Patent GB-496210-A (GB)
Title: Improvements in and relating to electrical resistances having negative temperature coefficients
IPC: H01B1/00
Filed: 1937-05-21
Abstract: A resistance having a substantially linear negative coefficient of resistance from 0 to 50 DEG  C. consists of tellurium, with or without an alloying of silver, formed in single crystals by progressive solidification from a molten state and annealed at between 105 and 125 DEG  C. for a time depending on the annealing temperature and the coefficient required.  In an example, an alloy of 15 per cent of silver and 85 per cent of tellurium is made by adding the silver to the molten tellurium in a porcelain crucible, the silver dissolving rapidly when tellurium is just above its melting point.  The operation is carried out in air or an oxidizing atmosphere while the mixture is stirred to promote oxidation.  The molten alloy is drawn into glass tubes by means of a partial vacuum. After progressive solidification so as to form a single crystal, it is either pushed out or the glass is dissolved by hydrofluoric acid. After heat treatment at between 115 and 125 DEG  C. for about 15 hours, an alloy is obtained which has a substantially linear temperature resistance curve from minus 40 to plus 50 DEG  C.  The negative temperature coefficient is from 1,2 to 1,3 per cent per degree according to the annealing temperature employed.  The alloy is made in the form of single crystal rods by passing the glass tubes containing the molten alloy from a furnace at 480 DEG  C. into an oil bath at from 25 to 100 DEG  C. at a uniform rate of 3/8 " per minute. The temperature coefficient may be reduced by reducing the annealing temperature or the annealing time, or the percentage of silver may be varied above or below 15 per cent.  For example, to obtain a negative temperature coefficient of 0,7 per cent per degree, an alloy of 15 per cent of silver and 85 per cent of tellurium may be annealed at 105 DEG  C. for about 15 hours or at 115 DEG  C. for about 4 1/4 hours.  To obtain a coefficient of 0,1 per cent, very little annealing is required.  The alloy rods may be plated at the ends with nickel or cobalt, copper terminals being soldered to the plated ends.ALSO:A resistance having a substantially linear negative coefficient of resistance from 0 to 50 DEG  C. consists of tellurium, with or without an alloying of silver, formed in single crystals by progressive solidification from a molten state and annealed at between 105 and 125 DEG  C. for a time depending on the annealing temperature and the coefficient required.  In an example, an alloy of 15 per cent of silver and 85 per cent of tellurium is made by adding the silver to the molten tellurium in a porcelain crucible, the silver dissolving rapidly when tellurium is just above its melting point.  The operation is carried out in air or an oxidizing atmosphere while the mixture is stirred to promote oxidation.  The molten alloy is drawn into glass tubes by means of a partial vacuum. After progressive solidification so as to form a single crystal, it is either pushed out or the glass is dissolved by hydrofluoric acid. After heat treatment at between 115 and 125 DEG  C. for about 15 hours, an alloy is obtained which has a substantially linear temperature resistance curve from minus 40 to plus 50 DEG  C.  The negative temperature coefficient is from 1,2 to 1,3 per cent per degree according to the annealing temperature employed.  The alloy is made in the form of single crystal rods by passing the glass tubes containing the molten alloy from a furnace at 480 DEG  C. into an oil bath at from 25 to 100 DEG  C. at a uniform rate of 3/8 per minute. The temperature coefficient may be reduced by reducing the annealing temperature or the annealing time, or the percentage of silver may be varied above or below 15 per cent.  For example to obtain a negative temperature coefficient of 0,7 per cent per degree, an alloy of 15 per cent of silver and 85 per cent of tellurium may be annealed at 105 DEG  C. for about 15 hours or at 115 DEG  C. for about 4 1/4 hours.  To obtain a coefficient of 0,1 per cent very little annealing is required.  The alloy rods may be plated at the ends with nickel or cobalt, copper terminals being soldered to the plated ends.