Some problems in sealing gas-filled glass ampoules

We have studied recently the ends of hand-sealed and machine-sealed, gas-filled ampoules of borosilicate glass. The hand-sealed ampoules were of two types: tip-sealed and draw-sealed. The openings in the tip-sealed ampoules were estimated to range from 5 to 10 mu; in the machine-sealed ampoules the helix-like openings were less than approximately 10 mu. From the dimensions and nature of the openings we conclude (1) that the usual, simple methods used to test for "leakers" are not successful for small bore channels because pressure differences are less than one atmosphere and the test-time period insufficient, (2) that the failure of ampoules to seal may be due to the physical properties of glass and if this is so, ampoules containing liquid or freeze-dried preparations under gases cannot be sealed completely by ordinary means, and (3) that complete, satisfactory sealing can be done by dipping the ends of the ampoules into an elastomer solution which when cured provides an effective barrier even when stored at -70 degrees C for 12 months.