>>> WEAR EYE PROTECTION when near the muffle furnace at or above 99C, and when using the hydraulic hand press. <<<


1. Heat CaF2 powder at 950C for four hours. One set of older notes indicates 900C, the other 1000C. The furnace is rated at 982C max for sustained operation. We settled on 950.

1b. The Ti crucibles are top-heavy, more so when filled. To avoid spillage, put them by hand in the furnace at room T. Heat for the indicated temperature and time. Dial down the furnace to room T and let it cool to that before removing the crucibles by hand. Allow an extra hour for heat-up, several hours for cool-down. Crucibles can of course be handled while hot, with use of tongs and proper protective apparel.

1c. Gently scrape away any flakes of TiO2 adhering to the now quite crumbly crucible-shaped billet of CaF2.


2. Crush and sieve. Suggested by others and done here is to use the 80-25 mesh size fraction for tube fabrication. Save leftover fines to be fired again.


3. Mix dry polyvinyl alcohol (PVA) with cold water, then heat and homogenize by stirring on a hot plate (or not, as below). In any case aiming for a consistency of thin and runny, like the cheapest of ersatz pancake syrup.

3b. Salvage the old already-mixed PVA. A long time ago someone mixed ~1L of the stuff, a supply that may outlast humankind.
     -Heat to ~90C with something to keep the groundglass lid open just a crack e.g. a paperclip.
     -Heat until mostly liquid with few lumps remaining
     -Add water and stir if it appears to be too viscous
     -Pour through a tea strainer into a beaker
     -Keep the filtrate, discard the lumps and mold
     -Clean the bottle and put back in the filtrate


4. Previous instructions state "Add to CaF2 ~20 wt% PVA and mix well." Since we don't know the PVA:water ratio of the already-mixed PVA, the preceding is meaningless. Add small amounts of PVA/water solution until its consistency is like brown sugar. Too much PVA and the mixture will stick to the glass. Too little and the pressed tubes might crumble.


5. Dry overnight at room temperature and then separate from the glass container if (because you added too much PVA) stuck. Dry in the warming oven ~ 90C until completely dry. Use the upper shelf in the oven, else the PVA may scorch.

6. Crush and sieve. Using a mixture of 80% of 25-80 mesh size fraction, but also adding 20% fines.... OR

6b. Crush *very* lightly, just enough to pass through 25 mesh. Then use as-is. Seems to work jut fine.

7. Press at 7000 psi (for an Enerpac 10 ton press) for at least five minutes. Longer certainly won't hurt. Aiming for a finished length of > 26.5 mm.

8. Anneal at 900C for 30 minutes.