 HV
Density3.52 g/cm3

Electrical and magnetic

Relative permeability1.0
Resistivity>1e13 Ω·cm
Dielectric strengthtan δ 1e-5, the reason it is the gyrotron window

Engineering

Corrosioninert
Joiningbrazed into a metal frame, and the braze is the hard part
Process notesthe only window that passes megawatt RF without melting
Availability and costElement Six and few others, very high cost

Brazing

Sourced pairings

WithFillerAtmosphereExpansion gap at set
Oxygen-free copper C10100 / C10200 / Kovar (FeNiCo) / Nickel and nickel plating / Austenitic stainless 304L / 316L / 316LN ESR / Titanium Gr 2 / Ti-6Al-4V / refractories (unspecified)Ticusilvacuum 1e-5 mm Hg or inert gas1.15 % at 780 °C
Oxygen-free copper C10100 / C10200 on the outside
over budget

Preparation

  • none

Compatibility

What documents state about this material faced with a filler metal, without the other member of the joint. A statement that names the exact filler comes first. A statement about a whole AWS class comes after it: a class covers dozens of alloys, so it is the weaker of the two, and the corpus never turns one into the other.

  • listedTiCuNi
    Ticuni is listed for brazing carbon to stainless steel, to copper, to nickel, to titanium and zirconium alloys, and to carbon itself.
    Conditions and source

    Book page 153, table 4.28, Selection guide to filler metals for brazing metal-ceramic joints, carbon row. Source Ref 9 264 as cited by Schwartz, selection guide not a qualification. The document does not name diamond in the row itself: note (c) of the table defines carbon as graphite and diamond, so the corpus writes the same statement under both keys and this condition says why. Nothing in the table distinguishes the two forms of carbon from one another. The identification of the filler rests on the commercial name alone: table 4.27 gives Ticuni as 70 Ti, 15 Cu, 15 Ni, while the corpus entry ti-cu-ni carries no composition to compare.

    [A]M. M. Schwartz, Brazing, 2nd edition, ASM International, 2003, chapter 4, Base Metals and Base-Metal Family Groups, DOI 10.1361/brse2003p063

    Chapter 4 of the second edition, book pages 63 to 162 in the copy read, which treats base metals family by family and states metallurgical reactions, atmosphere limits and filler selection guides. It is a handbook chapter, not a qualification record. The page of each statement is carried by the entry that uses it, never by this registry line.

  • listedTicusil
    Ticusil is listed for brazing carbon to stainless steel, to copper, to nickel, to titanium and zirconium alloys, and to carbon itself.
    Conditions and source

    Book page 153, table 4.28, Selection guide to filler metals for brazing metal-ceramic joints, carbon row. Source Ref 9 264 as cited by Schwartz, selection guide not a qualification. The document does not name diamond in the row itself: note (c) of the table defines carbon as graphite and diamond, so the corpus writes the same statement under both keys and this condition says why. Nothing in the table distinguishes the two forms of carbon from one another. Table 4.27 gives Ticusil as 68.8 Ag, 26.7 Cu, 4.5 Ti, which matches the corpus entry. The carbon row is marked with note (b), Includes alloys, while only note (c) says what carbon means, and the corpus reads the row under note (c).

    [A]M. M. Schwartz, Brazing, 2nd edition, ASM International, 2003, chapter 4, Base Metals and Base-Metal Family Groups, DOI 10.1361/brse2003p063

    Chapter 4 of the second edition, book pages 63 to 162 in the copy read, which treats base metals family by family and states metallurgical reactions, atmosphere limits and filler selection guides. It is a handbook chapter, not a qualification record. The page of each statement is carried by the entry that uses it, never by this registry line.

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: C, from the chemical name.

interfacial reaction that wets9 fillersTi against C1 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.

On a carbide or a carbon, titanium in the filler forms titanium carbide at the interface, and that layer is what the filler wets.wantedTi against C

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 862, closing paragraph on other nonoxide ceramics. The article states that titanium nitrides and carbides are known as the interfacial reaction products for titanium-containing active metal brazes. It immediately qualifies the reach of that statement, and the qualification is carried here rather than dropped: the wettability of such carbides and nitrides with metal liquids may be influenced by their stoichiometry, citing Ref 109. The article speaks of carbide ceramics. This corpus also holds two carbons, graphite and diamond, whose element is the same C, and the entry is served for them too because the reaction named is the one between titanium and carbon.

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.

Open in the brazing abacus →

Sources · 1
  1. CERN Accelerator School, vacuum and materials

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