Electrical contact material and method for manufacturing the same

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

[Technical Field]

[0001] The present disclosure relates to an electrical contact material for commutating an arc to an arc-extinguishing component disposed near the electrical contact when an arc is generated, and a method for manufacturing the same. [Background Art]

[0002] Various materials have been proposed as electrical contact materials used in air circuit breakers, switches, relays, and the like. Patent Document 1 discloses an electrical contact material obtained by adding an alkaline earth metal oxide such as CaO (calcium oxide), BaO (barium oxide), or SrO (strontium oxide) to an Ag (silver)-Gr (graphite) based contact. These alkaline earth metal oxides have a much lower work function 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 an alkaline earth metal oxide with a low work function in the electrical contact material, arcs are dispersed when the electrical contact is opened and closed. It is described that as a result, an electrical contact material excellent in wear resistance can be provided. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Laid-Open No. 2015-165041 [Summary of the Invention] [Problem to be Solved by the Invention]

[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 readily react with moisture in the air to form hydroxides or react with carbon dioxide in the air to transform into carbonate compounds. Furthermore, the graphite and alkaline earth metal oxides are physically separated within the electrical contact material. As a result, when an arc is generated, there is a problem that there are areas on the contact surface where the arc is easily commutated and areas where it is not easily commutated.

[0005] This disclosure has been made in view of the above, and aims to provide an electrical contact material that can make the ease of arc commutation on the surface more uniform compared to conventional materials while suppressing reactions with moisture and carbon dioxide in the air. [Means for solving the problem]

[0006] To solve the above-mentioned problems and achieve the objective, the electrical contact material according to this disclosure comprises a conductive component phase of Ag, an arc-resistant component oxide which is an oxide of an arc-resistant component element that suppresses the consumption of the conductive component phase when an arc is generated, and a rare earth oxide which is an oxide of a rare earth element having a work function lower than the work function of the conductive component phase and the arc-resistant component oxide, and the complex oxide particles are dispersed in the conductive component phase. The arc-resistant oxide component 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% to 15 vol%. [Effects of the Invention]

[0007] The electrical contact material relating to this disclosure has the effect of making the ease of arc commutation on the surface more uniform compared to conventional materials, while suppressing reactions with moisture and carbon dioxide in the air. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram schematically shows an example of the microstructure of an electrical contact material made of Ag-SnO2 containing a low work function component, before and after arc generation. [Figure 2]A schematic diagram showing an example of the microstructure of an electrical contact material before and after arc generation according to Embodiment 1. [Figure 3] A schematic diagram showing an example of the microstructure of an electrical contact material before and after arc generation according to Embodiment 1. [Figure 4] A diagram showing an example of the structure of a graphite mold. [Figure 5] A cross-sectional view showing an example of the procedure for filling a graphite mold with powder in the method for manufacturing an electrical contact material according to Embodiment 2. [Figure 6] A cross-sectional view showing an example of the procedure for filling a graphite mold with powder in the manufacturing method of an electrical contact material according to Embodiment 2. [Figure 7] A cross-sectional view showing an example of the procedure for filling a graphite mold with powder in the method for manufacturing an electrical contact material according to Embodiment 2. [Figure 8] A cross-sectional view showing an example of the procedure for filling a graphite mold with powder in the method for manufacturing an electrical contact material according to Embodiment 2. [Figure 9] A cross-sectional view showing an example of the procedure for filling a graphite mold with powder in the method for manufacturing an electrical contact material according to Embodiment 2. [Figure 10] A cross-sectional view showing an example of the procedure for filling a graphite mold with powder in the manufacturing method of an electrical contact material according to Embodiment 2. [Figure 11] A cross-sectional view showing an example of the procedure for filling a graphite mold with powder in the manufacturing method of an electrical contact material according to Embodiment 2. [Figure 12] This diagram schematically shows an example of the sintering process in a Spark Plasma Sinter (SPS) apparatus. [Figure 13] A perspective view showing an example of the structure of a sintered body composed of electrical contact material according to Embodiment 2. [Figure 14] A diagram showing an example of an electrical contact made from the electrical contact material according to Embodiment 2. [Figure 15] A schematic diagram illustrating an example of the procedure for manufacturing a fixed electrode. [Figure 16] A schematic diagram illustrating an example of the procedure for manufacturing a fixed electrode. [Figure 17] Diagram showing an overview of the open-pole operation test apparatus. [Figure 18] FIG. 1 is a diagram showing an image when an electrical contact is opened by a contact opening operation test device [Figure 19] FIG. 4 is a diagram showing an example of a waveform during commutation time measurement [Figure 20] FIG. 7 is a diagram showing an example of a waveform during commutation time measurement when the commutation time is short [Figure 21] FIG. 10 is a diagram schematically showing an example of a method for measuring contact resistance of an electrical contact [Figure 22] FIG. 13 is a diagram showing a scanning electron microscope (SEM) image of a cross-section near the surface of an Ag-SnO2-La2O3-based electrical contact after testing in Example 2 manufactured under the condition of SnO2:La2O3=15:10, and element mapping results obtained by wavelength dispersive X-ray spectroscopy (WDS) [Figure 23] FIG. 16 is a diagram showing a SEM image of a cross-section near the surface of an Ag-SnO2-CeO2-based electrical contact after testing in Comparative Example 6 manufactured under the condition of SnO2:CeO2=15:10, and element mapping results obtained by WDS [Figure 24] FIG. 19 is a diagram showing a SEM image of a cross-section near the surface of an Ag-SnO2-Sm2O3-based electrical contact after testing in Comparative Example 12 manufactured under the condition of SnO2:Sm2O3=15:10, and element mapping results obtained by WDS [Figure 25] FIG. 22 is a diagram showing an example of the configuration of a mold [Figure 26] FIG. 25 is a cross-sectional view showing an example of a procedure for filling powder into a mold in the method for manufacturing an electrical contact material according to Embodiment 3 [Figure 27] FIG. 28 is a cross-sectional view showing an example of a procedure for filling powder into a mold in the method for manufacturing an electrical contact material according to Embodiment 3 [Figure 28] FIG. 31 is a cross-sectional view showing an example of a procedure for filling powder into a mold in the method for manufacturing an electrical contact material according to Embodiment 3 [Figure 29] FIG. 34 is a cross-sectional view showing an example of a procedure for filling powder into a mold in the method for manufacturing an electrical contact material according to Embodiment 3 [Figure 30]A cross-sectional view showing an example of the procedure for filling a mold with powder in the manufacturing method of an electrical contact material according to Embodiment 3. [Figure 31] A cross-sectional view showing an example of the procedure for filling a mold with powder in the manufacturing method of an electrical contact material according to Embodiment 3. [Figure 32] A cross-sectional view showing an example of the procedure for filling a mold with powder in the manufacturing method of an electrical contact material according to Embodiment 3. [Figure 33] A cross-sectional view showing an example of the procedure for filling a mold with powder in the manufacturing method of an electrical contact material according to Embodiment 3. [Figure 34] A diagram showing an example of the structure of a sintered body after heat treatment. [Modes for carrying out the invention]

[0009] The electrical contact material and its manufacturing method according to embodiments of the present disclosure will be described in detail below with reference to the drawings.

[0010] Embodiment 1. Ag-SnO2 (tin oxide) is one of the electrical contact materials used in power distribution and control equipment such as air-insulated 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 has the advantage of superior resistance to welding and arcing, and is therefore often used in power distribution and control equipment products with a rated current of 50A or more. Furthermore, SnO2 has a higher decomposition temperature compared to CdO (cadmium oxide) and ZnO (zinc oxide), giving it the advantage of superior wear resistance among oxide-based electrical contact materials. However, it also has the disadvantage of easily remaining on the surface of the electrical contact and increasing the contact resistance of the electrical contact.

