Indium foil is used here in the HYPER lab to create gaskets for seals within cryogenic hydrogen systems. Research with cryogenic fluid systems requires uniquely shaped seals that do not degrade at the extreme cold temperatures, and Indium is recommended by several leading experts. The required gasket profiles are cut out of large thin sheets of Indium, this process produces scrap material that is not sufficiently large to use again. Due to a relatively low melting point we’re able to melt the scrap Indium to form an ingot that can then be re-rolled into a new sheet to be used. The preferred thickness of this sheet is 0.05-0.025 inch (1.27-.635mm) and the tooling in the WSU heat treatment lab has the ability to produce this thickness. Here’s a guide to the HYPER lab’s process for producing new sheets of foil from an ingot of Indium.
- Indium scrap ingot
- Wax paper
- Digital caliper
- Hydraulic cold rolling mill
- Retractable blade knife
- small container for indium scrap
- Using the retractable blade knife cut off any surface impurities from the indium ingot while collecting any material cut off for re-melting. Here’s a guide to safe use of a retractable blade knife.
- Slice the ingot into two, similarly, ~1 cm thick, ~3 cm in od, sized pucks so that the material will fit in the cold rolling mill.
- The rolling mill is in Dana 236. You need to get approval from either Dr. Field or Dr. Wo before using the mill. Turn on the cold rolling mill and position the pedal so that it is accessible from both sides of the machine.
- Cut a piece of wax paper that is large enough to fit through the mill while folded around the metal sample.
- Fold the wax paper in half and place the metal sample inside to prevent sticking to the rolling cylinders.
- Begin by setting the mill to the width of the first puck to be rolled.
- Start making passes through the mill reducing the thickness by .4mm (1/4 turn of the adjustment handle) per pass until the puck is roughly 5mm thick.
- After every 3-4 passes the thickness of the Indium measured with the caliper.
- After reaching 5mm thick the metal will have to be rotated 90 degrees to prevent curling and each pass was lowered to a .2mm size reduction, slowing the rolling process will reduce waves in the sample.
- At roughly 2.5mm sticking between the metal sample and roller will begin to become an issue that must be watched for and thickness measurements were taken after each pass.
- Continue making passes through the rolling mill until the Indium sheet reaches the required 1mm in thickness.
- Safe the rolling mill by backing off the adjustment handle, turning the machine off, and locking the room when you leave.
- Once the material has been rolled, store it in a ziplock baggy in the drawer labeled “Indium” in ETRL 221.
Now you too can make effective thermal interfaces for use at cryogenic temperatures. Thanks for reading!