Ceramic member for bonding, process for producing the same, vacuum switch and vacuum vessel

Abstract: A ceramic member for bonding comprises: a ceramic base which is a sintered ceramic; and a metallic layer formed on the ceramic base by metallization, wherein the metallic layer comprises 70 to 85% by weight of at least one of tungsten and molybdenum and 0.5 to 8.5% by weight of nickel.

Description: Background of the Invention 1. Field of the Invention The present invention relates to members required to have bonding strength, airtightness, and other properties as in the case of bonding a metal to a ceramic. More particularly, the invention relates to a process for producing a ceramic member for bonding and to a ceramic member for bonding, bonded objects, a vacuum switch, and a vacuum vessel. 2. Background Art The molybdenum-manganese method (Mo-Mn method; Telefunken method) has conventionally been known as a method for metallizing a surface of a ceramic base. In this Mo-Mn method, a metallizing ink prepared by adding bonding aids, which help bonding with ceramics, such as a manganese powder, titanium powder, and glass ingredient (SiO 2 ) to a powder of high-melting metals such as tungsten and molybdenum and mixing the powder mixture with an organic binder to make the mixture paste (hereinafter sometimes referred to as "metallizing ink") is applied to a ceramic base and the ink layer is baked (baking method). The technique of the related art described above necessitates a baking temperature as high as from 1,300 to 1,500°C for metallization and, hence, has had a problem that the sintering cost regarding furnace structure, utilities, expendable heat-resistant materials, etc. is high. Another problem is that the ceramic itself deforms in the high-temperature baking, resulting in a product which does not satisfy dimensional accuracy. Although a measure in overcoming the problem described above may be to bake a metallizing ink having a conventional composition at a temperature lower than 1,300°C, this low-temperature baking poses a problem that a sufficient bonding strength cannot be obtained. An improvement in this respect has been desired. Furthermore, in the case where a metallic layer formed by metallization by the Mo-Mn method is to be bonded to another metallic member or the like by brazing, it is necessary to improve the wettability thereof by a brazing material so as to obtain satisfactory bonding. Although it is hence inevitable to conduct post-treatments such as nickel plating and subsequent sintering, there has been a problem that these post-treatments make the production process complicated. JP-A-1 205 053 discloses a ceramic-metal joint for example comprising a Si 3 N 4 member soldered to a steel member with an interposed buffer material comprising two layers of 90 wt % W-(Fe, Ni), a layer of 70 wt % W-(Fe, Ni) and a metal layer comprising 12% Kovar. Summary of the Invention The invention has been achieved in order to eliminate the problems described above. An object of the invention is to provide a process by which a ceramic member for bonding having a metallization-deposited metallic film with sufficient bonding strength can be obtained even through low-temperature sintering. Another object of the invention is to provide a ceramic member for bonding, bonded objects, a vacuum switch, and a vacuum vessel. In the method of the related art of metallization, metals are bonded to a ceramic mainly by two actions, i.e., the sintering of high-melting metal particles and the diffusion and infiltration of a glass ingredient into spaces among the particles. When this method of the related art of metallization is conducted at a sufficiently high sintering temperature, not only the sintering of the high-melting metals proceeds to give a metallic layer having improved strength, but also a vitreous ingredient (e.g., SiO 2 ) contained in the ceramic or ink infiltrates into spaces among the high-melting metal particles to mechanically improve the bonding strength based on an anchoring effect. However, in order for the reactions which bring about these effects to proceed sufficiently, a temperature of 1,300°C or higher has been necessary. In contrast, sintering in the invention can be conducted at a lower temperature because nickel reacts with high-melting metals to accelerate the sintering. In the case where the ink contains SiO 2 , the metallic layer which is being formed by metallization is sufficiently filled with a vitreous ingredient due to the SiO 2 , so that baking can be conducted at