[0011] Considering that the contact resistance of electrical contacts composed of Ag-SnO2 tends to increase, it is desirable to commutate the arc to the arc extinguishing component, such as an arc runner, as quickly as possible during interruption, without allowing the arc to become stuck on the electrical contact. To efficiently commutate the arc generated between electrical contacts, it is necessary to move the arc along the electrical contact to the arc runner while maintaining the arc stably. Normally, the electrical contact material evaporates from the surface of the electrical contact as metal vapor, maintaining the arc. While a large amount of metal vapor evaporation makes it easier to maintain the arc, it also increases the wear of the electrical contact. Therefore, a method can be considered in which wear of the electrical contact is reduced while maintaining the arc by adding a material that has excellent thermionic emission properties and a lower work function compared to the conductive component Ag and the arc-resistant component SnO2. Compounds with lower work functions than pure metals such as Ag, Cu, and W (tungsten) that are commonly used in electrical contacts include metal oxides, metal carbides, and metal borides. Among these, the work function increases in the following order: alkaline earth metal oxides such as BaO and SrO, metal borides such as LaB6 (lanthanum hexaboride), and metal carbides such as WC (tungsten carbide). Below, a work function that is lower than the work functions of the conductive and arc-resistant components is referred to as "low work function." To maintain the arc and commutate, it is desirable to increase the amount of low work function material added.

[0012] Figure 1 schematically shows an example of the microstructure of an electrical contact material made of Ag-SnO2 containing a low work function component before and after arc generation. The electrical contact material 100 has a conductive component phase 111 that stably maintains the arc when an arc is generated, arc-resistant component particles 112 that suppress the consumption of the electrical contact material during arc generation, specifically the consumption of the conductive component phase 111 during arc generation, 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 SnO2. An example of the low work function component particles 113 is an alkaline earth metal oxide in the example in Figure 1. In one example, the conductive component phase 111 is composed of multiple conductive component particles.

[0013] Before arc generation, as shown in the left-hand diagram, in the electrical contact material 100, arc-resistant particles 112 and low work function particles 113 are dispersed in the conductive component phase 111. In other words, the arc-resistant particles 112 and low work function particles 113 are physically dispersed. Furthermore, microscopically, the low work function particles 113 are located at a greater distance from each other than the arc-resistant particles 112. When the arc-resistant particles 112 and low work function particles 113 are physically separated in this way, there will be areas on the electrical contact material 100 where arc commutation is easy and areas where it is difficult. Furthermore, after arc generation, as shown in the right-hand diagram of Figure 1, when the surface of the electrical contact material 100 melts and resolidifies due to the arc, the conductive component phase 111, arc-resistant component particles 112, and low work function component particles 113 also melt and resolidify, becoming the conductive component phase 111a, arc-resistant component particles 112a, and low work function component particles 113a, respectively. Because the arc-resistant component particles 112a and low work function component particles 113a melt and resolidify, the surface shape, specifically the interface shape between the arc-resistant component particles 112a and low work function component particles 113a and the conductive component phase 111a, becomes complex. Conventionally, even after arc generation, the arc-resistant component particles 112a and low work function component particles 113a maintain a physically separated state.

[0014] Thus, simply adding low work function component particles 113 to the electrical contact material 100 containing arc-resistant component particles 112 results in areas on the surface of the electrical contact material 100 that are easily commutated and areas that are not easily commutated. Furthermore, since 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 transform into carbonate compounds. Therefore, in this disclosure, the arc-resistant component particles 112 are made of oxides, and the low work function component particles 113 are made of oxides, and a complex oxide composed of these oxides is dispersed in the conductive component phase 111.

[0015] Figure 2 is a schematic diagram showing an example of the microstructure of an electrical contact material according to Embodiment 1 before and after arc generation. As shown in the left-hand diagram of Figure 2, the electrical contact material 1 comprises a conductive component phase 11 and complex oxide particles 12 that suppress wear of the electrical contacts during arc generation and commutate the arc. In other words, the complex oxide particles 12 include an arc-resistant component element, which is an arc-resistant component element, and a low-work-function component element, which is an element with a low work-function component. An example of the conductive component phase 11 is Ag. The complex oxide particles 12 are particles of a complex oxide mixture in which an arc-resistant component oxide, which is an oxide of the arc-resistant component element that suppresses wear of the conductive component phase 11 during arc generation, and a rare earth oxide, which is a low-work-function component having a work function lower than the work function of the conductive component phase 11 and the arc-resistant component oxide. An example of the arc-resistant component oxide is SnO2. In this case, the arc-resistant component element is Sn. Rare earth oxides are oxides of rare earth elements. Complex oxides are also called mixed oxides. The complex oxide particles 12 are dispersed in the conductive component phase 11. In other words, unlike in Figure 1, the arc-resistant component oxide and the low-work-function component rare-earth oxide do not separate, and a complex oxide is formed. Furthermore, after arc generation, as shown in the right-hand diagram of Figure 2, the conductive component phase 11 and complex oxide particles 12 that constitute the surface of the electrical contact material 1 melt and resolidify in the arc, becoming the conductive component phase 11a and complex oxide particles 12a, respectively. The conductive component phase 11a and complex oxide particles 12a have the same composition and crystal structure as the conductive component phase 11 and complex oxide particles 12, respectively. However, while the complex oxide particles 12 have a particulate shape externally, the complex oxide particles 12a have a complex surface shape due to melting and resolidifying.

[0016] In the electrical contact material 1 according to Embodiment 1, as shown in the left-hand diagram of Figure 2, before arc generation the complex oxide particles 12 are dispersed in the conductive component phase 11. However, as shown in the right-hand diagram of Figure 2, even after arc generation the complex oxide particles 12a remain dispersed in the conductive component phase 11a. The arc-resistant component oxide and the rare earth oxide with low work function are selected, more specifically, the arc-resistant element and the low work function element, so that even when the surface of the electrical contact material 1 melts and re-solidifies due to the arc, the arc-resistant component oxide and the rare earth oxide with low work function do not separate, and the complex oxide is maintained. As a result, the complex oxide particles 12 and 12a having the low work function element are uniformly distributed inside the electrical contact material 1, and areas where the arc is easily commutated are uniformly present on the electrical contact material 1. In other words, it is possible to suppress the presence of areas on the electrical contact material 1 where the arc is easily commutated and areas where it is not. Furthermore, unlike alkaline earth metal oxides, rare earth oxides with low work function components have their reactions with moisture and carbon dioxide in the air suppressed. This makes it possible to improve the commutation performance of the arc and reduce wear on electrical contacts.

[0017] In Figure 2, the state before arc generation, i.e., at the stage when the electrical contact material 1 was manufactured, was shown to consist of arc-resistant oxide particles and rare earth oxide particles with a low work function, forming the complex oxide particles 12. However, the electrical contact material 1 according to Embodiment 1 is not limited to this form. Specifically, before arc generation, the arc-resistant oxide particles and the rare earth oxide particles with a low work function may be independently dispersed in the conductive component phase 11. Alternatively, after arc generation, the arc-resistant oxide particles and the rare earth oxide particles with a low work function may form the complex oxide particles 12a, and these complex oxide particles 12a may be dispersed in the conductive component phase 11.

[0018] Figure 3 is a schematic diagram showing an example of the microstructure of an electrical contact material according to Embodiment 1 before and after arc generation. Normally, when fabricating electrical contacts by powder metallurgy, a compact made by mixing conductive component powders, Ag powder and oxide powder, is heated to near the melting point of Ag and sintered. In this case, if both the arc-resistant component oxide and the low-work-function component rare earth oxide used have high melting points, a complex 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 Figure 3, when fabricating the electrical contact, i.e., before arc generation, the arc-resistant component oxide particles 13 and the low-work-function component rare earth oxide particles 14 exist separately within the conductive component phase 11 of the electrical contact material 1A. However, the surface layer of the electrical contact material 1A melts and re-solidifies due to the generation of an arc at a high temperature, which is said to be over 3,000 degrees Celsius. As a result, as shown in the right-hand diagram of Figure 3, in the conductive component phase 11a, which is formed by melting and re-solidifying the conductive component phase 11, the arc-resistant component oxide particles 13 and the low-work-function component rare-earth oxide particles 14 mix to form complex oxide particles 12a. The electrical contacts of this disclosure may use such an electrical contact material 1A.

