Electrical contact material and production method therefor

Abstract

An electrical contact material (1) according to the present disclosure includes: Ag that is a conductive component phase (11); and complex-oxide particles (12) that contain complex oxides that are an arc-resistant component oxide that is an oxide of an arc-resistant component element that inhibits consumption of the conductive component phase (11) during arc generation, and a rare earth oxide that is an oxide of a rare earth element having a work function lower than the work functions of the conductive component phase (11) and the arc-resistant component oxide. The complex-oxide particles (12) are dispersed in the conductive component phase (11).

Description

Electrical contact material and method for producing the same

[0001] The present disclosure relates to an electrical contact material and a method for manufacturing the same, which diverts an arc when an arc occurs to an arc-extinguishing component located near the electrical contact.

[0002] Various materials have been proposed as electrical contact materials for use in air circuit breakers, switches, relays, and the like. Patent Document 1 discloses an electrical contact material in which alkaline earth metal oxides such as CaO (calcium oxide), BaO (barium oxide), and SrO (strontium oxide) are added to an Ag (silver)-Gr (graphite)-based contact. These alkaline earth metal oxides have much lower work functions than Ag and graphite. Specifically, the work function of CaO is 1.6 eV, the work function of BaO is 1.1 eV, and the work function of SrO is 1.27 eV. By dispersing such alkaline earth metal oxides with low work functions in the electrical contact material, arcs are dispersed when the electrical contact is opened or closed. It is described that this results in an electrical contact material with excellent wear resistance.

[0003] JP 2015-165041 A

[0004] However, the electrical contact material described in Patent Document 1 contains alkaline earth metal oxides such as CaO, BaO, and SrO, which have the problem that these alkaline earth metal oxides easily react with moisture in the air to form hydroxides or react with carbon dioxide in the air to turn into carbonate compounds. Furthermore, the graphite and alkaline earth metal oxides in the electrical contact material are physically separated. Therefore, when an arc occurs, there are problems in that some areas on the contacts are easy to commutate the arc and other areas are difficult to commutate.

[0005] The present disclosure has been made in view of the above, and aims to provide an electrical contact material that can make the ease of commutating an arc on its surface more uniform than before, while suppressing reaction with moisture and carbon dioxide in the air.

[0006] In order to solve the above-mentioned problems and achieve the object, the electrical contact material according to the present disclosure comprises Ag as a conductive component phase, an arc-resistant component oxide which is an oxide of an arc-resistant component element that suppresses consumption of the conductive component phase when an arc occurs, and a rare earth oxide which is an oxide of a rare earth element having a work function lower than the work functions of the conductive component phase and the arc-resistant component oxide, and the double oxide particles are dispersed within the conductive component phase.

[0007] The electrical contact material according to the present disclosure has the effect of suppressing reaction with moisture and carbon dioxide in the air, while making it possible to more uniformly commutate an arc on the surface than ever before.

[0008]

[0009] Hereinafter, an electrical contact material and a method for producing the same according to an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0010] Embodiment 1. Ag-SnO2 (tin oxide) is one of the electrical contact materials used in electrical contacts for power distribution control devices such as air circuit breakers, switches, and relays. In Ag-SnO2 electrical contact materials, Ag is the conductive component, and SnO2 is the arc-resistant component. Unlike pure metal electrical contacts such as Ag-Cu (copper) and Ag-Ni (nickel), Ag-SnO2 offers superior welding and arc resistance, making it widely used in power distribution control devices with rated currents of 50 A or more. Furthermore, SnO2 has a higher decomposition temperature than CdO (cadmium oxide) and ZnO (zinc oxide). While SnO2 offers superior wear resistance among oxide-based electrical contact materials, it also has the disadvantage of easily remaining on the surface of the electrical contact, increasing the contact resistance of the electrical contact.

[0011] Considering the tendency for contact resistance to increase in electrical contacts made of Ag-SnO2, it is desirable to commutate the arc to an arc-extinguishing component, such as an arc runner, as quickly as possible during interruption without allowing the arc to stick on the electrical contacts. To efficiently commutate an arc generated between electrical contacts, it is necessary to move the arc to the arc runner while maintaining its stability. Typically, the electrical contact material evaporates from the surface of the electrical contact as a metal vapor to maintain the arc. However, while a large amount of evaporated metal vapor facilitates arc maintenance, it also increases contact wear. Therefore, adding a material with excellent thermionic emission and a lower work function than the conductive component Ag and the arc-resistant component SnO2 can be considered to maintain the arc while reducing contact wear. Metal oxides, metal carbides, and metal borides are compounds with lower work functions than pure metals, such as Ag, Cu, and W (tungsten), which are commonly used in electrical contacts. Among these, the work functions increase in the order of alkaline earth metal oxides such as BaO and SrO, metal borides such as LaB6 (lanthanum hexaboride), and metal carbides such as WC (tungsten carbide). Hereinafter, a material with a work function lower than the work functions of the conductive and arc-proof components will be referred to as a "low work function." In order to maintain and commutate the arc, it is desirable to increase the amount of low work function material added.

[0012] FIG. 1 is a schematic diagram showing an example of the structure of an electrical contact material made of Ag—SnO containing a low work function component before and after arc generation. The electrical contact material 100 includes a conductive component phase 111 that stably maintains an arc when an arc is generated, arc-resistant component particles 112 that suppress wear of the electrical contact material when an arc is generated, specifically wear of the conductive component phase 111 when an arc is generated, and low-work-function component particles 113 that commutate the arc when an arc is generated. An example of the conductive component phase 111 is Ag. An example of the arc-resistant component particles 112 is SnO. An example of the low-work-function component particles 113 in the example shown in FIG. 1 is an alkaline earth metal oxide. In one example, the conductive component phase 111 is composed of a plurality of conductive component particles.

[0013] Before an arc occurs, as shown in the diagram on the left, in the electrical contact material 100, arc-proof component particles 112 and low-work-function component particles 113 are dispersed in the conductive component phase 111. In other words, the arc-proof component particles 112 and the low-work-function component particles 113 are physically dispersed. When viewed microscopically, the low-work-function component particles 113 are located farther apart from the arc-proof component particles 112. When the arc-proof component particles 112 and the low-work-function component particles 113 are physically separated in this way, there will be locations on the electrical contact material 100 where it is easy to commutate the arc and locations where it is difficult to commutate the arc. 1 , when the surface of the electrical contact material 100 melts and resolidifies due to the arc, the conductive component phase 111, the arc-resistant component particles 112, and the low-work-function component particles 113 also melt and resolidify to form the conductive component phase 111a, the arc-resistant component particles 112a, and the low-work-function component particles 113a, respectively. Because the arc-resistant component particles 112a and the low-work-function component particles 113a melt and resolidify, the surface shape, specifically the interface shape between the arc-resistant component particles 112a and the low-work-function component particles 113a and the conductive component phase 111a, becomes complex. Conventionally, the arc-resistant component particles 112a and the low-work-function component particles 113a remain physically separated even after the arc occurs.

[0014] Thus, simply adding low-work-function component particles 113 to the electrical contact material 100 containing the arc-proof component particles 112 results in some areas on the surface of the electrical contact material 100 where arc commutation is easy and other areas where it is difficult. Furthermore, because the low-work-function component particles 113 are composed of alkaline earth metal oxides, these alkaline earth metal oxides react with moisture and carbon dioxide in the air to form hydroxides or change into carbonate compounds. Therefore, in the present disclosure, the arc-proof component particles 112 and the low-work-function component particles 113 are oxides, and a composite oxide composed of these oxides is dispersed in the conductive component phase 111.

[0015] FIG. 2 is a diagram schematically illustrating an example of the structure of the electrical contact material according to the first embodiment before and after arc generation. As shown in the left diagram of FIG. 2, the electrical contact material 1 includes a conductive component phase 11 and composite oxide particles 12 that suppress wear of the electrical contact during arc generation and commutate the arc. That is, the composite oxide particles 12 contain an arc-resistant component element and a low-work-function component element. An example of the conductive component phase 11 is Ag. The composite oxide particles 12 are composite oxide particles that contain an arc-resistant component oxide, which is an oxide of an arc-resistant component element that suppresses wear of the conductive component phase 11 during arc generation, mixed with a rare earth oxide that serves as a low-work-function component having a work function lower than that of the conductive component phase 11 and the arc-resistant component oxide. An example of the arc-resistant component oxide is SnO. In this case, the arc-resistant component element is Sn. The rare earth oxide is an oxide of a rare earth element. The composite oxide is also referred to as a mixed oxide. The composite oxide particles 12 are dispersed in the conductive component phase 11. In other words, unlike the case of FIG. 1, the arc-resistant component oxide and the low-work-function rare earth oxide are not separated, but form a composite oxide. After an arc is generated, as shown in the right diagram of FIG. 2, the conductive component phase 11 and composite oxide particles 12 that constitute the surface of the electrical contact material 1 melt and resolidify, becoming the conductive component phase 11a and composite oxide particles 12a, respectively. The conductive component phase 11a and composite oxide particles 12a have the same composition and crystal structure as the conductive component phase 11 and composite oxide particles 12, respectively. However, while the composite oxide particles 12 have a particulate outer shape, the composite oxide particles 12a have a complex surface shape due to their melting and resolidification.

