| 摘要 |
1,168,134. Thermistors. GENERAL ELECTRIC CO. 18 April, 1967 [19 April, 1966], No. 17693/67. Heading H1K. [Also in Division C1] A thermistor usable over a large temperature range has a body of doped cubic boron nitride bearing two ohmic contacts. The dopant may be beryllium, sulphur, selenium, silicon, germanium, or boron and may be incorporated (in the proportion of 0À001-1À0% by weight of nitride) during the lithium nitride catalysed conversion at 1500-1900‹ C. and a pressure of 40-55 kilobars of hexagonal boron nitride to the cubic form. 300-500Ácrystals of the cubic material are separated by hand after dissolution in aqua region of remaining hexagonal material. To make the thermistor shown a crystal 1 cleaned in strong acid and then degreased is placed in contact with degreased heat sink-lead assemblies consisting of iron-cobalt-nickel leads 4 welded to molybdenum or tungsten bodies 3 each provided with a palladium coating 2. These parts were jigged with an alumino-silicate glass preform 5 in a gas-tight furnace containing oxygen-free forming gas of low dew-point and heated to form the ohmic contacts and seal the assembly, the leads being pushed inwards during the process. An outer envelope 7 of devitrified glass is applied to protect the lead-heat sink welds. Oxide on the exposed portions of the leads is removed and the leads chromium-plated. An alternative material for the ohmic contact is palladium-nickel alloy. In general, contact material may be applied by evaporation, as a slurry, or as a pre-form. Other lead materials are tungsten, molybdenum, and the following materials which require no protective chromium coat:-platinum, palladium, and palladiumcoated molybdenum. The atmosphere used in the firing stage and which is retained within the encapsulation may instead be argon, helium, nitrogen or hydrogen, or the firing may be effected in vacuo. |