[0019] The characteristics of the complex oxide particles 12,12a contained in the electrical contact material 1,1A according to Embodiment 1 will be described. Table 1 is a table showing the atomic radius and ionic radius for the names of rare earth elements of Group III. Examples of rare earth elements of Group III 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 is a table showing the atomic radius and ionic radius for arc-resistant elements that are often used in arc-resistant oxides. Examples of arc-resistant elements include Zn (zinc), Sn, Ti (titanium), and Zr (zirconium). Table 3 is a table showing the atomic radius and ionic radius for oxygen.

[0020] [Table 1]

[0021]

Table 2

[0022]

Table 3

[0023] Well-known composite oxides include perovskite compounds such as barium titanate BaTiO₃. One unit cell of this compound contains one metal element A, one metal element B, and three elements X, and is 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 forming a stable perovskite structure. When Ra is the ionic radius of metal element A, Rb is the ionic radius of metal element B, and Rx is the ionic radius of element X, the tolerance factor t is defined by the following formula (1).

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

[0025] For perovskite compounds, it is known that the tolerance factor t substantially satisfies 0.75<t<1. In perovskite compounds, the ionic radius of metal element A is large, and the combination of the ionic radius of metal element B is small. For example, in BaTiO₃, the ionic radius of Ba is 2.15Å, the ionic radius of Ti is 1.4Å, and the ionic radius of O is 0.6Å. When the tolerance factor t is calculated according to formula (1), the value is 0.97, which is close to 1.

[0026] Furthermore, in perovskite oxides represented by ABO₃, since the valence of O is -2, if metal element A is a divalent positive ion, there is a constraint that metal element B must be a tetravalent positive ion. In the case of BaTiO₃, metal element A is Ba 2+, wherein 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 the metal element A is a trivalent positive ion, the metal element B is also a trivalent positive ion. Furthermore, when the metal element A is a monovalent positive ion, the metal element B is a pentavalent positive ion.

[0027] As an example of the first embodiment, a case where the metal element A is Sn and the metal element B is La is proposed. However, Sn is an element of group IV and forms a tetravalent positive ion, while La is an element of group III and forms a trivalent positive ion. Therefore, even when the oxides form a composite, they do not satisfy the constitutional requirements for a perovskite. However, as shown in Tables 1 and 2, the difference in ionic radius serves as a significant indicator of whether the oxides readily form a composite.

[0028] The electrical contact material 1, 1A according to the first embodiment mainly contains: a complex oxide ABO3 which is an oxide of a rare earth element, the metal element A, having a large ionic radius whose tolerance factor t satisfies t>0.8, and the metal element B, which serves as an arc-resistant component and has an ionic radius smaller than that of the metal element A; and Ag.

[0029] Furthermore, for forming the complex oxide, if the amount of rare earth oxide is very small relative to the amount of arc-resistant component oxide, arc commutation performance during interruption is difficult to develop. For this reason, a certain amount of the rare earth oxide needs to be added as a low work function component.

[0030] Calculated values of tolerance factor t for combinations of rare earth oxides, which are low work function components, and arc-resistant component oxides are shown below. In the material combinations shown below, the tolerance factor t satisfies 0.75<t<1, so these material combinations are candidates for the complex oxide particles 12, 12a in the electrical contact material 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 shown in embodiments 2 to 4 below, among these, combinations of rare earth oxides and arc-resistant component oxides with an allowable factor t of 0.85 or more and less than 1 tend to form complex oxides.

[0032] The electrical contact material 1,1A according to Embodiment 1 includes Ag, which is a conductive component phase 11, and complex oxide particles 12 formed from arc-resistant component oxides and rare earth oxides with low work function components. Thus, in Embodiment 1, since alkaline earth metal oxides are not used, the reaction of the electrical contact material 1,1A with moisture and carbon dioxide in the air can be suppressed. Furthermore, the arc-resistant component oxides and rare earth oxides with low work function components form complex oxides and are uniformly distributed within the conductive component phase 11. Therefore, since complex oxide particles 12,12a containing low work function components are uniformly present at any point on the surface of the electrical contact material 1,1A, arc commutation is made easier. In other words, unlike conventional technology, there is no mixture of areas on the surface of the electrical contact material 100 where arc commutation is easy and areas where arc commutation is difficult, and the ease of arc commutation can be made more uniform on the surface of the electrical contact material 1,1A compared to conventional methods. This has the effect of enhancing the arc commutation effect.

[0033] Furthermore, the rare earth oxide with low work function is an oxide of the rare earth element A, and the arc-resistant oxide is an oxide of the metal element B. When the ionic radii of metal elements A and B are Ra and Rb, respectively, and the ionic radius of oxygen is Rx, the allowable factor expressed by equation (1) is 0.85 or more and less than 1. This makes it possible to form a complex oxide with metal elements A and B, which has the effect of making the ease of arc commutation on the surface more uniform compared to conventional methods while suppressing reactions with moisture and carbon dioxide in the air.

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

[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 electrical contact breakup test using the electrical contacts composed of the electrical contact material 1. First, the conductive component powder, the arc-resistant component oxide powder, and the low work function component rare earth oxide powder that constitute the conductive component phase 11, which are the raw materials for the electrical contact material 1, are weighed.

[0036] Specifically, the raw materials for electrical contact material 1 are Ag powder with an average particle size of 4 μm, SnO2 powder with an average particle size of 1 μm, and rare earth oxide powder. The rare earth oxide powder is La2O3 powder with an average particle size of 1.5 μm, CeO2 powder with an average particle size of 3 μm, or Sm2O3 powder with an average particle size of 3 μm. Table 4 shows the volume and mass percentages 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 is weighed so that the amount of Ag added is kept constant at 75 vol%, and the total value of SnO2 powder and rare earth oxide powder is 25 vol%.

[0037] [Table 4]

[0038] Next, the weighed conductive component powder, arc-resistant component oxide powder, and low work function component rare earth oxide powder are mixed. In one example, a dry mixing apparatus is used to separate the mixture into two combinations: one with Ag powder, SnO2 powder, and rare earth oxide powder, and another with only Ag powder and SnO2 powder, and each is mixed for 30 minutes.

[0039] Subsequently, the mixed powder is filled into a mold and molded at a predetermined molding pressure. In one example, after mixing the powders, the powder is filled into a graphite mold. Figure 4 shows an example of the configuration of a graphite mold. The graphite mold 30 has a die 31, an upper punch 32, and a lower punch 33, each of which is separate. The die 31 is provided with a through hole 31a that accommodates the powder to be molded and into which the upper punch 32 and lower punch 33 can be inserted. In one example, the diameter of the through hole 31a is Φ15 mm. The die 31 is provided with a small hole 31b for a thermocouple to measure temperature. A thermocouple 34 is inserted into this small hole 31b. The thermocouple 34 is positioned at a distance so that its tip does not directly touch the powder.

[0040] Figures 5 to 11 are cross-sectional views showing an example of the procedure for filling a graphite mold with powder in a method for manufacturing an electrical contact material according to Embodiment 2. As shown in Figure 5, a space 35 for filling the powder is formed by the die 31 of the graphite mold 30 and the lower punch 33 inserted into the through hole 31a provided in the die 31. At this time, BN (boron nitride) spray is applied to the surface of the graphite mold 30 that comes into contact with the powder to prevent the powder from sticking during the molding process. As shown in Figure 6, a mixed powder 51, which is a mixture of Ag powder, SnO2 powder, and rare earth oxide powder, or a mixed powder 51, which is a mixture of Ag powder and SnO2 powder, is filled into the space 35 formed by the die 31 and the lower punch 33 of the graphite mold 30. At this time, an amount that will result in a thickness of 2 mm when the electrical contact is completed is filled into the space 35. After that, as shown in Figure 7, the excess mixed powder 51 that is above the upper surface of the die 31 is scraped off with a scraping plate 36. This makes the surface of the mixed powder 51 filling the space 35 flat.