a temperature as low as, e.g., from 1,080 to 1,250°C (preferably from 1,100 to 1,250°C, more preferably from 1,100 to 1,200°C). A first aspect of the invention provides a ceramic member for bonding, which comprises: a ceramic base which is a sintered ceramic; and a metallic layer formed on the ceramic base by metallization, wherein the metallic layer comprises 70 to 85% by weight of at least one of tungsten and molybdenum and 0.5 to 8.5% by weight of nickel, and wherein the metallic layer further comprises at least one of 1 to 3% by weight of manganese and 0.05 to 2.5% by weight of titanium. Because the metallic layer formed by metallization contains 0.5 to 8.5 % by weight nickel, it has undergone sufficient sintering even at a temperature as low as, e.g., from 1,080 to 1,250°C because of the reactions of the nickel with high-melting point metals during the sintering for metallization. As a result, the sintering cost regarding furnace structure, utilities, expendable heat-resistant materials, etc. is low as compared with conventional ones. Moreover, since the ceramic itself is less apt to deform during the baking due to the low baking temperature, this ceramic member for bonding has high dimensional accuracy. Furthermore, even when the sintering is conducted at a low temperature, high bonding strength can be secured. The manganese ingredient and the titanium ingredient each functions as a bonding aid. Preferably, the metallic layer further comprises from 8 to 20% by weight SiO 2 in terms of silicon oxide amount. Furthermore, the silicon ingredient functions as vitreous SiO 2 . This SiO 2 infiltrates into spaces among high-melting metal particles to thereby mechanically improve bonding strength based on an anchoring effect. In particular, high bonding strength can be obtained even through low-temperature sintering. A further aspect of the invention provides a process for producing a ceramic member for bonding according to the first aspect of the invention which process comprises: mixing a mixture comprising nickel particles and at least one of tungsten particles and molybdenum particles with an organic binder, to produce a paste, wherein the paste further comprises at least one of 5 to 10% by weight of manganese particles and 0.5 to 2% by weight of at least one of titanium particles and TiH 2 particles; applying the paste to a ceramic base which is a sintered ceramic, to form a layer; and baking the layer to form a metallic layer. In this invention, since the metallizing ink (i.e. the paste) contains nickel, the nickel reacts with high-melting metals to accelerate sintering the layer which is being formed by metallization, as stated above. Because of this, the metal particles can be sufficiently sintered even at a temperature as low as, e.g., from 1,080 to 1,250°C. As a result, the sintering cost regarding furnace structure, utilities, expendable heat-resistant materials, etc. can be reduced as compared with conventional ones. Moreover, the baking conducted at a low temperature produces a marked effect that the ceramic itself is less apt to deform and high dimensional accuracy is obtained. A further advantage is that since the metal particles can be sufficiently sintered even at such a low temperature, high bonding strength can be secured. In this metallizing ink, the manganese ingredient, serving as a bonding aid, is oxidized by the moisture contained in the sintering atmosphere to thereby improve the wetting ability and flowability of a glass ingredient. The titanium ingredient, which also serves as a bonding aid, is exceedingly active and hence contributes to chemical bonding to the ceramic base. While the organic binder for use in the present invention is not limiting, an organic binder where solid binder (e.g., ethyl cellulose) is dissolved in a solvent (e.g., turpentine oil, butyl glycol) may be used. The organic binder may be used in an amount of about 10 to 35% by weight based on 100% by weight of the total amount of the organic binder and the particle mixture. The solid binder may be used in an amount of about 2 to 4.5% by weight based on 100% by weight of the total amount of the solid binder and the particle mixture. Preferably, in the process according to the further aspect of the invention, the mixture comprises 1 to 10% by weight of nickel, and 70 to 97% by weight of at least one of tungsten particles and molybdenum particles. Since the metallizing ink for use in this invention contains nickel in an amount of from 1 to 10% by weight, the nickel reacts with high-melting metals