Alumina 94 to 99.8 percent

Brazing

Sourced pairings

Preparation

• Mo-Mn 80/20 fired 1500 C under wet H2, coating 0.025-0.038 mm, Ni plating 0.003 mm refired 1000 C
• no metallisation
• none
• Mo-Mn then Ni plating
• 15 C/min to 975 C with a 10 minute soak, then 10 C/min to the peak temperature and its soak, then 25 C/min back to 975 C and 15 C/min to ambient
• the Ticusil foil placed in direct contact with the graphite surface on a tapered joint interface, with a slight pressure applied at the interface during brazing to obtain a void-free joint. On this joint the alumina is UNMETALLIZED.
• the graphite is metallized with a molybdenum, manganese and silica powder slurry brush-painted, dried and fired at 1600 C in dry hydrogen to form carbides with the graphite, the alumina ring is metallized on both its inner and outer circumferential surfaces, a thin copper coating overlaid on the graphite serves as the filler and protects the metallization from oxidation. Both brazes, Kovar to alumina and alumina to graphite, are made in a single operation.
• molybdenum-manganese metallization fired in wet hydrogen, then nickel plating, electrolytic from a nickel-chloride solution or electroless nickel-boron, the two compared with no difference in tensile strength attributable to either, brazing cycle of 10 minutes at 55 C above the liquidus, the parts placed into a preheated furnace and cooled in a water-cooled hydrogen-purged chamber
• for the metallized route, a coating of molybdenum, sometimes tungsten, and manganese particles mixed with silicates and glass additives, fired in wet hydrogen at 1450 to 1600 C to leave a glassy metallic coating 300 to 500 micro-inches thick, then plated with 0.001 to 0.003 inch of nickel sinter-fired at 850 to 950 C in hydrogen. For the thin-film route, a PVD titanium layer 0.05 to 0.25 micrometres thick under a noble over-layer of gold, platinum or palladium 0.25 to 1.0 micrometres thick.
• alumina cleaned in a three-step solvent process then resintered either in wet hydrogen at a 28 C dew point, 1500 C for 60 minutes, or air-fired at 1575 C for 120 minutes, Kovar pickled in deionized water and hydrochloric acid then bright-dipped in an acetic, nitric and hydrochloric solution, joint preload about 30 g per square centimetre, part of the Kovar carries a conformal ALD alumina coating of 1 to 20 nm. Cycle: 15 C/min to 925 C with a 15 minute soak, 10 C/min to 985 C with a 5 minute soak, 25 C/min back to 925 C, then furnace cool.
• a molybdenum or a tungsten barrier vacuum-evaporated onto the ceramic before brazing
• tungsten metallizing. Pure alumina with an addition of one half to 2 per cent yttria is coated with a suspension of 17 volume per cent tungsten powder in 83 volume per cent water, and the coating is sintered at 1700 C. The chapter prints the four reactions Cowan, Stoddard and Herrick summarise, ending with a final firing temperature of approximately 1700 C being necessary to densify the tungsten and cause the mixture of tungsten, yttrium tungstate and yttria to coalesce into a hard, dense structure.
• three metallizing paint formulations are printed on book page 447 and all three are used at the same laboratory, the document saying of them together that these compositions have been successfully used for a number of years at the W. W. Hansen Laboratories of Stanford University. PAINT NO. 5A, Eitel-McCullough, Inc., Report No. 7 of 1954, under contract AF33(600)-17125, Reliable Ceramic Tubes Adapted for Automatic Production: 176 g molybdenum powder at 400 mesh, 44 g manganese, MD 301 of the Metals Disintegrating Co., Inc., Elizabeth, N. J., 55 ml acetone, 25 ml methyl ethyl ketone, 50 ml Cellosolve of the Carbide Carbon Chemical Co., and 45 ml nitrocellulose lacquer of 600 to 1000 seconds. PAINT NO. 10A, Eitel-McCullough, Inc., Report No. 9 of 1954, under the same contract: 176 g molybdenum powder at 200 mesh, 44 g manganese powder at 200 mesh, 9 g titanium hydride, 45 ml nitrocellulose lacquer of 600 to 1000 seconds, 25 ml methyl ethyl ketone, 50 ml Cellosolve, which the document glosses as ethyl ether, and 55 ml acetone. PAINT NO. 2A, and this one the document attributes to the W. W. Hansen Laboratories of Stanford University themselves: 200 g molybdenum powder at 400 mesh, 40 g manganese powder at 400 mesh, 10 g hydrogen-reduced iron powder, 2 g silica in the form of silicic acid as a fine powder, 2 g calcium oxide at 200 mesh or finer, 50 ml nitrocellulose lacquer of 600 to 1000 seconds, 55 ml acetone, 30 ml methyl ethyl ketone and 50 ml Cellosolve. THE LACQUER ITSELF is prepared by mixing the following ingredients in the order shown: 400 g nitrocellulose, 1650 ml toluene, 750 ml ethyl alcohol or methyl ketone, 600 ml ethyl acetate. THE PROCESS: after ball-milling for 100 hours the paint is applied by brushing and sintered at the specified temperature, a second coating is superimposed and treated in the same manner, and the metallized area is then nickel-plated. WHICH PAINT ON WHICH BODY: Paint No. 5A is preferred for metallizing 94 per cent alumina that is then fired at 1525 C, which the document marks Tb, and for bodies of higher alumina content Paints 10A and 2A are being used. HANDLING, printed on book pages 445 and 446 and carried here because it conditions the bond: the ceramics must not be touched by bare hands after the cleaning operation has been performed, and they should be stored in heated, dust-free cabinets before use. Clean ceramics must not come into contact with any metal parts during handling, tweezers, spatulas and other tools should be bone-tipped or coated with plastic, and ceramic or fused-silica trays must be used during furnace treatment.
• a spongy layer of molybdenum formed on the ceramic by reducing a suspension of MoO3 in an amyl acetate and nitrocellulose solution, brushed on and reduced in wet hydrogen for 10 minutes at 1700 C or higher, higher sintering temperatures and higher humidity and longer firing times producing better results. Then a refractory alloy wetting agent of 40 weight per cent RuO2 and 60 weight per cent MoO3 in the same solution, brushed onto the spongy layer and reduced to metal by firing in hydrogen for a few minutes at 1300 C or higher.
• seven metallizing mixtures formulated at the Sperry Gyroscope Company, sintered between 1300 and 1600 C. Composition 65, 292.5 g Mo and 7.5 g Ti at 1500 C. Composition 91, 270 g Mo and 30 g LiMnO3 at 1500 C. Composition 141, 291 g Mo and 9 g talc MgO-SiO2 at 1600 C. Composition 72, 240 g Mo and 73.6 g CeO2 at 1500 C. Composition 50, 255 g Mo and 48 g SiO2 and 22 g Mn, at 1300 C on one body and 1500 C on another. Composition 49, 255 g Mo and 48 g SiO2 and 26 g MnO at 1500 C.

