GB852693A - Electrically heated infra-red radiant energy source - Google Patents

Abstract

852,693. Infra-red emitters. PERKINELMER CORPORATION. Dec. 11, 1957 [Dec. 13, 1956], No. 38465/57. Class 39(3). An electric heater emitting infra-red rays e.g. for measuring purposes, comprises a heating resistor 11 consisting of a metal of the platinum group (Ru, Rh, Pd, Os, Ir, Pt) especially Rh or an alloy of Rh, in a ceramic tube 10 which is completely filled with refractory insulating material 12. The ends of the tube 10 may be open, or closed by silver caps 13 through which the resistor passes and to which it is soldered, the caps 13 serving as terminals between spring clips. The tube 10 may be of aluminium oxide and may have one or more coatings modifying the emission of radiant energy, for example iron oxide or yttrium oxide. The insulation 12 may be a mixture of zirconium silicate, aluminium oxide, cobaltic oxide, molybdic acid and air is excluded to prevent oxidation of the resistor when operated at 1200‹-1500‹K. The resistor may be helical at 15 where maximum radiation is required and may have a loop 16 at each extended end to relieve mechanical stress between the wire and the end caps ; or silver leads may be spot welded to the ends of the resistor, the junction being embedded in the insulation, which may be fed into the tube under pressure. The sleeve with the resistor therein may be submerged in an aqueous suspension or slurry of the insulation, which is agitated and the surface of which is held under a vacuum to remove air. The insulation is then dried and that on the outside of the tube is removed. The slurry may be fed to a funnel inserting in a rubber tube over one end of the tube, the other end of which contains a plug of cotton wool and is attached to a vacuum system, and the unit is kept under a vacuum until the insulation is dry. The insulation is finally hardened by passing a current through the resistor.