to accelerate sintering in the layer which is being formed by metallization, as stated above. Because of this, the metal particles can be sufficiently sintered even at a temperature as low as, e.g., from 1,080 to 1,250°C. Preferably, in the process according to the further aspect of the invention, the paste further comprises from 2 to 15% by weight particles of SiO 2 . Furthermore, SiO 2 , which is vitreous, infiltrates into spaces among high-melting metal particles to thereby mechanically improve bonding strength based on an anchoring effect. In particular, when sintering is conducted at a low temperature, SiO 2 is less apt to be fed from the ceramic member for bonding. Even through such low-temperature sintering, however, high bonding strength can be obtained by using a metallizing ink to which SiO 2 has been added. Another aspect of the invention provides a bonded object comprising a ceramic member for bonding according to the first aspect of the invention, and a metallic member bonded to the ceramic member through the metallic layer of the ceramic member. The bonded object of this aspect of the invention is characterized in that a ceramic member for bonding is bonded to a metallic member with the above-described metallic layer comprising ingredients including nickel. Consequently, this bonded object comprising a ceramic member for bonding and a metallic member bonded thereto can be produced at a reduced cost, and the bonded object obtained has high bonding strength and high dimensional accuracy. Yet another aspect of the invention provides a bonded object comprising a ceramic member for bonding according to the first aspect of the invention, and another ceramic member for bonding, bonded to the ceramic member through the metallic layer of the ceramic member. The bonded object of this aspect of the invention is characterized in that two ceramic members for bonding are bonded to each other with the above-described metallic layers comprising ingredients including nickel. The bonding surface of each metallic layer is preferably plated prior to the bonding. A preferred method for the bonding is brazing. Consequently, this bonded object comprising two ceramic members bonded to each other can be produced at a reduced cost, and the bonded object obtained has high bonding strength and high dimensional accuracy. The present invention also provides a vacuum switch having the bonded object as defined in either preceding aspect. The vacuum switch of this invention is characterized by having either of the bonded objects described above. An example of this vacuum switch is an electric circuit switch employing a ceramic insulating valve, in particular one suitable for the switching of high-voltage large-current electricity. The present invention also provides a vacuum vessel comprising the bonded object as defined in either preceding aspect. The vacuum vessel of this invention (e.g., an insulating valve) is used in, e.g., the vacuum switch described above. A vacuum switch (electrical circuit switch) can be fabricated by disposing electrodes and other necessary members in this vacuum vessel. Brief Description of the Drawings Fig. 1 is a sectional view illustrating an important part of a bonded object shown in Example 1. Fig. 2 is a slant view illustrating a bonded object obtained in Example 1. Fig. 3 is a view illustrating a method of measuring the bonding strength of the bonded object obtained in Example 1. Fig. 4 is a sectional view illustrating an important part of a bonded object shown in Example 2. Fig. 5 is a partially cutaway view illustrating the vacuum switch shown in Example 3. Fig. 6 is a sectional view illustrating an important part of the vacuum switch shown in Example 3. Fig. 7 is a sectional view illustrating an important part of the vacuum switch shown in Example 4. Reference numerals in the drawing represent as follows. 