EP2831298B1 - Composite material - Google Patents

Description

For the production of electrical contacts in low-voltage switchgear, silver / metal and silver / metal oxide composites have proven themselves. The silver / metal composite most commonly used is silver / nickel, which has its main application at lower currents.

Certain additives, such as WO ₃ or MoO ₃ , have been proven in switching devices that have to withstand high thermal loads. AgSnO ₂ proved to be particularly suitable with these accessories in switchgear with rated currents of more than 100 A and under so-called AC4 load. At lower switching currents, however, the life of these materials is relatively short.

The AgSnO ₂ WO ₃ / MoO ₃ material is produced by powder metallurgy using the extrusion technique. The powder metallurgical production has the advantage that additives of any kind and quantity can be used. Thus, the material can be specifically optimized for certain properties, such as welding force or heating. In addition, the combination of powder metallurgy with the extrusion technology allows a particularly high efficiency in the production of the contact pieces. An internally oxidized AgSnO ₂ / In ₂ O ₃ material is also used. This material, described in DE-OS 24 28 147 , contains 5-10% SnO ₂ and 1-6% In ₂ O ₃ . A targeted change in the concentrations of the oxide additives to influence certain switching properties is often not always possible due to the oxidation kinetics.

In the DE-OS 27 54 335 a contact material is described which contains 1.6 to 6.5 Bi ₂ O ₃ and 0.1 to 7.5 SnO _{2 in} addition to silver. This material can be produced both by internal oxidation and powder metallurgy. However, such high Bi ₂ O ₃ contents lead to embrittlement, so that the material can be produced only by individual sintering, but not by the more economical extrusion technology. From the US 4,680,162 is an internally oxidized AgSnO ₂ material is known, which may contain at tin contents of more than 4.5% additions of 0.1-5 indium and 0.01-5 bismuth. The metal alloy powder is compacted and then internally oxidized. These additives inhibit the inhomogeneous oxide precipitations customary in internal oxidation. Optimal contact properties shows this Material not.

In the publication " Investigation into the Switching behavior of new Silver-Tin-Oxide Contact materials in Proc. of the 14th Int. Conf. on EI. Contacts, Paris, 1988 June 20-24, pp. 405-409 "reported on the switching behavior of powder-metallurgical electrical contacts made of silver-tin oxide, which may contain two more oxides from the series bismuth oxide, indium oxide, copper oxide, molybdenum oxide or tungsten oxide, said nothing about the exact composition of these materials.

In the US 4,695,330 describes a special process for producing an internally oxidized material with 0.5-12 tin, 0.5-15 indium and 0.01-1.5 bismuth.

The powder metallurgical production of contact materials based on silver-tin oxide by mixing the powder, cold isostatic pressing, sintering and extrusion to semi-finished is, for example, from DE 43 19 137 and DE 43 31 526 known.

From the US 4,141,727 Contact materials are known from silver containing bismuth tin oxide mixed oxide powder. Furthermore, in the DE 29 52 128 annealed the Zinnoxidpulver before mixing with silver powder at 900 ° C to 1600 ° C.

JP 50-19352 B1 shows a composite electrical contact material consisting of silver, cadmium oxide, magnesium oxide containing 0.1 to 0.3 wt .-% magnesium and tin oxide containing 2-4Gew .-% metallic tin, wherein a portion of magnesium and tin in the form of Mg ₂ SnO ₄ is present.

Due to increasing demands on the contact materials, the known materials do not always meet the requirements or for all applications.

description

1. 1. Electric, cadmium-free contact material consisting of a metal and 5 wt .-% to 60 wt .-% magnesium stannate Mg ₂ SnO ₄ , optionally optionally additionally wherein additionally oxides consisting of the group of magnesium oxide, copper oxide, bismuth oxide, tellurium oxide, tin oxide, indium oxide, tungsten oxide, molybdenum oxide, their mixed oxides or combinations thereof are contained in amounts of 0.5 wt .-% to 30 wt .-% and wherein the metal is silver or a silver alloy.
2. 2. contact material according to item 1, wherein 0.2 to 60 vol .-% magnesium stannate are included.
3. 3. Contact material according to item 1 to 2, wherein at least 60 wt .-% of the magnesium stannate present in the contact material has a particle size of 1 micron or more.
4. 4. Contact material according to one or more of the items 1 to 3, wherein the magnesium stannate present in the contact material wholly or partially has a particle size of 20 nm to 1 micron.
5. 5. Contact material according to one or more of the items 1 to 4, wherein the magnesium stannate present in the contact material wholly or partially has a particle size of 100 nm to 900 nm.
6. 6. Contact material according to one or more of items 1 to 5, obtainable by powder metallurgy production.
7. 7. Use of a contact material according to one or more of the items 1 to 11 for the production of electrical contact pieces.
8. 8. An electrical contact containing a contact material according to one or more of the items 1 to 11.
9. 9. Moving contact piece of a switching device or electrical switching device, containing an electrical contact according to item 14.
10. 10. A process for producing a contact material from the metal and magnesium stannate Mg ₂ SnO ₄ by mixing powdered magnesium stannate Mg ₂ SnO ₄ or a magnesium stannate precursor compound with the at least one metal powder and optionally the further oxides, pressing the mixture to obtain a compact and sintering the compact around a sintered compact.
11. 11. The method according to item 10, wherein the resulting sintered compact is shaped, in particular extruded, in a further process step,
12. 12. The method of item 10, wherein the sintered compact is a contact piece.
13. 13. The method of item 10, wherein the sintered article additionally contains copper oxide.
14. 14. Contact material obtainable by a method of items 10 or 11.

