Magnesia insulated heating elements and method of making the same
AssigneeGeneral Electric Company
InventorsMarcus P. Borom, John Schultz, Jr.
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Abstract
Compacted, granular, fused magnesia used as thermally-conducting electrical insulation in tubular, electrical resistance elements is substantially improved in thermal conductivity through the addition of 0.1 to 10.0 percent of a glass comprising CaO, B.sub.2 O.sub.3 and optionally Al.sub.2 O.sub.3 and method of making said tubular, electrical resistance elements.
Claims4
In a tubular heating element including a metal sheath and a coaxial coil resistor enclosed in the sheath, the combination of a compacted electrically insulating mass filling the space in the sheath between the resistor and the sheath and comprising fused magnesia and from about 0.1% to about 10% of a glass of softening temperature below about 700.degree. C. having resistivity greater than about 10.sup.7 ohm-cm at 600.degree. C. and being thermodynamically stable in oxygen partial pressure of 10.sup.-15 atmosphere at temperature in the range of 750.degree. to 1100.degree. C.
In the method of making a tubular heating element including the step of positioning the coil resistor coaxially within a metal sheath, the combination of the step of filling the metal sheath and thereby embedding the coil resistor with an electrically insulating mixture of fused magnesia and from about 0.1% to about 10% of a glass of softening temperature below about 700.degree. C. having resistivity greater than about 10.sup.7 ohm-cm at 600.degree. C. and being thermodynamically stable against metal oxide decomposition in the presence of oxygen partial pressure of 10.sup.-15 atmosphere at temperature in the range of 750.degree. to 1100.degree. C.
Dependencies are inferred from the claim text.