1 ceramic member for bonding 3 metallic member 5, 35, 162, 219, 221 brazing material 7, 37, bonded object 9 ceramic base 11 metallic layer formed by metallization 13 deposit layer formed by plating 31 first ceramic member for bonding 33 second ceramic member for bonding 39 first ceramic base 41 first metallic layer formed by metallization 45 second ceramic base 47 second metallic layer formed by metallization 161, 207 arc shield 101 insulating valve 100, 200, vacuum switch (high-load switch) 171, 211, 213 metallic layer formed by metallization 201 upper insulating valve 203 lower insulating valve 205 connecting member Description of the Preferred Embodiments Embodiments (examples) of the process for producing a ceramic member for bonding, the ceramic member for bonding, the bonded objects, the vacuum switch, and the vacuum vessel of the invention will be explained below by reference to the drawings. (EXAMPLE 1) A bonded object comprising a ceramic member for bonding and a metallic member is described as an embodiment. a) Fig. 1 diagrammatically shows this embodiment, which is a bonded object 7 comprising a ceramic member for bonding 1 and a metallic member 3 bonded thereto with a brazing material 5. More specifically, the ceramic member for bonding 1 comprises a ceramic base 9 and a metallic layer 11 formed thereon by metallization. A deposit layer (plating layer) 13 has been formed by plating on the metallic layer 11. The deposit layer 13 and the metallic member 3 have been bonded to each other with the brazing material 5, whereby the ceramic member for bonding 1 and the metallic member 3 have been united with each other. b) A process for producing a ring-shaped test piece as an example of this bonded object will be explained below together with a process for producing a ceramic member for bonding. (1) First, particulate metallizing-ink ingredients shown in Table 1 which will be given later were pulverized and mixed together, and this powder mixture (e.g., 87% by weight) was mixed with an organic binder (e.g., 13% by weight) such as, e.g., ethyl cellulose to obtain a paste. Thus, a metallizing ink was produced. (2) The metallizing ink thus produced was applied to a surface of an alumina-based ceramic base 9 (e.g., 92% by weight alumina) which was a sintered ceramic (e.g., a ring-shaped test piece having a thickness of 5 mm, an outer diameter of 30 mm, and an inner diameter of 8.5 mm) in a thickness of about from 10 to 20 µm. (3) Subsequently, the ceramic base 9 coated with the metallizing ink was placed in a furnace and sintered (metallized) at the temperatures of from 1,150 to 1,350°C shown in Table 2 below in an atmosphere of H 2 /N 2 (1:1) forming gas having a wetter temperature of 50°C. Thus, a ceramic member for bonding 1 was obtained which consisted of the ceramic base 9 and a metallic layer 11 formed thereon by metallization. (4) The surface of the metallic layer 11 (metallized side) was electroplated with nickel to form a deposit layer 13. This deposit layer 13 was sintered (sintered) in an H 2 atmosphere at a temperature of 830°C. (5) Thereafter, the ceramic member for bonding 1 and a metallic member 3 made of Kovar (Fe-Ni-Co) were brazed together. Specifically, a foil of a silver brazing material (BAg-8) 5 was interposed between the deposit layer 13 and the metallic member 3 (e.g., a Kovar disk having a thickness of 1 mm and an outer diameter of 16 mm). This assemblage was heated at a given brazing temperature and then cooled to braze the ceramic member for bonding 1 and the metallic member 3 together. Thus, a bonded object 7 was completed.Using the metallizing inks having different compositions as shown in Table 1 below, ring-shaped test pieces (samples) Nos. 3-5, 7, 8, 10-14, 16 and 17 as shown in Fig. 2 were produced, as bonded objects 7 to be tested, through the steps (1) to (5) described above. Sample No. 1 as a comparative example was further produced using a metallizing ink having a different composition (not containing nickel). Sample No. Content in metallizing ink [wt%] Remarks Item 1 Item 2 Mo Ni Mn Ti SiO 2 Total 1 91.5 0.0 7.3 1.2 0.0 100.0 comparative example 3 80.5 1.0 7.3 1.2 10.0 100.0 items 1-3 4 76.5 5.0 7.3 1.2 10.0 100.0 items 1-3 5 71.5 10.0 7.3 1.2 10.0 100.0 items 1-3 7 85.5 5.0 7.3 1.2 1.0 100.0 items 1, 2 8 71.5 5.0 7.3 1.2 15.0 100.0 items 1-3 10 76.5:W 5.0 7.3 1.2 10.0 100.0 items 1-3 11 81.3 5.0 2.5 1.2 10.0 100.0 items 1, 2 12 68.8 5.0 15.0 1.2 10.0 100.0 item 1 13 77.5 5.0 7.3 0.2 10.0 100.0 items 1, 2 14 84.7 5.0 7.3 3.0 10.0 10.0.0 items 1, 2 16 83.5 5.0 7.3 1.2 3.0 100.0 items 1-3 17 82.5 5.0 1.0 1.2 10.0 100.0 items 1, 2 Furthermore, during the production process described above, the metallic layer 11 of each ceramic member for bonding 1 produced was quantitatively analyzed to determine the contents of components. This quantitative analysis was made with an electron probe microanalyzer (accelerating voltage, 20 kV; spot diameter, 5 µm). The results obtained are shown in Table 2 below.With respect to each sample, the analysis was made on five points so as to reduce influences of segregation and the five found values obtained for each component were averaged. In Table 2, the contents of