Detailed description

It was the object to provide a new metal composite, which shows when used as contact material in electrical switching devices over common silver-based silver-tin oxide composite materials improved burn-off behavior and a lower contact resistance. This object is achieved by a metal composite containing at least one metal and 5% to 60% by weight magnesium stannate, wherein the metal is silver or a silver alloy. Magnesium stannate, Mg ₂ SnO ₄ , is a compound known from the literature, the preparation of which is described, for example, in US Pat Materials in Electronics, 16 (2005), pages 193 to 196 . Journal of Power Sources 97-98 (2001), pages 223-225 or Ceramics International 27 (2001), pages 325 to 334 , To prepare this compound, magnesium oxide MgO and tin oxide SnO ₂ in the corresponding molar ratio (ie MgO: SnO ₂ = 2: 1) can be intensively mixed (for example by wet or dry grinding), optionally dried and then at from about 15 to about 25 hours Temperatures of about 1200 ° C to about 1600 ° C calcined. In general, there are no special requirements for the atmosphere, so that it is possible to calcine in air. In this way, a mixture of magnesium stannate and magnesium oxide can be obtained as in FIG. 1 wherein about 4.4% magnesium oxide is present with about 95.6% magnesium stannate. By using an excess of about 10% magnesium oxide, up to 98% magnesium stannate Mg ₂ SnO ₄ can be achieved. The present patent application also relates to the use of a contact material containing at least one metal and magnesium stannate, wherein the metal is silver or a silver alloy, for the production of electrical contact pieces, as well as electrical contacts comprising such a contact material as further described. The metal used is silver or silver alloys. Well suited, for example, silver-nickel alloys. Silver alone also has excellent properties for many applications. Cadmium, on the other hand, is not included and may be present in the maximum range of unavoidable impurities. Magnesium stannate may generally be used in amounts of 0.02 to 60% by volume, or 0.02% by volume, in particular 0.2% by volume, to 25% by volume, (= up to 13% by weight), in particular 2% by volume .%, to 25 vol.%, or 0.02 vol.%, in particular 0.2 vol.%, To 60 vol.%. (= to% by weight), in particular 2% by volume, up to 60% by volume. or 0.02% by volume, in particular 0.2 In one embodiment, at least 60% of the further oxide, that is, for example, the tin oxide, particle sizes of 1 .mu.m or more, which is particularly advantageous in forming processes such as by extrusion.

In one embodiment, the further oxide can also be used particle sizes of 20 nm to 2 microns or 50 nm to less than 2000 nm, in particular 100 nm to 1800 nm or 200 nm to 900 nm. In this case, advantageously 60% of the further oxide particle sizes of 100 nm to 900 nm.

The contact material can be obtained by a manufacturing method selected from powder metallurgy production, internal oxidation or combinations thereof.

In the powder metallurgy production of the material by mixing a powder of the metal or an alloy with magnesium stannate Mg ₂ SnO ₄ or a magnesium stannate precursor compound and optionally other oxides, cold isostatic pressing the powder mixture, and sintering at temperatures of about 500 ° C to about 940 ° C and optionally forming the sintered material, such as by extrusion to wires or profiles, the contact material obtained. As Magnesiumstannat precursor compound of Magnesiumstannat various compounds can be used, which decompose under the process conditions in magnesium stannate and optionally further decomposition products. The further decomposition products must either be volatile in the process conditions or be substances whose presence does not disturb the properties of the product obtained, ideally substances whose presence is desired, such as the metal used or another oxide selected from the group consisting of magnesium oxide, copper oxide, Bismuth oxide, tellurium oxide, tin oxide, indium oxide, tungsten oxide, molybdenum oxide or their combinations, their mixed oxides or combinations thereof. Suitable compounds are, for example, alkoxides of tin and magnesium, such as hexakis [μ- (2-methyl-2-propanolato)] bis [(2-methyl-2-propanolato) tin] di-magnesium, CAS no. 139731-82-1.