[0016] In the electrical contact material 1 according to the first embodiment, the mixed oxide particles 12 are dispersed in the conductive component phase 11 before an arc is generated, as shown in the left diagram of Fig. 2 . However, even after an arc is generated, the mixed oxide particles 12a remain dispersed in the conductive component phase 11a, as shown in the right diagram of Fig. 2 . The mixed oxide and the rare earth oxide of the low-work-function component, more specifically, the mixed oxide element and the low-work-function component, are selected so that the mixed oxide remains formed without separation even when the surface of the electrical contact material 1 is melted and resolidified by an arc. This allows mixed oxide particles 12, 12a containing the low-work-function component to be uniformly distributed within the electrical contact material 1, resulting in uniform distribution of areas on the electrical contact material 1 where an arc is easily commutated. In other words, it is possible to prevent areas on the electrical contact material 1 from being divided into areas where an arc is easily commutated and areas where it is difficult to commutate. Furthermore, unlike alkaline earth metal oxides, rare earth oxides, which are low work function components, are less likely to react with moisture and carbon dioxide in the air, which improves the arc commutation performance and reduces the wear of electrical contacts.

[0017] 2 , before an arc is generated, that is, at the stage when the electrical contact material 1 is manufactured, the arc-resistant component oxide and the low-work-function rare earth oxide constitute the mixed oxide particles 12, but the electrical contact material 1 according to embodiment 1 is not limited to this form. Specifically, before an arc is generated, the arc-resistant component oxide particles and the low-work-function rare earth oxide particles may be independently dispersed in the conductive component phase 11, or after an arc is generated, the arc-resistant component oxide particles and the low-work-function rare earth oxide particles may constitute mixed oxide particles 12a, and these mixed oxide particles 12a may be dispersed in the conductive component phase 11.

[0018] FIG. 3 is a diagram showing an example of the structure of the electrical contact material according to the first embodiment before and after arc generation. Typically, when fabricating electrical contacts by powder metallurgy, Ag powder (conductive component powder) and oxide powder are mixed and compacted into a compact, which is then heated to near the melting point of Ag and sintered. If the melting points of the anti-arc component oxide and the low-work-function rare-earth oxide used are both high, a composite oxide may not be formed at a sintering temperature near the melting point of Ag. In this case, as shown in the left diagram of FIG. 3 , during fabrication of the electrical contacts, i.e., before arc generation, electrical contact material 1A contains arc-resistant component oxide particles 13 and low-work-function rare-earth oxide particles 14, which are separated within conductive component phase 11. However, the generation of a high-temperature arc, said to be above 3,000°C, melts and resolidifies the surface layer of electrical contact material 1A. As a result, as shown in the right diagram of Fig. 3, oxide particles 13 of the arc-proof component and rare earth oxide particles 14 of the low work function component are mixed to form composite oxide particles 12a in the conductive component phase 11a formed by melting and re-solidifying the conductive component phase 11. Such an electrical contact material 1A may be used in the electrical contacts of the present disclosure.

[0019] The characteristics of the mixed oxide particles 12, 12a contained in the electrical contact materials 1, 1A according to the first embodiment will be described. Table 1 shows the atomic and ionic radii of the group III rare earth elements. Examples of group III rare earth elements include Sc (scandium), Y (yttrium), La, Ce (cerium), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), and Dy (dysprosium). Table 2 shows the atomic and ionic radii of arc-resistant elements often used in arc-resistant oxides. Examples of arc-resistant elements include Zn (zinc), Sn, Ti (titanium), and Zr (zirconium). Table 3 shows the atomic and ionic radii of oxygen.

[0020]

[0021]

[0022]

[0023] Well-known double oxides include perovskite compounds such as barium titanate (BaTiO3). These compounds contain one metal element A, one metal element B, and three elements X within a unit cell, and are represented by the chemical formula ABX3. In the case of barium titanate, metal element A is Ba, metal element B is Ti, and element X is O. For perovskite compounds, the tolerance factor t is known as a condition for the formation of a perovskite structure. Here, assuming that the ionic radius of metal element A is Ra, the ionic radius of metal element B is Rb, and the ionic radius of element X is Rx, the tolerance factor t is defined by the following formula (1):

[0024] t=(Ra+Rx) / {2 1 / 2 (Rb+Rx)} ...(1)

[0025] It is known that the tolerance factor t for perovskite compounds satisfies the relationship 0.75<t<1. Perovskite compounds are made up of a combination in which the ionic radius of metal element A is large and the ionic radius of metal element B is small. For example, in BaTiO3, the ionic radius of Ba is 2.15 Å, the ionic radius of Ti is 1.4 Å, and the ionic radius of O is 0.6 Å. When the tolerance factor t is calculated according to equation (1), it becomes 0.97, a value close to 1.

[0026] In addition, in the perovskite oxide represented by ABO3, the valence of O is -2, so when the metal element A is a divalent positive ion, the metal element B must be a tetravalent positive ion. In the case of BaTiO3, the metal element A is Ba. 2+ and the metal element B is Ti 4+ Ba is an alkaline earth metal of Group II, and Ti is a metal of Group IV. When metal element A is a trivalent positive ion, metal element B is also a trivalent positive ion. When metal element A is a monovalent positive ion, metal element B is a pentavalent positive ion.

[0027] As an example of the first embodiment, a case is proposed in which metal element A is Sn and metal element B is La. However, since Sn is a group IV element and forms a tetravalent positive ion, and La is a group III element and forms a trivalent positive ion, even if oxides are combined, they do not meet the conditions for forming a perovskite. However, as shown in Tables 1 and 2, the difference in the size of the ionic radius is a significant indicator of the ease with which oxides are combined.

[0028] The electrical contact materials 1 and 1A according to the first embodiment contain, as main components, a double oxide ABO formed from an oxide of a rare earth element, which is a metal element A having a large ionic radius that satisfies the tolerance factor t of t>0.8, and a metal element B, which serves as an anti-arc component and has an ionic radius smaller than that of the metal element A, and Ag.

[0029] Furthermore, since a complex oxide is formed, if the amount of rare earth oxide is small compared to the amount of arc-resistant component oxide, the arc commutation performance during interruption is difficult to achieve. For this reason, a certain amount of rare earth oxide must be added as a low work function component.

[0030] Below are calculated tolerance factors t for combinations of rare earth oxides of low work function components and oxides of anti-arc components. For the material combinations shown below, the tolerance factor t satisfies 0.75<t<1, so these material combinations are candidates for the composite oxide particles 12, 12a in the electrical contact materials 1, 1A. La2O3 and SnO2: t=0.88 CeO2 and SnO2: t=0.845 Sm2O3 and SnO2: t=0.845 La2O3 and ZnO: t=0.92 CeO2 and ZnO: t=0.89 Y2O3 and SnO2: t=0.85

[0031] As will be shown in the following second to fourth embodiments, among these, combinations of rare earth oxides and anti-arc component oxides with a tolerance factor t of 0.85 or more and less than 1 tend to form double oxides.

[0032] The electrical contact material 1, 1A according to the first embodiment includes a conductive component phase 11 (Ag) and composite oxide particles 12 formed from an oxide of an arc-resistant component and a rare earth oxide of a low work function component. Thus, since the first embodiment does not use an alkaline earth metal oxide, the reaction of the electrical contact material 1, 1A with moisture and carbon dioxide in the air can be suppressed. Furthermore, the oxide of the arc-resistant component and the rare earth oxide of the low work function component form a composite oxide that is uniformly distributed within the conductive component phase 11. Therefore, composite oxide particles 12, 12a containing the low work function component are uniformly present at every location on the surface of the electrical contact material 1, 1A, facilitating arc commutation. In other words, unlike conventional techniques, the surface of the electrical contact material 100 does not have a mixture of areas where arc commutation is easy and areas where arc commutation is difficult. Therefore, the ease of arc commutation on the surface of the electrical contact material 1, 1A can be made more uniform than in the past. This has the effect of enhancing the arc commutation effect.