[0041] Next, as shown in Figure 8, the lower punch 33 is lowered by a predetermined distance to form a gap 35a above the mixed powder 51 in the die 31. Then, as shown in Figure 9, only the Ag powder 52 is filled into the gap 35a formed in the die 31. At this time, the Ag powder 52 laid on top of the mixed powder 51 is weighed so that it is 1 / 10 the thickness of the contact layer formed by the sintering of the mixed powder 51. Next, as shown in Figure 10, the excess Ag powder 52 above the top surface of the die 31 is scraped off with a scraping plate 36. This makes the surface of the Ag powder 52 filled in the gap 35a flat. Then, as shown in Figure 11, the upper punch 32 is placed over the Ag powder 52. When this is sintered, a two-layer molded body 53 is formed.

[0042] Next, the mixed powder 51 is sintered at a predetermined sintering temperature under pressure to form a sintered body. In one example, a graphite mold 30 filled with the mixed powder 51 and Ag powder 52 is set in the SPS apparatus. Figure 12 is a schematic diagram showing an example of the sintering process in the SPS apparatus. The SPS apparatus 60 comprises 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 is sandwiched between the upper electrode 62 and the lower electrode 63. At this time, the graphite mold 30 is temporarily fixed in place by a pre-pressure of about 3kN applied by the upper electrode 62 and the lower electrode 63. After that, the inside of the vacuum chamber 61 is evacuated using a vacuum pump (not shown) and waited until the vacuum level is 15 Pa or less. A rotary pump and 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 7kN. This results in a pressure of approximately 40MPa on the Φ15mm graphite mold 30. Additionally, current is passed between the upper electrode 62 and the lower electrode 63 to heat the molded body 53. In one example, the molded body 53 is heated at a rate of 20°C / min until it reaches 850°C, where it is held for 10 minutes, after which the current is stopped to allow it to cool. The maximum voltage during current application is approximately 2.5V, and the current is approximately 500A. If the mixed powder 51 consists only of Ag powder and SnO2 powder, sintering is performed at 850°C. However, since the mixed powder 51 is a mixture of Ag powder, SnO2 powder, and rare earth oxide powder, and the mixing ratio of SnO2 powder to rare earth oxide powder is 10:15 or 15:10, the Ag begins to melt at 850°C, so the temperature is lowered to 830°C to perform sintering. As a result, the molded body 53 becomes a sintered body.

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

[0045] The following describes the procedure for cutting out electrical contacts from a sintered body 70 made of the electrical contact material 1 shown in Figure 13, manufacturing a circuit breaker using the cut-out electrical contacts, and performing an evaluation test of the electrical contacts. Figure 14 shows 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 processed to obtain the electrical contacts. In one example, two rectangular electrical contacts 80 are cut out from the finished sintered body 70 shown in Figure 13 using an electrical discharge machine, as shown in Figure 14. The electrical contact 80 has a rectangular plate-shaped contact layer 81 made of sintered mixed powder 51, similar to the sintered body 70, and a rectangular plate-shaped Ag layer 82 made of sintered Ag powder 52, which is placed on one side of the contact layer 81. In one example, the electrical contact 80 is cut out to a size of 5.5 mm × 7 mm. Note that the scale of Figure 13 and Figure 14 are different.

[0046] Then, the fixed electrode and the movable electrode are manufactured using the electrical contacts 80. Here, the method for manufacturing the fixed electrode will be described. Figures 15 and 16 are schematic diagrams illustrating an example of the procedure for manufacturing the fixed electrode. Figure 15 is a perspective view, and Figure 16 is a cross-sectional view. As shown in Figure 15, a copper base 91 made of a rectangular block of copper is prepared. The copper base 91 is an electrode block that constitutes part of the fixed electrode and the movable electrode in the circuit breaker. Screw holes (not shown) are machined into the first surface 91a of the copper base 91. In one example, the size of the copper base 91 is 14 mm × 14 mm × 10 mm. In one example, the diameter of the screw holes is M8. The electrical contacts 80 cut out in Figure 14 are fixed to the second surface 91b of the copper base 91, which is opposite to the first surface 91a, i.e., the second surface 91b facing the first surface 91a. In one example, the brazing material 92 is placed on the second surface 91b of the copper base 91, and the brazing material 92 is sandwiched between the rectangular electrical contact 80 and the copper base 91 so that the Ag layer 82 side of the rectangular electrical contact 80 faces the brazing material 92 side. Then, the rectangular electrical contact 80 is brazed to the second surface 91b of the copper base 91 by heating with electricity. The brazing material 92 may be a silver brazing material such as BAg7, or a phosphorus copper brazing material such as BCuP5.

[0047] Next, as shown in Figure 16, the copper base 91 to which the electrical contacts 80 are brazed is fixed to the square bar 93, which 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 machined at one end of the square bar 93 at the position where it connects to the copper base 91. In one example, the diameter of the screw hole 93a is M8. Here, the screw hole 93a penetrates the square bar 93. The copper base 91 and the square bar 93 are aligned, and the fixing member, the screw 94, is screwed from the screw hole 93a of the square bar 93 to the screw hole 91c of the copper base 91, thereby fixing the copper base 91 to the square bar 93. The fixed electrode is thus manufactured.

[0048] Here, we have given an example of how to manufacture a fixed electrode, but a movable electrode is manufactured in a similar manner by fixing a copper base 91, to which electrical contacts 80 are brazed, to a square bar that constitutes part of the movable electrode using screws 94.

[0049] Figure 17 shows an overview of the open-pole operation test apparatus. Hereafter, 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 open-pole operation test apparatus 150 is a simple test apparatus that starts current flow with electrical contact 80b and electrical contact 80a in contact, and opens electrical contact 80b relative to electrical contact 80a to interrupt the current. 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 mechanism is such that the electrical contact 80b of the movable electrode 99 is rotated in an arc around the rotating shaft 95a to open the pole. In the stationary state, the electrical contact 80b and electrical contact 80a are pressed together with a constant force by a contact pressure spring 155, which is provided on the movable electrode 99 and is composed of a tension spring. An opening mechanism utilizing an electromagnet 154 is attached to the side of the movable electrode 99 opposite to the electrical contact 80b with respect to the rotation axis 95a. The opening mechanism includes an electromagnet 154, an iron plate 153, and an opening spring 156. The iron plate 153, which is attracted to the electromagnet 154, has an opening spring 156, which is made of a tension spring, attached to the opposite side of the attracting surface. While the iron plate 153 is attracted to the electromagnet 154, energy is accumulated by pulling the opening spring 156. However, because there is a small gap between the iron plate 153 and the movable electrode 99, even when energy is accumulated in the opening spring 156, the electrical contacts 80a and 80b remain pressed against each other by the contact pressure spring 155.

[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 do not make direct contact. On the other hand, on the movable electrode 99 side, iron plates are arranged at equal intervals and serve as the so-called grid 152 in the arc extinguishing chamber of the circuit breaker. Wiring for energizing 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 the variable reactor 161 are connected to the DC high-voltage power supply 164. The opening operation test device 150 is designed to change the test current by adjusting the impedance using the combination of the variable capacitor 163 and the variable reactor 161. In the example in Figure 17, the set of the DC high-voltage power supply 164 and the variable capacitor 163 corresponds to the capacitor bank power supply. The capacitor bank power supply is a power supply that uses a DC high-voltage power supply 164 to store charge in a variable capacitor 163, and can supply a large current when this charge is discharged. When DC charge is stored in the variable capacitor 163 and then discharged, an LC resonant circuit is formed between the variable reactor 161 (which is a coil) and the variable capacitor 163, and an artificial alternating current is generated. This artificially generated alternating current is used as the test current.