It is useful if the magnesium stannate used or the magnesium stannate precursor compound and / or other oxides already before mixing with the powder of the metal or an alloy such as silver powder, the desired particle size or particle size distribution, or more than 60 % By weight already before mixing with the powder of the metal or an alloy, such as In one embodiment, at least 60% of the further oxide, that is, for example, the tin oxide, particle sizes of 1 .mu.m or more, which is particularly advantageous in forming processes such as by extrusion.

In one embodiment, the further oxide can also be used particle sizes of 20 nm to 2 microns or 50 nm to less than 2000 nm, in particular 100 nm to 1800 nm or 200 nm to 900 nm. In this case, advantageously 60% of the further oxide particle sizes of 100 nm to 900 nm.

The contact material can be obtained by a manufacturing method selected from powder metallurgy production, internal oxidation or combinations thereof.

In the powder metallurgy production of the material by mixing a powder of the metal or an alloy with magnesium stannate Mg ₂ SnO ₄ or a magnesium stannate precursor compound and optionally other oxides, cold isostatic pressing the powder mixture, and sintering at temperatures of about 500 ° C to about 940 ° C and optionally forming the sintered material, such as by extrusion to wires or profiles, the contact material obtained. As Magnesiumstannat precursor compound of Magnesiumstannat various compounds can be used, which decompose under the process conditions in magnesium stannate and optionally further decomposition products. The further decomposition products must either be volatile in the process conditions or be substances whose presence does not disturb the properties of the product obtained, ideally substances whose presence is desired, such as the metal used or another oxide selected from the group consisting of magnesium oxide, copper oxide, Bismuth oxide, tellurium oxide, tin oxide, indium oxide, tungsten oxide, molybdenum oxide or their combinations, their mixed oxides or combinations thereof. Suitable compounds are, for example, alkoxides of tin and magnesium, such as, for example, hexakis [μ- (2-methyl-2-propanolato)] bis [(2-methyl-2-propanolato) tin] di-magnesium, CAS no. 139731-82-1.

It is useful if the magnesium stannate used or the magnesium stannate precursor compound and / or other oxides already before mixing with the powder of the metal or an alloy such as silver powder, the desired particle size or particle size distribution, or more than 60 % By weight already before mixing with the powder of the metal or an alloy, such as For example, silver powder, have a particle size of more than 1 micron. In this case, too fine magnesium stannate or else other oxides can be coarsened by a heat treatment in which, for example, annealed at temperatures of about 700 ° C to about 1400 ° C until more than 60 wt.% Of magnesium stannate or other oxides have a particle size of more than 1 micron. The use of these coarsened oxide powders, after sintering the compacts, provides a material which is more ductile than materials having smaller oxide particle sizes and therefore can be more easily deformed, which may be advantageous in further forming treatment, such as extrusion. In individual sintering of contacts, as described above, magnesium stannate (Mg ₂ SnO ₄ ) powders having smaller particle sizes may also be used, in which case additives such as sintering activators are advantageous, for example copper oxide CuO, nanoscale silver powder or other nanomaterials. In this case, of course, magnesium stannate can be used in which 60 wt.% Even before mixing with the metal powder have a particle size of at least 1 micron, but also magnesium stannate (Mg ₂ SnO ₄ ), in which 60% of magnesium stannate particle sizes of 50 nm to less than 1000 nm, in particular 60% of the magnesium stannate has particle sizes of 100 nm to 900 nm.

For example, when produced by internal oxidation, an alloy of silver with base metals is made pyrometallurgically and often heat-treated in pure oxygen under overpressure to form a contact material. Such methods are known from the literature and described for example in EP 1505164 and EP 0508055 ,

In the production by internal oxidation in combination with powder metallurgy production, for example, as a powder of the metal or an alloy, a metal powder may be used which is e.g. contains further oxides which have been produced by internal oxidation, such as, for example, silver containing tin oxide. The further processing then proceeds by powder metallurgy, that is to say by adding magnesium stannate and / or further oxides and / or metal powder, subsequent pressing, sintering and, if appropriate, shaping, such as, for example, Extrusion.

In one embodiment, the contact material contains in particular silver and magnesium stannate and moreover only conventional impurities. In a Embodiment contains the contact material magnesium stannate in an amount of 0.2 to 20 wt .-% and ad 100 wt .-% silver and conventional impurities.

In a further embodiment of the invention, the contact material comprises magnesium stannate which has at least 60% of a particle size of 1 μm or more, in an amount of 0.2 to 20% by weight and ad 100% by weight of silver and conventional impurities.

Examples example 1 Production of magnesium stannate

13.03 g SnO ₂ and 6.97 g MgO were weighed in and wet-ground for 2 × 5 minutes at 250 rpm (Fritsch Pulverisette 5, 2 mm ZrO ₂ balls, dry isopropanol). The powder mixture is dried in a drying oven (temperature) and then comminuted with a mortar.

