Abstract A process for forming a hermetic seal from a finely pulverized mixture of glass and 30-40 percent by weight of magnesium oxide. A finely pulverized mixture of a lead-potash-soda glass with 3040 percent by weight of magnesium oxide is loaded into the area around the electrical conductors to be sealed. The powdered mixture is ''''pressed'''' to reduce porosity and compact the particles. Thereafter, the mixture is heated to a temperature which drives off moisture and purges air from the mixture. Thereafter, the temperature is elevated at a rate to induce crystallization in the material without causing stratification while raising the temperature to the working point of the glass in the seal mixture. Thereafter, the composition is cooled until it becomes rigid.
A method for providing a sealed sheathed conductor comprising an outer sheath, an inner conductor and a primary insulant composed of a finely divided glass and a heat conducting material having a melting point above the softening point of the glass and selected from the class consisting of magnesium oxide, aluminum oxide, and beryllium oxide, with the glass being present in the mixture in the range of from 10 percent-30 percent by weight of the mixture, the primary insulant extending over a substantial portion of the sheath length to space the conductor from the sheath including the steps of: a. filling a volume defined by an end surface of the primary insulant and the sheath with a homogeneous mixture of magnesium oxide and a finely divided glass having a coefficient of thermal expansion intermediate the coefficients for the sheath and the conductors, the working temperature of the glass being less than the softening temperature for the finely divided glass in the primary insulant, the composition consisting of 30 percent-40 percent by weight of the magnesium oxide; b. compacting the mixture to reduce porosity in and to provide intimate contact between the particles; c. heating the sheathed conductor to remove moisture and purge air from the mixture; d. elevating the temperature of the sheathed conductor to the working temperature of the glass particles at a rate which induces some crystallization without stratification and thereafter maintaining the temperature at the working temperature for the glass for a time less than that which would otherwise induce stratification; and e. cooling the sheathed conductor at a rate which prevents stratification without thermally shocking the probe.
Claim 2
Dependent Claim
18 words
A method as recited in claim 2 wherein the finely divided glass is constituted by a soda-lead-potash glass.
Claim 3
Dependent Claim
22 words
A method as recited in claim 3 wherein the glass and magnesium are passed through a No. 325 mesh prior to mixing.
Claim 4
Dependent Claim
31 words
A method as recited in claim 4 wherein moisture is removed and air is purged from the mixture by maintaining the temperature at approximately 475* C. for more than four hours.