[0051] The test procedure in the open-pole operation test device 150 involves turning on switches 167 and 168 at both ends of the DC high-voltage power supply 164 to charge the variable capacitor 163. Once the variable capacitor 163 is charged, switches 167 and 168 at both ends of the DC high-voltage power supply 164 are turned off, and then the power supply start switch 162 on the variable reactor 161 side is turned on to start power supply to the open-pole operation test device 150. To measure the current, the power supply wiring is fitted with 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. When the arc is commutated to the arc runner 151, the current in the wiring on the arc runner 151 side increases. In addition, the voltage between the fixed electrode 98 and the movable electrode 99 is measured by a high-voltage measuring voltmeter 157.

[0052] Figure 18 shows an image of the electrical contacts opening in the open-contact operation test device. In Figure 17, the iron plate 153 is attracted to the electromagnet 154 and energy is stored in the opening spring 156. At the timing to open the electrical contacts 80a and 80b, that is, at the timing to turn on the power supply start switch 162, the power to the electromagnet 154 is turned off. As shown in Figure 18, the iron plate 153 is pulled away from the electromagnet 154 by the opening spring 156 and pushes the end of the square bar 95 of the movable electrode 99 opposite to the electrical contact 80b. Since the opening spring 156 is sufficiently stronger than the contact pressure spring 155, the electrical contacts 80a and 80b open. The timing of turning on the power supply start switch 162 and the timing of turning off the power to the electromagnet 154 can be freely adjusted, for example, by using a PLC. Furthermore, the contact pressure or opening speed can be freely changed by replacing the contact pressure spring 155 or the opening spring 156 with different spring constants. In the energization test, the contact pressure spring 155 and the 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 are in contact is 10 N, and the opening speed is 3 m / s.

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

[0054] At timing t1, approximately 2ms after the start of energization, when the current is increasing toward its maximum value, the power to the electromagnet 154 is turned off so that the opening of electrical contacts 80a and 80b begins. Immediately after the opening begins, i.e., 2ms after the start of energization, as shown in graph Vc, a voltage begins to rise between electrical contacts 80a and 80b and an arc begins to form. However, because the distance between electrical contacts 80a and 80b is still small, almost no commutation to the 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 positive and negative polarities reverse, and the second half-wave begins, commutation to the arc runner 151 begins. When the second half-wave ends, the interruption is successful, and the current value flowing through the entire system becomes zero. The time from the start of the second half-wave to the rise of the current to the arc runner 151 on graph Iar is the commutation time Δtc. The commutation time Δtc is also called the commutation start time. The arc runner 151 is positioned at the same height as the electrical contact 80a to facilitate commutation, but at a distance of 2 mm from the copper base 91 so as not to touch it. In one example, the grid 152, which is positioned on the movable electrode 99 side, is positioned 3 mm away from the trajectory of the electrical contact 80b of the movable electrode 99. Insulating tape is applied to the parts of the copper base 91 other than the electrical contacts 80a and 80b to prevent the arc from transferring to other parts when measuring the commutation time.

[0056] Figure 20 shows an example of a waveform during commutation time measurement when the commutation time is short. In this figure, the horizontal axis represents time t, and the vertical axis represents the current value I or voltage value V. In one example, Figure 20 shows the waveform during commutation time measurement when electrical contacts 80a and 80b are composed of Ag-SnO2-La2O3, that is, when complex oxide particles 12 composed of SnO2 and La2O3 are dispersed in a conductive component phase 11 composed of Ag. In Figure 20, it can be seen that commutation does not occur to the arc runner 151 in the first half-wave, but commutation occurs soon after the start of the second half-wave. In other words, the commutation time Δtc is shorter compared to the case in Figure 19.

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

[0058] Table 5 shows the measurement results of the characteristics of the electrical contacts when interruption tests were performed for Examples 1 to 4 and Comparative Examples 1 to 15. Here, the arc commutation time at each electrical contact 80a, 80b, the average wear amount of electrical contacts 80a, 80b, and the contact resistance of electrical contacts 80a, 80b before and after the test were summarized when the variable capacitor 163 and variable reactor 161 were adjusted so that the effective value (Root Mean Square value: RMS value) of the first half wave of the current flowing through the entire system was 5kA when the interruption test was performed. The shape of the electrical contacts 80a, 80b after the test was measured using a laser-type non-contact 3D measuring instrument, and the average volume wear amount from the new electrical contacts 80a, 80b, i.e., before the test, was calculated. Here, the average wear amount of the contacts is shown as the percentage of the average wear amount relative to the volume of electrical contacts 80a, 80b before the test. The contact wear ratio with Comparative Example 1 shows how much electrical contacts 80a and 80b, manufactured under different conditions, wear out compared to Comparative Example 1, which does not contain rare earth oxides, a low work function component.

[0059] [Table 5]

[0060] Referring to Table 5, the commutation time is shorter for the electrical junctions 80a and 80b containing La2O3 as the low work function component rare earth oxide in Examples 1 to 4 and Comparative Examples 2 and 3, and for the electrical junctions 80a and 80b containing CeO2 as the low work function component rare earth oxide in Comparative Example 9, compared to Comparative Example 1. However, even among the electrical junctions 80a and 80b containing La2O3 as the low work function component rare earth oxide, the electrical junctions 80a and 80b of Comparative Example 2, which have a volume content lower than 5 vol%, and the electrical junctions 80a and 80b containing other rare earth oxides as the low work function component rare earth oxide do not show as much improvement as the electrical junctions 80a and 80b containing La2O3.

[0061] When examining the contact resistance before and after the interruption test, i.e., the change in contact resistance before and after the test, the CeO2-based contacts 80a and 80b, which contain CeO2 as a rare earth oxide with a low work function component, had slightly higher resistance values ​​before the interruption test compared to Comparative Example 1. After the interruption test, the electrical contacts 80a and 80b made of Ag-SnO2 in Comparative Example 1 and the electrical contacts 80a and 80b made of Ag-SnO2-La2O3 in Examples 1 to 4 and Comparative Examples 2 and 3 had almost the same resistance values. However, the electrical contacts 80a and 80b made of Ag-SnO2-Sm2O3 were slightly higher than those in Comparative Example 1, and the electrical contacts 80a and 80b made of Ag-SnO2-CeO2 were even higher than those in Comparative Example 1.

[0062] Based on the above, the electrical contacts 80a and 80b manufactured under the condition of adding 5 vol% to 20 vol% of La2O3 as a rare earth oxide with a low work function component show improvement in commutation time and wear of electrical contacts 80a and 80b compared to comparative example 1, which consists of Ag-SnO2.

[0063] After testing, the electrical contacts 80a and 80b were observed using a cross-sectional SEM, and elemental analysis was performed using WDS to investigate the oxide structure. Figure 22 shows the SEM image of the cross-section near the surface of the Ag-SnO2-La2O3 system electrical contact after testing of Example 2, which was manufactured under the condition SnO2:La2O3=15:10, and the results of elemental mapping by WDS. The observation magnification here is 200x. Elemental mapping is performed on the area shown in the SEM image. In other words, Figure 22 shows the SEM image of the cross-section of the Ag-SnO2-La2O3 system electrical contacts 80a and 80b, and the elemental mapping diagram of Ag, O, Sn, and La in this SEM image. As shown in Figure 22, traces of melting and re-solidification of the surface of the electrical contacts 80a and 80b due to the arc during opening can be seen. It can also be seen that La, Sn, and O are detected in the same locations. This result remains the same even when the magnification is increased to 3,000x. In other words, it appears that La, Sn, and O precipitate in a mixed state, that is, in a complex oxide state.

[0064] Figure 23 shows the SEM image and WDS elemental mapping results of the cross-section near the surface of the electrical junction of the Ag-SnO2-CeO2 system after testing of Comparative Example 6, which was manufactured under the condition SnO2:CeO2 = 15:10. The observation magnification here is 1,000x. Elemental mapping is performed on the range shown in the SEM image. Also, the elemental mapping of Ag is omitted in Figure 23. In other words, Figure 23 shows the SEM image of the cross-section of the electrical junctions 80a and 80b of the Ag-SnO2-CeO2 system, and the elemental mapping diagram of O, Sn, and Ce in this SEM image. As shown in Figure 23, Sn and Ce are located in separate positions. Therefore, Sn, Ce, and O do not form a complex oxide.

