Replacing Al Crucible

Written by NTS from email 5/28/2016. Last updated by: SDM October 2016

• We will assume the GC has been vented.

Venting and Pumping the MBE System

• Make sure you have a new, clean Al crucible on hand and ultraclean Ta wire (at least 10") in a foil pack

Remove Al cell

1. Pull the Al cell

2. Cover port with clean foil

3. Put cell in transfer case

4. Blank port.

5. Do any other SF work, should be minimal

6. Pump down and Leak Check

7. Disconnect the Bravo glovebag and move the Al cell, ultraclean tools, etc. over to the BOS glovebag.

Replace Al Crucible

• This is done in the BOS glovebag.

• The new crucible will have to be baked on the BOS

• This is a pretty involved procedure, more than expected my first time

• It may be helpful for P1 to practice holding one small pliers in each hand in the bat cave prior to venting.

• The Al cell has, in order of removal: Ta wire to keep Ta foil semi-cylinders in place, Ta foil semi-cylinders, Ta foil heat shields around crucible neck, Al crucible.

1. Vent BOS

2. Take blank off of BOS and foil

   1. Gasket stayed on BOS, deal with it after Al cell work

3. Foil BOS port

4. Take Al cell out of transit case

   1. Open

      

      Removing transit case from Al cell. Be aware of how much space is needed relative to the size of the glovebag

5. Remove gasket from Al cell

   1. Noteworthy because this gasket did not want to budge and a gasket pullers might have been slightly damaged

6. Gasket vice grips were needed

7. Put down work space foil

   1. Big piece, not ultraclean, will catch junk that falls, is a good idea

8. Make a non-ultraclean boat for the old crucible, at least 8x6"

9. Make ultraclean boat for placing ultraclean (UC) cell pieces

   1. Get UC side of foil facing up with normal gloves, use clean gloves to bend sidewall

   2. I'd recommend about 9x9" and 1" tall sidewalls

10. This boat is your friend for resting pliers noses to adjust grip

11. Get two UC gloves and two UC pliers

    1. All of the handiwork coming up was done with these pliers

    2. Almost always two pliers: don't drop anything!

12. Note where the Ta wire is in relation to two cell characteristics

    1. Such as the flange label and the nearest feedthrough or leak check port

13. Remove Ta wire

    1. Slightly untwist Ta foil retaining wire and slip it up the cell tip to remove

    2. Don't fully untwist

    3. Place in the UC boat

    4. We can reuse the wire

    5. This may make later easier, if we can reuse it, as it is already circular and has twists

    6. If the Ta wire does not want to untwist, use wire cutters to snip. You will need a new piece of ~6 inch wire when replacing later

14. Remove Ta foil semi-cylinders

    1. Grab tiny top lip and bottom of Ta foil half, and pull straight out (away from cell, not up)

    2. Might need to wiggle a bit at first and go slightly off of straight out

    3. Place in UC boat

    4. P2 must keep the cell straight up and down when the Ta foil is on the cell but not wired together

    5. Open

       

       Removing semi-cylinder pieces

15. Remove Ta foil heat shields

    1. These are thin donut-shaped disks with a slit

    2. I'd recommend P2 rotates the cell so the next disk's slit is facing P1

    3. Grab a SINGLE disk on either side of the slit

    4. Part the halves carefully to make the slit wider

    5. Slide the disk off, with the crucible neck passing through the slit

    6. Place in the UC boat, don't stack them perfectly, but some overlap is OK

    7. These are fairly robust and flexible, but we do not want to deform or tear them, be patient

    8. It is easier with the crucible lifted a little, sometimes you can lift it a bit and it will stay there due to friction

    9. Open

       

       Removing Ta foil heat shield rings

16. Remove Al crucible, carefully

    1. Grab the lip with a firm but not forceful grip and lift straight up

    2. Watchout for any delaminating part of the crucible, we don't want to generate flakes

    3. There will be friction and some sticking points, be patient

    4. Slightly wiggle or rotate to help get it out

    5. Always have at least one pliers on it, but two is preferred, especially for lifting out

    6. The inside of the cell has some brittle materials like pBN, so patience and carefulness are key

    7. Place in crucible boat

    8. Open

       

       Pulling the old Al crucible. Note how large it is compared to the rest of the cell

17. Put pliers down and help P2 get new Al crucible ready

    1. The crucible can be treated like a gasket, outside of bag is normal clean, inside is UC

    2. Once the bag is open, look inside the crucible to make sure it is clean, watch out for dark spots

18. Get new UC gloves and get your pliers again, while P2 holds cell and open crucible bag (with crucible in it), and P3 opens/closes UC plier bin

19. Lift up new crucible and slowly install into cell

20. Install Ta foil heat shields

    1. Pick one up from UC boat

    2. Part middle slit and slide around crucible neck

    3. This part is harder than the removal, because the disks will want to catch on the crucible lip, bend weird, and catch on each other

    4. Be patient and careful

    5. Sometimes you will have to grab a disk with one pliers while the other pliers does something else, e.g. prevent the disk from getting caught on the crucible lip or another disk, lift up the crucible a bit

    6. Open

       

       Replacing the Ta foil heat shield rings

21. Center all of the heat shields and try to get them down into the birdcage lip

    1. This is easier said than done, or elaborated upon

22. Install Ta foil semi-cylinders

    1. Do actions in reverse of above

    2. Press the halves together to get them snug on the cell

    3. It is recommended that a P3 holds the first cylinder onto the cell while P1 gets the 2nd cylinder into place (see picture below)

    4. Open

       

       Replacing the Ta foil heat shield rings

23. Replace Ta wire

    1. If you saved the wire correctly, slip it back over the cell tip

    2. Place it about halfway down the Ta foil, and level

    3. Tighten the twists on the wire to snug back up

    4. When you can let go of the wire without it shifting you're close, until then always have a pliers nose under the wire to catch it when attempting

    5. When you can grab the wire and it won't move at all with light force, you should be good

    6. If you didn't save the wire properly, you can try to reuse what you did save (if anything), or cut yourself a new piece of wire and start from scratch

    7. We did both of the above, as our wire wasn't saved properly and we had to give up on it

    8. Cut yourself more wire than you'll need, you can cut it down but can't add a half-inch, 4.5" to 6" should be good

    9. Place wire around birdcage, make a loop and get your first half twist or full twist in

    10. Continue to twist, paying attention to: keep the loop in the middle of the Ta foil, levelness, position in relation to your two cell characteristics, tightening, prevent bunching in your twist (will make bending it down harder)

    11. It is more important to get the wire tight (without ripping) than the number of twists, but twisting helps tighten it

    12. I recommend the straightnose pliers for twisting (from the wrist)

    13. Cut any excess wire, leave a tiny bit so it can be grabbed for untwisting in the future (1/8 to 1/4 inch including twist and some untwisted wire)

24. Bend the twists part of the wire down toward the birdcage

    1. Be firm but gentle

    2. Open

       

       Replacing the Ta foil heat shield rings

Install on BOS

1. Wipe knife edge of cell

2. Put new gasket on cell

3. Remove gasket from BOS and wipe knife edge

4. Install on BOS

   1. Be careful to keep cell from hitting anything inside BOS arm (keep it at the proper angle and left-right/up-down position as you insert it

   2. Go slow for above and to keep gasket on it (no clips needed)

5. Pump down and leak check

Bake Cell

• See Baking Cells page: Insert Link when updated