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Publication numberUS2955145 A
Publication typeGrant
Publication dateOct 4, 1960
Filing dateJul 14, 1959
Priority dateJul 16, 1958
Publication numberUS 2955145 A, US 2955145A, US-A-2955145, US2955145 A, US2955145A
InventorsGustav Schrewelius Nils
Original AssigneeKanthal Ab
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Thermo-electric alloys
US 2955145 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

2,955,145 Patented Oct. 4, 1960 THERMO-ELE CTRIC ALLOYS Nils Gustav Schrewelius, Hallstahammar, Sweden, assignor to AB Kanthal, Hallstahammar, Sweden, a corporation of Sweden N Drawing. Filed .luly1'4, 1959, Ser. No. 826,916 Claims priority, application Sweden July 16, 1958 4 Claims. (Cl. "136-5) 7 This invention relates to thermo-electric alloys which are particularly suitable for use at very elevated temperatures, and which consist essentially of an intermetallic composition containing molybdenum, silicon and aluminium.

It is known (J. Appl. Phys. 24, p. 498, 1953), that MoSi within the range from -60 C. to +600 C. exhibits, with respect to platinum, a thermal which corresponds approximately to that of copper. Thus, highly temperature-resistant molybdenum disilicide can be used in a thermo-couple. It is also known (Austrian patent specification 193,632) that molybdenum disilicide with 3040% Si and various additions of other scaleresistant silicides or oxides or silicon carbide may be used in thermo-couples at elevated temperatures. Additions suggested in this patent are titanium silicide, tungsten silicide, chromiumsilicide, aluminium oxide, thorium oxide, titanium oxide, and zirconium oxide. Up to 25% of the silicon atoms of the molybdenum silicide may be replaced by carbon, boron or nitrogen.

"the thermo-electric alloys according to the present invention are distinguished from such previously known alloys in that they comprise molybdenum disilicide wherein 20-60 atomic percents of silicon have been replaced by aluminium. As a result, the crystal structure of the molybdenum disilicide, which is normally of the tetragonal C 11 lattice type, is converted entirely to the hexagonal C 40 lattice type. These lattice types are well known to those skilled in the art. (Compare Schwarzkopf et al., Refractory Hard Metals, 1953.) This conversion of the crystal structure results, surprisingly, in a considerably increased thermal for the alloys according to the present invention with respect to pure M0Si for example. Other advantages of these alloys are high mechanical strength, high oxidation resistance, and resistance to thermal shocks. By variations of the content of aluminium variations in the thermal E.M.F. can be readily obtained, and these variations are not accompanied by any significant deterioration of the mechanical or chemical properties of the alloys. In this respect, the alloys according to the present invention are distinguished from the previously known thermo-electric alloys based on molybdenum silicide.

The thermo-electric alloys according to the invention may also, if desired, comprise admixtures of other metals. Thus, up to 50 atomic percents as a maximum of molybdenum can be replaced by one or more of the metals titanium, zirconium, hafnium, tantalum, niobium, vanadium, tungsten, and chromium. The composition of the thermo-electric alloys according to the present invention may thus be expressed as wherein 0.2 x 0.6 and 0 y 0.5, and M represents one or more of the metals Ti, Zr, Hf, Ta, Nb, V, W or C1.

When the alloy contains no metal M, i.e. when y is 0,

then the alloy has the composition Mo(Si Al When a metal M is present, y preferably has a value of at least 0.05.

Thermo-couples comprising the alloys according to the invention are preferably made by a powder metallurgical process by sintering after admixture with 0.5 to 20 Wt. percent of a ceramic binding substance. Preferably, the ceramic binding substance is composed essentially of very finely powdered silica. However, it may also contain other oxides or silicon carbide. Conveniently, the final sintering is carried out in air, in which case a certain internal oxidation takes place. The ceramic component should preferably not exceed 30 percent'by weight of the material.