[0033] Furthermore, the rare earth oxide of the low work function component is an oxide of a rare earth element which is metal element A, and the arc-proof component oxide is an oxide of metal element B, and when the ionic radii of metal element A and metal element B are Ra and Rb, respectively, and the ionic radius of oxygen is Rx, the tolerance factor expressed by formula (1) is 0.85 or more and less than 1. This makes it possible for metal element A and metal element B to form a double oxide, which has the effect of suppressing reaction with moisture and carbon dioxide in the air while making it easier to commutate an arc on the surface more uniform than before.

[0034] Embodiment 2 In Embodiment 2, conditions under which an electrical contact material 1 can be formed having mixed oxide particles 12 selected from a combination of an arc-resistant component oxide containing Sn, which is the arc-resistant component element shown at the end of Embodiment 1, and a rare earth oxide of a low work function component element containing La, Ce or Sm, which is a low work function component element, will be described.

[0035] Here, we will first describe an example of a method for manufacturing the electrical contact material 1, and then the method and results of an interruption test using an electrical contact made of the electrical contact material 1. First, the conductive component powder constituting the conductive component phase 11, which are raw materials for the electrical contact material 1, the anti-arc component oxide powder, and the rare earth oxide powder of the low work function component are weighed.

[0036] Specifically, Ag powder with an average particle size of 4 μm, SnO powder with an average particle size of 1 μm, and rare earth oxide powder were prepared as raw materials for electrical contact material 1. The rare earth oxide powders were LaO powder with an average particle size of 1.5 μm, CeO powder with an average particle size of 3 μm, or SmO powder with an average particle size of 3 μm. Table 4 shows the volume and mass proportions of the raw materials for the electrical contact materials in Examples 1 to 4 and Comparative Examples 1 to 15. As shown in Table 4, each powder was weighed so that the amount of Ag added was constant at 75 vol% and the total amount of SnO powder and rare earth oxide powder was 25 vol%.

[0037]

[0038] Next, the weighed conductive component powder, anti-arc component oxide powder, and low work function rare earth oxide powder are mixed together. In one example, a combination of Ag powder, SnO powder, and rare earth oxide powder, and a combination of only Ag powder and SnO powder, are mixed using a dry mixer for 30 minutes each.

[0039] The mixed powder is then filled into a mold and compacted under a predetermined compacting pressure. In one example, after the powder is mixed, the powder is filled into a graphite mold. FIG. 4 shows an example of the configuration of a graphite mold. The graphite mold 30 includes a die 31, an upper punch 32, and a lower punch 33, which are separated from each other. The die 31 is provided with a through-hole 31a that accommodates the powder to be compacted and allows the upper punch 32 and the lower punch 33 to be inserted therein. The diameter of the through-hole 31a is, for example, 15 mm. The die 31 is provided with a small hole 31b for a thermocouple that measures temperature. A thermocouple 34 is inserted into this small hole 31b. The thermocouple 34 is installed at a distance so that the tip of the thermocouple 34 does not come into direct contact with the powder.

[0040] 5 to 11 are cross-sectional views showing an example of the procedure for filling a graphite mold with powder in the manufacturing method for an electrical contact material according to the second embodiment. As shown in FIG. 5, a space 35 for filling the powder is formed by the die 31 of the graphite mold 30 and a lower punch 33 inserted into a through-hole 31a provided in the die 31. At this time, the surface of the graphite mold 30 that comes into contact with the powder is sprayed with BN (boron nitride) to prevent the powder from adhering during the molding process. As shown in FIG. 6, a mixed powder 51 containing Ag powder, SnO powder, and rare earth oxide powder, or a mixed powder 51 containing Ag powder and SnO powder, is filled into the space 35 formed by the die 31 and the lower punch 33 of the graphite mold 30. An amount of mixed powder 51 is filled into the space 35 so that the thickness of the completed electrical contact will be 2 mm. Thereafter, as shown in FIG. 7, excess mixed powder 51 present above the top surface of the die 31 is leveled off using a leveling plate 36. This makes the surface of the mixed powder 51 filled in the space 35 flat.

[0041] Next, as shown in FIG. 8 , the lower punch 33 is lowered a predetermined distance to form a gap 35 a above the mixed powder 51 in the die 31. Thereafter, as shown in FIG. 9 , only Ag powder 52 is filled into the gap 35 a formed in the die 31. At this time, the Ag powder 52 spread on top of the mixed powder 51 is weighed so that the thickness is 1 / 10 of the thickness of the contact layer formed by sintering the mixed powder 51. Next, as shown in FIG. 10 , the excess Ag powder 52 present above the upper surface of the die 31 is leveled off using a leveling plate 36. This flattens the surface of the Ag powder 52 filled into the gap 35 a. Thereafter, as shown in FIG. 11 , the upper punch 32 is placed over the Ag powder 52. When this is sintered, a two-layered compact 53 is formed.

[0042] Next, the mixed powder 51 is sintered at a predetermined sintering temperature while applying pressure to form a sintered body. In one example, a graphite mold 30 filled with the mixed powder 51 and the Ag powder 52 is placed in an SPS apparatus. Figure 12 is a schematic diagram illustrating an example of sintering in an SPS apparatus. The SPS apparatus 60 includes a vacuum chamber 61, an upper electrode 62, and a lower electrode 63. The graphite mold 30 is introduced into the vacuum chamber 61 and sandwiched between the upper electrode 62 and the lower electrode 63. A preload of approximately 3 kN is applied to the graphite mold 30 by the upper electrode 62 and the lower electrode 63, temporarily fixing it in place. The vacuum chamber 61 is then evacuated using a vacuum pump (not shown), and the process waits until a vacuum of 15 Pa or less is reached. A rotary pump or a mechanical booster pump can be used as the vacuum pump.

[0043] Next, the pressure between the upper punch 32 and the lower punch 33 of the graphite mold 30 is increased to 7 kN. As a result, the pressure applied to the 15 mm diameter graphite mold 30 becomes approximately 40 MPa. Furthermore, current is passed between the upper electrode 62 and the lower electrode 63 to heat the compact 53. In one example, the compact 53 is heated at a temperature increase rate of 20°C / min. When the temperature reaches 850°C, it is held at 850°C for 10 minutes, and then the current is stopped to allow the temperature to decrease. The maximum voltage during current application is approximately 2.5 V, and the current is approximately 500 A. When the mixed powder 51 is composed of only Ag powder and SnO2 powder, sintering is performed at 850°C. However, when the mixed powder 51 is a mixture of Ag powder, SnO powder, and rare earth oxide powder, and the mixing ratio of SnO powder to rare earth oxide powder is 10:15 or 15:10, Ag begins to melt at 850° C., so the temperature is lowered to 830° C. for sintering, and the compact 53 becomes a sintered body.

[0044] After waiting for the temperature measured by thermocouple 34 to cool to 50°C or less, graphite mold 30 is removed from vacuum chamber 61, and the sintered body is then removed from graphite mold 30. Fig. 13 is a perspective view showing an example of the configuration of a sintered body made of the electrical contact material according to embodiment 2. As shown in Fig. 13, sintered body 70, which is sintered powder, is composed of a contact layer 71 formed by sintering mixed powder 51 and an Ag layer 72 formed by sintering Ag powder 52. In the state removed from graphite mold 30, the Ag layer 72 is on the upper side and the contact layer 71 is on the lower side, but Fig. 13 shows sintered body 70 upside down.

[0045] The following describes a procedure for cutting electrical contacts from a sintered body 70 made of the electrical contact material 1 shown in FIG. 13 , manufacturing a circuit breaker using the cut electrical contacts, and conducting an evaluation test of the electrical contacts. FIG. 14 is a diagram showing an example of an electrical contact made from the electrical contact material according to embodiment 2. After manufacturing the sintered body 70, the sintered body 70 is machined to obtain electrical contacts. In one example, two rectangular electrical contacts 80 are cut out from the finished sintered body 70 shown in FIG. 13 using an electric discharge machine, as shown in FIG. 14 . The electrical contacts 80 each have a rectangular plate-shaped contact layer 81 formed by sintering the mixed powder 51, similar to the sintered body 70, and a rectangular plate-shaped Ag layer 82 formed by sintering Ag powder 52 on one side of the contact layer 81. In one example, the electrical contacts 80 are cut out to a size of 5.5 mm × 7 mm. Note that the scale of FIG. 13 is different from the scale of FIG. 14 .