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.

• reacts71.5Ti-28.5Ni

  Kohl states that a very brittle intermetallic compound Ti2Ni forms in Ni/Ti active alloy seals once the eutectic composition of 28.5 nickel to 71.5 titanium is exceeded toward the nickel-rich side, and also toward the titanium-rich side, or when the sealing temperature drops below 955 C.

  [A]Walter H. Kohl, Handbook of Materials and Techniques for Vacuum Devices, chapter 15, Ceramic-to-Metal Sealing, pages 441 to 474, AIP Press, American Institute of Physics, New York, 1995 reprint of the Van Nostrand Reinhold edition of 1967, American Vacuum Society classics series, ISBN 1-56396-387-6, call number TK7871.72 .K64 1995

  Conditions and source

  Book page 453. The passage reads: It is important that the excessive formation of brittle phases be avoided during the sealing operation. This requires very careful temperature control and judicious proportioning of the alloy components. In the case of Ni/Ti active alloy seals, a very brittle intermetallic compound Ti2Ni is formed when the optimum eutectic composition of 28.5:71.5 Ni/Ti is exceeded toward the Ni-rich side on the phase diagram, or, for that matter, also when the composition moves toward the Ti-rich side, or when the sealing temperature drops below 955 C. THE MEASUREMENT THAT ESTABLISHES IT is printed on the same page, from Wisser and Hagadorn, who placed stacked rings of Ti and Ni of different thicknesses between two abutting cylinders of 96 per cent alumina ceramics and heated them to 1070 C for three minutes: Photomicrographs taken of seal sections disclose the presence of small cracks for a composition containing 32.1 per cent Ni and extensive cracks for a 35 per cent Ni-alloy. To obtain consistently good seals, it is recommended that the Ni content not exceed 28.5 per cent. THE REMEDY IS PRINTED TOO, on page 454: the authors also introduced massive titanium seals where a relatively thick Ti ring is used with a thin Ni washer on each side, so that the Ti/Ni alloy formed always remains on the Ti-rich side of the eutectic composition 28.5/71.5. WHY THE VERDICT IS reacts AND NOT proscribed OR attacks. The document names a reaction product and the composition window in which it appears, and it does not instruct anyone to avoid the filler, which would be proscribed, nor does it describe the filler eroding or dissolving the alumina, which would be attacks. The material of this entry is the alumina because that is the ceramic of the measurement, the 96 per cent alumina cylinders of Wisser and Hagadorn. The portee is stated and not derived-from-class because the corpus filler entered at this lot IS the eutectic the sentence names.

• listedCusil-ABA
  Schwartz reports Cusil ABA used as a titanium-containing filler metal to join alumina of 94 and 99 plus percent, over a brazing temperature range of 820 to 860 C.
  Conditions and source

  Book page 128, unnumbered table under the sentence that titanium-containing filler metals were used to join both 94 and 99 plus percent Al2O3 compositions. The alumina grades named match the corpus alumina entry, which covers technical alumina 94 to 99.8 percent. The sentence names no partner metal, and the figure that follows on the same page shows copper contacts, which is not recorded here because the sentence itself does not say it. The second filler of the same table, Incusil 10 ABA, is not written because the corpus carries Incusil-ABA under another name and another composition, and the two products are not established to be the same.

  [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: Al O, from the chemical name.

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