Thermocouples having one leg comprised of an alloy according to the invention, and another leg composed of MoSi for example, may also advantageously be used as heating resistors for producing high temperatures. In this case, the device defined by the two legs is suitably connected to serve as a thermocouple only for the short periods when the thermo-voltage is measured and to serve as an electrical heating resistor for the remaining periods. The resulting thermo-voltage may be used in practice for controlling the current supply to the resistor over a relay. Preferably the welded joint between the two legs should be disposed internally of the furnace, at or adjacent a lead-in electrode, so that it is not subjected to higher temperatures than those of the furnace room.

The following example illustrates the use of alloys according to the invention in a thermo-couple for 1600 to 1700 0:

The thermal increased regularly with the temperature and attained, inter alia, the following values:

Millivolts 800 C. 10 1000" C. 14 1200 C. l9 1400 C 24 1600 C 31 Both legs were 6 mm. cylindrical rods, made by extrusion and sintering, and joined by resistance butt welding. The most oxidation resistant negative leg may also, as an alternative, be formed as a tube which is closed at one end and surrounds the rod-shaped positive leg.

The above described leg combination may also be used as an electrical heating resistor and should then have the following dimensions: the positive leg is formed as a hair pin having one portion of 6 mm. diameter which acts as a glowing zone. One end of the loop is enlarged to 14 mm. and is long enough to extend out from the furnace as a cold lead-in electrode. The other end is Welded to a 9 mm. negative leg, which is similarly elongated to act as a cold lead-in electrode. As the alloy forming the negative leg has about half as high a specific resistance at 1600 C. as the alloy forming the positive leg, this lead-in electrode will also remain cool enough without special cooling devices. For the same reason, the welded joint will attain the same temperature as the furnace room, provided that it is disposed appropriately in the furnace, notwithstanding the fact that it is disposed adjacent the hot glowing Zone.

The alloy in accordance with the present invention described in the above example and used as the positive leg, was formed as follows; all parts being by weight; 98 parts of a metal powder made as set forth below were admixed with two parts of bentonite as a ceramic binding substance. Then this mixture was formed, dried and placedin a metal tube and sintered at 1400" C. for 30 minutes in an atmosphere of technical hydrogenl Final sintering was carriedout at 1550 C. in air for 2 minutes. The above mentionedmetal powder was of the composition (MoojjTid g)(Si0 8A1U 2 )2 and was formed in such a manner that Mo, Ti, Si and Al in theoretic quantities were heated in hydrogen gas to 1100 C. to start an exothermic reaction. The resulting sponge was then milled in a ball mill to a grain size of l-10 microns. The negative leg was formed in the same manner, using 95% MoSi and .5 bentonite.

- It'will be understood that thermocouples formed by the use of the alloys of the present invention may have' 4- in thermo-couples for elevated temperatures in oxidizing atmospheres, said alloy being of the hexagonal C 40 lattice type and having the composition (Mo M (Si 5;Al,;) Where M is at least one of the metals Ti, Zr, Hf, Nb, Ta, V, W, Cr, x has a value of 0.2 to 0.6 and y has a value of 0 to 0.5.

2. A thermo-electric alloy containing molybdenum, silicon and at least one other metal and adapted to be used in thermo-couples for elevated temperatures in oxidizing atmospheres, said alloy being ofthe hexagonal C 40 lattice type and having the composition (Mo Ti o.a o.2)z-

3. A thermo-couple having a positive leg comprising an alloy having the composition (Mo M (Si Al where M is at least one of the metals Ti, Zr, H f, Nb, Ta, V, W, Cr, x has a value of 0.2 to 0.6 and y has a value of 0 to 025, and a negative leg comprising Mosi r 4. A thermo-couple as defined in claim 3, wherein the alloy has the composition (Mo Ti )(Si Al References Cited in the file of'this'patent UNITED STATES PATENTS 2,745,928 Glasser May 5, 1955

