Silvac is a highly effective high vacuum cement for creating unmatched, vacuum tight, low vapor pressure bonds.   When properly applied, materials of differing thermal expansion characteristics can be joined together and subjected to temperatures ranging from cryogenic to bakeout.  Some limitations are imposed when the  expansion differences are great.  For example, a quartz window can be cemented to a stainless steel port and be subjected to a temperature range of –500C to +2500C provided the  diameter does not exceed 1".  Where the expansion differences are more moderate, as between quartz and borosilicate glass, the range can be extended from –2000C to +4000C in  diameters to 2".  The closer the expansion match the more tolerant the seal.