[0046] Then, the fixed electrode and the movable electrode are manufactured using the electrical contact 80. A method for manufacturing the fixed electrode will now be described. FIGS. 15 and 16 are diagrams schematically illustrating an example of the steps of the method for manufacturing the fixed electrode. FIG. 15 is a perspective view, and FIG. 16 is a cross-sectional view. As shown in FIG. 15 , a copper base 91 made of a rectangular copper block is prepared. The copper base 91 is an electrode block that constitutes part of the fixed electrode and the movable electrode of the circuit breaker. A screw hole (not shown) is drilled into a first surface 91 a of the copper base 91. The dimensions of the copper base 91 are, for example, 14 mm × 14 mm × 10 mm. For example, the diameter of the screw hole is M8. The electrical contact 80 carved out in FIG. 14 is fixed to a second surface 91 b of the copper base 91 opposite the first surface 91 a, i.e., the second surface 91 b facing the first surface 91 a. In one example, the brazing filler metal 92 is placed on the second surface 91b of the copper pedestal 91, and the brazing filler metal 92 is sandwiched between the rectangular electrical contact 80 and the copper pedestal 91 so that the Ag layer 82 side of the rectangular electrical contact 80 faces the brazing filler metal 92. Then, the rectangular electrical contact 80 is brazed to the second surface 91b of the copper pedestal 91 by electrical heating. The brazing filler metal 92 may be a silver brazing filler metal such as BAg7 or a phosphorus copper brazing filler metal such as BCuP5.

[0047] Next, as shown in FIG. 16 , the copper base 91 with the brazed electrical contacts 80 is fixed to a square bar 93 that constitutes part of the fixed electrode. The square bar 93 has a rectangular parallelepiped shape extending in one direction and is made of a conductive material such as copper. A screw hole 93a is drilled at one end of the square bar 93 at the position where it will be connected to the copper base 91. The diameter of the screw hole 93a is, for example, M8. In this example, the screw hole 93a penetrates the square bar 93. The copper base 91 and the square bar 93 are aligned, and a screw 94, which serves as a fixing member, is threaded from the screw hole 93a in the square bar 93 to the screw hole 91c in the copper base 91, thereby fixing the copper base 91 to the square bar 93. In this manner, the fixed electrode is manufactured.

[0048] Here, the manufacturing method of the fixed electrode has been given as an example, but the movable electrode is also manufactured in the same way by fixing a copper base 91 to which an electrical contact 80 is brazed to a square bar that forms part of the movable electrode using a screw 94.

[0049] FIG. 17 is a diagram illustrating an outline of an opening operation test device. Hereinafter, the electrical contact 80 attached to the fixed electrode 98 will be referred to as electrical contact 80a, and the electrical contact 80 attached to the movable electrode 99 will be referred to as electrical contact 80b. The opening operation test device 150 is a simple test device that starts current flow with electrical contact 80b and electrical contact 80a in contact and then breaks the current by opening electrical contact 80b relative to electrical contact 80a. In the movable electrode 99, a copper base 91 is fixed to a square bar 95, and a rotating shaft 95a is attached to the square bar 95. The electrical contact 80b of the movable electrode 99 is rotated in an arc around the rotating shaft 95a to open the contacts. In a stationary state, a pressure spring 155, which is a tension spring and attached to the movable electrode 99, presses electrical contact 80b and electrical contact 80a with a constant force. An opening mechanism utilizing an electromagnet 154 is attached to the movable electrode 99 on the opposite side of the rotation axis 95a from the electrical contact 80b. The opening mechanism includes the electromagnet 154, an iron plate 153, and an opening spring 156. An opening spring 156 composed of a tension spring is attached to the iron plate 153, which is attracted to the electromagnet 154, on the side opposite the attracting surface. With the iron plate 153 attracted by the electromagnet 154, the opening spring 156 is tensioned to store energy. However, because there is a small gap between the iron plate 153 and the movable electrode 99, the electrical contacts 80a and 80b remain pressed against each other by the contact pressure spring 155, even when energy is stored in the opening spring 156.

[0050] An arc runner 151 for commutating the arc is installed near the fixed electrode 98, but the electrical contact 80a and the arc runner 151 are not in direct contact. On the other hand, iron plates arranged at equal intervals on the movable electrode 99 side serve as the so-called grid 152 inside the circuit breaker arc extinguishing chamber. Current-carrying wiring is attached to the movable electrode 99, the fixed electrode 98, and the arc runner 151. A DC high-voltage power supply 164 is provided for charging the variable capacitor 163, and the variable capacitor 163 and a variable reactor 161 are connected to the DC high-voltage power supply 164. The opening operation test device 150 is designed to adjust the impedance by combining the variable capacitor 163 and the variable reactor 161 to change the test current. In the example shown in FIG. 17 , the set of the DC high-voltage power supply 164 and the variable capacitor 163 corresponds to a capacitor bank power supply. The capacitor bank power supply is a power supply that uses a DC high-voltage power supply 164 to store electric charge in a variable capacitor 163 and can pass a large current when this charge is discharged. When a DC charge is stored in the variable capacitor 163 and then discharged, an LC resonant circuit is formed by the variable reactor 161, which is a coil, and the variable capacitor 163, and an alternating current is generated artificially. The artificially generated alternating current is used as the test current.

[0051] The test procedure for the opening operation test device 150 is as follows: switches 167 and 168 on both ends of the DC high-voltage power supply 164 are turned on to charge the variable capacitor 163. Once the variable capacitor 163 is charged, switches 167 and 168 on both ends of the DC high-voltage power supply 164 are turned off, and then the current-carrying start switch 162 on the variable reactor 161 side is turned on to start the current flow to the opening operation test device 150. To measure the current, a fixed electrode side Rogowski coil current probe 165 for measuring the current of the entire system and an arc runner side Rogowski coil current probe 166 for measuring the arc current are attached to the current-carrying wiring. When the arc commutates to the arc runner 151, the current in the wiring on the arc runner 151 side increases. Furthermore, the voltage between the fixed electrode 98 and the movable electrode 99 is measured by a high-voltage measuring voltmeter 157.

[0052] FIG. 18 is a diagram illustrating the electrical contacts opening in the contact opening operation test device. In FIG. 17 , the iron plate 153 is attracted to the electromagnet 154, and the opening spring 156 is energized. The electromagnet 154 is deenergized when the electrical contacts 80a and 80b are to be opened, i.e., when the energization start switch 162 is turned on. Then, as shown in FIG. 18 , the iron plate 153 is attracted by the opening spring 156 and moves away from the electromagnet 154, pushing the end of the rectangular bar 95 of the movable electrode 99 opposite the electrical contact 80b. Because the opening spring 156 is sufficiently stronger than the contact pressure spring 155, the electrical contacts 80a and 80b are opened. The timing of turning on the energization start switch 162 and the timing of turning off the electrical contacts 80a and 80b can be freely adjusted, for example, by using a sequencer. In addition, the contact pressure or contact-parting speed can be freely changed by replacing the contact pressure spring 155 or contact-parting spring 156 with one having a different spring constant. In the current test, the contact pressure spring 155 and contact-parting spring 156 are selected so that the contact-parting distance between the electrical contacts 80a, 80b is 30 mm, the contact pressure when the electrical contacts 80a, 80b are in contact is 10 N, and the contact-parting speed is 3 m / s.

[0053] FIG. 19 shows an example of a waveform during commutation time measurement. In this diagram, the horizontal axis represents time t, and the vertical axis represents current value I or voltage value V. FIG. 19 shows, as an example, a waveform during commutation time measurement when electrical contacts 80a and 80b are made of Ag—SnO2. Graph Io shows the time change in current flowing through the entire system. The waveform of the current flowing through the entire system is a pseudo-AC waveform created by a resonant circuit consisting of variable capacitor 163 and variable reactor 161. When electrical contacts 80a and 80b are in a closed state, in which they are in contact, current begins to flow. The half-wave time is adjusted to 8.5 ms, which is approximately the same as the 8.33 ms half-wave time of 60 Hz AC.

[0054] At timing t1, approximately 2 ms after the start of current flow and when the current is increasing toward its maximum value, current flow to electromagnet 154 is turned off so that electrical contacts 80a, 80b begin to separate. Immediately after the contact separation begins, that is, 2 ms after the start of current flow, as shown in graph Vc, a voltage begins to rise between electrical contacts 80a, 80b and an arc begins to emerge, but because the distance between electrical contacts 80a, 80b is still small, almost no current commutation to arc runner 151 occurs, as shown in graph Iar.

[0055] When the first half-wave of the current flowing through the entire system ends, the polarity reverses, and the second half-wave begins, commutation to the arc runner 151 begins. At the end of the second half-wave, the current is successfully interrupted, and the current value of the current flowing through the entire system becomes zero. The time from the start of the second half-wave until the current to the arc runner 151 rises as shown in graph Iar is the commutation time Δtc. The commutation time Δtc is also referred to as the commutation start time. The arc runner 151 is positioned at the same height as the electrical contact 80a to facilitate commutation, but is spaced apart from the copper base 91 by 2 mm, for example. The grid 152, located on the movable electrode 99 side, is spaced apart from the path of the electrical contact 80b of the movable electrode 99, for example, 3 mm. During commutation time measurement, insulating tape is attached to the copper base 91 except for the electrical contacts 80a and 80b, to prevent the arc from transferring to other locations.

