A qualitative evaluation was made of the adherence between
borosilicate glass and the ceramics, steatite and alumina. Three
basic adherence studies were performed.
(1) A comparison between the x-ray diffraction patterns of
the ceramic and the fused glass-ceramic powder mixture was made
to determine if any new compounds were formed at 1200°C.
(2) A metallographic examination of the interfacial region of
actual seals made at 800°, 900°, 1000°, 1100°, and 1200°C was
made to observe the transition zone and any new phases formed.
(3) A hydrostatic rupture test and a metallographic and
stereoscopic examination of the resulting fracture surfaces were
made in order to get a qualitative evaluation of the adherence developed
in seals formed at various temperatures.
The results of each investigation indicated that good glass-ceramic adherence was achieved. The x-ray diffraction work suggested
that new compounds were formed at both glass-ceramic interfaces.
In the alumina system, the resulting diffraction pattern closely
resembled both an aluminum borate and an aluminum silicate. In
the steatite system, a close match was not made, but the new pattern
did resemble magnesium meta silicate.
The metallographic work revealed that, in the steatite system,
extensive interdiffusion of the glass and ceramic phases occurred.
Devitrivication was observed in seals made at 1200° C, and cracks
appeared when these seals were cooled. Neither phase in the alumina
system was so obviously affected by high temperatures. A few
small crystals were found on the ceramic at the interface, and glass
filled some of the ceramic voids near the interface, but evidence of
extensive diffusion was not observed.
The hydrostatic rupture test data showed that the strength of
the alumina seals improved with temperature. Similar data were
not collected for the steatite seals, for too many samples broke improperly.
Examination of the fracture surfaces in both systems indicated
that the crack generally propagated through the glass phase.
This suggests that the solid-liquid interfacial energy is somewhat
smaller than the solid-gas interfacial energy, or the energy of adherence
is large