silicon, aluminum, calcium, and magnesium are given in terms of oxide amount. Sample No. Found value after sintering (average) [wt%] Mo Ni Mn Ti SiO 2 Al 2 O 3 CaO MgO Total 1 77.8 0.0 2.4 0.6 11.3 6.5 1.0 0.4 100.0 3 75.4 0.6 2.7 0.7 12.2 6.8 1.1 0.5 100.0 4 78.6 2.2 2.6 0.7 9.1 5.7 1.1 0.0 100.0 5 70.0 7.6 2.0 1.4 11.2 6.5 1.1 0.2 100.0 7 79.4 2.3 2.7 0.7 8.4 5.4 0.9 0.2 100.0 8 72.0 2.2 1.7 0.5 16.3 6.2 1.0 0.1 100.0 10 78.8 2.1 2.5 0.7 9.0 5.8 1.1 0.0 100.0 11 77.9 2.2 1.4 0.7 10.8 5.9 1.0 0.1 100.0 12 75.3 2.3 3.0 0.7 11.2 6.2 1.1 0.2 100.0 13 76.2 2.1 2.5 0.1 11.5 6.4 1.1 0.1 100.0 14 75.6 2.8 2.6 2.1 10.2 5.7 1.0 0.0 100.0 16 78.4 2.4 2.8 0.6 8.8 5.8 1.0 0.2 100.0 17 78.2 2.3 0.5 0.6 11.1 6.1 1.0 0.2 100.0 In producing sample No. 10, tungsten was used in place of molybdenum. c) The bonded object samples produced by the process described above were examined for bonding strength. This examination was conducted in the following manner. As shown in Fig. 3, each bonded object 7 was placed so that the metallic member 3 faced downward and that the lower side of a peripheral part of the ceramic base 9 was supported on a cylindrical iron pedestal 21. A cylindrical punching rod 25 made of stainless steel was inserted from the upper side into the central through-hole 23 of the ceramic base 9 held in that state. The punching rod 25 was then moved downward at a rate of 0.5 mm/min. The strength (breaking strength) at the time when the metallic member 3 separated from the ceramic base 9 was measured with a load cell (not shown) disposed over the punching rod 25. This strength was taken as brazing strength. With respect to each sample, the brazing strengths for the respective sintering temperatures are shown in the following Table 3. Sample No. Brazing strength [MPa] Evaluation 1150°C 1200°C 1250°C 1300°C 1350°C 1 4.9 8.0 9.7 16.7 18.6 × 3 11.8 17.6 14.7 7.8 3.9 ○ 4 17.6 19.6 15.7 6.9 3.9 ○ 5 17.6 18.6 14.7 6.9 2.9 ○ 7 9.8 15.4 13.3 4.9 3.9 Δ 8 14.7 17.6 15.7 6.9 3.9 ○ 10 16.9 19.1 16.0 5.9 2.9 ○ 11 15.3 14.1 10.9 5.9 3.9 Δ 12 12.8 14.0 11.0 6.9 3.9 Δ 13 13.7 15.6 11.8 5.7 4.2 Δ 14 15.2 14.5 10.2 6.0 4.3 Δ 16 12.8 17.2 15.6 5.9 3.9 ○ 17 14.5 13.6 10.1 5.7 2.9 Δ In the column "Evaluation" in Table 3, ○ indicates that the sample had a peak not lower than 17 MPa in the range of from 1,150 to 1,250°C, Δ indicates that the sample had a peak of from 10 to 17 MPa in that temperature range, and × indicates that the sample had no peak of 10 MPa or higher in that temperature range. Table 3 shows the following. Samples Nos. 3-5, 7, 8, 10-14, 16 and 17, which are within the scope of the invention, advantageously have high brazing strengths because the metallic layers formed by metallization have sufficiently sintered even through low-temperature sintering. For example, these samples obtained through sintering at 1,150°C each has a strength of 6.9 MPa or higher. Those bonded objects have an advantage that the cost of sintering is low because the sintering can be conducted at low temperatures. There also is an advantage that since the metallic layers in those samples can be sufficiently sintered at low temperatures, the ceramic members for bonding can retain high dimensional accuracy as compared with the case where sintering is conducted at high temperatures. In contrast, sample No. 1, as a comparative example, obtained through sintering at low temperatures disadvantageously has low brazing strengths because the metallic layer formed by metallization has not sufficiently sintered through such low-temperature sintering. (EXAMPLE 2) In Example 2, explanations on the same points as in Example 1 are omitted. In this Example, a bonded object comprising two ceramic members bonded to each other is described as an embodiment. a) Fig. 4 diagrammatically shows this embodiment, which is a bonded object 37 comprising a first ceramic member for bonding 31 made of alumina and, bonded thereto with a brazing material 35, a second ceramic member for bonding 33 made of alumina and similar to the first ceramic member 31. More specifically, the first ceramic member for bonding 31 comprises a first ceramic base 39 and a first metallic layer 41 formed thereon by metallization. A first deposit layer 43 has been formed on this first metallic layer 41 by nickel plating. On the other hand, the second ceramic member for bonding 33 comprises a second ceramic base 45 and a second metallic layer 47 formed thereon by metallization. A second deposit layer 49 has been formed on this second metallic layer 47 by nickel plating. The first ceramic member for