[0056] FIG. 20 shows an example of a waveform obtained when measuring a commutation time when the commutation time is short. In this figure, the horizontal axis represents time t, and the vertical axis represents current I or voltage V. In one example, FIG. 20 shows a waveform obtained when measuring the commutation time when the electrical contacts 80a and 80b are made of Ag—SnO—LaO, i.e., when composite oxide particles 12 composed of SnO and LaO are dispersed in a conductive component phase 11 composed of Ag. In FIG. 20, while there is still no commutation to the arc runner 151 during the first half-wave, commutation occurs shortly after the start of the second half-wave. In other words, the commutation time Δtc is shorter than in FIG. 19.

[0057] Next, the contact resistance of the electrical contacts 80a, 80b is measured before and after the electrical test. FIG. 21 is a diagram schematically illustrating an example of a method for measuring the contact resistance of electrical contacts. The resistance of the electrical contacts 80a, 80b can be measured using an opening operation test device 150. To measure the resistance of the electrical contacts 80a, 80b before and after the electrical test, the capacitor bank power supply is removed and a DC constant current power supply 181 is connected. Then, with the electrical contacts 80a, 80b closed with a contact pressure of, for example, 10 N, the resistance of the electrical contacts 80a, 80b is measured using the four-terminal method. In one example, a current of 10 A is passed between the fixed electrode 98 and the movable electrode 99 by a DC constant current power supply 181, the current flowing between the electrical contacts 80 a and 80 b is measured by an ammeter 182, and the voltage between the electrical contacts 80 a and 80 b is measured by a voltmeter 183 connected to the two copper bases 91, and the resistance of the electrical contacts 80 a and 80 b is calculated using the measured current and voltage.

[0058] Table 5 shows the results of measuring the characteristics of the electrical contacts when an interruption test was conducted for Examples 1 to 4 and Comparative Examples 1 to 15. Here, variable capacitor 163 and variable reactor 161 were adjusted so that the root mean square (RMS) value of the first half-wave of the current flowing through the entire system was 5 kA. The table summarizes the arc commutation time at each of electrical contacts 80a and 80b, the average wear of electrical contacts 80a and 80b, and the contact resistance of electrical contacts 80a and 80b before and after the test. The shapes of electrical contacts 80a and 80b after the test were measured using a laser-type non-contact three-dimensional measuring device, and the average wear of the volume of electrical contacts 80a and 80b from when they were new, i.e., before the test, was calculated. The average wear of contacts is shown here as a percentage of the average wear of electrical contacts 80a and 80b relative to their pre-test volumes. The amount of wear of the electrical contacts 80a and 80b manufactured under other conditions is shown as a contact wear ratio to Comparative Example 1, which does not contain rare earth oxides, which are low work function components.

[0059]

[0060] Referring to Table 5, the commutation times of the electrical contacts 80a, 80b containing LaO as a rare earth oxide of a low work function component in Examples 1 to 4 and Comparative Examples 2 and 3, and the electrical contacts 80a, 80b containing CeO as a rare earth oxide of a low work function component in Comparative Example 9, are shorter than those of Comparative Example 1. However, even though the electrical contacts 80a, 80b contain LaO as a rare earth oxide of a low work function component, the electrical contacts 80a, 80b of Comparative Example 2, whose volume content is lower than 5 vol%, and the electrical contacts 80a, 80b containing other rare earth oxides as rare earth oxides of a low work function component, do not show as much improvement as the electrical contacts 80a, 80b containing LaO.

[0061] When examining the changes in contact resistance before and after the interruption test, that is, the contact resistance before and after the test, it was found that before the interruption test, the CeO2-based contacts 80a, 80b containing CeO2 as a rare earth oxide of a low work function component had a slightly higher resistance value than Comparative Example 1. After the interruption test, the electrical contacts 80a, 80b made of Ag—SnO2 in Comparative Example 1 and the electrical contacts 80a, 80b made of Ag—SnO2—La2O3 in Examples 1 to 4 and Comparative Examples 2 and 3 had almost the same resistance value, but the electrical contacts 80a, 80b made of Ag—SnO2—Sm2O3 had a slightly higher resistance value than Comparative Example 1, and the electrical contacts 80a, 80b made of Ag—SnO2—CeO2 had an even higher resistance value than Comparative Example 1.

[0062] From the above, the electrical contacts 80a, 80b manufactured under the condition of adding 5 vol% to 20 vol% of LaO as a rare earth oxide with a low work function component show improvements in the commutation time and wear of the electrical contacts 80a, 80b compared to the electrical contacts 80a, 80b made of Ag—SnO in Comparative Example 1.

[0063] The electrical contacts 80a and 80b after the test were observed by cross-section SEM, and elemental analysis was performed using WDS to examine the state of the oxides. Figure 22 shows a cross-sectional SEM image of the Ag-SnO2-La2O3-based electrical contacts near the surface after the test in Example 2, manufactured under the condition of SnO2:La2O3 = 15:10, and the results of elemental mapping by WDS. The observation magnification here was 200x. Elemental mapping was performed on the area shown in the SEM image. In other words, Figure 22 shows a cross-sectional SEM image of the Ag-SnO2-La2O3-based electrical contacts 80a and 80b, along with an elemental mapping diagram of Ag, O, Sn, and La in this SEM image. As shown in Figure 22, traces of melting and resolidification on the surfaces of the electrical contacts 80a and 80b due to the arc at the time of contact opening can be seen. It can also be seen that La, Sn, and O were detected in the same location. The results are the same even when the magnification is increased to 3,000 times. In other words, it is clear that La, Sn, and O are precipitated in a mixed state, i.e., in the state of a double oxide.

[0064] FIG. 23 shows an SEM image of a cross section near the surface of an Ag-SnO-CeO electrical contact manufactured under the condition of SnO:CeO = 15:10 after testing in Comparative Example 6, and the results of elemental mapping by WDS. The observation magnification here is 1,000x. Elemental mapping was performed on the area shown in the SEM image. Also, elemental mapping of Ag is omitted in FIG. 23. That is, FIG. 23 shows SEM images of the cross section of Ag-SnO-CeO electrical contacts 80a and 80b, along with elemental mapping of O, Sn, and Ce in the SEM image. As shown in FIG. 23, Sn and Ce are present in separate locations. Therefore, Sn, Ce, and O do not form a double oxide.

[0065] FIG. 24 shows an SEM image of a cross section near the surface of an Ag—SnO—SmO electrical contact manufactured under the condition of SnO:SmO = 15:10 after testing in Comparative Example 12, and the results of elemental mapping by WDS. The observation magnification here is 500x. Elemental mapping was performed on the area shown in the SEM image. The elemental mapping results for Ag are omitted in FIG. 24. In other words, FIG. 24 shows SEM images of the cross section of Ag—SnO—SmO electrical contacts 80a and 80b, along with elemental mapping diagrams of O, Sn, and Sm in the SEM images. As shown in FIG. 24, Sn and Sm are present in separate locations. Therefore, Sn, Sm, and O do not form a double oxide.

[0066] Cross-sectional analysis of electrical contacts 80a and 80b revealed that even if a low-work-function rare-earth oxide is added, if the type and amount of rare-earth oxide added is inappropriate, the rare-earth oxide will not form a composite oxide with the arc-proof oxide within electrical contacts 80a and 80b, but will instead separate. When the rare-earth oxide and the arc-proof oxide are separated, as shown in Table 5, the commutation time does not increase. This indicates that when the rare-earth oxide is not uniformly dispersed in the arc-proof oxide, thermionic emission is not stable at each location on electrical contacts 80a and 80b, resulting in insufficient suppression of arc sticking and accelerating commutation to arc runner 151. The tolerance factor t of the electrical contacts 80a, 80b containing LaO and SnO is t = 0.88, the tolerance factor t of the electrical contacts 80a, 80b containing CeO and SnO is t = 0.845, and the tolerance factor t of the electrical contacts 80a, 80b containing SmO and SnO is t = 0.845. From this, it can be said that the tolerance factor t for forming a double oxide between a rare earth oxide of a low work function component and an oxide of an anti-arc component is preferably greater than 0.845 and less than 1.

