Lead silicate glass insulation between coaxial electric leads - having lower thermal expansion then the leads to prevent fissuring

摘要

Vacuum-tight glass insulation between an inner electric lead and an outer electric lead coaxially surrounding the inner lead is improved in that the glass has lower thermal expansion than both the electric leads. The coefft. of the thermal expansion of the latter (pref. both made of the same alloyed steel) is 180-220 x 10-7 degrees C-1; whilst that of the glass is 40-120 x 10-7 degrees C-1. The glass is based on lead silicate; the weight ratio PbO:SiO2 is 55:45 to 85:15. In addition the glass may contain (in wt. % w.r.t. PbO+SiO)2: GeO2 6-18, Bi2O3 0-8, BaO 1-9, CaO 0-2. MgO 0-2, ZnO 0-13, CeO2 2-3, Al2O3 0-5, ZrO2 0-2, Na2O 0-2, K2O 0-2. If the glass is used in a nuclear plant it should be free of B and Co. This glass is esp. suitable for use in nuclear installations, but it can also be employed in other applications involving extensive temp. fluctuations. The use of a glass having a lower thermal expansion than both the electric leads proved to be better than the conventional arrangement in which the expansion of glass was intermediate between the expansion of the two electric leads (the highest in the expansion of the outer lead), because there was no fissuring tendency. The electric resistance was very high.