Patent GB-739780-A (GB)
Title: Electric resistor heaters and their production
IPC: H01B1/04
Filed: 1954-05-20
Abstract: An electric heater resistor comprises a continuous region consisting of molybdenum disilicide containing 5 to 50 per cent chromium boride in solid solution, preferably as a thin layer on a refractory material.  Alternatively the resistor comprises a continuous layer of a double carbide of molybdenum and silicon on an elongated carbonaceous body, having metal terminals at opposite ends.  The coating is 0.003 to 0.006 inch thick and formed by coating a graphite rod with molybdenum disilicide and heating it to above melting point in an inert atmosphere, e.g. argon, whereupon the molten coating penetrates the graphite to form the double carbide.  Several coatings may be similarly applied and may be heated by passing current through the rod.  A powder mixture of molybdenum silicide and chromium boride is hot pressed at 1500 DEG  C. into a cylindrical compact, is heated in hydrogen for 15 hours at 1300 DEG  C. and the alloy so formed is comminuted.  The alloy powder is then cold pressed into the desired shape, presintered, further shaped, e.g. as a rod and then sintered; or the alloy powder is extruded with an air free extrusion vehicle such as methyl or ethyl cellulose or with solution of cellulose acetate, and the extruded rods are sintered in hanging position in a vacuum.  The rod is fitted with water-cooled metal terminals and has a zero coefficient of resistivity at 1200-1700 DEG  C.  The alloy powder mixed with methyl cellulose may be applied to a ceramic rod and then sintered, the sintering temperature being reached within 10 minutes from room temperature.ALSO:An electric heater resistor comprises a continuous region consisting of molybdenum disilicide containing 5 to 50 per cent chromium boride in solid solution, preferably as a thin layer on a refractory material.  Alternatively the resistor comprises a continuous layer of a double carbide of molybdenum and silicon on an elongated carbonaceous body, having metal terminals at opposite ends.  The coating is 0.003 to 0.006 inch thick and formed by coating a graphite rod with molybdenum disilicide and heating it to above melting point in an inert atmosphere, e.g. argon, whereupon the molten coating penetrates the graphite to form the double carbide.  Several coatings may be similarly applied and may be heated by passing current through the rod.  A powder mixture of molybdenum silicide ano chromium boride is hot pressed at 1500 DEG C. intd a cylindrical compact, is heated in hydrogen for 15 hours at 1300 DEG  C. and the alloy so formed is comminuted.  The alloy powder is then cold pressed into the desired shape, presintered, further shaped, e.g. as a rod, and then sintered; or the alloy powder is extruded with an air-free extrusion vehicle such as methyl or ethyl cellulose or with solution of cellulose acetate, and the extruded rods are sintered in hanging position in a vacuum.  The rod is fitted with water-cooled metal terminals and has a zero coefficient of resistivity at 1200-1700 DEG  C.  The alloy powder mixed with methyl cellulose may be applied to a ceramic rod and then sintered, the sintering temperature being reached within ten minutes from room temperature.