Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
  • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
  • B22F9/20—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from solid metal compounds
  • B22F9/22—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from solid metal compounds using gaseous reductors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F9/00—Making metallic powder or suspensions thereof
  • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
  • B22F9/30—Making metallic powder or suspensions thereof using chemical processes with decomposition of metal compounds, e.g. by pyrolysis
  • B22F9/305—Making metallic powder or suspensions thereof using chemical processes with decomposition of metal compounds, e.g. by pyrolysis of metal carbonyls
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/0466—Alloys based on noble metals
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
  • H10N10/80—Constructional details
  • H10N10/85—Thermoelectric active materials
  • H10N10/851—Thermoelectric active materials comprising inorganic compositions
  • H10N10/854—Thermoelectric active materials comprising inorganic compositions comprising only metals

Definitions

• the present invention relates to a process for the production of noble metal, especially, platinum, thermoelectric wires of improved properties.
• Noble metal thermocouples are used in large numbers for high temperature measurement.
• the positive leg is formed of an alloy of platinum with 10% of rhodium and the negative leg is formed of pure platinum.
• the main field of use is for temperature measurements over 1100 C. to over 1600 C., preferably, between 1300 C. and 1500 C. Under these conditions of use the wires of the thermocouples are sub ect to various influences which may change their mechanical and electric properties from their original values.
• thermoelectric potential of the thermocouple may be changed by the take up of impurities, for instance, from the surrounding atmosphere and/or the surrounding ceramic parts because of the indirect action of the furnace atmospheres, especially, reducing furnace atmospheres, and therefore cause errors in the temperature indicated.
• materials may be taken up which form brittle intermetallic compounds with platinum engendering wire breakage or which form low melting eutectics with the platinum leading to fusion of the wires.
• the noble metal thermoelectric wires and especially the negative leg of very pure platinum in use at the high temperatures indicated are subjected to temperatures which are substantially higher than their recrystallization temperature and therefore undergo considerable grain growth.
• thermoelectric wires This grain growth which is observed in all pure metals leads to considerable reduction in mechanical strength and in elongation on break in comparison with the wires in their as produced state in which they are fine grained. This reduction in the mechanical properties during use of the thermoelectric wires renders them more susceptible to damage. Eventually, only strong mechanical shocks or vibrations sufiice to cause breakage of the coarse crystalline platinum thermoelectric wires.
• thermocouple wires which could be used as thermocouple wires.
• the various sintering processes described either led to wires which were not suited for long use at high temperatures and which at high temperatures lose the good properties which they possess at low temperatures or their thermoelectric potential did not meet the requirements as to exactness and consistency over periods of time unless used in oxidizing atmospheres. Oxidizing atmospheres are required in view of their oxide content as, otherwise, there is the danger that the oxides might be reduced and thereby alter the electrical and/or mechanical properties to such an extent that the wires are entirely unsuitable for use in thermocouples at high temperatures.
• the process according to the invention depends upon the use of an extremely finely divided noble metal, prefrably physically pure platinum powder of a grain size of less than 10,000 mesh per cm. and a highly fissured surface as is obtained by the reduction of noble metals at low temperatures, for example, of platinum ammonium chloride with hydrogen at temperatures between 200 and 500 C., preferably, below 350 C. or at about 300 C., followed by boiling out in acidified water to remove all ammonium chloride residues and to increase the surface area of the particles and drying at low temperatures.
• the reduction also can be carried out in a liquid medium with other known chemical reducing agents or it can be carried out electrochemically.
• thermoelectric wires gas phase decompositions or reductions of, for example, platinum carbonyl chloride at as low temperatures as possible produce powders suited for the production of thermoelectric wires according to the invention.
• powders are deep black in color and have a bulk factor of, at most 35 Compacts are produced from these powders in a known manner, taking care to maintain extreme purity as every i-mpurity leads to a change in the thermoelectric properties and therefore would make the charge unusable.
• the compacts with a pressed density of about 65% are then sintered in ceramic vessels, preferably, of very pure oxides such as, for example, aluminum oxide, at temperatures corresponding to the temperatures of intended use, preferably, at 1300 to 1500 C. for 2 to 8 hours, advantageously about 6 hours.
• thermoelectric wires of a diameter, for example, 0.5 mm., for instance, by forging and/ or rolling followed by wire drawing.
• the thermoelectric wires are then given a stress relieving anmeal for to 20 minutes, preferably, for about 10 minutes at 1300 to 1500 C., preferably, 1450 C. to remove all mechanical disturbances which could change the thermoelectric potential in a non-desirable manner.
• the platinum thermoelectric wires produced according to the invention after their production have a tensile strength of kg./mm. at room temperature and an elongation on break of about and a practically structureless texture, the grain size of which cannot be determined even upon 1000 enlargement.
• Platinum thermoelectric wires produced via smelting procedures have a tensile strength of 15 kg./mm. an elongation on break of and a grain texture of 700 grains per mm.
• After heating for 400 hours in uncontaminated air at 1450 C. which is the lowest period of utility expected of a PtRh-Pt thermocouple the tensile strength at room temperature of the sintered product according to the invention is practically unchanged at 14 kg./mm. and its elongation on break is still 28%.
• a process for the production of platinum metal thermoelectric wires having high hot strength and elongation and an almost structureless texture which is maintained even after heating for 400 hours at temperatures between 1300 and 1450 C. which comprises forming the platinum metal as a finely divided powder having a grain size below 10,000 mesh per cm. directly from a platinum metal compound at a temperature below 500 C., compressing such powder to form a compact, sintering such compact at a temperature between 1300 and 1500 C., cold working the sintered compact without an intermediate anneal to wire and subjecting such wire to a stress relieving anneal at a temperature between 1300 and 1500 C.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Powder Metallurgy (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=7047720

Family Applications (1)

Country Status (5)

Citations (2)

Family Cites Families (1)

• 1964
  • 1964-02-13 DE DED43610A patent/DE1274344B/de not_active Withdrawn
• 1965
  • 1965-01-25 CH CH101465A patent/CH454488A/de unknown
  • 1965-02-04 NL NL6501410A patent/NL6501410A/xx unknown
  • 1965-02-10 BE BE659549D patent/BE659549A/xx unknown
  • 1965-02-12 US US432405A patent/US3349467A/en not_active Expired - Lifetime

Patent Citations (2)

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