[0067] As described above, electrical contacts 80a, 80b according to the second embodiment are composite oxides formed of LaO, a rare earth oxide with a low work function, and SnO, an oxide of an arc-proof component, and the rare earth oxide content of electrical contacts 80a, 80b is 5 vol% or more and 20 vol% or less. Furthermore, the combination of the rare earth oxide with the arc-proof component is selected so that the tolerance factor t of electrical contacts 80a, 80b is greater than 0.845 and less than 1. This configuration has the effect of suppressing reaction with moisture and carbon dioxide in the air while making it easier to commutate an arc on the surface more uniform than in the past.

[0068] Embodiment 3 In embodiment 3, conditions under which an electrical contact material 1 can be formed having mixed oxide particles 12 selected from a combination of an arc-resistant component oxide containing Zn, which is the arc-resistant component element shown at the end of embodiment 1, and a rare earth oxide of a low work function component element containing La or Ce, which is a low work function component element, will be described.

[0069] Here, we will first describe an example of a method for manufacturing the electrical contact material 1, and then describe the method and results of an interruption test using an electrical contact made of the electrical contact material 1. Note that descriptions of the same parts as those described in embodiment 2 will be omitted. First, the conductive component powder constituting the conductive component phase 11, which are raw materials for the electrical contact material 1, the anti-arc component oxide powder, and the rare earth oxide powder of the low work function component are weighed.

[0070] Specifically, Ag powder with an average particle size of 4 μm, ZnO powder with an average particle size of 1 μm, and rare earth oxide powder were prepared as raw materials for electrical contact material 1. The rare earth oxide powder was LaO powder with an average particle size of 1.5 μm or CeO powder with an average particle size of 3 μm. Table 6 shows the volume and mass proportions of the raw materials for the electrical contact materials in Examples 5 to 7 and Comparative Examples 16 to 21. As shown in Table 6, each powder was weighed so that the amount of Ag added was constant at 80 vol%, and the total amount of ZnO powder and rare earth oxide powder was 20 vol%.

[0071]

[0072] Next, the weighed conductive component powder, anti-arc component oxide powder, and low work function rare earth oxide powder are mixed. The mixed powder is then filled into a mold and compacted at a predetermined compaction pressure. In one example, a dry mixer is used to mix two powders: a combination of Ag powder, ZnO powder, and rare earth oxide powder, and a combination of only Ag powder and ZnO powder. Each is mixed for 30 minutes. After mixing, the powder is filled into a rectangular mold. FIG. 25 shows an example of the mold configuration. The mold 200 includes a die 201, an upper punch 202, and a lower punch 203, each of which is separate. The die 201 contains the powder to be compacted and has a rectangular cross-sectional through-hole 201a through which the upper punch 202 and the lower punch 203 can be inserted. In one example, the mold 200 is made of SKD (Steel Kogu Dice) 11 steel. SKD11 steel is an alloy tool steel material defined in Japanese Industrial Standards (JIS) G 4404:2015.

[0073] 26 to 33 are cross-sectional views showing an example of a procedure for filling a mold with powder in the manufacturing method of an electrical contact material according to embodiment 3. As shown in FIG. 26 , a space 205 for filling the powder is formed by a die 201 of a mold 200 and a lower punch 203 inserted into a through-hole 201 a provided in the die 201. At this time, a thin layer of lubricant is applied to the surface of the mold 200 that comes into contact with the powder to prevent the powder from adhering during the molding process. Next, as shown in FIG. 27 , a mixed powder 221 obtained by mixing Ag powder, ZnO powder, and rare earth oxide powder, or a mixed powder 221 obtained by mixing Ag powder and ZnO powder, is filled into the space 205 formed by the die 201 and the lower punch 203 of the mold 200. At this time, the mixed powder 221 is filled in an amount such that the thickness of the contact layer formed by sintering the mixed powder 221 when the electrical contact is completed is 1.5 mm. 28, the excess mixed powder 221 present above the upper surface of the die 201 is leveled off by a leveling plate 226. This makes the surface of the mixed powder 221 filled in the space 205 flat.

[0074] Next, as shown in FIG. 29 , the lower punch 203 of the mold 200 is lowered a predetermined distance to form a gap 205a above the mixed powder 221 in the die 201. Thereafter, as shown in FIG. 30 , only Ag powder 222 is filled into the gap 205a formed in the die 201. At this time, the Ag powder 222 spread on top of the mixed powder 221 is weighed so that its thickness after sintering is 1 / 10 the thickness of the contact layer. Next, as shown in FIG. 31 , excess Ag powder 222 present above the upper surface of the die 201 is leveled off using a leveling plate 226. This flattens the surface of the Ag powder 222 filled into the gap 205a. Thereafter, as shown in FIG. 32 , the upper punch 202 is placed over the Ag powder 222. Then, as shown in FIG. 33 , the mold 200 is turned upside down and compacted at a predetermined compacting pressure. In one example, the compacting pressure is 640 MPa. As a result, a two-layered compact 223 is formed.

[0075] Thereafter, the compact 223 formed from the mixed powder 221 is sintered at a predetermined sintering temperature to form a sintered body. In one example, the two-layered compact 223 removed from the mold 200 is placed on an alumina tray with the Ag layer facing downward, and heat-treated in an atmospheric furnace, which is a heat treatment device, to sinter the two-layered compact 223 to form a sintered body. In one example, sintering is performed at 940°C for two hours. After sintering, the temperature in the atmospheric furnace is sufficiently lowered to about 50°C, and the sintered body is then removed. FIG. 34 is a diagram showing an example of the configuration of a sintered body after heat treatment. As shown in FIG. 34, the removed sintered body 240 has a contact layer 241 and an Ag layer 242 formed simultaneously.

[0076] The following describes a procedure for manufacturing a circuit breaker using this sintered body 240 as the electrical contact 80 and conducting an evaluation test of the electrical contact 80. Specifically, a fixed electrode and a movable electrode constituting the circuit breaker are manufactured using the sintered body 240 as the electrical contact 80. As in the manufacturing method shown in FIGS. 15 and 16 of the second embodiment, a brazing filler metal 92 is sandwiched between the second surface 91b of the copper pedestal 91 and the Ag layer 242 of the electrical contact 80, and then the electrical contact 80 is brazed to the copper pedestal 91 by resistance heating. In addition, the copper pedestal 91 to which the electrical contact 80 is brazed is fixed, using screws 94, to a square bar 93 constituting a part of the fixed electrode, and the copper pedestal 91 is fixed to a square bar 95 constituting a part of the movable electrode.

[0077] A fixed electrode 98 having copper base 91 and square bar 93 to which electrical contact 80a is brazed, and a movable electrode 99 having copper base 91 and square bar 95 to which electrical contact 80b is brazed are attached to the electrodes of opening operation test device 150 as shown in Fig. 17, and an electrical test is performed. In one example of the electrical test, contact pressure spring 155 and opening spring 156 are selected so that the opening distance between electrical contacts 80a and 80b is 30 mm, the contact pressure when electrical contacts 80a and 80b make contact is 7 N, and the contact opening speed is 3 m / s.

[0078] Table 7 shows the measurement results of electrical contact characteristics when an interruption test was conducted for Examples 5 to 7 and Comparative Examples 16 to 21. The variable capacitor 163 and variable reactor 161 were adjusted so that the effective value of the first half-wave of the current flowing through the entire system was 3 kA. The table summarizes the arc commutation time at each of the electrical contacts 80a and 80b, the average erosion of the electrical contacts 80a and 80b, and the contact resistance of the electrical contacts 80a and 80b before and after the test. The shapes of the electrical contacts 80a and 80b after the test were measured using a laser-type non-contact three-dimensional measuring device, and the average erosion of the volume of the electrical contacts 80a and 80b from when they were new, i.e., before the test, was calculated. The average erosion of the electrical contacts is shown as a percentage of the average erosion of the electrical contacts 80a and 80b relative to their pre-test volumes. The contact erosion ratio to Comparative Example 16 shows the erosion of electrical contacts 80a and 80b manufactured under other conditions compared to the erosion of Comparative Example 16, which does not contain a rare earth oxide, a low work function component.

[0079]

[0080] Referring to Table 7, the electrical contacts 80a, 80b containing LaO as a rare earth oxide of a low work function component in Examples 5 to 7 and Comparative Example 17, and the electrical contacts 80a, 80b containing CeO as a rare earth oxide of a low work function component in Comparative Example 20, exhibited shorter commutation times than Comparative Example 16. The electrical contacts 80a, 80b manufactured under the conditions of Examples 5 to 7 containing LaO as a rare earth oxide of a low work function component and with a rare earth oxide content in the range of 5 vol% to 15 vol% exhibited less wear than Comparative Example 16. Furthermore, the electrical contacts 80a, 80b manufactured under the conditions of Examples 5 to 7 containing LaO as a rare earth oxide of a low work function component and with a rare earth oxide content in the range of 5 vol% to 15 vol% exhibited lower contact resistances before and after the interruption test than Comparative Example 16. The tolerance factor t of electrical contacts 80a, 80b containing LaO and ZnO is t = 0.92. Combined with the case of embodiment 2, it can be said that the tolerance factor t for forming a double oxide between a rare earth oxide of a low work function component and an oxide of an anti-arc component is preferably greater than 0.845 and less than 1. However, since the tolerance factor t of electrical contacts 80a, 80b containing CeO and ZnO is t = 0.89, Ce must be excluded from the metal element A. In other words, it is desirable that metal element A be a rare earth element other than Ce, and that the tolerance factor t be greater than 0.845 and less than 1.