bonding 31 and the second ceramic member for bonding 33 have been united with each other by bonding the first deposit layer 43 to the second deposit layer 49 with the brazing material 35. b) A process for producing a ring-shaped test piece as an example of this bonded object will be explained below together with a process for producing ceramic members for bonding. (1) Using particulate metallizing-ink ingredients shown in Table 1 given above, metallizing inks for respective samples were produced in the same manner as in Example 1 (hereinafter, the points on which explanation is omitted here are the same as in Example 1). (2) Each of the metallizing inks thus produced was applied to a surface of a first ceramic base 39 and to a surface of a second ceramic base 45. (3) Subsequently, the first and second ceramic bases 39 and 45 coated with the metallizing ink were placed in a furnace and sintered at temperatures in the range of from 1,150 to 1, 350°C to obtain first and second ceramic members for bonding 31 and 33. (4) The surfaces of the first and second metallic layers 41 and 47 thus formed by metallization were nickel-plated to form first and second deposit layers 43 and 49. (5) Thereafter, a silver brazing material 35 was interposed between the two deposit layers 43 and 49 to braze the ceramic members for bonding 31 and 33 together. Thus, the ceramic members 31 and 33 were united with each other to complete a bonded object 37. c) The bonded object samples (test pieces of sample Nos. 1 to 17) produced by the process described above were examined for bonding strength by the same method as in Example 1. The results obtained are shown in Table 4 below. Sample No. Brazing strength [MPa] Evaluation 1150°C 1200°C 1250°C 1300°C 1350°C 1 16.6 28.5 37.8 58.8 63.7 × 3 47.0 63.7 60.8 32.3 14.7 ○ 4 60.8 66.6 63.7 27.4 15.7 ○ 5 62.7 63.0 60.8 26.5 9.8 ○ 7 32.3 52.2 46.1 20.6 15.7 Δ 8 56.8 62.7 62.7 27.4 14.7 ○ 10 58.9 64.3 63.5 25.1 13.3 ○ 11 59.4 59.6 45.3 23.8 11.2 Δ 12 44.3 48.7 40.2 26.2 10.4 Δ 13 58.8 58.6 48.4 28.4 8.4 Δ 14 58.2 56.1 51.2 21.4 10.1 Δ 16 51.2 62.4 58.4 27.8 11.3 ○ 17 56.3 54.1 49.6 21.8 9.7 Δ In the column "Evaluation" in Table 4, ○ indicates that the sample had a peak not lower than 60 MPa in the range of from 1,150 to 1,250°C, Δ indicates that the sample had a peak of from 40 to 60 MPa in that temperature range, and × indicates that the sample had no peak of 40 MPa or higher in that temperature range. Table 4 shows the following. Samples Nos. 3-5, 7, 8, 10-14, 16 and 17, which are within the scope of the invention, advantageously have high brazing strengths because the metallic layers formed by metallization have sufficiently sintered even through low-temperature sintering. Those bonded objects have an advantage that the cost of sintering is low because the sintering can be conducted at low temperatures. There also is an advantage that since the metallic layers in those samples can be sintered at low temperatures, the ceramic members for bonding can retain high dimensional accuracy as compared with the case where sintering is conducted at high temperatures. In contrast, sample No. 1, as a comparative example, obtained through sintering at low temperatures disadvantageously haslow brazingstrengths because the metallic layer formed by metallization has not sufficiently sintered through such low-temperature sintering. (EXAMPLE 3) In Example 3, explanations on the same points as in Examples 1 and 2 are omitted. This Example describes application of a bonded object comprising a ceramic member for bonding and a metallic member, such as that shown in Example 1, to a vacuum switch as an embodiment. This vacuum switch is a high-load switch which comprises a vacuum vessel having built-in electrodes and other components and is suitable for the switching of high-voltage large-current electricity. As shown in Fig. 5, this high-load vacuum switch 100 comprises an insulating valve 101, first and second end covers 102 and 103 attached to the insulating valve 101 so as to cover the respective ends thereof, a fixed electrode 104 attached to the first end cover 102 and projecting into the insulating valve 101, and a movable electrode 105 disposed so as to be freely slidable through the second end cover 103. The fixed electrode 104 and the movable electrode 105 constitute a contact point 106. The insulating valve 101 is a sintered ceramic which has an alumina content of 92% by weight and has a nearly cylindrical shape having an inner diameter of 80 mm, a wall thickness of about 5 mm, and a length