[0065] Figure 24 shows the SEM image and WDS elemental mapping results of the cross-section near the surface of the electrical junction of the Ag-SnO2-Sm2O3 system after testing of Comparative Example 12, which was manufactured under the condition SnO2:Sm2O3 = 15:10. The observation magnification here is 500x. Elemental mapping is performed on the range shown in the SEM image. Also, the elemental mapping results for Ag are omitted in Figure 24. In other words, Figure 24 shows the SEM image of the cross-section of the electrical junctions 80a and 80b of the Ag-SnO2-Sm2O3 system, and the elemental mapping diagrams of O, Sn, and Sm in these SEM images. As shown in Figure 24, Sn and Sm are located in separate positions. Therefore, Sn, Sm, and O do not form a complex oxide.

[0066] Cross-sectional analysis of electrical contacts 80a and 80b revealed that even when low-work-function rare-earth oxides are added, if the type and amount of rare-earth oxides are not appropriate, the rare-earth oxides will not form complex oxides with the arc-resistant oxides inside the electrical contacts 80a and 80b, but will remain separated. In this separated state, as shown in Table 5, the commutation time does not increase. This indicates that when the rare-earth oxides are not uniformly dispersed in the arc-resistant oxides, thermionic emission is unstable at each location on the electrical contacts 80a and 80b, resulting in insufficient suppression of arc stagnation and acceleration of commutation to the arc runner 151. Furthermore, the tolerance factor t for electrical contacts 80a and 80b containing La2O3 and SnO2 is t=0.88, the tolerance factor t for electrical contacts 80a and 80b containing CeO2 and SnO2 is t=0.845, and the tolerance factor t for electrical contacts 80a and 80b containing Sm2O3 and SnO2 is t=0.845. From this, it can be said that it is desirable for the tolerance factor t for the formation of a complex oxide by a low work function component rare earth oxide and an arc-resistant component oxide to be greater than 0.845 and less than 1.

[0067] As described above, the electrical contacts 80a and 80b according to Embodiment 2 are complex oxides formed from La2O3, a rare earth oxide with a low work function component, and SnO2, an arc-resistant component oxide, with the content of the rare earth oxide in the electrical contacts 80a and 80b being 5 vol% or more and 20 vol% or less. Furthermore, the combination of the rare earth oxide with a low work function component and the arc-resistant component oxide is selected so that the allowable factor t of the electrical contacts 80a and 80b is greater than 0.845 and less than 1. This configuration has the effect of making the ease of arc commutation on the surface more uniform compared to conventional methods while suppressing reactions with moisture and carbon dioxide in the air.

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

[0069] 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 electrical contact breakup test using the electrical contacts composed of the electrical contact material 1. Note that the same parts as those described in Embodiment 2 will be omitted. First, the conductive component powder, arc-resistant component oxide powder, and low-work-function component rare-earth oxide powder constituting the conductive component phase 11, which are the raw materials for the electrical contact material 1, are weighed.

[0070] Specifically, the raw materials for electrical contact material 1 are 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. The rare earth oxide powder is either La2O3 powder with an average particle size of 1.5 μm or CeO2 powder with an average particle size of 3 μm. Table 6 shows the volume and mass percentages 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 is weighed so that the amount of Ag added is kept constant at 80 vol%, and the total amount of ZnO powder and rare earth oxide powder is 20 vol%.

[0071] [Table 6]

[0072] Next, the weighed conductive component powder, arc-resistant component oxide powder, and low work function component rare earth oxide powder are mixed. Then, the mixed powder is filled into a mold and molded at a specified molding pressure. In one example, a dry mixing device is used to separate the mixture into two combinations: one containing Ag powder, ZnO powder, and rare earth oxide powder, and another containing only Ag powder and ZnO powder, and each is mixed for 30 minutes. After mixing, the powder is filled into a rectangular mold. Figure 25 shows an example of the mold configuration. The mold 200 has 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 molded and has a rectangular through-hole 201a into which the upper punch 202 and 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 specified in Japanese Industrial Standards (JIS) G 4404:2015.

[0073] Figures 26 to 33 are cross-sectional views showing an example of the procedure for filling a mold with powder in a method for manufacturing an electrical contact material according to Embodiment 3. As shown in Figure 26, a space 205 for filling the powder is formed by the die 201 of the mold 200 and the lower punch 203 inserted into the through hole 201a provided in the die 201. At this time, a thin layer of lubricating oil is applied to the surface of the mold 200 that the powder will come into contact with to prevent the powder from sticking during the molding process. Next, as shown in Figure 27, a mixed powder 221, which is a mixture of Ag powder, ZnO powder, and rare earth oxide powder, or a mixed powder 221, which is a mixture of 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, an amount of mixed powder 221 is filled into the space 205 such that the thickness of the contact layer formed by the sintering of the mixed powder 221 when the electrical contact is completed will be 1.5 mm. Subsequently, as shown in Figure 28, the scraping plate 226 scrapes off any excess mixed powder 221 that is above the top surface of the die 201. This makes the surface of the mixed powder 221 filling the space 205 flat.

[0074] Next, as shown in Figure 29, the lower punch 203 of the mold 200 is lowered by a predetermined distance to form a gap 205a above the mixed powder 221 in the die 201. Then, as shown in Figure 30, only the Ag powder 222 is filled into the gap 205a formed in the die 201. At this time, the Ag powder 222 laid 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 Figure 31, the excess Ag powder 222 above the top surface of the die 201 is scraped off with a scraping plate 226. This makes the surface of the Ag powder 222 filled in the gap 205a flat. Then, as shown in Figure 32, the upper punch 202 is placed over the Ag powder 222. Finally, as shown in Figure 33, the mold 200 is inverted upside down and molded at a predetermined molding pressure. In one example, the molding pressure is 640 MPa. This forms a two-layer molded body 223.

[0075] Subsequently, the molded body 223 formed from the mixed powder 221 is sintered at a predetermined sintering temperature to form a sintered body. In one example, the two layers of molded body 223 removed from the mold 200 are placed on an alumina tray with the Ag layer facing downwards, and heat treatment is performed in an atmospheric furnace, which is a heat treatment device, to sinter the two layers of molded body 223 and form a sintered body. In one example, sintering is performed at 940°C for 2 hours. After sintering, the temperature inside the atmospheric furnace is allowed to cool sufficiently to about 50°C before removing the sintered body. Figure 34 shows an example of the structure of the sintered body after heat treatment. As shown in Figure 34, the removed sintered body 240 has a contact layer 241 and an Ag layer 242 formed simultaneously.

[0076] The following describes the procedure for manufacturing a circuit breaker using the sintered body 240 as an electrical contact 80 and for performing an evaluation test of the electrical contact 80. Specifically, the fixed electrode and movable electrode constituting the circuit breaker are manufactured using the sintered body 240 as an electrical contact 80. Similar to the manufacturing method shown in Figures 15 and 16 of Embodiment 2, the electrical contact 80 is brazed to the copper base 91 by resistance heating after sandwiching a brazing material 92 between the second surface 91b of the copper base 91 and the Ag layer 242 of the electrical contact 80. The copper base 91 with the brazed electrical contact 80 is then fixed to a square bar 93 that constitutes part of the fixed electrode, and the copper base 91 is fixed to a square bar 95 that constitutes part of the movable electrode, using screws 94.