The crushed powder mixture is calcined at 1400 ° C for 20 hours in air and then ground to a particle size (d50) of 2 microns (Fritsch Pulverisette 5, 2 mm ZrO ₂ spheres, dry isopropanol). By X-ray diffraction on the reaction product and Rietveld refinement, the resulting product was found to consist of 95.6% dimagnesium stannate (Mg ₂ SnO ₄ ) and 4.4% cassiterite (SnO ₂ ).

Preparation of the Contact Material Containing Mg ₂ SnO ₄

914.4 g of silver powder (Umicore, atomized silver powder, sieved to <42 microns) with 17.07 volume percent Mg ₂ SnO ₄ powder (85.6 g) in a mixing unit (MTI mixer 8 min., 1000 U / min ) mixed. The powder mixture is filled into a plastic cylindrical shape and cold isostatically pressed into a bolt at a pressure of 800 bar. This stud is sintered for 2 h at 820 ° C and then extruded.

Comparative Example ₂ Production of the Contact Material Containing SnO ₂

880 g of silver powder (same silver powder as in Example 1) are mixed with 120 g corresponding to 17.07% by volume SnO ₂ powder in a mixing unit (MTI mixer, 8 min., 1000 U / min). The powder mixture is filled into a plastic cylindrical shape and cold isostatically pressed into a bolt at a pressure of 800 bar. This stud is sintered for 2 h at 820 ° C and then extruded.

Tensile tests according to EN ISO 6892-1 were carried out with samples of both contact materials and the elongation at break for both contact materials was determined to be 27%.

From the contact materials produced contact pieces are made after extrusion (5 mm wire, semi-finished, soldered and turned off, then switched) and with these contacts switching experiments in a circuit breaker with 500 circuits, a current of 350 A and Blasfeld: 30 mT / kA performed , The results are in Figures 2 and 3 shown.

FIG. 2 shows for both contact materials, which have an oxide content of 17.07 per cent by volume, the burnup in mg per switching operation. The lower column shows the change at the fixed contact, the upper column at the moving contact. It can be seen that the magnesium stannate (Mg ₂ SnO ₄ ) and silver based contact material exhibits improved burn-off properties.

FIG. 3 shows the contact resistances in mOhms for both contact materials, which are given as mean values (in each case right column) and as 99% values. It can be seen that the averages are comparable but the 99% values are significantly lower for the magnesium stannate (Mg ₂ SnO ₄ ) and silver-based contact material and thus significantly improved over the silver-tin oxide material.

Claims (14)

1. Electrical, cadmium-free contact material consisting of a metal and 5% by weight to 60% by weight of magnesium stannate Mg₂SnO₄ and optionally additionally oxides from the group consisting of magnesium oxide, copper oxide, bismuth oxide, tellurium oxide, tin oxide, indium oxide, tungsten oxide, molybdenum oxide, mixed oxides thereof or combinations thereof in amounts of 0.5% by weight to 30% by weight, wherein the metal is silver or a silver alloy.
2. Contact material according to Claim 1, wherein 0.2 to 60 percent by volume of magnesium stannate is present.
3. Contact material according to either of Claims 1 and 2, wherein at least 60% by weight of the magnesium stannate present in the contact material has a particle size of 1 µm or more.
4. Contact material according to one or more of Claims 1 to 3, wherein all or some of the magnesium stannate present in the contact material has a particle size of 20 nm to 1 µm.
5. Contact material according to one or more of Claims 1 to 4, wherein 60% of the magnesium stannate in the contact material has a particle size of 100 nm to 900 nm.
6. Contact material according to one or more of Claims 1 to 5, obtainable by powder metallurgy production.
7. Use of a contact material according to one or more of Claims 1 to 5 for production of electrical contact parts.
8. Electrical contact comprising a contact material according to one or more of Claims 1 to 5.
9. Moving switch part of a switch device or electrical switch device, comprising an electrical contact according to Claim 8.
10. Process for producing a contact material from the metal and magnesium stannate Mg₂SnO₄ according to one or more of Claims 1 to 5 by mixing pulverulent magnesium stannate Mg₂SnO₄ or a magnesium stannate precursor compound with the metal powder and optionally the further oxides, pressing the mixture in order to obtain a compact and sintering the compact to obtain a sintered body.
11. Process according to Claim 10, wherein the sintered body obtained is formed, especially extruded, in a further process step.
12. Process according to Claim 10, wherein the sintered body is a contact part.
13. Process according to Claim 10, wherein the sintered body additionally comprises copper oxide.
14. Contact material obtainable by a process according to either of Claims 10 and 11.

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