The role of ceramic voids and fracture propagation in shelf life failure of tubes

Small tubes having an internal volume of 0.1 cm
³
were found to become gassy during shelf life and subsequently to arc when turned on. Quadrupole mass analysis and Auger electron spectroscopy were used to identify internal gasses and deposits on electrodes of gassy tubes. Gasses released during ceramic fracture propagation were also studied. The results indicate that for the tubes investigated, the predominant failure mechanism involved the growth of ceramic micro cracks which are connected to the interior of the tube. As the crack propagates, it releases N
2
which was trapped in the voids of the ceramic. Cracks extending only a fraction of the ceramic wall thickness are sufficient to liberate enough N
2
into the tube to correspond to a pressure of 10
^-3
torr, which will result in an arc during turn-on.