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

[0078] Table 7 shows the measurement results of the characteristics of the electrical contacts when interruption tests were performed on Examples 5 to 7 and Comparative Examples 16 to 21. The table summarizes the arc commutation time at each electrical contact 80a, 80b, the average wear amount of electrical contacts 80a, 80b, and the contact resistance of electrical contacts 80a, 80b before and after the test, when 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 3kA when the interruption test was performed. After the test, the shape of the electrical contacts 80a, 80b was measured using a laser-type non-contact 3D measuring instrument, and the average volume wear amount from the new electrical contacts 80a, 80b, i.e., before the test, was calculated. Here, the average wear amount of the contacts is shown as the percentage of the average wear amount relative to the volume of electrical contacts 80a, 80b before the test. The contact wear ratio with Comparative Example 16 shows how much electrical contacts 80a, 80b manufactured under other conditions wear out compared to the wear amount of Comparative Example 16, which does not contain rare earth oxides, which are low work function components.

[0079] [Table 7]

[0080] Referring to Table 7, the electrical contacts 80a and 80b that exhibit less commutation time than Comparative Example 16 are those containing La2O3 as the low-work-function rare earth oxide in Examples 5 to 7 and Comparative Example 17, and those containing CeO2 as the low-work-function rare earth oxide in Comparative Example 20. The electrical contacts 80a and 80b that exhibit less wear than Comparative Example 16 are those manufactured under the conditions of Examples 5 to 7, which contain La2O3 as the low-work-function rare earth oxide and have a rare earth oxide content in the range of 5 vol% to 15 vol%. Furthermore, the electrical contacts 80a and 80b that exhibit less contact resistance before and after the interruption test than Comparative Example 16 are those manufactured under the conditions of Examples 5 to 7, which contain La2O3 as the low-work-function rare earth oxide and have a rare earth oxide content in the range of 5 vol% to 15 vol%. Furthermore, the tolerance factor t for electrical contacts 80a and 80b containing La2O3 and ZnO is t = 0.92. Combining this with the case of Embodiment 2, it can be said that it is desirable for the tolerance factor t for the formation of a complex oxide by a low work function component rare earth oxide and an arc-resistant component oxide to be greater than 0.845 and less than 1. However, since the tolerance factor t for electrical contacts 80a and 80b containing CeO2 and ZnO is t = 0.89, it is necessary to exclude Ce as metal element A. In other words, metal element A is a rare earth element excluding Ce, and it is desirable for the tolerance factor t to be greater than 0.845 and less than 1.

[0081] After the test, cross-sections of electrical contacts 80a and 80b were examined using SEM observation and elemental analysis with WDS. It was confirmed that the arc-resistant component ZnO and the added La2O3 formed a complex oxide, but the arc-resistant component ZnO and CeO2 did not form a complex oxide. This is thought to be because Ce, among rare earth oxides, takes on a tetravalent state as CeO2, and therefore does not form a complex oxide. For this reason, the acceptable factor for the combination of CeO2 and ZnO is t=0.89, but since the combination of CeO2 and ZnO does not form a complex oxide, it is excluded from the list of candidates for complex oxide particles 12 and 12a.

[0082] As described above, the electrical contacts 80a and 80b according to Embodiment 3 include a conductive component phase 11 formed by Ag, and complex oxide particles 12 formed by La2O3, a rare earth oxide with a low work function component, and ZnO, an arc-resistant component oxide, with the content of rare earth oxides in the electrical contact material 1 being 5 vol% to 15 vol%. This configuration has the effect of making the ease of arc commutation on the surface more uniform compared to conventional designs while suppressing reactions with moisture and carbon dioxide in the air.

[0083] Embodiment 4. Embodiment 4 describes the conditions under which an electrical contact material 1 having complex oxide particles 12 can be formed from a combination of arc-resistant oxides containing Sn, which is an arc-resistant component element shown at the end of Embodiment 1, and rare earth oxides containing Y, which is a low work function component element.

[0084] Here, we will first describe an example of a method for manufacturing the electrical contact material 1A, and then the method and results of an electrical contact breakup test using the electrical contacts composed of the electrical contact material 1A. Note that the same parts as those described in Embodiments 2 and 3 will be omitted. First, the conductive component powder, arc-resistant component oxide powder, and low-work-function component rare-earth oxide powder constituting the conductive component phase 11, which are the raw materials for the electrical contact material 1A, are weighed.

[0085] Specifically, the raw materials for electrical contact material 1A are Ag powder with an average particle size of 4 μm, SnO2 powder with an average particle size of 1 μm, and Y2O3 powder with an average particle size of 7 μm. The Y2O3 powder is a rare earth oxide powder with a low work function component. Table 8 shows the volume and mass percentages 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 is weighed so that the amount of Ag added is kept constant at 78 vol%, and the total value of SnO2 powder and rare earth oxide powder is 22 vol%.

[0086] [Table 8]

[0087] Next, the weighed conductive component powder, arc-resistant component oxide powder, and low work function component rare earth oxide powder are mixed. In one example, a dry mixing apparatus is used to separate the mixture into two combinations: one containing Ag powder, SnO2 powder, and Y2O3 powder, and another containing only Ag powder and SnO2 powder, and each is mixed for 30 minutes.

[0088] Subsequently, the mixed powder is filled into a mold and molded under a predetermined molding pressure. In one example, after mixing, the mixed powder 51 and Ag powder 52 are filled into a graphite mold 30 as shown in Figure 4, following the procedure shown in Figures 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. Furthermore, the Ag powder 52 that forms the Ag layer 72 on top of the contact layer 71 formed by sintering the mixed powder 51 is weighed so that it is about 1 / 10 the thickness of the contact layer 71.

[0089] Next, the mixed powder 51 is sintered at a predetermined sintering temperature under pressure to form a sintered body 70. In one example, a graphite mold 30 filled with mixed powder 51 and Ag powder 52 is sintered in the SPS apparatus 60 shown in Figure 12. Here, the pressure between the upper punch 32 and lower punch 33 of the graphite mold 30 is set to 7kN, and it is heated at a heating rate of 20°C / min. Once it reaches 850°C, it is held at 850°C for 10 minutes, and then the power is turned off to allow it to cool down. The maximum voltage during power application is approximately 2.5V, and the current is approximately 500A. If the mixed powder 51 consists only of Ag powder and SnO2 powder, sintering is performed at 850°C. However, when the mixed powder 51 is Ag powder, SnO2 powder, and Y2O3 powder, and the mixing ratio of SnO2 powder and Y2O3 powder is 10:15 or 15:10, the Ag begins to melt at 850°C, so the temperature is lowered to 830°C to perform sintering. As a result, the molded body 53 becomes a sintered body 70.

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

[0091] Using this electrical contact 80, the fixed electrode and movable electrode that constitute the circuit breaker are manufactured. Similar to the manufacturing method shown in Figures 15 and 16 of Embodiment 2, a brazing material 92 is placed between the second surface 91b of the copper base 91 and the Ag layer 82 of the electrical contact 80, and then the electrical contact 80 is brazed to the copper base 91 by resistance heating. The copper base 91 with the brazed electrical contact 80 is then fixed to a square bar 93 that constitutes part of the fixed electrode, and the copper base 91 is fixed to a square bar 95 that constitutes part of the movable electrode, using screws 94.

[0092] A fixed electrode 98 having a copper base 91 and square bar 93 to which an electrical contact 80a is brazed, and a movable electrode 99 having a copper base 91 and square bar 95 to which an electrical contact 80b is brazed, are attached to the electrodes of the opening operation test device 150 as shown in Figure 17, and an electrical conduction test is performed. In the electrical conduction test, in one example, the contact pressure spring 155 and the 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 are in contact is 10 N, and the opening speed is 3 m / s.