of 100 mm. The insulating valve 101 comprises a straight barrel part 110 having a constant inner diameter and a ridge part 112 projecting inward from the inner circumferential wall 111 and extending throughout the circumference along a circle located intermediately between both ends of the barrel part 110. The insulating valve 101 further has a glaze layer 115 on the outer circumferential surface thereof. The first and second end covers 102 and 103 are constituted of disk-shaped Kovar (Fe-Ni-Co) plates respectively having in the centers thereof holes 121 and 132 for securing the fixed electrode 104 and a guide 131 thereto. This guide 131 has been disposed so that the movable shaft 151 of the movable electrode 105 is readily slidable. The fixed electrode 104 consists of a fixed shaft 141, as one end thereof, which is firmly fitted to the hole 121 and a disk-shaped electrode 142, as the other end thereof, which projects into the insulating valve 101. The movable electrode 105 consists of the movable shaft 151, as a rear end part thereof, which slides within the guide 131 and an electrode 152, as a front end part thereof, which comes into contact with the electrode 142 of the fixed electrode 104. This movable electrode 105 is equipped with a metallic bellows 153 extending from that part of the movable shaft 151 which is near the electrode 152 to the second end cover 103. The bellows 153 enables the electrode 105 to perform its switching function while maintaining a vacuum. The metallic bellows 153 is surrounded by a bellows cover 154 so as to be prevented from coming into direct contact with a metal vapor generating from the electrodes 142 and 152 (i.e., contacts 143 and 155 disposed on the front ends thereof) upon current switching. The contact point 106 has such a structure that fusion bonding caused by a vacuum arc generated is less apt to occur. This has been accomplished by employing a high-melting tungsten-based metal sinter as the material of the contacts 143 and 155 where the electrodes 142 and 152 contact with each other. Furthermore, an arc shield 161 is disposed so as to surround the contact point 106. This arc shield 161 has been bonded by brazing to the ridge part 112 of the insulating valve 101 in order to prevent the metal vapor from depositing on the inner circumferential wall 111 of the insulating valve 101 to reduce insulation. Namely, like the bonded object of Example 1, the high-load switch 100 of this Example comprises the insulating valve 101, which is a ceramic member for bonding, and the arc shield 161, which is a metallic member, bonded by brazing with a brazing material 162 to the ridge part 112 of the insulating valve 101. Fig. 6 diagrammatically illustrates an important part of the switch 100. Specifically, the ridge part 112 of the insulating valve 101 has a metallic layer 171 formed on the top thereof by low-temperature metallization in the same manner as in Example 1. This metallic layer 171 is coated with a deposit layer 173 formed by nickel plating. This deposit layer 173 has been bonded to the arc shield 161 by brazing with the brazing material 162. Thus, the insulating valve 101 equipped with the arc shield 161 (and hence the high-load switch 100) can be produced at low cost, and high dimensional accuracy and high bonding strength can be realized. (EXAMPLE 4) In Example 4, explanations on the same points as in Example 3 are omitted. This Example describes application of a bonded object comprising a ceramic member for bonding and a metallic member to a vacuum switch as in Example 3. However, this vacuum switch differs from that of Example 3 in the structures of the arc shield and the insulating valve. An important part of the vacuum switch is diagrammatically shown in Fig. 7. This vacuum switch (high-load switch) 200 has a connecting member 205 made of oxygen-free copper interposed by brazing between an upper insulating valve 201 and a lower insulating valve 203, and further has an arc shield 207 bonded by brazing to the front end of the connecting member 205. In particular, in the part (fixing part 209) where the upper insulating valve 201 and lower insulating valve 203 are fixed to the connecting member 205, the upper and lower insulating valves 201 and 203 respectively have metallic layers 211 and 213 formed thereon by metallization in the same manner as in Example 1. These metallic layers 211 and 213 are coated with deposit layers 215 and 217, respectively, formed by nickel plating. These deposit layers 215 and 217 have been bonded to the connecting