[0081] After the test, cross sections of the electrical contacts 80a, 80b were examined by SEM observation and WDS elemental analysis, and it was confirmed that the arc-proof component ZnO and the co-added La2O3 formed a double oxide, but the arc-proof components ZnO and CeO2 did not form a double oxide. This is thought to be because, among rare earth oxides, Ce has a tetravalent valence, such as CeO2, and therefore does not form a double oxide. Therefore, the tolerance factor for the combination of CeO2 and ZnO is t = 0.89, but because the combination of CeO2 and ZnO does not form a double oxide, it is excluded from the candidates for the double oxide particles 12, 12a.

[0082] As described above, the electrical contacts 80a, 80b according to the third embodiment contain the conductive component phase 11 formed of Ag and the mixed oxide particles 12 formed of LaO, a rare earth oxide having a low work function, and ZnO, an arc-proof oxide, with the content of the rare earth oxide being 5 vol% or more and 15 vol% or less relative to the electrical contact material 1. This configuration has the effect of suppressing reactions with moisture and carbon dioxide in the air while making the ease of commutating an arc on the surface more uniform than before.

[0083] Embodiment 4 In embodiment 4, conditions for forming an electrical contact material 1 having mixed oxide particles 12 selected from a combination of an arc-resistant component oxide containing Sn, which is the arc-resistant component element shown at the end of embodiment 1, and a rare earth oxide of a low work function component element containing Y, which is a low work function component element, will be described.

[0084] Here, we will first describe an example of a manufacturing method for the electrical contact material 1A, and then describe the method and results of an interruption test using an electrical contact made of the electrical contact material 1A. Explanations of the same parts as those described in the second and third embodiments will be omitted. First, the conductive component powder constituting the conductive component phase 11, which are raw materials for the electrical contact material 1A, the anti-arc component oxide powder, and the rare earth oxide powder of the low work function component are weighed.

[0085] Specifically, the raw materials for electrical contact material 1A were prepared as follows: Ag powder with an average particle size of 4 μm, SnO powder with an average particle size of 1 μm, and Y2O3 powder with an average particle size of 7 μm. The Y2O3 powder was a rare earth oxide powder with a low work function. Table 8 shows the volume and mass proportions of the raw materials for the electrical contact materials in Examples 8 to 10 and Comparative Examples 22 to 23. As shown in Table 8, each powder was weighed so that the amount of Ag added was constant at 78 vol% and the total amount of SnO2 powder and rare earth oxide powder was 22 vol%.

[0086]

[0087] Next, the weighed conductive component powder, anti-arc component oxide powder, and low work function component rare earth oxide powder are mixed together. In one example, a combination of Ag powder, SnO powder, and YO powder, and a combination of only Ag powder and SnO powder are mixed together using a dry mixer, and each is mixed for 30 minutes.

[0088] The mixed powder is then filled into a mold and molded under a predetermined molding pressure. In one example, after mixing, mixed powder 51 and Ag powder 52 are filled into a graphite mold 30 as shown in Fig. 4 in the procedure shown in Figs. 5 to 11 to form a molded body 53. In this example, the diameter Φ of the through hole 31a of the graphite mold 30 is 15 mm. The Ag powder 52 forming the Ag layer 72 formed on the contact layer 71 formed by sintering the mixed powder 51 is weighed out to be about 1 / 10 the thickness of the contact layer 71.

[0089] Next, the mixed powder 51 is sintered at a predetermined sintering temperature while applying pressure to form a sintered body 70. In one example, a graphite mold 30 filled with the mixed powder 51 and Ag powder 52 is sintered using an SPS apparatus 60 shown in FIG. 12. Here, the pressure between the upper punch 32 and the lower punch 33 of the graphite mold 30 is set to 7 kN, and the mold is heated at a temperature increase rate of 20°C / min. Upon reaching 850°C, the mold is held at 850°C for 10 minutes, after which the current is stopped and the temperature is lowered. The maximum voltage during current application is approximately 2.5 V, and the current is approximately 500 A. When the mixed powder 51 is composed of only Ag powder and SnO2 powder, sintering is performed at 850°C. However, when the mixed powder 51 is composed of Ag powder, SnO powder, and Y2O3 powder and the mixing ratio of the SnO2 powder and the Y2O3 powder is 10:15 or 15:10, Ag begins to melt at 850° C., so the sintering temperature is lowered to 830° C. As a result, the compact 53 becomes the sintered body 70.

[0090] After waiting until the temperature measured by the thermocouple 34 has cooled to 50°C or less, the graphite mold 30 is removed from the vacuum chamber 61, and the sintered body 70 is then removed from the graphite mold 30. The completed sintered body 70 is machined using an electric discharge machine to cut out two rectangular electrical contacts 80, as shown in Fig. 14. In one example, the electrical contacts 80 are cut out to have a size of 5.5 mm x 7 mm.

[0091] The fixed electrode and movable electrode that constitute the circuit breaker are manufactured using this electrical contact 80. As in the manufacturing method shown in Figures 15 and 16 of the second embodiment, a brazing filler metal 92 is sandwiched between the second surface 91b of the copper pedestal 91 and the Ag layer 82 of the electrical contact 80, and then the electrical contact 80 is brazed to the copper pedestal 91 by resistance heating. Furthermore, the copper pedestal 91 to which the electrical contact 80 is brazed is fixed, using screws 94, to a square bar 93 that constitutes a part of the fixed electrode, and the copper pedestal 91 is fixed to a square bar 95 that constitutes a part of the movable electrode.

[0092] A fixed electrode 98 having copper base 91 and square bar 93 to which electrical contact 80a is brazed, and a movable electrode 99 having copper base 91 and square bar 95 to which electrical contact 80b is brazed are attached to the electrodes of opening operation test device 150 as shown in Fig. 17, and an electrical test is performed. In the electrical test, for example, contact pressure spring 155 and opening spring 156 are selected so that the opening distance between electrical contacts 80a and 80b is 30 mm, the contact pressure when electrical contacts 80a and 80b make contact is 10 N, and the contact opening speed is 3 m / s.

[0093] Table 9 shows the results of measuring the characteristics of the electrical contacts when interruption tests were conducted for Examples 8 to 10 and Comparative Examples 22 to 23. Table 9 summarizes the arc commutation time at each of the electrical contacts 80a and 80b, the average wear of the electrical contacts 80a and 80b, and the contact resistance of the electrical contacts 80a and 80b before and after the first and second interruption tests. During the first current application, the variable capacitor 163 and the variable reactor 161 were adjusted so that the effective value of the first half-wave of the current flowing through the entire system was 1 kA, and the first interruption test was conducted. Subsequently, with the same electrical contacts 80a and 80b in their states, the variable capacitor 163 and the variable reactor 161 were readjusted so that the effective value of the first half-wave of the current flowing through the entire system was 5 kA, and the second interruption test was conducted. The wear and resistance of the electrical contacts 80a and 80b were measured after each of the 1 kA and 5 kA interruptions. In Examples 8 to 10, the commutation time was not so short when a current of 1 kA was applied, but in the second current of 5 kA, the commutation time was clearly shorter than in Comparative Example 22, which was a condition in which no rare earth oxide was applied. In addition, the average wear of the contacts was also less than in Comparative Example 22, and the change in contact resistance was equivalent.

[0094]

[0095] Cross sections of electrical contacts 80a, 80b were examined before and after the test by SEM observation and elemental analysis using WDS. As shown in the left diagram of Fig. 3, in the contacts before the test, SnO2 of the arc-proof component oxide particles 13 and Y2O3 of the low work function component rare earth oxide particles 14 were confirmed to be present separately inside Ag, which is the conductive component phase 11. However, after the current test, as shown in the right diagram of Fig. 3, it was confirmed that SnO2 of the arc-proof component oxide particles 13 and Y2O3 of the low work function component rare earth oxide particles 14 formed composite oxide particles 12a. This is thought to be because the heat treatment below the melting point of Ag during the manufacture of the electrical contacts 80a, 80b was insufficient to form a double oxide between SnO2 and YO3. However, when the surfaces of the electrical contacts 80a, 80b were exposed to an arc during the first current test and melted and resolidified, SnO2 and YO3 formed a double oxide, which shortened the commutation time during the second current test. The tolerance factor t for electrical contacts 80a, 80b containing YO3 and SnO2 is 0.85. Combined with the cases of Embodiments 2 and 3, it can be said that the metal element A is a rare earth element excluding Ce, and the tolerance factor t for the formation of a double oxide between the rare earth oxide of the low work function component and the oxide of the arc-resistant component is preferably 0.85 or more and less than 1.