[0093] Table 9 shows the measurement results of the characteristics of the electrical contacts when interruption tests were performed for Examples 8 to 10 and Comparative Examples 22 to 23. Table 9 summarizes the arc commutation time at each electrical contact 80a, 80b, the average wear of electrical contacts 80a, 80b, and the contact resistance of electrical contacts 80a, 80b before and after the test when the first and second interruption tests are performed. For the first energization, the variable capacitor 163 and variable reactor 161 are adjusted so that the effective value of the first half-wave of the current flowing through the entire system is 1kA, and the first interruption test is performed. Then, with the same electrical contacts 80a, 80b, the variable capacitor 163 and variable reactor 161 are readjusted so that the effective value of the first half-wave of the current flowing through the entire system is 5kA, and the second interruption test is performed. The wear and resistance of electrical contacts 80a, 80b are measured after performing one 1kA and one 5kA interruption, respectively. In Examples 8 to 10, the commutation time was not significantly shorter with a 1kA current, but with a second 5kA current, the commutation time was clearly shorter compared to Comparative Example 22, which was under conditions without rare earth oxides. Furthermore, the average wear of the contacts was also less than in Comparative Example 22, and the change in contact resistance was comparable.

[0094] [Table 9]

[0095] Before and after the test, cross-sections of electrical contacts 80a and 80b were examined by SEM observation and elemental analysis using WDS. Before the test, as shown in the left diagram of Figure 3, it was confirmed that the SnO2 of the arc-resistant oxide particles 13 and the Y2O3 of the low-work-function rare-earth oxide particles 14 were separated and present inside the conductive component phase 11, Ag. However, after the energization test, as shown in the right diagram of Figure 3, it was confirmed that the SnO2 of the arc-resistant oxide particles 13 and the Y2O3 of the low-work-function rare-earth oxide particles 14 formed a complex oxide particle 12a. This is thought to be because, during the heat treatment of electrical contacts 80a and 80b at a temperature below the melting point of Ag, the temperature was insufficient, and SnO2 and Y2O3 did not form a complex oxide. However, during the first energization test, when the surfaces of electrical contacts 80a and 80b melted and re-solidified due to exposure to the arc, SnO2 and Y2O3 formed a complex oxide, thus shortening the commutation time in the second energization test. The allowable factor t for electrical contacts 80a and 80b containing Y2O3 and SnO2 is t = 0.85. Combining this with the cases of embodiments 2 and 3, it can be said that metal element A is a rare earth element excluding Ce, and it is desirable that the allowable factor t for the formation of a complex oxide between the low work function component rare earth oxide and the arc-resistant component oxide be 0.85 or more and less than 1.

[0096] In the case of the electrical contacts 80a and 80b according to Embodiment 4, before use, arc-resistant oxide particles 13 and rare earth oxide particles 14 with low work function components are dispersed in the conductive component phase 11. When used as a circuit breaker, the arc-resistant oxide particles 13 and rare earth oxide particles 14 with low work function components that are present in the melted and re-solidified portion are used to form a complex oxide. However, in order to form a complex oxide, the arc-resistant element of the arc-resistant oxide particles 13 and the rare earth element of the rare earth oxide particles 14 with low work function components must be a combination of elements that form a complex oxide. Thus, the electrical contacts 80a and 80b according to Embodiment 4 have a portion that has been melted by the arc and contains complex oxide particles 12a containing arc-resistant elements and rare earth elements, and a portion that has not been melted by the arc and contains arc-resistant oxide particles 13 and rare earth oxide particles 14 with low work function components dispersed in the arc.

[0097] Furthermore, in the electrical contact material 100 in which arc-resistant component particles 112 and low work function component particles 113 are dispersed in the conductive component phase 111, as shown in the figure on the right, the arc-resistant component particles 112a and low work function component particles 113a did not form a complex oxide even after arc generation and remained dispersed in the conductive component phase 111. This is thought to be because the arc-resistant component elements constituting the arc-resistant component particles 112 and the alkaline earth elements constituting the low work function component particles 113 were a combination that did not form a complex oxide. On the other hand, in Embodiment 4, the arc-resistant component elements constituting the arc-resistant component oxide particles 13 and the rare earth elements constituting the low work function component rare earth oxide particles 14 are a combination that does form a complex oxide. Therefore, in the part melted by the arc, the arc-resistant component oxide particles 13 and the low work function component rare earth oxide particles 14 can melt and re-solidify to form complex oxide particles 12a.

[0098] As described above, the electrical contacts 80a and 80b according to Embodiment 4 include Ag, which is a conductive component phase 11, arc-resistant component oxide particles 13, and rare earth oxide particles 14 with a low work function component. The arc-resistant component elements constituting the arc-resistant component oxide particles 13 and the rare earth elements constituting the rare earth oxide particles 14 with a low work function component are made of materials that form complex oxides. During the manufacture of the electrical contacts 80a and 80b, the arc-resistant component oxide particles 13 and the rare earth oxide particles 14 with a low work function component exist separately in the conductive component phase 11. When the surface of the electrical contacts 80a and 80b melts and resolidifies due to arcing caused by interruption, the arc-resistant component oxide particles 13 and the rare earth oxide particles 14 with a low work function component form complex oxide particles 12a. In other words, the arc-resistant component oxide particles 13 and the rare earth oxide particles 14 with a low work function component are made of materials that form complex oxides at a temperature higher than the melting point of Ag. In this configuration, the rare earth oxide is Y2O3, and the Y2O3 content can be between 5 vol% and 15 vol%. With this configuration, the commutation rate during the first arc generation does not change much compared to the case where rare earth oxide is absent, but during subsequent arc generation, the commutation rate can be improved, and the wear rate of the electrical contacts 80a and 80b can be reduced. In other words, it has the effect of making the ease of arc commutation on the surface more uniform compared to conventional methods while suppressing reactions with moisture and carbon dioxide in the air.

[0099] The configurations shown in the above embodiments are merely examples, and it is possible to combine them with other known technologies, combine different embodiments, and omit or modify parts of the configuration without departing from the gist of the invention. [Explanation of symbols]

[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 Trimmed plate, 51,221 Mixed powder, 52,222 Ag powder, 53,223 Molded body, 60 SPS device, 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 contacts, 91 Copper base, 91a First surface, 91b Second surface, 91c Screw hole, 92 Brazing material, 93, 95 Square bar, 93a Screw hole, 94 Screw, 95a Rotating shaft, 98 Fixed electrode, 99 Movable electrode, 112, 112a Arc-resistant component particles, 113, 113a Low work function component particles, 150 Open-pole operation test apparatus, 151 Arc runner, 152 Grid, 153 Iron plate, 154 Electromagnet, 155 Contact pressure spring, 156 Open-pole spring, 161 Variable reactor, 162 Power-on switch, 163 Variable capacitor, 164 DC high-voltage power supply, 165 Rogowski coil current probe on fixed electrode side, 166 Rogowski coil current probe on arc runner side, 167, 168 Switches, 181 DC constant current power supplies, 200 molds.

Claims

1. Ag, which is the conductive component phase, A complex oxide particle comprising a complex oxide of an arc-resistant component oxide, which is an oxide of an arc-resistant component element that suppresses the consumption of the conductive component phase when an arc is generated, and a rare earth oxide, which is an oxide of a rare earth element having a work function lower than the work function of the conductive component phase and the arc-resistant component oxide, It has, The complex oxide particles are dispersed within the conductive component phase. The aforementioned arc-resistant component oxide is ZnO, The rare earth oxide is an oxide of La, An electrical contact material characterized in that 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.

2. A method for manufacturing an electrical contact material comprising: a conductive component phase consisting of Ag; an arc-resistant component oxide which is an oxide of an arc-resistant component element that suppresses the consumption of the conductive component phase when an arc is generated; and a rare earth oxide which is an oxide of a rare earth element having a work function lower than the work function of the conductive component phase and the arc-resistant component oxide; and a complex oxide particle comprising a complex oxide of these two elements. A step of mixing the conductive component powder constituting the conductive component phase, the arc-resistant component oxide powder constituting the arc-resistant component oxide, and the rare earth oxide powder constituting the rare earth oxide to form a mixed powder, The process involves filling the aforementioned mixed powder into a mold or die, molding it at a predetermined molding pressure, and forming a molded body. The process involves sintering the molded body at a predetermined sintering temperature to form a sintered body, Includes, The aforementioned arc-resistant component oxide is ZnO, The rare earth oxide is an oxide of La, A method for producing an electrical contact material, characterized in that 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.

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