member 205 with brazing materials 219 and 221, respectively. Thus, the two insulating valves 201 and 203 have been united with the connecting member 205. The two insulating valves 201 and 203 have, on the outer circumferential surfaces thereof, glaze layers 223 and 225, respectively, which are the same as the glaze layer in Example 3. This Example brings about the same effects as Example 3. The invention should not be construed as being limited to the Examples give above in any way. It is a matter of course that the invention can be practiced in various modes unless these modes depart from the scope of the invention defined by the claims. As described above in detail, in the process for producing a ceramic member for bonding according to the invention defined in claim 3, a metallic layer formed by metallization can be sufficiently sintered at low temperatures. Consequently, the sintering cost regarding furnace structure, utilities, expendable heat-resistant materials, etc. can be reduced as compared with conventional ones. Furthermore, high dimensional accuracy and high bonding strength can be realized. The ceramic member for bonding according to the invention defined in claim 1 has a metallic layer formed by metallization which has undergone sufficient sintering even through low-temperature sintering. Consequently, this ceramic member is effective in reducing the sintering cost and has high dimensional accuracy and high bonding strength. Furthermore, the bonded objects of claims 7 and 8 likewise have advantages of cost reduction, high bonding strength, and high dimensional accuracy because they have the ceramic member for bonding described above. Moreover, the vacuum switch of claim 9 according to the invention and the vacuum vessel of claim 10 according to the invention likewise have advantages of cost reduction, high bonding strength, and high dimensional accuracy because they comprise a bonded object having the ceramic member for bonding described above.

Claims: A ceramic member for bonding, which comprises: a ceramic base which is a sintered ceramic; and a metallic layer formed on the ceramic base by metallization, wherein the metallic layer comprises 70 to 85% by weight of at least one of tungsten and molybdenum and 0.5 to 8.5% by weight of nickel, and wherein the metallic layer further comprises at least one of 1 to 3% by weight of manganese and 0.05 to 2.5% by weight of titanium. The ceramic member for bonding according to claim 1, wherein the metallic layer further comprises 8 to 20% by weight of SiO 2 . A process for producing a ceramic member for bonding according to claim 1, which comprises: mixing a mixture comprising nickel particles and at least one of tungsten particles and molybdenum particles with an organic binder, to produce a paste, wherein the paste further comprises at least one of 5 to 10% by weight of manganese particles and 0.5 to 2% by weight of at least one of titanium particles and TiH 2 particles; applying the paste to a ceramic base which is a sintered ceramic, to form a layer; and baking the layer to form a metallic layer. The process for producing a ceramic member for bonding according to claim 3, wherein the mixture comprises 1 to 10% by weight of nickel, and 70 to 97% by weight of at least one of tungsten particles and molybdenum particles. The process for producing a ceramic member for bonding according to either one of claims 3 or 4, wherein the paste further comprises 2 to 15% by weight of SiO 2 particles. The process for producing a ceramic member for bonding according to any one of claims 3 to 5, wherein the baking is carried out in a temperature of 1 080°C to 1250°C. A bonded object comprising a ceramic member for bonding according to either one of claims 1 or 2, and a metallic member bonded to the ceramic member through the metallic layer of the ceramic member. A bonded object comprising a ceramic member for bonding according to either one of claims 1 or 2, and another ceramic member for bonding, bonded to the ceramic member through the metallic layer of the ceramic member. A vacuum switch comprising a bonded object according to either one of claims 7 or 8. A vacuum vessel comprising a bonded object according to either one of claims 7 or 8.

Inventors: MAKINO YUSUKE, TAKASHIMA TSUNEAKI, MAKINO, YUSUKE, TAKASHIMA, TSUNEAKI, MAKINO, YUSUKE, C/O NGK SPARK PLUG CO., LTD., Takashima, Tsuneaki, c/o NGK Spar Plug Co., Ltd.
Applicants: NGK SPARK PLUG CO, NGK SPARK PLUG CO., LTD
Application year: 2001
Main classification: C04B41
IPC codes: C04B41, H01H33