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2745928 *Jun 3, 1953May 15, 1956American Electro Metal CorpHeater bodies and their production
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2998394 *May 25, 1960Aug 29, 1961Union Carbide CorpElectrical resistor composition
US3051924 *Jul 6, 1959Aug 28, 1962Kanthal AbSintered electric resistance heating elements and methods of producing such elements
US3072733 *Jul 17, 1961Jan 8, 1963Daizaburo ShinodaThermoelectric generator
US3248346 *Oct 16, 1962Apr 26, 1966Kanthal AbHeat-resistant and oxidation-proof materials containing molybdenum disilicide
US3256696 *Jan 29, 1962Jun 21, 1966Monsanto CoThermoelectric unit and process of using to interconvert heat and electrical energy
US3256697 *Jan 29, 1962Jun 21, 1966Monsanto CoThermoelectric unit and process of using to interconvert heat and electrical energy
US3256698 *Jan 29, 1962Jun 21, 1966Monsanto CoThermoelectric unit and process of using to interconvert heat and electrical energy
US3256699 *Jan 29, 1962Jun 21, 1966Monsanto CoThermoelectric unit and process of using to interconvert heat and electrical energy
US3256700 *Jan 29, 1962Jun 21, 1966Monsanto CoThermoelectric unit and process of using to interconvert heat and electrical energy
US3256701 *Jan 29, 1962Jun 21, 1966Monsanto CoThermoelectric unit and process of using to interconvert heat and electrical energy
US3256702 *Jan 29, 1962Jun 21, 1966Monsanto CoThermoelectric unit and process of using to interconvert heat and electrical energy
US3275572 *Oct 11, 1961Sep 27, 1966Ruben SamuelRefractory composition and electrical resistance made therefrom
US3285017 *May 27, 1963Nov 15, 1966Monsanto CoTwo-phase thermoelectric body comprising a silicon-germanium matrix
US3285018 *May 27, 1963Nov 15, 1966Monsanto CoTwo-phase thermoelectric body comprising a silicon-carbon matrix
US3285019 *May 27, 1963Nov 15, 1966Monsanto CoTwo-phase thermoelectric body comprising a lead-tellurium matrix
US3298777 *Dec 12, 1961Jan 17, 1967Du PontThermoelectric compositions of nbxta1-xsiyge2-y
US3330703 *May 18, 1962Jul 11, 1967Leon PodolskyThermoelectric elements of oriented graphite containing spaced bands of metal atoms
US3343373 *May 27, 1963Sep 26, 1967Monsanto CoTwo-phase thermo-electric body comprising a boron-carbon matrix
US3523832 *Jun 9, 1969Aug 11, 1970Siemens AgThermogenerator with germanium-silicon semiconductors
US4486651 *Jan 24, 1983Dec 4, 1984Nippon Soken, Inc.Ceramic heater
US4644133 *Feb 25, 1986Feb 17, 1987Nippondenso Co., Ltd.Ceramic heater
US5156688 *Jun 5, 1991Oct 20, 1992Xerox CorporationThermoelectric device
US5474619 *May 4, 1994Dec 12, 1995The United States Of America As Represented By The Secretary Of CommerceThin film high temperature silicide thermocouples
US6563095 *May 19, 2000May 13, 2003Sandvik AbResistance-heating element
US7164103 *Mar 7, 2003Jan 16, 2007Sandvik Intellectual Property AktiebolagElectrical heating resistance element
US8053710 *Mar 6, 2003Nov 8, 2011Sandvik Intellectual Property AktiebolagMethod of making a heating element of the molybdenum silicide type and a heating element
US20050236399 *Mar 6, 2003Oct 27, 2005Sandvik AbMethod of marking a heating element of the molybdenum silicide type and a heating element
US20050252909 *Mar 7, 2003Nov 17, 2005Jan AnderssonElectrical heating resistance element
Classifications
U.S. Classification136/239, 252/519.12, 419/19, 419/20, 136/240, 419/10, 136/236.1, 338/48
International ClassificationH01L35/12, H01L35/20
Cooperative ClassificationH01L35/20
European ClassificationH01L35/20