Binding glass to metal

Binding glass to metal (seal)

When making vacuum tubes it is essential to obtain good contact between the electrodes and the glass case. This is called "glass to metal seal".

This requires the glass and metal used to have similar coefficients of thermal expansion to avoid the glass near the connection cracking.

Some options:

• Soda-lime glass + copper wire
  • Soda-lime glass has a lower melting point leading to easier manufacturing
  • The soda-lime glass has TEC 8.5 and the copper has TEC 17, so the glass tends to easily crack.
• Borosilicate glass + tungsten wire
  • Borosilicate glass has a lower TEC of 3.3, so it is more resistant to cracking
  • Tungsten wire with TEC of 4.5 can be used, however tungsten wire can't be welded to the tube's insides and is also very hard

Note: other options should be researched.