[0096] Before use, electrical contacts 80a and 80b according to the fourth embodiment have arc-resistant component oxide particles 13 and low-work-function rare-earth oxide particles 14 dispersed in conductive component phase 11. When used as a circuit breaker, arc-resistant component oxide particles 13 and low-work-function rare-earth oxide particles 14 present in portions that melt and resolidify upon exposure to an arc form a double oxide. However, to form a double oxide, the arc-resistant component elements of arc-resistant component oxide particles 13 and the rare earth elements of low-work-function rare-earth oxide particles 14 must be a combination of elements that form a double oxide. Thus, electrical contacts 80a and 80b according to the fourth embodiment have a portion melted by the arc where double oxide particles 12a containing the arc-resistant component element and the rare-earth element are present, and a portion not melted by the arc where arc-resistant component oxide particles 13 and low-work-function rare-earth oxide particles 14 are dispersed.

[0097] 1 , in which arc-resistant component particles 112 and low-work-function component particles 113 are dispersed in conductive component phase 111, as shown in the diagram on the right, even after arc generation, arc-resistant component particles 112a and low-work-function component particles 113a do not form a double oxide and remain dispersed in conductive component phase 111. This is thought to be because the combination of the arc-resistant component element constituting arc-resistant component particle 112 and the alkaline earth element constituting low-work-function component particle 113 does not form a double oxide. On the other hand, in embodiment 4, the combination of the arc-resistant component element constituting arc-resistant component oxide particle 13 and the rare earth element constituting low-work-function component rare-earth oxide particle 14 forms a double oxide. Therefore, in the portion melted by the arc, arc-resistant component oxide particle 13 and low-work-function component rare-earth oxide particle 14 can melt and resolidify to form double oxide particle 12a.

[0098] As described above, electrical contacts 80 a, 80 b according to the fourth embodiment include Ag as conductive component phase 11, arc-resistant component oxide particles 13, and low-work-function rare-earth oxide particles 14, and the arc-resistant component elements constituting arc-resistant component oxide particles 13 and the rare-earth elements constituting low-work-function rare-earth oxide particles 14 are made of materials that form a double oxide. During manufacture of electrical contacts 80 a, 80 b, arc-resistant component oxide particles 13 and low-work-function rare-earth oxide particles 14 exist separately in conductive component phase 11, and when the surfaces of electrical contacts 80 a, 80 b melt and resolidify due to an arc caused by interruption, arc-resistant component oxide particles 13 and low-work-function rare-earth oxide particles 14 form double oxide particles 12 a. In other words, arc-resistant component oxide particles 13 and low-work-function rare-earth oxide particles 14 are made of materials that form a double oxide at a temperature higher than the melting point of Ag. In this case, the rare earth oxide is YO, and the YO content can be 5 vol% or more and 15 vol% or less. With this configuration, the commutation speed is not significantly different when the first arc is generated compared to when the rare earth oxide is not present, but when the second or subsequent arcs are generated, the commutation speed is improved and the wear rate of the electrical contacts 80a, 80b is reduced. In other words, this has the effect of suppressing reactions with moisture and carbon dioxide in the air while making the ease of commutation of the arc on the surface more uniform than before.

[0099] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0100] 1, 1A, 100 Electrical contact material, 11, 11a, 111 Conductive component phase, 12, 12a Complex oxide particles, 13 Arc-resistant component oxide particles, 14 Rare earth oxide particles, 30 Graphite mold, 31, 201 Die, 31a, 201a Through hole, 31b Small hole, 32, 202 Upper punch, 33, 203 Lower punch, 34 Thermocouple, 35, 205 Space, 35a, 205a Gap, 36, 226 Leveling plate, 51, 221 Mixed powder, 52, 222 Ag powder, 53, 223 Molded body, 60 SPS apparatus, 61 Vacuum chamber, 62 Upper electrode, 63 Lower electrode, 70, 240 Sintered body, 71, 81, 241 Contact layer, 72, 82, 242 Ag layer, 80, 80a, 80b electrical contact, 91 copper base, 91a first surface, 91b second surface, 91c screw hole, 92 brazing filler metal, 93, 95 square bar, 93a screw hole, 94 screw, 95a rotating shaft, 98 fixed electrode, 99 movable electrode, 112, 112a anti-arc component particles, 113, 113a low work function component particles, 150 opening operation test device, 151 arc runner, 152 grid, 153 iron plate, 154 electromagnet, 155 contact pressure spring, 156 opening spring, 161 variable reactor, 162 current start switch, 163 variable capacitor, 164 DC high voltage power supply, 165 fixed electrode side Rogowski coil current probe, 166 arc runner side Rogowski coil current probe, 167, 168 Switch, 181 DC constant current power supply, 200 Mold.

Claims

1. An electrical contact material comprising: a conductive component phase of Ag; an arc-resistant component oxide which is an oxide of an arc-resistant component element that suppresses wear of the conductive component phase when an arc occurs; and a rare earth oxide which is an oxide of a rare earth element having a work function lower than the work functions of the conductive component phase and the arc-resistant component oxide; and complex oxide particles which are dispersed within the conductive component phase.

2. The electrical contact material according to claim 1, characterized in that, when the rare earth element contained in the rare earth oxide is A and the arc-proof component element is B, the ion radii of the rare earth element A, the arc-proof component element B and oxygen are Ra, Rb and Rx, respectively, t calculated by the following formula (1) satisfies 0.85≦t<1. t=(Ra+Rx) / {2 1 / 2 (Rb+Rx)} ...(1) 3. The electrical contact material according to claim 1 or 2, characterized in that the arc-resistant component oxide is SnO2, the rare earth oxide is La2O3, and the content of the rare earth oxide relative to the total volume of the electrical contact material is 5 vol% or more and 20 vol% or less.

4. The electrical contact material according to claim 1 or 2, characterized in that the arc-resistant component oxide is ZnO, the rare earth oxide is an oxide of La, and the content of the rare earth oxide relative to the total volume of the electrical contact material is 5 vol. % or more and 15 vol. % or less.

5. An electrical contact material comprising: a conductive component phase of Ag; arc-resistant component oxide particles which are oxides of arc-resistant components which suppress wear of the conductive component phase when an arc occurs; and rare earth oxide particles which are oxides of rare earth elements having a work function lower than the work functions of the conductive component phase and the oxide of the arc-resistant component element, wherein the arc-resistant component oxide particles and the rare earth oxide particles are dispersed in the conductive component phase, and the arc-resistant component element and the rare earth element are a combination of elements which form a double oxide.

6. The electrical contact material according to claim 5, characterized in that the arc-resistant component element and the rare earth element are a combination of the arc-resistant component element and the rare earth element such that when the conductive component phase, the arc-resistant component oxide particles, and the rare earth oxide particles are melted and re-solidified by an arc, the arc-resistant component oxide particles and the rare earth oxide particles form a double oxide.

7. The electrical contact material according to claim 5, wherein the rare earth oxide particles are Y2O3 particles, and the content of the Y2O3 particles relative to the total volume of the electrical contact material is 5 vol % or more and 15 vol % or less.

8. The electrical contact material according to claim 6, characterized in that in the portion melted and re-solidified by the arc, complex oxide particles formed of the arc-resistant component oxide particles and the rare earth oxide particles are dispersed in the conductive component phase, and in the portion not melted by the arc, the arc-resistant component oxide particles and the rare earth oxide particles are dispersed in the conductive component phase.

9. A method for producing an electrical contact material having a composite oxide particle composed of a conductive component phase of Ag, an arc-resistant component oxide which is an oxide of an arc-resistant component element that suppresses consumption of the conductive component phase when an arc occurs, and a rare earth oxide which is an oxide of a rare earth element having a work function lower than that of the conductive component phase and the arc-resistant component oxide, the method comprising the steps of: mixing a conductive component powder constituting the conductive component phase, an arc-resistant component oxide powder constituting the arc-resistant component oxide, and a rare earth oxide powder constituting the rare earth oxide to form a mixed powder; filling the mixed powder into a mold or die and molding it at a determined molding pressure to form a molded body; and sintering the molded body at a determined sintering temperature to form a sintered body.

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